Development Of A 10-Channel Wavelength Division Multiplexer/Demultiplexer Fabricated By An X-Ray Micromachining Process

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Abstract
In fiber-optics communications wavelength division multiplexing constitutes a means of increasing the information capacity of fibers. For application in a multimode fiber-optics transmission line a passive grating multiplexer / demultiplexer is being developed using the LIGA technique (German acronym for Lithographie, Galvanoformung, Abformung), which is a combination of deep-etch synchrotron radiation lithography, galvanoforming, and moulding. The optical configuration consists of a polymer slab waveguide, structured by X-ray lithography, with an integrated selffocusing, blazed reflection grating and an integrated fiber alignment support. Optimized blaze angles over the whole grating width, varying grating constants, and a free choice of the grating curvature with an accuracy of 0.5 um can be realized for a grating. A grating design was worked out using Fermat's principle of geometric optics, including the light path function of a noncircular, cylindric grating with varying grating constants. For the 10 spectral channels (985 nm - 1300 nm, channel spacing 35 nm) coma and spherical aberration become negligible. In addition the focal conditions were examined by a ray trace procedure. The lateral dimensions of the device are about 2 cm x 1 cm. An X-ray mask for such a device was fabricated and first X-ray exposures of a polymethylmethacrylate (PMMA) resist served to examine the quality of the grating structure. Furthermore, a 125 μm thick 3-level X-ray resist with a PMMA core was fabricated and the structure accuracy after an X-ray exposure with a test pattern was examined.

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