Feature Of The Week 5/23/10: 140 kHz Optical Coherence Tomography by 2 Degree Of Freedom MEMS Scanner Based Swept Source
Feature Of The Week 5/23/10: Swept source detection optical coherence tomography (OCT) is becoming ever more popular as a chosen approach for clinical applications. This has to do with many factors including speed, compactness, costs, signal processing advantages, and center wavelength capability. Swept source technology continues to improve at a major rate but still achieving a high-speed sweep and long coherence length is one of the most demanding requirements for the swept source. Sweep rates beyond 100 kHz are routinely needed for faster acquisition in a time-limited medical procedure, faster 3D/4D capturing, or motion artifact-free imaging, such as for cardiology, or ophthalmology. When the swept rate is over 100 kHz, it is difficult to meet the overall specifications of the light source with available technologies. MEMS mirror /beam deflector in a diffraction grating based external cavity laser is one way to challenge this, but conventional MEMS design limits the scan angle at over several tens of kHz resulting in smaller wavelength range. Here researchers from Santec and the University of Tokyo show results of a novel two degree-of-freedom (2-DOF) MEMS scanner structure to overcome this mechanical limit. 2-DOF system is a classical model to treat the vibrational system with two mutually dependent spring constants. MEMS membrane is designed with two pair of torsion bars (hinges) where the mirror is supported by two actuators on the side. When appropriately designed by adjusting two spring constant of two pairs of hinges, scanning angle can be increased by a factor of X5-8, resulting in wider and faster scanning. Here they demonstrated a source that performs >100nm scan at 140kHz swept rate as well as SS-OCT image samples.