Fiber optic modules are important components in fiber optic communication that enable the process of optical-electrical and electrical-optical conversion in the transmission of optical signals. Working in the physical layer of the OSI model, they are one of the core components in fiber optic communication systems. They mainly consist of optoelectronic devices (optical transmitters, optical receivers), functional circuits, and optical interfaces, with the main function of implementing optical-electrical and electrical-optical conversion in fiber optic communication.
The sending interface inputs electrical signals of a certain bitrate, which are processed by the internal driver chip and emitted by the driver semiconductor laser (LD) or light-emitting diode (LED) as modulated optical signals of corresponding speed. After transmission via fiber optic, the receiving interface converts the optical signals into electrical signals using light detecting diodes, and the corresponding electrical signals are outputted after front-end amplification. Fiber optic modules come in various types and have different appearances, but their basic structure consists of the following parts. To meet the requirements of various transmission rates, there are different types of fiber optic modules available, such as 400GE, 100GE, 40GE, 25GE, 10GE, GE, and FE fiber optic modules. Fiber optic cables can be single-mode or multi-mode, accordingly there are single-mode and multi-mode modules.
What factors limit the transmission distance of fiber optic modules? Actually, the transmission distance of fiber optic modules is mainly restricted by loss and dispersion. Loss is caused by the loss of optical energy due to absorption, scattering, and leakage of the medium while transmitting in the fiber optic, this part of energy dissipates at a certain rate with increasing distance of transmission. Loss-limited distance can be estimated by the formula: loss-limited distance = (transmitting optical power-receiving sensitivity)/fiber attenuation. The greater the loss, the shorter the transmission distance of fiber optic modules, and vice versa.
Dispersion is mainly caused by the unequal speeds of electromagnetic waves of different wavelengths when propagating in the same medium, resulting in different wavelength components of the optical signal arriving at the receiving end at different times after accumulating over a certain transmission distance, causing pulse broadening and rendering signal values indistinguishable.