Detailed Explanation of the Internal Structure of Optical Transceivers

NADDOD Jason Data Center Architect Jan 30, 2023

As a key device in the optical communication system, the optical transceiver acts as a transmission medium between network devices, which is used to send and receive data. At present, there are many articles on optical transceivers on the market, but only a relatively small part mentions the internal structure of optical transceivers. This article will introduce the internal structure of optical transceivers in detail, so that you can understand the structure of optical transceiver components more clearly.

Internal structure of optical transceiver

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

Optical Devices

Optical devices are the core components of an optical transceiver. Different types of optical transceivers use different optical devices.

1.TOSA and ROSA in common optical transceivers

For common optical transceivers, there are two kinds of optical devices, TOSA and ROSA, which have opposite roles.

(1) What is TOSA?

TOSA is an optical transmitting 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, TOSA composition structure is not a layer of the same, different transmission distance or application of optical transceivers, TOSA may exist other components, such as filters.

Today, most optical transceivers are using laser diodes (LD) as the light source, unlike semiconductor light-emitting diodes (LED), which have lower power consumption, higher output power and higher coupling efficiency. However, there are still low-rate and short-range transmission using semiconductor light-emitting diodes because of their low cost and long service life. The following figure shows the structure of TOSA using laser diodes.


(2) What is ROSA?

A ROSA is an optical receiver assembly whose primary function is to convert the optical signal transmitted from a TOSA into an electrical signal. a ROSA consists of a photodiode, an optical interface, a metal or plastic housing, and an electrical interface. As with the TOSA, the specific components of the ROSA depend on the specific function and application of the optical transceiver, which may also have other components such as amplifiers designed to recover input signals that have been degraded due to long-distance transmission. In this case, the preamplifier converts the current signal into a voltage signal and amplifies it to a high voltage gain, while the postamplifier equalizes the signal output from 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 components of the optical transceiver for transmitting and receiving signals.

2.BOSA in BiDi optical transceiver

BOSA refers to the optical bi-directional transceiver assembly. As the name suggests, BOSA is related to BiDi optical transceivers, and BOSA has emerged with the development of optical transceiver manufacturing technology. Since optical transceivers tend to develop in small size, optical transceivers need to integrate TOSA and ROSA in the coupling process.BOSA, on the other hand, integrates TOSA, ROSA and WDM filter together, and uses WDM technology to couple two wavelengths into the same fiber for transmission.

Integrated Circuit Board

1. What is PCBA?

PCBA is an integrated circuit board, also known as a printed circuit board, SMT placement and DIP plug-in are the methods often used in the PCBA production process. Simply put, PCBA is actually a thin board with integrated circuits and other electronic components, which can fix integrated circuits and other electronic components to ensure the quality and functionality of electronic devices.

2. The difference between PCBA and PCB

Briefly, the main difference between PCBA and PCB is that PCB belongs to the bare board (empty board), PCBA is the finished board. PCB is the printed circuit board, is the carrier of the electrical connection of electronic components, PCBA is the PCB processing process. That is to say, PCB is an empty printed circuit board, there are no parts on it, after SMT placement or DIP plug-in processes, etc., before the PCBA.