Transmitting Optical Sub-Assembly (TOSA) mainly plays the role of electrical signals into optical signals (E/O), to determine its performance indicators are mainly optical power, threshold.TOSA mainly consists of lasers (TO-CAN), adapters, tube core sets, in the long-distance optical module, will also join the isolator and adjusting the ring, the isolator to play a role in the role of anti-reflective, while the adjusting the ring is to play a role in adjusting the focal length.

TOSA (Transmitting Optical Sub-Assembley) the main components of the optical transmitter module, mainly to complete the electrical signal to optical signal. The light source (semiconductor light-emitting diode or laser diode) is the core, LD chip, monitoring photodiode (MD) and other components are packaged in a compact structure (TO coaxial package or butterfly package), and then constitute the TOSA. the following figure is a conventional TOSA schematic.

In a TOSA, the LD laser diode is currently the most commonly used semiconductor transmitter device for optical modules, and it has two main parameters: threshold current (Ith) and slope efficiency (S). In order for the LD to operate quickly, we must supply the LD with a DC bias current IBIAS (DC Bias in the diagram above) that is slightly greater than the threshold current, i.e., the laser is emitted only when the forward current exceeds the threshold current.

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