JP4185697B2 - Two-dimensional photonic crystal surface emitting laser array and two-dimensional photonic crystal surface emitting laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a two-dimensional photonic crystal surface emitting laser array and a two-dimensional photonic crystal surface emitting laser.
[0002]
[Prior art]
Conventionally, various surface emitting lasers that emit laser light perpendicularly from a substrate surface have been developed and studied. Surface-emitting lasers can integrate (array) many elements on the same substrate, and coherent light is emitted in parallel from each element, so in the fields of parallel optical pickup, parallel optical transmission, and optical parallel information processing Applications are expected.
[0003]
As this type of surface emitting laser, a two-dimensional photonic crystal surface emitting laser using a photonic crystal is disclosed in Japanese Patent Application Laid-Open No. 2000-332351. A photonic crystal is a crystal having a refractive index period that is equal to or smaller than the wavelength of light. In a dielectric multidimensional periodic structure, the same principle as that in which a band gap occurs in an electronic state in a semiconductor crystal Thus, a wavelength band (photonic band gap) that suppresses light guiding is generated, and light can be confined in two dimensions or three dimensions.
[0004]
The two-dimensional photonic crystal surface emitting laser described in the above publication includes a photonic crystal periodic structure in which a refractive index period is two-dimensionally arranged in the vicinity of an active layer that emits light by carrier injection, and is resonated by the photonic crystal. As a result, surface emission occurs.
[0005]
[Problems to be solved by the invention]
By the way, when an attempt is made to array the two-dimensional photonic crystal surface emitting laser, since the light resonance direction is the in-plane direction, crosstalk occurs between adjacent lasers. In particular, if the polarization direction of light is not fixed, the light traveling direction (pointing vector) in the plane also faces in all directions, and crosstalk occurs regardless of how the lasers are arranged.
[0006]
Therefore, an object of the present invention is to provide a two-dimensional photonic crystal surface emitting laser array that can suppress the occurrence of crosstalk.
[0007]
Another object of the present invention is to provide a two-dimensional photonic crystal surface emitting laser in which an optical sensor for monitoring laser output can be easily arranged.
[0008]
Configuration, operation and effect of the invention
In order to achieve the above object, the first invention is a photonic crystal period in which an active layer that emits light by carrier injection is sandwiched between cladding layers, and a refractive index period is two-dimensionally arranged in the cladding layer or the active layer. in the two-dimensional photonic crystal surface-emitting laser array having a structure, in a direction different from the Poynting vector upper electrode provided on the clad layer is in the photonic crystal periodic structure within 45 the Poynting vector It is arranged in the range which intersects at the angle of ~ 90 ° .
[0009]
In the first invention, light amplified by resonance by the photonic crystal is emitted as coherent light from the light emitting region around the upper electrode. The upper electrode is a direction different from the traveling direction of light (Poynting vector) in the photonic crystal periodic structure in, since it is arranged within a range intersecting at 45 ° to 90 ° from the Poynting vector, adjacent Crosstalk between laser elements is less likely to occur.
[0010]
In particular , it is important to align the polarization direction of light. For this purpose, it is preferable that the unit cell shape of the photonic crystal periodic structure is an ellipse. In addition, the refractive index of the medium may be adjusted, or disturbances (lattice defects) may be introduced into the periodic structure. The lattice shape of the photonic crystal periodic structure is arbitrary, such as a square lattice or a triangular lattice, but a square lattice can be easily designed.
[0011]
According to a second aspect of the present invention, there is provided a photonic crystal periodic structure in which an active layer that emits light by carrier injection is sandwiched between cladding layers and a refractive index period is two-dimensionally arranged in the cladding layer or the active layer. in dimension photonic crystal surface-emitting laser, characterized in that the optical sensor for monitoring the laser output is provided at a position for receiving a plane substantially perpendicular to the pointing vector in the photonic crystal periodic structure in And
[0012]
In the two-dimensional photonic crystal surface-emitting laser, surface emission is performed using first-order diffraction, but second-order diffracted light is also leaked. In the second invention, the leaked light is detected by an optical sensor. Can be juxtaposed with the substrate, and the arrangement of the photosensor becomes easy.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a two-dimensional photonic crystal surface emitting laser array and a two-dimensional photonic crystal surface emitting laser according to the present invention will be described with reference to the accompanying drawings.
[0014]
(Refer to basic structure and resonance action, Fig. 1 and Fig. 2)
The two-dimensional photonic crystal surface emitting laser array according to the present invention is a two-dimensional photonic crystal surface emitting laser shown in FIG. 1 arranged in parallel on a single substrate.
[0015]
In the two-dimensional photonic crystal surface emitting laser 10, a lower clad layer 12, an active layer 13, and an upper clad layer 14 are roughly stacked on a substrate 11. A nick crystal 20 is incorporated.
[0016]
The substrate 11 is made of, for example, an n-type InP semiconductor material. The lower cladding layer 12 and the upper cladding layer 14 are, for example, n-type and p-type InP semiconductor layers, respectively, and have a refractive index lower than that of the active layer 13. The two-dimensional photonic crystal 20 is configured by holes (photonic crystal periodic structure 21) formed in the lower cladding layer 12, and a medium having a refractive index different from that of the lower cladding layer 12 is arranged in a two-dimensional period. It consists of square and triangular lattices. The pores may be filled with SiN or the like. The active layer 13 has, for example, a multiple quantum well structure using an InGaAs / InGaAsP semiconductor material, and emits light when carriers are injected.
[0017]
A double heterojunction is formed by sandwiching the active layer 13 between the lower clad layer 12 and the upper clad layer 14, and carriers contributing to light emission are concentrated in the active layer 13 by confining carriers.
[0018]
A lower electrode 16 and an upper electrode 17 made of gold or the like are formed on the bottom surface of the substrate 11 and the upper surface of the upper cladding layer 14. By applying a voltage between the electrodes 16 and 17, the active layer 13 emits light, and light leaked from the active layer 13 enters the two-dimensional photonic crystal 20. Light whose wavelength matches the lattice spacing of the two-dimensional photonic crystal 20 is amplified by resonance by the two-dimensional photonic crystal 20. Thereby, coherent light is surface-emitted from the upper surface of the upper clad layer 14 (the light emitting region 18 located around the electrode 17).
[0019]
Here, the resonance action of the two-dimensional photonic crystal 20 composed of a square lattice as shown in FIG. 2 will be described. The two-dimensional photonic crystal 20 is composed of a square lattice formed in the first medium 12 with the same period in two directions orthogonal to the second medium 21 such as holes. The square lattice has typical directions of the Γ-X direction and the Γ-M direction. If the distance between the second media 21 adjacent in the Γ-X direction is a, a basic lattice E having a square with a side of a with the second medium 21 as a lattice point is formed.
[0020]
When the light L whose wavelength λ coincides with the lattice interval a of the basic grating E travels in the Γ-X direction, the light L is second-order diffracted at the lattice point. Among these, only the light diffracted in the directions of 0 °, ± 90 °, and 180 ° with respect to the traveling direction of the light L satisfies the Bragg condition. Furthermore, since there are also lattice points in the traveling direction of the light diffracted in the directions of 0 °, ± 90 °, and 180 °, the diffracted light is again in the directions of 0 °, ± 90 °, and 180 ° with respect to the traveling direction. Diffraction.
[0021]
When the light L repeats one or more times of second-order diffraction, the diffracted light returns to the original lattice point, resulting in a resonance effect. Further, light that is first-order diffracted in a direction perpendicular to the paper surface also satisfies the Bragg condition. For this reason, light amplified by resonance is emitted through the upper clad layer 14 and has a surface emission function. In addition, since this phenomenon occurs at all lattice points, coherent laser oscillation is possible over the entire surface.
[0022]
(Photonic crystal periodic structure and pointing vector orientation, see FIGS. 3-5)
In order to prevent crosstalk, which is the subject of the present invention, it is important to make the traveling direction (pointing vector) of light in the photonic crystal 20 constant, that is, to align the polarization direction of light. In order to align the polarization direction, it is possible to adjust the refractive index of the medium 21 or introduce a disorder (lattice defect) in the periodic structure. However, in this embodiment, the photo incorporated in the lower cladding layer 12 is used. The unit cell shape forming the nick crystal periodic structure 21 was an elliptical shape. By making the periodic structure 21 into an ellipse, depending on the mode determined from the photonic band, when the major axis direction of the ellipse and the direction of the pointing vector P are the same (see FIG. 3A, modes A and D), There are different cases (see FIG. 3B, modes B and C).
[0023]
In any mode, the upper electrodes 17 formed on the upper surface of the upper clad layer 14 need not be arranged in the same direction as the pointing vector P in order to array the laser elements as narrowly as possible.
[0024]
4 and 5 show the positional relationship of each surface emitting laser 10 (upper electrode 17) with respect to the direction of the pointing vector P and the electric field (polarized light) D. FIG. As shown in FIG. 4, when the surface emitting laser array 30 is configured by arranging the upper electrodes 17 in the same direction as the pointing vector P, crosstalk occurs between adjacent lasers 10, and laser light emitted from each laser 10. May not be controlled independently. In order to prevent crosstalk, it is necessary to set the interval between the lasers 10 large, and this increases the size of the array.
[0025]
On the other hand, as shown in FIG. 5, when the surface emitting laser array 30 is configured by arranging the upper electrodes 17 in the direction orthogonal to the direction of the pointing vector P, the crosstalk between the adjacent lasers 10 is reduced. The interval between the lasers 10 can be set small.
[0026]
In order to reduce the crosstalk, it is most desirable to arrange the upper electrodes 17 in a direction orthogonal to the pointing vector P. However, even if the upper electrodes 17 are arranged in a direction intersecting with 45 °, the array is formed by suppressing the crosstalk. The effect of downsizing 30 is exhibited.
[0027]
(Optical sensor arrangement, see FIG. 6)
FIG. 6 shows a state in which an optical sensor 35 for monitoring the laser output is attached to the laser array 30 in which the two-dimensional photonic crystal surface emitting laser 10 is arrayed. Here, the optical sensor 35 is provided at a position orthogonal to the pointing vector P.
[0028]
In the two-dimensional photonic crystal surface emitting laser 10, laser light is emitted in the direction perpendicular to the paper surface of FIG. 6 using first-order diffraction, but second-order diffracted light also leaks from the side surface of the substrate 11. By providing the optical sensor 35 at a position substantially orthogonal to the pointing vector P and detecting the second-order diffracted light, the laser output can be monitored. In this case, the optical sensor 35 only needs to be juxtaposed with the substrate 11, and the arrangement is easy. The optical sensor 35 may be arranged not only in the laser array 30 but also in the surface emitting laser 10 alone.
[0029]
Incidentally, in the VCSEL known as a conventional surface emitting laser, it is necessary to arrange the optical sensor for monitoring on the lower surface of the substrate opposite to the emission surface, which makes it difficult to arrange the optical sensor. .
[0030]
(Other embodiments)
The two-dimensional photonic crystal surface-emitting laser array and the two-dimensional photonic crystal surface-emitting laser according to the present invention are not limited to the above-described embodiments, and can be variously modified within the scope of the gist.
[0031]
In particular, the semiconductor layer, photonic crystal, electrode material, structure for aligning the polarization of light, lattice shape, and the like are arbitrary. In the above embodiment, the photonic crystal periodic structure is provided in the lower cladding layer. However, the photonic crystal periodic structure may be provided in the vicinity of the active layer in the upper cladding layer or in the active layer.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a basic configuration of a surface emitting laser that is one unit of a two-dimensional photonic crystal surface emitting laser array according to the present invention.
FIG. 2 is an explanatory view showing a resonance action of the surface emitting laser.
FIG. 3 is an explanatory diagram showing the shape of a photonic crystal periodic structure and the direction of a pointing vector.
FIG. 4 is an explanatory diagram showing an arrangement relationship between the direction of a pointing vector and a surface emitting laser, and shows an undesirable relationship.
FIG. 5 is an explanatory diagram showing a positional relationship between a pointing vector direction and a surface emitting laser, and shows a preferable relationship.
FIG. 6 is a plan view showing a state in which an optical sensor is provided in a two-dimensional photonic crystal surface emitting laser array.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Two-dimensional photonic crystal surface emitting laser 11 ... Substrate 12 ... Lower clad layer (1st medium)
DESCRIPTION OF SYMBOLS 13 ... Active layer 14 ... Upper clad layer 16 ... Lower electrode 17 ... Upper electrode 20 ... Two-dimensional photonic crystal 21 ... Photonic crystal periodic structure (2nd medium)
30 ... Two-dimensional photonic crystal surface emitting laser array 35 ... Optical sensor P ... Pointing vector

Claims (4)

A two-dimensional photonic crystal surface emitting laser array comprising a photonic crystal periodic structure in which an active layer that emits light by carrier injection is sandwiched between clad layers and a refractive index period is two-dimensionally arranged in the clad layer or the active layer In
Wherein the Poynting vector upper electrode provided on the clad layer in the photonic crystal periodic structure in a different direction, that are arranged within a range intersecting at 45 ° to 90 ° from the Poynting vector,
A two-dimensional photonic crystal surface emitting laser array. 2-dimensional photonic crystal surface-emitting laser array of claim 1 Symbol mounting, characterized in that said photonic crystal periodic structure are arranged in a square lattice. 3. The two-dimensional photonic crystal surface emitting laser array according to claim 1, wherein the unit cell shape of the photonic crystal periodic structure is an ellipse. In a two-dimensional photonic crystal surface emitting laser comprising a photonic crystal periodic structure in which an active layer emitting light by carrier injection is sandwiched between clad layers and a refractive index period is two-dimensionally arranged in the clad layer or the active layer ,
The light sensor for monitoring the laser output is provided at a position for receiving a plane substantially perpendicular to the pointing vector in the photonic crystal periodic structure within
A two-dimensional photonic crystal surface emitting laser characterized by

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