Incoherent light sources based on superluminescent diodes (SLDs) are useful for optical coherence tomography (OCT) and in optical gyroscopes. However, typical SLDs produce a maximum optical output that is only a few to a few tens of milliwatts. Researchers at the National Metrology Institute of Japan (NMIJ; Tsukuba, Japan) have made a much more powerful incoherent light source by taking the 2.7 mW optical output of a SLD (master) and injecting it into a laser diode (slave), producing an incoherent output with a spectral linewidth of 7 nm and 140 mW of optical power at a center wavelength of about 855 nm. Reducing the laser diodes power to 15 mW broadens the spectral linewidth to 12 nm.
By itself, the SLD has a spectral linewidth on the order of 50 nm. With no master (SLD) light input, the slave (laser-diode) spectrum shows a typical very narrow laser-diode linewidth (a). Increasing the master light power to 0.3 mW starts adding a broader-band spectrum to the narrow peak (b). Boosting the master power to 0.8 mW eliminates the narrow laser line (c). The maximum SLD input of 2.7 mW creates a smoother broad peak (d). Because the slave light power output was substantially independent from the master input power, the researchers believe that, rather than stimulated emission of the master light, the slave spectrum is simply being broadened by the master input. Contact Akifumi Takamizawa at [email protected].
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.