A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Effective manipulation of cavity resonant modes is crucial for emission control in laser physics and applications. Using the concept of parity-time symmetry to exploit the interplay between gain and loss (i.e., light amplification and absorption), we demonstrate a parity-time symmetry-breaking laser with resonant modes that can be controlled at will. In contrast to conventional ring cavity lasers with multiple competing modes, our parity-time microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation with the selective whispering-gallery mode order. Exploration of parity-time symmetry in laser physics may open a door to next-generation optoelectronic devices for optical communications and computing.

http://science.sciencemag.org/content/sci/346/6212/972.full.pdf

Single-mode laser by parity-time symmetry breaking.

Sensing technology has been widely investigated and utilized for gas detection. Due to the different applicability and inherent limitations of different gas sensing technologies, researchers have been working on different scenarios with enhanced gas sensor calibration. This paper reviews the descriptions, evaluation, comparison and recent developments in existing gas sensing technologies. A classification of sensing technologies is given, based on the variation of electrical and other properties. Detailed introduction to sensing methods based on electrical variation is discussed through further classification according to sensing materials, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture absorbing materials. Methods based on other kinds of variations such as optical, calorimetric, acoustic and gas-chromatographic, are presented in a general way. Several suggestions related to future development are also discussed. Furthermore, this paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.

A Survey on Gas Sensing Technology

Quantitative phase imaging (QPI) has emerged as a valuable method for investigating cells and tissues. QPI operates on unlabelled specimens and, as such, is complementary to established fluorescence microscopy, exhibiting lower phototoxicity and no photobleaching. As the images represent quantitative maps of optical path length delays introduced by the specimen, QPI provides an objective measure of morphology and dynamics, free of variability due to contrast agents. Owing to the tremendous progress witnessed especially in the past 10–15 years, a number of technologies have become sufficiently reliable and translated to biomedical laboratories. Commercialization efforts are under way and, as a result, the QPI field is now transitioning from a technology-development-driven to an application-focused field. In this Review, we aim to provide a critical and objective overview of this dynamic research field by presenting the scientific context, main principles of operation and current biomedical applications. Over the past 10–15 years, quantitative phase imaging has moved from a research-driven to an application-focused field. This Review presents the main principles of operation and representative basic and clinical science applications.

Quantitative phase imaging in biomedicine

Many procedures in modern clinical medicine rely on the use of electronic implants in treating conditions that range from acute coronary events to traumatic injury. However, standard permanent electronic hardware acts as a nidus for infection: bacteria form biofilms along percutaneous wires, or seed haematogenously, with the potential to migrate within the body and to provoke immune-mediated pathological tissue reactions. The associated surgical retrieval procedures, meanwhile, subject patients to the distress associated with re-operation and expose them to additional complications. Here, we report materials, device architectures, integration strategies, and in vivo demonstrations in rats of implantable, multifunctional silicon sensors for the brain, for which all of the constituent materials naturally resorb via hydrolysis and/or metabolic action, eliminating the need for extraction. Continuous monitoring of intracranial pressure and temperature illustrates functionality essential to the treatment of traumatic brain injury; the measurement performance of our resorbable devices compares favourably with that of non-resorbable clinical standards. In our experiments, insulated percutaneous wires connect to an externally mounted, miniaturized wireless potentiostat for data transmission. In a separate set-up, we connect a sensor to an implanted (but only partially resorbable) data-communication system, proving the principle that there is no need for any percutaneous wiring. The devices can be adapted to sense fluid flow, motion, pH or thermal characteristics, in formats that are compatible with the body's abdomen and extremities, as well as the deep brain, suggesting that the sensors might meet many needs in clinical medicine.

Bioresorbable silicon electronic sensors for the brain

A reflective microring resonator is used as a wavelength selective nonlinear feedback element in a fiber ring laser to generate optical clock pulses. All components are driven by DC current.

Optical clock pulse generation using thermal nonlinearity in microring resonators

A $2 table-top experiment was devised to introduce optical imaging principles to precollege students. Using off-the-shelf parts, this project-based learning activity was implemented in many summer camps and schools to teach math and engineering concepts.

Pre-college students learn cross-cutting STEM concepts by building an optical imaging projector

We present the first continuous wave (CW) 1.50 /spl mu/m lasers grown on GaAs substrates. These GaInNAsSb lasers operated CW at room temperature with threshold current densities as low as 1.06 kA/cm/sup 2/ and output powers as high as 140 mW. Peak output power was limited by thermal dissipation and up to 670 mW was obtained under pulsed conditions. The CW slope efficiency was 0.26 W/A, corresponding to an external quantum efficiency of 31%. The lasers also featured high CW characteristic temperatures of 139 K over the range 10-60 /spl deg/C, making them ideal for use in uncooled optical communication networks.

Low threshold, CW, room temperature 1.49 /spl mu/m GaAs-based lasers

We present the first low-threshold 1.55-μm lasers grown on GaAs. The active layer was a single GaInNAsSb quantum well surrounded by strain-compensating GaNAs barriers. The room-temperature, continuous-wave, threshold current density was 579 A/cm2 and peak output power was 130 mW.

Low-threshold continuous-wave 1.55-μm GaInNAsSb lasers

We present design, fabrication and characterization of a single wavelength narrowband reflector made by integration of a DBR inside a ring resonator. The DBR covers half of the ring's circumference and is only reflective at one ring resonance.

Lynford L. Goddard

Papers

Optical clock pulse generation using thermal nonlinearity in microring resonators

Pre-college students learn cross-cutting STEM concepts by building an optical imaging projector

Low threshold, CW, room temperature 1.49 /spl mu/m GaAs-based lasers

Low-threshold continuous-wave 1.55-μm GaInNAsSb lasers

Realization of small footprint microring reflectors