JP2018085475A - Multiwavelength laser device and wavelength multiplex communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an optical loss of signal light to achieve a desired oscillation wavelength in the case of connecting a cycle wavelength filter and a wavelength spectral filter in series.SOLUTION: A multiwavelength laser device comprises: a semiconductor gain chip 1; a cycle wavelength filter 2; a wavelength spectral filter 3 connected in series with the cycle wavelength filter; a plurality of first mirrors 4 and a second mirror 5 which constitute an external resonator 11; a short wave-side monitor part 6 and a long wavelength-side monitor part 7 which are connected to the wavelength spectral filter, provided that the short wave-side monitor part includes a short wave-side photodetector 6A operable to detect a short wave-side monitoring light of a wavelength shorter by one cycle of a signal light wavelength, and the long wavelength-side monitor part includes a long wavelength-side photodetector 7A operable to detect a long wavelength-side monitoring light of a wavelength longer by one cycle of the signal light wavelength; and a control part 8 which performs control for matching a gain peak of a chip to a wavelength of short wave-side or long wave-side monitoring light with a peak wavelength of the cycle wavelength filter matched to a grid wavelength, and adjusting a wavelength position of the wavelength spectral filter so as to maximize an output of the short wave-side or long wave-side photodetector.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multiwavelength laser apparatus and a wavelength division multiplexing communication system.

  In recent years, it has been proposed to implement a multi-wavelength laser device capable of simultaneous oscillation at multiple wavelengths by inserting a periodic wavelength filter into the external resonator of an external resonator type quantum dot laser. (Division Multiplexing) Communication applications are expected.

International Publication No. 2009/119284 JP 2003-51786 A

Y. Zhanget al., “Quantum dot SOA / silicon external cavity multiwavelength laser,” Opt. Express 23 (4), pp.4666-4671, 2015

By the way, in the multi-wavelength laser apparatus as described above, for example, when phase control is performed for each wavelength, it is conceivable to connect a wavelength spectral filter in series with the periodic wavelength filter.
However, since the periodic wavelength filter and the wavelength spectral filter have different offsets with respect to the grid wavelength of the WDM communication system, it is very difficult to control to the desired oscillation wavelength.

  An object of the present invention is to suppress optical loss of signal light and obtain a desired oscillation wavelength when a periodic wavelength filter and a wavelength spectral filter are connected in series.

  In one aspect, a multiwavelength laser device includes a semiconductor gain chip, a periodic wavelength filter optically connected to the semiconductor gain chip, having a periodic peak wavelength, connected in series to the periodic wavelength filter, and a plurality of signals A wavelength spectral filter that divides light for each wavelength, a plurality of first mirrors that are optically connected to the wavelength spectral filter and reflect a part of each signal light divided by the wavelength spectral filter, and a period of the semiconductor gain chip Provided on the opposite side of the side where the wavelength filter is provided, and connected to the second mirror constituting the external resonator between the plurality of first mirrors and the wavelength spectral filter, and is the shortest of the plurality of signal lights A short-wave side monitor including a short-wave side photodetector that detects a short-wave side monitor light having a wavelength shorter than the wavelength by one period of the signal light wavelength, and a short-wave side mirror that reflects a part of the short-wave side monitor light. And a long wave side photodetector connected to the wavelength spectral filter for detecting a long wave side monitor light having a wavelength longer by one period of the signal light wavelength than the longest wavelength among the plurality of signal lights, and a long wave side monitor light A long-wave side monitor unit including a long-wave side mirror that partially reflects the peak wavelength of the periodic wavelength filter in accordance with the grid wavelength, and the gain peak of the semiconductor gain chip is set to the wavelength of the short-wave side monitor light or the long-wave side monitor light. And a control unit that performs control to adjust the wavelength position of the wavelength spectral filter so that the output of the short-wave side photodetector or the long-wave side photodetector is maximized in accordance with the wavelength.

  In one aspect, a wavelength division multiplexing communication system includes a transmitter including a multi-wavelength laser device and a receiver connected to the transmitter via a transmission path, and the multi-wavelength laser device includes the above-described configuration.

  As one aspect, when the periodic wavelength filter and the wavelength spectral filter are connected in series, the optical loss of the signal light is suppressed, and a desired oscillation wavelength can be obtained.

It is a figure which shows the structure of the multiwavelength laser apparatus concerning this embodiment. It is a figure which shows the specific structural example of the multiwavelength laser apparatus concerning this embodiment. (A)-(C) are figures which show the specific structural example of the periodic wavelength filter with which the multiwavelength laser apparatus concerning this embodiment is equipped. (A)-(C) are figures which show the specific structural example of the wavelength spectral filter with which the multiwavelength laser apparatus concerning this embodiment is equipped. It is a figure which shows the specific structural example of the wavelength spectroscopy filter with which the multiwavelength laser apparatus concerning this embodiment is equipped. It is a flowchart which shows the adjustment procedure of the wavelength position of the periodic wavelength filter and wavelength spectral filter with which the multiwavelength laser apparatus concerning this embodiment is equipped. (A)-(D) are the figures for demonstrating the filter for adjusting the wavelength position of the periodic wavelength filter with which the multiwavelength laser apparatus concerning this embodiment is equipped. (A), (B) is a figure for demonstrating adjustment of the wavelength position of the wavelength spectral filter with which the multiwavelength laser apparatus concerning this embodiment is equipped. It is a figure which shows the structural example in the case of performing phase control in an external resonator type | mold multiwavelength laser apparatus. It is a figure which shows the structure of a wavelength division multiplexing communication system.

Hereinafter, a multi-wavelength laser device and a wavelength division multiplexing communication system according to an embodiment of the present invention will be described with reference to FIGS.
The multi-wavelength laser device according to this embodiment is an external resonator type multi-wavelength laser device that includes a periodic wavelength filter in an external resonator of the laser and can simultaneously oscillate at multiple wavelengths. Note that the multi-wavelength laser device is also referred to as an optical semiconductor light-emitting device, a light-emitting device, or a multi-wavelength simultaneous laser.

In the present embodiment, as shown in FIG. 1, the multi-wavelength laser device includes a semiconductor gain chip 1, a periodic wavelength filter 2, a wavelength spectral filter 3, a plurality of first mirrors 4, a second mirror 5, A short wave side monitor unit 6, a long wave side monitor unit 7, and a control unit 8 are provided.
In FIG. 1, a multi-wavelength simultaneous oscillation laser 9 that simultaneously oscillates N wavelength signal lights (λ _{1 to} λ _N ) is shown as an example. Here, an example in which the semiconductor gain chip 1 is mounted on an integrated element in which the periodic wavelength filter 2 and the like are integrated on the substrate 10 will be described.

Here, the semiconductor gain chip 1 is a chip including a semiconductor gain medium. That is, the semiconductor gain chip 1 is a chip including a semiconductor optical amplifier (SOA).
For example, the semiconductor gain chip 1 is a quantum dot gain chip (QD gain chip) including a quantum dot gain medium. In this case, the multiwavelength laser device 9 is also referred to as a multiwavelength quantum dot laser device, an external resonator type multiwavelength quantum dot laser device, or an external resonator type quantum dot laser.

The periodic wavelength filter 2 is a filter having a periodic peak wavelength, and is optically connected to the semiconductor gain chip 1.
For example, the periodic wavelength filter 2 is a waveguide type periodic wavelength filter. For example, the periodic wavelength filter 2 is a filter using a ring resonator (see, for example, FIG. 2).
However, the present invention is not limited to this, and the periodic wavelength filter 2 may be a filter using a DBR (Distributed Bragg Reflector) 2A and a loop mirror 2B, for example, as shown in FIG. As shown in FIG. 3B, a filter using two DBRs 2C and 2D may be used. For example, as shown in FIG. 3C, a filter using DBR 2E and cleavage plane 2F may be used. good. The periodic wavelength filter 2 is also referred to as a wavelength periodic filter or a periodic filter.

The wavelength spectral filter 3 is a filter that divides a plurality of signal lights for each wavelength, and is connected in series to the periodic wavelength filter 2. The wavelength spectral filter 3 is also referred to as a wavelength distribution spectral filter.
Here, a wavelength spectral filter 3 is connected in series with the periodic wavelength filter 2 in order to perform phase control for each wavelength as will be described later. Here, the period of the transmission wavelength of the wavelength spectroscopic filter 3 coincides with the period of the transmission wavelength of the periodic wavelength filter 2. That is, the periods of the transmission wavelengths of the periodic wavelength filter 2 and the wavelength spectral filter 3 are the same.

For example, the wavelength spectral filter 3 is a filter using an arrayed waveguide diffraction grating (AWG) (see, for example, FIGS. 2 and 4A to 4C).
Further, for example, the wavelength spectral filter 3 is preferably provided with a multi-mode interference (MMI) portion 3A in the light input / output unit (see, for example, FIG. 4C). As described above, by adopting a structure in which the MMI portion 3A is integrated in the light input / output section of the wavelength spectral filter 3, the insertion loss of the wavelength spectral filter 3 can be reduced.

The wavelength spectroscopic filter 3 is not limited to this, and is a filter having a structure in which light incident on the diffraction grating surface 3B formed in the vertical direction is two-dimensionally dispersed, for example, as shown in FIG. May be.
The plurality of first mirrors 4 are mirrors that respectively reflect part of each signal light divided by the wavelength spectral filter 3, and are optically connected to the wavelength spectral filter 3. Here, N first mirrors 4 are provided. For example, the first mirror 4 is a loop mirror (see, for example, FIG. 2). The invention is not limited to this, and a DBR mirror or the like may be used.

The second mirror 5 is provided on the opposite side of the semiconductor gain chip 1 where the periodic wavelength filter 2 is provided, and constitutes an external resonator 11 between the plurality of first mirrors 4. Here, the second mirror 5 is a mirror (end face mirror) provided on the end face of the semiconductor gain chip 1. The invention is not limited to this, and a DBR mirror or the like may be used.
The shortwave side monitoring unit 6 includes a shortwave side photodetector 6A that detects a shortwave side monitor light having a wavelength shorter by one cycle of the signal light wavelength than the shortest wavelength among the plurality of signal lights (here, λ ₀ ), and a shortwave And a short-wave mirror 6B that reflects a part of the side monitor light, and is connected to the wavelength spectral filter 3.

  Here, the wavelength spectral filter 3 is provided with a short-wave side monitoring port for inputting / outputting short-wave side monitoring light having a wavelength shorter by one cycle of the signal light wavelength than the shortest wavelength among the plurality of signal lights, and the short-wave side monitoring port The monitoring waveguide 6C is connected, the shortwave side monitoring waveguide 6C is branched into two, the shortwave side mirror 6B is connected to one, the shortwave side photodetector 6A is connected to the other, and the shortwave side photodetector is connected. 6A is connected to the control unit 8 so that the output of the short wave side photodetector 6A is sent to the control unit 8.

The long wave side monitor unit 7 includes a long wave side photodetector 7A that detects a long wave side monitor light having a wavelength (λ _{N + 1 in this case} ) longer than the longest wavelength among the plurality of signal lights by one period, and a long wave And a long-wave mirror 7B that reflects part of the side monitor light, and is connected to the wavelength spectral filter 3.
Here, the wavelength spectroscopic filter 3 is provided with a long wave side monitor port for inputting / outputting a long wave side monitor light having a wavelength longer by one period of the signal light wavelength than the longest wavelength among the plurality of signal lights, and the long wave side thereof The monitoring waveguide 7C is connected, the long-wave side monitoring waveguide 7C is branched into two, the long-wave side mirror 7B is connected to one side, the long-wave side photodetector 7A is connected to the other side, and the long-wave side photodetector is connected. 7 A is connected to the control unit 8 so that the output of the long wave side photodetector 7 A is sent to the control unit 8.

As described above, the short-wave side monitoring port and the long-wave side monitoring port are provided on both sides of the signal light output port of the wavelength spectroscopic filter 3, and the wavelength (here, λ ₀ ) and one period of the short wave are one period longer than the signal light. The wavelength of the long wave (here, λ _{N + 1} ) can be monitored.
The controller 8 adjusts the gain peak of the semiconductor gain chip 1 to the wavelength of the short-wave monitor light (here, λ ₀ ) or the wavelength of the long-wave monitor light (here, in a state where the peak wavelength of the periodic wavelength filter 2 is matched to the grid wavelength. Then, in accordance with λ _{N + 1} ), control is performed to adjust the wavelength position of the wavelength spectral filter 3 so that the output of the short wave side photodetector 6A or the long wave side photodetector 7A is maximized. The control unit 8 is also referred to as a controller.

  In particular, the controller 8 adjusts the gain peak of the semiconductor gain chip 1 to the wavelength of the short-wave monitor light in a state where the peak wavelength of the periodic wavelength filter 2 is matched to the grid wavelength, and the output of the short-wave photodetector 6A is Control is performed to adjust the wavelength position of the wavelength spectral filter 3 so as to be maximized, and the output of the long wave side photodetector 7A is maximized by adjusting the gain peak of the semiconductor gain chip 1 to the wavelength of the long wave side monitor light. Thus, it is preferable to perform control for adjusting the wavelength position of the wavelength spectral filter 3.

Further, it is assumed that a photodetector 11 connected to the periodic wavelength filter 2 and detects monitor light branched from the periodic wavelength filter 2 is provided, and the control unit 8 is based on the output of the photodetector 11. It is also preferable to perform control to adjust the peak wavelength of this to the grid wavelength.
In this case, the periodic wavelength filter 2 is provided with a monitor port, to which the photodetector 11 is connected via the monitor waveguide 12, and the photodetector 11 is connected to the control unit 8. The output may be sent to the control unit 8.

The monitor light branched from the periodic wavelength filter 2 may be ASE light or oscillated light having an arbitrary wavelength.
It is also preferable that a plurality of phase adjustment mechanisms (phase control mechanisms) 13 provided between the wavelength spectral filter 3 and the plurality of first mirrors 4 are provided.
Here, the wavelength spectroscopic filter 3 is provided with a port for inputting / outputting each of a plurality of signal lights, each signal light waveguide 14 is connected thereto, and each signal light waveguide 14 is branched into two, The first mirror 4 is connected to the other, the other is connected to the output side, and the phase adjusting mechanism 13 is provided in one branch waveguide to which the first mirror 4 is connected. Here, N phase adjusting mechanisms 13 are provided. Here, the phase adjustment mechanism 13 is a phase adjuster in which phase control heaters H _{1 to} H _N are provided in the optical waveguide (see, for example, FIG. 2).

Further, a plurality of modulators (optical modulators) 15 that are optically connected to the wavelength spectral filter 3 and modulate each signal light divided by the wavelength spectral filter 3, and a plurality of modulators 15 are connected. And a multiplexer 16 that multiplexes the signal lights modulated by the modulators 15.
That is, as described above, a plurality of modulators 15 and a multiplexer 16 are further integrated (monolithically integrated in this case) on an integrated circuit substrate on which the periodic wavelength filter 2, the wavelength spectral filter 3, and the like are integrated, and wavelength spectroscopy is performed. Each signal light that is split by the filter 3 and output from each port may be modulated by each of the plurality of modulators 15, and each modulated light may be combined by the multiplexer 16 and output. .

Here, the modulator 15 is connected to the other branching waveguide that branches the signal light waveguides 14 connected to the wavelength spectral filter 3.
Since it is configured as described above, the light from the semiconductor gain chip 1 passes through the periodic wavelength filter 2 and the wavelength spectroscopic filter 3 and reaches the first mirror 4 on the extension line of the waveguide branched through each port. Reach and reflect. The reflected light is guided to the wavelength spectroscopic filter 3, the periodic wavelength filter 2, and the semiconductor gain chip 1, and reflected by the second mirror 5 provided on the opposite end face of the semiconductor gain chip 1. In this way, resonance occurs in the external resonator 11 composed of the first mirror 4 and the second mirror 5, and simultaneous oscillation occurs at the wavelength interval of the periodic wavelength filter 2 that is the wavelength interval of each signal light.

At this time, the oscillation wavelength is adjusted according to the following procedure.
First, as shown in FIG. 6, the offset of the periodic wavelength filter 2 is adjusted (step S1).
For example, the drive current of the semiconductor gain chip 1 is adjusted to the condition that the gain band covers N wavelengths (N wavelength oscillation condition), that is, the gain peak of the semiconductor gain chip 1 is the middle wavelength (λ _{N The} operating conditions are adjusted so as to be _{/ 2} ), the monitor light (transmitted light) guided from the monitor port of the periodic wavelength filter 2 is monitored, and the offset with respect to the WDM grid wavelength is adjusted.

Next, the offset of the wavelength spectral filter 3 is adjusted (step S2). That is, the offset of the wavelength spectral filter 3 with respect to the WDM grid wavelength is adjusted while maintaining the state of the periodic wavelength filter 2 that has been adjusted as described above.
First, adjustment is performed using short-wavelength monitor light (wavelength λ ₀ ) that is one cycle shorter than the simultaneous oscillation signal light (step S21).

For example, the drive current of the semiconductor gain chip is adjusted so that the gain peak becomes λ ₀ , the monitor light is oscillated at the wavelength λ ₀ on the short wave side, and the short wave side monitor provided on one side of the wavelength spectral filter 3 The short-wave side monitor light guided from the optical port is monitored, that is, the wavelength shift with the transmitted light from the periodic wavelength filter 2 is observed, and the offset of the wavelength spectral filter 3 with respect to the WDM grid wavelength is adjusted.

Next, adjustment is performed using the long-wave monitor light (wavelength λ _{N + 1} ) that is one cycle longer than the simultaneous oscillation signal light (step S22).
For example, the drive current of the semiconductor gain chip 1 is adjusted so that the gain peak becomes the wavelength λ _{N + 1} , the monitor light is oscillated at the wavelength λ _{N + 1} on the long wave side, and the long wave provided on the other side of the wavelength spectral filter 3 The long-wave side monitor light guided from the side monitor port is monitored, that is, the wavelength shift with the transmitted light from the periodic wavelength filter 2 is observed, and the offset of the wavelength spectral filter 3 with respect to the WDM grid wavelength is adjusted.

As a result, when the wavelength position of the wavelength spectral filter 3 determined by the adjustment using the short-wave monitor light is not changed by the adjustment using the long-wave monitor light, that is, readjustment is necessary. If not, the process proceeds to the NO route in step S3 to complete the adjustment.
On the other hand, if the wavelength position of the wavelength spectroscopic filter 3 determined by the adjustment using the short-wave monitor light previously performed is changed by the adjustment using the long-wave monitor light, the process proceeds to the YES route in step S3. Then, the adjustment (fine adjustment) is performed again using the short-wave monitor light (wavelength λ ₀ ) (step S21).

Thereafter, the adjustment is repeated until the wavelength position of the wavelength spectral filter 3 determined by the adjustment performed immediately before is not changed.
In this way, the transmitted light (signal light wavelength) from the periodic wavelength filter 2 and the wavelength spectral filter 3 can be matched with the WDM grid wavelength.
The readjustment may be performed only when the wavelength position is greatly changed with respect to the wavelength position of the wavelength spectral filter 3 determined by the adjustment performed immediately before.

In addition, here, the adjustment using the long-wave monitor light is performed after the adjustment using the short-wave monitor light. However, the adjustment is not limited to this, and the adjustment using the long-wave monitor light is performed. The adjustment using the short-wave monitor light may be performed later, or only one of the adjustments may be performed.
In this way, adjustment is performed using monitor light at wavelengths (λ _0, λ _{N + 1} ) different from those during actual operation, and signal light (λ _{1 to} λ _N ) for monitoring is branched during actual operation. Therefore, optical loss during actual operation can be suppressed.

By the way, the reason described above is as follows.
In recent years, a multiwavelength simultaneous oscillation laser has been realized with a structure in which a periodic wavelength filter is inserted in an external cavity of an external cavity type quantum dot laser, and a stable oscillation spectrum can be obtained (for example, see Non-Patent Document 1). Application to is expected.
In such a laser structure, since a periodic wavelength filter is used, a desired wavelength interval can be easily realized with good reproducibility.

However, for practical use, it is necessary to adjust the oscillation wavelength of the laser so that it oscillates within the grid required by the WDM system (offset wavelength adjustment). For example, the temperature of the periodic wavelength filter is changed. Wavelength adjustment is performed.
On the other hand, it is necessary that the relative intensity noise (RIN) of the signal light spectrum cut out by one wavelength is −135 dB / Hz or less.

However, it is difficult to suppress RIN to −135 dB / Hz or less at all oscillation wavelengths.
In order to obtain good RIN at all wavelengths, it is preferable that all wavelengths are in phase.
However, for example, when a multi-wavelength simultaneous oscillation laser oscillates four wavelengths simultaneously, it is difficult to adjust so as to obtain a desired phase at all four wavelengths in order to oscillate with the same resonator length.

Therefore, in order to avoid this problem, it is conceivable to perform phase control (phase adjustment) at each oscillation wavelength.
For this reason, it is possible to take out all the wavelengths into separate optical waveguides and to provide a phase adjustment mechanism for each wavelength (see, for example, FIG. 9).
In this case, a configuration in which a periodic wavelength filter and a wavelength spectral filter having the same filter transmission wavelength period are combined in series is adopted.

However, since the periodic wavelength filter and the wavelength spectral filter have different offsets with respect to the WDM grid wavelength, if they are connected in series, even if the oscillation wavelength is evaluated only by the output unit, the offset of the two filters is reduced. Since it cannot be estimated individually, it becomes very difficult to control to a desired oscillation wavelength.
Therefore, even when the periodic wavelength filter 2 and the wavelength spectral filter 3 are connected in series, the above-described configuration is performed so that a desired oscillation wavelength can be obtained.

  Thereby, by providing the phase adjustment mechanism 13, the signal light can be phase-adjusted at each wavelength, the relative intensity noise (RIN) of the signal light can be reduced, and the wavelength adjustment with respect to the grid wavelength of the signal light is possible. It becomes. As a result, the oscillation wavelength of each signal light can be adjusted and the phase can be controlled with a simple structure, and a high-performance multi-wavelength simultaneous oscillation laser can be realized.

Hereinafter, a specific example will be described with reference to FIG.
In this specific example, a ring resonator is used for the periodic wavelength filter 2, an AWG is used for the wavelength spectral filter 3, a ring mirror is used for the first mirror 4, and these are monolithically integrated on the Si substrate 10, and a Si fine line optical fiber is integrated. Further, the modulator 15 and the multiplexer 16 are monolithically integrated elements connected by the waveguide 17, the light oscillated by the external resonator 11 is modulated by the modulator 15, and each modulated light is multiplexed by the multiplexer 16. The light is combined (condensed) and transmitted from the output port of the integrated element to the optical fiber. The wavelengths of the plurality of signal lights are λ ₁ to λ _N.

Then, the ring resonator as a periodic wavelength filter 2 is provided with a wavelength control heater H _R, which are periodic wavelength filter power supply 19 is connected to, this period wavelength filter power supply 19, control unit 8 is controlled.
Further, the wavelength control heater H _AWG is also provided in the AWG as the wavelength spectral filter 3, and the wavelength spectral filter power source 20 is connected to the wavelength control heater H _AWG . To be controlled.

Further, each signal light waveguide 14 connected to the wavelength spectral filter 3 is branched into two, one side is connected to a ring mirror as the first mirror 4, and the other side is connected to the modulator 15, and the first mirror is connected. Phase control heaters H _{1 to} H _N constituting the phase adjustment mechanism 13 are provided in _one branch waveguide to which 4 is connected. A phase adjustment mechanism power source 21 is connected to the phase control heaters H _{1 to} H _N constituting the phase adjustment mechanism 13 so that the phase adjustment mechanism power source 21 is controlled by the control unit 8. It has become.

In addition, a Mach-Zehnder type modulator is used as the modulator 15, and a modulation signal source 22 is connected to a modulation electrode 23 provided on the modulator 15. The modulation signal source 22 is controlled by the control unit 8. It has become.
Further, as the short-wave side monitoring unit 6, a short-wave side monitoring waveguide 6C for guiding the short-wave side monitoring light (wavelength λ ₀ ) is connected to the wavelength spectral filter 3, and the two short-wave side monitoring waveguides 6C are connected. Branch, connect a loop mirror as the shortwave side mirror 6B to one side, connect a photodetector (PD) as the shortwave side photodetector 6A to the other side, connect the shortwave side photodetector 6A to the control unit 8, The output of the short wave side photodetector 6A is sent to the control unit 8.

Further, as the long wave side monitor unit 7, a long wave side monitor waveguide 7C for guiding the long wave side monitor light (wavelength λ _{N + 1} ) is connected to the wavelength spectral filter 3, and the long wave side monitor waveguide 7C is branched into two. Then, a loop mirror as the long wave side mirror 7B is connected to one side, a photodetector (PD) as the long wave side photodetector 7A is connected to the other side, the long wave side photodetector 7A is connected to the control unit 8, and the long wave side The output of the side light detector 7A is sent to the control unit 8.

  Further, a photodetector (PD) as a photodetector 11 is connected to the periodic wavelength filter 2 via the monitoring waveguide 12, and the photodetector 11 is connected to the control unit 8 so that the output of the photodetector 11 is controlled. It is sent to the part 8. Here, a filter 24 is provided in the monitoring waveguide 12. That is, when ASE light is used as the monitor light, a bandpass filter is provided as the filter 24 in the monitor waveguide 12, and when oscillation light is used as the monitor light, a band stop is provided as the filter 24 in the monitor waveguide 12. Provide a filter. As these filters 24, for example, a multilayer filter used in a spatial optical system may be used by being inserted into the Si substrate 10.

  In addition, a quantum dot gain chip is used as the semiconductor gain chip 1, an HR film provided on the end face of the quantum dot gain chip 1 is provided as the second mirror 5, and Si connected to the ring resonator as the periodic wavelength filter 2 is provided. The quantum dot gain chip 1 is mounted on the Si substrate 10 so as to be optically connected to the thin-line optical waveguide 17. A semiconductor gain chip power source 18 is connected to the semiconductor gain chip 1, and the semiconductor gain chip power source 18 is controlled by the control unit 8.

In the multi-wavelength laser device 9 of the specific example configured as described above, the wavelength position is adjusted as follows.
First, the offset of the periodic wavelength filter 2 is adjusted (wavelength position adjustment) (see, for example, step S1 in FIG. 6).
Here, a case where oscillation light is used as monitor light will be described as an example.

First, the control unit 8 controls the semiconductor gain chip power supply 18 so as to cover the drive current of the quantum dot gain chip 1 under the condition that the gain band covers the wavelengths λ _{1 to} λ _N of the signal light, that is, the signal light It is adjusted to a value (I _N ) that oscillates simultaneously at wavelengths λ _{1 to} λ _N. As a result, the external resonator 11 constituted by the end face mirror 5 and the loop mirror 4 provided in the quantum dot gain chip 1 is simultaneously oscillated at the wavelengths λ _{1 to} λ _N of the signal light.

Next, the monitor light guided from the monitoring port (transmission port) of the periodic wavelength filter 2 is monitored to adjust the offset with respect to the WDM grid wavelength.
Here, the control unit 8 controls the periodic wavelength filter power supply 19, to change the temperature of the wavelength control heater H _R provided the wavelength of the oscillation light in the period wavelength filter 2 periodically filtering.

Then, the control unit 8 is guided through the monitoring waveguide 12 and is detected by the photodetector (PD) 11 through the band stop filter as the filter 24 (for example, oscillation light having a wavelength λ ₁ ). The heater temperature is adjusted so that the intensity of the monitor light (light intensity) is minimized.
Here, the band-stop filter 24, as shown in FIG. 7 (D), a characteristic of blocking without transmitting light of wavelength lambda _1, i.e., the property of light of a wavelength other than the wavelength lambda ₁ is transmitted As shown in FIG. 2, it is installed immediately before the photodetector 11.

In this manner, by adjusting the heater temperature so that the intensity of the monitor light is minimized, the offset of the periodic wavelength filter 2 can be adjusted, that is, the offset with respect to the WDM grid wavelength can be adjusted on the grid. It can oscillate.
Here, the case where the wavelength offset adjustment is performed using the oscillation light as the monitor light is described as an example. However, the present invention is not limited to this. For example, the ASE of the quantum dot gain chip 1 is used as the monitor light. Wavelength offset adjustment may be performed using light. In this case, a band pass filter may be provided as the filter 24 in place of the band stop filter described above, and the heater temperature may be adjusted so that the intensity of the monitor light is minimized.

Here, the light from the transmission port of the ring resonator filter as the periodic wavelength filter 2 has a wavelength whose light intensity periodically decreases [see, for example, FIG. 7B], and this wavelength is a multiwavelength oscillation. It matches the wavelength. Therefore, for example, the light having the shortest wavelength λ ₁ of the signal light is used as the monitor light. For example, as shown in FIG. 7A, the bandpass filter 24 transmits the light having the wavelength λ _1. What is necessary is just to have. In this case, as shown in FIG. 7C, when the optical spectrum of the monitor light [see, for example, FIG. 7B] matches the transmission band (here, wavelength λ ₁ ) in the filter characteristics of the bandpass filter 24, the monitor The light intensity will be minimal.

Further, by using a narrow line width band stop filter or a narrow line width band pass filter as the filter 24, the periodic wavelength filter 2 can be adjusted so that signal light oscillates at the center of the grid. It becomes possible.
Here, the case where the monitor light is, for example, light having a wavelength λ ₁ is described as an example. However, in consideration of the manufacturing margin of the periodic wavelength filter 2, a band stop filter or a band pass filter as the filter 24 is used. Is preferably a narrow line width filter having a characteristic of blocking or transmitting light having a wavelength λ _{N / 2} near the center of the simultaneous oscillation wavelength.

Next, offset adjustment (wavelength position adjustment) of the wavelength spectral filter 3 is performed (see, for example, step S2 in FIG. 6). That is, the offset of the wavelength spectral filter 3 with respect to the WDM grid wavelength is adjusted while maintaining the state of the periodic wavelength filter 2 that has been adjusted as described above.
First, adjustment is performed using short-wavelength monitor light (wavelength λ ₀ ) that is one cycle shorter than the simultaneous oscillation signal light (see, for example, step S21 in FIG. 6).

First, the control unit 8 controls the power source 18 for the semiconductor gain chip to change the drive current of the quantum dot gain chip 1 so that the gain peak (the center wavelength of the gain spectrum) becomes the wavelength λ ₀ [Fig. 8 (A), adjust the position of reference X]. As a result, the monitor light is oscillated at the wavelength λ ₀ on the short wave side and used as the short wave side monitor light. In FIG. 8A, the symbol Z indicates the transmission spectrum of the periodic wavelength filter 2.

Next, the control unit 8 monitors the short-wave monitor light guided from the short-wave monitor port provided on one side of the wavelength spectral filter 3, and adjusts the offset of the wavelength spectral filter 3 with respect to the WDM grid wavelength. Do.
Here, the control unit 8 controls the wavelength spectral filter power source 20 to change the temperature of the wavelength control heater H _AWG provided in the wavelength spectral filter 3. As a result, the transmission spectrum of the wavelength spectral filter 3 [see, for example, symbol Y in FIG. 8A] moves.

Then, the control unit 8 monitors the intensity of the monitor light (oscillation light having the wavelength λ ₀ on the short wave side) guided by the short wave side monitoring waveguide 6C and detected by the short wave side photodetector (PD) 6A. Then, the heater temperature is adjusted so that the intensity of the monitor light (the output of the short-wave monitor unit) is maximized.
Next, adjustment is performed using long-wave monitor light (wavelength λ _{N + 1} ) that is one cycle longer than the simultaneous oscillation signal light (see, for example, step S22 in FIG. 6).

First, the control unit 8 controls the power source 18 for the semiconductor gain chip to change the drive current of the quantum dot gain chip 1 so that the gain peak (the center wavelength of the gain spectrum) becomes the wavelength λ _{N + 1} . 8 (B), adjust the position of reference X]. Thereby, the monitor light is oscillated at the wavelength λ _{N + 1} on the long wave side, and this is used as the long wave side monitor light. In FIG. 8B, the symbol Z indicates the transmission spectrum of the periodic wavelength filter 2.

Next, the control unit 8 monitors the long-wave monitor light guided from the long-wave monitor port provided on the other side of the wavelength spectral filter 3 and adjusts the offset of the wavelength spectral filter 3 with respect to the WDM grid wavelength. Do.
Here, the control unit 8 controls the wavelength spectral filter power source 20 to change the temperature of the wavelength control heater H _AWG provided in the wavelength spectral filter 3. As a result, the transmission spectrum of the wavelength spectral filter 3 [see, for example, symbol Y in FIG. 8B] moves.

Then, the control unit 8 monitors the intensity of the monitor light (oscillation light having the wavelength λ _{N + 1} on the long wave side) guided by the long wave side monitoring waveguide 7C and detected by the long wave side photodetector (PD) 7A. Then, the heater temperature is adjusted so that the intensity of the monitor light (the output of the long wave side monitor unit) is maximized.
Here, when performing adjustment using the long-wave side monitor light (wavelength λ _{N + 1} ), the wavelength is set so that the intensity of the monitor light is maximized when the intensity of the monitor light is not maximized (maximum value). When the temperature of the wavelength control heater H _AWG provided in the spectral filter 3 is adjusted (readjusted) and the intensity of the monitor light is maximized (maximum value), the wavelength control provided in the wavelength spectral filter 3 The temperature of the heater H _AWG is not adjusted (readjusted).

As a result, the wavelength position of the wavelength spectral filter 3 determined by the adjustment using the short-wave monitor light (wavelength λ ₀ ) performed earlier is not changed by the adjustment using the long-wave monitor light (wavelength λ _{N + 1} ). In other words, if the readjustment is not necessary, the adjustment is completed (for example, refer to the NO route in step S3 in FIG. 6).
Here, since the window of the wavelength spectral filter 3 is wide, in order to increase the accuracy of adjustment of the offset, in addition to the adjustment using the short-wave monitor light (wavelength λ ₀ ), such a long-wave monitor light (wavelength λ _{N + 1} ) is used for the adjustment and both are checked.

On the other hand, when the wavelength position of the wavelength spectral filter 3 determined by the adjustment using the short-wave monitor light (wavelength λ ₀ ) is changed by the adjustment using the long-wave monitor light (wavelength λ _{N + 1} ). In this case, adjustment (fine adjustment) is performed again using the short-wave monitor light (wavelength λ ₀ ) (see, for example, the YES route in step S3 in FIG. 6).
That is, it is confirmed whether or not the intensity of the monitor light is maximized by using the short wavelength side monitor light (wavelength λ ₀ ), and the intensity of the monitor light is maximized when the intensity of the monitor light is not maximized. As described above, the temperature of the wavelength control heater H _AWG provided in the wavelength spectral filter 3 is adjusted (finely adjusted).

Thereafter, the adjustment is repeated until the wavelength position of the wavelength spectral filter 3 determined by the adjustment performed immediately before is not changed.
That is, the light transmitted through the periodic wavelength filter 2 and the wavelength spectral filter 3 is the maximum value in both the adjustment using the short-wave monitor light (wavelength λ ₀ ) and the adjustment using the long-wave monitor light (wavelength λ _{N + 1} ). If they match, the adjustment of the wavelength spectral filter 3 is completed at that time.

In this way, by using the short-wave side monitor light (wavelength λ ₀ ) and the long-wave side monitor light (wavelength λ _{N + 1} ), the wavelength of the spectral filter 3 is adjusted by adjusting the heater temperature so that the intensity of the monitor light is maximized. Offset adjustment, that is, offset adjustment with respect to the WDM grid wavelength.
Here, since the full width at half maximum of the transmission spectrum of the wavelength spectral filter 3 is relatively wide, the two wavelengths of the short wavelength side monitor light (wavelength λ ₀ ) and the long wavelength side monitor light (wavelength λ _{N + 1} ) are used. By adjusting the offset, the adjustment can be performed with higher accuracy than in the case of performing the adjustment with one wavelength.

If adjustment can be performed with good accuracy by adjusting only one wavelength, for example, one of the short-wave monitor light (wavelength λ ₀ ) and the long-wave monitor light (wavelength λ _{N + 1} ), etc. The offset adjustment of the wavelength spectral filter 3 may be performed using two wavelengths.
After such adjustment, when using a multi-wavelength laser, the drive current of the semiconductor gain chip (quantum dot gain chip) 1 is covered, and the gain band covers the wavelengths λ _{1 to} λ _N of the signal light. Adjust to

In the specific example described above, the periodic wavelength filter 2 and the wavelength spectral filter 3 are provided with wavelength control heaters H _R and H _AWG , and wavelength control is performed using a refractive index change due to heating. However, the present invention is not limited to this. For example, wavelength control may be performed using current injection or voltage application, and a current injection electrode or a voltage application electrode may be provided.
By the way, the multi-wavelength laser device 9 as described above is used, for example, in a wavelength division multiplexing (WDM) optical communication system (wavelength multiplexing communication system) (see, for example, FIG. 10). In this case, the wavelength division multiplexing communication system is configured to include a transmitter including the multi-wavelength laser device 9 and a receiver connected to the transmitter via a transmission path.

  That is, for example, as shown in FIG. 10, a transmitter 26 including a multi-wavelength simultaneous oscillation laser (comb laser) 29, a duplexer (demultiplexer) 30, a modulator (modulator array) 31, and a multiplexer (multiplexer) 32; In a wavelength division multiplexing communication system 25, a demultiplexer (demultiplexer) 33 and a receiver 27 including a photodetector (detector array) 34 are connected by a transmission line 28 such as an optical fiber (for example, a single mode fiber link). The multi-wavelength laser device 9 can be used as the multi-wavelength simultaneous oscillation laser 29 and the duplexer 30 provided in the transmitter 26.

Therefore, the multi-wavelength laser device and the wavelength division multiplexing communication system according to this embodiment suppress the optical loss of signal light and obtain a desired oscillation wavelength when the periodic wavelength filter 2 and the wavelength spectral filter 3 are connected in series. Has the effect of being
In particular, in the present embodiment, the multi-wavelength simultaneous oscillation laser (quantum dot gain chip 1) can shift the gain peak wavelength by adjusting the drive current. The wavelength is changed to λ ₀ or λ _{N + 1} and used as a light source for offset adjustment. In the multi-wavelength simultaneous oscillation laser (quantum dot gain chip 1), when a current is injected (when the current injection amount is increased), the gain peak (the center wavelength of the gain spectrum) moves to the long wave side. Will go. For this reason, there is no need to provide a separate light source for offset adjustment, and there is no need to add an adjustment mechanism such as a complicated control circuit, and a multi-wavelength simultaneous oscillation laser with a monitoring function of the wavelength spectral filter 3 can be realized with a simple structure. can do.

Further, in the present embodiment, a method of monitoring the short-wave side monitor light (wavelength λ ₀ ) and the long-wave side monitor light (wavelength λ _{N + 1} ) is used, and a method of branching and monitoring the signal light is not used. It is also possible to make the optical loss relatively small during the multi-wavelength simultaneous oscillation operation.
In addition, this invention is not limited to the structure described in embodiment mentioned above, A various deformation | transformation is possible in the range which does not deviate from the meaning of this invention.

Hereinafter, additional notes will be disclosed regarding the above-described embodiment.
(Appendix 1)
A semiconductor gain chip;
A periodic wavelength filter optically connected to the semiconductor gain chip and having a periodic peak wavelength;
A wavelength spectroscopic filter that is connected in series to the periodic wavelength filter and divides a plurality of signal lights for each wavelength;
A plurality of first mirrors optically connected to the wavelength spectral filter and reflecting a part of each signal light divided by the wavelength spectral filter;
A second mirror provided on the opposite side of the semiconductor gain chip from the side on which the periodic wavelength filter is provided, and constituting an external resonator between the plurality of first mirrors;
A short-wave side photodetector connected to the wavelength spectroscopic filter and detecting a short-wave side monitor light having a wavelength shorter by one period of the signal light wavelength than the shortest wavelength among the plurality of signal lights; and the short-wave side monitor light A short-wave side monitor unit including a short-wave side mirror that partially reflects,
A long wave side photodetector connected to the wavelength spectroscopic filter and detecting a long wave side monitor light having a wavelength longer by one period of the signal light wavelength than the longest wavelength among the plurality of signal lights; and the long wave side monitor light A long-wave side monitor unit including a long-wave side mirror that partially reflects,
In a state where the peak wavelength of the periodic wavelength filter is matched with the grid wavelength, the short wavelength side photodetector or the gain peak of the semiconductor gain chip is matched with the wavelength of the short wavelength side monitor light or the long wavelength side monitor light. A multi-wavelength laser device comprising: a control unit that performs control to adjust a wavelength position of the wavelength spectral filter so that an output of the long wave side photodetector is maximized.

(Appendix 2)
In the state where the peak wavelength of the periodic wavelength filter is adjusted to the grid wavelength, the control unit adjusts the gain peak of the semiconductor gain chip to the wavelength of the shortwave monitor light, and the output of the shortwave photodetector is maximum. So that the wavelength position of the wavelength spectral filter is adjusted so that the gain peak of the semiconductor gain chip matches the wavelength of the long-wave monitor light, and the output of the long-wave photodetector is maximized. The multi-wavelength laser apparatus according to appendix 1, wherein control is performed to adjust the wavelength position of the wavelength spectral filter.

(Appendix 3)
A photodetector connected to the periodic wavelength filter and detecting monitor light branched from the periodic wavelength filter;
The multi-wavelength laser apparatus according to appendix 1 or 2, wherein the control unit performs control to adjust a peak wavelength of the periodic wavelength filter to a grid wavelength based on an output of the photodetector.

(Appendix 4)
The multi-wavelength laser device according to any one of appendices 1 to 3, further comprising a plurality of phase adjustment mechanisms respectively provided between the wavelength spectral filter and the plurality of first mirrors.
(Appendix 5)
The multi-wavelength laser device according to any one of appendices 1 to 4, wherein the semiconductor gain chip includes a quantum dot gain medium.

(Appendix 6)
A plurality of modulators that are optically connected to the wavelength spectral filter and modulate each signal light divided by the wavelength spectral filter;
6. The apparatus according to any one of appendices 1 to 5, further comprising a multiplexer that is connected to the plurality of modulators and multiplexes the signal lights modulated by the plurality of modulators. Multi-wavelength laser device.

(Appendix 7)
The multi-wavelength laser apparatus according to any one of appendices 1 to 6, wherein the wavelength spectral filter is a filter using an arrayed waveguide diffraction grating.
(Appendix 8)
The multiwavelength laser apparatus according to appendix 7, wherein the wavelength spectral filter is provided with a multimode interference coupler in an optical input / output unit.

(Appendix 9)
The multiwavelength laser device according to any one of appendices 1 to 8, wherein the periodic wavelength filter is a filter using a ring resonator.
(Appendix 10)
A transmitter comprising a multi-wavelength laser device;
A receiver connected to the transmitter via a transmission line;
The multi-wavelength laser device is
A semiconductor gain chip;
A periodic wavelength filter optically connected to the semiconductor gain chip and having a periodic peak wavelength;
A wavelength spectroscopic filter that is connected in series to the periodic wavelength filter and divides a plurality of signal lights for each wavelength;
A plurality of first mirrors optically connected to the wavelength spectral filter and reflecting a part of each signal light divided by the wavelength spectral filter;
A second mirror provided on the opposite side of the semiconductor gain chip from the side on which the periodic wavelength filter is provided, and constituting an external resonator between the plurality of first mirrors;
A short-wave side photodetector connected to the wavelength spectroscopic filter and detecting a short-wave side monitor light having a wavelength shorter by one period of the signal light wavelength than the shortest wavelength among the plurality of signal lights; and the short-wave side monitor light A short-wave side monitor unit including a short-wave side mirror that partially reflects,
A long wave side photodetector connected to the wavelength spectroscopic filter and detecting a long wave side monitor light having a wavelength longer by one period of the signal light wavelength than the longest wavelength among the plurality of signal lights; and the long wave side monitor light A long-wave side monitor unit including a long-wave side mirror that partially reflects,
In a state where the peak wavelength of the periodic wavelength filter is matched with the grid wavelength, the short wavelength side photodetector or the gain peak of the semiconductor gain chip is matched with the wavelength of the short wavelength side monitor light or the long wavelength side monitor light. A wavelength division multiplexing communication system comprising: a control unit that performs control to adjust a wavelength position of the wavelength spectral filter so that an output of the long wave side photodetector is maximized.

1 Semiconductor gain chip (quantum dot gain chip)
2 Periodic wavelength filter 2A DBR
2B Loop mirror 2C DBR
2D DBR
2E DBR
2F cleavage surface 3 wavelength spectral filter 3A MMI portion 3B diffraction grating surface 4 first mirror 5 second mirror 6 short wave side monitor unit 6A short wave side photodetector 6B short wave side mirror 6C short wave side monitor waveguide 7 long wave side monitor unit 7A Long wave side photodetector 7B Long wave side mirror 7C Waveguide for long wave side monitor 8 Control unit 9 Multi-wavelength laser device (multi-wavelength simultaneous oscillation laser)
DESCRIPTION OF SYMBOLS 10 Board | substrate 11 Photodetector 12 Waveguide for monitoring 13 Phase adjustment mechanism (phase control mechanism)
DESCRIPTION OF SYMBOLS 14 Signal light waveguide 15 Modulator 16 Mux 17 Si thin-line optical waveguide 18 Semiconductor gain chip power supply 19 Periodic wavelength filter power supply 20 Wavelength spectral filter power supply 21 Phase adjustment mechanism power supply 22 Modulation signal source 23 Modulation electrode 24 filters (band pass filter; band stop filter)
25 wavelength multiplex communication system 26 transmitter 27 receiver 28 transmission path 29 multi-wavelength simultaneous oscillation laser (comb laser)
30 demultiplexer
31 Modulator (Modulator array)
32 multiplexer (multiplexer)
33 Demultiplexer
34 Photodetector (detector array)

Claims (7)

A semiconductor gain chip;
A periodic wavelength filter optically connected to the semiconductor gain chip and having a periodic peak wavelength;
A wavelength spectroscopic filter that is connected in series to the periodic wavelength filter and divides a plurality of signal lights for each wavelength;
A plurality of first mirrors optically connected to the wavelength spectral filter and reflecting a part of each signal light divided by the wavelength spectral filter;
A second mirror provided on the opposite side of the semiconductor gain chip from the side on which the periodic wavelength filter is provided, and constituting an external resonator between the plurality of first mirrors;
A short-wave side photodetector connected to the wavelength spectroscopic filter and detecting a short-wave side monitor light having a wavelength shorter by one period of the signal light wavelength than the shortest wavelength among the plurality of signal lights; and the short-wave side monitor light A short-wave side monitor unit including a short-wave side mirror that partially reflects,
A long wave side photodetector connected to the wavelength spectroscopic filter and detecting a long wave side monitor light having a wavelength longer by one period of the signal light wavelength than the longest wavelength among the plurality of signal lights; and the long wave side monitor light A long-wave side monitor unit including a long-wave side mirror that partially reflects,
In a state where the peak wavelength of the periodic wavelength filter is matched with the grid wavelength, the short wavelength side photodetector or the gain peak of the semiconductor gain chip is matched with the wavelength of the short wavelength side monitor light or the long wavelength side monitor light. A multi-wavelength laser device comprising: a control unit that performs control to adjust a wavelength position of the wavelength spectral filter so that an output of the long wave side photodetector is maximized.   In the state where the peak wavelength of the periodic wavelength filter is adjusted to the grid wavelength, the control unit adjusts the gain peak of the semiconductor gain chip to the wavelength of the shortwave monitor light, and the output of the shortwave photodetector is maximum. So that the wavelength position of the wavelength spectral filter is adjusted so that the gain peak of the semiconductor gain chip matches the wavelength of the long-wave monitor light, and the output of the long-wave photodetector is maximized. The multi-wavelength laser apparatus according to claim 1, wherein control for adjusting a wavelength position of the wavelength spectral filter is performed. A photodetector connected to the periodic wavelength filter and detecting monitor light branched from the periodic wavelength filter;
The multi-wavelength laser device according to claim 1, wherein the control unit performs control to match a peak wavelength of the periodic wavelength filter with a grid wavelength based on an output of the photodetector.   4. The multi-wavelength laser device according to claim 1, further comprising a plurality of phase adjustment mechanisms respectively provided between the wavelength spectral filter and the plurality of first mirrors. 5.   The multi-wavelength laser device according to claim 1, wherein the semiconductor gain chip includes a quantum dot gain medium. A plurality of modulators that are optically connected to the wavelength spectral filter and modulate each signal light divided by the wavelength spectral filter;
6. The apparatus according to claim 1, further comprising: a multiplexer that is connected to the plurality of modulators and multiplexes each signal light modulated by each of the plurality of modulators. The multi-wavelength laser device described. A transmitter comprising a multi-wavelength laser device;
A receiver connected to the transmitter via a transmission line;
The multi-wavelength laser device is
A semiconductor gain chip;
A periodic wavelength filter optically connected to the semiconductor gain chip and having a periodic peak wavelength;
A wavelength spectroscopic filter that is connected in series to the periodic wavelength filter and divides a plurality of signal lights for each wavelength;
A plurality of first mirrors optically connected to the wavelength spectral filter and reflecting a part of each signal light divided by the wavelength spectral filter;
A second mirror provided on the opposite side of the semiconductor gain chip from the side on which the periodic wavelength filter is provided, and constituting an external resonator between the plurality of first mirrors;
A short-wave side photodetector connected to the wavelength spectroscopic filter and detecting a short-wave side monitor light having a wavelength shorter by one period of the signal light wavelength than the shortest wavelength among the plurality of signal lights; and the short-wave side monitor light A short-wave side monitor unit including a short-wave side mirror that partially reflects,
A long wave side photodetector connected to the wavelength spectroscopic filter and detecting a long wave side monitor light having a wavelength longer by one period of the signal light wavelength than the longest wavelength among the plurality of signal lights; and the long wave side monitor light A long-wave side monitor unit including a long-wave side mirror that partially reflects,
In a state where the peak wavelength of the periodic wavelength filter is matched with the grid wavelength, the short wavelength side photodetector or the gain peak of the semiconductor gain chip is matched with the wavelength of the short wavelength side monitor light or the long wavelength side monitor light. A wavelength division multiplexing communication system comprising: a control unit that performs control to adjust a wavelength position of the wavelength spectral filter so that an output of the long wave side photodetector is maximized.