In the
optical fiber communication system, the task of the optical receiver is to
recover the information carried by the optical carrier after optical fiber
transmission with minimal additional noise and distortion. Therefore, the
output characteristics of the optical receiver comprehensively reflect the
performance of the entire optical fiber communication system.
After
the optical signal transmitted by the optical transmitter is transmitted, not
only the amplitude is attenuated, but the pulse waveform is also broadened. The
function of the optical receiver is to detect the transmitted weak optical
signal, and amplify, shape, and regenerate the original transmission signal.
Its main components are:
(1) Photodetector: Its main function is to use the photoelectric effect
to convert optical signals into electrical signals. In optical communication
systems, the requirements for photodetectors are high sensitivity, fast
response, low noise, low cost and high reliability. The basic principle of the
photoelectric detection process is light absorption. At present, commonly used
photodetectors in optical communication systems are PIN photodiodes and
avalanche diodes (APD). Performance comparison of the two detectors: Compared
with the APD with the same performance, the price of the PIN is lower, and the
noise of the PIN is lower.
(2) Optical receiving system: At the
receiving end, the function of the receiving antenna is to collect and converge
the light field propagating in space on the surface of the detector.
(3) Signal processing
In the space optical communication system, the
signal received by the optical receiver is very weak, and in the case of high
background noise field interference, it will cause the S/N ratio of the
receiving end <1. So the processing of the signal is very necessary. The
usual measures are as follows: First, on the optical channel, an optical
narrowband filter is used to process the received optical signal to suppress
the interference of background stray light. The basic types of optical filters
include absorption filters, interference filters, birefringent filters and new
atomic resonance filters. The second is to use a preamplifier to convert the
weak photo-generated current signal generated by the photodetector into a
voltage signal on the electrical channel, and then further amplify the signal
through the main amplifier. Then the signal is shaped and processed by
equalization and filtering methods, and finally the information at the
transmitting end is recovered through clock extraction, decision circuit and
decoding circuit.
