A novel method is presented to manufacture multilevel diffractive optical elements (DOEs) in polymer by single-step KrF excimer laser ablation using a halftone mask. The DOEs have a typical pixel dimension of 5 µm and are up to 512 by 512 pixels in size. The DOEs presented are Fresnel lenses and Fourier computer generated holograms, calculated by means of a conventional iterative Fourier transform algorithm. The halftone mask is built up as an array of 5 µm-square pixels, each containing a rectangular or L-shaped window on an opaque background. The mask is imaged onto the polymer with a 5x, 0.13 NA reduction lens. The pixels are not resolved by the lens, so they behave simply as attenuators, allowing spatial variation of the ablation rate via the window size. The advantages of halftone mask technology over other methods, such as pixel-by-pixel ablation and multi-mask overlay, are that it is very fast regardless of DOE size, and that no high-precision motion stages and alignment are required. The challenges are that the halftone mask is specific to the etch curve of the polymer used, that precise calibration of each grey-level is required, and that the halftone mask must be calculated specifically for the imaging lens used. This paper describes the design procedures for multilevel DOEs and halftone masks, the calibration of the various levels, and some preliminary DOE test results.
Planar lightwave circuits (PLCs) made from photo-patternable sol-gel materials are attracting considerable R&D interest. This is due to the advantages they offer for applications in optical telecommunications and their compatibility with existing silicon technology process equipment. In particular, the ability to produce devices compatible with silica optical fibres using a straightforward, environmentally friendly, photolithographic process is very attractive. The approach is now well-established in the literature and typically involves the incorporation of an acrylate moiety in the sol-gel precursor mixture, thereby providing a photo-polymerisability function. In this work, we report on the fabrication of passive optical components and devices designed for datacomms applications using visible diode lasers or the 1 st telecom window. Silica-based sol-gel waveguides have been integrated in an opto-electronic multichip module (OE-MCM) demonstrator for optical interconnect applications. We have fabricated an 8-channel transmitter module for parallel optical interconnects (POI) based on 2 sub-modules: (a) an optical interface sub-assembly based on photo-patterned sol-gel optical waveguides, and (b) an optoelectronic component sub-module comprising an array of VCSELs. We describe here the fabrication, characterization and performance of the optical components and a POI Transmitter chip.
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