Characterization of integrated waveguides by atomic-force-microscopy-assisted mid-infrared imaging and spectroscopy.

A novel spectroscopy technique to enable the rapid characterization of discrete mid-infrared integrated photonic waveguides is demonstrated. The technique utilizes lithography patterned polymer blocks that absorb light strongly within the molecular fingerprint region. These act as integrated waveguide detectors when combined with an atomic force microscope that measures the photothermal expansion when infrared light is guided to the block.

1.4 million Q factor SiN micro-ring resonator at 780 nm wavelength for chip-scale atomic systems.

A silicon nitride micro-ring resonator with a loaded Q factor of 1.4 × 10 at 780 nm wavelength is demonstrated on silicon substrates. This is due to the low propagation loss waveguides achieved by optimization of waveguide sidewall interactions and top cladding refractive index.

Ge-on-Si waveguides for sensing in the molecular fingerprint regime.

Low loss, single mode, Ge-on-Si rib waveguides are used to demonstrated optical sensing in the molecular fingerprint region of the mid-infrared spectrum. Sensing is carried out using two spin-coated films, with strong absorption in the mid-infrared. These films are used to calibrate the modal overlap with an analyte, and therefore experimentally demonstrate the potential for Ge-on-Si waveguides for mid-infrared sensing applications.

Plasmonic mid-infrared third harmonic generation in germanium nanoantennas.

We demonstrate third harmonic generation in plasmonic antennas consisting of highly doped germanium grown on silicon substrates and designed to be resonant in the mid-infrared frequency range that is inaccessible with conventional nonlinear plasmonic materials. Owing to the near-field enhancement, the result is an ultrafast, subdiffraction, coherent light source with a wavelength tunable between 3 and 5 µm, and ideally overlapping with the fingerprint region of molecular vibrations. To observe the nonlinearity in this challenging spectral window, a high-power femtosecond laser system equipped with parametric frequency conversion in combination with an all-reflective confocal microscope setup is employed.

Midinfrared Plasmon-Enhanced Spectroscopy with Germanium Antennas on Silicon Substrates.

Midinfrared plasmonic sensing allows the direct targeting of unique vibrational fingerprints of molecules. While gold has been used almost exclusively so far, recent research has focused on semiconductors with the potential to revolutionize plasmonic devices. We fabricate antennas out of heavily doped Ge films epitaxially grown on Si wafers and demonstrate up to 2 orders of magnitude signal enhancement for the molecules located in the antenna hot spots compared to those located on a bare silicon substrate.