Limits on the performance of dispersive thin-film stacks

Dispersive thin-film stacks are interesting as compact, cost-effective devices for temporal dispersion compensation and wavelength multiplexing. Their performance depends on the total group delay or spatial shift that can be achieved. For general multilayer stacks, no analytic model exists relating the performance to the stack parameters such as the refractive indices and the number of layers. We develop an empirical model by designing and analyzing 623 thin-film stacks with constant dispersion. From this analysis we conclude that, for given stack parameters, the maximum constant dispersion value is inversely proportional to the wavelength range over which the dispersion is achieved. This is equivalent to saying that, for constant dispersion, there is a maximum possible spatial shift (or group delay) that can be achieved for a given material system and number of layers. This empirical model is useful to judge the feasibility of dispersive photonic nanostructures and photonic crystal superprism devices and serves as a first step in the search for an analytic performance model. We predict that an 8-channel wavelength multiplexer can be realized with a single 21-microm-thick SiO2-Ta2O5 thin-film stack.     

Microfluidic chip to produce temperature jumps for electrophysiology

We developed a microfluidic chip that provides rapid temperature changes and accurate temperature control of the perfusing solution to facilitate patch-clamp studies. The device consists of a fluid channel connected to an accessible reservoir for cell culture and patch-clamp measurements. A thin-film platinum heater was placed in the flow channel to generate rapid temperature change, and the temperature was monitored using a thin-film resistor. We constructed the thermal chip using SU-8 on a glass wafer to minimize the heat loss. The chip is capable of increasing the solution temperature from bath temperature (20 degrees C) to 80 degrees C at an optimum heating rate of 0.5 degrees C/ms. To demonstrate the ability of the thermal chip, we have conducted on-chip patch-clamp recordings of temperature-sensitive ion channels (TRPV1) transfected HEK293 cells. The heat-stimulated currents were observed using whole-cell and cell-attached patch configurations. The results demonstrated that the chip can provide rapid temperature jumps at the resolution of single-ion channels.     

Resonant-cavity-enhanced thin-film AlGaAs/GaAs/AlGaAs LED's with metal mirrors

Resonant-cavity-enhanced light-emitting diodes (RCE LED's) are of increasing interest as a low-cost alternative to lasers for short-distance applications. We report on the characteristics of thin-film AlGaAs/GaAs/AlGaAs double-heterostructure RCE LED's with metal mirrors on both sides fabricated by means of epitaxial liftoff and bonded to silicon host substrates. The devices exhibit typical turn-on voltages of 1.3 V, operating resistances of 31 Ω, linewidths of 10.4 nm, efficiencies of 1.4%, dispersion half-angles of 23.7°, and stable output over more than 1700 h. These devices exhibit significant improvement over conventional LED's without additional complicated processing or growth steps, resulting in a manufacturable, low-cost device.     

A Slab of Liquid Helium-4 with Two Free Surfaces

We describe a method of creating a freely suspended ‘slab’ of superfluid helium-II by using a dense array of 51 µm diameter parallel cylindrical holes in a glass disc of 190 µm thickness. By adjusting the chemical potential in the cell, the holes could be made to fill with liquid, and the surface-curvature controlled. We have measured the transmission of atom beams, generated by a thin-film heater and detected with a sensitive bolometer, through this slab at low temperature. The resugts show that R ⁺ rotons can undergo total internal reflection at the free liquid surfaces and confirm that the dominant transmission channel is atom-R ⁺ roton-atom with a maximum probability p～0.15 for 5 K atoms.     

Estimating materials parameters in thin-film BAW resonators using measured dispersion curves

The dispersion curves of Lamb-wave modes propagating along a multilayer structure are important for the operation of thin-film bulk acoustic wave (BAW) devices. For instance, the behavior of the side resonances that may contaminate the electrical response of a thin-film BAW resonator depends on the dispersion relation of the layer stack. Because the dispersion behavior depends on the materials parameters (and thicknesses) of the layers in the structure, measurement of the dispersion curves provides a tool for determining the materials parameters of thin films. We have determined the dispersion curves for a multilayer structure through measuring the mechanical displacement profiles over the top electrode of a thin-film BAW resonator at several frequencies using a homodyne Michelson laser interferometer. The layer thicknesses are obtained using scanning electron microscope (SEM) measurements. In the numerical computation of the dispersion curves, the piezoelectricity and full anisotropy of the materials are taken into account. The materials parameters of the piezoelectric layer are determined through fitting the measured and computed dispersion curves.     

Multicanonical comparison of polarization-mode dispersion compensator performance

We employ a modified version of the multicanonical algorithm to evaluate the system penalties and outage probabilities of different polarization-mode dispersion compensators. The procedure determines the optimal operating conditions for each compensator architecture far more efficiently than the standard Monte Carlo algorithm.     

Linear control of the spectral characteristics of wavelength-selective components with a high-index tapered thin-film planar waveguide and a single-mode half-coupler

A simple system of linearly tunable fiber-film wavelength-dependent components is demonstrated that includes a linearly tapered high-index thin-film planar waveguide (PWG) evanescently coupled by a single-mode-fiber half-coupler. We present experimental and theoretical results for the linear tuning of spectral responses such as coupled power, resonance position (lambda(0)), and fiber output-light polarization through position shifting of the linearly tapered PWG, in the direction of the propagating light in the fiber, over the half-coupler block. We achieved almost linear control of the spectral response by changing the temperature of mixture-of-oils and overlay-doped poly(methyl methacrylate) PWG's when the refractive index of the system decreases with temperature. The variation in thickness of the tapered film is along the direction of the interaction length of the system. Linear tapered PWG's that comprised a mixture of oils, BK7 glass, and overlay-doped PMMA with high refractive indices were fabricated that could operate the device at lower and higher modes. We investigated the dependence of tuning lambda(0) on the PWG mode. Tuning by shifting of a linear tapered PWG over a fiber half-block is mode dependent, whereas tuning by changing the refractive index of a uniform PWG is mode independent. Wavelength shift Dlambda(0) is found to decrease with an increase in the resonant PWG mode number m for linearly tapered PWG's. A fiber-to-asymmetric linear tapered-PWG coupler, which maintains the taper slope to within a specific limit, can function as a linearly tunable polarizer for the light in the fiber.     

空气源热泵热水器系统性能分析

为了预测空气源热泵热水器的运行性能,提高系统稳定性和降低能耗,建立空气源热泵热水器系统仿真模型,在焓差实验室对一台水箱容积为150L的一体式空气源热泵热水器样机进行变工况实验以验证模型的准确性,利用所建立的模型研究蒸发器入口空气流速及制冷剂质量流量对机组性能的影响。结果表明:系统制热量和COP都随环境温度的升高而不断增大;系统制热量随蒸发器入口空气流速的增大而呈增大趋势,在达到某值后,系统制热量变化趋于稳定;系统COP随制冷剂质量流量的不断增加呈先增大后减小的趋势,即制冷剂质量流量存在最佳值使得热泵性能系数最高。     

Thermal Conductivity Measurement of Liquids by Using a Suspended Microheater

In this paper, the traditional \(3\omega \) method is modified in order to measure the thermal conductivity of a droplet of liquid. The \(3\omega \) sensor is microfabricated using bulk silicon etching on a silicon wafer to form a microheater on a suspended bridge structure. The Si substrate of over 400 \(\upmu \hbox {m}\) thickness beneath the microheater is etched away so that the sample liquid can fill the gap created between the heater and the bottom boundary of the sensor. The frequency of the sinusoidal heating pulses that are generated from the heater is controlled such that the thermal penetration depth is much smaller than the thickness of the liquid layer. The temperature oscillation of the sample fluid is measured at the thin-film heater to calculate the thermal conductivity of the surrounding fluid. The thermal conductivity and measured values of the de-ionized water and ethanol show a good agreement with the theoretical values at room temperature.     

低环境温度空气源热泵的设计及其在我国寒冷地区的应用

基于低环境温度空气源热泵在寒冷地区应用的特点,针对产品设计及工程应用中遇到的若干问题,分别对融霜方式、系统控制方式、水/制冷剂换热器的选择、辅助电加热和末端方式的选择等进行分析和讨论,通过计算得到低环境温度空气源热泵作为北方寒冷地区单户采暖热源的一次能耗为35.9 kW·h/（m2·a）,与分户燃气炉相当,低于除大、中规模热电联产外其他热源形式的一次能耗,且运行费用低于目前的按面积收费标准,指出低环境温度空气源热泵具有推广使用价值。     

Oxidation of evaporated porous silicon rugate filters

Rugate filters are thin-film optical interference coatings with sinusoidal variation of the refractive index. Several of these filters were fabricated with glancing angle deposition, which exploits atomic competition during growth to create nanoporous materials with controllable effective refractive index. This method enables the fabrication of devices with almost arbitrary refractive index profiles varying between the ambient, 1.0, and the index of the film material, in this case silicon with an index of 4.0 (at 600 nm). As these filters are inherently porous, oxidation of the silicon can occur throughout the device layer, and here we study the intentional oxidation of silicon filters by high-temperature reaction with gaseous oxygen. We find that a significant portion of the silicon filter oxidizes in approximately 10 min when heated to 600 degrees C-650 degrees C in an oxygen environment; oxidation then continues slowly over several hours. The presence of water vapor has little apparent effect on the oxidation reaction, and attempts to oxidize with ozone at room temperature were unsuccessful. As silicon filters oxidize to become silica, spectral blueshifts and increased short-wavelength transmittance are observed. Measured and calculated transmittance spectra generally agree, although the lack of absorption and dispersion in the theoretical model limits detailed comparison.     

Development of thin-film multijunction thermal converters atPTB/IPHT

The thin-film multijunction thermal converter (PMJTC) developed in cooperation between Physikalisch-Technische Bundesanstalt (PTB) and Institut fur Physikalische Hochtechnologie e.V. (IPHT) is today's most sensitive and accurate standard for the precise measurement of electrical AC quantities in the frequency range of 10 Hz-1 MHz. Thin-film technology and micromechanics in silicon were essential for this success. The thin-film heater and bismuth/antimony thermocouples with high Seebeck effect deposited on a thin membrane of low heat conductance result in the attractively high sensitivity of the PMJTC which allows voltage measurements down to 100 mV to be performed. The statistics of the mass production of the PMJTCs show that PMJTCs built into a housing with an N-connector at the input can be reproducebly manufactured with an AC-DC voltage transfer difference smaller than 0.1 μV/V at 1 kHz, 8 μV/V up to 100 kHz, and below 40 μV/V up to 1 MHz for a heater resistance of 90 Ω. A compensation circuit has been added on the chip which results in low-frequency PMJTCs (LF-PMJTCs) with AC-DC transfer differences below 0.3 μV/V at 10 Hz     

Microfluidic device for airborne BTEX detection

We fabricated a microfluidic device for the optical detection of airborne benzene, toluene, ethylbenzene and xylenes (BTEX). The device consists of concentration and detection cells formed of 3 cm x 1 cm Pyrex plates. The concentration cell is composed of an adsorbent to concentrate the BTEX gases and a thin-film heater todesorb the concentrated gases from the adsorbent thermally. The collected gases are introduced into the detection cell, which is connected to optical fibers, to measure their absorption spectra. We optimized the device's operating conditions by studying the thermal characteristics of the concentration cell and the time profile of the gas concentration flowing in the detection cell. We used the device under optimized operating conditions to detect toluene gas as a typical example BTEX. The gas concentration amplification rate was approximately 2 orders of magnitude, and we successfully measured parts-per-million levels of toluene gas with this device.     

A magnetosensitive thin-film silicon Hall-type field-effect transistor with operating temperature range expanded up to 350°C

We describe a magnetosensitive device consisting of a combination of a thin-film Si transistor with built-in conducting channel (fabricated by the silicon-on-insulator technology) and a Hall-type sensor (HS). The transistor has a double-gate field control system of the metal–insulator–semiconductor–insulator–metal type and operates in the regime of carrier accumulation in the channel at partial depletion of adjacent regions of the Si film. It is established that the device can operate at temperatures up to about 350°C, which is 160–180°C higher than the maximum operating temperature of HSs based on bulk Si crystals and comparable with HSs based on wide-bandgap semiconductors.     

Toward tunable thin-film filters for wavelength division multiplexing applications

We provide a detailed analysis of the various problems connected with the development of tunable thin-film filters for wavelength-division multiplexing applications. We examine the relation between the change in layer thickness and the central wavelength shift for various configurations and point out the significance of the structure of the reflectors, the spacer thickness, and the location of the active layers. We describe and compare practical arrangements using either temperature or an electric field as the driving parameter.     

准二级压缩空气源热泵热水机的技术分析

文章对常规和过冷器准二级压缩的空气源热泵热水系统进行简要性能分析,通过实际测试不同工况下各性能参数随进水温度的变化规律,寻找过冷器准二级压缩空气源热泵热水机各工况点的最佳补气压力。结果表明,相对于常规空气源热泵热水系统,过冷器准二级压缩的空气源热泵热水系统可显著提高制热量及性能系数、降低排气温度、拓宽运行范围,可为过冷器准二级压缩热泵系统用于空气源热泵热水机的设计和应用提供参考。     

A tunable magnetic inductor

For integrated radio-frequency applications, tunable magnetic inductors are expected. A tunable magnetic inductor, based on magnetoimpedance effect, is presented in this paper. The proposed inductor is constructed with a magnetic inductor body, wound by an insulated coil, inducing a longitudinal dc bias magnetic field when a dc control current is flowing through. Formed by a conductive core coated by a high-permeability magnetic layer, the magnetic inductor body can be realized by either a thin-film structure or a composite wire. The reluctance models for both thin-film and composite wire structures are studied. A prototype tunable magnetic inductor, using a composite wire element, has been characterized. The results show that by varying the dc control current, the inductance L of the magnetic inductor can be tuned. The tunable range depends on the frequency of the current flowing through the inductor. A relative variation of inductance /spl Delta/L/L/sub 0/, up to 18% at low frequency (around 5 MHz), is achieved by applying a bias current of magnitude merely up to 15 mA. The quality factor varies from 5 to 17 in the measured frequency range. The proposed tunable inductor may be further optimized for high-frequency applications and has the potential to be realized in micro-electromechanical systems technology.     

Characteristics of heat flow in optical fiber devices that use integrated thin-film heaters

We describe the analysis of heat flow in a type of tunable optical fiber grating that uses thin-film resistive heaters microfabricated on the surface of the fiber. The high rate of heat loss from these microstructures and the relatively low thermal diffusivity of the glass yield unusual thermal properties. Approximate one-dimensional analytical calculations capture important aspects of the thermal characteristics of these systems. Comparison with experimental results that we obtained from devices with established designs validates certain features of the computations. This modeling also establishes the suitability of integrated thin-film heaters for several new types of tunable fiber grating devices.     

Theoretical study of amplitude and phase filtering of guided waves

The design of integrated optics filters by use of refinement software based on the Abelès thin-film computation method and the film mode matching method is studied. The results obtained with the two computation methods are compared. Good agreement is obtained provided that the fill factor of the guided mode in the component is high and that modal losses between waveguide sections are simulated by absorption with the Abelès computation method. Integrated optics devices that manage either the amplitude of guided waves such as a dense wavelength division multiplexing narrow-bandpass filter and a gain-flattening filter or the phase of guided waves such as a broadband dispersion compensator are     

On the Maintenance of Saturated Standard Cells at 3°C through the Use of Thermoelectric Cooling

Saturated standard cells at temperatures between 20°C and 40°C exhibit a high negative-voltage coefficient with respect to temperature and have required temperature stabilization within ±0.01°C over an extended period to achieve a voltage stability of ±1 ?V. Examination of standard cell data in the vicinity of 0°C, on the other hand, indicated higher voltages and a much lower temperature coefficient. In fact, the cell voltage reaches a maximum and consequently the voltage coefficient is zero at approximately 3°C, and is near zero over a range of several degrees. A cell maintenance temperature of 3°C, therefore, appears the most appropriate operating environment for a saturated cell in order to obtain maximum voltage stability. Heretofore, a convenient, high-stability, maintenance-free temperature bath operating near 3°C has not been available for laboratory use. The utilization of thermoelectricity to cool (Peltier effect) is currently available, and this method has been employed to provide a stable low-temperature ambient for saturated cells. This paper describes a practical air chamber-controller combination with thermoelectric heat pumping designed to test the behavior of saturated cells near 3°C. Details of the thermal and electrical characteristics of the unit will be discussed. Results show a ±0.2°C control is adequate to provide a primary voltage reference with ±1 ?V stability at 3.1°C. Advantages and precautions in maintaining cells at low temperatures will also be presented.