Comparing with the writing method of plane pattern, spherical pattern' has some remarkable different on several points.
Firstly, it is difficult to spin-coated a uniform photoresist film on a spherical substrate, especially the ratio of spherical
radius to caliber is smaller, and the spin-coated way must match the ratio of spherical radius to caliber. Secondly, if the
sphere couldn't be regarded as a plane, a so-called concentric optical scan movement way must be applied for the
generation of spherical pattern, because the reflex of substrate will affect the quantity of illumination. Commonly, an
alignment technique is indispensable with pattern generation of spherical surface by the concentric optical scan in order
to ensure the orthogonal intersection of focusing laser beam and writing surface. Thirdly, a uniform velocity control must
be considered for the laser direct writing method on a spherical substrate. Otherwise, the exposure time of photoresist
will be different, and the line widths of pattern will be also different at different areas. Fourthly, commonly, because the
errors of concentric machine and substrate surface shape are bigger, so focusing servo-control technique is also needful
for writing a pattern on a spherical substrate. Focusing servo-control may keep the focal spot on the spherical surface by
a focus detection and control system in the course of writing pattern. Using these techniques, we fabricated a line width
of 7μm and a period of 600μm isometric mesh on the concave of a spherical substrate.