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LIGA and Micromolding 4-73

Fiber-chip coupling

Protective layer LWL
Optical fiber

Spring elements
Fixed guide Step for coating
structure support
Cutting surface
Substrate

Space for insertion
of integrated
optical chip

FIGURE 4.54 Coupling for monomode fibers with nickel spring elements. (Courtesy of IMM, Germany.)

FIGURE 4.55 Pull-push LIGA connector. (Courtesy of IMM, Germany.)

submicron range as shown in Figure 4.54. The thermal expansion coefficient of the substrate material is
matched to the optical chip material — for example, a glass substrate is used for coupling fibers to glass
chips — and the use of spring elements simplifies the handling of the fibers [Rogner et al., 1991].
Alternatives involve the use of optical adhesives and silicon V-groove arrays (see chapter 3). Both tech-
nologies are more labor intensive and suffer from thermal expansion problems.
The use of micro-optical LIGA components is especially attractive for the coupling of multimode
fibers; here, the capability of exact lithographic positioning of mechanical mounting supports is used
advantageously to position the multimode fibers very precisely with respect to the micro-optical compo-
nents without the need for any additional adjusting operations [Gottert et al., 1992a, 1992b].
A pull-push LIGA connector for single-mode fiber ribbons, shown in Figure 4.55, incorporates a set of
precision microsprings coupling up to 12 fibers spaced at 250µm. It is now on the market and is one
of the LIGA products with mass-market appeal. To obtain good coupling efficiency, the fibers are posi-
tioned horizontally with a precision of 1 µm. LIGA is an excellent method to provide that precision. These

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