Superluminescent diode

A superluminescent diode (SLED or SLD) is an edge-emitting semiconductor light source based on superluminescence. It combines the high power and brightness of laser diodes with the low coherence of conventional light-emitting diodes. Its emission optical bandwidth, also described as full-width at half maximum, can range from 5 up to 750 nm. The superluminescent diode was reported for the first time by Kurbatov et al. (1971) and Lee, Burrus, and Miller (1973). By 1986 Dr. Gerard A. Alphonse at RCA Laboratories (now SRI International), invented a novel design enabling high power superluminescent diodes. This light source was developed as a key component in the next generations of fibre optic gyroscopes, low coherence tomography for medical imaging, and external cavity tunable lasers with applications to fiber-optic communications. In 1989 the technology was transferred to GE-RCA in Canada, which became a division of EG&G. Superluminescent light emitting diodes are also called sometimes superluminescent diodes, superluminescence diodes or superluminescent LEDs. A superluminescent light emitting diode is, similar to a laser diode, based on an electrically driven p-n junction that, when biased in forward direction, becomes optically active and generates amplified spontaneous emission over a wide range of wavelengths. The peak wavelength and the intensity of the SLED depend on the active material composition and on the injection current level. SLEDs are designed to have high single pass amplification for the spontaneous emission generated along the waveguide but, unlike laser diodes, insufficient feedback to achieve lasing action. This is obtained very successfully through the joint action of a tilted waveguide and anti-reflection coated (ARC) facets. When an electrical forward voltage is applied, an injection current across the active region of the SLED is generated. Like most semiconductor devices, a SLED consists of a positive (p-doped) section and a negative (n-doped) section.