TOSA stands for Transmit Optical Sub-Assembly, which bears the responsibility of converting an electrical signal into an optical signal. It is made up of light source (light emitting diode or laser diode), optical interface, monitor photodiode, metal and/or plastic housing, and. Optical modules are devices used to connect network devices, transmit and receive data between network devices, and can be used to convert optical and electrical signals. OSAs generally fall into three main categories: TOSA, ROSA, and BOSA. Among various optical module form factors, SFP (Small Form-Factor Pluggable).