VCSEL sweeps frequency via optomechanically coupled mirror
The device is potentially useful for lidar (for example, in self-driving cars) as well as for OCT.
|A self-sweeping vertical-cavity surface-emitting laser (VCSEL) couples an optical field with the mechanical motion of a high-contrast grating (HCG) mirror. The HCG mirror is supported by mechanical springs connected to layers of semiconductor material. The force of the light causes the top mirror to vibrate at high speed. The vibration allows the laser to automatically change color as it scans. (Schematic by Weijian Yang)|
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.
1. Weijian Yang et al., Scientific Reports (2015); doi: 10.1038/srep13700