JPS6267937A - Pulse analog optical communication system - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution of an optical transmitter and to prevent the deterioration of the reproducibility of a signal due to waveform distortion by using a pulsized FM signal to drive a light emitting element thereby sending an optical pulse signal at the transmission side and reproducing the said pulsized FM signal at the reception side to demodulate an analog signal from a voltage pulse train. CONSTITUTION:An analog signal S1 inputted to the transmitter is converted into a pulsize FM signal having a duty ratio 50% by a pulsized FM modulation circuit 1 and converted into the optical pulse signal S3 of the same waveform by an optical signal transmission circuit 2 and then sent. The optical pulse signal S3 is received by an optical signal reception circuit 3 in the same receiver, photoelectric-converted and the pulsized FM signal is reproduced. Then the leading of the pulsized FM signal is detected by a PFM modulation circuit 4, form which the signal is converted into the PFM modulation signal S4 having the prescribed width of pulse and the PFM modulation signal S4 is demodulated into the analog signal S5 by the PFM demodulation circuit 5. Thus, the control circuit is constituted simply and the stability of operation is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pulse analog optical communication system that converts an analog signal into an optical pulse signal and transmits the optical pulse signal.

Conventional technology] Generally, on the transmitting side of pulse analog optical communication system,
After the input analog signal is pulse-modulated by an electric circuit, a light emitting element is driven by the obtained pulse train to output an optical pulse signal with the same waveform as this pulse train.On the other hand, on the receiving side, the received optical pulse By the way, there are various methods of pulse modulation for converting the signal (original signal) into pulses. In addition to pulsed FM modulation that slices the FM modulation wave of the original signal, pulse frequency modulation (PFM) that changes the frequency of the pulse in proportion to the amplitude of the original signal,
Pulse width modulation (PWM) that changes the pulse width, Pulse number modulation (PNM) that changes the number of pulses within a unit time,
Change the pulse price by 1! Pulse position modulation (PPM)
etc. are used.

Among these pulse modulation methods, the one that can be realized with the simplest circuit configuration is pulsed FM modulation, and an example of the configuration of a conventional optical communication system that employs this pulsed FM modulation method is shown in Figure 4. First, an analog signal input to a pulsed FM modulation circuit 41 in an optical transmitter is subjected to pulsed FMI modulation and converted into a binary pulse signal. Next, this pulse signal is converted into an optical pulse signal with the same waveform by the optical signal transmitting circuit 42 and transmitted. This optical pulse signal is photoelectrically converted by the optical signal receiving circuit 43 of the optical receiver, and further demodulated into an analog signal by the FM demodulation circuit v844.

On the other hand, the PFM, PWM, PN, M, and P)) M modulation schemes are each implemented using similar circuit configurations; - As an example, the configuration of a conventional optical communication system employing the PFM modulation scheme is shown in Fig. 5. . In the optical transmitter, P
The analog signal input to the FM modulation circuit 51 is P F'
After being M-modulated and converted into two pulse signals, the signal goes up to the optical signal transmission circuit 52, where it is converted into an optical pulse signal with the same waveform and transmitted. This optical pulse signal is converted into an electrical signal by an optical signal receiving circuit 53 of the optical receiver, further waveform-shaped by a waveform shaping circuit 54 composed of a mono-multivibrator, etc., and then by a PFM demodulation circuit 55. demodulated into a signal.

[Problems to be Solved by the Invention] However, in the optical communication system using pulsed FM modulation, although the circuit configuration is in a cylinder, waveform distortion etc. are likely to occur during transmission, reception and reproduction of optical pulse signals. There was a problem in that the reproducibility of the A-JU1 signal obtained by FM demodulation deteriorated.

Furthermore, the PFM modulation circuit 51 used in the PFM modulation type optical transmitter shown in FIG. 5 is generally composed of a pulsed FM modulation circuit 51a and a mono-multiviparator 51b that keeps the output pulse width constant. Compared to the pulsed FM modulation method shown in FIG. 4, the configuration of the optical transmitter is particularly complicated. This applies not only to PFM modulation, but also to C in PWM, PNM, and l) l'M modulation. Furthermore, these modulation methods include pulsed FM modulation method and v4
As a result, the duty ratio of the optical pulse signal changes depending on the input ANO-II signal temperature level. Therefore, the light output for the light emitting element in the optical transmitter is automatic! 1111 (AP
C> Install a circuit or add automatic control (11 control) to the optical receiver.
When an AGC (AGC) circuit is provided, there is a problem that the configuration of these APC circuits or AGC circuits is complicated.

[Object of the invention] The object of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a pulse analog optical communication system that can simplify the circuit configuration of an optical communication system, particularly an optical transmitter, and prevent deterioration of signal reproducibility due to waveform distortion.

[Summary of the Invention 1] In order to achieve the above 2 objectives, the present invention converts an input analog signal into a pulse on the transmitting side [after converting the input analog signal into a pulsed FM signal with a duty ratio of 50% through M modulation, FM signal - A light emitting element is driven to transmit an optical pulse signal, and on the receiving side, the received optical pulse signal is photoelectrically converted into a pulsed FM (after reproducing No. 8, the frequency of this pulsed FM signal is changed to The average value of the pulse changes proportionally -
This voltage pulse train is converted into a voltage pulser 11 such as that shown in FIG.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an embodiment of a pulse analog optical communication system according to the present invention. In FIG. 1, the optical transmitter includes a pulsed FM modulation circuit 1 and an optical signal transmission circuit 2 connected thereto. The pulsed FM modulation circuit 1 inputs an analog signal 81, performs FM modulation on it, and generates a binary pulsed FM signal QS2 with a duty ratio of 50%.
It is composed of, for example, a VCO (voltage + controlled oscillator) IO. The optical signal transmission circuit 2 includes a light emitting element, and receives the pulsed "M signal S" output from the pulsed FM modulation circuit 1.
2 to drive the light emitting element (), pulse [M-signal QS2
An optical pulse signal S3 having the same waveform as @ is output. On the other hand, the optical receiver is composed of an optical signal receiving circuit 3, 1) an FM modulation circuit 4 connected to the output terminal thereof, and a PFM demodulation circuit 5 further connected to the output terminal of the PFM modulation circuit 4.

The optical signal receiving circuit 3 is a general-purpose digital optical receiver equipped with a light receiving element, and receives the optical pulse signal 83 and photoelectrically converts it into an electrical signal having the same waveform. The PFM modulation circuit 4
8 @ It converts the electrical signal output from the receiving circuit 3 into a PFM modulated signal S4, and is composed of, for example, a mono-multivibrator that reproduces pulses of a constant width. The PFM demodulation circuit 5 is composed of a low-pass filter, etc.
Converts the FM conversion signal @34 into an analog signal SS.

Next, the operation of this embodiment will be explained with reference to the signal waveform diagram in FIG.

First, the analog signal 81 input to the transmitter is converted into a pulsed FM signal @S2 with a duty ratio of 50% by the pulsed FM modulation circuit 1, and further converted into an optical pulse signal 83 with the same waveform by the optical signal transmission circuit 2. and sent. This optical pulse signal 83 is received by the optical signal receiving circuit 3 in the receiver, where it is photoelectrically converted and regenerated into a pulsed 1-M signal. Next, this pulsed FM signal is detected by an FM modulation circuit 4 whose rising edge is converted into a PFM FM modulation circuit 4 having pulses of a constant width, and the PFM modulation signal S4 is roughly converted into a PFM demodulation circuit 5. Wlli is applied to the analog signal S5.

In this embodiment, PFM modulation and demodulation is used in the receiver, but the present invention is not limited to this.

A modulation/demodulation method such as PNM or PPM may also be used.

Further, as the light emitting element in the optical signal transmitting circuit 2, a laser diode, a light emitting diode, etc. can be used, but the duty ratio of the optical pulse signal S3 to be output is 50.
Since it is fixed at %, an automatic light output control circuit can be easily constructed, especially when a laser diode is used, and stable light output can be obtained. In general, a general-purpose digital optical transmitter can be used.

On the other hand, for the light-receiving element in the optical signal receiving circuit 3, a photo diode, an avalanche A-type diode, and the like can be used. You can make a selection.

Furthermore, the output from the optical signal receiving circuit 3 is modulated by the next stage P[M modulation circuit 4 and converted into a new pulse train, so that
Even if some waveform distortion occurs due to the light receiving element in the optical signal receiving circuit 3, it will be corrected by the 11 FM modulation circuit 4. Therefore, there is no need to use an expensive, high-performance element as the light receiving element.

[Effects of the Invention] As explained above, the present invention exhibits the following excellent effects.

(1) Since the analog input is pulsed FM modulated and an optical pulse signal with a duty ratio of 50% is transmitted, the circuit configuration of the optical transmitter can be simplified, especially when a laser diode is used as the light emitting element. The automatic optical output control circuit of the optical receiver and the automatic control circuit of the optical receiver can be easily configured, thereby reducing the cost of the communication system and improving the stability of its operation.

(2) On the receiving side, the received optical pulse signal is
Since the signal is converted into another voltage pulse train using a modulation method such as FM, PWM, PNM, or PPM, and then demodulated into an analog signal, even if waveform distortion occurs during transmission, reception, and reproduction of the optical pulse signal, this distortion is not corrected. Therefore, the re-flatness of the signal is improved.

(3) Therefore, the present invention is extremely useful in transmission systems for analog image signals, audio signals, and other analog signals using optical fibers.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an optical communication system according to the present invention, FIG. 2 is an operational waveform diagram of the optical communication system of FIG. 1, and FIG. 3 is an explanatory diagram showing various pulse modulation methods. Fourth
5 and 5 are respectively block diagrams of a conventional optical communication system. In the figure, 1 is a pulse conversion [M modulation circuit, 2 is a Kohakuzuki transmission circuit, 3 is an optical signal receiving circuit, 4 is a 1) FM modulation circuit, and 5 is a P
PM demodulation N ways. Patent applicant: Hvt Electric Cable Co., Ltd. Attorney-[
Kinutani Butsu A (j4, 'I'FM history control circuit ~ 5: PFn demodulation circuit Figure 2

Claims (2)

[Claims] (1) On the transmitting side, the input analog signal is
After modulating and converting it into a pulsed FM signal with a duty ratio of 50%, this pulsed FM signal drives a light emitting element to transmit a light pulse signal.On the receiving side, the light received by the light receiving element is After reproducing a pulsed FM signal by photoelectrically converting the pulse signal, the pulsed FM signal is
A pulse analog optical communication system characterized in that an M signal is modulated into a voltage pulse train, and an analog signal is further demodulated from this voltage pulse train. (2) The modulation to the voltage pulse train mentioned above is pulse frequency modulation (PFM), pulse width modulation (PWM), pulse number modulation (
2. The pulse analog optical communication system according to claim 1, wherein the pulse analog optical communication system is one of PNM) and pulse position modulation (PPM).