JPH11145909A - Optical signal converter, photodetector and optical fiber transmission equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal converter, a photodetector and optical fiber transmission equipment with which high CNR characteristics are provided. SOLUTION: The optical signal converter receives signal light, to which intensity modulation is performed by a sub-carrier frequency-modulated by a multi-channel signal, and is provided with a light output limiter 22 for outputting light while the level of the waveform of that signal light is higher than a prescribed level so as to generate a first optical pulse stream, a light delay circuit 25 for delaying the first optical pulse stream so as to generate a second optical pulse stream, and an optical logic element 24 for outputting a third optical pulse stream having a pulse interval proportional to the multi- channel signal based on the first and second optical pulse streams. By performing photoelectric conversion to this third optical pulse stream, an electric signal proportional to the multi-channel signal can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal converter, an optical receiver, and an optical fiber transmission apparatus for transmitting multi-channel analog video signals, digital video signals, and the like in optical fiber transmission.

[0002]

2. Description of the Related Art Conventionally, as a method of transmitting and distributing a multi-channel video signal to a subscriber's house, a semiconductor laser is directly modulated with a multi-channel video signal, and the signal light generated thereby is transmitted through an optical fiber. After that, a method of performing direct detection with an optical receiver has been studied. However, existing
AM video signal transmission, which has high needs because it has excellent compatibility with CATV, requires high CNR characteristics and distortion characteristics, so the transmission distance and the number of optical branches are limited, and the reflection resistance of the optical connector is low. There was a problem of being small.

To overcome such a problem, a multi-channel video distribution system using an AM / FM batch converter using an optical heterodyne detection system has been proposed (K. Kikusima, et al .: Super- wide-band optical FM
modulation scheme and itsapplication to multichan
nel AM video transmission systems, IEEE Photonics
Technology Letters, pp. 839-841, 1996).

A conventional AM / FM batch conversion type optical fiber transmission apparatus will be described with reference to FIGS. 5 (a), 5 (b) and 5 (c).

As shown in FIG. 1A, an optical transmitter 1 of this optical fiber transmission device comprises an AM / FM converter 2 and a semiconductor laser 3 for transmission. The optical transmitter 1 generates an intensity-modulated signal light based on a microwave signal FM-modulated with an AM multi-channel video signal. The signal light output from the optical transmitter 1 is amplified by the optical fiber amplifier 4 and split by the optical splitter 5 before being transmitted through the transmission optical fiber 6. The signal light transmitted by the optical fiber 6 is received by the optical receiver 7. In the optical receiver 7, the signal light is received by an APD (avalanche photodiode) 8. The APD 8 converts the signal light into a microwave signal FM-modulated with the AM multi-channel video signal. The microwave signal is demodulated by the FM demodulator 9 into an AM multi-channel video signal.

FIG. 5B shows an internal configuration of the AM / FM converter 2. In the AM / FM converter 2,
First, the semiconductor laser 10 is FM-modulated by the AM multi-channel video signal. Next, output light from a local oscillation laser (hereinafter, referred to as “local laser”) 11 is combined with output light from a semiconductor laser 10 by an optical coupler 12. The multiplexed light is applied to the photodiode 14 and the photodiode 14
Performs heterodyne detection. As an output of the photodiode 14, a microwave signal FM-modulated with the AM multi-channel video signal is obtained. The frequency of the microwave signal is a beat frequency between the semiconductor laser 10 and the local laser 11 and is set to, for example, 3 GHz.

[0007] A part of the multiplexed light irradiates another photodiode 13 and is heterodyne-detected by the photodiode 13. The microwave signal formed as the output of the photodiode 13 is transmitted to the AFC control loop 15
Is fed back to the semiconductor laser 10 via the. The drive current of the semiconductor laser 10 is controlled by this feedback, and the carrier frequency is stabilized. AF
The C control loop 15 includes an FM demodulator 16 and a current control circuit 17.

Using the signal generated by the AM / FM converter 2 as described above, a transmission semiconductor laser (DFB) is used.
The intensity modulation of the laser 3 is performed. As a result, the above-described signal light is output from the optical transmitter 1.

FIG. 5C shows the configuration of the FM demodulator 9 in the optical receiver 7. The FM demodulator 9 includes AND gates 18 and 19, a delay line 20, and an amplifier 21, and demodulates a microwave signal output from the APD 8 into a multi-channel video signal.

According to such a transmission system, the minimum light receiving level can be improved by about 10 dB as compared with the conventional AM transmission, and the reflection resistance of the optical connector is greatly improved.

[0011]

In the conventional optical receiver 7, the signal light is received by a wide band (for example, 6 GHz) APD, and further, in the FM demodulator 9, high-speed AND gates 18 and 19 capable of operating at 6 GHz are provided. It is necessary to perform conversion into an electric signal by using. When the high-speed devices are connected in multiple stages as described above, the frequency characteristics of the amplitude deviation and the group delay deviation of each device are integrated, and as a result, noise characteristics and distortion characteristics are deteriorated. Although widening the band is effective in improving noise characteristics, as long as an electric device such as an AND gate is used, there is a limit to speeding up, and deterioration in noise characteristics and distortion characteristics due to band limitation is inevitable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a signal converter exhibiting high CNR characteristics, and an optical receiver and an optical fiber transmission using the same. It is to provide a device.

[0013]

SUMMARY OF THE INVENTION An optical signal converter according to the present invention receives a signal light intensity-modulated by a subcarrier frequency-modulated by a multi-channel signal, and the level of the signal light waveform is equal to or higher than a predetermined level. An optical output limiter for outputting light during that, thereby producing a first optical pulse train;
An optical delay circuit that delays the first optical pulse train to generate a second optical pulse train, and an optical pulse interval is proportional to the multi-channel signal based on the first optical pulse train and the second optical pulse train. And an optical logic element for outputting a third optical pulse train.

[0014] The optical output limiter may be constituted by a semiconductor laser having a saturable absorption region.

It is preferable that the optical delay circuit delays the second optical pulse train by a predetermined time from the first optical pulse train, and converts the second optical pulse train into an inverted one of the first optical pulse train.

The optical delay circuit has a Mach-Zehnder interference type configuration, branches the first optical pulse train output from the optical output limiter into two, and branches the first optical pulse train. Is delayed with respect to the other, thereby generating the second light pulse train, and then superimposing the first light pulse train and the second light pulse train.

The optical delay circuit delays one of the branched first optical pulse trains with respect to the other, and
It may be reversed.

It is preferable that the optical logic element is an optical AND gate element that calculates a logical sum of the first optical pulse train and the second optical pulse train.

[0019] The optical logic element may be an optical exclusive or element.

[0020] The optical logic element may be an optical bistable multivibrator element.

An optical receiver according to the present invention is a light receiving element for receiving the optical signal converter, the third optical pulse train output from the optical signal converter, and converting the third optical pulse train into an electric signal. And

The response speed of the light receiving element is sufficiently slower than the input interval of the third optical pulse train, and the electric signal output from the light receiving element shows a waveform proportional to the multi-channel signal. Is also good.

[0023] The device may further include an element which receives the electric signal output from the light receiving element and can function as a low-pass filter, and the output of the element shows a waveform proportional to the multi-channel signal.

An optical fiber transmission device according to the present invention comprises: an optical transmitter for generating signal light intensity-modulated by subcarriers frequency-modulated by a multi-channel signal; a transmission optical fiber for transmitting the signal light; An optical fiber transmission device comprising: an optical receiver that receives the signal light from the transmission optical fiber and demodulates the multi-channel signal from the signal light, wherein the optical receiver is based on the signal light. An optical signal converter that outputs an optical pulse train whose optical pulse interval is proportional to the multi-channel signal, and receives the optical pulse train,
A photoelectric conversion unit that converts the electric signal into an electric signal.

The optical transmitter receives the multi-channel signal and converts the multi-channel signal into a subcarrier signal frequency-modulated by the multi-channel signal, and a transmission semiconductor for performing intensity modulation at an output of the signal converter. Preferably, a laser is provided.

It is preferable that the optical signal converter is as described in any one of claims 1 to 8.

It is preferable that the optical receiver is one according to any one of claims 9 to 11.

Another optical fiber transmission device of the present invention comprises: an optical transmitter for generating signal light intensity-modulated by subcarriers frequency-modulated by a multi-channel signal; an optical fiber amplifier for amplifying the signal light; An optical splitter for splitting the signal light into a plurality, a plurality of transmission optical fibers for transmitting the split signal light, and the signal light received from the transmission optical fiber; and the multi-channel signal from the signal light. An optical fiber transmission device comprising: an optical receiver that demodulates an optical signal, wherein the optical receiver outputs an optical pulse train whose optical pulse interval is proportional to the multi-channel signal based on the signal light. And a photoelectric conversion unit that receives the light pulse train and converts the light pulse train into an electric signal. The optical transmitter is a signal converter that receives the multi-channel signal and converts it to a subcarrier signal frequency-modulated with the multi-channel signal, and a transmission semiconductor laser that performs intensity modulation with an output of the signal converter. Preferably, it is provided.

It is preferable that the optical signal converter is one according to any one of claims 1 to 8.

It is preferable that the optical receiver is one according to any one of claims 9 to 11.

[0031] The optical fiber amplifier and the optical splitter may be connected in multiple stages.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical signal converter according to the present invention receives a signal light carrying a subcarrier (microwave signal) frequency-modulated by a multi-channel video signal, and applies FM / AM to the signal light. Performs optical conversion processing required for conversion. After being subjected to such processing, the signal light is output from the optical signal converter and then applied to a photoelectric conversion element such as a photodiode. As the output of the photoelectric conversion element,
A multi-channel video signal (electrical signal subjected to amplitude modulation) is obtained.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Embodiment of Optical Signal Converter) First, reference will be made to FIG. The signal converter shown in FIG. 1 includes an optical output limiter element 22 that outputs an optical signal having an intensity saturated to a certain level when receiving an optical signal whose intensity exceeds a certain level (threshold). ing. As the light output limiter element 22, for example, a semiconductor laser having a saturable absorption region can be used. According to the semiconductor laser having the saturable absorption region, since the light input-light output characteristic has a differential characteristic, the light of several milliwatts (mW), for example, only when light having an intensity exceeding a certain threshold level is input. The output is obtained.

According to the signal converter of this embodiment,
First, the signal light propagating through the optical fiber is input to the optical output limiter element 22. FIG. 2 shows the intensity of the input signal light.
FIG. 2A has a waveform as shown in FIG.
Are carried. More specifically, the signal light in FIG. 2B is obtained by intensity-modulating a laser light with a subcarrier in a microwave region (for example, a frequency of 3 GHz), and the subcarrier is frequency-modulated with a multi-channel video signal. ing. The multi-channel video signal is an analog signal generated by, for example, frequency division multiplexing of 40-channel video information in a multi-channel signal generator (FDM-MUX). The carrier of 40 channels is, for example, from 90 MHz to 330 MHz on the frequency axis.
Are arranged at intervals of 6 MHz.

The signal light intensity-modulated by the subcarrier frequency-modulated by the multi-channel signal is shown in FIG.
Is generated by the optical transmitter shown in FIG.

When the signal light is input to the optical output limiter element 22, when the intensity of the signal light exceeds a threshold level and shows a large value, the optical output limiter element 22 outputs light having a certain intensity. I do. On the other hand, when the intensity of the signal light indicates a small value below the threshold level,
The output of the light output limiter element 22 becomes substantially zero.
As a result, the output of the optical output limiter element 22 is
As shown in (c), an optical pulse train (first optical pulse train) is obtained. As can be seen from FIG. 2C, when a portion having a relatively low frequency component in the intensity waveform of the input signal light (FIG. 2B) is input to the optical output limiter element 22, the optical output From the limiter element 22, relatively wide light pulses are output at wide time intervals. On the other hand, when a portion having a relatively high frequency component in the intensity waveform of the input signal light is input to the optical output limiter element 22, the relatively narrow width is output from the optical output limiter element 22. Light pulses are output at narrow time intervals. The interval between the optical pulse trains is determined by the frequency of the waveform in FIG. 2B (subcarrier frequency: 3 GHz, for example). When the subcarrier frequency is 3 GHz, for example, when the band is 4 GHz, the interval between the optical pulse trains shows a value in the range from 0.2 nanoseconds to 1.0 nanoseconds. Also, the average width of the optical pulse train can be changed by adjusting a “threshold” for switching on / off of the optical output limiter 22,
At most, it does not exceed the size of the average light pulse interval.

The optical pulse train thus obtained is input to an optical delay circuit 23 in the optical signal converter, as shown in FIG. 1, and is branched into two. Branching can be performed using a Mach-Zehnder interference type configuration. One of the branched optical pulse trains passes through the delay path 25. The optical pulse train is inverted and delayed by the output inverting element while propagating through the delay path 25 (the delay time is denoted by τ). As a result, at the end of the delay path 25, FIG.
Is obtained (second optical pulse train). The output inversion element is formed from, for example, a semiconductor laser. In this case, the semiconductor laser functioning as an output inversion element is
While operating in a continuous oscillation (CW) state, it is arranged in the delay path 25 so as to receive an input of an optical pulse train. However, the semiconductor laser oscillates continuously at a wavelength different from the wavelength of the received light pulse. In this case, when an optical pulse is input to the semiconductor laser, the gain of the laser is consumed for amplifying the optical pulse during that time, and the output of the semiconductor laser is turned off. Thus, an optical output obtained by inverting the input optical pulse train can be obtained.

The other of the branched optical pulse trains is input to the optical logic element (optical AND gate element) 24 without passing through the delay path 25. The optical pulse train that has passed through the delay path 25 is also input to the optical AND gate element 24, and the logical sum of both optical pulse trains (first and second optical pulse trains) is output. The optical AND gate element 24 is formed from an element having the same configuration as the optical output limiter element 22 described above, and the total light intensity when the two optical inputs are added exceeds the “threshold level”, In addition, with only one light input, the “threshold level” of the element is set so that the light intensity falls below the “threshold level”.

The optical AND gate element 24 having such a configuration
Is an optical pulse train (third optical pulse train) having the waveform shown in FIG. The output of the optical AND gate element 24 (third optical pulse train) has an optical pulse width equal to the delay time τ, and the optical pulse interval is inversely proportional to the frequency of the input signal light shown in FIG. That is, the number of optical pulse trains included in a unit time is proportional to the modulated frequency of the input signal light in FIG.
It is proportional to the amplitude of the other channel video signal shown in FIG. Therefore, when the light pulse train shown in FIG. 2E is photoelectrically converted using a photodiode whose response speed is sufficiently slower than the light pulse train interval, the light quantity obtained by integrating the light pulse train in a unit time is converted into an electric signal. Is done. Therefore, the electric signal output from the photodiode has a magnitude proportional to the modulated frequency of the input signal light, and a signal proportional to the multi-channel video signal of FIG. 2A is obtained.

The delay of the optical pulse train is caused by giving a difference to the length of the optical path (optical path length) through which the branched optical pulse train passes. The delay time τ is set to have a smaller value than the optical pulse width of the optical pulse train in FIG. In the present embodiment, the delay time τ is set to 90 picoseconds (p
sec), the optical path length difference is set.

As described above, according to the optical signal converter of the present embodiment, FM / AM conversion of a signal can be executed in a light state, and an electric device that can operate at high speed is not required. Therefore, a high CNR is obtained, and signal conversion with less distortion is realized.

It should be noted that, instead of using a photodiode whose response speed is sufficiently slower than the interval of the optical pulse train, the output of the light conversion element of this embodiment (light Signal)
An electric signal proportional to the multi-channel video signal can be obtained.

As the optical logic element, an optical exclusive OR element or an optical bistable multivibrator element may be used instead of the optical AND gate element 24.

(Embodiment of Optical Receiver) An embodiment of an optical receiver according to the present invention will be described with reference to FIG.

The optical receiver according to the present embodiment comprises an optical signal converter 26 shown in FIG. 1 and a light receiving element (photodiode) 27 which receives the output light of the optical signal converter 26 and converts it into an electric signal.
And an amplifier 28 for amplifying the output of the light receiving element 27.

An optical pulse train shown in FIG. 2 (e) is input to the light receiving element 27. The light receiving element 27 does not need to be an element that can operate in a wide band, but is sufficient if it can operate in a band of a multi-channel signal. Also, the light receiving element 2
Even if the band of 7 is wide, the amplifier 28 can function as a low-pass filter, so that after amplification by the amplifier 28, unnecessary high-frequency components are cut, and a necessary multi-channel signal is obtained.

In this embodiment, as the light receiving element 27 and the amplifier 28, low noise and low distortion elements conventionally used in a direct modulation / direct detection type transmission system can be used. Also, the number of required high-speed devices is reduced. For this reason, it is possible to solve the problem of deterioration of noise characteristics and distortion characteristics caused by amplitude deviation, group delay deviation, and band limitation.

(Embodiment of Optical Fiber Transmission Apparatus) An embodiment of an optical fiber transmission apparatus according to the present invention will be described with reference to FIG.

The optical fiber transmission device of this embodiment is similar to that of FIG.
And an optical fiber amplifier (erbium-doped fiber amplifier) 30 having the same configuration as the optical transmitter shown in FIG.
a, 30b, 30c, an optical splitter 31, a transmission optical fiber 32, and an optical receiver 33 according to the above embodiment. The optical fiber amplifier 30, the optical splitter 31, and the transmission optical fiber 32 may have a known configuration.

The signal light output from the optical transmitter 29 is amplified by the optical fiber amplifiers 30a, 30b, and 30c, and is then split by the optical splitter 31. The split signal light is
The light is transmitted by the transmission optical fiber 32 and received by the optical receiver 33. In the optical receiver 33, the received signal light is demodulated into a multi-channel video signal. Optical fiber amplifier 30
The optical splitter 31 may be connected in multiple stages.

According to the present embodiment, since the signal light further intensity-modulated by the microwave signal frequency-modulated by the multi-channel video signal is transmitted through the optical fiber, the minimum light receiving level is small and the reflection resistance is small. , The chromatic dispersion resistance increases. Further, since the optical signal converter described with reference to FIGS. 1 and 2 is provided in the optical receiver, a high CN is obtained.
R is achieved, and multi-channel video distribution with low distortion can be realized.

In the optical fiber transmission device of this embodiment, the wavelength of the output light of the optical transmitter is in the 1.55 μm band, but the wavelength of the output light may be in the 1.3 μm band. In that case, it is preferable to use a praseodymium-doped fiber amplifier as the optical fiber amplifier.

Although the present embodiment is a multi-distribution optical fiber transmission apparatus, it is needless to say that the present invention is applicable to an optical fiber transmission apparatus that does not include the optical fiber amplifier 30 and the optical splitter 31. No.

[0055]

According to the optical signal converter of the present invention, an optical pulse train is output at an interval inversely proportional to the modulated frequency of the input signal light, and the number of optical pulse trains included in a unit time is determined by multi-channel video. It is proportional to the signal amplitude. Thus, according to the optical signal converter of the present invention, FM
Since the / AM conversion is performed, there is no need to electrically perform the FM / AM conversion.

According to the optical receiver of the present invention, since the optical signal converter is provided, when the signal light intensity-modulated by the subcarrier frequency-modulated by the multi-channel signal is demodulated, it is directly modulated / directly modulated. A low-noise and low-distortion element conventionally used in a detection-type transmission system can be used, and the number of required high-speed devices is reduced. For this reason, it is possible to avoid deterioration of noise characteristics and distortion characteristics due to amplitude deviation, group delay deviation, and band limitation.

According to the optical fiber transmission apparatus of the present invention, when transmitting, via an optical fiber, signal light intensity-modulated by subcarriers frequency-modulated by a multi-channel signal, the optical receiver is used to demodulate the signal. Is used, the minimum light receiving level is small, not only the reflection proof strength and the wavelength dispersion proof strength are greatly improved, but also a high CNR characteristic is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an optical signal converter according to the present invention.

FIGS. 2A and 2B are diagrams showing signal waveforms obtained in respective portions of the embodiment of the optical signal converter according to the present invention, wherein FIG. 2A is a waveform diagram of a multi-channel signal, and FIG. (C) is an output waveform diagram of the optical output limiter;
(D) is an output waveform diagram of the optical delay circuit, and (e) is an output waveform diagram of the optical logic element.

FIG. 3 is a diagram showing a configuration of an embodiment of an optical receiver according to the present invention.

FIG. 4 is a diagram showing a configuration of an optical fiber transmission device according to the present invention.

FIG. 5A is a diagram showing a configuration of a conventional optical fiber transmission device, and FIG.
FIG. 1C is a diagram illustrating an internal configuration of an FM converter, and FIG. 2C is a circuit diagram illustrating a configuration of an FM demodulator in an optical receiver used in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical transmitter 2 AM / FM converter 3 DFB laser 4 Optical fiber amplifier 5 Optical splitter 6 Optical fiber 7 Optical receiver 8 Photodiode 9 FM demodulator 10 Semiconductor laser for transmission 11 Semiconductor laser for local oscillation 12 Optical coupler 13 Optical receiver 14 Optical receiver 15 AFC control loop 16 FM demodulator 17 Current control circuit 18 AND gate 19 AND gate 20 Delay element 21 Amplifier 22 Optical output limiter element 23 Optical delay circuit 24 Optical logic element 25 Delay path 26 Optical signal converter 27 Light receiving element 28 Amplifier 29 Optical transmitter 31 Optical splitter 32 Optical fiber 33 Optical receiver

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 31/10 // H01S 3/096

Claims (20)

[Claims] A signal light intensity-modulated by a subcarrier frequency-modulated by a multi-channel signal is received, and light is output while the level of the waveform of the signal light is equal to or higher than a predetermined level. An optical output limiter that generates a first optical pulse train and an optical delay circuit that generates a second optical pulse train; and an optical pulse based on the first optical pulse train and the second optical pulse train. An optical logic element that outputs a third optical pulse train whose interval is proportional to the multi-channel signal. 2. The optical signal converter according to claim 1, wherein said optical output limiter comprises a semiconductor laser having a saturable absorption region. 3. The optical delay circuit according to claim 2, wherein the second optical pulse train is delayed by a predetermined time from the first optical pulse train, and the first optical pulse train is inverted by an output inverting element. The optical signal converter according to claim 1, wherein 4. The optical delay circuit has a Mach-Zehnder interference type configuration, branches the first optical pulse train output from the optical output limiter into two, and branches the first optical pulse train. The method of claim 1 wherein one of the light pulse trains is delayed with respect to the other, thereby generating the second light pulse train, and then superimposing the first light pulse train and the second light pulse train. 2. The optical signal converter according to 1. 5. The optical delay circuit, comprising:
2. The optical signal converter according to claim 1, wherein one of the optical pulse trains is delayed with respect to the other and inverted by an output inverting element. 6. The optical signal according to claim 1, wherein the optical logic element is an optical AND gate element that calculates a logical sum of the first optical pulse train and the second optical pulse train. converter. 7. The optical signal converter according to claim 1, wherein said optical logic element is an optical exclusive OR element. 8. The optical signal converter according to claim 1, wherein the optical logic element is an optical bistable multivibrator element. 9. An optical signal converter according to claim 1, which receives the third optical pulse train output from the optical signal converter, and converts the third optical pulse train into an electric signal. An optical receiver comprising: a light receiving element that converts the light. 10. The response speed of the light receiving element is the third speed.
The optical receiver according to claim 9, wherein the electric signal output from the light receiving element has a waveform proportional to the multi-channel signal, which is sufficiently slower than the input interval of the optical pulse train. 11. The device according to claim 9, further comprising an element capable of receiving an electric signal output from said light receiving element and functioning as a low-pass filter, wherein an output of said element shows a waveform proportional to said multi-channel signal. An optical receiver according to claim 1. 12. An optical transmitter for generating a signal light intensity-modulated by a subcarrier frequency-modulated by a multi-channel signal, a transmission optical fiber for transmitting the signal light, and the signal from the transmission optical fiber. An optical receiver that receives light and demodulates the multi-channel signal from the signal light, wherein the optical receiver has an optical pulse interval based on the signal light. An optical fiber transmission device, comprising: an optical signal converter that outputs an optical pulse train proportional to a channel signal; and a photoelectric conversion unit that receives the optical pulse train and converts the optical pulse train into an electric signal. 13. The signal transmitter for receiving the multi-channel signal and converting the multi-channel signal into a subcarrier signal frequency-modulated by the multi-channel signal, and a transmission for performing intensity modulation on an output of the signal converter. The optical fiber transmission device according to claim 12, further comprising: a semiconductor laser for use. 14. The optical fiber transmission device according to claim 12, wherein the optical signal converter is one according to any one of claims 1 to 8. 15. The optical receiver according to claim 9, wherein the optical receiver is any one of claims 9 to 11.
3. The optical fiber transmission device according to 2. 16. An optical transmitter that generates signal light that is intensity-modulated by subcarriers that are frequency-modulated by a multi-channel signal, an optical fiber amplifier that amplifies the signal light, and light that splits the signal light into a plurality. A splitter, a plurality of transmission optical fibers that transmit the branched signal light, and an optical receiver that receives the signal light from the transmission optical fiber and demodulates the multi-channel signal from the signal light. An optical fiber transmission device, comprising: an optical signal converter that outputs an optical pulse train whose optical pulse interval is proportional to the multi-channel signal, based on the signal light, and receives the optical pulse train. A multi-distribution optical fiber transmission device comprising: a photoelectric conversion unit that converts the signal into an electric signal. 17. The signal transmitter for receiving the multi-channel signal and converting the multi-channel signal into a subcarrier signal frequency-modulated by the multi-channel signal, and a transmission for performing intensity modulation at an output of the signal converter. 17. The multi-distribution optical fiber transmission device according to claim 16, further comprising: a semiconductor laser for use. 18. The multi-distribution optical fiber transmission device according to claim 16, wherein said optical signal converter is one according to any one of claims 1 to 8. 19. The optical receiver according to claim 9, wherein the optical receiver is any one of claims 9 to 11.
7. The multi-distribution optical fiber transmission device according to 6. 20. The multi-distribution optical fiber transmission device according to claim 16, wherein said optical fiber amplifier and said optical splitter are connected in multiple stages.