Realization of free-space optical pickup head with stacked Si-based phase elements

We have developed a novel stacked silicon-based microoptical system, which is optical-on-axis and transmissible in both visible and infrared ranges. By using the new microoptical system techniques, we fabricated a miniaturized optical pickup head module. This optical pickup head consisted of a 650-nm laser diode, a 45degrees silicon reflector, a grating, a holographic optical element, and some aspherical Fresnel lenses. These optical phase elements fabricated on a SiNx membrane were suspended on Si chips. Each element was then stacked by chip bonding. We could obtain a circular focusing spot on the optical disc as small as 3.1 mum.