JP2671341B2 - Optical transceiver module - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical communication system, and more particularly to a signal transmission / reception system for bidirectional transmission in an optical fiber data link or the like.

[Conventional technology]

FIGS. 6 and 7 show an example of a method for bidirectional transmission using a single-core optical fiber.

In FIG. 6, a transmission signal is input from the recording terminal 1 of the module 11, converted into an optical signal by the driver 2 and the light emitting element 3, coupled to the optical fiber 6 through the optical coupler 4 and the optical connector 5, and Transmitted to the module. On the contrary, the received signal enters the light receiving element 7 from the optical fiber 6 through the optical connector 5 and the optical coupler 4. Light-to-electric conversion is performed by the light receiving element 7, and the converted signal is amplified by the preamplifier 8,
It is output to the output terminal 9.

Here, during transmission, reflection occurs in the optical connector 5, and the reflected light enters the light receiving element 7 to generate a crosstalk signal. Therefore, at the time of transmission, it is necessary to give a signal for stopping the operation to the preamplifier 8 from the reception cut terminal 10 so that the crosstalk signal is not output.
Therefore, the transmission method is half-duplex.

FIG. 7 shows an example of full-duplex transmission by wavelength division multiplexing (WDM). WDM module 12 consists of light emitting element 13 and light receiving element with wavelength λ _1.
14, WDM module 16 with built-in optical multiplexer / demultiplexer 15 and facing each other
Incorporates a light emitting element 17 having a wavelength λ _2, a light receiving element 14, and an optical multiplexer / demultiplexer 15. In this example, the transmitted / received signal is an optical demultiplexer
Since they are separated by 15, crosstalk does not occur even if there is reflection at the optical connector 5, and full-duplex transmission is possible.

[Problems to be solved by the invention]

The problems of the above-mentioned two types of optical data links will be described.

First, the drawback of the data link shown in FIG. 6 is that simultaneous bidirectional transmission cannot be performed due to the occurrence of crosstalk, and the transmission efficiency is significantly lower than in the full-duplex system.

One of the drawbacks of the WDM system for full-duplex transmission shown in Fig. 7 is its high price. The reason for this is that the optical multiplexer / demultiplexer becomes expensive as a result of the need for advanced thin film growth technology to manufacture the optical filter for wavelength separation used in the optical multiplexer / demultiplexer. In addition, since a light source of two kinds of wavelengths having high wavelength accuracy is required, the cost of the light source itself is high, which also leads to an increase in the cost of the module.

Moreover, in the WDM system, even if the wavelengths of transmission and reception are the same, the modules must face each other, and there is the disadvantage that the other party of communication cannot freely choose.

An object of the present invention is to provide an optical data link that uses a single-core optical fiber and is inexpensive and has high transmission efficiency.

[Means for solving the problem]

In addition to the light emitting element, the light receiving element, and the optical coupler, the optical transceiver module according to the present invention has a D latch for defining the transmission timing of a pulsed input terminal on the transmitting side, and a pulse width from the D latch. A pulse width compression circuit for compressing the pulse width, and the receiving side is provided with a clock generator that outputs a clock synchronized with the pulsed reception signal to the D latch as transmission timing information of the input signal. This reduces the pulse width of the input signal, and then uses the gap of the received pulse train to
The feature is that it is transmitted bit by bit.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

Referring to FIG. 1, the optical transceiver module of the present invention is
Outside the light emitting element 3, the optical coupler 4, the light receiving element 7, etc., the D-latch 18,
It has a pulse width compression circuit 19 and a clock generator 20.

The transmission signal input from the input terminal 1 is the D-latch 18,
It passes through the pulse width compression circuit 19 and is converted into an optical signal by the light emitting element 3. The received signal passes through the light receiving element 7 and the preamplifier 8 and is output to the output terminal 9 and the clock generator 20. Here, the clock generator 20 is in free run when there is no received signal, but when the received signal enters, it outputs a clock synchronized with it to the D-latch 18. The output of the pulse width compression circuit 19 is connected to the light emitting element 3 and the preamplifier 8, and the operation of the preamplifier 8 is stopped when there is a transmission pulse.

The operation will be further described with reference to FIG. Fig. 2 (a)
Is the output of the preamplifier 8, (b) is the clock generator
20 is an output, (c) is an input of the input terminal 1, (d) is an output of the D-latch 18, and (e) is an output of the pulse width compression circuit 19.

When there is no received signal, the timing of the transmitted signal is not particularly fixed, but when there is a received signal, the clock generator 20
The output of is synchronized with that, and a clock is applied to the D-latch 18 as transmission timing information of the input signal. The transmission signal passes through the pulse width compression circuit 19 to reduce its pulse width,
Similarly, it is transmitted by utilizing the gap of the received pulse train that is transmitted with the pulse width compressed.

In this method, although the transmission method of the half-duplex is basically adopted, since the transmission and reception can be performed simultaneously by using the pulse interval, the full-duplex transmission without the decrease of the transmission efficiency of the conventional half-duplex transmission module. It enables bidirectional transmission similar to the method. The modulation method of the input signal may be a pulse train with equal intervals. In addition to the PCM method, PAM which is a kind of pulse analog modulation
It is also applicable to (pulse amplitude modulation).

The maximum transmission distance of the optical transceiver module of the present invention depends on the output of the light emitting element, the sensitivity of the light receiving element and the preamplifier, as well as the interval of the pulse train. The relationship between the pulse train interval and the maximum transmission distance is described below.

When the pulse is alternately transmitted between the partner side and the self side as in the optical transceiver module of the present invention, the second pulse cannot be transmitted until the pulse from the partner arrives after the first pulse is transmitted. . That is, it is necessary that the interval between the pulses to be sent is larger than the time required for the pulses to make one round trip in the transmission path.

 This condition is expressed by equation (1).

2nL / C <T-τ (1) where n is the refractive index of the core, L is the transmission distance, C is the speed of light, T is the pulse period, and τ is the pulse width.

Now, n = 1.45, C = 3 × 10 ⁸ m, and bit rate B (≡1 / T) with the pulse duty ratio τ / T as a parameter.
FIG. 5 shows the relationship between the maximum transmission distance Lmax and the maximum transmission distance Lmax. At the same bit rate, the smaller the duty ratio, the wider the pulse interval, so long-distance transmission is possible.

 Next, specific examples of the present invention will be described.

FIG. 3 shows an example in which a one-shot multivibrator 21 is used as the pulse width compression circuit 19 in FIG. 1 and an analog switch 22 is used as an operation stop circuit of the preamplifier 8.

Also, FIG. 4 shows a D-latch 18, a pulse width compression circuit 1 as an external unit 24 of the conventional half-duplex module 23.
This is an example of easily improving the performance of an optical data link by installing a device consisting of a clock generator 20. If the output of the pulse width compression circuit 19 is connected to the input terminal 1 and the reception cut terminal 10, and the output of the output terminal 9 is connected to the clock generator 20, respectively, the transmission efficiency is greatly improved while using the conventional half-duplex module 23. it can.

〔The invention's effect〕

As described above, the optical transmission / reception module of the present invention can realize an inexpensive optical data link having a high transmission efficiency equivalent to that of the full-duplex method with a simple configuration, and can be expected to have a wide range of applications.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical transmitter / receiver module of the present invention, FIG. 2 is a diagram showing a signal pattern of each part of FIG. 1, and FIG. 3 is a block diagram showing more specifically FIG. FIG. 5 is a diagram showing a modification of the present invention, FIG. 5 is a characteristic diagram showing the relationship between the bit rate and the transmission distance of the optical transceiver module of the present invention, and FIGS. 6 and 7 are conventional optical transceiver modules. Block diagram of. 1 …… Input terminal, 2 …… Driver, 3 …… Light emitting device, 4 …… Optical coupler, 5 …… Optical connector, 6 …… Optical fiber, 7 …… Light receiving device, 8 …… Preamplifier, 9 …… Output terminal, 10 …… Reception cut terminal, 11 …… Module, 12,16 …… WDM module, 13…
… Light emitting element with wavelength λ ₁ , 14 …… Light receiving element, 15 …… Optical multiplexer / demultiplexer, 17 …… Light emitting element with wavelength λ ₂ , 18 …… D-latch, 19
...... Pulse width compression circuit, 20 …… Clock generator, 21
…… One-shot multivibrator, 22 …… Analog switch, 23 …… Conventional half-duplex module.

Claims (1)

(57) [Claims] 1. An optical transmission / reception module having a light emitting element, a light receiving element, and an optical coupler, and a D latch for defining a transmission timing of a pulsed input signal on a transmission side,
A pulse width compression circuit for compressing the width of the pulse from the D latch, and when there is a pulsed reception signal on the receiving side, a clock synchronized with this is used as the transmission timing information of the input signal for the D signal. An optical transceiver module comprising a clock generator for outputting to a latch so that the pulse width of the input signal is reduced and then the input signal is transmitted bit by bit by utilizing a gap of a received pulse train.