Selective Tuning of Silicon Photonic Crystal Cavities via Laser-Assisted Local Oxidation

Abstract

Ultra-high-Q nanocavity resonance tuning by laser-assisted thermal oxidation of silicon is demonstrated by using a 532 nm continuous wave laser. The resonance is blue-shifted by >2nm. The quality factor remains >200,000. OCIS codes: (230.5298) Photonic crystals; (140.3945) Microcavities; (130.5296) Photonic crystal waveguides 1. Introduction: Photonic crystal nanocavities are increasingly employed in a range of photonic studies and applications because of their high Q/V m ratios [1]. For applications such as optical EIT [2] and cavity QED [3], accurate control of the resonant wavelength is critical. However, due to fabrication imperfections, resonances will deviate from their desired values. Many post-fabrication tuning techniques have been proposed and demonstrated. These methods can be separated into two categories: global and local. Global tuning methods create uniform changes to the entire photonic chip. Local tuning methods only modify a specific cavity region [4]. Laser-assisted thermal-oxidation tuning has been demonstrated on a GaAs L3 photonic crystal cavity with low-Q of 1800 [5].Deutschmann and Huber have previously studied the local oxidation of SOI substrates [6,7]. Here we demonstrate local oxidation tuning of a silicon photonic crystal double-heterostructure with an initial ultra-high-Q > 300,000. A 532 nm wavelength continuous wave laser beam is focused onto the cavity center with a total incident power of approximately 20 mW. The experiment was conducted at ambient room conditions with a relative humidity of 20%. The cavity mode is blue-shifted > 2 nm while maintaining an ultra-high-Q > 200,000. A larger tuning range should also be achievable. Faster tuning times are also possible using higher incident powers. This tuning method is well suited for complete automation, by using a computer-controlled stage and in-situ monitoring. This would enable the post-fabrication fine-tuning of massive numbers of nanocavities.

Optomechanical creation of magnetic fields for photons on a lattice

“…In first experimental attempts, the optical and mechanical disorder is on the percent level, which makes especially the fluctuations of the optical resonance frequencies significant. Nevertheless, strong reductions of the disorder will be possible by post-fabrication methods [48][49][50], such as local laser-induced oxidation. These are expected to reduce the fluctuations down to the level of 10 −5 relative optical frequency fluctuations.…”