Optical Fiber Cavity Ring Down Measurement of Refractive Index With a Microchannel Drilled by Femtosecond Laser

A microchannel was inscribed in the fiber of a ring cavity which was constructed using two 0.1% : 99.9% couplers and a 10-m fiber loop. Cavity ring down spectroscopy was used to measure the refractive index (RI) of gels infused into the microchannel. The ring down time discloses a nonlinear increase with respect to RI of the gel and sensitivity up to 300 mus/RI unit and an index resolution of 1.4 times10^-4 was obtained.     

Cumulative Fading and Rainfall Distributions for a 2.1 km, 38 GHz, Vertically Polarized, Line-of-Sight Link

Between February 1,1997 and January 31,1998, a 2.1 km vertically polarized 38 GHz communications link was studied in the subtropical city of Brisbane, Australia. According to the current ITU fading prediction method the link would be expected to experience a rainfall intensity of approximately 50 mm/h for 52.6 min during the year, when averaged over a 60 s integration time. This should have caused approximately 20 dB of fading for 52.6 min [1]-[3]. However the link actually experienced 20 dB of fading for 150.5 min, with fading of 37 dB exceeded for 53.5 min during the year. A rainfall intensity of 84 mm/h was exceeded for 64 min at the receive end, and a rainfall intensity of 72 mm/h was exceeded for 52 min at the transmit end of the hop.     

Effects of PRMA on objective speech quality

When transmitting 32 kbit/s adaptive differential pulse code modulation (ADPCM) speech using Reed-Solomon error correction coding and 16 level quadrature amplitude modulation (16-QAM), a 20 slot packet reservation multiple access (PRMA) assisted cordless telecommunications (CT) scheme supported 36-38 speech users with negligible objective and subjective speech degradation. The average number of users per slot was nearly doubled due to deploying PRMA and toll quality speech was transmitted in a user bandwidth approximately 11.6 kHz. For a channel signal-to-noise ratio (SNR) in excess of 25 dB, a Rayleigh fading channel and mobile speeds above 2 mph the speech segmental SNR degradation was less than 0.3 dB.<>     

Spatially-multiplexed fibre-optic Bragg grating strain andtemperature sensor system based on interferometric wavelength-shiftdetection

A prototype fibre-optic system using interferometric wavelength-shift detection, capable of multiplexing up to 32 fibre-optic Bragg grating strain and temperature sensors with identical characteristics, has been demonstrated. This system is based on a spatially multiplexed scheme for use with fibre-based low-coherence interferometric sensors, reported previously. Four fibre-optic Bragg grating channels using the same fibre grating have been demonstrated for measuring quasi-static strain and temperature     

Two-port noise and impedance measurements for two-terminal deviceswith a resonant tunneling diode example

A two-port technique is presented for determining the circuit elements and noise sources of the equivalent circuit of a two-terminal device at microwave frequencies. The two-terminal device is connected as a two-port so that intrinsic and parasitic circuit elements can be obtained from full two-port S-parameter measurements. This measurement does not require one of the two contacts to be grounded, which makes it particularly well suited for the characterization of integrated devices where parasitic elements become important and cannot be easily calculated. The noise of the device is measured by employing a noise-figure meter and the intrinsic noise is computed from the measured terminal noise. As an example, the impedance and noise elements of a resonant tunneling diode (RTD) are measured over frequency ranges of 2-8 and 2-4 GHz, respectively     

Analysis of the infrared transmission data of hydrogenated amorphous silicon film fabricated by high rate PECVD

The optical properties of hydrogenated amorphous silicon thin films prepared by a new thermocatalytic plasma enhanced chemical vapor deposition (PECVD) method are here reported for the first time. The transmission spectrum of the film, deposited at a rate of 1.5 nm/s, was measured between 500 and 1100 nm. The envelopes of the transmission spectrum interference maxima and minima were analyzed to reveal the absorption coefficient α(λ@#@), the refractive indexn(λ), the average thickness of the film (791 nm) and the variation of the thickness (11.4 nm), using an analysis which takes into account film inhomogeneity. The modified Newton's method of numerical analysis was used to obtain the optical parameters. The optical band gap ε₀} was determined to be 1.69 eV from the absorption coefficient spectrum, commensurate with values quoted for lower deposition rate PECVD films. The value for ε₀}, the small variation of the film thickness, and a value for the defect density of 3.7 x 10¹⁵}cm^-3} determined for similar material in other work indicate that the thermocatalytic PECVD method can produce acceptable quality films at a high deposition rate.     

High-performance,transparent conducting oxides based on cadmium stannate

We discuss the modeling of thin films of transparent conducting oxides and we compare the predictions with the observed properties of cadmium stannate. Thin films of this material were deposited using radio-frequency magnetron sputtering. The Drude free-carrier model is used to model the optical and electrical properties. The model demonstrates the need for high mobilities. The free-carrier absorbance in the visible spectrum is used as a comparative figure-of-merit for cadmium stannate and tin oxide. This shows that free-carrier absorbance is much less in cadmium stannate than in tin oxide. X-ray diffraction shows that annealed films consist of a single-phase spinel structure. The post-deposition annealing sequence is shown to be crucial to forming a single phase, which is vital for optimal optical and electrical properties. The films are typically high mobility (up to 65 cm² V^?1 s^?1) and have carrier concentrations as high as 10²¹ cm^?3. Resistivities are as low as 1.3 10^?4 Ω. cm, the lowest values reported for cadmium stannate. Atomic force microscopy indicates that the root-mean-square surface roughness is approximately ±15Å. Cadmium stannate etches readily in both hydrofluoric and hydrochloric acid, which is a commanding advantage over tin oxide.     

Singular Tetrahedral Finite Elements for Vector Electromagnetics

The electromagnetic fields at reentrant edges made of conductor are generally singular and the polynomial basis functions used in traditional finite elements do not model the fields well in these regions. Two new tetrahedral elements are introduced with basis functions that incorporate the known asymptotic variation of the fields with distance from the edge. The basis is split into gradient and rotational parts. Additional vertex functions can be added to improve the conditioning of the global matrix system that arises in the time-harmonic case. Results are presented for the scattering parameters of a number of waveguide discontinuities. The new elements reduce the error considerably compared to the Whitney element, and generally outperform the second-order edge element, even though that has more degrees of freedom     

Full-wafer technology-A new approach to large-scale laserfabrication and integration

A concept for full-wafer processing (FWP) and full-wafer testing (FWT) for semiconductor laser fabrication in the AlGaAs-GaAs material system is presented. The approach is based on chemically assisted ion beam etching for the laser-mirror formation. Record values for mirror scattering, optimum mirror reflectivity, and equivalence to cleaved mirrors in terms of laser threshold and efficiency have been achieved. Promising results for uniformity and reproducibility for major laser diode characteristics on processed 2-in wafers have been found. The FWP technology has been extensively used for designing test sites to determine various materials, process, and laser parameters, such as sheet resistance, ridge dimensions, lithographic alignment errors, mirror surface leakage, etc     

防黑客设计技术

随着嵌入设备渗透进社会,并承担起更加重要的角色,安全失效会带来潜在的灾难性的后果。嵌入设备以无人干预方式运行在很多领域的数千种关键任务或安全相关系统中,如制造、健康保健、运输、金融和军事等。虽然我们不假思索地依赖于这些嵌入系统,但任何一种嵌入系统都可能成为临时黑客、犯罪团伙、恐怖分子,甚至敌对政府分子的潜在目标。阻止这些攻击的重任就落在了系统设计者的肩上,他不仅要保证通过或保存在嵌入设备中的数据的安全,而且还要保护产品本身的知识产权。