A fiber optic transmitter is a device that converts an electrical analog or digital signal into a corresponding optical signal. It is one of the components of fiber optics technology that uses long flexible glass-like fibers (optical fibers) for transmitting light signals over long distances. The other two components of the fiber optic transmission system are the fiber optic cable and the optical receiver. Some systems also possess the optical regenerator, which may be essential to boost the degraded light signal (for long distances).

The fiber optic transmitter includes a light emitting diode (LED), or a solid state laser diode, and signal conditioning electronics. Usually, the transmitter processes the signals of wavelengths of 850, 1310, or 1550 nm. LEDs are broadly used for short to moderate transmission distances, while laser diodes are meant for transmitting signals over long distances. Compared to LEDs, laser diodes can couple many times more power to optical fiber.

Separate fiber optic transmitters are available for single-mode fibers and multi-mode fibers. Also, some transmitters allow connecting both single mode and multimode cables in them. Biconic, D4, ESCON, FC, FDDI, LC, Loopback, MTP, MT-RJ, MU, SC, SMA, and ST are some of the common connectors.

Data rate (data bits transmitted per second), transmitter rise time (the time needed for a signal to change from a defined 10% to 90% of full power), wavelength (the output wavelength of the transceiver), spectral width (the spectral width of the output signal), and maximum optical output power are considered to be the important performance specifications while selecting a fiber optic transmitter. The speed of a transmitter is expressed in terms of its rise time.

To specify a fiber optic transmitter, it is necessary to refer to its operating temperature, signal inputs (such as TTL, ECL, CMOS video, and RF), pigtail, focusing lens (improving coupling between the transmitter and the fiber), and stand-alone.