Method and apparatus for combined active and passive athermalization of an optical assembly

Abstract

An athermalized optical assembly includes a laser beam source, such as a laser diode, and a collimator lens which are together mounted in an active thermally-compensated structure. The laser diode source is mounted in a beam source mount thermally isolated from a supporting base plate that serves as the assembly mounting surface. The collimating lens is mounted on a flexure plate having a kinematic hinge. The flexure plate is supported by concentric inner and outer compensation rings of dissimilar materials that are arranged to support the flexure plate at a predetermined distance above the base. The difference in the coefficient of thermal expansion (CTE) of each compensation ring is chosen such that the flexure plate kinematic hinge is passively operated to approximately compensate for thermal shifts in system focal length while maintaining radial and angular alignment of the lens relative to the laser diode source, so as to provide controlled axial movement of the collimating lens. A first thermal element, operatively connected to the beam source mount, and a second thermal element, operatively connected to the outer compensation ring and thermally isolated from the inner compensation ring, are controlled according to the inner compensation ring, outer compensation ring, and lens barrel temperatures. The thermal elements actively regulate the inner and outer compensation ring temperatures so as to supplant or correct any deficiencies in the accuracy or range of motion afforded by the passive operation of the kinematic hinge. Accordingly, the combination of passive and active athermalization provides more exact compensation for thermally-induced focal shifts than may be obtained by a passive or active system acting alone.

Dependencies are inferred from the claim text.