The LIGA process which is based on deep-etch lithography in combination with high-precision electroforming and moulding processes is a particularly promising method for the fabrication of three-dimensional microstructures. Some interesting applications can be seen in the field of integrated optics. Passive waveguide structures can be fabricated by deep-etch synchrotron radiation lithography of multilayer resist systems. Using this technique, multimode strip waveguides with a PMMA core and a P (TFPMA/MMA) cladding as well as a planar grating spectrograph have been realized. The attenuation of 0.18 dB/cm measured at a wavelength of 850 nm can be reduced, especially in the near IR-region, by the use of deuterated PMMA as a core material. For plastic fiber LAN applications, moulding processes for the replication of passive multimode waveguide components like Y-couplers or star couplers are under investigation. The advantages of the LIGA process--unrestricted design in the cross-sectional shape and a small surface roughness in the range of 10 - 20 nm--are of special interest for these developments. For coupling fibers to integrated-optical chips, structures of a coupling array have been fabricated. The fibers are guided by exactly positioned stop faces and then precisely located and prefixed by integrated spring elements. The main advantages are as follows: the thermal expansion coefficient of the array can be matched to the optical chip material, the use of spring elements for prefixing simplifies the handling, and adhesives and the connected problems can be avoided.
"Fabrication of light-guiding devices and fiber-coupling structures by the LIGA process", Proc. SPIE 1506, Micro-Optics II, (1 August 1991); doi: 10.1117/12.45961; https://doi.org/10.1117/12.45961