Waveguide-enhanced Raman spectroscopy of trace chemical warfare agent simulants.

We report the measurement of waveguide-enhanced Raman spectra from trace concentrations of four vapor-phase chemical warfare agent simulants: dimethyl methylphosphonate, diethyl methylphosphonate, trimethyl phosphate, and triethyl phosphate. The spectra are obtained using highly evanescent nanophotonic silicon nitride waveguides coated with a naturally reversible hyperbranched carbosilane sorbent polymer and exhibit extrapolated one-σ detection limits as low as 5 ppb. We use a finite-element model to explain the polarization and wavelength properties of the differential spectra. In addition, we assign spectral features to both the analyte and the sorbent, and show evidence of changes to both due to hydrogen bonding.

Suspended photonic waveguide devices.

This article describes recent research at the U.S. Naval Research Laboratory that focuses on the use of micro- and nanomachining techniques for photonic waveguide devices. By selectively etching a sacrificial layer that the waveguide core is supported by, in whole or in part, the waveguide obtains enhanced properties and functionality, such as mechanical flexibility, index contrast, birefringence, and evanescent field depth. We describe how these properties enable unique waveguide applications in areas such as cavity optomechanics, displacement sensing, electro-optics, and nonlinear optics.

Trace gas absorption spectroscopy using functionalized microring resonators.

We detect trace gases at parts-per-billion levels using evanescent-field absorption spectroscopy in silicon nitride microring resonators coated with a functionalized sorbent polymer. An analysis of the microring resonance line shapes enables a measurement of the differential absorption spectra for a number of vapor-phase analytes. The spectra are obtained at the near-infrared overtone of OH-stretch resonance, which provides information about the toxicity of the analyte vapor.

Spatial distribution of power coupling in self-pumped photorefractive reflection gratings.

The spatial distribution of the power transfer achieved by contradirectional two-beam coupling using self-pumped photorefractive reflection gratings is investigated in two materials with different photorefractive gain coefficients, LiNbO3:Fe and KNbO3:Fe. Incremental portions of the volume grating are erased optically by inducing thin optical damage planes, reducing the overall two-beam coupling efficiency. By monitoring the effect of local grating disruption, the distribution of power transfer is spatially resolved throughout the crystal, and the results are found to be in agreement with our theoretical predictions.