Jose E. Castillo

Parallel optical coherence tomography system

We present the design and procedures for implementing a parallel optical coherence tomography (POCT) imaging system that can be adapted to an endoscopic format. The POCT system consists of a single mode fiber (SMF) array with multiple reduced diameter (15 microm) SMFs in the sample arm with 15 microm center spacing between fibers. The size of the array determines the size of the transverse imaging field. Electronic scanning eliminates the need for mechanically scanning in the lateral direction. Experimental image data obtained with this system show the capability for parallel axial scan acquisition with lateral resolution comparable to mechanically scanned optical coherence tomography systems.

Thermal effects of the extended holographic regions for holographic planar concentrator

A model for the thermal properties of holographic planar concentrators on module performance is presented and verified with experimental data. The holographic planar concentrator modules consist of ribbons of volume holograms placed next to photovoltaic cells to achieve a low level concentration effect. The holographic ribbons increase the surface area required to produce a fixed amount of output power but reduce the cost of the module by eliminating approximately half of the photovoltaic cell material, in this case monocrystalline bifacial silicon cells. Due to the low concentration, the temperature reduction effect of the added surface area overcomes the added heat provided by the holograms. The theoretical point at which the added concentration by holograms overcomes the cooling effect provided by the extended region for varying theoretical holographic contributions is also presented.

Spectral-shifting and holographic planar concentrators for use with photovoltaic solar cells

Two types of solar concentrators for use with standard silicon photovoltaic cells are compared. The first is a spectral shifting luminescent concentrator that absorbs light in one spectral band and re-emits light at longer wavelengths where the absorption of standard silicon photovoltaic cells is more efficient. The second type is a holographic planar concentrator that selects the most useful bands of the solar spectrum and concentrates them onto the surface of the photovoltaic cell. Both types of concentrators take advantage of total internal reflected light, do not require tracking, and can operate with both direct and diffuse sunlight. The holographic planar concentrator provides a simpler and more cost effective solution with existing materials and construction methods.

Design and processing of high-density single-mode fiber arrays for imaging and parallel interferometer applications

The design and fabrication procedures for implementing a high-density (16-microm center spacing) single-mode fiber (SMF) array are described. The specific application for this array is a parallel optical coherence tomography system for endoscopic imaging. We obtained fiber elements by etching standard single-mode SMF-28 fibers to a diameter of 14-15 microm. We equalized 1-m lengths of fiber to within 1 mm by using a fiber interferometer setup, and we describe a method for packaging arrays with as many as 100 fibers.

Study of Multichannel Parallel Anti-Symmetric Waveguide Bragg Gratings for Telecom Applications

We theoretically demonstrate the viability of parallel anti-symmetric waveguide Bragg gratings within a two-mode waveguide. These gratings produce reflections with mode conversions. This is the functional equivalent of superimposed Bragg gratings in silica-on-silicon without requiring multilevel etches. Also, due to their weaker coupling constant, these gratings allow for devices with narrow spectral full-width at half-maximum that can process multiple wavelength channels for applications such as optical add-drop multiplexers and optical encoders in optical communication systems

Interleaved sampled Bragg gratings with concatenated spectrum

We design and demonstrate interleaved sampled Bragg gratings with concatenated spectrum which produce high channel counts with simple design and fabrication. These gratings can be applied in multichannel filtering, dispersion compensation, and many other functions. The devices were implemented as reduction-photolithographically written anti-symmetric Bragg gratings

Low holographic concentration effects on CIGS

We present the results of combining copper indium gallium (di)selenide (CIGS) photovoltaic cells with holographic planar concentrating film over a broad range of illumination levels. The film, originally designed for silicon bifacial solar applications worked well with the CIGS cells. The Voc, cell efficiency and fill factor reached full operating values at lower light levels; with a significant boost in performance being recorded. The holographic regions of the concentrator act as extended heat transfer surfaces, allowing the CIGS cells to operate at lower operational temperatures than they normally would in a traditional PV application.

Daily and seasonal performance of angularly dependent fixed mount dual aperture holographic planar concentrator photovoltaic modules

Dual aperture holographic planar concentrator (DA-HPC) technology consists of bifacial cells separated by strips of holographic film that diffract the light from the spacing into the cells for direct incident, diffuse, roof-reflected and albedo irradiance. The holographic film is angularly dependent of the seasonal sun angle. DA-HPC modules are compared to single aperture conventional modules for clear and cloudy days as well as for a seasonal period of eight months. Direct-current IV and alternating-current power curves are used to compare modules with comparable silicon active area and cell efficiency.

Response of Axially Stressed Edge-Illuminated Holographic Gratings in PQ/PMMA Photopolymers

A free-space unslanted, edge-illuminated, tunable Bragg filter in Phenanthrenquinone doped Poly(methyl methacrylate) (PQPMMA) operating at 1550 nm has been realized with a tuning range larger than 4 nm. The grating is ~1 cm long with a rejection efficiency of ~90% and a full-width at half-maximum spectral width of ~0.35 nm in its unstressed state. The tunability of the grating was achieved by stretching and compressing the sample.

Effect of silicon dioxide nanoparticles on the characteristics of PQ/PMMA holographic filters

The good optical properties of PQ (phenanthrenequinone)-doped PMMA (poly methylmethacrylate) and its flexibility to fabricate different substrate configurations make this material attractive for holographic recording. In previous work, filters in PQ/PMMA for Wavelength Division Multiplexing (WDM) and Optical Code Division Multiple Access (OCDMA) were demonstrated and shown to have a 0.03nm/°C thermal tuning range operating near 1550nm. In this paper we investigate the effect of adding silicon dioxide nanoparticles to PQ/PMMA in order to measure the thermal tuning range and investigate the performance of these filters.