Anisotropic distributed feedback fiber laser sensor

Details Anisotropic distributed feedback fiber laser sensor Anisotropic distributed feedback fiber laser sensor

2005-04-26

2005-04-26

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

Optical waveguide sensor

C385S037000, C372S006000

Reexamination Certificate

active

06885784

ABSTRACT:
The invention relates to a DFB fiber laser sensor (1). A measurement quantity makes it possible to induce a linear birefringence between mode pairs of the laser-amplifying fiber (2) and to measure an associated beat frequency (Δν1, Δν2, Δν3). According to the invention, the laser-amplifying fiber (2) has a nonrotationally symmetrical structure, so that it is possible to detect isotropic pressures p, acoustic waves or chemical substances that can be added radially to the laser-amplifying fiber (2). In a second aspect of the invention, an emission wavelength range and parameters (a, b, ΔN) of the laser-amplifying fiber (2) and also a grating period L of the fiber Bragg grating resonator (3) are coordinated with one another such that at least two different spatial modes (LP01, LP11even, LP11odd, LP21even) are propagatable and it is possible to measure beat frequencies (Δν1, Δν2, Δν3) between oscillatory longitudinal laser modes assigned to them. Exemplary embodiments relate to: rotationally asymmetrical fiber types, a choice of special spatial modes (LP11odd, LP21even) and/or multiple fiber Bragg gratings (3) for reducing the beat frequencies (Δν1, Δν2, Δν3) below 100 GHz; and elimination of temperature influences e.g. by the detection of a plurality of beat frequencies (Δνa, Δνb, Δνc, Δνd) between different pairs of spatial modes (LP01, LP11even, LP11odd, LP21even) and/or polarization modes (X, Y).

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