JPS6281829A - Two-way optical signal transmitter - Google Patents

Abstract

PURPOSE:To eliminate the effect of a reflected light in binary-coding a reception signal by providing an automatic gain control circuit synchronously with a transmission signal to an amplifier circuit of a reception section. CONSTITUTION:A transmission signal P inputted from an input terminal 1b equipments a light emitting element 1a via a drive circuit 1c at transmission and the transmitted light is sent via a T-coupler 3. On the other hand, the received light from a fiber C reaches a photodetecting element 2a via the T- coupler 3 at the reception, is subjected to photoelectric conversion and a binarization reception signal Q is outputted from an output terminal 2b via an amplifier circuit 2c and a binarization circuit 2d at the reception. In this case, since the automatic gain control circuit 5 uses a transmission signal P to change the amplification factor of the amplifier circuit 2c, the reflection signal after amplification is suppressed within the dynamic range of the binary coding circuit to eliminate the effect of the reflected light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an optical signal transmission device for bidirectional data transmission using a single optical fiber used in optical communications.

[Prior art and its problems]

As this type of bidirectional optical signal transmission device, the professional shown in Fig. 5 is used.
The configuration shown in the figure is known.

The light emitting section 1 includes a light emitting element 1a, an input terminal 1b, and a drive circuit 1c, and the light receiving section 2 includes a light receiving element 2a.

It consists of an output terminal 2b, an amplifier circuit 2C, and a binarization circuit 2d. The T-coupler 3 composed of a half mirror and the light emitting element 1a are coupled by a first optical fiber A, and the light receiving element 2a
are coupled by a second optical fiber C. C is a transmission optical fiber. At the time of transmission, the transmission signal P input from the input terminal 1b drives the light emitting element 1a via the drive circuit IC, and the transmitted light emitted from the light emitting element 1a is guided to the l-th original fiber and sent to the T-coupler 3. The signal is transmitted to the transmission optical fiber C via. At the time of reception, the reception source from the transmission optical fiber C is connected to the second optical fiber B via the T-coupler 3.
and reaches the light receiving section 2. Photoelectric conversion is performed by the light receiving element 2a of the light receiving section 2, and the amplifier circuit 2c.

The binarized received signal Q is output through the binarization circuit 2d to the output terminal 2b.
Output from Some bidirectional optical signal transmission devices include an automatic threshold control circuit in the binarization circuit 2d to absorb variations in transmission loss due to the length of the transmission fiber C, etc. This is called the dynamic range.

No. 611. FIG. 7 shows the configuration 3 and operation of this eye movement threshold control circuit 4. The control circuit 4 is composed of a comparator 4a, a resistor 4b, and a capacitor 4c, and the base blood voltage of the comparator 4a is shown in FIG. ■T is qualitatively determined according to the input voltage V1.
We are converting into value. Single optical fiber (for bidirectional data transmission, T-coupler 3 is used, so light emitting element 1
The transmitted light from the T-coupler 3 and the transmission optical fiber C enters the light receiving element 2a through end face reflection.

When the light intensity level of this reflected light exceeds the dynamic range of the receiver 2, as shown in FIG. There is a problem in that the pulse width distortion VL11 of the binarized output Vo increases because the pulse width distortion VL11 cannot be followed.

To solve this problem, increase the interval between transmission and reception to ensure the charging and discharging time of the capacitor, but if you increase the time interval, the transmission line will not be used during that time, resulting in poor data transmission efficiency. A weakness emerges. Another solution is to expand the dynamic range and include the light intensity level of the reflected light within the dynamic range, but in this case, the circuit is configured to expand the dynamic range beyond the dynamic range required for reception. The problem is that it becomes complicated and leads to unnecessary cost increases.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a bidirectional original signal transmission device that can eliminate the echo of reflected light when binarizing a received signal.

[Key points of the invention]

In order to achieve the above-mentioned purpose, this invention provides an automatic gain synchronization with the signal sent to the amplifier circuit of the receiving section. [An Ilj control circuit is provided, whereby when there is a high level of reflected light, the amplification degree of the amplifier circuit is lowered so that the pulse width distortion in the binarization circuit is not affected.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, and parts having the same configuration as in the conventional circuit (FIG. 5) are denoted by the same reference numerals.
The explanation will be omitted. The present invention differs from conventional circuits in that an automatic gain control circuit 5 is provided between the amplifier circuit 2c of the light receiving section 2 and the input terminal of the light emitting section l. This automatic gain control circuit 5 changes the amplification degree of the amplifier circuit 2c according to the transmission signal P.

2 and 3 show specific examples of a variable gain control circuit and an amplifier circuit, where 6 is a field effect transistor, 7 is an amplifier Ro is an input resistor, and RF l * l (F 2 is a fixed resistor).

In Fig. 2, the field effect transistor 6 is connected to the transmission signal PI.
is turned on and off to change the amplification degree of the amplifier 7. The degree of amplification is determined by the fixed resistor 1tP2 when the transmission signal is @l'', and is fixed when the transmission signal is ``Om''. In the case of FIG. 3, the output of the amplifier 7 is turned on and off by the sending signal P. When the transmitter 1g signal is "l", the output is turned off,
The received %i signal due to reflected light is not output.

FIG. 4 is chart 1 showing the molding of each part of the embodiment of this invention.
・In, (al is the transmission (g waveform diagram) of the transmission device, (bl is the transmission waveform diagram of the transmission device (not shown), (cl is the reception waveform diagram of the transmission device, and (dl is the change in amplification of the transmission device) (cl is an input waveform diagram of the binarization circuit of the transmission device, and (f) is an output waveform diagram of the binarization circuit of the transmission device. In other words, at the time of transmission, the amplification of the amplifier circuit is performed according to the transmission signal. By changing the frequency and suppressing the amplified reflected light signal within the dynamic range of the binarization circuit, pulse width distortion does not increase even if the time interval between the transmitted signal and the received signal is short.

[Effect of ejection ψ]

This invention provides automatic gain synchronized with the transmitted signal! 1J
By attaching the 411 circuit to the amplifier circuit, even if there is a high level of reflected light, the amplified signal can be kept within the dynamic range of the binarization circuit, and stable reception characteristics can be obtained, making it easy to transmit and receive. There is no need to widen the time interval, and the efficiency of using the transmission path can be increased.

[Brief explanation of drawings]

@Figure 1 is a professional diagram showing an embodiment of this invention, Figure 2,
FIG. 23 is a circuit diagram showing a specific example of an amplifier circuit and an automatic gain control circuit, FIG. 6 is an automatic threshold control circuit diagram, FIG. M7 is a waveform diagram showing the operation of FIG. 6, and FIG. 8 is a waveform diagram showing the influence of reflected light. l: light emitting section, la: light emitting element, lC: drive circuit, 2: light receiving section, 2a: light receiving element, 2c: amplifier circuit, 2d: binarization circuit, 3: 'l'l curler, 5: automatic gain control circuit. Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1) A T-coupler coupled to a transmission optical fiber and coupled to a light emitting element and a light receiving element through first and second optical fibers, and inputting a transmission signal to the light emitting element via a drive circuit to operate it. In a bidirectional optical signal transmission device comprising a light emitting section and a light receiving section that inputs the output of the light emitting element to a binarization circuit via an amplifier circuit, binarizes it, and outputs it as a received signal; A bidirectional optical signal transmission device comprising an automatic gain control circuit that lowers the amplification degree of the amplifier circuit when a transmission signal of the lever is at a high level.