Rayleigh, Brillouin and Raman scatterings in fibers result from the interaction of photons with local material characteristic features like density, temperature and strain. For example an acoustic/mechanical wave generates a dynamic density variation; such a variation may be affected by local temperature, strain, vibration and birefringence. By detecting changes in the amplitude, frequency and phase of light scattered along a fiber, one can realize a distributed fiber sensor for measuring localized temperature, strain, vibration and birefringence over lengths ranging from meters to one hundred kilometers. Such a measurement can be made in the time domain or frequency domain to resolve location information. With coherent detection of the scattered light one can observe changes in birefringence and beat length for fibers and devices. The progress on state of the art technology for sensing performance, in terms of spatial resolution and limitations on sensing length is reviewed. These distributed sensors can be used for disaster prevention in the civil structural monitoring of pipelines, bridges, dams and railroads. A sensor with centimeter spatial resolution and high precision measurement of temperature, strain, vibration and birefringence can find applications in aerospace smart structures, material processing, and the characterization of optical materials and devices.

Recent progress in distributed fiber optic sensors.

Optical Waveguide Theory

Robotic medical instrument systems and associated methods utilizing an optical fiber sensors such as Bragg sensor optical fibers. In one configuration, an optical fiber is coupled to an elongate instrument body and includes a fiber core having one or more Bragg gratings. A controller is configured to initiate various actions in response thereto. For example, a controller may generate and display a graphical representation of the instrument body and depict one or more position and/or orientation variables thereof, or adjust motors of an instrument driver to reposition the catheter or another instrument. Optical fibers having Bragg gratings may also be utilized with other system components including a plurality of working instruments that are positioned within a sheath lumen, an instrument driver, localization sensors, and/or an image capture device, and may also be coupled to a patient's body or associated structure that stabilizes the body.

Robotic instrument systems and methods utilizing optical fiber sensors

Structural Health Monitoring (SHM) can be understood as the integration of sensing and intelligence to enable the structure loading and damage-provoking conditions to be recorded, analyzed, localized, and predicted in such a way that nondestructive testing becomes an integral part of them. In addition, SHM systems can include actuation devices to take proper reaction or correction actions. SHM sensing requirements are very well suited for the application of optical fiber sensors (OFS), in particular, to provide integrated, quasi-distributed or fully distributed technologies. In this tutorial, after a brief introduction of the basic SHM concepts, the main fiber optic techniques available for this application are reviewed, emphasizing the four most successful ones. Then, several examples of the use of OFS in real structures are also addressed, including those from the renewable energy, transportation, civil engineering and the oil and gas industry sectors. Finally, the most relevant current technical challenges and the key sector markets are identified. This paper provides a tutorial introduction, a comprehensive background on this subject and also a forecast of the future of OFS for SHM. In addition, some of the challenges to be faced in the near future are addressed.

Fiber Optic Sensors in Structural Health Monitoring

We present a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample. The device is insensitive to the rotation of the sample in the plane perpendicular to ranging. Phase measurement accuracy is ±0.86°, but the reflectometer can distinguish local variations in birefringence as small as 0.05° with a distance resolution of 10.8 μm and a dynamic range of 90 dB. Birefringence-sensitive ranging in a wave plate, an electro-optic modulator, and a calf coronary artery is demonstrated.

Polarization-sensitive low-coherence reflectometer for birefringence characterization and ranging

We observe the spectral hole burning effect in a polarization maintain fiber (PMF) and a single-mode fiber (SMF) through the interaction between a continuous wave (CW) beam and a high power pulse with two frequency components located around the Stokes and anti-Stokes frequencies of the CW beam. The linewidth of the spectral burning hole is much narrower than that of the intrinsic Brillouin gain spectrum. We experimentally study the position dependent dip formation process in a PMF and an SMF, and explore the possibility of using this narrowed spectral width for distributed temperature and strain sensing with a higher accuracy. A hole burning peak with a linewidth of 9 MHz in a Brillouin gain spectrum with a full-width at half-maximum (FWHM) of 50 MHz is observed in a PMF. Since the frequency measurement accuracy of Brillouin sensor is inversely proportional to the FWHM of detected spectrum, the spectrum hole burning represents a potential for improving the Brillouin peak detection accuracy of distributed Brillouin sensor.

/pdf/spatially-resolved-brillouin-spectral-hole-burning-in-pmf-l5qirmckus.pdf

Spatially Resolved Brillouin Spectral Hole Burning in PMF and SMF

Slow-light effect in fibers with distance-depending Brillouin frequency provides large, optically controlled delay of picosecond pulses with a little shape distortion, when Brillouin frequency variation along the fiber corresponds to the whole pulse spectrum.

Slow Light of Gb/s Bit Streams via Stimulated Brillouin Scattering in Non-Uniform Optical Fibers

When the fiber is subjected to acoustic wave, the local refractive index will be modulated as function of time, which can be detected in time domain or frequency domain reflectometry in the fiber as acoustic sensor

Distributed acoustic wave detection with Rayleigh scattering

We present an analytical study of the output intensity fluctuations caused by the polarization mode dispersion (PMD) and the polarization dependent loss (PDL). An analytical expression for the Jones matrix autocorrelation function (ACF) in presence of the PMD and PDL is derived. The analytical ACF can be applied to different modulation formats leading to the analytical evaluation of the eye diagram.

Analytical eye diagram evaluation due to the existence of the polarization-mode dispersion and polarization-dependent loss in single-mode fibers

BER degradation, caused by a dynamic PMD emulator, is investigated in a 10Gb/s optical system. It is shown that dynamic PMD emulation more closely emulates rare field fiber BER events whereas standard emulators average away these events.

http://aix1.uottawa.ca/~dwaddy/publications/papers/2003-SPIE-BER.pdf

Liang Chen

Papers

Spatially Resolved Brillouin Spectral Hole Burning in PMF and SMF

Slow Light of Gb/s Bit Streams via Stimulated Brillouin Scattering in Non-Uniform Optical Fibers

Distributed acoustic wave detection with Rayleigh scattering

Analytical eye diagram evaluation due to the existence of the polarization-mode dispersion and polarization-dependent loss in single-mode fibers

System impact of dynamic PMD emulation