Chams Baker

Incoherent optical frequency domain reflectometry based on a Kerr phase-interrogator

We present a novel approach for incoherent optical frequency-domain reflectometry based on a frequency-swept sinusoidal optical signal and a Kerr phase-interrogator. The novel approach eliminates dependence on the laser coherence-length allowing for long-range operation. Long-range detection of reflection points as far as 151 km at a spatial-resolution of 11.2 cm is experimentally demonstrated.

Displacement sensor based on Kerr induced phase-modulation of orthogonally polarized sinusoidal optical signals

We present a novel short, medium, and long range displacement sensor using a Kerr phase-interrogator. Displacement induces relative phase variation between two orthogonally polarized sinusoidal optical signals. The Kerr phase-interrogator converts the phase variation into power variation through Kerr induced phase-modulation. Displacement sensing over a range of 12 mm with micron level resolution around the quadrature points is demonstrated.

Chromatic-dispersion measurement by modulation phase-shift method using a Kerr phase-interrogator

We present a novel approach for the measurement of chromatic-dispersion in long optical fibers using a modulation phase-shift method based on a Kerr phase-interrogator. This approach utilizes a Kerr phase-interrogator to measure the phase variation of a sinusoidal optical signal induced by traveling in a fiber under test as the laser carrier wavelength and the sinusoidal signal frequency are varied. Chromatic-dispersion measurement for several fibers including a standard single-mode silica fiber and a dispersion-shifted fiber is experimentally demonstrated. The ultrafast response of the Kerr phase-interrogator opens the way for real-time monitoring of chromatic-dispersion in kilometers-long optical fibers.

Group-Delay-Based Temperature Sensing in Linearly-Chirped Fiber Bragg Gratings Using a Kerr Phase-Interrogator

We present a novel temperature sensor based on temperature dependence of reflection group-delay in a linearly chirped fiber Bragg grating. The reflection group-delay of a chirped grating changes with temperature leading to a variation in the phase of a sinusoidal optical signal reflected from the grating. A Kerr phase-interrogator converts the phase variation into power variation allowing for high-precision temperature sensing. A temperature sensor with a resolution of 0.0089°C and a sensitivity of 1.122 rad/°C is experimentally demonstrated.

Enhancement of optical pulse extinction-ratio using the nonlinear Kerr effect for phase-OTDR.

We present a novel approach for the generation of high extinction-ratio square pulses based on self-phase modulation of sinusoidally modulated optical signals (SMOS). A SMOS in a nonlinear medium experiences self-phase modulation induced by the nonlinear Kerr effect leading to the generation of distinct sidebands. A small variation in the peak power of the SMOS leads to a large variation in the power of the sidebands. Impressing a square pulse on the SMOS and filtering a sideband component results in a higher extinction-ratio square pulse. The advantage of high extinction-ratio pulses is demonstrated by a reduced background noise level in the Rayleigh backscattering traces of a phase-OTDR vibration measurement system.

Sensitivity enhancement beyond the wavelength limit in a novel sub-micron displacement sensor.

We propose and demonstrate sub-micron displacement sensing and sensitivity enhancement using a two-frequency interferometer and a Kerr phase-interrogator. Displacement induces phase variation on a sinusoidally modulated optical signal by changing the length of the path that either of the signals two spectral components propagates through. A Kerr phase-interrogator converts the resulting phase variation into power variation allowing for sub-micron displacement sensing. The sensitivity of this novel displacement sensor is enhanced beyond the wavelength-limited sensitivity of the widely used Michelson interferometric displacement sensor. The proposed approach for sensitivity enhancement creates a whole new class of sensors with ultra-high sensitivity.

Recent Development in the Distributed Fiber Optic Acoustic and Ultrasonic Detection

Distributed acoustic sensors provide a powerful instrumentation for ultrasound testing to identify the internal crack and deformation with the location for assessing structural conditions and predicting the potential structural failure. This paper provides a tutorial review of the milestones leading to the development of the distributed acoustic sensor based on Rayleigh back scattering. It offers discussion on basic principles, optical configurations and system design requirement, various detection schemes, performance limitations and applications for the maximum measurable frequency, minimum detectable strain and highest spatial resolution. A final comment on the prospects of the further developments is presented.

Chromatic-Dispersion Monitor Based on a Differential Phase-Shift Method Using a Kerr Phase-Interrogator

We present a novel approach for real-time chromatic-dispersion (CD) monitoring using a Kerr phase-interrogator. CD induces a differential phase shift between two sinusoidal signals carried by two different wavelengths. A Kerr phase-interrogator converts the differential phase shift into power variation, and CD monitoring is achieved by measurement of the power variation in real time. A CD monitor with a resolution of 0.196 ps/nm is experimentally demonstrated. The high sensitivity and fast response of this CD monitoring approach opens the way for novel sensing applications.

Study of chromatic dispersion impact on nonlinear interaction between two sinusoidally modulated optical signals using theory of four-wave mixing

The impact of chromatic dispersion (CD) on the efficiency of the nonlinear interaction between two orthogonally polarized sinusoidally modulated optical signals (SMOSs) with identical or different carrier wavelengths is investigated theoretically and experimentally. The theory of four-wave mixing is used for studying the efficiency of the nonlinear interaction by analyzing the power of the first-order sideband that is generated through the nonlinear interaction between the orthogonally polarized SMOSs. The presented theoretical study accurately predicts the CD impact on the efficiency of the nonlinear interaction as confirmed by the close agreement between theoretical and experimental results. This study is essential for the understanding and the design of our newly developed Kerr phase-interrogator that allows for a new class of sensing devices utilizing the nonlinear Kerr effect.

Self-inscribed antisymmetric long-period grating in a dual-core As 2 Se 3 -PMMA fiber

We report for the first time that transmission of optical pulses centered at a wavelength of 1550 nm through a tapered dual-core As2Se3-PMMA fiber inscribes an antisymmetric long-period grating. The pulse power is equally divided between even and odd modes that superpose along the dual-core fiber to form an antisymmetric intensity distribution. A permanent refractive-index change that matches the antisymmetric intensity distribution is inscribed due to photosensitivity at the pulse central wavelength. The evolution of the transmission spectrum of the dual-core fiber is experimentally measured as the accumulated time that the fiber is exposed to the pulse is increased. A theoretical model of an antisymmetric long-period grating in a dual-core fiber computationally reproduces the experimentally observed evolution of the transmission spectrum. Experimental results indicate that antisymmetric long-period gratings induce effective group-velocity matching between the even and odd modes of the dual-core fiber, and reveal for the first time that long-period gratings can lead to slow light propagation velocities.