Among various nanostructures for low-dimensional photonics, the one-dimensional nanowire is of great importance owing to its capability of routing tightly confined light fields in single-mode with least space and material requirement, minimized optical path, and high mechanical flexibility. Free-standing optical nanowires or nanofibers fabricated by either chemical growth or physical drawing techniques surpass nanowaveguides fabricated by almost all other means in terms of sidewall smoothness and diameter uniformity, conveying their low waveguiding losses.With high index contrast between the core and the surrounding, a nanowire can guide light with tightly confined large fractional evanescent waves, which enables highly localized near-field interaction between the guided fields and the surrounding media. In this talk, we show the possibility of on-chip integration of free-standing optical nanofibers and nanowires. Firstly, by embedding nanofibers with microfluidic chips, we show ultrasensitive optical sensors for physical and bio-chemical detection. Secondly, by near-field coupling of free-standing nanowires/nanofibers with silicon-on-insulator waveguides, we show hybrid photonic circuits for optical modulation and light generation on silicon chips.

Single nanoparticle detection is of critical importance in many applications. Optical microcavities featuring high-Q factors and small mode volumes have been widely investigated in sensing applications. In general, the microcavity sensing depends mainly on reactive (i.e., dispersive) interactions, resulting in a resonance wavelength shift or mode splitting, which essentially responds to the real part of the polarizability of the targets. In the first part of this talk, we report the experimental demonstration of single nanoparticle detection using either resonance mode broadening or microcavity Raman laser splitting. In the second part, a dissipative sensing method is demonstrated to detect single lossy nanoparticles. This dissipative sensing method holds great potential in detecting nanoparticles of high absorption or ultralow polarizabilities, such as carbon nanotubes and metal nanoparticles, and in characterizing nanoparticle properties in combination with the reactive sensing method.

Optofluidics has become an appealing platform to fuse photonics and microfluidics for a large variety of applications. Here we demonstrated the use of optical fiber grating devices in the development of optofluidic devices, sensors and tunable lasers. A miniature microfluidic flowmeter and a microfluidic biochip are demonstrated through on-chip integration of microfiber Bragg grating and long-period grating, respectively. An optofluidic tunable mode-locked fiber laser using a microfluidic chip integrated with long-period grating will also be presented.

We report recent progresses on optical fiber photothermal interferometry for high sensitivity gas and liquid sensing. The basics of photothermal phase modulation with contentiously wavelength/intensity modulated and pulsed pump sources are described, and various interferometric probe configurations for phase detection are discussed. The all fiber configurations operated at the near infrared wavelengths would enable compact and cost-effective sensors with capability of remote detection, multiplexing and sensor networking, which could be used for a range of high performance applications in environmental, medical and safety monitoring.

Surface Plasmon resonance (SPR) optical fiber sensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for in-situ high sensitivity biochemical and electrochemical measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. Grating-assisted and polarization control are two key properties of fiber-optic SPR sensors to achieve unprecedented sensitivities and limits of detection. The biosensor configuration presented here utilizes a nano-scale metal-coated tilted fiber Bragg grating (TFBG) imprinted in a commercial single mode fiber core with no structural modifications. Such sensor provides an additional resonant mechanism of high-density narrow cladding mode spectral combs that overlap with the broader absorption of the surface Plasmon for high accuracy interrogation. In this paper, we briefly review our recent developments of plasmonic tilted fiber grating sensors, including the surface affinity studies of biomolecules for real life problems, electrochemical actives of electroactive biofilms for clean energy resources, the vector magnetic field measurement and the ultra-highly sensitive plasmonic sensing in gas.

This talk will give a systematic study for the ultra-precision machining technology for generating various optical microstructures, such as micro V-groove for optical fiber connectors, microlens array for microfluidic microcavity, etc. which includes the machining mechanism, tool path generation, modeling and simulation of surface generation, machining error prediction, process optimization, etc. A series of methods and approaches are also presented to measure and characterize such optical microstructures. The research work aims to provide an enabling solution for producing optical microstructures in high precision and efficiently.

The rapid development of biophotonics has advanced our understanding of the biological world through optical tools. On one hand, there is an increasing requirement to understand the heterogeneity of cells by precisely capturing and analyzing single cells. On the other hand, we have to develop biocompatible and implantable tools to explore the biological world. Although conventional optical tweezers have been widely used to immobilize single cells for further analysis, it has limitations, including manipulation inflexibility, use of bulky structures, diffraction limitations for nanoparticles, and limited trapping functions. We use a tapered optical fiber to realize optical trapping and manipulation with multiple functions and high flexibility, increased precision and high levels of integration. Both single particle/cell trapping for single cell analysis and multiple particle/cell assembly for biocompatible and implantable photonic devices construction have been realized. Using tapered optical fibers with different configurations, we achieved flexible trapping and controllable manipulation of different objects from microparticles to carbon nanotubes to single DNA molecules. Our tapered optical fiber-based single particle/cell trapping and multiple particle/cell assembly will advance our understanding of the biological world in a precise manner using biocompatible and implantable tools.

Optically tweezed microscopic aerosol droplets are characterized using Raman spectroscopy to quantify chemical and physical transformations that occur due to change in environment. Droplets are used as micro-chemical reactors to probe polymorphic calcium carbonate formation during ion exchange and droplets are used as sensors for the localized environment. Analysis of Raman spectral peak shifts during aqueous CaCl₂ and aqueous Na₂CO₃ droplet coalescence events provides detailed insight into chemical composition, and measurement of morphology dependent resonances provides droplet size, refractive index, morphology and phase information. We explore the reversibility of meta-stable vaterite and amorphous states and stable calcite formation through Raman peak deconstruction. This work has scope for extension to droplet flow systems for controlled chemical reactions that can promote higher yields and higher concentrations due to the super-saturated states accessible to aerosol droplets.

Distributed Bragg reflector (DBR) fiber laser, consisting of an active fiber sandwiched between two highly reflective fiber Bragg gratings, has attracted much research attention due to their compactness, multiplexing capability, and high stability with single-longitudinal-mode operation for the potential applications of wavelength-division multiplexing communication, optical microwave signal generation, optical sensing, and etc. Numerous efforts have been made in the past to fabricate high-performance sensors utilizing DBR fiber laser for detection of transverse pressure, magnetic field, torsion, high-frequency ultrasound, and etc. In most situations, however, the laser modes are mainly confined in the fiber core and are insensitive to external refractive index change. In this work, we demonstrate a CO2-laser carved DBR fiber laser for the purpose of refractive index detection. A parabola-like opening is firstly formed inside the laser cavity so that the laser output becomes tunable by the refractive index inside the opening. The structural parameter influence, the lasing threshold condition, and the temperature coefficient are investigated. We subsequently broaden the width of the opening using the laser-beam scanning technique and show that the beat frequency can be modified with changing external refractive index. The developed devices have advantages of high sensitivity, stability, and low cost compared to most other fiber counterparts and thus can have potential applications in tunable optical lasing, optical sensing, and etc.

Investigating brain activity during behavior has become one of the most attractive approaches for neuroscience researches. We developed a fiber-optic-based multi-modal optical imaging system that can detect optical fluorescent signal and hemodynamic changes simultaneously in awake animal. The imaging system integrates laser speckle contrast imaging (LSCI), spectral imaging of optical intrinsic signal (OIS), and wide-field fluorescent imaging together to provide the capability of recording the changes in calcium, blood flow, blood volume and blood oxygenation simultaneously. The imaging system consists of three parts: a multi-source illuminator, a fiber multi-channel optical imaging unit, and a head-mounted microscope. The imaging fiber bundle delivers optical images from the head-mounted microscope to the multi-channel optical imaging unit. Illuminating fiber bundles transmit light to the head-mounted microscope, which has a mass of less than 1.5 g and includes a gradient index lens. The internal optical components are adjustable, allowing for a change in the magnification and field of view. Using this system, hemodynamic and fluorescent changes during cortical spreading depression (CSD) in freely moving and anesthetized animals were investigated.