A silicon Fresnel lens was designed and fabricated using a greyscale lithography technique to shape optical emissions from an edge-emitting semiconductor diode laser. The laser beam was collimated in the fast axis and allowed a ±3° divergence in the slow axis along with bias angle accomplished through lens decentering. The lens had an aperture of 6.8 mm × 2.2 mm and 1 mm in total thickness. The lens was first designed as a contiguous surface using conventional raytracing methods, and then converted to a Fresnel sag model with an etch depth of 6.25 micrometers. The sag model along with the manufacturing tolerances were fed back through numerical tools to refine the design and modify the lens shape and laser position. Optical profilometry of fabricated lens element found deviations from design and nonuniformity across the entire aperture, with over-etching in the center and under-etching toward the edge of the lens. Characterization of the fabricated lenses showed less than 5% deviation in etch depth. Collimation performance was measured to be less than 2 milliradians, which was in close agreement with design models. Greyscale fabrication of the lens element enabled complex curvatures to be combined and provided a compact solution for direct, single optic coupling of diode laser to free-space projection.
Printing functional, metal parts for mass production using powder bed fusion additive manufacturing requires the ability to deposit more energy at the working plane to increase build rate. Conventional approaches serially add fiber lasers and scanners to create dual and quad laser machines, but scaling this strategy is limited by the size of powder bed while current scan parameters do not utilize the full output potential of available laser sources. Instead, a processing head containing an array of lower power laser sources can melt wider regions of a powder bed simultaneously to increase build rate. A 16 channel processing head comprised of fiber-coupled direct diodes capable of outputting up to 960W of combined power is presented. Fiber arrays arranged to melt widened tracks of CoCr powder demonstrated builds with >99% density at 2x the build rate of conventional, single laser systems. Details of the array layout, optical system and controls are presented along with scan strategies for melt tracks of varying widths. Most importantly, the array configuration can be scaled to multi-kW outputs spread over larger areas without requiring new parameter development as the energy per unit area remains unchanged with channel count.
Recently there has been increased interest on the part of federal and state regulators to detect and quantify emissions of methane, an important greenhouse gas, from various parts of the oil and gas infrastructure including well pads and pipelines. Pressure and/or flow anomalies are typically used to detect leaks along natural gas pipelines, but are generally very insensitive and subject to false alarms. We have developed a system to detect and localize methane leaks along gas pipelines that is an order of magnitude more sensitive by combining tunable diode laser spectroscopy (TDLAS) with conventional sensor tube technology. This technique can potentially localize leaks along pipelines up to 100 km lengths with an accuracy of ±50 m or less. A sensor tube buried along the pipeline with a gas-permeable membrane collects leaking gas during a soak period. The leak plume within the tube is then carried to the nearest sensor node along the tube in a purge cycle. The time-to-detection is used to determine leak location. Multiple sensor nodes are situated along the pipeline to minimize the time to detection, and each node is composed of a short segment of hollow core fiber (HCF) into which leaking gas is transported quickly through a small pressure differential. The HCF sensing node is spliced to standard telecom solid core fiber which transports the laser light for spectroscopy to a remote interrogator. The interrogator is multiplexed across the sensor nodes to minimize equipment cost and complexity.
We propose a compact directional optical receiver for free-space communications, where a microlens array and micro-optic structures selectively couple light from a narrow incidence angle into a thin slab waveguide and then to an edge-mounted detector. A small lateral translation of the lenslet array controls the coupled input angle, enabling the receiver to select the transmitter source direction. We present the optical design and simulation of a 10mm x 10mm aperture receiver using a 30μm thick silicon waveguide able to couple up to 2.5Gbps modulated input to a 10mm x 30μm wide detector.
The increase in domestic natural gas production has brought attention to the environmental impacts of persistent gas leakages. The desire to identify fugitive gas emission, specifically for methane, presents new sensing challenges within the production and distribution supply chain. A spectroscopic gas sensing solution would ideally combine a long optical path length for high sensitivity and distributed detection over large areas. Specialty micro-structured fiber with a hollow core can exhibit a relatively low attenuation at mid-infrared wavelengths where methane has strong absorption lines. Methane diffusion into the hollow core is enabled by machining side-holes along the fiber length through ultrafast laser drilling methods. The complete system provides hundreds of meters of optical path for routing along well pads and pipelines while being interrogated by a single laser and detector. This work will present transmission and methane detection capabilities of mid-infrared photonic crystal fibers. Side-hole drilling techniques for methane diffusion will be highlighted as a means to convert hollow-core fibers into applicable gas sensors.
CPV optics typically have multiple discrete apertures which each focus sunlight directly onto an associated PV cell. Waveguide based CPV systems instead couple light from multiple small apertures through a shared slab waveguide, avoiding individual optical alignment and electrical connection of multiple PV cells. We previously demonstrated the design and fabrication of a planar micro-optic waveguide concentrator, where incoming sunlight is focused through millimeter pitch lenslets onto mirrored micro-prisms which couple light into a slab waveguide toward common PV cells. This enables an efficient high concentrator system with a compact geometry. However, this design has the typical CPV limitation of low angular acceptance, requiring precise two-axis large-scale mechanical tracking. Here, we present the results of a design study to adapt the planar micro-optic design for use in combination with a one-dimensional mechanical tracker, tilted at latitude, to provide azimuthal alignment and altitude bias. Lateral mechanical micro-tracking can accommodate the residual altitude misalignment. The design shows that this relatively simple system can still provide over 72% annual optical efficiency for a 50x concentrator. Replacing the micro-tracking with passive optical altitude alignment further reduces system complexity, but also reduces efficiency. These waveguide based concentrators have primarily been designed for use with photovoltaic cells, which are index matched onto the waveguide either directly, or through output couplers. For concentrating solar power systems, sunlight is focused onto thermally isolated devices which can not be in direct contact. We will also present alternative output coupler designs, which allow extraction of light from the waveguide to an air or vacuum isolated coupler. The loss associated with these couplers is substantially identical to the reflection losses of one additional mirror.
Extremely low birth weight (ELBW) infants frequently require endotracheal intubation for assisted ventilation or as a route for administration of drugs or exogenous surfactant. In adults and less premature infants, the risks of this intubation can be greatly reduced using video laryngoscopy, but current products are too large and incorrectly shaped to visualize an ELBW infant's airway anatomy. We design and prototype a video laryngoscope using a miniature camera set in a curved acrylic blade with a 3×6-mm cross section at the tip. The blade provides a mechanical structure for stabilizing the tongue and acts as a light guide for an LED light source, located remotely to avoid excessive local heating at the tip. The prototype is tested on an infant manikin and found to provide sufficient image quality and mechanical properties to facilitate intubation. Finally, we show a design for a neonate laryngoscope incorporating a wafer-level microcamera that further reduces the tip cross section and offers the potential for low cost manufacture.
High-concentration photo-voltaic systems focus incident sunlight by hundreds of times by combining focusing lenses
with accurate, dual-axis solar tracking. Conventional systems mount large optical arrays on expensive tracking pedestals
to maintain normal incidence throughout the day. A recently proposed micro-optic solar concentrator utilizes a twodimensional
lens array focusing into a planar slab waveguide. Localized mirrors fabricated on the waveguide surface
reflect focused sunlight into guided modes which propagate towards an edge-mounted photovoltaic cell. This geometry
enables a new method of solar tracking by laterally translating the waveguide with respect to the lens array to capture
off-axis illumination. Using short focal length lenses, translations on the order of millimeters can efficiently collect 70°
full-angle incident fields. This allows for either one or two-axis tracking systems where the small physical motion is
contained within the physical footprint of a fixed solar panel. Here, we experimentally demonstrate lateral micro
tracking for off-axis light collection using table-mounted components. We also present a novel tracking frame based on
de-centered cams and describe a lens configuration optimized for off-axis coupling.
Conventional CPV systems focus sunlight directly onto a PV cell, usually through a non-imaging optic to avoid hot
spots. In practice, many systems use a shared tracking platform to mount multiple smaller aperture lenses, each
concentrating light into an associated PV cell. Scaling this approach to the limit would result in a thin sheet-like
geometry. This would be ideal in terms of minimizing the tracking system payload, especially since such thin sheets can
be arranged into louvered strips to minimize wind-force loading. However, simply miniaturizing results in a large
number of individual PV cells, each needed to be packaged, aligned, and electrically connected. Here we describe for the
first time a different optical system approach to solar concentrators, where a thin lens array is combined with a shared
multimode waveguide. The benefits of a thin optical design can therefore be achieved with an optimum spacing of the
PV cells. The guiding structure is geometrically similar to luminescent solar concentrators, however, in micro-optic
waveguide concentrators sunlight is coupled directly into the waveguide without absorption or wavelength conversion.
This opens a new design space for high-efficiency CPV systems with the potential for cost reduction in both optics and
tracking mechanics. In this paper, we provide optical design and preliminary experimental results of one implementation
specifically intended to be compatible with large-scale roll processing. Here the waveguide is a uniform glass sheet, held
between the lens array and a corresponding array of micro-mirrors self-aligned to each lens focus during fabrication.
Significant efficiency increases in photovoltaic power conversion are due to improved absorption over the broad
spectrum of the sun. Semiconductors have an efficiency peak at a specific wavelength associated with the material
band gap. The current trend towards high-efficiency photovoltaics involves multi-junction cells where several
semiconductors are grown on top of one another creating a layered device with a broad spectral response.
Fabrication is a difficult and expensive process that results in small area solar cells. An alternative approach uses
dielectric mirrors to optically separate the incident light by reflecting one spectral band while transmitting another.
Spectral splitting is simulated within a 10x non-imaging concentrator. The optical system may be concatenated into
large arrays and incorporates two separated ray paths exiting at a common plane. Optimized photovoltaic cells can
be interleaved on a single circuit board, improving packaging and thermal management compared to orthogonal
arrangements. The entire concentrator can be molded from glass or acrylic and requires a dichroic coating as the
only reflector. Average collection efficiencies above 84% are realized within 40°x16° angular acceptance.