Patent ID: 7319558

Claim:
A wide-band wave plate comprising at least two wave plates, each of which has a microstructure to generate a phase difference, each microstructure of the two wave plates having a cycle not shorter than 1/n min of a shortest wavelength of light in use, wherein the two wave plates are arranged so that microstructures of the two wave plates are disposed face to face with each other with main axes of the microstructures being non-parallel with each other, where, n min is a refractive index of a wave plate material of which at least one of the two wave plate are made with respect to the shortest wavelength of light in use, wherein 0°<δ1<135°, 0°<δ2<135°, 90°<δ1+δ2<270°, where, δ 1 and δ 2 are respectively phase differences of the two wave plates.