Optical transport in planar waveguide structures is of great importance for spectroscopic chemical and biological sensing
applications. We have fabricated a TiO2-polymer planar waveguide with an embedded grating coupler. The grating
coupler consists of a low index layer of SiO2 on a Si(100) substrate. The SiO2 layer has a grating pattern reactive ion
etched into the surface. On top of this surface is a high index TiO2 waveguide. The TiO2 film is generated from a spincoated
polymer solution, OptiNDEXTM EXP04054 from Brewer Science. The TiO2 film has low optical absorption, a
high refractive index, and good thermal and UV stability. It is possible to make up to a 420nm film in a single coating
operation. To form the TiO2 film the polymer solution is spin-coated onto a wafer and the wafer is baked at 300 °C for 10
minutes. Scanning electron microscopy and focused ion beam cross-sections verified that the TiO2 conformally fills the
groves of the grating. We made electrodynamic calculations based on the indices of the materials for our waveguiding
structure and the wavelength of the incident light for single-mode wave guiding. These calculations gave a projected
TiO2 thickness for our waveguides. Experimental results show that the waveguide structures that we fabricated were in
close agreement with these predictions.
Nanoscale electric field confinement and enhancement is a well known phenomenon for small particles and flat
interfaces. Senspex is using E-Beam lithography to develop nanosensors for the detection of biological and chemical
hazards. The sensors that are being developed are a square array of metallic cubes; each cube has dimensions of
approximately 100nm x 100nm x 30nm and a pitch of 125nm in the x- and y-directions. Senspex's numerical simulations
show that the intense electric field in the minute volume between the cubes will lead to a high probability of detection
for small concentrations of analyte in real world situations.
We report the calculation of the attenuation coefficient of a probing optical mode due to interaction with metallic nanoparticles randomly distributed in the air holes of a solid core photonic crystal fiber (PCF) for SERS-based sensing and detection. The approach employed is an approximation of the solid core PCF with conventional curricular fiber considering a similar total internal reflection mechanism for mode propagation and almost complete concentration of the mode flux in the core of PCF. Losses due to the absorption and radiative scattering of electromagnetic energy by nanoparticles are examined. The analysis demonstrates a critical dependence of the absorption losses approaching the resonant localized surface plasmon's excitation and very fast rise of radiative losses with the increase of nanoparticle size. The physics of proper integral Raman spectroscopy is also discussed.
We propose a design of the frequency-selective sub-mm-W detector, which must operate at room temperature. The idea is based on a standing wave enhancement of the detector responsivity. The detector contains a lateral semiconductor superlattice with electrons performing Bloch oscillations as an active medium, a broadband bow-tie terahertz (THz) antenna, a built-in resonator and an external dc circuit. As compared with well-known THz-photon detector based on one-dimensional layered superlattice the switch to the lateral superlattice leads to a necessary change in technology of antenna attachment to the superlattice and allows the additional growth of a resonator. The estimation calculations of the current responsivity of the proposed detector fulfilled by means of an equivalent transmission line model have proved that the detector responsivity can be enhanced in several hundred times near a resonance frequency due to the matching between the incident radiation and the superlattice provided by built-in resonator. The expected rise time of the proposed detector is in order of 10-11s.