A novel technique for distributed disturbance sensor is presented. It is based on Coherent Correlation OTDR operating in CW regime. The sensor utilizes a standard telecom CW DFB diode laser as a light source and a very simple configuration. Probe signals were generated by interferometer with OPD exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation function between the probe light intensity signal and the signal returned back from the sensing fiber. Perturbations are detected as time variation of correlation amplitude at disturbance locations. Preliminary experiments proved operability of the sensor.
We propose a very simple technique for multiplexing and interrogation of Fiber Bragg Gratings using a DFB diode
laser operating in CW mode. The technique is based on correlation detection of probe signals reflected by the fiber
Bragg gratings. Phase noise of the DFB diode laser converted into intensity noise was used as a probe signal.
Demultiplexing was performed by calculating the correlation between the probe signal and the signal reflected by the
fiber. The correlation function provide the reflectivity at the probe wavelength and position of each fiber Bragg gating.
Reflection spectra of FBGs can be obtained by tuning the diode laser wavelength with temperature and calculating the
correlation function for each probe wavelength. Results of experimental verification of the technique are presented.
We present an inexpensive technique capable to interrogate multiplexed sensors based on ultra-low-reflective Bragg
gratings written in a long standard telecom fiber. The technique is suitable for distributed detection and localization of
disturbances in security and early warning systems for pipeline monitoring, in linear temperature sensors for fire
detectors, etc. It is based on the correlation OTDR principle measuring cross-correlation between a noise-like probe
signal and the signal reflected back from the sensing fiber. In order to simplify the sensor configuration, an unmodulated
CW DFB diode laser was used as a light source. A noise-like probe signal was generated by conversion of phase noise
of the DFB laser into intensity noise with a help of unbalanced Michelson interferometer. Results of the experimental
verification of the proposed technique are presented.
We present very simple and sensitive techniques capable to interrogate ultra-weak Bragg gratings written in a long
SMF-28 fiber. The techniques are suitable for distributed detection and localization of alarm conditions in early warning
systems. Also, a high multiplexing capability was demonstrated in a multi-point measuring system utilizing an array of
identical FBGs. This technique is based on measuring correlation between the probe and reflected signal. A DFB laser
operating in a CW regime was used as a light source. We present results of experimental verification of the techniques in
different sensor configurations for static strain and vibration measuring. Multipoint sensor using Bragg gratings with
reflectivity of 0.01% printed in a 3-km long fiber was demonstrated.