Miniaturization through micro-optics and integrated photonics in special applications requires adhesive-free, stable fiber connections in terms of position and power. Our laser welding equipment directly joins fibers to these components.
In the last decades, coupling strategies of optical microresonators have been intensively explored to develop highly sensitive and label-free miniaturized biosensors. This work presents an innovative semi-automatic assembly approach for glass microbottles on a photonic integrated circuit (PIC) with single-mode waveguides. Microbottles are extraordinary whispering- gallery-mode structures with additional axial confinement of the light along the bottle shape. A high dense spectrum of resonances varying along the bottle curvature is typically observed. To excite these resonances, the evanescent field of waveguides is used, as it provides direct evanescent interaction, integration of multiple structures and mass production. Initial coupling tests in air yielded a Q factor of 104 at 1550 nm by employing an active alignment setup and a customized gripping tool. Lateral coupling tolerances of Δx = ±50 μm and Δy = ±2 μm for a bottle diameter of 180 μm were also found. An existing assembly machine including a visual system, alignment system, high precision glue dispenser and UV light was used for the identification, placement and fixation of microbottles. A highest Q factor of 105 was determined after the attachment of a microbottle. Similar results were obtained with bio-chemical modified samples. A laser cutting method was also applied for reducing the fiber length of the microbottle. In this way the hybrid PIC can be compatible with microfluidics. The dedicated assembly process is a promising tool to bring optical resonators into practical use for label-free biochemical sensing but also for other applications such as quantum sensing and communication.
Optical fiber components have the potential of enabling interconnections in compact systems because they provide reliable and efficient manipulation of light in application fields such as telecommunication, sensing and high power. A variety of glasses and fiber components including tapers, tips, bundles and couplers are typically fabricated using hydrofluoric acidbased etching processes. However, such a standard approach has some limitations related to the generation of surface defects (e.g., roughness and microcracks), poor process control and high chemical disposal costs. We propose an innovative glass etching process based on molten salts that will overcome these limitations. Molten salts can be thermally activated to etch glass materials with high precision. Initial plant development and industrial manufacturing capabilities are demonstrated on a modular etching system through a research collaboration. This system also has the advantage of managing a set of fibers simultaneously with an automatic process control. First results of etched glasses and especially, biconical fiber tapers show extremely smooth surfaces, good homogeneity, high reproducibility and potential scalability for further processing of fiber couplers. With respect to the fabrication tolerances, a value of ± 1 μm over a length of 10 mm has been found for the case of etched multimode tapers. The use of molten salts as an etching tool can be extended to economically create microstructures in glass panels for optical or fluidic purposes.
Demand for high integration of optoelectronic and micro-optical components into micro-electronic systems for communication, computing, medical, and sensing applications is increasing. Advanced hybrid packaging technologies are used to enhance glass-based substrates featuring electrical, thermal, and optical functionalities with laser diodes, modulators, isolators, photonic integrated circuits (PIC), beam-splitting components, and micro-lenses. Such glass-based substrates can be thin glass layers on large panels or more mini-bench-like boards that can be embedded into organic printed circuit boards (PCBs). Optical fiber interconnects, connectors, and electrical–optical integration platforms are used for higher level system integration and need to be miniaturized on module and board level to fulfill decreasing channel pitch requirements. We provide background on and discuss thin glass as a suitable base material for ion exchanged waveguide panels and interposers, precise glass structuring for posts and holders, the related high precision assembly techniques, and advanced fiber interconnects. Some examples of PCB photonic integration, micro-bench optical sub-assemblies, including PIC, and 3D optical resonator packages that combine most of these approaches will be shown.
Monitoring and controlling processes in industry, healthcare and environment encourage the demand and development of ultrasensitive sensors to detect physical and chemical analytes with very low concentrations. Optical methods based on resonant microstructures, that present high sensitivity, precision, selectivity, sensor lifetime and unit cost, are one of the most promising detection techniques. A fundamental limitation of optical microresonators is the realization of a reliable packaging approach that includes their readout element, e.g., tapered fibers. In this paper, the sensing response of packaged glass bottle microresonators have been demonstrated. Bottle-shaped structures support optical modes called whispering gallery modes along their curvature profile having a quality factor of 2.6 106 at 1550 nm in air. Two simple and robust packages fabricated by 3D printing and glass structuring methods were proposed for temperature and refractive index experiments. A temperature sensitivity of 9.9 pm/K in the range from 17.1°C to 22.5°C was obtained with a taper-coupled bottle system assembled into a plastic package. A similar value has been found when a bottle structure was mounted on a thermally-stable glass base and subjected to temperature changes from 18.6°C to 26.3°C. Both values were theoretically corroborated. For refractive index measurements, the fiber taper has been partially encapsulated employing a low refractive index glue. This provides a free-vibration package solution. Preliminary results shows a refractive index sensitivity of 13 nm/RIU under a constant temperature of 22°C. The proposed fiber-coupled bottle package enables new possibilities for the development of practical sensors.
The rapid development of nanophotonic chip devices combines the advantages of ultra-high miniaturization and largescale integrated circuit production, targeting a drastic decrease in the device costs. Such photonic devices based on single-mode waveguide structures are intensively used in optical communications but recently novel high power applications have emerged where it has been demonstrated that nano-sized waveguides support ultra-high optical power densities, giving rise to the generation of non-linear effects. However, all of the applications require a high efficient and stable fiber interface between the chip and the outside world. In this letter, we propose a stacked glass block technology in combination with a sub-micron alignment approach for the development of robust fiber connectors for lateral coupling. This technology offers a high degree of freedom during the assembly of glass parts, compensating undesired misalignments related to the shrinkage of the adhesive. Moreover, adhesive-based issues are minimized by stacking the glass parts with almost zero gap. The design of the glass fiber connector can be adapted for one or more optical fibers. Using an automated laser cutting system, small glass parts from glass panels are cut with high reproducibility and acceptable cut quality. Two different chips for photonic modules of specific output power level with a laser excitation wavelength at 1550 nm are addressed to show the potential use of fiber connectors based on stacked glass blocks.
Portable high-sensitivity biosensors exhibit a growing demand in healthcare, food industry and environmental monitoring sectors. Optical biosensors based on photonic integration platforms are attractive candidates due to their high sensitivity, compactness and multiplexing capabilities. However, they need a low-cost and reliable integration with the microfluidic system. Laser-micropatterned double-sided biocompatible adhesive tapes are promising bonding layers for hybrid integration of an optofluidic biochip. As a part of the EU-PHOCNOSIS project, double-sided adhesive tapes have been proposed to integrate the polymer microfluidic system with the optical integrated waveguide sensor chip. Here the adhesive tape should be patterned in a micrometer scale in order to create an interaction between the sample that flows through the polymer microchannel and the photonic sensing microstructure. Three laser-assisted structuring methods are investigated to transfer microchannel patterns to the adhesive tape. The test structure design consists of a single channel with 400 μm wide, 30 mm length and two circular receivers with 3 mm radius. The best structuring results are found by using the picosecond UV laser where smooth and straight channel cross-sections are obtained. Such patterned tapes are used to bond blank polymer substrates to blank silicon substrates. As a proof of concept, the hybrid integration is tested using colored DI-water. Structuring tests related to the reduction of channel widths are also considered in this work. The use of this technique enables a simple and rapid manufacturing of narrow channels (50-60 μm in width) in adhesive tapes, achieving a cheap and stable integration of the optofluidic biochip.
Miniaturization of medical imaging devices will significantly improve the workflow of physicians in hospitals. Photonic integrated circuit (PIC) technologies offer a high level of miniaturization. However, they need fiber optic interconnection solutions for their functional integration. As part of European funded project (InSPECT) we investigate fiber bundle probes (FBPs) to be used as multi-mode (MM) to single-mode (SM) interconnections for PIC modules. The FBP consists of a set of four or seven SM fibers hexagonally distributed and assembled into a holder that defines a multicore connection. Such a connection can be used to connect MM fibers, while each SM fiber is attached to the PIC module. The manufacturing of these probes is explored by using well-established fiber fusion, epoxy adhesive, innovative adhesive and polishing techniques in order to achieve reliable, low-cost and reproducible samples. An innovative hydrofluoric acid-free fiber etching technology has been recently investigated. The preliminary results show that the reduction of the fiber diameter shows a linear behavior as a function of etching time. Different etch rate values from 0.55 μm/min to 2.3 μm/min were found. Several FBPs with three different type of fibers have been optically interrogated at wavelengths of 630nm and 1550nm. Optical losses are found of approx. 35dB at 1550nm for FBPs composed by 80μm fibers. Although FBPs present moderate optical losses, they might be integrated using different optical fibers, covering a broad spectral range required for imaging applications. Finally, we show the use of FBPs as promising MM-to-SM interconnects for real-world interfacing to PIC’s.
We propose two low-cost and robust optical fiber systems based on the photonic lantern (PL) technology for operating at 635 nm and 1550 nm. The PL is an emerging technology that couples light from a multi-mode (MM) fiber to several single-mode (SM) fibers via a low-loss adiabatic transition. This bundle of SM fibers is observed as a MM fiber system whose spatial modes are the degenerate supermodes of the bundle. The adiabatic transition allows that those supermodes evolve into the modes of the MM fiber. Simulations of the MM fiber end structure and its taper transition have been performed via functional mode solver tools in order to understand the modal evolution in PLs. The modelled design consists of 7 SM fibers inserted into a low-index capillary. The material and geometry of the PLs are chosen such that the supermodes match to the spatial modes of the desired step-index MM fiber in a moderate loss transmission. The dispersion of materials is also considered. These parameters are studied in two PL systems in order to reach a spectral transmission from 450 nm to 1600 nm. Additionally, an analysis of the geometry and losses due to the mismatching of modes is presented. PLs are typically used in the fields of astrophotonics and space photonics. Recently, they are demonstrated as mode converters in telecommunications, especially focusing on spatial division multiplexing. In this study, we show the use of PLs as a promising interconnecting tool for the development of miniaturized spectrometers operating in a broad wavelength range.
Optical sensor systems for biological and medical applications have been widely developed in order to satisfy the current
requirements such as a miniaturization, cost reduction, label-free detection and fast response. Here, we demonstrate a
highly sensitive optical sensor based on two cascaded microring resonators (MRRs) exploiting the Vernier effect. The
architecture consists of a filter MRR connected to a sensor MRR via a common waveguide. The external medium of the
filter MRR is isolated with a top cladding layer, while the sensor MRR interacts with the analyte sample via an opening.
The sensor chip, that includes an array of five cascaded MRRs, was designed and fabricated on a silicon nitride platform.
A first test has been performed with sodium chloride (NaCl) concentrations in deionized (DI) water providing a
sensitivity of 1.03 nm/% (6317 nm/RIU). A limit of detection of 3.16 x 10-6 RIU was demonstrated for the current
sensor, respectively. Several concentrations of isopropanol in ethanol ranging from 0% to 10% were also investigated.
These preliminary measurements show a sensitivity as high as 0.95 nm/% at ~1535 nm compared to 0.02 nm/% from a
single sensor MRR. For a moderated alignment between the chip and cleaved optical fibers, tapered grating couplers are
included at the ends of waveguides. Hence, by combining the Vernier effect and the silicon nitride material, cascaded
MRRs will be a powerful optical configuration for biosensing applications in a wide operating wavelength range.
The progress in bioanalytics caused a growing demand of innovation in reliable, miniaturized and low cost optical sensor systems based on integrated optical devices. We present a detailed analysis of sensor elements for applications in aqueous solution based on two cascaded microring resonators (MRRs) by using the Vernier effect (VE). This approach is beneficial for ultra-high sensitivity at large fabrication tolerances, aspects of crucial importance for the practical detection of biomolecules such as peptides. The architecture consists of two silicon nitride microrings connected via a bus waveguide. The free spectral range (FSR) of individual rings is slightly different in order to achieve VE. Thereby the external refractive index of the reference ring is fixed; the second one varies due to the presence of the analyte. The precise operation is controlled by using spectral tuning via integrated micro-heaters. Theoretical analysis has been performed for different structural parameters. A sensitivity several orders of magnitude higher than in the case of a single ring can be predicted for TE and TM polarization, respectively. The first design of Vernier devices and its experimental characterization will be presented. The devices include tapered grating couplers in order to couple light between fibers and chip at moderate alignment tolerances in a reliable manner. Therefore, by combining the VE and the spectral tuning, cascaded MRRs are an optical configuration very promising for sensing applications.
Microcapillary resonators have great potential in sensors applications due to their high sensitivity and
compatibility with micro-fluidic systems. Capillaries show the unique property of being capable to sense
liquids with refractive index higher than the refractive index of the capillary. Whispering-gallery modes
resonances excited in the capillary shift as a function of the refractive index of the medium that fills the
capillary. The sensitivity, as well as the Q factor of the resonances, depends strongly on the structural
parameters of the capillary, i.e. radius and wall thickness. A detailed theoretical analysis is presented. As
a practical application, capillaries were used for the measurement of glucose concentration in water
solution. A collection of capillaries with different wall thickness and radius were tested. The sensitivity of
higher radial-order modes in large radius capillaries is also investigated. A best sensitivity of 1.24 nm / %
of glucose concentration in water is reported.
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