The Inside Structure of Optical Transceiver Module

As a key component in optical communication systems, optical modules act as transmission media between network devices and are used to send and receive data. Currently, there are many articles on optical modules on the market, but only a few of them mention the internal structure of the optical module. This article will introduce the internal structure of the optical module in detail to give you a clearer understanding of the optical module structure.

The optical transceiver module is mainly composed of three parts: housing, optical device and integrated circuit board. Uncover the metal casing of the optical module and you will find that the internal components are connected to each other. The following will focus on optical components and integrated circuit boards.

Optical Devices

Optical devices are the core components of optical modules. Different types of optical modules use different optical devices.

TOSA and ROSA in Common Optical Transceiver Modules

For ordinary optical transceiver modules, there are two optical devices, TOSA and ROSA, which have opposite effects.

What is TOSA?

TOSA refers to the light emitting component, whose main function is to convert electrical signals into optical signals. It consists of a light source (semiconductor light-emitting diode or laser diode), optical interface, monitoring photodiode, metal or plastic housing and electrical interface. However, the composition structure of TOSA is not a constant layer. For optical modules with different transmission distances or applications, TOSA may have other components, such as optical filters.

Nowadays, most optical transceiver modules use laser diodes (LDs) as light sources. Unlike semiconductor light-emitting diodes (LEDs), laser diodes have lower power consumption, higher output power and higher coupling efficiency. However, semiconductor light-emitting diodes are still used for low-speed and short-distance transmission because of their low cost and long service life. The figure below shows the TOSA structure using laser diodes.

What is ROSA?

ROSA refers to the optical receiving component, whose main function is to convert the optical signal transmitted from TOSA into an electrical signal. ROSA consists of a photodiode, optical interface, metal or plastic housing and electrical interface. The same as TOSA, the specific components of ROSA depend on the specific function and application of the optical module. There may also be other components such as amplifiers designed to restore the input signal degraded due to long-distance transmission. Among them, the preamplifier converts the current signal into a voltage signal and amplifies it into a high voltage gain, while the postamplifier equalizes the signal output by the preamplifier to an amplitude level suitable for output to subsequent digital circuits.

Such a pair of ROSA and TOSA components combine to form the main component of the optical module, which is used to send and receive signals.

BOSA in BiDi Optical Transceiver Modules

BOSA refers to optical bidirectional transceiver components. As its name suggests, BOSA is related to BiDi optical transceiver modules. BOSA emerged with the development of optical module manufacturing technology. Since optical modules tend to develop in small sizes, the optical modules need to integrate TOSA and ROSA during the coupling process. BOSA integrates TOSA, ROSA and WDM filters, and uses wavelength division multiplexing technology to couple two wavelengths into the same optical fiber for transmission.

What is PCBA?

PCBA refers to integrated circuit board, also known as printed circuit board. SMT patches and DIP plug-ins are commonly used methods in the PCBA production process. The entire process of the PCB blank board passing through SMT chip mounting parts or DIP plug-ins is called PCBA. Active and passive electronic components are soldered to the integrated circuit board and then placed inside the optical module. Simply put, PCBA is actually a thin plate with integrated circuits and other electronic components. It can fix integrated circuits and other electronic components to ensure the quality and functionality of electronic equipment.

The difference between PCBA and PCB

Briefly, the main difference between PCBA and PCB is that PCB is a bare board (empty board), while PCBA is a finished board. PCB is a printed circuit board, which is the carrier for electrical connections of electronic components, and PCBA is the process of PCB processing and manufacturing. In other words, PCB is an empty printed circuit board without any parts on it. After SMT patching or DIP plug-in and other processes, PCBA is created.