This study presents a real-time hardware implementation of a novel physical layer security algorithm developed for visible-light communications (VLCs) based on precoded spatial modulation (SM). The demonstration was carried out on a low-cost 70 cm × 40 cm × 40 cm miniature room model with four light-emitting diodes (LEDs) as a test-bed for conducting experiments in the field of VLC. The test-bed is a 10:1 shrunk replica of a conventional room and can be built with simple office supplies totaling <$10, excluding drive and collection optoelectronic components. While being cost-friendly, the test-bed also allows for (i) integrating optical components and (ii) carving desired window and door patterns with different cardboard color tones. Hence, the effects of reflections from different colored walls and the effect of external light sources can be observed on the performance of the secure VLC system. We successfully demonstrate the operation of the zero-forcing precoder and the SM on the built set up to provide robust and secure communication among the transmitting LEDs and the receivers, representing the legitimate user and the eavesdropper, for the first time in the literature. The secrecy capacity improvement is also noted, validating the proposed approach in realistic environments.
We present the design and characterization of a 3D-printed spiral actuator towards focus adjustment in endoscopes. The actuator, holding an aspherical lens, can be electromagnetically actuated to achieve ~0.5 mm displacement at 10 mW power.
We present a miniaturized actuator for volumetric tissue imaging. The device consists of a hydraulically actuated accordion-like part for axial scanning (focus adjustment), and an electromagnetically actuated 2D scanner for lateral scanning. The device is manufactured using selective laser sintering, allowing for very low cost and rapid production. We demonstrate 3D scanning capability through observing the lateral scan pattern at different axial locations with a CMOS camera, and through scanning of a multi-layered phantom. We further investigate reliability of the electromagnetically actuated lateral scanner, as well as the hysteresis behavior of the hydraulic scanner.
We present a two-dimensional piezoelectric fiber actuator and a novel actuation scheme to establish three different scan patterns with single device. The flexibility in choosing scan patterns offers multiple options for the operator to choose between improved uniformity, high frame-rate to image abrupt biological applications, or circular field-of- view to better image naturally cylindrical cavities (gastrointestinal tract, esophagus, etc.). The presented device is capable of achieving different scan patterns with a robust actuation scheme that demonstrated through first presenting its mechanical frequency behavior, then generating 256 pixel width or diameter raster, spiral, and Lissajous patterns at ≥20 frames-per-second.The presented device, along with the actuation strategy is a promising candidate for integration with miniaturized laser scanning devices towards clinical use.
We present a mode-optimized two-dimensional piezoelectric fiber actuator and a robust actuation scheme to establish three different scan patterns with the same device. Having multiple scan options, the operator of the actuator is free to choose between improved uniformity, high frame rate to image abrupt biological event, or circular field-of-view to better image cylindrical cavities (gastrointestinal tract, esophagus, etc.) that are cylindrical in nature. We demonstrate the capabilities of the device, through first presenting its mechanical frequency behavior, then offering an actuation scheme to achieve different scan patterns, and finally generating 256 pixel width or diameter raster, spiral, and Lissajous patterns at ≥20 frames per second. With further development, the presented actuator design and drive scheme could serve as a useful tool as part of a minimally invasive optomedical device in the clinic.
A magnetically actuated microscanner is used in a laser scanning microscopy application. Stress distribution along the circular-profiled flexure is compared with a rectangular counterpart in finite-element environment. Magnetic actuation mechanism of the scanning unit is explained in detail. Moreover, reliability of the scanner is tested for 3×106 cycle. The scanning device is designed to meet a confocal microscopy application providing 100 μm×100 μm field of view and <3-μm lateral resolution. The resonance frequencies of the device were analytically modeled, where we obtained 130- and 268-Hz resonance values for the out-of-plane and torsion modes, respectively. The scanning device provided an optical scan angle about 2.5 deg for 170-mA drive current, enabling the desired field of view for our custom built confocal microscope setup. Finally, imaging experiments were conducted on a resolution target, showcasing the desired scan area and resolution.
We present a disposable miniaturized confocal imager, consisting mostly of three-dimensional (3-D)-printed components. A 3-D printed laser scanner with 10×10 mm2 frame size is employed for Lissajous scan, with 180 and 315 Hz frequencies in orthogonal directions corresponding to ±8 deg and ±4 deg optical scan angles, respectively. The actuation is done electromagnetically via a magnet attached to the scanner and an external coil. A miniaturized lens with 6-mm clear aperture and 10-mm focal length is 3-D printed and postprocessed to obtain desired (≤λ/5 surface roughness) performance. All components are press-fitted into a 3-D-printed housing having 17 mm width, which is comparable to many of the MEMS-based scanning imagers. Finally, line-scan from a resolution target and two-dimensional scanning in the sample location were demonstrated with the integrated device.
KEYWORDS: Scanners, Confocal microscopy, 3D printing, Laser scanners, 3D scanning, Computer aided design, Imaging systems, 3D metrology, Polishing, Microelectromechanical systems
A low-cost confocal endoscope was developed consisting of a 3D printed laser scanner, a lens, and a housing. The developed tool, mainly made out of low cost polymer offers a disposable use. The scanner unit is overall 10x10mm and electromagnetically actuated in 2-dimensions using a magnet that is attached to the 3D printed scanner and an external miniaturized coil. Using 3D printer’s fabrication advantages the first two vibration modes of the scanner were tailored as out-of-plane displacement and torsion. The scanner employs lissajous scan, with 190 Hz and 340 Hz scan frequencies in the orthogonal directions and we were able to achieve ± 5° scan angles, respectively, with ~ 100 mA drive current. The lens which has 6-mm diameter and 10-mm focal length is 3D printed with Veroclear material and then polished in order to reach optical quality surface. Profilometer (Dektak) measurements indicate only x2 increase in rms roughness, with respect to a commercial glass lens having identical size and focal length.
We propose a novel fiber sensor utilizing a thermomechanical MEMS element at the fiber tip. Owing to its
Parylene/Titanium bimaterial structure, the MEMS membrane exhibits an out-of plane displacement with changing
temperature. Together with the MEMS element, the embedded diffraction grating forms an in-line interferometer, from
which the displacement as well as the temperature can be deduced. The fabricated detector is placed at the single-mode
fiber output that is collimated via a graded index lens. This novel architecture allows for integrating MEMS detectors on
standard optical fibers, and easy substitution of the MEMS detector element to alter the measurement range and the
response time of the sensor.Temperature and time-constant measurements are provided and verified with reference
measurements, revealing better than 20 mK temperature sensitivity and 2.5 msec response time, using low-cost laser
source and photodetectors.
KEYWORDS: Optical simulations, Beam shaping, Skin, Multiphoton microscopy, Point spread functions, Light scattering, Luminescence, Microscopes, Signal attenuation, Monte Carlo methods
Multiphoton fluorescence microscopy (MPM) is a method for high resolution, non-invasive investigations of biological tissue. The aim of introducing an annular shaped laser beam is to reduce the ouf-of-focus generated background signal improving imaging of light scattering tissue such as human skin. Simulations show that 50% of the beam radius can be blocked, while preserving the shape of the point spread function. Initial experiments performed on a phantom consisting of fluorescein and fluorescent beads embedded in agar by using a custom built MPM-set up show that by introducing a simple beam blocker to create an annular beam, the background signal is reduced with approximately 5%. Future work will include optimizing the set up, and creating phantoms with more light scattering properties.
Toward developing a new method for restoring tissue viscoelasticity in scarred vocal folds, we previously proposed a method to localize biomaterials within subepithelial voids ablated using ultrafast laser pulses. The clinical implementation of this method necessitates the quantification of the laser parameters for ablating scarred tissue. Here, we present a comprehensive study of these parameters including ablation threshold and bubble lifetime in healthy and scarred tissues. We also present a new method for extracting tissue-specific ablation threshold and scattering lengths of different tissue layers. This method involves finding the ablation threshold at multiple depths and solving the equations based on Beer’s law of light attenuation for each depth to estimate the unknown parameters. Measured threshold fluences were 1.75 J/cm 2 for vocal folds and 0.5 J/cm 2 for cheek pouches for 3-ps, 776-nm laser pulses. Scarred pouches exhibited 30% lower threshold than healthy pouches, possibly due to the degraded mechanical properties of scarred collagen during wound healing. The analysis of tissue architecture indicated a direct correlation between the ablation threshold and tissue tensile strength and that the bubble lifetime is inversely related to tissue stiffness. Overall, this study sheds light on the required laser parameters for successful implementation of ultrafast laser ablation for phonosurgery.
Vocal fold scarring is one of the major causes of voice disorders and may arise from overuse or post-surgical wound
healing. One promising treatment utilizes the injection of soft biomaterials aimed at restoring viscoelasticity of the
outermost vibratory layer of the vocal fold, superficial lamina propria (SLP). However, the density of the tissue and the
required injection pressure impair proper localization of the injected biomaterial in SLP. To enhance treatment
effectiveness, we are investigating a technique to image and ablate sub-epithelial planar voids in vocal folds using
ultrafast laser pulses to better localize the injected biomaterial. It is challenging to optimize the excitation wavelength to
perform imaging and ablation at depths suitable for clinical use. Here, we compare maximum imaging depth using two
photon autofluorescence and second harmonic generation with third-harmonic generation imaging modalities for healthy
porcine vocal folds. We used a home-built inverted nonlinear scanning microscope together with a high repetition rate (2
MHz) ultrafast fiber laser (Raydiance Inc.). We acquired both two-photon autofluorescence and second harmonic
generation signals using 776 nm wavelength and third harmonic generation signals using 1552 nm excitation
wavelength. We observed that maximum imaging depth with 776 nm wavelength is significantly improved from 114 μm
to 205 μm when third harmonic generation is employed using 1552 nm wavelength, without any observable damage in
the tissue.
The thermal sensor system presented in this paper is based on the mechanical bending due to the incident IR radiation. A
diffraction grating is embedded under each pixel to facilitate optical readout. Typically the first diffraction order is used
to monitor the sub-micron mechanical displacement with sub-nanometer precision. In this work; two different optical
readout systems based on diffraction gratings are analyzed.
First setup employs a conventional 4f optical system. In this one-to-one imaging system, collimated light is propagated
through a lens, filtered with an aperture and then imaged onto a CCD by a second lens.
Second system is more compact to improve image quality and to reduce noise. This is achieved by using an off-axis
converging laser beam illumination that forms the Fourier plane near the imaging lens. This approach has important
advantages such as reducing number of optical components and minimizing the optical path. The system was optimized
considering parameters such as laser converging angle, laser beam size at MEMS chip, and magnification of the imaging
system.
Diffraction gratings integrated with MEMS sensors offer sensitive displacement measurements. However, the sensitivity
of the interferometric readout may drop significantly based on the sensor position. A two wavelength readout method
was developed and tested previously in order to maintain the sensitivity of the readout > %50 maximum sensitivity over
a broad range (i.e. several um's for visible wavelengths). This work demonstrates the sensitivity enhancement of a
MEMS thermal imaging sensor array. Measurement of the target scene was performed using two lasers at different
wavelengths (633, 650 nm). The diffracted 1st order light from the array was imaged onto a single CCD camera for both
sources. The target scene was reconstructed by observing the change in the 1st diffracted order diffraction intensity for
both wavelengths. Merging of the data, acquired with two different sources, is performed by assigning each pixel in the
final image with the higher sensitivity pixel among two measurements. > 30% increase in the average sensitivity was
demonstrated for the sensor array.
Novel thermo-mechanical detector arrays with integrated diffraction grating for optical readout were designed and
fabricated. Parylene was used as the structural material due to its high thermal isolation and mismatch properties.
Calculations reveal that the NETD performance of a thermo-mechanical array using Parylene can be significantly better
than SiNx based designs and offer a theoretical NETD value <10mK assuming an optical readout with a high dynamic
range detector array. Finite Element simulations were performed with length of the bimaterial leg as the optimization
parameter. It was observed that only a few microns of isolation leg supported 30 fps applications, leaving rest of the leg
to be bimaterial and providing large thermo-mechanical deflections.
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