Miniature refractive multi-element molded-aspheric glass lens for multichannel reader-writer for phase-change tape data storage

Abstract

With an emphasis on the design and implementation of a miniature multi-element objective lens, this paper discusses the issues and challenges relating to hardware developed to demonstrate the viability of simultaneously writing and reading multiple-channels on phase-change media. A linear array of 850 nm single-mode vertical cavity surface emitting lasers (VCSELS) is used as a source for the noncontact phase-change on tape by means of an F/0.7 NA objective lens. The multichannel design and media characteristics required that an objective lens be developed having a full-field angle of 3 degrees and diffraction-limited performance of Strehl ratio > 0.88. Additionally, during the design process, simultaneous read-back through the same objective lens with 780 nm light, required consideration of the dispersive properties of glass. Because longitudinal and lateral movement of the objective lens in an actuator actively maintains focus, weight minimization related to material choices and mounting was also considered in the design. A successful breadboard implementation of the hardware was constructed demonstrating the capability for simultaneous high-speed writing and reading of multiple channels on tape. The breadboard also demonstrated the feasibility for fabricating a multi-element, molded aspheric, objective lens assembly meeting the unique requirements of the lightweight, high-numerical aperture, finite-field objective lens.