A hollow-core photonic bandgap fiber polarization controller was made by applying
lateral pressures to three segments along the fiber. The applied lateral pressures result in variable
birefringence along the fiber, which modifies the state of the polarization. This approach may be
applicable to a hollow-core photonic bandgap fiber with little or no inherent birefringence.
Detection of acoustic pressure with optical fiber interferometers has been studied for many years<sup>1-3</sup>. The conventional
solid silica fiber hydrophone was sufficient to prove the concept; however, it has low acoustic sensitivity. This is because
1) the silica glass material has relatively high Young's modulus, which makes the conventional fiber incompressible; 2)
the refractive index change resulted from fiber strain has opposite sign with respective to the strain term and hence
compromises the acoustic sensitivity. In a hollow-core photonic bandgap fiber (PBF), the fundamental mode is almost
entirely confined to the air core, the effective Young's modulus of fiber is expected to be reduced and the undesirable
"negative" index effect is anticipated to be greatly decreased. We experimentally measured that the phase sensitivity of
the commercial HC-1550-02 PBF and found it is improved by a factor of 15dB compared to a conventional (HNSM-155)
single mode fiber, which agrees well with theoretical prediction.
We proposed a kind of fiber-optic gradient hydrophone based on interferometer. Two arms of the interferometer are
sensing fibers, each of which can be regard as a scalar pressure sensing element, and then the phase gradient between the
two elements is transformed into the light intensity modulated output by the coupler. In this paper, a suit of analytical
models for researching the sensor performance are developed. The theoretical and experimental research was carried out
to demonstrate this kind of gradient hydrophone's phase sensitivity as the function of the measure frequency and the "8"
A real-time digital phase demodulation scheme is developed. This scheme, based on cos<sup>-1</sup> and channel-choosing
techniques, uses the two optical outputs from a 3×3 coupler to overcome the signal fading problem of fiber