Optical switch circuit with monitoring function

Abstract

An optical switch circuit (101) is provided with: an optical switch (21) in which element switches (11) capable of switching between a cross state and a bar state between two input terminals and two output terminals are disposed in a matrix structure of N rows and N columns; and a monitoring unit (61) for monitoring an optical connection state between an input port and an output port, wherein one of the two input terminals of each element switch in a first column is an input port (A) and the other is an input-side dummy port (A^), and one of the two output terminals of each element switch in an N-th column is an output port (B) and the other is an output-side dummy port (B^). The monitoring unit monitors the optical connection state on the basis of a position, in the matrix structure of the element switches, of an element switch in which detection light input from a detection light source (55) to the input-side dummy port or the output-side dummy port is detected.

Description

Optical switch circuit with monitoring function

[0001] The present invention relates to an optical switch circuit with a monitoring function that can selectively connect N input ports to N output ports in a one-to-one correspondence and has a function for monitoring the connection state.

[0002] In data centers and high-performance computers that handle large amounts of data, increasing bandwidth and reducing power consumption in signal processing technology are key challenges. One promising solution for achieving this is the introduction of optical switches, which switch optical signals along individual paths (optical paths), and various types of optical switches have been developed. For example, optical switches include those realized using MEMS (Micro Electro Mechanical Systems) and those realized using silicon photonics, which fabricates optical and electronic integrated circuits on a silicon substrate. Co-packaging, which integrates optical circuits and mounts them on the same substrate as electronic circuits, has also attracted attention as a technology that promotes low power consumption.

[0003] Optical switches generally consume less power than electronic switches, but are less reliable and have a higher failure rate. Therefore, their operational status must be constantly monitored so that any malfunctions can be addressed promptly. For example, some data centers that have introduced MEMS optical switches constantly monitor their operational status using surveillance cameras. Furthermore, optical switches using silicon photonics are compact and low-power, and various types have been developed. Among these, PILOSS (Pass-Independent Insertion Loss) optical switches, which are characterized by equal loss across all optical paths, have strictly non-blocking characteristics, and a switch chip capable of switching 32 optical signals has been developed (Non-Patent Document 1). Silicon photonics optical switches are suitable for co-packaging, but when implemented, their operational status must be monitored on the chip, just like MEMS optical switches. Various methods for monitoring the operation of typical non-blocking optical switches have been developed. However, these previously developed methods cannot be applied to PILOSS optical switches with different structures.

[0004] For example, the status of an optical switch can be monitored by adding a port identification signal to an input signal using intensity modulation or the like and reading the added port identification signal on the output side. However, once modulation is applied to the input signal, it cannot be completely removed. This causes practical problems, including degradation of signal quality. To avoid such problems, methods for monitoring the operation of an optical switch without modulating the input signal have also been developed. For example, Patent Document 1 discloses a method for monitoring the operating status of a wavelength selective switch (WSS), which switches optical signals on a wavelength-by-wavelength basis. When signal light is input from an input port and selectively output from an output port, monitor light is input from the output port, travels through the WSS along the same optical path as the signal light in the opposite direction to the propagation direction of the signal light, and is output from the input port. The monitor light is then separated from the signal light using a circulator and guided to a monitor unit for monitoring. Furthermore, Patent Document 2 discloses a method for monitoring the operating status of an optical cross-connect by modulating a portion of the signal light output from an output port, supplying the modulated light to the output port, reversing the optical path that the signal light passed through, and guiding it to a photodiode via an optical coupler or optical circulator for monitoring.

[0005] International Publication No. 2013 / 140493 Pamphlet Japanese Patent Application Laid-Open No. 2000-358261

[0006] T. Nishi et. al, “A polarization controlled free-space photonic switch based on a PILOSS switch”, Photonics Technology Letter, vol. 5, No. 9, p.1104-1106, 1993

[0007] In the methods described in Patent Documents 1 and 2, monitoring light is input from an output port, and the monitoring light is output from the input port by traveling back along the same optical path as the optical path from the input port to the output port through which the signal light passes. Therefore, a circulator or coupler (isolator) is required to prevent the monitoring light from leaking outside the switch. However, although circulators and couplers (isolators) are widely used in optical fiber products, their integration has not yet been realized. Therefore, the optical switch monitoring methods disclosed in Patent Documents 1 and 2 cannot be applied to monitoring the operating status of an optical switch using an integrated optical circuit.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to solve the problems present in the prior art and to make it possible to monitor the operating state of an optical switch without causing a deterioration in the quality of optical signals in an integrated optical circuit.

[0009] In view of the above object, the present invention provides an N×N matrix structure in which element switches each having at least two input terminals and two output terminals and capable of switching between a cross state and a bar state between the two input terminals and the two output terminals are arranged in N rows and N columns, and the output terminals of all element switches in the previous stage are connected in a one-to-one correspondence to the input terminals of all element switches in the next stage so that, for each element switch except for the Nth column, the two output terminals of each element switch in the previous stage are each connected to one input terminal of a different element switch in the next stage, and one of the two input terminals of each element switch in the first column is an input port and the other is an input-side dummy port, and one of the two output terminals of each element switch in the Nth column is an output port and the other is an output-side dummy port, and all Provided is an optical switch circuit with monitoring function that includes optical switches configured to establish an optical path between one of the input ports and one of the output ports by switching an element switch at any one position among the element switches from a cross state to a bar state, and further includes a monitoring unit that monitors the optical connection state between the input port and the output port, and a detection light source that is connected to the input side dummy port of each element switch in a first column or the output side dummy port of each element switch in an Nth column, and the monitoring unit monitors the optical connection state between the input port and the output port based on the position in the matrix structure of the element switch where detection light input from the detection light source is detected.

[0010] In the above-mentioned optical switch circuit with monitoring function, it is preferable that, where m is an integer from 2 to N-1 and n is an integer from 1 to N-1, one output terminal of the element switch located in the mth row and nth column is connected to one input terminal of the element switch located in the (m-1)th row and (n+1)th column, and the other output terminal of the element switch located in the mth row and nth column is connected to one input terminal of the element switch located in the (m+1)th row and (n+1)th column.

[0011] Furthermore, it is preferable that one output terminal of the element switch located in the first row, nth column is connected to one input terminal of the element switch located in the first row, (n+1)th column, and one output terminal of the element switch located in the Nth row, nth column is connected to one input terminal of the element switch located in the Nth row, (n+1)th column, where n is an integer from 1 to N-1.

[0012] For example, the element switch may have a first input terminal and a second input terminal and a first output terminal and a second output terminal, where m is an integer from 2 to N-1 and n is an integer from 1 to N-1, and the first output terminal of the element switch located in the mth row and nth column may be connected to the second input terminal of the element switch located in the (m-1)th row and (n+1)th column, and the second output terminal of the element switch located in the mth row and nth column may be connected to the first input terminal of the element switch located in the (m+1)th row and (n+1)th column.

[0013] In this case, it is preferable that the first output terminal of the element switch located in the first row, nth column is connected to the first input terminal of the element switch located in the first row, (n+1)th column, and the second output terminal of the element switch located in the Nth row, nth column is connected to the second input terminal of the element switch located in the Nth row, (n+1)th column, where n is an integer from 1 to N-1.

[0014] In one embodiment, each element switch is composed of one basic switch element having a first input optical path and a second input optical path and a first output optical path and a second output optical path, and the first input optical path and the second input optical path function as a first input terminal and a second input terminal of the element switch, respectively, and the first output optical path and the second output optical path function as a first output terminal and a second output terminal of the element switch, respectively, so that in a bar state, light input to the first input terminal is output from the first output terminal and light input to the second input terminal is output from the second output terminal, and in a cross state, light input to the first input terminal is output from the second output terminal and light output from the second input terminal is output from the first output terminal.

[0015] In the above embodiment, the detection light source is connected to each of the input side dummy ports of each element switch in the first column and one of the output side dummy ports of each element switch in the Nth column, and a photodetector is connected to each of the other of the input side dummy ports of each element switch in the first column and the output side dummy ports of each element switch in the Nth column, and a correspondence relationship between the positions of the input port and the output port through which an optical path is established and the positions of the input side dummy port and the output side dummy port through which the optical path is established when the element switch in the i-th row and j-th column is switched from a cross state to a bar state, where i and j are integers from 1 to N, is pre-stored in the monitoring unit, and it is preferable that the monitoring unit detects the input port and the output port through which an optical path is established based on the pre-stored correspondence relationship from the position of one of the input side dummy port and the output side dummy port into which the detection light is input and the position of the other of the input side dummy port and the output side dummy port that detected the detection light.

[0016] Furthermore, it is further preferable that the optical switch circuit with monitoring function further includes a control unit that switches the element switch selected so that an optical path is established between the input port and the output port at a desired position from a cross state to a bar state, and that when the element switch in the i-th row and j-th column is switched from the cross state to the bar state, the monitoring unit determines that the optical connection state is normal when the positions of the input port and the output port through which the optical path is established, which are determined from the position of one of the input side dummy port and the output side dummy port into which the detection light is input and the position of the other of the input side dummy port and the output side dummy port that detected the detection light, and the positions of the input port and the output port set by the control unit so that the optical path is established, match the pre-stored correspondence, and determine that the optical connection state is abnormal when they do not match.

[0017] For example, the detection light from the detection light source can be input to each of the input-side dummy ports or the output-side dummy ports in sequence by an optical path switcher.

[0018] In addition, the detection light source may be composed of an optical branching device that branches a portion of the signal light output from the output port of each element switch in the Nth column, and a modulator that modulates the light with different patterns or frequencies depending on the position of each output port and assigns port identification information to the light as a label, and the monitoring unit may be configured to detect the correspondence between the input port to which an optical path is established and the output port based on the port identification information of the detection light that is input from the detection light source to the output port and detected by the element switch.

[0019] In addition, the detection light sources are connected one by one to the input dummy port of each element switch in the first column or the output dummy port of each element switch in the Nth column, and a modulator is connected to each detection light source for modulating the detection light with a different pattern or frequency depending on the position of each element switch and assigning port identification information to the detection light as a label, and the monitoring unit may be configured to detect the correspondence between the input port and the output port to which an optical path is established based on the port identification information of the detection light that is input from the detection light source to one of the input dummy port of each element switch in the first column and the output dummy port of each element switch in the Nth column and detected from the other.

[0020] In another embodiment, each element switch is configured by connecting basic switch elements having a first input optical path and a second input optical path and a first output optical path and a second output optical path in two stages, and in the basic switch element, in a bar state, light input to the first input optical path is output from the first output optical path and light input to the second input optical path is output from the second output optical path, and in a cross state, light input to the first input optical path is output from the second output optical path and light output from the second input optical path is output from the first output optical path. In the element switch, the first input optical path of the basic switch element of the previous stage is used as a first input terminal and the second input optical path is used as an input side dummy terminal, the second output optical path of the basic switch element of the previous stage is connected to the second input optical path of the basic switch element of the subsequent stage, the first input optical path of the basic switch element of the subsequent stage is used as a second input terminal, and the The first output optical path is used as a first output terminal, and the second output optical path is used as an output-side dummy terminal, and the first output optical path of the previous-stage basic switch element is used as a second output terminal, and in a bar state, light input to the first input terminal is output from the first output terminal and light input to the second input terminal is output from the output-side dummy terminal, and in a cross state, light input to the first input terminal is output from the second output terminal and light output from the second input terminal is output from the first output terminal, and where m is an integer from 2 to N-1 and n is an integer from 2 to N-1, the first output terminal of the element switch located in the mth row and nth column can be connected to the second input terminal of the element switch located in the (m-1)th row and (n+1)th column, and the second output terminal of the element switch located in the mth row and nth column can be connected to the first input terminal of the element switch located in the (m+1)th row and (n+1)th column.

[0021] In the other embodiment described above, a photodetector is connected to at least one of the input dummy terminal and the output dummy terminal of each of the N×N element switches, and the detection light source is connected to the input dummy port of each element switch in the first column or the output dummy port of each element switch in the Nth column, and it is preferable that the monitoring unit determines that the element switch having the input dummy terminal or the output dummy terminal from which detection light is detected by the photodetector is set to a bar state.

[0022] Furthermore, it is further preferable that the optical switch circuit with monitoring function further includes a control unit that switches the element switch selected so that an optical path is established between the input port and the output port at a desired position from a cross state to a bar state, and when the element switch in the i-th row and j-th column is switched from the cross state to the bar state by the control unit, the monitoring unit compares the position of the element switch where the detection light was detected with the position of the element switch switched to the bar state by the control unit, and determines that the optical connection state is normal when they match, and determines that the optical connection state is abnormal when they do not match.

[0023] For example, the detection light from the detection light source can be branched and input to the output-side dummy ports of all the element switches in the Nth column.

[0024] According to the optical switch circuit with monitoring function of the present invention, detection light for checking the operating state of the optical switch circuit is input to an unused input-side dummy port or output-side dummy port, and is detected through an unused terminal in the optical path of the signal light of any of the element switches, including the element switches in the first or Nth column, via an optical path different from the optical path established between the input port and the output port. Therefore, the detection light does not affect the signal light input to the input port, preventing degradation of the signal light. Furthermore, when the corresponding element switch is switched to the bar state to set the output port from which the signal light input to a specific input port is output, an element switch having a terminal from which the detection light is output when the detection light is input from the output-side dummy port of the element switch having the output port from which the signal light is detected is identified. As a result, the relationship between the input-side dummy port and the output-side dummy port through which the optical path through which the detection light passes is identified, corresponding to the relationship between the input port and the output port through which the optical path through which the signal light passes. Alternatively, the detection light input to the input-side dummy port or the output-side dummy port is output from the element switch in the bar state, thereby identifying the element switch in the bar state. Therefore, the input port and output port to which an optical path is established can be detected based on the position of the element switch that outputs detection light input to the input-side dummy port or the output-side dummy port, and the detection light can be used to monitor the optical connection state between the input port and the output port. Furthermore, since the signal light and the detection light do not pass through the same optical path and the detection light can be detected simply by installing a photodetector at the terminal of the element switch from which the detection light can be output, optical couplers, optical circulators, etc. are not required, and integration of optical circuits is also facilitated.

[0025] It is an explanatory diagram showing the configuration of a single - gate type element switch using a Mach - Zehnder interferometer, and shows the configuration of the waveguide of the single - gate type element switch. It shows a simplified representation of the single - gate type element switch shown in FIG. 1A. In the simplified representation, it is an explanatory diagram showing the operating state of the single - gate type element switch shown in FIG. 1A, and shows the optical path in the cross state. In the simplified representation, it is an explanatory diagram showing the operating state of the single - gate type element switch shown in FIG. 1A, and shows the optical path in the bar state. It is an explanatory diagram showing the configuration of a double - gate type element switch using a Mach - Zehnder interferometer, and shows the configuration of the waveguide of the double - gate type element switch. It shows a simplified representation of the double - gate type element switch shown in FIG. 3A. In the simplified representation, it is an explanatory diagram showing the operating state of the double - gate type element switch shown in FIG. 3A, and shows the optical path in the cross state. In the simplified representation, it is an explanatory diagram showing the operating state of the double - gate type element switch shown in FIG. 3A, and shows the optical path in the bar state. It is a configuration diagram showing an example of the configuration of a (4×4) PILOSS optical switch having 4 input ports and 4 output ports, which is composed of single - gate type element switches arranged in a 4 - row and 4 - column matrix structure. It is an explanatory diagram showing an example of setting the optical path between the input port and the output port in an (8×8) PILOSS optical switch having 8 input ports and 8 output ports, which is composed of single - gate type element switches arranged in an 8 - row and 8 - column matrix structure. It is an explanatory diagram showing examples of different optical paths stretched between the input port and the output port and between the input - side dummy port and the output - side dummy port when one element switch in the (4×4) PILOSS optical switch shown in FIG. 5 is set to the bar state. It is a correspondence table showing the optical paths stretched between the input port and the output port and between the input - side dummy port and the output - side dummy port when the element switch in the m - th row and n - th column (= ID(m,n)) of the (4×4) PILOSS optical switch shown in FIG. 7 is set to the bar state, using the port numbers shown in FIG. 7.9 is an explanatory diagram showing an example of the configuration of a (5 × 5) PILOSS optical switch having five input ports and five output ports composed of single-gate element switches arranged in a 5-row, 5-column matrix structure, and an example of setting port numbers for the input ports, output ports, input-side dummy ports, and output-side dummy ports. It is a correspondence table showing, using the port numbers shown in FIG. 9, optical paths established between the input ports and output ports and between the input-side dummy ports and output-side dummy ports when the element switch in the mth row and nth column (= ID(m, n)) in the (5 × 5) PILOSS optical switch shown in FIG. 9 is set to the bar state. It is an explanatory diagram showing the flow of light when light is input from two input terminals and two output terminals in a double-gate element switch, showing a simplified representation of the element switches including the input-side dummy terminals. It is an explanatory diagram showing the flow of light when light is input from two input terminals and two output terminals in a double-gate element switch, showing the optical paths when light is input from the first output terminal and the second output terminal. 1 is an explanatory diagram showing the flow of light when light is input from two input terminals and two output terminals in a double-gate element switch, showing a simplified representation of the element switch including the output-side dummy terminal. FIG. 2 is an explanatory diagram showing the flow of light when light is input from two input terminals and two output terminals in a double-gate element switch, showing the optical path when light is input from the first input terminal and the second input terminal. FIG. 3 is an explanatory diagram showing the flow of signal light and detection light in a (4 × 4) PILOSS optical switch having four input ports and four output ports, which is composed of double-gate element switches arranged in a 4-row, 4-column matrix structure. FIG. 4 is a configuration diagram showing the overall configuration of a first embodiment of an optical switch circuit with monitoring function according to the present invention. FIG. 5 is a configuration diagram showing the overall configuration of a second embodiment of an optical switch circuit with monitoring function according to the present invention. FIG. 6 is a configuration diagram showing the overall configuration of a third embodiment of an optical switch circuit with monitoring function according to the present invention. FIG. 7 is a configuration diagram showing the overall configuration of a fourth embodiment of an optical switch circuit with monitoring function according to the present invention. FIG. 8 is a table showing the relationship between the operating state of a double-gate element switch and a monitored value.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0027] An (N × N) PILOSS optical switch to which the optical switch circuit with monitoring function of the present invention can be applied has N input ports and N output ports, and its structure includes input-side dummy ports and output-side dummy ports in numbers equal to the number of input ports and output ports, respectively. In the optical switch circuit with monitoring function of the present invention, detection light is introduced into the circuit from the output-side dummy port or the input-side dummy port and follows an optical path different from that of the signal light, making it possible to monitor the operating status of the PILOSS optical switch without affecting the optical signal input to the input port. Furthermore, because the detection light follows an optical path different from that of the signal light, there is no need to use an optical isolator or optical circulator to prevent the detection light from leaking outside the switch when separating the detection light from the signal light. This makes it possible to integrate the optical switch and monitor the operating status of the optical switch on a chip.

[0028] First, with reference to Figures 1A to 4B, the basic configuration and operation of an element switch that can be used in an optical switch circuit with monitoring function according to the present invention will be described. The element switch is configured using (2 x 2) basic switch elements having two input optical paths and two output optical paths that can be in a bar state or a cross state. As the (2 x 2) basic switch element, for example, a Mach-Zehnder interferometer (MZI) can be used. The element switches include a single-gate element switch configured using one basic switch element and a double-gate element switch configured using two basic switch elements connected in two stages.

[0029] 1A, 1B, 2A, and 2B show a single-gate element switch 11 configured by a Mach-Zehnder interferometer 1. FIG. 1A shows the configuration of the single-gate element switch 11, i.e., the configuration of the Mach-Zehnder interferometer 1, and FIG. 1B shows a simplified representation of the single-gate element switch 11. The Mach-Zehnder interferometer 1 is configured with a first input optical path 2 and a second input optical path 3, a first output optical path 4 and a second output optical path 5, two directional couplers 6 and 7, and a phase shifter 8 provided in at least one of two arm waveguides connecting the two directional couplers 6 and 7. The phase shifter 8 changes the refractive index of the arm waveguides to change the phase of the light passing through the two arm waveguides by π, thereby utilizing the interference of light to switch the Mach-Zehnder interferometer 1 between the bar state and the cross state. In the Mach-Zehnder interferometer 1, in the bar state, optical paths are formed to connect the first input optical path 2 and the first output optical path 4, and the second input optical path 3 and the second output optical path 5, and in the cross state, optical paths are formed to connect the first input optical path 2 and the second output optical path 5, and the second input optical path 3 and the first output optical path 4. Since the Mach-Zehnder interferometer 1 is a well-known technique, the configuration of the Mach-Zehnder interferometer 1 will not be described in further detail here.

[0030] The single-gate type element switch 11 is composed of one Mach-Zehnder interferometer 1. Therefore, if the terminal formed by the first input optical path 2 is represented as the input terminal A, the terminal formed by the second input optical path 3 is represented as the input terminal A^, the terminal formed by the first output optical path 4 is represented as the output terminal B, and the terminal formed by the second output optical path 5 is represented as the output terminal B^, in the single-gate type element switch 11, in the cross state, as shown in Fig. 2A, optical paths are established between the input terminal A and the output terminal B^ and between the input terminal A^ and the output terminal B, resulting in an optical connection state, and signal light input to the input terminal A^ is output from the output terminal B^, and signal light input to the input terminal A^ is output from the output terminal B. On the other hand, in the bar state, as shown in Figure 2B, an optical path is established between the input terminal A and the output terminal B, and between the input terminal A^ and the output terminal B^, resulting in an optical connection state, so that light input to the input terminal A is output from the output terminal B, and light input to the input terminal A^ is output from the output terminal B^. Here, in Figures 2A and 2B, the dashed lines connecting the input terminals A and A^ and the output terminals B and B^ represent waveguides, and the thick lines represent the optical paths through which light actually travels.

[0031] 3A, 3B, 4A, and 4B show a double-gate element switch 11' composed of two Mach-Zehnder interferometers 1A and 1B connected in two stages. FIG. 3A shows the configuration of the double-gate element switch 11', and FIG. 3B shows a simplified representation of the double-gate element switch 11'. The double-gate element switch 11' is composed of two basic element switches, a Mach-Zehnder interferometer 1A and a Mach-Zehnder interferometer 1B, connected in two stages. The Mach-Zehnder interferometer 1A is composed of a first input optical path 2A and a second input optical path 3A, a first output optical path 4A and a second output optical path 5A, two directional couplers 6A and 7A, and a phase shifter 8A provided in at least one of two waveguides connecting the two directional couplers 6A and 7A. Similarly, the Mach-Zehnder interferometer 1B is composed of a first input optical path 2B and a second input optical path 3B, a first output optical path 4B and a second output optical path 5B, two directional couplers 6B and 7B, and a phase shifter 8B provided in at least one of the two waveguides connecting the two directional couplers 6B and 7B. The operation of each of the Mach-Zehnder interferometers 1A and 1B is as described above, so a description thereof will be omitted here.

[0032] As shown in FIG. 3A, the double-gate element switch 11′ is configured by connecting two basic element switches, a Mach-Zehnder interferometer 1A and a Mach-Zehnder interferometer 1B, in two stages, with only one output optical path 5A of the Mach-Zehnder interferometer 1A in the front stage being connected to the Mach-Zehnder interferometer 1B in the rear stage. In detail, the second output optical path 5A of the Mach-Zehnder interferometer 1A in the front stage is connected to the second input optical path 3B of the Mach-Zehnder interferometer 1B in the rear stage, the first input optical path 2A of the Mach-Zehnder interferometer 1A in the front stage is used as the first input terminal A of the element switch 11′, the second input optical path 3A is used as the input side dummy terminal C1 of the element switch 11′, the first input optical path 2B of the Mach-Zehnder interferometer 1B in the rear stage is used as the second input terminal A^ of the element switch 11′, the first output optical path 4B of the Mach-Zehnder interferometer 1B in the rear stage is used as the first output terminal B of the element switch 11′, the second output optical path 5B is used as the output side dummy terminal C2 of the element switch 11′, and the first output optical path 4A of the Mach-Zehnder interferometer 1A in the front stage is used as the second output terminal B^ of the element switch 11′. With this configuration, in the cross state of the element switch 11′ in which both the two Mach-Zehnder interferometers 1A and 1B are in the bar state, as shown in FIG. 4A , an optical path is established between the first input terminal A and the second output terminal B^ and between the second input terminal A^ and the first output terminal B, resulting in an optical connection state, so that the signal light input to the first input terminal A is output from the second output terminal B^, and the signal light input to the second input terminal A^ is output from the first output terminal B. On the other hand, in the bar state of the element switch 11′ in which both the two Mach-Zehnder interferometers 1A and 1B are in the cross state, an optical path is established between the first input terminal A and the first output terminal B, resulting in an optical connection state, so that the light input to the first input terminal A is output from the first output terminal B, as shown in FIG. 4B . Therefore, in the double-gate type element switch 11′, usually, only the first input terminal A is used as a terminal for inputting the signal light, and the second input terminal A^ is not used as a terminal for inputting the signal light.In addition, when the element switch 11' is in the bar state, optical paths are established between the second input terminal A^ and the output-side dummy terminal C2, and between the input-side dummy terminal C1 and the second output terminal B^, resulting in an optical connection state, so that light input to the second input terminal A^ is output from the output-side dummy terminal C2, and light input to the second output terminal B^ is output from the input-side dummy terminal C1. Here, in Figures 4A and 4B, the dashed lines connecting the input terminals A and A^ and the output terminals B and B^ represent waveguides, and the thick lines represent the optical paths through which light actually travels.

[0033] Although the above describes an example of the configuration of an element switch using a Mach-Zehnder interferometer 1, the configuration of the element switch is not limited to those shown in Figures 1A and 1B or Figures 3A and 3B, and other types of element switches can also be used as long as they can switch the port from which signal light input to the input port is output by switching between the cross state and the bar state.

[0034] Next, the configuration of a PILOSS optical switch realized using the element switches described above will be described.

[0035] Generally, an (N×N) PILOSS optical switch having N input ports and N output ports, i.e., N inputs and N outputs, configured using single-gate element switches 11 or double-gate element switches 11′, is configured, for example, as follows.

[0036] First, element switches are arranged in a matrix structure of N rows and N columns, i.e., a lattice pattern. Next, where m is an integer between 2 and N-1 and n is an integer between 1 and N-1, one output terminal of an element switch located in the first row, n column is connected to one input terminal of an element switch located in the first row, (n+1) column, and one output terminal of an element switch located in the Nth row, n column is connected to one input terminal of an element switch located in the Nth row, (n+1) column. Also, one output terminal of an element switch located in the mth row, n column is connected to one input terminal of an element switch located in the (m-1)th row, (n+1) column, and the other output terminal of an element switch located in the mth row, n column is connected to one input terminal of an element switch located in the (m+1)th row, (n+1) column. One of the two input terminals of each element switch in the first column is used as an input port, and the other is an input-side dummy port. Also, one of the two output terminals of each element switch in the Nth column is used as an output port, and the other is an output-side dummy port.

[0037] The (N×N) PILOSS optical switch is preferably configured as follows: where m is an integer from 2 to N−1 and n is an integer from 1 to N−1, a first output terminal of an element switch located in the first row, n column is connected to a first input terminal of an element switch located in the first row, (n+1) column, a second output terminal of an element switch located in the Nth row, n column is connected to a second input terminal of an element switch located in the Nth row, (n+1) column, a first output terminal of an element switch located in the mth row, n column is connected to a second input terminal of an element switch located in the (m−1)th row, (n+1) column, and a second output terminal of an element switch located in the mth row, n column is connected to a first input terminal of an element switch located in the (m+1)th row, (n+1) column.

[0038] In an optical switch configured in this manner, a state in which all element switches constituting the optical switch are in the cross state is called the idle state. In the idle state, all input ports are connected to all ports except the output port, no optical path is established between the input and output ports, and signal light input to the input port is not output from the output port. When one element switch is switched from the cross state to the bar state in this idle state, an optical path is established between one input port and one output port, and signal light input to that input port is output from that output port. In this way, in a general (N × N) PILOSS optical switch, by switching N appropriately selected element switches from the cross state to the bar state, N optical paths can be established between N input ports and N output ports. Furthermore, by appropriately selecting N element switches and switching them from the cross state to the bar state, N! possible optical paths, i.e., optical connection states, can be realized.

[0039] 5 shows a (4×4) PILOSS optical switch 21 having four input ports and four output ports configured using the single-gate type element switch 11 as an example of the (N×N) PILOSS optical switch configured as described above. The (4×4) PILOSS optical switch 21 shown in FIG. ２The (4 x 4) PILOSS optical switch 21 is composed of 16 element switches 11. In the (4 x 4) PILOSS optical switch 21, only one of the two input terminals of each element switch 11 in the first column is used as an input port, and only one of the two output terminals of each element switch 11 in the fourth column is used as an output port. The port numbers of the input side ports (input ports) and output side ports (output ports) are assigned A1 to A4 and B1 to B4, respectively, starting from the top element switch 11, and are indicated by black circles. The other input terminals and output terminals not used for inputting or outputting signal light are indicated by white circles and "*" as dummy ports. In detail, for the input ports, starting from the element switch 11 arranged at the top of the first column, the first input terminal and the second input terminal are alternately used as input ports, and for the output ports, starting from the element switch 11 arranged at the top of the fourth column, the second output terminal and the first output terminal are alternately used as output ports.

[0040] In the (4x4) PILOSS optical switch 21 shown in Figure 5, in the idle state, all input ports A1 to A4 are connected to dummy ports on the output side, no optical paths are established between the input ports A1 to A4 and the output ports B1 to B4, and signal light input to the input ports A1 to A4 is not output from the output ports B1 to B4. It can also be seen that by switching one element switch 11 from the cross state to the bar state in the idle state, one optical path is established between the input port A and the output port B. For example, let the identifier ID of the element switch 11 in the mth row and nth column be represented as ID(m, n). Here, "row" refers to the arrangement of the element switches 11 in the horizontal direction in Figure 5, and "column" refers to the arrangement of the element switches 11 in the vertical direction in Figure 5. In the idle state, when the element switches ID(1,1), ID(1,3), ID(4,3), and ID(4,1) are switched from the cross state to the bar state, optical paths are established between input port A1 and output port B3, between input port A2 and output port B1, between input port A3 and output port B4, and between input port A4 and output port B2, respectively. Therefore, it can be seen that if four element switches 11 are appropriately selected and switched from the cross state to the bar state, four optical paths are established between the four input ports and the four output ports.

[0041] 6 shows, as another example of an (N×N) PILOSS optical switch, an (8×8) PILOSS optical switch having eight input ports and eight output ports configured using single-gate type element switches 11. The (8×8) PILOSS optical switch shown in FIG. ２5, in the (8 × 8) PILOSS optical switch, only one of the element switches 11 in the first column is used as an input port, and only one of the element switches 11 in the eighth column is used as an output port, and the port numbers of the input side ports (input ports) and output side ports (output ports) are assigned A1 to A8 and B1 to B8, respectively, starting from the element switch 11 at the top of the first column. In detail, for the input ports, starting from the element switch 11 located at the top of the first column, the first input terminal and the second input terminal are alternately used as the input port, and for the output ports, starting from the element switch 11 located at the top of the eighth column, the second output terminal and the first output terminal are alternately used as the output port. 6, the element switches 11 with ID(3,2), ID(3,5), ID(3,8), ID(4,5), ID(5,2), ID(5,8), ID(6,4), and ID(6,6) are selected and set to the bar state, and the other element switches 11 are set to the cross state, whereby the optical paths established between the input ports A1 to A8 and the output ports B1 to B8 are shown by thick solid lines. By setting the selected element switches 11 to the bar state as described above, it can be seen that optical paths are established between the input port A1 and the output port B4, between the input port A2 and the output port B1, between the input port A3 and the output port B2, between the input port A4 and the output port B8, between the input port A5 and the output port B5, between the input port A6 and the output port B6, between the input port A7 and the output port B3, and between the input port A8 and the output port B7.

[0042] Next, the principle of a method for monitoring the operating status of an (N×N) PILOSS optical switch using single-gate element switches 11 will be described. In the following description, for convenience of explanation, port numbers are also assigned to dummy ports that are not used for inputting or outputting signal light. Let i be an integer from 1 to N. Starting with the element switches 11 in the first column, the port number of their input ports is assigned as Ai, and starting with the element switches 11 in the Nth column, the port number of their output ports is assigned as Bi. In the idle state, the output dummy port connected to input port Ai is assigned as Xi, and the input dummy port connected to output port Bi is assigned as Yi. In an (N×N) PILOSS optical switch using single-gate element switches 11, when one element switch 11 is switched from the cross state to the bar state from the idle state, an optical path is established between input port A and output port B, as well as between output dummy port X and input dummy port Y.

[0043] 7 shows the optical paths established when one element switch 11 is changed from the idle state (all element switches 11 are in the cross state) to the bar state, using the (4x4) PILOSS optical switch 21 shown in Fig. 5 as an example. In Fig. 7, optical paths established between input ports and output ports are shown by thick solid lines, and optical paths established between input dummy ports and output dummy ports are shown by thick dashed lines. It can be seen that by switching the element switch 11 with ID (1, 4) from the cross state to the bar state, optical paths are established between input port A4 and output port B1, and between input dummy port Y1 and output dummy port X4.

[0044] 8 is a table showing optical paths established between input port A and output port B, and between input-side dummy port Y and output-side dummy port X, when the element switch 11 with ID (m, n) is switched from the idle state to the bar state in the (4×4) PILOSS optical switch 21. In the table shown in Fig. 8, when the element switch 11 with ID (m, n) is switched to the bar state, the port numbers of the input port A and output port B to which the optical path is established are shown on the left and right of the "→" in the upper row, respectively, indicating that an optical path is established between input port A of the left-hand port number and output port B of the right-hand port number, and light input to input port A of the left-hand port number is output from output port B of the right-hand port number. At the same time, the port numbers of the output dummy port X and the input dummy port Y to which the optical path is established are shown on the left and right of the "→" in the lower row, respectively, to indicate that an optical path is established between the output dummy port X of the left port number and the input dummy port Y of the right port number, and that light input to the output dummy port X of the left port number is output from the input dummy port Y of the right port number. Here, the port numbers of the input port A, output port B, output dummy port X, and input dummy port Y refer to the numbers next to A, B, Y, and X. For example, in the state shown in FIG. 7, the element switch with ID (1, 4) is set to the bar state, so that optical paths are established between the input port A4 and the output port B1 and between the output dummy port X4 and the input dummy port Y1. Therefore, in the table shown in FIG. 8, "4 → 1" is written in the upper row and "4 → 1" is written in the lower row of the column for m=1, n=4.

[0045] 8 , in the (4×4) PILOSS optical switch 21, when an element switch 11 at an arbitrary position (ID) is set to the bar state, the port numbers of the input port A and output port B of the optical path established always match the port numbers of the output-side dummy port X and input-side dummy port Y, respectively, to which the optical path is simultaneously established. Therefore, when an element switch 11 is set to the bar state, by monitoring the optical path established between the output-side dummy port X and the input-side dummy port Y, the port numbers of the input port and output port to which the optical path is established can be determined, and the switch state can be known. For example, by connecting a detection light source to the output-side dummy port X and a photodetector PD such as a photodiode to the input-side dummy port Y, and detecting the detection light input to the output-side dummy port X at the input-side dummy port Y, it is possible to determine which input port A and which output port an optical path is established between, and monitor the operating state of the optical switch.

[0046] As described above, when the element switch 11 at an arbitrary position is set to the bar state, the port numbers of the input port A and the output port B of the optical path stretched are always the same as the port numbers of the output-side dummy port X and the input-side dummy port Y where the optical path is stretched simultaneously. Therefore, conversely, a detection light source is connected to the input-side dummy port Y, a photodetector PD such as a photodiode is connected to the output-side dummy port X, and the operation state of the optical switch circuit can also be monitored by detecting the detection light input to the input-side dummy port Y at the output-side dummy port X. Also, since there is a correspondence relationship between the positions of the input port A and the output port B of the optical path stretched when the element switch 11 at an arbitrary position is set to the bar state and the positions of the output-side dummy port X and the input-side dummy port Y, regardless of the method of allocating the port numbers of the input port A, the input port B, the output-side dummy port X, and the input-side dummy port Y, if the correspondence relationship between the port numbers of the input port A and the output port B where the optical path is stretched and the port numbers of the input-side dummy port Y and the output-side dummy port X is grasped in advance as shown in the table shown in FIG. 8, similarly, by monitoring the optical path stretched between the output-side dummy port X and the input-side dummy port Y, the input port and the output port where the optical path is stretched can be detected, and the operation state of the optical switch can be known. Also, in the above-described method, since the detection light is not emitted outside the optical switch circuit, there is no need to use an optical isolator, an optical circulator, etc., and the integration of the optical switch circuit becomes easy.

[0047] Fig. 9 shows a (5 × 5) PILOSS optical switch 31 having five input ports and five output ports configured using single-gate element switches 11. Fig. 10 is a table showing optical paths established between input port A and output port B, and between input-side dummy port Y and output-side dummy port X, when the element switch 11 with ID (m, n) is switched from the idle state to the bar state in the (5 × 5) PILOSS optical switch 31. Even in the configuration shown in Fig. 9, if port numbers are assigned to the input port A, output port B, output-side dummy port X, and input-side dummy port Y according to the same rules as for the (4 × 4) PILOSS optical switch 21 shown in Fig. 7, as shown in the table in Fig. 10, the port numbers of input port A and output port B of the optical path established when the element switch 11 at any position is set to the bar state always match the port numbers of the output-side dummy port X and input-side dummy port Y, respectively, to which optical paths are simultaneously established. In this way, it can be seen that the above-described method for monitoring the operating state can be applied to an (N×N) PILOSS optical switch having N input ports and N output ports configured using single-gate type element switches 11, where N is any integer.

[0048] The operating state of an (N×N) PILOSS optical switch using the double-gate element switch 11′ can also be monitored in a similar manner.

[0049] First, with reference to Figures 11A to 11D, the flow of light in the double-gate type element switch 11' when light is input from each of the input side (two input terminals) and the output side (two output terminals) will be described. Figures 11B and 11D show the flow of light when light is input from the first input terminal A and the second input terminal A^ and the first output terminal B and the second output terminal B^ in the double-gate type element switch 11' shown in Figure 3B. In the double-gate type element switch 11' in the cross state, as shown in Figure 4A, the first input terminal A and the second output terminal B^ are optically connected, and the second input terminal A^ and the first output terminal B are optically connected. Therefore, when light is input from the output side, the light input to the first output terminal B is output from the second input terminal A^, and the light input to the second output terminal B^ is output from the first input terminal A. Furthermore, when light is input from the input side, light input to the first input terminal A is output from the second output terminal B^, and light input to the second input terminal A^ is output from the first output terminal B. On the other hand, in the double-gate element switch 11' in the bar state, the first input terminal A and the first output terminal B are optically connected, the second input terminal A^ and the output-side dummy terminal C2 are optically connected, and the second output terminal B' is optically connected to the input-side dummy terminal C1. Therefore, when light is input from the output side, if the element switch 11' including the input-side dummy terminal C1 is represented by the simplified representation shown in FIG. 11A, as shown in FIG. 11B, light input to the first output terminal B is output from the first input terminal A, but light input to the second output terminal B^ is output from the input-side dummy terminal C1 rather than the second input terminal A^. Furthermore, when light is input from the input side, if the element switch 11' including the output side dummy terminal C2 is represented in the simplified form shown in Figure 11C, as shown in Figure 11D, light input to the first input terminal A is output from the first output terminal B, but light input to the second input terminal A^ is output from the output side dummy terminal C2 rather than the second output terminal B^.

[0050] Therefore, when an (N×N) PILOSS optical switch is configured using double-gate element switches 11′, the arrangement and connection method of the element switches 11′ may be generally similar to when an (N×N) PILOSS optical switch circuit is configured using single-gate element switches 11. Of the two input terminals of each element switch 11′ in the first column, the first input terminal (the input terminal connected to the output terminal in the bar state) is used as an input port, and the second input terminal is an input-side dummy port. Of the two output terminals of each element switch 11′ in the Nth column, the first output terminal is used as an output port, and the second output terminal is an output-side dummy port. However, unlike the single-gate element switches 11, in the double-gate element switch 11′, an optical path is established only between the first input terminal A and the first output terminal B in the bar state. Therefore, in the first row, the element switches 11' are arranged in an orientation such that the first input terminal used as a terminal for inputting signal light becomes the input port, and in the second row and beyond, the element switches 11' are arranged in an orientation such that the first output terminal of the element switch 11' in the front row is connected to the second input terminal of the rear row, and the second output terminal of the element switch 11' in the front row is connected to the first input terminal of the rear row.

[0051] In an (N×N) PILOSS optical switch configured using double-gate element switches 11′, when at least one of the element switches 11′ of the optical switch is set to the bar state, in order to detect detection light input to the output dummy port of the Nth column or the input dummy port of the first column, a photodetector must be connected to the input dummy terminal C1 or the output dummy terminal C2 of each element switch 11′. That is, the photodetector for detecting the detection light must be connected to the input dummy terminal C1 or the output dummy terminal C2 of each element switch 11′ of the (N×N) PILOSS optical switch, rather than to the input dummy ports A1^ to A4^ of the first column or the output dummy ports B1^ to B4^ of the Nth column. When a photodetector is connected to the input-side dummy terminal C1 or the output-side dummy terminal C2 of each element switch 11' in this way, when the (N×N) PILOSS optical switch is in the idle state, the detection light is not detected by the photodetector, but when at least one element switch 11' in the (N×N) PILOSS optical switch circuit is in the bar state, the detection light is detected by the photodetector connected to the input-side dummy terminal C1 or the output-side dummy terminal C2 of the element switch 11' that has been switched to the bar state. Therefore, the position of the element switch 11' that has been switched to the bar state is detected, and based on the detected position of the element switch 11' in the bar state, the operating state of the (N×N) PILOSS optical switch, i.e., the operating state of which input port and which output port an optical path is established between, can be detected.

[0052] 12 shows a (4×4) PILOSS optical switch 41 having four input ports and four output ports configured using double-gate type element switches 11′ as an example of the (N×N) PILOSS optical switch configured as described above. The (4×4) PILOSS optical switch 41 shown in FIG. ２7, the (4 × 4) PILOSS optical switch 41 uses only one of the element switches 11′ in the first row as an input port, and only one of the two input terminals of each element switch 11′ in the fourth row as an output port, and the port numbers of the input side ports (input ports) and output side ports (output ports) are assigned A1 to A4 and B1 to B4 in order from the upper element switch 11′, respectively, and are shown by black circles, and the other second input terminals and second output terminals that are not used for inputting and outputting signal light are used as input side dummy ports and output side dummy ports, and the port numbers are assigned A1^ to A4^ and B1^ to B4^ in order from the upper element switch 11′, respectively, and are shown by white circles.

[0053] 12, the optical paths of the signal light input to each of the input ports A1 to A4 are indicated by thick solid lines, and the optical paths of the detection light input to each of the output dummy ports B1^ to B4^ are overlaid with thick dashed lines. Specifically, in the idle state, the element switches 11′ of ID(1,2), ID(1,4), ID(3,3), and ID(4,3) are selected and switched from the cross state to the bar state, and optical paths are established between the input port A1 and the output port B2, between the input port A2 and the output port B3, between the input port A3 and the output port B4, and between the input port A4 and the output port B1. As a result, it can be seen that the signal light input to the input port A1 is output from the output port B2, the signal light input to the input port A2 is output from the output port B3, the signal light input to the input port A3 is output from the output port B4, and the signal light input to the input port A4 is output from the output port B1. On the other hand, the detection light input to each of the output side dummy ports B1^ to B4^ passes through the element switch 11' in the cross state, and when it reaches the element switches 11' of ID(1,2), ID(1,4), ID(3,3) and ID(4,3) which are in the bar state, it is output from the input side dummy terminal C1 and is detected by the photodetector connected to the input side dummy terminal C1.

[0054] When the cross or bar state is set in the element switch 11' so that the desired optical path is realized between the input ports A1 to A4 and the output ports B1 to B4, if the state of the element switch 11' is set correctly as set, the position (i.e., ID) of the element switch 11' connected to the photodetector that detected the detected light should exactly match the position (i.e., ID) of the element switch 11' set to the bar state. Therefore, by monitoring the outputs of the photodetectors connected to the input-side dummy ports A1^ to A4^ of all the element switches 11' and comparing the position (ID) of the element switch 11' connected to the photodetector that detected the detected light with the position (ID) of the element switch 11' set to the bar state, it is possible to determine whether the optical switch is operating normally or abnormally. Even in this case, the detected light is not emitted outside the optical switch 41, so there is no need to use an optical isolator or optical circulator, and it goes without saying that the integration of the optical switch 41 is also facilitated.

[0055] 12 shows an example in which the detection light is input to the output dummy ports B1^ to B4^. However, the detection light may also be input to the input dummy ports A1^ to A4^. In this case, a photodetector can be connected to the output dummy terminal C2 of each element switch 11' so that the detection light can be detected. Furthermore, if a photodetector is connected to both the input dummy terminal C1 and the output dummy terminal C2 of each element switch 11', it becomes possible to handle both cases in which the detection light is input to the input dummy ports A1^ to A4^ and to the output dummy ports B1^ to B4^.

[0056] Thus, according to the optical switch circuit with monitoring function of the present invention, whether the optical switch is configured using single-gate type element switches 11 or double-gate type element switches 11', detection light for checking the operating state of the optical switch is input to an unused input-side dummy port A^ or output-side dummy port B^, passes through an optical path different from the optical path stretched between input port A and output port B, and is detected through an unused terminal in the signal light of any of element switches 11, 11' including the element switches in the first or Nth column. Therefore, the detection light does not affect the signal light input to input port A, and deterioration of the signal light can be prevented.

[0057] Furthermore, when the element switch 11 or 11' selected to set the output port B from which the signal light input to a specific input port A is output is switched to the bar state, the element switch 11 or 11' having a terminal from which the detection light is output when the detection light is input from the output-side dummy port B^ of the element switch 11 or 11' having the output port B from which the signal light is output is identified. As a result, when an optical switch is configured using a single-gate element switch 11, the relationship between the port numbers of the input-side dummy port and the output-side dummy port through which the optical path through which the detection light passes is identified in accordance with the relationship between the port numbers of the input port and the output port through which the optical path through which the signal light passes. Furthermore, when an optical switch is configured using a double-gate element switch 11', the detection light input to the input-side dummy port or the output-side dummy port is output from the output-side dummy terminal or the input-side dummy terminal of the element switch that has been set to the bar state, and the element switch that has been set to the bar state can be identified. Therefore, based on the position of the element switch that outputs the detection light input to an unused input side dummy port or output side dummy port, in the case of an optical switch configured using a single gate type element switch 11, it is possible to monitor the optical connection status between the input port and the output port from the correspondence between the positions (ID) of the input port and the output port to which the optical path is established and the positions (ID) of the input side dummy port and the output side dummy port, and in the case of an optical switch configured using a double gate type element switch 11', it is possible to monitor the optical connection status between the input port and the output port from the position (ID) of the element switch 11' that is in the bar state.

[0058] Furthermore, since the signal light and detection light do not pass through the same optical path, and the detection light can be detected simply by installing a photodetector at the terminal of the element switch where the detection light can be output, optical couplers, optical circulators, etc. are not required, and the integration of optical circuits is also facilitated.

[0059] Below, we will show embodiments having specific configurations when the optical switch circuit with monitoring function according to the present invention is implemented as a device. However, the embodiments shown below are merely examples, and the present invention is not limited to these embodiments. It goes without saying that the present invention can be modified and implemented within the scope of the invention.

[0060] Fig. 13 shows an optical switch circuit 101 with a monitoring function according to a first embodiment of the present invention, which is applied to a (4 × 4) PILOSS optical switch 21 configured using single-gate element switches 11 as shown in Fig. 7. The optical switch circuit 101 includes the (4 × 4) optical switch 21 shown in Fig. 7, a control unit 51 that sets the cross state or bar state of each element switch 11 constituting the optical switch 21 to achieve a desired switch state, an element switch driving unit 53 that drives each element switch 11 to switch the state according to the setting by the control unit 51, a detection light source 55, an optical path switcher 57 that selectively switches according to an instruction from the control unit 51 to input detection light from the detection light source 55 to a desired output-side dummy port B1^ to B4^ of the optical switch 21, a photodetector 59 connected to each input-side dummy port A1^ to A4^ to detect the detection light, and a monitoring unit 61 that monitors the operating state of the optical switch 21. In the optical switch circuit 101, the optical path established between the input port A and the output port B is detected based on the port number of the input side dummy port A1^ to A4^ connected to the photodetector 59 that detects the detection light input from the detection light source 55 to each output side dummy port B1^ to B4^, i.e., the position (ID) on the matrix structure of the element switch 11 that has the input side dummy port A1^ to A4^, and the optical connection status between the input port A and the output port B is monitored.

[0061] The control unit 51 can be configured with a central processing unit (CPU) such as a microprocessor. The control unit 51 determines and selects the element switches 11 to be set to the bar state in the optical switch 21 so that the desired switch state is realized (i.e., so that an optical path for signal light is established between the input ports A1 to A4 and the output ports B1 to B4 of the desired port numbers), and transmits position information, i.e., ID, of the selected element switches 11 in the matrix structure to the element switch driving unit 53 and the monitoring unit 61. The element switch driving unit 53 switches the element switches 11 to the cross state or the bar state by controlling the operation of the phase shifters 8 of the element switches 11. Each element switch 11 in the optical switch 21 is switched to the cross state or the bar state by the element switch driving unit 53 in accordance with instructions from the control unit 51. The optical switch 21 is configured to be in an idle state (i.e., a state in which all element switches 11 are in a cross state) under normal circumstances, and the control unit 51 selects the ID of the element switch 11 to be set to the bar state so that an optical path is established between the input ports A1 to A4 of the desired port number and the output ports B1 to B4, optically connecting them, and the element switch drive unit 53 switches the element switch 11 with the ID selected by the control unit 51 from the cross state to the bar state.

[0062] The control unit 51 also controls the optical path switch 57 to sequentially switch the optical path through which the detection light from the detection light source 55 passes, causing the detection light to be input to each of the output dummy ports B1^ to B4^, and the detection light input to each of the output dummy ports B1^ to B4^ is detected by the photodetector 59 connected to the input dummy ports A1^ to A4^. A laser diode (LD), a light-emitting diode (LED), or the like can be used as the detection light source 55. A general optical switch such as the optical switch 21 can be used as the optical path switch 57. Furthermore, a photodiode (PD), or the like can be used as the photodetector 59. In the illustrated embodiment, a laser diode (LD) is used as the detection light source 55, an optical switch (SW) is used as the optical path switch 57, and a photodiode (PD) is used as the photodetector.

[0063] Each time detection light is input to each output dummy port B^, information indicating which port number of the input dummy port A^ connected to the photodetector 59 detected the detection light is sent to the monitoring unit 61. Based on the port number information of the input dummy port A^ connected to the photodetector 59 that detected the detection light, the monitoring unit 61 compares the port numbers of the output dummy port B^ and the input dummy port A^ for the optical path of the detection light stretched between the output dummy ports B1^ to B4^ and the input dummy ports A1^ to A4^ with the port numbers of the input port A and the output port B for the optical path of the signal light set by the control unit 51 to be stretched between the input ports A1 to A4 and the output ports B1 to B4. The monitoring unit 61 pre-stores a correspondence table, such as that shown in FIG. 8, of the input and output ports through which the optical path of the signal light is established and the port numbers of the output dummy ports and input dummy ports through which the optical path of the detection light is established when the element switch 11 of each ID (m, n) is set to the bar state. If the correspondence between the port numbers of the input port A and the output port B for the optical path of the signal light set by the control unit 51 and the port numbers of the output dummy port B^ and the input dummy port A^ for the optical path of the detection light determined by detecting the detection light all match the information in the pre-obtained correspondence table, such as that shown in FIG. 8, the monitoring unit 61 determines normal operation. If the correspondence differs from the information in the pre-obtained correspondence table, the monitoring unit 61 determines abnormal operation. Silicon photonics optical switches have a switching speed of less than μseconds. Therefore, if a silicon photonics optical switch, for example, is used as the optical path switcher 57, the monitoring unit 61 can perform monitoring almost in real time.

[0064] In this way, the monitoring unit 61 can monitor the operating state of the optical switch 21, i.e., the optical connection state between the input port and the output port, based on the port number information of the input-side dummy port A^ connected to the photodetector 59 that detected the detected light, i.e., the position (ID) in the matrix structure of the element switch 11 that has the input-side dummy port A^ that detected the detected light. Furthermore, since the first embodiment can be configured using integrated components as described above, it can be realized on a chip.

[0065] In the optical switch 21, the correspondence between the input port A and output port B through which the optical path of the signal light is established, and the correspondence between the input-side dummy port A^ and output-side dummy port B^ through which the optical path of the detection light is established, is the same whether input is from the input side or the output side, as long as the settings of each element switch 11 of the optical switch 21 are the same. Therefore, in the first embodiment shown in Figure 13, the detection light is input to the output-side dummy port B^ and detected at the input-side dummy port A^, but the detection light may also be configured to be input to the input-side dummy port A^ and detected at the output-side dummy port B^.

[0066] 14 shows an optical switch circuit with monitoring function 201 according to a second embodiment of the present invention, which is applied to a (4×4) PILOSS optical switch 21 configured using a single-gate element switch 11 as shown in FIG. 7. In the optical switch circuit with monitoring function 201 according to the second embodiment, a portion of the signal light input to input port A of the optical switch 21 and output from output port B is branched and used as detection light. Therefore, this configuration is suitable for the case where signal light is input to all input ports A. Another advantage is that a separate detection light source is not required.

[0067] The monitoring function-equipped optical switch circuit 201 according to the second embodiment differs from the monitoring function-equipped optical switch circuit 101 according to the first embodiment in that it includes an optical branching device 63 that branches light from a light guide extending from an output port B, a modulator 65 that modulates the light, and a label assignment unit 67, instead of the detection light source 55 and the optical path switcher 57. The other configuration is the same as that of the monitoring function-equipped optical switch circuit 101 according to the first embodiment. In the monitoring function-equipped optical switch circuit 201 according to the second embodiment, the optical branching device 63 functions as a detection light source. An optical coupler, for example, can be used as the optical branching device 63.

[0068] In the optical switch circuit 201 with monitoring function according to the second embodiment, a portion of the signal light input to the input ports A1 to A4 of the optical switch 21 and output from the output ports B1 to B4 is branched by the optical branching device 63 as detection light, and is further modulated by the modulator 65 in accordance with the port number of the output dummy port B^ to which the signal light is input, and is assigned port identification information as a label, before being input to the output dummy port B^. The label assigning unit 67 controls the modulator 65 to modulate the detection light with a different pattern or frequency for each output dummy port B^ and assigns port identification information as a label. The detection light input to the output dummy port B^ is output from the input dummy port A^ and detected by the photodetectors 59 connected to each of the input dummy ports A1^ to A4^, and the detection information is sent to the monitoring unit 61. The monitoring unit 61 reads the labels attached to the detection light detected by the photodetectors 59 connected to each of the input dummy ports A1^-A4^, and detects the port number of the output dummy port B^ to which the detection light was input and the port number of the input dummy port A^ to which the detection light was output. Furthermore, the monitoring unit 61 compares the port numbers of the output dummy port B^ and the input dummy port A^ for the optical path of the detection light established between the output dummy ports B1^-B4^ and the input dummy ports A1^-A4^ with the port numbers of the input port A and the output port B for the optical path of the signal light established by the control unit 51 between the input ports A1-A4 and the output ports B1-B4. If the correspondences all match the information in a pre-obtained correspondence table such as that shown in FIG. 8, the monitoring unit 61 determines that the operation is normal. If the correspondences differ from the information in the pre-obtained correspondence table, the monitoring unit 61 determines that the operation is abnormal.

[0069] In this way, in the second embodiment as well, the monitoring unit 61 can monitor the operating state of the optical switch 21, i.e., the optical connection state between the input port and the output port, based on the port number information of the input-side dummy port A^ connected to the photodetector 59 that detected the detected light, i.e., the position (ID) in the matrix structure of the element switch 11 that has the input-side dummy port A^ where the detected light was detected. Furthermore, like the first embodiment, the second embodiment can also be realized on a chip.

[0070] 14, the detection light is input to the output dummy port B^ and detected at the input dummy port A^, but it is also possible to configure the detection light to be input to the input dummy port A^ and detected at the output dummy port B^. This configuration is more advantageous from the viewpoint of loss.

[0071] Fig. 15 shows an optical switch circuit with monitoring function 301 according to a third embodiment of the present invention, which is applied to a (4 × 4) PILOSS optical switch 21 configured using single-gate element switches 11 as shown in Fig. 7. In the optical switch circuit with monitoring function 301 according to the third embodiment, a detection light source is connected to each of the output-side dummy ports B1^ to B4^, and detection light labeled with port identification information is input to the output-side dummy ports B1^ to B4^.

[0072] The monitoring function-equipped optical switch circuit 301 according to the third embodiment differs from the monitoring function-equipped optical switch circuit 101 according to the first embodiment in that it includes four detection light sources 69 connected to the output side dummy ports B1^ to B4^, respectively, and a label providing unit 71, instead of one detection light source 55 and optical path switcher 57. The other configuration is the same as that of the monitoring function-equipped optical switch circuit 101 according to the first embodiment. As with the detection light source 55, a laser diode (LD), a light emitting diode (LED), or the like can be used as the detection light source 69.

[0073] In the optical switch circuit 301 with monitoring function according to the third embodiment, detection light to which port identification information has been assigned by a label assignment unit 71 according to the port number of the output dummy port B^ to which each detection light source 69 is connected is input from the detection light source 69 to the output dummy port B^ connected thereto. The label assignment unit 71 assigns the port identification information as a label to the detection light, for example, by modulating the drive current of the detection light source 69 to perform intensity modulation on the output of the detection light source 69. The detection light input to the output dummy port B^ is output from the input dummy port A^ and detected by the photodetectors 59 connected to each of the input dummy ports A1^ to A4^, and the detection information is sent to the monitoring unit 61. The monitoring unit 61 reads the labels assigned to the detection light detected by the photodetectors 59 connected to each of the input dummy ports A1^ to A4^, and detects the port number of the output dummy port B^ to which the detection light was input and the port number of the input dummy port A^ to which the detection light was output. Furthermore, the monitoring unit 61 compares the port numbers of the output-side dummy port B^ and the input-side dummy port A^ for the optical path of the detection light stretched between the output-side dummy ports B1^ to B4^ and the input-side dummy ports A1^ to A4^ with the port numbers of the input port A and the output port B for the optical path of the signal light set by the control unit 51 to be stretched between the input ports A1 to A4 and the output ports B1 to B4. If the correspondence relationships all match the information in a correspondence table obtained in advance as shown in Figure 8, the monitoring unit 61 determines that the operation is normal, and if the correspondence relationships differ from the information in the correspondence table obtained in advance, the monitoring unit 61 determines that the operation is abnormal.

[0074] In this way, in the third embodiment as well, the monitoring unit 61 can monitor the operating state of the optical switch 21, i.e., the optical connection state between the input port and the output port, based on the port number information of the input-side dummy port A^ connected to the photodetector 59 that detected the detected light, i.e., the position (ID) in the matrix structure of the element switch 11 that has the input-side dummy port A^ where the detected light was detected. Furthermore, like the first embodiment, the third embodiment can also be realized on a chip.

[0075] In the third embodiment shown in Figure 15, the detection light is input to the output side dummy port B^ and detected at the input side dummy port A^, but it may also be configured so that the detection light is input to the input side dummy port A^ and detected at the output side dummy port B^.

[0076] Fig. 16 shows an optical switch circuit 401 with a monitoring function according to a fourth embodiment of the present invention, which is applied to a (4 × 4) PILOSS optical switch 41 configured using double-gate type element switches 11' as shown in Fig. 12. The optical switch circuit 201 with a monitoring function according to the fourth embodiment uses an optical switch 41 configured using double-gate type element switches 11', and detection light branched from one detection light source is input to each of the output-side dummy ports B1^ to B4^, and a photodetector is connected to the input-side dummy terminal C1 of each element switch 11' that configures the optical switch 41.

[0077] The monitoring function-equipped optical switch circuit 401 according to the fourth embodiment differs from the monitoring function-equipped optical switch circuit 101 according to the first embodiment in that a detection light source 73 and a demultiplexer 75 are used instead of the detection light source 55 and optical path switch 57, an optical switch 41 composed of double-gate element switches 11' is used instead of the optical switch 21 composed of single-gate element switches 11, and a photodetector 77 connected to the input-side dummy terminal C1 of each element switch 11' is used instead of the photodetector 59 connected to the input-side dummy ports A1^ to A4^. The remaining configuration is the same as that of the monitoring function-equipped optical switch circuit 101 according to the first embodiment. The detection light source 73 may be a laser diode (LD), a light-emitting diode (LED), or the like, similar to the detection light source 55. An optical coupler may be used as the demultiplexer 75. Furthermore, a photodiode (PD) may be used as the photodetector 77, similar to the photodetector 59.

[0078] In the optical switch circuit 401 with monitoring function according to the fourth embodiment, detection light from the detection light source 73 is branched into four by the splitter 75 and input to all output dummy ports B1^ to B4^. Furthermore, a photodetector 77 is connected to the input dummy terminal C1 of each of the element switches 11' constituting the optical switch 41, and its output information is sent to the monitoring unit 61. The output voltage of the photodetector 77 is saturated to a predetermined value when detection light is incident. The detection light input to each output dummy port B1^ to B4^ passes through an element switch 11' in the cross state, and when it reaches an element switch 11' in the bar state, it is output from its input dummy terminal C1 and detected by the photodetector 77 connected to each input dummy terminal C1, and the detection information is sent to the monitoring unit 61. Based on the detection information, the monitoring unit 61 can detect whether each element switch 11' is in the cross state or the bar state. Furthermore, the monitoring unit 61 compares the position information (ID) of the element switch 11' that has been set to the bar state, obtained based on the detection information from the photodetector 77, with the position information (ID) of the element switch 11' that has been set to the bar state by the control unit 51 so as to be stretched between the input ports A1 to A4 and the output ports B1 to B4, and if they all match, it determines that the operation is normal, and if they differ, it determines that the operation is abnormal.

[0079] As an example, the control voltage (V Ｃ ) is, for example, 0 when in the cross state, and V when in the bar state. ０ The output voltage (V ＰＤ ) is 0 when the element switch 11' to which it is connected is in the cross state, and V ０ In this case, the monitor unit 61 monitors the difference between the control voltage and the output voltage of the photodetector 77, that is, the monitor value (V Ｃ -V ＰＤ) can be monitored. FIG. 17 shows the relationship between the state of the element switch 11' and the monitor value. In this case, if the monitor value is 0 for all element switches 11', the monitoring unit 61 can determine that the element switch is operating normally; otherwise, it can determine that the element switch is operating abnormally. If an abnormal operation is determined, it can be determined which of the following two patterns of state has occurred based on whether the monitor value is positive or negative. If the monitor value is negative, it can be assumed that the cross state has erroneously become the bar state, and if the monitor value is positive, it can be assumed that the cross state has not correctly changed to the bar state.

[0080] In this way, in the fourth embodiment as well, the monitoring unit 61 can monitor the operating state of the optical switch 41, i.e., the optical connection state between the input port and the output port, based on the position (ID) in the matrix structure of the element switch 11' having the input-side dummy terminal C1 from which the detected light is detected. Furthermore, the fourth embodiment can also be realized on a chip, as in the first embodiment.

[0081] 16, the detection light is input to the output dummy port B^, but the detection light may also be input to the input dummy port A^, or to both the input dummy port A^ and the output dummy port B^. In the latter case, more information can be obtained, which is effective in strengthening the monitoring function of the switch.

[0082] The optical switch circuit with monitoring function according to the present invention has been described above with reference to the illustrated embodiment, but the present invention is not limited to the illustrated embodiment. For example, in the illustrated embodiment, the detection light is input to an output dummy port, but the detection light may also be input to an input dummy port. Furthermore, as long as the port number of the port to which the detection light is input can be identified, the detection light source may have a configuration other than that of the illustrated embodiment.

[0083] REFERENCE SIGNS LIST 1 Mach-Zehnder interferometer 11 Element switch 13 21 Optical switch 31 Optical switch 41 Optical switch 51 Control unit 55 Detection light source 57 Optical path switcher 59 Photodetector 61 Monitoring unit 63 Optical branching device 65 Modulator 69 Detection light source 73 Detection light source 77 Photodetector 101 Optical switch circuit 201 Optical switch circuit 301 Optical switch circuit 401 Optical switch circuit

Claims

1. An optical switch circuit with a monitoring function, comprising optical switches configured such that element switches have at least two input terminals and two output terminals and can switch between a cross state and a bar state between the two input terminals and the two output terminals, the element switches being arranged in an N×N matrix structure with N rows and N columns, the output terminals of all element switches in the previous stage being connected in a one-to-one correspondence to the input terminals of all element switches in the next stage so that, for each element switch except for the Nth column, the two output terminals of each element switch in the previous stage are respectively connected to one input terminal of a different element switch in the next stage, one of the two input terminals of each element switch in the first column is an input port and the other is an input-side dummy port, and one of the two output terminals of each element switch in the Nth column is an output port and the other is an output-side dummy port, and an optical path is established between one of the input ports and one of the output ports by switching an element switch in any one position among all of the element switches from the cross state to the bar state, An optical switch circuit with monitoring function, further comprising a monitoring unit that monitors the optical connection status between the input port and the output port, and a detection light source connected to the input side dummy port of each element switch in the first column or the output side dummy port of each element switch in the Nth column, wherein the monitoring unit monitors the optical connection status between the input port and the output port based on the position in the matrix structure of the element switch where the detection light input from the detection light source is detected.

2. An optical switch circuit with monitoring function as described in claim 1, wherein, where m is an integer from 2 to N-1 and n is an integer from 1 to N-1, one output terminal of an element switch located in the mth row and nth column is connected to one input terminal of an element switch located in the (m-1)th row and (n+1)th column, and the other output terminal of the element switch located in the mth row and nth column is connected to one input terminal of an element switch located in the (m+1)th row and (n+1)th column.

3. An optical switch circuit with monitoring function as described in claim 2, wherein one output terminal of the element switch located in the first row and nth column is connected to one input terminal of the element switch located in the first row and (n+1)th column, and one output terminal of the element switch located in the Nth row and nth column is connected to one input terminal of the element switch located in the Nth row and (n+1)th column, where n is an integer from 1 to N-1.

4. An optical switch circuit with monitoring function as set forth in claim 3, wherein the element switch has a first input terminal and a second input terminal and a first output terminal and a second output terminal, and wherein, where m is an integer from 2 to N-1 and n is an integer from 1 to N-1, the first output terminal of the element switch located in the mth row and nth column is connected to the second input terminal of the element switch located in the (m-1)th row and (n+1)th column, and the second output terminal of the element switch located in the mth row and nth column is connected to the first input terminal of the element switch located in the (m+1)th row and (n+1)th column.

5. An optical switch circuit with monitoring function as described in claim 4, wherein the first output terminal of the element switch located in the first row and nth column is connected to the first input terminal of the element switch located in the first row and (n+1)th column, and the second output terminal of the element switch located in the Nth row and nth column is connected to the second input terminal of the element switch located in the Nth row and (n+1)th column, where n is an integer from 1 to N-1.

6. An optical switch circuit with monitoring function as claimed in any one of claims 1 to 5, wherein each element switch is constituted by one basic switch element having first and second input optical paths and first and second output optical paths, wherein the first and second input optical paths function as the first and second input terminals of the element switch, respectively, and the first and second output optical paths function as the first and second output terminals of the element switch, respectively, and wherein in a bar state, light input to the first input terminal is output from the first output terminal and light input to the second input terminal is output from the second output terminal, and in a cross state, light input to the first input terminal is output from the second output terminal and light output from the second input terminal is output from the first output terminal.

7. The detection light source is connected to one of the input dummy port of each element switch in the first column and the output dummy port of each element switch in the Nth column, and a photodetector is connected to the other of the unused input dummy port of each element switch in the first column and the unused output dummy port of each element switch in the Nth column, and a correspondence relationship between the positions of the input port and the output port through which an optical path is established and the positions of the input dummy port and the output dummy port through which an optical path is established when the element switch in the i-th row and j-th column is switched from a cross state to a bar state, where i and j are integers from 1 to N, is stored in advance in the monitoring unit; 7. The optical switch circuit with monitoring function described in claim 6, wherein the monitoring unit detects the input port and the output port to which an optical path is established based on the pre-stored correspondence relationship from the position of one of the input side dummy port and the output side dummy port to which detection light is input and the position of the other of the input side dummy port and the output side dummy port that detected the detection light.

8. The optical switch circuit with monitoring function according to claim 7, further comprising a control unit that switches the element switch selected so that an optical path is established between the input port and the output port at a desired position from a cross state to a bar state, and the monitoring unit determines, when the element switch in the i-th row and j-th column is switched from the cross state to the bar state, that the optical connection state is normal if the positions of the input port and the output port through which the optical path is established, determined from the position of one of the input dummy port and the output dummy port into which the detection light is input and the position of the other of the input dummy port and the output dummy port that detected the detection light, and the positions of the input port and the output port set by the control unit so that an optical path is established, match the pre-stored correspondence, and determines that the optical connection state is abnormal if they do not match.

9. The optical switch circuit with monitoring function according to claim 8, wherein the detection light from said detection light source is inputted to each of said input side dummy ports or said output side dummy ports in turn by an optical path switcher.

10. An optical switch circuit with monitoring function as described in claim 8, wherein the detection light source is composed of an optical branching device that branches a portion of the signal light output from the output port of each element switch in the Nth column, and a modulator that modulates the light with different patterns or frequencies depending on the position of each output port and assigns port identification information to the light as a label, and the monitoring unit detects the correspondence between the input port and the output port to which an optical path is established based on the port identification information of the detection light that is input from the detection light source to the output port and detected by the element switch.

11. The optical switch circuit with monitoring function described in claim 8, wherein the detection light sources are connected one by one to the input dummy port of each element switch in the first column or the output dummy port of each element switch in the Nth column, and a modulator is connected to each detection light source for modulating the detection light with a different pattern or frequency depending on the position of each element switch and assigning port identification information to the detection light as a label, and the monitoring unit detects the correspondence between the input port and the output port to which an optical path is established based on the port identification information of the detection light that is input from the detection light source to one of the input dummy port of each element switch in the first column or the output dummy port of each element switch in the Nth column and detected from the other.

12. Each elementary switch is constructed by connecting basic switch elements, each having a first input optical path and a second input optical path and a first output optical path and a second output optical path, in two stages, and in the basic switch element, in a bar state, light input to the first input optical path is output from the first output optical path and light input to the second input optical path is output from the second output optical path, and in a cross state, light input to the first input optical path is output from the second output optical path and light output from the second input optical path is output from the first output optical path. In the elementary switch, the first input optical path of the elementary switch element in the preceding stage is used as a first input terminal and the second input optical path is used as an input-side dummy terminal, the second output optical path of the elementary switch element in the preceding stage is connected to the second input optical path of the elementary switch element in the succeeding stage, the first input optical path of the elementary switch element in the succeeding stage is used as a second input terminal, and the first output optical path of the elementary switch element in the succeeding stage is used as a first output terminal. and a second output optical path is used as an output-side dummy terminal, and a first output optical path of the preceding basic switch element is used as a second output terminal, and in a bar state, light input to the first input terminal is output from the first output terminal and light input to the second input terminal is output from the output-side dummy terminal, and in a cross state, light input to the first input terminal is output from the second output terminal and light output from the second input terminal is output from the first output terminal, and 13. An optical switch circuit with monitoring function as described in claim 12, wherein a photodetector is connected to at least one of the input dummy terminal and the output dummy terminal of each of the N x N element switches, and the detection light source is connected to the input dummy port of each element switch in the first column or the output dummy port of each element switch in the Nth column, and the monitoring unit determines that the element switch having the input dummy terminal or the output dummy terminal from which detection light is detected by the photodetector is set to a bar state.

14. The optical switch circuit with monitoring function according to claim 13, further comprising a control unit that switches the element switch selected so that an optical path is established between the input port and the output port at a desired position from a cross state to a bar state, and when the element switch in the i-th row and j-th column is switched from the cross state to the bar state by the control unit, the monitoring unit compares the position of the element switch at which the detection light is detected with the position of the element switch switched to the bar state by the control unit, and determines that the optical connection state is normal when they match, and determines that the optical connection state is abnormal when they do not match.

15. The optical switch circuit with monitoring function according to claim 14, wherein the detection light from said detection light source is branched and input to said output-side dummy ports of all of said element switches in said N columns.

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