Optical module usually consists of a transmitter assembly (TOSA, containing a laser LD chip), a receiver assembly (ROSA, containing a photodetector PD chip), a driver circuit, an optoelectronic interface, a heat sink (some models), a housing, a pull ring and so on. There is also an Automatic Power Control (APC) function which monitors the PD current to control the LD driver current to keep the fiber output constant. When a current is passed across a junction between two different metals in series, heat is radiated or absorbed according the current direction. This document focuses on projection optical modules that incorporate Texas Instruments' DLP Display chips and are designed to project an image onto a surface for a variety of applications, including smartphones, tablets, display projectors, smart home displays, digital signage, AR glasses, and. An optical module is essentially a system-level device that enables electro-optical and opto-electrical signal conversion. Internally, it integrates multiple optical chips and electrical chips working together. The overall architecture can be divided into three main parts: 2. Laser chips, or light-emitting chips, are the heart of optical communication systems.