Purpose: We report that a large field-of-view (FOV) retinal image can be acquired by a smart fundus camera.
Approach: This handheld system consists of a Raspberry Pi board, a touch screen display, a customized optical lens group, a ring light-emitting diode, and a Li-battery.
Results: Wide FOV of ∼57 deg is observed with proper lens configuration and can be expanded using image stitching algorithms.
Conclusions: This customized handheld fundus camera provides better image quality than cellphone-based fundus imaging solutions and offers more operational features than traditional portable fundus cameras. It may benefit field-portable ophthalmic diagnostic applications.
We report that a large field of view (FOV) retinal image can be acquired by a low-cost smart fundus camera. This handheld system includes a Raspberry Pi board, a touch screen display, a customized optical lens group, a ring LED light, and a Li-battery. Based on the open hardware platform and Linux operating system, we have integrated the portable system with component switching and image processing functions. Wide FOV has been realized using image stitching and structure from motion algorithms. This customized low-cost handheld fundus camera provides better image quality than cellphone-based fundus imaging solutions and offers more operational features than traditional portable fundus cameras. It may benefit field portable ophthalmic diagnostic applications.
We report a multi-frame superresolution enhanced spectral domain optical coherence tomography (SD-OCT) for fast and high quality in vivo 3D imaging of subsurface fingerprint. After acquiring several sets of low resolution C-scans 3D fingerprint images with lateral sub-spot-spacing shifts, a high lateral resolution and high quality 3D image is reconstructed by multi-frame superresolution processing. In experiment, about 3 times lateral resolution improvement has been achieved from 25 to 7.81 μm with sample arm optics of 0.015 numerical aperture, as well as doubling the image quality. For in vivo 3D SD-OCT imaging, high quality 3D subsurface live fingerprint images have been obtained within a short scan time, showing beautiful and clear distribution of eccrine sweat glands that could be an effective indictor to SD-OCT lateral resolution. Without using any complex segment algorithm, our high quality 3D fingerprint image could be easily separated into three layers: the external fingerprint patterns, the distribution of eccrine sweat glands, and the internal fingerprint pattern. The latter two subsurface layers will benefit high security biometry applications against spoofing attacks.
We present herein the active PbS-photopolymer waveguide fabricated by vacuum assisted microfluidic (VAM) soft lithography technique. The PbS Quantum Dots (QDs) were synthesized using colloidal chemistry methods with tunable sizes and emission wavelengths, resulting in efficient light emission around 1000 nm center wavelength. The PbS QDs have demonstrated much better solubility in our newly synthesized UV curable polymer than SU-8 photoresist, verified by Photoluminescence (PL) testing. Through refractive index control, the PbS QDs-polymer core material and polymer cladding material can efficiently confine the infrared emitting light with a broad spectral bandwidth of ~180 nm. Both single-mode and multi-mode light emitting waveguides have been realized.
We report that wide field-of-view (FOV) optical coherence tomography images with high lateral resolution can be obtained by using superresolution and 3D image stitching techniques. About 3 times lateral resolution improvement from 6.20 μm to 2.19 μm using a focusing lens of 0.08 numerical aperture has been demonstrated. With such lens the FOV is generally small owing to off-axis focusing degradation. To enlarge the FOV while maintaining high lateral resolution, 3D image stitching technique is introduced to effectively reconstruct an ultra-wide FOV 3D image of 2.10x1.15 mm2 lateral area from ten C-scans of 500×500 μm2 FOV. Improved FOV with high lateral resolution should benefit various biomedical imaging applications.
We introduced a laser-based noncontact shallow water depth measurement technique from a flying unmanned aerial vehicle (UAV). The water depth is measured by imaging two laser beam spots scattered from the surface and bottom of the water. The effect of water surface waves and UAV tilt angles to the depth measurement has been studied for practical applications. We have further developed this laser-based detection system consisting of a green laser, a global positioning system, a camera with a narrow field of view lens, a laser range finder, and a single-board computer. The measurement system onboard of a UAV flying over a small lake has demonstrated satisfactory water depth measurement capability. The low-cost light weight UAV-based water depth measurement should benefit water depth monitoring, mapping, and reporting in a hazardous environment offering flexibility, mobility, and remote control safe operation.
Planar concave grating wavelength demultiplexers with a flattened spectral response are realized based on SU-8 polymer waveguides. The flattened spectral response is accomplished by using an optimized multimode interference (MMI) coupler as the input aperture of the planar waveguide for all spectrally separated channels. The mode field distribution at the input of the planar waveguide is controlled by adjusting the width of the input taper connected to the MMI coupler. The devices are fabricated by cost-effective one-step UV lithography. Experimental results show that the desired flattened spectral response has been realized. The on-chip loss, crosstalk, and nonuniformity of the fabricated device are −14.8, −22, and 2.5 dB, respectively.
A 4-channel planar concave grating device with a flattened spectral response based on SU-8 polymer is presented.
The flattened spectral response is accomplished by using an optimized multi-mode interference coupler as the input
aperture of the device for spectrally separated channels. The mode field distribution in the input plane is controlled
by adjusting the width of input taper coupled to the multi-mode interference coupler. The effects of the input taper
width on the flattened spectral response are demonstrated in detail through simulation results. The devices are
realized by using an SU-8 polymer strip waveguide with a UV lithography technology. Experimental results show
that the flattened spectral response can be easily controlled by adjusting the taper width.
Polymeric waveguides with tunable optofluidic couplers are fabricated by the vacuum assisted microfluidic technique for card-to-backplane optical interconnect applications. The optofluidic coupler on a backplane consists of polymer waveguides and a perpendicular microfluidic channel with inclined sidewalls. An index matching liquid and air bubbles are located in the microfluidic hollow channel. The activation or deactivation of the surface normal coupling of the optofluidic coupler is accomplished by setting air bubbles or index matching liquid to be in contact with the waveguide mirrors. 10 Gbps eye diagrams of the card-to-backplane optical interconnect link have been demonstrated showing the high performance of the interconnect system.
We report an integrated optical coherence tomography (OCT) and reflectometry system for ophthalmology imaging. The dual-functional device provides a complementary high-resolution tear film evaluation by reflectometry and anterior segment imaging by OCT, offering a more comprehensive anterior segment examination. The imaging measurement capabilities have been demonstrated on a human eye as well as on a model eye. The minimum measured tear film thickness is 0.3 μm with measurement resolution of less than ±0.58% of film thickness yet the OCT anterior segment offers a depth resolution of 7 μm with a 45-nm bandwidth superluminescent light source at 840-nm center wavelength. The integrated system has demonstrated the capability for three-dimensional imaging in the anterior segment of the eye.
We report on the fabrication of a light sensitive waveguide via vacuum assisted microfluidic (VAM) soft
lithographic technique. UV curable light insensitive waveguides function like typical polymer waveguides with
desired mode confinements while the light sensitive waveguides formed by an azobenzene based polymer resin can
achieve refractive index modulation through green or blue laser illumination. The refractive index modulation is
instant and reversible in the light sensitive waveguide. The VAM technique is used for the fabrication of multisection
waveguides using different resins at the same time which is unique compared to conventional single material
waveguide fabrication. The effective fabrication of various waveguide sections with the light sensitive azobenzene
based UV curable resin can result in many functional waveguide devices for photonics applications.
Polymeric waveguides with dynamic coupler array are fabricated by vacuum assisted microfluidic technique for
card-to-backplane optical interconnect applications. The dynamic optical coupler on backplane consists of 45°
integrated waveguide mirrors and a perpendicular microfluidic channel for flow motion of index matching liquid
and air bubbles. Controlled positioning of the air bubble or index matching liquid in contact with the integrated
mirror can effectively turn on or off each surface normal waveguide coupler for card-to-backplane optical
interconnection. The size of the integrated mirror determines the coupler efficiency. Effective surface normal optical
coupling is demonstrated.
We demonstrate cis-to-trans transition based red light holographic recording in an azobenzene-liquid crystal (LC)
polymer material following efficient crucial transition of trans-to-cis, which is prepared by selected wavelength light
pre-illumination. The presence and orientation of soft liquid crystal impregnating the polymer backbone allows the
cis intermediate states to hold for the stable red hologram recording and non-destructive readout. Using a 50 nm
bandwidth light source at the center wavelength of 575 nm, we have efficient pre-illumination on the material. The
diffraction efficiency of up to 2% can be achieved by a HeNe laser at 632.8 nm wavelength, and two-dimensional
holograms of USAF resolution target are successfully recorded.
We report on the fabrication of an eight-channel single-mode waveguide array via vacuum assisted microfluidic soft
lithographic technique. The incorporation of sectional flow tapers perpendicular to the waveguide direction allows
for the realization of long single-mode channel waveguide arrays, thus overcoming the waveguide length limitation
set by the viscosity of the UV curable resin. The refractive index and other properties of the synthesized UV curable
core waveguide resin can be tuned through the reformulation of material composition.
Three-dimensional (3D) microstructures are fabricated by prism-assisted inclined ultraviolet (UV) lithography. The
exposure angles of slanted structures ranging from 0° to 65° in SU-8 photoresist can be easily achieved without
immersion in index matching liquid. The sample surface reflection of UV light can be utilized for the fabrication of
symmetric structures. Tripod structures have been fabricated by one-step UV exposure with corner prism. Examples
of various achievable 3D microstructures are presented.
Polymer waveguides with 45° mirrors are fabricated by vacuum assisted microfluidic (VAM) soft lithographic
technique for card-to-backplane optical interconnect applications. Waveguide array structures with inclined surfaces
in SU-8 photoresist for PDMS mold are fabricated by prism assisted UV exposure. Sample surface reflected UV
light is utilized to eliminate undercut structures and to accomplish the inclined mirror surfaces on both ends of the
straight waveguide segments by one-step UV exposure. Polymer waveguides with 45° embedded mirrors
demonstrated about 0.49 dB/cm propagation loss and 67% mirror coupling efficiency.
We report an enhanced laser induced polarization switching and holography in a novel photo-reconfigurable material
system that contains polymer backbone impregnated by a soft liquid crystal material. The backbone of polymer chains is
reconfigurable and the surrounding movable liquid crystal molecules are reoriented collectively anchoring toward the
reconfigured polymer chains, resulting in remarkable enhancement of anisotropic refractive index modulation suitable
for updatable holographic recording. The dynamic polymer-liquid crystal network strengthening concept enables
significant enhancement of holographic performance with controllable updatability.
We report on the fabrication of single-mode channel waveguide structures via the vacuum assisted microfluidic
technique. The soft lithographic technique in conjunction with specially designed photomask patterns and UV curable
epoxy resins can result in a high yield, cost-effective method for fabrication of channel waveguides. In particular, the use
of microfluidic technique allows for the production of freestanding high quality single-mode channel waveguides on
various substrates. The viscosity limitation of the microfluidic fabrication of small cross-sectional waveguide structures,
especially single-mode channel waveguides at visible wavelengths, has been overcome through the introduction of
sectional flow tapers.
There are huge market demands for innovative, cheap and efficient light sources, including light emitting devices, such
as LEDs and lasers. However, the light source development in the visible spectral range encounters significant difficulties these years. The available visible wavelength LEDs or lasers are few, large and expensive. The main challenge lies at the lack of efficient light media. Semiconductor nanocrystal quantum dots (QDs) have recently
commanded considerable attention. As a result of quantum confinement effect, the emission color of these QDs covers the whole visible spectral range and can be modified dramatically by simply changing their size. Such spectral tunability, together with large photoluminescence quantum yield and photostability, make QDs attractive for potential applications in a variety of light emitting technologies. However, there are still several technical problems that hinder their application as light sources. One main issue is how to fabricate these QDs into a solid state device while still retaining
their original optical emission properties. A vacuum assisted micro-fluidic fabrication of guided wave devices has demonstrated low waveguide propagation loss, lower crosstalk, and improved waveguide structures. We report herein the combination of the excellent emission properties of QDs and novel vacuum assisted micro-fluidic photonic structure fabrication technique to realize single-mode efficient light sources.
We report on various single and multimode channel waveguide structures fabricated via microtransfer molding and
microfluidic techniques. These soft lithographic fabrication techniques can result in an inexpensive and rapid turnover of
various types of channel waveguide structures and general integrated optic devices. It may be particularly useful for
production of waveguides on user-desired surface substrates including those of a curved or distorted nature. Microscopic
cross-sectional images for both single and multimode waveguides are obtained and compared between the two
fabrication methods. The novel microfluidic technique results in superior waveguide formation and improved
propagation loss performance.
The market demands for innovative, efficient, small package and single-mode light sources are always high because of
their broad applications in scientific, medical, industrial, and commercial fields. The high photoluminescence quantum
yield, photophysical and photochemical stability, and tunable emission wavelength make quantum dots ideal for a new
generation of solid state light sources. We report on the realization of various single-mode light sources in the visible
spectral band by using semiconductor quantum dots. The effective use of a waveguide structure can help achieve the
divergence control of the output light beam. This technique may benefit the development for next generation light
emitting diodes, optical communication, intelligent optical sensors, microprocessors, and nanoscale optical imaging
systems.
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