Kiegon Im

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.

In-line Variable Optical Attenuator Based on the Bending of the Tapered Single Mode Fiber

We propose a simple in-line variable optical attenuator (VOA) based on the bending effect of tapered single mode fibers. The influence of the taper structure and the reflective index of the external medium surrounding the taper region on the bending loss of the tapered fiber have been investigated experimentally. An attenuation range exceeding 35 dB and a very low excess loss of < 0.2 dB at 1550 nm were achieved. The measured polarization dependent loss of the present VOA at the attenuation level of 10 dB, 20 dB, and 30 dB were 0.1 dB, 0.2 dB, and 0.5 dB, respectively.

Side-Coupled Asymmetric Plastic Optical Fiber Coupler for Optical Sensor Systems

This paper reports a side-coupled asymmetric

High Sensitivity Refractive Index Sensor Based on a Wet-Etched Fused Fiber Coupler

1{\times}2

Enhancement of FBG Multiplexing Capability Using a Spectral Tag Method

plastic optical fiber coupler for an optical sensor system. The dependence of the optical power coupling ratio on the coupling angle and refractive index of the adhesion layer in both the forward and backward directions was examined based on the geometrical optics. It was confirmed experimentally that the coupling ratios can be optimized by controlling the coupling angle and refractive index of the adhesion layer. A maximum forward coupling efficiency > 93% was achieved.

High temperature sensor based on a photonic crystal fiber interferometer

We propose a novel method for fabricating fused fiber couplers whose transmission spectrum and sensitivity can be controlled in the wet-etching process. A wide tuning of the transmission spectrum during wet etching was observed experimentally. It was demonstrated that etched fused fiber couplers with reduced waist size had high sensitivity to the refractive index of an external medium. The sensitivity achieved by the present fiber coupler sensor was a 1125 nm/refractive index unit.

Experimental Demonstration of a Dynamic 10 G bit/s WDM Header/Label Recognition Structure

Multiplexing of fiber Bragg grating (FBG) sensors is one of the most effective technologies to reduce both installation and operation costs for quasi-distributive strain and temperature measurements such as smart structure applications. We propose a novel method of enhancing the multiplexing capability of a multipoint FBG sensor system without increasing system complexity by providing a unique spectral response as an identification tag to each FBG. The number of sensors in the proposed spectral tag method can increase as N(N-1)/2 as the number of spectral codes N increases at the expense of the free spectral range.

Improved spectral tag method for FBG sensor multiplexing with equally spaced spectral codes and simulated annealing algorithm

We demonstrate a high temperature sensor by using an intrinsic photonic crystal fiber (PCF) based Mach-Zehnder interferometer. Air hole collapsed regions inside the PCF act as coupler between the core and cladding modes which form the two arms of the interferometer. The temperature measurements are obtained by measuring the shift in the peaks of the interference signal. The experiments confirm the reliability, repeatability and hysteresis. The small amount of hysteresis and deviation in the repeated experiments are within the experimental errors.

Spectral tag method for enhancing FBG multiplexing capability

In this paper, we experimentally demonstrate a dynamic wavelength-division-multiplexing (WDM) header/label recognition structure that processes on-the-fly WDM patterns. An opto-VLSI processor is used to dynamically generate digital phase holograms that control the wavelength components of the label/header to create digital wavelength profiles. An autocorrelation function of a high-peak is generated when a label bit pattern matches a digital wavelength profile. The main attractive feature of using an opto-VLSI processor is that the lookup table of matching digital wavelength profiles does not need modification when the data bit-rate is upgraded. The dynamic pattern recognition structure is experimentally demonstrated at 10 Gbit/s for 4-, 6-, and 8-bit labels.

Spectral analysis of the TEC fiber Bragg grating

We propose a multiplexing scheme for an FBG sensor system on the basis of wavelength division multiplexing (WDM). Each double grating sensor is assigned with a unique spectral tag of two different Bragg wavelengths. The simulated annealing algorithm was employed for the demultiplexing procedure of identifying spectral peaks in the measured reflection spectrum of the FBG sensor system. The peak detection accuracy was as good as 0.6 pm for overlapped spectral peaks in the simulated reflection spectrum. An array of four FBG strain sensors was tested experimentally and the maximum measurement error was 9.1 µε.