JPH0851411A - Frequency multiplexed light source - Google Patents

Abstract

PURPOSE:To facilitate control for stabilizing optrical frequency and to improve stability in light frequency multiplexed light source for detecting and error of each optical frequency from frequency multiplexed light obtained by multiplexing light beams having mutually different frequency bands lmitted from plural light sources and controlling respective light sources. CONSTITUTION:Frequency multiplexed light obtained by multiplexing output light beams from respective light sources 11 to 1n by a multiplexer 20 is made incident on an optical frequency discriminator 30 for changing a transmission factor correspondingly to deviations from the optical frequency bends set up in respective light sources 11 to 1n, transmitted light from the discriminator 30 is demultiplexed by a dimultiplexer 40, changes in the transmission factor by respective light frequency bands are detected by respective error detecting circuits 51 to 5n to detect respective light frequency errors, and respective light sources 11 to 1n are controlled based upon the detected results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used in optical frequency multiplex communication. In particular, it relates to generation of frequency-multiplexed light whose oscillation light frequencies are stabilized at different values.

[0002]

2. Description of the Related Art Optical frequency division multiplexing (FDM)
son multiplexing, which is synonymous with wavelength division multiplexing (FDM), is used to multiplex and transmit light of different frequencies from a plurality of light sources, and selectively receive only the light of a desired frequency by an optical filter or the like to obtain information. Demodulate. In such a case, if the oscillation frequency of the light source fluctuates, the light of the light source cannot be selected by the optical filter, or the frequency of the light from another light source may overlap and interfere with communication. Therefore, in the optical frequency multiplex communication system, it is necessary to stabilize the oscillation frequencies of a plurality of light sources at equal intervals.

FIG. 9 is a block diagram showing a conventional optical frequency multiplex light source with stabilized optical frequency. This conventional example is based on H.Toba and K.Nosu, "Optical Frequency Division
Multiplexing Systems ", IEICE TRANS.COMMMUN., VOL.
E75-B, NO.4, pp.243-255, 1992.

In this conventional example, n light sources 11, 12, ...
1n, and the optical frequencies output by each are f1 and f
2, ..., Fn are set. Actually, the light near the optical frequencies f1, f2, ..., Fn is output. The optical frequencies f1, f2, ..., Fn are evenly spaced, and the frequency spacing is Δf. These light sources 11, 12, ..., 1
The output of n is multiplexed by the star coupler 21, and the frequency multiplexed light extracted from the one output is guided to the channel selection filter 91. According to an instruction from the controller 92, the channel selection filter 91 selectively transmits only the light (light having an optical frequency near fj) from the light source 1j (where 1 ≦ j ≦ n). This transmitted light has a frequency interval Δf.
Then, the light passes through a Mach-Zehnder interferometer filter (hereinafter referred to as “MZ filter”) 31 whose transmission frequency changes periodically, and is photo-electrically converted by a photo detector 510. This gives an error signal. That is, the deviation between the frequency of the light from the light source 1j selectively transmitted by the channel selection filter 91 and the optical frequency fj is detected as an error signal.

The detected error signal is guided to the 1 × n switch 2. The 1 × n switch 2 switches its path in synchronization with the channel selection filter 91 according to an instruction from the controller 92. That is, when the channel selection filter 91 selectively transmits only the light of the light source 1j (the optical frequency is near fj), the 1 × n switch 2 feeds back the input error signal to the light source 1j. Select a route.

The light source 1j changes its optical frequency according to the error signal fed back.

That is, only the light near the optical frequency fj is selectively transmitted by the channel selection filter 91, and 1 ×
By guiding the error signal to the light source 1j by the n switch 2,
A feedback loop 7j is formed. Thus, the output light frequency of the light source 1j is fj by the feedback control.
Stabilized to.

The controller 92 sequentially switches the channel selection filter 91 and the 1 × n switch 2 synchronously and sequentially, so that the plurality of light sources 11, 12, ..., 1n can be stabilized. That is, for example, a feedback loop 71 is formed for a minimum of 1 second to stabilize the output light frequency of the light source 11 to f1, and a feedback loop 72 is formed for the next 1 second to set the output light frequency of the light source 12 to f.
The output optical frequency of the light source 1n is stabilized to fn by finally forming the feedback loop 7n in the same manner. Thereafter, this operation is repeated. In this way, each light source is feedback-controlled and stabilized for 1 second every n seconds.

[0009]

However, in the optical frequency multiplex light source shown as the conventional example, the control is complicated and the stability is insufficient. This will be described below.

First, in the optical frequency multiplex light source shown as the conventional example, it is necessary to synchronously switch the channel selection filter 91 and the 1 × n switch 2 by the controller 92. In this case, in the channel selection filter 91, it is necessary to control the transmission characteristics of the filter so as to extract any one channel from the n channels, and such control generally requires a complicated control system.

Further, the feedback loop for stabilizing the semiconductor laser is constructed only intermittently. Therefore, it is necessary to feed back the error signal to the semiconductor laser for 1 second of performing feedback control out of n seconds, and hold the error signal for the remaining (n-1) seconds. For this reason, a complicated control circuit is required. is necessary.

Further, since the feedback control is performed only once every n seconds, the control is not performed (n-1).
Fluctuations in seconds cannot be stabilized. For example, according to the above-mentioned literature, the frequency fluctuation can be stabilized only about 100 MHz peak-to-peak.

It is an object of the present invention to solve the above problems and provide an optical frequency multiplex light source which is easy to control and has excellent stability.

[0014]

The optical frequency multiplex light source of the present invention comprises a plurality of light sources whose output optical frequencies are set to different values, and a combining means for combining output lights of the plurality of light sources. , Demultiplexing means for demultiplexing the output light of each of the plurality of light sources from the combined light output from this multiplexing means, and detecting the optical frequency error of the output light of each of the plurality of light sources from the demultiplexed light of this demultiplexing means In the optical frequency multiplex light source including the error detecting means for controlling the output optical frequency of the corresponding light source according to the output of the error detecting means, a plurality of optical frequency multiplexing light sources are provided between the multiplexing means and the demultiplexing means. Each of the light sources is provided with an optical frequency discriminating means whose transmissivity changes with respect to a deviation from a set optical frequency, and the error detecting means includes means for detecting a transmissivity change by the optical frequency discriminating means. The features.

The error detecting means and the feedback loop are preferably provided in parallel corresponding to each of the plurality of light sources.

The optical frequencies output from the plurality of light sources are set at equal frequency intervals, and the optical frequency discriminating means preferably includes a periodic filter whose transmittance changes at a period equal to the frequency intervals. As the periodic filter, it is desirable to use a filter composed of a Mach-Zehnder interferometer, but it is also possible to use a Fabry-Perot filter or a ring resonator.

The optical frequency discriminating means is set so that the transmissivity becomes maximum with respect to the optical frequency set for each of the plurality of light sources, and the means for detecting the change in transmissivity is the transmission characteristic of the optical frequency discriminating means. And a photodetector for receiving the demultiplexed light of the demultiplexing unit, and a unit for performing phase-coherent detection by the modulation signal of the unit for modulating the received light output of the photodetector. Instead of modulating the transmission characteristics of the optical frequency discriminating means, the optical frequencies output by the plurality of light sources can be respectively modulated.

Further, the transmittance of the optical frequency discriminating means is set to a value which is half the maximum value with respect to the optical frequency set for each of the plurality of light sources, and the error of the optical frequency is detected by the intensity of the transmitted light. It can also be configured to.

The optical frequency discriminating means and the demultiplexing means can be formed as one element.

The multiplexing means and the demultiplexing means are formed as one element, and this element multiplexes lights having different frequencies respectively inputted to the n-1 input ports to output from one output port. The light having the same optical frequency component as the combined light output from the output port, which is output to the input port other than the n-1 input ports, is different from the light output from the one output port. It is also possible to include an optical multiplexing / demultiplexing device for demultiplexing to n-1 output ports, and to provide an optical path for optically connecting the one output port and the one input port.

[0021]

The transmission characteristic is changed corresponding to the deviation from the set value for each optical frequency of the frequency multiplexed light, and after separating each optical frequency, the error is detected for each individual optical frequency. Thereby, it becomes possible to detect an error for each optical frequency at the same time, and by providing the error detecting means and the feedback loop in parallel corresponding to each of the plurality of light sources, each light source can always be feedback-controlled.

When a periodic type filter is used as the optical frequency discriminating means for changing the transmission characteristic, the optical frequencies output from a plurality of light sources can be set corresponding to this period,
The optical frequencies can be set at equal frequency intervals in the cycle. This is convenient for use in optical frequency multiplex communication.

By setting the transmittance of the optical frequency discriminating means to be maximum for each of the multiplexed optical frequencies and modulating the transmission characteristic or the optical frequency output from the light source, the phase synchronous detection is performed. A frequency error can be detected. Further, if the transmittance is set to an intermediate value for each of the multiplexed optical frequencies, the intensity of the transmitted light fluctuates greatly due to the deviation of the optical frequencies. Therefore, the error of the optical frequency is detected by the optical intensity. be able to.

The optical frequency discriminating means and the multiplexing means, or the multiplexing means and the demultiplexing means, or three of them can be realized by one element, and the number of constituent parts can be reduced to reduce the cost and downsize.

[0025]

1 is a block diagram showing an optical frequency multiplex light source according to a first embodiment of the present invention, showing a basic configuration of the present invention. This optical frequency multiplex light source has a plurality of light sources 11, 12, ..., 1n whose output optical frequencies are set to different values f1, f2 ,.
A multiplexer 20 that multiplexes the output lights of 2, ..., 1n, and a plurality of light sources 11, 12 from the combined light that the multiplexer 20 outputs.
... and a demultiplexer 40 that demultiplexes the respective output lights of 1n,
From the demultiplexed light of the demultiplexer 40, a plurality of light sources 11, 12,
The error detection circuits 51, 52, ... 5n for detecting the optical frequency error of each output light of 1n, and the corresponding light sources 11, 12, ... According to the outputs of the error detection circuits 51, 52 ,. , 1n for controlling the output optical frequency of 1n. Here, the feature of this embodiment is that between the multiplexer 20 and the demultiplexer 40, the deviation from the optical frequency set for each of the plurality of light sources 11, 12, ... Each of the error detection circuits 51, 52, ..., 5n is provided with an optical frequency discriminator 30 whose transmittance changes.
It is configured to detect a change in transmittance due to

In this embodiment, the error detection circuit 51,
52, ..., 5n and feedback loops 71, 7
, 7n are provided in parallel corresponding to each of the plurality of light sources 11, 12, ..., 1n, and light near the optical frequency fj output from the light source 1j is input to the error detection circuit 5j.
However, 1 ≦ j ≦ n. The error detection circuit 5j uses the light source 1
The deviation between the light output by j and the transmission characteristic of the optical frequency discriminator 30 is detected and fed back to the light source 1j. In this way, the plurality of feedback loops 71, 72, ...
7n can be formed simultaneously, and an optical frequency multiplex light source that is easy to control and has excellent stability is realized.

The optical frequency discriminator 30 and the demultiplexer 40 can be formed as the same element. In addition, the multiplexer 20
And the duplexer 40 can be realized by the same element.
Further, the multiplexer 20, the optical frequency discriminator 30, and the demultiplexer 40 can be realized by the same element. Such a configuration will be described in a specific example below.

FIG. 2 is a block diagram showing the optical frequency multiplex light source of the second embodiment of the present invention, and shows a concrete configuration of the present invention. Here, for simplicity, the number of light sources will be described as five. Each light source is composed of a semiconductor laser and a variable current source that supplies a current for laser oscillation to the semiconductor laser. That is, this embodiment includes variable current sources 111 to 115 and semiconductor lasers 121 to 125. The variable current sources 111 to 115 change their output currents according to external input signals, thereby controlling the oscillation frequencies of the semiconductor lasers 121 to 125, respectively.

The semiconductor lasers 121 to 125 oscillate near the optical frequencies f1, f2, ..., F5, respectively. Here, the optical frequencies f1, f2, ..., F5 are arranged at equal intervals on the frequency axis, and the intervals are Δf.

The respective output lights of the semiconductor lasers 121 to 125 are guided to a star coupler 21 as a combining means,
The multiplexed light is output as a plurality of frequency-multiplexed lights.

One combined output of the star coupler 21 is
It is guided to the MZ filter 31 as an optical frequency discriminating means. FIG. 3 shows the transmission characteristics of the MZ filter 31. The MZ filter 31 exhibits a periodic transmission characteristic of a period Δf, and as shown by a thick line in FIG. 3, the MZ filter 31 is set so that its transmittance becomes maximum at the optical frequency fj (1 ≦ j ≦ 5). Also, M
The transmission characteristic of the Z filter 31 is modulated by the low frequency signal from the oscillator 501, and as shown by the thin line in FIG. 3, oscillates left and right on the frequency axis at a constant period T. Therefore, for example, when the frequency of the light output from the semiconductor laser 122 is smaller than f2, the transmittance of this light fluctuates in the cycle T, so that the intensity of this light after passing through the MZ filter 31 is also the cycle T. Vibrates at. Also, for example, the semiconductor laser 12
When the frequency of the light output by 4 is higher than f4, the intensity of this light still oscillates in the cycle T, but the phase of the oscillation is inverted. On the other hand, for example, when the frequency of the light output from the semiconductor laser 123 matches f3, the intensity of this light fluctuates, but its basic period is 2T,
There is no component that fluctuates in the cycle T.

The frequency-multiplexed light transmitted through the MZ filter 31 enters an arrayed waveguide grating type demultiplexer 41 as demultiplexing means and is demultiplexed according to the optical frequency. FIG. 4 schematically shows an example of demultiplexing characteristics realized by the arrayed waveguide grating type demultiplexer 41. The intensity of each demultiplexed light is converted into an electric signal by the photo detectors 511 to 515. That is, the photodetector 51j outputs an electric signal according to the intensity of the light from the semiconductor laser 12j (1 ≦ j ≦ 5).

The outputs of the photo detectors 511 to 515 are sent to the lock-in amplifiers 521 to 525, respectively, and the fluctuation component of the period T synchronized with the signal from the oscillator 501 is detected. Therefore, for example, the semiconductor laser 12
When the output light frequency of 2 is smaller than f2, the lock-in amplifier 522 outputs a positive signal, and when the output light frequency of the semiconductor laser 124 is larger than f4, the lock-in amplifier 524 outputs a negative signal. . On the other hand, for example, when the output optical frequency of the semiconductor laser 123 matches f3, the output of the lock-in amplifier 523 is zero. That is, the magnitude and direction of the deviation between the output frequency of the semiconductor laser 12j and the transmittance peak optical frequency value of the MZ filter 31 are detected by the photodetector 51j and the lock-in amplifier 52j.

The detection outputs of the lock-in amplifiers 521 to 525 are output as error signals from the variable current sources 111 to 11 respectively.
It is fed back to 5. Thus, the semiconductor laser 1
The oscillation frequencies of 21 to 125 are stabilized at the optical frequencies f1 to f5 by negative feedback control.

As described above, in this embodiment, one MZ filter 31 is passed at the stage of frequency-multiplexed light in which the output light of each light source is multiplexed, and the arrayed-waveguide grating type demultiplexer 41 is set. Provided to separate the frequency-multiplexed light from a plurality of light sources, the error of the optical frequency is detected for each light source by the photo detectors 511 to 515 and the lock-in amplifiers 521 to 52.
5 are separately detected, and are negatively fed back to each light source by different feedback loops. As a result, the oscillation frequency of the light source can always be controlled by negative feedback. In this way, compared to the conventional optical frequency multiplex light source, which could only intermittently realize the negative feedback control to each light source, it is possible to greatly improve the stability and to reduce the frequency fluctuation, for example, peak to peak. The peak can be set to 10 MHz or less. Negative feedback control can be realized simply by connecting the output of the lock-in amplifier to a variable current source, so it is complicated to switch the frequency selection filter or switch synchronously with the controller or hold the error signal value. The present invention can be carried out with a simple configuration without requiring any circuits.

In this embodiment, the photodetectors 511 to 515 are modulated by modulating the transmission characteristics of the MZ filter 31.
An error is detected by the lock-in amplifiers 521 to 525. On the other hand, the error can be detected by another method. For example, instead of modulating the transmission characteristics of the MZ filter 31, the oscillation light frequencies of the semiconductor lasers 121 to 125 may be oscillated on the frequency axis. Alternatively, the optical frequency error can be detected by the light intensity detected by the photodetectors 511 to 515 without applying modulation. That is, without using the modulator 501, a voltage comparator is provided instead of the lock-in amplifiers 521 to 525, and the transmittance of the MZ filter 31 is set to be half the maximum value at the optical frequencies f1 to f5. ,
An error in the optical frequency may be detected based on the change in transmitted light intensity.

Further, as the frequency discriminator, instead of the MZ filter 31, other means having a periodic transmission characteristic of the period Δf, such as a Fabry-Perot filter or a ring resonator, can be used to carry out the present invention in the same manner. . Further, M
It is also possible to omit the Z filter 31 and allow the array waveguide grating type demultiplexer 41 to have a frequency discriminating function. That is, the output of the oscillator 501 is used to output the arrayed-waveguide grating type duplexer 4
The demultiplexing characteristic can be oscillated on the frequency axis by changing the temperature of 1.

One of the plurality of light sources is used as a reference light source,
The optical frequency discriminating means (MZ filter 31) may be calibrated. For example, the semiconductor laser 12
1, the error signal output from the lock-in amplifier 521 is fed back to the MZ filter 31 instead of being fed back to the variable current source 11. As a result, the MZ filter 31 is stabilized based on the oscillation frequency of the semiconductor laser 121, and the oscillation frequencies of the other semiconductor lasers 122 to 125 are stabilized based on the MZ filter 31. By doing so, it is possible to obtain frequency-multiplexed light whose frequencies are arranged at equal intervals with the oscillation frequency of the semiconductor laser 121 as a reference. The semiconductor laser 121 serving as a reference light source may be arranged at a remote place, and in general, one wave of the frequency-multiplexed light propagated from a remote place may be demultiplexed and used as a reference light. it can.

FIG. 5 is a block diagram showing the optical frequency multiplex light source of the third embodiment of the present invention. In this embodiment, in order to combine the outputs of the semiconductor lasers 121 to 125, a multi-input 1
Secondly, it is possible to use the arrayed-waveguide grating type multiplexer 22 of the output and take out a part of the output by an optical branching element (optical coupler 23 in this embodiment) having no wavelength dependence and guide it to the MZ filter 31. Different from the example. With this configuration, light of a plurality of frequencies can be combined without distribution loss, so that a strong combined output can be obtained. Further, even if the light source goes out of control and outputs light of different frequencies, it is possible to prevent the light from appearing in the combined output. In addition, the array waveguide grating type multiplexer 2
In 2, if the high-order spatial mode, which is normally discarded as a loss and is not extracted, can be extracted, the combined output and the combined output used for stabilization can be extracted separately. An optical branching element such as the optical coupler 23 is unnecessary.

FIG. 6 is a block diagram showing the optical frequency multiplex light source of the fourth embodiment of the present invention. In this embodiment, the multiplexing means and the demultiplexing means are the same arrayed-waveguide grating type multiplexer / demultiplexer 2
What is realized by No. 4 is largely different from the second embodiment.

The semiconductor lasers 121 to 125 oscillate in the vicinity of the optical frequencies f1, f2, ..., F5, respectively, and the respective output lights are arrayed waveguide grating type multi / demultiplexers operating as 5 × 5 optical multi / demultiplexers. To the vessel 24. The multiplexing / demultiplexing characteristic of the arrayed-waveguide grating type multiplexer / demultiplexer 24 has a frequency f between the port a1 and the ports b1, b2, ..., B5.
, F5 are coupled to each other, and light of frequencies f2, f3, ..., F6 are coupled to each other between the port a2 and the ports b1, b2 ,. , b5 are designed to couple the lights of frequencies f5, f6, ..., F9 to each other between a5 and ports b1, b2 ,. Table 1 shows the multiplexing / demultiplexing characteristics.

[0042]

[Table 1] Due to such multiplexing / demultiplexing characteristics, the port ak (2 ≦ k ≦
When lights of frequency fk are respectively incident on 5), the lights are combined and all are output from the port b1. Therefore, the arrayed-waveguide grating type multiplexer / demultiplexer 24 functions as a multiplexer.

The frequency-multiplexed light output from the port b1 of the arrayed-waveguide grating type multiplexer / demultiplexer 24 is guided to the optical coupler 23 and branched into two, one is taken out as an output, and the other is used for frequency stabilization. To be done. The light used for frequency stabilization is frequency-discriminated by the MZ filter 31 as in the second embodiment shown in FIG. 2, and passes through the loopback optical path 61 to the port a1 of the arrayed-waveguide grating type multiplexer / demultiplexer 24. Is entered. The frequencies f2, f3, f4 input to the port a1,
According to the above-mentioned characteristics, the light of f5 has the port b.
2, b3, b4, b5. That is, the arrayed waveguide grating type multiplexer / demultiplexer 24 functions as a demultiplexing unit here.

The respective demultiplexed lights are photodetectors 512 to 515 and the lock-in amplifier 5 from the respective demultiplexed lights as in the second embodiment shown in FIG.
Stabilization is realized by detecting the optical frequency error by 22 to 525 and feeding back the error signal to the semiconductor lasers 122 to 125.

As described above, this embodiment uses the arrayed-waveguide-grating type multiplexer / demultiplexer 24 which operates in the same manner as the second embodiment and has the functions of the multiplexing means and the demultiplexing means. By doing so, the number of constituent parts can be reduced, which enables downsizing and cost reduction. Further, since the array waveguide grating type multiplexer / demultiplexer 24 having frequency selectivity is used as the demultiplexing means, even if the light source runs out and outputs light of different frequencies, it does not appear in the multiplexed output. It also has the advantage of. Also in this embodiment, if the array waveguide grating type multiplexer / demultiplexer is constructed so as to extract the higher-order spatial mode which is not normally extracted but is discarded as loss, it is used for combined output and stabilization. It becomes possible to take out separately the combined output for
Becomes unnecessary.

Also in this embodiment, as in the second embodiment,
The optical frequency error can be detected by other methods.
Further, the MZ filter 31 may be omitted and the array waveguide grating type multiplexer / demultiplexer 24 may have the function thereof. That is, the temperature of the arrayed waveguide grating type multiplexer / demultiplexer 24 may be changed by the output of the oscillator 501, and the multiplexing / demultiplexing characteristic may be vibrated on the frequency axis. In this case, the semiconductor lasers 122-
Since each output of 125 passes through the arrayed waveguide grating type multiplexer / demultiplexer 24 twice, in the second embodiment, the MZ filter 3 is used.
1 is omitted, and its function is arrayed waveguide grating type multiplexer / demultiplexer 4
There is also an advantage that the frequency discrimination sensitivity is improved as compared with the case where it is set to 1. This is because the arrayed-waveguide-grating-type multiplexer / demultiplexer 24 exhibits the transmission characteristic as shown in FIG. 4 in one pass, and the transmission characteristic becomes sharper in two passes (transmission bandwidth). Is, for example, 0.7 times).

Further, instead of vibrating the characteristics of the MZ filter 31 or the arrayed waveguide grating type multiplexer / demultiplexer 24,
The oscillation frequencies of the semiconductor lasers 122 to 125 may be oscillated on the frequency axis.

Similarly, using one of the plurality of light sources as a reference light source, the optical frequency discriminating means (the MZ filter 31 or the arrayed waveguide grating type multiplexer / demultiplexer 24 having the function).
May be configured to be calibrated. For example, in the configuration of FIG. 6, when the semiconductor laser 122 is used as the reference light source, instead of feeding back the error signal which is the detection output of the lock-in amplifier 522 to the variable current source 112, the MZ is used.
It may be configured to feed back to the filter 31. As a result of this, the MZ filter 31 causes the semiconductor laser 122 to
Of the other semiconductor lasers 123 to 125, while the oscillation frequencies of the other semiconductor lasers 123 to 125 are stabilized by the MZ filter 3.
Stabilized on the basis of 1. Thus, the semiconductor laser 12
It is possible to obtain frequency-multiplexed light in which the frequencies are arranged at equal intervals based on the oscillation frequency of 2. The semiconductor laser 122 serving as a reference light source may be arranged at a remote place, and the frequency-multiplexed light propagated from the remote place is directly input to the port a2 of the arrayed-waveguide grating type multiplexer / demultiplexer 24. May be. In this case, the light of the frequency f2 of the frequency multiplexed light acts as the reference light.

FIG. 7 is a block diagram showing the optical frequency multiplex light source of the fifth embodiment of the present invention. This embodiment differs from the first embodiment in that the loopback optical path 61 is connected to the port a2. In this case, the arrayed waveguide grating type multiplexer / demultiplexer 2
Table 2 shows the multiplexing / demultiplexing characteristics required for No. 4 above.

[0050]

[Table 2] In this way, p ≠ q for the port bp that outputs wavelength-multiplexed light and the port aq (1 ≦ p, q ≦ 5) that is looped back.
In this case, the multiplexing / demultiplexing characteristic of the arrayed waveguide grating type multiplexer / demultiplexer 24 may satisfy the circularity as shown in Table 2.

FIG. 8 is a block diagram showing the optical frequency multiplex light source of the sixth embodiment of the present invention. In this embodiment, a loopback optical path 65 is used instead of the loopback optical path 61, and M
The difference from the fifth embodiment is that the output of the Z filter 31 is input from the port bp of the arrayed waveguide multiplexer / demultiplexer 24.

The semiconductor lasers 122 and 124 oscillate in the vicinity of the optical frequencies f2 and f4, respectively, and the respective output lights are the ports a2 of the arrayed waveguide grating type multiplexer / demultiplexer 24.
Each is led to a4. Each light is output from the multiplexed port b1 according to the multiplexing / demultiplexing characteristics shown in Table 1.

The frequency-multiplexed light output from the port b1 is branched into two by the optical coupler 23, and the MZ filter 31
After the frequency is discriminated by (1), it is input to the port b2 of the arrayed-waveguide grating type multiplexer / demultiplexer 24 through the folding optical path 65. Light of frequencies f2 and f4 input to the port b2 is
According to the multiplexing / demultiplexing characteristics shown in Table 1, the ports a1 and
It is led to a3.

Hereinafter, similar to the second embodiment described with reference to FIG. 2, photodetectors 512 and 514 and lock-in amplifiers 522 and 52 are extracted from the respective demultiplexed lights.
An optical frequency error is detected by 4, and the error signal is fed back to the semiconductor lasers 122 and 124 to stabilize the oscillation frequency.

In the fourth and fifth embodiments described with reference to FIGS. 6 and 7, crosstalk of the arrayed waveguide grating type multiplexer / demultiplexer 24 may cause interference noise in the combined output. There was a nature. For example, referring to FIG. 6, a component used for frequency stabilization in the light output from the semiconductor laser 122 is re-input from the port a1 of the arrayed-waveguide grating type multiplexer / demultiplexer 24 and then port b2.
Is output to the port b1, but a small amount is also mixed in the port b1. Since this mixed light is the light from the same light source as the light included in the combined output extracted from the ports a2 and b1 which is the original output light, the mixed light interferes and the light intensity fluctuates.

On the other hand, in the sixth embodiment shown in FIG. 8, the component used for frequency stabilization is the array waveguide grating type multiplexer / demultiplexer from the port b2 on the same side as the port b1 for extracting the multiplexed output. Since it is re-inputted to 24, crosstalk light is not mixed in the multiplexed output. Therefore, the light intensity does not fluctuate due to the interference.

As described above, the present embodiment operates in the same manner as the fourth and fifth embodiments, and additionally, the individual output light from the light source and the frequency-multiplexed light multiplexed are arrayed waveguide gratings. By propagating in the opposite direction with the type multiplexer / demultiplexer 24,
It is possible to take out the combined output without deterioration due to interference noise.

Also in the case of the present embodiment, if the array waveguide grating type multiplexer / demultiplexer is constructed so as to extract the higher-order spatial mode which is normally discarded and is discarded as a loss, the combined output and the stability are obtained. It is also possible to separately take out the combined output used for conversion, and the optical coupler 23 becomes unnecessary.

Also in this embodiment, the frequency error may be detected by another method as in the above-mentioned embodiment. The MZ filter 31 may be omitted and the array waveguide grating type multiplexer / demultiplexer 24 may have the function thereof. The optical frequency discriminating means (the MZ filter 31 or the arrayed waveguide grating type multiplexer / demultiplexer 24 having the function) may be calibrated by using one of the plurality of light sources as a reference light source.

In the embodiment shown in FIG. 8, the combined output is taken out from the port b1 of the arrayed-waveguide grating type multiplexer / demultiplexer 24 and the folded optical path 65 is connected to the port b2.
The same operation can be performed by using the other ports bp and bq (1 ≦ p, q ≦ 5).

[0061]

As described above, the optical frequency multiplex light source of the present invention can simultaneously detect an error for each optical frequency of the frequency multiplex light, and it is possible to configure a plurality of feedback loops at the same time. . Therefore, there is an effect that it is possible to easily carry out without using a complicated control circuit such as loopback loop switching and to obtain frequency multiplexed light with excellent frequency stability.

Further, when the demultiplexing means is also used as the optical frequency discriminating means, the number of constituent parts can be reduced and the cost and the size can be reduced. Furthermore, by combining the demultiplexing means and the multiplexing means with a single element, or by using the demultiplexing means, the optical frequency discriminating means and the multiplexing means with a single element, the number of components can be further reduced to further reduce the cost. Reduction and miniaturization can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical frequency multiplex light source according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an optical frequency multiplex light source according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a transmission characteristic of an MZ filter.

FIG. 4 is a diagram schematically showing an example of demultiplexing characteristics of an arrayed waveguide grating type demultiplexer.

FIG. 5 is a block diagram showing an optical frequency multiplex light source according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing an optical frequency multiplex light source according to a fourth embodiment of the present invention.

FIG. 7 is a block diagram showing an optical frequency multiplex light source according to a fifth embodiment of the present invention.

FIG. 8 is a block diagram showing an optical frequency multiplex light source according to a sixth embodiment of the present invention.

FIG. 9 is a block diagram showing a conventional optical frequency multiplex light source.

[Explanation of symbols]

 11, 12, ..., 1n light source 111-115 variable current source 121-125 semiconductor laser 2 1 × n switch 20 multiplexer 21 star coupler 22 array waveguide grating type multiplexer 23 optical coupler 24 array waveguide grating type combination Demultiplexer 30 Optical frequency discriminator 31 MZ filter 40 Demultiplexer 41 Arrayed waveguide grating type demultiplexer 51, 52, ..., 5n Error detection circuit 501 Oscillator 510-515 Photodetector 521-525 Lock-in amplifier 61 Loopback optical path 65 Folded-back optical paths 71, 72, ..., 7n Feedback loop 91 Channel selection filter 92 Controller

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Claims (8)

[Claims] 1. A plurality of light sources whose output optical frequencies are set to different values, a combining means for combining the output lights of the plurality of light sources, and a plurality of the combined lights output from the combining means. Demultiplexing means for demultiplexing the output light of each light source, error detecting means for detecting the optical frequency error of the output light of each of the plurality of light sources from the demultiplexing light of the demultiplexing means, and the error detecting means An optical frequency multiplex light source including a feedback loop for controlling an output optical frequency of a corresponding light source according to an output, wherein the light set in each of the plurality of light sources is provided between the multiplexing unit and the demultiplexing unit. An optical frequency discriminating unit that changes the transmissivity with respect to a deviation from the frequency is provided, and the error detecting unit includes a unit that detects a transmissivity change by the optical frequency discriminating unit. Frequency multiplex light source. 2. The optical frequency multiplex light source according to claim 1, wherein the error detection means and the feedback loop are provided in parallel corresponding to each of the plurality of light sources. 3. The optical frequencies output from the plurality of light sources are set at equal frequency intervals, and the optical frequency discriminating means includes a periodic filter whose transmittance changes at a period equal to the frequency intervals. 2. The optical frequency multiplex light source according to 2. 4. The optical frequency multiplex light source according to claim 3, wherein the periodic filter is a filter composed of a Mach-Zehnder interferometer. 5. The optical frequency discriminating means is set so that the transmissivity is maximized with respect to the optical frequency set for each of the plurality of light sources, and the means for detecting a change in the transmissivity is the optical frequency discriminating means. A means for modulating the transmission characteristic of the frequency discriminating means, a photodetector for receiving the demultiplexed light of the demultiplexing means, and a means for phase-coherently detecting the received light output of the photodetector by the modulation signal of the modulating means. An optical frequency multiplex light source according to any one of 1 to 4. 6. The optical frequency discriminating means is set so that the transmissivity is maximized with respect to the optical frequency set for each of the plurality of light sources, and the means for detecting the change in the transmissivity is the plurality of light sources. Means for respectively modulating the optical frequency output by the light source, and a photodetector for respectively receiving the demultiplexed light of the demultiplexing means,
2. A means for phase-synchronizing detection of a light-receiving output of the photodetector by a modulation signal of the means for modulating.
5. An optical frequency multiplex light source according to any one of items 4 to 4. 7. The optical frequency multiplex light source according to claim 1, wherein the frequency discriminating means and the demultiplexing means are formed as one element. 8. The multiplexing means and the demultiplexing means are formed as a single element, and the element multiplexes lights having different frequencies respectively input to n-1 input ports to form a single element. Light having the same optical frequency component as that of the combined light output from the output port, which is output from the output port of the output port and is input to one input port different from the n-1 input ports. 2. An optical path including one optical multiplexing / demultiplexing device for demultiplexing to n-1 output ports other than the above, and an optical path optically connecting the one output port and the one input port. 7. The optical frequency multiplex light source according to any one of 7.