A sensor to sense a changing temperature or pressure or vibration or chemical reaction, the sensor comprising: a fiber comprising: a fiber core; a first coating at a first part of the fiber, the first coating having a first deformation coefficient; and a second coating at a second part of the fiber, the second part of the fiber being different from the first part of the fiber, the second coating having a second deformation coefficient, the second deformation coefficient being different from the first deformation coefficient, the first coating and the second coating causing radially asymmetric strain of the fiber in response to the changing temperature or pressure or vibration or chemical reaction, the radially asymmetric strain of the fiber causing the fiber to bend by itself as a result of the changing temperature or pressure or vibration or chemical reaction; a fiber laser cavity formed by a single fiber grating in the fiber core, the fiber laser cavity having at least two modes along at least part of its length, the fiber cavity including a first section that is bent in a non-linear shape, the non-linear shape having a radius of curvature, the changing temperature or pressure or vibration or chemical reaction causing a shift in a RF beat note (Δv), the Δv being a function of (1/R) 2; and at least one pump laser connected to the fiber laser cavity. a fiber comprising: a fiber core; a first coating at a first part of the fiber, the first coating having a first deformation coefficient; and a second coating at a second part of the fiber, the second part of the fiber being different from the first part of the fiber, the second coating having a second deformation coefficient, the second deformation coefficient being different from the first deformation coefficient, the first coating and the second coating causing radially asymmetric strain of the fiber in response to the changing temperature or pressure or vibration or chemical reaction, the radially asymmetric strain of the fiber causing the fiber to bend by itself as a result of the changing temperature or pressure or vibration or chemical reaction; a fiber laser cavity formed by a single fiber grating in the fiber core, the fiber laser cavity having at least two modes along at least part of its length, the fiber cavity including a first section that is bent in a non-linear shape, the non-linear shape having a radius of curvature, the changing temperature or pressure or vibration or chemical reaction causing a shift in a RF beat note (Δv), the Δv being a function of (1/R) 2; and a fiber core; a first coating at a first part of the fiber, the first coating having a first deformation coefficient; and a second coating at a second part of the fiber, the second part of the fiber being different from the first part of the fiber, the second coating having a second deformation coefficient, the second deformation coefficient being different from the first deformation coefficient, the first coating and the second coating causing radially asymmetric strain of the fiber in response to the changing temperature or pressure or vibration or chemical reaction, the radially asymmetric strain of the fiber causing the fiber to bend by itself as a result of the changing temperature or pressure or vibration or chemical reaction; a fiber laser cavity formed by a single fiber grating in the fiber core, the fiber laser cavity having at least two modes along at least part of its length, the fiber cavity including a first section that is bent in a non-linear shape, the non-linear shape having a radius of curvature, the changing temperature or pressure or vibration or chemical reaction causing a shift in a RF beat note (Δv), the Δv being a function of (1/R) 2; and at least one pump laser connected to the fiber laser cavity.