Design and Fabrication of Micro-electro-mechanical Systems Actuators for Application in External Cavity Tunable Lasers

• Author / Creator

  Amin, T M Fahim

• The limited availability of rugged and economical infra-red laser sources that can be tuned over a certain wavelength range is still a bottleneck for widespread application of spectroscopic methods to environmental, industrial, and medical trace gas monitoring. Conventional semiconductor lasers in distributed feedback (DFB) configuration offer only limited wavelength tuning around the center wavelength. External cavity lasers (ECLs) can provide the large tuning ranges needed for laser spectroscopy. Micro-electro-mechanical systems (MEMS) technology is a viable option for integrating and manipulating optical elements and thus fabricating a hybrid integrated ECL at chip level dimensions. With this thesis, I present a strong foundation for building a widely tunable MEMS based ECL. The major contributions are: 1) design and fabrication of different rotary comb actuators to build micro-opto-electromechanical systems (MOEMS) devices for various applications, including ECLs; 2) development of two silicon sidewall smoothing techniques which can provide optical quality reflecting surfaces; and 3) design of an extremely long arm MEMS actuator with zipped comb fingers and structural re-enforcement, and development of an efficient method of mounting external micro mirrors onto MEMS devices.

  The first rotary comb actuator presented in this thesis provides a large deflection angle of 3° at a, for MEMS technology, reasonably low voltage of 100 V. This actuator has a high resonance frequency (>1 kHz) and can be used for optical applications where kHz level frequency operation is required. The virtual pivot point actuator has a pivot point located distant from the physical actuator and offers more options for in-plane optical path alignment. The detailed design and the implementation of the virtual pivot point actuator are presented. The full rotation angle for this actuator is 3° (± 1.5°) for an applied voltage of 190 V. Both of these designs provide an accessible sidewall which can be used as a reflecting surface for on-chip integration. The sidewalls of the actuators were smoothed using either an over-passivated or a two-step oxidation + BOE (buffered oxide etch) technique. The over-passivated recipe uses controlled over-passivation during reactive ion etching with the Bosch process to obtain a smooth sidewall. An rms roughess of as low as 3.93 nm was achieved for the etched sidewall of the rotary comb actuator using this process. The second process uses a thermal oxidation step followed by buffered oxide etching. Repeating this process and using a carefully chosen temperature and oxidation time resulted in the desired optical quality sidewall. This method has no theoretical limitations in terms of smoothing thick structures and the rms roughness achieved for a 100 µm thick silicon sidewall was 2.56 nm. A third actuator was designed with a long movable arm that can support relatively large externally mounted optical components. This actuator will be especially useful for optical applications that require larger optical beams and therefore also large reflectors. For an ECL, a large, high quality external mirror can maximize the reflected light fed back into the gain medium and increase the wavelength tuning range.

• Subjects / Keywords

  • External cavity laser
  • MEMS
  • MOEMS
  • Sidewall smoothing
  • Tunable laser
  • Optical application
  • Micromirror

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3VT1GV7N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.