What is an Optical Transceiver?

What is an Optical Transceiver?

The term optical transceiver is an industry term within the communications industry that describes a component which converts high speed electrical signals into optical signal and to vice-versa. The term ‘transceiver’ is a short version of transmit and receive. 

An optical transceiver (also called a fibre optic transceiver) is component which ranges from the size of your index finger to the palm of your hand. These small and powerful pluggable devices transmit and receive data at speeds from Mbps (1000k bits per second) to several Tbps (Terabits per second). Optical transceivers typically used to plug into switches, routers, high performance computers, and directly into mobile antennas.

The inside of a transceiver consists of several parts:

  • Optical transmitter path (or Transmitter Optical Sub Assembly) which consists of one or more lasers driven by a laser driver which turns the laser on/off. The laser is typically connected a fibre or lens to guide the light out of the device and into a connected optical fibre via the module receptacle
  • Optical receiver path (or Receiver Optical Sub Assembly) which will consist of a fibre connected to the module receptacle which guides the light into the lens or fibre aligned to a PIN or APD optical diode/s, which is also bonded to a transimpedance amplifier (or TIA) to control the gain of the incoming electrical signal to a useable signal. The TIA and APD/PIN which is to convert the light into the electrical domain, which is then connected electrically via wire bonds or other contacts
  • A microcontroller is used to communicate with the host and to manage the power that is supplied along with any error or warning flags regarding the health and performance of the several parts

Optical transceivers are used in many industries, but they are prevalent in the IT and telecom industry due to the ability to send and receive high levels of data through a network.

Optical transceivers are available in a range of form factors (shapes and sizes) and would depend on the switch, router, or equipment in which it plugs into. To choose the form factor needed would depend on the type of data, speed required, and distance required within the network.

Form Factors

Optical transceivers form factor specify the size of the module, its shape, the speeds required to be sent/received, and its protocols.

Here are the range of Form Factors offered at Westbury Photonics:

  • SFP (Small Form Factor Pluggable)
  • SFP+ (10Gbps Small Form Factor Pluggable)
  • SFP28 (25Gbps Small Form Factor pluggable)
  • QFSP (10Gbps Quad channel Small Form Factor Pluggable)
  • QSFP+ (40Gbps Quad channel Small Form Factor Pluggable)
  • QSFP28 (100Gbps Quad channel Small Form Factor Pluggable)
  • QSFP56 (100Gbps Quad channel Small Form Factor Pluggable)

Transceiver Types

There are many types of optical transceiver, each with a different transmission distances. The following describes the commonly found single channel and quad/4-channel versions:

  • SR (Short Range) – SR transceivers support link distances up to 300M over MMF (multimode fibre). Transceivers of this type are of the original multimode optical specification and are widely available. Typical applications include intra-datacentre and within a building.
  • LR (Long Range) – LR transceivers support transmission distances up to 10km over single mode fibre. There is no minimum distance for LR modules. Typical applications would be a central office (CO) to an office building.
  • ER (Extended Reach or 10GBASE-ER) – ER transceivers are suitable for link lengths up to 40km across engineered links and 30km over standard SMF links. Typical application into CO to CO (central office) and metro to -point-to-point links.
  • EZ (Extended Reach or 10GBASE-ZR) – these transceivers are suitable for link distances up to 80km across single mode fibre (SMF). Application for EZ transceivers is typically city-to-city and can be used to span across countries with multiple hops using optical amplifiers and dispersion control.
  • SR4: “SR” refers to link distances up to 300m across MMF, and “4” means there are 4 optical channels. Each of the 4 optical channels from an SR4 module are carried on separate optical fibres, resulting in a total of 8 fibres (4 Tx and 4 Rx) with each channel operating at 50Gbps (200Gbps module) or 100Gbps (400Gbps module)
  • DR4: “DR” refers to 500m reach using SMF and “4” implies there are 4 optical channels. Each of the 4 optical channels from a DR4 module are carried on separate fibres, resulting in a total of 8 optical fibres (4 Tx and 4 Rx). Each optical channel operates at 50Gbps or 100Gbps.
  • FR4: “FR” refers to 2km reach using SMF, and “4” implies there are 4 optical channels. Unlike the DR4 and SR8, the 4 optical channels from an FR4 are multiplexed into a single fibre, totalling 2 fibres from the module (1 Tx and 1 Rx). Each optical channel operates at 100Gbps or higher. The FR4 module uses a duplex LC connector to connect to a single fibre pair.

The terms described above explains some of the more familiar terms for optical transceivers and the meanings behind the abbreviations which is to helps understand and to select the appropriate components for a network.

Get in touch with us to find out more about optical transceivers.

Back to blog