Analysis of TOSA and ROSA Devices in Optical Modules

1、TOSA

TOSA is the main component of the optical transmitter module, which mainly completes the conversion of electrical signals to optical signals. TOSA can be divided into SC TOSA, LC TOSA, FC TOSA and ST TOSA by adapter type. TOSA includes optical isolator, monitoring photodiode, LD drive circuit, thermistor, thermoelectric cooler, automatic temperature control circuit (ATC), automatic power control circuit (APT).

The light source (semiconductor light-emitting diode or laser diode) is the core, the LD chip, the monitoring photodiode and other components are packaged in a compact structure (TO coaxial package or butterfly package), and then constitute TOSA.

In TOSA, LD laser diode is the most commonly used semiconductor emission device for optical modules at present. It has two main parameters: threshold current (Ith) and slope efficiency (S). In order to make the LD work quickly, we must provide the LD with DC bias current IBIAS that is slightly greater than the threshold current, that is, the laser is emitted when the forward current exceeds the threshold current.

2、ROSA

ROSA is an optical receiving module. In a high data rate optical module, PIN or ADP photodiode and TIA are usually assembled in a sealed metal shell to form our optical receiving module.

The photoelectric detector, the main component of the receiving module ROSA, is mainly used to convert optical signals into electronic signals through photoelectric effects. The common photodetectors in optical communication are PIN photodiode and avalanche photodiode (APD). APD is a highly sensitive photodetector, which uses avalanche multiplication effect to double the photocurrent. Compared with PIN photodiode, the sensitivity of APD receiver can be improved by 6-10dB.