J.W. Yu

Novel all-fiber bandpass filter based on hollow optical fiber

We report an in-line all-fiber bandpass filter based on a hollow optical fiber (HOF) core mode blocker along with a long-period fiber grating (LPG) pair. It is theoretically and experimentally confirmed that selective core mode blocking at the HOF region located in the middle of the LPG pair could provide efficient passband channels corresponding to the resonant wavelengths of the LPGs. The filter characteristics in passbands and the nearfield patterns of guided modes in the proposed device are discussed.

Development of fiber optic BOTDA sensor for intrusion detection

We present a compact fiber optic Brillouin optical time domain analysis (BOTDA) sensor system, which has the capability of detecting and locating intrusion attempts over several tens of kilometers long paths. The system employs a laser diode and two electro-optic modulators. Simulation of an intrusion effect was achieved by use of a strain-inducing setup. Distance resolution of 3 m was obtained for a 4.81 km long optical fiber within 1.5 s. Actual intrusion detection experiment was also performed using a step-on stage setup and clearly discernable detection signals were obtained in less than 1.5 s. # 2002 Published by Elsevier Science B.V.

Analysis of Brillouin frequency shift and longitudinal acoustic wave in a silica optical fiber with a triple-layered structure

We report a thorough analysis on the Brillouin frequency shift as a function of geometrical parameters in a silica optical fiber consisting of triple-layered structure, GeO/sub 2/-doped core, P/sub 2/O/sub 5/, and F co-doped inner cladding, and pure silica outer cladding. General characteristic equations for the Brillouin frequency shift were analytically derived and analyzed for various fiber parameters. In experiments, three-layered optical fibers were fabricated and their Brillouin frequency shifts were measured in the wavelength region of 1.55 /spl mu/m by a pump-probe technique. The longitudinal acoustic velocity in each layer was found significantly affected by the thermal stress as well as the dopant concentrations. We confirmed both in theory and experiment that the inner cladding of a three-layered optical fiber does provide a new degree of freedom in precise control of the Brillouin frequency shift.

New in-line fiber band pass filters using high silica dispersive optical fibers

Abstract New types of in-line fiber filters whose core and cladding are composed of binary silica doped with either boron or fluorine are proposed. Utilizing dispersive characteristics of SiO 2 –B 2 O 3 and SiO 2 –F systems, we demonstrate that an optical fiber, with borosilicate core and fluorosilicate cladding, shows short-pass filter response. Experimentally, we fabricated a short-pass filter fiber that could be used as a 1310/1550 nm WDM filter. We also propose theoretically that a long-pass filter could be obtained in a fiber structure whose core is fluorosilicate with borosilicate cladding. In a special long-pass filter structure, we found that the normalized frequency can be kept uniform over a wide wavelength range from 1200 to 1700 nm, which will be applied in wideband wavelength division multiplexing devices.

Brillouin frequency shifts in silica optical fiber with the double cladding structure.

We report theoretical and experimental analysis on Brillouin frequency shift in silica optical fibers with the double cladding structures that are comprised of GeO2-doped core, P2O5- and F-codoped inner cladding and silica outer cladding. The intrinsic Brillouin frequency shift was calculated for various fiber parameters utilizing boundary conditions for longitudinal acoustic waves. Optical fibers with different fiber parameters were fabricated and the Brillouin frequency shifts were measured in the wavelength region of 1.55m. We confirmed that the inner cladding in an optical fiber could provide a new degree of freedom in controlling the Brillouin frequency shift.

Ultra-fast acoustically tunable all-fiber polarization controller based on a hollow optical fiber

Local deformation of circular HOF induced by traveling acoustic wave results in a versatile control of SOP by varying frequency and voltage of RF signal. Traces of SOP on Poincare sphere are reported for various frequency and RF voltage ranges.

Acousto-optic polarization-dependent mode coupling in a dual-mode hollow optical fiber

We report acousto-optic polarization-dependent coupling in two-mode hollow optical fiber. Local deformation of circular symmetry by traveling acoustic wave results in high birefringence making it suitable for polarization control devices.

Development of intrusion detection technique using fiber optic ROTDR sensor

The developing of buried fiber optic sensor with high sensitivity and broad-area detecting intruders is carried out using fiber optic ROTDR(Rayleigh Optical Time Domain Reflectometry). The sensing part was designed to be able to broad-area detect intrusion effect per optical fiber length under ground. The bending light losses in optical fibers are investigated by commercial mini ROTDR with wavelength , distance range 5km, pulse width 20ns, SNR

High silica dispersive optical fiber and its application as an in-line short pass fiber filter

Summary form only given. In this study, a dispersive fiber based on a high silica glass host is fabricated for the first time. The dispersive characteristics of the index difference was achieved using the index variation of SiO/sub 2/-B/sub 2/O/sub 3/ and SiO/sub 2/-F glass. To make a short-pass filter, the core and cladding compositions were chosen as SiO/sub 2/-B/sub 2/O/sub 3/ and SiO/sub 2/-F respectively.

A new in-line long-wavelength-pass filter using a high silica dispersive fiber

We propose an in-line fiber long-wavelength-pass filter using high silica dispersive fiber composed of SiO/sub 2/-B/sub 2/O/sub 3/ cladding and SiO/sub 2/-F core. The normalized frequency of this dispersive fiber was designed to be uniform over a wide wavelength range from 1.2 to 1.7 /spl mu/m which could be applied in wavelength-insensitive coupling devices for wavelength division multiplexing system.