Rapid frequency sweeping of a laser's output is an essential function in certain lidar and optical coherence tomography (OCT) instruments. Frequency sweeping can be achieved, for example, by using a microelectromechanical systems (MEMS) high-contrast grating (HCG) mirror as one cavity mirror for a vertical-cavity surface-emitting laser (VCSEL); the MEMS mirror is cyclically moved to sweep the laser's frequency.
But what if the swept mirror could be moved, not by an external electrically driven method, but instead by the light from the VCSEL itself? Researchers at the University of California, Berkeley (UC Berkeley) have done just this by suspending an HCG mirror on micromechanical springs that allow the VCSEL's optical field to couple with the mirror's motion.1 With an average force of just a few nanonewtons, the light exerts enough energy to cause the mirror to vibrate.
The researchers measured a self-oscillation amplitude of the mirror of 550 nm, which produced a 23 nm wavelength sweep in the IR without the need for external controls. The mirror itself has a mass of 130 pg.
In addition to lidar and OCT, the device could be integrated into on-chip photonic sensors.
The next stage, say the researchers, will be to incorporate the new laser design into current lidar or OCT systems and to demonstrate its application in 3D video imaging.
Source: http://news.berkeley.edu/2015/09/03/self-sweeping-laser/
REFERENCE:
1. Weijian Yang et al., Scientific Reports (2015); doi: 10.1038/srep13700
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.