Patent ID: 6262844
Filing Date: 2001-07-17
Classification: G02B,Y10S

Abstract:
A method for at least partially controlling a change in an optical property of an optical system resulting from a change in the temperature of at least a portion of the system, said system having an optical axis and comprising at least one lens element having an index of refraction, a shape, and a location within the optical system, said method comprising:(A) including at least one stepped diffractive surface in the system, said at least one stepped diffractive surface comprising N concentric planar zones which:(i) are orthogonal to the system's optical axis,(ii) are displaced from one another along the optical axis, the displacement between zone i and zone i+1 being d.sub.i, and(iii) define a base curve, said stepped diffractive surface having a clear aperture and a sag which changes monotonically from the optical axis to the clear aperture; and(B) selecting the base curve and the d.sub.i at least in part to compensate for a change in the index of refraction, shape, and/or location of said at least one lens element as a result of said change in temperature to at least partially control the change in the optical property.