JP5451367B2 - Three-dimensional photonic crystal and light emitting device - Google Patents

Description

  The present invention relates to a three-photonic crystal used for a functional element such as a light-emitting element, and more particularly to a three-dimensional photonic crystal in which a waveguide region and a mode conversion region are provided in the crystal.

  Yablonovitch has proposed the concept of controlling characteristics such as transmission / reflection of electromagnetic waves by periodically arranging structures having a size equal to or smaller than the wavelength (Non-Patent Document 1). Such a structure is known as a photonic crystal, and an optical element having a reflectance of 100% with no light loss can be realized in a certain wavelength region. Thus, the effect of setting the reflectance to 100% in a certain wavelength region is said to be a photonic band gap (action) from the comparison with the energy gap of a conventional semiconductor.

  By using a photonic crystal having a photonic band gap, an optical element having a new function can be realized. For example, by providing a point-like or linear defect in the photonic crystal, it can be operated as a resonator or a waveguide.

  When a linear defect portion operating as a waveguide is provided in the photonic crystal, light propagates in a state having an inherent electromagnetic energy distribution corresponding to the structure of the waveguide. In addition, light propagates in an external region of the photonic crystal with a unique electromagnetic energy distribution corresponding to the structure. Hereinafter, the state of light propagating with this inherent electromagnetic energy distribution is referred to as a “waveguide mode”. Further, the inherent electromagnetic energy distribution of the guided mode is referred to as “guided mode pattern”, and the frequency of light propagating with the inherent electromagnetic energy distribution is referred to as “guided mode frequency”. Furthermore, a region outside the photonic crystal is referred to as an “external region”.

  When the light propagating in the waveguide is close to the external region, the waveguide mode of the light propagating in the waveguide is combined with the waveguide mode of the light in the external region, converted into light propagating in the external region, and emitted. The Hereinafter, the waveguide mode of light propagating through the waveguide is referred to as “guided mode 1”, and the mode of light propagating through the external region is referred to as “guided mode 2”.

  When light is emitted from the photonic crystal to the external region, the electromagnetic energy distribution of light on the plane orthogonal to the light propagation direction is considered. When the external region is a uniform medium, when using light condensed or collimated by an optical element such as a lens, the electromagnetic energy distribution of the light is mirror-symmetric about multiple axes. It is preferable to have high symmetry. For this reason, it is necessary to make the shape of the waveguide mode pattern of the light just before being emitted from the photonic crystal to the external region a shape having as high symmetry as possible in the plane orthogonal to the light propagation direction. .

  In addition, when a waveguide (photonic crystal waveguide) provided in a photonic crystal and a waveguide (thin wire waveguide) formed by a thin wire are coupled, a waveguide mode pattern propagating through the thin wire waveguide is: Mirror symmetry about multiple axes. Therefore, if the waveguide mode pattern propagating through the photonic crystal waveguide immediately before coupling has a highly symmetric shape, it can be efficiently coupled to the thin wire waveguide.

  It is known to use a mode conversion structure as means for converting from the waveguide mode 1 of the photonic crystal waveguide to the waveguide mode 2 of the external region. For example, Non-Patent Document 2 and Patent Document 1 propose a structure in which a tapered defect portion is provided as a mode conversion structure between a photonic crystal waveguide and an external region in a photonic crystal. The tapered defect portion is a structure in which the width of the linear defect portion in the direction orthogonal to the light propagation direction is gradually enlarged toward the light propagation direction. A waveguide mode of light propagating through the mode conversion structure is referred to as “guided mode 3”.

  By arranging the mode conversion structure between the photonic crystal waveguide and the external region, the waveguide mode 1 light propagating in the photonic crystal waveguide has a waveguide mode pattern close to the waveguide mode 2. After being converted to mode 3 light, it can be converted to guided mode 2 light. By using the mode conversion structure in this manner, light propagating in the waveguide mode 1 in the photonic crystal waveguide can be efficiently converted into light in the waveguide mode 2 propagating in the external region.

  Since the three-dimensional photonic crystal can confine light in three dimensions, the loss can be reduced as compared with the two-dimensional photonic crystal. A diamond structure is known as a three-dimensional photonic crystal having a complete photonic band gap in which no mode can exist for light in all directions.

  Hereinafter, the unit structure for one period of the photonic crystal is referred to as “photonic crystal unit structure”. FIG. 28A shows a photonic crystal unit structure α having a diamond structure. FIG. 28B shows a projection view of the (110) plane of FIG. The (1-10) direction of the photonic crystal unit structure α is the x′-axis direction, the (001) direction is the y′-axis direction, and the (110) direction is the z′-axis direction. FIG. 28B shows a structure that is mirror symmetric with respect to at least one straight line parallel to the y ′ axis and is not mirror symmetric with respect to any straight line parallel to the x ′ axis.

JP 2003-315572 A

Physical Review Letters, Vol. 58, pp. 2059, 1987 Optics Communications, Vol. 223, pp. 339, 2003

  The waveguide and the mode conversion structure are configured by providing a linear defect inside the basic photonic crystal structure formed by arranging all the photonic crystal unit structures α in the same direction. Here, a direction in which the linear defect portion extends is defined as a z-axis direction, and two straight lines orthogonal to each other in a plane orthogonal to the z-axis are defined as an x-axis and a y-axis. In addition, it is assumed that the x-axis direction, the y-axis direction, and the z-axis direction of the photonic crystal basic structure coincide with the x′-axis direction, the y′-axis direction, and the z′-axis direction of the photonic crystal unit structure α, respectively. .

  At this time, the xy section of the waveguide and the mode conversion structure has a structure as shown in FIG. In the xy cross section shown in FIG. 29, when the x-axis and the y-axis pass through the center of the defect portion, the structure has mirror symmetry with respect to the y-axis and does not have mirror symmetry with respect to the x-axis.

  Since light propagating through the waveguide and the mode conversion structure concentrates on the defect portion and the structure in the vicinity thereof, the waveguide mode pattern is affected by the defect portion and the surrounding structure. In the xy cross section, if the structure around the defect portion is a structure having no mirror symmetry with respect to the x axis as shown in FIG. 29, the waveguide mode pattern has a shape having no mirror symmetry with respect to the x axis. Become. The guided mode pattern of light emitted to the external region is affected by the guided mode pattern immediately before being emitted. When the outer region is a uniform refractive index medium region, when light is emitted from the mode conversion structure having low symmetry that does not have mirror symmetry to the outer region, the electromagnetic energy of the emitted light The distribution also has a shape with low symmetry.

  Further, when the photonic crystal waveguide and the thin wire waveguide are coupled, if the waveguide mode pattern of the light propagating through the mode conversion structure is a shape having low symmetry that does not have mirror symmetry in the xy section. Can't combine light efficiently.

  The present invention has an electromagnetic energy distribution with high symmetry that is mirror-symmetric with respect to a plurality of axes, in light emitted from the photonic crystal waveguide having no mirror symmetry with respect to a plurality of axes to the external region. Provided is a three-dimensional photonic crystal.

  The three-dimensional photonic crystal as one aspect of the present invention has a waveguide region and a mode conversion region. The waveguide region has a first photonic crystal basic structure and a first defect provided inside the first photonic crystal basic structure, and the mode conversion region is a second photonic crystal. It has a crystal basic structure, a third photonic crystal basic structure, and a second defect portion. The waveguide region and the mode conversion region are connected so that light propagating in the respective modes is coupled at the first interface. Each of the first photonic crystal basic structure, the second photonic crystal basic structure, and the third photonic crystal basic structure is configured by arranging a plurality of photonic crystal unit structures. The photonic crystal unit structure has a second axis in a cross section parallel to the second and third axes when the three axes orthogonal to each other are the first axis, the second axis, and the third axis. It is not mirror-symmetric with respect to a parallel straight line, but has a mirror-symmetric structure with respect to a straight line parallel to the third axis. When the direction in which light propagates through the waveguide region and the mode conversion region is the first direction, and the two directions orthogonal to the first direction and orthogonal to each other are the second direction and the third direction, In the first photonic crystal basic structure and the second photonic crystal basic structure, the first direction, the second direction, and the third direction are respectively the first axis and the second axis of the photonic crystal unit structure. The photonic crystal unit structure is arranged so as to coincide with the direction in which the third axis extends. In the first cross section parallel to the second and third directions, the second photonic crystal basic structure extends in the second direction and passes through the center of the second defect portion in the third direction. It is arranged on one side.

  In the first cross section, the third photonic crystal basic structure is configured by arranging photonic crystal unit structures so as to have a mirror-symmetrical structure with the second photonic crystal basic structure with respect to the central axis. Has been. The second photonic crystal basic structure and the third photonic crystal basic structure are connected to each other at a connection surface that is parallel to the first and second directions and passes through the center of the second defect portion. The mode conversion region has a mirror-symmetric structure with respect to straight lines extending in the second direction and the third direction through the center of the second defect portion in the first cross section.

Incidentally, also constitutes another aspect of the present invention emitting light device using the three-dimensional photonic crystal.

  According to the present invention, it is possible to have a highly symmetrical electromagnetic energy distribution in the light emitted from the photonic crystal waveguide that does not have mirror symmetry with respect to a plurality of axes to the external region, and the photonic crystal guide. Light can be coupled (propagated) with high efficiency from the waveguide to the external region.

Sectional drawing which shows the concept of the three-dimensional photonic crystal of the Example of this invention. Sectional drawing of the waveguide area | region and mode conversion area | region in the photonic crystal of FIG. Sectional drawing of the three-dimensional photonic crystal which is Example 1 of this invention. 2 is a perspective view and a cross-sectional view showing a photonic crystal unit structure in the three-dimensional photonic crystal of Example 1. FIG. 1 is a perspective view showing a basic structure of a photonic crystal in Example 1. FIG. FIG. 3 is a diagram showing the structure of each layer of the basic structure of the photonic crystal in Example 1. 6 is a graph showing a calculation result of a photonic band gap of a photonic crystal basic structure in Example 1. FIG. FIG. 3 is a cross-sectional view of a waveguide region in the first embodiment. 6 is a graph showing a calculation result of a waveguide mode in a waveguide region in Example 1. Sectional drawing of the mode conversion area | region in Example 1. FIG. 3 is a graph showing the calculation result of the electric field intensity distribution of emitted light in Example 1. 6 is a graph showing calculation results of electric field intensity distribution of a comparative example of Example 1. The graph which shows the calculation result of the electric field intensity distribution of the emitted light in the comparative example of FIG. FIG. 6 is a cross-sectional view showing the structure of a three-dimensional photonic crystal that is a modification of the first embodiment. The perspective view of the photonic crystal unit structure which has the woodpile structure as another modification of Example 1. FIG. Sectional drawing of each layer of the photonic crystal unit structure of FIG. Sectional drawing which shows the structure of the three-dimensional photonic crystal which is Example 2 of this invention. Sectional drawing which shows the structure of the mode conversion area | region of the three-dimensional photonic crystal of Example 2. FIG. 10 is a graph showing the calculation result of the electric field intensity distribution of emitted light in Example 2. Sectional drawing of the three-dimensional photonic crystal which is a comparative example of Example 2. FIG. 6 is a graph showing a calculation result of an electric field intensity distribution of emitted light in a comparative example of Example 2. Sectional drawing which shows the structure of the three-dimensional photonic crystal which is Example 3 of this invention. FIG. 6 is a cross-sectional view showing the structure of the waveguide region of the three-dimensional photonic crystal of Example 3. 10 is a graph showing a calculation result of an electric field intensity distribution of emitted light in Example 3. 4 is a cross-sectional view of a three-dimensional photonic crystal that is a comparative example of Example 3. FIG. 10 is a graph showing a calculation result of an electric field intensity distribution of emitted light in a comparative example of Example 3. Sectional drawing which shows the structure of the photonic crystal light-emitting element which is Example 4 of this invention. The schematic diagram which shows the structure of the conventional photonic crystal. Xy sectional drawing of the waveguide and mode conversion structure in the photonic crystal of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  The concept of a three-dimensional photonic crystal including a mode conversion structure, which is an embodiment of the present invention, will be described with reference to FIG. A three-dimensional photonic crystal A shown in FIG. 1 includes a waveguide region 5 and a mode conversion region 6.

  The waveguide region 5 includes a photonic crystal basic structure (first photonic crystal basic structure) 1, and a linear defect portion (first defect portion) 3 provided in the photonic crystal basic structure 1. Consists of.

  The mode conversion region 6 includes a photonic crystal basic structure (second photonic crystal basic structure) 2, a photonic crystal basic structure (third photonic crystal basic structure) 2 ′, and a linear defect portion (second photonic crystal structure). Defective portion) 4.

  The waveguide region 5 and the mode conversion region 6 are connected at an interface (first interface) 7 so that light propagating through the waveguide region 5 and light propagating through the mode conversion region 6 are coupled.

  In the embodiment, the region outside the photonic crystal is the external region 9, and the interface between the end of the mode conversion region 6 and the external region 9 is the interface (second interface) 8 as shown in FIG. To do.

  The direction in which the linear defect portion 3 and the mode conversion region 6 and the linear defect portion 4 in the waveguide region 5 extend, that is, the direction in which light propagates, is the z-axis direction (first direction: hereinafter referred to as the z-axis direction). And Two straight lines that pass through the center of the linear defect portion 3 and are orthogonal to each other on the plane orthogonal to the z-axis direction are defined as an x-axis and a y-axis. The x-axis direction (second direction) and the y-axis direction (third direction) are hereinafter referred to as the x-axis direction and the y-axis direction, respectively.

  In the xy cross section (first cross section), the center of the linear defect portion 3 in the waveguide region 5 and the center of the linear defect portion 4 in the mode conversion region 6 coincide with each other.

  The photonic crystal basic structure 1, the photonic crystal basic structure 2 and the photonic crystal basic structure 2 ′ are formed by arranging a plurality of photonic crystal unit structures α in the same direction and in contact with each other. Is done. The photonic crystal unit structure α is a unit structure for one period of the three-dimensional photonic crystal, and is the diamond structure shown in FIGS. As described above, FIG. 28B shows a projection view of the (110) plane of FIG. The (101) direction of the photonic crystal unit structure α is the x′-axis (second axis) direction (hereinafter referred to as the x′-axis direction), and the (001) direction is the y′-axis (third axis). Direction (hereinafter referred to as the y′-axis direction). The direction of (110) is defined as the direction of the z ′ axis (first axis) (hereinafter referred to as the z ′ axis direction).

  Each of the photonic crystal basic structures 1, 2, 2 'has a complete photonic band gap. When a linear defect is provided inside the basic structure of the photonic crystal, it is possible to create a state in which light in a part of the frequency band included in the complete photonic band gap can exist in the linear defect. .

  FIG. 2A shows an xy cross section of the waveguide region 5. The photonic crystal basic structure 1 is photonic so that the x-axis direction, the y-axis direction, and the z-axis direction coincide with the x′-axis direction, the y′-axis direction, and the z′-axis direction of the photonic crystal unit structure α, respectively. It is formed by arranging the crystal unit structures α. At this time, the waveguide region 5 has a structure that is mirror-symmetric with respect to the y-axis and is not mirror-symmetrical with respect to the x-axis in the xy cross section.

  FIG. 2B shows an xy cross section of the mode conversion region 6. The photonic crystal basic structure 2 and the photonic crystal basic structure 2 ′ are arranged on the + y direction and the −y direction, that is, on one side of the y-axis direction from the xz cross section (center axis) passing through the center of the linear defect portion 4, respectively. Has been.

  Similar to the photonic crystal basic structure 1, the photonic crystal basic structure 2 is such that the x, y, and z axis directions coincide with the x ′, y ′, and z ′ axis directions of the photonic crystal unit structure α, respectively. It is formed by arranging a plurality of photonic crystal unit structures α.

  The photonic crystal basic structure 2 ′ has a photonic crystal unit structure α arranged so as to have a mirror-symmetrical structure with the photonic crystal basic structure 2 with respect to an xz cross section (center axis) passing through the center of the linear defect portion 4. It is formed by doing.

  The photonic crystal basic structure 2 and the photonic crystal basic structure 2 ′ are connected by an xz cross section (connection surface) passing through the center of the linear defect portion 4. At this time, the mode conversion region 6 has a mirror-symmetric structure with respect to two axes of the x axis and the y axis in the xy section (first section).

  The conventional mode conversion structure has a structure that is not mirror-symmetric with respect to the x-axis in the xy cross section, like the waveguide region 5. Since the mode conversion region 6 in the present embodiment has a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis in the xy section, it has a higher symmetry than the conventional mode conversion structure.

  A waveguide mode of light propagating through the waveguide region 5 is referred to as a waveguide mode 1, and a waveguide mode of light propagating through the external region 9 is referred to as a waveguide mode 2. The guided mode of light propagating through the mode conversion region 6 is referred to as a guided mode 3.

  In the three-dimensional photonic crystal A shown in FIG. 1, the light propagating through the waveguide region 5 is converted into light propagating through the mode conversion region 6 at the interface 7, and the light propagating through the mode conversion region 6 is transmitted at the interface 8. It is converted into light propagating through the external region 9 and emitted to the external region 9. By using the mode conversion region 6 having improved symmetry as compared with the conventional mode conversion structure, the symmetry of the guided mode pattern of light emitted to the external region 9 can be improved.

  Here, the reason why the symmetry of the waveguide mode pattern of the light emitted to the external region 9 can be improved by using the mode conversion region 6 will be described.

  Since the light propagating through the mode conversion structure concentrates on the linear defect portion inside the mode conversion structure and the structure in the vicinity thereof, the light is influenced by the linear defect portion through which the light propagates and the surrounding structure. If the structure around the linear defect portion of the mode conversion structure is a mirror-symmetric structure with respect to only one axis in the xy section as in the conventional mode conversion structure, the waveguide mode pattern also has only one axis. It becomes a mirror-symmetrical shape. When the structure around the linear defect portion of the mode conversion structure is a mirror-symmetric structure with respect to two axes orthogonal to each other as in the mode conversion region 6 of this embodiment, the waveguide mode pattern also has two orthogonal directions. The shape is symmetric with respect to the axis, and the symmetry can be increased.

Since the waveguide mode pattern of the light emitted to the external region 9 is affected by the waveguide mode pattern of the mode conversion structure immediately before being emitted, the symmetry of the mode conversion structure is increased so that the external region 9 The symmetry of the guided mode pattern of the emitted light can be improved. Therefore, by using the mode conversion region 6 in the present embodiment, light with improved symmetry of the waveguide mode pattern can be emitted to the external region 9. The waveguide region of the three-dimensional photonic crystal A shown in FIG. 5 and a mode conversion region 6 have an interface 7 in which the periodic structure of the photonic crystal A is disturbed. Therefore, there is a mode that propagates in the in-plane direction of the xy cross section of the interface 7 depending on the way of bonding. Here, a waveguide mode that propagates in the plane of the xy section of the interface 7 is referred to as a waveguide mode 4.

  If the light of the waveguide mode 1 propagates at a frequency different from the frequency band in which the light of the waveguide mode 4 propagates, the light of the waveguide mode 1 is not converted into the light of the waveguide mode 4, and the mode conversion region 6 is converted into light of guided mode 3. Even if the frequency of the light of the waveguide mode 1 is included in the frequency band in which the light of the waveguide mode 4 propagates, the waveguide region has the same frequency as the waveguide mode 4 and does not have the same polarization component. 5 and the mode conversion area 6 may be connected. Thereby, the light of the waveguide mode 1 is not converted into the light of the waveguide mode 4. Since modes that do not have the same polarization component (that is, the polarization directions are orthogonal) do not couple with each other, when the light of the waveguide mode 1 reaches the interface 7, the light of the waveguide mode 1 is guided by the waveguide mode 4 of the interface 7. Without being converted into light, the light in the waveguide mode 3 in the mode conversion region 6 is converted with high efficiency without loss.

  As described above, when the photonic crystal A includes the mode conversion structure 6, when light propagating in the waveguide region 5 is emitted to the external region 9, light having a waveguide mode pattern having high symmetry is emitted. Can do.

  Next, a three-dimensional photonic crystal B which is a specific structural example including the mode conversion structure 6 according to the above concept will be described with reference to FIG. The three-dimensional photonic crystal B includes a waveguide region 103 and a mode conversion region 104.

  The waveguide region 103 includes a photonic crystal basic structure (first photonic crystal basic structure) 101 and linear defect portions 10 and 11 provided inside the photonic crystal basic structure 101. .

  The mode conversion region 104 includes a photonic crystal basic structure (second photonic crystal basic structure) 102, the photonic crystal basic structure (third photonic crystal basic structure) 102 ′, a linear defect portion 12, and the like. It consists of

  The waveguide region 103 and the mode conversion region 104 are connected at the interface (first interface) 105 so that light propagating in the mutual waveguide mode is coupled. Further, an outer region of the three-dimensional photonic crystal B is an outer region 106, and an interface between the end portion of the mode conversion region 104 and the outer region 106 is an interface (second interface) 107.

  A direction in which the linear defect portion 10 extends in the waveguide region 103 is defined as a z-axis direction, and two straight lines that pass through the center of the linear defect portion 10 in the xy section and are orthogonal to each other are defined as an x-axis and a y-axis.

  In the xy cross section, the center of the linear defect portion 10 in the waveguide region 103 and the center of the linear defect portion 12 in the mode conversion region 104 coincide with each other.

  Each of the photonic crystal basic structures 101, 102, 102 'is formed by arranging the photonic crystal unit structures 100 in the same direction so that each surface is in contact with each other. The photonic crystal unit structure 100 is a unit structure for one period of a three-dimensional photonic crystal having a periodic refractive index distribution. FIG. 4A shows the photonic crystal unit structure 100.

  In the photonic crystal unit structure 100, the direction in which the columnar structures orthogonal to each other extend is the x′-axis direction and the z′-axis direction, and the stacking direction of these columnar structures is the y′-axis direction. FIG. 4B shows the x′y ′ cross section of FIG. The x′y ′ cross section of the photonic crystal unit structure 100 shown in FIG. 4B is mirror symmetric with respect to at least one straight line parallel to the y ′ axis, and is mirrored with respect to any straight line parallel to the x ′ axis. The structure is not mirror-symmetric.

FIG. 5 shows a basic photonic crystal structure in which a plurality of photonic crystal unit structures 100 are arranged in the x′-axis direction, the y′-axis direction, and the z′-axis direction so that their respective surfaces are in contact with each other. The basic structure is formed by laminating 12 layers 1000 to 1011. FIG. 6 shows the structure of the x′z ′ plane of each layer. 6, outer region 1 012 represents the magnitude of the basic structure surrounded by a dashed box.

  In the first layer 1000 and the seventh layer 1006, a plurality of columnar structures (first columnar structures) 1000a and 1006a extending in the x′-axis direction are arranged side by side in the z′-axis direction at equal intervals P. The columnar structures 1000a and 1006a are arranged at positions shifted from each other by P / 2 (half cycle) in the z′-axis direction.

  In the fourth layer 1003 and the tenth layer 1009, a plurality of columnar structures (second columnar structures) 1003a and 1009a extending in the z′-axis direction are arranged in the x′-axis direction at equal intervals P. . The columnar structures 1003a and 1009a are arranged at positions shifted from each other by P / 2 (half cycle) in the x′-axis direction.

  Thus, the photonic crystal unit structure 100 has a columnar structure layer (first layer, seventh layer) having a plurality of columnar structures extending in the x′-axis direction and a plurality of columnar structures extending in the z′-axis direction. It has a basic structure in which columnar structure layers (fourth layer, tenth layer) are alternately stacked. The columnar structure layer includes a first layer 1000, a fourth layer 1003, a seventh layer 1006, and a tenth layer 1009 corresponding to the first layer, the second layer, the third layer, and the fourth layer in this order. Are stacked.

  Between the first layer 1000 and the fourth layer 1003, a second layer 1001 and a third layer 1002 are arranged. In the second layer 1001 and the third layer 1002, the columnar structure 1000a of the first layer 10 and the columnar structure 1003a of the fourth layer 1003 have a position corresponding to the intersection (stereoscopic intersection position) in the y′-axis direction. Discrete structures 1001a and 1002a are arranged. The discrete structures 1001a and 1002a are discretely arranged so as not to contact each other in the x′z ′ plane.

  The second layer 1001 and the third layer 1002 are additional layers to the columnar structure layer. The discrete structures 1001a and 1002a have symmetry that overlaps each other by rotation of 90 degrees in the x'z 'cross section.

A fifth layer as an additional layer is also provided between the fourth layer 1003 and the seventh layer 1006 , between the seventh layer 1006 and the tenth layer 1009 , and between the tenth layer 1009 and the first layer 1000 in the next basic structure period. The layer 1004 and the sixth layer 1005, the eighth layer 1007 and the ninth layer 1008, the eleventh layer 1010 and the twelfth layer 1011 are arranged, respectively. The fifth layer 1004 and the sixth layer 1005, the eighth layer 1007, the ninth layer 1008, the eleventh layer 1010, and the twelfth layer 1011 are also configured in the same manner as the second layer 1001 and the third layer 1002. That is, the discrete structures 1004a, 1005a, 1007a, 1008a, 1010a, 1011a are arranged at positions corresponding to the intersections of the columnar structures as viewed in the y′-axis direction between the columnar structure layers including columnar structures extending in directions orthogonal to each other. Yes.

  In the columnar structure layer and the additional layer adjacent thereto, the columnar structure and the discrete structure are in contact with each other. It is possible to obtain a complete photonic band gap in a specific wide frequency band (wavelength band) by appropriately setting the structural parameters such as the refractive index, shape, spacing and thickness of each layer of the columnar structure and discrete structure material. it can. By using a photonic crystal having a wide complete photonic band gap, loss can be suppressed and the operating frequency band can be widened.

  The structural parameters of the photonic crystal unit structure 100 are shown in Table 1. In Table 1, the in-plane lattice period corresponds to the interval P between the columnar structures shown in FIG. The out-of-plane lattice period refers to the length (thickness) in the stacking direction of 12 layers 1000 to 1011 of the photonic crystal unit structure 100. The refractive index in Table 1 represents the refractive index of the medium (first medium) constituting the columnar structure and the discrete structure of the photonic crystal unit structure 100. The medium (second medium) other than the columnar structure and discrete structure of the photonic crystal unit structure 100 is air, and its refractive index is 1.0.

  The columnar structure width is the dimension of the columnar structure in a direction orthogonal to the direction in which the columnar structure extends, and the columnar structure height is the dimension of the columnar structure in the stacking direction (y′-axis direction). Further, as shown in FIG. 6, the discrete structure widths Dw1 and Dw2 respectively represent the dimensions in the long side direction and the short side direction of one discrete structure in each additional layer. Further, the discrete structure height Dh is a dimension in the stacking direction (y′-axis direction) of the discrete structure as shown in FIG.

  FIG. 7 shows a photonic band gap of a basic structure of a photonic crystal formed by aligning a plurality of photonic crystal unit structures 100 in the same direction and contacting each surface by a plane wave expansion (PWE) method. It is a graph which shows the result of calculation. The horizontal axis of the graph represents the wave number vector, that is, the incident direction of the electromagnetic wave incident on the photonic crystal basic structure.

  For example, the K point is a wave vector parallel to the x ′ axis (or z ′ axis), and the X point has an inclination of 45 ° with respect to the x ′ axis (or z ′ axis) in the x′z ′ plane. It represents a wave vector. The vertical axis of the graph indicates the frequency normalized by the grating period (normalized frequency). In the frequency band indicated by shading in FIG. 6, a complete photonic band gap in which no mode exists regardless of the incident direction of light is formed.

  When a defect portion whose period is disturbed is provided inside the basic structure of the photonic crystal, a mode having a frequency within the complete photonic band gap is generated. This mode is a mode in which the frequency (wavelength) and wave number vector are determined by the shape of the defect portion and the medium. At this time, if a linear defect is provided, the magnitude of the wave vector is not limited in the direction in which the linear defect extends, so the defect mode becomes a waveguide mode that guides in the direction in which the linear defect extends. .

The waveguide region 103 includes a photonic crystal basic structure 101, a first linear defect portion 10 provided in the photonic crystal basic structure 101 and extending in the z-axis direction, and the first linear defect portion 10. The second linear defect portion 11 is provided in a layer different from the layer containing the. The second linear defect portion 11 is formed by deforming or removing a part of the columnar structure extending in the z-axis direction.

  FIG. 8A shows an xy cross section of the waveguide region 103 when the first and second linear defect portions 10 and 11 extend in the z-axis direction. 8B and 8C are xz sectional views of the section i and the section ii shown in FIG. 8A, respectively.

  The photonic crystal basic structure 101 includes a plurality of x-axis directions, y-axis directions, and z-axis directions so as to match the x′-axis direction, the y′-axis direction, and the z′-axis direction of the photonic crystal unit structure 100, respectively. It is formed by arranging the photonic crystal unit structures 100.

  As shown in FIG. 8A, the waveguide region 103 has a structure that is mirror-symmetric with respect to the y-axis and is not mirror-symmetrical with respect to the x-axis, in the xy section.

  The first linear defect portion 10 has a width of 0.60 P and is formed of a medium having the same refractive index as that of the medium forming the columnar structure of the photonic crystal unit structure 100. The second linear defect portion 11 has a width of 0.00P. The structural parameters of the waveguide region 103 are shown in Table 2.

  The defect widths 10w and 11w are dimensions in the x-axis direction in the layers of the respective defect portions as shown in FIGS. 8 (b) and 8 (c). The defect height 10h is a dimension in the stacking direction (y-axis direction) of each defect portion as shown in FIG. Further, the defect portion refractive index 10n is the refractive index of the medium constituting each defect portion. The origin of the coordinates is the center of the first linear defect portion 10 in the xy cross section of FIG.

  FIG. 9 is a graph showing the result of calculating the waveguide mode for the waveguide region 103 using the transfer matrix method (TMM). The horizontal axis of the graph indicates the magnitude of the wave guide vector (z-axis direction) component of the wave vector normalized by the grating period P, and the vertical axis indicates the frequency (normalized frequency) normalized by the grating period P. Yes. Further, the frequency band indicated by the region γ is a frequency band other than the complete photonic band gap. The frequency band indicated by the region β indicates a frequency band in which a single guided mode due to the defect exists in the complete photonic band gap.

  As shown in FIG. 9, the waveguide region 103 is a waveguide having a single waveguide mode in the frequency band β. By setting the waveguide to be included in the waveguide region 103, light can be propagated to the first linear defect portion 10 in the waveguide region 103 in a waveguide mode in which light is strongly concentrated. It is possible to reduce scattering loss due to surface roughness of one linear defect portion 10.

  The mode conversion region 104 includes a photonic crystal basic structure 102, a photonic crystal basic structure 102 ′, and a linear defect portion 12. FIG. 10A shows an xy cross section of the mode conversion region 104 when the linear defect portion 12 extends in the z-axis direction. FIG. 10B shows an xz cross section of the mode conversion region 104 in the cross section i shown in FIG.

  The photonic crystal basic structure 102 and the photonic crystal basic structure 102 ′ are respectively arranged in the + y direction and the −y direction (that is, one side) from the xz section passing through the center of the linear defect portion 12.

  The photonic crystal basic structure 102 has a plurality of photonic crystal unit structures 100 arranged so that the x, y, and z axis directions thereof coincide with the x ′, y ′, and z ′ axis directions of the photonic crystal unit structure 100, respectively. It is formed by doing.

Photonic crystal base structure 102 'is formed by arranging the photonic crystal unit structure 100 so that the photonic crystal base structure 102 and the mirror-symmetrical structure with respect to xz section passing through the center of the line defect member 1 2 Has been. Photonic crystal 102 and photonic crystal 102 'is connected in the xz cross section passing through the center line defect member 1 2. The photonic crystal 2 and the photonic crystal 2 ′ are connected by an xz section passing through the center of the linear defect portion 4. At this time, as shown in FIG. 10A, the mode conversion region 6 has a structure having mirror symmetry with respect to the two axes of the x axis and the y axis in the xy cross section.

  Further, as shown in FIG. 3, the end 107 of the mode conversion area 104 is in contact with the external area 106.

  In the present embodiment, a structure including a linear defect portion 12 having a width of 1.00P and a height of 1.00P is shown. Table 3 shows the structural parameters of the mode conversion area 104. The defect width 12w is a dimension in the x-axis direction in the layer of each defect portion shown in FIG. The defect height 12h is a dimension in the stacking direction (y-axis direction) of each defect portion shown in FIG. The defect refractive index 12n is a refractive index of a medium constituting each defect portion. The defect portion length 12D is a dimension in the z-axis direction in the layer of the defect portion shown in FIG.

  In this embodiment, the external region 106 is a region having a uniform refractive index distribution, and the refractive index of the external region 106 is 106n.

  The defect portion refractive index 12n is a refractive index equal to or higher than the refractive index of the medium forming the photonic crystal unit structure 100. Thereby, light can be propagated to the linear defect portion 12 in a waveguide mode in which light is strongly concentrated, and scattering loss due to surface roughness of the linear defect portion 12 can be reduced.

  The waveguide mode of light propagating through the waveguide region 103 is “guided mode 1”, and the waveguide mode of light propagating through the external region 106 is “guided mode 2”. In addition, the waveguide mode of light propagating through the mode conversion region 104 is referred to as “guided mode 3”.

  In the three-dimensional photonic crystal B shown in FIG. 3, the light propagating through the waveguide region 103 is converted into light propagating through the mode conversion region 104 at the interface 105. The light propagating through the mode conversion region 104 is converted into light propagating through the external region 106 at the interface 107 and emitted to the external region 106.

  When the wavelength of light propagating through the external region 106 is λ, an xy cross section at a position 3λ away from the interface 107 between the mode conversion region 104 and the external region 106 in the + z direction is defined as an xy cross section A. FIG. 11A shows the result of calculating the electric field intensity distribution at the xy section A of the light emitted from the three-dimensional photonic crystal B including the mode conversion region 104 to the external region 106. FIG. 11 (b) shows the electric field strength distribution in the y-axis direction at x = 0 in FIG. 11 (a). The vertical axis represents the electric field strength normalized by the maximum value, and the horizontal axis represents the y-axis coordinate. Respectively.

  From FIG. 11A and FIG. 11B, the guided mode pattern of light emitted from the three-dimensional photonic crystal B including the mode conversion region 104 to the external region 106 is related to two axes, the x axis and the y axis. It can be seen that the shape is highly symmetric so as to be mirror symmetric.

  Here, for comparison, an electric field intensity distribution calculation result in the case where the structure of the mode conversion region is not mirror-symmetrical with respect to the x-axis as in the waveguide region 103 is shown. FIG. 12A shows a yz section of a three-dimensional photonic crystal including a mode conversion region 109 that is mirror symmetric with respect to the y axis and is not mirror symmetric with respect to the x axis. FIG. 12B shows an xy cross section of the mode conversion region 109.

  The photonic crystal 101 around the defect 12 in the mode conversion region 109 has the same structure as that of the waveguide region 103, and has a structure in which the photonic crystal unit structures 100 are oriented in the same direction and are in contact with each other. is there. The linear defect portion 12 has the same structure as the linear defect portion included in the mode conversion region 104 shown in FIG. FIG. 13A shows the calculation result of the electric field intensity distribution in the xy section A of the light emitted from the three-dimensional photonic crystal including the mode conversion region 109 shown in FIG. FIG. 13B shows the electric field strength distribution in the y-axis direction at x = 0 in FIG. 13A, where the vertical axis shows the electric field strength normalized by the maximum value, and the horizontal axis shows the y-axis coordinates. Represents each.

  Comparing FIGS. 11A and 11B with FIGS. 13A and 13B, the electric field intensity distribution of light emitted from the mode conversion region 104 that is mirror-symmetrical with respect to the two axes of the x-axis and the y-axis. It can be seen that (FIGS. 11A and 11B) are more symmetrical.

  The reason why the symmetry of the guided mode pattern of the emitted light is improved by using a mode conversion region having a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis is described in the explanation of the above concept. For the same reason.

  As described above, in this embodiment, the three-dimensional photonic crystal B including the mode conversion region 104 having a mirror-symmetric structure with respect to two axes orthogonal to each other is used. Accordingly, it is possible to emit light having a waveguide mode pattern having high symmetry that is mirror-symmetric with respect to two axes orthogonal to each other.

  In the interface 105 between the waveguide region 103 and the mode conversion region 104 of the three-dimensional photonic crystal B shown in FIG. 2, a surface in which the periodic structure of the photonic crystal is disturbed is generated. There is a mode that propagates in the in-plane direction. Here, the waveguide mode propagating in the plane of the xy section of the interface 105 is referred to as “guided mode 4”.

  If the light of the waveguide mode 1 propagates at a frequency different from the frequency band in which the light of the waveguide mode 4 propagates, the light of the waveguide mode 1 is not converted into the waveguide mode 4 but in the mode conversion region 113. It is converted into guided mode 3 light. Even if the frequency of the light of the waveguide mode 1 is included in the frequency band in which the light of the waveguide mode 4 propagates, the waveguide does not have a waveguide mode having the same polarization component at the same frequency as the waveguide mode 4 The area 103 and the mode conversion area 113 may be connected. Thereby, the light of the waveguide mode 1 is not converted into the light of the waveguide mode 4. Since modes that do not have the same polarization component are not coupled to each other, when the light of the waveguide mode 1 propagated through the waveguide region 5 reaches the interface 105, the light is converted into the light of the waveguide mode 4 at the interface 105. First, it is converted into light of the waveguide mode 3 in the mode conversion region 113 with high efficiency without loss.

  The ratio of the energy of light propagating in the xy cross section of the waveguide region 103, the xy cross section of the interface 105, and the xy cross section of the mode conversion region 104 to the waveguide mode 4 propagating through the xy cross section of the interface 105 is Calculated. As a result, the ratio of the light converted into the xy cross-section propagating through the interface 105 was about 1% with respect to the amount converted into the light in the mode conversion region 104. Therefore, it is considered that the light propagating through the waveguide region 103 is hardly converted into light propagating through the xy section of the interface 105 at the interface 105 and is converted into light propagating through the mode conversion region 104.

  Next, in this embodiment, a description will be given of a case where the waveguide also has a mirror-symmetric structure with respect to the two axes, the x axis and the y axis. FIG. 14A shows a three-dimensional photonic crystal in which both the waveguide and the mode conversion structure have a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis. FIG. 14B shows an xy cross section of the waveguide region 110 having mirror symmetry with respect to the two axes of the x axis and the y axis. Here, the mode conversion structure is the same as that of the mode conversion region 104 having a mirror-symmetric structure with respect to the two axes of the x axis and the y axis shown in FIG. 9 and Table 3.

  The waveguide region 110 is configured by providing the first linear defect portion 10 inside the structure in which the photonic crystal unit structures 100 are arranged, and is a mirror-symmetric structure with respect to two axes of the x axis and the y axis in the xy section. Have The first linear defect portion 10 in the waveguide region 110 has the same structure as the first linear defect portion 10 in the waveguide region 103 shown in FIG. At this time, the waveguide region 110 and the mode conversion region 104 have a mirror-symmetric structure with respect to the interface 111.

  At the interface 111 of the waveguide region 110, the period of the photonic crystal around the first linear defect 10 is disturbed. Therefore, there is a mode that propagates through the xz section of the interface 111, and the waveguide mode 1 that propagates through the waveguide is combined with the waveguide mode that propagates through the xz section of the interface 111, resulting in a loss. In particular, when light propagates through the waveguide region 110 over a long distance, the loss increases.

  In addition, since the structure of the first linear defect portion 10 in the waveguide region 110 is changed, a plurality of waveguide modes exist, and it is difficult to propagate with light of a desired single mode. Therefore, it is necessary to provide a mirror-symmetric region with respect to the two axes of the x-axis and the y-axis only in the region of the mode conversion structure immediately before being emitted to the external region 106, not in the waveguide.

  As described above, in this embodiment, the three-dimensional photonic crystal B including the mode conversion region 109 having a mirror-symmetric structure with respect to two axes orthogonal to each other is used. Thereby, the light of the waveguide mode pattern which has high symmetry can be inject | emitted.

  The photonic crystal unit structure may be a simple woodpile photonic crystal unit structure 112 as shown in FIG. In this case, the frequency band having a complete photonic bandgap is narrower than in the case where the above-described three-dimensional photonic crystal unit structure 100 is used, but the number of stacks is reduced, so that the number of manufacturing steps can be reduced. .

  FIG. 15B shows the photonic crystal unit structure 112 shown in FIG. 15A in which x′y ′ plane, y′z ′ plane, and x′z ′ plane are in contact with each other. , A basic structure of a photonic crystal composed of a plurality of elements arranged in the y ′ and z ′ axis directions.

Photonic crystal unit structure 112 is composed of 4 layers of a layer 1013-101 6 including the xz plane as the base period. Figure 16 shows the xz cross section of each layer 1013-101 6, the area of the broken lines 101 7 boxed represents the size of the basic structure.

In the first layer 1013 and the third layer 1015, a plurality of columnar structures 1013a and 1015a extending in the x-axis direction are arranged at equal intervals P in the z-axis direction. The columnar structures 1013a and 1015a are arranged at positions shifted from each other by P / 2 (half cycle) in the z-axis direction. In the second layer 1014 and the fourth layer 101 6, a plurality of columnar structures 1014a extending in the z-axis direction, 101 6 a are each arranged in the x axis direction at equal intervals P. Columnar structures 1014a, 101 6 a are arranged at positions shifted P / 2 (a half cycle) in the x-axis direction.

  By optimizing the refractive index of the material of the columnar structure, the shape and interval of the columnar structure, the thickness of each layer, etc., a complete photonic band gap can be obtained in a desired frequency band (wavelength band). Note that the photonic crystal basic structure may have a structure other than the above-described three-dimensional photonic crystal structure.

  FIG. 17 shows a configuration of a three-dimensional photonic crystal including a mode conversion structure, which is Embodiment 2 of the present invention. A three-dimensional photonic crystal C shown in FIG. 17 includes a waveguide region 103 and a mode conversion region 113.

  The waveguide region 103 includes a photonic crystal basic structure 101 and first and second linear defect portions 10 and 11 provided in the photonic crystal basic structure 101. FIG. 8 (a) to (c) and the same structure as shown in Table 2.

  The mode conversion region 113 includes a photonic crystal 102, a photonic crystal 102 ', and a tapered defect portion 13. The waveguide region 103 and the mode conversion region 113 are connected so that light propagating in the mutual mode is coupled at the interface 105. An interface between the end of the mode conversion region 113 and the external region 106 is referred to as an interface 107.

  As shown in FIG. 17, the direction in which the first linear defect portion 10 extends in the waveguide region 103 is defined as the z-axis direction, and passes through the center of the first linear defect portion 10 in the xy section and is orthogonal to each other. Let the straight line be the x-axis and the y-axis. In the xy cross section, the positions of the center of the first linear defect portion 10 and the center of the linear defect portion 13 coincide with each other.

  Each of the photonic crystal basic structures 101, 102, 102 'is formed by arranging the photonic crystal unit structures 100 all in the same direction and in contact with each other, and has a complete photonic band gap. The photonic crystal unit structure 100 has the same structure as that shown in FIGS. 4A and 4B and Table 1 of the first embodiment. The direction in which the columnar structure extends is the x′-axis direction and the z′-axis direction, and the stacking direction is the y′-axis direction. The x'y 'cross section has a structure that is mirror symmetric with respect to at least one straight line parallel to the y' axis and is not mirror symmetric with respect to any straight line parallel to the x 'axis.

  The photonic crystal basic structure 101 included in the waveguide region 103 has a photonic crystal so that the x, y, and z axis directions coincide with the x ′, y ′, and z ′ axis directions of the photonic crystal unit structure 100, respectively. It is formed by arranging unit structures 100. As shown in FIG. 8A of the first embodiment, the waveguide region 103 has a structure that is mirror-symmetric with respect to the y-axis and not mirror-symmetric with respect to the x-axis in the xy section.

  18A, 18B, and 18C show the configuration of the mode conversion area 113. FIG. FIG. 18A shows an xy cross section at the interface 105 in FIG. 18B shows an xy cross section at the interface 107 in FIG. 17, and FIG. 18C shows an xz cross section passing through the center of the defect portion 13, respectively.

  The photonic crystal basic structure 102 and the photonic crystal basic structure 102 ′ are respectively arranged in the + y direction and the −y direction with respect to the xz section passing through the center of the linear defect portion 13. Similar to the photonic crystal basic structure 101, the photonic crystal basic structure 102 is arranged so that the x, y, and z axis directions thereof coincide with the x ′, y ′, and z ′ axis directions of the photonic crystal unit structure 100, respectively. It is formed by arranging the photonic crystal unit structures 100. The photonic crystal basic structure 102 ′ is formed by arranging the photonic crystal unit structures 100 so as to have a mirror-symmetrical structure with the photonic crystal basic structure 102 with respect to the xz cross section passing through the center of the linear defect portion 13. ing.

The photonic crystal basic structure 102 and the photonic crystal basic structure 102 ′ are connected in an xz cross section passing through the center of the linear defect portion 13. At this time, as shown in FIG. 18A, the mode conversion region 113 has a mirror-symmetric structure with respect to the two axes of the x axis and the y axis in the xy section. Moreover, as shown in FIG. 17, the end 107 of the mode conversion region 113 is in contact with the external region 106. The width of the linear defect portion 13 at the interface 107 shown in FIG. The thickness is 0.25P. Further, the width of the defect portion 13 at the interface 107 shown in FIG. 18B is 2.10P, and the thickness is 2.55P. The length between the interfaces 105 and 107 shown in FIG. 18C is 7.00P. In FIG. 17 and FIG. 20, the linear defect portion 13 has a tapered shape in which the width and thickness in the xy section gradually change from the position indicated by the interface 105 to the position indicated by the interface 107. Have. The linear defect portion 13 is a region formed of a medium having the same refractive index as that of the medium forming the columnar structure included in the three-dimensional photonic crystal unit structure 100. As for the center coordinates of the xy section of the linear defect portion 13, the x coordinate is 0.00P and the y coordinate is 3.50P.

  Table 4 shows the structural parameters of the mode conversion area 113. The defect widths 13w1 and 13w2 are dimensions in the x-axis direction in the layer shown in FIG. The defect heights 13h1 and 13h2 are dimensions in the stacking direction (y-axis direction) of the defect portions shown in FIGS. 18 (a) and 18 (b). The defect portion length 13D is a dimension in the z-axis direction in the layer of the defect portion shown in FIG. The defect refractive index 13n is the refractive index of the medium constituting the defect portion.

  In the present embodiment, the external region 106 is a region having a uniform medium formed with a refractive index of 1.0, as in the first embodiment.

  The waveguide modes of light propagating through the waveguide region 103 and the external region 106 included in the three-dimensional photonic crystal C shown in FIG. 17 are respectively “guided mode 1” and “guided mode” as in the first embodiment. 2 ”. The waveguide mode of light propagating through the mode conversion region 113 is referred to as “guided mode 5”.

  In the three-dimensional photonic crystal C shown in FIG. 17, light propagated through the waveguide region 103 is converted into light propagated through the mode conversion region 113 at the interface 105. The light propagating through the mode conversion region 113 is converted into light propagating through the external region 106 at the interface 107 and emitted to the external region 106.

  When the wavelength of light propagating through the external region 106 is λ, an xy cross section at a position 3λ away from the interface 107 between the mode conversion region 113 and the external region 106 in the + z direction is defined as an xy cross section A.

  FIG. 19A shows the calculation result of the electric field intensity distribution at the xy section A of the light emitted from the three-dimensional photonic crystal B including the mode conversion region 113 to the external region 106. FIG. 19 (b) shows the electric field strength distribution in the y-axis direction at x = 0 in FIG. 19 (a). The vertical axis represents the electric field strength normalized by the maximum value, and the horizontal axis represents the y-axis coordinate. Represents each. The electric field strength distribution was calculated using a finite difference time domain (FDTD) method.

  19A and 19B, the waveguide mode pattern of light emitted from the three-dimensional photonic crystal B including the mode conversion region 104 to the external region 106 is reflected with respect to the two axes of the x axis and the y axis. It can be seen that the shape is highly symmetric so as to be symmetric.

  Here, for comparison, the calculation result of the electric field intensity distribution when the structure of the mode conversion region is not mirror-symmetrical with respect to the x axis as in the waveguide region 103 is shown below. FIG. 20A shows a yz section of a three-dimensional photonic crystal including a mode conversion region 114 having a structure that is mirror-symmetric with respect to the y-axis and is not mirror-symmetrical with respect to the x-axis. FIG. 20B shows an xy cross section of the mode conversion region 114. Similar to the waveguide region 103, the mode conversion region 114 includes a photonic crystal basic structure 101 having a structure that is not mirror-symmetric with respect to the x-axis, and a linear defect provided in the photonic crystal basic structure 101. It is formed with the part 13. Here, the linear defect portion 13 is the same linear defect portion as the linear defect portion included in the mode conversion region 113 shown in FIG. 18 and Table 4.

  FIG. 21A shows the result of calculating the electric field intensity distribution in the xy section A of the light emitted from the three-dimensional photonic crystal B including the mode conversion region 113 to the external region 106. FIG. 21 (b) shows the electric field strength distribution in the y-axis direction at x = 0 in FIG. 21 (a), where the vertical axis represents the electric field strength normalized by the maximum value, and the horizontal axis represents the y-axis coordinate. Represents each.

  When comparing FIGS. 19A and 19B with FIGS. 21A and 21B, the light emitted from the mode conversion region 113 having a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis. It can be seen that the electric field intensity distribution (FIGS. 19A and 19B) has a higher symmetry.

  Here, the reason why the symmetry of the guided mode pattern of the emitted light is improved by using the mode conversion region having a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis is shown in the first embodiment. For the same reason.

  As in the first embodiment, there is a waveguide mode 4 that propagates in the xy section of the interface 105 at the interface 105 between the waveguide region 103 and the mode conversion region 113. The waveguide region 103 and the mode conversion region 113 are connected so as not to be converted. If the guided mode 1 light propagates at a frequency different from the frequency band in which the guided mode 4 light propagates, the guided mode 1 light is not converted to the guided mode 4 and mode conversion is performed. The light is converted into guided mode 3 light in the region 113.

Even if the frequency of the light of the waveguide mode 1 is included in the frequency band in which the light of the waveguide mode 4 propagates, the waveguide does not have a waveguide mode having the same polarization component at the same frequency as the waveguide mode 4 The area 103 and the mode conversion area 113 may be connected. Thereby, the light of the waveguide mode 1 is not converted into the light of the waveguide mode 4. Since modes that do not have the same polarization component do not couple with each other, when the light of the waveguide mode 1 reaches the interface 105, the light is not converted into the light of the waveguide mode 4 of the interface 105, It is converted into light of the waveguide mode 5 with high efficiency without loss .

  As described above, according to the present embodiment, by using the three-dimensional photonic crystal B including the mode conversion region 109 that is mirror-symmetrical with respect to two axes orthogonal to each other, the light of the waveguide mode pattern having high symmetry can be obtained. Can be injected.

  Further, by using the mode conversion structure included in the mode conversion region 113, the light of the waveguide mode 1 propagating through the waveguide region 103 can be gradually converted into the light of the waveguide mode 2 in the external region 106. . Thereby, light can be efficiently emitted to the external region 106.

  FIG. 22 shows a structure of a three-dimensional photonic crystal D including a mode conversion structure, which is Embodiment 3 of the present invention. The three-dimensional photonic crystal D includes a waveguide region 115 and a mode conversion region 113.

  The waveguide region 115 is configured by providing linear defect portions 14, 15, 16, 17, and 18 inside the photonic crystal basic structure 101.

  The mode conversion region 113 is composed of the photonic crystal basic structure 102, the photonic crystal basic structure 102 ′, and the tapered linear defect portion 13, and FIGS. 18A to 18C of Example 2 and FIG. It has the same structure as shown in Table 4. The waveguide region 115 and the mode conversion region 113 are connected so that light propagating in the mutual mode is coupled at the interface 105. The interface between the end of the mode conversion region 113 and the external region 106 is referred to as an interface 107.

  As shown in FIG. 22, the direction in which the first linear defect 14 in the waveguide region 115 extends is defined as the z-axis direction, and passes through the center of the first linear defect 14 in the xy cross section. Let two straight lines be the x-axis and the y-axis. In the xy section, the center of the first linear defect 14 in the waveguide region 115 and the center of the tapered linear defect 13 in the mode conversion region 113 coincide with each other.

  Each of the photonic crystal basic structures 101, 102, 102 'is formed by arranging the photonic crystal unit structures 100 all in the same direction and in contact with each other, and has a complete photonic band gap. The photonic crystal unit structure 100 has the same structure as that shown in FIGS. 4A and 4B of Example 1 and Table 1. The direction in which the columnar structure extends is the x′-axis direction and the z′-axis direction, and the stacking direction is the y′-axis direction. The x'y 'cross section has a structure that is mirror symmetric with respect to at least one straight line parallel to the y' axis and is not mirror symmetric with respect to any straight line parallel to the x 'axis.

  The photonic crystal basic structure 101 included in the waveguide region 115 has a photonic crystal so that the x, y, and z axis directions coincide with the x ′, y ′, and z ′ axis directions of the photonic crystal unit structure 100, respectively. It is formed by arranging unit structures 100.

  The waveguide region 115 is located in the photonic crystal structure 101 in the first linear defect portion 14 extending in the z-axis direction and in a layer different from the first linear defect portion 14, and in the z-axis direction. And the second linear defect portions 15 to 18 formed by deforming a part of the columnar structure extending in the direction. The photonic crystal basic structure 101 has a structure in which the photonic crystal unit structures 100 are arranged in the same direction in the x, y, and z directions and are in contact with each other, and has a complete photonic band gap.

  The waveguide region 115 is shown in FIGS. In the present embodiment, a structure including the second linear defect portions 15 to 18 in which the width of the columnar structure extending in the z-axis direction is 0.20P is shown. Detailed structural parameters of the waveguide region 115 are shown in Table 5. The defect width indicates the dimension in the x-axis direction within each layer of each of the linear defect portions 14 to 15, and is written as 14 w to 18 w in Table 5 and FIG. The defect height indicates the dimension of the linear defect portions 14 to 15 in the stacking direction, and is indicated as 14h to 18h in Table 5 and FIG.

  In the present embodiment, the outer region 106 has a uniform refractive index of 1.0 as in the first and second embodiments.

  The waveguide region 115 has a structure that is mirror-symmetric with respect to the y-axis and not mirror-symmetrical with respect to the z-axis in the xy cross section. The mode conversion region 113 has a mirror-symmetric structure with respect to two axes of the x axis and the y axis in the xy cross section.

  The waveguide mode of light propagating through the waveguide region 115 is referred to as “guided mode 6”. In addition, the waveguide mode of light propagating through the external region 106 is “guided mode 2” as in the first and second embodiments, and the waveguide mode of light propagating through the mode conversion region 113 is the same as in the second embodiment. Similarly, “guided mode 5” is assumed.

  In the three-dimensional photonic crystal D shown in FIG. 22, the light propagating through the waveguide region 115 is converted into light propagating through the mode conversion region 113 at the interface 105. The light propagating through the mode conversion region 113 is converted into light propagating through the external region 106 at the interface 107 and emitted to the external region 106.

  When the wavelength of light propagating through the external region 106 is λ, an xy cross section at a position 3λ away from the interface 107 between the mode conversion region 113 and the external region 106 in the + z direction is defined as an xy cross section A.

  FIG. 24A shows the result of calculating the electric field intensity distribution in the xy section A of the light emitted from the three-dimensional photonic crystal D including the waveguide region 115 and the mode conversion region 113 to the external region 106. FIG. FIG. 24 (b) shows the electric field strength distribution in the y-axis direction at x = 0 in FIG. 24 (a). The vertical axis represents the electric field strength normalized by the maximum value, and the horizontal axis represents the y-axis coordinate. Represents each. The electric field strength distribution was calculated using a finite difference time domain (FDTD) method.

  24A and 24B, the guided mode pattern of the light emitted from the three-dimensional photonic crystal D including the waveguide region 115 and the mode conversion region 113 to the external region 106 is the x-axis and the y-axis. It can be seen that it has a high symmetry that is mirror-symmetric with respect to the two axes.

  Here, for comparison, the calculation result of the electric field intensity distribution in the case where the structure of the mode conversion region is not mirror-symmetric with respect to the x-axis is shown below. FIG. 25A shows a yz cross section of a three-dimensional photonic crystal including a mode conversion region 114 that is mirror-symmetric with respect to the waveguide region 115 and the y-axis and is not mirror-symmetrical with respect to the x-axis. The mode conversion region 114 has the same structure as that shown in FIG.

  FIG. 26A shows the electric field intensity distribution in the xy section A of the light emitted from the three-dimensional photonic crystal D including the waveguide region 115 and the mode conversion region 114. FIG. 26B shows the electric field strength distribution in the y-axis direction at x = 0 in FIG. 26A, where the vertical axis represents the electric field strength normalized by the maximum value, and the horizontal axis represents the y-axis coordinate. Represents.

Comparing FIGS. 24A and 24B with FIGS. 26A and 26B, the electric field of light emitted from the mode conversion region 113 having a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis. It can be seen that the intensity distribution (FIGS. 24A and 24B) has a shape with higher symmetry.
The reason why the symmetry of the guided mode pattern of the emitted light is improved by using the mode conversion region having a mirror-symmetric structure with respect to the two axes of the x axis and the y axis is the same as the reason described in the first embodiment. It is.

  In the interface 105 between the waveguide region 115 and the mode conversion region 113, there is a waveguide mode 4 that propagates in the xy section of the interface 105. In this embodiment, the waveguide mode 6 is not converted to the waveguide mode 4. The waveguide region 115 and the mode conversion region 113 are connected.

  If the light in the guided mode 6 propagates at a frequency different from the frequency band in which the light in the guided mode 4 propagates, the light in the guided mode 6 is not converted into the guided mode 4, and the mode conversion region 113 is converted into the light of the waveguide mode 5.

  Even if the frequency of the light of the waveguide mode 6 is included in the frequency band in which the light of the waveguide mode 4 propagates, the waveguide has a frequency that is the same as that of the waveguide mode 4 and that does not have the same polarization component. The region 115 and the mode conversion region 113 may be connected. Thereby, the light of the waveguide mode 6 is not converted into the light of the waveguide mode 4. Since modes that do not have the same polarization component are not coupled to each other, when the light of the guided mode 6 reaches the interface 105, the light is not converted into the guided mode 4 light of the interface 105, but is guided in the mode conversion region 113. It is converted into light of wave mode 5 with high efficiency without loss.

  As described above, in this embodiment, by using the three-dimensional photonic crystal B including the mode conversion region 113 having a mirror-symmetric structure with respect to two axes orthogonal to each other, light having a waveguide mode pattern having high symmetry can be obtained. Can be injected. Further, in this embodiment, it is possible to propagate light of a single waveguide mode by using the waveguide region having the above-described structure.

  In addition, you may form the linear defect parts 15-18 which comprise a waveguide by displacing a part of columnar structure.

  Hereinafter, a photonic crystal light-emitting element that is Embodiment 4 of the present invention using the three-dimensional photonic crystal described in Embodiments 1 to 3 will be described. The photonic crystal light-emitting device of this example includes a resonator provided by forming a point-like defect inside the three-dimensional photonic crystal basic structure described in Examples 1 to 3, and a linear defect. And a mode conversion structure are provided.

  The point defect can function as a resonator having a resonance mode at a desired frequency within the complete photonic band gap by optimizing the shape and medium. A light emitting medium (gain medium) having a resonance wavelength in the emission spectrum is arranged inside the resonator, and the light is excited by supplying energy to the light emitting medium from the outside by electromagnetic waves or current. generate. Light generated from the light emitting medium is amplified in the resonator.

  When a waveguide having a waveguide mode is arranged in the vicinity of such a point defect resonator at a frequency that the resonance mode of the resonator has, the light generated inside the resonator and amplified light is guided by the waveguide. Coupled with light propagating in wave mode, it is extracted out of the resonator. The extracted light propagates in the waveguide mode of the waveguide and the mode conversion structure. Thereby, light emitting elements, such as a laser and LED with high efficiency, are realizable.

  FIG. 27 shows the structure of the photonic crystal light-emitting element of this example. In FIG. 27, a resonator, an electrode, and a carrier conduction path are provided in the three-dimensional photonic crystal shown in the second embodiment (FIG. 17) as a representative of the three-dimensional photonic crystals described in the first to third embodiments. Has a structure.

  A direction in which the linear defect portion 10 extends in the waveguide region 103 is defined as a z-axis direction, and two straight lines that pass through the center of the linear defect portion 10 in the xy section and are orthogonal to each other are defined as an x-axis and a y-axis.

  The photonic crystal unit structure 100 has the structure shown in FIG. 4 in the first embodiment. The photonic crystal unit structure 100 is oriented in the x, y, and z-axis directions so that each surface is in contact with the photonic crystal unit structure 100 facing the same direction. The aligned structure has a complete photonic band gap.

  The light emitting device shown in FIG. 27 includes a resonator 116 formed by providing a point defect 19 in the three-dimensional photonic crystal basic structure 101, a p-type electrode 117, a p-type carrier conduction path 118, and an n-type. It has an electrode 119 and an n-type carrier conduction path 120.

  In the resonator 116, an active portion that exhibits a light emitting action by carrier injection is formed. Holes are supplied to the resonator 116 via the p-type electrode 117 and the p-type carrier conduction path 118, and electrons are supplied to the resonator 116 via the n-type electrode 119 and the n-type carrier conduction path 120. The supplied holes and electrons are combined inside the resonator 116 to emit light, and laser oscillation occurs.

  The waveguide region 103 has the same structure as the structure shown in FIGS. 8A to 8C of the first embodiment, and is a structure that is mirror symmetric with respect to the y axis and is not mirror symmetric with respect to the x axis in the xy section. Have The waveguide region 103 has a waveguide mode at a frequency that the resonance mode of the resonator 116 has. By arranging the waveguide region 103 at an appropriate position with respect to the resonator 116, light existing in the resonance mode of the resonator 116 can be efficiently converted into light propagating in the waveguide mode of the waveguide. it can.

  The waveguide region 103 and the mode conversion region 113 are connected by an interface 105. The mode conversion region 113 has the same structure as that shown in FIGS. 18A to 18C of the second embodiment, and has a mirror-symmetric structure with respect to the two axes of the x axis and the y axis in the xy section.

  In addition, the end of the mode conversion region 113 is in contact with the external region 106 at the interface 107.

  As in the second embodiment, the waveguide mode of light propagating through the waveguide region 103 is “guided mode 1”, and the waveguide mode of light propagating through the external region 106 is “guided mode 2”. A waveguide mode of light propagating through the mode conversion region 113 is referred to as “guided mode 5”.

  At the interface 105 between the waveguide region 103 and the mode conversion region 113, the waveguide mode 4 that propagates along the xy section of the interface 105 exists. However, also in this embodiment, the waveguide region 103 and the mode conversion region 113 are connected so that there is no waveguide mode having the same polarization component at the same frequency as the waveguide mode 1 in the waveguide mode 4. Yes.

  In such a photonic crystal light emitting device, light generated and amplified by the resonator 116 is converted into light propagating in the waveguide mode of the waveguide region 103 and propagates through the waveguide region 103. Then, the light is converted into light propagating through the mode conversion region 113 at the interface 105. The light propagating through the mode conversion region 113 is converted into light propagating through the external region 106 at the interface 107 and emitted to the external region 106.

  As described in the previous embodiment, in this embodiment, by using the mode conversion region 113 having a mirror-symmetric structure with respect to the two axes of the x-axis and the y-axis in the xy cross section, the outer region 106 is highly symmetrical. The light of the waveguide mode pattern which it has can be inject | emitted. In addition, since a light having a waveguide mode pattern having high symmetry can be emitted to the external region 106, a high-performance laser device can be realized.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  It is possible to provide a three-dimensional photonic crystal and a light emitting device that can propagate light to an external region with high efficiency.

100 photonic crystal unit structure 101 (first) photonic crystal basic structure 102 (second) photonic crystal basic structure 102 '(third) photonic crystal basic structure 103 waveguide region 104 mode conversion region 106 external region

Claims (9)

A three-dimensional photonic crystal having a waveguide region and a mode conversion region,
The waveguide region has a first photonic crystal basic structure and a first defect provided inside the first photonic crystal basic structure;
The mode conversion region has a second photonic crystal basic structure, a third photonic crystal basic structure, and a second defect portion,
The waveguide region and the mode conversion region are connected so that light propagating in each other mode is coupled at the first interface;
Each of the first photonic crystal basic structure, the second photonic crystal basic structure, and the third photonic crystal basic structure is configured by arranging a plurality of photonic crystal unit structures,
The photonic crystal unit structure has the second axis in a cross section parallel to the second and third axes when three axes orthogonal to each other are defined as a first axis, a second axis, and a third axis. A straight line parallel to the axis is not mirror symmetric but has a mirror symmetric structure with respect to the straight line parallel to the third axis,
The direction in which light propagates through the waveguide region and the mode conversion region is defined as a first direction, and two directions orthogonal to the first direction and orthogonal to each other are defined as a second direction and a third direction. When
In the first and second photonic crystal basic structures, the first direction, the second direction, and the third direction are the first axis of the photonic crystal unit structure, the second direction, respectively. The photonic crystal unit structure is arranged so as to coincide with the direction in which the axis and the third axis extend,
In the first cross section parallel to the second and third directions, the second photonic crystal basic structure extends from the central axis extending in the second direction and passing through the center of the second defect portion. Arranged on one side in the third direction,
In the first cross section, the photonic crystal unit structure is arranged so that the third photonic crystal basic structure has a mirror-symmetrical structure with the second photonic crystal basic structure with respect to the central axis. Composed of
The second photonic crystal basic structure and the third photonic crystal basic structure are connected by a connection surface that is parallel to the first and second directions and passes through the center of the second defect portion,
The mode conversion region has a mirror-symmetric structure with respect to straight lines extending in the second direction and the third direction through the center of the second defect portion in the first cross section, respectively. 3D photonic crystal.   The waveguide region and the mode conversion region are connected so that there is no mode having the same polarization component at the same frequency as light propagating through the first interface and propagating through the waveguide region. The three-dimensional photonic crystal according to claim 1. The photonic crystal unit structure is
A plurality of first columnar structures spaced apart from each other, and a first layer and a third layer periodically arranged in a direction orthogonal to the direction in which the first columnar structures extend;
A plurality of second columnar structures each extending in a direction perpendicular to the direction in which the first columnar structures extend are periodically arranged in a direction perpendicular to the direction in which the second columnar structures extend. Having a second layer and a fourth layer;
The first columnar structure included in the first layer and the first columnar structure included in the third layer are shifted from each other by a half cycle in a direction orthogonal to a direction in which the first columnar structure extends. The second columnar structure included in the second layer and the second columnar structure included in the fourth layer are orthogonal to the direction in which the second columnar structure extends. Placed half a cycle away from each other,
The first layer to the fourth layer are laminated in this order,
The first and second columnar structures are formed of a first medium, and the other regions are formed of a second medium different from the first medium. 3. A three-dimensional photonic crystal according to 2. Discretely arranged between the first layer and the fourth layer at a three-dimensional intersection of the first columnar structure and the second columnar structure in a plane parallel to the layers. An additional layer including at least one layer including a discrete structure is disposed;
The first columnar structure, the second columnar structure, and the discrete structure are formed of a first medium, and the other regions are formed of a second medium different from the first medium. The three-dimensional photonic crystal according to claim 3. The first defect is the pre-SL and the first line defect member extending in the same direction as the first or the second columnar structure extending direction, Ru extend in the same direction as the line defect member of said first three-dimensional photonic crystal according to claim 3 or 4, characterized in that it comprises a second linear defects, the. 6. The three-dimensional photonic crystal according to claim 5 , wherein the first linear defect portion is formed of a medium having the same refractive index as that of the first medium .   The said 2nd defect part is a linear defect part comprised by the medium which has a refractive index more than the refractive index of the medium which comprises the said photonic crystal basic structure, Any one of Claim 1 to 6 characterized by the above-mentioned. The three-dimensional photonic crystal according to claim 1.   The linear defect constituting the second defect portion is a tapered defect whose shape in a plane orthogonal to the direction in which the linear defect portion extends changes with respect to the direction in which the linear defect portion extends. The three-dimensional photonic crystal according to claim 7, wherein the three-dimensional photonic crystal is present. A light-emitting element using the three-dimensional photonic crystal according to any one of claims 1 to 7,
Having a resonator formed by providing a point defect inside the photonic crystal basic structure;
The resonator and the waveguide region are arranged so that at least a part of the light existing in the mode of the resonator is coupled with the light propagating in the waveguide mode of the waveguide region,
A gain medium is disposed inside the resonator, and light generated by exciting the gain medium is amplified by the resonator and propagates through the waveguide region and the mode conversion region to thereby generate the three-dimensional photo. light - emitting element characterized in that it is emitted to the outside region of the photonic crystal.