A low-loss real-time monitoring non-blocking optical switching network and its construction method

Abstract

The present invention discloses a low-loss, real-time monitoring, non-blocking optical switching network and its construction method. This optical switching network embeds an optical monitoring network within a Benes network, forming a novel, real-time, non-blocking optical switching network. The embedded optical monitoring network consists of thermo-optical switches, enabling real-time monitoring of the operating status of all optical switching units in the entire optical switching network while also ensuring low transmission loss. This invention eliminates the need for built-in optical power monitoring points within the optical switching chip, requiring only four monitoring ports to achieve real-time monitoring of the entire network. Furthermore, the status of the switch units can still be monitored in real time after the optical chip is packaged, significantly facilitating the testing of large-scale switching chips.

Description

Technical Field

[0001] The present invention relates to the technical field of optical switching networks, and in particular to a low-loss real-time monitoring non-blocking optical switching network and a construction method thereof. Background Art

[0002] With the emergence and technological development of a series of high-speed, high-bandwidth services such as big data, cloud computing, the Internet of Things, and data centers, these new services and technologies have placed higher demands on the carrying capacity of communication networks. Silicon-based photonics has become the most promising high-efficiency, low-cost on-chip solution. Among them, all-optical switching technology, with its advantages of low latency, high bandwidth, and low power consumption, is an inevitable choice for the development of future communication networks.

[0003] Current all-optical switching networks can be divided into three categories based on whether there is conflict in path switching: blocked networks, rearranged non-blocking networks, and strictly non-blocking networks. For large-scale optical switch arrays, it is necessary to meet the requirements of both non-blocking and a small number of switch units. The optical switch unit is the network structure with the least number of switch units to meet the non-blocking condition. However, for Benes network monitoring, the solution of built-in optical power monitoring point is generally adopted for network monitoring, that is, a DC coupler with a fixed splitting ratio is used to split one optical path as the optical power monitoring point. The N×N Benes network requires a total of The single optical power monitoring point not only limits large-scale applications but also makes it impossible to perform real-time monitoring of the optical switch unit. Summary of the Invention

[0004] The present invention aims to address the deficiencies of the prior art and provide a low-loss, real-time monitoring, non-blocking optical switching network and its construction method. The present invention only requires four monitoring ports to achieve real-time monitoring of the entire network.

[0005] The object of the present invention is achieved through the following technical solutions: In a first aspect, an embodiment of the present invention provides a low-loss real-time monitoring non-blocking optical switching network, the optical switching network comprising:

[0006] A Benes network, wherein the Benes network includes 2log2N-1 levels, each level is provided with N / 2 optical switch units from top to bottom, the optical switch unit includes two input ports and two output ports, wherein the ports of the optical switch units between adjacent levels from the 1st to the log2Nth level and from the log2N+1th to the 2log2N-1th level are connected; and

[0007] An optical monitoring network comprising three levels, each level having N / 2, N / 2+1, and N / 2 optical switch units, respectively, from top to bottom, wherein four optical switch units are connected end to end to form a ring network, and each ring network is connected in a row by an optical switch unit. The optical monitoring network comprises N / 2 ring networks connected end to end;

[0008] In which, the optical monitoring network is embedded between the log2Nth level and the log2N+1th level of the Benes network, the optical switch units in the ring network of the optical monitoring network are respectively connected to the optical switch units of the log2Nth level and the log2N+1th level of the Benes network, and the monitoring ports of the optical monitoring network are the first optical switch unit of the second level and the remaining ports of the last optical switch unit.

[0009] Furthermore, N is a positive integer greater than or equal to 4, and N is a power of 2.

[0010] Furthermore, the Benes network includes optical switch units, the optical monitoring network includes An optical switch unit.

[0011] Furthermore, the optical switch unit is a 2×2 optical switching unit, and the states of the 2×2 optical switching unit include a cross state, a straight-through state, and an intermediate cross state.

[0012] Furthermore, the number of the monitoring ports is 4.

[0013] A second aspect of an embodiment of the present invention provides a method for constructing a low-loss, real-time monitoring, non-blocking optical switching network, comprising the following steps:

[0014] (1) A 2×2 optical switch unit is selected as the basic unit of the entire optical switching network. The optical switch unit includes two input ports and two output ports.

[0015] (2) Iterate according to the topological rules of the Benes network to construct an N×N Benes network;

[0016] (3) Constructing an optical monitoring network according to the topological rules of the optical monitoring network;

[0017] (4) embedding an optical monitoring network between the log2Nth level and the log2N+1th level of the N×N Benes network, and connecting the optical monitoring network to the N×N Benes network;

[0018] (5) The states of the first-level optical switch unit and the third-level optical switch unit of the optical monitoring network are adjusted to the intermediate cross state, and the state of the second-level optical switch unit of the optical monitoring network is adjusted to the straight-through state, so as to realize real-time monitoring of the entire optical switching network.

[0019] Furthermore, the topology rule of the Benes network in step (2) is specifically as follows: the Benes network includes 2log2N-1 levels, each level is provided with N / 2 optical switch units from top to bottom, and the Benes network includes Optical switch units, the jth switch unit in the i-th level of the Benes network is represented as Sij, where i and j are integers, 1≤i≤2log2N-1, For the 1st to log2Nth levels and the log2N+1th to 2log2N-1th levels, the ports of the optical switch units between two adjacent levels are connected to construct an N×N Benes network.

[0020] Furthermore, the topology rule of the optical monitoring network in step (3) is specifically as follows: the optical monitoring network includes three levels, and each level is provided with N / 2, N / 2+1, and N / 2 optical switch units from top to bottom, respectively. The nth optical switch unit in the mth level is represented as Cmn, where m and n are integers, 1≤m≤3, Every four optical switch units are connected end to end to form a ring network, and each ring network is connected into a row through an optical switch unit. Two adjacent ring networks in N / 2 ring networks are connected through a shared optical switch unit to build an optical monitoring network.

[0021] Furthermore, after the optical monitoring network is constructed, the remaining four ports of the first optical switch unit and the last optical switch unit of the second stage are reserved as monitoring ports.

[0022] Furthermore, the step (4) includes the following sub-steps:

[0023] (4.1) Connect the first port on the right side of the optical switch unit of the log2Nth level of the Benes network to the first port on the left side of the first-level optical switch unit of the optical monitoring network, that is, connect the first port on the right side of Skj to the first port on the left side of C1n, where k = log2N.

[0024] (4.2) Connect the second port on the right side of the optical switch unit of the log2Nth level of the Benes network to the first port on the left side of the third-level optical switch unit of the optical monitoring network, that is, connect the second port on the right side of Skj to the first port on the left side of C3n, where k = log2N.

[0025] (4.3) Connect the two left ports of the optical switch unit in the log2N+1th level of the Benes network to the second right ports of the first-level optical switch unit and the third-level optical switch unit of the optical monitoring network, respectively. For the optical switch unit Stj in the log2N+1th level of the Benes network, the specific connection method is:

[0026] When j is an odd number, the first port on the left side of Stj is connected to the second port on the right side of the first-stage optical switch unit C1j of the optical monitoring network, and the second port on the left side of Stj is connected to the second port on the right side of the first-stage optical switch unit C1g of the optical monitoring network;

[0027] When j is an even number, the first port on the left side of Stj is connected to the second port on the right side of the third-level optical switch unit C3h of the optical monitoring network, and the second port on the left side of Stj is connected to the second port on the right side of the first-level optical switch unit C3j of the optical monitoring network;

[0028] Where, t = log2N + 1, g=j+1, h=j-1.

[0029] The beneficial effect of the present invention is that it eliminates the need for a built-in optical rate detector and can achieve real-time monitoring of the entire network optical switch through only four optical monitoring ports, solving the problem of large-scale optical switching monitoring; by adopting a solution that combines thermal-optical switches with electro-optical switches, it not only ensures the nanosecond-level switching rate of the optical switching chip, but also greatly reduces the additional losses caused by the monitoring network. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of a basic optical switch unit and its different working states in an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the structure of an 8×8 low-loss real-time monitoring non-blocking optical switching network in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of an 8×8 low-loss real-time monitoring non-blocking optical switching network in normal working condition according to an embodiment of the present invention;

[0033] Figure 4 Schematic diagram of an 8×8 low-loss real-time monitoring non-blocking optical switching network in a unit test state according to an embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of an 8×8 low-loss real-time monitoring non-blocking optical switching network in a real-time monitoring state according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. The low-loss, real-time monitoring of a non-blocking optical switching network in the present invention includes a Benes network and an optical monitoring network.

[0036] In this embodiment, the Benes network includes 2log2N-1 levels, each level is provided with N / 2 optical switch units from top to bottom, and the optical switch unit includes two input ports and two output ports. Among them, the ports of the optical switch units between the 1st to the log2Nth level and the log2N+1th to the 2log2N-1th level are connected.

[0037] In this embodiment, the optical monitoring network includes three levels, and each level is provided with N / 2, N / 2+1, and N / 2 optical switch units from top to bottom, respectively. Among them, every four optical switch units are connected end to end to form a ring network, and each ring network is connected into a column through an optical switch unit. The optical monitoring network includes N / 2 ring networks connected end to end.

[0038] The optical monitoring network is embedded between the log2Nth and log2N+1th stages of the Benes network. The optical switch units in the ring network of the optical monitoring network are connected to the log2Nth and log2N+1th optical switch units of the Benes network, respectively. The monitoring ports of the optical monitoring network are the remaining ports of the first and last optical switch units of the second stage. It is easy to understand that the first and last optical switch units of the second stage of the optical monitoring network have a total of four remaining ports, so there are four monitoring ports in total.

[0039] In this embodiment, N is a positive integer greater than or equal to 4, and N is a power of 2; for example, Figure 2 In the optical switching network shown, N=8, which meets the selection condition of N. It should be understood that N may also be other numbers that meet the condition, such as 16, 32, etc.

[0040] In this embodiment, the Benes network includes Optical switch units, the optical monitoring network includes The optical switching network includes a total of Nlog2N+N+1 optical switching units.

[0041] Preferably, the optical switch unit is a 2×2 optical switching unit, wherein, Figure 1As shown, the states of the 2×2 optical switching unit include a cross state, a bar state, and a mid-cross state.

[0042] It is worth mentioning that an embodiment of the present invention also provides a method for constructing a low-loss, real-time monitoring, non-blocking optical switching network, which specifically includes the following steps:

[0043] (1) A 2×2 optical switch unit is selected as the basic unit of the entire optical switching network.

[0044] The optical switch unit includes two input ports and two output ports, and its states include a cross state, a bar state, and a mid-cross state.

[0045] (2) Iterate according to the topological rules of the Benes network to construct an N×N Benes network.

[0046] The topology rule of the Benes network is as follows: The Benes network includes 2log2N-1 levels, each level has N / 2 optical switch units from top to bottom, and the Benes network includes The jth switch unit in the i-th level of the Benes network is represented as Sij, where i and j are integers, 1≤i≤2log2N-1, For the 1st to log2Nth levels and the log2N+1th to 2log2N-1th levels, the ports of the optical switch units between two adjacent levels are connected. According to the topological rules of the Benes network, an N×N Benes network can be constructed.

[0047] For example, N=8 is selected, and an 8×8 topology is taken as an example. According to the topology rule of the Benes network, an 8×8 Benes network is obtained by iteration, and the jth switch unit of the i-th level is represented as Sij, where i and j are integers, 1≤i≤5, 1≤j≤4, such as Figure 2 shown.

[0048] (3) Construct an optical monitoring network according to the topological rules of the optical monitoring network.

[0049] The topology rules of the optical monitoring network are as follows: the optical monitoring network consists of three levels, and each level is provided with N / 2, N / 2+1, and N / 2 optical switch units from top to bottom, respectively. The nth optical switch unit in the mth level is represented as Cmn, where m and n are integers, 1≤m≤3. Connect four optical switch units end to end to form a ring network, and each ring network is connected to form a row through an optical switch unit. According to the topology rules of the optical monitoring network described above, the optical monitoring network is constructed by sharing an optical switch unit between two adjacent ring networks in N / 2 ring networks.

[0050] After the optical monitoring network is constructed according to the above topological rules of the optical monitoring network, the optical monitoring network still has 2N+4 ports left. The remaining 4 ports of the first optical switch unit and the last optical switch unit of the second level are reserved as monitoring ports of the entire optical switching network.

[0051] For example, an optical monitoring network is constructed according to the topological rules of the optical monitoring network. Specifically, C11, C21, C31, and C22 are connected end to end to form a first ring network; C12, C22, C32, and C23 are connected end to end to form a second ring network; C13, C23, C33, and C24 are connected end to end to form a third ring network; and C14, C24, C34, and C25 are connected end to end to form a fourth ring network. That is, the first ring network is connected to the second ring network through C22, the second ring network is connected to the third ring network through C23, and the third ring network is connected to the fourth ring network through C24. The optical monitoring network still has 20 ports left unconnected, among which the remaining 4 ports of C21 and C25 are used as monitoring ports to monitor the status of the optical switch units in the entire optical switching network, such as Figure 2 shown.

[0052] (4) An optical monitoring network is embedded between the log2Nth level and the log2N+1th level of the N×N Benes network, and the optical monitoring network is connected to the N×N Benes network.

[0053] (4.1) Connect the first port on the right side of the optical switch unit of the log2Nth level of the Benes network to the first port on the left side of the first-level optical switch unit of the optical monitoring network, that is, connect the first port on the right side of Skj to the first port on the left side of C1n, where k = log2N.

[0054] For example, the first port on the right side of the optical switch unit of the third level (from S31 to S34) of the Benes network is connected in sequence with the first port on the left side of the first level optical switch unit (from C11 to C14) of the optical monitoring network, that is, the first port on the right side of S31 is connected to the first port on the left side of C11, the first port on the right side of S32 is connected to the first port on the left side of C12, the first port on the right side of S33 is connected to the first port on the left side of C13, and the first port on the right side of S34 is connected to the first port on the left side of C14.

[0055] (4.2) Connect the second port on the right side of the optical switch unit of the log2Nth level of the Benes network to the first port on the left side of the third-level optical switch unit of the optical monitoring network, that is, connect the second port on the right side of Skj to the first port on the left side of C3n, where k = log2N.

[0056] For example, the second port on the right side of the optical switch unit of the third level (from S31 to S34) of the Benes network is connected to the first port on the left side of the third level optical switch unit (from C31 to C34) of the optical monitoring network in sequence, that is, the second port on the right side of S31 is connected to the first port on the left side of C31, the second port on the right side of S32 is connected to the first port on the left side of C32, the second port on the right side of S33 is connected to the first port on the left side of C33, and the second port on the right side of S34 is connected to the first port on the left side of C34.

[0057] (4.3) Connect the two left ports of the optical switch unit in the log2N+1th level of the Benes network to the second right ports of the first and third optical switch units of the optical monitoring network, respectively. For the optical switch unit Stj in the log2N+1th level of the Benes network, the specific connection method is:

[0058] When j is an odd number, the first port on the left side of Stj is connected to the second port on the right side of the first-stage optical switch unit C1j of the optical monitoring network, and the second port on the left side of Stj is connected to the second port on the right side of the first-stage optical switch unit C1g of the optical monitoring network;

[0059] When j is an even number, the first port on the left side of Stj is connected to the second port on the right side of the third-level optical switch unit C3h of the optical monitoring network, and the second port on the left side of Stj is connected to the second port on the right side of the first-level optical switch unit C3j of the optical monitoring network;

[0060] Where, t = log2N + 1, g=j+1, h=j-1.

[0061] For example, the two ports on the left side of the fourth-level optical switch unit (from S41 to S44) of the Benes network are connected to the second port on the right side of the first-level optical switch unit and the third-level optical switch unit of the optical monitoring network, respectively. The specific connection method is: connect the first port on the left side of S41 to the second port on the right side of the first-level optical switch unit C11 of the optical monitoring network, and the second port on the left side of S41 to the second port on the right side of the first-level optical switch unit C12 of the optical monitoring network; connect the first port on the left side of S42 to the second port on the right side of the third-level optical switch unit C31 of the optical monitoring network. The first and second ports of S43 are connected to each other, the second port on the left side of S43 is connected to the second port on the right side of the first-level optical switch unit C13 of the optical monitoring network, and the second port on the left side of S43 is connected to the second port on the right side of the first-level optical switch unit C14 of the optical monitoring network; the first port on the left side of S44 is connected to the second port on the right side of the third-level optical switch unit C33 of the optical monitoring network, and the second port on the left side of S44 is connected to the second port on the right side of the first-level optical switch unit C34 of the optical monitoring network.

[0062] (5) The states of the first-level optical switch unit and the third-level optical switch unit of the optical monitoring network are adjusted to the intermediate cross state, and the state of the second-level optical switch unit of the optical monitoring network is adjusted to the straight-through (Bar) state to achieve real-time monitoring of the entire network.

[0063] The optical switching network in this embodiment has three working states, namely normal working state, unit test state and real-time monitoring state. By adjusting the state of the corresponding optical switch unit in the optical monitoring network, the switching between the three working states of the optical switching network can be achieved.

[0064] In this embodiment, the states of the first-stage optical switch units (i.e., C11 to C14) and the third-stage optical switch units (i.e., C31 to C34) of the optical monitoring network are adjusted to the cross state, and the 8×8 low-loss real-time monitoring non-blocking optical switching network is in normal working state. Figure 3 As shown, compared with the traditional Benes network, there is one more level of thermo-optical switch. Since the loss of the thermo-optical switch is extremely low, the impact on optical transmission can be ignored.

[0065] In this embodiment, the optical switch units (i.e., C21 to C25) of the second level of the optical monitoring network are adjusted to the straight-through (Bar) state, and then the optical switch units in the optical monitoring network corresponding to the optical switch units under test are adjusted to the straight-through (Bar) state, so that the optical switch units under test can be tested. At this time, the 8×8 low-loss real-time monitoring non-blocking optical switching network is in the unit test state, such as Figure 4As shown, for the optical switch unit S31 under test, in addition to adjusting the second-stage optical switch units (i.e., C21 to C25) to the straight-through (Bar) state, the corresponding C11 also needs to be adjusted to the straight-through (Bar) state, so that the state of the switch unit S31 under test can be monitored at the monitoring port 2.

[0066] In this embodiment, the states of the first-stage optical switch units (i.e., C11 to C14) and the third-stage optical switch units (i.e., C31 to C34) of the optical monitoring network are adjusted to the intermediate crossover state. In this state, the splitting ratio for the monitoring circuit is only 10%, which does not reduce the strength of the normal signal path. The state of the second-stage optical switch units (i.e., C21 to C25) of the optical monitoring network is adjusted to the straight-through (Bar) state. The 8×8 low-loss real-time monitoring non-blocking optical switching network is in the real-time monitoring state. Figure 5 As shown, it can work normally and also monitor the entire optical switching network in real time through the four monitoring ports.

[0067] The above embodiments are intended only to illustrate the design concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. The scope of protection of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design concepts disclosed in the present invention are within the scope of protection of the present invention.

Claims

1. A low-loss real-time monitoring system for non-blocking optical switching networks, characterized in that: The optical switching network includes: A Benes network, wherein the Benes network includes 2log2 N-1 stages, each stage is provided with N / 2 optical switch units from top to bottom, the optical switch unit includes two input ports and two output ports, wherein the ports of the optical switch units between adjacent stages from the 1st stage to the log2 Nth stage and from the log2 N+1th stage to the 2log2 N-1th stage are connected; and An optical monitoring network comprising three levels, each level having N / 2, N / 2+1, and N / 2 optical switch units, respectively, from top to bottom, wherein four optical switch units are connected end to end to form a ring network, and each ring network is connected in a row by an optical switch unit. The optical monitoring network comprises N / 2 ring networks connected end to end; The optical monitoring network is embedded between the log2 Nth level and the log2 N+1th level of the Benes network, the optical switch units in the ring network of the optical monitoring network are respectively connected to the optical switch units of the log2 Nth level and the log2N+1th level of the Benes network, and the monitoring ports of the optical monitoring network are the remaining ports of the first optical switch unit and the last optical switch unit of the second level.

2. The low-loss real-time monitoring non-blocking optical switching network according to claim 1, characterized in that: The N is a positive integer greater than or equal to 4, and N is a power of 2.

3. The low-loss real-time monitoring non-blocking optical switching network according to claim 1 or 2, characterized in that: The Benes network includes optical switch units, the optical monitoring network includes An optical switch unit.

4. The low-loss real-time monitoring non-blocking optical switching network according to claim 1, characterized in that: The optical switch unit is a 2×2 optical switching unit, and the states of the 2×2 optical switching unit include a cross state, a straight-through state, and an intermediate cross state.

5. The low-loss real-time monitoring non-blocking optical switching network according to claim 1, characterized in that: The number of monitoring ports is 4.

6. A method for constructing a low-loss, real-time monitoring, non-blocking optical switching network according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) A 2×2 optical switch unit is selected as the basic unit of the entire optical switching network. The optical switch unit includes two input ports and two output ports. (2) Iterate according to the topological rules of the Benes network to construct an N×N Benes network; (3) Constructing an optical monitoring network according to the topological rules of the optical monitoring network; (4) embedding an optical monitoring network between the log2 Nth level and the log2 N+1th level of the N×N Benes network, and connecting the optical monitoring network to the N×N Benes network; (5) The states of the first-level optical switch unit and the third-level optical switch unit of the optical monitoring network are adjusted to the intermediate cross state, and the state of the second-level optical switch unit of the optical monitoring network is adjusted to the straight-through state, so as to realize real-time monitoring of the entire optical switching network.

7. The method for constructing a low-loss, real-time monitoring, non-blocking optical switching network according to claim 6, characterized in that: The topology rule of the Benes network in step (2) is as follows: the Benes network includes 2log2 N-1 levels, each level is provided with N / 2 optical switch units from top to bottom, and the Benes network includes Optical switch units, the jth switch unit in the i-th level of the Benes network is represented as Sij, where i and j are integers, 1≤i≤2log2 N-1, For the 1st to log2 Nth levels and the log2 N+1th to 2log2 N-1th levels, the ports of the optical switch units between two adjacent levels are connected to construct an N×N Benes network.

8. The method for constructing a low-loss, real-time monitoring, non-blocking optical switching network according to claim 6, characterized in that: The topology rule of the optical monitoring network in step (3) is as follows: the optical monitoring network includes three levels, and each level is provided with N / 2, N / 2+1, and N / 2 optical switch units from top to bottom, respectively. The nth optical switch unit in the mth level is represented as Cmn, where m and n are integers, 1≤m≤3, Every four optical switch units are connected end to end to form a ring network, and each ring network is connected into a row through an optical switch unit. Two adjacent ring networks in N / 2 ring networks are connected through a shared optical switch unit to build an optical monitoring network.

9. The method for constructing a low-loss, real-time monitoring, non-blocking optical switching network according to claim 8, characterized in that: After the optical monitoring network is constructed, the remaining four ports of the first optical switch unit and the last optical switch unit of the second stage are reserved as monitoring ports.

10. The method for constructing a low-loss, real-time monitoring, non-blocking optical switching network according to claim 6, characterized in that: The step (4) includes the following sub-steps: (4.1) Connect the first port on the right side of the optical switch unit of the log2 Nth level of the Benes network to the first port on the left side of the first-level optical switch unit of the optical monitoring network, that is, connect the first port on the right side of Skj to the first port on the left side of C1n, where k = log2 N. (4.2) Connect the second port on the right side of the optical switch unit of the log2 Nth level of the Benes network to the first port on the left side of the third-level optical switch unit of the optical monitoring network, that is, connect the second port on the right side of Skj to the first port on the left side of C3n, where k = log2 N. (4.3) Connect the two left ports of the optical switch unit in the log2N+1th level of the Benes network to the second right ports of the first-level optical switch unit and the third-level optical switch unit of the optical monitoring network, respectively. For the optical switch unit Stj in the log2N+1th level of the Benes network, the specific connection method is: When j is an odd number, the first port on the left side of Stj is connected to the second port on the right side of the first-stage optical switch unit C1j of the optical monitoring network, and the second port on the left side of Stj is connected to the second port on the right side of the first-stage optical switch unit C1g of the optical monitoring network; When j is an even number, the first port on the left side of Stj is connected to the second port on the right side of the third-level optical switch unit C3h of the optical monitoring network, and the second port on the left side of Stj is connected to the second port on the right side of the first-level optical switch unit C3j of the optical monitoring network; Where, t = log2 N + 1, g=j+1, h=j-1.

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