The existence of three-dimensional photonic bandgaps in square spiral thin films, made using the Glancing Angle Deposition (GLAD) method, was recently verified. We further demonstrate the flexibility of the GLAD process to fabricate silicon photonic bandgap crystals with customizable bandgap centre frequencies. GLAD combines physical vapor deposition at highly oblique flux incidence angles with dual axis substrate motion control, creating porous thin films with three-dimensional submicrometer topographies. This makes it a near-ideal approach for diamond lattice based photonic crystal fabrication, with manipulation of the photonic properties through the deposition parameters. We have produced a range of different square spiral thin films, and present characterization results indicating bandgaps at wavelengths close to 2 micrometers. Such low wavelength bandgaps have not previously been achieved for square spiral architectures. Ongoing work towards optimization of the process holds the promise of square spiral photonic crystals with even lower bandgap centre wavelengths, approaching the telecommunications windows. In addition to its flexibility and mass-production suitability, we present how GLAD can be used to engineer defects inside the photonic crystals during the one-step growth process. Such defects may potentially be employed as stand-alone waveguides, or as elements of more complex photonic device and circuitry designs involving subsequent micromachining of the GLAD thin films.
Chiral thin films have been demonstrated to have significant optical activity and device applications for gratings, filters, retarders and optical switches. These helically nanostructured films may be microfabricated onto silicon or other substrates utilizing the Glancing Angle Deposition (GLAD) technique with various nanostructures such as helices, chevrons, or polygonal spirals. GLAD is a simple one-step process that enables ready integration of these structures onto optical chips. As proposed by Toader and John, the GLAD technique can be used to fabricate large bandwidth photonic crystals based on the diamond lattice. This structure yields a predicted photonic bandgap as much as 15% of the gap center frequency. Moreover, the corresponding inverse square spiral structure is predicted to have a photonic bandgap as much as 24% of the gap center frequency. We report the details of basic chiral thin film fabrication and calibration. We will also discuss optical characteristics of the chiral films such as the optical rotatory power. Finally, we present the results of our efforts to fabricate square spiral and inverse square spiral structures.