198 research outputs found
Multi-level diffractive optics for single laser exposure fabrication of telecom-band diamond-like 3-dimensional photonic crystals
Get PDFWe present a novel multi-level diffractive optical element for diffractive optic near-field lithography based fabrication of large-area diamond-like photonic crystal structure in a single laser exposure step. A multi-level single-surface phase element was laser fabricated on a thin polymer film by two-photon polymerization. A quarter-period phase shift was designed into the phase elements to generate a 3D periodic intensity distribution of double basis diamond-like structure. Finite difference time domain calculation of near-field diffraction patterns and associated isointensity surfaces are corroborated by definitive demonstration of a diamond-like woodpile structure formed inside thick photoresist. A large number of layers provided a strong stopband in the telecom band that matched predictions of numerical band calculation. SEM and spectral observations indicate good structural uniformity over large exposure area that promises 3D photonic crystal devices with high optical quality for a wide range of motif shapes and symmetries. Optical sensing is demonstrated by spectral shifts of the Γ-Z stopband under liquid emersion.Financial support from the Natural Science and Engineering Research Council of Canada and
the Canadian Institute for Photonics Innovation is gratefully acknowledged. Debashis Chanda
is grateful for financial support from the RICOH Canada Graduate Science and Technology
Award (OGSST)
Digital holographic-volumetric bio-printing using binary-phase HoloTile on a DMD
No full textWe present the option to use the patented [1, 2] Computer Generated Holography (CGH) modality, HoloTile, as a better alternative light delivery system for volumetric additive manufacturing (VAM). Holographic light delivery promises many of the qualities sought after in VAM, including higher photon efficiency, inherent wavefront shaping, full point spread function control, and lower mechanical complexity. These qualities, along with the unique control that is gained with HoloTile, may allow for the use of low-power light sources at low print times with real-time aberration and scattering compensation
Racializing white residues: seditious Anglo-Indians and others
Get PDFMy dissertation interrogates the discursive residues of the Anglo-Indian question in decolonized India. To problematize these residues, I structure my dissertation as a fragmented genealogy of colonial and post-colonial perceptions of Anglo-Indians. I open my dissertation by showing how, since the late-nineteenth century, Anglo-Indians were claimed to be only of part-European racial provenance, and tautologically had their bodies deemed sexually deviant. Their bodies being, like those of their non-Anglo-Indian counterparts, in fact of uncertain racial intermixture, I argue that Anglo-Indians inhabit mongrel bodies—bodies in a state of continual flux of class and race, inhabiting a multiplicity of pluralized communities. The ethical end of the decolonized Indian nation-state, I accordingly suggest, is to facilitate the recognition of mongrelism as an inevitable phenomenon across groups—one that fractures monolithic conceptions of race and community. To flesh out this argument, I conduct readings from an archive of novels, historiographic treatises, short stories, memoirs, films, and cartoons. The figures whose texts I examine include, among others, colonial Anglo-Indian ‘prostitute’ Amelia Horne, Anglo-Indian anti-racism activist Cedric Dover, Bengali novelist Sharadindu Bandyopadhyay, diasporic English writer Aubrey Menen, Indian cartoonist Mario Miranda, Bengali film director Satyajit Ray, Anglo-Indian politician and historiographer Frank Anthony, and British-Indian writer Ruskin Bond.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-08-01The student, Debojoy Chanda, accepted the attached license on 2018-07-04 at 01:48.The student, Debojoy Chanda, submitted this Dissertation for approval on 2018-07-04 at 02:33.This Dissertation was approved for publication on 2018-07-06 at 10:04.DSpace SAF Submission Ingestion Package generated from Vireo submission #12728 on 2018-09-27 at 11:16:29Made available in DSpace on 2018-09-27T16:30:17Z (GMT). No. of bitstreams: 2
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Previous issue date: 2018-07-06Embargo set by: Seth Robbins for item 107771
Lift date: 2020-09-27T16:30:34Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107771
Lift date: 2020-09-27T16:31:43Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107771
Lift date: 2020-09-27T16:34:29Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107771 on 2020-09-28T09:15:16Z
Femtosecond laser inscribed advanced calibration phantom for optical coherence tomography (OCT)
Get PDFOptical coherence tomography (OCT) has developed rapidly and is widely used in different fields such as biomedicine and optometry. The characterization and calibration of OCT systems is essential when testing the system and during normal use to ensure that there is no misalignment or distortion that could affect clinical decisions. Imaging distortion is a significant challenge for OCT systems when viewing through non-planar surfaces. Here we present a new multi-purpose plano-convex OCT phantom which is designed to be used for OCT characterization and calibration as well as to validate the post-processing algorithm for the imaging distortion of the OCT systems. A femtosecond laser direct writing technique is used to fabricate this phantom which consists of a landmark layer with radial lines at a 45-degree angular spacing inscribed at 50μm in apparent depth (AD) underneath the planar surface. Below that there are a further 8 layers of a spherical inscription pattern which has a 150μm (in AD) separation between each layer. The first spherical layer is located at 150μm (in AD) underneath the planar surface. Due to the laser power loss when travelling through the deeper layer, an increased power is applied to the deeper layers. The spherical pattern overcomes orientation issues seen with existing calibration phantoms. The landmark layer is applied so that it can easily tell the exact location when scanning which will also benefit the image distortion correction process
Holo Tile:a novel digital holographic light sculpting modality for volumetric 3D printing (Invited Paper)
No full textHoloTile is our novel and recently patent-filed approach [1,2] to obtain very fastreconfigurable and strongly speckle-reduced digital holography. Using HoloTile we haveexperimentally demonstrated more than 90 % photon-efficient phase-only projecteddynamic and static far field diffraction both with and without a lens. A key aim forinventing and innovating HoloTile has been to effectively solve the challenge of rapidand speckle-free coherent or semi-coherent light sculpting without the need for timeaveragingtechniques - a challenge that exists in several fields of optics and photonics. Inparticular, HoloTile provides four new unique key features as CGH-modality for highresolutionspatial light modulators, reconfigurable DOEs or new meta-surface MOEs: •A 100x speed improvement over standard CGH-modalities • Substantial specklereduction by matched tiling and PSF-shaping • Real-time dynamic and output 'pixel'discretized digital holograms • Lens-free scaling or zoom by software adapted HoloTilephase-encodin
Strong Light-Matter Interactions for Skin-like Flexible Color Display
No full textThe talk will focus on enhanced light-latter interactions on nanostructured surfaces for plasmonic full-color displays on flexible substrates. The newly developed printing techniques enable large area printing of such nanostructured surfaces for low cost manufacturing
Novel fabrication method for highly conformable THz metasurfaces
No full textThe continuously increasing interest in flexible and integrated photonics requires new strategies for device manufacturing on arbitrary complex surfaces and with lowest possible size, respectively. Terahertz (THz) technology can particularly benefit from this approach to implement compact systems for generation, detection and on-demand manipulation of THz radiation. Here we present a novel fabrication method to realize conformable metasurfaces. The flexible and versatile character of polymeric nanomembranes is combined with direct laser writing via two-photon polymerization and metal deposition to develop freestanding ultra-thin quasi-perfect plasmonic absorbers with an unprecedentedly high level of conformability. Moreover, revealing new flexible dielectric materials presenting low absorption and permittivity in the THz range, this work paves the way for the realization of ultra-thin, conformable hybrid or all-dielectric devices enhancing the application of THz technologies, and flexible/integrated photonics in general.</p
Temperature compensated strain sensor in fused silica by femtosecond laser inscription
No full textMeasuring strain without parasitic thermal influence is vital. A temperature compensated strain sensor is fabricated in fused silica using femtosecond laser micromachining. Utilizing femtosecond laser direct writing and femtosecond irradiation followed by chemical etching, two Bragg gratings are fabricated in the bulk of a fused silica substrate. By suspending one of the Bragg gratings in a cantilever, it is mechanically isolated from the rest of the substrate. Thermal and tensile characterization showed that both Bragg gratings are sensitive to thermal changes with a sensitivity around 10.5 pm/°C, while only the non-isolated Brag grating is sensitive to strain with a sensitivity of 1.1 pm/µϵ. Hence, it is proven that the parasitic thermal influence on the strain sensor can be compensated by taking into account the response of the isolated Bragg grating
Large-Area Scatterometry for Nanoscale Metrology
Get PDFMany applications across photonics and semiconductor industries require the fabrication of nanostructures with non-trivial geometries with a precision and reproducibility down to the nanometer scale. Slanted gratings and metamaterials are examples of such designs that have vast applications in Augmented Reality and LiDAR. State-of-the-art lithography techniques, such as nanoimprint lithography or UV lithography, can provide such levels of fabrication precision for high-volume production. However, a rapid in-line quality inspection method for such complex patterns is required to monitor the fabrication process, verify the sample quality, and to ensure reproducibility. Here, we demonstrate a novel technique that allows us to inspect the quality of the samples in a non-destructive and fast manner, and to extract geometrical parameters of the nanostructures over large areas, generating spatial variations maps across wafers.</p
High-efficiency fill factor recovery using refractive microlens arrays imprinted on 0.5–256 kpixel front-side illuminated SPAD imagers
No full textSilicon-based single-photon avalanche diodes (SPADs) implemented in front-side illuminated arrays and imagers have often suffered from fill factor limitations. The corresponding reduced sensitivity can be sometimes traded off with longer acquisition times thanks to SPAD’s noiseless read-out. The use of SPADs can however be critically affected in many applications, especially when photon-starved, or when several photons need to be detected in coincidence. The fill factor loss can be recovered by employing microlens arrays, which are difficult to build with relatively large pitch (> 10 μm) and low native SPAD fill factor (as low as 10%). To address these challenges, we have developed several generations of refractive microlenses by photoresist reflow used to fabricate molds. These structures were used to imprint UV-curable hybrid polymer microlenses on SPAD arrays. Replications were successfully carried out on large SPAD arrays with very thin residual layers (~10 μm), as required for higher numerical aperture (NA > 0.25). Replications were also carried out for the first time in a multi-chip operation regime at the wafer reticle level. By optimizing the lens sag and residual layer thickness, concentration factors (CFs) within 15-20% of the theoretical maxima were obtained for the smaller arrays (32×32 and 512×1). The spectral response was flat above 400 nm. CF values up to 4.2 with good uniformity were measured on large 512×512 arrays with 16 μm pixel pitch and a native fill factor of 10.5%. This result was confirmed by simulations when using the actual measured lens shape. We thus demonstrated good spectral and spatial uniformity and high CF, while moving to higher NAs and larger sensor sizes with respect to previous work.AQU
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