Optimized microlens-array geometry for Hartmann-Shack wavefront sensor: design, fabrication and test

AUTOR(ES)

Otavio Gomes de Oliveira

FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

29/02/2012

RESUMO

The Hartmann-Shack (H-S) wavefront sensor is now deployed in many different fields, from astronomy to industrial inspection, where the quality of optical media or components can be measured by the distortions (wavefront aberrations) they impart on a wavefront transmitted or reflected by them. In ophthalmology, this sensor is a core component of major aberrometers, used in the assessment of the visual quality of the eye, academic research and clinical diagnosis. The H-S wavefront sensor is also found in adaptive optics (AO) systems, which are used to improve the quality and the capabilities of optical systems, by compensating for wavefront aberrations that affect light waves. These image distortions can represent a serious problem in many different applications where high-quality images are demanded. The microlens array is an important element in the H-S sensor, responsible for sampling the aberrated wavefront into light spots on the focal plane. The position of each light spot relates to the average tilt of the wavefront over the respective microlens. These spot­position coordinates are then used in the modal reconstruction to approximate the wavefront topology with a combination of orthogonal basis functions. The wavefront reconstruction error describes the deviation of the reconstructed wavefront from the reference one. The wavefront sampling is influenced by the microlens distribution pattern in the array, lens contour and size, number of microlenses and fill factor. Adopted grids typically consist in either rectangular or hexagonal configurations. The influence of the array geometry on the wavefront reconstruction error was already discussed in the literature, which demonstrated that random arrays might perform better than regular ones. This work proposes the optimization of the microlens-array geometry to be used in a specific context, such as ophthalmology. The workflow consisted of three major steps: numerical optimization, to find the optimal microlens arrays; fabrication of the arrays; and test on an optical bench, to comparatively assess the performance of the fabricated and commercial arrays. The optimization comprises the minimization of the wavefront reconstruction error and/or the number of necessary microlenses in the array, considering a known aberration statistics. Within the ophthalmological context, as a case study, it was demonstrated by the numerical simulations that 10 or 16 suitably located microlenses can be used to produce reconstruction errors as small as those of a 36-microlens rectangular array. The optimized arrays were then fabricated in a clean room, where KOH anisotropic etching was used to obtain the silicon molds from which the microlens arrays were replicated on polymer by casting. Four arrays were fabricated: 10- and 16-microlens optimized arrays and 16 and 36-microlens rectangular arrays. All four arrays were tested and compared to a standard 127-microlens hexagonal commercial array, using an arbitrary wavefront aberration, which is compatible with the used ophthalmological wavefront-aberration statistics. The final results corroborate with the predictions of the computational simulations.

ASSUNTO(S)

engenharia elétrica teses.

Documentos Relacionados

• Comparações quantitativas entre o sensor Hartmann-Shack e o sensor de Castro e resultados preliminares para um olho mecânico
• Resultados preliminares com refratrômetro de alta resolução, usando sensor de frente de onda de Hartmann-Shack: parte I
• Variability of wavefront aberration measurements in small pupil sizes using a clinical Shack-Hartmann aberrometer
• Design, Fabrication and Flight Demonstration of a Remotely Controlled Airship for Snow Scientists
• Projeto, fabricação e teste de uma microbomba sem valvulas