Title of Paper: Free space optical data transfer using cat's eye modulating retro-reflectors

Principal Author: Dr. William Rabinovich

Abstract: Using short range free space optical interconnects can be attractive for on-board data transfer in spacecrafts. Such links do not require long wiring harnesses, have no susceptibility to RF interference, can provide point-to-point connectivity and can, in some cases, be self-configuring. However most schemes for free space optical interconnects rely on arrays of small lasers and/or modulators directed via microlens arrays or gratings to a detector plane. These systems have very tight alignment tolerances both positionally and angularly and may be difficult to employ reliably on a spacecraft.

An alternative approach for free space optical data transfer uses modulating optical retro-reflectors (MRR). An optical retro-reflector is a passive optical device that reflects light exactly back along its path of incidence over a large field of view. An MRR couples an electro-optic modulator to the retro-reflector. In operation a cw interrogating beam paints the MRR with light which the retro-reflects back to the interrogating source. By driving the modulator with a signal the retro-reflected light is modulated and carries that data back to the interrogator with no need for pointing or tracking on one end of the link.

We will discuss an MRR system that works between two fixed points and greatly relaxes the alignment requirements for the link while at the same time preventing cross-talk between nodes. This system uses nodes consisting of catís eye modulating retro-reflectors that contain semiconductor multiple quantum well modulator/receivers. The nodes also have cw diode laser emitters. In operation each node sends out a broad cw beam to an identical node. The second node retro-reflects the broad beam in a narrow cone that contains the desired information. The designs and preliminary evaluations of the optical and electro-optical components of the system will be discussed and some sample