JPS6212221A - Optical transmission system - Google Patents

Abstract

PURPOSE:To improve the operating efficiency of optical transmission energy by sending a forward optical signal and a reverse optical signal caused in response to the intermission of a semiconductor laser light intermitted in an external modulator by a modulation signal via an optical transmission line provided respectively and detecting differentially the two signals at the reception side. CONSTITUTION:The light generated from a laser diode of a light emitting element 1 is made incident in an external modulator 3, that is, an optical switch. The incident light is modulated externally by using an information signal 12 and sent to optical transmission lines 6, 7 from ports A, B as an intermittent signal. The forward, reverse optical signals are outputted from the points A, B. The optical signal is sent through the optical transmission lines 6, 7 comprising an optical fiber, the two signals are received at the same time by photoelectric converters 8, 9 at the reception side, signals (a, b) being electric outputs are subject to difference by a subtractor of a difference detection circuit 10, and the result is outputted as a signal (c). The received power is doubled in comparison with a conventional system in this case and the reception signal level is increased.

Description

[Detailed description of the invention] In an optical transmission system that externally modulates laser light, the laser light switched by an external modulator is transmitted via two optical fibers and differentially detected on the receiving side. , which increases the optical reception sensitivity.

[Industrial application field]

The present invention relates to improvements in optical transmission systems.

In the optical transmission method, laser light generated from a light emitting element, such as a semiconductor laser diode, is modulated with an electrical signal and transmitted to a receiving end as intermittent optical pulses.

Optical signals received via the optical transmission line are converted back into electrical signals. In this case, even when optical energy is transmitted over a long distance, it is desirable to be able to receive it with high sensitivity so that it can be converted into an original electrical signal.

[Conventional technology]

Conventionally, external modulators have been used to transmit information signals as optical signals over optical fibers. This modulator is equipped with an electro-optic crystal, whose refractive index is controlled by the electrical signal to be transmitted, and the path of the light incident on the optical crystal from the laser diode is electrically switched, so that the optical signal is converted into intermittent light. Supply to the transmission line.

In order for the transmitted optical signal to be correctly received at a far receiving end, it must be able to receive with sufficient energy.In order to reduce the loss during transmission and increase the transmitted optical output, Various measures have been taken, such as increasing the output of the laser diode.

[Problem that the invention seeks to solve]

However, there is a limit to increasing the output of the diode or reducing the loss of the transmission line.

In conventional external modulation methods, the entire light emitted by the laser diode is not used for signal transmission.

That is, since the light supplied to the external modulator is sent out as intermittent light, a portion of the light does not become signal transmission energy at all and is wasted.

An object of the present invention is to improve the efficiency of using optical transmission energy and to increase the receiving sensitivity at the receiving end.

[Means for solving problems]

The above problem is caused by external change due to the modulation signal! A normal optical signal and an inverted optical signal generated in response to the interruption of the semiconductor laser light that is interrupted in the IL device are transmitted through respective optical transmission lines, and the two signals are differentially detected on the receiving side. This problem is solved by the optical transmission system according to the present invention configured as follows.

[Effect]

According to the present invention, the entire light emission output of the intermittent laser beam is used for signal transmission as a normal optical signal and an inverted optical signal generated in response to the intermittent laser beam, and wasteful consumption of optical energy is avoided.

In addition, by transmitting the normal optical signal and the inverted optical signal generated in response to the discontinuity through respective optical transmission lines, and differentially detecting the two signals on the receiving side, the detection level is lower than that of the conventional optical signal. This is twice the amount compared to the conventional method, and the receiving sensitivity can be increased.

〔Example〕

Hereinafter, the present invention will be described in detail according to illustrated embodiments.

Figure 1 is a principle block circuit diagram of the optical transmission system of the present invention.
FIG. 2 is a waveform diagram of the principle operation.

In FIG. 1, light generated from a laser diode of a light emitting device 1 enters an external modulator 3, ie, an optical switch.

The incident light is externally modulated by the information signal 12 and sent out as an intermittent signal from ports A and B to the optical transmission line 6.7. A
A normal rotation optical signal and an inversion optical signal are output from the B port.

These optical signals are transmitted through an optical transmission line 6.7 consisting of an optical fiber, and on the receiving side, these two signals are simultaneously received by a photoelectric converter 8.9 and their electrical outputs are a and b.
A difference is created between the signals by a subtracter in the differential detection circuit 10, and the result is output as a signal C.

At this time, the received light power is doubled compared to the conventional method, and the received signal level is increased by 6 dB.

FIG. 2 is an operating waveform diagram, in which the continuous signal of the light emitting element ii) is intermittent in the modulator 3 by the information signal 12 of i), and the intermittent signals of iii) A and iv) B with mutually inverted phases occurs. This optical signal is converted into electrical signals a and b of v) and vi) by a photoelectric converter 8.9 on the receiving side, and the difference is taken by a differential detection circuit 10, resulting in a combined output signal C of νii). becomes.

FIG. 3 is a block diagram of one embodiment of the method of the present invention.

Laser light from the light emitting element 1 is supplied via an optical fiber 2 to a modulator 3 consisting of an optical switch.

The information signal is input to the signal processing section 4, and after being subjected to signal processing such as multiplexing processing, is input to the optical drive circuit 5.

The optical switch of the modulator 3 is turned on and off by this electrical signal, and external modulation is performed.

The intermittent optical signal enters an optical transmission line 6.7 consisting of an optical fiber and is transmitted.

The output light from the two optical fibers is sent to each photoelectric converter 8.
The signal is received by the photodiodes 81 and 91 included in the optical diode 9, converted into an electrical signal, and amplified by each amplifier.The signal difference is amplified and detected by the differential detection circuit 10 consisting of a differential amplifier. The detection output signal is converted into an original electrical signal by the signal processing section 11.

In FIG. 3, photoelectric converters are provided independently for each of the electrical signals obtained from the normal optical signal and the inverted optical signal.

FIG. 4 shows another embodiment of the photoelectric converter.

In this case, the normal signal and the inverted signal converted into electrical signals are configured to be amplified by one amplifier. By doing so, it is possible to reduce the common mode noise in the photoelectric converter, and it is possible to improve the optical reception sensitivity and reduce the circuit scale.

〔Effect of the invention〕

According to the present invention, receiving sensitivity can be improved and the minimum receiving level can be increased by 1 dB compared to conventional transmission systems. It is also possible to improve the utilization efficiency of light energy, and its effects are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a principle block circuit diagram of the optical transmission system of the present invention, FIG. 2 is a principle operational waveform diagram of the optical transmission system of the present invention, FIG. 3 is a block circuit diagram of an embodiment of the present invention system, and FIG. The figure shows another embodiment of the photoelectric converter of the invention. In the figure, 1 is a light emitting element, 2 is an optical fiber, 3 is a modulator, 6.7 is an optical transmission line, 8 and 9 are photoelectric converters, and 10
12 is a differential detection circuit, 12 is an information signal, and 81.91 is a photodiode. i) /2 Lyudingto1ii) A k Vi) b-”]”- Grass 2 figure

Claims (1)

[Claims] The laser beam of the light emitting element (1) is interrupted in the external modulator (3) by the information signal (12), and an optical transmission line (6
, 7), and the two signals are differentially detected (
10) An optical transmission system characterized by being configured as follows.