KEYWORDS: Solar cells, Solar energy, Visible radiation, Holographic optical elements, Photovoltaics, Holograms, Solar energy systems, Solar concentrators, Energy efficiency, Holographic concentrators
We demonstrate a novel hybrid solar photovoltaic electrical and thermal energy cogeneration system with high
efficiency, at potentially reduced overall weight and size compared with current solar energy systems. The new system is
based on highly efficient photovoltaic solar cells and tubular water thermal receivers, incorporating holographic spectral
beam light guide concentrators resulting in a more cost-effective solution. Details of fabrication and preliminary
experimental testing results are presented.
We demonstrate a novel spectral imaging device based on an imaging Fourier transform spectrometer (FTS) with phase
delays electro-optically controlled by fast tuning liquid crystal (LC) elements. The electro-optic (EO) tunable
multispectral/hyperspectral imaging give the spectral imager significant advantages, including reduction in size and mass
for simultaneous 2D spectral imaging, with a high spatial and spectral resolution. The technology is made very attractive
for its potential military, medical and remote sensing applications where hyperspectral imaging plays a significant role in
detection.
We demonstrate a new material composed of isotropic liquid crystal (ILC) blended with semiconductor nanoparticles,
which could result in a novel high-speed, multiple-notch broadband passive optical switch to selectively discriminate
bands of electromagnetic radiation in intelligence, surveillance, or reconnaissance systems. The new material has been
demonstrated high nonlinear 3rd order optical Kerr coefficients (light-induced refractive index change, n2) exceeding 100
times of classic nonlinear material CS2 with n2 = 1.2E-11 esu. Details of fabrication and experimental results are
presented.
In this paper, Bayesian inference is applied to performance metrics definition of the important class of recent Homeland
Security and defense systems called binary sensors, including both (internal) system performance and (external)
CONOPS. The medical analogy is used to define the PPV (Positive Predictive Value), the basic Bayesian metrics
parameter of the binary sensors. Also, Small System Integration (SSI) is discussed in the context of recent Homeland
Security and defense applications, emphasizing a highly multi-technological approach, within the broad range of clusters
("nexus") of electronics, optics, X-ray physics, γ-ray physics, and other disciplines.
System-on-chip (SoC) single-die electronic integrated circuit (IC) integration has recently been attracting a great
deal of attention, due to its high modularity, universality, and relatively low fabrication cost. The SoC also has low
power consumption and it is naturally suited to being a base for integration of embedded sensors. Such sensors can
run unattended, and can be either commercial off-the-shelf (COTS) electronic, COTS microelectromechanical
systems (MEMS), or optical-COTS or produced in house (i.e., at Physical Optics Corporation, POC). In the
version with the simplest electronic packaging, they can be integrated with low-power wireless RF that can
communicate with a central processing unit (CPU) integrated in-house and installed on the specific platform of
interest. Such a platform can be a human body (for e-clothing), unmanned aerial vehicle (UAV), unmanned ground
vehicle (UGV), or many others. In this paper we discuss SoC-centric embedded unattended sensors in Homeland
Security and military applications, including specific application scenarios (or CONOPS). In one specific example,
we analyze an embedded polarization optical sensor produced in house, including generalized Lambertian light-emitting
diode (LED) sources and secondary nonimaging optics (NIO).
The broadband optical absorption properties of silicon nanowire (SiNW) films fabricated on glass substrates by wet etching and chemical vapor deposition (CVD) have been measured and found to be higher than solid thin films of equivalent thickness. The observed behavior is adequately explained by light scattering and light trapping though some of the observed absorption is due to a high density of surface states in the nanowires films, as evidenced by the partial reduction in high residual sub-bandgap absorption after hydrogen passivation. Finite difference time domain simulations show strong resonance within and between the nanowires in a vertically oriented array and describe the experimental absorption data well. These structures may be of interest in optical films and optoelectronic device applications.
Polymers have been studied as an alternate material to silica for optical interconnects and photonic devices for the last decade. In this paper we review the work performed at GE Global Research in the area of polymer based material systems for photonic applications. A description of the application of the technology to several different areas is presented. Some of these application areas include optical interconnects, optoelectronic integration and electro-optical devices using polymer material systems. The overall effort includes areas of research from the basic chemistry of polymer optical materials to the development of photonic components. Specifically the use of polymer materials as a platform technology for hybrid integration in the development of multi-functional sub systems is reviewed.
The development of a photonic backplane for high-speed and high-bandwidth communications is presented. This hybrid, multimode, multi-channel backplane structure contains both electrical and optical interconnects, suitable for next-generation high-speed servers with terabit backplane capacity. Removable and all-passively aligned high density interconnects on this backplane are achieved by polymer based optical waveguides with integrated micro-optics and VCSEL arrays on conventional printed circuit boards. The fabrication of this photonic backplane requires few additional steps outside a traditional board-manufacturing environment and is largely compatible with existing processes.
Complex photonic bands and strong anisotropic dispersion characteristics of artificially engineered periodic dielectric structures have been widely investigated. In this paper we explore the self-guiding effect possessed by photonic crystals and the possible applications for integrated photonics. Since this approach does not require a full photonic bandgap, low refractive index materials (i.e. glass or organic polymers) are considered as an alternative with advantages over conventional semiconductor materials. Sensitivity analysis reveals how structural variations influence the performance of this type of photonic crystal based system.
A new method of interconnecting various optoelectronic components is discussed. Offset error up to 25 microns can be corrected to achieve single mode alignment accuracies. Several planar optical devices were photocomposed using the adaptive photolithographic method and these have been shown to perform with the desired characteristics.
Based on radiation mode coupling through a self-formed polymer waveguide extension, efficient single-mode optical coupling can be achieved between active and passive chips while relaxing the stringent positioning requirements. A 20dB improvement can be achieved according to simulation results. Single-mode waveguides have been successfully demonstrated using GE photo-definable polymer materials.
A photo patterned fabrication process for manufacture of passive polymer composite waveguide structures and devices is presented. The process takes advantage of compatibility between certain polymer/high vapor pressure monomer blends and their refractive index differences to directly photo define passive waveguide structures. With suitable catalysts, monomers present in the composite blend are polymerized in exposed areas, while allowed to evaporate in unexposed areas during a brief post exposure bake. Areas thus produced will have a different composition (i.e. refractive index) in exposed vs. unexposed areas and different thickness due to reactant loss. Composite blends consisting of polysulfone/epoxy or acrylic/epoxy have excellent compatibility for providing photo defined waveguide core regions in either the unexposed areas or exposed areas of processed thin films. Optical loss measurement comparisons for bulk polymer samples and composite thin films to the photo patterned waveguides indicate loss in the patterned waveguides are similar to the polymer intrinsic loss. Additionally, by taking advantage of the process providing control over refractive index and surface topography, other photonic components such as micro lenses can be fabricated.
We investigate a self-aligning method used to couple a vertical emitting laser (flip-chip) to a planar single-mode waveguide through a 45° mirror based upon solder self-alignment. The alignment tolerances to achieve targeted coupling loss of 3.5dB or better were determined for all axes by modeling the optical behavior of the vertical waveguide/45° mirror interconnect. Simulation models for optical design are carried out using commercial software "FullWAVE" from Rsoft, Inc. The design and optimization of the joint's parameters are performed using a public-domain software "Surface Evolver" for surface energy minimization in conjunction with GE proprietary Six Sigma regression and optimization tools. The parameters that were considered for the models included the misalignment along all axes, solder volume, the height of the joints, the radius of the metallization pads, the initial placement error, and the solder reflow time. It has been assumed that intermetallic growth at the solder/metallization/air triple line does not couple with the self-alignment process in order to simplify this problem. The study shows that, given good control over noise parameters such as vibration and reflow temperature fluctuations, solder self-alignment can be harnessed to achieve the targeted coupled efficiency.
Feasibility studies and statistical analyses generated using specially tailored software tools of 2D photonic bandgap waveguides containing structural deviations are presented. Waveguide structures comprising two wide angle bends within a photonic bandgap structure were used in this analysis. The results demonstrate that small variations in the location and size of ordered media create significant changes in the photonic bandgap properties of the material. Deviations with a statistical mean of 20 nm in locaiton and size of this particular model designed for 1.55 μm wavelength are enough to cause the waveguide transmission to reduce by up to 90%.
We have studied the optical nonlinearities of aligned nematic liquid crystalline films in the near IR communication spectral region (1.55 micrometers ). The measured refractive index coefficients are on the order of 10-3 cm2/W. The origins of the refractive index changes are thermal indexing effect and director axis reorientation. Phase modulation of several (pi) s can be generated with mW-power near IR lasers in micron thick films.
A quantitative model for nonlinear photonic absorption processes in a liquid and their effects in the nonlinear transmission and limiting of a laser pulse are studied. The theoretical simulation results accounting for two-photon- and excited-state absorption processes, and the dynamic evolution of the molecular level populations and propagation of picosecond and nanosecond laser pulses through a fiber core formed by such liquid are in good agreement with experimental observations. In pump-prove studies using picosecond and nanosecond laser pump pulses and cw probe, we have also observed oscillatory transmission associated with laser induced thermal/density effects. We also discuss applications of the supra optical nonlinearity of nematic liquid crystal film for anti-laser jamming and optical limiting operation against long-pulse or cw lasers.
We found that in nematic liquid crystals doped with methyl-red dye or an azobenzene liquid crystal, the orientational optical nonlinearity can be dramatically enhanced. A concise review of the fundamental mechanisms involved and some application in all-optical image processing, optical limiting and switchable storage lens holograms is presented.
All-optical holography of azobenzene-liquid-crystal (ALC) doped nematic liquid crystals (NLC) is investigated by means of polarization and intensity grating methods. The holographic grating is formed upon a total optical power as low as 200 (mu) W/cm2 without any external biases, and can be switched within hundreds of milliseconds. The polarization dependence of the probe beam on the diffraction intensity reveals that the grating formation is attributed to reorientation and order-parameter change of the NLC molecules induced by the photoisomerization of the ALC molecules.
Preliminary attempts at aligning nematic liquid crystals using windows having sub-wavelength surface gratings show that good planar aligned cells can be fabricated. We also demonstrate all-optical nonlinear diffraction effect using methyl-red doped nematic liquid crystal that possess a large intensity refractive index change coefficient.
We present a review of the basic mechanisms for laser induced refractive index changes associated with director axis reorientation in nematic liquid crystals. In methyl-red doped nematic liquid crystal, an index change coefficient of more than 10 cm2/GW has been obtained, allowing us to perform image conversion and optical limiting processes at very low optical intensities. In particular, we demonstrated a very large dynamic range twisted nematic liquid crystal limiter that will protect sensor from cw or long-pulse laser jamming.
Using nematic liquid crystal films doped with photocharge producing dyes, we have demonstrated the feasibility of optical limiting of long pulse - cw lasers at nanowatt power, and clamped transmission of < < 1(mu) J. We also demonstration incoherent-coherent image conversion capability with optical intensity in the (mu) Watt/cm2 level.
We have developed compact millimeter thick optical fiber arrays with nonlinear optical liquid guiding cores. These image transmitting fiber arrays are capable of passive optical limiting action against frequency agile short (picosecond- nanosecond) laser pulses in the visible spectrum. We present the results of further studies of their limiting performance. We also discuss how a recently discovered extraordinarily large nonlinear optical response of methyl-red doped nematic liquid crystal film may be employed for limiting action on longer pulse or cw lasers with nanowatt threshold power.
Recently observed optical limiting effects of nano- and pico- second laser pulses through a fiber
array are analyzed using a model that accounts for various nonlinear and excited state absorption, and
subsequent thermal and density effects occurring in the fiber guiding core materials. The nonlinear liquid
cored-fiber arrays we have constructed are capable of low optical limiting threshold and clamped output, as
well as high resolution image transmission.
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