Optical Signal Processing Apparatus

Abstract

To provide an optical signal processing device capable of reducing the crosstalk while narrowing the space between switch elements for downsizing, the optical signal processing device includes a plurality of input optical waveguides, a plurality of output optical waveguides, a plurality of optical waveguide elements arranged between the plurality of input optical waveguides and the plurality of output optical waveguides, and a connection optical waveguide. The connection optical waveguide positioned closely to the optical waveguide element is differentiated in propagation constant from the optical waveguide configuring the closely arranged optical waveguide element. The connection optical waveguide positioned closely to the optical waveguide element is a connection optical waveguide having one end or both ends connected to the optical waveguide element, or a connection optical waveguide having both ends not connected to the optical waveguide elements.

Claims

1. An optical signal processing device including a plurality of input optical waveguides, a plurality of output optical waveguides, a plurality of optical waveguide elements arranged between the plurality of input optical waveguides and the plurality of output optical waveguides, and a connection optical waveguide, wherein the connection optical waveguide positioned closely to the optical waveguide element is differentiated in propagation constant from the optical waveguide configuring the closely arranged optical waveguide element.

2. The optical signal processing device according to claim 1, wherein the connection optical waveguide includes a first connection optical waveguide having at least one end connected to the optical waveguide element, and the first connection optical waveguide is differentiated in propagation constant from the optical waveguide configuring the closely arranged optical waveguide element.

3. The optical signal processing device according to claim 1, wherein the connection optical waveguide includes a second connection optical waveguide having at least one end not connected to the optical waveguide element, and the second connection optical waveguide is differentiated in propagation constant from the optical waveguide configuring the closely arranged optical waveguide element, or the second connection optical waveguide is differentiated in propagation constant from the first connection optical waveguide having at least one end connected to the optical waveguide element.

4. An optical signal processing device including a plurality of input optical waveguides, a plurality of output optical waveguides, and a plurality of optical waveguide elements arranged between the plurality of input optical waveguides and the plurality of output optical waveguides, wherein optical waveguides configuring two optical waveguide elements arranged closely in a direction orthogonal to an optical waveguide direction, of the plurality of optical waveguide elements, are differentiated in propagation constant.

5. The optical signal processing device according to claim 1, wherein two optical waveguides mutually different in propagation constant are differentiated in optical waveguide width.

6. The optical signal processing device according to claim 1, wherein the optical waveguide element includes a Mach-Zehnder interferometer.

7. The optical signal processing device according to claim 1, wherein the plurality of optical waveguide elements configure a multi-input/multi-output optical switch in which a PIOSS configuration including multi-stage optical waveguide elements is arranged in a direction orthogonal to an optical waveguide direction.

8. The optical signal processing device according to claim 7, wherein the multi-input/multi-output optical switch functions as a multicast switch.

9. The optical signal processing device according to claim 2, wherein the connection optical waveguide includes a second connection optical waveguide having at least one end not connected to the optical waveguide element, and the second connection optical waveguide is differentiated in propagation constant from the optical waveguide configuring the closely arranged optical waveguide element, or the second connection optical waveguide is differentiated in propagation constant from the first connection optical waveguide having at least one end connected to the optical waveguide element.

10. The optical signal processing device according to claim 2, wherein two optical waveguides mutually different in propagation constant are differentiated in optical waveguide width.

11. The optical signal processing device according to claim 3, wherein two optical waveguides mutually different in propagation constant are differentiated in optical waveguide width.

12. The optical signal processing device according to claim 4, wherein two optical waveguides mutually different in propagation constant are differentiated in optical waveguide width.

13. The optical signal processing device according to claim 2, wherein the optical waveguide element includes a Mach-Zehnder interferometer.

14. The optical signal processing device according to claim 3, wherein the optical waveguide element includes a Mach-Zehnder interferometer.

15. The optical signal processing device according to claim 4, wherein the optical waveguide element includes a Mach-Zehnder interferometer.

16. The optical signal processing device according to claim 5, wherein the optical waveguide element includes a Mach-Zehnder interferometer.

17. The optical signal processing device according to claim 2, wherein the plurality of optical waveguide elements configure a multi-input/multi-output optical switch in which a PIOSS configuration including multi-stage optical waveguide elements is arranged in a direction orthogonal to an optical waveguide direction.

18. The optical signal processing device according to claim 3, wherein the plurality of optical waveguide elements configure a multi-input/multi-output optical switch in which a PIOSS configuration including multi-stage optical waveguide elements is arranged in a direction orthogonal to an optical waveguide direction.

19. The optical signal processing device according to claim 4, wherein the plurality of optical waveguide elements configure a multi-input/multi-output optical switch in which a PIOSS configuration including multi-stage optical waveguide elements is arranged in a direction orthogonal to an optical waveguide direction.

20. The optical signal processing device according to claim 5, wherein the plurality of optical waveguide elements configure a multi-input/multi-output optical switch in which a PIOSS configuration including multi-stage optical waveguide elements is arranged in a direction orthogonal to an optical waveguide direction.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1(a) is a diagram illustrating a switch element (MZI switch) configured by optical waveguides, and FIG. 1(b) is a diagram illustrating an optical signal processing device (switch) configured by a plurality of switch elements connected with each other.

[0018] FIG. 2 is a diagram illustrating an optical signal processing device (switch) including a plurality of switch elements arranged in the y-axis and z-axis directions, and is configured to connect the output of one switch element to the input of another switch element.

[0019] FIG. 3(a) is a diagram illustrating a configuration of an optical signal processing device of a first embodiment, and FIG. 3(b) is a diagram illustrating a part of FIG. 3(a) and is an enlarged view illustrating a region where an optical waveguide connecting switch elements and an optical waveguide not connected to a switch element are positioned closely.

[0020] FIG. 4 is a diagram illustrating a configuration of an optical signal processing device of a second embodiment.

[0021] FIG. 5 is a diagram illustrating a configuration of an optical signal processing device of a third embodiment.

DESCRIPTION OF EMBODIMENTS

[0022] The basic idea of the present invention can be summarized by the following items (i) to (iii), for example.

[0023] (i) A multi-input/multi-output optical switch having a PILOSS configuration includes switch elements connected in multiple stages and has a configuration in which, among the switch elements, an output of a front-stage switch element and an input of a rear-stage switch element are connected.

[0024] (ii) In the case of connecting switch elements while skipping a switch element of a specific stage, for example, it is necessary to provide an optical waveguide between the switch elements. (For example, in a p-th row, switch elements are arranged in multiple stages, and when connecting an output of an nth stage switch element and an input of an (n+2)th switch element among the switch elements, it is necessary to form an optical waveguide for skipping an (n+1)th switch element so that the optical waveguide is connected between the (n+1)th switch element in the p-th row and the (n+1)th switch element in the (p+1)th row (or (p−1)th row).)

[0025] (iii) Differentiating the optical waveguide formed between the switch elements in the above description (ii), in propagation constant, from the optical waveguide configuring the switch element can suppress the crosstalk (TX) of optical signals, which may occur between the optical waveguide configuring the switch element and the optical waveguide formed between the switch elements.

[0026] Configuring an optical signal processing device so as to satisfy the above features can narrow the space between the switch elements while securing low crosstalk characteristics.

[0027] Since the switch element is usually configured by an element mainly including an optical waveguide such as MZI, for example (see FIG. 1(a)), it is referred to as an optical waveguide element in the following description.

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In the drawings of respective embodiments described below, the left end of an optical signal processing device is defined as the input side and the right end is defined as the output side. However, in the optical waveguide elements and in the optical waveguide connecting them, the propagation direction of light is reversible, and the right end may be defined as the input side and the left end may be defined as the output side. Further, the optical signal processing device may have a multi-stage configuration, so that the optical waveguide on the output side of an optical waveguide element in each stage is connected to the optical waveguide on the input side of an optical waveguide element in the next stage. Alternatively, the optical waveguide element on the output side in the front stage may be the optical waveguide element on the input side in the rear stage.

First Embodiment

[0029] FIG. 3(a) is a plan view illustrating connection optical waveguides and switch elements of an optical signal processing device according to a first embodiment of the present invention.

[0030] In FIG. 3(a), to simplify the description, the illustrated optical signal processing device includes eight optical waveguide elements, four of which are arranged on the input side at the left end and another four of which are arranged on the output side at the right end, like the conventional example illustrated in FIG. 1. The optical signal processing device further includes eight optical waveguide elements arranged between the four optical waveguide elements on the input side and the four optical waveguide elements on the output side. The 16 optical waveguide elements in total are arranged in a pattern of four lines and four rows in the y-z plane. Four connection optical waveguides of two sets connect between the optical waveguide elements on the input side and the optical waveguide elements on the output side. Further, in FIG. 3(a), an optical waveguide not connected to the 16 switch elements illustrated in the drawings is arranged so as to extend from left to right between the switch elements (between the switch elements arranged in the second row and the switch elements arranged in the third row in the y-axis direction). As described above, if the space between the optical waveguide elements in the y-axis direction is narrow, the propagation modes of the optical waveguides will be combined and the crosstalk may occur between the optical waveguides.

[0031] FIG. 3(b) is a diagram illustrating an optical waveguide formed between third-stage (third from the left) switch elements of the second and third rows in the y-axis direction in FIG. 3(a). FIG. 3(b) is an enlarged view illustrating a region where the optical waveguides (or the optical waveguides configuring the switch elements) respectively connecting the second-stage (second from the left) switch elements and the fourth-stage (fourth from the left) switch elements in the second and third rows in the y-axis direction in FIG. 3(a) and the optical waveguide not connected to the illustrated switch element are positioned closely, in the case where each switch element is MZI.

[0032] The propagation mode coupling strength of optical waveguides positioned closely becomes stronger as the space between the optical waveguides becomes narrower regardless of shortness of distance in positioning closely. Therefore, if the optical waveguides are positioned so closely, the crosstalk of optical signals will occur. Further, the coupling strength is maximized when propagation constants thereof are the same, and becomes smaller when propagation constants thereof are different.

[0033] The propagation constant of an optical waveguide changes depending on the difference in refractive index between a core and a clad, the refractive index distribution, and the shape of the core. When the optical signal processing device is configured by optical waveguides formed on one chip, the refractive indices of the core and the clad are usually determined at the time of formation, but it is possible to control the propagation constant by changing the shapes of the optical waveguides positioned closely. In particular, the thickness of the optical waveguide can be controlled by an exposure mask to be used when the core is formed and can be easily changed.

[0034] In the present embodiment, as illustrated in FIG. 3(b), the optical waveguides positioned closely are differentiated in thickness so as to change the propagation constants thereof. As a result, it is possible to suppress the propagation mode coupling therebetween and the resulting crosstalk. In FIG. 3(b), the central optical waveguide of three neighboring optical waveguides is configured to be larger in thickness (width in the y-axis direction) than two other optical waveguides. In the case where two optical waveguides other than the central optical waveguide illustrated in FIG. 3(b) are positioned closely to the optical waveguides configuring the third-stage (third from the left) switch elements of the second and third rows in the y-axis direction in FIG. 3(a), in order to reduce the crosstalk between optical signals propagating them, the two optical waveguides other than the central optical waveguide illustrated in FIG. 3(b) may be differentiated in propagation constant from the optical waveguides configuring the switch elements illustrated in FIG. 3(a).

[0035] For example, when the space (distance in the y-axis direction) between neighboring optical waveguides is 40 μm, configuring the two optical waveguides in such a manner that the ratio in thickness (width in the y-axis direction) between two optical waveguides is 1.03, thereby differentiating propagation coefficients thereof, can suppress the crosstalk.

[0036] In the above-described embodiment, an optical waveguide having both ends connected to switch elements may be replaced by an optical waveguide having at least one end connected to a switch element, and/or an optical waveguide having both ends not connected to switch elements may be replaced by an optical waveguide having at least one end not connected to a switch element. Alternatively, in the above-described embodiment, either the optical waveguide having both ends connected to switch elements or the optical waveguide having both ends not connected to switch elements may be omitted. In this case, the optical waveguide having at least one end connected to a switch element may be differentiated in propagation constant from the optical waveguide configuring a switch element closely arranged in the y-axis direction. Alternatively, the optical waveguide having at least one end connected to a switch element may be differentiated in propagation constant from the optical waveguide configuring a switch element closely arranged in the y-axis direction.

[0037] Further, in the above-described embodiment, the optical waveguide having both ends connected to switch elements and the optical waveguide having both ends not connected to switch elements may be omitted. In switch elements closely arranged in the y-axis direction, optical waveguides configuring these switch elements may be differentiated in propagation constant.

Second Embodiment

[0038] FIG. 4 is a diagram illustrating a simplified configuration of an optical signal processing device according to a second embodiment of the present invention. The optical signal processing device of the present embodiment is a 4-input/3-output PILOSS switch. The above-described optical signal processing device includes input and output optical waveguides, switch elements, and connection optical waveguides connecting the switch elements. The above-described switch elements are MZI switches arranged two-dimensionally in the y-z plane. In such a PILOSS switch whose input and output are asymmetrical, there exists a connection optical waveguide that skips each stage of the switch elements arranged in multiple stages and connects to the switch element of the next stage.

[0039] As described above, the overall switch size can be reduced by setting the space between the switch elements as narrow as possible. However, if the space between two switch elements in the y-axis direction is too small, the propagation mode coupling and the crosstalk of optical signals will occur between the connection optical waveguide formed between the switch elements and the optical waveguide configuring the switch element (configuring the MZI switch).

[0040] To the contrary, differentiating the connection optical waveguide formed between the switch elements in thickness from the optical waveguide configuring the switch element can change the propagation constants thereof and can weaken the propagation mode coupling. As a result, the crosstalk of optical signals can be suppressed. Therefore, the optical waveguide space in the optical signal processing device can be reduced and the chip can be downsized.

[0041] Further, in order to skip the MZI switch of each stage, not only in the optical waveguide formed between the MZI switches but also in the closely positioned MZI switches, changing the propagation constants of the optical waveguides configuring the MZI switches can suppress the crosstalk of optical signals between the MZI switches. This can be achieved by adopting optical waveguides that are different in width, in the neighboring MZI switches.

Third Embodiment

[0042] FIG. 5 is a diagram illustrating a simplified configuration of an optical signal processing device according to a third embodiment of the present invention. The optical signal processing device of the present embodiment is a multicast switch (MCS) in which a 4-input/3-output PILOSS configuration is adopted. The above-described optical signal processing device includes input and output optical waveguides, switch elements, connection optical waveguides connecting the switch elements, and optical splitters. The above-described switch elements are MZI switches arranged two-dimensionally in the y-z plane. According to this kind of switch adopting the PILOSS configuration whose input and output are asymmetrical, similar to the second embodiment, there exists a connection optical waveguide that skips each stage of the switch elements arranged in multiple stages and connects to the switch element of the next stage. Therefore, similar to the second embodiment, differentiating the connection optical waveguide formed between the switch elements in thickness from the optical waveguide configuring the switch element can change the propagation constants thereof and can weaken the propagation mode coupling. As a result, the crosstalk of optical signals can be suppressed. Further, in order to skip the MZI switch of each stage, not only in the optical waveguide formed between the MZI switches but also in the closely positioned MZI switches, changing the propagation constants of the optical waveguides configuring the MZI switches can suppress the crosstalk of optical signals between the MZI switches.