Here we report progress in the fabrication, calibration, and testing of a compact spectral imaging camera. The camera uses a micro-array of Fabry-Perot etalons bonded directly to a broadband focal plane array sensor. The array of etalons adds negligible size and weight to the system compared to a panchromatic imager. Other recent demonstrations of compact spectral imagers in the visible and near infrared (VNIR) have commonly used arrays of etalons in a single order, thereby reducing the system bandwidth and sensitivity to achieve the required spectral resolution. Here, we demonstrate a camera utilizing multiple etalon orders in a spectral multiplexing scheme known as Multiple Order Staircase Etalon Spectrometry (MOSES). An important characteristic of the MOSES system is that there is a relaxed tradeoff between spectral resolution and sensitivity (or etalon throughput). Unlike single-order etalon techniques, MOSES allows for the reconstruction of the spectrum to the bandwidth limit of the detector and reflecting layers. This is important in coastal environmental sensing, where IR spectral features may be desired at the same time as UV light transmitted through shallow water layers. This VNIR system demonstration indicates the feasibility of MOSES devices in other wavebands.
Modern nano-metrology instruments require calibration references with nanometer accuracy in the x, y, and z directions.
A common problem is the accurate calibration in the z direction (height). For example, it is generally not difficult to
obtain accurate x- and y- calibration references for a Scanning Probe Microscope (SPM). It is, however, much more
difficult to obtain accurate z-axis results. It is difficult to control z-axis piezo dynamics because during scanning in the
xy-plane the x-and y-axes move at a constant rate whiles the z axis does not. Furthermore due to the high cost of
producing calibration standards, the microscope is often calibrated at only one height. However, if the relationship
between the measured z height and the actual z height is not linear, then the height measurements will not be correct. In
this paper, we will present a method for the fabrication of calibration references with: (i) sub-10 nm features and (ii)
multiple step heights on one reference, allowing for better calibration of the non-linearity in the z direction.
Hyperspectral instruments with physical sizes comparable to that of a bare sensing array are now possible. Compact Fabry-Perot (FP) etalon arrays allow for different spectral sensitivities to be assigned to the different pixels of a sensing array. Such arrays for hyperspectral imaging are commercially available but underutilized due to cost and performance tradeoffs. FP arrays were first made possible by binary or logarithmic fabrication, which reduces the number of lithography steps to log<sub>2</sub>(k) where k is the number of distinct levels of material required for the integrated optical element. However, significant yield loss results from the several lithography steps required in this process. We introduce a new binary etching technique that allows for the creation of an arbitrary number of distinct levels with a single greyscale lithography technique. Our technique has been used for the fabrication of distinct levels of 1 nm rms flatness with a controlled 10 nm resolution. This technique has been used to fabricate a staircase structure with greater than 100 distinct steps directly on a COTS optical imager. Details of the fabrication technique and characteristics of the optical element will be presented.
Traditional Fabry-Perot (FP) spectroscopy is bandwidth limited to avoid mixing signals from different transmission
orders of the interferometer. Unlike Fourier transformation, the extraction of spectra from multiple-order interferograms
resulting from multiplexed optical signals is in general an ill-posed problem. Using a Fourier transform approach, we
derive a generalized Nyquist limit appropriate to signal recovery from FP interferograms. This result is used to derive a
set of design rules giving the usable wavelength range and spectral resolution of FP interferometers or etalon arrays
given a set of accessible physical parameters. Numerical simulations verify the utility of these design rules for moderate
resolution spectroscopy with bandwidths limited by the detector spectral response. Stable and accurate spectral recovery
over more than one octave is accomplished by simple matrix multiplication of the interferogram. In analogy to recently
developed single-order micro-etalon arrays (Proc. of SPIE v.8266, no. 82660Q), we introduce Multiple-Order Staircase
Etalon Spectroscopy (MOSES), in which micro-arrays of multiple order etalons can be bonded to or co-fabricated with a
sensor array. MOSES enables broader bandwidth multispectral and hyperspectral instruments than single-order etalon
arrays while keeping a physical footprint insignificantly different from that of the detection array.
Pulse shape discrimination (PSD) is a common method to distinguish between pulses produced by gamma rays and neutrons in scintillator detectors. This technique takes advantage of the property of many scintillators that excitations by recoil protons and electrons produce pulses with different characteristic shapes. Unfortunately, many scintillating materials with good PSD properties have other, undesirable properties such as flammability, toxicity, low availability, high cost, and/or limited size. In contrast, plastic scintillator detectors are relatively low-cost, and easily handled and mass-produced. Recent studies have demonstrated efficient PSD in plastic scintillators using a high concentration of fluorescent dyes. To further investigate the PSD properties of such systems, mixed plastic scintillator samples were produced and tested. The addition of up to 30 wt. % diphenyloxazole (DPO) and other chromophores in polyvinyltoluene (PVT) results in efficient detection with commercial detectors. These plastic scintillators are produced in large diameters up to 4 inches by melt blending directly in a container suitable for in-line detector use. This allows recycling and reuse of materials while varying the compositions. This strategy also avoids additional sample handling and polishing steps required when using removable molds. In this presentation, results will be presented for different mixed-plastic compositions and compared with known scintillating materials
Cell-based sensors are being developed to harness the specificity and sensitivity of biological systems for sensing
applications, from odor detection to pathogen classification. These integrated systems consist of CMOS chips
containing sensors and circuitry onto which microstructures have been fabricated to transport, contain, and nurture the
cells. The structures for confining the cells are micro-vials that can be opened and closed using polypyrrole bilayer
actuators. The system integration issues and advances involved in the fabrication and operation of the actuators are
Bilayer microactuators of gold and polypyrrole doped with dodecylbenzene sulfonate, PPy(DBS), are characterized with respect to their response times and the influence of operation temperature. These parameters are needed for biomedical applications such as microvalves. To fully open and close the valves, the bilayer hinges must be able to rotate within a few seconds at body temperature. Bilayers were subjected to potential steps to switch the PPy between the oxidized and reduced states. Actuation was viewed through an optical microscope and recorded by a digital camera. The velocity profiles during reduction and oxidation follow the same trends. Two different phases of actuation can be identified. In the first phase there is rapid movement, and in the second phase the velocities slowly decrease until the position reaches steady-state. In order to investigate the effects of elevated temperature on the actuators, the operation temperature was varied stepwise from 25 °C to 55 °C. The curvature increased irreversibly by up to 45% at elevated temperatures, and the output force dropped.
Polypyrrole/gold bilayer microactuators are being developed in our laboratory for biomedical applications such as microvalves. To fully open and close the valves, the bilayer hinges must be able to rotate between 0° and 180° within a few seconds against external forces. The layer thicknesses and hinge lengths must therefore be properly designed for the application. However, existing models fail to predict the correct behavior of microfabricated PPy/Au bilayer microactuators. Therefore, additional experimental data are needed to correctly forecast their performance. Bilayer actuators were fabricated with ranges of PPy thicknesses and hinge lengths. Bending angles were recorded through a stereomicroscope in the fully oxidized and reduced states. Isometric forces exerted by the hinges were measured with a force transducer, the output of which was read by a potentiostat and correlated with the applied potentials.
We present the use of electroactive polymer actuators as components of a biolab-on-a-chip, which has potential applications in cell-based sensing. This technology takes full advantage of the properties of polypyrrole actuators as well as the wide range of CMOS sensors that can be created. System integration becomes an important issue when developing real applications of EAP technologies. The requirements of the application and the constraints imposed by the various components must be considered in the context of the whole system, along with any opportunities that present themselves. In this paper, we discuss some of these challenges, including actuator design, the use of complementary actuation techniques, miniaturization, and packaging.
We present in this paper the development of novel mid-to-far IR filters that are based on porous silicon structures. The diameters of the pores in such filters are by orders of magnitude less than the central wavelength of the transmission band, leading to effective averaging of the porous structure by the light waves. Such filters have a number of important advantages over multilayer interference filters. Since the filters are made from a single material by means of an electrochemical etching process (rather than through deposition), these filters do not exhibit delamination problems and are well suited for operation at extreme temperatures (for example, in the environment of space). Our fabrication technique permits the fabrication of filters up to 200 mm (8 inches) in diameter, suitable for any wavelength from below 1.1 μm to more than 45 μm. The results of experimental testing of such filters are shown to prove the main predictions.
Currently used optical filters exhibit strong limitations in the deep UV and shorter wavelength ranges. We propose an entirely different type of UV filter to solve many of the problems due to inadequate materials and fabrication techniques. These filters consist of three-dimensionally ordered Macroporous Silicon (MPSi), with the pores used as waveguide cores separated by the reflective silicon host. Ordered pores serve as a two-dimensional array of optical waveguides. Multilayer coating of the pore walls results in the band-pass, short-pass, or band-blocking transmittance spectra of MPSi filters. Such filters have a number of advantages. They do not exhibit spectral shifts of the passed or blocked spectral bands with the angle of incidence, permitting operation in tilted and divergent light beams to simplify optical system design and fabrication. Due to their structures (fewer and thinner layers on the pore walls required to gain the same level of rejection), the filters do not exhibit delamination problems and are well suited for operation at extreme temperatures (for space as well as for terrestrial environments). The fabrication process is different from that used for multilayer interference filters. This process permits the fabrication of filters up to 200mm in diameter that are suitable for wavelengths from longer than 400 nm to shorter than 100 nm. Far-UV filters can be manufactured as simply and economically as the near UV ones. The theory of light propagation through the MPSi layers is developed, the main predictions of the theory are experimentally validated, and the fabrication procedure for MPSi UV filters is reported.
The optical properties of photonic bandgap (PBG) structures are highly sensitive to the geometry and refractive index. This makes PBG structures a good host for sensor applications. The binding of target species inside the PBG structure changes the refractive index of the material, which can be detected by monitoring the optical response of the device. One-dimensional PBG biosensors based on porous silicon (PSi) have been fabricated. The device is a microcavity, made of a symmetry breaking PSi layer (defect layer) inserted between two PSi Bragg mirrors. Narrow resonances are introduced in the photoluminescence and reflectance spectra. The large internal surface of the sensor is functionalized for the capture of target biological materials. When the sensor is exposed to the target, binding to the internal surface increases the effective optical thickness of the microcavity and thus causes a red shift of the optical spectrum. The sensor's sensitivity is determined by the morphology and geometry of the device. We will present the details of the materials science, sensor fabrication and optimization, and also describe experiments performed with biological targets.
Currently used transmission-type polarizers exhibit strong limitations in the deep UV and shorter wavelength. We propose an entirely different type of polarizer to solve many of the problems caused by the absence of adequate materials in this spectral range. The new polarizers consist of three-dimensionally ordered Macroporous Silicon (MPSi), with the pores used as waveguide cores separated by the reflective silicon host. Ordered pores serve as a two-dimensional array of optical waveguides. Multilayer coating of the pore walls, together with the rectangular shape of the pores (with the length along one axis being several times greater than that of the second axis) results in polarized transmission. Calculations demonstrate potentially very high extinction. In addition, the extinction achieved by such polarization components does not exhibit degradation with the angle of incidence, permitting operation in tilted and divergent light beams to simplify optical system design and fabrication. The fabrication process is different from that used in the fabrication of multilayer interference filters. It permits the fabrication of deep UV polarizers up to 200mm in diameter, suitable for wavelengths from above 600nm to less than 50nm. Far-UV polarizers can be manufactured as simply and economically as the near UV ones. The theory of light propagation through such MPSi layers is developed, the main predictions of the theory are experimentally validated, and the fabrication procedure for MPSi UV polarizers is described.