PhD Defence by Hitesh Kumar Sahoo

Title: “Wavelength tunable MEMS VCSELs”

Principal supervisor: Assoc. Prof. Kresten Yvind, DTU Fotonik
Co-supervisor: Prof. Ole Hansen, DTU Nanotech

Evaluation Board:
Prof. Erik Thomsen, DTU Nanotech
CTO, Dr. Dan Birkedal, Alight Technologies ApS, Danmark
Prof. Dr.-Ing Franko Küppers, TU Darmstadt, Germany

Master of the Ceremony:
Senior Researcher Minhao Pu


MEMS VCSELs are one of the most promising swept source lasers for optical coherence tomography 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 solely based on the III-V material system, which is expensive and challenging to work with. Furthermore, the actuating part, i.e., MEMS, is on the top of the structure which brings a strong dependence on packaging to reduce its sensitivity to the operating environment.

This thesis addresses these design drawbacks and proposes a novel design framework. The proposed device uses a high contrast grating mirror on a MEMS stage as the bottom mirror, all of which defined in an SOI wafer. The SOI wafer is then bonded to an InP wafer with the desired active layers, thereby sealing the MEMS. Finally, the top mirror, a dielectric DBR is deposited on top. A systematic study on the integration of InP to Si using a low­temperature bonding process with Ah03 as the intermediate layer is presented.

The proposed 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 i.e. wider free spectral range to increase the wavelength sweep. Fabrication of the proposed device is outlined and the results of device characterization are reported.   


tir 20 mar 18
13:30 - 16:30


DTU Fotonik



Lyngby Campus
Building 341, aud. 22