JPH06296165A - Optical transmitter - Google Patents

Abstract

PURPOSE:To allow an optical transmission side to set optical modulation by receiving an output voltage of a detection circuit providing a voltage output in response to a level of an output signal from an optical-to-electric conversion circuit and producing a gain control signal for an ampfifier circuit whose gain is variable. CONSTITUTION:The optical transmitter driving a light emitting element 21 with a frequency multiplex signal to execute optical modulation is provided with a gain variable amplifier circuit section 2 whose gain is controlled in response to a control signal to amplify the frequency multiplex signal and a circuit section employing a light receiving element 6 and a level detection circuit 7 to detect a modulation signal level from the optical output of the light emitting element 21, and also with a control circuit section 9 controlling the gain of the gain variable amplifier circuit 2 depending on the detected modulation signal level to control the frequency multiplex signal level received by the light emitting element 21 to a desired level so that the effect due to nonlinear distortion of the light emitting element 21 is not received. Since a modulation signal level is obtained as information corresponding to the optical modulation is obtained from the optical output of the light emitting element 21, even a party other than the optical reception side obtains the optical modulation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called optical communication transmission device for transmitting an optical signal through an optical fiber as a transmission line, and more particularly to a multi-channel CATV signal which is converted into an electro-optical signal.
The present invention relates to an optical transmission device of a CATV system that transmits by an optical fiber.

[0002]

2. Description of the Related Art Generally, when a light emitting element such as a laser diode is subjected to optical modulation by applying a signal of high power or a plurality of frequency-multiplexed signals, a non-linear distortion occurs due to the non-linearity of the current of the light emitting element versus the light emission output. Therefore, in the conventional optical transmission device, the optical modulation is performed so as not to be affected by the nonlinear distortion.
Depending on the number of channels of the multiplex signal, the level of the multiplex signal input to the light emitting element is adjusted, or the optical modulation degree for the level of the multiplex signal is obtained by checking the optical modulation degree on the light receiving side, and the optical modulation degree is set or It was a method of adjusting. As a conventional optical transmission apparatus, there is no mention of a method for automatically adjusting the optical modulation degree, as disclosed in JP-A-4-37329 and JP-A-4-65930.

[0003]

In the above-mentioned conventional optical transmission apparatus, an optical CAT for directly brightness-modulating a laser diode by frequency-multiplexing an RF signal obtained by amplitude-modulating a television signal.
In the V system, when the number of channels is increased after the system is installed, it is difficult to adjust the level of multiple signals. Further, when the optical transmitting unit and the optical receiving unit are far apart, the method of adjusting the transmitting side by the information of the receiving side takes time for adjustment, and there is a problem that it becomes complicated.

In view of the above problems, an object of the present invention is to provide an optical transmission device capable of setting the optical modulation degree only on the optical transmission side.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a variable gain for controlling a gain in accordance with a control signal and amplifying a frequency multiplex signal in an optical transmission device for driving a light emitting element by a frequency multiplex signal to perform optical modulation. An amplifier circuit section, a circuit section that detects the signal level of modulation from the light output of the light emitting element using the light receiving element and the level detection circuit, and a control circuit section that controls the gain of the variable gain amplifier circuit by the detected modulation signal level are provided. This is achieved by controlling the frequency-multiplexed signal level input to the light emitting element so as to maintain a desired level so as not to be affected by the non-linear distortion of the light emitting element.

[0006]

According to the present invention, since the modulation signal level detection circuit using the light receiving element is provided in the optical transmitter, the modulation signal level can be obtained from the light output of the light emitting element as the information corresponding to the optical modulation degree. It is possible to obtain the optical modulation degree even if it is not on the receiving side. Further, since the gain of the variable gain amplifier circuit is controlled by the modulation signal level and the level of the frequency multiplexed signal input to the light emitting element is set to a desired level, the frequency multiplexed signal level corresponding to the number of channels of the frequency multiplexed signal is set. It is possible to set the optical modulation degree according to the number of channels of the frequency-division multiplexed signal.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows the configuration of an optical transmission device according to an embodiment of the present invention.

In FIG. 1, a laser diode module (hereinafter abbreviated as LD module) 20 includes a laser diode (hereinafter abbreviated as LD) 21 as a light emitting element,
The output part includes an optical isolator 22, a monitor photodiode (hereinafter abbreviated as PD) 23, a thermistor 24, and a Peltier element 25. The output of the monitor PD 23 is supplied to an automatic optical output control (APC) circuit 30 and an automatic temperature controller. Control (A
The TC) circuit 31 controls the temperature of the Peltier element 25 by the output signal of the thermistor 24. The frequency-multiplexed signal is input from the input terminal 1, amplified by the variable gain amplifier circuit 2, added by the DC current of the current source 4 which supplies the DC bias of the LD by the adder 3, and drives the LD 21. The output of the optical isolator 22 in the LD module 20 is the optical waveguide 4
0 to the optical distributor 5, and the output of the distributor 5 is transmitted to the PD via the optical waveguide 41 and the optical connector 50.
Connect to 6. The optical signal of the LD 21 is transmitted from the optical connector 50 to the optical receiving section 70 by the single mode optical fiber 60, partially converted into an electric signal by the PD 6, and input to the level detection circuit 7. The level detection circuit 7 outputs a voltage corresponding to the signal level input to the detection circuit 7. The arithmetic circuit 8 determines the gain of the variable gain amplifier circuit 2 corresponding to the output voltage of the level detection circuit 7, and the control circuit 9 sets the gain of the variable gain amplifier circuit 2 to the gain obtained by the arithmetic circuit 8. The gain of the variable gain amplifier circuit 2 is controlled so that

In the optical transmission device of the present invention having the above structure, the frequency-multiplexed signal output from the LD can be directly monitored on the optical transmission side,
The degree of modulation can be confirmed. Further, as a calculation method for obtaining the gain of the variable gain amplifier circuit 2 in the calculation circuit 8, by using the number of channels of the multiplexed signal and the LD setting current value of the APD circuit, the degree of optical modulation can be optimized. Become.

As another embodiment of the present invention, FIG. 2 shows the configuration of an optical transmission apparatus for selecting an arbitrary one channel from a frequency-multiplexed signal by using a variable bandpass filter to obtain an LD input level.

In FIG. 2, the same numbers are used for the same parts as in FIG. The LD module 20 has a built-in LD 21 as a light emitting element, an optical isolator 22, a monitor PD 23, a thermistor 24, and a Peltier element 25, which are outputs of the LD 21, and the output of the monitor PD 23 is supplied to the APC circuit 30.
The TC circuit 31 controls the temperature of the Peltier element 25 by the output signal of the thermistor 24. The frequency-multiplexed signal is input from the input terminal 1 and amplified by the variable gain amplifier circuit 2.
The DC current of the current source 4 that supplies the DC bias of the LD is added by the adder 3 to drive the LD 21. The output of the optical isolator 22 in the LD module 20 is connected to the optical distributor 5 via the optical waveguide 40, and the output of the distributor 5 is connected to the optical waveguide 4.
1 to connect to the PD 6 via the optical connector 50 and the optical waveguide 42. The optical signal of the LD 21 is transmitted from the optical connector 50 to the optical receiving unit 70 through the single mode optical fiber 60, and partially converted into an electric signal by the PD 6. The output signal of the PD 6 is input to the level detection circuit 7 after being band-limited through the bandpass filter 10 having a variable center frequency of the passband width of one channel of the frequency multiplexed signal. The bandpass filter 10 can change the number of central edges with a signal applied to the control terminal 11 and can select an arbitrary channel of a frequency-multiplexed signal. The level detection circuit 7 outputs a voltage corresponding to the signal level input to the detection circuit 7. The arithmetic circuit 8 determines the gain of the variable gain amplifier circuit 2 corresponding to the output voltage of the level detection circuit 7, and the control circuit 9 sets the gain of the variable gain amplifier circuit 2 to the gain obtained by the arithmetic circuit 8. The gain of the variable gain amplifier circuit 2 is controlled so that

In the optical transmission device of the present invention having the above structure, the frequency-multiplexed signal output from the LD can be directly monitored on the optical transmission side,
The degree of modulation can be confirmed. Further, since the channel for level detection is one arbitrary channel, the optical modulation degree can be set by selecting the channel that is most affected by the non-linear distortion of the LD, and it is possible to reduce the modulation interference. Further, by using the number of channels of the multiplexed signal and the LD setting current value of the APD circuit as the calculation method for obtaining the gain of the variable gain amplifier circuit 2 in the calculation circuit 8, the degree of optical modulation can be optimized. Become.

As another embodiment of the present invention, FIG. 3 shows the configuration of an optical transmission apparatus for selecting an LD input level by selecting one channel from a frequency multiplexed signal by a tuner apparatus having a frequency conversion circuit.

In FIG. 3, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals. The LD module 20 includes an LD 21 as a light emitting element and an optical isolator 2 at its output section.
2, a monitor PD 23, a thermistor 24, and a Peltier element 25 are built in, and the output of the monitor PD 23 is the APC circuit 3
At 0, the ATC circuit 31 controls the temperature of the Peltier element 25 by the output signal of the thermistor 24. The frequency-multiplexed signal is input from the input terminal 1, is amplified by the variable gain amplifier circuit 2, and is the DC of the current source 4 that supplies the DC bias of the LD.
The current is added by the adder 3 to drive the LD 21. LD
The output of the optical isolator 22 in the module 20 is connected to the optical distributor 5 via the optical waveguide 40, and the output of the distributor 5 is connected to the PD 6 via the optical connector 41 and the optical waveguide 42 via the optical waveguide 41. The optical signal of LD21 is the optical connector 50
From the single mode optical fiber 60 to the optical receiver 70
And is partially converted into an electric signal by PD6. PD
The output signal of 6 is input amplification circuit 101, mixer 102,
Voltage controlled oscillator 103 for local oscillation, band pass filter 1
04, a tuner device 100 including an IF amplifier circuit 105
Then, a desired channel is selected from the frequency-multiplexed signal and input to the level detection circuit 7. Channel tuning is performed by applying a tuning voltage to the control terminal 106 and setting the oscillation frequency of the local oscillation voltage-controlled oscillator 103.
The level detection circuit 7 outputs a voltage corresponding to the signal level input to the detection circuit 7. The arithmetic circuit 8 determines the gain of the variable gain amplifier circuit 2 corresponding to the output voltage of the level detection circuit 7, and the control circuit 9 sets the gain of the variable gain amplifier circuit 2 to the gain obtained by the arithmetic circuit 8. The gain of the variable gain amplifier circuit 2 is controlled so that

In the optical transmission device of the present invention having the above configuration, the frequency-multiplexed signal output from the LD can be directly monitored on the optical transmission side,
The degree of modulation can be confirmed. Further, since the channel for level detection is one arbitrary channel, the optical modulation degree can be set by selecting the channel that is most affected by the non-linear distortion of the LD, and it is possible to reduce the modulation interference. Further, by using the number of channels of the multiplexed signal and the LD setting current value of the APD circuit as the calculation method for obtaining the gain of the variable gain amplifier circuit 2 in the calculation circuit 8, the degree of optical modulation can be optimized. Become.

As another embodiment of the present invention, FIG. 4 shows the configuration of an optical transmission device for selecting an LD input level by selecting one channel from a frequency-multiplexed AM television signal by a tuner device having a frequency conversion circuit. Show.

In FIG. 4, the same numbers are used for the same parts as in FIG. The LD module 20 has a built-in LD 21 as a light emitting element, an optical isolator 22, a monitor PD 23, a thermistor 24, and a Peltier element 25, which are outputs of the LD 21, and the output of the monitor PD 23 is supplied to the APC circuit 30.
The TC circuit 31 controls the temperature of the Peltier element 25 by the output signal of the thermistor 24. The frequency-multiplexed signal is input from the input terminal 1 and amplified by the variable gain amplifier circuit 2.
The DC current of the current source 4 that supplies the DC bias of the LD is added by the adder 3 to drive the LD 21. The output of the optical isolator 22 in the LD module 20 is connected to the optical distributor 5 via the optical waveguide 40, and the output of the distributor 5 is connected to the optical waveguide 4.
1 to connect to the PD 6 via the optical connector 50 and the optical waveguide 42. The optical signal of the LD 21 is transmitted from the optical connector 50 to the optical receiving unit 70 through the single mode optical fiber 60, and partially converted into an electric signal by the PD 6. The output signal of the PD 6 includes an input amplifier circuit 101, a mixer 102, a local oscillation voltage control oscillator 103, a band pass filter 104, and I.
The tuner device 100 including the F amplifier circuit 105 selects a desired channel from the frequency-multiplexed signal and inputs it to the level detection circuit 7. The level detection circuit 110 follows the sync pulse input to the sync pulse input terminal 111,
The detection voltage corresponding to the signal level input to the detection circuit 110 within the synchronization period of the AM television signal is output. The arithmetic circuit 8 determines the gain of the variable gain amplifier circuit 2 corresponding to the output voltage of the level detection circuit 110, and the control circuit 9 sets the gain of the variable gain amplifier circuit 2 to the gain obtained by the arithmetic circuit 8. The gain of the variable gain amplifier circuit 2 is controlled so that

In the optical transmission device of the present invention having the above configuration, the frequency-multiplexed signal output from the LD can be directly monitored on the optical transmission side,
The degree of modulation can be confirmed. Further, since the channel for level detection is one arbitrary channel, the optical modulation degree can be set by selecting the channel that is most affected by the non-linear distortion of the LD, and it is possible to reduce the modulation interference. Further, by using the number of channels of the multiplexed signal and the LD setting current value of the APD circuit as the calculation method for obtaining the gain of the variable gain amplifier circuit 2 in the calculation circuit 8, the degree of optical modulation can be optimized. Become.
As a characteristic effect of the present embodiment, since the signal amplitude of the AM television signal during the synchronization period is constant, when the LD input level is controlled by the detection voltage within the synchronization period, the input level of the variable gain amplifier circuit is Even if it fluctuates, the LD input level can be kept constant even if the gain temperature of the variable gain amplifier circuit fluctuates, and the fluctuation of the modulation factor can be reduced.

[0020]

According to the present invention, since it is not necessary to monitor the modulation degree on the optical receiving side and adjust the optical transmitting unit as in the conventional case, the adjustment can be performed in a short time and the accuracy can be improved. Furthermore, the degree of optical modulation can be optimized, and it is effective in reducing the modulation interference.

[Brief description of drawings]

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

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Gain variable amplification circuit, 3 ... Addition part, 4 ... Current source, 5 ... Optical distributor, 6 ... PD, 7 ... Level detection circuit, 8 ... Arithmetic circuit, 9 ... Control circuit, 10 ... Band pass filter, 11 ... Control terminal, 20 ... LD module, 21 ... LD, 40, 41, 42 ... Optical waveguide, 50 ... Optical connector, 60 ... Single mode optical fiber, 100 ... Tuner device power supply terminal, 110 ... Level detection Circuit, 111 ... Sync pulse input terminal.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H04N 7/16 A 7251-5C 7/20 7251-5C 9372-5K H04B 9/00 E

Claims (4)

[Claims] 1. A variable gain amplifier circuit for amplifying a frequency-multiplexed signal, and a light emitting element is driven by the amplified frequency-multiplexed signal to perform optical modulation, and the optical signal is a first optical waveguide and a first optical waveguide. And an optical connector for connecting the optical fiber of the latter stage and an optical transmission device for transmitting through a single mode optical fiber, which is a means for distributing the light to be input to the first optical waveguide and an electric signal for inputting the distributed optical signal. A photoelectric conversion circuit that outputs a signal, a detection circuit that outputs a voltage according to the output signal level of the photoelectric conversion circuit, and a unit that inputs the detection circuit output voltage and generates a gain control signal of the gain variable amplification circuit An optical transmission device comprising: 2. A variable gain amplifier circuit for amplifying frequency-multiplexed multi-channel signals, a light emitting element is driven by the amplified frequency-multiplexed signals to perform optical modulation, and the optical signal is transmitted to the first optical waveguide and the first optical waveguide. Is an optical transmission device for transmitting through a single mode optical fiber and an optical connector for connecting the optical waveguide of the second optical fiber and the optical fiber of the latter stage, and means for distributing the light to be input to the first optical waveguide, and the distributed optical signal. An opto-electric conversion circuit that inputs and outputs an electric signal, a selection circuit that selects a desired one channel from the output signals of the opto-electric conversion circuit, and a detection circuit that outputs a voltage according to the selection circuit output signal level,
An optical transmission apparatus comprising means for inputting an output voltage of a detection circuit and generating a gain control signal of the variable gain amplifier circuit. 3. The optical transmission device according to claim 2, wherein a frequency conversion circuit including an input signal amplification circuit, a local oscillator and a mixer is used as a selection circuit for selecting a desired one channel from the output signals of the photoelectric conversion circuit. An optical transmission device comprising a circuit, a bandpass filter, and a tuner device including an IF amplifier circuit. 4. A variable gain amplifier circuit for amplifying a frequency-multiplexed multi-channel AM television signal, and a light-emitting element driven by the amplified frequency-multiplexed signal to perform optical modulation,
An optical transmission device that transmits an optical signal through a first mode optical fiber, an optical connector that connects the first optical waveguide and a subsequent optical fiber, and a single mode optical fiber. Means, a photoelectric conversion circuit that inputs the distributed optical signal and outputs an electric signal, an amplifier circuit that amplifies the output signal of the photoelectric conversion circuit, a frequency conversion circuit that includes a local oscillator and a mixer, and a band. A pass filter,
A tuner device including an IF amplifier circuit selects a desired one channel and demodulates the tuner device output signal, a detection circuit that detects the voltage of the demodulation circuit output signal in the synchronization period, and a detection circuit output voltage that is input. An optical transmission apparatus comprising means for generating a gain control signal of the variable gain amplifier circuit.