Low-noise high-reliability 680-nm optical head enables robust 14.8-gigabyte/disk product

A high reliability and ow noise 680 nm optical head is described. This head enables a high data integrity, 14.8 GByte/Disk product (KODAK Optical Disk System 2000). The laser intensitynoise is measured to be -133 to -137 dB/Hz at the data frequencies. This allows phase margin forthe system to exceed 50%. The laser with drive electronics is shown to have a pulse lifetime of greater than 40,000 hours at exaggerated drive conditions.Keywords: Write-Once Optical Data Storage, Red Optical Head, Laser Intensity Noise, LaserReliability 1. INTRODUCTION We have achieved a high reliability and high data integrity 14.8 Gigabyte/Disk product by using a very low noise and high reliability 680 nm optical head. This product (KODAK OpticalDisk System 2000) is based on Kodak's proprietary write-once phase change recording layer.12. OPTICAL HEADThe layout of the red optical head is shown in Figure 1. The light source is a 30 mW, 680 nm laser diode from SDL, Inc. The beam is collimated with a Kodak precision glass molded lens witha focal length of 7.5 mm. A beam expander/partial polarization beamsplitter expands the beam by