Hongyun Meng

Single-Mode-Multimode Fiber Structure Based Sensor for Simultaneous Measurement of Refractive Index and Temperature

A fiber sensor for simultaneous measurement of refractive index (RI) and temperature in solutions based on multimode interference is presented. The intensity and the wavelength of the interference minimum will vary with the RI and the temperature of the solution, respectively. The sensitivity of the RI and the temperature are 94.58 dB/RI and 0.0085 nm/°C, respectively. Its ease of fabrication and low-cost offer the attractive applications in chemical and biological sensing.

Three Channel-Spacing Switchable Multiwavelength Fiber Laser With Two Segments of Polarization-Maintaining Fiber

A three channel-spacing tunable multiwavelength fiber ring laser by using two segments of polarization-maintaining fiber (PMF) is experimentally demonstrated. By adjusting the polarization controllers, the wavelength spacing could be efficiently switched among 0.48, 0.73, and 1.45 nm. Moreover, we also analyzed theoretically the equivalent Lyot birefringence fiber filter with two segments of PMF. Theoretical prediction was verified by experimentally obtained multiwavelength outputs.

Simultaneous Measurement of Refractive Index and Temperature Based on Modal Interference

A simple optical fiber sensor configuration for simultaneous measurement of refractive index (RI) and temperature based on modal interference is proposed and experimentally demonstrated. The sensing configuration is formed by splicing two multimode fibers among three single mode fibers. Due to the different sensitivity responses of the two wavelength transmission dips formed by the cladding modes interfering with the core mode, it is possible to measure the RI and temperature by monitoring the wavelength shifts of the two transmission dips. The experimental results indicate that the sensing sensitivities of RI and temperature are -37.9322 nm/RIU and 0.0522 nm/°C within the RI range from 1.3105 to 1.3517 and the temperature range from 25°C to 85°C, respectively. The proposed sensor configuration features the advantages of easy to fabricate, robust, cost effective, and high sensitivity, making it exhibit potential applications in physical, biological, and chemical sensing.

Long distance fiber-optic displacement sensor based on fiber collimator

A simple fiber-optic displacement sensor based on reflective intensity modulated technology is demonstrated using a fiber collimator. The sensing range is over 30 cm, which is over 100 times that of the conventional fiber-optic displacement sensor based on the normal single-mode fiber. The measured data are fitted into linear equation very well and the values of R-square are more than 0.995. The sensitivity of the device achieves 0.426 dB∕cm over the range of 5-30 cm. By applying the relative technique, the errors resulted from the fluctuation of light source and influences of environment are effectively eliminated, and the stability for wide range measurement can be improved. The simplicity of the design, high dynamic range, stability and the ease of the fabrication make it suitable for applications in industries.

Polarization-Independent All-Fiber Quasi-Flat-Top Comb Filter Based on a Dual-Pass Mach–Zehnder Interferometer With High Birefringence Fiber in the Second Loop

A polarization-independent all-fiber comb filter with quasi-flat-top spectral response based on a dual-pass Mach-Zehnder (M-Z) interferometer is proposed and demonstrated. The proposed filter consists of a dual-pass M-Z interferometer with a section of high birefringence fiber (HBF) and a polarization controller (PC) in the second loop. The theoretical analysis shows that the apparatus allows to operate as a polarization-independent multiwavelength periodic filter and to gain the quasi-flat-top passband filter by adjusting the polarization state of the PC. Theoretical prediction was verified by experimental demonstration.

Simultaneous measurement of temperature and strain by combining a fiber Bragg grating and the pigtail fiber covered with epoxy resin

A fiber sensor for simultaneous measurement of temperature and strain based on a fiber Bragg grating (FBG) with the pigtail fiber covered with epoxy resin is presented. The side mode suppression ratio of the FBG will vary with the temperature due to the Fresnel reflection from the interface between the pigtail fiber and the epoxy resin whose refractive index is sensitive to the temperature. The sensor is also capable of simultaneous measurement temperature and strain by combining the Bragg wavelength shift characteristics as the temperature and strain of the FBG.

Visible-wavelength metalenses for diffraction-limited focusing of double polarization and vortex beams

In recent years, two-dimensional functional optical devices utilizing metasurfaces to manipulate phases of light develop rapidly. In this paper, we demonstrated metalenses according to the geometric Pancharatnam–Berry phase concept based on zinc sulfide (ZnS) material. Metalenses at the visible wavelengths λ=405, 532 and 633 nm have the capacity to focus incident light down to diffraction-limited spots with corresponding transfer efficiencies of 72%, 65%, 67%, respectively. A full-hybrid metalens was developed to adapt for double-polarized light focusing, which altered the condition that metalenses designed by geometric phase concepts could not focus different polarized light into one spot. In addition, we realized the conversion of the circularly polarized plane light into a vortex beam and focusing the vortex beam simultaneously by one device.

Multifunctional Sensors and Switch in MDM Waveguide With Symmetric Dual Side-Coupled Nanodisks

A multirole waveguide with symmetric dual side-coupled nanodisk resonators, which can act as refractive index sensor, temperature sensor, and optical switch, is proposed and investigated numerically. By the finite-difference time-domain simulations, it is demonstrated that the value of the refractive index sensitivity of the nano-sensor can reach 1333 nm/RIU. And with ethanol fully filled in the resonators, it can act as a temperature sensor with temperature sensitivity of 0.52 nm/°C. Furthermore, by filling with liquid crystal material, the transmittance of the optical switch is up to 73.6% at the wavelength of 1310 nm. This letter may pave a way for multifunctional applications in the on-chip nano-sensing area.

A novel titration method based on fiber-optic refractive index sensing for the determination of deacetylation degree of chitosans

We describe a novel method for determining the degree of deacetylation (DD) of chitosans from fiber-optic measurements of refractive index. Theory analyses and the experimental setup of the method are introduced and discussed. The analytical performance of the method is described for the determination of alkaline titration end-points. Experimental results reveal that the equivalence point can be directly identified from the titration curve. The proposed method is simple, low-cost, accurate, reliable, and easy to operate for industrial application. The DD values of four chitosan samples obtained with this new method show good agreement with those yielded from 1H NMR. Such a mechanism of refractive-index monitor should open up a new application in the field of chitosanolytic enzymes, such as chitosanase, pectinase that are important in bioprocesses.

Analogue of electromagnetically induced absorption with double absorption windows in a plasmonic system

We report the observation of an analog of double electromagnetically induced absorption (EIA) in a plasmonic system consisting of two disk resonators side-coupled to a discrete metal-insulator-metal (MIM) waveguide. The finite-difference time-domain (FDTD) simulation calculations show that two absorption windows are obtained and can be easily tuned by adjusting the parameters of the two resonance cavities. The consistence between the coupled-model theory and FDTD simulation results verify the feasibility of the proposed system. Since the scheme is easy to be fabricated, our proposed configuration may thus be applied to narrow-band filtering, absorptive switching, and absorber applications.