JPH0446424A - Optical transmission equipment - Google Patents

Abstract

PURPOSE:To attain optimum AGC(automatic gain control) automatically even in the case of long or short range transmission by providing an equalization amplifier means, a gain control amplifier means and a control means. CONSTITUTION:In the case of long distance optical transmission, gain control amplifier means 221, 222 control the gain of a photoelectric conversion means 201, 202 and an equalization amplifier means 21 with a control voltage in response to an output level of the equalization amplifier means 21 to form 2 system of AGC loops. On the other hand, in the case of short distance optical transmission, a control means 23 inactivate the means 202 in the means 201, 202 to activate only one system in the 2 system of AGC loops. Thus, in the case of short distance optical transmission, the AGC loop of one system only is formed automatically and optimum AGC is applied to the system without deviation of AGC dynamic range. Thus, optimum AGC is applied automatically even in any of the long or short range transmission.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical transmission device used for a long-distance optical transmission system and a short-distance optical transmission system, the present invention automatically performs optimal AGC during transmission in any case.
(automatic gain control), two optical/electrical conversion means, an equalization amplification means that equalizes and amplifies the signal obtained by adding these respective outputs, and a control voltage corresponding to the output level. two gain control amplification means that control the respective gains of the optical/electrical conversion means and equalization amplification means, and one that outputs the output level as it is when the output level of the equalization amplification means is below a threshold value. , and control means for controlling one of the two photo/electric conversion means to become inoperable when the output level exceeds the threshold.

[Industrial application field]

The present invention relates to an optical transmission device used in a long-distance optical transmission system and a short-distance optical transmission system.

Optical transmission equipment used in long-distance optical transmission systems performs AGC so that the reception gain is maximized during transmission over the longest distance (for example, 40 km to 50 km).

However, this optical transmission device can be used over extremely short distances (for example, several tens of
It may be used for transmission over distances of 0 m to several km), and in such cases, the dynamic range of AGC is out of range. Therefore, even in such a case, it is necessary to perform transmission by applying optimal AGC.

[Conventional technology]

As shown in Figure 4, a long-distance optical transmission system includes, for example, four
Optical transmission equipment 1 installed at a distance of 0km to 50km,
An optical information signal is transmitted and received between the two via an optical fiber cable 3. Each of the optical transmission devices 1.2 is provided with a receiving system circuit as shown in FIG. 5 as a part thereof, and each converts information signals transmitted from the other side into electrical signals and performs predetermined processing. Do this.

FIG. 5 shows a conventional receiving system circuit when an optical transmission device used in a long-distance optical transmission system is used over a very short distance, for example, from several hundred meters to several tens of meters. In FIG. 5, optical information sent through an optical fiber cable 3 is attenuated by an optical attenuator 4, which will be described later, and then converted into an electrical signal by an optical/electrical conversion circuit (hereinafter referred to as a conversion circuit) 5. Equalization amplifier circuit 6
The frequency characteristics are corrected, and predetermined processing is performed in a subsequent circuit (not shown). In this case, the output signal of the equalization amplifier circuit 6 is supplied to the AGC amplifier 7 and is made into a gain control voltage according to the output signal level, and the conversion circuit 5 (bias current) and the amplification gain of the equalization amplifier circuit 6, respectively.

By the way, in long-distance optical transmission systems, this AG
C is designed to maximize the reception gain at the longest distance.
If this is used as it is for transmission over a very short distance, the input optical information level (received light power) to the device will be too large and will be out of the dynamic range of AGC. Therefore, as shown in FIG. 5, conventionally, an optical attenuator 4 is provided at the input stage to attenuate the optical information level so that the received light power falls within the dynamic range of the AGC.

[Problem to be solved by the invention]

Since the conventional circuit is configured with an optical attenuator 4, manual adjustment must be made to activate the optical attenuator 4 during extremely short distance transmission, making it cumbersome to handle. In this case, it is necessary to check the received light power with a power meter or the like before making adjustments. Alternatively, instead of the conventional optical attenuator 4, two conversion circuits may be provided and the two conversion circuits may be used depending on the received light power, or either one of the conversion circuits may be used. There is also a method in which multiple conversion circuits are prepared and used by replacing them depending on the received light power.

All of these conventional examples require time to operate, making it impossible to set up an optical transmission system in a short time.
There are some problems that are extremely inconvenient for outdoor transportation systems used in emergencies.

An object of the present invention is to provide an optical transmission device that can automatically apply optimal AGC during both long-distance and short-distance transmission.

[Means to solve the problem]

FIG. 1 shows a diagram of the principle of the present invention. In the same figure (A), 20+
, 20* is an optical/electrical conversion means that converts an optical information signal into an electrical signal. 21 is an equalization amplification means, and a photo/electrical conversion means 20
The signal obtained by adding the respective outputs of + and 20t is equalized and amplified. 2
21 and 221 are gain control amplification means, equalization amplification means 2
The photo/electrical conversion means 20 is controlled by a control voltage according to the output level of 1.
1.20 and the gain of the equalization amplification means 21. 23 is a control means which outputs the output level as it is when the output level of the equalization amplification means 21 is below a threshold value, while when the output level of the equalization amplification means 21 exceeds the threshold value, it outputs the output level as it is; 20. .

20 (200) is controlled to be inoperable. In addition, the present invention, as shown in FIG.
Optical/electric conversion means 20. , 201, equalization amplification means 21, and gain control amplification means 22I.

222, a receiving system 24 consisting of a control means 23, and an electric/
A transmitting system 26 including an optical conversion means 25 is constituted as one unit.

[Effect]

In the case of long-distance optical transmission, gain control amplification means 22+, 22
．． controls the respective gains of the optical/electric conversion means 201.degree. 20 and the equalization amplification means 21 using a control voltage corresponding to the output level of the equalization amplification means 21. In other words, in this case, two systems of A
A GC loop is configured. On the other hand, in the case of short-distance optical transmission,
Since the received light power becomes high, the control means 23 makes one of the optical/electrical conversion means 20+ and 20* (20) inoperable, and turns the A of only one of the two AGC loops into an inoperable state.
Operate the GC loop. This effectively reduces the received light power to 1/2 of that in the case of a two-system loop, and in the case of short-distance optical transmission, an AGC loop with only one system is automatically configured, and the AGC dynamic Optimal AGC can be applied without going out of range.

Therefore, optimal AGC can be automatically applied for both long-distance and short-distance situations.

〔Example〕

FIG. 2 shows a block diagram of an embodiment of the present invention, and in the figure, the same components as those in FIG. 5 are given the same numbers and their explanations will be omitted. In Figure 2, 10. .

10 is a photo/electric conversion circuit (hereinafter referred to as a conversion circuit),
Its output is connected to an equalization amplifier circuit 6 via an adder 11. 12 is a control circuit that performs control according to the output level of the equalization amplifier circuit 6, that is, when the output level of the equalization amplifier circuit 6 is below a preset threshold, the output level is directly applied to the AGC amplifiers 1.3. ．． 13. AGC amplifier 13+, 13 which has two systems only when the threshold is exceeded.
For example, the AGC amplifier 13.t. The configuration is such that control is performed to reduce the output voltage to zero, for example.

AGC amplifier with 2 systems 13. ．． 132 is connected to the conversion circuits 10□ and 102, respectively, and the adder 14
It is connected to the equalization amplifier circuit 6 via. In this way, the present invention has a configuration in which two AGC loops are provided.

Conversion circuit 10. ．． 10. are provided close to each other in the case 15, as shown in FIG. 3(A), for example, and their circuit diagram is as shown in FIG. 3(B).

First, a case will be described in which the present invention is used in a long-distance optical transmission system of, for example, 40 km to 501 ann. In Figure 2,
The optical information sent through the optical fiber cable 3 is sent to the conversion circuit 10. ．． 10! is converted into an electrical signal by adder 11
After being added in the equalizing amplifier circuit 6, the frequency characteristics are corrected and output.

At this time, the output signal of the equalization amplifier circuit 6 is supplied to the control circuit 12, and the control circuit 12 determines that the output signal level is below the threshold value (this is because the received light power is relatively low due to long-distance optical transmission). It detects this and supplies the output signal as it is to the amplifier 131-13. AGC amplifier I
3+ and 132 output a control voltage according to the output signal level of the equalization amplifier circuit 6, and the respective gains (bias currents) of the conversion circuits 10+ and +02 are adjusted so that the output signal level of the equalization amplifier circuit 6 is constant. At the same time, the amplification gain of the equalization amplifier circuit 6 is controlled by the control voltage added by the adder 14.

Next, a case will be described in which the present invention is used in an extremely short distance optical transmission system of, for example, several hundred meters to several meters. In this case, since the received light power is relatively high, the correction circuit 12 detects that the output signal level of the equalization amplifier circuit 6 exceeds the threshold value, and the amplifier 13! Control is performed to make the output voltage of the other side zero. As a result, the conversion circuit 10t is rendered inoperable, and the gain of the equalization amplifier circuit 6 is lowered. In this way, when the received light power becomes high, the conversion circuit 10+ is automatically activated.

Adder 11. Equalization amplifier circuit 6. Amplifier 13. An AGC loop with only one system is constructed by each circuit, and the received light power is substantially equivalent to I/2 in the case of a two-system loop. Therefore, by using only one AGC loop, optimal AGC can be applied without going outside the AGC dynamic range.

The optical transmission device according to the present invention is provided with a transmitting circuit in addition to the receiving circuit shown in FIG. 2.

The transmission system circuit is provided with one system of electrical/optical conversion circuit.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to apply optimal AGC in both long-distance optical transmission and short-distance optical transmission, and manually adjust the optical attenuator during short-distance optical transmission as in the conventional example. Since there is no need to do anything like this, an optical transmission system for outdoor use can be immediately set up in case of an emergency.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, and Fig. 3 is a diagram of the principle of the present invention.
FIG. 4 is a block diagram of an electrical conversion circuit, FIG. 4 is a block diagram of an optical transmission system, and FIG. 5 is a block diagram of a conventional example. In the figure, 1.2 is an optical transmission device, 3 is an optical fiber cable, 6 is an equalization amplifier circuit, 10, . 101 is a photo/electric conversion circuit, 11.14 is an adder, 12 is a control circuit, 13, . 11 is an AGC amplifier, 20, . 201 is an optical/optical conversion means, 21 is an equalization amplification means, 22+, 22* is a gain control amplification means, 24 is a reception system, 25 is an electric/optical conversion means, and 26 is a transmission system. (A) Principle diagram of the present invention (Fig. 1) Patent applicant: Fujitsu Limited (Professional diagram of an embodiment of the present invention) (Fig. 2)

Claims (2)

[Claims] (1) Two optical/electrical conversion means (20_1, 20_2), and an equalization amplification means (21 )
and 2 for controlling the respective gains of the two optical/electric conversion means (20_1, 20_2) and the equalization amplification means (21) with a control voltage according to the output level of the equalization amplification means (21). When the output level of the equalizing amplifying means (21) is below the threshold value, the output level of the equalizing amplifying means (21) is output as is, while the output of the equalizing amplifying means (21) When the level exceeds the threshold, 2 above
1. An optical transmission device comprising: a control means (23) for controlling one (20_2) of the optical/electrical conversion means (20_1, 20_2) to be in an inoperable state. (2) The two photo/electric conversion means (20_1, 20_2
), a reception system (24) comprising the equalization amplification means (21), the two gain control amplification means (22_1, 22_2), and the control means (23), and an electrical/optical conversion means. 2. The optical transmission device according to claim 1, wherein the transmission system (26) including the transmission system (25) is configured as one unit.