In this paper, we tailor the evanescent field coupling between two metal layers with subwavelength slit arrays and created a half-wave plate that imparts a half-wave phase delay to one component of linear polarization. The polarization of linearly polarized light at 1.55 μm wavelength can be rotated by up to 90 degrees, with polarization extinction ratio exceeding 22 dB. One advantage of this device over conventional polarization rotators is that the wavelength of operation can be chosen by fabricating subwavelength slit arrays with different parameters. Moreover, future devices can be designed to be mechanically tunable by suspending one of the metal plates. Nanomechanical motion between the two metal layers changes the evanescent field coupling between them, allowing real time control of the polarization of the transmitted light.

The threat of nuclear proliferation remains a critical issue in our society. Prevention requires knowledge, and there is no greater indicator of the capability and intent of a nation than observation of actual detonation tests being conducted. Ground-based monitoring systems have proven to be very capable in identifying nuclear tests, and can provide somewhat precise information on the location and yield of the explosive device. Making these measurements, however, currently requires very expensive and bulky seismometers that are difficult to deploy in places where they are most needed. A high-performance, compact device can enable rapid deployment of large scale arrays, which can in turn be used to provide higher quality data during times of critical need. We are pursuing a design that is based upon a proven optical sensing modality, and will combine this interferometric transducer with a new mechanical system design in order to achieve the required sensor self-noise of 0.5 nano-g/Hz 1/2 , with a total dynamic range of more than 150 dB. This will be accomplished in a form factor that is approximately 1 cm 3 per axis, and a power consumption below 30 mW. These metrics would represent substantial advancements over the existing state of the art. Lower cost, smaller sensors will enable wide-scale deployment of sensor arrays, which will also greatly enhance our understanding of the earth and provide early-warning systems for earthquakes and tsunami. Slight variations in the sensor design will also find extensive use in oil and gas exploration.

We demonstrate a half wave plate whose principle of operation is based on the strong evanescent field coupling between two metal layers with arrays of subwavelength slits. The device is divided into two kinds of pixels in which the slits are oriented in orthogonal directions. By tuning the phase delay of the transmitted light through the lateral displacement between the top and bottom layers, the polarization of linearly polarized light at 1.55 μm can be rotated by up to 90°. The polarization extinction ratio of the transmitted light exceeds 22 dB.

We have successfully demonstrated a series of results that push the limits of optical sensing, acceleration sensing and lithography. Previously, we built some of the most sensitive displacement sensors with displacement sensitivities as low as 12fm/Hz at 1kHz. Using reference detection circuitry in conjunction with correlated double sampling methods, we lowered the 1/f noise floor to 10mHz, hence improving the detection limit at low frequencies (10mHz) by 77dB to 50fm/Hz. We converted these highly sensitive displacement sensors to highly sensitive acceleration sensors through a direct mass integration processes. Our accelerometers have resonant frequencies as low as 36Hz and thermal noise floors as low as 8nG/Hz (where 1G=9.8m/s2). We have pushed the limits of shaker table experiments to independently verify acceleration measurements as low as 10μG/Hz. Direct measurements with our integrated sub-wavelength optical nano-grating accelerometers have shown device sensitivities of 590V/G and noise floors corresponding to 17nG/Hz (at 1Hz).

We demonstrate that the phase of light transmitted through double-layer subwavelength metallic slit arrays can be controlled through lateral shift of the two layers. Our samples consist of two aluminum layers, each of which contains an array of subwavelength slits. The two layers are placed in sufficient proximity to allow coupling of the evanescent fields at resonance. By changing the lateral shift between the layers from zero to half the period, the phase of the transmitted electromagnetic field is increased by pi, while the transmitted intensity remains high. Such a controllable phase delay could open new capabilities for nanophotonic devices that cannot be achieved with single-layer structures.

We have successfully demonstrated a series of results that push the limits of optical sensing, acceleration sensing and lithography. We previously built some of the most sensitive displacement sensors with displacement sensitivities as low as 12 fm/root Hz at 1 kHz. Using reference detection circuitry in conjunction with correlated double sampling methods, we have lowered the 1/f noise floor to 10 milli-Hz, hence improving the detection limit at low frequencies (10 milli-Hz) from 37 pm/root Hz to 50 fm/root Hz i.e. by 57.3 dB. We have developed the capability to convert these highly sensitive displacement sensors to highly sensitive acceleration sensors through innovative low-stress mass addition and direct mass integration processes. We have built accelerometers with resonant frequencies as low as 43 Hz and thermal noise floors as low as 10 nG/root Hz. We have pushed the limits of shaker table experiments to verify direct acceleration measurements as low as 10 mu G/root Hz.

A method of stress control in microelectromechanical systems (MEMS) devices is presented that consists of creating counterbalancing structures to position stressed layers at the neutral plane of the device, eliminating the bending momentum acting on the device. Upon metallization, many MEMS elements such as silicon membranes show substantial bow under the stress developed as a result of the difference in the thermal expansion coefficients of a metal and silicon. The proposed membranes with the counterbalancing structures remain flat in the entire test temperature range (25–150°C). The method gives material-independent solution to stress-induced curvature problems in a variety of ultrathin devices.

A new method of controlling trains based on constant communications with each train is known as communications based train control (CBTC). This method allows more traffic and trains closer together at the same time improving safety. This paper looks at an open on-board CBTC controller for subway cars using a modified model of n-version programming to create a system that guarantees the highest level of safety, at the same time performing the on-board functions required by CBTC

We present measurements of transmission of infrared radiation through double-layer metallic grating structures. Each metal layer contains an array of subwavelength slits and supports transmission resonance in the absence of the other layer. The two metal layers are fabricated in close proximity to allow coupling of the evanescent field on individual layers. The transmission of the double layer is found to be surprisingly large at particular wavelengths, even when no direct line of sight exists through the structure as a result of the lateral shifts between the two layers. We perform numerical simulations using rigorous coupled wave analysis to explain the strong dependence of the peak transmission on the lateral shift between the metal layers.

Submitted for the MAR05 Meeting of The American Physical Society Optical transmission through metallic bilayers with subwavelength apertures H. B. CHAN, Z. MARCET, KWANGJE WOO, D. B. TANNER, Department of Physics, University of Florida, D.W. CARR, Sandia National Laboratories — The optical transmission through a periodical array of subwavelength apertures in a metal film can be strongly enhanced by resonance of the incident light with surface plasmon polaritons on the metal surfaces. The excitation of surface plasmons is accompanied by a dramatic enhancement of the local electromagnetic field on the metal surfaces. We have fabricated subwavelength structures consisting of two layers of metal. The metal layers are positioned sufficiently close to each other such that the evanescent fields of the surface plasmons generated in the first layer excite surface plasmons in the second layer. In some cases the two metal layers are laterally displaced such that no direct line of sight exists through the structure. Nevertheless, the transmission through a number of these devices remains remarkably high at resonance, comparable to the single layer value. We will discuss the dependence of the optical transmission on various sample parameters, including metal layer thickness, separation, lateral shift and incident angle of light.