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We demonstrate the use of a low-cost liquid-crystal-based wavelength-tunable filter and CMOS video camera to add hyperspectral imaging capabilities to a probe station equipped with a simple optical microscope. The resultant setup is used to rapidly resolve the spectral and spatial variations in electroluminescence typically observed for InxGa1−xN/GaN light-emitting diodes. Applying standard statistical analyses of variation within the multivariate datasets, such as moments and principal components, we observe inhomogeneities on a spectral scale significantly smaller than the bandwidth of the tunable filter. The resultant tool offers an alternative to scanning beam luminescence techniques for high-throughput hyperspectral analysis of optoelectronic devices. [ABSTRACT FROM AUTHOR]

Zero incidence angle spatial filters of a compact design can be very useful, among others, for intracavity spatial filtering in high-power micro-lasers. Typically, micro-lasers, especially in high-power operation regimes, emit beams of low spatial quality due to the large aspect ratio of the laser resonator. A promising proposal for compact spatial filtering is the integration of the Photonic Crystals structures into the micro-resonator of the laser. Here, we report efficient spatial filters with desired filtering properties engineered by the inverse design. Such filters can be designed not only separately for both polarizations of the incident radiation but also simultaneously for both S and P polarizations. Moreover, we fabricate the inverse-designed structure by physical vapor deposition and highlight good correspondence of the angle-wavelength transmission map to the target one. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a back-illuminated metal-semiconductor-metal AlGaN heterostructure solar-blind ultraviolet (UV) photodetector integrated with a SiO2/Si3N4 one-dimensional photonic crystal (1D PC). The light absorption outside solar-blind ultraviolet caused by impurity and defect energy levels is significantly suppressed by the 1D PC. The fabricated device exhibits extremely low dark current of 2 pA at 20 V applied voltage, where light/dark current ratio exceeds 4000. Meanwhile, the photodetector demonstrates a manifest narrow-band solar-blind detection property. The optical modulations of heterostructure energy-band engineering and photonic crystal filter both contribute to the solar-blind absorbing selectivity. In addition, the finger-scaling effects are also investigated based on carrier transport mechanism. These results are anticipated to promote the evolution on design and fabrication of solar-blind UV photodetector. [ABSTRACT FROM AUTHOR]

Broad aperture semiconductor lasers usually suffer from low spatial quality of the emitted beams. Due to the highly compact character of such lasers, the use of conventional intracavity spatial filters is problematic. We demonstrate that extremely compact photonic crystal spatial filters, incorporated into a laser resonator, can improve the beam spatial quality and, correspondingly, increase the brightness of the emitted radiation. We report the decrease in the M2 value from 47 down to 28 due to photonic crystal spatial intracavity filtering and the increase in the brightness by a factor of 1.5, giving a proof of principle of intracavity photonic crystal spatial filtering in broad area semiconductor lasers. [ABSTRACT FROM AUTHOR]

The integration of gaseous plasma elements into a microwave photonic crystal band gap cavity structure allows for active tuning of the device. An alumina rod array microwave photonic crystal waveguide resonator is simulated and characterized through finite difference time domain methods. A gaseous plasma element is integrated into the cavity structure and the effect of plasma density on the transmission properties of the structure is investigated. We show, through both simulations and experiments, that the permittivity of the plasma can be adjusted to shift the peak resonance to allow for both switching and tunability of transmission. The experimentally measured peak shifts in transmission are compared to those simulated and the electron density of the gaseous plasma element is calculated and compared to values determined from the measured discharge current density. [ABSTRACT FROM AUTHOR]

We have monitored the cathodoluminescence (CL) emitted upon injection of free electrons into a hybrid structure consisting of a thin magnetic Fe layer deposited on a p-GaAs substrate, in which InGaAs quantum wells are embedded. Electrons transmitted through the unbiased metal/ semiconductor junction recombine radiatively in the quantum wells. Because of the electron spinfiltering across the Fe/GaAs structure, the CL intensity, collected from the backside, is found to depend on the relative orientation between the injected electronic spin polarization and the Fe layer magnetization. The spin asymmetry of the CL intensity in such junction provides a compact optical method for measuring spin polarization of free electrons beams or of hot electrons in solid-state devices. [ABSTRACT FROM AUTHOR]

We demonstrate an infrared spectrometer based on waveguide-coupled nanocavity filters in a planar photonic crystal structure. The input light is coupled into the waveguide, from which spectral components are dropped into the cavities and radiated off-chip for detection on a commercial InGaAs camera. The spectrometer has a footprint of only 60 µm by 8 µm. The spectral resolution is about 1 nm in the operation bandwidth of 1522-1545 nm. By substituting the membrane material and structure parameters, this design can be easily extended into the visible regime and developed for a variety of highly efficient, miniature photonic applications. [ABSTRACT FROM AUTHOR]

To optimize the performance of multifunctional carbon nanotube-ferroelectric devices, it is necessary to understand both the polarization and charge dynamics effects on their transconductance. Directly comparing ferroelectric Pb(Zr0.2Ti0.8)O3 and dielectric SrTiO3 field effect transistors, we show that the two effects strongly compete, with transient charge dynamics initially masking up to 40% of the ferroelectric field effect. For applications, it is therefore crucial to maximize the quality of the ferroelectric film and the interface with the carbon nanotube to take full advantage of the switchable polarization. [ABSTRACT FROM AUTHOR]

We propose a simple, yet highly efficient and robust device for producing valley polarized current in graphene. The device comprises of two distinct components; a region of uniform uniaxial strain, adjacent to an out-of-plane magnetic barrier configuration formed by patterned ferromagnetic stripes. We show that when the amount of strain, magnetic field strength, and Fermi level are properly tuned, the output current can be made to consist of only a single valley contribution. Perfect valley filtering is achievable within experimentally accessible parameters. [ABSTRACT FROM AUTHOR]

Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystals have been developed recently, which can increase the operating temperature by at least 20 °C compared to PMN-PT crystals. We have measured a complete set of material properties of single domain PIN-PMN-PT crystal, which is urgently needed in theoretical studies and electromechanical device designs using this crystal. Because the rotated values of d33*=1122 pC/N and k33*=89% along [001]c calculated using the single domain data obtained here are in good agreement with the [001]c poled multidomain PIN-PMN-PT crystals, one may conclude that the physical origin of the ultrahigh piezoelectric properties mainly come from orientation effect. [ABSTRACT FROM AUTHOR]

We report on a microelectromechanical tunable optical filter incorporating strain-tunable nanoimprinted elastomeric grating with a pitch varied by 18%. This device enables tuning of optical fiber-guided laser wavelength between λ=473 and 532 nm within 0.5 ms by mechanically modulating the pitch with a silicon microactuator. We also demonstrate the use of the device for obtaining two-color images of live/dead-stained cells with the color intensity ratio varied by the actuator voltage applied. The small structure of the device integrated on a silicon chip may be used in portable systems for optical switching and spectroscopy. [ABSTRACT FROM AUTHOR]

Based on recent improvements of growth of In-rich InGaN quantum wells with low defect density, we demonstrate current driven InGaN laser diodes at wavelengths as long as 500 nm. The laser structures are grown on c-plane GaN substrate and are processed as broad oxide-insulated stripe laser diodes. We discuss the impact of the piezoelectric field on the emission energy of long wavelength laser diodes for this growth orientation. The combination of low threshold current density of 8.2 kA/cm2 with high slope efficiency of 650 mW/A enables high output powers up to several tens of milliwatts. [ABSTRACT FROM AUTHOR]

A guided-mode resonant filter incorporating an electro-optically tunable liquid crystal refractive index is demonstrated at a wavelength of 655 nm and a tuning range of 4 nm. Rigorous coupled wave analysis and finite difference time domain analysis are used to simulate the characteristics of the filter during liquid crystal reorientation. Tuning performance is demonstrated that is consistent with the device simulations. Tunable filters in the visible wavelength range that are inexpensively fabricated over large surface areas are expected to find applications in optical limiting and video display. [ABSTRACT FROM AUTHOR]

The electrical performance of the polycrystalline silicon (poly-Si) thin-film transistors (TFTs) is greatly affected by the microstructure of the poly-Si. The crystal filtering method is employed to improve the electrical properties of poly-Si TFTs using metal-induced lateral crystallization by the ordering of Si grains. Experimental results indicated that the field-effect mobility of TFTs having crystal filtered poly-Si is more than 2.5 times higher than that of conventional poly-Si TFTs. It is found that the ordered microstructure is one of the key parameters to improve the electrical performance in poly-Si TFTs. [ABSTRACT FROM AUTHOR]

The authors demonstrate a flexible terahertz pulse-shaping technique, manipulating spatially dispersed multifrequency components generated by optical rectification in a fanned-out periodically poled lithium niobate crystal. Spatial masks of low pass, high pass, and double slit in front of the crystal manipulate the spatial pattern of the optical excitation beam on the crystal, which is mapped onto the intensity profile of the terahertz spectrum. The spatial dispersion of the terahertz spectrum is removed by the line-to-point imaging of a spherical mirror. [ABSTRACT FROM AUTHOR]

A metallic photonic crystal filter has been demonstrated at terahertz frequencies, with the passband tunable over the range of 365–386 GHz. Tuning is achieved by a relative lateral shift of two metallic photonic crystal plates. Each plate is comprised of two orthogonal layers of gratings and integral mounting lugs. The plates are micromachined from silicon wafers then coated in gold to provide metallic electromagnetic behavior. An insertion loss of 3–7 dB and Q in the range of 20–30 was achieved. A shift of 140 μm gave a tuning range of 21 GHz, tuning sensitivity of 150 GHz/mm, and a fractional tuning range of 6%. [ABSTRACT FROM AUTHOR]

We show how to fabricate three basic photonic crystal structures with simple cubic, fcc, and bcc translational symmetry by interference lithography. The structures are fabricable by tile interference of beams launched from the same half space. The simple cubic structure is size scalable while the structure with fcc translational symmetry possesses two band gaps. Both these structures are experimentally realized. [ABSTRACT FROM AUTHOR]

An in-plane-type channel-drop filtering device with input/output waveguides and a point defect cavity in a two-dimensional photonic crystal slab is investigated. The in-plane operation becomes possible by employing a point defect cavity with an extremely high Q factor to suppress the radiation loss for the out-of-plane direction. 60° bends are also introduced in the output waveguide to avoid interference between the input/output waveguides. The transmission frequency range of the output waveguide with bends is tuned by changing the size of the air holes at the apex of the corner so that the resonant frequency of the point defect cavity is within the transmission band. A channel drop operation with a very high resolution of 0.12 nm is successfully observed at 1.55 μm wavelengths. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A tunable metallic photonic crystal filter with a mechanical tuning mechanism is demonstrated. The performance is predicted with rigorous full-vector electromagnetic simulations (finite-difference time domain). A prototype has been built and characterized in the W band (70–110 GHz) using a vector network analyzer configured for free-space measurement of S parameters. The measured filter’s passband has a quality factor of 11, a tuning range of 3.5 GHz, and insertion loss of only 1.1–1.7 dB. Device fabrication is straightforward, yielding an inexpensive, robust and compact tunable filter. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a design of the surface-emitting-type channel drop filters based on point defect cavities and line defect waveguides in two-dimensional photonic crystal slabs, which aim to improve the filtering resolution and light emission characteristics. Since the filters are passive, the mode volume size of the defects needs not be minimized, but the interaction between the defect cavity and the line defect waveguide must be considered. By adopting a donor-type point defect with three missing holes of linear shape, the quality factor of the filter theoretically increases to values as high as 2900 while it reached only 500 in the previously utilized acceptor-type defect. The results suggest that this donor-type defect is very useful for the development of ultrasmall channel add/drop devices. [ABSTRACT FROM AUTHOR]

Omnidirectional (omni-) reflector and transmission filter optimized at a wavelength of 1.55 µm have been realized using Si/SiO[sub 2] one-dimensional photonic crystals (1D PCs). Photonic band structures in the PCs with and without a defect layer have been also analyzed. The 1D PCs fabricated have very large omnidirectional photonic band gaps (omni-PBGs), and their measured reflectance spectra are in very good agreement with the calculated results. The omni-PBG in a six-pair Si/SiO[sub 2] 1D PC (no defect layer, a filling factor η=0.406) exists in a normalized frequency range of 0.223-0.297. Introducing a defect layer generates a defect state in the PBG, and it behaves like electronic impurity levels in the gap with a change in thickness of the defect layer (d[sub D]). A six-pair Si/SiO[sub 2] 1D PC with the structure parameters of η=4.060, d[sub H] (Si thickness)=95.3 nm, d[sub L] (SiO[sub 2] thickness)=234.9 nm, and d[sub D] = 2.336·d[sub H] could act as a 1.55 µm-transmission filter for normal incidence light. [ABSTRACT FROM AUTHOR]

Energy transmission efficiency and working bandwidth are the two major factors limiting the application of current acoustic diodes (ADs). This letter presents a design of high efficiency and broadband acoustic diodes composed of a nonlinear frequency converter and a linear wave filter. The converter consists of two masses connected by a bilinear spring with asymmetric tension and compression stiffness. The wave filter is a linear mass-spring lattice (sonic crystal). Both numerical simulation and experiment show that the energy transmission efficiency of the acoustic diode can be improved by as much as two orders of magnitude, reaching about 61%. Moreover, the primary working band width of the AD is about two times of the cut-off frequency of the sonic crystal filter. The cut-off frequency dependent working band of the AD implies that the developed AD can be scaled up or down from macro-scale to micro- and nano-scale. [ABSTRACT FROM AUTHOR]

Electric field induced changes in the x-ray diffraction pattern of nylon 11 films containing a mixture of the alpha and gamma crystal phases are presented. These changes indicate an orientation of crystallites such that dipoles are aligned in the direction of the poling field. Correlation between this crystal orientation and piezoelectric activity was observed. [ABSTRACT FROM AUTHOR]