There is provided a cutting element for use in a hair cutting device. The cutting element comprises an optical waveguide having a sidewall, wherein a portion of the sidewall forms a cutting face for contacting hair. The optical waveguide includes a plurality of optical structures spaced along its length, the optical structures being configured to reflect light at one or more wavelengths. When broadband light is directed along the optical waveguide the optical waveguide is such that: if the cutting face of the optical waveguide is not in contact with a target object, then each of the plurality of optical structures reflects light having a first wavelength； and if the cutting face of the optical waveguide is in contact with a target object, then at least one of the optical structures reflects light having a second wavelength different to the first wavelength. A hair cutting device comprising the cutting element and a method of operating the hair cutting device are also provided.
