Holographic Free-Space Optical Interconnects

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Holographic Free-Space Optical Interconnects
The Interconnect
receiver
emitter

• surface relief or refractive index modulated
  hologram as diffractive optical element
• in-situ recording and development results in
  precise alignment
• back or front-coating to obtain reflection
  hologram

real-time hologram
Mechanism of Hologram Recording in Candidate
Materials
Photoconducting Thermoplastic
conductor
illumination




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photogenerated free charges migrate to surface

• non-uniform electrostatic pressure
• heating causes deformation of thermoplastic
• rapid cooling fixes surface relief pattern
• surface deposition of aluminum

• re-charge to constant surface potential
• added charge deposited in exposed regions
• variation of surface charge density
• developable electrostatic latent image

• non-uniform electrostatic field
• non-uniform surface potential

Dichromated Gelatin
Photopolymers

• photochemical reaction is a reduction of Cr(VI)
  to Cr(III)
• cross-links form in regions of higher exposure
• gelatin hardens and becomes less soluble
• develop by water wash and alcohol rinse
• density changes and nano-sized cracks and voids
• refractive index modulated holograms

• free-radical polymerization of acrylamide
• diffusion of products to re-establish
  equilibrium
• density changes produce refractive index changes
• develop by uniform exposure to UV radiation

Reflective Coating Process
back-coating
front-coating

• metal deposition or use of mirrored substrate
• coating backside of refractive index modulated
  hologram
• signals propagate in diffracting material two
  times
• investigate diffractive effect of second trip
• can implement using existing architectures

• aluminum or other reflective metal deposition
• coating of surface relief hologram
• dependable reflective-diffractive optical
  element produced
• new architectures will need to be designed to
  implement

Research by Professor Clark Guest and Crescentia
Miscisin