Hai Xiao

Spatially continuous distributed fiber optic sensing using optical carrier based microwave interferometry

This paper reports a spatially continuous distributed fiber optic sensing technique using optical carrier based microwave interferometry (OCMI), in which many optical interferometers with the same or different optical path differences are interrogated in the microwave domain and their locations can be unambiguously determined. The concept is demonstrated using cascaded weak optical reflectors along a single optical fiber, where any two arbitrary reflectors are paired to define a low-finesse Fabry-Perot interferometer. While spatially continuous (i.e., no dark zone), fully distributed strain measurement was used as an example to demonstrate the capability, the proposed concept may also be implemented on other types of waveguide or free-space interferometers and used for distributed measurement of various physical, chemical and biological quantities.

All-in-fiber optofluidic sensor fabricated by femtosecond laser assisted chemical etching

An all-in-fiber prototype optofluidic device was fabricated by femtosecond laser irradiation and subsequent selective chemical wet etching. Horizontal and vertical microchannels can be flexibly created into an optical fiber to form a fluidic cavity with inlets/outlets. The fluidic cavity also functions as an optical Fabry-Perot cavity in which the filled liquid can be probed. The assembly-free microdevice exhibited a fringe visibility of 20xa0dB and was demonstrated for measurement of the refractive index of the filling liquids. The proposed all-in-fiber optofluidic micro device is attractive for chemical and biomedical sensing because it is flexible in design, simple to fabricate, mechanically robust, and miniaturized in size.

Microwave Interrogated Sapphire Fiber Michelson Interferometer for High Temperature Sensing

We present, for the first time to our knowledge, a microwave interrogated sapphire fiber Michelson interferometer for high temperature sensing. By sending a microwave-modulated optical wave to a sapphire fiber Michelson interferometer, a high quality interference spectrum was reconstructed in the microwave domain with a fringe visibility exceeding 40 dB. The sensor showed good sensitivity, reversibility and stability in the temperature range of 100 °C-1400 °C. The proposed sensing configuration has a number of unique advantages including low dependence to the multimodal influences, high signal quality, relieved fabrication precision, and insensitivity to the background blackbody radiation when used in high temperature.

Simultaneous measurement of temperature and pressure with cascaded extrinsic Fabry-Perot interferometer and intrinsic Fabry-Perot interferometer sensors

Abstract. This paper presents an approach for simultaneous measurement of temperature and pressure using miniaturized fiber inline sensors. The approach utilizes the cascaded optical fiber inline intrinsic Fabry–Perot interferometer and extrinsic Fabry–Perot interferometer as temperature and pressure sensing elements, respectively. A CO2 laser was used to create a loss between them to balance their reflection power levels. The multiplexed signals were demodulated using a Fast Fourier transform-based wavelength tracking method. Experimental results showed that the sensing system could measure temperature and pressure unambiguously in a pressure range of 0 to 6.895×105u2009u2009Pa and a temperature range from 20°C to 700°C.

In vitro study of improved wound-healing effect of bioactive borate-based glass nano-/micro-fibers

Because of the promising wound-healing capability, bioactive glasses have been considered as one of the next generation hard- and soft-tissue regeneration materials. The lack of understanding of the substantial mechanisms, however, indicates the need for further study on cell-glass interactions to better interpret the rehabilitation capability. In the present work, three bioactive glass nano-/micro-fibers, silicate-based 45S5, borate-based 13-93B3 and 1605 (additionally doped with copper oxide and zinc oxide), were firstly compared for their in vitro soaking/conversion rate. The results of elemental monitoring and electron microscopic characterization demonstrated that quicker ion releasing and glass conversion occurred in borate-based fibers than that of silicate-based one. This result was also reflected by the formation speed of hydroxyapatite (HA). This process was further correlated with original boron content and surrounding rheological condition. We showed that an optimal fiber pre-soaking time (or an ideal dynamic flow rate) should exist to stimulate the best cell proliferation and migration ability. Moreover, 13-93B3 and 1605 fibers showed different glass conversion and biocompatibility properties as well, indicating that trace amount variation in composition can also influence fibers bioactivity. In sum, our in vitro rheological module closely simulated in vivo niche environment and proved a potentially improved wound-healing effect by borate-based glass fibers, and the results shall cast light on future improvement in bioactive glass fabrication.

Microwave interrogated large core fused silica fiber Michelson interferometer for strain sensing

A Michelson-type large core optical fiber sensor has been developed, which is designed based on the optical carrier-based microwave interferometry technique, and fabricated by using two pieces of 200-μm diameter fused silica core fiber as two arms of the Michelson interferometer. The interference fringe pattern caused by the optical path difference of the two arms is interrogated in the microwave domain, where the fringe visibility of 40xa0dB has easily been obtained. The strain sensing at both room temperature and high temperatures has been demonstrated by using such a sensor. Experimental results show that this sensor has a linear response to the applied strain, and also has relatively low temperature-strain cross talk. The dopant-free quality of the fused silica fiber provides high possibility for the sensor to have promising strain sensing performance in a high temperature environment.

Comparison of Silica and Sapphire Fiber SERS Probes Fabricated by a Femtosecond Laser

Different types of fibers were compared for construction of reflection-based surface-enhanced Raman-scattering (SERS) fiber probes. The probes were made by direct femtosecond (fs) laser micromachining of nanometer structures on the fiber endface and subsequent chemical plating of a thin layer of silver. Rhodamine 6G solutions were used to evaluate the performance of the SERS probes. In comparison with the silica fibers, the single-crystal sapphire fiber has much lower background Raman scattering. The fs laser is found effective to fabricate high-quality sapphire fiber SERS probes for detection of weak Raman signals in a reflection configuration.

Interferogram Reconstruction of Cascaded Coaxial Cable Fabry-Perot Interferometers for Distributed Sensing Application

This paper describes a distributed sensing concept using coaxial cable-based Fabry-Perot interferometers (CCFPIs). Multiple reflectors are implemented along a coaxial cable, where every two consecutive reflectors can be considered as a low finesse CCFPI, which has a relatively weak reflection coefficient and insertion loss. The interferogram in a frequency domain of each individual CCFPI could be reconstructed through the proposed signal processing method, so that the phase detection could be applied to any CCFPIs on one cable to achieve high measurement accuracy. A large capacity sensor network with a relatively high measurement accuracy can be implemented simultaneously. The concept takes advantage of the time-domain multiplexing method and the pure frequency domain measurement, which is herein called a joint-time-frequency demodulation technique. Due to its effectiveness and robustness, the device is especially attractive for structural, downhole, or underwater applications.

Highly efficient Er/Yb-codoped fiber amplifier with an Yb-band fiber Bragg grating

In this Letter, a high-power Er/Yb-codoped fiber amplifier (EYDFA) with a high-reflection Yb-band fiber Bragg grating (FBG) at the pump end is experimentally investigated. The FBG was inscribed on a piece of double-clad fiber with a center wavelength of 1032 nm. Due to the selective reflection of the backward Yb-band amplified spontaneous emission (Yb ASE) by the FBG, a co-pump-propagating Yb-band auxiliary signal was generated. Because of the stimulated amplification and reabsorption of the auxiliary signal, the Yb ASE was dramatically suppressed and the pump conversion efficiency (PCE) of the EYDFA was notably improved. An output power of 6.48 W was achieved at a pump power of 16.5 W, which is equivalent to a PCE of ∼39%. The slope efficiency relative to applied pump power was ∼40%. The maximum output power was improved ∼20% because of the introduction of the FBG.

Fano resonances in cone-shaped inwall capillary based microsphere resonator

In this paper, we demonstrate a cone-shaped inwall coupler for excitation of the whispering-gallery modes (WGMs) of a microsphere resonator. The coupler is composed of a single mode fiber (SMF) and a capillary with an inner diameter of 5 μm. After immersing the capillary front end vertically into Hydrofluoric acid to obtain a cone inside the capillary, light in the SMF couples into the capillary efficiently while the hollow core is wide enough for a microsphere to be inserted. Because the front end face of the capillary acts as a reflector, a Fano resonance with an asymmetric line shape and a Q-factor of 2.57 × 104 is observed in the reflection spectrum using a barium titanite glass microsphere with a diameter of 45 μm. The integrated resonator structure has the advantages such as the reflective type, alignment-free and mechanically robust, making it have great potential in sensing applications and optical switching.