Yana Shang

Distributed OTDR-interferometric sensing network with identical ultra-weak fiber Bragg gratings

We demonstrate a distributed sensing network with 500 identical ultra-weak fiber Bragg gratings (uwFBGs) in an equal separation of 2m using balanced Michelson interferometer of the phase sensitive optical time domain reflectometry (φ-OTDR) for acoustic measurement. Phase, amplitude, frequency response and location information can be directly obtained at the same time by using the passive 3 × 3 coupler demodulation. Lab experiments on detecting sound waves in water tank are carried out. The results show that this system can well demodulate distributed acoustic signal with the pressure detection limit of 0.122Pa and achieve an acoustic phase sensitivity of around -158dB (re rad/μPa) with a relatively flat frequency response between 450Hz to 600Hz.

The Measurement System of Birefringence and Verdet Constant of Optical Fiber

The Faraday magneto-optical effect of optical fiber has many applications in monitoring magnetic field and electric current. When a linearly polarized light propagates in the direction of a magnetic field, the plane of polarization will rotate linearly proportional to the strength of the applied magnetic field, which following the relationship of θF =VBl. θF is the Faraday rotation angle, which is proportional to the magnetic flux density B and the Verdet constant V . However, when the optical fiber contains the effect of linear birefringence, the detection of Faraday rotation angle will depend on the line birefringence. In order to determine the Verdet constant of an optical fiber under a linear birefringence, the fiber birefringence needs to be accurately measured. In this work, a model is applied to analyze the polarization properties of an optical fiber by using the Jones matrix method. A measurement system based on the lock-in amplifier technology is designed to test the Verdet constant and the birefringence of optical fiber. The magnetic field is produced by a solenoid with a DC current. A tunable laser is intensity modulated with a motorized rotating chopper. The actuator supplies a signal as the phase-locked synchronization reference to the signal of the lock-in amplifier. The measurement accuracy is analyzed and the sensitivity of the system is optimized. In this measurement system, the Verdet constant of the SMF-28 fiber was measured to be 0.56±0.02 rad/T·m at 1550nm. This setup is well suitable for measuring the high signal-to-noise ratio (SNR) sensitivity for lock-in amplifier at a low magnetic field strength.

Remote detection of the surface-enhanced Raman spectrum with the optical fiber nanoprobe

Optical fiber nanoprobe with gold nanoparticles substrate on the surface was prepared by electrostatic self-assembly technology. Surface-enhanced Raman spectrum of the cells was measured using the optical fiber nanoprobe by remote detection method and direct detection method using confocal Raman micro-spectroscopy. The spectrum were analyzed with the detailed chemical components. The remote detection method using the optical fiber nanoprobe could make the probe inserting into the cells or tissue, and that may be helpful for the online SERS measurement of the cells in the biomedical research and diagnosis in the future.

Cerium doped silica scintillating fiber sensor for γ radiation measurement

Remote optical fiber sensors for radiation measurement are very useful in high radiation fields. In this paper, we fabricated scintillating optical fiber by using a cerium-doped silica rod. In the drawing process, we obtained different fiber samples by changing the drawing temperature and speed. The drawing temperature is from 1900 to 2200 °C and the speed is from 1 to 10 m/min. The experimental results showed that the optical rod physical properties such as viscosity, tension and scintillating efficiency can be controlled by the parameters of temperature and speed. The optical properties and chemical composition of the scintillating optical fiber have been analyzed by Raman spectra and X-ray fluorescence spectrometer (XRF-1800, SHIMADZU). The concentration of the doped cerium is 0.55%. Moreover, a test system is proposed to measure the scintillating performance of the fabricated optical fibers. For the scintillating properties, the effect of fiber length, the number of fiber bundle and the detection angle were analyzed. Experimental results showed that the optimal length of the cerium doped fiber is ~15 cm. The scintillating light intensity increases linearly with the number of the fiber bundle. With two low intensity 60Co (0.2784 μCi) and 137Cs (1.0865 μCi) gamma radiation sources, the scintillating light can be detected the gamma sources by using the scintillating fiber sensor which is connected a MMF.

PbS Quantum Dots Filled Photonic Crystal Fiber for All-fiber Amplifier

In this paper, we have proposed a novel type of fiber amplifier by filling the PbS semiconductor quantum dots into the holes of photonic crystal fibers (PCFs) for the first time. Based on simulation results, we have found that the loss of PCF filled with PbS is slightly increased compared with the one without PbS at wavelength of 1310 nm. Furthermore, we have successfully fabricated the PbS-filled PCF with selective air-hole cladding by a new perfusion technique that can optimize the overall loss.

Decrease scattering loss induced by surface roughness through waveguide structure optimization

This paper focuses on a method to decrease the scattering loss induced by surface roughness through waveguide structure optimization. First, the concept of roughness is discussed briefly, and the diagram of waveguide surface roughness tested by optical profiler is given. Then, this report mainly analyzes the influence on scattering loss coefficient and total loss coefficient induced by surface roughness under different waveguide parameters. The study finds that the scattering loss coefficient and the total loss coefficient increase as roughness increasing. Last, the part produces a method to decrease scattering loss induced by roughness through waveguide structure optimization importantly. It is found that the total scattering loss coefficient can be decreased greatly if waveguide core size is in range from 60 μm to 80 μm or the parameter Δ is smaller than 0.016. When surface roughness is 200 nm, the correlation length is 4 μm, waveguide length is 100 cm, and core width (height, a=b) is from 30 μm to 70 μm, the total scattering loss coefficient can decrease from 3.37×10-2 dB/cm to 1.65×10-2 dB/cm.

Physical characteristics and optical properties of PbS nanoclusters: DFT simulation and experimental study

The physical characteristics and optical properties of PbS nanoclusters are investigated by using density functional theory (DFT) of first-principles. Microstructure models of (PbS)n (n=1-9) nanoclusters and bulk materials are built on Materials Studio platform, and its energy band structures, highest occupied molecular orbital-lowest unoccupied molecular orbital gap (HOMO-LUMO gap), density of state (DOS), and optical properties are calculated, respectively. Compared to PbS bulk materials, PbS nanoclusters show a discrete energy gap as well as the DOS, because of the quantum confinement effect. It is interesting that the HOMO-LUMO gap of (PbS)n (n=1-9) shows oscillates with the increasing of the n number. However, when its size is large enough, the HOMO-LUMO gap is gradually decrease with the increasing of size (>27 atoms). And, the HOMO-LUMO gap of PbS nanoclusters of different sizes is range from 2.575 to 0.58 eV, which covers the low loss communication band of optical communication. In addition, PbS nanomaterials (NMs) with small size are synthesized by using oleylamine as ligands. Sizes of PbS NMs can be accurately controlled through control of the reaction time as well as the growth temperature. The photoluminescence (PL) spectra show strong size dependence, which is large red shift with increasing size of the NMs. This trend is basically in agreement with the theoretical calculation above. Moreover, transmission electron microscopy (TEM) further reveals the morphology of PbS NMs. PbS NMs can be used in optical fiber amplifiers and fiber lasers because of its unique optical properties in optical communication bands.

Fabrication of a Miniature Fiber-optic EFPI Pressure Sensor

A miniature(Φ300μm) fiber optic EFPI pressure sensor using SU-8 photoresist is fabricated. Both pressure and temperature characteristics have been studied, and it shows a good linearity within 100~700Pa with a sensitivity of 0.765nm/kPa.

The structural and optical properties of (PbS) n clusters in the silica optical fiber material

The structures and optical properties of (PbS)n cluster in silica optical fiber material are investigated. The microstructures models of (PbS)n (n=1-4) and PbS-(SiO2)n (n=1-6) have been built and calculated by Gaussian-03 software using density functional theory with the B3LYP level. The gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) is also calculated for microstructures. Compared with the (PbS)n clusters and (SiO2)n clusters, The HOMO-LUMO gaps of (PbS)n clusters combined with (SiO2)n clusters make a big difference. The geometry structures of (PbS)n-(SiO2)4 (n=2-4) clusters are calculated by using the singles configuration interaction (CIS) method. The calculation results show that the excitation energies of (PbS)n-(SiO2)4 clusters changed as the sizes or the structures are changed. The PbS-doped silica optical fiber is fabricated, and the optical properties are measured to compare with the theoretical results.