JPS59105612A - Separating element for plane of polarization of light - Google Patents

Abstract

PURPOSE:To permit easy production, efficient sepn. of planes of polarization and control of polarized light and to decrease the loss of guided light by disposing two optical waveguides in proximity to each other and providing control electrodes to the respective optical waveguides. CONSTITUTION:The 1st optical waveguide which is made larger in both extraordinary refractive index and ordinary refractive index than a base plate 21 and the 2nd optical waveguide 23 which is made larger only in the extraordinary refractive index than the base plate are disposed in parallel, and electrode groups 24-26 are constituted. Only the TM mode polarized light of the light P incident to the waveguide 22 is then led out to the waveguide 23 and the difference in the phase velocities of respective polarization modes is controlled by the groups 24-26. Such device is usable as a modulator, switch and synthesizing element for planes of polarization. Both waveguides can be formed independently, and since the high refractive index forming materials are respectively of one kind, diffusion control is easy and there is no induction of crystal strain. Since the element is linear-shaped, the loss of the guided light is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to an optical polarization separation element that separates incident light into light with a specific polarization top.

(Prior Art and its Problems) Conventionally, as this type of optical polarization plane splitting element, for example, the one shown in FIG. 1 is known. In the figure, the substrate 1 is a
On this substrate 1, a Y-branch waveguide 2 consisting of a coupling waveguide 2a, branch waveguides 2b and 2C is formed as follows. First, the coupling waveguide 2a and one branch waveguide 2b are formed by diffusing titanium, and then the other branch waveguide 2c is formed by diffusing silver. At this time, silver is also diffused into the coupling waveguide 2a. As a result, both the extraordinary refractive index and the ordinary refractive index of the branch waveguide 2b increase, and the branch waveguide 2C becomes one in which only the extraordinary refractive index increases. Further, the increase value of the extraordinary refractive index in the branch waveguide 2G is much larger than that in the branch waveguide 2b. Therefore, in the coupling waveguide 2a, the increase value of the extraordinary refractive index is approximately equal to that of the branch waveguide 2c, and the increase value of the ordinary refractive index is equal to that of the branch waveguide 2b.

With the above configuration J5, the light P incident on the coupling waveguide 2a
In the coupling waveguide section 2a, polarized wave modes 1 to 1 corresponding to the extraordinary ray and pairs I, i5'Tl8 (Iii wave mode (2) of the ordinary ray are generated, and they propagate at different phase velocities.

At this time, since the substrate 1 is a-c1~, the polarization mode corresponding to the extraordinary ray has a vibration direction in the C-axis direction -1
The polarization mode corresponding to the ordinary ray is the M mode whose vibration direction is in the a-axis direction. Depending on the magnitude of the bar value, the T mode is guided to the branch waveguide 2C,
The T M waves 1 to 5) are guided to a branch 9 wavepath 21).

However, such a Y-branch type polarization plane separation element has the following problems. First, the coupling waveguide 2a diffuses titanium and further diffuses silver, but silver is difficult to diffuse into the titanium diffusion region.
This diffusion of silver also causes distortion in the crystal. In addition, in order to efficiently split the TM mode such as TE mode, the value of the extraordinary refractive index of the branching waveguide 2C must be made larger than the value of 83 in the branching waveguide. As mentioned above, since it is difficult to control the diffusion of silver, the difference in the increase in the extraordinary refractive index between the two waveguides 2b and 2c is small, and the T [mode is
1) The wave is also guided to the side. In other words, the polarization plane separation is insufficient. Furthermore, since the waveguide is of a branched type, a loss due to branching occurs in addition to a loss due to bending. lastly,
In this Y-branch type optical polarization plane separation element, it is not possible to control the separated polarized light simply by separating the optical polarization planes.

・〈Object of the invention〉This invention provides two optical waveguides that are arranged close to each other and
In addition, by providing a bridge electrode in each optical waveguide, manufacturing is easy, polarization planes can be split efficiently, polarized light can be controlled, and loss of guided light can be reduced by increasing θ1. It is an object of the present invention to provide an optical polarization plane splitting element that can reduce the amount of light.

・<Structure and Effects of the Invention> In order to achieve the above object, the present invention provides a first optical waveguide on an optical/new crystal substrate in which both the extraordinary refractive index and the ordinary refractive index are larger than that of the substrate. and a second optical waveguide in which only the abnormal layer 11θy is larger than the substrate are arranged in parallel for a predetermined length, and the first optical waveguide is divided into a plurality of parts in the optical propagation direction. and a second electrode group formed in series on the second optical waveguide.

According to this configuration, 4 of the 8111=1 lights transmitted to the first optical waveguide by the first electrode group a3 and the second electrode? Light with a polarization moat constant j is guided to the second leading wavepath. In this case, the first electrode group 63J:
and the second electrode. Since it is possible to control the mode of optical wave coupling in the second leading waveguide and the phase velocity difference of each polarization mode that is separated into eight waveguides and guided, the extraordinary refractive index values of each waveguide (or unequal By using these control 1ffi poles, the optical polarization plane component #l element according to the present invention can be used as a modulator, a switch, and a polarization plane combining element. In addition, both waveguides can be formed independently, and only one type of high refractive index forming material is required for each waveguide, so there are no problems with conventional methods such as difficulty in controlling diffusion and induction of crystal distortion. Problem 1
．． It is easy to make 'JA'. Furthermore, each waveguide can be formed into a substantially straight line, significantly reducing the loss of guided light.
Rir.

(Description of the Embodiment) At d3 in FIG. 2, a substrate 21 is made of C-C-1- lithium diAbutate, and on this substrate 21 there are two leading waveguides 22, 23 over a length of 1. are formed in parallel at regular intervals, and two electrodes 2 are formed on the optical waveguide 22.
4.25 (Lz: 1+/2), and an electrode 26 having a length Ll is provided on the optical waveguide 23. A positive voltage is applied to the electrode 24 by the power source E+, a negative voltage is applied to the TG pole 25 by the power source E2, and the electrode 26 is held at ground potential.

The guide waveguide 22 is formed by attaching titanium to the top surface of the substrate 21 by vapor deposition or the like so that the waveguide has a planar shape (L+X5 μm).
This was left in an atmosphere at 1000°C for 5 hours and thermally diffused, and both the ordinary refractive index and the extraordinary refractive index were 10-
The value has increased by three orders of magnitude.

''-The light distribution waveguide 23 is formed by depositing aluminum on the substrate 21.
A window with a size of +X5 μm was installed at a distance of 5 μm in parallel from Even after removing , only the abnormal layer JJi ratio has increased to a value of 10-"7!-da. After forming each optical waveguide 22 and 23 on this,
Each of the above electrodes is formed by vapor deposition or the like.

Since the above J: jη configuration is adopted, the light P incident on the optical waveguide 22 from the end face becomes two polarized waves in the optical waveguide 22 as in the previous case. At this time, the substrate 21
is C-k1~, so the pair 1ii5' for the extraordinary ray
The J1 polarization mode is a TM mode whose vibration direction is in the C-axis direction, and the polarization mode corresponding to the ordinary ray is a TE mode whose vibration direction is in the a-axis direction.

As is well known, when two optical waveguides are adjacent to each other, light waves are transferred from one optical waveguide to the other optical waveguide by optical wave coupling, but in this embodiment, the optical waveguide 23 has only an extraordinary refractive index. Since it is an increased waveguide, T M
Only the polarized light of the mode will be transferred to the optical waveguide 23.

What should be noted here is the electrode 24 to which a voltage of opposite polarity is applied. ．． 25 and an electrode 26 held at ground potential. In other words, the length L of the waveguide covered by the electrode 24? The equation for the optical wave coupling between the optical waveguides 22 and 23 in the region () is as follows, and the optical wave coupling between the optical waveguides 22 and 23 in the region () with the waveguide length L2 where the electrode 25 is provided is as follows. The force equation becomes. Here, a and b are the complex amplitudes of the guided light passing through the two optical waveguides 22 and 23, β1 and β2 are the phase velocities of both waveguides, and C is the coupling coefficient between the two outer waveguides.

As is clear from the above two equations, when voltages opposite to each other are applied to the electrodes 24 and 25, the voltage 4iiA24 is
The sign of the coupling coefficient ' is reversed between the region where the current is applied to the electrode 25 and the region J5 is connected to the electrode 25, and the 1"1 of the phase velocity difference β1 to β2 is also reversed. At this time, the 1 M The mode shift amount (energy amount) is as shown in FIG. 3.

This means that the extraordinary refractive index values of both optical waveguides 22 and 23 are not equal, and that the T M It's meant to be waved. Furthermore, as is clear from the following explanation, by using this electrode structure, the optical polarization plane PJJ element according to the present invention can be used as an optical modulator, a switch, and an optical polarization plane separation element. It can be used.

In addition, in Example 11, two electrodes to which opposite voltages are applied to each other were provided on the optical waveguide, but this invention is not limited to this. It goes without saying that a plurality of electrodes to which a voltage is applied may be arranged on the optical waveguide 22 in multiple stages.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of a conventional optical polarization splitter, FIG. 2 is a schematic perspective view of an optical i-wavefront splitter according to an embodiment of the present invention, and FIG. 3 is a schematic perspective view of a conventional optical polarization splitter. FIG. 1 shows the coupling characteristics. 21......Optical crystal substrate 22.23
... Optical waveguide 24.25 ... First electrode group 2G ...... Electrode P ......... Incident light P1. ...
...Polarized light (]-[mode)])2...
......Polarized light (1-M mode) 1-+, L
2... Parallel distance of optical waveguide Fl, E2... Power supply patent applicant Tateishi Electric Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] 1) On an optical crystal substrate, a first guiding waveguide having both an extraordinary refractive index and an ordinary refractive index larger than that of the substrate, and a second optical waveguide having only an extraordinary refractive index larger than that of the substrate. a first electrode JIY arranged in parallel with a predetermined height and divided into a plurality of parts in the light propagation direction A on the first optical waveguide and to which a reverse voltage is alternately applied; a second electrode formed in series on the optical S wavepath of 41; An optical polarization plane splitting element characterized in that light in a mode is guided to the second optical waveguide.