Electro-optic modulators are analog or digital devices that use an electric field to alter the characteristics (e.g., band gap and index of refraction) of a material through which light is traveling, changing the characteristics of the light itself. Most electro-optic modulators use changes to the index of refraction in a lithium niobate crystal for electrical potential. The change in the index of refraction is then used to modify the light passing through the material. Some electro-optic modulators vary the amplitude or frequency of the light beam. Others shift the light beam’s phase. Electro-optic modulators can be free standing or rack mounted. Optional features include attached fiber pigtails and maintained polarization of the incoming signal.
Electro-optic modulators use many different types of connectors. Biconic connectors have precision-tapered ends for low insertion loss. D4 and FC connectors are durable, zirconia-ceramic ferrules with a keyed body for repeatability. FC connectors are used primarily with single-mode fibers, but are also used in telephone systems, instruments, and high-speed communication links. Designed for use in FDDI networks, FDDI connectors are 2.5 mm ferrules that include a fixed shroud. ESCON connectors have the same measurements, but use an adjustable shroud. LC connectors are high-precision, zirconia-ceramic ferrules that feature an RJ-45 push-pull housing and latching. MT-RJ connectors hold two fibers with a ferrule that is smaller than the one used in MTP connectors, devices that are threaded and well-suited for high-density applications. ST connectors are easy-to-assemble devices that feature a bayonet mounting system. They are used with both single-mode and multi-mode fibers in communications applications. SMA connectors include a low-cost, multi-mode coupling that is suitable for military applications. Loop back connectors are used to test transceiver systems with electro-optic modulators.
Performance specifications for electro-optic modulators include wavelength range, data rate, rise time, insertion loss, frequency shift range, and bias voltage. Typically, wavelength range is measured in nanometers (nm) and data rate is measured in gigabytes per second (GB/Sec). In the approximation of a step function, rise time is the time required for a signal to change from a specified 10% to 90% of full power. Rise time provides a way to express the speed of electro-optic modulators and is usually measured in seconds. Insertion loss is the amount of attenuation caused by the insertion of an optical component. Bias voltage is a low DC voltage typically supplied by a body-pack wireless transmitter. Unlike phantom power, bias voltage does not require a balanced circuit.
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Acousto-optic modulators are devices that use sound waves to modify the amplitude, frequency, or phase of light passing through an acousto-optic material.