High-performance nanowire-grid polarizers

We developed a new type of wire-grid polarizer that has achieved excellent optical performance and reliability. The nanowire-grid polarizer is based on a fully optimized innovative design structure that consists of not only the core nanowire grid but also the surrounding multilayer thin-film structures. The surrounding structures are designed for antireflectivity to provide the best possible efficiency as well as for device reliability to provide the best possible handling robustness and environmental durability. The core nanowire grid utilizes nanosized high-aspect-ratio dielectric walls as a support for forming a high-aspect-ratio metal nanowire grid that significantly reduces energy loss as a result of metal absorption for the transmitted beam while providing a high extinction ratio of the blocked beam. The developed high-quality nanowire-grid polarizer has potential for use in many integrated optical applications.     

Fabrication of wire-grid polarizers and dependence of submillimeter-wave optical performance on pitch uniformity

We describe a device for fabricating high-precision free-standing grids of fine wire, suitable for use as polarizing elements for radiation at millimeter and submillimeter wavelengths. Computer control of the winding process makes changing grid parameters particularly convenient and flexible. We present measurements of the mechanical uniformity and of the optical performance of wire grid polarizers made with 25 m and 10 m diameter wire. The flexibility of computer control is exploited to introduce a known degree of randomness in the grid pitch (center-to-center wire spacing), allowing the dependence of polarizer quality on uniformity to be quantified. This information allows prediction of the fabrication tolerances required for polarizers to be used at very high frequencies.     

Inverse metal-stripe polarizers

Received: 18 May 1998/Revised version: 17 August 1998     

Preparation and electrochemical performance of spherical MnOx with high capacitance

A promising electrode material, MnO_x, was prepared by chemical precipitation method using MnSO₄?·?H₂O as manganese source and (NH₄)₂CO₃ as precipitant. The as-prepared manganese oxide was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and X-ray diffraction (XRD), respectively. The effects of reaction temperature and calcination temperature on the electrochemical properties of the electrode materials were investigated. The results show that MnO_x with a spherical morphology exhibits an excellent performance in the energy storage field. Under the optimal experimental conditions, the specific capacitance of pure MnO_x reaches up to 592 F g^?2 in the alkaline media when the current density is 5 mA cm^?2 over the potential window from ?0.3 to +0.4 V. The combination resistance and transfer resistance of MnO_x are 0.86 and 0.08 Ω, respectively. These findings make MnO_x a promising electrode material for electrochemical capacitors.     

Planar silicon-based light polarizers

Silicon-based thin-film polarizers operating in the visible and near-infraed spectral range are fabricated by electrochemical etching of bulk silicon wafers. Anisotropically etched (110) porous silicon layers exhibit a strong in-plane anisotropy of the refractive index. Stackes of alternating layers with different mean refractive indices and thicknesses act as dichroic Bragg reflectors or microcavities, respectively. Both structures have two distinct reflection and transmission bands depending on the polarization of the incident linearly polarized light. Planar polarizers are realized through the combination, in one structure, of a dichroic reflector with either a second reflector or a microcavity with different spectral responses.     

Mismatch limitations on metal-fibre polarizers

If a fibre polarizer is spliced into a single-mode fibre, the achievable extinction ratio of the polarizer is modified because of the coupling to higher-order modes at one end of the polarizer and coupling back into the fundamental mode at the other end.     

Calculation of parameters of diffraction polarizers

The results of calculations of two types of reflective polarizers made up of thin-film diffraction grating formed by birefringent plane-parallel elements are presented. One of the two orthogonal linear polarizations can be separated almost without any losses because of a strong zero-order reflection. A polarizer of the first type represents a grating formed by asperities of a dielectric coating with a columnar structure produced upon oblique deposition of the dielectric. The second polarizer represents a thin mica plate grating. In this case, comparison with previous experiments can be performed.     

Theoretical and experimental research on spectral performance and laser induced damage of Brewster's thin film polarizers

Polarizers respectively with broad polarizing region bandwidth, large layer thickness error tolerance and high extinction ratio are designed and prepared. Transmittance spectra of the prepared samples are measured at Brewster's angle, and the results show that different requirements can be fulfilled by optimized designs. Spectral performance of designs with higher layer thickness error tolerance coincides better with the theoretical spectra. Laser induced damage threshold of the prepared samples are evaluated. Electric field distribution, defect, film absorption, and damage morphology are investigated, and the results indicate that electric field distribution in high index layers is the main reason that causes the difference of laser induced damage threshold. For both p polarized and s polarized light, the lower the electric field peak value and the farther the layer, which has the strongest electric field away from air, the higher the laser induced damage threshold.     

Polymer thin-film transistors with high dielectric constant gate insulators

Field-effect transistors consisting of poly(3-hexylthiophene) have been fabricated with high dielectric constant SrBi₂Ta₂O₉ films working as the gate insulator. Significantly enhanced gate effects were observed in these devices compared to similar transistors with conventional SiO₂ gate dielectric. Our devices exhibited operating voltages around 10 V, as compared to about 100 V for devices employing SiO₂ as the gate dielectric. Moreover, inverters based on such polymer transistors were demonstrated with nice input–output characteristics. PACS 82.35.Cd     

Grid polarizers for infrared fourier spectrometers

Infrared grid polarizers consisting of copper lines with a 3.6 μm grid constant on a 4 μm thick mylar polyester substrate have been prepared by the techniques of photolithography and sputter-etching. Their polarization properties have been measured and found to be suitable for use at infrared frequencies below 700cm⁻¹. The polarizers have been used to extend the useful frequency range of a Martin-Puplett polarizing interferometer designed for Fourier transform spectroscopy. The efficiency of the interferometer has been measured over a frequency range from 50 to 700cm⁻¹ and compared to that of a conventional Michelson interferometer. The results are shown to be consistent with the measured properties of the polarizers. Methods are suggested for improving the efficiency of a Martin-Puplett interferometer which employs these polarizers.     

Grating polarizers in waveguide miter bends

Rectangular grooved gratings have been fabricated on mirrors of waveguide miter bends. When the HE₁₁ mode was propagated in corrugated waveguide with diameter equal to approximately 12 wavelengths, these gratings performed in the same manner as predicted using plane wave theory. Two gratings with different groove depths in successive miter bends are sufficient to generate a rather wide range of polarizations. These gratings are particularly convenient in waveguide, which offers ease of alignment, compact transverse dimensions, and the possibility of vacuum operation.     

On the preparation of high reflectance aspherical mirrors by thin-film deposition

The replacement of thick aluminium layers by dielectric films during the manufacture of high reflectivity aspherical mirrors was investigated. Aluminium oxide was found to be a suitable material for this purpose.     

Influence of thermal treatment on the performance of copper phthalocyanine thin-film transistors

Organic thin-film transistors (OTFTs) with bottom-gate and bottom-contact configuration based on copper phthalocyanines (CuPc) as active layer were fabricated. The performance of CuPc OTFTs was studied before and after thermal treatment on CuPc layer. The values of the threshold voltage before and after thermal treatment are −6.3 and −5.7 V, respectively. The field-effect mobility values in saturation regime of CuPc thin-film transistors before and after thermal treatment are 0.014 cm²/Vs and 0.0068 cm²/Vs, respectively. The experimental results indicate that there is a heavy decay on the mobility of CuPc based OTFTs mostly due to the crystalline morphology change induced by the thermal treatment, and absolute value of the threshold voltage after thermal treatment decreases with the decrease of the CuPc film thickness and the roughness.     

Polymer thin-film transistor based on a high dielectric constant gate insulator

In this paper full polymer thin-film transistors (PTFTs) based on Poly (acrylonitrile) (PAN) as the gate dielectric and poly (2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) as the semiconductor layer were investigated by using different channel width/length ratios. Relatively high dielectric constant of the polymer dielectric layer (6.27) can remarkably reduce the threshold voltage of the transistors to below -3V. Hole field-effect mobility of MEH-PPV of the PTFTs was about 4.8×10^-4cm²/Vs, and on/off current ratio was larger than 10², which was comparable with that of transistors with widely used Poly (4-vinyl phenol) (PVP) or SiO₂ as gate dielectrics.     

High-coercivity magnetic mirror polarizers for thermal neutrons

Mirror polarizers for thermal neutrons are proposed and developed. In contrast to the widespread practice where mirrors are constantly in an external magnetizing field of more than 1 kOe, we have solved the problem of the efficient operation of a polarizer when a weak magnetic field of about 50 Oe is applied perpendicular to its surface.