Diffractive optical elements, designed by computer optimization techniques, can provide high coupling efficiencies between components in optical communications systems, and can be reproduced accurately in large numbers by the same technology employed to make microcircuits. This applications-led development was for optimized f/0.48 Fresnel lenses to couple light from arrays of semiconductor lasers into monomode optical fibers. The lenses were fabricated as four phase level structures in fused quartz using electron-beam lithography and reactive ion etching. The low f number needed to match between the laser and fiber numerical apertures required 0.2 μm feature sizes in the outer region of the lenses etched 2.1 μm deep. Effective use was made of focused ion beam etching and imaging to obtain cross sections of these high aspect ratio structures during process development. Differing lens designs have achieved 34% and 50% coupling efficiencies between 30° full width half peak 1.55 μm lasers and cleaved, monomode system fibers. In the former case, lens to fiber alignment tolerance was ±6 μm, making passive assembly of the lens fiber arrays feasible.

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A BD-ROM production-capable Electron Beam Recorder (EBR) has been developed, resulting from an optimization program conducted on a prior prototype. The key technical improvements are a comprehensive upgrade of the mechanical master driving system to reduce the track pitch deviations and the implementation of a dynamic focus system, including an axial run-out checker to obtain a uniform jitter. And the multi-pulse write strategy was adopted to control the pit shapes. The resulting masters show a typical radial track pitch variation comprised in the range 6.6nm across the entire recorded area. The corresponding push-pull signal deviation is found to be less than 18% on the whole disc and less than 14% in one revolution. The signal jitter of dual layered BD-ROM disc less than 6.1% on layer 0, and less than 6.7% on layer 1 with large enough push-pull amplitude through the whole radius. These results are fully compliant with the requirements for the dual layered BD-ROM disc of 50GB capacity.

full-length masters of 15GB capacity were produced which were both playable and of good quality. The development of this system continued to today's system, which is a production ready machine capable of making full-length 50GB masters. A second e -Beam Mastering System has been built which has been shipped to a major optical disc developer in Japan and a third machine is now under construction, which is due for shipment to the US later this year.