We are building prototype chip-scale low-power integrated-optic gas-phase chemical sensors based on mid-infrared
(3-5μm) Tunable Diode Laser Absorption Spectroscopy (TDLAS). TDLAS is able to sense many gas phase chemicals
with high sensitivity and selectivity. Novel gas sensing elements using low-loss resonant photonic crystal cavities or
waveguides will permit compact integration of a laser source, sampling elements, and detector in configurations suitable
for inexpensive mass production. Recently developed Interband Cascade Lasers (ICLs) that operate at room temperature
with low power consumption are expected to serve as monochromatic sources to probe the mid-IR molecular spectral
transitions. Practical challenges to fabricating these sensors include: a) selecting and designing the high-Q microresonator
sensing element appropriate for the selected analyte; b) coupling laser light into and out of the sensing
element; and c) device thermal management, especially stabilizing laser temperature with the precision needed for
sensitive spectroscopic detection. This paper describes solutions to these challenges.
We propose a waveguide integrated plasmonic platform in order to deliver excitation power to and collect signal
efficiently from a nanoantenna. The system consists of a silicon waveguide with an integrated nanoantenna and a fiber
spot size converter. The nanoantenna is designed to have a broad resonance around 1.5 microns with an estimated
surface enhanced Raman scattering (SERS) enhancement of 6 orders of magnitude and collection efficiency up to 80%.
The device is fabricated on a silicon-on-insulator (SOI) wafer. The proposed and fabricated device can be used in
applications such as on-chip SERS spectroscopy, infrared spectroscopy and gas sensing.
We propose and demonstrate a new labyrinth based metamaterial structure that solves two major problems related to the split-ring resonator based structures. One of the problems related to the
split-ring resonator structure is the bianisotropy, and the other problem is the electric coupling to the magnetic resonance of the split-ring resonator structure. These two problems introduce difficulties in obtaining isotropic left-handed metamaterial mediums. The new structure that we propose here solves both of these problems. We further show that in addition to the magnetic resonance, when combined with a suitable wire medium, the structure that we propose exhibits left-handed transmission band. A two-dimensional metamaterial based on the labyrinth structure is used to study imaging of a point source. Our experimental results show that it is possible to image the point source with half widths as small as λ/4 by using the labyrinth based metamaterial.
We report a true left-handed (LH) behavior in a composite metamaterial consisting of periodically arranged split ring resonator (SRR) and wire structures. The magnetic resonance of the SRR structure is demonstrated by comparing the transmission spectra of SRRs with that of closed SRRs. We confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined left-handed transmission band with a peak value of -1.2 dB (-0.3 dB/cm) is obtained. We also report the transmission characteristics of a 2D composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement. The experimental results agree extremely well with the theoretical calculations.
In this work, we have experimentally and theoretically studied the emission of radiation from a monopole source embedded in a two and three dimensional photonic crystal. We have demonstrated the enhancement of radiation at the band edges and at the cavity modes including coupled cavity modes. We have shown that the emission
of radiation from a source depends on the group velocities of the modes and on the electric field intensities of the modes at the source location. Moreover, we have studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal.
We investigate the localized coupled-cavity modes in two- dimensional dielectric photonic crystals. The transmission, phase, and delay time characteristics of the various coupled-cavity structures are measured and calculated. We observed waveguiding through the coupled cavities, splitting of electromagnetic waves in waveguide ports, and switching effect in such structures. The corresponding field patterns and the transmission spectra are obtained from the finite- difference-time-domain (FDTD) simulations. We also develop a theory based on the classical wave analog of the tight- binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation.