An optical filter for generating a filter output signal from a filter input signal, the filter output signal consisting of light from the filter input signal in a predetermined bandwidth. The filter includes a grating, a first optical assembly and an optical signal path. A portion of the input signal traverses the optical signal path such that it is diffracted from the grating to form a first intermediate beam that is input to the first optical assembly, which generates a second intermediate beam therefrom. The second intermediate beam is directed back to the grating and is diffracted by the grating, a portion of the diffracted second intermediate beam forming a portion of the filter output signal. The second intermediate beam is the inverted image of the first intermediate beam, and hence, the second reflection from the grating compensates for the time dispersion introduced by the first reflection from the grating.