JP4596346B2 - Optical add / drop switch - Google Patents

Description

  The present invention relates to a method for controlling an optical add / drop switch, and more particularly to an optical add / drop switch control method for switching an arbitrary wavelength path in a node in a wavelength division multiplexing communication system.

  There is known a wavelength division multiplexing communication system in which a plurality of nodes are connected in a ring shape or a bus shape via an optical fiber transmission line using wavelength division multiplexing (WDM). Each node is equipped with an optical switch that switches connections for each wavelength, and the configuration of the wavelength path can be easily changed. Therefore, this is called a reconfigurable optical add-drop multiplexing (ROADM) system. The switching operation of each node consists of a through mode that outputs an optical signal of an arbitrary wavelength input from one optical fiber transmission line to the other optical fiber transmission line, and an arbitrary wavelength input from the optical fiber transmission line. An add / drop mode that outputs an optical signal of any wavelength input from the terminal device to the optical fiber transmission line (add operation). have. With such a switching operation, an arbitrary number of wavelength paths can be set between arbitrary nodes. Therefore, the wavelength division multiplexing communication system is characterized in that it can flexibly cope with traffic fluctuations by changing the configuration of the wavelength path, and can easily cope with a failure in a transmission path or a terminal device.

  FIG. 1 shows the configuration of a conventional ROADM system node. Here, two nodes connected adjacently are called a west node and an east node for convenience, respectively, and the signal light flows from the west node to the east node clockwise, and the signal light from the east node to the west node The flow is defined as counterclockwise. The clockwise wavelength multiplexed signal light is input from the optical fiber 105R to the optical demultiplexer 102R via the pre-amplifier 104R. The optical demultiplexer 102R separates the input wavelength multiplexed signal light into n signal lights for each wavelength. The optical add / drop switches 101R-1 to 101-n operate in the through mode or the add / drop mode for each of the n signal lights separated. The optical multiplexer 103R multiplexes the optical signals from the optical add / drop switches 101R-1 to 101R-1n into the wavelength multiplexed signal light. The wavelength-multiplexed signal light is output from the optical fiber 107R to the east node via the rear optical amplifier 106R. The counterclockwise wavelength multiplexed signal light can be described in the same manner by changing the sign of the figure from R to L (see, for example, Patent Document 1).

  FIG. 2 shows the function of a conventional optical add / drop switch. The optical add / drop switches 101R-1 to n, 101L-1 to n (hereinafter, R and L are omitted and 101-1 to n or subscripts are omitted and 101) are two-input two-output optical switches, There are two input ports (In, Add) and two output ports (Out, Drop). In the through mode, the In port and the Out port are connected. In the add / drop mode, the In port and the Drop port are connected, and the Add port and the Out port are connected.

  FIG. 3 shows a detailed configuration of a conventional optical add / drop switch. The optical add / drop switch 101 includes an optical switch 121 that branches the signal light input from the In port to a drop port or a variable optical attenuator (VOA) 122, an output of the VOA 122, and an output of the VOA 123 connected to the Add port. And an optical switch 124 for selecting. Furthermore, the optical add / drop switch 101 includes a control circuit (CONT) 125 that controls the attenuation amount of the VOAs 122 and 123, a branch circuit 126 that branches the output of the optical switch 124, and a control circuit that monitors the branched output light. And a photodetector 127 for feeding back to 125.

  The optical add / drop switch 101 is integrated by one quartz optical waveguide substrate, and the optical switch and the VOA are configured by a Mach-Zehnder interferometer. By mounting n optical add / drop switches 101 clockwise (R) and counterclockwise (L), the node shown in FIG. 1 can be configured.

  The Mach-Zehnder interferometer has a configuration in which a 3 dB coupler connected to two input waveguides and a 3 dB coupler connected to two output waveguides are connected by two arm waveguides. ing. A thin film heater for phase adjustment is disposed on one arm waveguide. Since the refractive index of the silica-based glass constituting the waveguide changes depending on the temperature due to the thermo-optic effect, the optical path difference between the two arm waveguides can be arbitrarily controlled by energization heating of the thin film heater. . In this way, by changing the optical path length difference, that is, the interference phase condition of the Mach-Zehnder interferometer, the signal light input from one of the input waveguides can be output from one of the output waveguides, or any branching ratio Can be branched into two output waveguides. Therefore, it can be operated as both an optical switch and a variable optical attenuator.

Japanese Patent Laid-Open No. 2004-37968 (FIGS. 5 and 6)

  In a conventional ROADM system node, whether signal light input to the node is input at a predetermined input level or signal light is output from the node at a predetermined output level in order to determine a failure of the system. Is monitoring. Then, the output level of the signal light is adjusted in the node as necessary so that the signal light has a predetermined output level.

  In the conventional ROADM system, there are many connection points using optical connectors, and there are many monitoring points for monitoring the level of signal light. Therefore, it is necessary to provide a large number of photodetectors in the node, and there is a problem that the scale of the monitor circuit increases.

  In a wavelength division multiplexing communication system, it is important that signal light of each wavelength output to the optical fiber transmission line is output with a predetermined power. Therefore, in order to monitor the power of the signal light of each wavelength, it is necessary to monitor using a photodetector with a wavelength sweep filter such as an optical spectrum analyzer. Therefore, it is necessary to provide a complicated measuring means in the node, and there is a problem that it takes time to measure in order to sweep all wavelengths.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical add / drop switch with a small scale of a monitor circuit for measuring optical power. Another object of the present invention is to provide a method of controlling an optical add / drop switch that can easily monitor the power of wavelength division multiplexed signal light (WDM signal light) in a wavelength division multiplexing system.

In order to achieve such an object, the present invention according to claim 1 multiplexes a plurality of optical add / drop switches corresponding to a plurality of wavelengths, and outputs of the plurality of optical add / drop switches. and have you in wavelength division multiplex communication system node comprising an optical multiplexer, a control method of the optical add drop switch for calculating the power of the signal light of each wavelength, the optical add drop switches from the through port A first variable optical attenuator for inputting the signal light, a second variable optical attenuator for inputting the signal light from the add port, and either the first variable optical attenuator or the second variable optical attenuator. An optical switch that selects an output and outputs signal light from an output port; and a photodetector connected to the output of the optical switch, corresponding to the drive currents of the first and second variable optical attenuators Attenuation amount -Determine the insertion loss at each wavelength from the port to the output port and from the add port to the output port, the insertion loss of the optical multiplexer and the branching ratio of the optical tap for connecting the photodetector, The control circuit stores the optical power measured by the photodetector, the attenuation corresponding to the drive current of the first variable optical attenuator stored in the control circuit, and the through port. The optical power of the signal light input to the through port is calculated by the sum of the insertion loss at each wavelength up to the output port, and the optical power measured by the photodetector is stored in the control circuit. Further, the sum of the attenuation corresponding to the drive current of the second variable optical attenuator and the insertion loss at each wavelength from the add port to the output port Calculate the optical power of the signal light input to the add port, and subtract the difference between the insertion loss of the multiplexer and the branching ratio of the tap from the optical power measured by the photodetector. characterized Rukoto issuing calculate the optical power of the signal light of each wavelength at the output of the vessel.

  As explained above, according to the present invention, the optical power measured by the photodetector connected to the output of the optical add / drop switch, the drive current of the variable optical attenuator, and the insertion stored in the control circuit Since the optical power of the signal light in the optical add / drop switch is calculated from the loss, the scale of the monitor circuit for measuring the optical power can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 4 shows a configuration of an optical add / drop switch according to an embodiment of the present invention. Optical add / drop switches 201W and 201E (hereinafter, W and E are abbreviated as 201. Port names and the like are the same) branch signal light input from the In port to the Drop port or ThrOut port. An optical switch 221 is provided. This block is referred to as DropSW211.

  The optical add / drop switch 201 includes an optical switch 224 that selects an output of the VOA 222 connected to the ThrIn port and an output of the VOA 223 connected to the Add port, and a control circuit that controls the attenuation amount of the VOAs 222 and 223. (CONT) 225. Furthermore, a branch circuit 226 that branches the output light to the Out port, and a photodetector 227 that detects the level of the branched output light and feeds back the detection result to the control circuit 225 are provided. This block is called AddSW212.

  The optical add / drop switch 201 is integrated by a quartz optical waveguide, and the optical switch and the VOA are configured by a Mach-Zehnder interferometer.

  In the through mode, the In port and the ThrOut port are connected in the DropSW 211, and the ThrIn port and the Out port are connected in the AddSW 212, respectively. In the add / drop mode, the In port and the Drop port are connected in the Drop SW 211, and the Add port and the Out port are connected in the Add SW 212, respectively.

  The optical add / drop switch 201 is disposed in each of the west node 201W and the east node 201E, the ThrOutW port and the ThrInE port are connected, and the ThrOutE port and the ThrInW are connected. The DropW port and AddW port, and the DropE port and AddE port are connected to the terminal device as a transmission / reception pair, respectively. When each of the optical add / drop switches 201W and 201E is set to the through mode, clockwise and counterclockwise communication paths are generated so as to pass through this node. On the other hand, when the optical add / drop switches 201W and 201E are respectively set to the add / drop mode, the transmission / reception signal pair via the west node and the transmission / reception signal pair via the east node are connected to the terminal device. From the viewpoint of the terminal equipment, it is possible to adopt a redundant configuration in which one through the west node or the east node is the active system and the other is the standby system.

  According to this configuration, since the active and standby optical fiber transmission lines pass through different nodes, the failure of the optical fiber transmission line can be remedied even when the bidirectional switching method is applied. In addition, since the active and standby systems are housed in separate optical add / drop switches, the optical add / drop switch can remedy failures of the optical add / drop switch even when the bidirectional switching method is applied. it can. Therefore, the failure of the optical fiber transmission line and the failure of the optical add / drop switch can be remedied.

  FIG. 5 shows a configuration of a node according to an embodiment of the present invention. The clockwise wavelength multiplexed signal light is input from the optical fiber 205W to the optical demultiplexer 202W via the pre-optical amplifier 204W. The optical demultiplexer 202W separates the input wavelength multiplexed signal light into n signal lights for each wavelength. The optical add / drop switches 201W-1 to 201n switch the n separated signal lights to the optical add / drop switches 201E-1 to 201n in the through mode and to the terminal equipment in the add / drop mode, respectively. The optical multiplexer 203E multiplexes the optical signals from the optical add / drop switches 201E-1 to 201-n into the wavelength multiplexed signal light. The wavelength multiplexed signal light is output from the optical fiber 207E to the east node via the post-amplifier 206E. The counterclockwise wavelength multiplexed signal light can be described in the same manner by changing W and E in the figure.

  Here, the optical add / drop switches 201W and 201E are accommodated in separate maintenance / replacement packages 208W and 208E. By configuring the maintenance / replacement package in this way, it is possible to relieve the failure of the optical fiber transmission line and the package failure of the optical add / drop switch.

  The optical add / drop switch 201, the optical demultiplexer 202, and the optical multiplexer 203 are accommodated in the same maintenance replacement package 208. This is because the connection connectors between the optical add / drop switch 201 and the optical demultiplexer 202 and between the optical add / drop switch 201 and the multiplexer 203 are omitted. Further, a photodetector for monitoring the WDM signal light is provided on the input side of the optical demultiplexer 202.

  The node configured by the optical add / drop switch according to the present invention is not limited to the configuration of FIG. 5, but as described above, since there are many advantages of configuring the ROADM node, FIG. 4 and FIG. This will be described based on the configuration of No. 5.

In the present embodiment, the level Pmon of the signal light of each wavelength is measured by the photodetector 227. The signal light level Pthr input to the ThrIn port, the signal light level Padd input to the Add port, and the signal light level Poutλ of each wavelength in the WDM signal light combined by the optical multiplexer 203 are: Based on Pmon measured by the detector 227, the following calculation is performed.
Pthr [dBm] = Pmon [dBm] + Lthr [dB] + Athr [dB] where Athr is the attenuation amount of the VOA 222, and Lthr is the insertion loss from the ThrIn port to the photodetector 227 when Athr is zero. .

    Padd [dBm] = Pmon [dBm] + Ladd [dB] + Aadd [dB] Here, Aadd is the attenuation amount of VOA 223, and Ladd is the insertion loss from the Add port to the photodetector 227 when Aadd is zero. .

Poutλ [dBm] = Pmon [dBm] −Lmux [dB] + Rtap [dB]
Here, Lmux is the insertion loss of the corresponding wavelength port in the optical multiplexer 203, and Rtap is the branching ratio of the optical tap that partially branches the optical signal to the optical detector 227, that is, the output to the optical multiplexer 203. Is the ratio of the branched light to the photodetector 227 when.

  Originally, in order to monitor the level of the signal light input to the ThrIn port, it is necessary to provide a photodetector between the ThrIn port and the VOA 222, and the level of the signal light input to the Add port is monitored. In order to achieve this, it is necessary to provide a photodetector between the Add port and the VOA 223. In the present embodiment, since means for calculating the level of the signal light at these monitoring points according to the above formula is provided, the branch circuit and the photodetector at these monitoring points can be omitted.

  Further, the power of the signal light of each wavelength in the WDM signal light can be easily monitored without providing complicated measuring means. Furthermore, since each signal light of each wavelength is monitored without having a mechanical sweeping mechanism such as an optical spectrum analyzer, all wavelengths can be measured at a very high speed.

  In this embodiment, the branch circuit 226 and the photodetector 227 are arranged between the Out port and the optical switch 224. By disposing at this position, in the case of either the through mode or the add / drop mode, measurement can be performed with the same photodetector 227, and there is an advantage that the number of photodetectors can be minimized. For example, it can be arranged between the optical switch 224 and the VOA 222 and between the optical switch 224 and the VOA 223, or between the VOA 222 and the ThrIn port and between the VOA 223 and the Add port, but the number of photodetectors is doubled. It becomes.

  FIG. 6 shows an optical power monitoring method according to an embodiment of the present invention. A specific method for monitoring the level of signal light input to the ThrIn port, the level of signal light input to the Add port, and the level of signal light of each wavelength in the WDM signal light will be described. In the method of this embodiment, the loss value of each component of the optical add / drop switch 201 is measured in advance. Specifically, the output power Pin of the measurement light source 301 is measured in advance. Then, the measurement light source 301 is connected to the ThrIn port, and the optical power MonThr detected by the photodetector 227 is measured.

  Next, the measurement light source 301 is connected to the Add port, and the optical power MonAdd detected by the photodetector 227 is measured. Further, the measurement light source 301 is connected to the ThrIn port or the Add port, the optical power MonOut detected by the photodetector 227 is measured, and the optical power Pout output from the optical multiplexer 203 is measured. Measure with In the above measurement, the output wavelength of the measurement light source 301 is matched with the wavelength of the port to be connected.

As a result,
Lthr [dB] + Athr [dB] = Pin [dB] −MonThr [dB]
Ladd [dB] + Aadd [dB] = Pin [dB] −MonAdd [dB]
Lmux [dB] -Rtap [dB] = MonOut [dB] -Pout [dB]
Thus, the values of (Lthr + Athr), (Ladd + Aadd), and (Lmux-Rtap) are obtained.

By changing the drive currents I ₂₂₂ and I ₂₂₃ of the thin film heaters of the VOA ₂₂₂ and VOA ₂₂₃ , the values of MonThr and MonAdd with respect to the current value of the drive current are measured, and the values of (Lthr + Athr) and (Ladd + Aadd) are obtained. At this time, the minimum values of (Lthr + Athr) and (Ladd + Aadd) are set to Lthr and Ladd, and the values of Athr and Aadd for the drive currents I ₂₂₂ and I ₂₂₃ are calculated.

The calculated values of Lthr, Ladd, (Lmux−Rtap), the correspondence between the drive current I ₂₂₂ and Athr, and the correspondence between the drive current I ₂₂₃ and Aadd are stored in the memory of the CONT 225. Further, the same measurement is performed for each wavelength, and the measurement result is stored in the memory of the CONT 225 for each optical add / drop switch.

During operation of the optical add / drop switch, the value of Pmon is measured by the photodetector 227. The CONT ₂₂₅ reads the values of Athr and Aadd from the drive currents I ₂₂₂ and I ₂₂₃ of the VOA from the memory, and further reads the values of Lthr, Ladd and (Lmux−Rtap) from the memory. Next, the values of Pthr, Padd, and Poutλ can be calculated using the above-described equations. Therefore, by measuring the value of Pmon, the level of the signal light input to the ThrIn port, the level of the signal light input to the Add port, and the level of the signal light of each wavelength in the WDM signal light are measured. Can do.

It is a block diagram which shows the node of the conventional conventional wavelength division multiplexing communication system. It is a figure which shows the function of the conventional optical add / drop switch. It is a block diagram which shows the detail of the conventional optical add / drop switch. It is a block diagram which shows the optical add / drop switch concerning one Embodiment of this invention. It is a block diagram which shows the structure of the node concerning one Embodiment of this invention. It is a figure which shows the monitoring method of the optical power concerning one Embodiment of this invention.

Explanation of symbols

101, 201 Optical add / drop switch 102, 202 Optical demultiplexer 103, 203 Optical multiplexer 104, 204 Pre-optical amplifier 105, 107, 205, 207 Optical fiber 106, 206 Post-optical amplifier 121, 124 Optical switch 122, 123 VOA
125 Control circuit (CONT)
301 Light Source for Measurement 303 Monitor Circuit for Measurement

Claims (1)

A plurality of optical add drop switches corresponding to a plurality of wavelengths, and have your a node of a wavelength division multiplexing communication system including an optical multiplexer for multiplexing the outputs of the plurality of optical add-drop switch, the signal light of each wavelength In the control method of the optical add / drop switch for calculating the power of
The optical add / drop switch includes a first variable optical attenuator for inputting signal light from a through port, a second variable optical attenuator for inputting signal light from an add port, and the first variable optical attenuator or the first variable optical attenuator. An optical switch that selects one of the outputs of the two variable optical attenuators and outputs the signal light from the output port; and a photodetector connected to the output of the optical switch;
An attenuation amount corresponding to a drive current of the first and second variable optical attenuators, an insertion loss at each wavelength from the through port to the output port and from the add port to the output port, and the optical multiplexer Find the insertion loss and the branching ratio of the optical tap for connecting the photodetector, store in the control circuit,
The control circuit includes optical power measured by the photodetector, attenuation corresponding to the drive current of the first variable optical attenuator stored in the control circuit, and each from the through port to the output port. The optical power of the signal light input to the through port is calculated by the sum of the insertion loss at the wavelength of the optical signal, the optical power measured by the photodetector, and the second variable light stored in the control circuit The optical power of the signal light input to the add port is calculated from the sum of the attenuation corresponding to the drive current of the attenuator and the insertion loss at each wavelength from the add port to the output port. By subtracting the insertion loss of the multiplexer and the difference in the branching ratio of the tap from the measured optical power, the signal of each wavelength at the output of the optical multiplexer is subtracted. Method of controlling an optical add-drop switch, characterized in Rukoto issuing calculate the optical power of the light.

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