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All of the communication equipment such as routers, switches, firewalls and wireless access points we see today are electronic equipment. Electronic equipment understands only electrical signals. Electrical signals are used to transmit or receive information in the form of bits. When the electronic equipment is interfaced with fiber optic networks, transceivers are used. Transceivers provide the conversion of electrical signal to optical signal and vice versa. Transceivers are an important component of any network. Inside the metal casing of an transceiver, there are several components and sub-assemblies that join together to form the transceiver. The most important components inside of transceivers are:
- Transmitter Optical Sub Assembly (TOSA)
- Receiver Optical Sub Assembly (ROSA)
- Bi-Directional Optical Sub Assembly (BOSA)
Transmitter Optical Sub Assembly (TOSA)
TOSA is the component inside the transceiver which is responsible for converting the electrical signal into an optical signal and then transmitting it over the optical fiber strand connected to it. The transmitter optical sub assembly consists of an electrical connection, a monitor photodiode, a laser diode, a housing which can be of metal or plastic and an optical interface. The TOSA is an essential component of every fiber optic transceiver.
Receiver Optical Sub Assembly (ROSA)
ROSA is the other component in the transceiver. The ROSA is responsible for receiving the optical signal transmitted by the TOSA of the opposite end’s transceiver and converting it back to an electrical signal so that the communication equipment can understand it. The Receiver optical sub assembly consists of a photodiode, a housing and the electrical interface. The Photodiode receives the optical signal, the housing provides the metal or plastic cover and the electrical interface connects to the communication equipment. The ROSA is also an essential component of every fiber optic transceiver. A pair of TOSA and ROSA combined together forms the optical transceiver. The ROSA may also contain amplifier to enhance the received signal.
Bi-Directional Optical Sub Assembly (BOSA)
TOSA and ROSA are essential components in the uni-directional transceivers which transmit on one fiber optic strand and receive on the other fiber optic strand. In case of bi-directional transceivers, BOSA is used which is a combination of a TOSA, a ROSA and additionally a WDM filter. The WDM filter enables the bi-directional transceiver to split the wavelengths into two separate wavelengths. After the wavelengths are split, transmit and receive functions can work on a single strand of fiber.
