Patent ID: 7379160

Claim:
An optical integrator, comprising: an integrally formed plurality of first minute refraction surfaces; and an integrally formed plurality of second minute refraction surfaces, which are provided closer to a light emission side than the plurality of first minute refraction surfaces so that the plurality of second minute refraction surfaces optically correspond to the plurality of first minute refraction surfaces, wherein a parameter β satisfies the following conditions: |β|<0.2 (where β=(γ−1) 3 ·NA 2 /Δn 2 ), where a refracting power ratio φa/φb between φa, a refracting power of the first minute refraction surfaces and φb, a refracting power of the second minute refraction surfaces is γ, numerical aperture on the emission side of the optical integrator is NA, and a difference between a refraction index of a medium on a light entrance side of the second minute refraction surfaces and a refraction index of a medium on a light emission side of the second minute refraction surfaces is Δn.