CONTINUOUS-RELIEF FAN-OUT ELEMENTS WITH OPTIMIZED FABRICATION TOLERANCES

The design of kinoform fan-out elements with high efficiency and reduc ed sensitivity to vertical profile scaling errors is presented, We sta rt from a high-efficiency continuous-phase fan-out solution and optimi ze the position of the 0-2 pi transitions in the phase function, in or der to achieve a high fabrication-error tolerance. The sensitivity of Fourier-transform and focusing fan-out elements to vertical etch-depth errors is analyzed. The limitations for the fabrication of such struc tures by laser-beam writing are discussed, In particular, the influenc e of the finite writing-spot diameter on the fan-out performance is in vestigated. Design rules for fan-out elements, which consider fabricat ion constraints, are derived, Experimental results are presented for c ylindrical focusing fanout elements With Small uniformity error (2%) a nd weak profile scaling dependence.