Bimodal waveguide interferometer RI sensor fabricated on low-cost polymer platform

A refractive index sensor based on bimodal waveguide interferometer is demonstrated on the low-cost polymer platform for the first time. Different from conventional interferometers which make use of the interference between the light from two arms, bimodal waveguide interferometers utilize the interference between the two different internal modes in the waveguide. Since the utilized first higher mode has a wide evanescent tail which interacts with the external environment, the interferometer can reach a high sensitivity. Instead of vertical bimodal structure which is normally employed, the lateral bimodal waveguide is adopted in order to simplify the fabrication process. A unique offset between the centers of single mode waveguide and bimodal waveguide is designed to excite the two different modes with equal power which contributes to the maximum fringe visibility. The bimodal waveguide interferometer is finally fabricated on optical polymer (Ormocore) which is transparent at both infrared and visible wavelengths. It is fabricated using the UV-based soft imprint technique which is simple and reproductive. The bulk sensitivity of fabricated interferometer sensor with a 5 mm sensing length is characterized using different mass concentration sodium chloride solutions. The sensitivity is obtained as 316 pi rad/RIU and the extinction ratio can reach 18 dB

All-optical photoacoustic microscopy

AbstractThree-dimensional photoacoustic microscopy (PAM) has gained considerable attention within the biomedical imaging community during the past decade. Detecting laser-induced photoacoustic waves by optical sensing techniques facilitates the idea of all-optical PAM (AOPAM), which is of particular interest as it provides unique advantages for achieving high spatial resolution using miniaturized embodiments of the imaging system. The review presents the technology aspects of optical-sensing techniques for ultrasound detection, such as those based on optical resonators, as well as system developments of all-optical photoacoustic systems including PAM, photoacoustic endoscopy, and multi-modality microscopy. The progress of different AOPAM systems and their representative applications are summarized

Integrated nanophotonic waveguide-based devices for IR and Raman gas spectroscopy

On-chip devices for absorption spectroscopy and Raman spectroscopy have been developing rapidly in the last few years, triggered by the growing availability of compact and affordable tunable lasers, detectors, and on-chip spectrometers. Material processing that is compatible with mass production has been proven to be capable of long low-loss waveguides of sophisticated designs, which are indispensable for high-light–analyte interactions. Sensitivity and selectivity have been further improved by the development of sorbent cladding. In this review, we discuss the latest advances and challenges in the field of waveguide-enhanced Raman spectroscopy (WERS) and waveguide infrared absorption spectroscopy (WIRAS). The development of integrated light sources and detectors toward miniaturization will be presented, together with the recent advances on waveguides and cladding to improve sensitivity. The latest reports on gas-sensing applications and main configurations for WERS and WIRAS will be described, and the most relevant figures of merit and limitations of different sensor realizations summarized

Study and manufacturing of biosensors based on plasmonic effects and built on silicon

Abstract: Lab-on-a-chip (or LOC) devices scale down the laboratory processes for detecting illnesses and monitoring sick patients without the need of medical laboratories. Well-known examples of LOC are pregnancy test kits or portable HIV sensors. To be useful, LOC devices must be sensitive, specific, compact, and affordable. These criteria are made possible with a transducer that can convert the biological presence of the target molecule into electrical information. Since the early 2000s, integrated photonics have offered a possible solution for a transducer compatible with LOC needs. In particular, silicon micro-ring resonators represent a compact and sensitive choice to use as a transducer in LOC devices. In agreement with the requirements of LOC devices, the objective of this project is to design and assess the performance of a compact photonic biosensor. The system will be based on integrated photonic transduction. The requirements are that it is compatible with an industrial fabrication platform and fluidic systems, with a sensitivity equal to or higher than the state-of-the-art and simple to functionalize in order to localize the target molecules in the sensitive regions of the sensor. This project details the design, fabrication, and characterization of such a biosensor. We found that ring resonators with a Hybrid Plasmonic Waveguide (HPWG) cross-section fulfill the LOC requirements and outperform the state-of-the-art biosensor. Furthermore, based on a principle called mode lift, we patented new geometry of HPWG, which will be the object of an article. We simulated the HPWG structure to understand the coupling mechanisms of the modes inside the structure (more specifically, the plasmonic and the ridge dielectric modes). The fabrication was possible thanks to the collaboration of the industrial and university cleanrooms. An advantage of industrial production is that we can reproducibly create the geometric components necessary for the LOC in a high-throughput manner, thus lowering the cost per unit cell. Once the 300 mm Si wafers were patterned, the university cleanroom fabrication process adds the metallic waveguides. The Au nanopatterning on the devices characterized in this project was created using the lift-off method. The preliminary measures define the optimal testing liquid (glucose monohydrate) and the uncertainty of the measures. The HPWG samples showed an experimental sensitivity lower than the simulations. After adjusting the fabrication parameters (mainly Au and Cr deposition rates and thicknesses), the second-generation HPWG devices suggest that the mode lift improves the sensitivity for waveguides below cutoff (the sensitivity increases from 210 nm/RIU to 320 nm/RIU when only 10% of the ring resonator has an HPWG section and the rest is a ridge waveguide). Even in the case where ridge waveguides are above the cutoff, the sensitivity increases by 40 nm/RIU when using mode lift. We also showed the compatibility of the fabricated devices’ surface with differential functionalization, by means of fluorescent nanoparticles. Due to time limitations, the presence of the nanoparticles will be measured with the fabricated devices in future experiments.Les dispositifs laboratoire sur puce (ou Lab-on-a-chip ou LOC) visent à miniaturiser les procédés de laboratoires pour la détection des maladies et la surveillance des patients malades, sans avoir besoin de laboratoires médicaux. Deux exemples bien connus de LOC sont les kits de test de grossesse ou les capteurs portables du VIH. Pour être efficaces, les appareils LOC doivent être sensibles, spécifiques à l’analyte concerné, compacts et abordables. Ces critères sont possibles grâce à un transducteur, qui peut convertir la présence biologique de la molécule cible en informations électriques. Depuis le début des années 2000, la photonique intégrée a offert une solution pour un système de transduction compatible avec les besoins du LOC. En particulier, les micro-résonateurs à anneaux en silicium représentent un transducteur compact et sensible adapté aux appareils LOC. En accord avec les exigences des dispositifs LOC, l’objectif de ce projet est de concevoir et d’évaluer les performances d’un biocapteur photonique compact. Le système sera basé sur une transduction photonique intégrée. Les exigences sont : une simple fonctionnalisation, la compatibilité avec une plateforme de fabrication industrielle et des systèmes fluidiques, avec une sensibilité égale ou supérieure à l’état de l’art. Ce projet détaille la conception, la fabrication et la caractérisation d’un tel biocapteur. Nous avons constaté que les résonateurs en anneau avec une section transversale de guide d’ondes hybrides plasmoniques (HPWG) remplissent les exigences LOC et sont compétitifs en comparaison avec l’état de l’art des biocapteurs photoniques. Par ailleurs, basée sur un principe appelé mode lift, une nouvelle géométrie de HPWG a été brevetée et fera l’objet d’un article. Nous avons simulé la structure HPWG pour comprendre les mécanismes de couplage des modes photoniques à l’intérieur de la structure (plus précisément les modes plasmoniques et les modes diélectriques du guide d’onde à ruban). La fabrication a été possible grâce à la collaboration de la salle blanche industrielle de STMicroelectronics et des salles blanches universitaires de l’université de Sherbrooke et de l’Institut de Nanotechnologies de Lyon. Un avantage de la production industrielle est que nous pouvons créer de manière reproductible la géométrie des composants nécessaires pour le LOC à haut débit, réduisant ainsi le coût par unité. Une fois que les wafers de 300 mm ont été structurés, le processus de fabrication en salle blanche universitaire permet d’ajouter le métal des guides d’ondes plasmoniques. La méthode du lift-off a été utilisée pour la nanostructuration Au sur les dispositifs caractérisés dans ce projet. Des mesures préliminaires ont permis de définir le liquide d’essai optimal (glucose monohydrate) ainsi que l’incertitude des mesures. Les échantillons HPWG ont montré une sensibilité expérimentale inférieure aux simulations. Après avoir ajusté les paramètres de fabrication (principalement les taux et les épaisseurs de dépôt d’Au et de Cr), les dispositifs HPWG de deuxième génération suggèrent que le mode lift améliore la sensibilité des guides d’ondes en dessous de la coupure (la sensibilité augmente de 210 nm/RIU à 320 nm/RIU lorsque seulement 10 % du résonateur en anneau a une section HPWG). Même par rapport aux guides d’ondes au-dessus de la coupure, la sensibilité augmente de 40 nm/RIU lors de l’utilisation du mode lift. Nous avons également montré la compatibilité de la surface des appareils fabriqués avec la fonctionnalisation différentielle en utilisant des nanoparticules fluorescentes. Pour des contraintes de temps, la présence des nanoparticules ne sera mesurée que dans des futures expériences

On-chip optical sensors

Adding more functionality to chips is an important trend in the advancement of technology. During the past couple of decades, integrated circuit developments have focused on keeping Moore\u27s Law alive More of Moore . Moore\u27s law predicts the doubling of the number of transistors on an integrated circuit every year. My research objectives revolve around More than Moore , where different functionalities are sought to be integrated on chip. Sensing in particular is becoming of paramount importance in a variety of applications. Booming healthcare costs can be reduced with early diagnosis, which requires improved sensitivity and lower cost. To halt global warming, environmental monitoring requires miniature gas sensors that are cheap enough to be deployed at mass scale. First, we explore a novel silicon waveguide platform that is expected to perform well as a sensor in comparison to the conventional 220 nm thick waveguide. 50 and 70 nm shallow silicon waveguides have the advantage of easier lithography than conventional 220 nm thick waveguides due to the large minimum feature size required of 1 µm. 1 µm wide waveguides in these shallow platforms are single mode. A multi-mode interference device is designed in this platform to function as the smallest MMI sensor, giving sensitivity of 427 nm / refractive index unit (RIU) at a length of 4 mm. The silicon photonic MMI sensor is based on detecting refractive index changes. Refractometric techniques such as the MMI sensor require surface functionalization to achieve selectivity or specificity. Spectroscopic methods, usually reserved for material characterization in a research setting, can be adapted for highly specific label-free sensing. Chapter 4 explores the use of a highly doped III-V semiconductor for on chip infrared spectroscopy. Finite element method and finite different time domain were both used to design a plasmonic slot waveguide for gas sensing. On chip lasers and detectors have been designed using InAs. While InAs is still considered more expensive than silicon, the electronics industry expects to start incorporating more materials in standard fabrication processes, including III-V semiconductors for their superior properties including mobility. Thus, experimental realization of this sensor is feasible. A drawback with infrared spectroscopy is that it is difficult to use with biological fluids. Chapter 5 explores the use of Raman spectroscopy as a sensing method. To adapt Raman spectroscopy for sensing, the most important task is to enhance the Raman signal. The way the Raman signal is generated means that the number of photons is generally very low and usually bulk material or concentrated fluids are used as samples. To measure low concentrations of a probe molecule, the probe molecule is placed on a surface enhanced Raman spectroscopy (SERS) substrate. A typical SERS substrate is composed of metal nanostructures for their surface plasmon resonance property, which causes a large amplification in the electric field in particular hot spots. By decorated silicon nanowires with silver nanoparticles, an enhancement factor of 1011 was realized and picomolar concentrations of pyridine were detected using Raman spectroscopy. In conclusion, this thesis provides new concepts and foundations in three directions that are all important for on chip optical sensing. First, silicon photonics is the technology of choice that is nearest to the market and a multi-mode interference sensor based on shallow silicon waveguides was designed. Further work can explore how to cascade such MMIs to increase sensitivity without sacrificing the free spectral range. Second, infrared plasmonics is a promising technology. Before semiconductor plasmonics, on chip devices operated in the visible or near IR and then microwave region of the electromagnetic spectrum. By using highly doped semiconductors, it is possible to bridge the gap and operate with mid-infrared wavelengths. The implications are highlighted by designing a waveguide platform that can be used for next generation on chip infrared spectroscopy. Third, Raman spectroscopy was exploited as a sensing technique by experimental realization of a SERS substrate using equipment-free fabrication methods

Recent advances in solid-state organic lasers

Organic solid-state lasers are reviewed, with a special emphasis on works published during the last decade. Referring originally to dyes in solid-state polymeric matrices, organic lasers also include the rich family of organic semiconductors, paced by the rapid development of organic light emitting diodes. Organic lasers are broadly tunable coherent sources are potentially compact, convenient and manufactured at low-costs. In this review, we describe the basic photophysics of the materials used as gain media in organic lasers with a specific look at the distinctive feature of dyes and semiconductors. We also outline the laser architectures used in state-of-the-art organic lasers and the performances of these devices with regard to output power, lifetime, and beam quality. A survey of the recent trends in the field is given, highlighting the latest developments in terms of wavelength coverage, wavelength agility, efficiency and compactness, or towards integrated low-cost sources, with a special focus on the great challenges remaining for achieving direct electrical pumping. Finally, we discuss the very recent demonstration of new kinds of organic lasers based on polaritons or surface plasmons, which open new and very promising routes in the field of organic nanophotonics

Simulation and analysis of microring electric field sensor based on a lithium niobate-on-insulator

With the increasing sensitivity and accuracy of contemporary high-performance electronic information systems to electromagnetic energy, they are also very vulnerable to be damaged by high-energy electromagnetic fields. In this work, an all-dielectric electromagnetic field sensor is proposed based on a microring resonator structure. The sensor is designed to work at 35 GHz RF field using a lithium niobate-on-insulator (LNOI) material system. The 2.5-D variational finite difference time domain (varFDTD) and finite difference eigenmode (FDE) methods are utilized to analyze the single-mode condition, bending loss, as well as the transmission loss to achieve optimized waveguide dimensions. In order to obtain higher sensitivity, the quality factor (Q-factor) of the microring resonator is optimized to be 106 with the total ring circumference of 3766.59 μm. The lithium niobate layer is adopted in z-cut direction to utilize TM mode in the proposed all-dielectric electric field sensor, and with the help of the periodically poled lithium niobate (PPLN) technology, the electro-optic (EO) tunability of the device is enhanced to 48 pm·μm/V

Miniaturization of optical spectrometers

Spectroscopic analysis is one of the most widely used analytical tools across both scientific research and industry. Whilst laboratory bench-top spectrometer systems offer superlative resolution and spectral range, their miniaturization is crucial for applications where portability is paramount, or in-situ measurements must be made. Advancement in this field over the last three decades is now yielding microspectrometers with performance and footprint near those viable for lab-on-a-chip systems, smartphones and other consumer technologies. In this review, we briefly summarize the technologies that have emerged toward achieving these aims - including miniaturized dispersive optics, narrowband filter systems, Fourier transform interferometers and reconstructive microspectrometers - and discuss the challenges associated with improving spectral resolution while device dimensions shrink ever further.EPSRC: EP/L016087/1 National Natural Science Foundation of China (51706141, 51976122