JPH0897775A - Wavelength monitor - Google Patents

Abstract

PURPOSE: To realize the wavelength monitor suitable for optical signal integration by discriminating each wavelength of a wavelength multiplex light multiplexed at a prescribed wavelength interval (frequency interval) with high accuracy strictly. CONSTITUTION: The monitor is provided with a variable light filter 12 outputting a signal light of each wavelength of a wavelength multiplex light through the sweep of a transmission center wavelength, a reference light source 11 providing an output of a reference wavelength light, a periodic optical filter 15 having a periodic transmission center wavelength corresponding to the wavelength interval of the wavelength multiplex light, and a control circuit 16 making the transmission center wavelength of the periodic optical filter 15 stable wavelength of the reference wavelength light, also with a wavelength error detection circuit 17 receiving the transmitted light with respect to the signal light of each wavelength received by the periodic filter 15 to detect a relative wavelength error with respect to each transmitted center wavelength of the periodic optical filter 15, and changeover means 14-1, 14-2 switching a path connecting a variable optical filter 12 to the periodic optical filter 15 and the wavelength error detection circuit 17 and the path connecting the control reference light source, the periodic optical filter 15 and the control circuit 16 at a prescribed period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength monitoring device for monitoring each wavelength of wavelength multiplexed light with high accuracy.

[0002]

2. Description of the Related Art A conventional wavelength monitoring device for monitoring each wavelength of wavelength-multiplexed light sweeps a transmission center wavelength of a sweeping optical filter (for example, a sweeping Fabry-Perot interferometer) in time to detect a wavelength error in a time domain. Is configured to perform wavelength discrimination.

FIG. 11 shows a configuration example of a conventional wavelength monitoring device (Mizuchi, et al., “622-electrode MQWDFB-LD is used.
Mbit / s-16ch FDM coherent optical transmission system ", IEEJ, Vol.J77-BI, No.5, pp.294-303, 1994).

In the figure, the reference wavelength light and the wavelength multiplexed light are multiplexed by an optical coupler 71 and input to a swept Fabry-Perot interferometer 72. Swept Fabry-Perot interferometer 7
2 is swept by a sawtooth wave (FIG. 12A) generated by a sawtooth wave generator 76 synchronized with the oscillator 75, and light having a wavelength matching the transmission center wavelength is received by the photodetector 73. Photo detector 7
The peak position of the output pulse of FIG. 3 (FIG. 12 (b)) is differentially detected by the differentiator 78 (FIG. 12 (c)), and the sampling pulse corresponding to the peak position is detected by the sampling circuit 79 (FIG. 12 (d)). ). The sampling pulse and the output signal of the oscillator 75 (FIG. 12E) are input to the synchronous detector 80, and the output thereof is input to the sample hold circuit 81. Since the sawtooth wave (Fig. 12 (a)) and the output signal of the oscillator 75 (Fig. 12 (e)) are synchronized, the output signal of the oscillator 75 (Fig. 12 (e)) is generated by the sampling pulse (Fig. 12 (d)). ) Is detected, and the sample hold circuit 81 holds the detected output, so that an error signal (FIG. 12 (f)) can be obtained. The selector 74 sequentially switches and outputs a relative error signal between each wavelength of the reference wavelength light and the wavelength multiplexed light and the transmission center wavelength of the sweeping Fabry-Perot interferometer 72.

The error signal corresponding to the reference wavelength light is added to the sawtooth wave output from the sawtooth wave generator 76 by the adder 77 and applied to the sweeping type Fabry-Perot interferometer 72 to obtain the light corresponding to the reference wavelength light. The position of the output pulse of the detector 73 is controlled to be the bias point of the sawtooth wave. As a result, the transmission center wavelength of the swept Fabry-Perot interferometer 72 can be stabilized at the wavelength of the reference wavelength light, and a temperature compensating function for fluctuations in ambient temperature can be provided.

Further, by negatively feeding back an error signal corresponding to each wavelength of the wavelength-multiplexed light to each light source of the wavelength-multiplexed light and controlling the injection current or temperature thereof, wavelength stabilization of the wavelength-multiplexed light can be achieved. .

The above-described swept Fabry-Perot interferometer used in the conventional configuration requires a mechanism for sweeping the resonator length by a piezoelectric element, but can be realized by a relatively simple optical circuit. In addition, by appropriately selecting the transmission center wavelength and passband width of the swept Fabry-Perot interferometer,
There is an advantage that a wide range of wavelength changes can be monitored with a desired resolution.

[0008]

In the conventional configuration, the displacement amount of the piezoelectric element and the transmission center wavelength are proportional to the voltage applied to the piezoelectric element of the swept Fabry-Perot interferometer. However, actually, FIG. 13 (1)
As shown in, the amount of displacement of the piezoelectric element is not proportional to the applied voltage and has hysteresis. Therefore, when it is attempted to set the transmission center wavelengths corresponding to the displacement amount of the piezoelectric element at equal intervals, the applied voltage does not become equal intervals (V _{1 to} V ₆ ), and FIG.
It is necessary to apply a correction voltage shown by a broken line in _{(2) (V 2 '~V} 5').

That is, in the case where the sweep voltage has a linear waveform of a sawtooth wave as in the conventional configuration, the transmission center wavelength cannot be swept linearly. Therefore, in the conventional configuration in which sampling is performed in synchronization with the same clock, it is difficult to perform precise wavelength discrimination in a wide wavelength range, and highly accurate monitoring of wavelength multiplexed light multiplexed at arbitrary wavelength intervals is impossible. Met.

Further, in the configuration using the Fabry-Perot interferometer, it is possible to relatively monitor each wavelength change of the wavelength multiplexed light with the wavelength of the reference wavelength light as a reference, but the wavelength of the reference wavelength light is strictly stable. It is difficult to measure the absolute wavelength because it has not been standardized.

The present invention has a predetermined wavelength interval (frequency interval).
It is an object of the present invention to provide a wavelength monitoring device which can discriminate each wavelength of the wavelength-division-multiplexed light multiplexed in 1. with high accuracy and strictness and which is suitable for optical integration.

[0012]

According to a first aspect of the present invention, there is provided a wavelength monitoring apparatus in which wavelength-multiplexed light is input, and variable signal light having a wavelength corresponding to a transmission center wavelength swept by a predetermined sweep signal is sequentially output. An optical filter, a reference light source for outputting a reference wavelength light stabilized at a predetermined wavelength, a periodic optical filter having a periodic transmission center wavelength corresponding to the wavelength interval of wavelength multiplexed light, and an input to the periodic optical filter. The transmitted light with respect to the reference wavelength light is received, the transmission characteristics are controlled according to the relative wavelength error between one transmission center wavelength of the periodic light filter and the reference wavelength light, and the transmission center wavelength of the periodic light filter is the wavelength of the reference wavelength light. A control circuit that stabilizes in accordance with the above, and a wavelength error detection that receives the transmitted light for the signal light of each wavelength input to the periodic optical filter and detects the relative wavelength error with each transmission center wavelength of the periodic optical filter. Comprising road and a path connecting the tunable optical filter and the periodic optical filter and the wavelength error detecting circuit, and a switching means for switching the path connecting the control circuit and the control reference source and the periodic optical filter at a predetermined period.

According to a second aspect of the present invention, there is provided a wavelength monitoring device in which the switching means and the periodic optical filter according to the first aspect are integrated with a plurality of periodic optical filters and their transmission characteristics are controlled in synchronization with each other. It is characterized in that a reference light source and a control circuit, and a variable optical filter and a wavelength error detection circuit are always connected through a tracking periodic optical filter instead of a filter.

According to a third aspect of the wavelength monitoring apparatus, the variable optical filter of the second aspect is replaced with an optical demultiplexer, and a wavelength error detection circuit corresponding to each wavelength is further provided. The fourth aspect limits the configuration of the control circuit of the wavelength monitoring device. The control circuit includes an oscillator for generating a predetermined reference signal, a means for finely modulating the transmission center wavelength of the periodic optical filter or the tracking periodic optical filter by the reference signal, and the transmitted light of the periodic optical filter or the tracking periodic optical filter. , A wavelength error detecting means for synchronously detecting with a reference signal to detect a relative wavelength error between the transmission center wavelength and the reference wavelength light, and a periodic optical filter or a tracking periodic optical filter by adding a signal corresponding to the relative wavelength error to the reference signal. And means for negative feedback to.

The fifth aspect limits the configuration of the wavelength error detection circuit of the wavelength monitoring device. The wavelength error detection circuit is configured to receive the transmitted light of the periodic optical filter or the tracking periodic optical filter, synchronously detect it with the reference signal generated by the control circuit, and detect the relative wavelength error with respect to the transmission center wavelength.

[0016]

The wavelength monitoring device of the present invention enables the wavelength discriminating operation in synchronization with the absolute wavelength by controlling the transmission center wavelength of the periodic optical filter to the reference wavelength light stabilized at a predetermined wavelength.

Each wavelength discrimination of the wavelength division multiplexed light is performed by detecting a relative wavelength error from the periodic transmission center wavelength of the periodic optical filter. In the wavelength monitoring device according to the first and second aspects, the wavelength-multiplexed light is separated into the signal light of each wavelength by using the variable optical filter whose transmission center wavelength is swept, and is input to the periodic optical filter or the tracking periodic optical filter. In the wavelength monitoring device according to the third aspect, the wavelength division multiplexed light is separated from the signal light of each wavelength by using the optical demultiplexer, and the signal light is input to the tracking periodic optical filter. The former discriminates each wavelength of wavelength-multiplexed light by time division, and the latter discriminates each wavelength of wavelength-multiplexed light at the same time.

Further, in the wavelength monitoring device according to claims 2 and 3,
By using the tracking periodic optical filter, the wavelength error of the wavelength multiplexed light can be discriminated with high accuracy while stabilizing the transmission center wavelength of the tracking periodic optical filter to the wavelength of the reference wavelength light.

In the control circuit and the wavelength error detection circuit of the wavelength monitoring device according to claims 4 and 5, the transmission center wavelength of the periodic optical filter or the tracking periodic optical filter is finely modulated by the reference signal, and the transmitted light is synchronized with the reference signal. A relative wavelength error can be detected by performing detection.

The wavelength error signal obtained by the wavelength monitoring device of the present invention is negatively fed back to the light source corresponding to each wavelength of the wavelength multiplexed light, and the injection current or the temperature thereof is controlled,
It is possible to stabilize the wavelength (optical frequency).

[0021]

【Example】

(First Embodiment) FIG. 1 shows the construction of the first embodiment of the present invention (claim 1).

In the figure, a reference light source 11 outputs a reference wavelength light having a stabilized wavelength on an absorption line of an atom or a molecule. The wavelength multiplexed light to be monitored is a tunable optical filter 1
Entered in 2. The variable optical filter 12 is the waveform generator 1
A swept Fabry-Perot interferometer or an acousto-optic variable filter in which the transmission center wavelength is swept in accordance with the swept signal a outputted from 3 is used, and the optical signals of the respective wavelengths of the wavelength multiplexed light are sequentially outputted. The optical signal of each wavelength and the reference wavelength light are switched by the optical switch 14-1 and input to the periodic optical filter 15. As the periodic optical filter 15, a Fabry-Perot interferometer or a Mach-Zehnder interferometer having a periodic transmission center wavelength is used. The output light is the optical switch 14
It is switched at -2 and input to the control circuit 16 or the wavelength error detection circuit 17. The control circuit 16 sends the control signal b to the periodic optical filter 15 and the reference signal c to the wavelength error detection circuit 17. The output of the wavelength error detection circuit 17 is input to the selector 18 and separated into each wavelength error signal of the wavelength multiplexed light. Sync signal d output from the waveform generator 13
Is input to the optical switch control circuit 19 and the selector 18. The optical switch control circuit 19 sends a switching signal e corresponding to the synchronization signal d to the optical switches 14-1 and 14-2.

FIG. 2 shows an example of the structure of the reference light source 11. This configuration is based on the literature (Y. Sakai et al., "Frequency stabili
zation of laser diodes using 1.51-1.55μm absorpt
ionlines of ¹² C ₂ H ₂ and ¹³ C ₂ H ₂ ", IEEE J. Quantum
Electron, Vol.28, No.1, pp.75-81, 1992).

In the figure, a temperature-stabilized semiconductor laser 21 is applied with a modulation signal output from an oscillator 23 superimposed on a bias current supplied from a DC power supply 22. The output light of the semiconductor laser 21 frequency-modulated by this modulation signal is received by the photodetector 25 via the C ₂ H ₂ gas cell 24. The output of the photodetector 25 is detected by the synchronous detector 26 by the modulation signal, and a wavelength error with one of the peaks of the absorption line of the gas (molecule) is detected. By negatively feeding back this error signal to the semiconductor laser 21 by the control circuit 27, the oscillation wavelength of the semiconductor laser 21 can be stabilized at the wavelength of the absorption line of the gas (molecule) for a long time.

FIG. 3 shows a configuration example of the control circuit 16. In the figure, a photodetector 31 that receives the output light of the periodic optical filter 15 that is input via the optical switch 14-2, an oscillator 32 that outputs a reference signal c, and an output of the photodetector 31 are synchronized with the reference signal c. Synchronous detector 33 for detecting and synchronous detector 3
3 is composed of a low-pass filter (LPF) 34 for removing harmonic components from the output of No. 3, and an adder 35 for adding the output of the low-pass filter 34 and the reference signal c to generate a control signal b to be sent to the periodic optical filter 15. It

FIG. 4 shows a configuration example of the wavelength error detection circuit 17. In the figure, a photodetector 4 that receives the output light of the periodic optical filter 15 that is input via the optical switch 14-2.
1. A synchronous detector 42 that synchronously detects the output of the photodetector 41 with the reference signal c, and a low-pass filter (LPF) 43 that removes harmonic components from the output of the synchronous detector 42. The output of the low pass filter 43 is sent to the selector 18.

FIG. 5 shows each signal of the first embodiment. In the figure, the sweep signal a is a multilevel step signal that sequentially sets the transmission center wavelength of the tunable optical filter 12 in correspondence with the wavelength interval of the wavelength multiplexed light. The number of steps in one cycle is
The number of wavelength multiplexing is +1 (corresponding to the reference wavelength light). In addition,
The sweep signal voltage at the timing corresponding to the reference wavelength light is arbitrary. The synchronization signal d is a signal synchronized with the step of the sweep signal a, that is, the switching timing of the transmission center wavelength of the tunable optical filter 12, and the selector 18 sequentially switches the output ports at the switching timing. The switching signal e is
The optical switch control circuit 19 generates the synchronization signal d at a predetermined cycle (one cycle of the sweep signal a), and the optical switch 14-
1, 14-2 are switched simultaneously.

FIG. 6 shows the operating principle of the first embodiment. In the figure, (1) is the wavelength arrangement of the wavelength multiplexed light and the transmission characteristics of the variable optical filter 12, (2) is the wavelength arrangement of the reference wavelength light, (3) is the transmission characteristics of the periodic optical filter 15, and (4) is the synchronization. It is the differential transmission characteristic of the periodic optical filter 15 obtained by the detectors 33 and 42.

The feature of this embodiment is that the reference light source 11, the optical switch 14-1, the periodic optical filter 15, and the optical switch 14- are used.
2. The control circuit 16 constitutes a stabilizing circuit to stabilize the transmission center wavelength of the periodic optical filter 15 to the wavelength of the reference wavelength light stabilized to the absorption line of atoms or molecules. Further, the variable optical filter 12, the optical switch 14-
1, the periodic optical filter 15, the optical switch 14-2, and the wavelength error detection circuit 17 constitute a wavelength discriminating circuit, and discriminate each wavelength of the wavelength multiplexed light by utilizing the periodicity of the transmission center wavelength of the periodic optical filter 15. Where it is.

The operation of the stabilizing circuit and the wavelength discriminating circuit will be described below with reference to FIGS. To operate the stabilization circuit, the optical switch 14-
1, 14-2 are switched, the reference light source 11, the periodic light filter 15, and the control circuit 16 are connected, and the reference wavelength light output from the reference light source 11 is input to the periodic light filter 15.
The central transmission wavelength of the periodic optical filter 15 is finely modulated by the reference signal c generated by the oscillator 32 of the control circuit 16. The control circuit 16 outputs the output light of the periodic optical filter 15.
Received by the photodetector 31 and the output thereof is synchronously detected by the synchronous detector 33 by the reference signal c, and the lowpass filter 34
By removing the higher harmonic component, the relative wavelength error between the wavelength of the reference wavelength light and one transmission center wavelength of the periodic optical filter 15 can be detected. A signal corresponding to this relative wavelength error is negatively fed back to the periodic optical filter 15 as the control signal b via the adder 35, and a loop for making the relative wavelength error zero works, and one transmission center of the periodic optical filter 15 is operated. The wavelength can be stabilized to the wavelength of the reference wavelength light.

Since the wavelength of the reference wavelength light is stabilized by the absorption line of an atom or a molecule, each transmission center wavelength of the periodic optical filter 15 is extremely stably controlled to a predetermined wavelength. Further, since the operation of the stabilizing circuit is repeated for each cycle of the sweep signal a by the switching signal e, each transmission center wavelength of the periodic optical filter 15 can be stabilized for a long period of time.

To operate the wavelength discriminating circuit, the optical switches 14-1 and 14-2 are switched by the switching signal e.
The variable optical filter 12, the periodic optical filter 15, and the wavelength error detection circuit 17 are connected. The sweep signal a applied to the tunable optical filter 12 is a multilevel step signal adjusted so that its transmission center wavelength changes corresponding to the wavelength interval of the wavelength division multiplexed light, and is an optical signal of each wavelength of the wavelength division multiplexed light. The (channels) are sequentially switched and sent to the periodic optical filter 15.
On the other hand, the interval between the transmission center wavelengths of the periodic optical filter 15 corresponds to the regular wavelength interval of the wavelength multiplexed light. Therefore, the output light of the periodic optical filter 15 is output to the wavelength error detection circuit 1
The photodetector 41 of No. 7 receives the light, and the output is received by the synchronous detector 42.
At the low-pass filter 4
By removing the harmonic component at 3, the relative wavelength error between each wavelength of the wavelength multiplexed light and each transmission center wavelength of the periodic optical filter 15 can be sequentially detected at the sweep period. A signal corresponding to the relative wavelength error is input to the selector 18, and the output port is sequentially switched by the synchronization signal d synchronized with the switching of each channel of the sweep signal a, thereby obtaining the wavelength error signal corresponding to each wavelength of the wavelength multiplexed light. Can be separated and taken out.

As described above, the transmission center wavelength of the tunable optical filter 12 is wavelength-multiplexed by using the sweep signal (multilevel step signal) a for calibrating the nonlinearity of the transmission center wavelength change with respect to the applied voltage of the tunable optical filter 12. By accurately sweeping at the wavelength intervals of light, the signal light of each wavelength can be separated and sequentially output. Moreover, since one transmission center wavelength of the periodic optical filter 15 is stabilized at the wavelength of the reference wavelength light, the periodic optical filter 15 can be a wavelength discriminator synchronized with the absolute wavelength. Therefore, by combining the variable optical filter 12 and the periodic optical filter 15, the wavelength error of the wavelength multiplexed light to be monitored can be discriminated with high accuracy.

(Second Embodiment) FIG. 7 shows the configuration of a second embodiment of the present invention (claim 2). This embodiment is characterized in that the optical switches 14-1 and 14-2 and the periodic optical filter 15 in the first embodiment are replaced with a tracking periodic optical filter 50. The first embodiment is characterized in that the periodic optical filter 15 constituting the wavelength discriminating circuit is switched to the stabilizing circuit side at a predetermined period to stabilize the transmission center wavelength to the wavelength of the reference wavelength light. In the present embodiment, a tracking periodic optical filter 5 that integrates a plurality of periodic optical filters is used.
0, and the stabilizing circuit and the wavelength discriminating circuit are operated in parallel. Other configurations are similar to those of the first embodiment, and corresponding components are designated by the same reference numerals and will not be described.

FIG. 8 shows a tracking periodic optical filter 50.
A configuration example of is shown. In the figure, (1) shows a Fabry-Perot interferometer type using a piezoelectric element. Two reflectors 51-
1, 51-2 are spatially opposed to each other with the piezoelectric element 52 interposed therebetween, and a plurality of input / output waveguides 53 are connected to integrally configure a plurality of Fabry-Perot interferometers. By collectively controlling the resonator length according to the voltage applied to the piezoelectric element 51,
The transmission center wavelength of each Fabry-Perot interferometer can be changed simultaneously.

(2) shows a Fabry-Perot interferometer type using a heater. The two reflecting mirrors 51-1 and 51-2 are opposed to each other via the plurality of optical waveguides 55 formed on the waveguide substrate 54, and the plurality of input / output waveguides 53 are connected to each other to form a plurality of Fabry-Perot interferometers. Are integrally configured. This waveguide substrate 54
The central transmission wavelength of each Fabry-Perot interferometer can be changed at the same time by heating the heater 56 in contact with and controlling collectively the refractive index (resonator length) of each optical waveguide.

(3) shows a Mach-Zehnder interferometer type. A plurality of Mach-Zehnder interferometers 57 are integrally formed on the waveguide substrate 54, and a plurality of input / output waveguides 53 are connected to form a plurality of Fabry-Perot interferometers. This waveguide substrate 5
The central transmission wavelength of each Mach-Zehnder interferometer can be collectively changed by heating the heater 56 in contact with 4 to collectively control the optical path length difference of each Mach-Zehnder interferometer.

(4) shows a ring resonator type. The plurality of ring resonators 58-1 to 58-n are integrally configured. By collectively controlling the length of each ring waveguide according to the voltage applied to the piezoelectric element 51, the transmission center wavelength of each ring resonator can be simultaneously changed.

As described above, the tracking periodic optical filter 50 has a structure in which a plurality of periodic optical filters are integrated,
By simultaneously changing the cavity length, the refractive index, the optical path length difference, etc., the transmission characteristics can be controlled to be the same. Therefore, by using this tracking periodic optical filter 50, the stabilizing circuit and the wavelength discriminating circuit can be operated in parallel. That is, while stabilizing the transmission center wavelength of the tracking period optical filter 50 to the wavelength of the reference wavelength light, a wavelength discriminating circuit (variable optical filter 12, tracking period optical filter 5 that operates at the same time).
0, the wavelength error detection circuit 17) can discriminate the wavelength error of the wavelength multiplexed light with high accuracy. It should be noted that one period of the sweep signal a given to the tunable optical filter 12 is shortened by one channel for the reference wavelength light.

(Third Embodiment) FIG. 9 shows the structure of a third embodiment of the present invention (claim 3). The present embodiment is characterized in that the variable optical filter 12 in the second embodiment is replaced with an optical demultiplexer 60 having the same transmission characteristic. The second embodiment has a configuration in which the tunable optical filter 12 is swept with a sweep signal a, wavelength discrimination of wavelength multiplexed light is time-divisionally performed for each wavelength, and each wavelength error signal is individually output from the selector 18. There is. In the present embodiment, the optical demultiplexer 60 separates the wavelength division multiplexed light for each wavelength, and the tracking periodic optical filter 5
By utilizing the feature of 0, each wavelength discrimination is performed simultaneously. Therefore, wavelength error detection circuits 17-1 to 17-n corresponding to each wavelength are provided. Other configurations are similar to those of the first and second embodiments, and corresponding parts are designated by the same reference numerals and will not be described.

In the structure of the present embodiment, the wavelength discriminating circuit (optical demultiplexer 60, tracking periodic light 60) corresponding to each wavelength is operated simultaneously while stabilizing the transmission center wavelength of the tracking periodic optical filter 50 to the wavelength of the reference wavelength light. Filter 50,
The wavelength error detection circuits 17-1 to 17-n) can discriminate each wavelength error of the wavelength multiplexed light simultaneously and with high accuracy.

By the way, in the embodiment shown above, one of the periodic optical filter 15 and the tracking periodic optical filter 50 is used.
Although the configuration is such that one transmission center wavelength is stabilized to the wavelength of the reference wavelength light by the synchronous detection method, the wavelength of the reference wavelength light and the transmission center wavelength do not necessarily have to match. For example, there is a method of stabilizing the transmission characteristic slope (point A) of the periodic optical filter 15 as shown in FIG. Literature
(K. Kuboki et al., "Frequency offset locking of A
lGaAs semiconductor lasers ", IEEE Journalof Quantu
m Electronics, Vol.QE-23, No.4, pp.388-394, 1987)
Shows that the oscillation wavelength of the semiconductor laser is stabilized at the center of the slope of the transmission characteristics of the Fabry-Perot interferometer. In the configuration of the present invention, since the wavelength fluctuation of the reference light source stabilized to the absorption line of atoms or molecules is better than the stability of the periodic optical filter, the periodic optical filter 15 or the tracking periodic optical filter 50 and the control circuit 16 are By forming a control loop between them, the transmission center wavelength can be stabilized.

Although the wavelength discrimination of the wavelength division multiplexed light has been described in each of the above embodiments, the optical frequency discrimination can be similarly explained.

[0044]

As described above, the wavelength monitoring device of the present invention uses the periodic optical filter or the tracking periodic optical filter which is synchronized with the reference wavelength light stabilized at a predetermined wavelength, and The wavelength accuracy of the tracking periodic optical filter can be improved, and the wavelength discrimination of the wavelength division multiplexed light can be performed by the absolute wavelength. Further, since it is possible to cope with a change in the transmission center wavelength of the periodic optical filter or the tracking periodic optical filter due to a change in the ambient temperature, stable wavelength discrimination can be performed for a long period of time.

Further, in the configuration in which the optical demultiplexer and the tracking period optical filter are combined, the wavelength sweeping function is not required, and thus the optical integrated circuit can be easily formed. As a result, it can be configured with a small number of optical circuit components, and the load on the control circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of a reference light source 11.

FIG. 3 is a block diagram showing a configuration example of a control circuit 16.

FIG. 4 is a block diagram showing a configuration example of a wavelength error detection circuit 17.

FIG. 5 is a diagram showing each signal of the first embodiment.

FIG. 6 is a diagram for explaining the operating principle of the first embodiment.

FIG. 7 is a block diagram showing the configuration of a second embodiment of the present invention.

FIG. 8 is a diagram showing a configuration example of a tracking periodic optical filter 50.

FIG. 9 is a block diagram showing the configuration of a third embodiment of the present invention.

FIG. 10 is a diagram illustrating another stabilization method of the periodic optical filter.

FIG. 11 is a block diagram showing a configuration example of a conventional wavelength monitoring device.

FIG. 12 is a diagram illustrating the operation of a conventional wavelength monitoring device.

FIG. 13 is a diagram showing a relationship between an applied voltage of a sweeping type Fabry-Perot interferometer, a displacement amount of a piezoelectric element, and a transmission center wavelength.

[Explanation of symbols]

11 Reference Light Source 12 Variable Optical Filter 13 Waveform Generator 14 Optical Switch 15 Periodic Optical Filter 16 Control Circuit 17 Wavelength Error Detection Circuit 18 Selector 19 Optical Switch Control Circuit 21 Semiconductor Laser 22 DC Power Supply 23 Oscillator 24 C ₂ H ₂ Gas Cell 25 Optical Detection 26 Synchronous detector 27 Control circuit 31 Photodetector 32 Oscillator 33 Synchronous detector 34 Low-pass filter (LPF) 35 Adder 41 Photodetector 42 Synchronous detector 43 Low-pass filter (LPF)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H04J 14/02 (72) Inventor Hitoshi Ohara 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Co., Ltd. (72) Inventor Masami Kihara 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Co., Ltd. (72) Kenichi Sato 1-1-6 Uchiyuki-cho, Chiyoda-ku, Tokyo Nihon Telegraph Phone Co., Ltd.

Claims (5)

[Claims] 1. A variable optical filter for inputting wavelength-multiplexed light, which is a signal light of a plurality of wavelengths, and sequentially outputting a signal light of a wavelength corresponding to a transmission center wavelength swept by a predetermined sweep signal; A reference light source that outputs a wavelength-stabilized reference wavelength light, a periodic optical filter having a periodic transmission center wavelength corresponding to the wavelength interval of the wavelength multiplexed light, and the reference wavelength input to the periodic optical filter The transmitted light for the light is received, the transmission characteristics are controlled according to the relative wavelength error between one transmission center wavelength of the periodic optical filter and the reference wavelength light, and the transmission center wavelength of the periodic optical filter is changed according to the wavelength of the reference wavelength light. A control circuit that stabilizes, and a wavelength error that receives transmitted light for the signal light of each wavelength input to the periodic optical filter and detects a relative wavelength error with each transmission center wavelength of the periodic optical filter. Switching means for switching the output circuit, the path connecting the variable optical filter, the periodic optical filter and the wavelength error detection circuit, and the path connecting the control reference light source, the periodic optical filter and the control circuit at a predetermined cycle. And a wavelength monitoring device. 2. A variable optical filter for inputting wavelength-multiplexed light obtained by multiplexing signal light of a plurality of wavelengths, and sequentially outputting signal light of a wavelength corresponding to a transmission center wavelength swept by a predetermined sweep signal, and a predetermined optical filter. A reference light source that outputs a wavelength-stabilized reference wavelength light and a plurality of periodic optical filters that have a periodic transmission center wavelength corresponding to the wavelength interval of the wavelength multiplexed light are integrated, and their transmission characteristics are synchronized. And a tracking periodic optical filter controlled by the tracking periodic optical filter, the transmitted light with respect to the reference wavelength light input to the tracking periodic optical filter is received, and a relative wavelength error between one transmission center wavelength of the tracking periodic optical filter and the reference wavelength light is determined. A control circuit for controlling the transmission characteristic in accordance with the tracking period optical filter and stabilizing the transmission center wavelength of the tracking periodic optical filter in accordance with the wavelength of the reference wavelength light; A wavelength error detection circuit for receiving transmitted light with respect to the signal light of each wavelength input to the optical filter and detecting a relative wavelength error with each transmission center wavelength of the tracking periodic optical filter. Wavelength monitoring device. 3. An optical demultiplexer for inputting wavelength-multiplexed light in which signal lights of a plurality of wavelengths are multiplexed, and an optical demultiplexer for demultiplexing the signal light of each wavelength, and outputting a reference wavelength light stabilized at a predetermined wavelength. A reference light source, a plurality of periodic optical filters having a periodic transmission center wavelength corresponding to the wavelength interval of the wavelength-division-multiplexed light, and a tracking periodic optical filter whose transmission characteristics are controlled in synchronization, The transmitted light with respect to the reference wavelength light input to the tracking period optical filter is received, the transmission characteristic is controlled according to the relative wavelength error between one transmission center wavelength of the tracking period optical filter and the reference wavelength light, and the tracking period optical filter A control circuit that stabilizes the transmission center wavelength of the signal light according to the wavelength of the reference wavelength light, and a transmission light for the signal light of each wavelength input to the tracking periodic optical filter. Each received, a wavelength monitoring device, characterized in that a wavelength error detecting circuit of each wavelength corresponding to detecting the relative wavelength error between the transmission center wavelength of the tracking period optical filter. 4. The wavelength monitoring device according to claim 1, wherein the control circuit includes an oscillator that generates a predetermined reference signal, and a periodic optical filter or a tracking periodic optical filter that uses the reference signal. A means for minutely modulating the transmission center wavelength, and a wavelength error for receiving the transmitted light of the periodic optical filter or the tracking periodic optical filter and synchronously detecting with the reference signal to detect a relative wavelength error between the transmission central wavelength and the reference wavelength light. A wavelength monitoring device comprising: a detection unit; and a unit that adds a signal corresponding to the relative wavelength error to the reference signal and negatively feeds back to the periodic optical filter or the tracking periodic optical filter. 5. The wavelength monitoring device according to claim 4, wherein the wavelength error detection circuit receives the transmitted light of the periodic optical filter or the tracking periodic optical filter, and synchronously detects by the reference signal generated by the control circuit. A wavelength monitoring device having a configuration for detecting a relative wavelength error with respect to a transmission center wavelength.