Yijian Huang

Asymmetrical in-fiber Mach-Zehnder interferometer for curvature measurement.

We demonstrated a compact and highly-sensitive curvature sensor based on a Mach-Zehnder interferometer created in a photonic crystal fiber. Such a Mach-Zehnder interferometer consisted of a peanut-like section and an abrupt taper achieved by use of an optimized electrical arc discharge technique, where only one dominating cladding mode was excited and interfered with the fundamental mode. The unique structure exhibited a high curvature sensitivity of 50.5 nm/m-1 within a range from 0 to 2.8 m-1, which made it suitable for high-sensitivity curvature sensing in harsh environments. Moreover, it also exhibited a temperature sensitivity of 11.7 pm/°C.

Surface plasmon resonance biosensor based on gold-coated side-polished hexagonal structure photonic crystal fiber

The refractive index sensing characteristics of the side-polished photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor are detailed investigated in this paper. We used the finite element method (FEM) to study the influences of the side-polished depth, air hole size, lattice constant, and the refractive index (RI) of the PCF material on sensing performance. The simulation results show that the side-polished depth, air hole size, lattice pitch have significant influence on the coupling strength between core mode and surface plasmon polaritons (SPPs), but have little influence on sensitivity; the coupling strength and sensitivity will significant increase with the decrease of RI of the PCF material. The sensitivity of the D-shaped PCF sensor is obtained to be as high as 21700 nm/RIU in the refractive index environment of 1.33-1.34, when the RI of the PCF material is controlled at 1.36. It revealed a new method of making ultra-high sensitivity SPR fiber sensor. Then we experimental demonstrated a SPR refractive sensor based on the side-polished single mode PCF and investigated the sensing performance. The experimental results of the plasmon resonance wavelength sensitivity agree well with the theoretical results. The presented gold-coated D-shaped PCF SPR sensor could be used as a simple, cost-effective, high sensitivity device in bio-chemical detection.

Liquid modified photonic crystal fiber for simultaneous temperature and strain measurement

A liquid modified photonic crystal fiber (PCF) integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids. The refractive index of the filled liquid is higher than that of background silica, which can not only support the transmitting rod modes but also the “liquid modified core” modes propagating between the PCF core and the liquid rods. Hence, the light propagating in the liquid modified core can be efficiently coupled into the satellite waveguides under the phase-matching conditions, resulting in a dramatic decrease of the resonant wavelength intensity. Furthermore, there is a multi-mode interference produced by modified core modes and rod modes. Such a compact (∼0.91  cm) device integrated with an embedded coupler and interferometer is demonstrated for high-sensitivity simultaneous temperature (∼14.72  nm/°C) and strain (∼13.01  pm/μϵ) measurement.

Broadband Thermo-Optic Switching Effect Based on Liquid Crystal Infiltrated Photonic Crystal Fibers

We demonstrate a liquid-crystal-filled photonic crystal fiber (PCF) and investigate its temperature response with a unique liquid crystal (LC) clearing point of 58 °C. Opposite temperature responses are observed at the temperature that is lower and higher than the LCs clearing point, respectively. Such a LC-filled PCF could be used to develop a promising optical switch with a broadband operation range of 102.5 nm via a small temperature change of less than 1.5 °C. Moreover, the LC-filled PCF exhibited an ultrahigh temperature sensitivity of 105 nm/°C and could find potential applications in the field of temperature sensors.

Ultra-sensitive temperature sensor based on liquid crystal infiltrated photonic crystal fibers

We investigated experimentally liquid crystal (LC) filled photonic crystal fiber’s temperature responses at different temperature ranging from 30 to 80°C. Experimental evidences presented that the LC’s clearing point temperature was 58°C, which is consistent with the theoretical given value. The bandgap transmission was found to have opposite temperature responses lower and higher than the LC’s clearing point temperature owing to its phase transition property. A high bandgap tuning sensitivity of 105 nm/°C was achieved around LC’s clearing point temperature.

Mechanism and Characteristics of Humidity Sensing with Polyvinyl Alcohol-Coated Fiber Surface Plasmon Resonance Sensor

A surface plasmon resonance (SPR) sensor based on a side-polished single mode fiber coated with polyvinyl alcohol (PVA) is demonstrated for relative humidity (RH) sensing. The SPR sensor exhibits a resonant dip in the transmission spectrum in ambient air after PVA film coating, and the resonant wavelength shifts to longer wavelengths as the thickness of the PVA film increases. When RH changes, the resonant dip of the sensor with different film-thicknesses exhibits interesting characteristics for optical spectrum evolution. For sensors with initial wavelengths between 550 nm and 750 nm, the resonant dip shifts to longer wavelengths with increasing RH. The averaged sensitivity increases firstly and then drops, and shows a maximal sensitivity of 1.01 nm/RH%. Once the initial wavelength of the SPR sensor exceeds 850 nm, an inflection point of the resonant wavelength shift can be observed with RH increasing, and the resonant dip shifts to shorter wavelengths for RH values exceeding this point, and sensitivity as high as −4.97 nm/RH% can be obtained in the experiment. The sensor is expected to have potential applications in highly sensitive and cost effective humidity sensing.

Photonic crystal fiber with selective infiltration for high sensitivity simultaneous temperature and strain measurement

A selectively infiltrated photonic crystal fiber integrated with an embedded directional coupler and a multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids. The light propagated between the fiber core and the rods can efficiently be coupled into the satellite waveguides under the phase-matching conditions Furthermore, there is a multi-mode interference produced by fiber core modes and rod high order modes. Such a compact device is demonstrated for high sensitivity simultaneous temperature (∼14.72 nm/°C) and strain (∼13.01 pm/μs) measurement.

High-sensitivity bend sensor based on Mach-Zehnder interferometer using photonic crystal fiber

An optical fiber bend sensor assisted with a photonic crystal fiber(PCF) has been fabricated by splicing a section of photonic crystal fiber between two single mode fibers. Such a structure could be developed a Mach-Zehnder interferometer (MZI). The PCF-based MZI is sensitive to structure bending with a sensitivity of 6dB/m-1 and is independent on temperature only with a sensitivity of 0.01 dB/°C. Such a bend sensor can effectively reduce the cross-sensitivity between bend and temperature.