Fiber optic switches route an optical signal without electro-optical and opto-electrical conversions. Fiber optic switches can interface with two types of cables, single mode and multimode. Single mode is an optical fiber that will allow only one mode to propagate. The fiber has a very small core diameter of approximately 8 µm. It permits signal transmission at extremely high bandwidth and allows very long transmission distances. Multimode describes a fiber optic cable, which supports the propagation of multiple modes. Multimode fiber may have a typical core diameter of 50 to 100 µm with a refractive index that is graded or stepped. It allows the use of inexpensive LED light sources and connector alignment and coupling is less critical than single mode fiber. Distances of transmission and transmission bandwidth are less than with single mode fiber due to dispersion. Some fiber optic switches can be used for both single mode and multimode cables.
Important switch performance parameters to consider when searching for fiber optic switches include wavelength range, number of input ports, and number of output ports, switching time, insertion loss, polarization dependent loss, cross-talk, data rate, and switching voltage. The wavelength range specifies the wavelength range the switch is designed to operate in. The number of input and output ports is important to consider. The switching time is the amount of time it takes for switching to occur. The insertion loss is the attenuation caused by the insertion of an optical component. Polarization dependent loss is the attenuation caused by polarization. Cross-talk is the ratio of the output power produced by the desired input to the output power produced by undesired inputs. It is a measure of switching effectiveness. Data rate is the number of data bits transmitted in bits per second. Data rate is a way of expressing the speed of the switch. Switches are active components. The switching voltage is the voltage needed for switching.
Control signal choices for fiber optic switches include RJ-45, RS232, RS422, and TTL. Common switch features include rack mountable and LED indicators. An important environmental parameter to consider for fiber optic switches is the operating temperature.