Robust Design of an Optical Micromachine for an Ophthalmic Application

This article describes an approach to the robust design of an optical micromachine consisting of a freeform optics, an amplification linkage, and an actuator. The robust design approach consists of monolithic integration principles to minimize assembly efforts and of an optimization of the functional components with respect to robustness against remaining assembly and manufacturing tolerances. The design approach presented involves the determination of the relevant tolerances arising from the domains manufacturing, assembly, and operation of the micromachine followed by a sensitivity analysis with the objective of identifying the worst offender. Subsequent to the above-described steps, an optimization of the functional design of the freeform optics with respect to a compensation of the effects of the tolerances is performed. The result leads to a robust design of the freeform optics and hence ensures a defined and optimal minimum performance of the micromachine in the presence of tolerances caused by the manufacturing processes and the operation of the micromachine. The micromachine under discussion is the tunable optics of an ophthalmic implant, an artificial accommodation system recently realized as a demonstration model at a scale of 2:1. The artificial accommodation system will be developed to replace the human crystalline lens in the case of a cataract

Variable optical elements for fast focus control

In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications

Microfluidics based phantoms of superficial vascular network

Several new bio-photonic techniques aim to measure flow in the human vasculature non-destructively. Some of these tools, such as laser speckle imaging or Doppler optical coherence tomography, are now reaching the clinical stage. Therefore appropriate calibration and validation techniques dedicated to these particular measurements are therefore of paramount importance. In this paper we introduce a fast prototyping technique based on laser micromachining for the fabrication of dynamic flow phantoms. Micro-channels smaller than 20 µm in width can be formed in a variety of materials such as epoxies, plastics, and household tape. Vasculature geometries can be easily and quickly modified to accommodate a particular experimental scenario

Enhancement of High-Resolution 3D Inkjet-rinting of Optical Freeform Surfaces Using Digital Twins

3D-inkjet-printing is just beginning to take off in the optical field. Advantages of this technique include its fast and cost-efficient fabrication without tooling costs. However, there are still obstacles preventing 3D inkjet-printing from a broad usage in optics, e.g., insufficient form fidelity. In this article, we present the formulation of a digital twin by the enhancement of an optical model by integrating geometrical measurement data. This approach strengthens the high-precision 3D printing process to fulfil optical precision requirements. A process flow between the design of freeform components, fabrication by inkjet printing, the geometrical measurement of the fabricated optical surface, and the feedback of the measurement data into the simulation model was developed, and its interfaces were defined. The evaluation of the measurements allowed for the adaptation of the printing process to compensate for process errors and tolerances. Furthermore, the performance of the manufactured component was simulated and compared with the nominal performance, and the enhanced model could be used for sensitivity analysis. The method was applied to a highly complex helical surface that allowed for the adjustment of the optical power by rotation. We show that sensitivity analysis could be used to define acceptable tolerance budgets of the process

Investigation of a fibre-optic Fizeau interferometer configuration and coherent fibre-optic imaging bundles for optical coherence tomography

Currently several medical imaging techniques are in operation in clinical environments that help the doctors to diagnose diseases before proceeding to treatment. This research investigated and implemented configurations for a medical imaging technique called Optical Coherence Tomography (OCT). The Michelson interferometer has been the principal configuration for OCT systems. For endoscopic OCT applications though such a configuration is susceptible to polarisation induced signal fading due to environmental changes within the sample arm, like fibre bending and temperature fluctuations. The development and testing of a Fizeau interferometer based OCT system demonstrate the elimination of this polarisation induced signal fading as the sample and reference arm of the interferometer experience the same environmental changes. The Fizeau interferometer is formed between the end of the fibre and the sample itself. A secondary processing interferometer is used in this configuration, to compensate the path difference inherent to the Fizeau configuration. Longitudinal resolution is about 19 m in air, and lateral resolution about 23 m. A signal-to-noise ratio of about 80 dB was achieved with this system and several sets of image data were collected from laboratory and biological samples. An OCT system based on a Fizeau interferometer incorporating a coherent fibre imaging bundle was also investigated. Fibres in the bundle are accessed sequentially by a beam focused onto the input face of the bundle, allowing 2D information to be acquired using point detection. Incorporating a fibre optic imaging bundle in Fizeau based interferometer OCT allows mechanical scanning parts to be removed from the sample arm, resulting in a passive probe. Such a configuration can form a compact, robust and “downlead insensitive” OCT system and is a strong candidate for in vivo applications. The performance of leached and wound coherent fibre optic bundles was accessed and an analysis is presented. The longitudinal resolution of the system developed was about 10 m in air, and lateral resolution about 9 m. This thesis demonstrates several sets of image data that were collected from various samples using a Fizeau interferometer based OCT incorporating coherent imaging bundles. 2D image data captured by such a configuration are presented and reported for the first time in this thesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Minimally invasive diagnostic imaging using high resolution Optical Coherence Tomography

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references.Advances in medical imaging have given researchers unprecedented capabilities to visualize, characterize and understand biological systems. Optical Coherence Tomography (OCT) is a high speed, high resolution imaging technique that utilizes low coherence interferometry to perform cross-sectional tomographic imaging of tissue in real time and in vivo. The design, development, and implementation of ultrahigh resolution OCT systems in both laboratory and clinical experiments has been pursued in this work. Biomedical imaging studies in the areas of arthroscopy, cardiology, and endoscopy have been investigated with ultrahigh resolution capability achieved through the use of broadband femtosecond oscillators such as Ti:Sapphire and Cr:Forsterite light sources. OCT image resolutions of 1-5um in tissue have been realized, an order of magnitude greater than conventional MRI or ultrasound resolutions. In addition, through the use of coherent heterodyne detection techniques, the capability to visualize pathological tissue architecture in vivo for both animal and human experimental trials has been demonstrated. Because OCT can perform such "optical biopsy" with resolutions approaching that of conventional excisional biopsy and histology, it has the potential to become a powerful diagnostic tool in the field of medical imaging. In combination with small fiber-optic catheters, endoscopes, and other imaging devices, minimally invasive OCT imaging was carried out with novel diagnostic devices also developed in this work. The development and implementation of advanced OCT systems for both research and clinical applications will be presented as well as future directions for the technology.by Paul R. Herz.Ph.D

Desenvolvimento e otimização de sensores em fibra ótica produzidos por laser de femtosegundo

In this work, optical fibre sensors were developed and optimized using a pulsed femtosecond laser. In addition to the inherent advantages of using femtosecond pulses, by emitting radiation in the NIR band, it was possible to modify the refractive index inside dielectric materials, namely silica and polymer optical fibres. Prior to the manufacturing of optical structures, a theoretical study was carried out on the peculiarities of writing-systems based on femtosecond lasers, as well as on the most common devices inscribed in optical fibres, namely Bragg gratings, long period gratings, and Fabry-Pérot interferometers. After assembling femtosecond NIR laser system, Bragg gratings, long period gratings, Fabry-Pérot interferometers, and interferometers based on the optical Vernier effect were manufactured using the direct-writing and phase mask methods. Using the micromachining setup, different structures were created in already existing optical fibre sensors, namely channels in hollow Fabry-Pérot cavities and laser etching around Bragg gratings inscribed in polymers optical fibres. The spectral responses of all devices were extensively characterized to, mainly, variations of temperature and strain, revealing unique sensitivity values, especially for the interferometers based on the optical Vernier effect (> 1 nm/°C and 0.1 nm/µε for temperature and strain, respectively). To demystify the thermal stability of fibre Bragg gratings, a theoretical and experimental study was carried out where several Bragg gratings were inscribed by different techniques, involving different lasers as well as silica and polymer optical fibres. The experimental results corroborated the theoretical predictions, where it was concluded that the gratings inscribed by the point-to-point method using a femtosecond laser have a greater thermal stability and lifetime, even when subjected to longer and higher temperature regimes. Finally, a bridge was stablished between the fundamental research developed during the manufacture of the elementary optical fibre sensors, and possible applications. Five different sensor concepts were demonstrated and tested, capable of detecting variations in magnetic fields, fluids refractive index, temperature, strain and humidity. As results, astonishing sensitivity values were attained, and several cross-sensitivity problems were mitigated, thus establishing the foundations for the development of new prototypes for the future.Neste trabalho foram desenvolvidos e otimizados sensores em fibra ótica através de um laser pulsado de femtosegundo. Para além das vantagens inerentes de usar pulsos da ordem do femtosegundo, ao emitir radiação na banda do infravermelho foi possível modificar o índice de refração no interior de materiais dielétricos, nomeadamente fibras óticas de sílica e polímero. Antes de proceder ao fabrico das estruturas óticas, foi realizado um estudo teórico sobre as peculiaridades dos sistemas de escrita baseados em lasers de femtosegundo, bem como sobre os principais dispositivos inscritos em fibra ótica, nomeadamente redes de Bragg, redes de período longo, e interferómetros de Fabry-Pérot. Após montado o sistema laser NIR de femtosegundo, através de inscrição direta e por máscara de fase foram fabricadas redes de Bragg, redes de período longo, interferómetros de Fabry-Pérot, e interferómetros baseados no efeito ótico de Vernier. Com a montagem de micromaquinação, diferentes estruturas foram criadas em sensores já existentes, nomeadamente buracos em cavidades Fabry-Pérot e remoção de material ao redor de redes de Bragg. As respostas espetrais de todos os dispositivos foram extensivamente caracterizadas, nomeadamente a variações de temperatura e tensão, revelando elevados valores de sensibilidades, especialmente para os interferómetros baseados no efeito ótico de Vernier (> 1 nm/°C e 0.1 nm/µε para temeprature e tensão, respetivamente). Para desmistificar a estabilidade térmica de redes de Bragg em fibra ótica, foi feito um estudo teórico e experimental onde várias redes de Bragg foram gravadas por diferentes técnicas, envolvendo diferentes lasers e fibras óticas de sílica e polímero. Os resultados experimentais corroboraram as previsões teóricas, onde se concluiu que as redes gravadas pelo método de ponto-a-ponto usando um laser de femtosegundo detêm uma maior estabilidade térmica e tempo de vida, mesmo quando submetidas a regimes longos de altas temperaturas. Por fim, foi feita a ponte entre a investigação fundamental desenvolvida durante o fabrico de dispositivos elementares em fibras óticas e possíveis aplicações. Foram demonstrados e testados cinco conceitos diferentes de sensores, capazes de detetar variações de campos magnéticos, índice de refração de fluídos, temperatura, tensão e humidade. Foram atingidos valores de sensibilidade surpreendentes, bem como mitigados problemas de sensibilidade cruzada, tendo sido assim estabelecidas as fundações para o desenvolvimento de novos protótipos para o futuro.Programa Doutoral em Engenharia Físic