The femtosecond laser-induced fiber Bragg grating is an effective sensor technology that can be deployed in harsh environments. Depending on the optical fiber chosen and the inscription parameters that are used, devices suitable for high temperature, pressure, ionizing radiation and strain sensor applications are possible. Such devices are appropriate for aerospace or energy production applications where there is a need for components, instrumentation and controls that can function in harsh environments. This paper will present a review of some of the more recent developments in this field.

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Plane-by-plane fabrication of fiber Bragg gratings in optical fibers using a short-pulse femtosecond IR laser is proposed and demonstrated. By incorporating a cylindrical lens in the fabrication setup, a plane of index modification can be directly inscribed in the fiber core by a single laser pulse. The planes of index modification are produced in the core of a free-standing fiber without an oil immersion objective. This plane-by-plane method simplifies the direct grating inscription process and allows for the fabrication of complicated grating structures.

Periodic planar nanostructures are found in Type II-IR Bragg gratings produced in SMF-28 fiber by side-illuminating it with infrared femtosecond-laser pulses through a phase mask. The planar nanostructures are aligned perpendicular to the laser polarization, as demonstrated using scanning electron microscopy analysis of cleaved fiber samples. Dark field optical microscopy is employed for real-time monitoring of structural changes occurring inside the fiber during the inscription process.

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