Summary of optical module product knowledge

1、 What is an optical module?

The optical module is a photoelectric conversion module, whose function is to convert the electrical signal of the equipment into an optical signal, so that the optical signal can be transmitted in the optical fiber, and then convert the optical signal into an electrical signal after reaching the destination.

2、 Structure of optical module

The optical module is composed of optoelectronic devices, PCB boards and optical interfaces. The main devices are TOSA (optical emission), ROSA (optical reception) and BOSA (optical transceiver). Among them, the key core component of TOSA is the laser emission optical chip, and the current mainstream laser types are DFB, EML, FP, VCSEL. DFB is a common direct modulation semiconductor laser, which is mainly used for medium and long distance transmission. VCSEL transmitter has a short optical transmission distance, which is generally suitable for short distance transmission of 500m. EML is an electro absorption modulated laser composed of DML and EAM modulators, which is suitable for long distance optical transmission. The key core component of ROSA is the detector chip. At present, the mainstream detector types are PIN and APD.

BOSA is called optical bidirectional transceiver module. It is an optical component of BIDI single fiber optical module. Its difference from TOSA and ROSA is that BOSA uses optical filter to transmit signals in full duplex by using wavelength division multiplexing technology in one fiber.

3、 What are the parameters of the optical module?

The parameters of optical module mainly include transmission rate, center wavelength, transmission distance, single-mode/multi-mode, interface type, etc. Multimode is suitable for short distance transmission due to its large loss but small dispersion during transmission, while single-mode is suitable for long distance transmission due to its small loss but large dispersion during transmission.

Loss is the loss of optical energy caused by the absorption, scattering and leakage of the medium when the light is transmitted in the optical fiber. This part of energy is dissipated at a certain rate with the increase of the transmission distance.

Dispersion is mainly caused by the unequal speed of electromagnetic waves with different wavelengths propagating in the same medium, which causes the different wavelength components of optical signals to arrive at the receiving end at different times due to the accumulation of transmission distance, leading to pulse broadening, and thus unable to distinguish the signal value.