The photographic assessment of the optic nerve has been one of the original and most extensively used methods to evaluate patients for glaucoma. The depth evaluation of the optic disc in the retinal fundus is important for the early detection of glaucoma. Conventional fundus cameras have a limited field-of-view for imaging of the retina and its peripheral areas. In this article, we report the design and fabrication of a non-mydriatic wide-field fundus camera using a contact-free trans-scleral illumination that is capable of taking 3D images of the optic disc using oblique illumination. We demonstrate that, using oblique illumination through sclera, a quasi 3D image of the optic disc along with its shadow can be obtained. The shadow provides important information on the shape and depth of the optic disc. The depth values of the optic disc obtained by our proposed method using shadow length measurements are in good agreement with the values obtained using an optical coherence tomography device. The results indicate that our fabricated fundus camera could be an easy-to-handle and low-cost tool for remote detection and diagnosis of ocular diseases without the need of an ophthalmologist.
.We report the use of digital holographic microscopy to study harmonic evolution of dynamic deformation of two orthogonal modes of resonating piezoelectric MEMS mirror with a gimbal frame suspension. For the bending mode, the results show a linear relationship between dynamic deformation and the optical scan angle. For the torsional mode, a hysteretic behavior is observed, showing a significant difference depending on the scan direction. The difference was measured to be 45 nm, representing 18% of the total dynamic deformation of this mode. To investigate this effect, a point-by-point Fourier expansion method of the deformation cycle was employed and mechanical harmonics were extracted. From studying the first harmonic, we conclude that the origin of the hysteresis can be attributed to the phase difference in the oscillation of the two extrema points at the edge of the mirror, defining the peak-to-value deformation. In addition, higher-order harmonic terms (3rd and 5th) were identified and are affecting the hysteresis shape. Next, a modulation transfer function, corresponding to the measured angle-resolved dynamic deformation was estimated. Results show small contrast loss originating from the torsional mode, with an almost negligible effect of the hysteresis. The loss of contrast is dominated by the dynamic deformation of bending mode and was estimated to be 96% already at 0.18 normalized spatial frequency.
Age-related cataracts are reported to be responsible for over 50% of world blindness and are considered a priority eye disease by the World Health Organization. Cataracts progress slowly and often have no subjective symptoms, so regular examination is required for early detection and treatment. We report on the design and development of a portable slit-light-based cataract detection device using near-infrared light and a scanning mirror. Imaging results were obtained by scanning cataract model eyes made from dimethylpolysiloxane and starch mixture and enucleated swine eye with induced cataracts. The fabricated system has adequate sensitivity to detect the smallest cataract formation and progress of cataract in the induced cataract eye and such measurements are useful for early detection of cataract. The results indicate that our fabricated slit-light device could be an easy-to-handle and low-cost tool for remote/routine detection and diagnosis of ocular diseases (like cataracts) without a need for an ophthalmologist.
A multileveled tunable silicon grating array is designed and fabricated on a large-scale-integration (LSI) substrate. The grating consists of 250 single crystalline silicon ribbons of 260 nm in thickness, 400 μm in length, and 10 μm in period. The LSI substrate generates voltages to vary the heights of respective grating ribbons addressed by digital signal input. Each grating ribbon is attracted by an electrostatic force generated by 6-bit applied voltage in the range from 0 to 5 V. In the fabrication, the LSI substrate and a silicon-on-insulator wafer are bonded by the two kinds of polymers. A photosensitive polyimide polymer is used for patterning the bonding pads and also for bonding the wafers at the pressure of 0.25 MPa and the temperature of 350°C. Another epoxy polymer fills the space underneath the grating ribbons for subsequent process, which is finally removed by sacrificial etching to make the grating ribbons freestanding. The tunability of the grating is examined experimentally under the basic operation conditions.
We have fabricated a simple and compact scanning laser optical system using microelectromechanical system (MEMS) scanner that can be incorporated into portable health monitoring devices. The two-dimensional (2-D) MEMS scanner used in this system is much smaller and light in weight compared to galvanometer scanners and polygon scanners used in the commercially available ophthalmic devices. MEMS scanners have many advantages and also limitations compared to galvanometer and polygon scanners. An easy to use and compact device is more useful for rapid alignment for measurement and data acquisition. Sensitivity of the system was quantified by measuring signal-to-noise ratio (SNR) for both high and low reflectivity materials. SNR was 10 for the high reflectance materials and about 4 for low reflectance materials, which is sufficient for biological imaging. Distortion generated using large scanning angle of 2-D MEMS scanner was corrected in real time by custom made LabVIEW program. Ocular safety is important to consider when using a laser for ophthalmic devices. We calculated the maximum permissible beam power for thermal damage and photochemical damage considering the specification of our system such as visual angle and wavelength of the laser beam. The measured laser intensity in the front of model eye was 6 μW, which is much smaller than the maximum permissible beam power recommended by the American National Standards Institute.
We propose, design and fabricate here an electrostatically actuated continuous single-crystal-silicon membrane deformable mirror (DM) for astronomical observation. To get a large stroke, a bimorph spring array is used to generate a large air gap between the mirror membrane and the electrode. A DM with a 1.8mm×1.8mm mirror membrane are fabricated by combining Au-Si eutectic wafer bonding and the subsequent all-dry release process. The stroke of the DM is 3.5μm at 115V. The influence function on the nearest neighbor is 51%. The fill factor of the DM is 99.9%.
The surface grating technologies enable to control the thermal radiation spectrum. We are applying this
technique to promote the chemical reaction to produce hydrogen in the methane steam reforming process by
spectrally resonant thermal radiation. The thermal radiation spectrum is adjusted to vibrational absorption
bands of methane and water molecules near 3 μm by making a two-dimensional surface grating of period
Λ=2.6 μm on the radiative surface. By matching the peak of thermal radiation to the absorption bands of
gases, it is clearly observed that the hydrogen production is promoted five times as much as the case without
spectrally resonant thermal radiation by the optical excitation of vibrational energy levels of molecules.
From a series of experiments and analysis, it is suggested that radiative gas effectively excited the molecules
up of high energy vibrational and rotational levels, and this lead to the high production rate of hydrogen in
methane steam reforming process.
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