JPH0870280A - Optical modulation control method for optical transmitter - Google Patents

Abstract

PURPOSE: To provide the method capable of controlling modulation of a light source of the optical transmitter without using a pilot signal. CONSTITUTION: A light source 2 of the optical transmitter 1 is subject to intensity modulation by using an electric signal processed by frequency division multiplexing (FDM signal), the amplitude of the electric signal is made constant by an AGC to control the intensity modulation with respect to the light source 1 thereby allowing the light source 1 to provide an output of an optical signal. In the optical modulation control method for the optical transmitter, total power of the electric signal processed by frequency division multiplexing is used for the AGC signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling the optical modulation degree of an optical transmission device used for optical communication, for example, an electric / optical converter (E / O converter).

[0002]

2. Description of the Related Art A conventional optical transmission device, for example, an electric / optical converter (E / O converter) 1 as shown in FIG.
Frequency-multiplexed (FDM) electrical signal (hereinafter referred to as FDM
Signal), and the optical signal is transmitted after being intensity-modulated. At this time, in order to keep the modulation of the light source constant, F
A pilot signal is superimposed on a DM signal, a part of this FDM signal is branched as shown in FIG. 1, a pilot signal is extracted from the branched signal by a filter 3, and the pilot signal is extracted by an AGC RF amplifier 4. The amplified signal is detected by the detector 5, the detected pilot signal and the reference voltage (setting value) are compared by the differential amplifier 6, and the variable attenuator (variable ATT) 7 is output by the differential amplifier 6. Change F
An AGC method (pilot AGC) for controlling the DM signal so as to match the reference voltage has been adopted. Note that FIG.
8 is a preamplifier for amplifying the FDM signal, 9 is a main amplifier, and 10 is an optical fiber.

[0003]

However, Pilot A
The GC method has the following problems. ． Since the power applied to the light source 2 is increased by the power of the pilot signal, the optical output is distorted. By the way, when the effective modulation degree of the light source 2 (usually mN ^1/2 : m is the modulation degree per wave, N is the wave number) exceeds a certain value, the nonlinear distortion generated in the light source 2 is rapidly deteriorated. It is necessary to keep the effective modulation degree below a certain value in order to maintain the transmission characteristics of the optical signal generated from the light source 2. ． A pilot signal generator is required. ． In a system in which E / O-O / Es are cascaded as shown in FIG. 3 and the number of signals to be FDM increases with the number of relay stages of E / O-O / E, each E / O
Since the number of FDM signals applied to (E / O1) is different,
In order to keep the effective modulation factor (total power of the FDM signal) applied to the light source of O1 constant, it is necessary to individually set the reference voltage of the pilot AGC, which complicates the system. ． If the pilot signal is cut off, the modulation will not be stable and
/ O operates at the maximum gain value in the electric stage, and the modulation becomes unstable.

It is an object of the present invention to provide a method capable of controlling the modulation degree of a light source of an optical transmission device without using a pilot signal in order to solve the above-mentioned problems of the pilot AGC system.

[0005]

An optical modulation degree control method for an optical transmission apparatus according to the present invention comprises intensity-modulating a light source 2 of an optical transmission apparatus 1 with an electric signal (FDM signal) that is frequency-multiplexed as shown in FIG. In the optical modulation degree control method of the optical transmission device, the intensity modulation for the light source 1 is controlled by making the electric signal constant by the AGC, and the optical signal is output from the light source 1. The total electric power of the multiplexed electric signal is used.

[0006]

According to the optical modulation degree control method of the optical transmission device of the present invention,
The FDM signal that intensity-modulates the light source 2 of the optical transmission device is transmitted to the AGC.
In doing so, since the total power of the FDM signal is used as the AGC signal, the total power of the FDM signal that drives the light source 2 can be made constant without the need to prepare a pilot signal for AGC. The effective value of the modulation power to the light source 2 is kept constant, and the transmission characteristic of the optical signal generated from the light source 2 is maintained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical modulation degree control method for an optical transmission device according to the present invention will be described in detail with reference to FIG. FIG. 1 shows an E / O converter which is one of optical transmission devices. It comprises a preamplifier 8 for amplifying an input FDM signal, a variable attenuator 7, a main amplifier 9, a light source 2, an optical fiber 10, and an AGC circuit 11. The AGC circuit 11 is composed of an amplifier 4, a detector 5, and a differential amplifier 6.

In the E / O converter of FIG. 1, the total power of all the FDM signals NO branched from the output signal of the main amplifier 9 is amplified by the amplifier 4 of the AGC circuit 11, and the amplified signal is detected by the detector 5. The detected signal is compared with the reference voltage (setting value) in the differential amplifier 6, and the attenuation amount of the variable attenuator 7 is changed by the output voltage based on the result, and the FDM signal is converted into the reference voltage. It is controlled so that it agrees with.

Various uses of the E / O converter shown in FIG. 1 are conceivable. One of them is incorporated into the trunk line of the optical transmission system shown in FIG. 3, for example, as a relay electric / optical converter E / O1. In this case, since the number of FDM signals applied to each relay E / O1 is different, in the conventional pilot AGC method, the setting value of the pilot AGC is individually adjusted so that the effective modulation degree applied to the light source of the E / O1 is constant. I was doing. However, in the present invention, the E / O converter of FIG.
Since the total power of the DM signal is used as the AGC signal, the effective modulation degree applied to the light source of E / O1 can be made constant even if there is no pilot signal or if the same reference voltage is set. become.

[0010]

The optical modulation control method for an optical transmission device according to the present invention has the following effects. ． The total power of the FDM signal that drives the light source 2 of the optical transmission device can be made constant without bothering to prepare the pilot signal for AGC, and the effective value of the modulation power to the light source 2 can be kept constant. The transmission characteristics of the optical signal generated from the optical fiber 2 are maintained. ． Since there is no pilot signal, the total power applied to the light source 2 is reduced and the optical output is less likely to be distorted. Also,
As in the conventional case, when the pilot signal is cut off, the degree of modulation is not stable, and the modulation does not become unstable due to the operation at the maximum gain value in the E / O electric stage. ． No pilot signal generator is required. ． Even in a system in which E / O-O / E is cascaded and the number of signals to be FDM increases with the number of relay stages of E / O-O / E, it is not necessary to individually set the reference voltage of the pilot AGC. The optical transmission system becomes simple.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an E / O converter used in the present invention.

FIG. 2 E / O incorporating a conventional pilot AGC circuit
Explanatory drawing which shows an example of a converter.

3 is a configuration diagram of a signal transmission system from multiple points in which the E / O converter of FIG. 1 is incorporated.

[Explanation of symbols]

 1 Optical transmission device 2 Light source

Claims (1)

[Claims] 1. A light source (2) of an optical transmission device (1) is intensity-modulated with a frequency-multiplexed electric signal, and the electric signal is AG
In the optical modulation degree control method of an optical transmission device, wherein the intensity modulation for the light source (2) is controlled by making it constant by C, and an optical signal is output from the light source (2). An optical modulation degree control method for an optical transmission device, characterized in that the total electric power of multiplexed electric signals is used.