High sensitivity magnetic field sensors have been applied to biotechnology problems such as magnetoencephalography and magnetocardiography. Unfortunately, the high cost and/or development of the sensors often limit the widespread use of these medical diagnostic systems. Fiber optic magnetostrictive sensors offer high sensitivities with competitive fabrication cost. Magnetostrictive sensors have experimentally demonstrated resolutions as low as 23 pT/√Hz without any mu-metal shielding. With respect to the sensor cost, fiber-optic-based magnetic field sensors leverage the advanced component development and the economies of scale of the telecommunications industry. In addition, the trend in interferometric sensor development has been to transfer the demodulation complexity from hardware to the digital signal processing algorithm. This reduction in hardware significantly reduces the cost of the overall sensor system. In this paper, we present a demodulation algorithm for an interferometric magnetic field sensor. The sensing mechanism is based on the magnetostriction of a material bonded to the optical fiber in the sensing leg of the interferometer. A phase-generated-carrier demodulation scheme is assumed. The algorithm features real-time demodulation of arbitrary signal waveforms. We present the theoretical derivation of the algorithm and verify its operation through computer simulation.
Magnetostrictive fiber sensors combine the phase sensitivity of interferometry with the magnetically induced strain of ferromagnetic materials. Configurations include fiber wrapped around mandrel halves separated by a magnetostrictive rod, fiber bonded to a magnetostrictive ribbon and fiber jacketed with a magnetostrictive film. Processing advances in the deposition of dense, uniform films on the cylindrical surface of the fiber offer the advantage of reduced demagnetization of the magnetostrictive material. In this paper, we investigate the design of a sensor based on a magnetostrictive film jacketing the fiber. We analyze the system resolution and minimum film thickness of the fiber sensor using nickel, Metglas and Terfenol-D films. For each of these magnetostrictive films, we present simulation results on the resolution as a function of the film-fiber interaction length. In our analysis, we assume a phase generated carrier demodulation scheme. We next analyze the magnetostrictive strain of the compound film-fiber system as a function of film thickness. This analysis sets the minimum film thickness for effective strain on the system. Finally, we propose a geometry which allows a compact sensor package with a reasonable film-fiber interaction length.
In this paper, we present a novel approach for the collection of computed tomography data. Non-uniform increments in
projection angle may be used to reduce data acquisition time with minimal reduction in the accuracy of the reconstructed
profile. The key is to exploit those projection angles which correspond to regions where the object contains few high
spatial frequency components. This technique is applicable to optical phase computed tomography, as well as X-ray
computed tomography. We present simulation results on intraocular lenses used in cataract surgery.
Fluorescent imaging of cells and tissues cultured within a rotating wall vessel bioreactor offers quantitative assessment
of the 3-dimensional aggregation of cells into tissue constructs. We present the design of a rotating wall vessel system
optimized for real-time fluorescent analysis. The modulation transfer function of our system is found to be superior to
the commercially-available vessel used in previous fluorescence imaging studies. We demonstrate dynamic fluorescent
imaging of DAPI-stained porcine pancreatic islets.
KEYWORDS: Microelectromechanical systems, Interferometers, Demodulation, Optical fibers, Finite element methods, Actuators, Fiber optics, Interferometry, Digital signal processing, Systems modeling
We present the integration of an optical fiber interferometer with a MEMS probe station for measuring the out-of-plane
displacement of MEMS structures. The interferometric system presented uses a phase generated carrier demodulation
scheme. Digital signal processing techniques provide a theoretical measurement dynamic range greater than 108.
Experimental results characterizing a novel vertical-lift
electro-thermal actuator are presented. These results are in good
agreement with modeling data based on finite element analysis.
In this paper, we present a metrology system to characterize the refractive index profile of intraocular lenses (IOLs).
Our system is based on interferometric optical phase computed tomography. We believe this metrology system to be a
key enabling technology in the development of the next generation of IOLs. We propose a Fizeau-based optical
configuration and present a simulation study on the application of computed tomography to IOL characterization.
KEYWORDS: Interferometry, Sensors, Demodulation, Calibration, Digital signal processing, Interferometers, Data acquisition, Signal processing, Fiber optics, Fiber couplers
We have developed a ballistic shock sensor based on interferometric velocimetry. The requirements of the sensor are that
it should measure the motion of an impacted armored plate with velocities up to 10 m/s, frequencies up to 100 kHz, and
displacements not exceeding about 3 mm. Our fiber optic system uses a 3 × 3 fiber directional coupler and digital
demodulation for passive stabilization of the interferometer. In this paper, we describe the digital signal processing for
phase drift compensation and automatic calibration of the system. Simulation results will be presented.
KEYWORDS: Detection and tracking algorithms, Digital signal processing, Microelectromechanical systems, Demodulation, Interferometry, Interferometers, Calibration, Signal processing, Modulation, Algorithm development
Microelectromechanical systems (MEMS) are under development as radio-frequency (RF) switches for a broad range of applications, where active and passive components can be switched into or out of RF circuits. Optical interferometry is well-suited to the characterization of MEMS structures due to its wide dynamic range, its fine resolution, and its non-invasive qualities. However, RF MEMS operate at frequencies ranging from a few megahertz to tens of gigahertz. These high operating frequencies offer challenges in the demodulation of the interferometric system. Our demodulation system consists of photodetecting the optical interferometric signal, converting the analog electronic signal to a digital signal, and digitally processing the signal to compute the MEMS structure's vibration amplitude. In this paper, we present a digital signal processing algorithm for demodulating an interferometer developed for characterizing RF MEMS. Our algorithm is based on a phase-generated carrier modulation system and assumes that the target structure is oscillating at a fixed frequency. A key feature of our algorithm is that it permits determination of a structure’s vibration amplitude, where the structure's vibration frequency is greater than the analog-to-digital converter's (ADC's) sample frequency. Therefore, commercially-available low-cost ADCs and microprocessor systems may be used for real-time demodulation. Both simulation and experimental results will be presented.
KEYWORDS: Interferometers, Digital signal processing, Demodulation, Ferroelectric materials, Microelectromechanical systems, Algorithm development, Signal processing, Detection and tracking algorithms, Modulation, Interferometry
The rapid expansion of the microelectromechanical systems (MEMS) industry and the increasing number of applications in communications, displays, and sensing has led to an increasing demand for robust characterization techniques capable of in situ characterization of MEMS structures. Interferometry is well suited to such characterization due to its wide measurement dynamic range, its fine resolution, and its non-invasive qualities. We have constructed a fiber optic interferometer for the in situ characterization of MEMS structures. We report the development and implementation of a real-time digital signal processing (DSP) algorithm to demodulate the interferometer. We have developed a computationally efficient algorithm for both stabilization of the interferometer at quadrature and determination of the target’s vibration amplitude. We have verified our demodulation scheme using a piezoelectric transducer driven mirror as the target. Our current system will measure vibration amplitudes down to 10 nm. Both theoretical and experimental results are presented.
We present the theoretical operation and experimental results of a fiber optic interferometer, which we have used to measure the surface displacement of a collagen gel. Dispersed within the collagen gel are fibroblast cells. We describe a measurement system to assist in the detailed study of the biochemical and mechanical processes involved in fibroblast cell contraction. The interferometric system is non-contacting and offers a large dynamic range of measurement. Digital demodulation of a phase generated carrier results in an experimental sensitivity limit on the order of tens of nanometers with a measurement range of up to 2 mm. Computer-controlled data acquisition allows measurement of the contracting gel host over a period of several hours. We describe the optical interferometric system and present experimental results on a contracting collagen gel.
Imaging polarimetry is a novel method of characterizing the polarization effects of optoelectronic devices. From the Mueller matrix image, any polarization property of a device can be determined. High resolution polarization images of the outcoupling faces of several self-imaging GaAs/AlGaAs waveguide beamsplitters were made in the Mueller matrix imaging polarimeter at the University of Alabama in Huntsville. Interesting polarization states of the device modes (TE and TM), the magnitude of linear retardance varied significantly across a device. Polarization losses were also observed to vary across the faces of the devices. These effects could not have been observed by simply measuring the crosstalk between the TE and TM modes. The results of this study could lead to the detection of defect mechanisms in optoelectronic devices through Mueller matrix measurements.
Mueller matrix imaging polarimetry represents a novel means of characterizing the polarization effects of optoelectronic devices. The Mueller matrix contains the complete polarization properties of a sample, and can therefore be used to calculate properties such as phase retardance, polarization dependant losses and polarization crosstalk. The complete polarization properties of a series of GaAs/AlGaAs self-imaging waveguide beamsplitters were measured with an imaging Mueller matrix polarimeter. Polarization properties were mapped across high resolution images of the devices' outcoupling faces, and the uniformity of the polarization properties was measured. Properties investigated include magnitude and orientation of linear retardance, polarization dependant losses, and crosstalk between TE and TM modes.
The maturation in the state-of-the-art of optical components is enabling increased applications for the technology. Most notable is the ever-expanding market for fiber optic data and communications links, familiar in both commercial and military markets. The inherent properties of optics and photonics, however, have suggested that components and processors may be designed that offer advantages over more commonly considered digital approaches for a variety of airborne sensor and signal processing applications. Various academic, industrial, and governmental research groups have been actively investigating and exploiting these properties of high bandwidth, large degree of parallelism in computation (e.g., processing in parallel over a two-dimensional field), and interconnectivity, and have succeeded in advancing the technology to the stage of systems demonstration. Such advantages as computational throughput and low operating power consumption are highly attractive for many computationally intensive problems. This review covers the key devices necessary for optical signal and image processors, some of the system application demonstration programs currently in progress, and active research directions for the implementation of next-generation architectures.
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