JPH10247893A - Optical sub-carrier transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure high communication quality, to enlarge light transmission distance and to construct a more inexpensive system by providing the respective means of code generation, spectrum diffusion and electric/optic conversion for a light-transmitting device and providing the respective means of optic/ electric conversion and spectrum inverse diffusion for a light-receiving device. SOLUTION: In a light-transmitting device 10, a code generation means 13 generates a diffusion code P1 and inputs it to a spectrum diffusion means 12. An electric signal S1 becomes an electric signal SS1 which is spectrum-diffused in a spectrum diffusion means 12, is converted into a light signal and is transmitted to an optical fiber 30. In the light-receiving device 20, a code generation means 23 generates a diffusion code P1a and inputs it to a spectrum inverse diffusion means 22. The light signal which is taken in from the optical fiber 30 is converted again into the electric signal SS1, which is spectrum-diffused by E/O21. The electric signal SS1 is spectrum-fiffused by the spectrum inverse diffusion means 22 and becomes the original electric signal S1 and is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical CATV transmission for transmitting an analog signal such as a frequency-multiplexed video signal through an optical fiber and an optical subcarrier transmission system for transmitting an image light.

[0002]

FIG. 8 is a block diagram of a conventional optical subcarrier transmission system. First, the configuration will be described. In the figure, reference numeral 10 denotes an optical transmitter which is a CATV transmitting station such as a head end for transmitting an analog signal such as a video signal as an optical signal, and reference numeral 20 denotes an optical receiver which is an optical / coaxial conversion node for receiving the optical signal. . An optical fiber 30 is connected between them.

[0003] As a main configuration, an optical transmission device 10 is electrically / electronically operated.
An optical conversion unit (hereinafter, referred to as “E / O”) 11 is provided, and the optical receiver 20 includes an optical / electrical conversion unit (hereinafter, referred to as “O / E”) 21.

Next, the operation will be described. To accommodate multiple subscribers, the frequency multiplexed electrical signal s1 is:
The signal is converted into an optical signal by the E / O 11 and transmitted to the optical fiber 30. Then, the optical signal taken in from the optical fiber 30 is reconverted into the original electric signal s1 by the O / E 21 and taken out.

In the optical subcarrier transmission system having such a configuration, an extremely low noise light source (for example, a DFB-LD (for example, a DFB-LD)) is used in the E / O 11 in order to reduce deterioration of a signal due to transmission and maintain good communication quality. Distributed Feed Bac
k-Laser Diode) must be used. Further, in order to process a frequency-multiplexed wideband signal (electrical-optical conversion processing), it is necessary to use a wideband light source and a photodetector in the E / O 11 and the O / E 21. Further, in order to suppress generation of unnecessary signals when processing the frequency-multiplexed signal, it is necessary to use a light source and a photodetector with low distortion characteristics in the E / O 11 and the O / E 21. When a plurality of optical signals are combined by an optical combiner and transmitted, the E / O
In order to stabilize the emission wavelength of the light source in 11, the emission wavelength control with high precision is required.

[0006]

Since the conventional optical subcarrier transmission system is configured as described above, it is necessary to obtain a high communication quality, a wide band, a low distortion characteristic, and a high optical wavelength stability. There is a problem that parts and high-precision control must be performed, and the cost of the parts and thus the entire system increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its main object to suppress noise degradation during transmission, obtain high communication quality, and transmit a plurality of signals corresponding to a plurality of subscribers. An object of the present invention is to provide an optical subcarrier transmission system capable of suppressing the signal band and suppressing the generation of unnecessary waves even when performing the above, and realizing these performances without using high-performance components and high-precision control.

[0008]

In an optical subcarrier transmission system according to the present invention, an optical transmitter and an optical receiver are connected by an optical fiber, and when performing optical subcarrier transmission, the optical transmitter is connected to the optical transmitter. Is a code generating means for generating a spread code, a spectrum spread means for spreading and outputting an input analog signal based on the spread code, and an electric signal which is an output signal from the spread spectrum means is converted into an optical signal, An optical / electrical conversion means for transmitting the optical signal to the optical fiber; an optical / electrical conversion means for converting an optical signal transmitted through the optical fiber into an electric signal; Spectrum despreading means for despreading an output signal from the conversion means based on a predetermined spreading code and outputting an original analog signal.

In addition, when an optical transmitter and a plurality of optical receivers are connected by an optical fiber and an optical distributor, and optical subcarrier transmission is performed, the optical transmitter has a plurality of input analog signals. Code generating means for generating a plurality of different spread codes, spectrum spread means for spreading and outputting the plurality of input analog signals based on the corresponding spread codes, and combining a plurality of output signals from the spread spectrum means. Synthesizing means for converting and outputting an electric signal, which is an output signal from the synthesizing means, into an optical signal, and sending the optical signal to the optical fiber.
Each of the optical receivers has an optical / electrical conversion means for converting an optical signal transmitted via the optical fiber into an electric signal, and an output signal from the optical / electrical conversion means for performing spectrum inversion based on a predetermined spreading code. Spectrum despreading means for spreading and outputting an original analog signal.

A plurality of optical transmitters and an optical receiver are connected by an optical fiber and an optical combiner, and when performing optical subcarrier transmission, each optical transmitter has a code generating means for generating a spread code. A spread spectrum unit that spreads an input analog signal based on the corresponding spread code and outputs the spread spectrum code, and an electric signal that is an output signal from the spread spectrum unit converted into an optical signal and transmitted to the optical fiber. / Optical conversion means, wherein the optical receiving device includes: an optical / electric conversion means for converting an optical signal transmitted through the optical fiber into an electric signal; and an output signal from the optical / electric conversion means. Distributing means for distributing and outputting, and spectrum despreading for despreading a plurality of output signals from the distributing means based on a predetermined spreading code and outputting a plurality of original analog signals. It is obtained as comprising a means.

The electric / optical conversion means uses a Fabry-Perot type semiconductor laser as a light source.

The plurality of input analog signals have the same carrier frequency.

The spread spectrum means spreads the input analog signal by frequency hopping based on a spread code and outputs the spread spectrum.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Embodiment 1 of the optical subcarrier transmission system according to the present invention will be described below. FIG. 1 is a block diagram of the optical subcarrier transmission system according to the first embodiment. First, the configuration will be described. An optical transmitter 10 is a CATV transmitting station such as a head end that transmits an analog signal such as a video signal as an optical signal, and an optical receiver 20 is an optical / coaxial conversion node that receives the optical signal. An optical fiber 30 is connected between them.

The main components of the optical transmitter 10 are a code generating means 13 for generating a spread code, a spectrum spread means 12 for spreading an input analog signal based on the spread code and outputting the spread signal, and a spread spectrum output as an electric signal. An E / O 11 for converting the optical signal into an optical signal and outputting the optical signal is provided.

The optical receiver 20 is a CATV transmitting station 1
Code generating means 23 for generating the same spreading code as the spreading code from the code generating means 13 within 0, O / E 21 for converting an optical signal into an electric signal, and spread-spectrum electric signal from the O / E 21 It has a spectrum despreading means 22 for despreading the spectrum based on the code and outputting the original analog signal.

Next, the operation will be described. Optical transmission device 1
The operation in 0 is as follows. Here, it is assumed that the electric signal s1 is frequency-multiplexed in order to correspond to a plurality of subscribers. The code generating means 13 generates the spread code p
1 is generated and input to the spread spectrum means 12. The electric signal s1 is an electric signal ss that is spectrum-spread by the spectrum spread means 12 based on the spread code p1.
It becomes 1. The electric signal ss1 is converted into an optical signal by the E / O 11 and transmitted to the optical fiber 30.

The operation in the optical receiver 20 is as follows. The code generator 23 generates the same spread code p1a as the spread code from the code generator 13 in the optical transmitter 10 and inputs the same to the spectrum despreader 22. The optical signal taken in from the optical fiber 30 is reconverted into an electric signal ss1 whose spectrum has been spread by the O / E 21. The electric signal ss1 is subjected to spectrum despreading by the spectrum despreading means 22 based on the spread code p1a, and is taken out as the original electric signal s1.

As a spread spectrum technique based on a spread code, a direct spread (DS) method (a method of directly multiplying (modulating) an input signal by a spread code having a narrow code width of code bits and performing spread spectrum). ) And a method based on frequency hopping (FH) (a method in which an input signal is not directly modulated by a spreading code, but is modulated by a plurality of modulation signals having different frequencies corresponding to the spreading code and spread spectrum). is there. In the case of the present invention, since the signal to be subjected to spectrum spreading is an analog signal, spectrum spreading by FH is preferable to DS in terms of simplification of the device configuration. If the digitization of the signal progresses in the future, the spread spectrum by DS will become realistic.

Here, the processing gain G due to the spread spectrum is used.
p is as follows: Gp = Bp / Bs (1) Here, Bp is the bandwidth of the spread spectrum electric signal ss1, and Bs is the bandwidth of the original electric signal s1. Accordingly, the carrier-to-noise ratio (C / N) between E / O11 and O / E21 is improved by the processing gain Gp, so that the optical transmission / reception level difference can be increased and the optical transmission distance can be increased. It is possible.

Conventionally, a light source in the E / O is required to have a low noise (for example, the DFB-LD). However, as described above, the C / N is improved by the processing gain Gp. As a light source, a light source such as a Fabry-Perot type LD (Laser Diode) which is inferior in noise characteristics to a DFB-LD but has a simple element structure and is inexpensive in cost can be applied.

As described above, according to the first embodiment, a processing gain by spectrum spreading can be obtained.
If the same light source as that of the related art is used, higher communication quality can be obtained, and there is an effect that the optical transmission distance can be extended. Also, if the communication quality is kept the same, there is an effect that a cheaper light source can be used.

Embodiment 2 FIG. Hereinafter, a second embodiment of the optical subcarrier transmission system according to the present invention will be described. Embodiment 2 shows an application example of an optical demand service for a plurality of subscribers in an optical CATV to a downlink. FIG. 2 is a block diagram of an optical subcarrier transmission system according to the second embodiment. First, the configuration will be described. Reference numeral 10 denotes an optical transmission device which is a CATV transmission station such as a head end for transmitting an analog signal such as a video signal as an optical signal, and reference numerals 201 to 203 denote subscriber receiving terminals provided for each subscriber receiving the optical signal. An optical receiver. The space between them is connected by an optical distributor 31 and an optical fiber 30.

As a main configuration, the optical transmitting apparatus 10 comprises a code generating means 1 for generating a plurality of spread codes different for each subscriber.
3. Spread spectrum means 121 to 123 for spreading and outputting a different input analog signal for each subscriber based on a spread code corresponding to the subscriber, combining means 14 for combining and outputting the plurality of spread spectrum signals, electric signal And an E / O 11 for converting the synthesized spread spectrum output into an optical signal and outputting the optical signal.

Each of the optical receiving devices 201 to 203 generates a spread code corresponding to the same subscriber as the spread code from the code generation device 13 in the optical transmission device 10.
3. O / E 21 for converting an optical signal into an electric signal;
A spectrum despreading unit 22 is provided for despreading the spectrum-spread electric signal from E21 based on the spread code and outputting an original analog signal.

Next, the operation will be described. Optical transmission device 1
The operation in 0 is as follows. Sign generation means 1
3 generates spread codes p1, p2, and p3 corresponding to the subscribers and inputs the generated spread codes to corresponding spread spectrum means 121 to 123. s1, s2, and s3 are CATs corresponding to each subscriber
V signal, and the electric signals s1, s
2, s3 are electric signals ss1, ss2, s which are respectively spread spectrum by the spread spectrum means 121 to 123 based on the corresponding spread codes p1, p2, p3.
s3. After the electric signals ss1, ss2, and ss3 are combined by the combining means 14, they are converted into optical signals by the E / O 11 and sent out to the optical fiber 30. The optical signal transmitted through the optical fiber 30 is distributed to each subscriber by the optical distributor 31 and is input to the optical receivers 201, 202 and 203 for each subscriber.

The operations in the optical receivers 201 to 203 are as follows. The code generating means 23 is a spreading code p1a, p2a, p3a for the same despreading as the spreading code from the code generating means 13 for each subscriber in the CATV transmitting station 10.
Is generated and input to the spectrum despreading means 22. The optical signal taken in from the optical fiber 30 is reconverted into electric signals ss1, ss2, and ss3 spread by the O / E 21. The electric signals s1, s2, ss3 are despread by the spectrum despreading means 22 based on the spread codes p1a, p2a, p3a, and the original electric signals s1, s2, s3 are taken out for each subscriber.

Here, the optical receiver 201 for each subscriber,
At 202 and 203, the spread spectrum signals ss1 and ss
To extract the original electric signals s1, s2, s3 from 2, ss3, spreading codes p1a, p2a, p3 determined for each subscriber
A despreading process based on a is required. For example, as for the spread spectrum signal ss1, only the optical receiving terminal 201 of the subscriber having the spread code p1a can extract the original electric signal s1.

The identification of the signal for each subscriber is based on the spreading code p.
Since the processing is performed at 1a, p2a, and p3a, the spread spectrum signals ss1, ss2, and ss3 can use overlapping frequency bands. In other words, frequency multiplexing is not necessary, and there is no need to expand the frequency band due to an increase in the number of subscribers and distribution services.

As described above, in the second embodiment, different spreading codes can be assigned to a plurality of subscribers, so that the number of subscribers and the distribution service can be increased without expanding the frequency band using the same frequency band. There is an effect that it is possible to increase. In addition, there is an effect that a cheaper system can be constructed without using various components of a wide band.

Embodiment 3 Embodiment 3 of the optical subcarrier transmission system according to the present invention will be described below. The third embodiment shows an application example of an optical demand service for a plurality of subscribers in an optical CATV to an uplink. FIG. 3 is a block diagram of an optical subcarrier transmission system according to the third embodiment. First, the configuration will be described. Reference numerals 101 to 103 denote optical transmitters which are subscriber transmission terminals provided for each subscriber transmitting the optical signal, and reference numeral 20 denotes a CATV receiving station such as a head end which receives an analog signal such as a video signal as an optical signal. An optical receiver. This is connected by a light combiner 32 and an optical fiber 30.

As a main configuration, the optical transmitters 101 to 10
Numeral 3 is a code generating means 13 for generating a different spread code for each subscriber, a spread spectrum means 12 for spreading and outputting a different input analog signal for each subscriber based on a spread code corresponding to the subscriber, and an electric signal. E / O1 for converting the spread spectrum output into an optical signal and outputting the signal
1 is provided.

The optical receiving device 20 is an optical transmitting device 101
Code generating means 23 for generating a plurality of spreading codes corresponding to the same subscribers as the spreading codes from the code generating means 13 in 103, an O / E 21 for converting an optical signal into an electric signal, Distributing means 25 for distributing the spectrum-spread composite electric signal; despreading the distributed electric signal based on a spreading code corresponding to each subscriber;
Spectral despreading means 22 for outputting the original analog signal
1 to 223.

Next, the operation will be described. Optical transmission device 1
The operations in 01 to 103 are as follows. The code generating means 13 includes spreading codes p1, p2,
p3 is generated and input to the spread spectrum means 12.
s1, s2, and s3 are electric signals that are CATV signals corresponding to the respective subscribers, and are electric signals s1, s2, and s3.
Are electric signals ss1, ss2, and ss3, respectively, which have been spectrum-spread by the spectrum spreading means 12 based on the corresponding spreading codes p1, p2, and p3. The electric signals ss1, ss2, and ss3 are converted into optical signals by the E / O 11 and sent out to the optical fiber 30. Optical signals transmitted through the optical fiber 30 are combined by the optical combiner 32 and input to the optical receiver 20.

The operation in the optical receiver 20 is as follows. The code generation means 23 includes optical transmission devices 101 to 10
3 generates spread codes p1a, p2a, p3a for the same despreading as the spread codes from the code generating means 13 for each subscriber, and inputs them to the spectrum despreading means 221 to 223. The optical signal captured from the optical fiber 30 is O / E
The electric signals ss1, ss spread spectrum by 21
2. Re-converted to ss3. These electric signals ss1, ss
2 and ss3 are distributed by the distribution means 25 and then spectrum despread by the spectrum despreading means 22 based on the spreading codes p1a, p2a and p3a, and the original electric signals s1,
s2 and s3 are extracted for each subscriber.

Here, the despreading means 221 to 221 for each subscriber
At 223, spread spectrum signals ss1, ss2, ss
In order to extract the original electric signals s1, s2, s3 from No. 3, a despreading process based on spreading codes p1a, p2a, p3a determined for each subscriber is required. For example, the spread spectrum signal ss1 is a despreading means 2 of the subscriber having the spreading code p1a.
Only 21 can extract the original electric signal s1.

The signal for each subscriber is identified by a spreading code p.
Since the processing is performed at 1a, p2a, and p3a, the spread spectrum signals ss1, ss2, and ss3 can use overlapping frequency bands. In other words, frequency multiplexing is not necessary, and there is no need to expand the frequency band due to an increase in the number of subscribers and distribution services.

When optical signals from a plurality of E / Os are combined by an optical combiner, if the light emission wavelengths of the E / Os are slightly different, beat noise occurs when the optical signals are converted into electric signals, resulting in communication. This will result in quality degradation. The following describes that the invention of the third embodiment is also effective as a measure against the beat noise. FIG. 4 shows the spectrum of the output signal of the O / E 21 and the spectrum despreading means 221. ss
1, ss2 and ss3 are spread spectrum signals, which are wide band signals. On the other hand, beat noise is a signal in a narrow band of an arbitrary frequency because it is generated by a difference in emission wavelength of the light source in the E / O. Therefore, when such a signal is despread, the beat noise component is spread and only the original signal can be extracted.

As described above, in the third embodiment, different spreading codes can be assigned to a plurality of subscribers, so that the same frequency band is used and the number of subscribers and the distribution service are increased without expanding the frequency band. There is an effect that it is possible to increase. In addition, there is an effect that a cheaper system can be constructed without using various components of a wide band. In addition, there is an effect that the influence of beat noise can be eliminated without performing complicated call control or control of the emission wavelength in the CATV uplink.

Embodiment 4 FIG. Embodiment 4 of the optical subcarrier transmission system according to the present invention will be described below. The fourth embodiment shows an example of application in a case where a conventional optical transmission means not subjected to spread spectrum is mixed. FIG. 5 is a block diagram of an optical subcarrier transmission system according to the fourth embodiment. First, the configuration will be described. An optical transmitter 10 is a CATV transmitting station such as a head end that transmits an analog signal such as a video signal as an optical signal, and an optical receiver 20 is an optical / coaxial conversion node that receives the optical signal. An optical fiber 30 is connected between them.

The main components of the optical transmitter 10 are a code generating means 13 for generating a spread code, a spectrum spread means 12 for spreading and outputting an input analog signal based on the spread code, and another input analog which is not subjected to spread spectrum. The signal s2 and the spread spectrum signal ss
Combining means 14 for combining and outputting 1 and the combining means 14
And an E / O 11 for converting the spread spectrum output, which is an electric signal, into an optical signal and outputting the optical signal.

The optical receiver 20 is a CATV transmitting station 1
Code generating means 23 for generating the same spreading code as the spreading code from code generating means 13 within 0, O / E 21 for converting an optical signal into an electric signal, distribution means for distributing an electric signal output from the O / E 21 25, a spectrum despreading unit 22 that despreads the electric signal from the distribution unit 25 based on the spread code and outputs an original analog signal;
An output terminal 2 for directly outputting a signal from the distribution means 25
6. An output terminal 27 for outputting a signal from the spectrum despreading means 22 is provided.

Next, the operation will be described. Optical transmission device 1
The operation in 0 is as follows. Here, it is assumed that the electric signals s1 and s2 are frequency-multiplexed in order to correspond to a plurality of subscribers. S2 of this electric signal
Is not spread, and s1 is spread. The code generation means 13 generates a spread code p1,
It is input to the spread spectrum means 12. The electric signal s1
Is based on the spread code p1.
Becomes an electric signal ss1 whose spectrum is spread. This electric signal ss1 is combined with the electric signal s2 and
After being combined, the signal is converted into an optical signal by the E / O 11 and transmitted to the optical fiber 30.

The operation in the optical receiver 20 is as follows. The code generator 23 generates a spread code p1a for spectrum despreading, which is the same as the spread code from the code generator 13 in the optical transmitter 10, and inputs the spread code p1a to the spectrum despreader 22. The optical signal taken in from the optical fiber 30 is reconverted into an electric signal that is spread spectrum by the O / E 21. This electric signal is distributed by the distribution means 25. One of the divided signals is the spreading code p1a.
, And the original electric signal s1 is extracted from the output terminal 27. The other signal is extracted from the output terminal 26 as an electric signal s2.

Here, the signal s2 is transmitted as it is (without spread spectrum), and the signal s1 is spread spectrum and transmitted as ss1. Therefore, as shown in FIG. 6, in the output signal of the output terminal 26, the ss1 component is spread over a wide band.
s1 has almost no adverse effect. On the other hand, from the output of the spectrum despreading means 22, the original signal s1 is extracted from ss1, as shown in FIG. 6, and s2 is spread to ss2. s2
Ss2 has almost no adverse effect on the reception of.

As described above, according to the fourth embodiment, even when the frequency bands of the input signals are overlapped with each other when the conventional optical transmission means which is not subjected to the spread spectrum is used, the influence is not exerted on each other. Can be synthesized and separated with almost no effect.

Embodiment 5 Hereinafter, Embodiment 5 of the optical subcarrier transmission system according to the present invention will be described. The fifth embodiment shows an example of application to a remote monitoring system using images. FIG. 7 is a block diagram of an optical subcarrier transmission system according to the fifth embodiment. First, the configuration will be described. 101
Reference numerals 103 to 103 denote optical transmitters which are local nodes provided at each monitoring point for transmitting optical signals, and reference numeral 20 denotes an optical receiver which receives analog signals such as video signals installed in a control room or the like as optical signals. An optical fiber 30 is connected between them.

As a main configuration, the optical transmitters 101 to 10
Reference numeral 3 denotes a monitoring camera 18, code generation means 13 for respectively generating a different spread code for each optical transmission device, and spectral spread of different input analog signals from the monitoring camera 18 for each optical transmission device based on the corresponding spread code. It has a spread spectrum means 12 for outputting, and an E / O 11 for converting the spread spectrum output, which is an electric signal, into an optical signal and outputting it. Each of the optical transmitters 101 and 102 has an optical combiner 32 that combines an optical signal from itself and an optical signal from another optical transmitter.

The optical receiving device 20 is an optical transmitting device 101
Code generating means 23 for generating a plurality of spread codes corresponding to each of the optical transmitters, which are the same as the spread codes from code generation means 13 in O.E.
1. A spectrum despreading means 22 for despreading the spectrum of the combined electric signal from the O / E 21 based on a spread code corresponding to each optical transmitter and outputting an original analog signal.

Next, the operation will be described. Optical transmission device 1
The operations in 01 to 103 are as follows. The code generation means 13 has a spreading code p1 corresponding to each optical transmitting device,
p2 and p3 are generated and input to the spectrum spreading means 12. s1, s2, and s3 are electric signals that are video signals from the monitoring cameras, and the electric signals s1, s2, and s3
Are electric signals ss1, ss2, and ss3, respectively, which have been spectrum-spread by the spectrum spreading means 12 based on the corresponding spreading codes p1, p2, and p3. The electric signals ss1, ss2, and ss3 are converted into optical signals by the E / O 11 and sent out to the optical fiber 30. Optical signals transmitted through the optical fiber 30 are sequentially combined by the optical combiner 32 and input to the optical receiver 20.

The operation in the optical receiver 20 is as follows. The code generation means 23 includes optical transmission devices 101 to 10
3, the spread codes p1a, p1 for the same spectrum despreading as the spread code from the code generation means 13 for each optical transmitting apparatus.
2a and p3a are cyclically generated and input to the spectrum despreading means 22. The optical signal taken in from the optical fiber 30 is reconverted into electric signals ss1, ss2, and ss3 which are spread spectrum by the O / E 21. The electric signals ss1, ss2, ss3 are cyclically despread by the spectrum despreading means 22 based on the cyclically generated spreading codes p1a, p2a, p3a.
The original electrical signals s1, s2, and s3 for each optical transmission device are cyclically extracted.

Here, the electric signal of each optical transmission device can be identified by a spread code. Therefore, the fact that the frequency bands of s1, s2, and s3 may overlap is described in the second and third embodiments.
As described in the above. Further, as described in the third embodiment, it is possible to eliminate the influence of beat noise generated when optical signals from a plurality of E / Os are combined by an optical combiner.

As described above, in the fifth embodiment, different spreading codes can be assigned to a plurality of monitoring points, so that the number of monitoring points can be increased using the same frequency band without expanding the frequency band. There is an effect that can be done. In addition, there is an effect that a cheaper system can be constructed without using various components of a wide band. Further, there is an effect that the influence of beat noise can be eliminated without controlling the emission wavelength.

[0054]

As described above, according to the present invention, it is possible to obtain a processing gain by spectrum spreading, so that higher communication quality can be obtained and an optical transmission distance can be extended. There is. In addition, there is an effect that a cheaper system can be constructed.

Since different spreading codes can be assigned to a plurality of subscribers, the same frequency band can be used and the number of subscribers and the distribution service can be increased without expanding the frequency band. is there. Also,
As a result, there is an effect that a less expensive system can be constructed without using various components in a wide band.

Further, since different spreading codes can be assigned to a plurality of subscribers, the same frequency band can be used and the number of subscribers and the distribution service can be increased without expanding the frequency band. is there. Also,
As a result, there is an effect that a less expensive system can be constructed without using various components in a wide band. In addition, there is an effect that the influence of beat noise can be eliminated without performing complicated call control or control of the emission wavelength in the CATV uplink.

Further, since a processing gain by spectrum spreading can be obtained, there is an effect that a cheaper light source can be used.

Since different spreading codes can be assigned to a plurality of subscribers, the number of subscribers and the number of distribution services can be increased using the same frequency band without expanding the frequency band. is there. Also,
As a result, there is an effect that a less expensive system can be constructed without using various components in a wide band.

Further, since different spreading codes can be assigned to a plurality of optical transmission devices, there is an effect that the number of monitoring points can be increased using the same frequency band without expanding the frequency band. In addition, there is an effect that a cheaper system can be constructed without using various components of a wide band. In addition, there is an effect that the influence of beat noise can be eliminated without performing complicated call control and emission wavelength control on the uplink line of the monitoring camera.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical subcarrier transmission system according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram of an optical subcarrier transmission system according to Embodiment 2 of the present invention.

FIG. 3 is a block diagram of an optical subcarrier transmission system according to Embodiment 3 of the present invention.

FIG. 4 is an explanatory diagram of an operation of an optical subcarrier transmission system according to a third embodiment of the present invention.

FIG. 5 is a block diagram of an optical subcarrier transmission system according to Embodiment 4 of the present invention.

FIG. 6 is an operation explanatory diagram of an optical subcarrier transmission system according to Embodiment 4 of the present invention.

FIG. 7 is a block diagram of an optical subcarrier transmission system according to Embodiment 5 of the present invention.

FIG. 8 is a block diagram of a conventional optical subcarrier transmission system.

[Explanation of Code] 12 Spread spectrum means, 13 Code generation means, 14
Synthesis means, 18 surveillance camera, 22 spectrum despreading means, 23 code generation means, 25 distribution means, 31
Optical distributor, 32 optical combiner, 101 optical transmitter, 10
2 optical transmission device, 103 optical transmission device, 121 spread spectrum means, 122 spread spectrum means, 123
Spectral spreading means, 201 light receiving device, 202 light receiving device, 203 light receiving device, 221 spectrum despreading means, 222 spectrum despreading means, 223 spectrum despreading means

Claims (6)

[Claims] 1. An optical subcarrier transmission system in which an optical transmitter and an optical receiver are connected by an optical fiber to perform optical subcarrier transmission, the optical transmitter includes a code generator for generating a spread code. A spread spectrum means for spreading an input analog signal based on the spread code and outputting the spread signal; and an electric / optical conversion means for converting an electric signal which is an output signal from the spread spectrum means into an optical signal and sending it to the optical fiber. And an optical receiving device comprising: an optical / electrical conversion unit for converting an optical signal transmitted via the optical fiber into an electric signal; and a predetermined spread code for an output signal from the optical / electrical conversion unit. An optical subcarrier transmission system, comprising: spectrum despreading means for despreading a spectrum based on the spectrum and outputting an original analog signal. 2. An optical subcarrier transmission system in which an optical transmitter and a plurality of optical receivers are connected by an optical fiber and an optical distributor to perform optical subcarrier transmission. Code generating means for generating a plurality of different spreading codes corresponding to analog signals; spectrum spreading means for spreading and outputting the plurality of input analog signals based on the corresponding spreading codes, respectively; Combining means for combining and outputting the output signals of the above, and electrical / optical converting means for converting an electric signal, which is an output signal from the combining means, into an optical signal and sending the optical signal to the optical fiber. Optical / electrical conversion means for converting an optical signal transmitted through the optical fiber into an electric signal, and an output signal from the optical / electrical conversion means, An optical subcarrier transmission system, comprising: spectrum despreading means for despreading a spectrum based on a spreading code and outputting an original analog signal. 3. An optical subcarrier transmission system in which a plurality of optical transmitters and an optical receiver are connected by an optical fiber and an optical combiner to perform optical subcarrier transmission, wherein each optical transmitter has a spreading code. Code generating means for generating, spread spectrum means for spreading and outputting an input analog signal based on the corresponding spread code, and converting an electric signal, which is an output signal from the spread spectrum means, into an optical signal; An optical / electrical conversion unit for transmitting the optical signal to the optical fiber; an optical / electrical conversion unit for converting an optical signal transmitted through the optical fiber into an electrical signal; and the optical / electrical conversion unit. A distributing means for distributing and outputting the output signal from the plurality of analog signals based on a predetermined spreading code; An optical subcarrier transmission system, comprising: spectrum despreading means for outputting a signal. 4. The optical subcarrier transmission system according to claim 1, wherein said electric / optical conversion means uses a Fabry-Perot semiconductor laser as a light source. 5. The optical subcarrier transmission system according to claim 2, wherein the plurality of input analog signals have the same carrier frequency. 6. The optical subcarrier transmission system according to claim 1, wherein the spread spectrum means spreads the spectrum of the input analog signal by frequency hopping based on a spread code and outputs the spread spectrum signal.