Simple ultraviolet-based soft-lithography process for fabrication of low-loss polymer polysiloxanes-based waveguides

A simple ultraviolet (UV)-based soft-lithography process is used for fabrication of polymer polysiloxanes (PSQ-L) waveguides. The imprint process is first done on the cladding PSQ-LL layer and is followed by a spin-coating step to fill the imprinted features with core PSQ-LH layer material. The optical loss of the straight PSQ-L waveguides is characterised by the Fabry-Perot method for the first time. Even with non-polished facet of the waveguide, the Fabry-Perot resonance spectrum is obtained. An upper limit scattering loss of the waveguide is extracted to be less than 0.8 +/- 0.2 dB/cm for TE mode and 1.3 +/- 0.2 dB/cm for TM mode at 1550 nm. The fully transferred pattern and low scattering loss proves it to be an effective way to replicate low-loss polymer PSQ-L-based waveguides

Low loss high index contrast nanoimprinted polysiloxane waveguides

Nanoimprint lithography is gaining rapid acceptance in fields as diverse as microelectronics and microfluidics due to its simplicity high resolution and low cost. These properties are critically important for the fabrication of photonic devices, where cost is often the major inhibiting deployment factor for high volume applications. We report here on the use of nanoimprint technology to fabricate low loss broadband high index contrast waveguides in a Polysiloxane polymer system for the first time

Development of microfabricated optical chemical sensor platforms using polymer processing technology

This work describes the design and fabrication of enhanced polymer waveguide platforms for absorption-based optical chemical sensors and the use of soft lithographic techniques for the fabrication of optical sensor chips. The design of the enhanced polymer waveguide platforms was based on a previously reported theoretical model that was verified experimentally in this work. The platforms were fabricated by micro-injection moulding and subsequently coated with sol-gelderived sensing layers doped with a colorimetric indicator compound. The sensor response to both gaseous ammonia and solution pH was examined using a LEDbased prototype sensor head. Soft lithographic patterning techniques, based on the use of a poly(dimethylsiloxane) (PDMS) patterning element, were employed to produce a variety of sol-gel-based structures with applications in optical sensing. These included discrete sensor spots, surface corrugation grating couplers and ridge waveguides. As a proof of principle, these techniques were applied to the development of an integrated optical oxygen sensor based on the quenching of fluorescence from a sol-gel-encapsulated ruthenium complex that was deposited as a sensor spot onto a ridge waveguide. This work highlights the feasibility of using rapid prototyping technology to fabricate sensitive, mass-producible sensor platforms that employ generic configurations, thereby facilitating their use in a broad range of applications

Development of a generic multi-analyte optical sensor platform for fluorescence-based sensing

This work describes the development of two advanced sensor platforms based on different spectroscopic techniques. The first, and the primary focus of this work, is an enhanced generic multi-analyte sensor platform for fluorescence-based sensors and the second is an absorbance-based portable sensor for the detection of nitrates in groundwater. A generic multi-analyte sensor platform can be applied to a broad range of areas such as food packaging and blood gas analysis. A multi-analyte optical sensor platform for enhanced capture of fluorescence was modelled, designed and fabricated. The sensor platform was developed using a range of microfabrication techniques. Films sensitive to oxygen, relative humidity and carbon dioxide respectively were developed for the context of indoor air-quality monitoring. Deposition methods for printing the sensor solutions onto the sensor platforms were also investigated. The sensor films and platforms were integrated into a working sensor chip with both a fluorescence intensity and phase fluorometric detection system. An absorbance-based portable sensor for the detection of nitrates in groundwater was also developed. This was based on the direct absorbance of UV-light by the nitrate ion. Other contaminants, which could be found in groundwater and interfere with the nitrate detection, such as humic acid and chlorides, were investigated and compensated for

Integrated polymer photonics : fabrication, design, characterization and applications

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Optically pumped planar waveguide lasers, part I: fundamentals and fabrication techniques

The tremendous interest in the field of waveguide lasers in the past two decades is largely attributed to the geometry of the gain medium, which provides the possibility to store optical energy on a very small dimension in the form of an optical mode. This allows for realization of sources with enhanced optical gain, low lasing threshold, and small footprint and opens up exciting possibilities in the area of integrated optics by facilitating their on-chip integration with different functionalities and highly compact photonic circuits. Moreover, this geometrical concept is compatible with high-power diode pumping schemes as it provides exceptional thermal management, minimizing the impact of thermal loading on laser performance. The proliferation of techniques for fabrication and processing capable of producing high optical quality waveguides has greatly contributed to the growth of waveguide lasers from a topic of fundamental research to an area that encompasses a variety of practical applications. In this first part of the review on optically pumped waveguide lasers the properties that distinguish these sources from other classes of lasers will be discussed. Furthermore, the current state-of-the art in terms of fabrication tools used for producing waveguide lasers is reviewed from the aspects of the processes and the materials involved

Polymer Waveguide Amplifiers

Polymer-based optical waveguides are a promising technology for integrating optical links onto standard printed circuit boards as they enable cost-effective manufacturing and assembly as well as offer high bandwidth. The motivation for this work is to address the lack of amplifying components the currently demonstrated polymer interconnects, which limits the complexity, functionality and reach of these systems. This dissertation studies combination of rare-earth-doped material with polymer platform to create compact erbium-doped waveguide amplifiers (EDWAs) for board-level interconnect applications. Siloxane polymer materials developed by Dow Corning are used as they have shown the necessary optical, mechanical and thermal properties required for EDWA designs (such as the ability to withstand temperatures in excess of 350 °C). The feasibility of two approaches for integrating Er-doped materials into siloxane polymer layers is investigated, namely: (i) ultrafast laser plasma implantation (ULPI) and (ii) solution-based dispersion of Er-doped nanoparticles (NP). Er-doped thin films are prepared with these two methods and their properties investigated. The maximum dopant concentrations and lifetimes are determined to be 16.3, 4.4 and 1.5 × 10$^{20}$ cm$^{-3}$ and 12.1, 4.2 and 5.7 ms for ULPI into silica glass, ULPI into polymer and the dispersion of erbium NPs in a polymer matrix, respectively. An EDWA numerical modelling framework is developed to optimise the erbium-ytterbium ratio to maximise the device gain while accounting for various potential integration methods and waveguide design parameters. Using a channel geometry based on the measured optical properties of Er-doped glass, an internal gain of 9.6 dB/cm is predicted at the optimal Er:Yb ratio of 9.0:7.3 × 10$^{20}$ cm$^{-3}$ when pumped at an optical power of 200 mW. A hybrid, polymer-glass strip-loaded design is proposed to combine the highly doped glass layer with the polymer material. While a slightly lower gain of 7.4 dB/cm is projected in the re-optimised design under the same operating conditions, it benefits from a simpler fabrication procedure. An experimental study of devices prepared through the direct Er integration into polymer waveguides enables a comparison with developed theoretical models. A good agreement between measured and modelled results show that a practical amplifier operation with erbium concentration of 1.5 × 10$^{20}$ cm$^{-3}$ is prevented by the dopant NP clustering and the potential gain limited by the absence of ytterbium co-doping. The excess scattering loss of 9.3 dB/cm could not be further reduced only with the proposed additional ultrasonication and filtering fabrication steps indicating alternative approaches such as core-shell structures are required.Engineering and Physical Sciences Research Council (EPSRC

Biochemical sensing using Siloxane polymer waveguides

The objective of this work presented here is to extend the capabilities of siloxane waveguide technology in the field of biochemical sensing. Recent advances in the integration of polymeric optical waveguides with electronics onto standard printed circuit boards (PCBs) allow the formation of cost-effective lab-on-achip modules suitable for mass production. This technology has been primarily designed for on-board data communication. The focus of this research is to investigate the possibility of realising a Siloxane polymer based lab-on-chip sensor. Different siloxane-polymer-based optical waveguide sensor structures have been designed and analysed from the aspect of biochemical sensing. An evanescent-wave absorption sensor based on mode-selective asymmetric waveguide junctions is proposed for the first time. The device mitigates the common optical effect of spurious response in absorption sensors due to the analyte transport fluid. Head injury is the leading cause of death in the population of people under 40 years. Currently, 3 out of 5 deaths in emergency rooms are due to severe brain injuries in the developed world. Researchers at the Neurosciences Critical Care Unit (NCCU) at Addenbrooke’s Hospital have managed to correlate biochemical changes with the severeness of the injury and the likelihood of patient recovery. Considerable progress has been made to develop a lab-on-chip sensor capable of continuously monitoring glucose, lactate and pyruvate concentrations in the brain fluid, hence the contribution to the current trend in the advancement of portable lab-on-chip technologies for the deployment of point-of-care diagnostic tools. A novel recognition layer has been developed based on porphyrin in combination with glucose, lactate and pyruvate oxidase for measuring all the analytes, enabling fast and reversible chemical reactions to be monitored by optical interrogation. The operational wavelength of the developed recognition layer is 425 nm, which required the formation of polymer features that were beyond the fabrication capabilities at the time. Through considerable process development and the adoption of nanoimprinting lithography, siloxane polymer based optical waveguides were fabricated allowing the realisation of highly sensitive optical sensors. Based on the results that are presented here, it can be concluded the functionalization of siloxane polymer waveguide have a potential for realising biochemical sensors in the future. The new fabrication technique will allow the formation of more robust and complex lab-on-chip sensors based on this material.ESPR

Photolithographic and replication techniques for nanofabrication and photonics

In the pursuit of economical and rapid fabrication solutions on the micro and nano scale, polymer replication has proven itself to be a formidable technique, which despite zealous development by the research community, remains full of promise. This thesis explores the potential of elastomers in what is a distinctly multidisciplinary field. The focus is on developing innovative fabrication solutions for planar photonic devices and for nanoscale devices in general. Innovations are derived from treatments of master structures, imprintable substrates and device applications. Major contributions made by this work include fully replicated planar integrated optical devices, nanoscale applications for photolithographic standing wave corrugations (SWC), and a biologically templated, optical fiber based, surface-enhanced Raman scattering (SERS) sensor. The planar devices take the form of dielectric rib waveguides which for the first time, have been integrated with long-period gratings by replication. The heretofore unemployed SWC is used to demonstrate two innovations. The first is a novel demonstration of elastomeric sidewall photolithographic mask, which exploits the capacity of elastomers to cast undercut structures. The second demonstrates that the corrugations themselves in the absence of elastomers, can be employed as shadow masks in a directional flux to produce vertical stacks of straight lines and circles of nanowires and nanoribbons. The thesis then closes by conceptually combining the preceding demonstrations of waveguides and nanostructures. An optical fiber endface is em ployed for the first time as a substrate for patterning by replication, wherein the pattern is a nanostructure derived from a biological template. This replicated nanostructure is used to impart a SERS capability to the optical fiber, demonstrating an ultra-sensitive, integrated photonic device realized at great economy of both time and money, with very real potential for mass fabrication

Nanoimprint Lithography Technology and Applications

Nanoimprint Lithography (NIL) has been an interesting and growing field in recent years since its beginnings in the mid-1990s. During that time, nanoimprinting has undergone significant changes and developments and nowadays is a technology used in R&D labs and industrial production processes around the world. One of the exciting things about nanoimprinting process is its remarkable versatility and the broad range of applications. This reprint includes ten articles, which represent a small glimpse of the challenges and possibilities of this technology. Six contributions deal with nanoimprint processes aiming at specific applications, while the other four papers focus on more general aspects of nanoimprint processes or present novel materials. Several different types of nanoimprint processes are used: plate-to-plate, roll-to-plate, and roll-to-roll. Plate-to-plate NIL here also includes the use of soft and flexible stamps. The application fields in this reprint are broad and can be identified as plasmonics, superhydrophibicity, biomimetics, optics/datacom, and life sciences, showing the broad applicability of nanoimprinting. The sections on the nanoimprint process discuss filling and wetting aspects during nanoimprinting as well as materials for stamps and imprinting