JPH10326939A - Wavelength stabilization device for multiple wavelength light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength stabilization device for a multiple wavelength light source, capable of making the small number of photodetectors be sufficient, thus eliminating the need of a highly accurate circuit device and reducing ambient temperature dependency. SOLUTION: A signal light outputted from laser diodes 791 -79N inside an N wave multi-wavelength light source 61 is multiplexed in an optical multiplexer 63, and the part of it is demultiplexed in an optical demultiplexer 65 and turned to monitor light 67. The monitor light 67 is inputted to a wavelength variable filter 68, one kind of each of the wavelengths is successively selected and inputted to an optical cycle filter 72, and the signal light P1 and P2 of a through port and a cross port is detected. A control part 71 computes a feedback amount based on them, and the temperature of the corresponding laser diode 79 is adjusted in a temperature adjustment circuit 74. Thus, the two pieces of the photodetectors 73 are sufficient, and when the sweeping of the wavelength is performed, the need for a highly accurate circuit is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength stabilizing device for a multi-wavelength light source for stabilizing a light source in a multi-wavelength optical transmission system.

[0002]

2. Description of the Related Art In a multi-wavelength optical transmission system, light sources having a plurality of different wavelengths are prepared, and optical signals output from these light sources are multiplexed and transmitted.

[0003] FIG. 8 is a diagram showing wavelength reduction for a conventional multi-wavelength light source.
It is a representation of a stabilizing device. This device uses multi-wavelength light
Source 11 and a plurality of waves output from this multi-wavelength light source 11
Long λ ₁, Λ_Two, …… λ_NOptical multiplexer 12 for multiplexing
Is connected to the optical multiplexer 12 to transmit an optical signal.
The transmission line 13 is provided. The multi-wavelength light source 11
A wavelength meter 14 for monitoring is connected.

An optical demultiplexer 15 is arranged in the middle of the transmission line 13 so that a part of an optical signal transmitted through the transmission line 13 is demultiplexed as monitor light.
The demultiplexed monitor light is input to the sweep type variable wavelength filter 16. The sweep type variable wavelength filter 16 is connected to a filter sweep control circuit 17 for performing sweep control, and also connected to a photodetector 18 for detecting monitor light after passing through the filter. The detection output of the photodetector 18 is input to a peak detection and error calculation circuit 19. The filter sweep control circuit 17 is also connected to the peak detection and error calculation circuit 19 and the feedback loop selection control unit 21 and controls these.

Meanwhile, multi-wavelength light source 11 is lambda ₁ and the, lambda _2, ...... lambda _N laser diodes 23 ₁ ~ 23 _N of the first to N for outputting the optical signal of each wavelength separately in
When a temperature control circuit 24 for adjusting the temperature of these laser diodes 23 ₁ ~ 23 _N, and one wavelength monitoring laser diode 25, the wavelength monitor laser diode 2
And an AFC (Auto Frequency Control) circuit 26 for driving the drive 5. Here, the wavelength of the wavelength monitoring laser diode 25 is constantly monitored by the wavelength meter 14. The feedback loop selection control unit 21
... λ _N corresponding to the wavelengths of the wavelengths λ ₁ , λ ₂ ,... λ _N , and sequentially selects the error signals 27 output from the error detection circuit 19 and sends them to the temperature control circuit 24. 1st to Nth laser diodes 23 ₁
２３23 _N temperature control is performed.

In the wavelength stabilizing device for a multi-wavelength light source having such a configuration, the optical signals of the respective wavelengths λ ₁ , λ ₂ ,... Λ _N output from the multi-wavelength light source 11 shown in FIG. Table 12
And transmitted to the transmission line 13. A part thereof is input from the optical demultiplexer 15 to the sweep type variable wavelength filter 16 as monitor light. Filter sweep control circuit 1
7 periodically sweeps the wavelength to the sweep type variable wavelength filter 16, and the information of each peak wavelength of the monitor light is detected by the photodetector 18 on the electric pulse signal 3 on the time axis.
1 and converts it into a peak detection and error calculation circuit 1.
9.

FIG. 9 illustrates the operation of the filter sweep control circuit. FIG. 7A shows a state of the sweep filter 32 that changes the wavelength by the sweep type variable wavelength filter 16 shown in FIG. FIG. 6B shows an optical signal (WDM signal light wavelength) 33 of each of the wavelengths λ ₁ , λ ₂ ,... Λ _N as monitor light input to the sweep type variable wavelength filter 16. Figure (c)
Represents the waveform of the electric pulse signal 31 output from the photodetector 18 as a sweep result of the sweep filter 32. Here, as an example, each wavelength λ ₁ ,
The peak of the optical signal of λ ₂ ,... λ _N appears.

Returning to FIG. 8, the description will be continued. The peak detection and error calculation circuit 19 detects the respective peak positions of the electric pulse signal 31 and calculates the wavelengths λ ₁ , λ ₂ ,.
_A series of error signals 27 is calculated by comparing with a position set in advance as a position corresponding to _N. Error signal 27
Are sequentially input to the feedback loop selection control unit 21. The filter sweep control circuit 17 sequentially selects ones corresponding to the wavelengths λ ₁ , λ ₂ ,... Λ _N and sends them to the temperature control circuit 24 as error signals 27 _{1 to} 27 _N. Temperature control circuit 24
Are the _{first to first} error signals using these error signals 27 _{1 to} 27 _N.
By controlling the temperature of the laser diode 23 ₁ ~ 23 _N of the N, each wavelength λ _1, λ _2, to adjust the ...... λ _N. The wavelength of the wavelength monitoring laser diode 25 is constantly monitored by the wavelength meter 14, and an error from a specified wavelength is fed back to the AFC circuit 26. Therefore, by fixing the wavelength of the wavelength monitoring laser diode 25, all the wavelengths λ ₁ , λ ₂ ,.
Absolute wavelength stability for _N will be ensured.

FIG. 10 shows another example of a conventional wavelength stabilizing device for a multi-wavelength light source. In FIG.
The same reference numerals are used for the same parts as those described above, and the description thereof will be appropriately omitted. In FIG. 10, the multi-wavelength light source 41 is the first
To Nth laser diodes 23 ₁ to 23 _N and a temperature control circuit 24. An optical signal of each wavelength λ ₁ , λ ₂ ,... Λ _N output from the multi-wavelength light source 41 and an optical signal of an absolute wavelength serving as a reference output from the absolute reference light source 42 are input to the optical multiplexer 12. The signals are multiplexed and sent to the transmission line 13. Some of them are used as monitor light by the optical demultiplexer 15.
Is input to the wavelength discriminator 44.

[0010] The wavelength discriminator 44 operates for each wavelength.
The two transmitted light outputs, whose phases have been inverted, to adjacent ports
To get it. Each of these wavelengths λ₁, Λ_Two…
… Λ _NAnd the two transmitted light outputs for each absolute wavelength
Is input to the corresponding detection element of the output unit 45 and converted into an electric signal.
Is replaced. The pair of electrical signals for each wavelength is
Each wavelength λ₁, Λ_Two, …… λ_NError detector 46 corresponding to
₁~ 46_NAnd the error detector 47 corresponding to the absolute wavelength
Is entered.

The respective error detectors 46 _{1 to} 46 _N , 4
7, as shown in FIG. 11, each wavelength λ ₁ , λ ₂ ,.
The error signals 27 _{1 to} 27 _N and 48 are output so that the output power ratio of the adjacent ports becomes 1 for each λ _N. The error signals 27 _{1 to} 27 _N corresponding to the respective wavelengths λ ₁ , λ ₂ ,... Λ _N are supplied to the temperature control circuit 24 to perform feedback control based on the temperature. control of the wavelength of the diode 23 ₁ ~ 23 _N is performed. The error signal 48 output from the error detector 47 is fed back to the temperature control circuit 49, and based on this, the temperature control for the absolute wavelength is performed. As a result, stable wavelength discrimination characteristics against environmental temperature changes are guaranteed.

[0012]

Among the conventional wavelength stabilizing devices for a multi-wavelength light source, the device shown in FIG. 8 has the following problems. First, as the sweep type variable wavelength filter 16, a filter having a sufficiently narrow transmission bandwidth and good wavelength selectivity is required, which leads to an increase in the cost of the apparatus. This is because, when a peak is detected by the peak detection circuit portion in the peak detection and error calculation circuit 19, if the transmission bandwidth of the sweep type variable wavelength filter 16 is wide, the peak position is accurately detected due to the influence of noise or the like. It is because they cannot do it.

The second problem of the apparatus shown in FIG. 8 is that the wavelength sweep characteristic of the filter sweep control circuit 17 for driving the sweep type variable wavelength filter 16, that is, the linearity and stability of the transmission peak wavelength with respect to the sweep time. High precision is required, and this is also a factor that leads to an increase in the cost of the apparatus. In this device, since the information on the relative peak wavelength position of the multi-wavelength light source is converted into an electric pulse signal train on the time axis, the linearity and stability of the transmission peak wavelength characteristic with respect to the sweep time are improved. This is a factor that determines the wavelength accuracy of the light.

A conventional multi-wavelength light source shown in FIG.
In the wavelength stabilization device, first, in principle, optical detection
The number of detecting elements constituting the detector 45 is different from each wave of the multi-wavelength light source 41.
Long λ ₁, Λ_Two, …… λ_NNeed twice the total number of
This causes a problem of increased costs.
Was. Also, as a second problem, the absolute reference light source 42
To stabilize the overall temperature of the wavelength discriminator 44
However, the wavelength discriminator 44 itself is relatively large.
High-precision optical device
There is a problem that it is difficult to stabilize the temperature at an appropriate level. This
This makes it difficult to expect high wavelength accuracy.
Was. Further, in the apparatus shown in FIG.
The number of wavelengths of multi-wavelength light sources that can be handled is limited
There was also the problem of getting lost.

Accordingly, an object of the present invention is to provide a wavelength stabilizing device for a multi-wavelength light source which requires only a small number of photodetectors, does not require a high-precision circuit device, and can reduce environmental temperature dependence. Is to do.

[0016]

According to the first aspect of the present invention, (a) a multi-wavelength light source provided with a plurality of laser diodes, each of which is temperature-controlled by a temperature control circuit, for outputting signal light of each wavelength. Wavelength selecting means for inputting signal light of multiple wavelengths and sequentially selecting signal light of wavelengths corresponding to these laser diodes one by one, and (b) inputting signal light of a wavelength selected by the wavelength selecting means. An optical periodic filter that outputs two transmitted lights having different phases from each other;
(C) a photodetector that detects two transmitted lights output from the optical periodic filter and converts them into electric signals, respectively.
The amount of feedback for controlling the temperature of the laser diode corresponding to the wavelength selected by the wavelength selection means by calculating these two types of detection results of the photodetector is determined each time the wavelength selection means selects a wavelength. And a feedback loop provided to the temperature control circuit by sequentially switching the temperature control circuit.

That is, according to the first aspect of the present invention, by selecting one kind of signal light from the multi-wavelength signal lights one by one by the wavelength selecting means and inputting the selected signal light to the optical periodic filter, the light arranged on the output side is selected. The minimum number of detectors is sufficient irrespective of the number of laser diodes. Further, since the optical periodic filter outputs two types of signal light having different phases such that the phase of the input signal light is, for example, 180 degrees, the wavelength is shifted to a wavelength stable point based on this. Is fed back to the temperature control circuit to control the temperature of the laser diode one by one.

According to a second aspect of the present invention, the wavelength selecting means of the wavelength stabilizing device for a multi-wavelength light source according to the first aspect is constituted by a sweep-type tunable filter, and a signal light having a wavelength corresponding to each of the laser diodes. Is selected, the temperature control of the corresponding laser diode is completed by the feedback control of the feedback loop, and the sweep is temporarily stopped until the calculated value of the two types of detection results reaches a predetermined value.

That is, according to the second aspect of the present invention, the wavelength selecting means is constituted by a sweep-type wavelength tunable filter. Temperature control can be performed.

According to a third aspect of the present invention, the wavelength stabilizing device for a multi-wavelength light source according to the first aspect includes an optical periodic filter temperature adjusting means for adjusting the temperature of the optical periodic filter, and the wavelength output from the multi-wavelength light source. When the wavelength selecting means selects a wavelength output from the predetermined reference light source at a wavelength other than the above, the feedback amount obtained by calculating the detection result of the photodetector is given to the optical periodic filter temperature adjusting means to control the temperature of the optical periodic filter. It is characterized by performing.

That is, according to the third aspect of the present invention, the temperature of the optical periodic filter, which only needs to be adjusted in the wavelength stabilizing device for the multi-wavelength light source, is adjusted, so that it is possible to accurately control the fluctuation of the environmental temperature. To be able to deal with.

According to a fourth aspect of the present invention, the optical periodic filter of the wavelength stabilizing device for a multi-wavelength light source according to the first aspect is constituted by a Mach-Zehnder type frequency optical multiplex coupler. This invention is characterized in that this is constituted by an optical fiber grating.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows a circuit configuration of a wavelength stabilizing device for a multi-wavelength light source according to an embodiment of the present invention. This device includes an N-wave multi-wavelength light source 61, an absolute reference light source 62 serving as a reference, and a plurality of wavelengths λ ₁ , λ
₂ ,... An optical multiplexer 63 composed of a fusion-type optical fiber coupler for multiplexing λ _N and λ _S ;
3, an optical splitter 65 for splitting the signal light transmitted to the transmission line 64, a wavelength tunable filter 68 for inputting the monitor light 67 split from the optical splitter 65, and a wavelength tunable filter 68. , A single wavelength is selected, and a tunable filter sweep circuit 69 for temporarily stopping the sweep at the position of the peak wavelength, a control unit 71 for controlling the tunable filter sweep circuit 69, and a selected output from the tunable filter 68 are selected. An optical periodic filter 72 for inputting wavelength monitor light, and an optical periodic filter 72
And a temperature control circuit 74 that controls the temperature of the optical periodic filter 72.

In this embodiment, the optical splitter 65 splits the input signal light into monitor light 67 at a ratio of 10: 1, and supplies the monitor light 67 to the wavelength variable filter 68. The signal light of a specific single wavelength selected by the wavelength tunable filter 68 is input to the optical periodic filter 72, and the output of the photodetector pair 73 obtained by this is input to the control unit 71. . The control unit 71 includes a control CPU (central processing unit), and includes a wavelength tunable filter control circuit 76, a peak detection and feedback amount calculation circuit 77.
And the feedback loop selection control circuit 78 are functionally realized. Then, the output of the photodetector pair 73 is input to a peak detection and feedback amount calculation circuit 77 to perform peak detection and calculation of the feedback amount of each wavelength, and to provide the feedback amount to the feedback loop selection control circuit 78. Has become. Feedback loop selection control circuit 78, corresponding to the N multiplexed each laser diode 79 ₁ to 79 _N in wavelength light source 61, supplies a feedback amount to the temperature adjusting circuit 74 is adapted to adjust the temperature.

The first to Nth laser diodes 79
_{1 to} 79 _N are each constituted by a DFB laser module having a thermistor (temperature detector) (not shown) and a Peltier element for temperature adjustment. The Peltier element is an element for heating and cooling the laser diode 79. Each of the laser diodes 79 _{1 to} 79 _N includes a photodiode (not shown) for monitoring the output power thereof, and an APC for controlling the output power to be constant using the output thereof.
(Auto Power Controll) circuit. Thereby, the power of the signal light output from each of the laser diodes 79 _{1 to} 79 _N is kept constant. Temperature control circuit 74
Has a function of performing temperature control together with these thermistors and Peltier elements, and uses the voltage value given from the control unit 71 as a control reference voltage to control the temperature of the corresponding laser diodes 79 _{1 to} 79 _N. Adjustments are made.

The tunable filter 68 uses an acousto-optic filter in this embodiment. The acousto-optic filter has a light input / output port and an RF signal input port.
This is an optical device in which a transmission peak wavelength for input light of a filter changes in accordance with a change in the frequency of an F signal. The wavelength tunable filter sweep circuit 69 is a circuit that generates an RF signal to be provided to the wavelength tunable filter 68 composed of an acousto-optic filter. Wavelength variable filter sweep circuit 69
Is R for outputting an RF signal to the wavelength tunable filter 68.
It has an F signal output port and an input voltage port input from the wavelength tunable filter control circuit 76. The wavelength tunable filter sweep circuit 69 of this embodiment uses a built-in voltage controlled oscillator (VCO) to generate an RF signal having a frequency proportional to the input voltage.
It has a function of generating a signal and amplifying the signal to a power required for driving the wavelength variable filter 68.

FIG. 2 shows the configuration of the optical periodic filter. The optical periodic filter 72 includes one input port 81, one through port 82, and one cross port 8.
3 comprises a system multiplexed optical coupler. In the present embodiment, a Mach-Zehnder type frequency optical multiplex coupler is used. As described above, the single-wavelength signal light selectively output from the tunable filter 68 is input to the input port 81. The outputs of the through port 82 and the cross port 83 are connected to a photodetector pair 73.
The light is incident on the separate photodiodes constituting (FIG. 1).

FIG. 3 shows a transmission wavelength characteristic of an optical periodic filter constituted by a Mach-Zehnder type frequency optical multiplexing coupler. Now, the input port 81 of the optical periodic filter 72 (FIG. 2), it is assumed that the monitor light of a first wavelength lambda ₁ of the signal light output from the laser diode 23 ₁ is input. When the wavelength is represented on the horizontal axis and the relative output intensity is represented on the vertical axis, a signal light characteristic 91 of the through port 82 as shown by a solid line and a signal light characteristic 92 of a cross port 83 as shown by a dotted line are obtained. Now, focusing on a certain wavelength λ _X , the output of the signal light of the through port at this time is P
_1, the output of the signal light of the cross port becomes P _2. These will be separately detected by a pair of photodiodes in the photodetector pair 73 (FIG. 1). The detected current amount is converted into a voltage value using a built-in current-voltage conversion circuit (not shown) and output to the control unit 71.

The peak detection and feedback amount calculation circuit 77 in the control unit 71 receives the detection output of the photodetector pair 73,
As described above, the detection outputs of the pair of photodiodes are equal, i.e. the error component as the output P ₁ of the two signal lights, P ₂ is the wavelength that is equal to the arithmetic as feedback amount, the feedback loop selection control this Supply to circuit 78. The feedback loop selection control circuit 78 controls the laser diode 79 in association with the tunable filter control circuit 76 causing the tunable filter sweep circuit 69 to select a single specific wavelength.
(In this case, the feedback amount corresponding to the laser diode 79 ₁ ) is supplied to the temperature adjustment circuit 74. As a result of such feedback control is performed, the temperature control of the first laser diode 23 ₁ so that the wavelength of the wavelength stabilizing point 93 shown in FIG. 3 are performed.

Thus, the first laser diode 2
3₁When the temperature adjustment for is completed,
The peak detection and feedback amount calculation circuit 77 has a wavelength tunable filter.
The second laser diode 23 is connected to the filter control circuit 76._TwoWaves
Long λ_TwoRequest adjustment of signal light. This allows wavelength
The variable filter sweep circuit 69 sets the wavelength variable filter 68
λ_TwoIs set to a filter characteristic that allows the signal light to pass through. So
Then, the second laser die is controlled by the same control as described above.
Aether 23_TwoWill be adjusted. This
, The feedback loop selection control circuit 78
Diode 23 _TwoThe amount of feedback in the path corresponding to
An output port is selected so as to supply to the path 74. control
The unit 71 calculates the feedback amount, controls the sweep, and selects the feedback loop.
Also manages the timing control. Similarly, the third
Laser diode 23_ThreeTemperature control for the rest continues
Will do.

When the temperature adjustment for the wavelength λ _{N up} to the N-th laser diode 23 _N is completed, the same control is repeated again from the wavelength λ ₁ , whereby it is possible to cope with fluctuations in the environmental temperature. In addition, the control of the wavelength λ _S of the absolute reference light source 62 is performed between the control of the wavelengths of the _first to _N-th laser diodes 231 to 23N. As an example, the control of the absolute reference light source 62 immediately before the first control of the laser diode 23 ₁ is started is performed each time. At this time, the feedback amount output from the feedback loop selection control circuit 78 is supplied to the temperature adjustment circuit 74. By fixing the temperature of the optical periodic filter 72 with respect to the absolute reference light source 62, the absolute wavelength accuracy of the wavelength stabilizing device for a multi-wavelength light source according to the present embodiment is guaranteed. Note that the numerical value “N” is “4” in the wavelength stabilizing device for a multi-wavelength light source of the present embodiment.
It is free to take a larger value or a smaller value.

In the wavelength stabilizing device for a multi-wavelength light source according to the present embodiment, 1548 and 15 are used as the N-wave multi-wavelength light source 61 (FIG. 1).
It is assumed that four light sources of 50, 1552, and 1554 nm, each having an interval of 2 nm, are used. First to fourth
The laser diode 23 _{1-23 4} are used close to each wavelength, and the temperature adjustment for the laser diode module, having the characteristics that can be tailored to four wavelengths. The signal light output from the _first to _fourth laser diodes 231 to 234 is 4: 1.
Input to the optical multiplexer 63 composed of optical star couplers
It is multiplexed into the optical fiber.

FIG. 4 shows the flow of the temperature adjustment control by the control unit. The control unit 71 has a built-in CPU,
A series of controls are realized by executing a program stored in a built-in ROM (read only memory). That is, when the control is started, the control unit 71 performs initialization (step S101), and initializes a wavelength counter variable "counter" for counting the number of wavelengths ("counter = 0") (step S101). S102). Subsequently, sweeping is started from the short wavelength side via the wavelength variable filter sweeping circuit 69 (steps S103 and S104).

The output light of the wavelength tunable filter 68 is input to the input port of the optical periodic filter 72, and outputs P ₁ and P ₂ are obtained. When the control unit 71 detects the maximum value of the transmitted light power of the variable wavelength filter 68 based on this (step S105; Y), the sweep is temporarily stopped (step S106). In this state, the control unit 71 detects an error between the output of the through port and the output of the cross port, and controls the laser to be controlled to a wavelength at which the output power of these ports becomes equal (the wavelength of the wavelength stable point 93 in FIG. 3). The amount of feedback to the temperature control circuit 74 is calculated so that the wavelength of the diode 79 is stabilized (step S107). The calculation of the feedback amount is based on PID control, that is, control that defines the feedback amount by a linear combination of proportional, integral, and differential elements.

When the feedback amount is calculated in this manner, C
The PU checks whether the wavelength number counter variable “counter” is “0” (Step S108). In this embodiment, since “counter = 0” is assigned as the absolute reference light source 62, the calculated feedback amount corresponds to the absolute reference light source 62.
This is to determine whether the feedback amount is for the temperature control circuit 74 and set the destination of the feedback amount. That is, if it is "0" (Y), an output port for the temperature control circuit 74 is selected (step S109), and the feedback amount is output to this (step S110). Thereafter, the value of the wavelength counter variable "counter" is counted up by "1" (step S111). Then, the value of the wavelength number counter variable “counter” after counting up is set to “N”.
It is checked whether the value is “+1” (“4 + 1” in this embodiment) (step S112) In this example, since the value of the wavelength number counter variable “counter” is “1” (N), Returning to S104, the first wavelength λ ₁
Is started.

On the other hand, if the wavelength counter variable "counter" is other than "0" in step S108 (N), the feedback loop selection control circuit 78 outputs the output port of the feedback loop selection loop number equal to the count value. Is selected (step S113). For example, when the feedback amount for the first wavelength λ ₁ is calculated, the first output port for adjusting the temperature of the first laser diode 79 ₁ is selected, and the feedback amount is output. (Step S114). Temperature control circuit 74 executes a first temperature adjustment of the laser diode 79 ₁ using the feedback amount. Similarly, the second to fourth output ports also have the wavelength counter variable “co”.
unter ". Step S1
When the feedback amount is output in step 14, the process proceeds to step S111, and the wavelength counter variable "counter" is counted up by "1". As a result, the value of the wavelength number counter variable “counter” after counting up is set to “N + 1”.
(Y), it means that the temperature adjustment up to the N-th laser diode module has been completed. Therefore, in this case, the process returns to step S102 to restart the adjustment cycle from the beginning.

As described above, in the wavelength stabilizing device for a multi-wavelength light source according to the present embodiment, the deviation from the set wavelength is defined by the ratio of the optical output of the two output ports 91 and 92 of the optical periodic filter 72. did. Therefore, the wavelength tunable filter 68 only needs to sequentially select each of the wavelengths λ ₁ , λ ₂ ,... Λ _N , λ _S. That is, the wavelength stability does not depend on the transmission bandwidth of the filter as the wavelength selectivity of the wavelength variable filter 68 or the accuracy of the wavelength variable filter sweep circuit 69. Further, regardless of the number of wavelengths of the multi-wavelength light source, the number of necessary detection elements of the photodetector is sufficient for two, and compared with the detection elements constituting the photodetector 45 shown in FIG. The configuration can be greatly simplified. Also, since the only device having temperature dependency is the relatively small optical periodic filter 72, high-precision temperature control can be performed as a whole of the wavelength stabilizing device for the multi-wavelength light source, and the temperature dependency is reduced. become.

Modification

FIG. 5 shows a circuit configuration of a wavelength stabilizing device for a multi-wavelength light source according to a modification of the present invention.
In this figure, the same parts as those of the previous embodiment shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.
As shown in this figure, in the wavelength stabilizing device for a multi-wavelength light source of a modification, an optical fiber grating 101 is used instead of the Mach-Zehnder type frequency optical multiplexing coupler used as the optical periodic filter 72 in the previous embodiment. . The optical fiber grating 101 is one in which a diffraction grating is written near the boundary between the core and the clad of the optical fiber, and reflects only light of a specific wavelength by Bragg reflection and transmits light of other wavelengths. Optical fiber type optical device.

In this modification, utilizing such characteristics of the optical fiber grating 101, it is used as a transmission type band rejection filter. Tunable filter 6
The output light of No. 8 passes through an optical isolator 102 for preventing the reflected light from the optical fiber grating 101 from returning to the N-wave multi-wavelength light source 61 (FIG. 1), and thereafter, a one-to-one light such as a fused optical coupler. The light is split by the splitter 103. And
The split light is passed through the optical fiber grating 101.

FIG. 6 specifically shows an optical fiber grating. Optical fiber grating 10
Reference numeral 1 denotes a configuration in which N stages are connected in series, and signal light is detected by a photodetector pair 73 connected to the last stage. Here, the respective optical fiber grating portions 101 _{1 to} 101 _N sequentially have wavelengths λ ₁ , λ ₂ ,
And it is shifted by ± δ than ...... λ _N.

FIG. 7 shows the relationship between each wavelength of the signal light and the relative output intensity obtained by the photodetector in the optical fiber grating of this modified example. Each wavelength lambda ₁ each output intensity of the signal light, lambda _2, is as shown by the solid line 111 or broken line 112 relative ...... λ _N,
By feeding back a feedback amount corresponding to the difference between the detection of the two detection elements in the photodetector 73, the wavelength at which the difference becomes “0” (the characteristic curves shown by the solid line 111 and the dotted line 112 intersect) Wavelength). In the wavelength stabilizing device for a multi-wavelength light source of the previous embodiment, N
Although the wave multi-wavelength light source 61 is limited to the wavelength arrangement at equal intervals,
This modified example can be applied to an N-wave multi-wavelength light source in which the wavelength intervals are not equal.

[0045]

As described above, according to the first aspect of the present invention, one type of signal light is selected one by one from multi-wavelength signal light by the wavelength selecting means, and the light having periodic bandpass characteristics is selected. Since the input is made to the periodic filter, the number of photodetectors arranged on the output side can be suppressed to two irrespective of the number of laser diodes. As a result, even if the number of laser diodes constituting the multi-wavelength light source increases, the number of photodetectors does not need to be changed. There is an advantage that cost increase can be prevented. Further, the optical periodic filter can be constituted by a small frequency multiplexing optical coupler. In this case, the temperature can be easily controlled, and highly accurate temperature stabilization can be easily realized.

According to the second aspect of the present invention, since the wavelength selecting means is constituted by the sweep type wavelength tunable filter, the wavelength stability of the multi-wavelength light source does not depend on the wavelength transmittance of the filter and the accuracy of the sweep circuit. There is an advantage that these sweep-type variable wavelength filters and sweep circuits can be manufactured at low cost.

Further, according to the third aspect of the present invention, the feedback amount for adjusting the temperature is sequentially fed back to the laser diode of each wavelength, so that the fluctuation of the environmental temperature can be dealt with with high accuracy. There is an advantage that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a wavelength stabilizing device for a multi-wavelength light source according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing each port of an optical periodic filter used in the present embodiment.

FIG. 3 is an explanatory diagram showing a relationship between a transmission wavelength characteristic of the optical periodic filter used in the present embodiment and a wavelength control principle.

FIG. 4 is a flowchart showing a flow of temperature adjustment control by a control unit in the embodiment.

FIG. 5 is a block diagram showing a circuit configuration of a wavelength stabilizing device for a multi-wavelength light source according to a modification of the present invention.

FIG. 6 is an explanatory diagram showing an optical fiber grating and its periphery in a modification of the present invention.

FIG. 7 is an explanatory diagram showing a relationship between a transmission wavelength characteristic of an optical fiber grating and a wavelength control principle in a modification of the present invention.

FIG. 8 is a block diagram showing a configuration of a first example of a conventional wavelength stabilizing device for a multi-wavelength light source.

FIG. 9 is a diagram showing various waveforms for explaining the operation of the filter sweep control circuit.

FIG. 10 is a block diagram showing a configuration of a second example of a conventional wavelength stabilizing device for a multi-wavelength light source.

11 is an explanatory waveform diagram for explaining the operation of the error detector shown in FIG.

[Explanation of symbols]

 41 Multi-wavelength light source 61 N-wave multi-wavelength light source 62 Absolute reference light source 63 Optical multiplexer 65 Optical demultiplexer 67 Monitor light 68 Wavelength variable filter 71 Controller 72 Optical periodic filter 73 Photodetector pair 74 Temperature control circuit 79 Laser diode 101 Light Fiber grating 103 1: 1 optical demultiplexer

Claims (5)

[Claims] 1. A multi-wavelength signal light output from a multi-wavelength light source provided with a plurality of laser diodes, each of which is temperature-controlled by a temperature control circuit, for outputting a signal light of each wavelength, is input to these laser diodes. Wavelength selecting means for sequentially selecting signal lights of corresponding wavelengths one by one; an optical periodic filter for inputting signal light of the wavelength selected by the wavelength selecting means and outputting two transmitted lights having different phases; A photodetector that detects two transmitted lights output from the periodic filter and converts them into electric signals, respectively, and calculates these two types of detection results of the photodetectors to correspond to the wavelength selected by the wavelength selection means. A feedback loop for switching the feedback amount for feedback controlling the temperature of the laser diode to be applied to the temperature control circuit by sequentially switching the wavelength each time the wavelength selection unit selects a wavelength. A wavelength stabilizing device for a multi-wavelength light source, comprising: 2. The method according to claim 1, wherein the wavelength selecting means is constituted by a sweep-type tunable filter, and when a signal light having a wavelength corresponding to each of the laser diodes is selected, the temperature of the corresponding laser diode is controlled by feedback control of the feedback loop. 2. The wavelength stabilizing device for a multi-wavelength light source according to claim 1, wherein the sweeping is temporarily stopped until the adjustment is completed and the calculated value of the two types of detection results reaches a predetermined value. 3. An optical periodic filter temperature adjusting means for adjusting the temperature of the optical periodic filter, wherein the wavelength selecting means selects a wavelength output from a predetermined reference light source at a wavelength other than the wavelength output from the multi-wavelength light source. 2. The wavelength for a multi-wavelength light source according to claim 1, wherein when (1) is selected, a feedback amount obtained by calculating the detection result of the photodetector is supplied to the optical periodic filter temperature adjusting means to control the temperature of the optical periodic filter. Stabilizer. 4. The wavelength stabilizing device for a multi-wavelength light source according to claim 1, wherein said optical periodic filter is constituted by a Mach-Zehnder type frequency optical multiplex coupler. 5. The wavelength stabilizing device for a multi-wavelength light source according to claim 1, wherein said optical periodic filter is constituted by an optical fiber grating.