Michael Ponting

Tunable Polymer Lens

A new type of solid-state variable focal length lens is described. It is based on shape changes in an elastomeric membrane driven by compression of a reservoir of a polymer gel. A novel fabrication process based on individual lens components allows for customization of lens power based on the desired application. The lens shape as a function of applied compressive strain is measured using direct surface profile measurements. The focal length of a solid state lens was reversibly changed by a factor of 1.9. Calculated back focal lengths of the lens were consistent with experimental measurements.

Optical properties of a bio-inspired gradient refractive index polymer lens

The design, fabrication, and properties of one of a new class of gradient-index lenses are reported. The lens is an f/2.25 GRIN singlet based on a nanolayered polymer composite material, designed to correct for spherical aberration. The light gathering and focusing properties of the polymer lens are compared to a homogeneous BK7 glass singlet with a similar f-number. The modulation transfer function of the polymer GRIN lens exceeded that of the homogeneous glass lens at all spatial frequencies and was as much as 3 times better at 5 cyc/mm. The weight of the polymer lens was approximately an order of magnitude less than the homogeneous glass lens.

Optical Coherence Tomography Enabling Non Destructive Metrology of Layered Polymeric GRIN Material

Gradient Refractive INdex (GRIN) optical components have historically fallen short of theoretical expectations. A recent breakthrough is the manufacturing of nanolayered spherical GRIN (S-GRIN) polymer optical elements, where the construction method yields refractive index gradients that exceed 0.08. Here we report on the application of optical coherence tomography (OCT), including micron-class axial and lateral resolution advances, as effective, innovative methods for performing nondestructive diagnostic metrology on S-GRIN. We show that OCT can be used to visualize and quantify characteristics of the material throughout the manufacturing process. Specifically, internal film structure may be revealed and data are processed to extract sub-surface profiles of each internal film of the material to quantify 3D film thickness and homogeneity. The technique provides direct feedback into the fabrication process directed at optimizing the quality of the nanolayered S-GRIN polymer optical components.

Polymeric nanolayered gradient refractive index lenses: technology review and introduction of spherical gradient refractive index ball lenses

Abstract. A nanolayered polymer films approach to designing and fabricating gradient refractive index (GRIN) lenses with designer refractive index distribution profiles and an independently prescribed lens surface geometry have been demonstrated to produce a new class of optics. This approach utilized nanolayered polymer materials, constructed with polymethylmethacrylate and a styrene-co-acrylonitrile copolymer with a tailorable refractive index intermediate to bulk materials, to fabricate discrete GRIN profile materials. A process to fabricate nanolayered polymer GRIN optics from these materials through thermoforming and finishing steps is reviewed. A collection of technology-demonstrating previously reported nanolayered GRIN case studies is presented that include: (1) the optical performance of a f/# 2.25 spherical GRIN plano-convex singlet with one quarter (2) the weight of a similar BK7 lens and a bio-inspired aspheric human eye GRIN lens. Original research on the fabrication and characterization of a Luneburg inspired GRIN ball lens is presented as a developing application of the nanolayered polymer technology.

Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms

The fabrication of high-performance spherical gradient refractive index (S-GRIN) optics requires nondestructive metrology techniques to inspect the samples. We have developed an angular-scan, swept-source-based, Fourier-domain optical coherence tomography (OCT) system centered at 1318 nm with 5 mm imaging depth capable of 180° polar scan and 360° azimuthal scan to investigate polymeric S-GRIN preforms. We demonstrate a method that enables simultaneous mapping of the group optical thickness, physical thickness, the radially-averaged group refractive index, and the transmitted wavefront of the S-GRIN preforms. The angular scan OCT imaging and metrology enables direct visualization, molding uniformity characterization, and optical property evaluations of the preforms. The results on two generations of S-GRIN preforms are discussed that showcase the evolution of the manufacturing process in response to the OCT metrology feedback.

Simultaneous estimation of thickness and refractive index of layered gradient refractive index optics using a hybrid confocal-scan swept-source optical coherence tomography system.

A hybrid confocal-scan swept-source optical coherence tomography metrology system was conceived for simultaneous measurements of the refractive index and thickness profiles of polymeric layered gradient refractive index (GRIN) optics. An uncertainty analysis predicts the metrology capability of the system and guides the selection of an optimum working numerical aperture. Experimental results on both a monolithic and a GRIN layered sheet are demonstrated to be in close agreement with theoretical predictions. Index measurement precision reached 0.0001 and 0.0008 for measuring 2.8 mm and ~300 µm thick layers, respectively. The thicknesses of these layers were simultaneously measured with a precision of 0.28 and 0.17 µm, respectively.

Gradient index polymer optics

We developed novel lenses from gradient index, multi-polymer sheets. The sheets were processed into lenses with spherically-symmetric index profiles. An F/2.25 GRIN singlet produced images with 4times better contrast than a commercial F/2.25 glass singlet.

Volumetric rendering and metrology of spherical gradient refractive index lens imaged by angular scan optical coherence tomography system

In this paper, we develop the methodology, including the refraction correction, geometrical thickness correction, coordinate transformation, and layer segmentation algorithms, for 3D rendering and metrology of a layered spherical gradient refractive index (S-GRIN) lens based on the imaging data collected by an angular scan optical coherence tomography (OCT) system. The 3D mapping and rendering enables direct 3D visualization and internal defect inspection of the lens. The metrology provides assessment of the surface geometry, the lens thickness, the radii of curvature of the internal layer interfaces, and the misalignment of the internal S-GRIN distribution with respect to the lens surface. The OCT metrology results identify the manufacturing defects, and enable targeted process development for optimizing the manufacturing parameters. The newly fabricated S-GRIN lenses show up to a 7x spherical aberration reduction that allows a significantly increased utilizable effective aperture.

SWaP advantage of replacing high performance glass achromatic doublet with a polymeric nanolayer GRIN achromatic singlet

Custom formulated nanolayered Gradient-Index (LGRIN) polymeric optical materials offer capabilities not possible in conventional GRIN or monolithic optics. Large scale processing of nanolayered polymer films with custom refractive indices has enabled production of polymer GRIN lenses with arbitrary spherical refractive index distribution in optics ranging from 6 to 90 mm diameters. Utilizing this nanolayered polymer film material a design and fabrication case study was performed to compare the performance of a LGRIN achromatic singlet to a traditional commercial glass lens achromatic doublet. High performance LGRIN achromatic singlet lenses were designed with non-linear, spherical refractive index distributions using specially developed ZEMAX design tools and fabricated. The performance of an f/5 LGRIN Achromatic Singlet is compared to a high-quality commercial glass f/5 Achromatic Doublet. Optical performance of LGRIN optics was shown to significantly reduce optical system mass, volume, and optical element count as compared to a commercial glass achromatic doublet while simultaneously improving performance. The LGRIN lens exhibits significantly smaller on-axis RMS spot radius of 2.8μ, compared to the glass doublet 3.5μ, with similar reduction off-axis as well, higher MTF, and better color correction while lowering total optic weight from 9.84g for the glass doublet to 3.80g in the same volume for LGRIN. LGRIN achromatic singlet fabrication and metrology is discussed within an accompanying manufacturing methodology overview of the LGRIN lens fabrication process. Additional information on the technology manufacturing/design space will be presented as a bridge toward SWaP advantages for incorporating the technology into more robust Vis-NIR optical systems and devices.

Reduced SWAP Polymeric, Nanolayered, Spherical, Gradient Refractive Index (GRIN) Lenses in Imaging Systems

Night vision goggle eye piece and objective systems are described leveraging spherical gradient refractive index lenses fabricated from polymeric nanolayered materials. A reduction in objective length, 15%, weight, 28%, and eyepiece weight, 24%, was achieved.