Optical Transceivers are BOSA (Bi-directional Optical Sub-Assembly) Assemblies and packaged Laser Diode and Photo Diode Modules. The Laser Emitting part of optical transceivers is called TOSA (Transmit Optical Sub-Assembly), its key device is Laser Diode; the Laser Receiving part is called ROSA (Receiver Optical Sub-Assembly), the key device is Photo Diode.

BOSA
BOSA is mainly composed of Laser Diodes, Adapter, Filter, Base, Detector, Isolator and Die Sleeve.
1. Transmitting Laser Diodes and Receiving Photo Diode-TIA;
2. Optical Filter (0 and 45 degree) is needed for the transmitting and receiving of optical path.
3. Adapter and pigtail fibers are selected according to different cost and application scenarios.
4.Optical Isolators, with different light wavelengths, but now are generally omitted by manufacturers due to cost and process, which causes the output visual problem.

TOSA & Laser Diodes
TOSA is a Laser Transmit part to convert electrical signals into optical signals (E/O), and optical power and threshold are the key to performance judgement. It is mainly composed of a semiconductor Laser Diode (LD) , an adapter, and a die sleeve. An optical isolator and adjustment ring will be added into the LR optical module. The isolator acts as an anti-reflection function. And the adjustment ring adjusting the focus.

ROSA & Photo Diodes
ROSA is a Laser Receiving part to convert optical signals into electrical signals (O/E) at the receiving end. Sensitivity (SEN) is the key to performance judgement. It is composed of a detector and an adapter. The detectors can be divided into PIN-TIA and APD-TIA, and the adapters have two types of metal and plastic PE parts.

TIA
TIA refers to the transimpedance amplifier, which converts current signals into voltage signals.

PIN-TIA
PIN is to add intrinsic semiconductor between the PN junction.

APD-TIA
APD is short for Avalanche Photodiode.

The PIN Diode or Avalanche photodiode (APD) converts the received light into signal current. PIN diodes are relatively cheap and work at the same voltage as other electronic components. However, for a given optical power, it generates much less electrons than APD. Therefore, the receiver manufactured by APD has higher sensitivity and the transmitter has a longer transmission distance.