Patent ID: 6968096

Claim:
A diffraction device for periodically dividing an electromagnetic wave, the diffraction device comprising: a diffraction grating; an input medium contacting the diffraction grating; and an output medium contacting the diffraction grating, with at least either one of the input medium and output medium comprising a photonic crystal having a periodic characteristic in single direction, or the diffraction grating comprising a photonic crystal, which periodically divides electromagnetic waves to produce a phase difference in a wave front with differences in optical propagation distances between the divided electromagnetic waves, wherein the photonic crystal satisfies the condition of 2≦|(Δλ/λ 0 )/(Δω/ω 0 )|, whereas λ 0 represents the wavelength of a propagating wave when an electromagnetic wave having frequency ω 0 propagates in a specific direction in the photonic crystal, and Δλ represents the change of wavelength relative to an electromagnetic wave having frequency Δω+ω 0 when the frequency ω 0 is changed by a slight amount.