Simulation of distributed optical fiber disturbance detection system based on Sagnac/Mach-Zehnder interferometer and cross-correlation location

A distributed optical fiber disturbance detection system consisted of a Sagnac interferometer and a Mach-Zehnder interferometer is demonstrated. Two interferometers outputs are connected to an electric band-pass filter via a detector respectively. The central frequencies of the two filters are selected adaptively according to the disturbance frequency. The disturbance frequency is obtained by either frequency spectrum of the two interferometers outputs. An alarm is given out only when the Sagnac interferometer output is changed. A disturbance position is determined by calculating a time difference with a cross-correlation method between the filter output connected to the Sagnac interferometer and derivative of the filter output connected to the Mach-Zehnder interferometer. The frequency spectrum, derivative and cross-correlation are obtained by a signal processing system. Theory analysis and simulation results are presented. They show that the system structure and location method are effective, accurate, and immune to environmental variations.

Monitoring of time-resolved singlet oxygen luminescence at 1270 nm by an optical fiber detection system

Singlet oxygen(^(1)O_(2))is the main cytotoxic substance in Type II photodynamic therapy(PDT).The luminescence of ^(1)O_(2) at 1270nm is extremely weak with a low quantum yield,making the direct detection of'O2 at 1270 nm very challenging.In this study,a set of highly sensitive optical fiber detection system is built up to detect the luminescence of photosensitized ^(1)O_(2) We use this system to test the luminescence characteristics of ^(1)O_(2) in pig skin tissue ex vrivo and mouse auricle skin in vivo.The experimental results show that the designed system can quantitatively detect photosensitized ^(1)O_(2) luminescence.The ^(1)O_(2) luminescence signal at 1270 nm is successfully detected in pig skin exr vivo.Compared with RB in an aqueous solution,the lifetime of ^(1)O_(2) increases to 17.4±12pus in pig skin tissue ex vivo.Experiments on living mice suggest that an enhancement of ^(1)O_(2) intensity with the increase of the TMPyP concentration.When the dose is 25 mg/kg,the vasoconstriction can reach more than 80%。The results of this study hold the potential application for clinical PDT dose monitoring using an optical fiber detection system.

DISTRIBUTED OPTICAL FIBER SENSOR FOR LONG-DISTANCE OIL PIPELINE HEALTH

A fully distributed optical fiber sensor （DOFS） for monitoring long-distance oil pipeline health is proposed based on optical time domain reflectometry （OTDR）. A smart and sensitive optical fiber cable is installed along the pipeline acting as a sensor, The experiments show that the cable swells when exposed to oil and induced additional bending losses inside the fiber, and the optical attenuation of the fiber coated by a thin skin with periodical hardness is sensitive to deformation and vibration caused by oil leakage, tampering, or mechanical impact. The region where the additional attenuation occurred is detected and located by DOFS based on OTDR, the types of pipeline accidents are identified according to the characteristics of transmitted optical power received by an optical power meter, Another prototype of DOFS based on a forward traveling frequency-modulated continuous-wave （FMCW） is also proposed to monitor pipeline. The advantages and disadvantages of DOFSs based on OTDR and FMCW are discussed. The experiments show that DOFSs are capable of detecting and locating distant oil pipeline leakages and damages in real time with an estimated precision of ten meters over tens of kilometers.

Intra-Cavity Absorption Gas Sensors Using Wavelength Modulation and Wavelength Sweep

Wavelength modulation technique （WMT） and wavelength sweep technique （WST） are introduced into intra-cavity absorption gas sensors （ICAGS） for low concentration gas detection. The optimized parameters of the system maximizing the signal-to-noise ratio （SNR） are found. Calibration of acetylene concentration and gas recognition are both realized.