JPH0514280A - Light frequency dividing multiplex transmitter - Google Patents

Abstract

PURPOSE:To obtain a light frequency dividing multiplex transmitter having a local frequency in which a light receiver is stably controlled even when the trouble of a transmitting light source and the disconnection of an optical fiber occur. CONSTITUTION:An optical filter having a periodical light transmission characteristic is arranged at respective light frequency dividing multiple transmitter and a light frequency dividing multiple receiver and each optical filter is stabilized by an absolutely stabilized reference light frequency. That is, the transmitter is equipped with an optical filter, a transmitting optical filter stabilizer 2 and the N number of light transmitters 3. Each light signal frequency is stabilized to the periodical transmission characteristic of the optical filter arranged to the transmitter and each local frequency is respectively stabilized to the periodical transmission characteristic of the optical filter arranged to the receiver. Thus, since the light signal frequency and the local frequency are respectively independently stabilized, even when a light signal is not inputted to the receiver, the local frequency continues to be controlled stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device using an optical frequency division multiplexing technique for transmitting a large amount of information on one optical fiber.

[0002]

2. Description of the Related Art Optical frequency division multiplexing transmission equipment (hereinafter frequency division multiplexing is called FDM. However, FDM is Frequency
The division multiplexing is usually an optical FDM transmitter having a plurality of (N, N is a natural number of 1 or more) transmission light sources, an optical fiber for transmitting an optical FDM signal, and a plurality (N
Optical FDM receiver having a heterodyne optical receiver. The frequency interval of the transmission light source is normally stabilized at a constant value D _op . In addition, each heterodyne optical receiver (for example, n-th, n is a natural number, 1 ≦ n
≦ N) receives only the optical signal output from the corresponding transmission-side light source (nth). For a conventional example of the optical FDM transmission device, see, for example, I-A-I-A, Photonics Technology Letters, Volume 2, Number 1.
2, pages 914-916 (IEEE Photonics Technol
ogy Letters, vol.2, No.12, pp.914-916). In a conventional optical FDM transmission apparatus, the frequency of a local light source (hereinafter,
By controlling the local oscillation frequency), the difference frequency between them (hereinafter referred to as the intermediate frequency) is stabilized at a constant value f _IF .

[0003]

In the conventional apparatus, the local frequency is controlled so that the intermediate frequency becomes constant. Therefore, the optical signal is transmitted to the optical FDM receiving apparatus due to the failure of the transmission light source or the disconnection of the optical fiber. However, there is a problem that the control of the local oscillation frequency becomes impossible when is input.

[0004]

The above problem is caused by disposing an optical filter having a periodic light transmission characteristic in each of the optical FDM transmitter and the receiver, and each optical filter has an absolutely stabilized reference optical frequency. And each optical signal frequency is stabilized by the periodical transmission characteristic of the optical filter arranged in the optical FDM transmitter, and each local frequency is periodical transmission characteristic of the optical filter arranged in the optical FDM receiver. It can be realized by stabilizing each.

The object of the present invention is to solve the above problems,
That is, an optical FDM transmission device capable of controlling the local oscillation frequency of the optical FDM reception device is realized even when an optical signal is not input to the optical FDM reception device due to a failure of the transmission light source or a break of the optical fiber. To do.

[0006]

A Fabry-Perot resonator (hereinafter abbreviated as FP resonator) is taken as an example of a typical optical filter. The light transmission characteristics of the FP resonator are determined by the refractive index n ₀ peculiar to the resonator material and the resonator length L (normally called FSR.
Stands for Free Spectral Range). It is known that the value of FSR is given by c / 2Ln ₀ (where c is the speed of light in vacuum). Therefore, the FSR of the FP resonator can be freely designed by determining L and n ₀ .

In the present invention, an optical FDM transmitter and an optical FDM are provided.
Each DM receiver has one FP resonator (transmit F
P resonator and receiving FP resonator). In particular, the FSR of the transmitting FP resonator and the receiving FP resonator (FSR1
And FSR2) satisfy the following equation, the device of the present invention can be realized with a simple configuration.

FSR1 = (1 / m ₁ ) · D _op (where m ₁ is a natural number) ... (Equation 1) FSR2 = (1 / m ₂ ) · D _op (where m ₂ is a natural number) ... (Equation 2) ) FSR2 = (1 / k) · f _IF (where k is a natural number) (Equation 3) An example of the transmission characteristics of the FP resonator satisfying the above three equations is shown in FIG.
Shown in (a) and (b). In the figure, the horizontal axis represents the optical frequency, and the vertical axis represents the power density of light and the transmittance of the FP resonator. The broken line represents the transmission characteristic of each FP resonator. In the figure (a), FSR1 = D _op (however,
m ₁ = 1), and in the same figure (b), FSR2 = (1 /
4) -D _op = f _IF (however, m ₂ = 4, k = 1) are shown.

In the present invention, the transmission characteristics of these two FP resonators are independently stabilized with respect to the absolutely stabilized reference optical frequency F ₀ . The example of FIG. 2 has two FPs so that the transmittance has a peak at the reference optical frequency F ₀ .
The case where the resonator is stabilized is shown. Next, with respect to the FP resonator thus stabilized, the optical signal frequency of channel 1, channel 2, ..., Channel N in the optical FDM transmitter is set to each optical frequency at which the transmittance of the transmitting FP resonator reaches a peak. Stabilizes to. As a result, channel 1, channel 2,
..., the optical signal frequencies of the channel N are F ₀ + D _op , respectively.
F ₀ + 2D _op , ..., F ₀ + ND _op , and the optical signal frequency interval is stabilized at D _op . On the other hand, in the optical FDM receiver, the transmission characteristics of the local luminescence 1, local luminescence 2, ..., Local luminescence N used for heterodyne detection of the optical signals of channel 1, channel 2, ... The optical frequency at which the peak is F ₀ + D _op + f _IF , F ₀ + 2D _op
Stabilize at + f _IF , ..., F ₀ + ND _op + f _IF at D _op intervals. As a result, the frequency difference between a certain optical signal frequency and the corresponding local oscillation frequency is f _{IF for} any channel. Therefore, when the optical signal of channel n is received by the heterodyne detector having the local oscillation light source (n), the intermediate frequency of the obtained signal is always f _IF . At this time, since the optical signal frequency and the local oscillation frequency are independently stabilized, the local oscillation frequency continues to be stably controlled even if the optical signal is not input to the heterodyne detector.

As described above, according to the present invention, the optical signal frequency is stabilized by the optical FDM transmitter and the local oscillation frequency is stabilized by the optical FDM receiver, respectively. Optical FDM due to fiber breakage, etc.
Even if an optical signal is not input to the receiving device, the local oscillation frequency can be stably controlled.

[0011]

[Example] 1. First Embodiment FIGS. 1 and 2 show a first embodiment of the present invention. The optical FDM transmission apparatus is an optical FD that inputs N information signals (channel 1 signal-channel N signal) and outputs an optical FDM signal.
An M transmitter (FIG. 1), an optical fiber (1 in the figure) for transmitting an optical FDM signal, and an optical FDM receiver (FIG. 2) for inputting an optical FDM signal and outputting a channel 1 signal-channel N signal. It consists of As a modulation method applied to each optical signal, frequency shift keying, amplitude shift keying, phase shift keying, and the like can be considered.

1.1 Optical FDM Transmitter The optical FDM transmitter is a transmission optical filter, a transmission optical filter stabilizing device (2 in the figure), and N optical transmitters (channel 1).
(Optical transmitter-channel N optical transmitter) (3 in the figure), an optical multiplexer for multiplexing optical signals output from N optical transmitters and outputting an optical FDM signal, and an optical FDM signal. It is composed of an optical coupler that branches into two.

(1) Transmitter Optical Filter Stabilizer First, the structure will be described. The constituent elements of the transmission optical filter stabilizing device are an optical frequency reference light source that outputs an absolutely stabilized reference optical frequency F _0, and an optical frequency modulator that performs frequency modulation on the light output from the light source at a frequency f _0. , An optical coupler for multiplexing the frequency-modulated light and the optical FDM signal and inputting them to the transmission Fabry-Perot resonator (transmission characteristics are indicated by the broken line in FIG. 3A), and output from the transmission Fabry-Perot resonator From a photodiode that obtains a detection signal by converting the generated light into an electric signal, a bandpass filter (BPF in the figure, center frequency f ₀ ) that extracts a signal component of frequency f ₀ from the detection signal, and the extraction signal and oscillator and the signal (frequency f ₀₎ and multiplier for multiplying the low-pass filter for extracting an error signal from the multiplication signal (LPF in the figure, the cutoff frequency f _LPF, f _LPF «f ₀₎ and, Send by error signal It is a temperature control circuit that controls the temperature of the signal Fabry-Perot resonator. The optical frequency reference light source is, for example, the document I-A-A-I, Photonics Technology Letters, Volume 1, No. 6, pages 140-141 (IEEE Photonics Techn
ology Letters, vol.1, No.6, pp.140-141) etc. The optical frequency modulator can be realized by using lithium niobate or the like having an electro-optical effect. In addition, the transmission FP resonator is
For example, it can be realized by using a material such as synthetic quartz or BK-7. Since these materials have a non-zero expansion coefficient with respect to changes in temperature, it is possible to control the length of the resonator by changing the temperature.

Next, the operation principle will be described. FIG. 4 shows the waveforms of the signals obtained in each part when the transmission FP resonator is stabilized by using the light of the frequency F ₀ output from the reference light source. FIG. 4A shows a voltage signal of frequency f ₀ applied to the optical frequency modulator. As a result of the voltage application, an optical signal (center frequency F ₀ , frequency deviation ± ΔF, ΔF << D _op / 2) that has been frequency-modulated can be obtained as the output of the optical frequency modulator (FIG. 2B). . When this optical signal is input to a transmission FP resonator having a transmission characteristic as shown in FIG. 3A and its output is detected by a photodiode, FIG.
A detection signal as shown in (c) can be obtained. Such a waveform is obtained because the transmission FP resonator has a frequency F.
_This is because the transmittance has a peak at ₀ and the power of the light output from the transmission FP resonator is maximized every time the optical frequency of the frequency-modulated signal matches F ₀ . This time,
The frequency of fluctuation of the detection signal is 2f ₀ . Therefore, this detection signal is removed by the bandpass filter. As a result, the error signal output from the low-pass filter becomes zero, and the temperature control circuit keeps the temperature of the transmission FP resonator constant without changing it. That is, the frequency at which the transmittance of the transmission FP resonator reaches its peak continues to be stabilized at F ₀ . However, the transmission characteristics of the transmission FP resonator fluctuate and the frequency F ₀ +
When the transmittance peaks at ΔF, the detection signal has a waveform as shown in FIG. This detection signal has a frequency f ₀ and passes a bandpass filter. When the signal (frequency f ₀ ) from the oscillator is multiplied, a positive signal whose frequency is near zero (near DC) is generated. When this signal is input to the low pass filter, a positive error signal is output. This error signal, the frequency at which the transmittance of the transmission FP resonator has a peak F ₀ + temperature control circuit back to the F ₀ from ΔF is operated. On the other hand, when the transmission characteristic of the transmission FP resonator fluctuates and has a transmittance peak at the frequency F ₀ −ΔF, the detected signal is as shown in FIG.
The waveform as shown in (e) (the frequency is f ₀ ,
The phase is shifted by 180 degrees compared to the case of (d)), and a negative error signal is obtained. As a result, the temperature control circuit operates in the opposite direction to the case of FIG. (D), returning the frequency of transmission of the transmission FP resonator has a peak of F ₀ -.DELTA.f to F _0. From the above, with the transmission Fabry-Perot resonator stabilizing device shown in FIG. 1, the transmission characteristic of the transmission FP resonator is frequency F _0.
Is controlled to have a peak at. Although the optical FDM signal is input to the transmission FP resonator in addition to the reference optical frequency F ₀ , the frequency f ₀ can be set sufficiently large compared to the transmission rate of each optical signal that constitutes the optical FDM signal. If
The influence of the optical FDM signal is due to the band pass filter (center frequency f
_It can be removed by ₀ ). That is, the optical FDM signal is transmitted by the transmission FP
Even if input to the resonator, the same signal as shown in FIG. 4 can be obtained.

(2) Optical transmitter An example of the structure of an apparatus for stabilizing the frequency of each transmission light source with respect to the transmission FP resonator is shown as the optical transmitter in FIG. The optical transmitter comprises a transmission light source, an adder, and an optical signal frequency stabilizing circuit. The optical transmitter of each channel has the same configuration. The transmission light source in the channel n optical transmitter will be called a transmission light source (n). In this configuration, the optical FDM signal is transmitted to the transmission FP via the optical coupler.
Input to the resonator. The correspondence between the frequency at which the transmittance of the transmission FP resonator reaches its peak and the frequency of each optical signal is shown in FIG.
As shown in. The detection signal output from the photodiode is branched and distributed to the optical signal frequency stabilizing circuit in each channel optical transmitter. The detection signal includes information on frequency fluctuations of all the transmission light sources. For this reason,
For example, in the optical transmitter of channel 1, only the information of the frequency fluctuation of the transmission light source of channel 1 (correlation signal) is extracted by multiplying the detection signal by the signal of channel 1 and taking the correlation. A high-pass component is further removed from the correlation signal by a low-pass filter (LPF in the figure, cutoff frequencies f _LPF , f _LPF << transmission speed f _{0 of} each signal), and the correlation signal is output as an error signal. The error signal is added to the channel 1 signal and the bias signal and injected into the transmission light source (1). The error signal is injected with a polarity such that the optical frequency of the transmission light source (1) is stabilized at the frequency F ₀ + D _op at which the transmittance of the transmission FP resonator reaches its peak. By the same operation, the transmission light sources (2) to (N) of the other channels are stabilized at the transmittance peaks of the corresponding transmission FP resonators. That is, the channel 1, channel 2, ..., Channel N optical signal frequencies are stabilized to F ₀ + D _op , F ₀ + 2D _op , ..., F ₀ + ND _op , respectively. The principle of the above-mentioned stabilization method is described in, for example, Literature, Electronics Letters, Volume 23, Number 14, 750 to 752 (Electronics Lett).
ers vol.23, No.14, pp.750-752).

1.2 Optical FDM Receiving Device FIG. 2 shows a device configuration example on the receiving side. The optical FDM receiver includes a reception optical filter, a reception optical filter stabilizer (6 in the figure), and N heterodyne optical receivers (channel 1 heterodyne optical receiver-channel N heterodyne optical receiver) (7 in the figure). ) And an optical demultiplexer for demultiplexing the optical FDM signal into N heterodyne optical receivers.

(1) Receiving Optical Filter Stabilizing Device The operation of the receiving optical filter stabilizing device is the same as that of the transmitting Fabry-Perot resonator stabilizing device in the optical FDM transmitter.
The structure in which an optical multiplexer is added to the transmission Fabry-Perot resonator stabilizer is to combine the local oscillation light output from each heterodyne optical receiver and input it to the reception Fabry-Perot resonator. A Mach-Zehnder type optical filter or a star coupler can be used as the optical multiplexer.

(2) Heterodyne optical receiver First, the configuration will be described. The configuration will be described by taking a channel 1 heterodyne optical receiver as an example. The components of the channel 1 heterodyne optical receiver are driven by the output of the adder, and output a local oscillation light source with an optical frequency F ₀ + D _op + f _IF ; an optical coupler for branching the local oscillation light; A polarization diversity optical receiver that receives an optical signal using one output of a coupler and outputs a baseband signal, and an identification reproduction circuit that identifies and reproduces a channel 1 signal from the signal output from the polarization diversity optical receiver. And a local oscillation frequency stabilizing circuit for obtaining an error signal from the detection signal obtained by the receiving Fabry-Perot resonator stabilizing device. Further, the components of the local oscillation frequency stabilizing circuit can detect the frequency f ₁ from the detection signal.
A band-pass filter (BPF, center frequency f ₁ ) for extracting the component of, an oscillator (a frequency is the same as the center frequency of the band-pass filter, f ₁ ) that outputs a sine wave signal, an extraction signal and a sine wave signal A multiplier for multiplying, and a low-pass filter (LP for extracting an error signal from the multiplied signals)
F, cutoff frequencies f _LPF , f _LPF << f ₁ ) and an adder for adding the error signal, the sine wave signal, and the bias signal. The heterodyne optical receiver for each channel has a similar configuration. However, the frequency of the oscillator and the center frequency of the bandpass filter are channel 1, channel 2, ..., Channel N.
, F ₁ , f ₂ , ..., F _N , which are different for each channel (f ₁ ≠ f ₂ ≠ ... ≠ f _N ≠ f ₀ ). Also, channel n
The local light source in the heterodyne optical receiver will be referred to as a local light source (n). The above-mentioned polarization diversity optical receiver is disclosed in, for example, the literature, IEE, EEE, Journal of Lightwave Technology, Vol.
Lightwave Technology, vol.LT-5, no.2, pp.274-276)
It can be realized by the configuration described in.

Next, the operation principle will be described. In the heterodyne optical receiver, channel 1, channel 2, ..., Channel N
Receiving the optical frequency of the local light source (local light source (1) -local light source (N)), the corresponding peak transmittance frequencies (F ₀ + D _op + f _IF , F ₀ + D _op + 2f _IF , ... , F ₀ + D
_In order to stabilize at _op + Nf _IF ), the local light source is frequency-modulated with a minute sine wave current. The modulation frequency f ₁ , for each of channel 1, channel 2, ..., Channel N,
f _2, ..., assign _{f N (f 1 ≠ f 2} ≠ ... ≠ f N ≠ f 0). The stabilization operation will be described by taking a channel 1 heterodyne optical receiver as an example. FIG. 5 shows the signal waveform of each part. FIG. 6A shows the waveform of the modulation current. As a result of the modulation, an optical signal frequency-modulated around the frequency F ₀ + D _op + f _IF can be obtained ((b) of the same figure). When this optical signal is input to the receiving FP resonator having the transmission characteristics shown by the broken line in FIG. 1B and the output is detected by the photodiode, a detection signal as shown in FIG. 5C is obtained. be able to. Such a waveform is obtained by the receiving FP
The resonator has a peak of transmittance at the frequency F ₀ + D _op + f _IF , and the optical frequency of the frequency modulation signal is F ₀ + D
_This is because the power of the light output from the receiving FP resonator is maximized every time it matches _op + f _IF . At this time, the frequency of fluctuation of the detection signal becomes 2f ₁ . Therefore, this detection signal is removed by the bandpass filter. As a result, the error signal output from the low pass filter becomes zero, and the frequency of the local light source (1) is kept constant. However, the frequency of the local light source (1) fluctuates and the center frequency becomes F ₀ + D _op +
When f _IF −ΔF, the detection signal has a waveform as shown in FIG. This detection signal has a frequency f ₁ , passes through a bandpass filter, and has a frequency near zero (near DC) by multiplication with the signal from the oscillator (frequency f ₁ ).
Generate a positive signal. As a result, a positive error signal is output from the low pass filter. With this error signal,
The frequency of the local light source (1) is returned to F ₀ + D _op + f _IF . On the other hand, when the frequency of the local light source (1) fluctuates and the center frequency becomes F ₀ + D _op + f _IF + ΔF, the detection signal is as shown in FIG.
The waveform becomes as shown in (e), and a negative error signal is obtained.
As a result, the frequency of the local light source (1) is F ₀ + D _op + f _IF +
It is returned from ΔF to F ₀ + D _op + f _IF . The receiving FP
In addition to the light from the local light source (1), light from other local light sources (2)-(N) is also input to the resonator, but each light is frequency-modulated at a different frequency. Therefore, the band pass filter (BPF) included in each heterodyne optical receiver can extract only the information on the fluctuation of the local oscillation light source frequency. That is, even if other light is input to the receiving FP resonator, it is possible to obtain a signal having the same waveform as that shown in FIG. From the above, the optical frequencies of the local light sources of channel 1, channel 2, ..., Channel N of the heterodyne optical receiver are F ₀ + D _op + f _IF , F ₀ + 2D _op + f _IF , respectively.
…, Stabilized to F ₀ + ND _op + f _IF .

1.3 Optical FDM Transmission Device As described above, when the optical FDM transmission device having the configuration of FIG. 1 receives an optical signal of channel n (1 ≦ n ≦ N) at the channel n heterodyne optical receiver, it is obtained. The intermediate frequency of the signal is always f _IF . At this time, since the optical signal frequency and the local oscillation frequency are independently stabilized, the local oscillation frequency can be stably controlled even if the optical signal is not input to the heterodyne detector.

2. Second Embodiment FIG. 6 shows the configuration of the second embodiment of the optical FDM receiver.
The second embodiment is an improvement of the optical FDM receiver of the first embodiment for an information distribution type optical FDM transmission system. The optical FDM signal obtained by the optical FDM transmitter (the configuration is the same as that of FIG. 1) is distributed to the tunable optical FDM receivers arranged at different places via different optical fibers. In the optical FDM receiver, the transmitted optical FDM
One channel of the desired optical signal is selected from the signals and received. It is necessary to switch the frequency of the local oscillation light source in order to switch the channel of the optical signal to be received, and a tunable heterodyne optical receiver is installed on the receiving device side.

The optical FDM receiver of this embodiment comprises a receiving optical filter, a receiving optical filter stabilizing device, and a tunable heterodyne optical receiver (11 in the figure). The configuration of the receiving optical filter stabilizing device is as shown as 10 in FIG. 6, and is equivalent to the configuration of the device 6 of the first embodiment from which the optical coupler is removed. This is because the present optical receiver has only one local light source. A first method is to stabilize the reception Fabry-Perot resonator at the reference optical frequency F ₀ .
This is similar to the case of the embodiment.

The difference between this embodiment and the first embodiment is that the frequency of the local light source is switched according to the channel of the received optical signal. The configuration of the tunable heterodyne optical receiver is shown at 11 in FIG. In addition to the configuration in which the optical tuner 13 is added to the heterodyne optical receiver 7 of FIG. 2, a switch 14 is added to the local oscillator frequency stabilizing circuit 12. Light tuner removes a signal component of the frequency f ₁ low pass filter (LPF, a cutoff frequency f ₁ ', f _1' <f
₁ ) is compared with the pulse counter that counts the number of pulses generated as a detection signal when switching the local oscillation frequency, and the counted number of pulses and the number of pulses that should be generated when switching channels (depending on the requested channel) It is composed of a comparator and a controller for controlling the frequency of the tunable station light source and turning on / off the switch according to the output of the comparator. When the switch is in the ON state, the local oscillation frequency is stabilized at a certain peak transmittance frequency of the receiving FP resonator, but when in the OFF state, it is not stabilized. The operation of this optical tuner will be described below with reference to FIGS. As an example, consider the case of switching from channel 1 to channel N. In FIG. 7, the reception F
The transmission characteristics of the P resonator and the arrangement of local frequencies before and after frequency switching are shown. The transmission characteristics of the receiving FP resonator are the same as those in the first embodiment, and the characteristics are stabilized so that the transmittance has a peak at the reference optical frequency F ₀ . In the figure, in order to switch the received signal from channel 1 to channel N, the local oscillation frequency is changed from F ₀ + D _op + f _IF to F ₀ + ND _op + f.
Switching to _IF . Frequency F ₀ + D _op + f _IF to F ₀ +
The receiving FP resonator is 4 (N-1) between ND _op + f _IF.
-1 has a transmittance peak (however, the transmittance peaks at the frequencies of the start point and the end point are excluded). As a result, a pulse is generated in the detection signal output from the reception FP resonator every time the local oscillation frequency passes through the transmittance peak. FIG. 8 shows a correspondence relationship between pulse generation, switch on / off states, and local oscillation frequencies. FIG. 7A is a diagram showing whether the switch is in an on state or an off state. Channel 1
When a channel request signal to switch to the channel N is input to the optical tuner while receiving the signal, the switch is turned off and the local frequency stabilization to the peak transmittance frequency is stopped. Next, as shown in FIG.
The local oscillation frequency is swept from F ₀ + D _op + f _IF toward F ₀ + ND _op + f _IF . During the sweep process, a pulse as shown in FIG. 7C is generated in the detection signal. The pulse counter counts the number of generated pulses, and the number of pulses is 4 (N-
1) -Stop the sweeping of the local oscillator frequency by the next pulse that has become -1 and turn the switch on again to set the local oscillator frequency to F _0.
Stabilize to the peak transmittance frequency of the receiving FP resonator at + ND _op + f _IF . The optical signal frequency of the channel N is F ₀ +
Since it is ND _op , the intermediate frequency of the signal obtained by heterodyne detection becomes f _IF , and reception of channel N is immediately started (tuning completed). By the same principle,
When trying to select channel 1, channel 2, ..., Channel (N-1), the optical frequencies of the local light source are F
₀ + D _op + f _IF , F ₀ + 2D _op + f _IF , ..., F ₀ + (N−
1) It is stabilized after being switched to D _op + f _IF, and reception can be started immediately. Here, since the control of the local frequency is performed in the optical FDM receiver, the optical FD
Even if the M signal is not input to the optical receiver, the local oscillation frequency can be stably controlled. Furthermore, optical FDM
There is also an effect that no tuning error occurs even if a certain channel in the signal is missing.

3. Embodiment of Connection of Transmission Device FIG. 9 shows an example of connection of the transmission device of the present invention. FIG. 1A shows two transmission devices of the present invention capable of transmitting N-channel signals, which are connected in cascade. With such a configuration, the total transmission distance can be increased as compared with the case where only one transmission device is used. The total transmission distance can be increased by increasing the number of connected devices (3 or more) or by connecting the optical amplifier to the optical fiber. FIG. 9B shows a transmission device of the present invention capable of transmitting N-channel signals, and a transmission device capable of m-channel transmission (transmission of channel 1 to channel m),
Transmission device capable of (N-m) channel transmission (channel m +
1 to channel N) are connected). With this configuration, it is possible to divide the N channel and transmit one part of the channel to different places. For example, an optical FDM receiver which is a transmitter capable of transmitting m channels and (N-
m) If the optical FDM receivers of the transmission devices capable of channel transmission are arranged in different places, the signals of channel 1 to channel m and the signals of channel m + 1 to channel N are transmitted to different places. The number of transmission locations can be increased by changing the channel division method and the number of divisions.
Further, by combining the configuration shown in FIG. 9B with the configuration shown in FIG. 9A, it is possible to divide and transmit the necessary channels to different places greatly separated in distance. In FIG. 9C, the transmission device of the second embodiment is connected after the transmission device of the first embodiment of the present invention. According to this configuration,
It is possible to distribute N-channel signals to different places. Furthermore, by combining the configurations of (a), (b), and (c) of FIG. 9, N-channel signals can be distributed to a plurality of locations that are widely separated in distance. The transmission distance can be further increased by connecting the optical amplifier to the optical fiber. In addition, in FIGS. 9A to 9C, the light F at the transmission end is
Optical FD other than DM transmitter and optical FDM receiver at receiving end
If a part or all of the M transmission and reception devices are replaced with optical amplifiers, the configuration of the optical FDM transmission device can be further simplified.

4. Other Embodiments The present invention is not limited to the above embodiments. For example, the transmitting and receiving Fabry-Perot resonators do not necessarily have to have transmission characteristics as shown in FIG. Figure 1
It shows in 0. In the figure, the local light 1 is the transmission Fabry-Perot (F
P) at the peak transmittance frequency of the resonator, at the local oscillation light 2 at an optical frequency at which the transmittance is other than the peak value and the minimum value, and
The local light 3 is stabilized at an optical frequency where the transmittance becomes minimum. Stabilization to an optical frequency where the transmittance of the FP resonator is other than the peak value and the minimum value can be achieved by controlling the error signal so that it approaches a nonzero reference voltage, not by controlling it so as to approach zero. . Further, the stabilization to the optical frequency at which the transmittance becomes minimum can be realized by, for example, inverting the polarity of the error signal of the receiving optical filter stabilizing device in FIG. That is, F in the transmitter and the receiver
The transmission characteristics of the P resonator are stabilized by the reference optical frequency,
Moreover, if the frequencies of the transmission light source and the local oscillation light source in the transmission device and the reception device are stabilized on the basis of the transmission characteristics of the respective optical filters, the same effect as in the above embodiment can be obtained. Further, even if the frequency of the optical frequency reference light source is different between the transmitting device and the receiving device, if the respective frequencies are known, the same effect as in the above embodiment can be obtained. Also, when N is 1, that is, when FDM transmission is not performed, the same effect is obtained. Further, the same effect can be obtained even if the optical signal frequency interval is not a constant value. Also, the transmission rate may be different for each channel. In any case, it suffices that the intermediate frequency obtained by the heterodyne optical receiver substantially matches the design value. Further, a similar effect can be obtained by using a Mach-Zehnder type optical filter or the like instead of the FP resonator. Further, the method of stabilizing the optical signal frequency in the optical FDM transmitter may be another method. For example, as in the optical FDM receiver, an oscillator and a bandpass filter having different frequencies are installed in each optical transmitter to obtain an optical FD.
The optical signal frequency can be stabilized by the same principle as that of the M receiver. As a result, for example, the above effect can be obtained if the optical signal frequency as shown in FIG. 3 is obtained. Further, the optical multiplexer and the optical demultiplexer used in the optical FDM transmitter and the receiver may be an optical star coupler, or may be a combination of the optical multiplexer / demultiplexer and the optical star coupler. good. Further, in FIG. 3, both the signal frequency and the local oscillation frequency are stabilized at the frequency at which the transmittance of the FP resonator reaches the peak, but it is not always necessary to stabilize at the frequency at which the peak occurs. For example, it may be a frequency at which the transmittance is a minimum, or may be an appropriate point between the peak and the minimum value of the transmittance. As a result, the difference between the optical signal frequency and the local oscillation frequency should be equal to the desired intermediate frequency f _IF . The same applies to the relationship between the reference optical frequency and the transmittance of the FP resonator. Also, in the transmitting and receiving optical filter stabilizer, the light from the optical frequency reference light source is frequency-modulated by using the optical frequency modulator, but the optical frequency reference light source is directly modulated to perform the frequency modulation. You may get For example, when the optical frequency reference light source is a semiconductor laser, it is well known that frequency-modulated light can be obtained by modulating the current injected into the semiconductor laser. FIG. 11 shows an example of the configuration of the transmitting optical filter stabilizing device when the light source is directly modulated. Also, the optical filter on the transmission side may be shared with the optical multiplexer in the optical FDM transmission device. Such sharing can be realized by using a Mach-Zehnder type optical filter as an optical filter on the transmission side. FIG. 11 shows an example of the configuration of the optical FDM transmitter when shared. Transmitter optical filter stabilizer (1 in the figure)
5) and the configuration of each optical transmitter are the same as in the case of FIG.
However, the optical coupler in the transmission optical filter stabilizing device is unnecessary, and the output light from each optical transmitter is also input to the Mach-Zehnder type optical filter (16 in the figure). The optical FDM signal output from the optical filter is split into two, one is sent to the optical fiber, and the other is input to the photodiode in the transmission optical filter stabilizing device, and each optical signal is output by the same principle as in FIG. The signal frequency is stabilized. With this configuration, the configuration of the optical FDM transmitter can be simplified compared to the case of FIG. Similarly, also in the optical FDM receiver, the configuration of the apparatus can be simplified as compared with the case of FIG. 2 and FIG. 6 by sharing the multiplexer for multiplexing a plurality of local oscillation lights and the optical filter on the receiving side.

[0026]

As described above, according to the present invention, the optical signal frequency is controlled independently by the optical FDM transmitter, and the local oscillation frequency is controlled independently by the optical receiver (stabilization and tuning).
Therefore, even if the optical signal is not input to the optical FDM receiver due to a failure of the transmission light source or a break of the optical fiber, the local oscillation frequency can be stably controlled.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of an optical FDM transmitter.

FIG. 2 is a configuration diagram of a first embodiment of an optical FDM receiver.

FIG. 3 Transmission characteristics of Fabry-Perot resonator and frequency distribution of signal light and local light

FIG. 4 is a diagram showing a signal waveform in each part in the transmission optical fiber stabilizing device.

FIG. 5 is a diagram showing signal waveforms at various parts in a channel 1 heterodyne optical receiver.

FIG. 6 is a configuration diagram of a second embodiment of an optical FDM receiver.

FIG. 7: Transmission characteristics of Fabry-Perot resonator and frequency allocation of local light

FIG. 8: Correspondence relationship between pulse generation, switch on / off state, and local oscillation frequency

FIG. 9 is a diagram showing a connection example of a transmission device of the present invention.

FIG. 10 is another example of the transmission characteristics of the Fabry-Perot resonator and the frequency allocation of the local oscillation light.

FIG. 11 is a configuration diagram of another embodiment of the optical FDM transmitter.

[Explanation of symbols]

1 ... Optical fiber, 2 ... Transmit optical filter stabilizing device, 3 ...
Optical transmitter, 4 ... Transmission Fabry-Perot resonator, 5 ... Optical signal frequency stabilizing circuit, 6 ... Receiving optical filter stabilizing device, 7 ...
Heterodyne optical receiver, 8 ... Receiving Fabry-Perot resonator,
9 ... Local frequency stabilizing circuit, 10 ... Receiving optical filter stabilizing device, 11 ... Tunable heterodyne optical receiver, 1
2 ... Local frequency stabilizing circuit, 13 ... Optical tuner, 14 ...
Switch, 15 ... Transmitting optical filter stabilizing device, 16 ... Optical filter.

Claims (45)

[Claims] 1. An optical frequency division multiplex reception having an optical frequency division multiplex transmission device for frequency division multiplexing and outputting a plurality of optical signals of different wavelengths, and a plurality of heterodyne optical receivers for respectively receiving the plurality of optical signals. An optical frequency division multiplex transmission apparatus including a device, the optical frequency division multiplex transmission apparatus includes a first optical filter having periodic light transmission characteristics on a frequency axis, and stable transmission characteristics of the first optical filter. An optical signal frequency stabilizing circuit for stabilizing the center frequencies of the plurality of optical signals based on the transmission characteristics of the first optical filter, and the optical frequency division multiplexing The receiving device includes a second optical filter having a periodic light transmission characteristic on the frequency axis, a second optical filter stabilizing device for stabilizing the transmission characteristic of the second optical filter, and a second optical filter transmitting device. Properties based on the provided and local oscillator frequency stabilization circuits for the plurality of heterodyne optical receiver respectively stabilize the frequency of the local light source having respectively,
Characterizing that the difference between the center frequency of the stabilized plurality of optical signals and the frequency of the stabilized local oscillation light source corresponding to each optical signal is substantially matched to the optimum intermediate frequency for each heterodyne optical receiver. Optical frequency division multiplex transmission device. 2. The optical frequency according to claim 1, wherein the period 1 of the transmission characteristic of the first optical filter is set to 1 / natural number (1 / natural number) of the center frequency intervals of the optical signal. Division multiplexing transmission equipment. 3. The optical frequency according to claim 1, wherein the period 2 of the transmission characteristic of the second optical filter is set to 1 / natural number (1 / natural number) of the center frequency intervals of the optical signal. Division multiplexing transmission equipment. 4. The optical frequency division multiplexing transmission device according to claim 3, wherein the period 2 is set to a natural number 1 / (natural number) of the intermediate frequency. 5. The first optical filter stabilizing device according to claim 1, wherein the first optical frequency reference light source outputs an absolutely stabilized reference optical frequency, and the frequency f _{0 of} the light output from the light source. An optical frequency modulator for performing frequency modulation with an optical coupler, an optical coupler for multiplexing the frequency-modulated light and the optical frequency division multiplexed signal and inputting to the first optical filter, and an optical coupler for outputting the light output from the optical filter. A photodiode for converting into a signal to obtain a detection signal, a bandpass filter for extracting a signal component near the frequency f ₀ from the detection signal, an oscillator for outputting a sine wave signal of the frequency f ₀ , the extraction signal and the sine A multiplier for multiplying the wave signal, a low-pass filter (cutoff frequencies f _LPF , f _LPF << f ₀ ) for extracting the error signal from the multiplied signal, and the temperature of the first optical filter by the error signal. Control the temperature And an optical frequency division multiplexing transmission device. 6. The second optical filter stabilizing device according to claim 1, wherein the second optical frequency reference light source outputs an absolutely stabilized reference optical frequency, and the light output from the light source has a frequency f ₀ . An optical frequency modulator for performing frequency modulation, a star coupler for multiplexing the plurality of local oscillation lights, a frequency-modulated light and the combined local oscillation light are multiplexed and input to the second optical filter. An optical coupler, a photodiode for converting the light output from the optical filter into an electric signal to obtain a detection signal, a bandpass filter for extracting a signal component of frequency f ₀ from the detection signal, and a sine wave signal of frequency f ₀ An oscillator for outputting the signal, a multiplier for multiplying the extracted signal by the sine wave signal, and a low-pass filter (cutoff frequencies f _LPF , f _LPF << f ₀ ) for extracting an error signal from the multiplied signal. , The second optical filter by the error signal An optical frequency division multiplexing transmission device comprising: a temperature control circuit for controlling the temperature of the optical filter. 7. An optical frequency division multiplexing transmission device, wherein the optical frequency of the first optical frequency reference light source according to claim 5 and the optical frequency of the second optical frequency reference light source according to claim 6 are matched. 8. The cycle of the transmission characteristic of the first optical filter is set to 1 / natural number (1 / natural number) of the center frequency interval of the optical signal according to claim 7, and the second optical filter is The cycle 2 of the transmission characteristic is set to one natural number (1 / natural number) of the center frequency interval of the optical signal, and the cycle 2 is one natural number of the intermediate frequency (1 / natural number).
An optical frequency division multiplex transmission device characterized in that: 9. The optical frequency of the optical frequency reference light source, the frequency at which the transmission characteristic of the first optical filter is maximum or minimum, and the transmission characteristic of the second optical filter is maximum or minimum. The optical frequency division multiplexing transmission device is characterized in that the same frequency is matched. 10. The optical signal frequency stabilizing circuit according to claim 8, wherein the center frequencies of the plurality of optical signals are respectively stabilized to optical frequencies at which the transmission characteristics of the first optical filter become maximum or minimum. Optical frequencies characterized by stabilizing the frequencies of the local oscillation light sources respectively included in the plurality of heterodyne optical receivers at frequencies at which the transmission characteristics of the second optical filter become maximum or minimum, by the local oscillation frequency stabilizing circuit. Division multiplexing transmission equipment. 11. The optical frequency of the optical frequency reference light source, the frequency at which the transmission characteristic of the first optical filter is maximum or minimum, and the transmission characteristic of the second optical filter is maximum or minimum. Match the frequency
The optical signal frequency stabilizing circuit stabilizes the center frequencies of the plurality of optical signals to different optical frequencies at which the transmission characteristic of the first optical filter becomes maximum or minimum, and the transmission characteristic of the second optical filter is obtained. An optical frequency division multiplex transmission device, wherein the frequencies of the local oscillation light sources respectively included in the plurality of heterodyne optical receivers are stabilized by the local oscillation frequency stabilizing circuit at the frequencies at which the maximum and minimum values are obtained. 12. The optical frequency division multiplexing transmission device according to claim 1, wherein Fabry-Perot optical resonators are used as the first optical filter and the second optical filter. 13. The optical frequency division multiplexing transmission device according to claim 1, wherein a Mach-Zehnder type optical filter is used as the first optical filter and the second optical filter. 14. The optical signal frequency stabilizing circuit according to claim 5, wherein the optical signal frequency stabilizing circuit multiplies the information signal input to the optical frequency division multiplexing transmission device by the detection signal, and an error from the multiplied signals. An optical frequency division multiplex transmission device comprising a low pass filter for extracting a signal. 15. The local frequency stabilizing circuit according to claim 6, wherein the bandpass filter extracts a component of frequency f ₁ from the detection signal, an oscillator (frequency f ₁ ) outputs a sine wave signal, A multiplier for multiplying the extracted signal and the sine wave signal, and a low-pass filter (cutoff frequency f _LPF , f _LPF << f ₁ ) for extracting an error signal from the multiplied signal.
And an adder for adding the error signal and the sine wave signal bias signal, the optical frequency division multiplex transmission device. 16. The optical frequency division multiplexing transmission device according to claim 15, wherein the frequencies of the oscillators in the local oscillator frequency stabilizing circuits respectively included in the plurality of heterodyne optical receivers are different from each other. 17. The heterodyne optical receiver according to claim 1, wherein the local frequency stabilizing circuit, the local light source, an optical coupler for branching the local light, and one output of the optical coupler are used. A polarization diversity optical receiver that receives an optical signal and outputs a baseband signal, and an identification reproduction circuit that identifies and reproduces an information signal from the signal output from the polarization diversity optical receiver. A characteristic optical frequency division multiplex transmission device. 18. The polarization diversity optical receiver according to claim 17, wherein the polarization splitter separates an optical signal into a horizontally polarized light signal and a vertically polarized light signal, and the local oscillation light is emitted from the first and second stations. An optical coupler for branching to light emission, a first balanced receiver for heterodyne detection of a horizontally polarized optical signal using first local light emission, and a first intermediate frequency signal output from the first balanced receiver for a first baseband signal. A second demodulation circuit for converting a vertical polarization optical signal into a heterodyne by using a second local oscillation light; and a second intermediate frequency signal output from the second balanced receiver in a second baseband. A second demodulation circuit for converting into a signal, and an adder for adding the first baseband signal and the second baseband signal to output a baseband signal according to claim 17. Light frequency Division multiplexing transmission apparatus. 19. An optical frequency division multiplex transmission device comprising the optical frequency division multiplex transmission device according to claim 1 and the optical frequency division multiplex reception device according to claim 1 connected by an optical fiber. 20. The optical frequency division multiplexing transmission device according to claim 19, wherein an optical amplifier is connected to the optical fiber. 21. The first optical filter stabilizing device according to claim 1, wherein the first optical filter stabilizing device outputs a light frequency-modulated at a frequency f ₀ centered on an absolutely stabilized reference optical frequency. , An optical coupler for multiplexing the light output from the light source and the optical frequency division multiplexed signal and inputting to the first optical filter, and a detection signal by converting the light output from the optical filter into an electrical signal. With a photodiode to get,
A bandpass filter for extracting a signal component near the frequency f ₀ from the detection signal, an oscillator for outputting a sine wave signal of the frequency f ₀ , a multiplier for multiplying the extracted signal by the sine wave signal, and a multiplier It is composed of a low-pass filter (cutoff frequencies f _LPF , f _LPF << f ₀ ) for extracting an error signal from the signal, and a temperature control circuit for controlling the temperature of the first optical filter by the error signal. And an optical frequency division multiplexing transmission device. 22. The second optical filter stabilizing device according to claim 1, wherein the second optical filter stabilizing device outputs a light frequency-modulated at a frequency f ₀ centered on an absolutely stabilized reference optical frequency. A star coupler for multiplexing the plurality of local oscillation lights, an optical coupler for multiplexing the frequency-modulated light and the multiplexed local oscillation light, and inputting the multiplexed light to the second optical filter,
A photodiode for converting the light output from the optical filter into an electric signal to obtain a detection signal, and a frequency f from the detection signal.
A bandpass filter for extracting a signal component of ₀ , and a frequency f ₀
Of the sine wave signal, a multiplier for multiplying the extracted signal by the sine wave signal, and a low pass filter (cutoff frequencies f _LPF , f _LPF << for extracting the error signal from the multiplied signal). f ₀ ), and a temperature control circuit for controlling the temperature of the second optical filter according to the error signal. 23. An optical frequency division multiplexing transmission device for frequency-division-multiplexing and outputting a plurality of optical signals of different wavelengths, and a tunable heterodyne optical receiver for selectively receiving one optical signal from the plurality of optical signals. In an optical frequency division multiplex transmission device including an optical frequency division multiplex reception device having the optical frequency division multiplex transmission device, the optical frequency division multiplex transmission device includes a first optical filter having periodic light transmission characteristics on a frequency axis, A first optical filter stabilizing device for stabilizing the transmission characteristics of the filter, and an optical signal frequency stabilizing circuit for stabilizing the center frequencies of the plurality of optical signals based on the transmission characteristics of the first optical filter are provided. The optical frequency division multiplexing receiver includes a second optical filter having a periodic light transmission characteristic on the frequency axis and a second optical filter stabilizing device for stabilizing the transmission characteristic of the second optical filter. And a local oscillator frequency stabilizing circuit for stabilizing the frequency of the tunable local oscillator source included in the heterodyne optical receiver based on the transmission characteristic of the second optical filter, and for tuning the frequency of the local oscillator source. The optical tuner is provided to make the difference between the center frequency of the plurality of stabilized optical signals and the frequency of the local oscillation light source at the time of receiving each optical signal substantially equal to the optimum intermediate frequency for the heterodyne optical receiver. A characteristic optical frequency division multiplex transmission device. 24. The first optical filter stabilizing device according to claim 23, wherein the first optical frequency reference light source outputs an absolutely stabilized reference optical frequency, and the frequency f _{0 of} the light output from the light source. An optical frequency modulator that performs frequency modulation with
An optical coupler for multiplexing the frequency-modulated light and the optical frequency division multiplexed signal and inputting to the first optical filter, and a photodiode for obtaining the detection signal by converting the light output from the optical filter into an electric signal And a bandpass filter for extracting a signal component near the frequency f ₀ from the detection signal, and a frequency f
An oscillator that outputs a sine wave signal of ₀ , a multiplier that multiplies the extracted signal and the sine wave signal, and a low-pass filter (cutoff frequency f that extracts an error signal from the multiplied signal).
An optical frequency division multiplexing transmission device comprising _LPF , f _LPF << f ₀ ) and a temperature control circuit for controlling the temperature of the first optical filter by an error signal. 25. The second optical filter stabilizer according to claim 23, wherein the second optical frequency reference light source outputs an absolutely stabilized reference optical frequency, and the light output from the light source has a frequency f ₀ . An optical frequency modulator for performing frequency modulation, an optical coupler for multiplexing the frequency-modulated light and the local oscillation light and inputting to the second optical filter, and converting the light output from the optical filter into an electrical signal. , A bandpass filter for extracting a signal component of frequency f ₀ from the detection signal, an oscillator for outputting a sine wave signal of frequency f ₀ , and a multiplication of the extracted signal and the sine wave signal. A multiplier, a low-pass filter (cutoff frequencies f _LPF , f _LPF << f ₀ ) for extracting an error signal from the multiplied signal, and a temperature control circuit for controlling the temperature of the second optical filter by the error signal Made up of An optical frequency division multiplexing transmission device characterized in that 26. The optical frequency of the first optical frequency reference light source according to claim 24 and the optical frequency of the second optical frequency reference light source according to claim 25 are matched, and the cycle of the transmission characteristic of the first optical filter. 1 is set to 1 / (natural number) of the center frequency interval of the optical signal, and the period 2 of the transmission characteristic of the second optical filter is set to 1 / (1) of the center frequency interval of the optical signal. / Natural number), and the cycle 2 is set to 1 / natural number of the intermediate frequency (1 / natural number). 27. The optical frequency of the optical frequency reference light source, the frequency at which the transmission characteristic of the first optical filter is maximum or minimum, and the transmission characteristic of the second optical filter is maximum or minimum. The optical signal frequency stabilizing circuit stabilizes the center frequencies of the plurality of optical signals at optical frequencies at which the transmission characteristics of the first optical filter are maximized or minimized. 2. An optical frequency division multiplexing transmission device, wherein the frequency of the local oscillation light source of the heterodyne optical receiver is stabilized by the local oscillation frequency stabilizing circuit to a frequency at which the transmission characteristic of the two optical filters becomes maximum or minimum. 28. The local oscillation frequency stabilizing circuit according to claim 25, wherein a band pass filter for extracting a component of frequency f ₁ from the detection signal, an oscillator (frequency f ₁ ) for outputting a sine wave signal, A multiplier for multiplying the extracted signal and the sine wave signal, and a low-pass filter (cutoff frequency f _LPF , f _LPF << f ₁ ) for extracting an error signal from the multiplied signal.
And an adder for adding the error signal and the sine wave signal bias signal, the optical frequency division multiplex transmission device. 29. The heterodyne optical receiver according to claim 23, wherein one of the local oscillator frequency stabilizing circuit, the tunable local oscillator light source, an optical coupler for branching local oscillator light, and one of the optical couplers. It is composed of a polarization diversity optical receiver that receives an optical signal using an output and outputs a baseband signal, and an identification reproduction circuit that identifies and reproduces an information signal from the signal output from the polarization diversity optical receiver. An optical frequency division multiplexing transmission device characterized in that 30. The optical frequency division multiplex transmission apparatus according to claim 23, wherein the local oscillation frequency stabilizing circuit has a built-in switch for switching between stopping and resuming stabilization. 31. The optical tuner according to claim 30, wherein the optical tuner includes a low-pass filter for removing a signal component of a frequency f ₁ , a pulse counter for counting the number of pulses generated as a detection signal when switching the local oscillation frequency, and a count. It comprises a comparator for comparing the number of generated pulses with the number of pulses expected to occur when switching channels, and a controller for controlling the frequency of the tunable station light source and the switch according to the output of the comparator. And an optical frequency division multiplexing transmission device. 32. The heterodyne optical receiver according to claim 23, wherein the local oscillator frequency stabilizing circuit according to claim 30, the optical tuner according to claim 31, the tunable local light source, and local light are provided. An optical coupler that branches, a polarization diversity optical receiver that receives an optical signal by using one output of the optical coupler and outputs a baseband signal, and an information signal from a signal output from the polarization diversity optical receiver An optical frequency division multiplex transmission device comprising: an identification / reproduction circuit for identifying and reproducing. 33. An optical frequency division multiplex transmission device, characterized in that the optical frequency division multiplex transmission device according to claim 23 and the optical frequency division multiplex reception device according to claim 23 are connected by an optical fiber. 34. The optical frequency division multiplexing transmission device according to claim 33, wherein an optical amplifier is connected to the optical fiber. 35. N light sources for converting a plurality of N-channel information signals into optical signals, respectively, and an optical multiplexer for multiplexing the N-channel optical signals and outputting an optical frequency division multiplexed signal.
An optical coupler that branches the optical frequency division multiplexed signal into two, an optical filter that receives one of the branched lights and has periodic light transmission characteristics on the frequency axis, and stabilizes the transmission characteristics of the optical filter. An optical filter stabilizing device, and N optical signal frequency stabilizing circuits for respectively stabilizing the center frequencies of the N-channel optical signals based on the transmission characteristics of the optical filter. Frequency division multiplexing transmitter. 36. An optical demultiplexer for separating frequency-division-multiplexed optical signals of a plurality of N channels, and a plurality of N heterodyne optical receivers for respectively receiving the separated optical signals and reproducing information signals, An optical multiplexer that multiplexes the local oscillator light output from the local oscillator light source that each of the plurality N of heterodyne optical receivers has, and has the light transmission characteristics that receives the multiplexed light and that is periodic on the frequency axis. An optical filter, an optical filter stabilizing device that stabilizes the transmission characteristics of the optical filter, and an N-unit station oscillation frequency stabilizing circuit that stabilizes the frequency of each local light source based on the transmission characteristics of the optical filter. An optical frequency division multiplexing receiver comprising: 37. A tunable heterodyne optical receiver for selectively receiving one channel from frequency-division-multiplexed optical signals of N channels, and a station for outputting from a tunable station light source included in the heterodyne optical receiver. An optical coupler that splits the emitted light into two, and one of the branched lights as an input, and
An optical filter having a periodic light transmission characteristic on the frequency axis, an optical filter stabilizing device for stabilizing the transmission characteristic of the optical filter, and a frequency of the local light source based on the transmission characteristic of the optical filter. And an optical tuner for tuning the frequency of the local oscillation light source. 38. N light sources for converting a plurality of N-channel information signals into optical signals, respectively, and multiplexing the N-channel optical signals to output an optical frequency division multiplexed signal, and on the frequency axis. An optical filter having a periodic light transmission characteristic, an optical coupler for branching the optical frequency division multiplexed signal into two, an optical filter stabilizing device for stabilizing the transmission characteristic of the optical filter, and a transmission characteristic of the optical filter as a reference. And N optical signal frequency stabilization circuits for respectively stabilizing the center frequencies of the N-channel optical signals. 39. An optical demultiplexer for demultiplexing frequency-division-multiplexed optical signals of a plurality of N channels, and a plurality of N heterodyne optical receivers for respectively receiving the demultiplexed optical signals and reproducing information signals, An optical filter that multiplexes the local oscillation light output from the local oscillation light sources that each of the plurality N of heterodyne optical receivers has, and that has a periodic optical transmission characteristic on the frequency axis, and the transmission characteristic of the optical filter is stable. Optical frequency stabilizing device for stabilizing the frequency of each local oscillation light source based on the transmission characteristics of the optical filter, and an optical frequency stabilizing circuit for stabilizing each frequency of each local oscillation light source. Division multiplexing receiver. 40. An optical frequency division multiplex transmission device comprising a plurality of optical frequency division multiplex transmission devices according to claim 1 connected thereto. 41. The optical system according to claim 1, wherein m channels (m is a natural number) of the N channels are transmitted after the optical frequency division multiplexing transmission system according to claim 1, which transmits information signals of a plurality of N channels. A frequency division multiplex transmission device and the remaining Nm channels of the N channels are transmitted.
An optical frequency division multiplexing transmission device, characterized in that the optical frequency division multiplexing transmission device described above is connected. 42. An optical frequency division multiplexing transmission device according to claim 1, which transmits m channels (m is a natural number) of information signals.
The optical frequency division multiplex transmission device according to claim 1, which transmits a p-channel (p is a natural number) information signal, and is provided with m + p.
An optical frequency division multiplex transmission device, to which the optical frequency division multiplex transmission device according to claim 1 capable of transmitting channels simultaneously is connected. 43. An optical frequency division multiplex transmission device comprising a plurality of optical frequency division multiplex transmission devices according to claim 23 connected to a stage subsequent to the optical frequency division multiplex transmission device according to claim 1. 44. The optical frequency division multiplex transmission device according to claim 41 is connected to the subsequent stage of the optical frequency division multiplex transmission device according to claim 40, and the optical frequency division multiplex transmission device according to claim 42 is connected to the subsequent stage. An optical frequency division multiplexing transmission device characterized in that a plurality of units are connected. 45. An optical frequency division multiplex transmission apparatus according to claim 40, further comprising an optical frequency division multiplex transmission and reception apparatus other than the optical frequency division multiplex transmission apparatus at the transmitting end and the optical frequency division multiplex receiving apparatus at the receiving end. An optical frequency division multiplexing transmission device, characterized in that a part or all of the optical amplifier is replaced with an optical amplifier.