Optical receiver

Abstract

Provided is an optical receiver, which has wide dynamic range characteristics to reproduce burst signals of different light receiving levels stably and which is excellent in a high-speed responsiveness and in an identical code continuation resistance. The optical receiver comprises a preamplifier for converting an output from a light receiving element into a voltage signal, a level detecting circuit having a first level detecting unit of a short time constant and a second level detecting unit of a long time constant and switched to either of the level detecting units on the basis of a time constant switching signal thereby to detect the voltage level of the voltage signal outputted from the preamplifier, an amplifier for controlling the conversion gain of the preamplifier variably on the basis of the detection result, and time constant switching control means for outputting a time constant switching signal on the basis of the output voltage signal from the preamplifier. The time constant switching control circuit outputs the time constant switching signal to the level detecting means so that the first level detecting unit may be selected in case the identical code continuation number of the bit series of a packet of the burst signals received is smaller than a predetermined number, and so that the second level detecting unit may be selected in case the same is larger than a predetermined number.

Description

technical field [0001] The present invention relates to an optical communication system, in particular to an optical receiver applied to a PON (Passive Optical Network: Passive Optical Network) system, which is one of access optical communication systems. Background technique [0002] Currently, a point-to-multi-point access optical communication system called a PON (Passive Optical Network) system is widely used as a system for realizing a public line network using optical fibers. [0003] The PON system is composed of one OLT (Optical Line Terminal: Optical Line Terminal) as a station-side device, and ONU (Optical Network Unit: Optical Network Unit) as a plurality of subscriber terminal devices connected via an optical star coupler. Most ONUs can share most of the optical fiber as the transmission path with the OLT, so it can be expected to save the cost of use, and it can be easily installed outdoors without power supply to the optical star coupler as the driven part, and...

AI Technical Summary

Problems solved by technology

However, on the other hand, since the gain control is performed based on the amplitude of the first bit of the data packet, there is a problem that when the received burst signal (burst signal) changes in level transiently, especially when the excess In case of convergence to a certain level after glowing, causing switching to wrong conversion gain

[0011] In addition, in the technology shown in the above-mentioned Patent Document 2, in order to realize high-speed response, the time constant of the AGC loop needs to be shortened, but in this case, the conversion gain is likely to depend on the pattern sequence of the received signal, and the same code length continues become worse

That is, there is a problem that it is difficult to realize high-speed responsiveness and the same code length continuity at the same time

Images