Setup of the autofocusing system for LDW on non-planar surfaces.
The waves for detecting the defocus z 0 when tilt angle α = 10°. (a) The wave for driving the pinhole. (b) The waves of normalized intensity response. The lengths of time Δt 1, Δt 2, and T/2 of curves C, B, and A correspond to defocuses 15 μm, −15 μm, and 0 μm, respectively, of the curved surface.
The FES curve as a function of the defocus z 0.
The FES generation module of SPC circuits.
Block diagram of focus positioning control.
The variation of PZT average control voltage towards the upper limit (b) when the curved substrate moves in the direction of arrow (a). Panel (b) shows that in the case of the voltage reaching the upper threshold, the stepper motor runs a certain distance to bring the voltage back to the median value of the lower and upper limits.
The different synchronous configurations of the stepper motor and PZT when the average control voltage of PZT reaches the upper threshold. (a) The motor first moves downwards and the PZT then contracts upwards. (c) The PZT contracts upwards while the motor moves downwards, and the PZT then expands downwards. These two configurations cause spurs (b) and no spurs (d) in the focusing control when the objective lens tracks the curved substrate.
(a) Photograph of the autofocusing system for LDW on non-planar surfaces. (b) The step response of the system in the case of a 3.7 μm defocus and the stepper motor not working. (c) The step response of the system in the case of a −7.7 μm defocus and the stepper motor working.
Curves of autofocusing errors (in absolute values) as a function of substrate movement speed at different tilt angles of substrate. Curves C, B, and A are for tilt angles 3°, 5°, and 10°, respectively.
Fabrication result on the curved substrate. (a) Lateral view photo. (b) Overhead view photo. (c) Partially enlarged view.
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