JP2014002198A - Optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an optical waveguide which can easily control a waveguide mode and a polarization direction capable of guiding.SOLUTION: A core 1 and clads 2a and 2b are configured by using a uniaxial birefringence crystal material in which a refractive index with respect to a main coordinate axis of a crystal which coincides with an optical axis is larger than a refractive index with respect to the other main coordinate axis. The optical axis of the birefringence crystal material used for the core 1 is arranged in the thickness direction of the core 1. The birefringence crystal material used for the clads 2a and 2b is arranged with an inclination with respect to the optical axis direction of the core 1 in a plane that is parallel to a plane formed by the direction of the optical axis of the core 1 and the travelling direction of light.

Description

  The present invention relates to an optical waveguide for confining light in a core and propagating using total reflection caused by a difference in refractive index between a core and a clad.

The optical waveguide is composed of a flat core and two clads joined to the upper and lower surfaces of the core, and the refractive index difference between the core and the clad (the refractive index of the clad is lower than the refractive index of the core). Utilizing the total reflection that occurs, light is confined in the core and propagated (see, for example, Non-Patent Document 1).
At this time, in the optical waveguide, a waveguide mode is formed according to the thickness and refractive index of the core, the refractive index difference between the core and the clad, the wavelength of light, and the incident light is coupled to the waveguide mode and propagates. To do.

Here, an optical waveguide capable of propagating only a single waveguide mode is referred to as a “single mode waveguide”.
In some cases, the light output from the optical waveguide is preferably a spatial single-mode Gaussian beam from the viewpoint of light collection characteristics and propagation characteristics, and a single-mode waveguide may be required.
In general, the number of modes that can be guided decreases as the core thickness decreases, the refractive index difference between the core and the cladding decreases, and the wavelength of light increases.
Therefore, a single mode waveguide can be manufactured by appropriately setting the thickness of the core, the refractive index difference, and the like.

The optical waveguide is manufactured by joining the core and clad members. Alternatively, it is manufactured by laminating an optical material to be a clad on the core.
At this time, since it is necessary to reduce the difference between the linear expansion coefficients of the core and the clad, usable materials are limited.
Further, in order to reduce the difference in refractive index between the core and the cladding, for example, the refractive index of the material may be adjusted by adding impurities.
At this time, since the change in refractive index varies depending on the material, a desired refractive index may not be obtained. In addition, the optical characteristics of the material may change.

Further, when an isotropic material is used, the polarization direction of incident light propagating through the core cannot be maintained.
By using a material with a different refractive index depending on the polarization direction as the cladding material, the polarization direction that can be guided is controlled and patented by making the refractive index lower than that of the core for only one polarization direction. There are some methods, but the materials that can be used are limited.

Jacob I. Mackenzie, “Multi-Watt, High Efficiency, Diffraction-Limited Nd: YAG Planar Waveguide Laser”, IEEE Journal of Quantum Electronics, Vol. 39, No. 3, March 2003

  Since the conventional optical waveguide is configured as described above, the desired refractive index cannot be easily set, and the waveguide mode and the polarization direction that can be guided cannot be easily controlled. was there.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain an optical waveguide capable of easily controlling the waveguide mode and the polarization direction capable of being guided.

  In the optical waveguide according to the present invention, the core and the clad are formed using a uniaxial birefringent crystal material in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is larger than the refractive indexes with respect to the other main coordinate axes. The optical axis of the birefringent crystal material used for the core is arranged in the thickness direction or the lateral direction of the core, and the birefringent crystal material used for the clad is parallel to the plane formed by the direction of the optical axis of the core and the light traveling direction. In the plane, it is arranged with an inclination with respect to the direction of the optical axis of the core.

  According to this invention, the core and the clad are configured using a uniaxial birefringent crystal material in which the refractive index with respect to the main coordinate axis of the crystal coinciding with the optical axis is larger than the refractive index with respect to the other main coordinate axis, The optical axis of the birefringent crystal material used for the core is arranged in the thickness direction or the transverse direction of the core, and the birefringent crystal material used for the clad is in a plane parallel to the plane formed by the optical axis direction of the core and the light traveling direction. Thus, since it is arranged so as to be inclined with respect to the direction of the optical axis of the core, there is an effect that the waveguide mode and the polarization direction capable of being guided can be easily controlled.

It is a perspective view which shows the optical waveguide by Embodiment 1 of this invention. It is explanatory drawing which shows a refractive index change when the polarization direction of a laser beam changes with respect to an optical axis. It is a perspective view which shows an optical waveguide in case the inclination | tilt angle (theta) of the optical axis of clad 2a, 2b is 90 degrees. It is a perspective view which shows the optical waveguide by Embodiment 2 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 3 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 3 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 4 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 4 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 5 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 6 of this invention. It is a perspective view which shows the optical waveguide by Embodiment 7 of this invention.

Embodiment 1 FIG.
1 is a perspective view showing an optical waveguide according to Embodiment 1 of the present invention.
In FIG. 1, a flat core 1 is formed using a uniaxial birefringent crystal material having a refractive index with respect to a principal coordinate axis of a crystal coinciding with an optical axis that is larger than a refractive index with respect to another principal coordinate axis. Has been.
The clads 2a and 2b are formed using a uniaxial birefringent crystal material of the same base material as the core 1, the clad 2a is bonded to the upper surface of the core 1, and the clad 2b is bonded to the lower surface of the core 1. Yes.

Here, the optical axis 5 of the birefringent crystal material used for the core 1 is disposed in the thickness direction of the core 1, and the birefringent crystal material used for the clads 2 a and 2 b corresponds to the direction of the optical axis 5 of the core 1 and the light. It is arranged with an inclination with respect to the direction of the optical axis 5 of the core 1 in a plane parallel to the plane formed by the traveling direction.
Hereinafter, in order to specifically describe the above arrangement, coordinates in which the three axes are orthogonal to each other, where the thickness direction of the core 1 is the y axis, the lateral direction of the core 1 is the x axis, and the depth direction of the core 1 is the z axis. Use the system.
Further, a shaft of the main axes of the crystal, b-axis, and the c-axis, the refractive index with respect to a axis n _a, the refractive index with respect to the b-axis n _b, the refractive index with respect to the c-axis and n _c.

Here, the core 1 and the clad 2a, 2b because it is configured using the uniaxial birefringent crystal _material, and a _{n a = n b <n c} . At this time, the c-axis becomes the optical axis.
The optical axis 5 of the core 1 is parallel to the y-axis, and the optical axes 6a and 6b of the claddings 2a and 2b are inclined by an angle θ with respect to the y-axis in the yz plane. However, 0 ° <θ ≦ 90 °.

The laser beam 3 propagated in the z-axis direction by the optical waveguide is a linearly polarized laser beam, and the polarization direction 4 of the laser beam 3 is parallel to the y-axis. That is, the polarization direction 4 of the laser beam 3 is also parallel to the optical axis 5 of the core 1.
Since the polarization direction 4 of the laser beam 3 is parallel to the optical axis 5 of the core 1, it can propagate through the core 1 while maintaining linear polarization without being affected by birefringence.
Further, since the optical axes 6a and 6b of the clads 2a and 2b are in the yz plane, the components of the laser light 3 that propagates through the core 1 to the clads 2a and 2b are not affected by birefringence.

FIG. 2 is an explanatory diagram showing a change in refractive index when the polarization direction of laser light is changed with respect to the optical axis.
In FIG. 2, 11 is a refractive index with respect to the laser light 3, 12 is a refractive index of the core 1 with respect to the laser light 3, and 13 is a refractive index of the clads 2 a and 2 b with respect to the laser light 3.
The refractive index of the crystal that the laser beam feels changes on an ellipse having _a major axis of 2 × n _c and a minor axis of 2 × na as shown by the refractive index 11 in FIG. 2 depending on the angle of the polarization direction with respect to the optical axis.
Refractive index is maximum at n _c when the polarization direction of the laser beam 3 is parallel to the optical axis, smallest at n _a when the polarization direction of the laser beam 3 becomes the optical axis and perpendicular.
Refractive index of the core 1 with respect to the laser beam 3, as the refractive index 12 of FIG. 2, the polarization direction of the laser beam 3 is n _c for being parallel to the optical axis.

Further, the refractive index n _clad of the _clads 2a and 2b with respect to the laser beam 3 is inclined by the angle θ with respect to the optical axis (c axis), as in the refractive index 13 of FIG. Therefore, it is expressed as follows.

Here, since it is 0 ° <θ ≦ 90 °, a _{n a ≦ n clad <n c} .
That is, the clad 2a, the refractive index of 2b, the optical axis 6a, by 6b of the tilt angle theta, because changes in the range from _{n a} to _{n c,} a theta ≠ 0 ° or theta ≠ 180 °, from _{n c} Becomes smaller.
Thus, since the refractive index of the clads 2a and 2b with respect to the laser beam 3 is smaller than the refractive index of the core 1, the optical waveguide shown in FIG. 1 can guide the laser beam 3.

In the above configuration, the refractive indexes of the clads 2a and 2b with respect to the laser light 3 can be changed by the inclination angle θ of the optical axes 6a and 6b of the clads 2a and 2b.
Therefore, the refractive index difference between the core 1 and the clads 2a and 2b can be adjusted by the inclination angle θ of the optical axes 6a and 6b, so that only the low-order waveguide mode is propagated by making the refractive index difference small. For example, by appropriately setting the inclination angle θ of the optical axes 6a and 6b of the clads 2a and 2b, an optical waveguide can be configured while controlling the waveguide mode.

Further, the difference in refractive index between the core 1 and the clads 2a and 2b is maximized when the tilt angle θ of the optical axes 6a and 6b of the clads 2a and 2b is 90 ° as shown in FIG. 3 (clad 2a , 2b is parallel to the z-axis). At this time, the clad 2a, the refractive index of 2b becomes _{n a.}

With the configuration shown in FIG. 1, the refractive index of the clads 2a and 2b with respect to the laser light 3 propagating through the core 1 can be changed by the inclination angle θ of the optical axes 6a and 6b of the clads 2a and 2b. The refractive index difference between 1 and the clads 2a and 2b can be adjusted, and an optical waveguide can be configured by controlling the waveguide mode.
Further, since the refractive index with respect to the optical axis is determined by the crystal material, a desired refractive index difference can be easily obtained.
Furthermore, since a birefringent crystal material of the same base material can be used for the core 1 and the clads 2a and 2b, material characteristics such as a thermal expansion coefficient at the junction between the core 1 and the clads 2a and 2b when forming the waveguide. The influence of can be reduced.

Further, in the optical waveguide shown in FIGS. 1 and 3, for the laser beam is polarized in the x-axis direction, the core 1 and the clad 2a, 2b refractive index for the laser light coincides with a n _a.
As a result, there is no difference in refractive index between the core 1 and the clads 2a and 2b, so that the laser beam that does not function as an optical waveguide and is polarized in the x-axis direction is radiated and guided to the clads 2a and 2b. I can't.
In these waveguides, only laser light polarized in the y-axis direction can be guided, and an optical waveguide capable of guiding only single polarized light is obtained.

In addition, when linearly polarized laser light having an inclination with respect to the y-axis is incident on the y-x plane, birefringence generated in the core 1 causes the laser light to be polarized in the y-axis direction and polarized in the x-axis direction. Separated into components.
At this time, as described above, the polarization component in the y-axis direction can be guided, but since the polarization component in the x-axis direction is not guided, it is propagated through the optical waveguide and output from the end surface is the y-axis. Only the polarization component of the direction.
Thus, it also has a function as a polarizer that transmits only the polarization component in the y-axis direction.
As described above, the optical waveguide can have polarization selectivity, and an optical waveguide capable of guiding only a single polarized light can be configured.

  As is apparent from the above, according to the first embodiment, the core 1 and the clads 2a and 2b are uniaxial in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is larger than the refractive indexes with respect to the other main coordinate axes. The birefringent crystal material used for the core 1 is disposed in the thickness direction of the core 1, and the birefringent crystal material used for the clads 2 a and 2 b is the core 1. In the plane parallel to the plane formed by the direction of the optical axis 5 and the light traveling direction, the core 1 is arranged so as to be inclined with respect to the direction of the optical axis 5. There is an effect that the polarization direction capable of being guided can be easily controlled.

In the first embodiment, the case where the optical axes 6a and 6b of the clad 2a and the clad 2b are parallel to each other is shown, but they may not be parallel.
However, when the optical axes 6a and 6b of the clad 2a and the clad 2b are not parallel, the refractive indexes of the clad 2a and the clad 2b which are felt by the laser beam 3 propagating through the core 1 become different values. In this case, the waveguide mode is limited by the clad side having a smaller optical axis tilt angle, that is, a higher refractive index.

When the optical axes 6a and 6b of the clads 2a and 2b are surfaces other than the yz plane (for example, when the optical axes 6a and 6b are inclined with respect to the y axis in the yz plane), they propagate through the core 1. The component of the laser beam 3 that leaks into the clads 2a and 2b is affected by birefringence.
As a result, a polarization component that cannot be recombined with the laser beam 3 propagating through the core 1 is generated, so that loss occurs.

Embodiment 2. FIG.
In the first embodiment, the optical axis 5 of the birefringent crystal material used for the core 1 is arranged in the thickness direction of the core 1, and the birefringent crystal material used for the clads 2 a and 2 b is the optical axis 5 of the core 1. In the plane parallel to the plane formed by the direction of the light and the direction of light travel, it is shown to be inclined with respect to the direction of the optical axis 5 of the core 1, but the birefringent crystal material used for the core 1 is shown. The optical axis is arranged in the transverse direction of the core 1, and the birefringent crystal material used for the clads 2 a and 2 b is in a plane parallel to the plane formed by the direction of the optical axis of the core 1 and the light traveling direction. You may arrange | position with inclination with respect to the direction of an optical axis.

4 is a perspective view showing an optical waveguide according to Embodiment 2 of the present invention. In the figure, the same reference numerals as those in FIG.
The core 1 and the clads 2a and 2b are configured using a uniaxial birefringent crystal material of the same base material, and have the same refractive index characteristics as those of the first embodiment.
However, unlike the first embodiment, the optical axis 21 of the core 1 is parallel to the x-axis, and the optical axes 22a and 22b of the clads 2a and 2b are in the xz plane and have an angle θ ( It is inclined by 0 ° <θ ≦ 90 °).

  The laser beam 3 propagated in the z-axis direction by the optical waveguide is a linearly polarized laser beam, and the polarization direction 23 of the laser beam 3 is parallel to the X axis. That is, the polarization direction 23 of the laser beam 3 is also parallel to the optical axis 21 of the core 1.

With the configuration described above, as in the first embodiment, the laser light 3 propagating in the core 1 and the component that exudes to the clads 2a and 2b propagate without being affected by birefringence. The refractive index of the clads 2a and 2b with respect to the laser beam 3 can be changed by the inclination angle θ of the optical axes 22a and 22b of the clads 2a and 2b.
Therefore, the refractive index difference between the core 1 and the clads 2a and 2b can be adjusted by the inclination angle θ of the optical axes 22a and 22b of the clads 2a and 2b. For this reason, by setting the inclination angle θ of the optical axes 22a and 22b of the claddings 2a and 2b appropriately, for example, by allowing only a low-order waveguide mode to be propagated by making the refractive index difference small, it is It is possible to configure the optical waveguide by controlling the wave mode.

Further, since the refractive index with respect to the optical axis is determined by the crystal material, a desired refractive index difference can be easily obtained.
Furthermore, since a birefringent crystal material of the same base material can be used for the core 1 and the clads 2a and 2b, material characteristics such as a thermal expansion coefficient at the junction between the core 1 and the clads 2a and 2b when forming the waveguide. The influence of can be reduced.

Further, in the optical waveguide shown in FIG. 4, for the laser beam is polarized in the y-axis direction, the core 1 and the clad 2a, 2b refractive index for the laser light coincides with a n _a.
As a result, there is no difference in refractive index between the core 1 and the clads 2a and 2b, so that the laser beam that does not function as an optical waveguide and is polarized in the y-axis direction is radiated and guided to the clads 2a and 2b. I can't.
In this waveguide, only laser light polarized in the x-axis direction can be guided, and an optical waveguide capable of guiding only a single polarized light is obtained.

Further, when linearly polarized laser light having an inclination with respect to the x axis in the y-x plane is incident, the birefringence generated in the core 1 causes the laser light to be polarized in the y axis direction and in the x axis direction. Separated into components.
At this time, as described above, the polarization component in the x-axis direction can be guided, but since the polarization component in the y-axis direction is not guided, it is propagated through the optical waveguide and output from the end surface is the x-axis. Only the polarization component of the direction.
Thus, it also has a function as a polarizer that transmits only the polarization component in the x-axis direction.
As described above, the optical waveguide can have polarization selectivity, and an optical waveguide capable of guiding only a single polarized light can be configured.

  As is apparent from the above, according to the second embodiment, the core 1 and the clads 2a and 2b are uniaxial in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is larger than the refractive indexes with respect to the other main coordinate axes. The birefringent crystal material used for the core 1 is arranged in the lateral direction of the core 1, and the birefringent crystal material used for the clads 2a and 2b is the core 1. Since it is arranged so as to be inclined with respect to the direction of the optical axis 21 of the core 1 in a plane parallel to the plane formed by the direction of the optical axis 21 and the traveling direction of light, the waveguide mode and the waveguide There is an effect that it is possible to easily control the polarization direction capable of wave generation.

In the second embodiment, the case where the optical axes 22a and 22b of the clad 2a and the clad 2b are parallel to each other is shown, but these may not be parallel.
However, when the optical axes 22a and 22b of the clad 2a and the clad 2b are not parallel, the refractive index of the clad 2a and the clad 2b felt by the laser beam 3 propagating through the core 1 is different, and the waveguide mode is an inclination angle of the optical axis. Becomes smaller. That is, the refractive index is limited by the larger cladding side.

When the optical axes 22a and 22b of the clads 2a and 2b are surfaces other than the xz plane (for example, when the optical axes 22a and 22b have an inclination with respect to the x axis in the yz plane), they propagate through the core 1. The component of the laser beam 3 that leaks into the clads 2a and 2b is affected by birefringence.
As a result, a polarization component that cannot be recombined with the laser beam 3 propagating through the core 1 is generated, so that loss occurs.

Embodiment 3 FIG.
In the first and second embodiments, the core 1 and the clads 2a and 2b are uniaxial birefringent crystal materials in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is larger than the refractive indexes with respect to the other main coordinate axes ( Although an example is shown in which n _a < _{bi is} a birefringent crystal material), the core 1 and the clads 2a and 2b have a refractive index with respect to the main coordinate axis of the crystal that coincides with the optical axis, and other main coordinate axes. uniaxial birefringent crystal material (n _a> n birefringent crystal material _c) may be configured with less than the refractive index with respect.

FIG. 5 is a perspective view showing an optical waveguide according to Embodiment 3 of the present invention. In the figure, the same reference numerals as those in FIG.
The optical axis 31 of the birefringent crystal material used for the core 1 is arranged in parallel with the light traveling direction, and the birefringent crystal material used for the clads 2a and 2b is the direction of the optical axis 31 of the core 1 and the thickness of the core 1. It is disposed with an inclination with respect to the direction of the optical axis 31 of the core 1 in a plane parallel to the plane formed by the direction.

In the third embodiment, a birefringent crystal material used core 1 and cladding 2a, and 2b is _n a> _{n c.}
When the polarization direction 4 of the laser beam 3 is parallel to the y-axis, the optical axis 31 of the core 1 is parallel to the z-axis, and the optical axes 32a and 32b of the claddings 2a and 2b are in the yz plane, Is inclined by an angle θ. However, 0 ° <θ ≦ 90 °.

With the configuration described above, as in the first embodiment, the laser light 3 propagating in the core 1 and the component that exudes to the clads 2a and 2b propagate without being affected by birefringence. The refractive index of the clads 2a and 2b with respect to the laser beam 3 can be changed by the inclination angle θ of the optical axes 32a and 32b of the clads 2a and 2b.
Therefore, the refractive index difference between the core 1 and the clads 2a and 2b can be adjusted by the inclination angle θ of the optical axes 32a and 32b of the clads 2a and 2b. For this reason, by setting the inclination angle θ of the optical axes 32a and 32b of the claddings 2a and 2b appropriately, for example, by allowing only a low-order waveguide mode to be propagated by making the difference in refractive index small, the guide can be derived. It is possible to configure the optical waveguide by controlling the wave mode.

In addition, when linearly polarized laser light having an inclination with respect to the y-axis is incident on the y-x plane, birefringence does not occur in the core 1, but regarding the polarization component in the x-axis direction, the core 1 a clad 2a, the refractive index of 2b coincides next _{n a.} Therefore, similarly to the first embodiment, only the polarization component in the y-axis direction can be guided.
As a result, as in the first embodiment, the optical waveguide can have polarization selectivity, and an optical waveguide capable of guiding only a single polarized light can be configured.

  In the optical waveguide of FIG. 5, the optical axes 32 a and 32 b of the clads 2 a and 2 b are tilted by an angle θ with respect to the z axis in the yz plane, but as shown in FIG. 6. The optical axes 33a and 33b of the clads 2a and 2b may be inclined by an angle θ with respect to the z axis in the xz plane (the birefringent crystal material used for the clads 2a and 2b is the core 1). In a plane parallel to the plane formed by the direction of the optical axis of the core 1 and the lateral direction of the core 1 with an inclination with respect to the direction of the optical axis of the core 1). However, 0 ° <θ ≦ 90 °.

By configuring as shown in FIG. 6, the laser light 3 propagating in the core 1 and the seepage component to the clads 2a and 2b propagate without being affected by birefringence, as in the second embodiment. The refractive index of the clad 2a, 2b with respect to the laser beam 3 can be changed by the inclination angle θ of the optical axes 33a, 33b of the clad 2a, 2b.
Therefore, the refractive index difference between the core 1 and the clads 2a and 2b can be adjusted by the inclination angle θ of the optical axes 33a and 323 of the clads 2a and 2b. For this reason, by setting the inclination angle θ of the optical axes 33a and 33b of the claddings 2a and 2b appropriately, for example, by allowing only a low-order waveguide mode to be propagated by making the difference in refractive index very small, It is possible to configure the optical waveguide by controlling the wave mode.

In addition, when linearly polarized laser light having an inclination with respect to the x-axis is incident on the y-x plane, birefringence does not occur in the core 1, but regarding the polarization component in the y-axis direction, the core 1 a clad 2a, the refractive index of 2b coincides next _{n a.} Therefore, similarly to the second embodiment, only the polarization component in the x-axis direction can be guided.
As a result, as in the second embodiment, the optical waveguide can have polarization selectivity, and an optical waveguide capable of guiding only a single polarized light can be configured.

As apparent from the above, the core 1 and the clad 2a, 2b is, be constructed using n _a> n _c birefringent crystal material, by appropriately arranging the direction of the optical axis, the clad 2a, Since the refractive index of the clad 2a, 2b with respect to the laser beam 3 propagating through the core 1 can be changed by the inclination angle θ of the optical axes 32a, 32b of 2b, the refractive index difference between the core 1 and the clad 2a, 2b can be easily achieved. The optical waveguide can be configured by controlling the waveguide mode.
In addition, since the optical waveguide can have polarization selectivity, an optical waveguide capable of guiding only a single polarized light can be configured.

Embodiment 4 FIG.
FIG. 7 is a perspective view showing an optical waveguide according to Embodiment 4 of the present invention. In FIG. 7, the same reference numerals as those in FIG.
The flat core 41 is made of a biaxial birefringent crystal material.
The clads 42a and 42b are made of a biaxial birefringent crystal material that is the same base material as the core 41. The clad 42a is joined to the upper surface of the core 41, and the clad 42b is joined to the lower surface of the core 41. Yes.

Here, the main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core 41 is arranged parallel to the thickness direction of the core 41, and the refractive index of the birefringent crystal material used for the clads 42a and 42b. The main coordinate axis of the crystal having the maximum is disposed in a plane parallel to the plane formed by the thickness direction of the core 41 and the light traveling direction, and is inclined with respect to the main coordinate axis where the refractive index of the core 41 is maximum. ing.
Hereinafter, in order to specifically describe the above arrangement, coordinates in which the three axes are orthogonal to each other, where the thickness direction of the core 41 is the y-axis, the lateral direction of the core 41 is the x-axis, and the depth direction of the core 41 is the z-axis. Use the system.
Also, the main coordinate axes of the crystal are the a-axis, b-axis, and c-axis, the a-axis 43a and the x-axis of the core 41 are parallel, the b-axis 43b and the z-axis of the core 41 are parallel, and the c-axis of the core 41 43c and the y-axis are parallel.

The a-axes 44a and 45a of the clads 42a and 42b are parallel to the x-axis, and the c-axes 44c and 45c of the clads 42a and 42b are inclined with respect to the y-axis by an angle θ in the yz plane. However, 0 ° <θ ≦ 90 °.
Incidentally, the refractive index with respect to a axis _n a, the refractive index _n b for b-axis, the refractive index with respect to the c-axis as _{n c,} and an n _{a <n} b _{<n c.}

ｎ_ｃｌａｄ＜ｎ_ｃ Accordingly, the refractive indexes n _clad of the _clads 42a and 42b with respect to the laser light 3 having the polarization direction 4 parallel to the y axis propagating through the core 41 are expressed as follows, and the same effect as in the first embodiment is obtained. can get.

n _clad <n _c

  In the optical waveguide of FIG. 7, the a-axes 44a and 45a of the clads 42a and 42b are parallel to the x-axis, and the c-axes 44c and 45c of the clads 42a and 42b are an angle θ with respect to the y-axis in the yz plane. As shown in FIG. 8, the b-axes 46b and 47b of the clads 42a and 42b are parallel to the x-axis, and the c-axes 46c and 47c of the clads 42a and 42b are yz planes. May be inclined at an angle θ with respect to the y-axis (the main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the clads 42a and 42b is the horizontal direction of the core 41 and the light propagation) In a plane parallel to the plane formed by the direction, the core 41 is arranged with an inclination with respect to the main coordinate axis where the refractive index is maximum). However, 0 ° <θ ≦ 90 °.

ｎ_ｃｌａｄ＜ｎ_ｃ Accordingly, the refractive indexes n _clad of the _clads 42a and 42b with respect to the laser light 3 having the polarization direction 4 parallel to the y axis propagating through the core 41 are expressed as follows, and the same effect as in the first embodiment is obtained. can get.

n _clad <n _c

7 and 8, the a-axis 43a and the x-axis of the core 41 may be parallel, and the b-axis 43b and the z-axis of the core 41 may be parallel.
Also in this case, the refractive indexes of the clads 42a and 42b can be adjusted with respect to the laser light 3 having the polarization direction 4 parallel to the y-axis propagating through the core 41 by the angle θ of the c-axis of the clads 42a and 42b. it can.
However, in the case of FIG. 7, for the laser beam 3 having a polarization direction parallel to the x-axis, the refractive index of the core 41 is n _b, and the cladding 42a, the refractive index of 42b becomes n _a. At this time, it becomes n _b> that n _a total reflection condition is satisfied because, the waveguide regardless of the polarization direction of incident light, the selectivity of the polarization is eliminated becomes possible waveguide.

Embodiment 5 FIG.
FIG. 9 is a perspective view showing an optical waveguide according to Embodiment 5 of the present invention. In the figure, the same reference numerals as those in FIG.
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core 41 is arranged in the lateral direction of the core 41, and the main coordinate axis of the crystal having the minimum refractive index of the birefringent crystal material is the core 41. It is arranged in parallel with the thickness direction.
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the clads 42a and 42b is arranged in parallel to the main coordinate axis having the maximum refractive index of the core 41, and the refraction of the birefringent crystal material is The main coordinate axis of the crystal having the minimum refractive index is arranged in a plane parallel to the plane formed by the thickness direction of the core 41 and the light traveling direction, and is inclined with respect to the main coordinate axis with the minimum refractive index of the core 41. Has been.

The above arrangement will be specifically described below.
In the optical waveguide of FIG. 9, the main coordinate axes of the crystal are the a-axis, b-axis, and c-axis, the a-axis 51a and the y-axis of the core 41 are parallel, the b-axis 51b and the z-axis of the core 41 are parallel, The c-axis 51c and the x-axis of the core 41 are parallel.
Further, the a-axes 52a and 53a of the clads 42a and 42b are parallel to the y-axis, and the c-axes 52c and 53c of the clads 42a and 42b are inclined by an angle θ with respect to the x-axis in the xz plane. However, 0 ° <θ ≦ 90 °.
The refractive index _n a for a-axis, the refractive index _n b for b-axis, the refractive index with respect to the c-axis is _{n c,} is assumed to be n _{a <n} b _{<n c.}

With the configuration described above, as in the second embodiment, the laser light 3 propagating through the core 41 and the component that exudes to the clads 42a and 42b can propagate without being affected by birefringence. The refractive index of the clads 42a and 42b with respect to the laser beam 3 can be changed by the inclination angle θ of the c-axes 52c and 53c of the clads 42a and 42b.
Therefore, the refractive index difference between the core 41 and the clads 42a and 42b can be adjusted by the inclination angle θ of the c-axes 52c and 53c of the clads 42a and 42b. For this reason, by setting the inclination angle θ of the c-axes 52c and 53c of the claddings 42a and 42b appropriately, for example, by allowing only a low-order waveguide mode to be propagated by making the refractive index difference small, the guide is It is possible to configure the optical waveguide by controlling the wave mode.

  In the optical waveguide of FIG. 9, the main coordinate axis of the crystal that maximizes the refractive index of the birefringent crystal material used for the core 41 is arranged in the lateral direction of the core 41, and the refractive index of the birefringent crystal material is minimized. The main coordinate axis of the crystal is arranged parallel to the thickness direction of the core 41, and the main coordinate axis of the crystal where the refractive index of the birefringent crystal material used for the clads 42a and 42b is maximum is the maximum refractive index of the core 41. In the plane parallel to the plane formed by the thickness direction of the core 41 and the light traveling direction, the main coordinate axis of the crystal is arranged in parallel with the main coordinate axis and the refractive index of the birefringent crystal material is minimum. Although the core 41 is arranged with an inclination with respect to the main coordinate axis that minimizes the refractive index, the a-axis and the b-axis of the clads 42a and 42b are interchanged as in the fourth embodiment. It may be arranged. Also in this case, the same effect as in the second embodiment can be obtained.

Furthermore, the a-axis and the b-axis of the core 41 may be replaced with each other. Also in this case, the same effect as in the second embodiment can be obtained.
However, when the b-axis of the core 41 is parallel to the y-axis and the a-axis of the clads 42a and 42b is parallel to the y-axis, for the laser light having a polarization direction parallel to the y-axis, the core refractive index of the 41 _{n b,} clad 42a, the refractive index of 42b becomes _{n a,} consisting of a _n b> n _a to satisfying the total reflection condition. Therefore, the optical waveguide can be guided regardless of the polarization direction of the incident light, and the polarization selectivity is lost.

Embodiment 6 FIG.
FIG. 10 is a perspective view showing an optical waveguide according to Embodiment 6 of the present invention. In the figure, the same reference numerals as those in FIG.
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core 41 is arranged parallel to the light traveling direction, and the main coordinate axis of the crystal having the minimum refractive index of the birefringent crystal material is the core. 41 is arranged in parallel with the horizontal direction.
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the clads 42a and 42b is arranged in parallel to the main coordinate axis having the minimum refractive index of the core 41, and the birefringent crystal material has a refractive index. The main coordinate axis of the crystal with the minimum refractive index is arranged in a plane parallel to the plane formed by the thickness direction of the core 41 and the light traveling direction, and is inclined with respect to the main coordinate axis with the maximum refractive index of the core 41. Has been.

The above arrangement will be specifically described below.
In the optical waveguide of FIG. 10, the main coordinate axes of the crystal are the a-axis, b-axis, and c-axis, the a-axis 61a and the z-axis of the core 41 are parallel, the b-axis 61b and the y-axis of the core 41 are parallel, The c-axis 61c and the x-axis of the core 41 are parallel.
Further, the c-axes 62c and 63c of the clads 42a and 42b are parallel to the x-axis, and the b-axes 62b and 63b of the clads 42a and 42b are inclined by an angle θ with respect to the y-axis in the yz plane. However, 0 ° <θ ≦ 90 °.
The refractive index _n a for a-axis, the refractive index _n b for b-axis, the refractive index with respect to the c-axis is _{n c,} is assumed to be n _{a <n} b _{<n c.}

ｎ_ｃｌａｄ＜ｎ_ｂ Accordingly, the refractive indexes n _clad of the _clads 42a and 42b with respect to the laser light 3 having the polarization direction 4 parallel to the y axis propagating through the core 41 are expressed as follows, and the same effect as in the first embodiment is obtained. can get.

n _clad <n _b

ｎ_ｃｌａｄ＞ｎ_ｂ In this configuration, the core 41 may be arranged so that the a-axis and the c-axis are switched so that the c-axis is parallel to the z-axis, but the c-axis of the clads 42a and 42b is not parallel to the x-axis. Don't be.
When the a-axis of the clads 42a and 42b is parallel to the x-axis, the refractive index n _clad of the _clads 42a and 42b is expressed as follows, and the laser beam cannot be guided because it is not totally reflected. .

n _clad > n _b

Embodiment 7 FIG.
FIG. 11 is a perspective view showing an optical waveguide according to Embodiment 7 of the present invention. In the figure, the same reference numerals as those in FIG.
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core 41 is arranged parallel to the light traveling direction, and the main coordinate axis of the crystal having the minimum refractive index of the birefringent crystal material is the core. 41 is arranged in parallel with the thickness direction.
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the clads 42a and 42b is arranged in parallel to the main coordinate axis having the minimum refractive index of the core 41, and the birefringent crystal material has a refractive index. The main coordinate axis of the crystal having the minimum refractive index is arranged in a plane parallel to the plane formed by the lateral direction of the core 41 and the light traveling direction, and is inclined with respect to the main coordinate axis with the maximum refractive index of the core 41. ing.

The above arrangement will be specifically described below.
In the optical waveguide of FIG. 11, the main coordinate axes of the crystal are the a-axis, b-axis, and c-axis, the a-axis 71a and the z-axis of the core 41 are parallel, the b-axis 71b of the core 41 and the x-axis are parallel, The c-axis 71c and the y-axis of the core 41 are parallel.
Also, the c-axes 72c and 73c of the clads 42a and 42b are parallel to the y-axis, and the b-axes 72b and 73b of the clads 42a and 42b are inclined by an angle θ with respect to the x-axis in the xz plane. However, 0 ° <θ ≦ 90 °.
The refractive index _n a for a-axis, the refractive index _n b for b-axis, the refractive index with respect to the c-axis is _{n c,} is assumed to be n _{a <n} b _{<n c.}

ｎ_ｃｌａｄ＜ｎ_ｂ As a result, the refractive indexes n _clad of the _clads 42a and 42b with respect to the laser light 3 having the polarization direction 23 parallel to the x axis propagating through the core 41 are expressed as follows, and the same effects as those of the second embodiment are obtained. can get.

n _clad <n _b

ｎ_ｃｌａｄ＞ｎ_ｂ In this configuration, the core 41 may be arranged so that the a-axis and the c-axis are switched so that the c-axis is parallel to the z-axis, but the c-axis of the clads 42a and 42b is not parallel to the y-axis. Don't be.
When the a-axis of the clads 42a and 42b is made parallel to the y-axis, the refractive index n _clad of the _clads 42a and 42b is expressed as follows, and the laser beam cannot be guided because it is not totally reflected. .

n _clad > n _b

In the above third to seventh embodiments, an example in which the tilt angles of the clads 42a and 42b are the same is shown, but the tilt angles of the clads 42a and 42b may not be the same.
However, in this case, the refractive indexes of the clad 42a and the clad 42b that are felt by the laser light 3 propagating through the core 41 have different values, and the waveguide mode has a smaller inclination angle of the optical axis. For this reason, the refractive index is limited by the larger clad side.

In the configuration shown in FIG. 7, the a-axis of the clad 42a may be arranged parallel to the x-axis, and the b-axis of the clad 42b may be arranged to be parallel to the x-axis.
Also in this case, since the waveguide mode is limited by the clad side having a higher refractive index, the waveguide mode can be controlled by the inclination angle of the axes of the clads 42a and 42b.

In the first to seventh embodiments described above, the case of an optical waveguide for guiding laser light has been described. However, the core 41 is configured using a crystal material to which active ions serving as a laser medium are added. Thus, a waveguide type laser element can also be configured.
Also in this case, since the refractive index difference can be adjusted by the inclination angle of the crystal axes of the clads 42a and 42b, the spatial mode of the laser light output from the waveguide can be easily controlled.
In addition, the polarization direction of the laser light that can be guided can be selected depending on the arrangement of the main axes of the crystals, and a single polarized output can be obtained.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Core, 2a, 2b Cladding, 3 Laser light, 4 Polarization direction of laser light 3, 5 Optical axis of core 1, 6a, 6b Optical axis of clad 2a, 2b, 11 Refractive index with respect to laser light, 12 Core with respect to laser light Refractive index, 13 refractive index of cladding for laser light, 21 optical axis of core 1, 22a, 22b optical axis of cladding 2a, 2b, 23 polarization direction of laser light 3, 31 optical axis of core 1, 32a, 32b cladding 2a, 2b optical axis, 33a, 33b clad 2a, 2b optical axis, 41 core, 42a, 42b clad, 43a, 51a, 61a, 71a core 41 a axis, 43b, 51b, 61b, 71b core 41 b Axis, 43c, 51c, 61c, 71c c-axis of core 41, 44a, 46a, 52a, 62a, 72a of clad 42a Axis 44b, 46b, 52b, 62b, 72b B axis of clad 42a, 44c, 46c, 52c, 62c, 72c C axis of clad 42a, 45a, 47a, 53a, 63a, 73a A axis of clad 42b, 45b, 47b 53b, 63b, 73b C-axis of the clad 42b, 45c, 47c, 53c, 63c, 73c C-axis of the clad 42b.

Claims (10)

In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a uniaxial birefringent crystal material in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is larger than the refractive index with respect to the other main coordinate axes,
The optical axis of the birefringent crystal material used for the core is arranged in the thickness direction or the lateral direction of the core,
The birefringent crystal material used for the cladding is disposed with an inclination with respect to the direction of the optical axis of the core in a plane parallel to the plane formed by the optical axis direction of the core and the light traveling direction. An optical waveguide characterized by In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are made of a uniaxial birefringent crystal material in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is smaller than the refractive index with respect to the other main coordinate axes,
The optical axis of the birefringent crystal material used for the core is arranged parallel to the traveling direction of light,
The optical axis of the birefringent crystal material used for the clad is inclined with respect to the direction of the optical axis of the core in a plane parallel to the plane formed by the optical axis direction of the core and the thickness direction of the core. An optical waveguide characterized by being arranged. In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are made of a uniaxial birefringent crystal material in which the refractive index with respect to the main coordinate axis of the crystal coincident with the optical axis is smaller than the refractive index with respect to the other main coordinate axes,
The optical axis of the birefringent crystal material used for the core is arranged parallel to the traveling direction of light,
The optical axis of the birefringent crystal material used for the clad is arranged with an inclination with respect to the direction of the optical axis of the core in a plane parallel to the plane formed by the direction of the optical axis of the core and the lateral direction of the core. An optical waveguide characterized by being made. In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a biaxial birefringent crystal material,
The main coordinate axis of the crystal that maximizes the refractive index of the birefringent crystal material used for the core is arranged parallel to the thickness direction of the core,
The refractive index of the core is maximized when the principal coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the cladding is parallel to the plane formed by the thickness direction of the core and the light traveling direction. An optical waveguide characterized by being arranged with an inclination with respect to the main coordinate axis. In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a biaxial birefringent crystal material,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core is arranged in the transverse direction of the core,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the clad is in a plane parallel to the plane formed by the transverse direction of the core and the light traveling direction. An optical waveguide characterized by being arranged with an inclination with respect to a coordinate axis. In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a biaxial birefringent crystal material,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core is arranged in the transverse direction of the core, and the main coordinate axis of the crystal having the minimum refractive index of the birefringent crystal material is the core. Arranged parallel to the thickness direction of
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the cladding is arranged in parallel with the main coordinate axis having the maximum refractive index of the core, and the refractive index of the birefringent crystal material is minimum. The main coordinate axis of the crystal is arranged in a plane parallel to the plane formed by the thickness direction of the core and the light traveling direction, and is inclined with respect to the main coordinate axis where the refractive index of the core is minimum. An optical waveguide characterized by In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a biaxial birefringent crystal material,
The main coordinate axis of the crystal in which the refractive index of the birefringent crystal material used for the core is maximized, and is arranged in parallel with the thickness direction of the core, and the refractive index of the birefringent crystal material is minimized. Are arranged parallel to the direction of light travel,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the cladding is arranged in parallel with the main coordinate axis having the maximum refractive index of the core, and the refractive index of the birefringent crystal material is minimum. The main coordinate axis of the crystal is arranged in a plane parallel to the plane formed by the transverse direction of the core and the light traveling direction, and is inclined with respect to the main coordinate axis where the refractive index of the core is minimum. Characteristic optical waveguide. In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a biaxial birefringent crystal material,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core is arranged in parallel to the light traveling direction, and the main coordinate axis of the crystal having the minimum refractive index of the birefringent crystal material is the above Arranged parallel to the transverse direction of the core,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the cladding is arranged in parallel with the main coordinate axis having the minimum refractive index of the core, and the refractive index of the birefringent crystal material is minimum. The main coordinate axis of the crystal is arranged in a plane parallel to the plane formed by the thickness direction of the core and the light traveling direction, and is inclined with respect to the main coordinate axis where the refractive index of the core is maximum. An optical waveguide characterized by In an optical waveguide comprising a flat core and two clads bonded to the upper and lower surfaces of the core,
The core and the clad are configured using a biaxial birefringent crystal material,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the core is arranged in parallel to the light traveling direction, and the main coordinate axis of the crystal having the minimum refractive index of the birefringent crystal material is the above Arranged parallel to the thickness direction of the core,
The main coordinate axis of the crystal having the maximum refractive index of the birefringent crystal material used for the cladding is arranged in parallel with the main coordinate axis having the minimum refractive index of the core, and the refractive index of the birefringent crystal material is minimum. The main coordinate axis of the crystal is arranged in a plane parallel to the plane formed by the transverse direction of the core and the light traveling direction, and is inclined with respect to the main coordinate axis where the refractive index of the core is maximum. Characteristic optical waveguide.   The optical waveguide according to any one of claims 1 to 9, wherein the birefringent crystal material used for the core is a crystal to which a laser active medium is added.

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