JPH0450807A - Waveguide type optical polarized wave separating device - Google Patents

Abstract

PURPOSE:To separate input light beam into two each orthogonal polarized light with high isolation and low loss by constituting the device of a polarized wave separating device which utilizes a difference of coupling length of a TE mode and a TM mode of a waveguide type directional coupler, and a polarizer placed on the way of two pieces of output waveguides of the same device. CONSTITUTION:The device is constituted of polarized wave separating devices 11, 12 which utilize a difference of coupling length of a TE mode and a TM mode of a waveguide type directional coupler, and polarizers 3, 4 which are placed on the way of two pieces of output waveguides 15, 16, respectively of its device and have an azimuth conforming to a polarized light of a predominant mode propagated along the output waveguides 15, 16. When light of no- polarization is inputted to an input waveguide 10 of this device, light consisting of only almost the TM mode is outputted from one output waveguide, and from the other output waveguide, light consisting of only almost the TE mode is outputted. In such a way, the inputted light beam can be separated into two each orthogonal polarized light with high isolation and low loss, and accumulation to other device, for instance, the directional coupler can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is a method for dividing light propagating in a leading wave path into two waves perpendicular to each other.
The present invention relates to a waveguide type optical polarization separation device that separates polarized light (TE mode and TM mode) into two waveguides. More specifically, the present invention relates to a waveguide type optical polarization separation device that can ensure high isolation even if there are manufacturing variations.

<Prior art> An optical polarization separation device is a device that separates light propagating in an optical fiber or optical waveguide into two linearly polarized lights perpendicular to each other. It is possible to achieve a stable reception power regardless of the polarization state of the signal light, and it is an essential component along with a directional coupler in the reception section of polarized divergent coherent communication.

Up until now, there have been two types of optical polarization separation devices: fiber type and waveguide type. This uses the difference in the bond length of the eigenmodes.

However, ] 1 Inoku Kabra 11 output ports are fighting
Because it is an 1
Yo, this Fino size Kabra has no drawbacks and is suitable for accumulation, and it is suitable for fire (same as Kabra, patent application Hei 1-397)
There was a waveguide type polarization separator disclosed in No. 911.

The former is constructed by utilizing the polarization dependence of a waveguide type directional coupler, but it has been considered to intentionally increase the polarization dependence in order to make it smaller. For example, R, A, BET
TS is ELECTRONIC8LETTER8 magazine, 19
In the configuration reported in No. 26, 1990, p. 450, the distance between the parallel waveguides in the coupling region of the directional coupler is made very small to increase the difference in coupling coefficient due to polarization.

This configuration has the advantage that polarization separation can be performed using only the waveguide. The latter utilizes polarization separation due to the birefringence effect of a uniaxial crystal plate inserted into a waveguide, and has the advantage of being easy to design and manufacture, as well as providing large isolation.

<Problems to be Solved by the Invention> However, each of the conventional waveguide type optical polarization separation devices has the following inherent drawbacks.

Devices that use the polarization dependence of a directional coupler have a problem in that the output waveguide has an isolane tangent of at most 10 to 15 dBL.

In a device using polarization separation using a -axis crystal, an isolene tan of 20 (18 or more) can be easily obtained, but since a groove is formed in the middle of the waveguide, an insertion loss of a few tenths of a dB is unavoidable.

For this reason, it is a waveguide type that is suitable for integration with a light receiving element.
There has been a desire for an optical polarization separator device that has low insertion loss and can provide an isolating condenser of about 20 clB.

<Means for solving the problems> The present invention solves the above-mentioned drawbacks by dividing the input light into two
It is an object of the present invention to provide a waveguide type optical polarization separation device that can separate light into two orthogonal polarizations with high isolation and low loss, and can be integrated with other devices such as directional couplers.

The present invention provides a polarization separation device that utilizes the difference in coupling length between the TE mode and TM mode of a waveguide type directional coupler, and a polarization separation device that is disposed in the middle of two output waveguides of the device,
A waveguide type optical polarization separation device is constructed from a polarizer having an azimuth that matches the polarization of the dominant mode propagating through the output waveguide.

When unpolarized light is input to the input waveguide of the above device, one output waveguide outputs light consisting almost only of TM mode, and the other output waveguide outputs light consisting almost only of TE mode. A certain amount of light is output.

<Example> Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing a waveguide structure of an embodiment of a waveguide type optical polarization separation device according to the present invention.

The substrate 1 is a borosilicate glass substrate on which a waveguide can be formed by ion exchange. A single mode waveguide with a pattern as shown in the figure was formed on the substrate 1 by a two-stage thermionic exchange method. 1o is an input waveguide, 11.12 is a directional coupler section,
13.14 is an output coupling part, and 16.16 is an output waveguide. The directional coupler sections 11 and 12 are arranged in parallel with a narrow waveguide axis interval and are optically coupled. Output connection 13.14
is a waveguide pair whose waveguide spacing is gradually widened to terminate the directional coupler section. The output coupling 13.14 leads to mutually parallel output waveguides 15.16. A groove 2 is formed diagonally across the output waveguide 15, 16. The width of the groove is 25 μm1 and the depth is 300 μm.
It is m. A polarizer 3.4 is inserted and fixed in the groove 2.

In general, it is desirable that the waveguide axis spacing S be smaller, since the polarization dependence is greater. In the example, the length is 12 μm, and the length of the directional coupler portion 11.12 is 18 mm. The slope of 42 is to prevent residual reflections from returning in the opposite direction, and is usually
It is good if it is more than a degree. Polarizing plate 3.4 is a laminated polarizer (trade name: Lamiball) made by laminating 5I02 film and A1 film, element thickness 20 μm, insertion loss 0.15 dB,
Extinction ratio is 25 (IB).

When unpolarized light with a wavelength of 1.55 μm is input to this waveguide type optical wave separation device from the input waveguide, 99.8% of the total output is TM mode light in the output waveguide 14. The light output in TE mode was only 0.2%. Output waveguide 1
6, the TM mode light is 99.7% of the total output.
The tip of E mode is 0. Output was only 3%. That is, the amount of TE mode light leaking into the TM port is less than -27 dB, and the amount of TM mode light 1 leaking into the TE boat is -25 dB.
It was below B. When the TE mode was input to the input waveguide 1o, the insertion loss from the input waveguide 1o to the output waveguide 15 was 0.8 dBm', including the coupling loss between the waveguide and the external single mode fiber.

Furthermore, when the TM mode was input to the input waveguide 10, the insertion loss from the input waveguide 10 to the output waveguide 16 was 0.9 dB, including the above-mentioned coupling loss.

The above embodiment is used when only the function of polarization separation is required. Next, a method of applying the waveguide type optical polarization separation device according to the present invention will be explained. FIGS. 2 and 3 are diagrams showing a device configuration in which a waveguide type optical polarization separation device is integrated with a waveguide type directional coupler. This device can be used in the optical receiving section (mixing of signal light and local light for each polarization component) of a reception module for polarization diversity coherent communication systems.

In the first configuration example shown in Figure 2, the input light is first separated into two polarized lights using a part of the waveguide type optical polarization separation device, and then the signal light and the local light are separated for each polarization using two directional couplers. They are mixed, and finally, unnecessary polarized light is removed by a part of the waveguide type optical polarization separation device.

The waveguides from IOA to 14A in the figure are part of one optical polarization separation device, IOA is a manual waveguide, IIA
, 12A is a directional coupler section, 13A% 14A is an output connection section. Same (, the waveguide from IOB to 14B in the figure is part of another optical polarization separation device, and the IO
B is the input waveguide, IIB, 12B is the directional coupler section, 1
3B and 14B are output connections. The parameters of the two directional couplers were the same as in the previous embodiment.

After the output connection parts 13A and 13B intersect and switch positions, the output connection parts 14A and 13B connect to the first directional coupler 3.
0, and the output waveguide sections 13A and 14B are connected to the second directional coupler 40. Grooves 2 are formed at positions across the output waveguides 5L52, 53, and 54 of the directional couplers 30 and 40.

In the middle of the groove 2 corresponding to the positions of the output waveguides 51 and 52,
A first polarizer 3 whose azimuth matches the TM mode is inserted and fixed. A second polarizer 4 whose azimuth angle matches that of the TE mode is inserted and fixed in the polarizer corresponding to the positions of the output waveguides 53 and 54.

Input waveguide! The signal light 2°A and the local light 20B entering from the OA and IOB are sent to the directional coupler sections 11A, 112A and II.
B, 12B is roughly separated into TM mode and TE mode,
In the TM mode, the output waveguides 14A and 13B are used, and in the TE mode, the output waveguide 13A is used.

Output to 14B. TE of signal light 20A and local light 20B
Focusing only on the mode component, the directional coupler 30 has 50:
50, unnecessary TE mode components are removed by polarizer 3, and the signal reaches output waveguides 51 and 52. Therefore, the polarization separated output lights 23 and 24 are the signal light 20A and the local light 2
Only the TM mode component of 0B is the light mixed at a ratio of 60:60. Focusing only on the TE mode components of the signal light 20A and the local light 20B, they are mixed at a ratio of 50:50 in the directional coupler 40, and unnecessary TM mode components are further removed in the polarizer 4, reaching the output waveguides 53 and 54. . Therefore, the polarization separation output light 25.26 is the TE of the signal light 2OA and the local light 20B.
Only the mode component is light mixed at a ratio of 50:50.

In this application example, the combination of the directional couplers 11A, 12A and the polarizer 3.4 constitutes the waveguide type optical polarization separation device of the above embodiment. Same (, directional coupler section 11B,
12B and the polarizer 3.4 constitute the waveguide type optical polarization separation device of the above embodiment.

When unpolarized light with a wavelength of 1.55 μm is input into this waveguide type optical polarization separation device from the input waveguide, the TM mode light of the signal light 20A and the local light 20B is transmitted to the output waveguides 23 and 24. 50%: A branching ratio of 50% is obtained with a deviation of ±1.0% or less, and the output waveguide 25.26 has a signal light of 20 A and a local light of 20 B] TE mode light is 50% = 50% branching ratio was obtained with a deviation of ±1°0% or less. Amount of light in TE mode leaking into the TM port, TM leaking into the TE port
The light intensity of both modes was less than -25 dB.

In the second configuration example shown in Fig. 3, input light and signal light are mixed before polarization separation and taken out to two output waveguides, and then
The light in each of the two output waveguides is completely separated into two polarized lights. 50 in the figure is a directional coupler, and the waveguides 10C to 14C and the polarizer 3.4 are one optical polarization separation device. IOC is the input waveguide, IIC, 12
C is a directional coupler section, and 13C and 14C are output coupling sections. Similarly, the waveguides 10D to 14D and the polarizer 3.4 are another optical polarization separation device. I
OD is the input waveguide, IID, 12D is the directional coupler section,
13D and 14D are output coupling parts. Output waveguide section 13
C and 13D intersect and switch positions, and the output waveguide section 5
1-52-53-54''.

Grooves 2 are formed at positions crossing the output waveguides 51'', 51'', 53'' and 54-. Output waveguide 51-52
A first polarizer 3 whose azimuth matches the TM mode is inserted and fixed in the full 2 corresponding to the - position.

In the groove 2 corresponding to the position of the output waveguide 5354-,
Azimuth matches the TE mode1. A second polarizer 4 is inserted and fixed.

The signal light 2OA and the local light 20B are mixed by a directional coupler 50, and then separated into TM mode and TE mode.
The mode is output to the output waveguide 5l-152-TE mode is output to the output waveguide 53''54-.

Therefore, from the output waveguide 51" 52-, the signal light 2
Polarization-separated output light 23 and 24 of only the TM mode component of light that is a mixture of 0A and local light 20B is output. Output waveguide 5
From 3.54, polarization separation output light 25.26 of only the TE mode component of the light mixed with the signal light 20A and the local light 20B is obtained.
outputs.

When unpolarized light with a wavelength of 1.55 μm is input into this waveguide type optical polarization separation device from the input waveguide, the TM mode light enters the output waveguides 23 and 24 with a branching ratio of 50% = 50%. is obtained with a deviation of ±1.0% or less, and the output waveguide 25.
26, the TE mode light is 50% = 50% branching ratio is shifted by ±1. It was obtained at 0% or less. The amount of light in the TM mode leaking into the TE boat and the amount of light in the TE mode leaking into the TM boat were both less than -25 dB.

In the embodiment, a laminated ball was used as the polarizer 3.4, but a plate cut out of a uniaxial crystal such as a calcite plate in an appropriate direction may also be used. In order to increase the polarization dependence of the directional coupler sections 11, 12, the cross-sectional shape of the waveguide may be flattened, or the waveguide may be loaded with a metal film overlayer. Also, although only the output connection part 14 is bent,
The design of the bending method is arbitrary.

<Effects of the Invention> As described above, according to the present invention, a waveguide type optical polarization separation device is provided which spatially separates and outputs input light as two mutually orthogonal polarized outputs.

The excess loss can be less than 1 dB and the isolation sun can be more than 25 dB. In the present invention, the difference in polarization of the coupling length of the directional coupler is utilized, but this part requires a guard to reduce the loss of the polarizer that follows, and the polarization separation characteristic is It doesn't have to be perfect as long as it does not affect the output waveguide. , the loss increases by Q,2(IB).

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of a waveguide type optical polarization separation device/< device according to the present invention, and FIG. 2 is a plan view showing an application example of the waveguide type optical polarization separation device of the present invention. 3 are plan views showing another example of application of the differential chair of the present invention. In the figures, 1...substrate 10...input waveguide 11. 12... Directional coupler section 15.16
......Output waveguide 2...Groove 3. 4. It is a polarizer. Figure Figure

Claims (1)

[Claims] a polarization separation device that utilizes the difference in coupling length between the TE mode and TM mode of the waveguide type directional coupler; A waveguide type optical polarization separation device consisting of a polarizer with an azimuthal angle that matches the polarization of the dominant mode propagating.