JP5777095B2 - Multimode interference device, 1 × 2 optical distributor, cross-polarization element between different polarizations, 2 × 2 optical distributor and 2 × 2 optical switch - Google Patents

Description

  The present invention relates to a multi-mode interference device having a novel structure, and a 1 × 2 optical splitter, which uses this and is made polarization independent so that it can be used without depending on TE polarized light and TM polarized light, The present invention relates to a crossed polarization element, a 2 × 2 optical distributor, and a 2 × 2 optical switch.

  The multi-mode interference device is a known technique as disclosed in Non-Patent Document 1 and the like, for example, a 1 × N optical splitter with 1 input N output based on a semiconductor optical waveguide or N with N input N output. It is used when manufacturing a × N optical distributor, an N × N switch, or the like.

A standard 1 × 2 optical distributor (one input and two output optical distributor) and a 2 × 2 optical distributor (two inputs and two output optical distributor) constituted by multimode interference devices are shown in FIGS. 9 and 10, respectively. Is shown in As shown in FIG. 9, in the 1 × 2 optical distributor, when the width is W, the input port is provided at the center of the input side end (that is, the position of W / 2), and two An output port is provided at a position on the inner side (side closer to the center) by W / 4 from both ends of the output side end. Further, as shown in FIG. 10, in the 2 × 2 optical splitter, when the width is W, the two input ports are respectively positioned at the inner side by W / 4 from both ends of the input side end. Provided, and two output ports are provided at positions inside by W / 4 from both ends of the output side end. A two-output optical splitter constituted by such a multimode interference device can appropriately select the length L of the multimode interference part (that is, the distance between the input side end and the output side end), It is generally known that a 3 dB optical distributor in which light is equally distributed to the two output ports, and the length L of the multimode interference unit is approximately given by the following equation.

なお、β₀、β₁は何れも多モード干渉部の厚さ、幅Ｗ及び偏波の種類（ＴＥ偏波、ＴＭ偏波）に依存する定数である。すなわち、多モード干渉部の長さＬは、多モード干渉部の厚さ、幅Ｗ及び偏波の種類に依存して変化する。 Here, k is a non-negative integer. L _c is called a coupling length, and is defined by the following equation, where β ₀ is a zero-order mode propagation constant and β ₁ is a first-order mode propagation coefficient.

Β ₀ and β ₁ are constants that depend on the thickness, width W, and polarization type (TE polarization, TM polarization) of the multimode interference unit. That is, the length L of the multimode interference unit varies depending on the thickness, width W, and type of polarization of the multimode interference unit.

L.B.Soldano, E.C.M.Pennings, "Optical Multi-Mode InterferenceDevices Based on Self-Imaging: Principles and Applications", J. LightwaveTechnology, vol.13, no.4, pp.615-627 (1995)

  Optical circuits using silicon optical waveguides are promising for large-scale integration, but they often have birefringence due to the aspect ratio of the waveguide core cross section, and the characteristics of optical circuits are polarization dependent. Have That is, the characteristics of the optical circuit depend on whether the light transmitted through the optical circuit is TE polarized or TM polarized. However, it is desirable that the optical circuit can be used regardless of the type of polarization.

For example, conventional multimode interference devices, the optical distributor or an optical switch configured by using a hand, as described above, the coupling length L _c to be used in selecting the length L of the multimode interference portion polarization Since it changes depending on the type, it has polarization dependency. For this reason, multimode interference devices, and conventional optical distributors and optical switches configured using multimode interference devices are designed exclusively for TE-polarized light or TM-polarized light. It is desirable to make it available for polarized light. However, the conventional multimode interference device and the conventional optical distributor or optical switch configured using the same are not polarized so that they can be used for both TE polarized light and TM polarized light. Did not exist.

  Accordingly, it is an object of the present invention to provide a multimode interference device that can solve the problems in the prior art and can make the optical distributor, the cross-polarization crossing element, and the optical switch polarization independent. .

  In view of the above object, the present invention is a multi-mode interference device having a width W and having a first end and a second end at both ends in the optical transmission direction, the center of the first end in the width direction. A first port provided on the second end, a second port provided on the inner side by W / 4 from either one of both ends in the width direction of the first end, and both ends in the width direction of the second end A third port and a fourth port provided on the inner side by W / 4 respectively, and when TE polarized light is input from the first port, the TE polarized light is transmitted to the third port and the second port. The multimode in the optical transmission direction so that the TM polarized light is evenly distributed to the third port and the fourth port when the TM polarized light is input from the second port evenly distributed to the four ports. A multimode interference device having a length L of the interference device is provided.

  In the multimode interference device, the TE polarized light is input to the first port and the TM polarized light is input to the second port, so that the input light is transmitted to the third port and the second polarized light in both cases of the TE polarized light and the TM polarized light. It is possible to output evenly distributed to four ports.

In the multimode interference device, a function of the width W representing the coupling length of the multimode interference device with respect to TE polarized light is L _c ^TE (W), and the width W representing the coupling length of the multimode interference device with respect to TM polarized light is When the function is L _c ^TM (W), it is preferable that L and W satisfying the following simultaneous equations are the length and width of the multimode interference device, respectively. However, L _c is a constant determined by Equation (2).

  The present invention also includes an input port, a TE polarization output port, and a TM polarization output port. When light is input to the input port, TE polarization light is output from the TE polarization output port and the TM polarization is output. A polarization separation element that outputs TM polarized light from an output port; and the multimode interference device as described above, and connects the TE polarization output port of the polarization separation element to the first port, and The TM polarization output port of the polarization separation element is connected to the second port to provide a polarization-independent 1 × 2 optical distributor. In the 1 × 2 optical distributor, since the input light is evenly distributed regardless of the type of polarization, it can be used without depending on the type of polarization.

  Further, according to the present invention, the multi-mode interference device as described above is arranged so that the second ends face each other, and the third port of one multi-mode interference device and the fourth of the other multi-mode interference device are arranged. And a fourth port of the one multimode interference device is connected to a third port of the other multimode interference device and is input to the first port of the one multimode interference device. TE polarized light is output from the first port of the other multimode interference device, and TM polarized light input to the second port of the one multimode interference device is output from the second port of the other multimode interference device. Provided is a cross element for cross-polarizations which is configured to be output. In the cross-polarized crossing element, the second end portions are arranged to face each other, and the third port and the fourth port of one multimode interference device are the fourth port and the third port of the other multimode interference device, respectively. Since it is connected to the port, the position of the second port of one multimode interference device and the position of the second port of the other multimode interference device are arranged on opposite sides of the first port. Therefore, when TE polarized light input to the first port and TM polarized light input to the second port are output, the relative positions with respect to each other are reversed, and the TE polarized light and the TM polarized light intersect. The function to make it play.

Above cross polarization cross elements, two of the multimode interference devices, the fourth port of the multimode interference device of the third port and the other the one multimode interference devices, the fourth one multimode interference devices port and said by other integrally as if connected by the end What happened the third port is the second to face of the multimode interference device formed so that the width W, is 2L length It may be.

  The present invention also provides a first polarization separation element and a second polarization separation element each having an input port, a TE polarization output port, and a TM polarization output port, an input side first port, and an input side. A first cross-polarization crossing element such as the cross-polarization crossing element having the second port, the output first port and the output second port, each having two input ports and two output ports. A 2 × 2 optical splitter for TE polarization and a 2 × 2 optical splitter for TM polarization, an input side first port, an input side second port, an output side first port, and an output side second port; A first cross-polarization element having a TE polarization input port, a TM polarization input port, and an output port, and Two polarization combining elements in order, and the TE polarization output of the first polarization separation element And a TM polarization output port of the second polarization separation element is connected to the input of the first cross polarization element of the first cross polarization element. 2 × 2 light for the TM polarization, the TM polarization output port of the first polarization separation element and the output second port of the first cross-polarization crossing element are connected to the second side port. The TE polarization output port of the second polarization separation element and the output first port of the first cross polarization element for the TE polarization are connected to the two input ports of the distributor. The 2 × 2 optical splitter is connected to the two input ports, and one of the two output ports of the TM polarized 2 × 2 optical splitter is connected to the input of the second cross-polarized cross element. The two output ports of the 2 × 2 optical splitter for TE polarization One side is connected to the input side first port of the second cross-polarization element of the second different polarization, and between the other of the two output ports of the 2 × 2 optical splitter for TM polarization and the second different polarization The output side first port of the crossing element is connected to the two input ports of the first polarization combining element, and the other of the two output ports of the 2 × 2 optical splitter for the TE polarization 2 × 2 optical distributor in which the second input port of the second cross polarization crossing element is connected to the two input ports of the second polarization combining element to make the polarization independent. I will provide a.

  The present invention also provides a first polarization separation element and a second polarization separation element each having an input port, a TE polarization output port, and a TM polarization output port, an input side first port, and an input side. A first cross-polarization crossing element such as the cross-polarization crossing element having the second port, the output first port and the output second port, each having two input ports and two output ports. It has a 2 × 2 optical switch for TE polarization and a 2 × 2 optical switch for TM polarization, an input side first port, an input side second port, an output side first port, and an output side second port. A second polarization crossing element such as the above-mentioned cross polarization crossing element, a first polarization combining element each having a TE polarization input port, a TM polarization input port, and an output port; And a polarization beam combining element in order, the TE polarization output of the first polarization separation element And a TM polarization output port of the second polarization separation element is connected to the input of the first cross polarization element of the first cross polarization element. 2 × 2 light for the TM polarization, the TM polarization output port of the first polarization separation element and the output second port of the first cross-polarization crossing element are connected to the second side port. The TE polarization output port of the second polarization separation element and the output-side first port of the first cross-polarization element for the TE polarization are connected to the two input ports of the switch. The two output ports of the 2 × 2 optical switch for TM polarization are connected to the two input ports of the 2 × 2 optical switch, and one of the two output ports of the 2 × 2 optical switch for TM polarization is connected to the second input side of the second cross-polarized cross element. And the two outputs of the 2 × 2 optical switch for TE polarization. One of the ports is connected to the first input-side port of the second cross-polarized cross element, and the other of the two output ports of the 2 × 2 optical switch for TM polarization and the second differential The output side first port of the wave crossing element is connected to the two input ports of the first polarization combining element, and the other of the two output ports of the 2 × 2 optical switch for TE polarization And the output-side second port of the second cross-polarization crossing element are connected to the two input ports of the second polarization-combining element to make a polarization-independent 2 × 2 optical switch provide.

  According to the multimode interference device of the present invention, the input port dedicated to the TE polarized light and the input port dedicated to the TM polarized light are provided, and the input light is transmitted in both cases of the TE polarized light and the TM polarized light. It becomes possible to distribute evenly to one port. If the multimode interference device is used, the 1 × 2 optical distributor can be made polarization independent. Furthermore, if the multimode interference device is used, it is possible to provide a cross-polarized cross element that functions to cross TE-polarized light and TM-polarized light. A two-light distributor and a 2 × 2 optical switch are provided. Such a polarization-independent 1 × 2 optical distributor, 2 × 2 optical distributor, and 2 × 2 optical switch are particularly useful as an element incorporated in an optical node device such as an optical cross-connect as an element element. .

It is a top view which shows the whole structure of the multimode interference device by this invention. The relationship between the length L and the width W of the multimode interference part to be satisfied in order that the TE polarized wave input from the center first port on the input side is distributed to the third port and the fourth port on the output side. Multimode to be satisfied in order for the TM polarization input from the second port on the input side provided at a position deviated from the first port to be distributed to the third port and the fourth port on the output side It is a graph which shows the curve showing the relationship between the length L and width W of an interference part. Calculation using the finite-difference time-domain method to propagate the TE polarization input from the first port on the input side and the TM polarization input from the second port on the input side through the multimode interference unit Results are shown. It is a top view which shows the whole structure of the 1 * 2 optical splitter made into polarization independent using the multimode interference device shown by FIG. It is a top view which shows the whole structure of the cross element between different polarizations made into polarization independence using the multimode interference device shown by FIG. It is a top view which shows the modification of the cross element between different polarizations shown by FIG. It is a top view which shows the whole structure of the 2 * 2 optical splitter made into polarization independence using the cross element between different polarizations shown by FIG. It is a top view which shows the whole structure of the 2 * 2 optical switch made polarization independent using the cross element between different polarizations shown by FIG. It is a top view which shows the whole structure of the conventional 1x2 optical splitter comprised using the multimode interference device. It is a top view which shows the whole structure of the conventional 2 * 2 optical splitter comprised using the multimode interference device.

  Embodiments of a multimode interference device according to the present invention will be described below with reference to the drawings.

First, the overall configuration of the multimode interference device 10 according to the present invention will be described with reference to FIG. The multimode interference device 10 includes a multimode interference portion 12 formed of a silicon thin plate, a first port 14 formed at one end portion (first end portion 12 a) in the length direction of the multimode interference portion 12, and a first port 14. The second port 16 includes a third port 18 and a fourth port 20 formed at the other end portion (second end portion 12b) in the length direction of the multimode interference unit 12, and each port 14, 16, 18 , 20 is connected to an input / output waveguide (not shown) surrounded by, for example, SiO ₂ (silicon dioxide). In the following, the distance between the first end 12a and the second end 12b of the multimode interference unit 12 is the length L, the direction perpendicular to the length L is the width W, and the length direction is perpendicular to the width direction. This direction is referred to as thickness D.

  The first port 14 is provided at the center in the width direction of the first end portion 12a, that is, at a position on the inner side by W / 2 from the side end of the first end portion 12a toward the center in the width direction. The center is provided at a position on the inner side by W / 4 from either one of both side ends of the first end portion 12a toward the center in the width direction. In FIG. 1, the second port 16 is centered at a position on the inner side by W / 4 from the right end of the first end portion 12a toward the center in the width direction. As shown, the center may be provided at a position on the inner side by W / 4 from the left end of the first end portion 12a toward the center in the width direction.

  The TE polarized light is input to the first port 14, and the TE polarized light input to the first port 14 is output by being equally distributed to the third port 18 and the fourth port 20 with a loss of 3 dB. It has become. Also, TM polarized light is input to the second port 16, and the TM polarized light input to the second port 16 is evenly distributed and output to the third port 18 and the fourth port 20 with a loss of 3 dB. It is like that.

ここで、Ｌ_c ^TE（Ｗ）はＴＥ偏波光に対する多モード干渉デバイスの結合長を表す幅Ｗの関数、Ｌ_c ^TM（Ｗ）はＴＭ偏波光に対する多モード干渉デバイスの結合長を表す幅Ｗの関数である。 In the multimode interference device 10, the TE polarized light input to the first port 14 and the TM polarized light input to the second port 16 are both output to the third port 18 and the fourth port 20. The width W and the length L of the multimode interference part are determined so as to satisfy the following simultaneous equations (1).

Here, L _c ^TE (W) is a function of the width W representing the coupling length of the multimode interference device with respect to TE polarized light, and L _c ^TM (W) is the width W representing the coupling length of the multimode interference device with respect to TM polarization light. Is a function of

The above equation is obtained as follows.
In order for the light input to the first port 14 to be distributed and output to the third port 18 and the fourth port 20, when the function representing the coupling length is L _c (W), the 1 × 2 distributor As in the case of, the width W and the length L of the multimode interference unit 12 must satisfy the following expressions.

In addition, in order for the light input to the second port 16 to be distributed and output to the third port 18 and the fourth port 20, when the function representing the coupling length is L _c (W), 2 × 2 As in the case of the distributor, the width W and the length L of the multimode interference unit 12 must satisfy the following expressions.

  Therefore, if the width W and the length L corresponding to the intersection of the curve represented by the expression (2) and the curve represented by the expression (3) are respectively the dimensions of the multimode interference part, the input from the first port 14 is performed. The two-branch output can be obtained from the third port 18 and the fourth port 20 for both the TE polarized light and the TM polarized light input from the second port 16.

  The present inventor inputs TE polarized light to the first port 14 and TM polarized light to the second port 16, and sets k = 1 in equation (2) and k = 0 in equation (3). As shown in FIG. 4, a curve 22 representing the relationship between L and W satisfying the equation (2) and a curve 24 representing the relationship between L and W satisfying the equation (3) produce an intersection, and the equation (2) and It was found that L and W simultaneously satisfying the formula (3) existed, and based on this, the formula (1) was obtained.

  As an example, FIG. 3 shows TE polarized light (FIG. 3A) and TM polarized light (FIG. 3) when the thickness D is 220 nm, the core width of the input / output waveguide is 450 nm, and the width W is 7.4 μm. The simulation result when the propagation state of 3 (b) is two-dimensionally calculated by the finite difference time domain method is shown. When simultaneous equations (1) are solved under the same conditions, the length L of the multimode interference section 12 is 153 μm. Also from the simulation results, it can be confirmed that the TE polarized light and the TM polarized light propagate to two common locations at a position separated by 153 μm from the input side end (first end 12a in FIG. 1). . Therefore, if the third port 18 and the fourth port 20 are provided at these two common locations, both the TE polarized light input to the first port 14 and the TM polarized light input to the second port 16 are the first. It can be seen that two branches from the third port 18 and the fourth port 20 are output evenly.

  As described above, in the multimode interference device 10 of the present invention, if the TE polarized light is input to the first port 14 and the TM polarized light is input to the second port 16, the TM polarized light is also applied to the TE polarized light. On the other hand, a two-branch output can be obtained from the third port 18 and the fourth port 20 with a loss of 3 dB.

  By using such a multimode interference device 10 according to the present invention, various element elements that are made polarization-independent can be configured. Hereinafter, with reference to FIGS. 4 to 8, various polarization-independent element elements configured by using the multimode interference device 10 according to the present invention will be described.

  FIG. 4 shows a polarization-independent 1 × 2 optical splitter 26 constructed using the multimode interference device 10 shown in FIG. The 1 × 2 optical splitter 26 shown in FIG. 4 includes the multimode interference device 10 shown in FIG. 1 and a polarization separation element 28 provided in the front stage of the multimode interference device 10. The polarization separation element 28 has an input port 30, a TE polarization output port 32, and a TM polarization output port 34. The TE polarization output port 32 of the polarization separation element 28 is multimode interference by an optical waveguide. The TM polarization output port 34 of the polarization separation element 28 is connected to the first port 14 of the device 10 and is connected to the second port 16 of the multimode interference device 10 by an optical waveguide. As the polarization separation element 28, for example, a directional coupler can be used. According to the 1 × 2 optical distributor 26 having such a configuration, one input light is evenly distributed into two regardless of whether it is TE polarized light or TM polarized light, and polarization independent. Is done.

  FIG. 5 shows an element element 40 configured by using two multimode interference devices 42 and 44 as shown in FIG. The element element 40 shown in FIG. 5 has the same configuration as the multimode interference device 10 shown in FIG. 1 and has a first multimode interference device 42 and a second multimode arranged in tandem. An interference device 44 is provided. The first multimode interference device 42 has a first port 46 and a second port 48 provided at the first end, and a third port 50 and a fourth port 52 provided at the second end. Similarly, the second multi-mode interference device 44 includes a first port 54 and a second port 56 provided at the first end, and a third port 58 and a fourth port 59 provided at the second end. Have The first multimode interference device 42 and the second multimode interference device 44 face each other on the second end side (the side on which the third ports 50 and 58 and the fourth ports 52 and 59 are provided). The third port 50 of the first multimode interference device 42 to the fourth port 59 of the second multimode interference device 44 and the fourth port 52 of the first multimode interference device 42 It is connected by an optical waveguide so as to be connected to the third port 58 of the second multimode interference device 44.

  In the element element 40 configured as described above, the TE polarized light input from the first port 46 (the lower left port in FIG. 5) of the first multimode interference device 42 is the first port of the multimode interference device 44. The TM polarized light output from 54 (upper right port in FIG. 5) and input from the second port 48 (lower right port in FIG. 5) of the first multimode interference device 42 is second multimode interference. Output from the second port 56 of the device 44 (upper left port in FIG. 5). That is, the element element shown in FIG. 5 outputs the cross-polarized cross element 40 that crosses the TE polarized light and the TM polarized light by outputting the TE polarized light and the TM polarized light in the width direction. Function.

  The cross function of the cross-polarization element 40 shown in FIG. 5 is the same as that of the cross-polarization element 40 ′ of the modified form shown in FIG. Even if the mode interference device 42 and the second multimode interference device 44 are connected and integrally formed, they can be maintained. Accordingly, the length L of the multimode interference device 10 shown in FIG. 1 is doubled, and the third port 18 is connected to the second end of the first end 12a opposite to the side near the second port 16. Side end of the end portion 12b (for example, in FIG. 1, the second port 16 of the multimode interference device 10 is provided on the side close to the right end of the first end portion, so the left end of the second end portion) When W / 4 is provided at the center side of the second end portion and the fourth port 20 is provided at the center of the second end portion, the cross polarization element 40 'shown in FIG. 6 is obtained.

  If the function of crossing the TE polarized light and the TM polarized light of the cross polarization element 40 or 40 'shown in FIG. 5 or 6 is used, a 2 × 2 optical distributor or 2 × 2 light is used. It becomes possible to make the switch polarization independent.

  FIG. 7 shows a 2 × 2 optical distributor (two-input two-output optical distributor) 60 that is made polarization independent by using the cross-polarization element 40 ′ shown in FIG. 5 or 6. In the embodiment shown in FIG. 7, the cross polarization element 40 ′ shown in FIG. 6 is used, but instead of the cross polarization element 40 ′, the cross polarization element 40 is used. Of course, it may be used.

  The 2 × 2 optical distributor 60 shown in FIG. 7 includes a first polarization separation element 62, a second polarization separation element 64, a first cross-polarization element 66 between different polarizations, and a TE polarization polarization element. 2 × 2 optical distributor 68, 2 × 2 optical distributor 70 for TM polarization, second cross-polarization element 72, first polarization combining element 74, and second polarization combining element 76 in order.

  The first polarization separation element 62 has an input port 62a, a TE polarization output port 62b, and a TM polarization output port 62c. Similarly, the second polarization separation element 64 has an input port 64a, a TE polarization output port 64b, and a TM polarization output port 64c. As the first polarization separation element 62 and the second polarization separation element 64, any kind of polarization separation element may be used as long as the input light can be separated into TE polarization light and TM polarization light. Can do.

  The first polarization beam combining element 74 has a TE polarization input port 74a, a TM polarization input port 74b, and an output port 74c. Similarly, the second polarization beam combining element 76 has a TE polarization input port 76a, a TM polarization input port 76b, and an output port 76c. As the first polarization combining element 74 and the second polarization combining element 76, any kind of polarization combining element can be used as long as it can synthesize and output TE polarized light and TM polarized light. Can be used.

  The 2 × 2 optical splitter 68 for TE polarization has two input ports 68a and 68b and two output ports 68c and 68d dedicated to TE polarization, and a 2 × 2 optical splitter 70 for TM polarization. Similarly, it has two input ports 70a and 70b dedicated to TM polarization and two output ports 70c and 70d. The TE polarization 2 × 2 optical distributor 68 and the TM polarization 2 × 2 optical distributor 70 have two input ports and two output ports, and are either TE polarized light or TM polarized light. Any type of 2 × 2 optical distributor can be used as long as light input to the two input ports can be evenly distributed to the two output ports. For example, as a 2 × 2 optical distributor 68 for TE polarization and a 2 × 2 optical distributor 70 for TM polarization, a 2 × 2 MMI (multimode interference optical waveguide) dedicated to TE polarization or TM polarization is used. Can be used.

  The first cross polarization element 66 having different polarizations has an input side first port 66a, an input side second port 66b, an output side first port 66c, and an output side second port 66d. The wave crossing element 72 has an input side first port 72a and an input side second port 72b, an output side first port 72c, and an output side second port 72d. As the first cross-polarization crossing element 66 and the second cross-polarization crossing element 72, cross-polarization crossing elements 40 and 40 'as shown in FIG. 5 or 6 are used.

  The TE polarization output port 62b of the first polarization separation element 62 is connected to the input side first port 66a of the first cross-polarization element 66 of the first different polarization by an optical waveguide. The TM polarization output port 62c is connected to one of the two input ports 70a and 70b of the 2 × 2 optical distributor 70 for TM polarization by an optical waveguide. The TE polarization output port 64b of the second polarization separation element 64 is connected to the input-side second port 66b of the first cross-polarization element 66 of the first different polarization by an optical waveguide, and the second polarization separation element The 64 TM polarization output ports 64c are connected to one of the two input ports 68a and 68b of the 2 × 2 optical distributor 68 for TE polarization by an optical waveguide. Further, the output-side first port 66c of the first cross-polarization element 66 between the different polarizations is connected to the other input port 68a of the two input ports 68a and 68b of the 2 × 2 optical distributor 68 for TE polarization by an optical waveguide. The output-side second port 66d of the first cross-polarization element 66 having different polarizations is connected to the other 70a of the two input ports 70a and 70b of the 2 × 2 optical splitter 70 for TM polarization by an optical waveguide. .

  One of the two output ports 68c and 68d of the 2 × 2 optical distributor 68 for TE polarization is connected to the input side first port 72a of the second cross-polarization element 72 by the optical waveguide. The other 68d of the two output ports 68c and 68d of the 2 × 2 optical distributor 68 for polarization is connected to the TE polarization input port 76a of the second polarization beam combiner 76 by an optical waveguide. One of the two output ports 70c and 70d of the TM polarization 2 × 2 optical distributor 70c is connected to the input-side second port 72b of the second cross-polarization element 72 having different polarization by an optical waveguide. The other of the two output ports 70c and 70d of the 2 × 2 optical distributor 70 for TM polarization is connected to the TM polarization input port 74b of the first polarization beam combiner 74 by an optical waveguide. Further, the output-side first port 72c of the second cross polarization element 72 with different polarizations is connected to the TE polarization input port 74a of the first polarization beam combining element by an optical waveguide, so The output second port 72d of 72 is connected to the TM polarization input port 76b of the second polarization beam combiner 76 by an optical waveguide.

  With this configuration, the two input lights are separated into the TE polarized light and the TM polarized light by the first polarization separation element 62 and the second polarization separation element 64, and the first different polarization is separated. After the position is changed by the crossing element 66, two inputs for each polarized light are connected to 2 × 2 optical distributors 68 and 70 designed exclusively for each polarized light, and the 2 × 2 optical distributors 68 and 70 are connected. Is output again by the second cross-polarization crossing element 72, and the TE polarization and TM polarization are combined by the first polarization combining element 74 and the second polarization combining element 76. It becomes two output. Therefore, a polarization-independent 2 × 2 optical distributor 60 that functions without depending on the type of polarized light is realized.

  Similarly, as shown in FIG. 8, in place of the TE polarization dedicated 2 × 2 optical distributor 68 and the TM polarization dedicated 2 × 2 optical distributor 70 in FIG. A TM polarized wave having 2 × 2 optical switch 78 dedicated to TE polarization having input ports 78a and 78b and two output ports 78c and 78d, two input ports 80a and 80b, and two output ports 80c and 80d. By using the dedicated 2 × 2 optical switch 80, a polarization-independent 2 × 2 optical switch 60 ′ that functions without depending on the type of polarization is realized. Since the operation is the same as that of the 2 × 2 optical distributor 60, it will not be described in detail here. It is well known that the 2 × 2 optical switches 78 and 80 dedicated to TE polarization or TM polarization can be configured by, for example, two general 2 × 2 optical distributors and phase shifters.

  As described above, when the multimode interference device 10 according to the present invention is used, the 1 × 2 optical distributor 26, the cross polarization elements 40, 40 ′, the 2 × 2 optical distributor 60, the 2 × 2 optical switch 60 ′, etc. Polarization independence can be achieved. Such a polarization-independent element can be incorporated as an element in an optical node device such as an optical cross connect.

  The multimode interference device 10 according to the present invention and various devices or elements 26, 40, 40 ′, 60, 60 ′ using the multimode interference device 10 according to the present invention have been described with reference to the illustrated embodiments. It is not limited. For example, in the multimode interference device 10 shown in FIG. 1, the second port 16 is provided on the right side in the figure with respect to the first port 14, but is provided on the left side in the figure with respect to the first port 14. May be.

DESCRIPTION OF SYMBOLS 10 Multimode interference device 12 Multimode interference part 12a 1st edge part 12b 2nd edge part 14 1st port 16 2nd port 18 3rd port 20 4th port 26 1x2 optical splitter 28 Polarization separation element 30 Input Port 32 TE Polarization Output Port 34 TM Polarization Output Port 40 Cross Polarization Cross Element 40 ′ Cross Polarization Cross Element 42 First Multimode Interference Device 44 Second Multimode Interference Device 46 First Port 48 First 2 port 50 3rd port 52 4th port 54 1st port 56 2nd port 58 3rd port 59 4th port 60 2x2 optical splitter 62 1st polarization separation element 62a Input port 62b TE polarization output port 62c TM polarization output port 64 Second polarization separation element 64a Input port 64b TE polarization output port 64c TM polarization output port G 66 First cross polarization element 66a Input side first port 66b Input side second port 66c Output side first port 66d Output side second port 68 2 × 2 optical splitter 68a, 68b Input port 68c, 68d Output Port 70 2 × 2 optical distributor 70a, 70b Input port 70c, 70d Output port 72 Second cross-polarization element 72a Input side first port 72b Input side second port 72c Output side first port 72d Output side second Port 74 First polarization combiner 74a TE polarization input port 74b TM polarization input port 74c Output port 76 Second polarization combiner 76a TE polarization input port 76b TM polarization input port 76c Output port 78 2 × 2 optical switch 78a, 78b input port 78c, 78d output port 80 2 × 2 optical switch 80a, 0b input port 80c, 80d output port

Claims (7)

A multi-mode interference device of width W having a first end and a second end at both ends in the optical transmission direction,
A first port provided at the center in the width direction of the first end, a second port provided on the inner side by W / 4 from either one of the ends in the width direction of the first end, A third port and a fourth port provided inward by W / 4 from both ends in the width direction of the second end portion, respectively, and when TE polarized light is input from the first port, the TE port Polarized light is evenly distributed to the third port and the fourth port, and when TM polarized light is input from the second port, the TM polarized light is evenly distributed to the third port and the fourth port. Thus, the multimode interference device is characterized in that the length L of the multimode interference device in the optical transmission direction is determined. A function of width W representing the coupling length of the multimode interference device with respect to TE polarized light is L _c ^TE (W), and a function of width W representing the coupling length of the multimode interference device with respect to TM polarized light is represented by L _c ^TM (W The multimode interference device according to claim 1, wherein L and W satisfying the following simultaneous equations are defined as a length and a width of the multimode interference device, respectively. Where L _c is the coupling length, and β ₀ is the zero-order mode propagation constant and β ₁ is the first-order mode propagation coefficient, and the thickness, width W, and type of polarization ( The constant is determined by Equation (8) depending on TE polarization and TM polarization.

  When a light is input to the input port having an input port, a TE polarization output port, and a TM polarization output port, TE polarization light is output from the TE polarization output port and TM polarization light is output from the TM polarization output port. A polarization separation element for output and the multimode interference device according to claim 1, wherein the TE polarization output port of the polarization separation element is connected to the first port, and the polarization A 1 × 2 optical splitter, wherein the TM polarization output port of the wave separation element is connected to the second port to make the polarization independent.   Two multi-mode interference devices according to claim 1 or 2 are arranged so that the second ends face each other, and the third port of one multi-mode interference device and the other multi-mode interference device And a fourth port of the one multimode interference device is connected to a third port of the other multimode interference device and input to the first port of the one multimode interference device. The polarized TE polarized light is output from the first port of the other multimode interference device, and the TM polarized light input to the second port of the one multimode interference device is the second of the other multimode interference device. Cross-polarized element with different polarizations, characterized in that it is output from a port. The two multimode interference devices, the third port and the fourth port of the other of the multi-mode interference device, a fourth port and the other of the multi-mode of the one multimode interference devices of said one multimode interference devices the third port of the interfering device or integrally formed as connected with the second end What happened to face, width W, length was set at 2L, in claim 4 The crossed element between different polarizations described . A first polarization separation element and a second polarization separation element each having an input port, a TE polarization output port and a TM polarization output port; an input side first port; an input side second port; and an output side The first cross-polarized cross element according to claim 4 or 5 having a first port and an output-side second port, and a TE polarized wave each having two input ports and two output ports. The 2 × 2 optical distributor and the 2 × 2 optical distributor for TM polarization, the input side first port, the input side second port, the output side first port, and the output side second port, or 6. A second polarization combining element and a second polarization combining element according to claim 5 , each having a TE polarization input port, a TM polarization input port, and an output port. In order,
The TE polarization output port of the first polarization separation element is connected to the input first port of the first cross-polarization element of the first different polarization and the TM polarization output port of the second polarization separation element is connected Connected to the second port on the input side of the first cross-crossing element of different polarizations,
The TM polarization output port of the first polarization separation element and the output-side second port of the first cross-polarization element of the first different polarization are the two input ports of the 2 × 2 optical splitter for TM polarization. The TE polarization output port of the second polarization separation element and the output-side first port of the first cross polarization crossing element of the 2 × 2 optical splitter for the TE polarization Connect to the two input ports,
One of the two output ports of the 2 × 2 optical splitter for TM polarization is connected to the second port on the input side of the second cross polarization crossing element, and 2 × for the TE polarization. One of the two output ports of the two-light distributor is connected to the first port on the input side of the second cross-polarization device of different polarizations;
The other of the two output ports of the 2 × 2 optical splitter for TM polarization and the output first port of the second cross-polarization crossing element are connected to the second of the first polarization combining element. The second output port of the 2 × 2 optical splitter for TE polarization and the output second port of the second cross-polarization crossing element are connected to the second input port. A 2 × 2 optical distributor, which is connected to the two input ports of the polarization beam combining element and made polarization independent. A first polarization separation element and a second polarization separation element each having an input port, a TE polarization output port and a TM polarization output port; an input side first port; an input side second port; and an output side The first cross-polarized cross element according to claim 4 or 5 having a first port and an output-side second port, and a TE polarized wave each having two input ports and two output ports. claim 4 or having a 2 × 2 optical switch for the 2 × 2 optical switches and the TM polarization, the input-side first port and the input-side second port and the output-side first port and the output-side second port a second cross polarization cross element according to 5, and a first polarization combining element and the second polarization combining element having an each with TE polarization input ports and the TM polarization input ports and output ports In order,
The TE polarization output port of the first polarization separation element is connected to the input first port of the first cross-polarization element of the first different polarization and the TM polarization output port of the second polarization separation element is connected Connected to the second port on the input side of the first cross-crossing element of different polarizations,
The TM polarization output port of the first polarization separation element and the output-side second port of the first cross-polarization element of the first different polarization are used as the two input ports of the 2 × 2 optical switch for TM polarization. The TE polarization output port of the second polarization separation element and the output-side first port of the first cross polarization crossing element are connected to the two of the 2 × 2 optical switches for the TE polarization. Connect to one input port,
One of the two output ports of the TM polarization 2 × 2 optical switch is connected to the input-side second port of the second cross-polarization element, and the TE polarization 2 × 2 One of the two output ports of the optical switch is connected to the input-side first port of the second cross-polarization element of different polarizations,
The other of the two output ports of the 2 × 2 optical switch for TM polarization and the output first port of the second cross-polarization crossing element are connected to the two of the first polarization combining elements. In addition to being connected to an input port, the other of the two output ports of the 2 × 2 optical switch for TE polarization and the output-side second port of the second cross-polarization element are connected to the second polarization port. 2. A 2 × 2 optical switch characterized in that it is connected to the two input ports of the wave synthesis element to make it polarization independent.

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