Second Harmonic and Sum Frequency Generation in Sub-Micron 3D Photonic Crystal Microcavities

The second harmonic radiation emitted into the top half space from three dimensionally localized modes of L3 defect cavities in InP-based planar photonic crystals is studied using both CW and pulsed excitation. The far field harmonic radiation patterns observed from modes with resonant wavelengths ~ 1550 nm, excited by a tunable CW laser with less than 1 mW power, reveal strong local field enhancement (> 1000 X). A detailed comparison with FDTD modeling allows us to conclude that the bulk InP second order susceptibility tensor dominates the second order response of these microcavities. When a broadband, sub picoseconds source is used to simultaneously excite two of the microcavity modes, the harmonic spectrum in general consists of three contributions, the second harmonic from each of the excited modes, and a third peak due to the second order (sum frequency) mixing of the two modes. By using short and long pulse excitation simultaneously, we demonstrate how the emission frequency due to sum frequency processes can be used to continuously tune the harmonic emission frequency dependent on the occupation of various cavity modes.