We study the modal birefringence behaviour of a near-elliptic core index-guiding photonic crystal fiber (PCF) intended
for high birefringence applications. The analysis is based on a semi-vectorial field convergence algorithm combined
with the perturbation correction technique of mode calculation. The approach is accurate, simple to implement, and
much faster than any of the existing methods. The efficacy of our design analysis has been verified by comparing the
results with otherwise known solutions. Using this analysis as a design recipe, we have realized PCF of reasonably high
birefringence characteristics.
The paper describes the design features and characteristics of an embedded fiber Bragg grating (FBG) pressure sensor that has been developed to measure forces applied in the direction perpendicular to the fiber axis. This FBG-based pressure sensor provides an absolute measurement in terms of wavelength shift, which avoids problems of signal intensity fluctuation often encountered by conventional intensity-modulated or phase-modulated pressure sensors. The initial outcome of our study indicates that direct sensing using bare-FBG is infeasible for real applications due to its non-linearity and limited range of force sensing. However, when the FBG is embedded into some composite material, the sensor exhibits excellent linearity, high stability and reliability over a wider force-sensing range, making it a potentially viable sensing element. When an FBG is embedded into some fiber-reinforced composites, a level of sensing force of up to 60N with a sensitivity of 3.96 pm/N and resolution of 1pm (equivalent to 0.8με) is achievable without causing permanent deformation to the FBG.
We present an analysis of fused fiber couplers by simultaneously considering the coupling of guided modes through the overlap of the evanescent fields in the weakly interacting 'taper transition' region as well as the beating of cladding modes in the strongly interaction 'taper waist' region. We have incorporated geometrical parameters to account for the 'degree of fusion' and the 'shape of taper', thus representing a realistic coupler structure. The results of our model are in very good agreement with the measured characteristics of coupler components fabricated in our laboratory.
We report in-house development of a real time monitoring system with programmable fabrication parameters for fabricating fused-fiber coupler based branching components. A number of branching components of varied specifications and with fibers of different make have been fabricated; these exhibited low excess loss and other features akin to commercially available couplers. Fabricated WDM couplers for operation at 1310/1550 nm exhibited high degree of isolation, large isolation bandwidth and reasonably low excess loss. Characteristics of the fabricated couplers have been investigated for optimizing design and fabrication parameters with regard to channel isolation and excess loss in the device. An equivalent planar waveguide (EPG) model has also been used to model these couplers and to correlate with the experimental findings.
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