JPH04207645A - Agc circuit for fsk system optical direct amplifier repeater - Google Patents

Abstract

PURPOSE:To attain gain control with immunity from the effect of natural radiation light from an Er doped fiber by using an amplitude of a beat signal resulting from self-delay homodyne detection from an FSK modulation light as a reference signal so as to control a drive current of an excitation laser diode. CONSTITUTION:A light wave A is an FSK modulation light and its optical frequency changes as f1, f2 according to a data. A light wave B is delayed by 1 bit or over with respect to the light wave A and when the light waves A, B are synthesized and the result is subjected to photoelectric conversion, then a beat signal of f1-f2 is detected by square detection. When only the beat signal is extracted by a band pass filter 9 whose center frequency is f1-f2, a burst signal C is obtained and when the burst signal C is subjected to peak detection with a peak detection circuit 10 with a sufficiently small charge time constant and a sufficiently large discharge time constant, a peak signal D is obtained. Then a laser diode drive circuit 11 controls a drive current of an excitation laser diode 12 so that the peak signal D is always constant. Thus a problem that an output light intensity cannot simply be formed into a reference signal with a natural radiation light from an Er doped fiber is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical direct amplification repeater, and more particularly to an AGC circuit of an FSK type optical direct amplification repeater.

Prior Art and Problems to be Solved by the Invention In conventional optical direct amplification repeaters, when automatic gain control is performed, the output light intensity is simply used as a reference signal because there is a lot of spontaneous emission from the Er-doped fiber. The problem was that I couldn't do it.

The present invention has been made in view of the above-mentioned conventional situation,
Therefore, an object of the present invention is to provide a novel AGC circuit for an FSK type optical direct amplification repeater, which makes it possible to solve the above-mentioned problems inherent in the conventional technology.

Means for Solving the Problems In order to achieve the above object, the AGC circuit of the FSK type optical direct amplification repeater according to the present invention includes a pumping laser diode that outputs pumping light, and a pumping laser diode that outputs pumping light and a signal light to be amplified. a first optical multiplexer that multiplexes the light, an Er-doped fiber that inputs and amplifies the light multiplexed by the first multiplexer;
an optical isolator that prevents the output light of the r-doped fiber from returning to the Er-doped fiber; a first optical demultiplexer that branches the output light into an output signal light and a reference destination; and a first optical demultiplexer that branches the reference light further. a delay optical fiber for delaying one of the lights branched by the second optical branching filter, and the other light branched by the second optical branching filter. a second optical multiplexer that multiplexes the output light of the delay optical fiber again; a photoreceiver that photoelectrically converts the output light of the second optical multiplexer; and a bead signal from the output signal of the optical receiver. a bandpass filter that extracts only the amplitude of the bead signal, a peak detection circuit that detects the peak of the amplitude of the bead signal, and a laser diode drive circuit that controls the drive current of the excitation laser diode using the output signal of the peak detection circuit as a control signal. It is composed of:

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a diagram showing signal waves of each part in FIG. 1.

As shown in FIG. 1, the input signal light is multiplexed with the pumping light of a pumping laser diode 12 by an optical multiplexer 1 and amplified by an Er-doped fiber 2. After passing through an optical isolator 3, the amplified light is split into two directions by an optical demultiplexer 4.
One is output as an output signal light, and the other is further branched into light waves A and B by an optical demultiplexer 5. The light wave B is delayed by one bit or more with respect to the light wave A in the delay fiber 6, and then is multiplexed with the light wave A in the optical multiplexer 7, received by the light receiver 8, and subjected to photoelectric conversion.

As shown in FIG. 2, the light wave A is FSK modulated light, and the optical frequency changes from fl to f2 depending on the data. Light wave B
is delayed by one bit or more with respect to A. When light waves A and B are combined and subjected to photoelectric conversion, a bead signal of fl-f2 is detected by square law detection. If only this bead signal is extracted by a band pass filter 9 with center frequencies f and -f2, we get
A burst signal C is obtained. When the peak of this burst signal C is detected by a peak detection circuit 10 having a sufficiently high charging time constant and a sufficiently large discharging time constant, a peak signal C is obtained. In order to keep the peak signal constant, the excitation laser diode 12 is controlled by the laser diode drive circuit 11.
control the drive current.

As described in detail, according to the present invention, a bead signal is detected by self-delayed homodyne detection of FSK modulated light, and the drive current of the excitation laser diode is determined using the amplitude of the bead signal as a reference signal. Therefore, it is possible to control the gain without being influenced by the spontaneous emission light from the Er-doped fiber.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a signal trowel diagram of each part. 1.7... Optical multiplexer, 2... Er-doped fiber,
3... Optical isolator, 4.5... Optical demultiplexer, 6.
... Delay optical fiber, 8... Light receiver, 9... Bandpass filter, 10... Peak detection circuit, 11...
・Laser diode drive circuit, 12... Laser diode for excitation Patent applicant: NEC Co., Ltd. Representative: Patent attorney: Yutabe Kumagai

Claims (1)

[Claims] In an FSK optical direct amplification repeater, a pumping laser diode outputs pumping light, a first optical multiplexer combines the pumping light and the signal light to be amplified, and the first optical multiplexer performs multiplexing. an Er-doped fiber that inputs and amplifies the optically transmitted light; an optical isolator that prevents the output light of this Er-doped fiber from returning to the Er-doped fiber; and an optical isolator that branches the output light of this optical isolator into an output signal light and a reference light. 1st
a second optical demultiplexer that further branches the reference light; a delay optical fiber that delays one of the lights branched by the second optical demultiplexer; a second optical multiplexer that recombines the other light branched by the second optical demultiplexer and the output light of the delay optical fiber; and photoelectrically converts the output light of the second optical multiplexer. a light receiver, a bandpass filter that extracts only the bead signal from the output signal of the light receiver, a peak detection circuit that detects the amplitude peak of the bead signal, and an output signal of the peak detection circuit that is used as a control signal for the excitation. An AGC circuit for an FSK type optical direct amplification repeater, comprising a laser diode drive circuit that controls a drive current of a laser diode.