JPH02266333A - Waveguide type optical switch - Google Patents

Abstract

PURPOSE:To eliminate polarization dependency and to decrease the arrangement number of control electrodes by providing 1st and 2nd waveguides almost along the Z axis of the crystal axis of a substrate and using the control electrodes as electrodes which produce electric fields in the 1st and 2nd waveguides almost along the X axis of the crystal axis of the substrate. CONSTITUTION:The 1st and 2nd waveguides 26 and 28 are provided extending almost along the Z axis of the crystal axis of the substrate 24 and the control electrodes 30 product the electric fields in the 1st and 2nd waveguides 26 and 28 almost along the X axis of the crystal axis of the substrate 24. Axes of polarization of polarized light I and II are different in direction from each other, but the both slant almost at 45 deg. from the X axis of the substrate crystal axis, so the refractive indexes of the 1st waveguide 26 and 2nd waveguide 28 to the polarized light I and II are controlled electrically to control the phase difference between the polarized light I and II or perform switching control so that the polarization dependency is eliminated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an optical switch that eliminates polarization dependence, and is suitable for application to, for example, a branching interferometer type or directional coupler type optical switch. be.

(Prior Art) Research and development of waveguide type optical switches that eliminate polarization dependence have been progressing for some time.
es in Electronics and Pho
tonics 26Guided-Wave 0pto
electronics (Guideirado-Wave Optoelectronics) January 1988 p1
98-199J.

The conventional optical switch shown in this document will be briefly explained below with reference to FIG.

FIG. 5 is a diagram schematically showing the configuration of a conventional optical switch. In the figure, 10 is a substrate, 12 and 14 are waveguides,
Roughly 16 and 18 indicate Y branches.

In the optical switch shown in the figure, a waveguide 12.14 and a Y branch 16.18 are formed on the substrate 10 by Ti diffusion, and one end of the Y branch 16 and the other branch are connected to one end of the waveguide 12 and the other branch of the Y branch 16, respectively. It is coupled to one end of the waveguide 14, and similarly, one and the other branch of the Y branch 18 are coupled to the other end of the waveguide 12 and the other end of the waveguide 14, respectively. A Z-cut LiNb○3 substrate is used as the substrate 10, and the waveguide 12 and the 14% i plate 10 are provided in a direction substantially along the X axis of the crystal axis.

Reference numeral 20.22 indicates a control electrode for controlling the propagation path of light, and the control electrode 20 is an electrode provided to form an electric field in the waveguide 10J2 in a direction substantially along the Y axis of the crystal axis of the substrate 10. The control electrode 22 is composed of electrode members 22a, 22b, 22c, and 22d, which are provided so as to form an electric field in the waveguide 12.14 in a direction substantially along the Y-axis of the crystal axis of the substrate 10. Consists of.

In the conventional switch having such a configuration, the propagation path of one polarized light (TE wave) propagating through the waveguide 12J4 is connected to the control electrode 2.
0 and the propagation path of the other polarized light (TM wave) can be controlled by the control electrode 22.

(Problems to be Solved by the Invention) However, in the conventional switch described above, two sets of control electrodes are provided, and one set of control electrodes controls the propagation path of the TE wave propagating in the waveguide, and the propagation path of the TM wave propagates in the waveguide. Control is performed by the other set of control electrodes.

Therefore, a drive circuit must be provided for each set of control electrodes, which poses a problem in that the scale of the drive circuit becomes large.

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide an optical switch that eliminates polarization dependence and can reduce the number of control electrodes provided compared to the conventional optical switch.

(Means for Solving the Problems) In order to achieve this object, the waveguide type optical switch of the present invention includes first and second waveguides juxtaposed on a LIXTA+-xNb03 substrate. , and a control electrode for controlling the refractive index, the first and second waveguides are provided to extend in a direction substantially along the Y axis of the crystal axis of the substrate, and the control electrode is provided to control the refractive index. The present invention is characterized in that the electrode is used to form an electric field in the first and second waveguides in a direction substantially along the X-axis of the crystal axis of the substrate.

In carrying out the present invention, it is preferable that the control electrode be composed of a plurality of electrode members spaced apart in directions substantially along two crystal axes of the substrate.

(Function) According to the waveguide optical switch having such a configuration, the first and second waveguides are provided to extend in directions substantially along two crystal axes of the substrate, and the control electrode is used to control the crystallization of the substrate. An electric field is formed in the second and second waveguides in a direction substantially aligned with the X axis.

Therefore, when forming an electric field in the direction approximately along the X-axis in the first and second waveguides, approximately 45° clockwise from the X-axis.
(+45°) What to do with the tilted polarization axis and one polarizer and
The other polarized light (1), which has a polarization axis tilted approximately 45 degrees (-45 degrees) counterclockwise from the axis, can be excited in the first and second waveguides.

Although the polarization axes of the polarized lights I and H are different from each other, they are both tilted approximately 45 degrees from the X axis of the substrate crystal axis, so the refractive index of the first waveguide and the second waveguide for these polarized lights I and H is Each can be electrically controlled to control the phase difference between the polarized lights I and H, or to perform switching control so as to eliminate polarization dependence.

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

Note that the drawings are merely shown schematically to the extent that the present invention can be understood, and therefore the shapes, dimensions, and arrangement values 1 of each component are not limited to the illustrated examples.

FIG. 1 is a perspective view schematically showing the structure of a first embodiment of the present invention.

The optical switch of the first embodiment includes a first waveguide 26 and a second waveguide 28 provided on a LiNt)03 substrate 24, and a control electrode 30 for controlling the refractive index. The waveguides 26.28 are provided extending in a direction substantially along the Y axis of the substrate crystal axis, and the control electrode 30 applies an electric field in a direction substantially along the X axis of the substrate crystal axis to the waveguide 26.2. It has a configuration in which the electrodes are formed in the same manner.

This embodiment will be described in more detail below with reference to the drawings.

The optical switch of the first embodiment is an example in which a one-manpower one-output optical switch is constructed using a branching interferometer.

In this example, the L i N b O3 substrate 24! &X
The substrate 24 is provided with waveguides 26.28, a Y branch 32 coupled to one end of these waveguides 26.28, and a Y branch 34 coupled to the other end. 26.28 and the Y branch 32.34 constitute a branching interferometer.One branch of the two branches of the Y branch 32 is coupled to one end of the waveguide 26, and the other branch is coupled to the waveguide 28. Similarly, one and the other branch of Y-branch 34 are coupled to the other end of waveguide 26 and the other end of waveguide 28. One end of Y-branch 32. The branch and the waveguide 26 form one arm (A
rm) At and the other branch of the Y branch 32, 34 and the waveguide 28 constitute the other arm A2 of the branch interferometer.

The Y branch 32.34 is made into 7 symmetrical branches, and the confluence of these branches 32.34 (shown with hatching in the figure)
are provided so as to extend in directions substantially along two axes of the substrate crystal axes. The input boat 36 is located at the end of the confluence of the Y-branch 32.
An output boat 38 is provided at the end of the confluence of the Y-branch 34 and the waveguide 26.28 and the Y-branch 32.34 are formed, for example, by diffusing Ti7 onto the substrate 24.

Furthermore, in this embodiment, the control electrode 30 is connected to the first waveguide 2.
6 and an electrode member 30b provided on the second waveguide 28. By applying a positive (or negative) voltage to the electrode member 30a and a positive (or positive) voltage to the electrode member 30b, an electric field in a direction substantially along the X-axis of the substrate crystal axis can be created in the waveguide 26.28.

Next, the operation of this embodiment will be explained.

The light input from the input boat 28 enters the branch point P of the Y branch 32.
After propagating through the waveguides 26 and 28, the zero-branched lights enter the Y branch 34 and merge at the branch point Q of the Y branch 34.

If the phase difference of the lights that merge at the branching point Q is 2nπ, the merged lights will be output from the output boat on the 3rd day and will be in the ON state) and (
2n+1)tt, the combined lights weaken each other and are not output from the output boat 38 (C0FF state), however,
n=o, 1.2, . . .

When the refractive index of the waveguides 26, 28 is electrically changed via the control electrode 30, the phase difference of the merging lights also changes, and therefore, the phase difference of the merging lights can be controlled by controlling the refractive index of the waveguides 26, 28. I can do l.

Figure 2 is a diagram showing an example of the index ellipsoids of the first and second waveguides when a voltage is applied to the control electrode, and is a cross-sectional view taken along the line ■-■ in Figure 1. .

When no voltage is applied to the electrode members 30a, 30b, the refractive index of the waveguides 26, 28 does not change, and therefore the refractive index ellipsoid 40 and the second waveguide 2 for the light of the first waveguide 26 do not change.
Although not shown, the refractive index ellipsoid 42 for light No. 8 has a circular shape and is isotropic. At this time, when light is input to the waveguides 26.28, TE waves and TM waves are excited in the waveguides 26.28.

When no voltage is applied, the light branches at the branch point P in equal phase and merges at the branch point Q in the same phase, thus turning on.

On the other hand, when a voltage is applied to the electrode members 30a and 30b of the control electrode 30 as described above to form an electric field in the direction substantially along the X-axis of the substrate crystal axis in the waveguide 26, 28, the electro-optic effect causes the waveguide 26. The refractive index of .28 changes, resulting in anisotropy in the index ellipsoid 40.42. The amount of change in this refractive index is the electro-optic coefficient γ6. and the amount of change depending on the strength of the electric field.

By arbitrarily setting the magnitude of the voltage applied to the electrode members 30a and 30b, the long axis 4 of the refractive index ellipsoid 401v
It is possible to change the refractive index ellipsoid 42 into an ellipse with the major axis 42a and minor axis 42b tilted approximately 45 degrees from the X axis. can. The long axes 40a and 42b are (K
+45° or -45° tilt, short axis 40b, 42b
In FIG. 2, as an example, the major axis 40ai is shown tilted approximately +45 degrees from the X axis, and the major axis 42a is tilted approximately -45 degrees from the X axis.

When the refractive index ellipsoid 40 is an ellipse as described above, the waveguide 26
When light is input to , the polarized light with the long axis 40a as the polarization axis and the polarized light with the short axis 40b as the polarization axis are excited, so that the polarized light I211 has the polarization axis tilted approximately +45 degrees from the X axis and the polarized light I211 has the polarization axis tilted approximately +45 degrees from the X axis. Polarized light 112B having a tilted polarization axis is excited in the waveguide 26. Similarly, when the refractive index ellipsoid 42 is an ellipse as described above, when light is input to the waveguide 28, polarized light I2a and polarized light 11za are excited in the waveguide 28.

Refractive index of waveguide 26 for polarized light I211 and waveguide 28
The refractive index difference between the refractive index of the waveguide 26 for the polarized light 1za and the refractive index of the waveguide 26 for the polarized light 112JI and the refractive index of the waveguide 28 for the polarized light 112B is expressed by the following equation (1).
It can be expressed as △n.

△n = 2-2"・7g,'r'Ex ------
-(1) However, no is the refractive index of the waveguide 2δ, 28 with respect to ordinary light, `` is the correction coefficient, and Ex is the electric field intensity in the direction along the X axis in the waveguide 26.28.

Here, the electrode member 30a in the Y-axis direction of the substrate crystal axis,
Let L be the M plane distance between the starting point 'IIS and the ending point T of 30b. Since the Y branch 32 is a symmetrical branch, the phases of the branched lights at the starting point Its are equal in phase. Therefore, the terminal value is 1 [the phase difference between the polarizations I211 and I2a at T, and the phase difference between the polarizations Hze and I12a].

Since the Y branch 34 is a symmetrical branch, the branched lights reach the branch point Q and merge while maintaining the phase difference at the terminal value MT.

If the electric field strength Ex is set, the light output is turned ON, and if the electric field strength Ex is set, the light output is turned OFF.

Next, the optical switch of this example will be analyzed using the coupling equation. The following equation (2) is obtained as a coupling equation of the optical switch of this embodiment.

However, εi (1=1.2) is the amplitude at the starting point MS of polarized light (TM wave) in the direction along the X axis, and ε1° is the amplitude at the starting point MS of polarized light (TE wave) in the direction along the Y axis. is the amplitude,
ε5 and εD represent the amplitude of polarized light excited in the waveguide 26 if i=1, and the amplitude of polarized light excited in the waveguide 28 if i=2.Roughly speaking, γ is the electro-optic effect. TM:TE moat conversion term due to the off-diagonal component of . The equivalent refractive index difference between this TE wave and TM wave is
This occurs because there is a difference between the optical structure in the X-axis direction and the optical structure in the Y-axis direction of 6.28.

2 represents the distance in the Y-axis direction of the substrate crystal axis, and j represents an imaginary number.

The solution to coupling equation (2) is equation (3) on the next page, where i = 1.2 and B = γ2 + 62 ε1° is the amplitude at the terminal value i1T of the TM wave, and ε10' is the terminal end of the TE wave. is the amplitude of the value MT. Further, in equation (3), when i=1, the decoding is -, and when i=2, the decoding is 10.

Since the light input from the input boat 36 is split at the Y branch 32 with equal power and merged at the Y branch 34 with equal power, the output power can be expressed by equation (4) on the next page. However, ε(=ε1+ε2) and ε°(=ε, °ε1°10ε2
The amplitude of the light at the bifurcation point Q, also ε. (=ε, .+ε20)
and ε. ', ε1o°1ε2°) is the amplitude of the light at the branch point P.

It can be seen that the FF state can be obtained.

By shifting the optical axes of the waveguides 26, 28 in the same manner as in the case where the optical axes of the waveguides 26, 28 are shifted in the 12-axis direction, the equivalent refractive index of the waveguides for TM waves when no voltage is applied to the control electrode 30 can be changed. The difference between the equivalent refractive index of the waveguide for the TE wave becomes smaller, and as a result, in this embodiment, the substrate 2
Since the X plate was used as 4, it has the following advantages 1)
~3) can be obtained.

1) Waveguides 26, 28 and Y branch 3 that constitute the optical propagation path
When Ti is diffused to form 2.34, the diffusion width of Ti in the waveguide width direction becomes wider than the design conditions compared to the case of Y plate or Z plate, and therefore the light It is possible to reduce the number of bends at curved portions of the propagation path.

2) Optical loss Ii of the optical switch can be reduced.

3) Deterioration of the optical output characteristics of the optical switch due to the pyroelectric effect can be reduced.

In the embodiment described above, the waveguides 26 and 28 and the control electrode 30 are operated under specific conditions that allow ON and OFF states of optical output to be formed.
, Y-branch 32, 34, and other constituent components have been described, however, the production conditions for each constituent component may be arbitrarily and suitably changed as long as ON and OFF states can be formed.

In this embodiment, the optical axis directions of the waveguides 26 and 28 are shifted, but if the optical output can be controlled to ON and 0FFilJ, the optical axis directions of the waveguides 26 and 28 can be changed to the biaxial directions of the substrate crystal axes. It is also preferable to match the direction of the electric field formed in the waveguides 26 and 28 by the control electrode with the X-axis direction of the substrate crystal axis, but if the phase difference of the branched light can be controlled. The direction of the electric field does not have to be exactly aligned with the X-axis direction, and the direction of the electric field may be shifted from the X-axis direction.

FIG. 3 is a perspective view schematically showing the structure of a second embodiment of the present invention. Note that constituent components corresponding to those explained in the above-mentioned embodiments will be described with the same reference numerals, and detailed explanation thereof will be omitted.

The optical switch of the second embodiment includes a first waveguide 40 and a second waveguide 42 provided on a L i N b 03 substrate 24, and a control electrode 44 for controlling the refractive index. A waveguide 40.42 is provided extending in a direction substantially along the Z axis of the substrate crystal axis, and a control electrode 44 applies an electric field in a direction substantially parallel to the X axis of the substrate crystal axis to the waveguide 40.42. It has a configuration with electrodes formed inside.

This embodiment will be explained in more detail below with reference to the drawing IFr.

The optical switch of the second embodiment is an example in which the present invention is applied to a directional coupler type optical switch. In this embodiment, portions of the waveguides 40, 42 are placed in close proximity to allow optical interaction. In FIG. 3, a portion adjacent to the waveguide 40 is designated by the symbol a, and a portion adjacent to the waveguide 42 is designated by the symbol bv. At least the adjacent parts a and b,
It is provided so as to extend in a direction substantially along two axes of the substrate crystal axes.

Input boats 46 and 48 are provided at one end of waveguides 40 and 42, and output boats 50 and 52 are provided at the other end of waveguides 40 and 42.

In this embodiment, the control electrode 44 is composed of an electrode member 44a provided on the adjacent portion a and an electrode member 44b provided on the adjacent portion. An electric field can be generated by the control electrode 44 in a direction substantially aligned with the X axis of the crystal axis.

In this embodiment, in order to eliminate the phase term 6 in the coupling equation, the optical axis directions of adjacent parts a and b are changed to
The optical axis direction v of the 0 portions a and b is preferably shifted from the Z-axis direction so that they do not coincide so that the dispersion of the TE wave and the TM wave is substantially eliminated in b! For example, it may be shifted by about 2 degrees from the two axial directions.

The coupling equation of this embodiment when the phase term 6 is ignored is the following equation (5).

However, ei (i=1.2) is the amplitude of the TM wave and e1
゛ is the amplitude of the TE wave, and these el and el' are i=1
If i = 2, it represents the amplitude of the polarized light excited by the adjacent part aT:vJ, and k is the coupling coefficient, (e + e,') and (e2 ±
e2゛) is the amplitude of light at the terminal position of the electrode members 44a, 44b in the Z-axis direction and (e+±eI.
±82')o is the electrode member 44a, 44 in the Z-axis direction
It represents the amplitude of light at the starting position of b.

From the coupling equation (5), equation (6) on the next page (decoded in the same order) is obtained.

As is clear from equation (6), (e+±e, °) and (e2
±e2°) and therefore adjacent parts a and b
The polarizer excited by the polarizer and the polarizer (1) can be controlled independently, so switching control without polarization dependence can be performed.

The solution to the coupling equation (5) is the equation (7) on the next page (decoding same IIN
).

In the second embodiment as well, since the substrate 24 is an X-plate, the effects 1) to 3) described above can be obtained as in the first embodiment.

(Modification) FIG. 4 is a perspective view schematically showing the configuration of a modification of the second embodiment.

This modification has the same structure as the second embodiment described above, except that the control electrode 44 is composed of a plurality of electrode parts +l+1 materials arranged at 11 intervals in a direction substantially along two axes of the substrate crystal axes. have

In this modification, the control electrode 44 is an inverted ΔB electrode type electrode, and the electrode members 44a and lt, for example, two electrode members 44
a1 and 44a2, and the electrode member 44b is divided into, for example, two electrode members 44b1 and 44b2.

By making the control electrode 44 an inverted ΔB electrode type electrode, there is an advantage that it is easy to create a light switch.
To inversion 〇 Electrode-type control electrode 44 closes adjacent parts a and b
Inside, there is an electric field whose electric field direction is approximately +X-axis direction, and an electric field whose direction is approximately -
When an electric field is formed in the X-axis direction, the TM:TE mode conversion term γ is generated between the adjacent parts a and b that form the electric field in the +X-axis direction and the adjacent parts a and b that form the electric field in the -X-axis direction.
has the opposite sign.

In this way, the sign of the TM:TE mode conversion term γ becomes the opposite sign, and since solution (7) is obtained, the control electrode 44
Even when the electrode is an inverted Δβ electrode type, switching control without polarization dependence can be performed.

The present invention is not limited to the embodiments described above, and therefore, the dimensions, shapes, locations, forming materials, and other conditions of each component can be changed as desired.

For example, if LiNbO2 is used as a substrate material, LIX
Ta+-x NbO3 (however, O≦X≦1) may be used, and the first and second waveguides can be formed by extending in a direction substantially along two axes of the substrate crystal axes, and the first and second waveguides may be As long as an electric field can be formed in the two waveguides in a direction substantially along the X-axis of the substrate crystal axis, the cutting direction of the substrate and the arrangement position of the electrode MIFr are not limited to the above-mentioned embodiments, but can be changed as desired. good.

It is preferable that the optical axes of the first and second waveguides be aligned with the substrate crystal axis in each of the embodiments described above.
In addition, it is not necessary to use any conventionally known suitable technique 1.

Further, in carrying out the present invention, it is preferable that the control electrode is an electrode that produces a non-diagonal component of the electro-optic effect.

(Effects of the Invention) As is clear from the above description, the waveguide optical switch of the present invention has a polarization axis tilted approximately 45° (+45°) clockwise from the X axis of the substrate crystal axis. With one polarizer, approximately 45' (-4
5') The other polarized light (2) having a tilted polarization axis can be excited in the first and second waveguides.

Although the polarization axes of the polarizer and H are different from each other, since they are both tilted approximately 45 degrees from the - It is possible to electrically control the refractive index of the waveguide and the second waveguide, respectively, to control the phase difference between the polarized lights I and H, or to perform switching control.Moreover, the phase difference between the polarized lights I and H can be controlled. The number of control electrodes for control and switching control can be reduced compared to the conventional method.Therefore, it is possible to provide an optical switch that eliminates polarization dependence and can reduce the scale of the drive circuit for the control electrodes.

Further, according to the waveguide type optical switch of the present invention, the refractive index of the first and second waveguides for polarized light excited in these waveguides is substantially approximately the same in the X-axis direction and the Y-axis direction of the substrate crystal axis. Since they can be made the same (because the anisotropy can be reduced), it is easy to create.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing the configuration of the first embodiment of the present invention, and FIG. 2I21 shows an example of the index ellipsoid of the first and second waveguides when voltage is applied to the control electrode. 3 is a perspective view schematically showing a configuration IFrW1 of a second embodiment of the present invention, FIG. 4 is a perspective view schematically showing a configuration 8 of a modification of the second embodiment of the present invention, and FIG. 1 is a plan view schematically showing the configuration of a conventional optical switch. 24... Substrate, 26.40... First waveguide 28.42... Second waveguide, 30.44-... Control electrode. Patent applicant: Oki Electric Industry Co., Ltd. 40. 42: Refractive index ellipsoid 40a, 42a Long axis 40b, 42b: Short axis Refractive index ellipsoid when voltage is applied to the control electrode Figure 2 24: LiNbO2 26: First Waveguide 28/Second waveguide 30: Control electrodes 30a, 30b: Electrode members 32, 34: Y branch 36: Input boat 38: Output port board Perspective view of the first embodiment FIG. 1 40, First waveguide 42: Second waveguide 44: Control electrodes 44a, 44b: Electrode members 46. 48: Input boat 50. 52: Output port Perspective view of the second embodiment FIG.

Claims (2)

[Claims] (1) A waveguide optical switch comprising first and second waveguides juxtaposed on a Li_xTa_1_-_xNbO_3 substrate and a control electrode for controlling the refractive index, wherein the first and second waveguides are The control electrode is provided to extend in a direction substantially along the Z axis of the crystal axis of the substrate, and the control electrode forms an electric field in the first and second waveguides in a direction substantially along the X axis of the crystal axis of the substrate. A waveguide type optical switch characterized by having electrodes that (2) The waveguide optical switch according to claim 1, wherein the control electrode is constituted by a plurality of electrode members spaced apart in a direction substantially along the Z-axis.