JP2001244895A - Optical transmission equipment - Google Patents

Abstract

(57) [Problem] To provide an optical transmission device having a wide dynamic range by applying the principle of an envelope feedback system without increasing the rank of noise characteristics and distortion characteristics of components. SOLUTION: In an optical transmission apparatus 10, an amplitude modulator 12 generates a signal EB (t) which is amplitude-modulated based on an input signal E (t), and an electric / optical converter 13 converts the signal EB (t) to obtain an optical intensity. The modulated optical signals PA and PB are output to the optical fiber transmission lines F1 and F20. The splitter 11 splits the signal DA (t) from the input signal E (t), and the envelope detector 15 outputs an envelope DB (t) from the signal DA (t). The optical splitter 14 splits the optical signal PC from the optical signal PA,
The optical / electrical converter 16 converts the optical signal PC into a signal CA (t), and the envelope detector 17 outputs an envelope CB (t) from the signal CA (t). The differentiator 18 compares the envelope DB (t) with the CB (t), detects the difference SM, and modulates the amplitude modulator according to the detected difference SM.
By suppressing the modulation degree of 12, the dynamic range for the input signal can be widened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device and, more particularly, to a transmission signal whose amplitude is modulated by an amplitude modulator based on a high-frequency input signal to be transmitted, and converting the transmission signal into an electric / optical signal. Accordingly, the present invention relates to an optical transmission device that generates an optical signal that has been subjected to optical intensity modulation and transmits the optical signal to a destination via an optical fiber transmission line.

[0002]

2. Description of the Related Art In recent years, a technique for transmitting a high-frequency signal through an optical fiber has become widespread. FIG. 6 is a block diagram showing a typical conventional example of an optical transmission system to which the high-frequency transmission technology is applied. In this case, the electrical / optical converter 110 generates an optical signal that has been subjected to analog modulation with the high-frequency input signal E (t), transmits the optical signal to the other party via the optical transmission medium 120, and Then, the optical / electrical converter 130 performs optical / electrical conversion on the received optical signal,
The output signal Eq (t) is extracted. According to this technique, it is possible to transmit a high-frequency signal using an optical fiber having excellent characteristics as a low-loss, light-weight and small-diameter transmission medium as the optical transmission medium 120. Compared with a conventional transmission technique using a metal wire, the present invention is particularly excellent in the case of transmitting a high-frequency signal or the case of performing long-distance transmission. As a general modulation method in this case, there is a light intensity modulation method of modulating the intensity of an optical signal with a high-frequency signal. In addition to the light intensity modulation method, there is a method of modulating the frequency of light, but it has not been widely used.

One of the features of the light intensity modulation method is that it is easy to convert a high-frequency signal into an optical signal. That is, when a semiconductor laser is used for a light emitting device, direct modulation of an optical signal can be performed by directly applying intensity modulation to a driving current of the light emitting device using a high-frequency signal. Further, when a plurality of high-frequency signals are multiplexed by a method such as frequency division multiplexing, code division multiplexing, or time division multiplexing, the multiplexed signal can be transmitted as it is. It is also possible to receive the formatted signal and reproduce the original signal. As described above, since a high frequency signal can be transmitted by a relatively simple device, as an application field of the optical analog transmission method, transmission of a plurality of video signals on a cable television (CATV) and mobile communication are currently available. And so on.

[0004]

As described above, in the method of transmitting a signal by using an analog-modulated optical signal, the transmission quality in the optical transmission system becomes an important item, and particularly, the transmission quality in the optical transmission system is generated. It is important that the transmission quality is limited by noise and distortion. The noise generated in the optical transmission unit includes a noise generated by a light emitting device (laser) and a noise generated by a light receiving device. If the analog signal to be transmitted has a finite band and the other band is not used, the distortion signal, especially the odd-order distortion signal, occurs in the same signal band near the transmission signal. Becomes For example, in the field of mobile communication, when trying to transmit a mobile phone signal having a band of several tens of MHz at 800 MHz, the second-order distortion occurs near DC and twice in the 1600 MHz band. Since it is far away from the target signal of 800 MHz transmission, it can be easily removed by a frequency filter. However, the third-order distortion signal occurs near the signal to be transmitted in the 800 MHz band, and it is not easy to remove this distortion signal by a frequency filter. In other words, the odd order (particularly, 3
Next, the amount of distortion limits the transmission quality of the transmission system, and the dynamic range for an input signal is limited by the amount of noise generated in the optical transmission system and the amount of signal that causes distortion.

In the above-described optical transmission system, when an optical signal that is analog-modulated with an input signal is generated, the transmission quality changes depending on the optical modulation degree of the optical signal. On the other hand, the absolute value of the amount of noise generated in the optical transmission system is almost irrelevant to the degree of light modulation and depends on devices such as a light emitting device (laser), a light receiving device, and an optical fiber. That is, when the degree of light modulation is increased, the ratio of the signal to be transmitted to noise (CNR) increases. However, as for the relationship between the distortion signal and the optical modulation factor, the amount of the distortion component included increases as the optical modulation factor increases. Therefore, it is necessary to set a light modulation degree that balances the noise and the distortion amount. There is a problem in that the dynamic range of the optical transmission system due to the set optical modulation degree depends on the laser, the light receiver, and the optical transmission loss.

By the way, in the above-mentioned optical transmission system,
It is necessary to set a light modulation degree that balances noise and distortion. Considering the base station equipment for mobile communication such as a mobile phone, the base station equipment is composed of a modulator for modulating a radio signal and a power amplifier for amplifying the signal. Further, since a single base station normally transmits radio signals of a plurality of frequencies, the modulation apparatus has facilities for the number of frequencies. On the other hand, the power amplifying device
Conventionally, an amplification device for each frequency is installed, and the output is combined and transmitted. However, in recent years, a common amplification method using a “common amplification device” that amplifies signals of a plurality of frequencies collectively is common. is there. In this common amplification method, since a plurality of signals are amplified, unnecessary signals due to the intermodulation distortion as described above are generated. The method of reducing the unnecessary signal can be realized by using a low distortion amplifier. However, a low-distortion amplifier is generally realized by a high-output amplifier. However, a high-output amplifier consumes a large amount of power, generates a large amount of heat, and is not economical. Therefore, several methods for reducing a distortion signal (distortion compensation method) have been proposed so that amplification with low distortion can be performed without using an amplifier having such a large output. As a method of the distortion compensation, there are a negative feedback method, an envelope feedback method, a heterodyne feedback method, a predistortion method, a Cuban predistortion method, a feedforward method, and the like, and each has an effect having a characteristic.

FIG. 7 shows one of the various distortion compensation methods described above.
FIG. 2 is a block diagram illustrating the principle of an amplifier that has performed distortion compensation by an envelope feedback method. The input signal E (t) input to the amplifier shown in FIG. 7 is split by the splitter 111, one signal Ea (t) is input to the amplitude modulator 112, and the other signal Ea (t) is input to the envelope detector 115. The amplitude modulator 112 modulates the input signal from the splitter 111 with the modulation signal SM.
It performs amplitude modulation (AM). Envelope detector 11
5 outputs a signal proportional to the envelope of the input signal. Signal E subjected to amplitude modulation by amplitude modulator 112
b (t) is input to the main amplifier 113. The main amplifier 113 has a distortion signal component I corresponding to the input signal Eb (t).
Generate M (t). Therefore, the main amplifier 1 having the amplification degree A
The output Eq (t) of the thirteen is substantially expressed by the following equation (1) Eq (t) = AＡEb (t) + IM (t) (1)

Here, the distortion signal component in the main amplifier 113 is generated according to the input signal Eb (t).
When (t) is large, the amount of the distortion signal also becomes large. In this way, the signal amplified by main amplifier 113 is input to splitter 114, and one of its outputs is output from amplifier output Eq.
(T), and the other is input to the envelope detector 117. The outputs of the envelope detector 117 and the envelope detector 115 are input to a differentiator 118. The differentiator 118 includes these two envelope detectors 115 and 11
7, and compares the output signal envelope with the output signal envelope and outputs the difference. This difference output is used as a difference output SM for controlling the amplitude modulator 112.
2 given. In such an amplifier with distortion compensation by the envelope detection method, the input signal becomes large, and the main amplifier 1
When distortion occurs at 13, the input signal envelope and the output signal envelope deviate from the proportional relationship by the distortion component. The deviated amount is provided to the amplitude modulator 112 as a difference output, and the amplitude modulator 112 performs amplitude modulation based on the difference output SM so as to reduce the envelope of the signal Eb (t), and outputs the main amplifier. The signal Eb (t) of 113 is reduced, and the amount of distortion signal of the main amplifier is reduced.

The present invention provides an optical transmission device capable of expanding a dynamic range by utilizing the principle of the above-described envelope feedback method for an amplifier in an optical transmission device, particularly, an optical transmission device using a laser module. The purpose is to provide.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to generate a transmission signal whose amplitude is modulated by an amplitude modulator based on a high-frequency input signal to be transmitted.
The transmission signal is converted from electrical to optical by a modulation output electrical / optical converter, thereby generating an optical signal subjected to optical intensity modulation, and transmitting the optical signal to a destination via an optical fiber transmission line. Input branching means for branching an input monitor signal from the input signal, input signal envelope detection means for detecting an input signal envelope detected by the input branching signal as an input signal envelope, and an optical fiber transmission line. Optical branching means for splitting an output monitoring optical signal from the optical signal transmitted to the other end via an optical signal, and an output monitoring optical / electrical converter for converting the output monitoring optical signal into an output monitor signal And output signal envelope detection means for detecting the envelope of the output monitor signal as an output signal envelope, comparing the input signal envelope and the output signal envelope, detecting the difference, and according to the detected difference. Said shake And a difference detecting means for suppressing the modulation degree of the modulator.

According to such a configuration, the difference detecting means compares the input signal envelope output from the input signal envelope detecting means and the output signal envelope detecting means with the output signal envelope, whereby the difference is obtained. From the difference, it is possible to detect the distortion component generated by the modulation and the electrical / optical conversion and included in the optical signal output to the optical fiber transmission line, and if the component tends to increase, the modulation degree of the amplitude modulator is suppressed. , To prevent its components from increasing. Therefore, the dynamic range for the input signal can be expanded.

In the embodiment of the present invention, based on a high-frequency input signal E (t) to be transmitted, the amplitude modulator 12 generates an amplitude-modulated transmission signal EB (t). The electrical / optical converter 13 for modulation output performs electrical / optical conversion, and thereby converts the optical signals PA, PA,
An optical transmission device for generating a PB and transmitting the PB to a destination via the optical fiber transmission lines F1 and F20, wherein the input signal E (t)
Input branching means 11 for branching an input monitor signal DA (t) from the input monitor signal D (t);
An input signal envelope detection means 15 for detecting the envelope of A (t) as an input signal envelope DB (t), and an output monitor optical signal from an optical signal PA transmitted to the other end via the optical fiber transmission line 20. An optical branching unit 14 for branching the PC; an output monitoring optical / electrical converter 16 which optically / electrically converts the output monitoring optical signal PC into an output monitor signal CA (t);
The envelope of the output monitor signal CA (t) is converted to an output signal envelope C
Output signal envelope detection means 17 for detecting as B (t)
, The input signal envelope DB (t) and the output signal envelope CB
(T), a difference SM is detected, and a difference detecting unit 18 that suppresses the degree of modulation of the amplitude modulator 12 according to the detected difference SM is disclosed.

Further, in the present invention, the output monitoring optical / electrical converter and the output signal envelope detecting means are constituted by photodiodes whose operation speed is reduced.

According to such a configuration, the number of constituent members is reduced, and the circuit can be simply configured.

According to the present invention, a transmission signal whose amplitude is modulated by an amplitude modulator is generated based on a high-frequency input signal to be transmitted, and the transmission signal is subjected to optical-to-optical conversion to perform light intensity modulation. An optical transmission device for generating an optical signal and transmitting the signal to a destination via an optical fiber transmission line, comprising: an input branching unit for branching an input monitor signal from the input signal; and an input monitor signal branched by the input branching unit. Signal envelope detection means for detecting the envelope of the input signal as an input signal envelope, and a laser chip, an optical coupler, and a photodiode. Generates an intensity-modulated optical signal, outputs the generated optical signal to the optical fiber transmission line via an optical coupler, and monitors the output of the laser chip with a photodiode to output the signal. An electrical / optical conversion module for outputting as a monitor signal, output signal envelope detection means for detecting, as an output signal envelope, an envelope of an output monitor signal of a photodiode of the electrical / optical conversion module, an input signal envelope and an output signal A difference detection unit that compares the envelope with the envelope, detects the difference, and suppresses the degree of modulation of the amplitude modulator according to the detected difference.

According to such a configuration, the output of the amplitude modulator is subjected to electrical / optical conversion by the laser chip to generate an optical signal subjected to optical intensity modulation, and the generated optical signal is transmitted through the optical coupler. Output to the optical fiber transmission line, the output of the laser chip is monitored by a photodiode, and output as an output monitor signal can be collectively processed by an electric / optical conversion module. By comparing the input signal envelope which is the output of the detection means and the output signal envelope detection means with the output signal envelope, the difference is generated by modulation and electric / optical conversion and output to the optical fiber transmission line. The distortion component contained in the modulated optical signal can be detected, and when the component tends to increase, the modulation degree of the amplitude modulator is suppressed to prevent the component from increasing. To. Therefore, the dynamic range for the input signal can be expanded.

In the embodiment of the present invention, the amplitude modulator 12 generates an amplitude-modulated transmission signal EB (t) based on the high-frequency input signal E (t) to be transmitted, and generates the transmission signal EB (t). An optical transmission device that generates an optical signal P subjected to optical intensity modulation by electrical / optical conversion, and transmits the optical signal P to a destination via an optical fiber transmission line 20. The input branching means 11 for branching the monitor signal DA (t), and the envelope of the input monitor signal DA (t) branched by the input branching means 11 is converted to an input signal envelope DB
(T) an input signal envelope detection means 15 for detecting
The laser chip 23a includes a laser chip 23a, an optical coupler 23b, and a photodiode 23c, and the output of the amplitude modulator 12 is subjected to electrical / optical conversion by the laser chip 23a, thereby generating an optical signal P subjected to light intensity modulation and generating the generated light. Signal P is coupled to optical coupler 2
An electrical / optical conversion module 23 that outputs the output to the optical fiber transmission line 20 via the optical fiber 3b, monitors the output of the laser chip 23a with the photodiode 23c, and outputs the output as an output monitor signal CA (t). 23 output monitor signal C of the photodiode 23c
The output signal envelope detection means 17 for detecting the envelope of A (t) as the output signal envelope CB (t) is compared with the input signal envelope DB (t) and the output signal envelope CB (t). A difference detecting means for detecting the difference SM and suppressing the modulation degree of the amplitude modulator 12 in accordance with the detected difference SM.

Further, in the present invention, the photodiode of the electrical / optical conversion module and the output signal envelope detecting means are constituted by the photodiode of the electrical / optical conversion module whose operation speed is reduced.

According to such a configuration, the number of constituent members is reduced, and the circuit can be simply configured.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the embodiments, the present invention is described as being applied to a system for amplifying the power of a high-frequency signal at a point where optical transmission is performed, for example, a base station device of a mobile phone. That is, the present invention is applied to an application in which a high-frequency signal such as a wireless signal of a mobile phone is transmitted for several hundred meters to several kilometers by an optical fiber, and the power is amplified and output therefrom.

Embodiment 1 FIG. 1 is a block diagram showing an optical transmission system in which Embodiment 1 of the optical transmission device of the present invention is used. The optical transmission system 1 converts an electrical input signal E (t) into an optical signal PB.
0 and an optical fiber 2 having one end connected to the optical transmission device 10.
0 and the other end of the optical fiber 20
The optical / electrical converter 30 converts an optical signal sent through the O.0 into an electric signal and outputs an output signal EQ (t). In this case, the optical transmission device 10 includes a splitter 11, an amplitude modulator 12, an electric / optical converter 13, an optical splitter 14, an optical / electric converter 16, and an envelope detector 1
5 and 17, a difference device 18, and optical fibers F1 and F2. The splitter 11 splits the input signal E (t), which is an electrical high-frequency signal, into two paths and outputs a signal D
Output as A (t) and EA (t). One of the branched signals EA (t) is supplied to the amplitude modulator 12 and the other signal DA.
(T) is input to the envelope detector 15. The signal DA (t) input to the envelope detector 15 undergoes envelope detection, and outputs an output DB (t) corresponding to the envelope to the differentiator 18. The other branched signal EA (t) is input to the amplitude modulator 12. The amplitude modulator 12 outputs the signal EA
The amplitude modulation is performed based on (t), and the signal EB (t) is output. The modulation degree is controlled (suppressed) by the difference output SM of the differentiator 18.

Electric / optical converter (for example, semiconductor laser)
13 converts the electrical signal EB (t) into an optical signal PA
And output to the optical fiber F1. In this case, in the electrical / optical converter 13, the generation level of the distortion signal included in the optical signal PA differs according to the level of the input signal EB (t). The optical splitter 14 converts the optical signal PA of the electrical / optical converter 13 provided via the optical fiber F1 into an optical signal P
The light is branched to B and PC. One optical signal PB that is optically branched
Is output to the optical transmission system including the optical fiber 20 and the like, is subjected to optical / electrical conversion by the optical / electrical converter 30 at the transmission destination, and is output as an electrical output signal EQ (t). The other optical signal PC that has been optically branched is provided to the optical / electrical converter 16 via the optical fiber F2. The optical / electrical converter 16 converts the applied optical signal PC into an electric signal CA (t). The envelope detector 17 receives the electric signal CA (t) output from the optical / electrical converter 16, and receives an envelope CB of the signal CA (t).
(T) is output. The difference unit 18 calculates a difference between the envelope DB (t) from the envelope detector 15 and the envelope CB (t) from the envelope detector 17, and outputs a difference output SM according to the difference. This difference output SM is output to the amplitude modulator 12.
Given to. This difference output SM is output to the electrical / optical converter 1
Since the output corresponds to the amplitude of the distortion amount of the distortion component generated from No. 3, when the distortion amount is large, the amplitude modulator 12 performs the amplitude modulation so as to reduce the amplitude. The input signal strength is reduced and the electrical / optical converter 1
3 can suppress generation of a distortion signal.

Embodiment 2 FIG. Next, an optical transmission device according to a second embodiment will be described with reference to FIG. In the first embodiment, the signal optically / electrically converted by the optical / electrical converter 16 is supplied to the envelope detector 17 to perform the envelope detection. However, in the optical transmission device 40 of FIG. FIG.
A photodiode 26 is used instead of the optical / electrical converter 16 and the envelope detector 17 of FIG. In this case, by adjusting the operation speed of the photodiode 26 to a low speed, it is possible to output the envelope of the optical signals PA and PB whose optical intensity has been modulated. That is, by setting the operation speed of the photodiode 26 to be low, the circuit configuration can be simplified with one member, and the envelope of the light intensity modulation signal can be directly output. Thus, the output signal of the photodiode 26 is the optical signal P
Since the signal corresponds to the envelope of A and PB, the signal SM can be input to the differentiator to compensate (cancel) the distortion signal as described above.

Embodiment 3 FIG. Next, a third embodiment of the optical transmission device will be described with reference to FIG. The optical transmission device 50 shown in FIG. 3 is different from the optical transmission device 10 of FIG. 1 in that the electrical / optical converter 13, the optical fibers F1 and F2, the optical splitter 14, the optical / optical The electric converter 16 is replaced by an electric / optical conversion module 23. In this case, the electric / optical conversion module 23 is
3a, the optical coupling system 23b, and the photodiode 23c are integrally formed, and have a module structure suitable for the name as shown in FIG. Parts having the same structure as the optical transmission device 10 of FIG. The laser chip 23a of the electrical / optical conversion module 23 receives the output EB (t) of the amplitude modulator 12 and performs electrical / optical conversion to generate an optical signal that has been subjected to optical intensity modulation. The output optical signal is output to the optical fiber 20 via the optical coupling system 23b disposed in front. The optical signal P output to the optical fiber 20 is optically / electrically converted by the optical / electrical converter 30 at the transmission destination, and output as an electrical output signal EQ (t).

In the above case, the photodiode 23c is
The laser chip 2 is disposed behind the laser chip 23a.
By receiving the light leaking according to the output of 3a, the output of the optical signal emitted from the laser chip 23a is monitored. The photodiode 23c converts the monitored optical signal into an electrical signal CA (t) and outputs the electrical signal CA (t) to the envelope detector 17. As in the optical transmission device 10 of FIG. 1, the differentiator 18 also includes the envelope DB (t) from the envelope detector 15 and the envelope detector 17 in the optical transmission device 50 of FIG.
And outputs an output SM corresponding to the difference from the envelope CB (t). The difference output SM is provided to the amplitude modulator 12. Since the difference output SM is an output according to the amplitude of the distortion amount of the distortion component generated from the electrical / optical conversion module 23, when the distortion amount is large, the amplitude modulator 12 performs the amplitude modulation so that the amplitude decreases. Is controlled, the input signal strength of the electric / optical conversion module 23 is reduced, and generation of a distortion signal in the electric / optical conversion module 23 can be suppressed. Therefore, the dynamic range for the input signal can be widened.

Embodiment 4 Further, a fourth embodiment of the optical transmission device shown in FIG. 5 will be described. In the third embodiment of FIG. 3, the signal from the photodiode 23c is subjected to envelope detection by the envelope detector 17, but in the optical transmission device 60 of FIG. 5, the envelope detector 17 of FIG. Is not used, and the operating speed of the photodiode 23c is adjusted to be slow to output the envelope of the light intensity modulation signal. That is, by setting the operation speed of the photodiode 23c to be slow, the photodiode 23c can directly output the envelope of the light intensity modulation signal without using the envelope detector 17. I have. In this case, since the output signal of the photodiode 23c is a signal corresponding to the envelope of the optical signal P, the distortion signal can be compensated as described above by inputting the signal CB (t) to the differentiator. It becomes possible.

[0027]

As described in detail above, according to the optical transmission apparatus of the present invention, the difference detecting means is provided with the input signal envelope which is the output of the input signal envelope detecting means and the output signal envelope detecting means. By comparing the output signal envelope with the output signal, the distortion component generated by the modulation and the electrical / optical conversion and included in the optical signal output to the optical fiber transmission line can be detected from the difference, and the component is likely to increase. This can be prevented by suppressing the modulation degree of the amplitude modulator. Therefore, the dynamic range of the transmission signal can be expanded without improving the noise characteristics and distortion characteristics inherent to the optical transmission system using the light emitting device, the light receiving device, and the transmission path. That is, when the same device is used, the transmission characteristics can be further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an optical transmission system using an optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating an optical transmission system using an optical transmission device according to a second embodiment of the present invention;

FIG. 3 is a block diagram showing an optical transmission system using an optical transmission device according to a third embodiment of the present invention;

FIG. 4 is a diagram showing a structure of an electric / optical conversion module used in Embodiment 3 of FIG. 3;

FIG. 5 is a block diagram showing an optical transmission system using an optical transmission device according to a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional example of a typical optical transmission system to which a technique for transmitting a high-frequency signal through an optical fiber is applied. This

FIG. 7 is a block diagram showing the principle of an amplifier that performs distortion compensation by a wireless signal envelope feedback method in a base station facility for mobile communication such as a mobile phone.

[Explanation of symbols]

 1, 2, 3, 4 Optical transmission system 10, 40, 50, 60 Optical transmission device 11 Splitter 12 Amplitude modulator 13 Electric / optical converter 14 Optical splitter 15, 17 Envelope detector 16, 30 Optical / electric Converter 18 Difference device 20, F1, F2 Optical fiber 23 Electric / optical conversion module 23a Laser chip 23b Optical coupling system 23C, 26 Photodiode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/18

Claims (4)

[Claims] An amplitude modulator generates a transmission signal whose amplitude is modulated based on a high-frequency input signal to be transmitted, and a modulation output electric / optical converter performs electric / optical conversion on the transmission signal. An optical transmission device for generating an optical signal subjected to optical intensity modulation and transmitting the optical signal to a destination via an optical fiber transmission line, wherein input branching means for branching an input monitor signal from the input signal, and input branching means. Input signal envelope detection means for detecting an envelope of the branched input monitor signal as an input signal envelope, and an optical branch for branching an output monitoring optical signal from the optical signal transmitted to the other end via an optical fiber transmission line Means, an optical / electrical converter for optically / electrically converting an optical signal for output monitoring to produce an output monitor signal, and an output signal envelope detector for detecting an envelope of the output monitor signal as an output signal envelope. Means for comparing an input signal envelope with an output signal envelope, detecting a difference therebetween, and suppressing a modulation degree of the amplitude modulator according to the detected difference. Transmission equipment. 2. The optical transmission device according to claim 1, wherein the output monitoring optical / electrical converter and the output signal envelope detecting means are constituted by photodiodes whose operation speed is reduced. 3. An amplitude modulator generates an amplitude-modulated transmission signal based on a high-frequency input signal to be transmitted, and performs electrical / optical conversion on the transmission signal to convert the optical signal subjected to light intensity modulation. An optical transmission device for generating and transmitting an input monitor signal from an input signal to an opposite end via an optical fiber transmission line, comprising: an input branching unit that branches an input monitor signal from the input signal; An input signal envelope detecting means for detecting as an input signal envelope; and a laser chip, an optical coupler, and a photodiode. And outputs the generated optical signal to an optical fiber transmission line via an optical coupler, and monitors the output of the laser chip with a photodiode to generate an output monitor signal. Signal-to-output conversion module, output signal envelope detection means for detecting the envelope of the output monitor signal of the photodiode of the signal-to-light conversion module as an output signal envelope, input signal envelope and output signal envelope And a difference detecting means for detecting the difference, and for suppressing the degree of modulation of the amplitude modulator in accordance with the detected difference. 4. The light according to claim 3, wherein the photodiode of the electrical / optical conversion module and the output signal envelope detection means are constituted by the photodiode of the electrical / optical conversion module whose operation speed is reduced. Transmission equipment.