JP2000151559A - Optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the communication system that transmits a signal by having only to provide one optical fiber line in transmission and reception directions without provision of the optical fiber line to each signal in the case that a main line signal and a data signal are transmitted between devices. SOLUTION: An RF synthesis section 13 and an RF distribution section 19 are provided to the system in addition to conventional circuits. An RF signal substantially to be sent, a base band signal used to monitor and control devices and a data signal such as a voice band signal for maintenance are transmitted by having only to provide one optical fiber line 15 in transmission and reception directions without causing mutual interference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical communication system,
In particular, the present invention relates to an optical communication system for transmitting a data signal such as a baseband signal and a voice band signal used for monitoring and controlling between devices using an optical fiber.

[0002]

2. Description of the Related Art In recent years, in a communication system using subcarrier analog optical transmission, compared to a metal cable, an optical fiber capable of realizing communication over a wide band with low transmission loss has been developed due to non-crosstalk characteristics due to non-induction. It is used more frequently, and is used as a transmission system between a relay amplifying device and a base station particularly in a mobile phone, a CATV or the like.

In the subcarrier analog optical transmission using such an optical fiber, apart from the main line signal, a baseband signal for monitoring / control of the apparatus, a voice band signal for maintenance personnel talking during maintenance, etc. When transmitting a data signal, a transmission signal and a data signal are transmitted as shown in FIG. 4, optical fibers 92 and 95 are provided respectively, and a modulation 97 on the transmission side and a demodulation 98 on the reception side are performed. Was adopted.

In addition, when an inexpensive FP-LD is used as the E / O, it has been reported that the distortion characteristic of the LD itself is improved by superimposing a signal having a frequency of about 20 to 30 MHz on the main line signal. ("Study on application of Fabry-Perot laser to optical SCM transmission for wireless base stations" by Sasai, Yamamoto, Utsumi and Fujito, "The 3rd Tohoku University Research Institute of Electrical Communication, Joint Research on Millimeter-wave Charged Waves" Research on ").

[0005]

However, in the conventional optical transmission system, when transmitting the main signal and the data signal, one optical fiber must be used for each signal, so that the cost is inevitably increased. There was a problem that.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a communication system using subcarrier analog optical transmission, in which a single optical fiber line is provided and monitoring between devices is performed without affecting an RF signal to be transmitted. , Baseband signals used for control, etc.,
An object of the present invention is to provide an optical communication system capable of transmitting a data signal such as a voice band signal for communication between a base station and a relay station by maintenance personnel during maintenance.

[0007]

To solve the conventional problems, according to the invention described in claim 1, the transmitting side modulates a signal having a frequency outside the occupied band of the RF signal to be transmitted as a carrier wave. The data signal filtered by the low-pass filter is combined with the RF signal to be transmitted, which is filtered by the high-pass filter, in an RF combining circuit, and the combined electric signal is converted into an electro-optical conversion element (E / O). The analog signal is converted to an analog optical signal and transmitted, and on the receiving side, the analog optical signal transmitted from the transmitting side is converted into an electric signal by an optical-electrical conversion element (O / E), and the electric signal is converted to an RF distribution circuit. To separate the RF signal and the modulated data signal, filter the RF signal obtained by the separation with a high-pass filter, and filter the modulated signal obtained by the separation with a low-pass filter. An optical communication system characterized by extracting the original data signal by filtering and demodulating the data signal can be provided.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an RF circuit in addition to a conventional circuit.
By providing a combining unit and an RF distribution unit, an RF signal that should be transmitted over a single optical fiber line in the transmission and reception directions, a baseband signal used for monitoring and control between devices, and a base station for maintenance Provide a device capable of transmitting data signals such as voice band signals for inter-relay communication without affecting each other. Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. On the transmitting side, in order to use a low-frequency wave outside the occupied band of the RF signal to be transmitted (hereinafter, main line signal) as a carrier,
The modulation circuit 20 modulates the data signal.
The low band of the modulated signal thus obtained is filtered by the low-pass filter 12, and the filtered low band signal is
The RF signal is combined with the main signal by the RF combining unit 13. Such a combined electric signal is converted into an optical signal by an electro-optical conversion element (E / O) 14 and transmitted to a receiving side via an optical fiber line 15. On the receiving side, the optical signal transmitted from the transmitting side is converted into an electric signal by an optical-electrical conversion element (O / E) 16. This electric signal is separated into a main signal and a modulation signal by the RF distributor 19. Since the modulated signal is demodulated by the demodulation circuit 21, the original data signal can be extracted.

FIG. 2 shows an embodiment in which the data signal is a voice band signal. Each of the base station 30 and the relay station 40 is provided with a transmission unit and a reception unit, and is capable of two-way communication. The voice signal from the base station 30 to the relay station 40 is modulated by the modulation circuit 33, combined with the main signal by the RF combining unit 31, and electrically transmitted by the E / O 32.
After the optical conversion, it is transmitted to the relay station 40 through the optical fiber 51. Then, in the relay station 40, after the optical / electrical conversion by the O / E 41, the signal is separated from the main line signal by the RF distribution unit 42, demodulated by the demodulation circuit 43, and extracted as an audio signal. From the relay station 40 to the base station 30
The audio signal transmitted to the modulation circuit 4
4, RF combining section 45, E / O 46, optical fiber 52, O
/ E26, RF distribution section 35, and demodulation circuit 34. Thereby, at the time of maintenance, the base station 30 is
And the communication between the relay station 40 and the relay station 40 are enabled.

FIG. 3 shows an embodiment in which a baseband signal such as control / monitoring information output from the CPU is modulated using a modem, and the modulated baseband signal is used as a data signal. The base station 60 and the relay station 70 have a transmission unit and a reception unit, respectively, and are capable of two-way communication. The baseband signal transmitted from the base station 60 to the relay station 70 is modulated by the modem 64 and then modulated by the modulation circuit 63.
Are subjected to secondary modulation, are combined with the main signal by the RF combining unit 61, are electro-optically converted by the E / O 62, and are transmitted to the relay station 70 through the optical fiber 81. In the relay station 70, after the optical / electrical conversion by the O / E 71, it is separated from the main line signal by the RF distribution unit 72, and the secondary-modulated baseband signal is demodulated by the demodulation circuit 73 and further demodulated by the modem 74. As a result, it is extracted as an original baseband signal.

The baseband signal transmitted from the relay station 70 to the base station 60 is processed in the same procedure as the modem 74, the modulation circuit 75, the RF combining section 76, the E / O 77, the optical fiber 8
2, transmitted to the O / E 67, the RF distribution unit 66, the demodulation circuit 65, and the modem 64. As a result, alarm information, control information, and the like of each station can be communicated, remote control and setting of each device can be performed, and monitoring, adjustment, and maintenance of each device are facilitated.

As a configuration of the modulation circuit, an oscillation (resonance) circuit using an inductor L and a capacitor C may be used.
In this case, FM modulation is performed by changing the resonance frequency by using a varicap whose capacitance changes according to the signal voltage. Alternatively, FM modulation may be performed directly by changing the oscillation frequency according to the voltage of the data signal using a voltage-controlled crystal oscillation circuit (VCXO). Also, as already described in the paragraph 4, when an inexpensive FP-LD is used as the E / O, 2
By superimposing a signal having a frequency of about 0 to 30 MHz on the main signal, the distortion characteristics of the LD itself are improved.

[0014]

According to the present invention, a main signal and a data signal such as a voice band signal and a base band signal are superimposed with only one optical fiber, and transmission is performed without distortion of the main signal affecting the data signal. It is possible to do. In addition, by adding simple circuits such as a modulation / demodulation circuit and a synthesis / distribution circuit, it is possible to communicate by voice between devices and to communicate alarm information and control information of the devices. And monitoring, adjustment and maintenance of the device become easy. Therefore, in the modulation of the baseband modem signal, the modulation method has a constant amplitude and the carrier frequency is 20 to 30 MHz.
By using a frequency of about z, the distortion characteristics of the LD can be improved, and the cost can be reduced while improving the characteristics of the system.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a second embodiment relating to transmission of a voice band signal of the present invention.

FIG. 3 is a block diagram showing a third embodiment relating to baseband signal transmission of the present invention.

FIG. 4 is a block diagram showing an example of a conventional system.

[Explanation of symbols]

11, 17 High-pass filter 12, 18 Low-pass filter 13, 31, 45, 61, 76 RF synthesis unit 14, 32, 46, 62, 77, 91, 94 E / O
(Electric / optical converter) 15, 51, 52, 81, 82, 92, 95 Optical fiber 16, 36, 41, 67, 71, 93, 96 O / E
(Optical / Electric Conversion Unit) 19, 35, 42, 66, 72 RF Distribution Unit 20, 33, 44, 63, 75, 97 Modulation Circuit 21, 34, 43, 65, 73, 98 Demodulation Circuit 30, 60 Base Station 40,70 relay station 64,74 modem

Continued on the front page F term (reference) 5K002 AA01 AA03 AA05 AA06 BA13 CA01 CA17 DA01 DA04 FA01 GA02 GA03 5K042 AA08 BA06 CA10 EA02 FA21 LA04 LA05 MA01

Claims (1)

[Claims] On the transmitting side, a signal having a frequency outside the occupied band of an RF signal to be transmitted is modulated as a carrier, and a data signal filtered by a low-pass filter is transmitted by a high-pass filter. An RF signal;
The electric signal is synthesized by an RF synthesizing circuit, and the synthesized electric signal is converted into an analog optical signal by an electro-optical conversion element (E / O) for transmission. On the receiving side, the analog optical signal transmitted from the transmitting side is converted. The signal is converted into an electric signal by an optical-electrical conversion element (O / E), the electric signal is separated into the RF signal and the modulated data signal by an RF distribution circuit, and the RF signal obtained by the separation is filtered by a high-pass filter. An optical communication system characterized in that a modulated signal obtained by the separation is filtered by a low-pass filter, and an original data signal is extracted by demodulation.