Sensing RF and microwave energy with fiber Bragg grating heating via soft ferromagnetic glass-coated microwires

We present results from a fiber Bragg grating-based microwave energy sensor. The sensor relies on a soft ferromagnetic glass-coated microwire that is bonded to the cladding of the grating. The microwire absorbs microwave energy and heats up thus raising the temperature of the fiber Bragg grating. Compared to a similar sensor that uses gold to absorb electromagnetic radiation, the microwire yields a sensor with greater sensitivity (∼10 times at f = 3.25 GHz) relative to the perturbation of the microwave field. With the sensor reported here, the best sensitivity to electromagnetic radiation corresponds to AC electric fields that have an average electric energy density of approximately 1.3 μJ/m3.