Date of Award
Master of Applied Science (MASc)
Thermally tunable planar Bragg gratings in silicon-on-insulator (SOl) rib waveguides with external and integrated heaters were simulated, fabricated, and measured. Planar Bragg gratings were fabricated using selective silicon self-implantation at a dose of 2 x 10^15 ions/cm^2 to amorphize and increase the refractive index by 0.3 due to the induced damage. External heating resulted in a positive shift of 0.080 nm/degree in a good agreement with the 0.082 nm/degree predicted by theory. This demonstrated the tunability of planar Bragg gratings in SOl rib waveguides and motivated the fabrication of integrated heaters on waveguides. The planar surface of implanted Bragg gratings makes it desirable for subsequent processing such as surface bonding and its tunability makes it applicable as an active device.
Simulations performed with the heat transfer module of COMSOL in conjunction with beam propagation method (BPM) simulations predicted that application of 200 mA current to 100 nm thick aluminum strips is sufficient to generate a 10 degree temperature increase in a waveguide and that a minimum thickness of 300 nm of oxide layer is required to prevent mode loss in a waveguide due to the presence of the metal layer on top. Due to temperature restrictions on implanted damage and high temperatures involved in growth of oxide, non-cured spin-on-glass was used as the insulating layer between the rib waveguide and metal strips. Although, the combination of spin-on-glass (SOG) and aluminum worked on the test samples, it was unsuccessful on the device samples, such that the integrated heaters failed and the deposited aluminum affected the propagation optical mode.
The use of Bragg gratings to couple a broad spectrum of surface illuminating light to a multimode SOl slab waveguide was also demonstrated. This has potential applications in enhancing the long wavelength performance of solar cells. The addition of Bragg gratings on top of slab waveguides promotes light coupling, trapping reflected light and also increasing the optical path length of the incident beam, which increases the efficiency of the solar cells. Bragg gratings with a pitch of 500 nm were fabricated on part of the surface of a multimode planar SOl waveguide and the coupling of light into waveguides with and without Bragg gratings were measured. The measurements and the simulations were in good agreement, confirming that broadband Bragg grating couplers are a good candidate for coupling in more light with higher efficiencies.
Homampour, Shabnam, "Thermal Tuning of Planar Bragg Gratings in Silicon-on-Insulator Rib Waveguides" (2010). Open Access Dissertations and Theses. Paper 4095.
McMaster University Library