Fiber Optic Transmitters

Fiber optic transmitters are devices that include an LED or laser source, and signal conditioning electronics, to inject a signal into fiber. The modulated light may be turned on or off, or may be linearly varied in intensity between two predetermined levels.  Light Emitting Diodes (LEDs) have relatively large emitting areas and as a result are not as good light sources as laser diodes.  However, they are widely used for short to moderate transmission distances because they are much more economical.  Laser diodes can couple many times more power to optical fiber than LEDs.  They are primarily used for applications that require the transmission of signals over long distances.  

Fiber optic transmitters 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 transmitters can be used for both single mode and multimode cables.  Common connector types for fiber optic transmitters include Biconic, D4, ESCON, FC, FDDI, LC, Loopback, MTP, MT-RJ, MU, SC, SMA, and ST.

Important performance specifications to consider when searching for fiber optic transmitters include data rate, transmitter rise time, wavelength, spectral width, and maximum optical output power.  Data rate is the number of data bits transmitted in bits per second.  Data rate is a way of expressing the speed of the transceiver.  In the approximation of a step function, the transmitter rise time is the time required for a signal to change from a specified 10% to 90% of full power.  Rise time is a way of expressing the speed of the transmitter.  Wavelength refers to the output wavelength of the transceiver.  The spectral width refers to the spectral width of the output signal.

Features to consider when specifying fiber optic transmitters include signal inputs, pigtail, focusing lens, and stand-alone.  Signal input choices include TTL, ECL, CMOS video, and RF.  Transmitters can have a fiber pigtail attached.  A focusing lens is used to improve coupling between the fiber and the transmitter.  Some transmitters are stand alone, as opposed to a chip.  An important environmental parameter to consider when searching for fiber optic transmitters includes the operating temperature.

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Part Numbers for Fiber Optic Transmitters