Ultraviolet-induced birefringence in hydrogen-loaded optical fiber

Abstract

A precision phase-shifting approach to fabricate various phase-shifted gratings using different combinations of polarized ultraviolet ͑UV͒ light is demonstrated. In doing so, the difference between s-and p-polarized light reported by others is confirmed. However, we reveal added complexity for the role of hydrogen and deuterium in the UV-induced process. Previous arguments for the origins are systematically ruled out by reviewing existing literature. We note that the birefringence is made up of at least two components with different thermal stabilities, one consistent simply with molecular hydrogen being present in the system. Overall the birefringence, by deduction, is associated with anisotropy in hydrogen reactions within the fiber. As a result they lead, through known mechanisms of dilation in glass, to anisotropic stress relaxation that can be annealed out, with or without hydrogen remaining, at low temperatures close to 125°C.

Fibre gratings and devices for sensors and lasers

“…Very large red shift in Bragg (>10nm, >10 -2 index change is possible). Similar properties to type In gratings suggests anisotropic stress equilibration through anisotropic OH formation occurs [25]. In GeO 2 doped fibres, stable between (500-800) 0 C, depending on preparation and length required duration.…”

Measurement of photo-induced birefringence in germanosilicate fibers

“…Eq. (12) indicates that the photo-induced normalized birefringence of the germanosilicate fiber is multi-decaying-exponentially proportional to the exposure, and the normalized birefringence of the can attain not more than 6.92×10 −5 , which is two orders of magnitude higher than that of the communication fiber. This result coincides with the result measured by a fiber loop [13].…”

“…In 1991, this result was also obtained by using external writing with UV light [10]. Ouellette et al studied the photo-inducd birefringence by using classical optics method, and showed that it was enhanced by increasing the Ge concentration in the core or by submitting the fiber to a thermal hydrogen treatment [11,12]. Zhang et al measured photo-induced birefringence by using a fiber loop and its value can attain 10 −5 [13].…”

An optical fibre system design enabling simultaneous point measurement of magnetic field strength and temperature using low-birefringence FBGs

“…Where linear birefringence in FBGs is not minimised, any input polarisation will be corrupted within the grating. Recent improvements in knowledge of the mechanisms underlying UV-induced linear birefringence in H 2 -loaded fibres have led to the reliable fabrication of FBGs that exhibit birefringences as small as 10 −6 [4]. These gratings, referred to hereafter as lo-bi gratings, allow polarised light to pass without altering substantially the state of polarisation, and hence can be used in a polarisation dependant sensor system even where multiplexing is required.…”