NxN Optical Switch

Abstract

There is provided an NN optical switch configured by connection between output ports of input side optical switches and input ports of output side optical switches by using optical waveguides on the same substrate and capable of reducing the crossing loss in a port connected to an optical waveguide having a maximum number of crossings and a higher crossing loss. In a 44 optical switch (10) having four input side 14 optical switches (SW11-SW14) each having four output ports (P1-P4), four output side 41 optical switches (SW21-SW24) each having four input ports (Q1-Q4), and connection optical waveguides (OW) connecting the output ports and the input ports, part of the connection optical waveguides OW are allowed to cross two or more of the other connection optical waveguides OW in one point.

Claims

1. An NN optical switch comprising: N input side 1N optical switches each having N (where N is an integer equal to or greater than 3) output ports; N output side N1 optical switches each having N input ports; and connection optical waveguides connecting the output ports and the input ports, wherein part of the connection optical waveguides cross two or more of the other connection optical waveguides in one point, and an MMI crossing structure is used in a crossing portion in which the connection optical waveguide crosses the other connection optical waveguides.

2. (canceled)

3. The NN optical switch according to claim 1, wherein the input side 1N optical switches and the output side N1 optical switches are separately aligned such that the output ports and the input ports are opposite to each other, the output port in one end of the input side 1N optical switch being located in one end among the input side 1N optical switches is connected to the input port in one end of the output side N1 optical switch being located in one end among the output side N1 optical switches by the connection optical waveguide that does not cross the other connection optical waveguides, the output port in the other end of the input side 1N optical switch being located in the other end among the input side 1N optical switches is connected to the input port in the other end of the output side N1 optical switch being located in the other end among the output side N1 optical switches by the connection optical waveguide that does not cross the other connection optical waveguides, the output ports located other than in one end of the input side 1N optical switch being located in one end among the input side 1N optical switches are connected to the input ports of the output side N1 optical switches being located other than in one end among the output side N1 optical switches and being different from each other by the connection optical waveguides that cross the other connection optical waveguides, the output ports located other than in the other end of the input side 1N optical switch being located in the other end among the input side 1N optical switches are connected to the input ports of the output side N1 optical switches being located other than in the other end among the output side N1 optical switches and being different from each other by the connection optical waveguides that cross the other connection optical waveguides, and the output ports of the input side 1N optical switches being located other than in two ends among the input side 1N optical switches are connected to the input ports of the output side N1 optical switches being different from each other by the connection optical waveguides that cross the other connection optical waveguides.

4. The NN optical switch according to claim 1, wherein the input side 1N optical switches and the output side N1 optical switches are alternately arranged in alignment, the output ports located in two ends of the input side 1N optical switch are connected to the input ports located in end portions of the output side N1 optical switches being adjacent to the input side 1N optical switch and being different from each other by the connection optical waveguides that do not cross the other connection optical waveguides, and among the output ports of the input side 1N optical switch, the output ports located other than in two ends are connected to the input ports located other than in two ends of the output side N1 optical switches not being adjacent to the input side 1N optical switch and being different from each other by the connection optical waveguides that cross the other connection optical waveguides.

5. The NN optical switch according to claim 1, wherein the input side 1N optical switches, the output side N1 optical switches, and the connection optical waveguides are formed as monolithic integration on a same semiconductor substrate.

6. The NN optical switch according to claim 1, wherein crossing angles in the crossing portion in which the connection optical waveguide crosses the other connection optical waveguides are equal.

7. The NN optical switch according to claim 3, wherein the input side 1N optical switches, the output side N1 optical switches, and the connection optical waveguides are formed as monolithic integration on a same semiconductor substrate.

8. The NN optical switch according to claim 3, wherein crossing angles in the crossing portion in which the connection optical waveguide crosses the other connection optical waveguides are equal.

9. The NN optical switch according to claim 4, wherein the input side 1N optical switches, the output side N1 optical switches, and the connection optical waveguides are formed as monolithic integration on a same semiconductor substrate.

10. The NN optical switch according to claim 4, wherein crossing angles in the crossing portion in which the connection optical waveguide crosses the other connection optical waveguides are equal.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0042] FIG. 1 is a configuration diagram showing an example of a tree-type optical switch applied to an NN optical switch according to an embodiment of the present invention.

[0043] FIG. 2 is a configuration diagram showing an NN optical switch according to the first embodiment of the present invention.

[0044] FIG. 3 is a configuration diagram showing an MMI crossing structure in a case where three waveguides cross each other.

[0045] FIG. 4 is a configuration diagram showing an NN optical switch according to the second embodiment of the present invention.

[0046] FIG. 5 is a configuration diagram showing an example of a conventional NN optical switch.

[0047] FIG. 6 is a perspective view of a conventional 22 optical switching element.

[0048] FIG. 7 is a configuration diagram showing another example of the conventional NN optical switch.

DESCRIPTION OF EMBODIMENTS

[0049] An NN optical switch according to an embodiment of the present invention is configured by connection between output ports of N input side 1N optical switches and input ports of N output side N1 optical switches by using connection optical waveguides formed on a substrate, wherein the connection optical waveguides are placed to have a waveguide crossing portion in which three or more connection optical waveguides cross each other in one point, and a multi-mode interference (MMI) crossing structure is used in the waveguide crossing portion where the connection optical waveguide crosses other connection optical waveguides connecting ports.

[0050] According to the NN optical switch according to an embodiment of the present invention, this configuration allows one connection optical waveguide to have a reduced number of waveguide crossing portions and also can achieve a low loss and low crosstalk crossing in the waveguide crossing portion, thereby reducing the optical loss caused by the crossing of the waveguides.

[0051] Here, with reference to FIG. 1, a tree-type optical switch used in one embodiment of the present invention will be described. The optical switch is not limited to a 14 optical switch. A 18 optical switch or a 1N optical switch having a larger number of ports may be employed. Hereinafter, a typical tree-type 14 optical switch will be described.

[0052] As shown in FIG. 1, a 14 optical switch SW10 is achieved by connecting 22 optical switches SW10a, SW10b, SW10c in a tree manner. The light output is split into two in the first 22 optical switch SW10a, and then the split light output is individually split into two in the next 22 optical switches SW10b, SW10c, so that the output is consequently split among four ports. Each of the 22 optical switches SW10a, SW10b, SW10c may be achieved by using, for example, a MZI.

[0053] The 22 optical switches SW10a, SW10b, SW10c first use a multimode interference optical coupler (hereinafter referred to as an MMI optical coupler) for input light entering an optical waveguide (for example, an OW.sub.1 shown in FIG. 1) and split the input light between two optical waveguides (not shown). At this time, the length of the MMI optical coupler is designed to split the optical intensity into two equal parts. The two parts of the split input light receive a phase difference between two optical waveguides and then are coupled again by using the MMI optical coupler. As a result, due to an interference effect, if the phase difference between the two optical waveguides is n, the input light is outputted from an optical waveguide (for example, an OW.sub.2 shown in FIG. 1) opposite to the optical waveguide which the input light has entered, while if the phase difference between the two optical waveguides is (2n+1)/2, the input light is outputted from an optical waveguide (for example, an OW.sub.3 shown in FIG. 1) in the same side of the optical waveguide which the input light has entered (where n is an integer).

[0054] Accordingly, by placing and controlling a phase modulation area in either one of the optical waveguides, a 22 switching operation can be obtained. To obtain phase modulation, a refractive index of an optical waveguide may be changed. Accordingly, a switching operation may be performed in the following manner: in a PLC or the like, current is applied through a heater to control the temperature and a refractive index of an optical waveguide is changed by using a TO effect; in an InP based optical waveguide, a Franz-Keldysh (FK) effect and a quantum confined stark effect (QCSE) produced by voltage application or a plasma effect produced by current infusion is used to change a refractive index of an optical waveguide; and in an LN based optical waveguide, a Pockels effect produced by voltage application is used to change a refractive index of an optical waveguide. Furthermore, a directional coupler and the like may be used for the MMI optical coupler that splits the optical intensity into two equal parts.

First Embodiment

[0055] With reference to FIG. 2 and FIG. 3, a detailed description will be given of an NN optical switch according to the first embodiment of the present invention.

[0056] In the present embodiment, as an optical switch, an NN optical switch comprises N input side 1N optical switches each having N output ports, N output side N1 optical switches each having N input ports, and connection optical waveguides connecting the output ports and the input ports. FIG. 2 shows an example of a basic connection configuration, where N=4.

[0057] As shown in FIG. 2, a 44 optical switch 10 comprises four input side 14 optical switches SW11-SW14 and four output side 41 optical switches SW21-SW24. The input side 14 optical switches SW11-SW14 are aligned, and the output side 41 optical switches SW21-SW24 are aligned opposite to the input side 14 optical switches SW11-SW14.

[0058] Each of the input side 14 optical switches SW11-SW14 has four output ports P1-P4. Furthermore, each of the output side 41 optical switches SW21-SW24 has four input ports Q1-Q4.

[0059] The four output ports P1-P4 of the respective input side 14 optical switches SW11-SW14 are connected to the input ports Q1-Q4 of the output side 41 optical switches SW21-SW24 that are different from each other by connection optical waveguides OW.

[0060] As a specific connection method between the input side 14 optical switches SW11-SW14 and the output side 41 optical switches SW21-SW24, FIG. 2 shows the following example. The output ports P1-P4 of the input side 14 optical switch SW11 are respectively connected to the input ports Q1 of the output side 41 optical switches SW21-SW24; the output ports P1-P4 of the input side 14 optical switch SW12 are respectively connected to the input ports Q2 of the output side 41 optical switches SW21-SW24; the output ports P1-P4 of the input side 14 optical switch SW13 are respectively connected to the input ports Q3 of the output side 41 optical switches SW21-SW24; and the output ports P1-P4 of the input side 14 optical switch SW14 are respectively connected to the input ports Q4 of the output side 41 optical switches SW21-SW24.

[0061] In other words, the output port P1 in one end of the input side 14 optical switch SW11 in one end is connected to the input port Q1 in one end of the output side 41 optical switch SW21 in one end by a connection optical waveguide OW that does not cross another connection optical waveguide OW.

[0062] Meanwhile, the output port P4 in the other end of the input side 14 optical switch SW14 in the other end is connected to the input port Q4 in the other end of the output side 41 optical switch SW24 in the other end by a connection optical waveguide OW that does not cross another connection optical waveguide OW.

[0063] Furthermore, the output ports P2-P4 located other than in one end of the input side 14 optical switch SW11 in one end are respectively connected to the input ports Q1 of the output side 41 optical switches SW22-SW24 that are located other than in the other end and are different from each other by connection optical waveguides OW that cross other connection optical waveguides OW.

[0064] Moreover, the output ports P1-P3 located other than in the other end of the input side 14 optical switch SW14 in the other end are respectively connected to the input ports Q4 of the output side 41 optical switches SW21-SW23 that are located other than in the other end and are different from each other by connection optical waveguides OW that cross other connection optical waveguides OW.

[0065] The output ports P1-P4 of the input side 14 optical switches SW12, SW13 located other than in the two ends are respectively connected to the input ports Q2, Q3 of the output side 41 optical switches SW21-SW24 that are different from each other by connection optical waveguides OW that cross other connection optical waveguides OW.

[0066] It should be noted that the input side 14 optical switches SW11-SW14, the output side 41 optical switches SW21-SW24, and the connection optical waveguides OW are formed as monolithic integration on the same semiconductor substrate.

[0067] In this case, the connection optical waveguides OW having a maximum number of crossings include the connection optical waveguide OW connecting the output port P4 of the input side 14 optical switch SW11 to the input port Q1 of the output side 41 optical switch SW24 and the connection optical waveguide OW connecting the output port P1 of the input side 14 optical switch SW14 to the input port Q4 of the output side 41 optical switch SW21.

[0068] Here, in the conventional configuration of the optical switch shown in FIG. 5, two connection optical waveguides OW are allowed to cross each other in the crossing point of the connection optical waveguides OW, whereas in the present embodiment, as shown in FIG. 2, three or more connection optical waveguides OW are allowed to cross each other in one crossing point, thereby reducing the number of crossings. FIG. 2 shows an example of the case where a maximum of three connection optical waveguides OW are allowed to cross each other in one crossing point. The points where three connection optical waveguides OW are allowed to cross in one crossing point are encircled by broken lines in FIG. 2.

[0069] It should be noted that in the present embodiment, all of the crossings of the connection optical waveguides OW are made by using MMI optical waveguides OW.sub.MMI as shown in FIG. 3 (the structure using the MMI optical waveguides OW.sub.MMI is referred to as an MMI crossing structure). The MMI optical waveguide OW.sub.MMI has a structure having any width with 1 input 1 output, and has a length that is twice the beat length.

[0070] In the MMI crossing structure, the connection optical waveguides OW are allowed to cross each other in a center portion (hereinafter referred to as the position corresponding to the beat length) of the MMI optical waveguide OW.sub.MMI corresponding to the beat length. If loss and crosstalk in the MMI crossing structure having three connection optical waveguides OW crossing in one point are equivalent to the performance (loss, crosstalk) in the structure having two connection optical waveguides OW crossing in one point without using the MMI crossing structure, it is possible to achieve low loss and low crosstalk by reducing the number of crossings, thereby greatly contributing to the increase in the number of ports.

[0071] It should be noted that according to the present embodiment, as can be seen from FIG. 2, the number of crossings can be reduced by N/2 for the conventional connection optical waveguide OW having a maximum number of crossings.

[0072] Furthermore, in general, regarding the crossing of the connection optical waveguides OW, the connection optical waveguides OW are allowed to cross each other one by one, and as a crossing angle is closer to orthogonal, loss and crosstalk are reduced. Meanwhile, in the present embodiment, the MMI crossing structure is introduced into all of the crossing parts of the connection optical waveguides OW, so that multiple crossings with low loss and low crosstalk can be achieved.

[0073] For example, in the case of an MMI crossing structure having a width for exciting a 1.sup.st mode, a proportion of a 0.sup.th mode reaches a peak in the position corresponding to the beat length with respect to a waveguide direction, and the MMI crossing structure becomes less likely to be affected by the side wall of the connection optical waveguides OW. Accordingly, it is possible to prevent light from leaking out to other connection optical waveguides OW that are allowed to cross in the position corresponding to the beat length, reduce crosstalk, and further reduce dispersion caused by other connection optical waveguides OW, and thus crossing loss can be reduced.

[0074] In addition, even in a case where three or more connection optical waveguides OW are allowed to cross each other and a crossing angle is set at an acute angle, it is expected to reduce loss and crosstalk in the MMI crossing structure in the same manner, and thus it is possible to further reduce loss per unit crossing by collecting multiple crossings at one point.

[0075] Note that although crossing angles are preferably equal as shown in FIG. 3 in the MMI crossing structure, it is expected to produce the same effect in various embodiments other than the above embodiment.

[0076] In the present embodiment, it is possible to reduce the number of crossings as compared to the case where a maximum number of crossings of the connection optical waveguides OW is (N1)(N1) in the conventional optical switch shown in FIG. 5, i.e., in a case where three connection optical waveguides OW are allowed to cross each other in one point, a maximum number of crossings of the connection optical waveguides OW is expressed by (N1)(N1)N/2.

[0077] In this case, regarding the number of crossings and a loss value, comparison on the assumption of the actual number of ports is shown in Table 1.

TABLE-US-00001 TABLE 1 Maximum value The number of Loss The number of crossings in (@0.1 dB) crossings in the Loss (@0.1 dB) in the the first conventional in the first conventional N embodiment example embodiment example 4 7 9 0.7 0.9 8 45 49 4.5 4.9 16 217 225 21.7 22.5

[0078] As shown in Table 1, according to the NN optical switch 10 of the present embodiment, it is possible to reduce the number of crossings of the connection optical waveguides OW, thereby reducing crossing loss caused by the crossing of the waveguides.

[0079] In Table 1, an example of allowing three connection optical waveguides OW to cross each other at the same time is shown in the present embodiment, but the optical loss can be further reduced by increasing the number of connection optical waveguides OW crossing each other at the same time.

[0080] Note that in the present embodiment, the example of making the crossing of the connection optical waveguides OW by using the MMI optical waveguides OW.sub.MMI is shown, but the present invention is not limited to the above-described embodiment. By employing a structure having three or more connection optical waveguides OW crossing each other in one point (a structure having one connection optical waveguide OW crossing other two or more connection optical waveguides OW in one point), it is possible to reduce loss and crosstalk as compared to the conventional structure.

Second Embodiment

[0081] With reference to FIG. 4, an NN optical switch according to the second embodiment of the present invention will be described. As an example, a case where N=4 will be described.

[0082] First, FIG. 7 shows a 44 optical switch 200, which has achieved reduction of the number of crossings by changing the alignment of input side 14 optical switches SW11-SW14 and output side 41 optical switches SW21-SW24 by referring to PTL 2. The 44 optical switch 200 shown in FIG. 7 has a structure of alternately arranging the input sides and the output sides instead of aligning the input side 14 optical switches SW11-SW14 and aligning the output side 41 optical switches SW21-SW24 opposite to the input side 14 optical switches SW11-SW14 as shown in FIG. 5.

[0083] More specifically, on one end surface, the input side 14 optical switch SW11, the output side 41 optical switch SW24, the input side 14 optical switch SW12, and the output side 41 optical switch SW23 are arranged in this order, and on the other end surface, the output side 41 optical switch SW21, the input side 14 optical switch SW14, the output side 41 optical switch SW22, and the input side 14 optical switch SW13 are arranged in this order.

[0084] Output ports P1-P4 of the respective input side 14 optical switches SW11-SW14 and input ports Q1-Q4 of the respective output side 41 optical switches SW21-SW24 are connected in the following state.

[0085] More specifically, the output ports P1, P4 located in the two ends of the input side 1N optical switch SW11 are respectively connected to the input ports Q1, Q4 located in the end portions of the output side N1 optical switches SW21, SW24 that are adjacent to the input side 1N optical switch SW11 and are different from each other by connection optical waveguides that do not cross other connection optical waveguides; and among the output ports of the input side 1N optical switch SW11, the output ports P2, P3 located other than in the two ends are respectively connected to the input ports Q2, Q3 located other than the two ends of the output side N1 optical switches SW22, SW23 that are not adjacent to the input side 1N optical switch SW11 and are different from each other by connection optical waveguides that cross other connection optical waveguides.

[0086] Furthermore, the output ports P1, P4 located in the two ends of the input side 1N optical switch SW12 are respectively connected to the input ports Q1, Q4 located in the end portions of the output side N1 optical switches SW24, SW23 that are adjacent to the input side 1N optical switch SW12 and are different from each other by connection optical waveguides that do not cross other connection optical waveguides; and among the output ports of the input side 1N optical switch SW12, the output ports P2, P3 located other than in the two ends are respectively connected to the input ports Q2, Q3 located other than in the two ends of the output side N1 optical switches SW21, SW22 that are not adjacent to the input side 1N optical switch SW12 and are different from each other by connection optical waveguides that cross other connection optical waveguides.

[0087] Furthermore, the output ports P1, P4 located in the two ends of the input side 1N optical switch SW13 are respectively connected to the input ports Q1, Q4 located in the end portions of the output side N1 optical switches SW23, SW22 that are adjacent to the input side 1N optical switch SW13 and are different from each other by connection optical waveguides that do not cross other connection optical waveguides; and among the output ports of the input side 1N optical switch SW13, the output ports P2, P3 located other than in the two ends are respectively connected to the input ports Q2, Q3 located other than in the two ends of the output side N1 optical switches SW24, SW21 that are not adjacent to the input side 1N optical switch SW13 and are different from each other by connection optical waveguides that cross other connection optical waveguides.

[0088] Furthermore, the output ports P1, P4 located in the two ends of the input side 1N optical switch SW14 are respectively connected to the input ports Q1, Q4 located in the end portions of the output side N1 optical switches SW22, SW21 that are adjacent to the input side 1N optical switch SW14 and are different from each other by connection optical waveguides that do not cross other connection optical waveguides; and among the output ports of the input side 1N optical switch SW14, the output ports P2, P3 located other than in the two ends are respectively connected to the input ports Q2, Q3 located other than in the two ends of the output side N1 optical switches SW23, SW24 that are not adjacent to the input side 1N optical switch SW14 and are different from each other by connection optical waveguides that cross other connection optical waveguides.

[0089] With such an arrangement, it is possible to reduce the number of crossings as compared to the configuration of the NN optical switch shown in FIG. 5, i.e., the number of crossings of the connection optical waveguide OW with respect to other connection optical waveguides OW is (N2)(N/2) times at the maximum ((42)(4/2)=4 times if N=4). Also to this configuration, the structure of the present invention can be applied.

[0090] As compared to the 44 optical switch 200 shown in FIG. 7, the 44 optical switch 20 shown in FIG. 4 has different paths of the connection optical waveguides OW. The arrangement of the input side 1N optical switches SW11-SW14 and the output side 41 optical switches SW21-SW24 and the connection state between the output ports P1-P4 of the respective input side 14 optical switches SW11-SW14 and the input ports Q1-Q4 of the respective output side 41 optical switches SW21-SW24 are the same as those in FIG. 7, so a detailed description will be omitted.

[0091] As shown in FIG. 4, in the present embodiment, the 44 optical switch 20 has not only crossings of two waveguides but also crossings of three waveguides like the first embodiment. Points in which three connection optical waveguides OW are allowed to cross each other are encircled by broken lines in FIG. 4. In this case, a maximum number of crossings can be greatly reduced as compared to the conventional NN optical switch shown in FIG. 5, i.e., the number of crossings is (N1)(N2)/2 times at the maximum ((41)(42)/2=3 times if N=4). In this case, regarding the number of crossings and a loss value, comparison on the assumption of the actual number of ports is shown in Table 2.

TABLE-US-00002 TABLE 2 Maximum value The number of Loss The number of crossings in (@0.1 dB) Loss (@0.1 dB) crossings in the in the in the the second conventional second conventional N embodiment example embodiment example 4 3 9 0.3 0.9 8 21 49 2.1 4.9 16 105 225 10.5 22.5

[0092] As shown in Table 2, according to the NN optical switch 20 of the present embodiment, it is possible to reduce the number of crossings of the connection optical waveguides OW, thereby reducing crossing loss caused by the crossing of the waveguides.

[0093] In Table 2, an example of allowing three connection optical waveguides OW to cross each other at the same time is shown, but the optical loss can be further reduced by increasing the number of connection optical waveguides OW crossing each other at the same time. Note that also in the present embodiment, by using an MMI crossing structure in a waveguide crossing portion, crossings with low loss and low crosstalk can be achieved.

REFERENCE SIGNS LIST

[0094] 10, 20 44 optical switch (NN optical switch) [0095] SW11-SW14 input side 14 optical switch (input side 1N optical switch) [0096] SW21-SW24 output side 41 optical switch (output side N1 optical switch) [0097] P1-P4 output port of input side optical switch [0098] Q1-Q4 input port of output side optical switch [0099] OW connection optical waveguide [0100] OW.sub.MMIMMI optical waveguide