JPS59105733A - Optical space transmission monitoring system - Google Patents

Abstract

PURPOSE:To monitor accurately the C/N state due to the background light by providing a means which measures the C/N after comparing the carrier detected from an electric signal delivered from a photodetecting element with the mean photodetecting current flowing through the photodetecting element. CONSTITUTION:An optical signal 1 is supplied to a photodetecting element 2 and converted into a premodulation signal to be delivered through an output terminal 6 via an amplifier 3, a filter 4 and an amplifier 5. While the output of the filter 4 is supplied to a carrier detecting circuit 7, and the carrier signal detected by the circuit 7 is supplied to a comparator 11. The signal 1 is supplied to the element 2 along with the background light 10, and a photodetecting element current Ib' is flowed. In this case, a fixed noise No is generated by a photodetecting element current Ib' produced by the signal 1, and a noise Nb is produced by the current Ib generated by the light 10. The current Ib' is amplified by an amplifier 12, and the current Ib' produced by the light 10 is detected by a wave detecting circuit 13. This detected Ib' is supplied to the comparator 11 and compared with a carrier for measurement of C/N. The value of the C/N is read by an indicator 14.

Description

DETAILED DESCRIPTION OF THE INVENTION jal Technical Field of the Invention The present invention relates to a C/
The present invention relates to an optical space transmission monitoring method for monitoring N.

(1) 1 Background of the technology Conventionally, as a monitoring method for the premodulation No. 13 method, the light No. 1 incident on the light receiving part of an optical transmission device is pre-empted by the light receiving element, and the light No. 1 is pre-modulated by the sub signal and converted into a A method is used in which the carrier component of the premodulated signal is extracted and the (,'/N of the light receiving system is monitored).

The above method is a suitable monitoring method for optical fiber communication signals that are not affected by ambient light such as background light, but as in optical space transmission methods, the noise in the light receiving system is affected by the back-piercing level. In this case, it is not possible to accurately monitor the C/N simply by monitoring the carrier level. Therefore, there is a need for a monitoring system that incorporates noise measurement of the light receiving line based on the background light level.

(cl. Prior Art and Problems FIG. 1 shows the control 7R1 method of the light receiving system of the conventional optical space transmission method) In FIG. 1, the original signal 1 enters the light receiving element 2, and the signal 4.
In this case, a part of the premodulation signal is output from the output terminal 6 via the amplifier 5, and the carrier component of the premodulation debit side is detected by the carrier detection circuit 7, and the detected signal is compared with the reference level of the carrier by the comparison circuit 8. The comparison results are displayed on the level meter 9.

As a result of adding the external source, that is, background light 10 to the optical signal wire ζ, the background light 10 is added to the light receiving current Ib flowing to the receiver C cable 2. I felt a sense of pride flowing through my mouth.

FIG. 2 shows the relationship between the light flow Ib and the background light pb. In the figure, the relationship between I b / P b is a linear relationship C in the range A-H. Figure 8S3 shows the relationship between the range of light reception and the noise Nb generated by the light receiving element. In the same figure, Nb/lb has a linear relationship in the range a-bO) 3 From Figures 2 and 3, the background ye I
The relationship between 'b and the noise Nb generated by the light receiving element is also IF
It can be seen that there is an L-line relationship. This means that when the background yL is optical 2f' and the JI transmission system is used, the noise will increase, and the reception of the system that is conventionally performed by simply detecting the carrier level of the premodulation code will be difficult. 6 series C
The disadvantage is that it is difficult to judge /N.

ldl Purpose of the Invention The purpose of the invention is to solve the above-mentioned drawbacks (this is a novel space transfer method that measures both the carrier level and the light-receiving current level of the light-receiving element and determines the C/N7E of the damaged system from this). The purpose of the invention is to provide a comprehensive system for monitoring. In order to achieve the above-mentioned object, an optical signal from a light emitting element is received by a light receiving element through space, thereby performing optical communication. In the monitoring method of the optical transmission equipment used in the optical space transmission method, the average reception f flowing through the light receiving element is compared with the carrier detected from the ``Kairy reconnaissance signal'' output from the light receiving element with the flow. Having means for measuring N7i-
Features.

(fl Embodiments of the Invention Noises in the light receiving system of optical fiber communication include: ■ Darkness t Ui of the light receiving element, ■ Noise N generated from the light receiving unit electric circuit, etc.
There is an O. This NO is independent of background light level.

In view of the above points, when the noise N L+ due to the background noise No. 0, the noise No. of the light receiving element, and the carrier C are measured simultaneously, the C/N is displayed as ``/N=717 u□a.

Here, NO is No)Nb in the optical fiber connection 1, and therefore can be expressed as C/No in C/N. Here, NO is approximately a constant value of 0-10,000, and in the optical space transmission targeted by the present invention, it is Nb)NO, and Nb is proportional to the background light level. Therefore,
C/N can be measured by setting the light receiving element current Ib, which is proportional to Nb, by 6111.

Next, we decided to measure the C/N using the example shown in FIG. 4. In FIG. be done. The preshock 11 polarization signal passes through an amplifier 3, a filter 4, and an amplifier 5, and is outputted from an output terminal 6. The output of the filter 4 is input to a carrier detection circuit 7, where a carrier is detected, and each detected signal is input to a comparison circuit 11.

10,000, the optical signal 1 is applied to the light receiving element 2 together with the background light 10, and the light receiving element current Ib/ flows. In this case, a certain noise No is generated by the light receiving element current Ib' caused by the optical signal J, and noise Nb is generated by the light receiving element current 11) caused by the back Jlt source IOJ. Since the relationship between this noise Nb and the light receiving element current 1b' is proportional as described above, Ib
Compare ' with carrier tobel C. 1- C/N is determined from Rukoyoshi. In the figure, the photodetector current ■1]' is the amplifier 1
2 is amplified by the detection circuit 13 and the background light is detected by the light receiving element 1'.
J, % i b' detected. The detected background light lb/ is input to the ratio soft circuit 11, compared with the carrier, and the C/N value added to the C/N titer is read by the indicator 14.

In addition, a reference voltage for determining the threshold value of C/Thi is given to the comparator circuit 11 (J makes it easy to measure C/N).

(gi) As explained in detail about the invention, in the conventional dead space transmission system, noise in the light receiving system of the transmission device was monitored by monitoring the gear rear level, but the back noise increased. When the light-receiving element σJC/I%I could not be monitored accurately due to the noise generated by the light-receiving element, the light-receiving element current Ib, which is proportional to the noise of the background light, was detected. By comparing Ib and C, the C/N of the light receiving system can be measured.This allows the state of Cc due to background light to be accurately monitored. Cultivate the benefits of maintaining the thread stably.

[Brief explanation of drawings]

Figure 1 shows a conventional U/N monitoring circuit, and Figure 2 shows 11)/
3 is a T diagram showing the relationship with Nb/Ib, and FIG. 4 is a diagram showing an embodiment of the invention. In the figures, 1 is light No. 1J, 2 is a light receiving element, 3, 5.12 is an amplifier, 4 is a filter, 6 is an output terminal, 7.13 is a detection circuit, 8 is a comparison circuit having a reference voltage, 9 is a level meter, 10 is a background light, and 14 is an indicator.

Claims (1)

[Claims] In the monitoring method of optical transmission equipment used in the optical space transmission method, which performs optical communication by receiving signals through space with a light receiving element, the carrier detected from the electrical signal output from the light receiving element and flowing through the light receiving element. An optical spatial transmission monitoring system characterized by having a means for measuring C/N by comparing it with an average received light current.