An optical module is a typically hot-pluggable optical transceiver used in high-bandwidth data communications applications. Optical modules typically have an electrical interface on the side that connects to the inside of the syst. An optical module is a typically hot-pluggable optical transceiver used in high-bandwidth data communications applications. Optical modules typically have an electrical interface on the side that connects to the inside of the system and an optical interface on the side that connects to the outside world through a fiber optic cable. The form factor and electrical interface are often specified by an interested group using a (MSA). Optical modules can either plug into a front panel socket or an on-board socket. Sometimes the optical module is replaced by an electrical interface module that implements either an active or passive electrical connection to the outside world. A large industry supports the manufacturing and use of optical modules. There have been multiple variants of the electrical interface of optical modules that have been used over the years. The earliest forms of optical modules had an analog electrical interface. In the transmit direction, the optical module would directly drive the laser or LED with the analog signal coming from the front system card. In the receive direction, the module would directly drive the receive electrical interface with the output of the analog optical-to-electrical receiver circuit. As speeds increased, the electrical interface was changed to a retimed digital interface. The (CEI), defined by the (OIF) served as the central defining document for these interfaces. The IEEE 802.3 working group has also been influential in the definition of the module interface. In order to save power within the module, optical modules have been made that used the digital interface definition, such as the CEI, but without retiming the signals within the module. These modules delivered an analog connection between the two ends. The in 2016 published the CFP2-ACO or CFP2 - Analog Interoperability Agreement (IA). This IA supports a configuration where the (DSP) is on the main board and analog optical components are on the module. This IA is useful in the case when the DSP exceeds the module power envelope. The ACO interface can be used in coherent optics applications when the link delivers a flexible amount of bandwidth to the system, for example when combined with. The initial ACO IA is for the CFP2 module. The typical optical modulation that are used include Dual Polarization Quadrature Phase Shift Keying (DP-QPSK) and QAM-16. These modules put the DSP on the module and use a conventional retimed digital interface. These modules can use the same optical modulation techniques as the ACO interfaces do. Many different forms of optical modulation and multiplexing have been employed in optical modules. The most common modulation technique historically has been or NRZ. (PAM-4) has also been extensively used. In the 2010s, has been used. Techniques include (DP-QPSK) and. Tunable lasers are sometimes used to allow a module to support various forms of network-based optical switching such as needed in certain cases by an or a (ROADM). In these, the transmit laser can be tuned to a different optical frequency/wavelength. Similarly, the receiver is able to receive different optical frequencies. Different optical wavelengths, also referred to as lambdas, of light are multiplexed in some optical modules using (WDM). Variants include Coarse WDM (CWDM), Dense WDM (DWDM). Optical modules have a series of components inside, some of which have received attention from standards development organizations. In many cases, the baud rate of the optical interface does not equal the baud rate of the electrical interface. In these cases, a gearbox is used within the module to convert between the two rates. For example if the module supports 4 x 25 Gb/s electrical inputs and 2 wavelengths of 50 Gb/s optical interface, then a gearbox must convert between 25 and 50 GBaud. Particularly in the long-reach module market, in-module (FEC) has been included. This has been in both proprietary and standards-based forms. The OIF has created interoperability agreements to create multi-vendor interoperability for a series of in-module components, particularly focused on coherent transmission. These have included • High Bandwidth Integrated Polarization Multiplexed Quadrature Modulators • Integrated Polarization Multiplexed Quadrature Modulated Transmitters • Integrated Dual Polarization Micro-Intradyne Coherent Receivers The OIF has created interoperability agreements to create multi-vendor interoperability for the tunable lasers that are sometimes used in optical modules. These have included • Integrable Tunable Laser Assembly Multi Source Agreement • Micro Integrable Tunable Laser Assembly Implementation Agreement The Transmit Optical Sub-Assembly or TOSA in the optical module converts electrical signals into optical signals for optical transmitters. Sometimes the optical module is replaced by an electrical interface module that implements either an active or passive electrical connection to the outside world. This is used when the link is short, particularly when connecting to a top of rack switch.
