Optics and optical subsystems are playing a larger role in consumer electronics. With that role comes extraordinary developments in size and weight reduction as well as high volume manufacturing methods, driving down both cost and size. Optical elements, as well as lasers and detectors will be fabricated lithographically and configured using the packaging technologies developed for ICs and multi-chip modules. A miniature laser-based optical sensor recently developed for a particularly low cost, high volume application takes advantage of these advanced fabrication methods. The application is the LS120TM disk drive which features a conventional magnetic floppy disk with an optical tracking servo to permit a much finer magnetic track pitch on the media. The 120 MB disk drive has been in the desktop computer market for several years. but the recent effort to develop a smaller version for laptop and notebook computers required major size and mass reduction in the optical sensor. For desktop personal computers, the standard drive bay is 25.4mm high. The standard LSl201M drive features an optical tracking head which is large. with macroscopic lenses, difIractive elements., lasers and detectors which are assembled into a molded chassis . Extension of LS120Thi technology to laptop computers required reducing the drive height to fit in a 12.7 mm slot. This necessitated a significant reduction in the size and mass of the optics head. The device would be required to have the structural integrity to carry the electrical leads for servo interfacing while maintaining precise alignment to the magnetic head. The new size and mass constraints required a fundamental change from the conventional optical system construction. The new sensor was produced using Integrated Micro-Optical System (IMOS) technology . In IMOS. the optical elements are lithographically generated with integrated alignment and bonding features. The source and detector elements are assembled into the system at the chip level, using flip-chip techniques to mechanically and electrically connect them.
The Floptical 3.5 inch floppy disk drive uses optical track sensing for 'Very High Density' (VHD) mode, and is also downward compatible with the DD and HD formats. A new optical head for Floptical Technology developed by Iomega uses a laser diode and a Computer Generated Hologram (CGH) to accomplish high signal levels and signal-to-noise ratio, long depth of focus, and low manufacturing cost. The new optical head uses a detection scheme of projecting--with very long depth of focus--a patch of sinusoidal grating pattern with the same spacing as the VHD tracks onto the disk surface, and detects the amount of reflected light. The track detection function is the convolution of the light pattern and the reflectivity function of the disk tracks. Depth of focus of the head is hundreds of microns. Integration across several tracks improves signal-to-noise ratio of the tracking signals. Utilization of a laser diode provides high signal levels. A computer generated binary hologram replaces several conventional optical elements. The HOE is replicated at much lower cost than conventional optics, and mechanically it simplifies head assembly, saving head cost on both counts.