The super luminescent diode (SLD) is an infrared emitter that has the advantages of both the laser diode and the LED, high radiant flux density and low coherence. The SLD was developed as a device that compensates for the disadvantages of laser diodes such as their coherent noise and is therefore ideal for applications where a higher S/N ratio is essential. A photodiode chip has also been mounted within the same package for monitoring the SLD output. They are used in fiber gyroscopes and optical coherence tomography (OCT).