Rotating disc optical synchronization system using alternating binary diffractive optical elements

An optical synchronization system for a scanning system on a rotating disc comprising:

• a light source for emitting a coherent light beam,
• means to collimate said coherent light beam,
• scanning elements disposed on said rotating disc,
• a continuous plurality of alternating first binary diffractive optical elements and second binary diffractive optical elements and third binary diffractive optical elements with equal numbers of said first and second binary diffractive optical elements and fewer of said third binary diffractive optical elements, said first, second and third binary diffractive optical elements disposed circumferentially on said rotating disc, said continuous plurality of first, second and third binary diffractive optical elements being separate from said scanning elements, such that said collimated light beam is alternately diffracted and focussed by said first binary diffractive optical elements onto a first photodetector, diffracted and focussed by said second binary diffractive optical elements onto a second photodetector, and diffracted and focussed by said third binary diffractive optical elements onto a third photodetector, said first photodetector, said second photodetector, and said photodetector generating a continuous synchronization signal for rotation of said rotating disc.