JPS6134305B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to an optical transmission system in so-called optical communication, in which an electric signal is transmitted through electrical-to-optical conversion on a transmitting side, and an electrical signal is regenerated from an optical signal on a receiving side.

(2) Prior art Semiconductor light emitting elements such as semiconductor lasers and light emitting diodes are used as light sources in optical communication equipment, but due to their nonlinearity, Bi-
Binary codes such as phase and RZ codes are used. However, the RZ code has drawbacks such as difficulty in timing extraction, large effect of low-frequency cutoff, and difficulty in constantly monitoring errors. Bi
-Phase codes eliminate these drawbacks, but
Since the mark rate is always 50% and the current density increases, this tends to shorten the life of the semiconductor light emitting device, which is a major problem in ensuring the reliability of the transmission system.

(3) Purpose of the Invention The purpose of the present invention is to solve the problem of Bi-
It is an object of the present invention to provide an optical transmission system that performs transmission using a code with a small mark rate while retaining the characteristics of a phase code.

(4) General description of the invention The present invention is characterized in that the "1" level of the Bi-phase code is shortened to an arbitrary time width and then transmitted. In this case, an NRZ-Bi-phase code converter is used on the transmitting side, but a Bi-phase-
It has the advantage of not requiring an NRZ code converter, and
It is possible to construct a device with the same or lower cost than a transmission device using phase codes. In addition, in the explanation of the example, Bi-
FM code is used as the phase code.

(5) Examples Hereinafter, the present invention will be explained in detail with reference to examples. FIG. 1 is a time chart showing the operation of the present invention. In the same figure, a is the original signal NRZ, b is Bi-
It is a phase code, and its conversion is performed by an existing code converter. In the conventional example, this Bi-phase code was transmitted as is, but in the present invention, this and the inverted code of b, which is delayed by an arbitrary time τ (1/4 time slot in Fig. 1), are combined. The code (d) in FIG. 1 obtained by calculating the logical product is transmitted as a transmission code.
FIG. 1e shows an example of the waveform of d that has been photoelectrically converted on the receiving side, and when this is equalized to obtain the optimum waveform for identification, the waveform as shown in FIG. 1f is obtained. The signal of f is 2
₀ (time slot T=1/ ₀ ), so if this is extracted and shaped, a timing pulse g can be obtained. If the signal f is identified from this, a signal h can be obtained. This signal becomes the output of the repeater, and the NRZ code can be directly reproduced from it. For this, the signal in Figure 1 h and this 1
The exclusive OR signal with signal i delayed by time slot T can be identified by clock ₀ of j. Signal k is obtained by performing a negative exclusive OR of signal h and signal i at the timing of clock j. Signal k is nothing but a reproduction of original signal a.

FIG. 2 is a block diagram showing one embodiment of the present invention. This will be explained below with reference to FIG. First, the original signal NRZ in FIG.
Convert it to phase, and then use the pulse width setting device 3 to
The transmission code shown in FIG. 1d is generated. In order to optically transmit this, this code is first converted from voltage to current in the drive circuit 4, and then the semiconductor light emitting device 5 is modulated with the current, thereby obtaining an optical signal of the same form as shown in Fig. 1d. can. Next, this optical signal is sent to the optical transmission line 6, and on the receiving side, it is photoelectrically converted by the optical receiver 7 and equalized and amplified by the equalizing amplifier 8. This output signal is shown in _FIG . Here, automatic gain control can also be performed by the AGC circuit 8 using the signal shown in FIG. 1 f. The signal shown in FIG. 1f is identified by the timing clock 1g in the discriminator 9, and the signal shown in FIG. 1h is obtained as its output.

In Fig. 2, the part surrounded by the broken line is the constituent block of the optical repeater, and the output of this repeater is the first one.
The two signals h and g in the figure are obtained and are supplied to the reproducing circuit 11. In the reproduction circuit 11, these two
The original signal is reproduced from the two signals through the processes h to k in FIG. 1, and is output to the terminal 12.

Next, the specific contents of the pulse amplification setter 3 and the original signal regeneration circuit 11 will be explained. FIG. 3 is a connection diagram showing the third embodiment. Terminal 21 is an input terminal for a signal (FIG. 1b) supplied from 2, and one side of this input signal is input to the first terminal of AND circuit 23.
The other input terminal is supplied to the second input terminal 23 after its polarity is inverted with a delay of time τ in the delay circuit 22, and the logical product is performed at 23. Therefore, after this operation, a signal as shown in FIG. 1d is obtained at the terminal 24.

FIG. 4 is a connection diagram showing one embodiment of the original signal reproducing circuit 11. The terminal 31 is a signal input terminal supplied from the discriminator 9, one of the discrimination outputs (h in FIG. 1) is input to the first terminal of the negative exclusive OR circuit 33, and the other is input to the delay circuit 32 for one time slot. After being given a delay of T, the signal is supplied to the second terminal of 33 and is configured to perform a negative exclusive OR at 33, and the output of 33 is supplied to the Data input terminal of the discriminator 34. On the other hand, the clock at ₂₀ is at terminal 3.
7, but in order to reproduce the original signal,
Since it is necessary to create a ₀ original clock,
After dividing this signal by a frequency dividing circuit 35, it is supplied to a clock terminal 34. If the phase difference between the data input signal and the clock input signal is set as shown in FIG. 1, the original signal k in FIG. 1 can be immediately obtained at the output terminal 36.
Note that it is obvious that a phase difference of up to 1/2 time slot can be tolerated. Further, 33 may be an exclusive OR circuit, and in this case, the output of 34 is taken out from a terminal. It will be clear that error monitoring can be easily performed by taking advantage of the fact that the "1" level shown in FIG. 1h does not last for more than two time slots.

(6) Summary As explained above, according to the present invention, Bi-
Without losing the advantages of phase codes, such as easy timing extraction, resistance to low-frequency cutoff, and error monitoring, the mark rate of optical transmission signals can be significantly lowered, and semiconductor light emitting The life of the element can be extended. Another advantage is that the Bi-phase-NRZ converter can be omitted, and the scale of the equipment can be the same as or smaller than conventional systems, so it can be expected to have great effects when applied to the field of optical communications.

[Brief explanation of the drawing]

FIG. 1 is a time chart for explaining the operating principle of the present invention, FIG. 2 is a diagram showing a block configuration of an optical transmission device realizing the present invention, and FIG. 3 is a diagram showing a transmission code according to the present invention. FIG. 4 is a connection diagram showing an embodiment of the original signal reproducing circuit according to the present invention.

Claims (1)

[Claims] 1. In an optical transmission system that converts an NRZ signal into a biphasic code, transmits the biphasic code as an optical signal, and receives the optical signal to reproduce the NRZ signal, the biphasic code is composed of a frequency modulation signal, and the biphasic code is An AND signal of a modulated signal and a signal obtained by inverting the frequency modulation signal and delaying the frequency modulation signal by an arbitrary time within 1/2 time slot is transmitted as the optical signal, and the optical signal is photoelectrically converted. identify and generate a reproduced signal from the received signal and the timing pulse extracted from the received signal;
An optical transmission system characterized in that the reproduced signal is discriminated from a signal delayed by one time slot at a period of 1/2 of the timing pulse, and the NRZ signal is reproduced.