JPS58171137A - Optical attenuating agc system - Google Patents

Abstract

PURPOSE:To constitute a high-linearity light receiving part, by providing controllable optical attenuator between an optical input and a photoelectric transducer and performing AGC in an optical region. CONSTITUTION:An optical input L1 is inputted to a photoelectric transducer APD through a controllable optical attenuator OAT and is converted to an electric signal. This signal is not only outputted as a base band output OUT through an amplifier RA but also detected by a detector DET and is impressed to a comparison amplifier AGC. The comparison amplifier AGC compares an output Eo of the detector DET and a reference voltage Er with each other, and an output EC controls the optical attenuator OAT so that the level of the base band output OUT is constant. An optical attenuating plate (ND filter) whose rotation is controlled or the like is used as the optical attenuator OAT.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optically attenuated AGC system with good baseband signal linearity and a wide dynamic range.

(Background Art) A system diagram of the AGC method of a conventional optical receiver is shown in FIG. In FIG. 1, Ll is an optical input signal, APD is a photoelectric conversion element, RA is a light receiving amplifier, OUT is a baseband output, DET is a detection circuit that detects the baseband output,
Eo is the detection circuit output, Er is the reference voltage, and AGC is E. A comparison amplification circuit compares and amplifies E and E, and Ec is configured as the output of the comparison amplification circuit.
A, GC control is performed by changing the reverse bias of the avalanche photodiode (avalanche photodiode), and when the optical input is large, distortion may occur, and the photoelectric conversion element APD may not be set under optimal conditions (the best S/N point). There was a drawback that it could not be operated.

(Problem of the Invention) The present invention aims to improve the above-mentioned drawbacks of the conventional technology, and is characterized by: a photoelectric conversion element that converts optical input into electrical output and outputs the electrical output; In the optical receiving apparatus, a controllable optical attenuator is provided in the optical path between the pre-input and the photoelectric conversion element, and the amount of attenuation by the optical attenuator is a light attenuation type AG controlled according to the deviation;
It is in method C. AG that changes the reverse bias of the APD in the electrical domain and changes the amplifier gain by controlling the control voltage.
An important feature of the present invention is to perform AGC in the optical domain instead of C.

(Structure and operation of the invention) FIG. 2 shows an embodiment of the invention, in which Ll is an optical input, OA
T is an optical attenuator, L2 is an optical attenuator, APD is a photoelectric conversion element (avalanche photo diode), R and A are light receiving amplifiers, OUT is a baseband output, and DET is a detection device that detects the baseband output. circuit, Eo is the detection circuit output, Er is the reference voltage, and AGC is E. A comparison amplifier circuit compares and amplifies Er and Er, and Ec is the output of the comparison amplifier circuit.

The operation will be explained below.

For optical attenuator OAT, control voltage E. For example, as shown in FIG. 3, the transmitted light L2 changes in response to a change in the control voltage E0. The optical attenuator power L2 with respect to the optical input L1 changes as shown in FIG. This is the output E of the detector DET in proportion to the optical input L2 of the photoelectric conversion element. increases and becomes thicker than the reference voltage E (
Then, the output E of the comparator amplifier AGC. is the optical attenuator 0AT
It operates to keep the optical attenuator amount L2 constant by changing the O reduction amount and keep the base band output OUT constant.

As explained above, in the embodiment, since the light L2 entering the photoelectric conversion element APD can be kept constant, the operating point of the electrical system can be set to the best value with good baseband signal linearity and S/N ratio. There is an advantage that the dynamic range can be increased by setting a large attenuation ratio of the optical attenuator OAT. Furthermore, there is an advantage that there is no need to attach an external optical attenuator even for large-level optical input.

The first specific example of the optical attenuator OAT of the embodiment shown in FIG.
As shown in the figure. As the optical attenuator, an optical attenuation plate (ND filter) NDI, which is rotated by a motor MOT, is used. The configuration of the optical attenuator is shown in Figure 6. AX connects the motor MOT and the optical attenuation plate. The transmittance of the light attenuation plate is changed by rotating the axis AX. Figure 7 shows the light attenuator in Figure 6 mounted on an APD mount) MT.
This is a cross-section of the device. FA is a fiber with an optical connector. The operation is similar to that of the embodiment shown in FIG.

(Effects of the Invention) The present invention performs gain control in an optical system without performing gain control in an electrical system, and has good linearity and a wide dynamic range, so it can be used in a receiving section of an optical terminal device.

[Brief explanation of the drawing]

Figure 1 is a system diagram of the AGC system of a conventional optical receiver;
The figure is a system diagram of the present invention, FIG. 3 is a diagram showing the optical attenuator control input vs. transmitted output, and FIG. 4 is a diagram showing the optical attenuation capacitor input vs. output.
FIG. 5 is a specific example of the configuration of the device shown in FIG. 2, FIG. 6 is a structural diagram of an optical attenuator, and FIG. 7 is a mounting diagram of the optical attenuator. Ll... optical input, L2... optical attenuator power, APD... photoelectric conversion element, RA... light receiving amplifier, OUT... base band output, DET... Detector, Eo...Detector output, Er...Reference voltage, AGC...
Comparison amplifier, Ec... Comparison amplifier output, O
AT: optical attenuator, L2: optical attenuator,
NDF...Optical attenuation plate, MOT...Motor, AX
...Curved shaft, FA...Fiber with optical connector Patent applicant Oki Electric Industry Co., Ltd. Patent application representative Patent attorney Megumi Yamamoto - Yan, / Yanio 2 Diagram 2 5 Diagram 6 Diagram 7 figure

Claims (3)

[Claims] (1) In an optical receiver having a photoelectric conversion element that converts an optical input into an electrical output and outputs it, and a means for performing AGC control of an optical signal according to a deviation between the electrical output and a reference voltage, the optical input and the photoelectric conversion An optically attenuated AGC system, characterized in that a controllable optical attenuator is provided in an optical path between elements, and the amount of attenuation by the optical attenuator is controlled according to the deviation. (2) The optical attenuation type AGC system according to claim 1, wherein the optical attenuator is an ND filter whose concentration changes depending on the rotation angle and can be rotated according to the deviation. (3) The optical attenuation type AGC system according to claim 1, wherein the optical attenuator is a BSO element whose transmittance changes according to the deviation.