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As a basic component in optical communication networks, optical transceivers operate as media between different types of devices to receive and transmit data. Today, we have plenty of online and offline information available on transceiver modules from the perspective of their construction and packaging. However, we believe many people still have limited information about the most common, internal elements. In this article, we are going to provide you with some basic yet useful and interesting information about various components that are usually found inside optical transceivers.

Optical Transceivers – Internal Components

We can categorize the basic components of optical transceivers into three parts; PCBA, Optoelectronic devices, and the external housing.

Optoelectronic Devices

Optoelectronic Devices are considered as core components of transceivers. For diverse application optical transceivers, a different type of optoelectronic devices is used.

ROSA and TOSA in General Application Optical Transceivers

ROSA and TOSA are the two most widely used types of optoelectronic devices. A combination of these devices is used in general-purpose transceivers. In the following paragraphs, you will be able to understand the functions of ROSA and TOSA.


What is TOSA?

TOSA means Transmit Optical Sub-Assembly. TOSA covers the electrical signal into an equivalent optical signal. A typical TOSA consists of a light source (laser diode or light-emitting diode), monitor photodiode, an optical interface, plastic or metal housing, and an electrical interface. As required for the applications of the host optical module or the transmission distance additional components such as a filter element may also be used with the TOSA.

These days, a laser diode (LD) is preferred to be used as a light source in optical modules. Compared with LEDs, LDs consumes lesser power while providing higher output and at a higher coupling efficiency. However, even today LEDs are still used in short distances and low-speed transmission hardware because of their long service life and low cost.

What is ROSA?

ROSA is Receiver Optical Sub-Assembly. The primary function of ROSA is to convert the optical signal into an electrical signal. A typical ROSA consists of an optical interface, a photodiode (PD), plastic and/or metal housing, and an electrical interface.

 Like TOSA, additional filters or amplifiers may also be used in conjunction with ROSA depending upon the transmission requirements. There are two possible types of amplifiers; preamplifiers and post-amplifiers. The preamplifier converts the current signal into the voltage signal and amplifies it. Whereas, the post-amplifier receives the amplified signal and outputs a signal suitable for the downstream digital circuitry.

A combination of TOSA and ROSA are deployed inside an optical transceiver, forming its core elements and enabling it for transmitting and receiving data.


BOSA in BiDi Transceivers

BOSA means Bi-Directional Optical Sub-Assembly. BOSAs are used in the construction of BiDi type transceivers. BOSAs comes integrated with a WDM filter, ROSA, and a TOSA – enabling it to support multiple wavelengths on a single fiber through bidirectional technology.

What is PCBA?

PCBA stands for Printed Circuit Board Assembly and it is also known as Printed Circuit Assembly or PCB Assembly. Dual-in-line Package (DIP) and Surface Mounted Technology (SMT) are two of the most common methods used in PCB assembly. The active and passive electronic or optoelectronic components of a transceiver are soldered on PCBs. In short, Printed Circuit Board Assemblies helps in integrating various electronic components of an optical transceiver.

PCBA Vs. PCB – what`s the difference?

Well, these two terms are often used interchangeably. The basic difference between PCBA and PCB is that PCBA is a finished board and PCB refers to a bare board. PCB can be considered as an empty board that can be used as a carrier for electrical components. Whereas, the PCBA represents a completed assembly. A PCB is assembled utilizing the Surface Mounted Technology (SMT) or another suitable technology to get transformed into PCBA.


Optical transceivers consist of various components. The outer jacket of these transceivers is utilized for the packaging of sensitive electronic and optoelectronic components. General-purpose modules come equipped with a ROSA and a TOSA. In Bidi type transceivers BOSA is used. All the electronic components contained by an optical transceiver are soldered on a printed circuit board. The light source is another crucial component used in optical transceivers.