JP4908387B2 - Light modulator - Google Patents

Description

  The present invention relates to an optical modulator, and more particularly to an optical modulator using an electro-optic crystal having a secondary electro-optic effect.

  Currently, demands for large capacity, high speed and high functionality of optical communication systems are increasing rapidly. One of the promising optical signal processing devices used in such an optical communication system is an optical modulator, and an optical modulator using an electro-optic crystal is being developed.

An optical phase modulator using an electro-optic crystal changes the phase of light by changing the speed of light passing through the crystal by changing the refractive index of the crystal. When the electro-optic crystal is installed in one of the optical waveguides of the Mach-Zehnder interferometer and the Michelson interferometer, the light intensity of the output of the interferometer changes according to the voltage applied to the crystal. These interferometers can be used as optical switches and optical modulators. In Patent Document 1, KTN (KTa _1-x Nb _x O ₃ (0 <x <1)) and KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1) are used as electro-optic crystals. , 0 <y <1)) is disclosed.

  1A and 1B show a configuration of an optical phase modulator using an electro-optic crystal disclosed in Patent Document 1. FIG. 1A and 1B, the optical phase modulator has a positive electrode 2 and a negative electrode 3 that are equal in width on opposite surfaces of a rectangular electro-optic crystal 1. In such a configuration, when a voltage V is applied between the positive electrode 2 and the negative electrode 3, the phase of light propagating through the electro-optic crystal 1 changes according to the voltage V.

International Publication No. 2006/137408 Pamphlet

  Since KTN or KLTN is a dielectric crystal having a cubic crystal structure and a large secondary electro-optic effect, low-voltage driving can be realized without depending on polarization, and a large secondary electro-optic effect can be obtained depending on the composition. Therefore, it is preferable to use it for an optical modulator.

  In particular, since the relative permittivity changes greatly in the vicinity of the ferroelectric transition, it is preferable to operate by setting the vicinity of the phase transition as the operating temperature.

  However, in this temperature range, the dielectric constant of KTN or KLTN is high as described above, so that a large refractive index change can be caused efficiently, which is very effective from the viewpoint of operating the optical modulator efficiently. At the same time, the electric capacity between the positive electrode and the negative electrode is increased. For example, when switching is performed, charging / discharging corresponding to the electric capacity is performed, but power consumption corresponding to the switching speed is generated. Therefore, when KTN or KLTN is used, the electric capacity becomes high at an operating temperature at which modulation can be performed efficiently, so that the burden on the drive power supply becomes very large, making practical application difficult.

  In addition to KTN and KLTN, there is a demand for reducing the burden on the driving power source due to the high electric capacity without impairing the modulation effect for all electro-optic crystals having secondary electro-optic effect. .

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical modulator capable of reducing the burden on the drive power supply.

In order to achieve such an object, the invention described in claim 1 is an optical modulator, and is arranged on a first surface of an electro-optic crystal having a secondary electro-optic effect and the electro-optic crystal. A first electrode formed, and a second electrode disposed on a second surface opposite to the first surface of the electro-optic crystal ;
A concave portion formed on at least one of the first surface, the second surface, the incident light incident surface, and the two opposing surfaces other than the emitting surface of the electro-optical crystal; Has at least a region having a width narrower than the width of the first surface, and the width of the first electrode and the width of the second surface are wider than the width of the region, The region is formed between the first electrode and the second electrode, and the region is formed by the recess .

According to a fourth aspect of the present invention, in the first aspect of the present invention, the concave portion is provided with a low dielectric constant material having a dielectric constant lower than that of the electro-optic crystal. To do.

According to a sixth aspect of the present invention, in the first or second aspect of the invention, the width of the region is larger than the diameter of incident light incident on the optical modulator, and the incident light is incident on the region. It is incident.

The invention according to claim 7 is the invention according to any one of claims 1 to 3 , wherein the material of the first electrode and the second electrode is Pt, Co, Ge, Au, Pd, Ni, Ir , Pt, Se, Cs, Rb, K, Sr, Ba, Na, Ca, Li, Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb , Ag, Al, V, Nb, Ti, Zn, Sn, B, Hg, Cr, Si, Sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, Be, Rh It is characterized by.

  According to the present invention, the width of a part of the region to which the electric field is applied for modulation of the electro-optic crystal is narrower than at least one of the surfaces on which the electrodes are arranged. Therefore, it is possible to reduce the load on the drive power source.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
In one embodiment of the present invention, KTN (KTa _1-x Nb _x O ₃ (0 <x <1)) and KLTN (K _1-y Li _y Ta _1-x Nb _x O ₃ (0 <x <1, 0 <y <1)), etc., and an optical modulator using an electro-optic crystal having a secondary electro-optic effect, wherein electrodes are arranged on opposite surfaces of the electro-optic crystal, , A width of a part of a region between the two electrodes, that is, a width of a part of a region to which an electric field is applied by the two electrodes is larger than a width of at least one of surfaces on which the electrodes are arranged It is narrow. That is, in the electro-optic crystal, the electrode is not disposed, and at least one of two opposing surfaces other than the incident surface on which light is incident and the emitting surface to be emitted, between the incident surface and the emitting surface, A part of the region along the light passing direction is removed.

  In one embodiment of the present invention, it is preferable that the region where the width is narrowed is a region through which light passes (light modulation region). The light modulation region is a region where an electric field is applied to the electro-optic crystal constituting the light modulator and through which light to be modulated passes. In the case of this configuration, the electrode of the electro-optic crystal is not disposed, and at least one of the two opposing surfaces other than the incident surface and the emitting surface is left at least a region larger than the diameter of the incident light. Thus, a part of area | region along the direction through which light passes between an entrance plane and an output surface is removed.

  In one embodiment of the present invention, when the width of the region through which light passes in the electro-optic crystal is narrower than the width of both surfaces on which the electrodes are disposed (detailed in the first and second embodiments) By removing the electro-optic crystal, which is the dielectric in the narrowed region, the capacitor can be obtained without increasing the area of the electrodes or reducing the distance between the electrodes, that is, the thickness of the electro-optic crystal. It is possible to reduce the electric capacity of the optical modulator provided with electrodes on the opposing surfaces of the electro-optic crystal.

  In another embodiment of the present invention, when the width of the region through which light passes in the electro-optic crystal is narrower than one width of the surface on which the electrode is disposed (detailed in the third embodiment). Although it is one of the electrodes forming the capacitor, the area of the electrode can be increased, so that the electric capacity can be reduced.

  Now, since KTN and KLTN have a large dielectric constant, the electric capacity of the modulator increases and places a burden on the drive power supply, but the large dielectric constant allows efficient modulation operation. Therefore, the electro-optic crystal having a large dielectric constant such as KTN or KLTN can realize the efficiency of the modulation operation, but the modulation capacitor has a large electric capacity and leads to an increase in the load on the drive power supply. And the burden on the drive power supply.

  Therefore, in the present invention, an electric field is applied for modulation of the electro-optic crystal in order to achieve a reduction in the electric capacity of the optical modulator while exhibiting a highly efficient modulation operation which is an advantage of a large dielectric constant. A part of the region to be removed, that is, the region between the two electrodes arranged on the opposite surfaces of the electro-optic crystal is removed. That is, in the region between the two electrodes of the electro-optic crystal, by removing one region along the light traveling direction from the incident surface toward the emitting surface, an electric field is generated in the light modulation region. Since an applied electro-optic crystal is used, a highly efficient modulation operation can be realized, and part of the region through which light does not pass is removed from the electro-optic crystal to which an electric field is applied. The electric capacity of can be reduced. Therefore, the burden on the drive power supply can be reduced while increasing the modulation efficiency.

  In this specification, the “width” is generated between each electrode (electro-optic crystal, electrode, etc.) included in the optical modulator and the traveling direction of light passing through the optical modulator and between the electrodes. It is defined as the length in the direction perpendicular to both the electric field directions. Therefore, for each member included in the optical modulator, the “thickness” refers to the length in the direction matching the electric field direction.

The above KTN and KLTN exhibit a large secondary electro-optic effect when an electric field is applied in the crystal axis direction. The value is (1200 to 8000 pm / V), which is significantly larger than the nonlinear constant 30 pm / V of LiNO ₃ (LN), which is a material having a primary electro-optic effect. Furthermore, KTN and KLTN can change the phase transition temperature from paraelectricity to ferroelectricity from almost absolute zero to 400 ° C. by changing the composition ratio of Ta and Nb. Therefore, the operating temperature can be set as desired, such as room temperature, without using a temperature controller. Thus, KTN and KLTN are preferable materials for the optical modulator.

In one embodiment of the present invention, the material used as the modulation region of the optical modulator is not limited to KTN or KLTN. An object of one embodiment of the present invention is not to perform a modulation operation at a low voltage, but to reduce the capacitance of the electrode when a material having a secondary electro-optic effect is applied to the modulation region. Therefore, the material used for the modulation material is not limited to KTN and KLTN, but LiTaO ₃ , LiIO ₃ , KNbO ₃ , KTiOPO ₄ , BaTiO ₃ , SrTiO ₃ , Ba _1-x Sr _x TiO ₃ (0 <x <1). _{, Ba 1-x Sr x Nb} 2 O 6 (0 <x <1), Sr 0.75 Ba 0.25 Nb 2 O 6, Pb 1-y La y Ti 1-x Zr x O 3 (0 <x <1,0 <Y <1), Pb (Mg _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ , KH ₂ PO ₄ , KD ₂ PO ₄ , (NH ₄ ) H ₂ PO ₄ , BaB ₂ O ₄ , LiB ₃ O ₅ , CsLiB ₆ O ₁₀ , GaAs, CdTe, GaP, ZnS, ZnSe, ZnTe, CdS, CdSe, and ZnO, and any dielectric material having a secondary electro-optic effect may be used.

  The material of the electrode for applying an electric field to the electro-optic crystal is Pt, Co, Ge, Au, Pd, Ni, Ir, Pt, Se, Cs, Rb, K, Sr, Ba, Na, Ca, Li Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb, Ag, Al, V, Nb, Ti, Zn, Sn, B, Hg, Cr , Si, Sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, Be, and Rh can be used. Further, an alloy using a plurality of the above materials may be used.

(First embodiment)
In this embodiment, among the regions to which the electric field is applied of the electro-optic crystal constituting the optical modulator, a region whose width is narrowed is a light modulation region that is a region through which incident light passes. That is, in order to achieve a reduction in the electric capacity of the optical modulator while exhibiting a high-efficiency modulation operation, at least an electro-optic crystal such as KTN or KLTN is left in the region that substantially functions as the light modulation region. Other than that, the extra electro-optic crystal is removed.

  Thus, the width of at least one of the surfaces on which the electrodes are arranged and the width of the electrodes arranged on the surfaces of the electro-optic crystal are made wider than the width of the light modulation region (region through which light passes). Thus, the electric field strength to the light modulation region can be increased while reducing the electric capacity of the optical modulator. Thereby, the voltage applied to the electrode can be lowered.

FIG. 2 is a diagram illustrating a configuration of the optical modulator according to the present embodiment.
In FIG. 2, the optical modulator 20 according to the present embodiment includes an electro-optic crystal 21 having a secondary electro-optic effect. A positive electrode 22 is disposed on the first surface of the electro-optic crystal 21, and a negative electrode 23 is disposed on the second surface opposite to the first surface. In the present embodiment, the electro-optic crystal 21 is KTN.
The “width” of each member (electro-optic crystal 21, positive electrode 22, negative electrode 23) indicates the length in the arrow direction P of FIG.

In the present embodiment, the electro-optic crystal 21 includes a first region 24 having a width l ₁ and second regions 25a and 25b having a width l ₂ that is wider (larger) than the width l _1. ing. The first region 24 and the second region 25a, 25b are respectively opposed surfaces of the electro-optic crystal 21 where the positive electrode 22 and the negative electrode 23 are not disposed and other than the incident surface and the exit surface of the incident light 27. On both sides (side surfaces of the electro-optic crystal 21), concave portions 26a and 26b are formed from the incident surface to the emission surface, and the first region 24 having a width l ₁ slightly larger than the diameter of the incident light 27 remains. In this way, the electro-optic crystal 21 is removed.

Further, since the incident light 27 is incident on the first region 24, the first region 24 becomes a light modulation region. Therefore, the width l ₁ of the first region 24 is made larger than the diameter of the incident light 27 in order to allow the incident light 27 to enter all the first regions 24. By setting the width l ₁ in this way, the portion of the electro-optic crystal 21 to which the electric field is applied by the positive electrode 22 and the negative electrode 23 while the electro-optic crystal is used as the light modulation region is not used as the light modulation region. Therefore, it is possible to reduce the capacitance of the capacitor formed by the positive electrode 22, the negative electrode 23, and the electro-optic crystal 21 while realizing high-efficiency modulation.

  As described above, in the present embodiment, since the first region 24 functions as a light modulation region, the positive electrode 22 and the negative electrode 23 are disposed so as to sandwich the first region 24. That is, the positive electrode 22 and the negative electrode 23 are arranged so that the first region 24 is located in the region between the positive electrode 22 and the negative electrode 23, and a predetermined voltage is applied to the positive electrode 22 and the negative electrode 23. An electric field is applied to the first region 24.

Here, from the viewpoint of reducing the electric capacity of the capacitor formed by the positive electrode 22, the negative electrode 23, and the electro-optic crystal 21, incident light is included in the electro-optic crystal 21 existing between the positive electrode 22 and the negative electrode 23. Therefore, it is necessary to remove an excessive portion while leaving at least a region (the first region 24) for favorably propagating 27. In consideration of this, the widths of the positive electrode 22 and the negative electrode 23 are set wider (larger) than the width l ₁ that is the width of the first region 24.

In the present embodiment, the second regions 25a and 25b function as a base for stably holding the positive electrode 22 and the negative electrode 23. In this embodiment, since the positive electrode 22 and the negative electrode 23 are set wider than the width l ₁ of the first region 24 as described above, at least the positive electrode 22 and the negative electrode 23 of the electro-optic crystal 21 are arranged. If the positive electrode 22 and the negative electrode 23 do not fit within the surface, it will be difficult to stably dispose the positive electrode 22 and the negative electrode 23 on the electro-optic crystal 21. Therefore, in the present embodiment, the arrangement of the positive electrode 22 and the negative electrode 23 is stabilized by providing the second regions 25a and 25b having a width l ₂ that is larger than the width of the positive electrode 22 and the negative electrode 23. Yes.

Further, by setting the width l ₂ of the second regions 25a and 25b to be equal to or larger than the widths of the positive electrode 22 and the negative electrode 23, all the electric fields generated between the positive electrode 22 and the negative electrode 23 become light modulation regions. The first region 24 can be guided.

In the present embodiment, air exists in the recesses 26a and 26b, and KTN, which is the electro-optic crystal 21, has a very large dielectric constant compared to the dielectric constant of air. No leakage from the region 24 into the recesses 26a, 26b. As described above, since the positive electrode 22 and the negative electrode 23 are wider than the width l ₁ of the first region 24, the positive electrode 22 and the negative electrode 23 are wider than the width l _{2 of} the second regions 25a and 25b. In this case, a portion protruding from the electro-optic crystal 21 is generated in both the positive electrode 22 and the negative electrode 23, and an electric field generated between the protruding electrode portions is generated between the recesses 26a and 26b where the electro-optic crystal 21 does not exist. Will do. Therefore, the electric field generated by the positive electrode 22 and the negative electrode 23 cannot be efficiently used for the modulation operation.

However, in the present embodiment, since the widths l ₂ of the second regions 25a and 25b are equal to or larger than the widths of the positive electrode 22 and the negative electrode 23, the positive electrode 22 and the negative electrode 23 are in contact with the electro-optic crystal 21. Since the electric field generated between the electrode 22 and the negative electrode 23 does not leak into the recesses 26 a and 26 b due to the large dielectric constant of the electro-optic crystal 21, all of the electric field can be applied to the first region 24. is there.

  In such a configuration, when a voltage is applied from the drive power source to the positive electrode 22 and the negative electrode 23 during the modulation operation, the incident light 27 incident on the electro-optic crystal 21 propagates from the positive electrode 22 toward the negative electrode 23. An electric field is generated in a direction perpendicular to the direction. At this time, the generated electric field is applied to the first region 24 via the second regions 25 a and 25 b, so that the incident light 27 undergoes predetermined modulation when passing through the first region 24.

In the present embodiment, the electro-optic crystal 21 has the second regions 25a and 25b which are wide regions and the first region 24 which is a region narrower than the second regions 25a and 25b. Since the recesses 26a and 26b are formed, a region (first region 24) necessary for modulation is secured in the region where the electric field between the positive electrode 22 and the negative electrode 23 is applied in the electro-optic crystal 21. However, the amount of the electro-optic crystal 21 having a high dielectric constant can be reduced. That is, it is possible to reduce the region other than the region serving as the light modulation region in the electro-optic crystal 21 to which the electric field is applied. Further, since the width l ₂ of the second regions 25a and 25b including the surface on which the electrodes are disposed is wider than the width l ₁ of the first region 24 that is a light modulation region, the positive electrode 22 and the negative electrode The width of 23 can be set to the width l ₁ or more, and the area of the electrode can be increased. Accordingly, the electric capacity of the optical modulator 20 can be reduced while realizing modulation with high efficiency.

Further, since the recesses 26a and 26b are formed with a uniform depth from the incident surface to the exit surface along the traveling direction of the incident light 27, the width l ₁ of the first region 24 is made uniform. The electric field intensity applied to the first region 24 can be made uniform at any location along the traveling direction of the first region 24. Therefore, good modulation can be performed on the incident light 27.

In addition, as described above, with the configuration according to the present embodiment, the electric field generated from the positive electrode 22 and the negative electrode 23 having a width wider than the width l ₁ of the first region 24 as the light modulation region can be reduced. 1, the first region 24 can be applied compared to the case where the width of the light modulation region is the same as the width of the positive electrode 22 and the negative electrode 23 as in the configuration shown in FIG. The electric field strength applied to can be increased. Therefore, compared with the conventional configuration as shown in FIGS. 1A and 1B, the voltage required for the predetermined modulation can be reduced. In other words, in the present embodiment, the concave portions 26a and 26b are provided to form the first region 24, and the electro-optic crystal in the region other than the region necessary for light modulation is reduced as much as possible, thereby reducing the electric capacity. However, in addition to this, the first region 24 and the recesses 26a and 26b also function to concentrate the electric field in a region necessary for light modulation.

  Further, by making the incident light 27 incident on the first region 24, that is, by setting the first region 24 as a light modulation region, the thickness of the optical modulator 20 can be further reduced. The electric capacity can be further reduced. That is, in the present embodiment, it is important to reduce the drive voltage of the optical modulator 20, and for that purpose, it is preferable to reduce the thickness of the electro-optic crystal 21. Therefore, the incident light 27 is incident on a region of the electro-optic crystal 21 sandwiched between the positive electrode 22 and the negative electrode 23 and the width thereof is narrowed to reduce the capacitance, and the region is defined as a light modulation region. By doing so, the region can be used effectively, and the thickness of the electro-optic crystal 21 can be reduced.

  In the present embodiment, the form in which all of the incident light 27 is incident on the first region 24 has been described. However, the incident light 27 extends across the first region 24 and the second region 25a (25b). May be incident (FIG. 3A), or may be incident on the second region 25a or 25b (FIG. 3B).

  Moreover, although the recessed part 26a and the recessed part 26b are formed in both the side surfaces of the optical modulator 20, you may make it form a recessed part only in one side of the said side surface. That is, what is important in the present embodiment is that the width of a part of the region to which the electric field of the electro-optic crystal 21 is applied is made narrower than the width of the other region, and the region where the width becomes narrower. In order to form, a concave portion is formed on the side surface of the optical modulator. Therefore, if the concave portion is formed on at least one of the side surfaces of the optical modulator, a region where the width is narrowed can be formed, and the electric capacity of the optical modulator can be reduced.

  Further, in the present embodiment, one recess 26a and one recess 26b are formed on the side surface of the optical modulator 20, but the number of recesses to be formed is not limited to one, and a plurality of recesses may be formed. good.

Next, a method for manufacturing the optical modulator 20 according to this embodiment will be described. 4A to 4E are diagrams for explaining a method of manufacturing the optical modulator 20.
An electro-optic crystal 41 having a thickness l ₂ (in this embodiment, KTN) is prepared (FIG. 4A). The surface 42a of the electro-optic crystal 41 and the surface 42b facing the surface 42a will later become the side surfaces of the optical modulator.

Next, as shown in FIG. 4B, grooves 43a, 43b, and 43c are formed on the surface 42a of the electro-optic crystal 41 using a dicing saw so as to be parallel to each other. Also, on the surface 42b of the electro-optic crystal 41, grooves 44a, 44b, and 44c are formed at a predetermined interval so as to be parallel to each other using a dicing saw. At this time, the groove 43a and the groove 44a are formed so that the groove 43a and the groove 44a face _{each other} and a region between the groove 43a and the groove 44a has the width l ₁ . Similarly, the groove 43b and the groove 44b are formed so that the groove 43b and the groove 44b face each other, and the region between the groove 43b and the groove 44b has a width l _1. The grooves 43c and 44c are formed so as to face _{each other} and the region between the grooves 43c and 44c has a width l ₁ .

  In the present embodiment, the grooves 43a to 43c and the grooves 44a to 44c are formed using a dicing saw, but the present invention is not limited to this method. In the present embodiment, any method may be used as long as it can form the grooves 43a to 43c and the grooves 44a to 44c appropriately, for example, dry etching or wet etching.

  Next, a portion between the grooves (along the broken line in FIG. 4B) is cut along the long axis direction of the groove with a dicing saw to separate the portion where the groove is formed on the side surface, and light modulation is performed. Electro-optic crystals 45a, 45b, and 45c having recesses (grooves) formed on the side surfaces, which are the base of the vessel, are formed (FIG. 4C).

  Next, the separated electro-optic crystals 45a, 45b, and 45c are each rotated by 90 ° (FIG. (4d)), and each of the electro-optic crystals 45a to 45c has no groove (concave portion) formed on the opposing surface. Electrode is vapor-deposited respectively to form a positive electrode and a negative electrode. That is, the positive electrode 48 is formed on the surface 46a of the electro-optic crystal 45a where the grooves 43a and 44a are not formed, and the negative electrode 49 is formed on the surface 47a opposite to the surface 46a (FIG. 4E). Similarly, a positive electrode is formed on the surface 46b of the electro-optic crystal 45b where the grooves 43b and 44b are not formed, and a negative electrode is formed on the surface 47b opposite to the surface 46b. Further, a positive electrode is formed on the surface 46c of the electro-optic crystal 45c where the grooves 43c and 44c are not formed, and a negative electrode is formed on the surface 47c facing the surface 46c. In this way, the optical modulator 20 shown in FIG. 2 is formed.

(Second Embodiment)
In the optical modulator 20 described in the first embodiment, when the aspect ratio in the recesses 26a and 26b is high, the first region 24 may be easily broken. Therefore, in this embodiment, the strength of the optical modulator 20 is improved by providing a low dielectric constant material as a supporter in the recesses 26a and 26b.

FIG. 5 is a diagram for explaining the optical modulator according to the present embodiment.
In FIG. 5, a low dielectric constant material 51 is provided in each of the recesses 26 a and 26 b of the optical modulator 20.
In the present specification, “low dielectric constant material” refers to a material having a dielectric constant lower than the dielectric constant of the electro-optic crystal 21 to be used. The value of the dielectric constant of the low dielectric constant material is preferably as low as possible, that is, as the difference from the dielectric constant of the electro-optic crystal 21 is large. However, even if the difference is not so large, the optical modulator 20 The effect of reducing the electric capacity can be exhibited. That is, by providing the low dielectric constant material 51 in the recesses 26 a and 26 b, a part of the region to which the electric field is applied in the electro-optic crystal 21 is replaced with a material having a dielectric constant lower than that of the electro-optic crystal 21. Therefore, the electric capacity of the optical modulator 20 is all smaller than that of the electro-optic crystal 21.

  Note that the greater the difference in the dielectric constant, the greater the effect of reducing the electric capacity of the optical modulator 20, and the electric field leakage to the low dielectric constant material 51 is also reduced. Therefore, in consideration of a reduction in electric capacity and an increase in electric field strength, it is preferable to use a material having a dielectric constant much smaller than that of the electro-optic crystal 21 as the low dielectric constant material. It is preferable to use a glass or polymer material.

  Thus, in this embodiment, since the low dielectric constant material 51 which functions as a supporter is provided in the recesses 26a and 26b, even if the aspect ratio of the recesses 26a and 26b is large, Since the low dielectric constant material 51 exists outside the region where the width is narrow (the first region 24), it is possible to prevent the optical modulator 20 from being broken with the first region 24 having the narrow width as a fulcrum. it can.

  Further, by setting the dielectric constant of the low dielectric constant material 51 to be lower than the dielectric constant of the electro-optic crystal 21, it is possible to improve the strength of the optical modulator 20 while exhibiting the effect of reducing the capacitance.

(Third embodiment)
In the first and second embodiments, the width l ₁ of the region (first region 24) whose width is narrowed in the electro-optic crystal is made smaller than the width l ₂ of both surfaces on which the electrodes are arranged. However, in the present embodiment, the first width of the region to be narrowed in the electro-optic crystal is made narrower than the second width of one surface on which the electrode of the electro-optic crystal is arranged, and the other surface It is equal to the width. And, by making the width of the electrode arranged on the surface having the second width wider than the first width, it is equivalent to reducing the amount of the electro-optic crystal to which the electric field is applied by the counter electrode, The electric capacity of the optical modulator can be reduced.

FIG. 6 is a diagram illustrating a configuration of the optical modulator according to the present embodiment.
In FIG. 6, the optical modulator 60 according to the present embodiment includes an electro-optic crystal 61 having a secondary electro-optic effect. A positive electrode 62 is disposed on the first surface of the electro-optic crystal 61, and a negative electrode 63 is disposed on the second surface opposite to the first surface. In the present embodiment, the electro-optic crystal 61 is KTN.
In the present embodiment, the electro-optic crystal 61 has a first region 64 having a width l ₃ and a second region 65 having a width l ₄ that is larger than the width l ₃ . That is, the width l ₃ of the first region 64, which is a region whose width is narrowed in the electro-optic crystal 61, is greater than the width l ₄ of the second surface, which is one surface on which the electrode of the electro-optic crystal 61 is disposed. The width of the first surface, which is the other surface, is narrowed, and is equal to the width l ₃ of the first region 64, which is the region where the width is narrowed.

Further, considering that the incident light 6 is incident on the first region 64, the width l ₃ of the first region 64 is set larger than the diameter of the incident light 66.

Furthermore, in the present embodiment, the width of the positive electrode 62 is made equal to the width l ₃ of the first region 64, and the width of the negative electrode 63 is made wider than the width of the positive electrode 62. Therefore, the electric capacity of the optical modulator 60 can be reduced. That is, in the conventional optical modulator, as shown in FIG. 1B, the widths of the positive electrode 2 and the negative electrode 3 are the same. Since the width of one electrode (the negative electrode 63 in FIG. 6) of the counter electrode to be arranged can be made wider than the width of the other electrode (the positive electrode 62 in FIG. 6), FIG. 1 (a) and FIG. Compared to the conventional optical modulator as shown, the electric capacity of the optical modulator can be reduced.

As described above, in this embodiment, the electric capacity of the optical modulator 60 can be reduced. However, the first embodiment removes a region that does not function as a modulation region from the electro-optic crystal to which an electric field is applied. And since the area of both electrodes of a counter electrode can be enlarged, the reduction effect of an electrical capacitance can be acquired more. However, in the present embodiment, the width of the first surface of the electro-optic crystal 61 is made equal to the width l ₃ of the first region 64, which is a narrow region, and the width of the second surface of the electro-optic crystal 61 is increased. By making l ₄ wider than the width l ₃ , the width of the negative electrode 63 is made wider than the width of the positive electrode 62, so that the second region 65 having the width l ₄ is formed on the negative electrode 63 side of the electro-optic crystal 61. Therefore, the strength can be improved more than in the first embodiment. Therefore, mounting on other members becomes easy.

In the present embodiment, the second region 65 functions as a base for stably holding the negative electrode 63. In the present embodiment, since the width of the negative electrode 63 is set wider than the width l ₃ of the first region 64 as described above, at least the negative electrode 63 is disposed in the plane where the negative electrode 63 of the electro-optic crystal 61 is disposed. Unless 63 is accommodated, it is difficult to stably dispose the negative electrode 63 on the electro-optic crystal 61. Therefore, in this embodiment, the arrangement of the negative electrode 63 is stabilized by providing the second region 65 having a width l ₄ larger than the width of the negative electrode 63.

Next, a method for manufacturing the optical modulator 60 according to this embodiment will be described. 7A to 7D are views for explaining a method for manufacturing the optical modulator 70. FIG.
First, an electro-optic crystal 71 (in this embodiment, KTN) having a surface 72a and a surface 72b opposite to the surface 72a is prepared (FIG. 7A).
Next, as shown in FIG. 7B, grooves 73a, 73b, and 73c are formed on the surface 72a of the electro-optic crystal 71 so as to be parallel to each other at a predetermined interval using a dicing saw. At this time, the grooves 73a to 73c are formed such that the predetermined interval is larger than the diameter of incident light to be incident.

  In the present embodiment, the grooves 73a to 73c are formed using a dicing saw, but the present invention is not limited to this method. In the present embodiment, any method may be used as long as the grooves 73a to 73c can be appropriately formed, for example, dry etching or wet etching.

  Next, the center of each groove (along the broken line in FIG. 7B) is cut along the long axis direction of the groove with a dicing saw, and the portion where the groove is formed on the side surface is separated, and light modulation is performed. Electro-optic crystals 74a and 74b that are the base of the vessel are formed (FIG. 7C).

  Next, for each of the electro-optic crystals 74a and 74b, electrodes are vapor-deposited on the opposing surfaces to form a positive electrode and a negative electrode. That is, the positive electrode 77 is formed on the surface 75a of the electro-optic crystal 74a, and the negative electrode 78 is formed on the surface 76a opposite to the surface 75a (FIG. 7D). Similarly, a positive electrode is formed on the surface 75b of the electro-optic crystal 74b, and a negative electrode is formed on the surface 76b facing the surface 75b. In this way, the optical modulator 60 shown in FIG. 6 is formed.

(A) is sectional drawing which shows the structure of the optical phase modulator using the conventional electro-optic crystal, (b) is a front view of the optical phase modulator shown to (a). 1 is a perspective view showing a configuration of an optical modulator according to an embodiment of the present invention. It is a figure which shows the structure of the optical modulator which concerns on one Embodiment of this invention. (A)-(e) is a figure for demonstrating the manufacturing method of the optical modulator which concerns on one Embodiment of this invention. 1 is a perspective view showing a configuration of an optical modulator according to an embodiment of the present invention. 1 is a perspective view showing a configuration of an optical modulator according to an embodiment of the present invention. (A)-(d) is a figure for demonstrating the manufacturing method of the optical modulator which concerns on one Embodiment of this invention.

Explanation of symbols

20, 60 Light modulator 21, 61 Electro-optic crystal 22, 62 Positive electrode 23, 63 Negative electrode 24, 64 First region 25a, 25b, 65 Second region 26a, 26b Recessed portion 27, 66 Incident light

Claims (4)

An electro-optic crystal having a secondary electro-optic effect;
A first electrode disposed on a first surface of the electro-optic crystal;
A second electrode disposed on a second surface opposite to the first surface of the electro-optic crystal ;
A concave portion formed on at least one of the first surface, the second surface, the incident light incident surface, and the two opposing surfaces other than the emission surface of the electro-optic crystal ;
The electro-optic crystal has at least a region having a width narrower than the width of the first surface;
The width of the first electrode and the width of the second surface are wider than the width of the region,
The region is located between the first electrode and the second electrode ;
The optical modulator, wherein the region is formed by the concave portion . The optical modulator according to claim 1 , wherein the concave portion is provided with a low dielectric constant material having a dielectric constant lower than that of the electro-optic crystal. The width of the region is larger than the diameter of incident light incident on the light modulator,
The incident light, the light modulator according to claim 1 or 2, characterized in that it is incident on the region. The materials of the first electrode and the second electrode are Pt, Co, Ge, Au, Pd, Ni, Ir, Pt, Se, Cs, Rb, K, Sr, Ba, Na, Ca, Li, Y, Sc, La, Mg, As, Ti, Hf, Zr, Mn, In, Ga, Cd, Bi, Ta, Pb, Ag, Al, V, Nb, Ti, Zn, Sn, B, Hg, Cr, Si, sb, W, Mo, Cu, Fe, Ru, Os, Te, Re, be, optical modulator according to any one of claims 1 to 3, characterized in that either Rh.

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