We report an experimental and theoretical study of the birefringence of two-dimensional photonic crystals in the spectral region below the first photonic band gap. Transmission spectroscopy is used to measure the birefringence of a sample composed of a triangular lattice of air cylinders in silicon, with a cylinder radius of $0.644\hspace{0.5em}\mu \mathrm{m}$ and a lattice pitch of $1.5\hspace{0.5em}\mu \mathrm{m}.$ The measured birefringence (defined as the difference in the effective refractive indices of the electric fields polarized parallel and perpendicular to the cylinder axis) reaches a maximum value of 0.366 near the first photonic band edge at a wavelength of $6.52\hspace{0.5em}\mu \mathrm{m}.$ The results show excellent agreement with theory and demonstrate the potential use of two-dimensional photonic crystals for highly birefringent optically integrated devices.

• Received 11 October 2000

DOI:https://doi.org/10.1103/PhysRevB.63.161101