Nanofabrication of high refractive index contrast two-dimensional photonic crystal waveguides

We present the fabrication of high refractive index contrast two-dimensional photonic crystal (2D-PC) slab waveguides. 2D photonic crystal structures, consisting of a periodic array of holes in a GaAs matrix, are obtained by nanopatterning of epitaxially grown GaAs/AlGaAs heterostructures. Two different PC structures will be described in detail: (i) an asymmetric 2D-PC slab waveguide obtained by selective oxidation which transforms the Al-rich AlGaAs cladding layer underneath the PCs into aluminium oxide and (ii) a symmetric 2D-PC slab waveguide obtained by removing the oxide (free standing structure)

Second-harmonic generation in reflection and diffraction by a GaAs photonic-crystal waveguide

Nonlinear reflection and diffraction measurements have been performed on a GaAs/AlGaAs photonic-crystal waveguide patterned with a square lattice: The basis in the two-dimensional unit cell consists of rings of air in the dielectric matrix. The measured angles of diffracted second-harmonic beams agree with those predicted for nonlinear diffraction conditions, Results for second-harmonic intensities as a function of incidence angle, polarization, and pump wavelength show that the reflected second-harmonic signal is dominated by the crystalline symmetry of GaAs, whereas nonlinear diffraction is determined by the photonic-crystal structure

Resonant second-harmonic generation in a GaAs photonic crystal waveguide

Second-harmonic generation (SHG) measurements in reflection on a GaAs/Al0.25Ga0.75As photonic crystal waveguide show a resonant enhancement when the pump beam is frequency and momentum matched with the photonic modes in the slab. The enhanced SH signal is observed in the form of resonant peaks, unlike in linear reflectance spectra. The observations are in very good agreement with a full 3D calculation of the anisotropic mode dispersion in the photonic crystal slab. The present results open the way towards realizing the extraordinary enhancement of SHG which was recently predicted [A. R. Cowan and J. F. Young, Phys. Rev. B 65, 085106 (2002)], and also demonstrate the potential of SHG as a nonlinear spectroscopic tool for optical studies of photonic crystals

High-resolution complex structures for two-dimensional photonic crystals realized by x-ray diffraction lithography

The fabrication of two-dimensional photonic band gap structures by using x-ray lithography combined with ion etching on metalorganic chemical vapor deposition grown GaAs/AlGaAs waveguides was discussed. The optical characterizations of photonic crystal samples were also performed. The characterizations showed the presence of well-defined photonic band gap structures and second harmonic property generation

Fabrication by means of X-Ray lithography of 2D GaAs/AlGaAs photonic crystals with unconventional unit cell

Two-dimensional photonic crystals have been fabricated by x-ray lithography and reactive ion etching on an air/GaAs/AlGaAs asymmetric waveguide. The shape of the lattice unit cell has been varied by exploiting x-ray diffraction effects and nonlinear response of resists during the development process. Rings with or without a central pillar have been fabricated with a resolution down to 50 nm. Lithographic details are described to show the accuracy of this fabrication technique. Optical characterization has been performed showing the presence of a well defined photonic band structure as well as band anti-crossing. The results are discussed and compared with theoretical calculations of the photonic band dispersion. Structures with high dielectric fraction are shown to yield photonic modes with small line widths and low propagation losses. The reliability and the precise control of the fabricated sample structures make this lithographic method useful for a full investigation of optical properties on the dependence of the lattice unit cell shape