Optical switch module

Abstract

The purpose of the present disclosure is to make it possible to achieve the function of looping back from an add-side optical switch to a drop-side optical switch in an optical switch module in which an MCS is used, without incurring any increase in circuit size.　The present disclosure relates to an optical switch module comprising an add-side optical switch in which two optical switches are connected by a 2 × 1 optical switch, and a drop-side optical switch in which two optical switches are connected by a 2 × 1 optical switch, the optical switch module being such that: ports provided to cross paths of the two optical switches are used as Degree ports; ports provided to through paths of the optical switch that is connected to the cross-side path of the 2 × 1 optical switch, among the two optical switches, are used as loopback ports; the port numbers of the Degree ports differ between the add-side optical switch and the drop-side optical switch; and the loopback ports of the add-side optical switch and the drop-side optical switch are connected to each other.

Description

Optical Switch Module

[0001] The present disclosure relates to an optical switch module.

[0002] An MCS (multicast switch) is used for inserting (Add) an optical signal into a ROADM (Reconfigurable Optical Add / Drop Multiplexer) node and branching (Drop) the optical signal from the node. For the purpose of verifying the operation of a transponder that transmits and receives optical signals to and from a ROADM, in an optical switch module using an MCS, there may be a requirement for a function of loop-backing a transmitted optical signal input from a channel (hereinafter sometimes abbreviated as Ch) port of an add-side optical switch that inserts an optical signal to a Ch port of a drop-side optical switch that branches the optical signal.

[0003] In an optical switch module using an M×N channel MCS, in order to add one port to the Degree port (hereinafter sometimes abbreviated as Deg port) arranged on the splitter side, based on its topology, it is necessary to add one 1×N splitter and set the branching number of the M×1 switch to M + 1. If the additional Deg port can be directly connected by the add-side optical switch and the drop-side optical switch simply as a loop-back, the 1×N splitter is not necessarily required.

[0004] Considering device cost and reliability, it is desirable to monolithically realize the MCS as a waveguide-type integrated device. Also, a Mach-Zehnder interferometer (sometimes abbreviated as MZI) is generally used as a waveguide-type switch element. From the viewpoints of miniaturization and cost reduction of the optical switch module, it is effective for the configuration of the MCS circuit using a waveguide-type MZI to adopt a PILOSS type [for example, see Patent Document 1].

[0005] In the case of M / 2≧N such as a 16×8 channel MCS, rather than being composed of a single switch block with a PILOSS structure, as in Patent Document 2, adding a 2×1 optical switch to the Ch port side and adopting a 2×(M / 2×N) configuration that bundles two M / 2×N channel MCSs is more desirable in terms of the number of waveguide crossings.

[0006] When adding a loopback port to a 2x (M / 2xN) configuration, one possible method is to add a 2x1 optical switch on the Ch port side to switch between the main path and the loopback path, as described in Patent Document 3. In this case, an additional N 2x1 optical switches would be required on both the add and drop sides. This would involve a large increase in the circuit size, including the control circuit, which is undesirable from the standpoint of module size and manufacturing cost.

[0007] As shown in Patent Document 4, another method is to use the through-side path of the switch element as an expansion port. In an M x N channel MCS, there are a total of N through-side paths, one for each channel port. By bundling these with a 1 x N splitter, an expansion port usable for loopback can be implemented without increasing the number of switches. However, since the through-side path is a path that conducts when the optical switch is OFF, there is a problem that the generally required interrupted state for an MCS is lost.

[0008] Japanese Patent Publication No. WO1012111316, Japanese Patent Publication No. 2014-533018, Japanese Patent Publication No. 2016-213554, Japanese Patent Publication No. 2004-242149

[0009] This disclosure aims to enable a loopback function from the add-side optical switch to the drop-side optical switch in an optical switch module using MCS, without increasing the circuit size.

[0010] The optical switch module of the present disclosure comprises an add-side optical switch in which two optical switches are connected by a 2x1 optical switch, and a drop-side optical switch in which two optical switches are connected by a 2x1 optical switch, wherein a port on the cross path of the two optical switches is used as a Degree port, a port on the through path of the optical switch connected to the cross path of the 2x1 optical switch is used as a loopback port, the port numbers of the Degree ports are different for the add-side optical switch and the drop-side optical switch, and the loopback ports of the add-side optical switch and the drop-side optical switch are connected to each other.

[0011] The port number assigned to the Degree port of the optical switch connected to the through-side path of the 2x1 optical switch among the two optical switches in the add-side optical switch may be assigned to the Degree port of the optical switch connected to the cross-side path of the 2x1 optical switch among the two optical switches in the drop-side optical switch, and the port number assigned to the Degree port of the optical switch connected to the through-side path of the 2x1 optical switch among the two optical switches in the drop-side optical switch may be assigned to the Degree port of the optical switch connected to the cross-side path of the 2x1 optical switch among the two optical switches in the add-side optical switch.

[0012] The optical switch is an MCS (Multicast Switch) that connects M Degree ports and N channel ports, and the number of Degree ports M and the number of channel ports N may be even and equal for the drop-side optical switch and the drop-side optical switch.

[0013] Furthermore, the above disclosures can be combined as much as possible.

[0014] According to this disclosure, in an optical switch module using MCS, a function to loop back from the add-side optical switch to the drop-side optical switch can be realized without increasing the circuit size.

[0015] This document shows an example configuration of the optical switch module of this disclosure. It also shows an example of port numbers when M=8 and N=4. Finally, it shows an example of a connection configuration for the optical switch module of this disclosure. It also shows an example of an embodiment of the optical switch module of this disclosure.

[0016] Embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments shown below. These examples are illustrative, and this disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0017] (First Embodiment) Figure 1 shows an example of the configuration of the optical switch module of the present disclosure. The optical switch module of the present disclosure comprises an add-side optical switch 91 and a drop-side optical switch 92. The add-side optical switch 91 and the drop-side optical switch 92 are connected by a 2x1 optical switch.

[0018] In this embodiment, an example is shown in which two optical switches are MCSs connecting M Deg ports and N Ch ports. The 2x1 optical switch has a through-side path, which is set when the optical switch is turned OFF, and a cross-side path, which is set when the optical switch is turned ON. In this embodiment, the MCSs connected to the through-side path of the 2x1 optical switch are referred to as main MCSs 11 and 21, and the MCSs connected to the cross-side path of the 2x1 optical switch are referred to as sub-MCSs 12 and 22.

[0019] Furthermore, the ports reached when following the cross path of the two optical switches are used as Deg ports D1 to DM. The ports reached when following the through path of sub-MCS 12 and 22 are used as loopback ports LB1 to LBN. Deg ports D1 to DM can be connected to any Deg port for a single channel port. For example, Ch port C1 can be connected to any of Deg ports D1 to D8, and Ch port C2 can also be connected to any of Deg ports D1 to D8. This makes it possible to insert (Add) or branch (Drop) optical signals to the ROADM node. In contrast, loopback ports LB1 to LBN can only be connected to one location for a single channel. For example, Ch port C1 can only be connected to loopback port LB1 and cannot be connected to loopback port LB2.

[0020] The add-side optical switch 91 has the main MCS 11 and sub-MCS 12 of the M x N channel connected by a 2 x 1 optical switch 13. The drop-side optical switch 92 has the main MCS 21 and sub-MCS 22 of the M x N channel connected by a 2 x 1 optical switch 23.

[0021] One side of the 2x1 optical switches 13 and 23 is connected to the channel port. As a result, the add-side optical switch 91 and the drop-side optical switch 92 have a 2x (M / 2xN) configuration with the 2x1 optical switch 13 on the Ch-side port.

[0022] The loopback ports LB1, LB2, LB3, and LB4 located on the splitter side of the sub-MCS 12 and 22 are connected to each other, thereby forming a loopback path 93. For this reason, the optical switch module of this embodiment can configure a loopback path without the need for additional switches.

[0023] Here, the port number assigned to the Deg port of the main MCS11 in the add-side optical switch 91 is different from the port number assigned to the Deg port of the main MCS21 in the drop-side optical switch 92. For example, the port number assigned to the Deg port of the main MCS11 in the add-side optical switch 91 is assigned to the Deg port of the sub-MCS22 in the drop-side optical switch 92. Also, the port number assigned to the Deg port of the sub-MCS12 in the add-side optical switch 91 is assigned to the Deg port of the main MCS21 in the drop-side optical switch 92.

[0024] Figure 2 shows an example of port numbers when M=8 and N=4. On the add-side optical switch 91, Deg ports D1, D2, D3, and D4 are assigned to the sub-MCS 12, and Deg ports D5, D6, D7, and D8 are assigned to the main MCS 11. On the drop-side optical switch 92, Deg ports D1, D2, D3, and D4 are assigned to the main MCS 21, and Deg ports D5, D6, D7, and D8 are assigned to the sub-MCS 22.

[0025] In a ROADM node, the connection path on the add side is defined as equal to the connection path on the drop side. As long as this rule of (connection path on the add side) = (connection path on the drop side) is followed, Ch ports C1 to C4 can be freely combined to be blocked, connected to Deg ports D1 to D8, or connected to loopback ports LB1 to LB4. Loopback ports LB1 to LB4 can also be used to transmit optical signals, similar to Deg ports D1 to D8.

[0026] As shown in Figure 3, if Ch ports C1 to C4 are not connected to any of the Deg ports D1 to D8 or loopback ports LB1 to LB4, Ch ports C1 to C4 will be in the OFF (through connection) state. In this case, the 2x1 optical switches 13 and 23 conduct to the unconnected ports C1 OFF to C4 OFF of the main MCS 11 and 21, and do not send optical signals outside the module.

[0027] Each Deg port D1 to D8 will be OFF (through connection) in the following cases: (i) When all Ch ports C1 to C4 are blocked. (ii) When all Ch ports C1 to C4 are connected to a Deg port other than the corresponding Deg port. (iii) When all Ch ports C1 to C4 are connected to loopback ports LB1 to LB4, as shown in Figure 4. That is, when all Ch ports C1 to C4 are not connected to Deg ports D1 to D8.

[0028] Loopback ports LB1 to LB4 will be OFF (through connection) in the following cases: (i) When the corresponding Ch ports C1 to C4 are blocked. (ii) When the corresponding Ch ports C1 to C4 are connected to Deg ports D1 to D8. In other words, when the corresponding Ch ports C1 to C4 are not connected to loopback ports LB1 to LB4.

[0029] Therefore, by combining the 2x (M / 2xN) configuration and through path used, and the cross / through connection settings of the Ch-side 2x1 optical switch and the assignment of port numbers on the Deg port, the present disclosure allows the paths leading to the sub-MCS 12 and 22 connected to the cross-side paths of the Ch-side 2x1 optical switches 13 and 23 to be used as the through-side paths. For this reason, the present disclosure allows the operation of the transponder to be verified without adding a 1xN splitter.

[0030] Furthermore, this disclosure employs a 2×(M / 2×N) configuration that bundles two M / 2×N MCS switch blocks, thereby reducing the circuit size and the number of waveguide crossovers. In particular, by setting the number of Deg ports M and the number of Ch ports N to M=N and making both M and N even numbers, the circuit size and the number of waveguide crossovers can be minimized, and the symmetry of the circuit configuration is maximized, thus reducing insertion loss and crosstalk.

[0031] (Second Embodiment) In this embodiment, the extinction of crosstalk between Ch ports will be described. The amount of light leakage from the optical switch is less from the cross-side path when the optical switch is OFF than from the through-side path when the optical switch is ON. Therefore, crosstalk can be reduced by designing the system so that there is one or more cross-side paths between the input port and the output port where the optical switch is OFF.

[0032] In this disclosure, Deg ports D5-D8 connected to the through-side path of the 2x1 optical switch 13 at the add-side optical switch 91 are connected to the cross-side path of the 2x1 optical switch 13 at the drop-side optical switch 92, and Deg ports D1-D4 connected to the cross-side path of the 2x1 optical switch 23 at the drop-side optical switch 92 are connected to the through-side path of the 2x1 optical switch 23 at the add-side optical switch 91. Therefore, in all cases when each Ch port C1-C4 is shut off and when Ch ports C1-C4 are connected to Deg ports D1-D8, one or more of the 2x1 optical switches 13 and 23 become the through (OFF) side path. With this definition, even if there is leakage light from the loopback path 93, crosstalk extinction due to the 2x1 optical switches being connected as through-side paths will always occur.

[0033] For example, in the add-side optical switch 91, the Deg ports D5-D8 are connected to the through-side path of the 2x1 optical switch 13. At this time, between the loopback ports LB1-LB4 of the sub-MCS 12 and this connection path, there is a cross-side path of the 2x1 optical switch 13 that is in the OFF state. Therefore, when the Ch ports C1-C4 are connected to the Deg ports D5-D8 in the add-side optical switch 91, crosstalk in the add-side optical switch 91 can be reduced.

[0034] In the add-side optical switch 91, the Deg ports D1-D4 are connected to the cross-side path of the 2x1 optical switch 13. At this time, there are no OFF cross-side paths between the loopback ports LB1-LB4 of the sub-MCS 12 and this connection path. Therefore, when the Ch ports C1-C4 are connected to the Deg ports D1-D4 in the add-side optical switch 91, the leaked light from the sub-MCS 12 will exit through the loopback ports LB1-LB4.

[0035] For example, as shown in Figure 5, when the Ch port C1 is connected to the Deg port D2 in the add-side optical switch 91, leaked light from the sub-MCS 12 flows into the loopback port LB1 of the sub-MCS 22. At this time, in the drop-side optical switch 92, a connection path is formed from the Ch port C1 of the drop-side optical switch 92 to the Deg port D2. Here, in the drop-side optical switch 92, the Deg port D2 is located in the main MCS 21, and the 2x1 optical switch 23 of the drop-side optical switch 92 is in the OFF state. Therefore, there is an OFF cross-side path between the loopback ports LB1-LB4 of the sub-MCS 22 and this connection path.

[0036] Thus, in this disclosure, in all cases when each Ch port C1 to C4 is blocked and when Ch ports C1 to C4 are connected to Deg ports D1 to D8, at least one of the 2x1 optical switches 13 and 23 becomes the through-path for the same channel. Therefore, this disclosure can reduce crosstalk in the add-side optical switch 91 and the drop-side optical switch 92.

[0037] Figure 6 shows an example of an embodiment of the optical switch module of the present disclosure. In this embodiment, M=4 and N=2, and waveguide-type MZIs are used for MCS 41-44 and 51-54. Each of MCS 41-44 and 51-54 is equipped with four directional couplers 40.

[0038] In MZI-type optical switches, the extinction ratio of the through-side path depends on the coupling ratio of the directional coupler and is therefore susceptible to manufacturing variations, generally being worse than that of the cross-side path. In this regard, the present disclosure offers good symmetry in the circuit configuration of the add-side optical switch 91 and the drop-side optical switch 92, allowing the crosstalk generated in the add-side optical switch 91 and the drop-side optical switch 92 to be made almost equal. As a result, crosstalk can be reduced by adopting this embodiment.

[0039] 11, 21: Main MCS 12, 22: Sub MCS 13, 23: 2x1 optical switch 91: Add-side optical switch 92: Drop-side optical switch

Claims

1. An optical switch module comprising: an add-side optical switch in which two optical switches are connected by a 2x1 optical switch; and a drop-side optical switch in which two optical switches are connected by a 2x1 optical switch, wherein a port on the cross path of the two optical switches is used as a Degree port; a port on the through path of the optical switch connected to the cross path of the 2x1 optical switch is used as a loopback port; the port numbers of the Degree ports are different for the add-side optical switch and the drop-side optical switch; and the loopback ports of the add-side optical switch and the drop-side optical switch are connected to each other.

2. The optical switch module according to claim 1, wherein the port number assigned to the Degree port of the optical switch connected to the through-side path of the 2x1 optical switch among the two optical switches in the add-side optical switch is assigned to the Degree port of the optical switch connected to the cross-side path of the 2x1 optical switch among the two optical switches in the drop-side optical switch, and the port number assigned to the Degree port of the optical switch connected to the through-side path of the 2x1 optical switch among the two optical switches in the drop-side optical switch is assigned to the Degree port of the optical switch connected to the cross-side path of the 2x1 optical switch among the two optical switches in the add-side optical switch.

3. The optical switch module according to claim 1, wherein the optical switch is an MCS (Multicast Switch) connecting M Degree ports and N channel ports, and the number of Degree ports M and the number of channel ports N are even and equal for the drop-side optical switch and the drop-side optical switch.

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