JP4399571B2 - Communication system using optical fiber - Google Patents

Description

BACKGROUND OF THE INVENTION
The present invention relates to a transmission system that converts an analog signal into a PWM wave of 5 MHz or less to transmit a plurality of voices and the like and performs communication using a single optical fiber.
[Prior art]
In the conventional method of transmitting a plurality of analog signals, all signals to be transmitted by the transmission unit are A / D converted to a carrier wave of 20 MHz or more, further converted into an optical signal, incident on an optical fiber, and received by a reception unit. Many methods have been used that convert the converted signal into a digital signal, perform D-A conversion, and transmit.
[Problems to be solved by the present invention]
The conventional transmission method has the following problems.
First, A-D conversion is performed in the light emitting unit to obtain an optical signal. Therefore, when digitalization is performed, a high frequency of 20 MHz or more is often required, the conversion unit is required to have high accuracy, and the light emitting unit performs high-speed blinking. Therefore, the performance of the light emitting element is also required. Even in the light receiving portion, there is a drawback that the circuit becomes complicated due to the performance of the light receiving element and the accuracy required for the DA conversion, and the cost increases.
[Means for solving the problems]
The present invention has been devised to solve these problems.
First, when one of the two types of audio analog signals is A and the other is B, B is input to the primary modulation unit and modulated to the PWM signal B ′, and is synthesized by the synthesis unit to be A + B ′, and the signal is converted into a PWM wave. The light is converted into (A + B ′) ′ and converted into an optical signal (A + B ′) in the light emitting section. This signal enters the optical fiber from the transmitter and is transmitted.
The receiving unit has a light receiving unit that converts a received signal into an electrical signal via an optical fiber, converts it to (A + B ′) ′, converts it into an A + B ′ signal in the primary demodulation unit, and branches this signal. One is passed through the LPF and the other is passed through the HPF, and after passing through the LPF on one side, the A signal is output from the amplifier. The other side passes through the waveform shaping section that has passed through the HPF, and is secondarily demodulated and then output through the LPF. After passing through the HPF, there is a B ′ signal and an A signal (residual signal) a that cannot be completely deleted by the HPF. When it reaches the waveform shaping unit, it is shaped into a stable PWM wave by the comparator, the time when the rising waveform falls by using a one-shot multivibrator can be corrected, and other than B 'signal can be removed. Since the signal frequency can be transmitted and demodulated through an optical fiber without changing to a high frequency carrier wave such as 20 MHz or higher, it is not necessary to widen the frequency band interval to provide a margin, thereby solving the above problem.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a communication system, and 1 is an analog signal generator for generating an analog signal A. An analog signal generator 2 generates an analog signal B. The analog signal B is PWM-converted by the primary modulation unit 3 and converted into a B ′ signal. A combining unit 4 combines the A signal and the B ′ signal and transmits it as an A + B ′ signal. The secondary modulation unit 5 performs PWM conversion on the A + B ′ signal, modulates it to an (A + B ′) ′ signal, converts it to an optical signal OPT (A + B ′) ′ by the light emitting unit 6, and inputs it to the optical fiber 7 from the transmission unit X. When the light output from the optical fiber 7 reaches the receiving unit Y, the light receiving unit 8 converts it into an electrical signal (A + B ′) and transmits it. The primary demodulator 9 converts the signal into an A + B ′ signal, branches one of the LPFs 10 and the other HPF 11. When the LPF 10 is reached, the B ′ signal is deleted, becomes an A signal, and is amplified and output by the amplifier 17.
After branching, when the A + B ′ signal on the other side reaches the HPF 11, the A signal is deleted. However, the HPF with a simple configuration has a poorer frequency characteristic than the LPF with a simple configuration, so the residual component a of the A signal Is transmitted together with the B ′ signal, the B ′ + a signal reaches the waveform shaping unit YY, is shaped into a stable PWM wave by the comparator 12, and further, the waveform is determined by the one-shot multivibrator 13 from the rise to the fall. Therefore, the residual component a can be removed, and the demodulated circuit can be demodulated by a circuit that is less complicated than the case of demodulating an analog signal encoded using A-D conversion or the like. After the waveform shaping, the B ′ signal from which the residual component has been deleted is demodulated by the secondary demodulator 14, and the demodulated B signal passes through the LPF 15 and is amplified and output by the amplifier 16.
【effect】
As described above, it is possible to modulate and synthesize a plurality of analog signals without transmitting complicated A-D conversion and D-A conversion, and transmit them through a single optical fiber. By using a multivibrator, separation performance can be improved, transmission can be performed without requiring a complicated and high-performance circuit, and cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a communication system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Analog generator 2 ... Analog generator 3 ... Primary modulation part 4 ... Synthesis | combination part 5 ... Secondary modulation part 6 ... Light emission part 7 ... Optical fiber 8 ... Light reception part 9 ... 1 Next demodulator 10 ... LPF 11 ... HFP
12 …… Comparator 13 …… One-shot multivibrator 14 …… Secondary demodulation unit 15 …… LPF 16 …… Amplification unit 17 …… Amplification unit X …… Transmission unit Y …… Reception unit YY …… Waveform shaping unit

Claims (1)

In the case of transmitting two types of audio analog signals over a single optical fiber, the signals are multistage modulated and synthesized, converted to a PWM wave of 5 MHz or less, converted into an optical signal, and then transmitted into two types of audio analog. One of the signals is A, the other is B, B is input to the primary modulation unit and modulated to the PWM signal B ′, synthesized at the synthesis unit to be an A + B ′ signal, and the A + B ′ signal at the secondary modulation unit (PWM signal ( It has a transmitter that modulates to A + B ′) ′, converts it into an optical signal {OPT (A + B ′) ′} in the light emitting unit, and transmits it. After OPT (A + B ′) ′ reaching the receiving unit is converted into an electrical signal (A + B ′) ′ by the light receiving unit, it is demodulated by the primary demodulating unit to be an A + B ′ signal, branched, and one of them passes through a low-pass filter (LPF). The other side passes through a high pass filter (HPF), and the A signal after passing through the LPF is output from the amplifying unit on one side. The other side is a comparator for deleting the residual component a when B ′ + a reaches the waveform shaping section when the B ′ + a reaches the waveform shaping unit after passing through the HPF and the combined signal of the B signal and the residual signal a of the A signal that cannot be deleted by the HPF. Then, a is deleted using a one-shot multivibrator, and the B ′ signal that has passed through the waveform shaping unit passes through the secondary demodulation unit, becomes a B signal, passes through the LPF, and is output from the amplification unit. With the configuration as described above, a plurality of analog signals can be transmitted by a single optical fiber with a carrier wave of 5 MHz or less by synthesizing and separating analog signals without performing complex A-D conversion. system.

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