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.
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.
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.
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