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We describe the implementations of Drude-critical point model for describing dispersive media into flnite difierence time domain algorithm using piecewise-linear recursive-convolution and auxiliary difierential equation methods. The advantages, accuracy and stability of both implementations are analyzed in detail. Both implementations were applied in studying the transmittance and re∞ectance of thin metal fllms, and excellent agreement is observed between analytical and numerical results.

We present a fiber-optic multibeam Mach-Zehnder interferometer (m-MZI) for simultaneous multi-parameter measurement. The m-MZI is comprised of a section of photonic crystal fiber integrated with two independent cores of distinct construction and birefringence properties characterized for torsion, strain and temperature sensing. Due to the presence of small core geometry and use of a short fiber length, the sensing device demonstrates inter-modal interference in the small core alongside the dominant inter-core interference between the cores for each of the orthogonal polarizations. The output spectrum of the device is characterized by the three-beam interference model and is polarization-dependent. The two types of interferometers present in the fiber m-MZI exhibit distinct sensitivities to torsion, strain and temperature for different polarizations, and matrix coefficients allowing simultaneous measurement of the three sensing parameters are proposed in experiment.

Photonic crystal fibers (PCFs) with regularly placed air holes running along the fiber oer flexible design and unique transmission characteristics, like unlimited single-mode operation, that are hard to obtain in conventional optical fibers. In this paper, we will discuss the design, fabrication and sensor applications of photonic crystal fibers, particularly twin-core photonic crystal fibers (TCPCFs) and highly birefringent photonic crystal fibers (HB-PCFs). A numerical analysis of PCFs with various design was performed using a computer code developed with finite element method (FEM). Fabrication of PCFs is mainly based on the well-known stack-and-draw method. Controlled gas pressurization was employed during the fiber drawing process, and the microstructure of PCFs was well preserved by pressurizing the core and cladding regions independently. We will also describe the sensor applications of the fabricated PCFs for measuring the strain, bending, and transverse loads, e.g., TC-PCF-based in-line interferometers and HB-PCF-based birefringent interferometers. In the case of a TC-PCF-based in-line sensor, the small dierence in the eective indices of the two core modes leads to interference fringes, and the birefringence due to the twin cores results in polarization-dependent fringe spacing. A novel intensity-based bend sensor is demonstrated utilizing the bend-induced spatial fringe shift. With a HB-PCF inserted between two linear polarizers, the resulting interference pattern can be used to obtain the transverse load sensitivity for dierent angles of the applied load.

We have experimentally investigated the multi-parameter sensing characteristics in a novel all-fiber Sagnac loop hybrid interferometer based on a highly birefringent photonic crystal fiber with two asymmetric cores. The sensor device was based on a combination of two types of in-fiber interferences, the intra-core-mode Sagnac interference and the inter-core-mode Mach-Zehnder interference due to the distinct birefringent properties associated with the asymmetric cores. Fast Fourier transform analysis on the transmission spectra of the device exhibited six clear peaks in the spatial frequency domain. By examining the phase shift responses of two distinct Sagnac and one Mach-Zehnder interference peaks, the response matrix that enable simultaneous measurement of torsion, strain, and temperature could be obtained. The proposed all-fiber Sagnac loop hybrid interferometer has the advantages such as simplicity of the device structure, compact device size, and capability for simultaneous sensing of multiple parameters.

The transmission characteristics of multi-channel long period fiber gratings (LPFGs) in terms of the physical parameters like the separation distance, grating length and number of gratings will be discussed. Their transmission characteristics such as channel spacing, number of channels, loss peak depth, and channel bandwidth can be easily controlled by physical parameters. Based on the experimental results, their applications to optical multiwavelength Raman lasers and optical sensors will be investigated. A multiwavelength Raman fiber ring laser with 9 WDM channels with 100 ㎓ spacing and 19 channels with 50 ㎓ spacing using tunable multi-channel LPFGs will be experimentally demonstrated. The fiber-optic sensing applications with high resolution and sensitivity based on multi-channel LPFGs will be also presented.

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A novel method for auto-correction of fiber optic distributed temperature sensor using anti-Stokes Raman back-scattering and its reflected signal is presented. This method processes two parts of measured signal. One part is the normal back scattered anti-Stokes signal and the other part is the reflected signal which eliminate not only the effect of local losses due to the micro-bending or damages on fiber but also the differential attenuation. Because the beams of the same wavelength are used to cancel out the local variance in transmission medium there is no differential attenuation inherently. The auto correction concept was verified by the bending experiment on different bending points.

We will discuss fabrication of twin core photonic crystal fiber (TC-PCF) using the stack-and-draw method and its application for in-line Mach-Zehnder interferometers. The small difference in the effective indexes of the two core modes leads to interference fringes and the birefringence of the twin cores results in polarization-dependent fringe spacing. The strain sensitivity was negative and wavelength-dependent. A novel intensity-based bend sensor is also demonstrated with bend-induced spatial fringe shift. High air filling fraction of fabricated TC-PCF cladding provides immunity to bend-induced intensity fluctuation.

We propose and experimentally demonstrate a novel method for multi-wavelength erbium-doped fiber laser by using fiber Bragg gratings written in few-mode side-hole fiber with an elliptical core. The resonance peaks can be made to split by properly adjusting the polarization state due to the high birefringence of the fiber with the elliptical core. The number of lasing wavelengths can thus be switched using the polarization controller. This multi-wavelength laser has the advantages of low cost, novel and simple configuration.

A novel and simple multi-wavelength linear-cavity tunable fiber laser source using a chirped fiber Bragg grating (CFBG) and a few-mode fiber Bragg grating (FMFG) is demonstrated using erbium-doped fiber (EDF) as the gain medium. In our linear-cavity configuration, the FMFG acts as full-reflecting mirror and wavelength selector while the CFBG with the 3-dB bandwidth of over 30 nm acts as a broadband partially reflecting mirror. The number of lasing wavelengths can be controlled by changing the state of polarization inside the cavity using a polarization controller. The large bandwidth of the CFBG enables continuous tuning of the lasing wavelengths by application of mechanical strain or thermal heating on the FMFG.

We propose a simple erbium-doped fiber laser configuration for obtaining multi-wavelength oscillation at room temperature, in which a few-mode fiber Bragg grating was used as the wavelength-selective component. An amplitude variation of 1.6 dB over 120 second period was obtained for three-wavelength oscillation at room temperature, which demonstrates stability of the output power. This multi-wavelength laser can be switched between dual- and triple-wavelength operations by properly adjusting polarization controller in the cavity. This multi-wavelength laser has the advantage of simple configuration, high stability, low cost and stable operation at room temperature.

We propose a new fiber-type all-optical switching device based on the optical nonlinearity of Yb(3+) doped fiber and a long-period fiber gratings(LPG) pair. The all-optical ON-OFF switching with the continuous wave laser signal at ~1556nm in the LPG pair including the 25.5cm long Yb(3+) doped fiber was demonstrated up to ~200Hz upon pumping with the modulated square wave pulses at 976nm, where a full optical switching with the ~18dB extinction ratio was obtained at the launched pump power of ~35mW.

A tunable comb filter based on a fiber loop mirror setup, which incorporates a piece of pumped erbium-ytterbium co-doped polarization maintaining fiber, is newly presented. It is accomplished by controlling the pump power or adjusting a polarization controller in the loop mirror, which results from the fact that the effective birefringence of the erbium-ytterbium co-doped polarization maintaining fiber depends on the pump power and polarization state of the traversing signal. By using the proposed comb filter, a continuously tunable multiwavelength fiber ring laser in the L-band is successfully demonstrated.

The effect of CO2 laser irradiation on the refractive-index change in optical fibers is investigated by measuring the interference fringe shift formed by a long-period fiber grating pair. The refractive-index decrease on CO2 laser irradiation was due to relaxation of the residual stress, which was formed in optical fibers during the drawing process, and the refractive-index decrease was found to increase linearly with the drawing force. The effect of the CO2 laser output power on residual-stress relaxation, and fiber elongation was also studied.

The Advanced Photon Source (APS) storage ring will utilize a closed-orbit feedback system in order to produce a more stable beam. The specified orbit measurement resolution is 25 microns for global feedback and 1 micron for local feedback. The system will sample at 4 kHz and provide a correction bandwidth of 100 Hz. At this bandwidth, standard rf BPMs will provide a resolution of 0.7 micron, while specialized miniature BPMs positioned on either side of the insertion devices for local feedback will provide a resolution of 0.2 micron (1). The measured BPM noise floor for standard BPMs is 0.06 micron per root hertz mA. Such a system has been designed, simulated, and tested on a small scale (2). This paper covers the actual hardware design and layout of the entire closed-loop system. This includes commercial hardware components, in addition to many components designed and built in-house. The paper will investigate the large-scale workings of all these devices, as well as an overall view of each piece of hardw...

Beam position monitors using stripline pickups for 30 ns long electron and positron beam bunches have been built and responses were measured in the vertical and horizontal directions. Log amplifiers used for signal processing have a dynamic range of 40 dB and are scaled for 50 mV/dB sensitivity. In this paper we describe the design of the detectors, the signal processing electronics, and the results of the position‐to‐signal mapping using a wire. Beam position measurements using a prototype detector and electronics on the APS linac test stand are discussed.

We report a simple fiber sensor for measurement of high temperature with high sensitivity. The sensing head is a multimode-single mode-multimode (MM-SM-MM) fiber configuration formed by splicing a section of uncoated single mode fiber (SMF) with two short sections of multimode fibers (MMF) whose core is composed of pure silica. Because of the mode-field mismatch at the splicing points of the SMF with 2 sections of MMFs, as well as index matching between the core of the MMF and the cladding of the SMF, optical power from the lead-in fiber can be partly coupled to the cladding modes of the SMF through the MMF. The cladding modes of the SMF then re-coupled to the lead-out fiber, in the same fashion. Due to the effective index difference between the core and cladding modes, an interference pattern in the transmission spectrum of the proposed device was obtained. The interference pattern was found to shift to the longer wavelength region with respect to temperature variation. The temperature sensor can measure temperature stably up to more than 900 degrees C with sensitivity of 0.088 nm/ degrees C.

We firstly report on the fabrication of Cu(2+)-doped germano-silicate glass fiber for nonlinear optical devices application by using modified chemical vapor deposition and solution doping processes. Broadband absorption near 700nm due to the 3d-shell electron transitions of Cu(2+) ions from the ground state to the excited states was observed. The resonant nonlinearity of the Cu(2+)-doped fiber was estimated to be 5.5x10(-17)m(2)/W by measuring the phase shift of the fringes obtained from the long-period fiber grating pair upon pumping with a laser diode at 980nm and non-resonant nonlinearities were also measured to be 4.114x10(-21)m(2)/W by the continuous wave self-phase modulation method.

The temperature sensitivity of modal birefringence (dB/dT) of different types of polarization-maintaining fibers with side holes was measured using a Sagnac loop interferometer. The thermal expansion coefficient can be varied by controlling the amount of germanium doped in the core region. Using this method, dB/dT could be made higher (~10(-7)/ degrees C) than that of standard PMFs (~10(-8)/ degrees C) or comparable to that of standard PMFs (~10(-9)/ degrees C).

We propose and experimentally demonstrate a tunable multi-wavelength SOA fiber laser based on a Sagnac loop mirror using elliptical core side-hole fiber. We fabricated different types of elliptical core side-hole fiber with elliptical or circular cladding shape. The measured modal birefringence of the fabricated fiber was 1.7x10(-4) (elliptical shape) and 1.16x10(-4) (circular shape), respectively. By carefully adjusting the polarization controller inside the cavity, we could obtain 18 discrete channels with SNR over 30 dB and channel spacing of 0.8 nm and 10 discrete channels with SNR over 30 dB and channel spacing of ~1.4 nm. The proposed fiber laser was rather stable and the temporal power fluctuation was less than 0.8 dB. In addition, by thermally heating the elliptical core side-hole fiber in the Sagnac loop, we could obtain a tunable multi-wavelength fiber laser.

We present an upstream transmission method in- dependent of temperature characteristics of the remote node (RN) in a WDM-PON. This method employs a self-injection locked Fabry-Perot laser diode (F-P LD) for upstream trans- mission in the optical network unit (ONU). Using this method, the sidemodes of the F-P LD are suppressed, and the F-P LD is matched to the center wavelength of the wave- length distributor/combiner placed at the RN. The experi- mental results confirm that bidirectional error-free transmis

A practically tunable multiwavelength Raman fiber laser based on few-mode fiber Bragg gratings without additional multichannel filters is investigated. We achieved high quality of the Raman laser output with a high extinction ratio of more than 45 dB. The number of lasing wavelengths can be adjusted by the properties of few-mode Bragg gratings with multiple resonant wavelengths. The lasing wavelength of Raman fiber laser can be readily controlled by the tension and compression strain, which correspond to the directional bending curvature change. The dynamic range of lasing wavelength change was more than 15 nm.

Unambiguous simultaneous measurement of strain and temperature based on dual long-period fiber gratings by controlling their thermal and strain sensitivities is proposed and experimentally demonstrated. The difference in the wavelength peak shift and the separation with the variation of strain and temperature allows discrimination between the strain and temperature effects, respectively.

We developed a Finite Element package to analyze cladding mode field extensions into the air-holes of photonics crystal fiber for refractive index sensing. Our analysis could determine the most sensitive cladding mode for liquid sensing.

25th International Conference on Optical Fibre Sensors (OFS), SOUTH KOREA, APR 24-28, 2017; International audience; Fiber Bragg Gratings (FBGs) are used to measure shock velocity, detonation velocity, shock wave profile or pressure profile in inert and energetic materials. Such thin probe, with a diameter below 150 µm, can be inserted directly into materials without disturbing the physical phenomena. Chirped FBGs are used to track the shock wave in the grating using wavelengths. The velocity (few km/s) and shock wave profile measurements are realized by recording the CFBG's reflected spectral width. Pressure measurements at few GPa levels use dynamic spectrometers, two approaches are compared: parallel acquisition using an Arrayed-Waveguide-Grating and time-multiplexing by wavelength-to-time conversion using dispersion.