Transmit Optical Sub-Assembly (TOSA) components generally consist of optical isolators, monitoring photodiodes, LD driver circuits, thermistors, thermoelectric coolers, automatic temperature control circuits (ATC), and automatic power control circuits (APT). As the core of the transmitter side, TOSA determines key performance metrics such as wavelength. The key components that perform electro-optical conversion in optical modules are called optical sub-assemblies (OSA). OSAs generally fall into three main categories: TOSA, ROSA, and BOSA. The function of the optical module is to carry out the photoelectric and electro-optic conversion.