Working Principle and Application of Optical Module in Optical Transmission

In the field of communication, the transmission of electric interconnection of metal wires is greatly limited due to electromagnetic interference, inter symbol interference and loss, wiring cost and other factors.

Therefore, optical transmission is born. Optical transmission has the advantages of high bandwidth, large capacity, easy integration, low loss, good electromagnetic compatibility, no crosstalk, light weight, small size, etc., so optical output is widely used in digital signal transmission.

Basic structure of optical module

Optical module is the core device in optical fiber transmission, and its indicators determine the overall performance of transmission. The optical module is the carrier used for transmission between the switch and the equipment, and its main function is to convert the electrical signal of the equipment to the optical signal at the transmitting end. The basic structure is composed of two parts: "optical emission component and its driving circuit" and "optical receiving component and its receiving circuit".

The optical module consists of two channels, namely the transmitting channel and the receiving channel.

Composition and working principle of transmission channel

The transmitting channel of the optical module is composed of an electrical signal input interface, a laser driver circuit, an impedance matching circuit and a laser module TOSA.

Its working principle is to input the electrical interface of the transmission channel, complete the coupling of electrical signals through the electrical interface circuit, then modulate through the laser drive circuit in the transmission channel, and then perform impedance matching through the impedance matching part to complete the modulation and driving of signals, and finally send them to the laser (TOSA) for electro-optical conversion into optical signals for optical signal transmission.

Composition and working principle of receiving channel

The optical module receiving channel is composed of a photodetector assembly ROSA (consisting of a photodetector diode (PIN) and a transimpedance amplifier (TIA)), an impedance matching circuit, a limiting amplifier circuit, and an electrical signal output interface circuit.

Its working principle is that PIN converts the collected optical signal into electrical signal in a positive proportion, TIA converts this electrical signal into voltage signal, amplifies the converted voltage signal to the required amplitude, and transmits it to the limiting amplifier circuit through the impedance matching circuit to complete the re amplification and shaping of the signal, improve the signal-to-noise ratio, reduce the bit error rate, and finally the electrical interface circuit completes the signal output.

Application of optical modules

Optical modules are widely used in data centers as the core devices to realize photoelectric conversion in optical communication. Traditional data centers mainly use 1G/10G low-speed optical modules, while cloud data centers mainly use 40G/100G high-speed modules. Generally, we choose optical modules mainly considering application scenarios, data transmission rate requirements, interface types, optical transmission distance (fiber mode, required optical power, center wavelength, laser category) and other factors.