JPS6292552A - Optical signal turning-off detecting system - Google Patents

Abstract

PURPOSE:To allow for the turning-off detecting level of the optical signal by dividing the comparing identification of the light receiving signal into the identification for the data signal and for the clock signal. CONSTITUTION:The identifier of the light receiving signal is divided and provided into two for a data signal 1 and for a clock signal 8. An identifier 8 for the data signal identifies the input optical signal, outputs it to an FF2 and on the other hand, an identifier 8 for the clock signal triggers a tank 3 for extracting the timing. Here, an identifying level 6 of the data signal is held to the optimum condition, and an identifying level 9 of the identifier 8 is dislocated a little so that the level cannot be identified by the noise level. Consequently, the noise signal of the logical level does not occur and the tank 3 is also not triggered by the noise. Since the edge component is extracted in the clock signal system, the edge component, the level may be dislocated. Thus, the allowance can be made for the turning-off detecting level of the optical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for detecting the front of an optical signal in an optical receiving circuit in optical communication, and in particular to an optical signal interruption method suitable for detecting a transmission/monitoring signal that requires high reliability. Regarding detection method.

[Background of the invention]

Conventionally, especially in optical receiving circuits that do not wait for an automatic gain control function (AGC), interruption of the original signal has been detected based on the output level of a timing extraction tank. Literature related to this type of method includes, for example, The Bell.
System Technical Journal Vol. 57 No. 6 18
There is a paper titled ``Practical 45-Mb/s Regenerator for Light Unique Transmissions'' published in 37-Sei. (American
Telephone and Telegraph C
company+THE BFJLL SYSTEM
TECHNICAL JOURNAL, Vol.
57, No, 6. JulF-August
1978 “Practical 45-Mb/s
Regenerator for Lightwave
Transmission') FIG. 2 shows the circuit configuration of a conventional optical receiving circuit. In FIG. 2, the discriminator 1 inputs the optical reception signal, and triggers the timing extraction tank 3 when the input signal (i) exceeds a certain level as shown in FIG. As shown in the figure, when the noise signal is larger than the discrimination sensitivity of the discriminator 1, the timing extraction circuit 3 is triggered even when the optical signal is cut off, and a clock signal is output.

In this way, in the conventional method, if a highly sensitive discriminator is used for the optical reception signal, even if the optical signal is cut off, the input minute noise is converted to a logic level and the timing extraction tank is used. The problem was that there was almost no difference in level between the disconnected state and the communication state.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical signal disconnection detection method that widens the detection level margin between an optical signal disconnection state and a communication state, and enables highly accurate detection.

[Summary of the invention]

A feature of the present invention is that the comparison and identification of received optical signals is performed separately for data signals and clock signals, thereby widening the margin of optical signal disconnection detection level.

[Embodiments of the invention]

FIG. 1 shows an embodiment of an optical receiving circuit for implementing the present invention. In the figure, 1.8 is a discriminator, 2 is a flip-flop, 3 is a timing extraction tank, 4 is a level detection filter, and 5 is a disconnection detection comparator.

In this embodiment, the optical reception signal discriminator is divided into two, one for data signals and one for clock signals. The data signal discriminator 1 discriminates the input optical signal and outputs it to the flip-flop 2, while the clock signal discriminator 8 triggers the timing extraction tank 3. Here, the discrimination level 6 of the data signal is kept at the optimum state, and the discrimination level 9 of the discriminator 8 is slightly shifted so as not to be discriminated by the noise level. Therefore, no logic level noise signal is generated. The timing extraction tank 3 is also not triggered by noise. Furthermore, since edge components are extracted in the clock signal system, there is no problem at all even if the discrimination level 9 is shifted.

Since shot noise is large in an optical receiving system, this embodiment is particularly effective for a light receiving circuit using an APD, and since a large margin can be provided for the comparison level 7 of the comparator 5, power fluctuations and temperature fluctuations in the entire circuit can be suppressed. There is enough leeway to take this into account.

〔Effect of the invention〕

According to the present invention, there is a margin in the optical signal disconnection detection level,
Can detect call/no call signals with high reliability.

Particularly in optical subscriber communications, the only difference is whether or not IM modulation is applied to the data signal, and output is always performed regardless of whether there is a call or no call.

Therefore, if the optical fiber transmission line is short, a large amount of power will be input, which will increase the shot noise and result in less than 1g.
Although the signal detection margin becomes smaller, according to the present invention, the detection level difference does not change depending on the distance of the optical fiber transmission line, and stable operation can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an optical receiver circuit for implementing the present invention, FIG. 2 is a block diagram of a conventional optical receiver circuit, and FIGS. 3 and 4 show input waveforms of a discriminator. It is a diagram. 1.8... Discriminator, 2... Flip 70 tube, 3... Timing extraction tank, 4...
・Level name 3 times b 4-l Kinranbetsu Netsu "Wind"

Claims (1)

[Claims] 1. In a method of detecting a disconnection of a digital optical signal based on a level difference in the clock output of a timing extraction tank circuit, the method is characterized in that the optical reception signal is compared and identified into two types: one for the data signal and one for the clock signal. Optical signal disconnection detection method.