Diffractive Optical Analysis for Refractive Index Sensing using Transparent Phase Gratings.
ABSTRACT: We report the implementation of a micro-patterned, glass-based photonic sensing element that is capable of label-free biosensing. The diffractive optical analyzer is based on the differential response of diffracted orders to bulk as well as surface refractive index changes. The differential read-out suppresses signal drifts and enables time-resolved determination of refractive index changes in the sample cell. A remarkable feature of this device is that under appropriate conditions, the measurement sensitivity of the sensor can be enhanced by more than two orders of magnitude due to interference between multiply reflected diffracted orders. A noise-equivalent limit of detection (LoD) of 6 × 10(-7) was achieved with this technique with scope for further improvement.
Project description:Diffractive optical elements can be realized as ultra-thin plates that offer significantly reduced footprint and weight compared to refractive elements. However, such elements introduce severe chromatic aberrations and are not variable, unless used in combination with other elements in a larger, reconfigurable optical system. We introduce numerically optimized encoded phase masks in which different optical parameters such as focus or zoom can be accessed through changes in the mechanical alignment of a ultra-thin stack of two or more masks. Our encoded diffractive designs are combined with a new computational approach for self-calibrating imaging (blind deconvolution) that can restore high-quality images several orders of magnitude faster than the state of the art without pre-calibration of the optical system. This co-design of optics and computation enables tunable, full-spectrum imaging using thin diffractive optics.
Project description:Purpose:To present the outcomes of hybrid multifocal and monofocal intraocular lenses (IOLs) and to compare with refractive and diffractive multifocal IOLs (MFIOLs). Methods:Three hundred twenty eyes (160 patients) underwent cataract surgery with randomized IOLs bilateral implantation. Changes in uncorrected and distance-corrected logMAR distance, intermediate and near (UNVA and DCNVA) visual acuity (VA), contrast sensitivity (CS), presence of dysphotopsia, spectacle independence, and patient satisfaction were analyzed. Results:Postoperative VA in the hybrid (OptiVis) group was improved in all distances (p < 0.001). OptiVis acted superiorly to monofocal IOLs in UNVA and DCNVA (p < 0.001 for both) and to refractive ones in DCNVA (p < 0.005). Distance, mesopic, without glare CS in OptiVis was lower than in the monofocal group and similar to other MFIOLs. No differences in dysphotopsia pre- and postoperatively and spectacle independence in near for OptiVis and refractive MFIOLs were detected. OptiVis patients were more satisfied than those with monofocal IOLs (p=0.015). Conclusions:After cataract surgery, patients with OptiVis improved VA in all distances. Near and intermediate VA was better than monofocal, and DCNVA was better than the refractive group. CS was lower in OptiVis than in the monofocal group, but there was no difference between MFIOLs. Patient satisfaction was higher in OptiVis than in the monofocal group. This trial is registered with NCT03512626.
Project description:Multilevel diffractive lenses (MDLs) have emerged as an alternative to both conventional diffractive optical elements (DOEs) and metalenses for applications ranging from imaging to holographic and immersive displays. Recent work has shown that by harnessing structural parametric optimization of DOEs, one can design MDLs to enable multiple functionalities like achromaticity, depth of focus, wide-angle imaging, etc. with great ease in fabrication. Therefore, it becomes critical to understand how fabrication errors still do affect the performance of MDLs and numerically evaluate the trade-off between efficiency and initial parameter selection, right at the onset of designing an MDL, i.e., even before putting it into fabrication. Here, we perform a statistical simulation-based study on MDLs (primarily operating in the THz regime) to analyse the impact of various fabrication imperfections (single and multiple) on the final structure as a function of the number of ring height levels. Furthermore, we also evaluate the performance of these same MDLs with the change in the refractive index of the constitutive material. We use focusing efficiency as the evaluation criterion in our numerical analysis; since it is the most fundamental property that can be used to compare and assess the performance of lenses (and MDLs) in general designed for any application with any specific functionality.
Project description:We designed and fabricated a photonic crystal surface emitting laser (PCSEL) with vertically integrated diffractive optical elements on their top to study the mechanism of static beam steering on a single chip. The deflected output beam by the self-formed periodic ITO cladding layer of the PCSEL can be further steered by changing the grating period and azimuthal angle of the diffractive gratings relative to the photonic crystal. Through the analysis of photonic band structure and lasing characteristics, the periodic ITO structure is coupled to the photonic crystal band, whereas the integrated grating serves the diffractive function only. The findings pave the way for the design of PCSELs enabling single or multiple output beam with varying direction capability. This type of laser is regarded as an ideal light source for various applications, such as light detection and ranging and three-dimensional sensing systems.
Project description:The efficient light-matter interaction and discrete level structure of atomic vapors made possible numerous seminal scientific achievements including time-keeping, extreme non-linear interactions, and strong coupling to electric and magnetic fields in quantum sensors. As such, atomic systems can be regarded as a highly resourceful quantum material platform. Recently, the field of thin optical elements with miniscule features has been extensively studied demonstrating an unprecedented ability to control photonic degrees of freedom. Hybridization of atoms with such thin optical devices may offer a material system enhancing the functionality of traditional vapor cells. Here, we demonstrate chip-scale, quantum diffractive optical elements which map atomic states to the spatial distribution of diffracted light. Two foundational diffractive elements, lamellar gratings and Fresnel lenses, are hybridized with atomic vapors demonstrating exceptionally strong frequency-dependent, non-linear and magneto-optic behaviors. Providing the design tools for chip-scale atomic diffractive optical elements develops a path for compact thin quantum-optical elements.
Project description:Diffractive optical elements suffer from large chromatic aberration due to the strong wavelength-dependent nature in diffraction phenomena, and therefore, diffractive elements can work only at a single designed wavelength, which significantly limits the applications of diffractive elements in imaging. Here, we report on a demonstration of a wavefront coded broadband achromatic imaging with diffractive photon sieves. The broadband diffraction imaging is implemented with a wavefront coded pinhole pattern that generates equal focusing power for a wide range of operating wavelength in a single thin-film element without complicated auxiliary optical system. Experimental validation was performed using an UV-lithography fabricated wavefront coded photon sieves. Results show that the working bandwidth of the wavefront coded photon sieves reaches 28?nm compared with 0.32?nm of the conventional one. Further demonstration of the achromatic imaging with a bandwidth of 300?nm is also performed with a wavefront coded photon sieves integrated with a refractive element.
Project description:Purpose:To review refractive, visual acuity, defocus curve and subjective visual quality results after bilateral implantation of an apodized diffractive toric intraocular lens (IOL) with a moderate add in the dominant eye and a higher add in the non-dominant eye. Setting:One site in Gainesville, GA, USA. Design:Single arm, non-randomized prospective study. Methods:This was a single-arm prospective study of visual acuity and subjective visual quality after implantation of a toric low-add apodized diffractive multifocal IOL in the dominant eye and a higher add IOL of the same type in the non-dominant eye three months after surgery. Binocular visual acuity at 4 m, 60 cm and 40 cm was tested. Other tests included refraction, defocus curve measurement and evaluation of the quality of vision. Toric IOL orientation was also measured. Results:A total of 29 subjects were enrolled. There were no statistically significant differences in the mean keratometry, corneal astigmatism or IOL sphere power implanted in the dominant and non-dominant eyes. Vision was preferred without any correction in more than half of the eyes tested (32/58, 55%). The residual refractive astigmatism was ? 0.50 D in 100% of eyes. Seventy-five percent of subjects (22/29) had 0.10 logMAR (20/25 Snellen) binocular uncorrected visual acuity at all tested distances. Glare and haloes were the most common visual disturbances, but most subjects (22/29, 76%) reported that they were not bothered by any visual disturbances. In 97% of eyes (56/58), the measured difference in orientation between 1 month and 3 months was less than 5 degrees, with no change more than 14 degrees. Conclusion:This blended bifocal IOL modality appears to be well-tolerated by subjects with a good range of vision and minimal bother from visual disturbances.
Project description:Background:We compared the efficacy between trifocal and bifocal diffractive intraocular lens (IOL) implantation. Methods:Through PubMed, MEDLINE, EMBASE, and CENTRAL, we searched potentially relevant articles published from 1990 to 2018. Defocus curves, visual acuities (VAs) were measured as primary outcomes. Spectacle dependence, postoperative refraction, contrast sensitivity (CS), glare, and higher-order aberrations (HOAs) were measured as secondary outcomes. Effects were pooled using random-effects method. Results:We included 11 clinical trials, with a total of 787 eyes (395 subjects). The trifocal IOL group showed better binocular distance VA corrected with defocus levels of -0.5, -1.0, -1.5, and -2.5 diopter than the bifocal IOL group (All P ? 0.004). The trifocal IOL group showed better monocular uncorrected distance and intermediate VAs (mean difference [MD], -0.04 logarithm of the minimum angle of resolution [logMAR]; 95% confidence interval [CI], -0.07, -0.01; P = 0.006 and MD, -0.07 logMAR; 95% CI, -0.13, -0.01; P = 0.03, respectively). Postoperative refraction, glare, CS, and HOAs were not significantly different from each other. Conclusion:The overall findings indicate that trifocal diffractive IOL implantation is better than the bifocal diffractive IOL in intermediate VA, and provides similar or better in distance and near VAs without any major deterioration in the visual quality.
Project description:Thermally induced refractive index gratings in Yb-doped fibers lead to transverse mode instability (TMI) above an average power threshold, which represents a severe problem for many applications. To obtain a deeper understanding of TMI, the evolution of the strength of the thermally induced refractive index grating with the average output power in a fiber amplifier is experimentally investigated for the first time. This investigation is performed by introducing a phase shift between the refractive index grating and modal interference pattern, which is obtained by applying a pump power variation to the fiber amplifier. It is demonstrated that the refractive index grating is sufficiently strong to enable modal energy coupling at powers that are significantly below the TMI threshold if the induced phase shift is sufficiently large. The experiments indicate that at higher powers, the refractive index grating becomes more sensitive to such phase shifts, which will ultimately trigger TMI. Furthermore, the experimental results demonstrate beam cleaning above the TMI threshold via the introduction of a positive phase shift. This finding paves the way for the development of a new class of mitigation strategies for TMI that are based on controlling the phase shift between the thermally induced refractive index grating and modal interference pattern.
Project description:Diffractive optics have increasingly caught the attention of the scientific community. Classical diffractive optics are 2D diffractive optical elements (DOEs) and computer-generated holograms (CGHs), which modulate optical waves on a solitary transverse plane. However, potential capabilities are missed by the inherent two-dimensional nature of these devices. Previous work has demonstrated that extending the modulation from planar (2D) to volumetric (3D) enables new functionalities, such as generating space-variant functions, multiplexing in the spatial or spectral domain, or enhancing information capacity. Unfortunately, despite significant progress fueled by recent interest in metasurface diffraction, 3D diffractive optics still remains relatively unexplored. Here, we introduce the concept of azimuthal multiplexing. We propose, design, and demonstrate 3D diffractive optics showing this multiplexing effect. According to this new phenomenon, multiple pages of information are encoded and can be read out across independent channels by rotating one or more diffractive layers with respect to the others. We implement the concept with multilayer diffractive optical elements. An iterative projection optimization algorithm helps solve the inverse design problem. The experimental realization using photolithographically fabricated multilevel phase layers demonstrates the predicted performance. We discuss the limitations and potential of azimuthal multiplexing 3D diffractive optics.