Femtosecond Laser Modification of Silicon Photonic Integrated Devices

• Author / Creator

  Bachman, Daniel T

• Silicon photonics is an emerging technology with many applications in communications and computing. Light is guided on chip through waveguides with a crystalline silicon core on top of a buffer oxide layer. Silicon is transparent at telecommunications wavelengths with a high index of refraction that enables miniaturization of photonic integrated circuits. However, this high index of refraction also makes resonant and interferometric based silicon photonic devices, like microring resonators and MachZender interferometers, extremely sensitive to waveguide fabrication errors. Current fabrication techniques for silicon photonics are not accurate enough on a wafer scale to allow for proper phase control in these photonic elements and therefore, in most circumstances, post-fabrication tuning of these devices is required. In this thesis, a new, permanent tuning technique is proposed and demonstrated for phase trimming silicon photonic devices. It utilizes single femtosecond laser pulses to change the optical properties of the crystalline silicon waveguide core. Microring resonators were fabricated and used as the test devices to investigate the femtosecond laser tuning mechanism. Using single pulses with a femtosecond laser wavelength of 400 nm, both positive and negative resonance shifts wavelength shifts were achieved. Positive resonance wavelength shifts were attributed to amorphization of a thin layer of the crystaline silicon at the waveguide surface and a linear relationship between resonance wavelength shift and the applied laser fluences was observed. Negative resonance wavelength shifts at higher fluences were attributed to laser ablation of a thin layer of material from the waveguide surface. The technique was also demonstrated to work through a thick SiO2 cladding layer and beam shaping allowed for very fine tuning of microring resonance wavelengths. The same experiment was conducted at a femtosecond laser wavelength of 800 nm and it was found that the threshold fluence for permanent change to silicon at this wavelength occured about 5x lower than previously reported values. Finally the technique was successfully demonstrated on advanced silicon photonic devices including resonance alignment in high-order microring filters and phase correction in polarization diversity circuit.

• Subjects / Keywords

  • Femtosecond laser
  • Photonic Integrated Circuits
  • Amorphization

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3959CJ7W

• 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.