Angle- and polarization-independent mid-infrared narrowband optical filters using dense arrays of resonant cavities.

We report design and experimental verification of narrowband mid-infrared optical filters with transmission characteristics that are practically constant over a wide range of incident angles. The filter employs a dense array of dielectric resonant cavities in a metal film, where the transmission of each cavity depends upon localized rather than travelling fields, making the filter fundamentally angle-independent. We show experimentally a transmission around 90% from normal incidence up to 60°.

Experimental Studies and Numerical Simulation of Polypyrrole Trilayer Actuators.

Conducting polymer actuators have shown wide application prospects in the field of biomedical sensors and micro-/nanorobotics. In order to explore more applications in biomedical sensing and robotics, it is essential to understand the actuator static behavior from an engineering perspective, before incorporating them into a design. In this article, we have established the mathematical model of a trilayer polypyrrole (PPy) cantilever actuator and validated it experimentally.

All-reflective ring illumination system for photoacoustic tomography.

Given that breast cancer is the second leading cause of cancer-related deaths among women in the United States, it is necessary to continue improving the sensitivity and specificity of breast imaging systems that diagnose breast lesions. Photoacoustic (PA) imaging can provide functional information during in vivo studies and can augment the structural information provided by ultrasound (US) imaging. A full-ring, all-reflective, illumination system for photoacoustic tomography (PAT) coupled to a full-ring US receiver is developed and tested.

Enhancing Sensitivity of a Miniature Spectrometer Using a Real-Time Image Processing Algorithm.

A real-time image processing algorithm is developed to enhance the sensitivity of a planar single-mode waveguide miniature spectrometer with integrated waveguide gratings. A novel approach of averaging along the arcs in a curved coordinate system is introduced which allows for collecting more light, thereby enhancing the sensitivity. The algorithm is tested using CdSeS/ZnS quantum dots drop casted on the surface of a single-mode waveguide.

Local field enhancement on demand based on hybrid plasmonic-dielectric directional coupler.

The concept of local field enhancement using conductor-gap-dielectric-substrate (CGDS) waveguide structure is proposed. The dispersion equation is derived analytically and solved numerically. The solution of the dispersion equation reveals the anti-crossing behavior of coupled modes.

Platinum germanides for mid- and long-wave infrared plasmonics.

Platinum germanides (PtGe) were investigated for infrared plasmonic applications. Layers of Pt and Ge were deposited and annealed. X-ray diffraction identified PtGe(2) and Pt(2)Ge(3) phases, and x-ray photo-electron spectroscopy determined vertical atomic composition profiles for the films.

Asymmetric photonic resonances in GaN slab waveguide for mid infrared selective filters.

We demonstrate a spectrally selective reflector that exploits asymmetric photonic resonances of a 1D photonic crystal. The proposed spectrally selective reflector has a very simple structure - essentially just a single high-index slab of GaN, properly perforated, and supported by a transparent sapphire substrate. With the proper 1D array design, nearly 100% reflection is achieved with a narrow spectral width between 10 cm⁻¹ - 18 cm⁻¹, while the background reflection remains low across the entire mid-IR range.

Variational analysis of the mouse and rat eye optical parameters.

Rodent models are increasingly used to study refractive eye development and development of refractive errors; however, there is still some uncertainty regarding the accuracy of the optical models of the rat and mouse eye primarily due to high variability in reported ocular parameters. In this work, we have systematically evaluated the contribution of various ocular parameters, such as radii of curvature of ocular surfaces, thicknesses of ocular components, and refractive indices of ocular refractive media, using variational analysis and a computational model of the rodent eye. Variational analysis revealed that not all variation in ocular parameters has critical impact on the refractive status of the eye.

Photopic visual input is necessary for emmetropization in mice.

It was recently demonstrated that refractive errors in mice stabilize around emmetropic values during early postnatal development, and that they develop experimental myopia in response to both visual form deprivation and imposed optical defocus similar to other vertebrate species. Animal studies also suggest that photopic vision plays critical role in emmetropization in diurnal species; however, it is unknown whether refractive eye development is guided by photopic vision in the mouse, which is a nocturnal species. We used an infrared mouse photorefractor and a high-resolution MRI to clarify the role of photopic visual input in refractive eye development in the mouse.

Phase-matched sum frequency generation in strained silicon waveguides using their second-order nonlinear optical susceptibility.

Using analysis and numerical simulation, we have investigated near-infrared and mid-infrared second-harmonic generation (SHG) and sum frequency generation (SFG) in crystal silicon (SOI) waveguides that possess a strong second-order nonlinear susceptibility by virtue of a Si(3)N(4) straining layer applied directly to the top surface of the waveguide. This layer induces anisotropic compressive strain in the waveguide core. Using the technique of TE/TM mode birefringence, we have derived waveguide geometries for both slab and strip channel waveguides that offer perfect phase matching of three lightwaves for SHG/SFG along a uniform waveguide, thereby offering the prospect of efficient wavelength conversion in monolithic silicon photonics.

Mid-infrared optical parametric oscillators based on uniform GaP waveguides.

Integrated chip-scale optical systems are an attractive platform for the implementation of non-linear optical interactions as they promise compact robust devices that operate reliably with lower power consumption compared to analogs based on bulk nonlinear crystals. The use of guided modes to facilitate nonlinear parametric interactions between optical fields, as opposed to bulk beams, has certain implications on optical parametric oscillations, the most important of which are additional methods for achieving phase synchronism and reduced threshold power due to the tight confinement associated with the guided modes. This work presents a theoretical investigation on the use of polarization dependent mode dispersion in guided wave structures as a means to achieve non-linear parametric oscillations from continuous wave sources with outputs in the mid-infrared region of the spectrum.

Sub-wavelength plasmonic modes in a conductor-gap-dielectric system with a nanoscale gap.

We study guided modes in a conductor-gap-dielectric (CGD) system that includes a low-index dielectric gap layer of deep sub-wavelength thickness sandwiched between a conductor and a high-index dielectric cladding. Analysis of the dispersion equation for CGD modes provides an analytical estimation for the cut-off thickness of the gap layer. This guided mode is unusual because it exists when the gap thickness is less than the cutoff thickness.

Optical properties of Al2O3 thin films grown by atomic layer deposition.

We employed the atomic layer deposition technique to grow Al(2)O(3) films with nominal thicknesses of 400, 300, and 200 nm on silicon and soda lime glass substrates. The optical properties of the films were investigated by measuring reflection spectra in the 400-1800 nm wavelength range, followed by numerical fitting assuming the Sellmeier formula for the refractive index of Al(2)O(3). The films grown on glass substrates possess higher refractive indices as compared to the films on silicon.

Two-dimensional colloidal crystal corrugated waveguides.

We demonstrate, for what is to our knowledge the first time, two-dimensional (2D) corrugated waveguides at optical wavelengths obtained by use of 2D colloidal crystals. We report experimental studies of light coupling into and out of the waveguide structure. The diffracted light shows interesting optical properties that exist only in such 2D grating structures.

Surface-plasmon-assisted resonant tunneling of light through a periodically corrugated thin metal film.

We present experimental results and a numerical model confirming that surface plasmons can resonantly enhance light transmission through a corrugated metal film. A new interpretation in terms of plasmon-assisted light tunneling is given to recent experiments on light penetration through periodic subwavelength holes in a thin metal film. We designed a narrow-band filter suitable for applications in optical communication by optimizing the film and the grating parameters.

Waveguide grating mirror for large-area semiconductor lasers.

We have fabricated and tested a waveguide grating mirror that uses anomalous reflection of light associated with excitation of waveguide modes. Sharp features are observed in the reflection spectra in both the wavelength and the angular domains. We confirm experimentally that, when the waveguide grating mirror is placed a short distance in front of a large-area semiconductor laser, it can control the emission spectrum.

Concept of a miniature optical spectrometer using integrated optical and micro-optical components.

We describe the concept of a super compact diffractive imaging spectrometer, with optical components a few millimeters across in all dimensions, capable of detecting optical fluorescence spectra within the entire visible spectral range from 400 nm to 700 nm with resolution of the order of 2 nm. In addition, the proposed spectrometer is capable of working simultaneously with multiple, up to 35, independent input optical channels. A specially designed diffractive optical element integrated with a planar optical waveguide is the key component of the proposed device.

Model-independent method for the determination of guiding thin-film optical parameters.

A method for the determination of the optical constants of thin films based on the combination of a waveguide measurement procedure with the spectroscopic measurements made from the UV to the IR is presented. As a test material AlN thin film on sapphire substrates is investigated.

A simple miniature optical spectrometer with a planar waveguide grating coupler in combination with a plano-convex lens.

A miniature optical spectrometer with a thin-film planar waveguide grating coupler in combination with a miniature plano-convex focusing lens has been investigated. With optical part of the spectrometer as small as 0.2 cubic cm, the spectral resolution varies from 0.

Sub-micron grating fabrication on hafnium oxide thin-film waveguides with focused ion-beam milling.

Uniform period sub-micron gratings have been fabricated using focused ion beam milling on hafnium oxide waveguides. Atomic force microscopy indicates that the gratings have smooth and uniform profiles. At the period of 330 nm, the largest peak-to-peak height that was achieved was 85 nm.

Titania, silicon dioxide, and tantalum pentoxide waveguides and optical resonant filters prepared with radio-frequency magnetron sputtering and annealing.

Mixing dielectric materials in solid-thin-film deposition allows the engineering of thin films' optical constants to meet specific thin-film-device requirements, which can be significantly useful for optoelectronics devices and photonics technologies in general. In principle, by use of radio-frequency (rf) magnetron sputtering, it would be possible to mix any two, or more, materials at different molar ratios as long as the mixed materials are not chemically reactive in the mixture. This freedom in material mixing by use of magnetron sputtering has an advantage by providing a wide range of the material optical constants, which eventually enables the photonic-device designer to have the flexibility to achieve optimal device performance.

Experimental characterization of simultaneous spatial and spectral filtering by an optical resonant filter.

Simultaneous spatial and spectral filtering by an optical resonant filter has been characterized experimentally to furnish additional insight into the operation and applications of optical resonant filters. Our experimental study can be useful for applications that depend on spatial filtering, spectral filtering, spatial-spectral filtering, and polarization selectivity. One significant application is the integration of an optical resonant filter with semiconductor lasers to control the spatial-spectral radiation for optimum performance.

Fabrication methods of optical resonant filters with a close-to-rectangle filtering profile.

The potential applications of optical resonant filters for optical communication systems can be significant. Three approaches to achieve a close-to-rectangle filtering profile for optical resonant filter were investigated and proven experimentally. The combination of the filtering sharpness, which comes from the resonance nature, and a flattened filtering window realized the close-to-rectangle filtering profile that can enhance the bandwidth efficiency.

High-resolution photometric optical monitoring for thin-film deposition.

Real-time monitoring of thin-film deposition with high resolution is important for precise fabrication of thin-film devices in a technological environment with ever-increasing demands for smaller size and better performance. Using photometry, we were able to achieve a real-time optical monitoring resolution of film thickness that is comparable with a single atomic layer scale (i.e.

Heat treatment for reduction of surface roughness on holographic gratings.

Controlled postdevelopment heat treatment of the photoresist polymer used in the preparation of holographic gratings has been shown to enhance the diffraction efficiency of gratings and reduce the scattering losses. We prove this effect by analyzing the resonant reflection spectra of a waveguide grating and observing the reduction in the arc-shaped light scattering associated with the excitation of waveguide modes.