JP5632337B2 - Optical communication system, wavelength tunable laser, and wavelength switching method - Google Patents

Description

  The present invention relates to an optical communication system, a wavelength tunable laser, and a wavelength switching method.

  A wavelength switch that combines a wavelength tunable laser and a circular AWG (Arrayed Waveguide Grating) switches the output port of the circular AWG by changing the wavelength of the laser. The wavelength of the laser is switched by changing the value of the current supplied to the wavelength control terminal of the wavelength tunable laser, but another wavelength is generated while switching to the desired wavelength depending on the wavelength before and after switching. This other wavelength may cause crosstalk in other output ports and cause bit errors. This problem will be described with reference to FIG. 11 and FIG.

  As shown in FIG. 11, when a laser having an oscillation wavelength λA is input from the wavelength tunable laser 61 to the modulator 62, the optical signal modulated by the modulator 62 corresponding to the signal to be transmitted is transmitted by the circular AWG 65. After being routed, it is output from the output port 51. Further, when a laser having an oscillation wavelength λB is input from the wavelength tunable laser 63 to the modulator 64, an optical signal modulated by the modulator 64 corresponding to the signal to be transmitted is wavelength-routed by the circulating AWG 65, Output from the output port 52. The wavelength tunable laser has a mechanism in which wavelengths are switched discretely at regular intervals by parameter control.

  When the current value supplied to the wavelength tunable laser 61 is changed in order to switch the output port of the optical signal transmitted by the laser of the wavelength tunable laser 61 from the output port 51 to the output port 53 from the above state, the oscillation wavelength of the laser is changed. A signal of wavelength λB is generated in the middle of switching from λA to λC and leaks to the output port 52. As shown in FIG. 12, at the output port 52, the signal of wavelength λB output from the modulator 64 (white rectangle) and the signal of wavelength λB output from the modulator 62 (rectangle shown by hatching) become crosstalk. And mix. If a 0 level signal changes to a 1 level signal due to crosstalk, a bit error occurs on the receiving side. An example of a wavelength switch is disclosed in Non-Patent Document 1.

Toru Segawa, et al., "All-optical wavelength-routing switch with monolithically integrated filter-free tunable wavelength converters and an AWG", OPTICS EXPRESS, 1 March 2010, Vol. 18, No. 5, pp.4340-4345

  Non-Patent Document 1 describes that static crosstalk is −22 dB or less, but does not consider crosstalk when switching wavelengths (dynamic). In addition, when the number of input / output ports is increased, there is a problem that the possibility of crosstalk increases in proportion to the number of ports when wavelength switching occurs simultaneously in a plurality of wavelength tunable lasers. At present, crosstalk at the time of wavelength switching is not particularly taken into consideration, and no measures for reducing crosstalk are taken.

  The present invention has been made to solve the above-described problems of the technology, and an optical communication system, a wavelength tunable laser, and a wavelength switching capable of reducing the crosstalk generated when the oscillation wavelength of the laser is switched. It aims to provide a method.

In order to achieve the above object, an optical communication system of the present invention comprises:
A phase control region that changes the wavelength of the cavity mode according to the supplied current, a wavelength control region that changes the resonance peak according to the supplied current, and the cavity mode and the resonance when a current exceeding a threshold value is supplied A tunable laser including an output control region that oscillates the laser at a wavelength matching the peak;
A modulator that switches on / off of a gate corresponding to a signal to be transmitted, modulates a laser input from the wavelength tunable laser, and outputs an optical signal;
An arrayed waveguide diffraction grating including a plurality of filters for classifying the wavelength group of the optical signal input from the modulator for each wavelength band;
When an instruction to switch the oscillation wavelength is input , the current value supplied to the phase control region is changed by changing the oscillation wavelength before the change and the cavity mode at the center wavelength of the filter. The cavity mode is changed from the center wavelength of the filter to a wavelength near the intersection between the filters of the arrayed waveguide grating, and then the resonance peak is changed by changing the value of the current supplied to the wavelength control region. After setting the previous wavelength, by changing the value of the current supplied to the phase control region, a control circuit that matches the cavity mode with the center wavelength of the filter at the changed wavelength ,
It is the structure which has.

The wavelength tunable laser of the present invention is a wavelength tunable laser connected to the arrayed waveguide diffraction grating via a modulator,
A phase control region that changes the wavelength of the cavity mode according to the supplied current;
A wavelength control region that changes a resonance peak according to a supplied current; and
When a current equal to or higher than a threshold is supplied, an output control region that oscillates a laser at a wavelength that matches the cavity mode and the resonance peak;
When an instruction to switch the oscillation wavelength is input , the current value supplied to the phase control region is changed by changing the oscillation wavelength before the change and the cavity mode at the center wavelength of the filter. The cavity mode is changed from the center wavelength of the filter to a wavelength near the intersection between the filters of the arrayed waveguide grating, and then the resonance peak is changed by changing the value of the current supplied to the wavelength control region. After setting the previous wavelength, by changing the value of the current supplied to the phase control region, a control circuit that matches the cavity mode with the center wavelength of the filter at the changed wavelength ,
It is the structure which has.

Further, the wavelength switching method of the present invention is connected to the arrayed waveguide grating via the modulator, and changes the cavity mode wavelength according to the supplied current, and the resonance peak according to the supplied current. And a wavelength switching method for a tunable laser including an output control region that oscillates a laser at a wavelength that matches the cavity mode and the resonance peak when a current equal to or greater than a threshold is supplied ,
When an instruction to switch the oscillation wavelength is input, the oscillation wavelength before change and the cavity mode are supplied to the phase control region from a state where the center wavelength of the filter included in the arrayed waveguide diffraction grating is the same. By changing the value of the current, the cavity mode is changed from the center wavelength of the filter to the wavelength near the intersection between the filters of the arrayed waveguide grating ,
After changing the wavelength position of the cavity mode, by changing the value of the current supplied to the wavelength control region, the resonance peak is set to the change destination wavelength,
A filter included in the arrayed waveguide diffraction grating at the wavelength of the change destination by changing the value of the current supplied to the phase control region after setting the resonance peak at the position of the wavelength of the change destination. It is made to coincide with the center wavelength.

  According to the present invention, the crosstalk at the time of switching the oscillation wavelength is reduced, and the occurrence of bit errors can be suppressed.

It is a block diagram which shows one structural example of the optical communication system of 1st Embodiment. FIG. 2 is a schematic plan view illustrating a configuration example of a wavelength tunable laser illustrated in FIG. 1. It is a figure for demonstrating oscillation control and wavelength control. It is a figure for demonstrating the oscillation principle of a wavelength variable laser. It is a flowchart which shows the operation | movement procedure of wavelength switching in 1st Embodiment. It is a figure for demonstrating phase control and wavelength control. It is explanatory drawing corresponding to the step of the flowchart shown in FIG. It is a figure for demonstrating in detail the process of step 101 of the flowchart shown in FIG. It is a flowchart which shows the operation | movement procedure of wavelength switching in 2nd Embodiment. It is a block diagram which shows another structural example of the wavelength tunable laser in any one of 1st and 2nd embodiment. It is a block diagram which shows the example of 1 structure of the wavelength switch which combined the wavelength variable laser and the revolving AWG. It is a figure for demonstrating the problem of the wavelength switch shown in FIG.

(First embodiment)
In this embodiment, when changing the wavelength of the wavelength tunable laser, the wavelength is not changed directly, but the wavelength is changed while allowing the signal in the wavelength changing process to pass through the path where the loss in the AWG filter increases. It is.

  The configuration of the optical communication system according to the present embodiment will be described. FIG. 1 is a block diagram illustrating a configuration example of an optical communication system according to the present embodiment. FIG. 2 is a schematic plan view showing a configuration example of the wavelength tunable laser shown in FIG.

  As shown in FIG. 1, the optical communication system includes wavelength tunable lasers 11-1 to 11-n (n is an integer of 2 or more), modulators 12-1 to 12-n, AWG 13, and receiver 14-. 1 to 14-n and a control circuit 15 for controlling the wavelength tunable lasers 11-1 to 11-n. In the configuration example shown in FIG. 1, the number of input ports and output ports of the AWG 13 is the same, but the number of input ports and output ports may be different. In addition, since the control executed by the control circuit 15 is the same for each of the wavelength tunable lasers 11-1 to 11-n shown in FIG. In the following description, it is simply expressed as “11” and the code of the modulator connected to the wavelength tunable laser 11 is simply expressed as “12”.

  The modulator 12 switches the gate on / off in response to an input signal corresponding to the signal to be transmitted, modulates the laser input from the wavelength tunable laser 11, generates an optical signal, and converts the optical signal to Send to AWG13. However, the modulator 12 cannot completely shut off the laser output from the wavelength tunable laser 11 even when the gate is off, and has a property that a low-level optical signal leaks to the AWG 13 side.

  The AWG 13 is a recurring AWG that includes a plurality of AWG filters that classify wavelength groups of optical signals received from the modulator 12 into predetermined wavelength bands at a constant frequency interval (Free Spectral Range: FSR).

  As shown in FIG. 2, the wavelength tunable laser 11 has an output control region 21, a phase control region 22, and a wavelength control region 23. FIG. 3A is a diagram for explaining oscillation control in the output control region, and FIG. 3B is a diagram for explaining wavelength control in the wavelength control region. In FIG. 3A, the horizontal axis indicates the value of the current supplied to the output control region, and the vertical axis indicates the optical output power.

  As shown in FIG. 3A, the output control region 21 oscillates the laser when the value of the supplied current exceeds a certain threshold value. The phase control region 22 changes the wavelength of the cavity mode according to the value of the supplied current. The wavelength control region 23 changes the oscillation wavelength by changing the position of the resonance peak according to the value of the supplied current and selecting the wavelength of the cavity mode close to the resonance peak. The graph shown in FIG. 3B shows λ1 to λ9 as an example of selectable oscillation wavelengths, and the current value I1 (horizontal axis) and the current supplied to the wavelength control region 23 for wavelength selection and The case where it controls using two types of electric current values of electric current value I2 (vertical axis) is shown. Two types of current values are used to control two resonance peaks.

  When an instruction for setting or switching the oscillation wavelength is input, the control circuit 15 supplies a current value to be supplied to the output control region 21, the phase control region 22, and the wavelength control region 23 so that the oscillation wavelength becomes the specified wavelength. To control. The control circuit 15 may be a semiconductor integrated circuit in which a dedicated logic circuit is formed, or may include a memory that stores a program and a CPU (Central Processing Unit) that executes processing according to the program.

  Here, a general oscillation principle in a wavelength tunable laser having a mode selection mechanism will be described. FIG. 4 is a diagram for explaining the oscillation principle of the wavelength tunable laser, and shows a case where the oscillation wavelength is changed from λ3 to λ5.

  When the oscillation wavelength is set to λ3, a current value equal to or greater than the threshold value is supplied to the output control region 21, and a predetermined current value is supplied to each of the phase control region 22 and the wavelength control region 23. The wavelength control region 23 controls two resonance peaks using two current values. As a result, as shown in FIG. 4A, the laser oscillates in the cavity mode closest to the wavelength λ3 where the resonance peak 1 and the resonance peak 2 coincide. Subsequently, when the oscillation wavelength is changed from λ3 to λ5, as shown in FIG. 4B, by changing the current value supplied to the wavelength control region 23, the resonance peaks 1 and 2 are moved, and the wavelength λ5 When the resonance peak 1 and the resonance peak 2 coincide with each other in the vicinity of the cavity mode, the laser oscillates at the wavelength λ5.

  Next, the wavelength switching operation by the control circuit 15 in the optical communication system of the present embodiment will be described. Here, it is assumed that the oscillation wavelength is changed from λ4 to λ6. In the present embodiment, it is assumed that the wavelength tunable laser 11 and the AWG 13 are a combination capable of matching the cavity mode of the wavelength tunable laser and the center wavelength of the AWG filter of the revolving AWG.

  FIG. 5 is a flowchart showing an operation procedure of wavelength switching in the present embodiment. FIG. 6 is a diagram for explaining phase control and wavelength control. FIG. 7 is an explanatory diagram corresponding to the steps of the flowchart shown in FIG. FIG. 8 is a diagram for explaining in detail the processing of step 101 in the flowchart shown in FIG.

  First, when an instruction to set the oscillation wavelength to λ4 is input, the control circuit 15 supplies a current value equal to or greater than the threshold value to the output control region 21 as described with reference to FIG. By supplying a predetermined current value to each of the control region 22 and the wavelength control region 23, the cavity mode, the resonance peak 1, and the resonance peak 2 are matched at the wavelength λ4.

  FIG. 8A shows a state where the resonance peak 1 and the resonance peak 2 coincide with each other in the cavity mode of the wavelength λ4. FIG. 8B is a schematic diagram showing a part of the state in which the wavelength group is classified into a plurality of bands in one FSR of the AWG 13. Referring to FIGS. 8A and 8B, the cavity mode is located at the center wavelength of the AWG filter at wavelengths λ4, λ5, and λ6, and the cavity mode, resonance peak 1 and resonance peak 2 are at wavelength λ4. You can see that they match.

  When an instruction to change the oscillation wavelength from λ4 to λ6 is input, the control circuit 15 adjusts the value of the current supplied to the phase control region 22, shifts the cavity mode from the center wavelength of the AWG filter, and generates a loss. Is changed to a position of a large wavelength (step 101). The position of the wavelength having a large loss is a region near the boundary between adjacent AWG filters, as shown in FIG. FIG. 6 shows that the wavelength has changed from λ4 to λ4 ′ by changing the value of the current supplied to the phase control region 22 by the control circuit 15 (phase control current value). FIG. 7A shows that the position of the cavity mode is changing. In this way, the cavity mode is changed to a wavelength position where the loss of the AWG filter is large.

  Subsequently, the control circuit 15 adjusts the current value supplied to the wavelength control region 23 and changes the resonance peak 1 and the resonance peak 2 so as to be in the vicinity of a desired wavelength (step 102). Here, the wavelength λ6 corresponds to a desired wavelength. FIG. 6 shows that the wavelength is λ4 by increasing the wavelength control current value I1 without changing the wavelength control current value I2 as the value of the current supplied to the wavelength control region 23 by the control circuit 15 (wavelength control current value). This represents a change from 'to λ6'. By changing the wavelength control current I1, the resonance peaks 1 and 2 move to the vicinity of the wavelength λ6. FIG. 7B shows a state where the resonance peak 1 and the resonance peak 2 coincide with each other at the wavelength λ6. Note that when the resonance peak moves, there is a wavelength at which the resonance peaks 1 and 2 oscillate in the middle. However, since the loss is large because it deviates from the center wavelength of the AWG filter, the crosstalk is small enough not to cause a problem.

  Thereafter, the control circuit 15 adjusts the current value supplied to the phase control region 22 and changes the cavity mode so that it becomes λ6, which is the center wavelength of the AWG filter, as shown in FIG. 7C (step 103). .

  According to this embodiment, since the loss of the laser output at the time of switching the oscillation wavelength is large, it is possible to reduce crosstalk and prevent bit errors from occurring. Further, since the crosstalk is reduced by controlling the laser output, it is not necessary to add a new part for the crosstalk reduction measure, and the manufacturing cost can be suppressed.

  Further, in the optical communication system including the wavelength switch in which the tunable AWG is combined with the tunable AWG as in the present embodiment, when the output port is switched in accordance with the switching of the oscillation wavelength in the circulatory AWG, Crosstalk can be reduced.

(Second Embodiment)
In this embodiment, the output power of the wavelength tunable laser is turned off or the current for laser oscillation is made smaller than the threshold value, so that the wavelength change is performed after the signal causing the crosstalk is almost zero. After completion, the output power of the wavelength tunable laser is turned on or the current for laser oscillation is set to a threshold value or more.

  Since the configuration of the optical communication system according to the present embodiment is the same as that of the first embodiment, detailed description thereof is omitted. In the present embodiment, differences from the first embodiment will be described in detail.

  In the optical communication system of the present embodiment, the wavelength switching operation by the control circuit 15 will be described. FIG. 9 is a flowchart showing an operation procedure of wavelength switching in the present embodiment.

  When the wavelength switching instruction is input, the control circuit 15 stops supplying current to the output control region 21 (step 201). Subsequently, the control circuit 15 changes the value of the current supplied to the wavelength control region 23 so that the oscillation wavelength becomes the wavelength to be changed (desired wavelength) (step 202). Specifically, the control circuit 15 changes the position of the resonance peaks 1 and 2 by changing the value of the current supplied to the wavelength control region 23, and changes the cavity mode, resonance peak 1, and resonance peak at the wavelength to which the oscillation wavelength is changed. Resonance peak 2 is matched. Thereafter, the control circuit 15 resumes the supply of current to the output control region 21 (step 203).

  In step 201 shown in the flowchart of FIG. 9, the case where the control circuit 15 stops supplying current to the output control region 21 has been described as a method for stopping laser oscillation. You may perform control which makes the value of the electric current supplied smaller than a threshold value. In this case, when the laser oscillation is resumed in step 203, the control circuit 15 may perform control so that the value of the current supplied to the output control region 21 is equal to or greater than the threshold value.

  According to the present embodiment, since the signal that causes crosstalk becomes substantially zero, the effect of preventing crosstalk is further improved.

  In the first and second embodiments, the control circuit 15 is provided separately from the wavelength tunable laser 11. However, the control circuit 15 may be provided in the wavelength tunable laser 11. FIG. 10 is a block diagram showing an example when the control circuit shown in FIG. 1 is provided in a wavelength tunable laser. A control unit 24 is provided in the wavelength tunable laser 16 shown in FIG. The control unit 24 has the same configuration as the control circuit 15 and will not be described in detail. In this case, the control circuit 15 may not be provided in the optical communication system illustrated in FIG.

  In the second embodiment, the case where the optical communication system has a circular AWG has been described. However, the configuration connected after the modulator 12 is not limited to the circular AWG, and a configuration in which crosstalk is a problem is modulated. The second embodiment can be applied to an optical communication system connected after the device 12. In the second embodiment, in addition to the wavelength tunable laser having the mode selection mechanism, a wavelength tunable laser whose wavelength is continuously changed according to the value of the supplied current can be used.

11, 16 Tunable laser 12 Modulator 13 AWG
14 Receiver 15 Control Circuit 21 Output Control Area 22 Phase Control Area 23 Wavelength Control Area 24 Control Unit

Claims (3)

A phase control region that changes the wavelength of the cavity mode according to the supplied current, a wavelength control region that changes the resonance peak according to the supplied current, and the cavity mode and the resonance when a current exceeding a threshold value is supplied A tunable laser including an output control region that oscillates the laser at a wavelength matching the peak;
A modulator that switches on / off of a gate corresponding to a signal to be transmitted, modulates a laser input from the wavelength tunable laser, and outputs an optical signal;
An arrayed waveguide diffraction grating including a plurality of filters for classifying the wavelength group of the optical signal input from the modulator for each wavelength band;
When an instruction to switch the oscillation wavelength is input , the current value supplied to the phase control region is changed by changing the oscillation wavelength before the change and the cavity mode at the center wavelength of the filter. The cavity mode is changed from the center wavelength of the filter to a wavelength near the intersection between the filters of the arrayed waveguide grating, and then the resonance peak is changed by changing the value of the current supplied to the wavelength control region. After setting the previous wavelength, by changing the value of the current supplied to the phase control region, a control circuit that matches the cavity mode with the center wavelength of the filter at the changed wavelength ,
An optical communication system. A tunable laser connected to an arrayed waveguide grating via a modulator,
A phase control region that changes the wavelength of the cavity mode according to the supplied current;
A wavelength control region that changes a resonance peak according to a supplied current; and
When a current equal to or higher than a threshold is supplied, an output control region that oscillates a laser at a wavelength that matches the cavity mode and the resonance peak;
When an instruction to switch the oscillation wavelength is input , the current value supplied to the phase control region is changed by changing the oscillation wavelength before the change and the cavity mode at the center wavelength of the filter. The cavity mode is changed from the center wavelength of the filter to a wavelength near the intersection between the filters of the arrayed waveguide grating, and then the resonance peak is changed by changing the value of the current supplied to the wavelength control region. After setting the previous wavelength, by changing the value of the current supplied to the phase control region, a control circuit that matches the cavity mode with the center wavelength of the filter at the changed wavelength ,
A tunable laser having: Phase control region that is connected to the arrayed waveguide diffraction grating via the modulator and changes the wavelength of the cavity mode according to the supplied current, the wavelength control region that changes the resonance peak according to the supplied current, and the threshold value or more When the current is supplied, a wavelength switching method for a tunable laser including an output control region that oscillates the laser at a wavelength that matches the cavity mode and the resonance peak ,
When an instruction to switch the oscillation wavelength is input, the oscillation wavelength before change and the cavity mode are supplied to the phase control region from a state where the center wavelength of the filter included in the arrayed waveguide diffraction grating is the same. By changing the value of the current, the cavity mode is changed from the center wavelength of the filter to the wavelength near the intersection between the filters of the arrayed waveguide grating ,
After changing the wavelength position of the cavity mode, by changing the value of the current supplied to the wavelength control region, the resonance peak is set to the change destination wavelength,
A filter included in the arrayed waveguide diffraction grating at the wavelength of the change destination by changing the value of the current supplied to the phase control region after setting the resonance peak at the position of the wavelength of the change destination. Wavelength switching method to match the center wavelength of.

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