JP3490617B2 - Optical transmitter and optical communication system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter and an optical communication system whose transmission waveform changes in an analog manner.

[0002]

2. Description of the Related Art An optical communication system in which optical power is modulated by a signal whose waveform varies in an analog manner, such as a band signal for wireless communication or broadcasting, is part of a communication system such as a CATV or a wireless base station accommodation system. Is used for.

The light source used for optical communication is usually a semiconductor laser. When the output current power is directly modulated by modulating the drive current of the semiconductor laser, the distortion component that occurs because the relationship of the output light power corresponding to the drive current is not perfectly linear in a signal whose waveform changes in an analog manner. It can be a problem.

In order to solve such a problem, conventionally, a method of electrically compensating for distortion has been adopted. Japanese Patent Laid-Open No. 8-172232 utilizes the property that the distortion characteristic of the laser changes depending on the amount of DC bias current, and the amount of DC bias current that minimizes distortion changes depending on the magnitude of the drive modulation signal. Create a table in which the distortion characteristics of the laser are recorded in advance, detect the magnitude of the drive modulation signal, and refer to the table for the bias point that produces the minimum distortion characteristic with the magnitude of the drive modulation signal. The laser is searched for and the bias current value of the laser is controlled based on that value. By doing so, the bias point with the smallest distortion value can be used regardless of the magnitude of the drive modulation signal. However, as can be seen in claim 3 of this patent,
How the distortion appears depends not only on the magnitude of the drive modulation signal but also on the frequency of the drive modulation signal. This patent proposes to create a table that also takes into account the frequency of the drive modulation signal, but the factors that cause changes in distortion are not limited to these two factors, but also changes in the ambient temperature of the laser and reflected return light. There are various factors such as the amount of. Therefore, in order to deal with such a situation with the method of this patent, it is necessary to create a table in consideration of all possible factors. However, the effective amount of the reflected return light changes depending on the polarization, and it is very difficult and unrealistic to measure the effective amount during the actual operation of the system. In addition, there may be other unknown factors, and it is not possible to deal with the strain fluctuations caused by such factors. Furthermore, the distortion characteristics of semiconductor lasers vary greatly from individual to individual, and it is not realistic to make such a table for each semiconductor laser.

[0005]

As described above, in the conventional method, in order to determine the optimum bias point, it is necessary to prepare a table in which all factors are taken into consideration. However, it is difficult to identify all the factors in advance, and some parameters are very difficult to measure, which is not realistic.

The present invention provides an apparatus which always operates at an optimum bias point regardless of fluctuation factors.

[0007]

In order to solve such a problem, in the first invention of the present application, an optical transmission in which an injection current of a semiconductor laser is driven by a signal that can take an arbitrary level and its output light is transmitted. Of the semiconductor laser
Can take any of the levels caused by non-linearity
Distortion component for detecting the magnitude of signal distortion component from the output light
Detecting means and magnitude of signal that can take the arbitrary level
Before entering the semiconductor laser or from the output light.
The output signal detecting means, the magnitude of the distortion component and the signal
From the magnitude of the signal detected by the signal detection means
The non-linearity calculation means for calculating the non-linearity and the non-linearity calculation method
In order to minimize the non-linearity calculated by the step,
A bar for controlling the bias amount of the injection current of the semiconductor laser.
An optical transmitter comprising: an ear control means .

[0008] distortion when driving a semiconductor laser with a signal analog manner waveform changes like a frequency multiplexed electrical signal generated by non-linearity of the laser is a problem. In the present invention, the component generated by the laser distortion of the drive modulation signal is extracted from the electric signal obtained by photoelectrically converting the output light of the semiconductor laser. The magnitude of the distorted component varies depending on the distortion amount of the semiconductor laser , that is, the non-linearity. Therefore, the amount of strain of the semiconductor laser can be detected from the component generated by the strain. As described in [Prior Art], the semiconductor laser generally has a characteristic that the amount of strain (non-linearity) changes depending on the amount of bias of the injected current. Therefore, in the present invention, the bias amount of the injection current is controlled so that the detected strain amount becomes small. By doing this, regardless of the factors that change the amount of distortion,
It is possible to control the amount of bias current so that the amount of distortion at that time is minimized, and the table for distortion control corresponding to various situations of the semiconductor laser used in advance becomes unnecessary, and the distortion is highly feasible. It becomes possible to control.

With respect to the distortion amount detecting method, in the fourth invention of the present application, the semiconductor laser is detected by a signal that can take an arbitrary level.
Optical transmitter that drives the injection current of the laser and transmits the output light
And is different from the signal that can take any level
A dummy generator for generating one or more dummy signals,
The dummy signal generated from the dummy generator is
When the nonlinearity of the body laser is deteriorated from the target,
The distortion of the dummy signal is of a size that can be detected.
The dummy signal is added to the signal that can take the level of
One of the output light obtained by driving the injection current of the semiconductor laser
Before extracting from the signal obtained by photoelectrically converting all or part
Based on the distortion component of the dummy signal, the semiconductor laser of the
The injection voltage of the semiconductor laser is adjusted so that the nonlinearity is minimized.
Provided is an optical transmitter characterized by controlling a flow bias amount .

A dummy signal such as an unmodulated carrier is added to the transmission data signal for driving the semiconductor laser.
In the case of a data signal, depending on the form of the system, the magnitude thereof may not be constant, or in some cases there may be no signal, so that the component generated by the distortion cannot always be detected. Therefore, in the present invention, the dummy signal is added to the data signal to drive the semiconductor laser, and the component generated by the distortion of the dummy signal is detected from the electric signal obtained by photoelectrically converting the output light. The amount of strain of the semiconductor laser is detected from there, and the amount of bias current of the semiconductor laser is controlled so that the amount of strain is minimized. Further, the size of the dummy carrier is set so that the distortion can always be detected when the nonlinearity of the semiconductor laser is deteriorated from the target. As a result, the amount of distortion of the laser can be constantly monitored and detected, and more stable control can be performed.

Next, in the fifth invention of the present application, an arbitrary level is set.
Drive the injection current of the semiconductor laser with a signal that can take
Optical transmitter that operates and transmits the output light, and optical fiber transmission
Receives output light transmitted from the optical transmitter through the optical path
An optical communication system comprising an optical receiver,
The signal is different from the signal that can take any level 1
Equipped with a dummy generator that generates one or more dummy signals
The dummy signal generated from the dummy generator is
With the laser nonlinearity deteriorated from the target,
When the dummy signal distortion is large enough to be detected,
The dummy signal to the signal that can take any level.
Signal is applied to drive the injection current of the semiconductor laser.
Means for photoelectrically converting a part or all of the output light
The dummy extracted from the signal obtained by photoelectric conversion
The nonlinearity of the semiconductor laser based on the distortion component of the signal
And means for calculating the calculated semiconductor laser
The laser diode so that the nonlinearity of the laser is minimized.
Optical communication characterized by controlling the amount of input current bias
Provide the system .

The mode of the present invention is a mode in which the amount of strain is detected and fed back to the amount of bias current of the semiconductor laser, but the amount of strain changes relatively slowly, and high-speed feedback is not required. In the present invention, the strain amount of the semiconductor laser may be detected in a device having the semiconductor laser therein, but the invention is not particularly limited thereto. In the fifth aspect of the present invention, the amount of distortion is detected by the optical receiver connected to the optical transmitter via the optical fiber. The detected strain amount or information for controlling the semiconductor laser is transmitted to a device having an optical transmitter through some communication line. When the device having the optical transmitter receives the information, it controls the bias current amount of the semiconductor laser based on the information. One of the applicable areas of the present invention is a system in which an antenna station for wireless communication is accommodated by an optical fiber. In such a case, it is desirable to downsize the antenna station device. By taking the form as the fifth invention of the present application,
The size of the optical transmitter installed in the antenna station can be reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. It should be noted that in the following description, only the parts that are essentially related to the present application are shown, and parts that are not directly related to the operation of the present application are not shown, although they are necessary for implementation such as amplifiers and power supplies.

FIG. 1 is a block diagram showing an embodiment of the first invention of the present application. A data signal such as a CATV signal or a wireless signal is input from the signal input 4. This signal is made to have a magnitude suitable for driving the semiconductor laser 1 by the signal driver 5. The combiner 6 combines the output signal of the signal driver 5 and the bias current output from the bias current source 8. The semiconductor laser 1 is driven by the output of the coupler 6 and outputs an optical signal whose light intensity changes substantially in proportion to the change in injection current. A part of the output optical signal is branched by the optical branching / coupling device 2 and is converted into an electric signal by the photoelectric converter 9. The obtained electric signal is input to the distortion amount detector 7 and the distortion amount is detected. Bias current control device 3
Controls the bias current source 8 by determining the bias current amount so that the strain amount detected by the strain amount detection unit 7 is minimized.

The bias current control device 3 controls the bias current so that the amount of strain detected by the strain amount detector 7 is minimized. For example, a method such as a hill climbing method is used to find and control the direction of change in the bias current in which the amount of distortion is small. If there is a maximum allowable strain amount, control so that it is less than that. If it is within the permissible range, no particular control is required during that time.

In the present invention, the only parameter to be controlled is the bias current. There is an optimum point for the amount of bias current that minimizes the amount of distortion, but even at the optimum point, the amount of distortion differs depending on the state at that time (temperature, reflected return light amount, etc.).
Although the method of the present invention can set the optimum point with the minimum distortion, the minimum distortion amount does not always satisfy the specific reference value. Therefore, the control method is preferably a method of finding the optimum point, rather than a method of controlling so as to satisfy the reference value. Alternatively, both of them may be used. That is, if a certain reference value is set and the amount of distortion becomes smaller than that, no further control is performed. If the amount of distortion does not become smaller than the reference value even if the control is performed, control is performed so that it is fixed to the minimum amount of bias current .
It

A method of detecting the amount of strain in the strain amount detector 7 will be described. FIG. 3 illustrates how distortion occurs in a band signal. The spectrum of the band signal 10 existing within a limited band around a certain center frequency Fs is shown in FIG.
Is like. When passing through a semiconductor laser having poor linearity, distortion occurs as shown in FIGS. 3B and 3C. In FIG. 3B, side lobes 11 are generated around the original band of the band signal 10.
In (c), the harmonic 12 of the band signal 10 is generated. FIG. 4 shows some forms of configuration examples of the distortion detection unit. FIG. 4A shows a relatively simple configuration, in which the magnitude of the strain itself generated by the non-linearity of the semiconductor laser is output instead of detecting the coefficient indicating the strain amount (non-linearity) of the semiconductor laser. To do. A desired distortion component from the electric signal obtained by the photoelectric converter 9, for example, the side lobe 11 in FIG.
The harmonics 12 are extracted by the filter 13, and the magnitude thereof is detected by the detector 14. The detector 14 may be an asynchronous detector such as a diode or may be a synchronous detector. With such a configuration, the bias current of the semiconductor laser is controlled not to decrease the coefficient indicating nonlinearity but to reduce the generated distortion component.

With this arrangement, for example, even if the bias current amount is such that the semiconductor laser has a large non-linearity, the generated distortion component is sufficiently small because the power of the drive signal is small. May be judged. In such a state, if a band signal with a large power is suddenly input, the control may not catch up and a large amount of distortion may be generated. Therefore, the configuration of FIG. 4A is not suitable for a system in which the power of the band signal varies greatly. However, because of the extremely simple configuration, CA
A system with a small dynamic range such as a TV signal and almost no power fluctuation, or even when transmitting a wireless signal to an antenna station, and automatic power control etc. is inserted before inputting to the signal driver, and power fluctuation is small. It can be used for systems that have become.

In the form of FIG. 4A, only the main part for detecting the distortion component is shown. When the frequency of the distortion component is high and difficult to handle, or when it is desired to reduce the frequency of the distortion component in order to detect it with a filter having a low Q value, it is advisable to appropriately insert a frequency down converter.

Although FIG. 4B is a little more complicated than the structure of FIG. 4A, it is a structure for detecting the distortion amount of the semiconductor laser, that is, a coefficient indicating non-linearity. Similar to FIG. 4A, the output light of the semiconductor laser is converted into an electric signal by the photoelectric converter 9, cut out by the filter 13, and the magnitude thereof is detected by the detector 14. At the same time, the original data signal is filtered 15
The size is detected by the detector 16 and the size thereof is detected by the detector 16. These are input to the calculator 17. Calculator 17
Divides these inputs by an appropriate ratio and an appropriate power, and outputs a coefficient indicating the distortion amount of the semiconductor laser to the bias controller. In this way, the nonlinearity of the semiconductor laser is controlled so as to be minimized, so that there are no restrictions on the dynamic range of signals and the speed of fluctuation.

Even with the configuration of FIG. 4C, the coefficient indicating the distortion amount of the semiconductor laser can be detected in the same manner. In the configuration of FIG. 4B, both the data signal and the distortion component are extracted from the optical signal, but in FIG. 4C, the data signal is branched from the drive signal before being input to the semiconductor laser. In this case, since the data signal has no distortion component, no filter is required before the detector 16. The distortion component is extracted by the filter 13 from the signal converted into the electric signal by the photoelectric converter 9. The output of the filter 13 is input to the wave detector 14, and the magnitude of the distortion component is detected. On the other hand, the original signal is partially distributed by the distributor 18, is input to the detector 16, and its magnitude is detected. The output of the detector 14 and the output of the detector 16 are input to the calculator 17, are divided by an appropriate ratio and an appropriate power, and a coefficient indicating the distortion amount of the semiconductor laser is output.

In the above embodiment, the amount of distortion is obtained from the component generated by the distortion of the data signal. In order to obtain the amount of distortion more stably, a dummy signal is added to the data signal and the component generated by the distortion of the dummy signal is detected. FIG. 5 shows an example of the configuration when a dummy signal is used. The data signal is input from the signal input 4, and is combined with the dummy signal output from the dummy signal generator 20 by the combiner 19. The output of the combiner 19 is amplified by the signal driver 5 and combined with the bias current by the combiner 6 to drive the semiconductor laser 1. The output light of the semiconductor laser 1 is partially branched by the optical branching / coupling device 2 and input to the photoelectric converter 9. From the output signal of the photoelectric converter 9, the distortion amount detector 21 detects the distortion component generated by the distortion of the dummy signal, and based on this, the semiconductor laser 1
Is detected. The detected distortion amount is input to the bias current control device 3, and the bias current source 8 is controlled so that the distortion amount is minimized.

Since the dummy signal is always supplied with stable power and frequency, even if the power and frequency of the original band signal fluctuate, the distortion component for detecting the distortion amount can be detected stably. Therefore, it is possible to stably detect the amount of distortion even in a system having a large dynamic range or a system in which the frequency of a data signal varies.

Even when the distortion of the dummy signal is detected, the distortion component itself may be controlled so as to be small as in the case of detecting the distortion of the data signal, or it may be compared with the magnitudes of the data signal and the dummy signal. The amount of strain of the semiconductor laser, that is, the coefficient of nonlinearity may be detected.

A modulated signal may be used as the dummy signal, but more simply, an unmodulated carrier may be used. The operation when the unmodulated carrier is used as a dummy signal will be described with reference to FIG. FIG. 2A shows a coupler 19
It is the spectrum after the data signal and the dummy carrier are combined at. A band signal 10 which is a data signal and two dummy carriers 34-1 and 34-2 are multiplexed.
When the semiconductor laser 1 is driven by this, a distortion component is generated as shown in FIG. 2B due to the non-linearity of the semiconductor laser. FIG. 2B is a spectrum when third-order distortion occurs.
Side lobes 11-1 and 11-2 are components generated by distortion of band signal 10, and distortions 35-1 and 35-2 are intermodulation distortions of dummy carriers 34-1 and 34-2. In the distortion detector 21, the distortion 35-1 or 35-2 of the dummy carrier is generated.
Is detected, and the amount of distortion is detected based on that. In the frequency arrangement as shown in FIG. 2, the distortion 35-2 of the dummy carrier is close to the side lobe 11-2 of the band signal 10 and is difficult to separate. Therefore, it is preferable to extract the distortion 35-1.

The optimum value of the bias current of the laser that minimizes the amount of strain may vary depending on the order of strain. Therefore, it is necessary to control the bias current so as to minimize the distortion of the order which is a problem in the applied system. Figure 2
In the above example, two dummy carriers are prepared, cross-modulation due to the third-order distortion of the semiconductor laser is detected, and feedback is applied so that the third-order distortion is minimized. If the second-order distortion is a problem, the difference frequency or the sum frequency of the two dummy carriers may be detected and fed back.

If the system is capable of detecting the higher harmonics of the dummy carrier, only one dummy carrier may be used to detect the higher harmonics. In that case, if the third-order distortion is detected, the third-order harmonic wave may be detected, and if the second-order distortion is detected, the second-order harmonic wave may be detected.

The system for detecting the amount of strain is the same as in FIG. In the case of the method of controlling so that the absolute amount of the distortion component of the dummy carrier becomes small, the distortion of the dummy carrier is selected by the filter 13 in FIG. If you want to detect and control the amount of laser distortion (coefficient of non-linearity) as well, see Fig. 4 (b).
Or as shown in FIG. 4 (c). At this time, filter 1
In 3, the component generated by the distortion of the dummy carrier is detected. The size of the dummy carrier is detected by the filter 15 and the detector 16. The computing unit 17 divides these by an appropriate ratio and a power, and detects the amount of distortion.

The component detected by the filter 15 and the detector 16 may be not the dummy carrier but the magnitude of the data signal or the magnitude of the entire signal including all of the data signal and the dummy carrier. When detecting the magnitude of the entire signal, the filter 15 may be omitted in FIG. Although the magnitude of the data signal input from the signal input 4 may change depending on the operating condition of the system, the dummy carrier is generated in the optical transmitter and its magnitude is known. Although the size of the dummy carrier included in the signal detected by the photoelectric converter 9 slightly fluctuates due to the change in the electric-optical conversion efficiency of the semiconductor laser 1, the fluctuation width is narrow. The power of the generated distortion depends not only on the original signal forming the distortion but also on the magnitude of the entire signal applied to the laser 1. Therefore, the amount of distortion can be detected more accurately by detecting the size of the data signal or the size of the entire signal. At this time, the arithmetic unit 17 stores a constant corresponding to the size of the dummy carrier, and the ratio of the size of the dummy carrier to the size of the entire signal,
Also, the amount of distortion of the laser is calculated and output from the ratio (power ratio) of the size of the distortion component to the size of the dummy carrier.

In order to detect the distortion amount more accurately in response to the fluctuation of the laser electro-optical conversion efficiency, the size of the dummy carrier, the size of the data signal (or the entire signal), as shown in FIG. You may detect the magnitude of each distortion component. In the configuration of FIG. 6A, the output of the photoelectric converter 9 is branched into three, the distortion component of the dummy carrier is extracted by the filter 13, the dummy carrier is extracted by the filter 15, and the data signal (or the entire signal) is extracted by the filter 22. . The magnitude of each output is detected by the detector and input to the calculator 17.
The calculator 17 calculates these values and outputs the distortion amount of the semiconductor laser.

In FIG. 6B, only the distortion component is detected from the output of the photoelectric converter 9. The dummy carrier and the data signal are distributed by the distributor 18 in the subsequent stage of the signal driver 5 and branched, and the dummy carrier is then filtered.
5. The data signal is extracted by the filter 22.

In FIG. 6 (c), the data signal branches in the latter stage of the signal input 4, and the dummy carrier branches the output of the dummy signal generator 20 in the distributor 24 to detect the detectors 16 and 2, respectively.
The size is detected in 3. The distortion component of the dummy carrier is extracted from the output of the photoelectric converter 9. FIG. 6 (c)
In the above configuration, no filter is required when detecting dummy carriers and data signals.

In the above embodiments, distortion is detected inside the optical transmitter. However, the factors that change the nonlinearity of the laser are very slow, such as deterioration of the laser and changes in the ambient temperature. The time constant of the loop for detecting the distortion and applying the feedback may be a long time such as several tens of seconds to several minutes and several tens of minutes. Therefore, in the present invention, the detection of distortion is
It is performed in an apparatus having an optical receiver that receives an optical signal from an optical transmitter. The detected distortion (the magnitude of the distortion component or the distortion quantity of the laser) is notified from the device having the optical receiver to the optical transmitter through some communication line. The optical transmitter controls the bias current of the laser based on the notified information on the strain.

FIG. 7 shows an embodiment. The optical signal output from the device 25 having an optical transmitter is transmitted through the optical fiber transmission medium 26 to the device 27 having an optical receiver. The optical fiber transmission medium 26 may be a single optical fiber that connects the device 25 having an optical transmitter and the device 27 having an optical receiver, or a device having an optical transmitter in addition to the device 25 having an optical transmitter. PON (p
It may be in the form of an assured optical network). The information on the distortion detected by the device 27 having the optical receiver is notified to the device 25 having the optical transmitter via the communication medium 32. The communication medium 32 may be an optical fiber transmission medium similar to the optical fiber transmission medium 26, or may be a completely different line such as a telephone line or ISD.
It may be N or the like.

FIG. 8 shows a form of an apparatus having an optical receiver. The optical receiver 2 receives an optical signal from the optical fiber transmission medium 26.
At 8, it is converted into an electric signal. The obtained electric signal is branched,
The data processing section 29 demodulates the data section. The other branch is input to the distortion detector 30 and detects information about distortion. The detected distortion information is sent to the communication interface 31, where it is in a form suitable for being sent to the communication medium 32, and then sent to the communication medium 32.

The structure of the distortion detector 30 is shown in FIG.
It may be similar to (b) and FIG. 6 (a). Alternatively, if the data processing unit 29 is configured to detect the size of the data signal, the distortion detecting unit does not detect the size of the data signal independently, and the data processing unit 29 may receive it.

FIG. 9 shows the configuration of the optical transmitter. Unlike FIG. 1, there is no optical branching / coupling device, photoelectric converter, or distortion amount detector. The distortion information input 33 of the bias control device 3 includes the communication medium 32.
The information regarding the distortion transmitted from the device 27 having the optical receiver is input via the. The bias controller 3 controls the bias current based on the information so that the distortion amount (or distortion component) is minimized.

In a device having an optical receiver, not only information about distortion but also information for controlling the bias of the laser may be created. In that case, the optical transmitter receives information that controls the bias of the laser and controls the bias of the laser accordingly.

For example, in the case where the control algorithm is the hill-climbing method, an example of the difference in control when strain information is received and when bias control information is received will be shown. When the optical transmitter receives the distortion information, the bias control device 3 changes the laser bias current by a small amount and waits until the device 27 having the optical receiver sends information concerning the resulting change in the distortion amount. Upon receiving the notified result, the control operation of the laser bias current is determined and executed.

When the optical transmitter receives the information for controlling the bias current, the device 27 having the optical receiver gives an instruction to change the laser bias current of the optical transmitter by a small amount, and the optical transmitter receives the laser bias current. Change the current by a small amount. The resulting change in distortion amount is detected by the device 27 having the optical receiver, the control operation of the laser bias is determined, and the determined control operation is notified to the device having the optical transmitter via the communication medium 32. The optical transmitter changes the laser bias as instructed.

As described above, by performing a part of the control processing by the device having the optical receiver, the device having the optical transmitter can be downsized. In particular, in a configuration in which a device having a plurality of optical transmitters is connected to a device having an optical receiver, such as a PON, there is an advantage that the distortion detection unit can be shared.

[0042]

According to the present invention, the distortion of the semiconductor laser which becomes a problem when optically transmitting the band data signal is detected from the output light of the semiconductor laser, and the bias current of the semiconductor laser is set so as to reduce the distortion. I gave you feedback. As a result, no matter what causes the amount of distortion to change,
It became possible to control the bias current so that the distortion was always the minimum, and it was possible to maintain good transmission quality.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of the present invention.

FIG. 3 is a diagram for explaining the principle of the present invention.

FIG. 4 is a diagram showing a part of an embodiment of the present invention.

FIG. 5 is a diagram showing an embodiment of the present invention.

FIG. 6 is a diagram showing a part of an embodiment of the present invention.

FIG. 7 is a diagram showing an embodiment of the present invention.

FIG. 8 is a diagram showing a part of an embodiment of the present invention.

FIG. 9 is a diagram showing a part of an embodiment of the present invention.

[Explanation of symbols]

1 Semiconductor laser 2 Optical branch coupler 3 Bias control device 4 signal input 5 signal driver 6 combiner 7 Distortion amount detection 8 Bias current source 9 Photoelectric converter 10 band signal 11 Sidelobe 12 harmonics 13 filters 14 Detector 15 filters 16 detector 17 arithmetic unit 18 distributor 19 combiner 20 Dummy signal generator 21 Strain amount detector 22 filters 23 Detector 24 distributor Device with 25 optical transmitters 26 Optical Fiber Transmission Medium 27 Device having optical receiver 28 Optical receiver 29 Data processing unit 30 strain detector 31 Communication interface 32 communication media 33 Distortion information input 34 dummy carrier 35 Distortion of dummy carrier

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04B 10/28

Claims (6)

(57) [Claims] 1. An optical transmitter that drives an injection current of a semiconductor laser by a signal that can take an arbitrary level and transmits its output light.
Signal generator, wherein the arbitrary generated by the non-linearity of the semiconductor laser
The magnitude of the distortion component of the signal that can take the level of
The distortion component detecting means for detecting from the semiconductor device, and the magnitude of the signal that can take the arbitrary level.
Signal detection before entering the laser or detecting from the output light
Output means, before the magnitude of the distortion component and the signal detection means
Non-linearity calculation for calculating the non-linearity from the magnitude of the signal
A light source, and a bias control means for controlling the bias amount of the injection current of the semiconductor laser so that the nonlinearity calculated by the nonlinearity calculation means is minimized. Transmitter. 2. A semiconductor that is driven by a signal that can have an arbitrary level.
Light source that drives the injection current of the body laser and transmits its output light
Signal from the optical transmitter via the optical fiber transmission line.
An optical communication system consisting of an optical receiver that receives the output light that is received.
A Temu, said optical receiver, nonlinearities of the semiconductor laser
The large distortion component of the generated signal that can take the arbitrary level
A distortion component detecting means for detecting the intensity from the output light;
The magnitude of the signal that can take an arbitrary level can be calculated from the output light.
Signal detecting means for detecting, the magnitude of the distortion component and the
Based on the magnitude of the signal detected by the signal detecting means,
And a non-linear calculation means for calculating the line resistance, the nonlinearity calculated by the nonlinearity calculation means
Via a communication line connecting the optical transmitter and the optical receiver.
Then transferred to the optical transmitter,
Implanting the semiconductor laser to minimize non-linearity
Optical communication characterized by controlling the amount of current bias
system. 3. The optical transmitter is installed in an antenna station for wireless communication.
The non-linearity calculated by the non-linearity calculation means.
Linearity is the communication that connects the antenna station and the optical receiver.
Characterized in that it is transferred to the optical transmitter via a line.
The optical communication system according to claim 2, wherein 4. A semiconductor according to a signal which can have an arbitrary level.
Light source that drives the injection current of the body laser and transmits its output light
A belief, One or more signals different from the signal that can take any level
A dummy generator for generating a dummy signal,
The dummy signal generated by the generator is the semiconductor laser of the semiconductor laser.
When the nonlinearity is worse than the target, the dummy signal
Signal distortion is large enough to be detected, The dummy signal is added to the signal that can take any level.
The output obtained by driving the injection current of the semiconductor laser
Extracted from the signal obtained by photoelectrically converting part or all of the power light.
Based on the distortion component of the generated dummy signal, the semiconductor
The semiconductor laser so that the laser nonlinearity is minimized.
The light is characterized by controlling the bias amount of the injection current of
Transmitter. 5. A semiconductor is provided by a signal that can have an arbitrary level.
Light source that drives the injection current of the body laser and transmits its output light
Signal from the optical transmitter via the optical fiber transmission line.
An optical communication system consisting of an optical receiver that receives the output light that is received.
System, The optical transmitter is a signal that can have the arbitrary level.
A dummy generator that generates one or more different dummy signals
The dummy signal generated from the dummy generator is
State in which the nonlinearity of the semiconductor laser is degraded from the target
Then, the distortion of the dummy signal is a size that can be detected, The optical receiver outputs a signal that can have any level.
A dummy signal is added to drive the injection current of the semiconductor laser.
To convert part or all of the output light obtained by moving
Dan and this Extracted from the signal obtained by photoelectric conversion of
Based on the distortion component of the dummy signal, the semiconductor laser
A means for calculating the non-linearity of The calculated nonlinearity of the semiconductor laser is minimized.
Control the bias amount of the injection current of the semiconductor laser.
An optical communication system characterized by controlling. 6. The optical transmitter is provided in an antenna station for wireless communication.
The non-linearity installed and calculated in the optical receiver
Is a communication line that connects the antenna station and the optical receiver.
Transfer to the optical transmitter via
Item 5. The optical communication system according to item 5.