Novel optical properties of two-dimensional silicon photonic crystals

Macroporous silicon two-dimensional photonic crystals with photonic band gaps in the near- and mid-infrared are investigated through a number of theoretical and experimental studies. The bulk properties of crystals with a triangular lattice of air pores in silicon (and a 1.5 μm lattice pitch) are measured via Fourier transform infrared spectroscopy and laser spectroscopy. Broadband measurements show deep band gaps in the mid-infrared, in agreement with band structure calculations. Calculations also predict the existence of many high-frequency band gaps in addition to the well-known fundamental band gap. Transmission measurements within the photonic band gap of thin crystals reveal a large attenuation of approximately 10 dB per crystal row, demonstrating that only a few crystal rows are needed to approximate a semi-infinite crystal. The transmission of orthogonally polarized beams through a thick crystal is used to measure birefringence within the first photonic band. The measured birefringence shows excellent agreement with band structure calculations and reaches a maximum value of 0.366 ± 0.002, significantly exceeding the birefringence of naturally anisotropic crystals. Single-mode transmission is demonstrated in photonic crystal waveguides formed by a missing row of air pores. Broadband transmission with novel Fabry-Perot oscillations is measured within the 3.3–5.5 μm bulk crystal band gap, in good agreement with band structure calculations and finite-difference time-domain transmission calculations. A tunable two-dimensional photonic crystal is demonstrated via the temperature dependence of a nematic liquid crystal infiltrated into the crystal pores. The 4.4 μm band edge is tuned over 70 nm and band structure calculations are used to infer the alignment of the liquid crystal within the pores. Finally, ultrafast all-optical switching is achieved using free-carriers to shift the 1.9 μm band edge of a photonic crystal with a 500 nm lattice pitch. Pump and probe spectroscopy is used to measure a band edge blueshift of 29 ± 1 nm (for a maximum pump fluence of 2.1 ± 0.4 mJ·cm−2) that occurs over a 400 fs timescale. The many new properties demonstrated in this thesis highlight the exciting possibility of using macroporous silicon photonic crystals to create a new generation of unique and highly-integrated photonic devices.