JPH04167633A - Optical digital transmission method - Google Patents

Abstract

PURPOSE:To detect an optical digital signal by a simple code string by driving a light emitting element by a signal that is a pulse signal generated in a different direction in accordance with a direction of change at the change point of a binary signal, and whose peak on the side shows nearly zero. CONSTITUTION:The light emitting element is driven by the signal (D) that is the pulse signal generated in the different direction in accordance with the direction of change at the change point of the binary signal and whose peak on one side shows nearly zero. In other words, an input signal is an NRZ signal, and it is converted to a ternary signal like the signal (D) by a signal converter 2, and dries a laser diode 4 by a modulator 3. When such optical output is received by a light receiving element 11, a detection signal almost similar to the signal (D) can be obtained. When a mean value is detected by passing the detection signal through, for example, a low-pass filter LPF 17, the output of the LPF 17 can be detected as far as the optical signal is detected. Thereby, when no optical signal is transmitted, no output of the LPF 17 is detected, therefore, a fault can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for transmitting optical digital signals used in optical communication systems and the like.

(Prior Art) Conventionally, NRZ signals have been used in optical digital link transmitters. The NRZ signal is a binary signal of "1" and r OJ, as shown in Figure 3 (A).
1" continues, it continues to take a high (H) value, and r
While OJ continues, the signal continues to take a low (L) value. Usually, in the case of L, the value is zero. In a receiver receiving such a signal, there is no optical input when the signal is zero. Since there is no optical input even when the optical transmission line is disconnected, various techniques are used for transmission codes to distinguish between a zero signal state and a disconnected optical transmission line state.

The burst transmission method using subcarriers and the Manchester code conversion method, which sends a constant pulse train even when the signal is zero, are known as code conversion methods that can distinguish between a zero signal state and an optical transmission line disconnection state. There is.

However, in the burst transmission method, the transmission band of the subcarrier is required to be at least five times the transmission band of the transmission signal, which places a heavy burden on the transmitting and receiving circuit. In addition, in the Manchester code conversion method, in order to create a pulse train to be added, N
A clock signal is required along with the RZ signal.

Therefore, none of the conventional code conversion methods is sufficient.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and it is possible to transmit an optical digital signal using a simple code string, and also easily obtain a signal for automatic output adjustment. The object of the present invention is to provide an optical digital transmission method that performs transmission using a signal that can be used.

(Means for Solving the Problems) In an optical digital transmission method, the present invention provides a pulse signal that is generated in different directions depending on the direction of change at a change point of a binary signal, and that has one peak. This is characterized in that the light emitting element is driven by a signal whose value is approximately zero.

The NRZ signal can be differentiated into a signal in which one peak of the signal is approximately zero, and the light emitting element can be driven by the converted signal.

(Function) When the NRZ signal in Figure 3 (A) is differentiated, as shown in Figure 3 (B), it is positive when the NRZ signal rises from L to H, negative when it falls from H to L, and negative when it falls from H to L. Alternatively, when L does not change, a ternary signal becomes zero. The signal obtained by shaping this waveform is shown in FIG. 3(C). For example, by adding a DC component that is half the difference between the positive peak and the negative peak to this signal, one peak, the negative peak, is made to be approximately O, as shown in Figure (D). . This is the drive signal that drives the light emitting element.

When the light output of the light emitting element modulated by this drive signal is received by a light receiving element, a detection signal substantially similar to that shown in FIG. 2(D) can be obtained. When the detection signal is passed through, for example, a low pass filter (LPF) and the average value is detected, the output of the LPF can be detected as long as the optical signal is detected. If the optical signal is not sent due to a failure such as a break in the optical transmission line, the failure can be detected although the output of the LPF cannot be detected. Of course, even if the zero state continues, LP
The output of F is present and can be easily distinguished from a failure.

In addition, since the output of the LPF is related to the energy of the optical signal, this output allows automatic output adjustment (
APC) can be performed.

Furthermore, automatic gain control (AGC) can be performed on the receiving side.

(Embodiment) FIG. 1 is a schematic configuration diagram of a transmitter for explaining an embodiment of the optical digital transmission method of the present invention.

In the figure, 1 is an input signal, 2 is a signal converter, 3 is a modulator, and 4
is a laser diode (LD), 5 is a photodiode (PD), 6 is an amplifier, 7 is an integrator, 8 is a comparator, 9
is a reference voltage setting circuit.

The signal converter 2 is a circuit that converts the NRZ signal into a ternary signal as shown in FIG. 3(D). As explained in Fig. 3, the differential signal is not limited to an analog differential signal as shown in Fig. 3 (B), but the NRZ signal and its inverted signal can be input to the trigger circuit. By a method such as generating a pulse signal with a predetermined width at the rising edge, inverting one signal and combining it with the other signal, as shown in FIG.
A differential signal may be generated that is high (H) at the change point from H to H, low (L) at the change point from H to L, and medium (M) when H or L does not change. . Of course, it is not necessary to create the differential signal while creating the NRZ signal, and the differential signal may be created directly.

Further, in this embodiment, an integrated element in which the laser diode 4 and the photodiode 5 are formed in the same element is used, so that a part of the modulated light from the laser diode area is manually applied to the photodiode area. I made it.

The operation will be explained. The human power signal 1 is an NRZ signal, which is converted by a signal converter 2 into a ternary signal as shown in FIG. A part of the modulated light output from the laser diode 4 is input to the photodiode 5, converted into an electrical signal, amplified by the amplifier 6, and integrated by the integrator 7.

The output of the integrator 7 is compared with the set voltage of the reference voltage setting circuit 9 by a comparator 8, and the difference voltage is outputted from the comparator 8 to set the bias voltage of the modulator 3.

FIG. 4 is a diagram showing an example of the input terminal-optical output characteristics of a laser diode. The bias voltage set in the modulator 3 determines the bias current, and the signal current output by the signal converter 2 1. , H, M, L by
It is possible to obtain three-value optical output. Since the bias current 8 can be changed by the bias voltage of the modulator 3, the optical output can be controlled, and since the manual light of the photodiode is part of the output light of the laser diode, automatic output adjustment can be performed. I can do it.

FIG. 2 is a schematic configuration diagram of an example of a receiver.

In the figure, 11 is a photodiode (PD), 12 is a preamplifier, 13 is a differential amplifier, 14 is a discriminator, 15 is a demodulator, 16 is a reproduction signal, 17 is a low-pass filter, 18 is a comparator, and 19 is a reference voltage The setting circuit 20 is a detection signal.

The optical signal received by the photodiode 11 is amplified by a preamplifier 12 and a differential amplifier 13, separated into H and L signals by a discriminator 14, and guided to a demodulator 15.

The demodulator 15 is constituted by an RS flip-flop, and is set by an H signal and reset by an L signal. Therefore, the reproduced signal 16 is a reproduced NRZ signal. On the other hand, the average value of a portion of the output of the photodiode is detected by a low-pass filter 17, compared with the voltage from a reference voltage setting circuit 19 by a comparator 18, and monitored as a detection signal 20. Detection signal 20
always exceeds a certain value when an optical signal is received by the photodiode, and never exceeds a certain value when the optical signal does not arrive due to a failure or the like. Therefore, in the receiver, it is possible to monitor the optical signal with a simple configuration such as a low-pass filter. Also, 70-
It is also possible to apply AGC to the output of the pass filter 17.

(Effects of the Invention) As is clear from the above explanation, the optical digital transmission method according to the present invention has a band equivalent to that of the Manchester code conversion method, and does not use a clock signal (
Can detect optical signals. In addition, the transmitter can easily perform automatic output adjustment regardless of the mark rate or transmission speed of the transmission signal, and the receiver can similarly adjust the output.
Another advantage is that automatic gain adjustment can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a transmitter for explaining an example of the optical digital transmission method of the present invention, FIG. 2 is a schematic configuration diagram of an example of a receiver, and FIG. 3 is a schematic configuration diagram of an example of a receiver. Detailed illustrations,
FIG. 4 is a diagram showing an example of input terminal-light output characteristics of a laser diode. DESCRIPTION OF SYMBOLS 1... Input signal, 2... Signal converter, 3... Modulator, 4... Laser diode, 5... Photodiode, 6... Amplifier, 7... Integrator, 8 ...Comparator, 9...Reference voltage setting circuit. Patent applicant: Shimadzu Corporation

Claims (1)

[Claims] A light characterized in that a light emitting element is driven by a pulse signal generated in different directions depending on the direction of change at a change point of a binary signal, and one of the peaks of which is approximately zero. Digital transmission method.