What is Optical Transceiver?

The optical transceiver is the core device of optical communication, which accomplishes the opto-electrical (O-E) and electrical-optical (E-O) conversion of optical signals. It consists of two parts: the receiving part and the transmitting part. The receiving part performs O-E conversion, while the transmitting part performs E-O conversion.

Transmitting Part:

Input electrical signals of a certain bit rate are processed by internal driving chips to drive semiconductor lasers (LD) or light-emitting diodes (LED) to transmit modulated optical signals at the corresponding rate. It incorporates an automatic power control circuit (APC) to maintain the stability of the output optical signal power.

Receiving Part:

Optical signals of a certain bit rate are input to the module and converted to electrical signals by photodetectors. After amplification by a pre-amplifier, the corresponding bit rate electrical signals are output, usually in PECL levels. Simultaneously, an alarm signal will be output when the input optical power is below a certain threshold.

Main Parameters of Optical Modules

Transmission Rate

Transmission rate refers to the number of bits transmitted per second, measured in Mb/s or Gb/s. Main rates include 100 Mbps, 1 Gbps, 2.5 Gbps, 4.25 Gbps, and 10 Gbps, 25Gbps, 40Gbps, 50Gbps, 100Gbps, 200Gbps, 400Gbps, 800Gbps.

Transmission Distance

The transmission distance of optical modules is categorized into short, medium, and long distances. Typically, distances of 2 km and below are considered short-range, 10-20 km are medium-range, and 30 km or more are long-range.

The transmission distance of optical modules is limited primarily due to losses and dispersion of optical signals in the fiber.

Loss

Occurs due to absorption, scattering, and leakage of light energy in the fiber, dissipating energy at a certain rate with increasing transmission distance.

Dispersion

Arises from the unequal propagation speeds of electromagnetic waves of different wavelengths in the same medium, causing different wavelength components of the optical signal to arrive at the receiver at different times due to accumulated transmission distance, resulting in pulse broadening and difficulty in distinguishing signal values.

Therefore, users need to choose suitable optical modules based on their actual network conditions to meet different transmission distance requirements.

Center Wavelength

Center wavelength refers to the optical wavelength used for signal transmission. The commonly used center wavelengths for optical modules are:

850nm: Mostly used for short-range transmission (≤ 2 km)

1310nm and 1550nm: Mostly used for medium to long-range transmission (over 2 km).