As one of the cores of medium and long-distance optical communication, the optical module plays a role in photoelectric conversion. It is composed of optical devices, functional circuit boards, and optical interfaces. Today, ETU-LINK will introduce to you the components of the optical module—TOSA and ROSA.

1、TOSA

TOSA is the main component of the optical transmitter module, whose main function is to convert electrical signals to optical signals. TOSA can be divided into SC TOSA, LC TOSA, FC TOSA, ST TOSA according to the adapter type. TOSA includes components such as optical isolator, monitoring photodiode, LD drive circuit, thermistor, thermoelectric cooler, automatic temperature control circuit (ATC), and automatic power control circuit (APT).

The light source (semiconductor light-emitting diode or laser diode) is the core. LD chip, 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 currently the most commonly used semiconductor emitting device for optical modules. 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 a DC bias current IBIAS slightly larger than the threshold current, that is, the laser is emitted when the forward current exceeds the threshold current.

2、ROSA

ROSA is a light receiving component. In high data rate optical modules, PIN or ADP photodiodes and TIA are usually assembled in a sealed metal casing to form our light receiving components.

The photodetector, the main component of the receiving component ROSA, is mainly used to convert optical signals into electronic signals through the photoelectric effect. Common photodetectors in optical communication are PIN photodiodes and avalanche photodiodes (APD). APD is a high-sensitivity photodetector that uses avalanche multiplication effect to double the photocurrent. Compared with PIN photodiodes, the sensitivity of APD receivers can be increased by 6~10dB.

The above is the TOSA and ROSA related knowledge compiled by ETU-LINK. TOSA and ROSA, as the core components of the optical module, play an important role in photoelectric conversion.