The function of the optical transmitter is to convert the HDB3 signal code sent from the multiplexing device into the NRZ code; then the NRZ code is encoded into a code pattern suitable for transmission on the optical cable line; and finally the electrical/optical conversion is performed to convert the electrical signal into an optical signal and coupled into the optical fiber.
Constitute
The optical transmitter is composed of an input interface, a light source, a driving circuit, a monitoring circuit, and a control circuit. The core is the light source and the driving circuit. In digital communication, the input circuit reshapes the input signal (such as PCM pulse), transforms it into a code pattern suitable for line transmission and then drives the circuit light source, or sends it to the light modulator to modulate the continuous light wave output by the light source. In order to stabilize the output average optical power and operating temperature, an automatic temperature control and power control circuit is usually set up.
Light source modulation
Information processing is done in the field of electricity. In optical fiber communication, electrical signals must be converted into optical signals so that they can be propagated on optical fibers. In an optical fiber communication system, information is carried by light waves emitted by LEDs or LDs. The light waves are carrier waves, and the process of loading information on the light waves is modulation. The optical modulator is a device that realizes the conversion from electrical signals to optical signals.
The system has high requirements on the light source, including:
1. Wavelength stability requirements: WDM systems have higher requirements for the stability of the light source emission wavelength, and wavelength drift will cause crosstalk between channels.
2. Power stability requirements: The drift of the power of a certain channel not only affects the transmission performance of this channel, but also affects the performance of other channels through the transient effect of EDFA.
The control circuit of the light source mainly includes temperature control and power control circuits. Their function is to eliminate the effects of temperature changes and device aging, and stabilize the transmitter performance. Other control circuits include a light source slow start protection circuit, a laser reverse impulse current protection circuit, a laser overcurrent protection circuit and a laser shutdown circuit.
Classification
Optical transmitters are mainly divided into two categories: 1310 optical transmitters and 1550 optical transmitters.
1550 optical transmitters are divided into two categories: externally modulated optical transmitters and direct-modulated optical transmitters.
Post time: 2021-01-29
