We demonstrate a compact power-referenced fiber-optic accelerometer using a weakly tilted fiber Bragg grating (TFBG) combined with an abrupt biconical taper. The electric-arc-heating induced taper is located a short distance upstream from the TFBG and functions as a bridge to recouple the TFBG-excited lower-order cladding modes back into the fiber core. This recoupling is extremely sensitive to microbending. We avoid complex wavelength interrogation by simply monitoring power change in reflection, which we show to be proportional to acceleration. In addition, the Bragg resonance is virtually unaffected by fiber bending and can be used as a power reference to cancel out any light source fluctuations. The proposed sensing configuration provides a constant linear response (nonlinearity < 1%) over a vibration frequency range from DC to 250 Hz. The upper vibration frequency limit of measurement is determined by mechanical resonance, and can be tuned by varying the sensor length. The tip-reflection sensing feature enables the sensor head to be made small enough (20~100 mm in length and 2 mm in diameter) for embedded detection. The polymer-tube-package makes the sensor sufficiently stiff for in-field acceleration measurement.

/pdf/tilted-fiber-grating-accelerometer-incorporating-an-abrupt-4ak1u44q1r.pdf

Tilted fiber grating accelerometer incorporating an abrupt biconical taper for cladding to core recoupling

A type of D-shaped photonic crystal fiber sensor based on surface plasmon resonance (SPR) is proposed for refractive index sensing and analyzed by the finite element method. The SPR effect between surface plasmon polariton modes and fiber core modes of the designed D-shaped photonic crystal fiber is used to measure the refractive index of the analyte. Numerical results show that the sensor can detect a range of refractive index ranging from 1.33 to 1.38. When the thickness of metal film is t=20  nm, the maximum sensitivity of 10,493  nm/RIU is obtained with a very high resolution of 9.53×10−6  RIU. The good sensing performance makes the proposed sensor a competitive candidate for environmental, biological, and biochemical sensing applications.

D-shaped photonic crystal fiber refractive index sensor based on surface plasmon resonance.

We propose As2S3 ring photonic crystal fiber (PCF) for supercontinuum generation of optical vortex modes. Due to the large material index contrast between As2S3 and air holes in the designed ring PCF, there is a two-orders-of-magnitude improvement of the difference between the effective refractive indices of different vortex modes compared with regular ring fiber. The design freedom of PCFs enables a low dispersion (<60  ps/nm/km variation in total) over a 522 nm optical bandwidth. Moreover, the vortex mode has a large nonlinear coefficient of 11.7/W/m at 1550 nm with a small confinement loss of <0.03  dB/m up to 2000 nm. An octave-spanning supercontinuum spectrum of the vortex mode is generated from 1196 to 2418 nm at −20  dB by launching a 120 fs pulse with a 60 W peak power at 1710 nm into a 1 cm long As2S3 ring PCF.

Octave-spanning supercontinuum generation of vortices in an As_2S_3 ring photonic crystal fiber

In this article, a hybrid photonic crystal fiber has been proposed for chemical sensing. A FEM has been applied for numerical investigation of some propagation characteristics of the PCF at a wider wavelength from 0.7 to 1.7 µm. The geometrical parameters altered to determine the optimized values. The proposed PCF contains three rings of circular holes in the cladding where the core is formulated with microstructure elliptical holes. The simulation result reveals that our proposed PCF exhibits high sensitivity and low confinement loss for benzene, ethanol and water than the prior PCFs. We have also shown that our proposed PCF shows high birefringence for benzene 1.544 × 10−3, for ethanol 1.513 × 10−3 and for water 1.474 × 10−3 at λ = 1.33 µm. The proposed PCF is simple with three rings which can be used for the sensing applications of industrially valuable lower indexed chemicals.

/pdf/hybrid-photonic-crystal-fiber-in-chemical-sensing-143vpjx2rs.pdf

Hybrid photonic crystal fiber in chemical sensing.

Highly nonlinear and highly birefringent dispersion compensating photonic crystal fiber

We propose a novel polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core and a cladding with squeezed-hexagonal-lattice elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental modes in such PCFs. Numerical result shows that very high modal birefringence with a magnitude of the order of 10−2 around 1550 nm has been obtained. Furthermore, large normal dispersion appears over a wide range of wavelengths in both orthogonal polarizations.

Highly birefringent elliptical-hole photonic crystal fiber with squeezed hexagonal lattice

In this letter, we propose a novel design for a polarization-maintaining index-guiding photonic crystal fiber (PCF). It is composed of a solid silica core, two big circular air holes near the core, and a cladding with elliptical air holes. Using a full-vector finite-element method, we study the modal birefringence of the fundamental mode in such a PCF. The numerical result shows that very high modal birefringence with magnitude of order of 10-3 has been obtained, which are higher than the birefringence induced by adding two big air holes near the core or using elliptical air holes in cladding separately

Highly Birefringent Elliptical-Hole Photonic Crystal Fiber With Two Big Circular Air Holes Adjacent to the Core

Coupling characteristics of dual-core photonic bandgap fibers with triangular photonic crystal cladding are investigated by use of a vector plane-wave expansion method and a vector finite-element method. We demonstrate the eigenmodes and the coupling length for two orthogonal polarizations. A decoupling phenomenon is found at a certain wavelength in this fiber configuration. The decoupling effect is attributed to the effect of surface modes on the eigenmodes. The decoupling wavelength decreases as the ratio of core radius to cladding air-hole pitch increases from 1.05 to 1.15.

Coupling and decoupling of dual-core photonic bandgap fibers.

Temperature-insensitive dynamic pressure measurement using a single fiber Bragg grating (FBG) based on reflection spectrum bandwidth modulation and optical power detection is proposed A specifically designed double-hole cantilever beam is used to provide a pressure-induced axial strain gradient along the sensing FBG and is also used to modulate the reflection bandwidth of the grating The bandwidth modulation is immune to spatially uniform temperature effects, and the pressure can be unambiguously determined by measuring the reflected optical power, avoiding the complex wavelength interrogation system The system acquisition time is up to 85Hz for dynamic pressure measurement, and the thermal fluctuation is kept less than 12% full-scale for a temperature range of −10°C to 80°C

Temperature-insensitive fiber Bragg grating dynamic pressure sensing system.

Transformation of an optical transmission mechanism was achieved when the holes of normal silica-guiding microstructure fiber (MF) were filled with nematic liquid crystal (NLC). Moreover, two photonic bandgaps (PBGs) were obtained by using a plane-wave method to create the pattern. The wavelength dependence of the effective mode area, leakage loss, and group velocity dispersion (GVD) has been theoretically investigated by using a full-vector finite-element method with anisotropic perfectly matched layers. The results reveal that the characteristics of the NLC-filled PBG-MFs are particularly wavelength dependent. This research gives a physical insight into the propagation mechanism in MFs and is crucial for future transmission applications.

Chunshu Zhang

Papers

Highly birefringent elliptical-hole photonic crystal fiber with squeezed hexagonal lattice

Highly Birefringent Elliptical-Hole Photonic Crystal Fiber With Two Big Circular Air Holes Adjacent to the Core

Coupling and decoupling of dual-core photonic bandgap fibers.

Temperature-insensitive fiber Bragg grating dynamic pressure sensing system.

Transformation of a transmission mechanism by filling the holes of normal silica-guiding microstructure fibers with nematic liquid crystal.