Three-dimensional microfabrication through a multimode optical fiber

Additive manufacturing, also known as 3D printing, is an advanced manufacturing technique that allows the fabrication of arbitrary macroscopic and microscopic objects. All 3D printing systems require large optical elements or nozzles in proximity to the built structure. This prevents their use in applications in which there is no direct access to the area where the objects have to be printed. Here, we demonstrate three-dimensional microfabrication based on two-photon polymerization (TPP) with sub diffraction-limited resolution through an ultra-thin, 50 mm long printing nozzle of 560 micrometers in diameter. Using wavefront shaping, femtosecond infrared pulses are focused and scanned through a multimode optical fiber (MMF) inside a photoresist that polymerizes via two-photon absorption. We show the construction of arbitrary 3D structures of 500 nm resolution on the other side of the fiber. To our knowledge, this is the first demonstration of microfabrication through a multimode optical fiber. Our work represents a new area which we refer to as endofabrication

Three-dimensional femtosecond laser processing for lab-on-a-chip applications

AbstractThe extremely high peak intensity associated with ultrashort pulse width of femtosecond laser allows us to induce nonlinear interaction such as multiphoton absorption and tunneling ionization with materials that are transparent to the laser wavelength. More importantly, focusing the femtosecond laser beam inside the transparent materials confines the nonlinear interaction only within the focal volume, enabling three-dimensional (3D) micro- and nanofabrication. This 3D capability offers three different schemes, which involve undeformative, subtractive, and additive processing. The undeformative processing preforms internal refractive index modification to construct optical microcomponents including optical waveguides. Subtractive processing can realize the direct fabrication of 3D microfluidics, micromechanics, microelectronics, and photonic microcomponents in glass. Additive processing represented by two-photon polymerization enables the fabrication of 3D polymer micro- and nanostructures for photonic and microfluidic devices. These different schemes can be integrated to realize more functional microdevices including lab-on-a-chip devices, which are miniaturized laboratories that can perform reaction, detection, analysis, separation, and synthesis of biochemical materials with high efficiency, high speed, high sensitivity, low reagent consumption, and low waste production. This review paper describes the principles and applications of femtosecond laser 3D micro- and nanofabrication for lab-on-a-chip applications. A hybrid technique that promises to enhance functionality of lab-on-a-chip devices is also introduced

Femtosecond Laser Micromachining of Advanced Fiber Optic Sensors and Devices

Research and development in photonic micro/nano structures functioned as sensors and devices have experienced significant growth in recent years, fueled by their broad applications in the fields of physical, chemical and biological quantities. Compared with conventional sensors with bulky assemblies, recent process in femtosecond (fs) laser three-dimensional (3D) micro- and even nano-scale micromachining technique has been proven an effective and flexible way for one-step fabrication of assembly-free micro devices and structures in various transparent materials, such as fused silica and single crystal sapphire materials. When used for fabrication, fs laser has many unique characteristics, such as negligible cracks, minimal heat-affected-zone, low recast, high precision, and the capability of embedded 3D fabrication, compared with conventional long pulse lasers. The merits of this advanced manufacturing technique enable the unique opportunity to fabricate integrated sensors with improved robustness, enriched functionality, enhanced intelligence, and unprecedented performance. Recently, fiber optic sensors have been widely used for energy, defense, environmental, biomedical and industry sensing applications. In addition to the well-known advantages of miniaturized in size, high sensitivity, simple to fabricate, immunity to electromagnetic interference (EMI) and resistance to corrosion, all-optical fiber sensors are becoming more and more desirable when designed with characteristics of assembly free and operation in the reflection configuration. In particular, all-optical fiber sensor is a good candidate to address the monitoring needs within extreme environment conditions, such as high temperature, high pressure, toxic/corrosive/erosive atmosphere, and large strain/stress. In addition, assembly-free, advanced fiber optic sensors and devices are also needed in optofluidic systems for chemical/biomedical sensing applications and polarization manipulation in optical systems. Different fs laser micromachining techniques were investigated for different purposes, such as fs laser direct ablating, fs laser irradiation with chemical etching (FLICE) and laser induced stresses. A series of high performance assembly-free, all-optical fiber sensor probes operated in a reflection configuration were proposed and fabricated. Meanwhile, several significant sensing measurements (e.g., high temperature, high pressure, refractive index variation, and molecule identification) of the proposed sensors were demonstrated in this dissertation as well. In addition to the probe based fiber optic sensors, stress induced birefringence was also created in the commercial optical fibers using fs laser induced stresses technique, resulting in several advanced polarization dependent devices, including a fiber inline quarter waveplate and a fiber inline polarizer based on the long period fiber grating (LPFG) structure

Lab-on-fiber technology: a new avenue for optical nanosensors

The "lab-on-fiber" concept envisions novel and highly functionalized technological platforms completely integrated in a single optical fiber that would allow the development of advanced devices, components and sub-systems to be incorporated in modern optical systems for communication and sensing applications. The realization of integrated optical fiber devices requires that several structures and materials at nano- and micro-scale are constructed, embedded and connected all together to provide the necessary physical connections and light-matter interactions. This paper reviews the strategies, the main achievements and related devices in the lab-on-fiber roadmap discussing perspectives and challenges that lie ahead

New Trends and Applications in Femtosecond Laser Micromachining

This book contains the scientific contributions to the Special Issue entitled: "New Trends and Applications in Femtosecond Laser Micromachining". It covers an array of subjects, from the basics of femtosecond laser micromachining to specific applications in a broad spectra of fields such biology, photonics and medicine

3D laser nano-printing on fibre paves the way for super-focusing of multimode laser radiation

Multimode high-power laser diodes suffer from inefficient beam focusing, leading to a focal spot 10–100 times greater than the diffraction limit. This inevitably restricts their wider use in ‘direct-diode’ applications in materials processing and biomedical photonics. We report here a ‘super-focusing’ characteristic for laser diodes, where the exploitation of self-interference of modes enables a significant reduction of the focal spot size. This is achieved by employing a conical microlens fabricated on the tip of a multimode optical fibre using 3D laser nano-printing (also known as multi-photon lithography). When refracted by the conical surface, the modes of the fibre-coupled laser beam self-interfere and form an elongated narrow focus, usually referred to as a ‘needle’ beam. The multiphoton lithography technique allows the realisation of almost any optical element on a fibre tip, thus providing the most suitable interface for free-space applications of multimode fibre-delivered laser beams. In addition, we demonstrate the optical trapping of microscopic objects with a super-focused multimode laser diode beam thus rising new opportunities within the applications sector where lab-on-chip configurations can be exploited. Most importantly, the demonstrated super-focusing approach opens up new avenues for the ‘direct-diode’ applications in material processing and 3D printing, where both high power and tight focusing is required

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

Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

Recent advances in biomedical photonic sensors: a focus on optical-fibre-based sensing

In this invited review, we provide an overview of the recent advances in biomedical pho tonic sensors within the last five years. This review is focused on works using optical-fibre technology, employing diverse optical fibres, sensing techniques, and configurations applied in several medical fields. We identified technical innovations and advancements with increased implementations of optical-fibre sensors, multiparameter sensors, and control systems in real applications. Examples of outstanding optical-fibre sensor performances for physical and biochemical parameters are covered, including diverse sensing strategies and fibre-optical probes for integration into medical instruments such as catheters, needles, or endoscopes.This work was supported by Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-107270RB-C21/AEI/10.13039/501100011033), and TeDFeS Project (RTC-2017- 6321-1) co-funded by European FEDER funds. M.O. and J.F.A. received funding from Ministerio de Ciencia, Innovación y Universidades of Spain under Juan de la Cierva-Formación and Juan de la Cierva-Incorporación grants, respectively. P.R-V. received funding from Ministerio de Educación, Cultura y Deporte of Spain under PhD grant FPU2018/02797