Patent ID: 7847952

Claim:
An interferometer, comprising: a splitting element which splits an incident light beam into a first split beam and a second split beam; and a first phase compensator which is positioned in an optical path of the first split beam, and which compensates a phase difference occurring between the first split beam and the second split beam upon splitting of the incident light beam by said splitting element, wherein said first phase compensator is a phase retardation plate comprising a uniaxial crystal, and a thickness of said first phase retardation plate is set according to the phase difference between the first split beam and the second split beam, said phase retardation plate includes a first phase retardation plate and a second phase retardation plate, said first phase retardation plate is laminated to said second phase retardation plate, said first phase retardation plate has a first thickness and is positioned such that an optical axis of said first phase retardation plate is either perpendicular to or parallel to a plane of incidence of the incident light on said splitting element, and said second phase retardation plate has a second thickness and is positioned such that an optical axis of said second phase retardation plate is perpendicular to the optical axis of said first phase retardation plate, the second thickness is different from the first thickness, and a difference in thickness between the first thickness and the second thickness is set according to the phase difference between the first split beam and the second split beam, and the difference in thickness between the first thickness and the second thickness is derived from Equation (2): L =(λ×Δ f )/(Δ n×FSR ) Equation (2) wherein L is the difference in thickness between the first thickness and the second thickness, λ is a wavelength of the incident light beam, Δn is a difference in refractive indices of said phase retardation plate along a retarded-phase axis and an advanced-phase axis, and FSR is a frequency phase shift of an interference pattern of the interferometer.