Wavelength tunable MEMS VCSELs for OCT imaging

Abstract

MEMS VCSELs are one of the most promising swept source (SS) lasers for optical coherence tomography (OCT) and one of the best candidates for future integration with endoscopes, surgical probes and achieving an integrated OCT system. However, the current MEMS-based SS are processed on the III-V wafers, which are small, expensive and challenging to work with. Furthermore, the actuating part, i.e., the MEMS, is on the top of the structure which causes a strong dependence on packaging to decrease its sensitivity to the operating environment. This work addresses these design drawbacks and proposes a novel design framework. The proposed device uses a high contrast grating mirror on a Si MEMS stage as the bottom mirror, all of which is defined in an SOI wafer. The SOI wafer is then bonded to an InP III-V wafer with the desired active layers, thereby sealing the MEMS. Finally, the top mirror, a dielectric DBR (7 pairs of TiO 2 -SiO 2 ), is deposited on top. The new device is based on a silicon substrate with MEMS defined on a silicon membrane in an enclosed cavity. Thus the device is much more robust than the existing MEMS VCSELs. This design also enables either a two-way actuation on the MEMS or a smaller optical cavity (pull-away design), i.e., wider FSR (Free Spectral Range) to increase the wavelength sweep. Fabrication of the proposed device is outlined and the results of device characterization are reported.

Low-coherence semiconductor light sources: devices and applications

“…More specifically, the FD-OCT can be classified into spectrometer-based OCT (SB-OCT), which requires highresolution spectrophotometer, and swept source OCT (SS-OCT) which relies on wavelength-tunable narrowband laser sources. While highcoherence wavelength-tuning VCSELs are crucial for SS-OCTs, both SB-OCT and TD-OCT benefit from low-coherence light sources 163,165,166 . For example, TD-OCT employs temporal low-coherent light sources in an interferometer setup, as shown in Fig.…”