What are Fiber Optic Transceivers?

A fiber optic transceiver is a single, packaged device that uses fiber optic technology to transmit and receive data, also known as an optical module. The transceiver is a combination of, transmitter and receiver, which share common circuitry. It is an important part of optical network equipment that has electronic components to encode/decode data from incoming light pulses and then send them to the other end as electrical signals. To send data as light, it makes use of a light source, such as Vertical Cavity Surface Emitting Lasers (VCSELs), FP (Fabry-Perot) lasers, DFB (Distributed Feedback Laser) which is controlled by the electronic parts, and to receive light pulses, it makes use of a photodiode semiconductor such as PIN photodetector, avalanche photodiode (APD). Data can usually travel only one way in a fiber optic cable, so most transceivers have two ports for bidirectional communication: one for sending and the other for receiving signals.

Structure of a Fiber Optic Transceiver

From the above figure, it can be seen that the fiber optic transceiver comprises:

1. Latch: The latch mechanism allows the user to selectively extract the transceiver module from the port by moving an attached plug between the first and second positions.
2. Optical Receivers: These are used to convert light signals into electrical signals for use by equipment such as computer networks.
3. Optical Transmitter: These are the parts of a fibre optic network that convert an electronic signal into an optical one. This signal is then sent through glass optical fibres as a pulse of light.
4. Transceiver Shell: This is the covering for a fiber optic transceiver.
5. Label: Fiber optic transceivers use labels so that the cable connected to the transceiver can be reconnected correctly after depluging.
6. Dust Plug: Dust plug plays a vital role in the optical fiber system, it protects the fiber optic connector, fiber optic adapter, optical interface, and other ports of equipment from the external environment. It prevents severe network deceleration or network failure.

Fiber optic transceiver is classified into various types depending on the type of data to be transported, and over what distance:

• Grey (standard) transceivers: A standard transceiver, often referred to as a grey transceiver, is a single-channel device. Any signal that is not wavelength division multiplexed (WDM) or colored wavelength channels is typically referred to as an uncolored, or a grey signal. WDM is a technique of multiplexing multiple optical carrier signals through a single optical fiber channel by varying the wavelengths of laser light. WDM allows communication in both directions in the fiber cable. Grey transceivers have two main applications. Firstly, they can be connected directly to a single fiber channel or Ethernet data switch to transport data in the form of light over fiber. Secondly, they are used as an optical interface in transponder devices for receiving a radio signal and automatically transmitting a different signal.
• Single fiber (bi-directional) transceiver: A bi-directional transceiver uses two independent wavelength channels, one to transmit and one to receive signal over a single fiber strand. It uses channels 1310nm and 1550nm, but for longer distances, two coarse wavelength division multiplexers (CWDM) channels are used, usually 1510nm and 1570nm.

The Fiber Optic Transceiver uses the following parameters:

• Data Rate:  It is the number of bits transmitted per second.
• Transmission distance: It is the maximum distance over which optical signals can transmit. Optical signals sent from different types of sources can transmit over different distances due to the negative effects of optical fibers, such as dispersion and attenuation. When connecting optical interfaces, select optical modules, and fibers based on the maximum signal transmission distance.
• Central wavelength: It represents the wave band used for optical signal transmission. At present, there are mainly three central wavelengths for common fiber transceiver modules: 850 nm, 1310 nm, and 1550 nm, respectively representing three wavebands.
• Optical Transmit power: The output optical power of an optic transceiver is said to be working properly, when two optical transceivers are connected, the transmit optical power of one end must be within the range of received optical power on the other end.
• Receiving sensitivity: The power at which the receiver of a fiber optic transceiver can receive optical signals within a range of bit error rate (BER = 10-12), in dBm.
• Fiber mode: Mode of optical fibers defined based on core diameters and features of optical fibers. Optical fibers are classified into single-mode (SMF) and multi-mode fibers (MMF). The multi-mode fibers have large core diameters and can transport light in multiple modes. However, the inter-mode dispersion is greater so they are used to transmit optical signals over short distances. Single-mode fibers (SMF) have a small core size and can transmit light in only one mode with a small dispersion, so they can transmit optical signals for long-reach communication distances.
• Connector Type: These are types of the interface on an optic transceiver to accommodate a fiber. The commonly used connector types are Lucent connectors, standard connectors (SC), Multi-fiber push-on connectors, etc.
• Extinction ratio: The minimum ratio of the average optical power with signals transmitted against the average optical power. The extinction ratio indicates the capability of an optical module to identify signal 0 and signal 1. This parameter is a quality indicator for fiber optic transceivers.
• Eye diagram: An oscilloscope display in which a digital signal from a receiver is sampled and fed into vertical input fiber optic cable.

Applications of Fiber Optic Transceivers

Optical transceivers are used in most industries, and they are of utmost importance in telecom applications due to their ability to transport high levels of data over a network. This versatile component can either be plugged into or embedded into a network device. They come in a variety of shapes and sizes.

Fiber Optic Transceiver is used in wired networking applications such as:

• Ethernet: A networking technology used for connecting several computer systems to form a local area network, control the passing of information, and avoid simultaneous transmission by two or more systems.
• Fibre Channel: It is also a high-speed networking technology used to connect computer data storage to servers. Fibre Channel typically runs on optical fiber cables.
• SONET (Synchronous Optical Network) and Synchronous Digital Hierarchy (SDH): These are standard technology for synchronous data transmission on optical media. Both technologies provide faster and less expensive network interconnection than traditional equipment.

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