Microcavity physics and design will be reviewed. Following an overview of applications in quantum optics, communications and biosensing, recent advances in ultra-high-Q research will be presented.

Optical microcavities

Organic semiconductor lasers.

Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201707035

Soft Robotic Grippers.

We report the fabrication and accurate measurement of propagation and bending losses in single-mode silicon waveguides with submicron dimensions fabricated on silicon-on-insulator wafers. Owing to the small sidewall surface roughness achieved by processing on a standard 200mm CMOS fabrication line, minimal propagation losses of 3.6+/-0.1dB/cm for the TE polarization were measured at the telecommunications wavelength of 1.5microm. Losses per 90 masculine bend are measured to be 0.086+/-0.005dB for a bending radius of 1microm and as low as 0.013+/-0.005dB for a bend radius of 2microm. These record low numbers can be used as a benchmark for further development of silicon microphotonic components and circuits.

/pdf/losses-in-single-mode-silicon-on-insulator-strip-waveguides-2xwu3irgp8.pdf

Losses in single-mode silicon-on-insulator strip waveguides and bends.

Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

Monitoring of Vital Signs with Flexible and Wearable Medical Devices

We report on the fabrication and characterization of silicon oxynitride (SiON) layers for applications as planar optical waveguides in the 1550 nm wavelength region. The optically guiding SiON waveguide core layer has a relatively high refractive index of 1500 and is sandwiched between two silicon oxide cladding layers with a lower refractive index of 1450. The SiON layer is deposited by plasma-enhanced chemical vapor deposition using silane, nitrous oxide, and ammonia as gaseous precursors. Waveguide bends with a radius of curvature as small as 1.5 mm can be realized because of the high refractive index difference achievable between core and cladding layers. This allows the fabrication of compact, relatively complex integrated optical waveguide devices, The deposition process and the characterization of the SiON films are discussed. The strengths of this high refractive index contrast planar waveguide technology are illustrated using the example of an optical add/drop filter for wavelength division multiplexing applications in the field of optical communication systems.

Silicon Oxynitride Layers for Optical Waveguide Applications

To reduce the coupling loss of a fiber-to-ridge waveguide connection, a planar silica spot-size converter for a wavelength of 1.55 /spl mu/m is implemented in the form of a nonperiodic segmented waveguide structure with irregular tapering. A simple single-step lithography process is sufficient for the fabrication of the planar structures. An evolutionary algorithm has been successfully applied for the optimization. The simulated results obtained with a three-dimensional (3-D) finite difference beam propagation method (FD-BPM) program are compared with measurements of implemented couplers, showing very good agreement. A waveguide-to-fiber coupling efficiency improvement exceeding 2 dB per converter is shown. Structures obtained with this approach are very short (/spl sim/140 /spl mu/m) and simple to integrate on the same wafer with other planar structures such as phased arrays or ring resonator structures.

A very short planar silica spot-size converter using a nonperiodic segmented waveguide

A monolithic ring resonator of KNbO3 was used for efficient frequency doubling of a 856 nm GaAlAs diode laser. A special electronic servo technique was devised to lock the diode laser frequency to the KNbO3 cavity so that stable generation of blue output was obtained. With 105 mW of incident near‐infrared power, 41 mW of 428 nm radiation were produced. The conversion efficiency from electrical input power into the diode laser to blue output was ∼10%.

Generation of 41 mW of blue radiation by frequency doubling of a GaAlAs diode laser

This paper describes a quad optical transceiver for low-power high-density short-distance optical data communication. Each channel transmits 10 Gb/s over a multimode (MM) fiber and features a link margin of 5.2 dB at a bit error rate (BER) of 10/sup -12/. The transmit and receive amplifying circuits are implemented in an 80-nm digital CMOS process. Each driver consumes 2 mW from a 0.8-V supply, and each vertical cavity surface-emitting laser (VCSEL) requires 7 mA from a 2.4-V supply. The receiver excluding the output buffer consumes 6 mW from a 1.1-V supply per channel and achieves a transimpedance gain of 80.1 dB/spl Omega/. The isolation to the neighboring channels is >30dB including the bond wires and optical components. A detailed link budget analysis takes the relevant system impairments as losses and power penalties into account, derives the specifications for the electrical circuits, and accurately predicts the link performance. This work presents the highest serial data rate for CMOS transceiver arrays and the lowest power consumption per data rate reported to date.

A 100-mW 4/spl times/10 Gb/s transceiver in 80-nm CMOS for high-density optical interconnects

Long-term monitoring with optical fibers has moved into the focus of attention due to the applicability for medical measurements. Within this Review, setups of flexible, unobtrusive body-monitoring systems based on optical fibers and the respective measured vital parameters are in focus. Optical principles are discussed as well as the interaction of light with tissue. Optical fiber-based sensors that are already used in first trials are primarily selected for the section on possible applications. These medical textiles include the supervision of respiration, cardiac output, blood pressure, blood flow and its saturation with hemoglobin as well as oxygen, pressure, shear stress, mobility, gait, temperature, and electrolyte balance. The implementation of these sensor concepts prompts the development of wearable smart textiles. Thus, current sensing techniques and possibilities within photonic textiles are reviewed leading to multiparameter designs. Evaluation of these designs should show the great potential of optical fibers for the introduction into textiles especially due to the benefit of immunity to electromagnetic radiation. Still, further improvement of the signal-to-noise ratio is often necessary to develop a commercial monitoring system.

/pdf/body-monitoring-and-health-supervision-by-means-of-optical-1futeiw0hq.pdf

Gian-Luca Bona

Papers

Silicon Oxynitride Layers for Optical Waveguide Applications

A very short planar silica spot-size converter using a nonperiodic segmented waveguide

Generation of 41 mW of blue radiation by frequency doubling of a GaAlAs diode laser

A 100-mW 4/spl times/10 Gb/s transceiver in 80-nm CMOS for high-density optical interconnects

Body-Monitoring and Health Supervision by Means of Optical Fiber-Based Sensing Systems in Medical Textiles