Patent ID: 8000210

Claim:
A quarter-wave plate which transmits a plurality light fluxes with wavelengths that are different from each other, the quarter-wave plate comprising: a base member comprising a ridge and trough periodic structure with a structural period of λ min /2<P<λ min arranged on one side of the base member, where λ min is a minimum wavelength among the plurality of wavelengths, wherein a refractive index n min of a ridge portion of the ridge and trough periodic structure for the wavelength λ min satisfies 1.5<n min <1.6, wherein a light transmittance of the quarter-wave plate for the wavelength λ min is 85% or more, wherein the ridge and trough periodic structure satisfies the expression (1): H= 3.5 ×f− 5.65 ×n min +8.55+α (1) (−0.35<α<+0.35) where P is a structural period of the ridge and trough periodic structure, H is a structural height (μm) of the ridge portion, L is a structural width of the ridge portion, and f is a filling factor (=L/P), wherein the structural period P is 0.31 um or more, and wherein each of the plurality of wavelengths is within a range of 380 nm to 820 nm.