JPH1048582A - Modulation device, transmission device, modulation method, and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an optical modulation device capable of suppressing deterioration of transmission signal in quality caused by drift of a working point of a modulation device, by adding dither signal on a bias voltage of an optical modulation device. SOLUTION: This optical modulation device comprises a source of light 1, an optical modulator 3, a modulator driving circuit 24, a dither signal generator 12, a peak detector 15 for detecting a low frequency dither signal from output signal, a synchronous detection circuit 7 for detecting synchronization of the dither signal generated from the low frequency and dither signal generator detected in the peak detector 15, and a bias circuit 10 for controlling a bias applied to the optical modulator 3 according to the result of the synchronization detection by the synchronous detection circuit 7. And, adding a low frequency signal on the bias makes it easily possible to control the operation of the modulator even in modulating a high frequency signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitter for modulating and outputting a data signal, and more particularly to an optical transmitter of an external light modulation system.

[0002]

2. Description of the Related Art In a conventional optical communication system, a direct modulation system in which a laser diode is modulated with a driving current to obtain a light intensity signal proportional to an electric signal has been used.
However, in an ultra-high speed / broadband optical communication system having a transmission speed exceeding several Gbit / s, the chirping phenomenon in which the wavelength of light changes during direct modulation has been a factor limiting transmission capacity. On the other hand, the external modulation method has a very small chirping, and an operation band of 10 GHz or more can be obtained relatively easily, so that application to a large-capacity optical communication system has begun. The most common external modulator is a lithium niobate (LiNbO3: Lithium Niobate) Mach-Zehnder type optical modulator.

[0003] The lithium niobate modulator modulates the modulated signal S
The output optical signal I (t) when modulated by (t) is expressed by the following equation. I (t) = k {1 + cos (β · S (t) + δ)} (1) where k is a proportional coefficient, β is a modulation factor, and δ is a phase of an operating point. Consider a binary digital signal as the modulation signal S (t). If β = π and an appropriate DC voltage is applied and the initial phase δ is selected to be π / 2, an optical signal that is completely turned on / off in proportion to the modulation signal can be obtained. If δ is constant, there is no problem, but a normal lithium niobate modulator has a problem that the operating point drifts. Drift includes thermal drift due to pyroelectric effect caused by temperature change,
There is a DC drift due to a charge distribution formed on the element surface by a DC voltage applied to the electrode. In order to compensate for the variation of the operating point due to these drifts, it is necessary to apply a DC voltage (bias voltage) so that an optimum operating point is obtained.

A technique for stabilizing the bias voltage of a lithium niobate modulator is disclosed in, for example, Japanese Patent Laid-Open No. 5-142.
504 is known. FIG. 16 is a rewrite of the block diagram shown in JP-A-5-142504. 16, reference numeral 1 denotes a light source that emits continuous light, 3 denotes an optical modulator, 14 denotes a terminator, 4 denotes a splitter that splits an output signal, and 5 denotes a photodiode (PD) that converts an optical signal into an electric signal. ), 6 is a preamplifier for amplifying an electric signal output from the PD, 12 is a dither signal generator for generating a low frequency, 13 is a dither signal superimposing circuit for superimposing a dither signal on a data signal, and 7 is a low level signal output from the preamplifier 6. A synchronous detection circuit for synchronously detecting the frequency component and the dither signal in the dither signal generator 12.

A bias circuit 10 generates a bias voltage to be applied to the optical modulator 3, a modulator driving data signal input terminal 21, a modulator driving circuit 24 for driving the optical modulator,
1 is a bias T. The synchronous detection circuit 7 includes an amplifier 8, a mixer 17, and a low-pass filter 9.

Next, the operation will be described. Continuous light emitted from the light source 1 is input to the optical modulator 3. The data signal is input from the modulator drive data signal input terminal 21 and output from the modulator drive circuit 24 as a modulator drive signal. In the low frequency superimposing circuit 13, the low frequency signal (fHz) output from the dither signal generator 12 is superimposed on the modulator driving signal. At the bias T, the modulator driving signal on which the bias signal and the low frequency signal (fHz) are superimposed is synthesized, and is then input to the optical modulator 3. The optical signal modulated based on the data signal in the optical modulator 3 is split by the splitter 4 and then emitted from the optical output terminal 20.

The output optical signal demultiplexed by the demultiplexer 4 is converted into an electric signal by the PD 5 and amplified by the preamplifier 6, and then the low-frequency component of the output signal and the dither signal generation means are output by the synchronous detection circuit 7. The generated low frequency (fHz) is synchronously detected. The bias signal is controlled in the bias circuit based on the synchronous detection result in the synchronous detection circuit 7.

Next, the bias control based on the dither signal will be specifically described with reference to FIGS. 17, 18 and 19. FIG. The low frequency signal (fHz) output from the dither signal generator 12 is superimposed on the modulator drive signal by the low frequency superimposing circuit 13. FIG. 17A illustrates a signal at the bias T11 input to the optical modulator 3. FIG.
(B) shows an operation characteristic curve of the optical modulator 3 given by the equation (1), and shows an example in which the bias voltage (phase δ) is appropriately set. FIG. 17C shows an optical signal waveform output from the optical modulator 3. Low frequency component fH
It can be understood that z is not observed and a 2 fHz component is generated. Therefore, when the synchronous detection circuit 7 performs synchronous detection, the output of the synchronous detection circuit becomes 0.

FIG. 18 shows the operation of the optical modulator 3 when the bias voltage is slightly higher than an appropriate value. FIG.
(A) shows a signal at the bias T11 input to the optical modulator 3. FIG. 18B shows an operation characteristic curve of the optical modulator 3, and FIG. 18C shows an optical modulator output optical signal.
The phase of the low frequency signal (fHz) in the output signal is the low frequency signal (fH) generated by the dither signal generator 12.
It can be seen that the phase is inverted from that of z). Therefore, the output signal voltage of the synchronous detection circuit 7 becomes negative.

FIG. 19 shows the operation of the optical modulator 3 when the bias voltage is slightly lower than an appropriate value. FIG.
(A) shows an output signal from the bias T11 input to the optical modulator. FIG. 19B shows an operation characteristic curve of the optical modulator 3, and FIG. 19C shows an optical modulator output optical signal.
It can be seen that the phase of the low frequency signal (fHz) in the output signal matches the phase of the low frequency signal (fHz) generated by the dither signal generator. Therefore, the output signal voltage of the synchronous detection circuit 7 becomes positive.

As shown on the right, an error signal corresponding to the deviation of the bias voltage from the optimum point is output from the synchronous detection circuit 7, so that the error signal is fed back to the bias circuit 10 to operate the optical modulator 3. Point drift can be suppressed. In this prior art, it is assumed that the amplitude of the modulator drive signal has an optimum value.

[0012]

The above prior art discloses a technique for compensating for a drift of an operating point. However, it is not easy to superimpose a low-frequency signal on an optical modulator drive signal, especially for a high-frequency signal. In order to superimpose a low frequency on a drive signal, it is necessary to input the drive signal to a "voltage drive attenuator" or a "gain control amplifier" and drive these devices at a low frequency. The drive signal has a spectral component of about DC to twice the modulation frequency, and the device needs to attenuate or amplify this spectral component equally.

However, the operating frequency of these devices is DC to about 5 GHz, or has a non-flat frequency characteristic, thereby deteriorating the driving signal quality. It is generally known that variable gain type amplifiers are more difficult to realize than fixed gain amplifiers. For this reason, it is difficult to superimpose a low frequency on a drive signal of 5 GHz or more without waveform deterioration. Also, there is no dispute that the passive device (bias T) is easier to realize a wideband characteristic than the active device (amplifier).

In the amplitude of the data signal for driving the optical modulator, since I (t) changes from 0 to K in the equation (1), in the prior art, the quality of the optical transmission signal is degraded and the operation is performed at the same time. There is a problem that perfect control cannot be performed even in point control. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a modulator that can perform optimum operation even when performing modulation based on a high-frequency signal.

[0015]

According to a first aspect of the present invention, there is provided a modulating device for modulating a carrier wave with a data signal and outputting an output signal, and a modulating device for controlling an operation of the modulating device. Bias applying means for applying a bias, dither signal generating means for generating a dither signal, and dither for superposing a dither signal generated by the dither signal generating means on a bias in the bias applying means without superimposing the dither signal on the data signal Signal superimposing means, dither signal detecting means for detecting the superimposed dither signal component from the output signal output from the modulating means, and a phase of the detected dither signal component and dither generated by the dither signal superimposing means. A phase comparing means for comparing the phase of the signal with the signal; Those having a bias control means for controlling the application of the bias in. Here, applying a bias to the modulating means includes all methods of applying to the modulating means, such as applying to a data signal or applying directly to the modulating means. The same applies to the means for solving the following problems.

A modulator according to a second aspect of the present invention includes a modulator for modulating a carrier wave with a data signal and outputting an output signal, a dither signal generator for generating a dither signal, and the dither signal generator for the modulator. Dither signal applying means for applying a dither signal generated by the above, dither signal detecting means for detecting the superimposed dither signal component from the output signal output from the modulating means, and a phase of the detected dither signal component. Phase comparing means for comparing the phase of the dither signal generated by the dither signal generating means,
An amplitude control unit that controls the amplitude of the data signal based on the comparison result in the phase comparison unit. Here, applying the dither signal generated by the dither signal generation means to the modulation means means a data signal,
It includes all methods of applying to the modulating means, such as applying to the bias or applying directly to the modulating means. This point is the same in the means for solving the following problems.

A modulator according to a third aspect of the present invention includes a modulating means for modulating a carrier wave by a data signal and outputting an output signal, and a bias applying means for applying a bias to the modulating means for controlling the operation of the modulating means. Means, first dither signal generating means, dither signal superimposing means for superimposing a first dither signal generated by the first dither signal generating means on a bias in the bias applying means without superimposing the first dither signal on a data signal; First dither signal detecting means for detecting the superimposed first dither signal component from the output signal output from the modulation means, and detecting the phase of the detected first dither signal component and the first dither signal. First phase comparing means for comparing the phase of the first dither signal generated by the signal generating means with the first dither signal; Bias control means for controlling the application of a bias in the bias application means, second dither signal generation means for generating a second dither signal having a frequency different from the first dither signal, and a second dither signal generation means Dither signal application means for applying the generated second dither signal to the modulation means, and second dither signal detection for detecting the superimposed second dither signal component from the output signal output from the modulation means Means, a second phase comparing means for comparing the detected phase of the second dither signal component with the phase of the second dither signal generated by the second dither signal generating means, An amplitude control means for controlling the amplitude of the data signal based on the result of the comparison by the phase comparison means.

The modulating device according to the fourth invention has the first,
In the modulation device according to the second or third aspect, the data signal input to the modulation means has a frequency of 5 GHz or more.

The transmitting apparatus according to the fifth invention has the first,
In the modulation device according to the second, third or fourth invention, a monitoring signal generating means for generating a monitoring signal, a monitoring signal applying means for applying a monitoring signal generated by the monitoring signal generating means to the modulation means, The modulation device further includes monitoring signal detection means for detecting the monitoring signal component from the return signal of the output signal from the transmission path of the output signal and monitoring the state of the transmission path. Here, the application of the monitoring signal in the monitoring signal generation means to the modulation means includes all methods of applying to the modulation means, such as applying to a data signal, a bias, or directly applying to the modulation means. This point is the same in the means for solving the following problems.

A communication system according to a sixth aspect of the present invention is a communication system having a transmitting device and a receiving device, wherein the transmitting device is a modulation device according to the first, second, third or fourth aspect of the present invention. A monitoring signal generating means for generating a monitoring signal having the following, and a modulation device further comprising a monitoring signal applying means for applying a monitoring signal generated by the monitoring signal generating means to the modulation means, wherein the receiving apparatus comprises: It has a monitoring signal detecting means for detecting the monitoring signal component from an output signal from the device, and a detecting means for detecting information on the communication system based on the detected monitoring signal. Here, the receiving device includes a repeater and the like as long as it receives a transmission signal. This point is the same in the means for solving the following problems.

A communication system according to a seventh aspect of the present invention is a communication system having a transmission device and a reception device, wherein the transmission device generates a monitor signal, particularly in the modulation device according to the first, second, third, or fourth invention. Monitoring signal generating means for
A modulation device that further includes a monitoring signal application unit that applies a monitoring signal generated by the monitoring signal generation unit to the modulation unit, wherein the reception device detects the monitoring signal component from an output signal from the transmission device It has monitoring signal detection means and gain control means for controlling the gain of the output signal based on the detected monitoring signal.

A transmitting apparatus according to an eighth aspect of the present invention includes a modulating means for modulating a carrier wave with a data signal and outputting an output signal, a monitoring signal generating means for generating a monitoring signal, and a monitoring signal generating means for generating the monitoring signal. Monitoring signal applying means for applying a monitoring signal to the modulation means without superimposing the monitoring signal on the carrier; and monitoring signal detection for detecting the monitoring signal component from a return signal of the output signal from the transmission path and monitoring the state of the transmission path. Means.

A communication system according to a ninth aspect of the present invention is a communication system having a transmitting device and a receiving device, wherein the transmitting device generates a monitor signal, and a modulating means for modulating a carrier wave by a data signal and outputting an output signal. Monitoring signal generating means, and monitoring signal applying means for applying the monitoring signal generated by the monitoring signal generating means to the modulation means without superimposing the monitoring signal on the carrier wave, wherein the receiving device outputs an output from the transmitting device. It has a monitoring signal detecting means for detecting the monitoring signal component from the signal, and a gain control means for controlling the gain of the output signal based on the detected monitoring signal.

A communication system according to a tenth aspect is a communication system having a transmitting device and a receiving device, wherein the transmitting device modulates a carrier wave by a data signal and outputs an output signal, and information on the communication system. Monitoring signal generating means for generating a monitoring signal having, and a monitoring signal applying means for applying the monitoring signal generated by the monitoring signal generating means to the modulation means without superimposing on the carrier, the receiving device, A monitoring signal detection unit configured to detect the monitoring signal component from an output signal from the transmission device; and a detection unit configured to detect information regarding the communication system based on the detected monitoring signal.

The modulating device according to the eleventh aspect is a modulating means for modulating a plurality of single wavelength carriers with a data signal and outputting an output signal, a dither signal generating means for generating a dither signal, and a modulating means for the modulating means. A bias applying unit for applying a bias to the modulating unit to control an operation, a dither signal applying unit for applying a dither signal generated by the dither signal generating unit to the modulating unit, and an output signal of the modulating unit. Carrier detecting means for detecting one carrier component of the plurality of carrier waves, dither signal detecting means for detecting the superimposed dither signal component from the carrier components detected by the carrier detecting means, and the detected dither signal component Phase comparing means for comparing the phase of the dither signal with the phase of the dither signal generated by the dither signal generating means; Those having a bias control means for controlling the application of the bias in the application means of the bias based on a comparison result in.

According to a twelfth aspect of the present invention, in the modulator according to the first, second, third or fourth aspect, the modulating means modulates a plurality of single-wavelength carriers by a data signal. And the dither signal detecting means has carrier detecting means for detecting one carrier component of the plurality of carrier waves from the output signal of the modulating means, and the superimposed carrier component is detected by the carrier detecting means. It is characterized by detecting a dither signal component.

The modulating method according to the thirteenth aspect of the present invention provides a modulating means for modulating a carrier wave with a data signal in a modulating means and outputting an output signal, a dither signal generating step for generating a dither signal, A dither signal applying step for applying a dither signal generated in the signal generating step, a dither signal detecting step for detecting the superimposed dither signal component from an output signal output from the modulation means, and the detected dither signal component detected Phase comparison step of comparing the phase of the dither signal generated by the dither signal generation step,
An amplitude control step of controlling an amplitude of the data signal based on a comparison result in the phase comparison step.

The modulation method according to a fourteenth aspect of the present invention is a modulation method for modulating a carrier wave with a data signal in a modulation means and outputting an output signal, and applying a bias to the modulation means for controlling the operation of the modulation means. A dither signal generating step of generating a dither signal; a dither signal superimposing step of superimposing a dither signal generated in the dither signal generating step on a bias in the bias applying step without superimposing the dither signal on the data signal. A dither signal detecting step of detecting the superimposed dither signal component from an output signal output from the modulating means; a phase of the detected dither signal component and a phase of the dither signal generated by the dither signal generating step And a phase comparison step of comparing
A bias control step of controlling a bias application in the bias applying step based on a comparison result in the phase comparing step.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a block diagram showing the configuration of an optical transmission apparatus according to an embodiment of the present invention. In FIG. 1, 1 is a light source that emits continuous light, 3 is an optical modulator, 14 is a terminator,
4 is a splitter for splitting an output signal, 5 is a photodiode (PD) for converting an optical signal into an electric signal, 6 is a preamplifier for amplifying the output electric signal of the PD, and 12 is a dither signal generating a low frequency. 15 is a peak detector for detecting a low frequency signal from the output signal, and 7 is a synchronous detection circuit for synchronously detecting the low frequency detected by the peak detector 15 and the dither signal generated by the dither signal generator 12. . 10
Is a bias circuit for generating a bias voltage applied to the optical modulator 3, 21 is a modulator drive data signal input terminal having a frequency of 5 GHz or more, 24 is a modulator drive circuit for driving the optical modulator, and 11 is a bias T. .

The synchronous detection circuit 7 is, as in this embodiment,
For example, it includes a bandpass filter 16a, an amplifier 8a, a mixer 17, an amplifier 8b, and a low-pass filter 9. Here, the band pass filter selectively transmits the low frequency signal component output from the dither signal generator. The amplifiers 8a and 8b can be configured using operational amplifiers. In addition, since the output amplitude from the amplifier 8a can be made constant by using the amplifier 8a as a limiter amplifier, more efficient synchronous detection becomes possible. The peak detector 7 is usually easily formed using a diode and a capacitor, and is easily available on the market as a peak detector.

As in the present embodiment, the bias circuit 10 can be realized by, for example, adding a DC voltage source output, a dither signal generator output, and a synchronous detection circuit output using an operational amplifier. It is desirable that the PD 5 and the preamplifier 6 have a sufficient band to receive and amplify the optical modulator drive signal.
As long as a low-frequency signal can be extracted, it may be a part of the modulator drive signal band. Here, the dither signal detecting means is constituted by the PD 5, the preamplifier 6, the peak detector 15, and the like.
The synchronous detection circuit 7 and the like constitute a phase comparison unit, and the bias circuit 10 and the like constitute a bias application unit, a dither signal application unit, and a bias control unit.

Next, the operation will be described. Continuous light emitted from the light source 1 is input to the optical modulator 3. The data signal is input from the modulator drive data signal input terminal 21 and output from the modulator drive circuit 24 as a modulator drive signal. In the bias circuit 10, the low frequency signal (fHz) output from the dither signal generator 12 is superimposed on the bias signal.
At the bias T11, the bias signal on which the low-frequency signal (fHz) is superimposed and the modulator driving signal are combined, and then input to the optical modulator 3. The optical signal modulated and output based on the data signal in the optical modulator 3 is output to the splitter 4.
The light is then output from the optical output terminal 20.

The output optical signal split by the splitter 4 is converted into an electric signal by the PD 5, amplified by the preamplifier 6, and then input to the peak detector 15. After the peak detector 15 detects the low-frequency signal superimposed on the output signal, the synchronous detector 7 detects the low-frequency signal and the low-frequency signal (f) generated by the dither signal generator 12.
Hz) is synchronously detected. The bias signal is controlled in the bias circuit 10 based on the synchronous detection result in the synchronous detection circuit 7.

Next, the bias control based on the dither signal will be specifically described with reference to FIGS. 2, 3 and 4. FIG.
The low frequency signal (fH) output from the dither signal generator 12
z) is superimposed on the bias voltage signal by the bias circuit 10. FIG. 2A shows a signal at the bias T11 input to the optical modulator 3. FIG. 2B shows an operation characteristic curve of the optical modulator 3 given by Expression (1), and shows an example in which the bias voltage (phase δ) is appropriately set. FIG. 2C shows an optical signal waveform output from the optical modulator 3.

FIG. 2D shows the output waveform of the peak detector when the output optical signal is received by the PD 5 and amplified by the preamplifier 6 and then subjected to peak detection by the peak detector 15. No low-frequency component fHz was observed and 2 fHz
It can be understood that the components are generated. Therefore, when the peak detector output signal is synchronously detected by the synchronous detection circuit 7 with the low frequency signal (fHz) output from the dither signal generator 12, the output of the synchronous detection circuit becomes zero. FIG. 3 shows the operation of the optical modulator 3 when the bias voltage is slightly higher than an appropriate value. FIG. 3A shows a signal at the bias T11 input to the optical modulator 3. FIG.
3B shows an operation characteristic curve of the optical modulator 3, and FIG. 3C shows an optical modulator output optical signal.

The low-frequency signal (fHz) shown in FIG. 3D can be detected by receiving the output optical signal by the PD 5 and amplifying it by the preamplifier 6 and then performing peak detection by the peak detector 15. The phase of the detected low-frequency signal (fHz) is the low-frequency signal (fH) generated by the dither signal generator.
It can be seen that the phase is inverted from that of z). Therefore, the output signal voltage of the synchronous detection circuit 7 becomes negative.

FIG. 4 shows the operation of the optical modulator 3 when the bias voltage is slightly lower than an appropriate value. FIG. 4 (a)
Represents an output signal from the bias T11 input to the optical modulator. FIG. 4B shows an operation characteristic curve of the optical modulator 3 and FIG. 4C shows an optical modulator output optical signal. The low-frequency signal (fHz) shown in FIG. 4D can be detected by receiving the output optical signal by the PD 5, amplifying the output optical signal by the preamplifier 6, and detecting the peak by the peak detector 15. It can be seen that the phase of the detected low frequency signal (fHz) matches the phase of the low frequency signal (fHz) generated by the dither signal generator. Therefore, the output signal voltage of the synchronous detection circuit 7 becomes positive.

As shown on the right, an error signal corresponding to the deviation of the bias voltage from the optimum point is output from the synchronous detection circuit 7, so that the error signal is fed back to the bias circuit 10 to operate the optical modulator 3. Point drift can be suppressed.

If the amplitude of the low-frequency signal superimposed on the bias voltage is set to several percent or less of the optical modulator drive signal, the quality of the output optical signal does not deteriorate. Also, by using the band-pass filter 16 and the limiter amplifier 8a for the synchronous detection circuit 7,
Since a constant output can be obtained even when the dither signal frequency is effectively extracted and the data signal amplitude fluctuates, an error signal of the bias voltage can be obtained without being affected by the light intensity fluctuation output from the light source 1. be able to. Providing an optical filter immediately before the PD 6 is also effective. When an optical signal output from the light source 1 contains unnecessary wavelength components and noise components, the control accuracy can be improved by providing an optical filter that selectively transmits the signal light wavelength.

As described above, according to the present invention, it is possible to suppress the drift of the operating point of the modulator, and in particular, it is possible to easily prevent the deterioration of the quality of the transmission signal due to the drift of the operating point in a high-frequency signal. In the above embodiment, the modulator drive signal and the bias signal are combined with the bias T and then applied to the optical modulator 3. For example, the bias is directly applied to the optical modulator 3 from an input terminal different from the modulator drive signal. For example, a signal may be applied. Further, the modulator is not limited to the visible light, but includes a wide range using an electromagnetic wave. This is the same in the embodiments described below.

Embodiment 2 FIG. 5 is a block diagram showing the configuration of an optical transmitter according to an embodiment of the present invention, similarly to the first embodiment, in which the peak detector 15 in the first embodiment is replaced with a first synchronous detection circuit 7a. It is. 1 to
6, 8a, 8b, 9-12, 14, 16, 17, 20,
Reference numerals 21 and 24 denote the same or corresponding parts in the configuration described in FIG. 1, and a description thereof will be omitted. In FIG. 5, 7a is a first synchronous detection circuit, 7b is a second synchronous detection circuit, and 18 is a delay controller. Here, the PD 5, the preamplifier 6, the first synchronous detection circuit 7a, the delay controller 18 and the like constitute a dither signal detecting means.

The operation will be described. The basic operation is the same as in the first embodiment. The difference from the first embodiment is that the operation of the peak detector 15 in the first embodiment is realized by the first synchronous detection circuit 7a. After a part of the data signal input from the modulator drive data signal input terminal 21 is adjusted for the delay time by the delay controller 18,
The signal is input to the first synchronous detection circuit 7a. By adjusting the delay time, the first synchronous detection circuit 7 is controlled by the delay controller 18.
The efficiency of the first synchronous detection circuit 7a can be increased by adjusting the phases of the two signals input to "a".
Since the signal output from the PD 5 is a dither signal using the modulator drive data signal as a carrier, the dither signal component can be detected from the output signal from the PD 5 by synchronous detection with the modulator drive data signal in the synchronous detection circuit 7a. .

Regarding the bias control by the dither signal, the output waveform of the synchronous detection circuit 7a having the configuration of FIG. 5 is the same as that of the first embodiment shown in FIGS.
This is the same as (d), and the description is omitted. As described above, according to the present invention, it is possible to suppress the drift of the operating point of the modulator, and it is possible to easily prevent the deterioration of the quality of the transmission signal due to the drift of the operating point particularly in a high-frequency signal.

Embodiment 3 FIG. FIG. 6 is a configuration block diagram of an optical transmission device according to an embodiment of the present invention, similarly to the second embodiment. The configuration other than the clock input terminal 26 is the same or equivalent to that of the second embodiment (FIG. 5), and the description is omitted. The difference from the second embodiment is that the delay controller 18 receives a clock signal from a clock input terminal 26 instead of the modulator drive data signal from the modulator drive data signal input terminal 21. . Clock input terminal 26
Is supplied with a clock signal synchronized with the modulator drive data signal.

The operation will be described. First synchronous detection circuit 7a
In step 2, a dither signal component is detected from an output signal from the PD 5 by synchronous detection with the clock signal. Other points are the same as those of the second embodiment, and the description is omitted. As described above, according to the present invention, it is possible to suppress the drift of the operating point of the modulator, and it is possible to easily prevent the deterioration of the quality of the transmission signal due to the drift of the operating point particularly in a high-frequency signal.

Embodiment 4 FIG. FIG. 7 is a configuration block diagram of an optical transmission device according to an embodiment of the present invention, similarly to the first embodiment. The configuration other than the pulse light source 2 is the same as or equivalent to that of the first embodiment (FIG. 1), and the description is omitted. The difference from the first embodiment is that the light source 1 in the first embodiment is a pulse light source 2. The pulse light source 2
A pulse light source synchronized with the modulator drive data signal at the modulator drive data signal terminal 21.

As the pulse light source, a light source obtained by switching a gain of a semiconductor laser, a ring oscillator using a fiber type optical amplifier, a light source obtained by modulating a continuous light into a pulse by an optical modulator, or the like can be used. Pulse light source 2
Since the optical pulse output from is modulated by the optical modulator,
The signal output from the optical output terminal 20 is a pulse-modulated optical signal (RZ signal). The signal detected by the PD 5 is also an RZ signal, and the operation band of the PD 5 and the preamplifier 6 includes the clock frequency component of the modulator drive data signal, so that the low frequency dither signal can be efficiently extracted.

As described above, according to the present invention, in particular, RZ
Since the signal has a line spectrum component equal to the data transmission speed, there is an advantage that the operation of the first synchronous detection circuit 7a has high sensitivity by effectively detecting this line spectrum component. Note that the light source 1 described in the second embodiment (FIG. 5) or 3 (FIG. 7) can be the pulse light source 2 in the same manner.

Embodiment 5 FIG. 8 is a configuration block diagram of an optical transmission device according to an embodiment of the present invention, similarly to the first embodiment. Single wavelength light source 23 outputting different wavelengths
The configuration other than a, 23b, 23c and the optical filter 27 is the same or equivalent to that of the first embodiment (FIG. 1), and a description thereof will be omitted. The difference from the first embodiment is that the light source includes a plurality of single wavelength light sources. Reference numerals 23a, 23b, and 23c denote single-wavelength light sources that output different wavelengths.

The operation will be described. Since the optimum bias point of the optical modulator 3 varies depending on the wavelength of the light source, it is desirable to selectively detect only the operating point at one wavelength to compensate for the bias point drift. An optical filter 27 is provided at the output of the demultiplexer 4, and the single wavelength light sources 23a, 23b, 2
Only the light of the wavelength output by any one of 3c is selectively transmitted. Other operations are the same as those in the first embodiment.

In particular, it is known that the optimum operating point of a Mach-Zehnder type lithium niobate modulator differs depending on the wavelength. Therefore, when light of a plurality of wavelengths is input, there is a problem that an error signal cannot be stably obtained because the bias is too high or too low depending on the wavelength. As described above, according to the present invention, even when a plurality of single wavelengths are collectively modulated, bias control can be performed for each wavelength, and appropriate operating point control of the modulator can be performed.

It goes without saying that the number of wavelengths contained in the light source 1 may be four or more. When the single wavelength light source is turned on / off according to time, it is desirable to control the transmission wavelength of the optical filter in accordance with the output wavelength of the single wavelength light source that is turned on.

Embodiment 6 FIG. FIG. 9 is a configuration block diagram of an optical transmission device according to an embodiment of the present invention. 5a is a first PD, 6a is a first preamplifier, 5b is a second P
D and 6b are second preamplifiers, 22 is a monitor signal generation circuit, and 25 is a monitor signal detection circuit. The demultiplexer 4 is a two-input two-output coupler, and the optical output signal of the optical modulator 3 is branched to the first PD 5a and the optical output terminal 20, and the optical output terminal 20
The return light from is input to the second PD 5b. The output of the first PD 5a is amplified by the first preamplifier 6a, and the output of the second PD 5b is amplified by the second preamplifier 6b.
Is amplified by Other components are the same as those in the first embodiment.
This is the same as or equivalent to (FIG. 1), and the description is omitted.

Here, the monitor signal generating means and the monitor signal applying means are constituted by the monitor signal generating circuit 22 and the like, and the monitor signal detecting means is constituted by the PD 5b, the preamplifier 6b, the monitor signal detecting circuit 25 and the like. Next, the operation will be described. The operation other than the operation related to the monitoring signal is the same as that of the first embodiment (FIG. 1).
The monitoring signal generating circuit 22 generates a predetermined monitoring signal, for example, a pulse signal generated at a constant interval. The low frequency signal output from the dither signal generator 12 is modulated according to the monitoring signal. As the modulation format, for example, intensity modulation, phase modulation, frequency modulation and the like can be used. A transmission path optical fiber is connected to the optical output terminal 20. For example, when a failure such as a disconnection or an increase in loss occurs in the transmission line, the reflection at the failure point increases, and the return light intensity observed by the PD 5b increases.

As described above, according to the present invention, the monitor signal detected by the monitor signal detection circuit 25 is monitored by changing the monitor signal generated by the monitor signal generation circuit 22 with the passage of time, for example. Then, the time when the return light generated by the failure is output from the optical modulator 3 is specified,
The distance from the optical modulator 3 to the fault point can be specified. As a result, the same effect as that of the fault point identification system called OTDR can be obtained without preparing a special light source.

In this embodiment, the monitor signal from the monitor signal generating circuit 22 is applied to the dither signal generator 12, but the monitor signal is applied directly to the bias, the carrier or the optical modulator 3. And so on. This point is the same in the embodiments described below. Further, in the present embodiment, the operation point control of the modulator 3 by the dither signal and the monitoring of the transmission line by the monitor signal are performed at the same time, but only the monitor by the monitor signal may be performed.

Embodiment 7 FIG. FIG. 10 is a schematic configuration diagram of an optical transmission system according to an embodiment of the present invention. 22
Is a monitor signal generation circuit, 28 is a transmission line, and 29 is an optical repeater. The optical repeater 29 includes a monitor signal detection circuit 25 and a gain control circuit 30. The transmission path 28 is the optical output terminal 20
And the optical repeater 29. Other components are the same as or equivalent to those of the first embodiment (FIG. 1), and description thereof is omitted. Here, the receiving device is constituted by the optical repeater 29 and the like, the monitoring signal detecting means in the receiving device is constituted by the monitoring signal detecting circuit 25 and the like, and the gain control means in the receiving device is constituted by the gain control circuit 30 and the like.

The operation will be described. The operation other than the operation related to the monitoring signal is the same as that of the first embodiment (FIG. 1). The frequency of the monitoring signal output from the monitoring signal generating circuit 20 is set to a frequency sufficiently lower than the low frequency signal output from the dither signal generator 12. The monitoring signal output from the monitoring signal generation circuit 20 is superimposed on the dither signal, superimposed on the optical output signal from the optical output terminal 20, and applied to the optical repeater 29 via the transmission line. The monitoring signal is detected by a monitoring signal detection circuit 25 built in the optical repeater 29 and frequency-voltage converted. The gain control circuit 30 controls the gain of the optical repeater 29 based on the voltage output from the monitor signal detection circuit 25. With this operation, the optical transmission system according to the present embodiment can control the gain of the optical repeater 29.

As described above, according to the present invention, since the gain control of the transmission signal in the receiving apparatus is performed by the monitoring signal from the transmitting apparatus, it is possible to effectively suppress the deterioration of the quality of the transmission signal. It is also possible to perform system management and the like by transmitting system information such as the transmitter wavelength to the network by the monitoring control signal and detecting it in the optical repeater 29. Further, in the present embodiment, the operating point control of the modulator 3 by the dither signal and the gain control in the optical repeater 29 by the monitor signal are performed at the same time, but only the gain control by the monitor signal may be performed. The gain control in the optical repeater 29 and the control of the data signal by the dither signal can be performed simultaneously. Further, repeater 29 in the present embodiment may be a receiver.

Embodiment 8 FIG. FIG. 11 is a schematic configuration diagram of a transmission device according to an embodiment of the present invention. 31 is a variable gain optical amplifier as a modulator driving circuit. The output of the synchronous detection circuit 7 is input to the variable gain amplifier 31.
Other components are the same as or equivalent to those of the first embodiment (FIG. 1), and description thereof is omitted. Although the dither signal is applied to the bias circuit 11 in this embodiment, the dither signal may be applied directly to the data signal, the carrier wave, or the optical modulator 3. Here, an amplitude control means is constituted by the variable gain optical amplifier 31 and the like.

The operation will be described. Application of data signal, bias and dither signal to optical modulator 3, demultiplexing of optical output signal output from optical modulator 3 in demultiplexer 4, conversion of optical signal in PD 5 to electric signal, and preamplifier 6 The amplification operation is the same as in the first embodiment (FIG. 1).
The low frequency dither signal in the output signal is supplied to the synchronous detection circuit 7
Is synchronously detected with the low frequency generated by the dither signal generator 12. Based on the synchronous detection result in the synchronous detection circuit 7, the gain of the variable gain optical amplifier 31 is controlled according to the output voltage of the synchronous detection circuit 7.

Next, amplitude control using a dither signal will be described with reference to FIGS. The low frequency signal (fHz) output from the dither signal generator 12 is superimposed on the bias voltage signal by the bias circuit 10. FIG. 12A shows a bias T input to the optical modulator 3.
11 represents an output signal. FIG. 12B shows the equation (1).
5 shows an operation characteristic curve of the optical modulator 3 given by
FIG. 12B shows an example in which the modulator drive amplitude is set appropriately. FIG. 12C shows an optical signal waveform output from the optical modulator 3. It can be understood that the low frequency component fHz is not observed and the 2 fHz component is generated.
Therefore, when the PD5 output signal is synchronously detected with the low frequency signal (fHz) output from the dither signal generator 12, the output of the synchronous detection circuit 7 becomes 0.

FIG. 13 shows the operation of the optical modulator 3 when the modulator drive amplitude is larger than an appropriate value. FIG.
13A shows a bias T11 output signal input to the optical modulator, FIG. 13B shows an operation characteristic curve of the optical modulator 3, and FIG.
(C) is an optical modulator output optical signal. It can be seen that the phase of the low frequency signal (fHz) in the output signal is inverted from the phase of the low frequency signal (fHz) generated by the dither signal generator. Therefore, the output signal voltage of the synchronous detection circuit 7 becomes negative.

FIG. 14 shows the operation of the optical modulator 3 when the modulator drive amplitude is smaller than an appropriate value. FIG.
14A shows a bias T11 output signal input to the optical modulator 3, FIG. 14B shows an operation characteristic curve of the optical modulator 3, and FIG.
(C) is an optical modulator output optical signal. It can be seen that the phase of the low frequency signal (fHz) in the output signal matches the phase of the low frequency signal (fHz) generated by the dither signal generator. Therefore, the output signal voltage of the synchronous detection circuit 7 becomes positive.

As described above, since the error signal corresponding to the deviation of the modulator drive amplitude from the optimum point is output from the synchronous detection circuit 7, the error signal is fed back to the variable gain optical amplifier 31 so that the optical modulator 3 can optimize the amplitude of the drive signal. As described above, according to the present embodiment, the amplitude of the drive signal of modulator 3 can be optimized by the error signal, so that a high-quality transmission signal can be transmitted regardless of the fluctuation of the amplitude of the data signal. it can.

If the amplitude of the low-frequency signal superimposed on the bias voltage is set to several percent or less of the optical modulator drive signal, the quality of the output optical signal does not deteriorate. Further, by using the band-pass filter 16 and the limiter amplifier 8a for the synchronous detection circuit 7, as in the first embodiment, the amplitude of the optical modulator drive signal amplitude is not affected by the fluctuation of the optical signal intensity output from the light source 1. An error signal can be obtained. The same operation can be obtained by inputting the output signal of the PD 5 to the synchronous detection circuit after performing peak detection or the like.

Embodiment 9 FIG. 15 is a schematic configuration diagram of an optical transmission device according to an embodiment of the present invention. 7a is a first synchronous detection circuit, 7b is a second synchronous detection circuit, 12a is a first dither signal generator, 12b is a second dither signal generator, and 31 is a variable gain optical amplifier as a modulator driving circuit. It is. Other components are the same as or equivalent to those of the first embodiment (FIG. 1), and description thereof will be omitted. In this embodiment, the second dither signal is applied to the bias circuit.
The second dither signal may be applied directly to a data signal, a carrier wave, or an optical modulator.

The operation will be described. First synchronous detection circuit 7a
Output the error signal of the bias voltage of the optical modulator 3, and the output of the second synchronous detection circuit 7b outputs the error signal of the amplitude of the modulator drive signal. According to the output of the first synchronous detection circuit 7a, the operating point of the optical modulator 3 is determined in the same manner as in the first embodiment, and based on the output of the second synchronous detection circuit 7b, the eighth embodiment is performed.
The amplitude of the modulator drive signal can be controlled in the same manner as described above. In order to output the two error signals independently, the frequencies of the first low-frequency signal and the second low-frequency signal are different from each other. For example, they can be 10 kHz and 1 kHz. The cut-off frequency of the low-pass filter 9a is set according to the frequency of the first low-frequency signal, and the cut-off frequency of the low-pass filter 9b is set according to the frequency of the second low-frequency signal. By optimizing the amplitude of the modulator drive signal, it becomes possible to control the operating point of the optical modulator 3 more efficiently.

According to the present embodiment, since the operating point control of the modulator 3 and the amplitude control of the drive signal are performed simultaneously, the quality degradation of the transmission signal due to the drift of the operating point of the modulator can be suppressed more effectively. Therefore, a high-quality transmission signal can be transmitted regardless of fluctuations in the amplitude of the data signal. The first low-frequency signal and the second low-frequency signal can also be detected by synchronously detecting the data signal or clock signal and the PD output signal without using the peak detector 15. As the light source, a pulse light source or a multi-wavelength light source can be used.

[0070]

According to the first aspect of the present invention, there is provided a modulating device for modulating a carrier wave by a data signal and outputting an output signal, and applying a bias to the modulating device to control the operation of the modulating device. Bias applying means; dither signal generating means for generating a dither signal; dither signal superimposing means for superimposing a dither signal generated by the dither signal generating means on a bias in the bias applying means without superimposing the dither signal on the data signal; A dither signal detecting means for detecting the superimposed dither signal component from the output signal output from the modulating means, and a phase of the detected dither signal component and a phase of the dither signal generated by the dither signal generating means. And a bias comparing means based on the comparison result of the phase comparing means. Since those having a bias control means for controlling the application of the scan, there is an effect that it is possible to suppress the quality degradation of the transmit signal due to drift of the operating point of the modulator.

The modulator according to the second aspect of the present invention includes a modulating means for modulating a carrier wave with a data signal and outputting an output signal, a dither signal generating means for generating a dither signal, and the dither signal generating means for the modulating means. Dither signal applying means for applying a dither signal generated by the above, dither signal detecting means for detecting the superimposed dither signal component from the output signal output from the modulating means, and a phase of the detected dither signal component. Phase comparing means for comparing the phase of the dither signal generated by the dither signal generating means,
Since it has amplitude control means for controlling the amplitude of the data signal based on the comparison result in the phase comparison means, it is possible to transmit a high-quality transmission signal regardless of fluctuations in the amplitude of the data signal. Play.

A modulator according to a third aspect of the present invention includes a modulating means for modulating a carrier wave with a data signal and outputting an output signal, and a bias applying means for applying a bias to the modulating means for controlling the operation of the modulating means. Means, first dither signal generating means for generating a first dither signal, and the bias applying means without superimposing the first dither signal generated by the first dither signal generating means on the data signal. Dither signal superimposing means for superimposing on the bias;
First dither signal detection means for detecting the superimposed first dither signal component from the output signal output from the modulation means, and the phase of the detected first dither signal component and the first dither signal First phase comparing means for comparing the phase of the first dither signal generated by the generating means, and bias control means for controlling the application of a bias in the bias applying means based on the comparison result in the first phase comparing means And a second dither signal generating means for generating a second dither signal having a frequency different from the first dither signal, and a second dither signal generated by the second dither signal generating means to the modulation means. Dither signal applying means for applying, second dither signal detecting means for detecting the superimposed second dither signal component from the output signal output from the modulating means, A second phase comparison means for comparing the phase of the second dither signal component with the phase of the second dither signal generated by the second dither signal generation means; and Since it has amplitude control means for controlling the amplitude of the data signal based on the comparison result, by simultaneously controlling the operating point of the modulator and the amplitude of the data signal, the transmission signal due to the drift of the operating point of the modulator is controlled. It is possible to more effectively suppress the quality deterioration and to transmit a high-quality transmission signal irrespective of the fluctuation of the amplitude of the data signal.

The modulation device according to the fourth invention is particularly suitable for the first,
In the modulation device according to the second or third invention, the data signal input to the modulation means includes a frequency of 5 GHz or more.
In particular, in the modulation of a high-frequency signal, it is possible to easily suppress the quality deterioration of the transmission signal due to the drift of the operating point of the modulator,
In addition, the present invention has the effect that the quality degradation of the transmission signal due to the fluctuation of the data signal can be easily suppressed.

The transmitting apparatus according to the fifth invention is particularly suitable for the first,
In the modulation device according to the second, third or fourth invention, a monitoring signal generating means for generating a monitoring signal, a monitoring signal applying means for applying a monitoring signal generated by the monitoring signal generating means to the modulation means, Since the modulation device further includes monitoring signal detecting means for detecting the monitoring signal component from the return signal of the output signal from the transmission path of the output signal and monitoring the state of the transmission path, particularly monitoring the state of the transmission path And efficient management of the communication system can be realized.

A communication system according to a sixth aspect of the present invention is a communication system having a transmitting device and a receiving device, wherein the transmitting device is a modulation device according to the first, second, third or fourth aspect of the present invention. A monitoring signal generating means for generating a monitoring signal having the following, and a modulation device further comprising a monitoring signal applying means for applying a monitoring signal generated by the monitoring signal generating means to the modulation means, wherein the receiving apparatus comprises: It has monitoring signal detecting means for detecting the monitoring signal component from an output signal from the device, and detecting means for detecting information on the communication system based on the detected monitoring signal. Can be obtained, and efficient management of the communication system can be realized.

A communication system according to a seventh aspect of the present invention is a communication system having a transmitting device and a receiving device, wherein the transmitting device generates a monitor signal, particularly in the modulation device according to the first, second, third, or fourth aspect. Monitoring signal generating means for
A modulation device that further includes a monitoring signal application unit that applies a monitoring signal generated by the monitoring signal generation unit to the modulation unit, wherein the reception device detects the monitoring signal component from an output signal from the transmission device Monitor signal detection means, since it has a gain control means for performing the gain control of the output signal based on the detected monitor signal, especially by performing the gain control of the output signal in the receiving device,
This has the effect of suppressing quality degradation of the transmission signal.

The transmitting apparatus according to the eighth aspect of the present invention includes a modulating means for modulating a carrier wave by a data signal to output an output signal, a monitoring signal generating means for generating a monitoring signal, and a monitoring signal generating means for generating the monitoring signal. Monitoring signal applying means for applying a monitoring signal to the modulation means without superimposing the monitoring signal on the carrier; and monitoring signal detection for detecting the monitoring signal component from a return signal of the output signal from the transmission path and monitoring the state of the transmission path. Since it has means, efficient management of the communication system can be realized by monitoring the state of the transmission path.

A communication system according to a ninth aspect of the present invention is a communication system having a transmitting device and a receiving device, wherein the transmitting device generates a monitor signal, and a modulating means for modulating a carrier wave by a data signal and outputting an output signal. Monitoring signal generating means, and monitoring signal applying means for applying the monitoring signal generated by the monitoring signal generating means to the modulation means without superimposing the monitoring signal on the carrier wave, wherein the receiving device outputs an output from the transmitting device. Since it has monitoring signal detection means for detecting the monitoring signal component from the signal and gain control means for controlling the gain of the output signal based on the detected monitoring signal, it is possible to control the gain of the output signal in the receiving device. Accordingly, the effect of suppressing the quality deterioration of the transmission signal is achieved.

A communication system according to a tenth aspect of the present invention is a communication system having a transmitting device and a receiving device, in particular, modulating means for modulating a carrier wave with a data signal and outputting an output signal, and a monitoring signal having information on the communication system. A monitor signal generating unit that generates, and a monitor signal applying unit that applies the monitor signal generated by the monitor signal generating unit to the modulation unit without superimposing the monitor signal on the carrier wave. Since it has monitoring signal detection means for detecting the monitoring signal component from the output signal and detection means for detecting information on the communication system based on the detected monitoring signal, it is possible to obtain information on the transmitting apparatus by the receiving apparatus. And efficient management of the communication system can be realized.

The modulator according to the eleventh aspect of the present invention includes a modulator for modulating a plurality of single-wavelength carriers with a data signal and outputting an output signal, a dither signal generator for generating a dither signal, and a modulator for the modulator. A bias applying unit for applying a bias to the modulating unit to control an operation, a dither signal applying unit for applying a dither signal generated by the dither signal generating unit to the modulating unit, and an output signal of the modulating unit. Carrier detecting means for detecting one carrier component of the plurality of carrier waves, dither signal detecting means for detecting the superimposed dither signal component from the carrier components detected by the carrier detecting means, and the detected dither signal component Phase comparing means for comparing the phase of the dither signal with the phase of the dither signal generated by the dither signal generating means; Since the bias control means for controlling the bias application in the bias applying means based on the comparison result in the above, even when a plurality of single wavelength carriers are modulated collectively, the transmission signal due to the drift of the operating point of the modulation device is There is an effect that quality deterioration can be suppressed.

According to a twelfth aspect of the present invention, in the modulator according to the first, second, third or fourth aspect, in particular, the modulating means modulates a plurality of single wavelength carriers with a data signal. Wherein the dither signal detection means has a carrier detection means for detecting one carrier component of the plurality of carrier waves from the output signal of the modulation means, and the superimposition is performed based on the carrier component detected by the carrier detection means. It is characterized by detecting a dither signal component that has been modulated, so that even when multiple single-wavelength carriers are modulated collectively, a high-quality transmission signal can be transmitted regardless of fluctuations in the amplitude of the data signal. This has the effect that it can be performed.

The modulating method according to the thirteenth aspect of the present invention provides a modulating means for modulating a carrier wave with a data signal in a modulating means to output an output signal, a dither signal generating step for generating a dither signal, A dither signal applying step for applying a dither signal generated in the signal generating step, a dither signal detecting step for detecting the superimposed dither signal component from an output signal output from the modulation means, and the detected dither signal component detected Phase comparison step of comparing the phase of the dither signal generated by the dither signal generation step,
Since it has an amplitude control step of controlling the amplitude of the data signal based on the comparison result in the phase comparison step, an effect that a high-quality transmission signal can be transmitted irrespective of fluctuations in the amplitude of the data signal is obtained. Play.

A modulation method according to a fourteenth aspect of the present invention provides a modulation method for modulating a carrier with a data signal in a modulation means and outputting an output signal, and applying a bias to the modulation means to control the operation of the modulation means. A dither signal generating step of generating a dither signal; a dither signal superimposing step of superimposing a dither signal generated in the dither signal generating step on a bias in the bias applying step without superimposing the dither signal on the data signal. A dither signal detecting step of detecting the superimposed dither signal component from an output signal output from the modulating means; a phase of the detected dither signal component and a phase of the dither signal generated by the dither signal generating step And a phase comparison step of comparing
Since the method includes the bias control step of controlling the bias application in the bias application step based on the comparison result in the phase comparison step, it is possible to suppress the quality degradation of the transmission signal due to the drift of the operating point of the modulation device. Play.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a basic configuration of an optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a basic operation of the optical transmission device according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a basic operation of the optical transmission device according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a basic operation of the optical transmitting apparatus according to the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating a basic configuration of an optical transmission device according to a second embodiment of the present invention.

FIG. 6 is a block diagram illustrating a basic configuration of an optical transmission device according to a third embodiment of the present invention.

FIG. 7 is a block diagram illustrating a basic configuration of an optical transmission device according to a fourth embodiment of the present invention.

FIG. 8 is a block diagram illustrating a basic configuration of an optical transmission device according to a fifth embodiment of the present invention.

FIG. 9 is a block diagram illustrating a basic configuration of an optical transmission device according to a sixth embodiment of the present invention.

FIG. 10 is a block diagram illustrating a basic configuration of an optical transmission system according to a seventh embodiment of the present invention.

FIG. 11 is a block diagram illustrating a basic configuration of an optical transmitting apparatus according to an eighth embodiment of the present invention.

FIG. 12 is a diagram illustrating a basic operation of the optical transmitting apparatus according to the eighth embodiment of the present invention.

FIG. 13 is a diagram showing a basic operation of the optical transmitting apparatus according to the eighth embodiment of the present invention.

FIG. 14 is a diagram illustrating a basic operation of the optical transmission apparatus according to the eighth embodiment of the present invention.

FIG. 15 is a block diagram illustrating a basic configuration of an optical transmission device according to a ninth embodiment of the present invention.

FIG. 16 is a block diagram showing a basic configuration of an optical transmission device in a conventional technique.

FIG. 17 is a diagram illustrating a basic operation of an optical transmission device according to a conventional technique.

FIG. 18 is a diagram illustrating a basic operation of an optical transmission device according to a conventional technique.

FIG. 19 is a diagram illustrating a basic operation of an optical transmission device according to a conventional technique.

[Explanation of symbols]

1 light source, 2 pulse light sources, 3 optical modulators, 4 splitters, 5 PD, 5 a PD, 5 b PD, 6 preamplifier, 6 a preamplifier, 6 b preamplifier, 7 synchronous detection circuit, 7 a synchronous detection circuit, 7 b synchronous detection circuit, 8
Amplifier, 8a amplifier, 8b amplifier, 8c amplifier, 8
d amplifier, 9 low frequency transmission filter, 9a low frequency transmission filter, 9b low frequency transmission filter, 10 bias circuit, 11 bias T, 12 dither signal generator,
12a dither signal generator, 12b dither signal generator, 13 low frequency superimposing circuit, 14 terminator, 15 peak detector, 16 BPF, 17 mixer, 17a mixer, 17b mixer, 18 delay controller, 19 multiplexer,
Reference Signs List 20 optical output terminal, 21 modulator drive data signal input terminal, 22 supervisory signal generation circuit, 23a single wavelength light source,
23b single wavelength light source, 23c single wavelength light source, 24
Modulator drive circuit, 25 monitoring signal detection circuit, 26 clock input terminal, 27 optical filter, 28 transmission line fiber, 29 optical repeater, 30 gain control circuit, 31 variable gain optical amplifier.

Claims (14)

[Claims] 1. A modulating means for modulating a carrier wave with a data signal and outputting an output signal, a bias applying means for applying a bias to the modulating means for controlling the operation of the modulating means, and a dither signal for generating a dither signal Generating means, dither signal superimposing means for superimposing a dither signal generated by the dither signal generating means on a bias in the bias applying means without superimposing the data signal on the bias, and an output signal output from the modulation means. Dither signal detection means for detecting the superimposed dither signal component, phase comparison means for comparing the detected phase of the dither signal component with the phase of the dither signal generated by the dither signal generation means, and the phase comparison means Control means for controlling the application of the bias by the bias applying means based on the comparison result in Modulator having. 2. A modulating means for modulating a carrier wave with a data signal to output an output signal; a dither signal generating means for generating a dither signal; and applying a dither signal generated by the dither signal generating means to the modulating means. Dither signal application means, dither signal detection means for detecting the superimposed dither signal component from the output signal output from the modulation means, and the phase of the detected dither signal component and the dither signal generated by the dither signal generation means. A modulation device comprising: a phase comparison unit that compares a phase of a dither signal; and an amplitude control unit that controls an amplitude of the data signal based on a comparison result of the phase comparison unit. 3. A modulating means for modulating a carrier with a data signal and outputting an output signal, a bias applying means for applying a bias to the modulating means for controlling the operation of the modulating means, and a first dither signal generating means. A dither signal superimposing means for superimposing a first dither signal generated by a first dither signal generating means on a bias in the bias applying means without superimposing the data signal on the bias; and an output outputted from the modulation means. First dither signal detection means for detecting the superimposed first dither signal component from the signal,
First phase comparing means for comparing the detected phase of the first dither signal component with the phase of the first dither signal generated by the first dither signal generating means, and the first phase comparing means A bias control means for controlling the application of a bias in the bias application means based on the comparison result, a second dither signal generation means for generating a second dither signal having a frequency different from the first dither signal, Dither signal applying means for applying the second dither signal generated by the dither signal generating means to the modulating means, and detecting the superimposed second dither signal component from the output signal output from the modulating means. A second dither signal detecting means for comparing a phase of the detected second dither signal component with a phase of a second dither signal generated by the second dither signal generating means; Modulator having a second phase comparing means, an amplitude control means for controlling the amplitude of the data signal based on the comparison result of the second phase comparator for. 4. A data signal input to the modulation means,
4. The modulator according to claim 1, wherein the modulator has a frequency of 5 GHz or more. 5. A monitor signal generating means for generating a monitor signal,
Monitoring signal applying means for applying a monitoring signal generated by the monitoring signal generating means to the modulating means; and detecting the monitoring signal component from a return signal of the output signal from the transmission path of the output signal and detecting a state of the transmission path. A transmission device comprising the modulation device according to claim 1, further comprising a monitoring signal detection unit that monitors the signal. 6. A communication system having a transmitting device and a receiving device, wherein the transmitting device generates a monitoring signal having information regarding the communication system, and a monitoring signal generated by the monitoring signal generating device. Further comprising a monitoring signal applying means for applying the monitoring signal to the modulation means, wherein the receiving apparatus converts the monitoring signal component from an output signal from the transmitting apparatus. A communication system comprising: a monitoring signal detecting unit for detecting; and a detecting unit for detecting information on the communication system based on the detected monitoring signal. 7. In a communication system having a transmitting device and a receiving device, the transmitting device applies a monitoring signal generating means for generating a monitoring signal and a monitoring signal generated by the monitoring signal generating means to the modulation means. 5. The monitoring signal detection device according to claim 1, further comprising a monitoring signal applying unit for performing the monitoring signal detection, wherein the receiving device detects the monitoring signal component from an output signal from the transmission device. A communication system comprising: a receiver; and a receiver having gain control means for controlling a gain of the output signal based on the detected monitor signal. 8. A modulating means for modulating a carrier with a data signal and outputting an output signal, a monitor signal generating means for generating a monitor signal, and superimposing a monitor signal generated by the monitor signal generating means on the carrier. And a monitor signal applying unit for applying the output signal to the modulation unit, and a monitor signal detecting unit for detecting the monitor signal component from a return signal of the output signal from the transmission line and monitoring the state of the transmission line. 9. A communication system having a transmitting device and a receiving device, wherein the transmitting device modulates a carrier with a data signal and outputs an output signal; monitoring signal generating means for generating a monitoring signal; A monitor signal applying unit that applies a monitor signal generated by a monitor signal generating unit to the modulation unit without superimposing the monitor signal on the carrier, the receiving device converts the monitor signal component from an output signal from the transmitting device. A communication system having a receiving device including a monitoring signal detection unit for detecting, and a gain control unit for performing gain control of the output signal based on the detected monitoring signal. 10. A communication system having a transmitting device and a receiving device, wherein the transmitting device modulates a carrier with a data signal and outputs an output signal, and a monitor for generating a monitoring signal having information on the communication system. A signal generation unit, and a monitoring signal application unit that applies a monitoring signal generated by the monitoring signal generation unit to the modulation unit without superimposing the monitoring signal on the carrier, wherein the reception device outputs an output signal from the transmission device. 1. A communication system comprising: a monitoring signal detection unit configured to detect the monitoring signal component from the control unit; and a reception device including a detection unit configured to detect information regarding the communication system based on the detected monitoring signal. 11. A modulating means for modulating a plurality of single-wavelength carriers with a data signal and outputting an output signal; a dither signal generating means for generating a dither signal; and the modulating means for controlling the operation of the modulating means. Bias applying means for applying a bias to, dither signal applying means for applying a dither signal generated by the dither signal generating means to the modulating means, and one carrier component of the plurality of carrier waves from the output signal of the modulating means. And a dither signal detecting means for detecting the superimposed dither signal component from the carrier component detected by the carrier detecting means, and a phase of the detected dither signal component and the dither signal generating means. Phase comparing means for comparing the phase of the generated dither signal with the phase of the generated dither signal; Modulator having a bias control means for controlling the biasing of the astigmatism applying means. 12. The modulation means modulates a plurality of single-wavelength carriers with a data signal, and the dither signal detection means detects one carrier wave of the plurality of carrier waves from an output signal of the modulation means. 5. The method according to claim 1, further comprising a carrier detection unit for detecting a component, wherein the superimposed dither signal component is detected from a carrier component detected by the carrier detection unit. Modulation device. 13. A modulating means for modulating a carrier wave with a data signal in a modulating means to output an output signal; a dither signal generating step for generating a dither signal; and a dither signal generated in said dither signal generating step by said modulating means. A dither signal applying step, a dither signal detecting step of detecting the superimposed dither signal component from an output signal output from the modulating means, and a phase of the detected dither signal component and the dither signal generating step. A modulation method, comprising: a phase comparison step of comparing a phase of a generated dither signal; and an amplitude control step of controlling an amplitude of the data signal based on a comparison result in the phase comparison step. 14. A modulating step of modulating a carrier with a data signal in a modulating means and outputting an output signal; a bias applying step of applying a bias to said modulating means to control an operation of said modulating means; and generating a dither signal. A dither signal generating step, a dither signal superimposing step of superimposing a dither signal generated in the dither signal generating step on a bias in the bias applying step without superimposing the dither signal on the data signal, and an output output from the modulating means. A dither signal detecting step of detecting the superimposed dither signal component from the signal; a phase comparing step of comparing a phase of the detected dither signal component with a phase of the dither signal generated in the dither signal generating step; Based on the comparison result in the phase comparison step, Modulation method having a bias control step of controlling the application of the bias in the astigmatism applying step.