Quantum optical communications system for micro robots

One way to improve the acquisition of planetary information from robotic landers is to use many smaller robotic explorers that can cover more ground than a single conventional rover. The development of such robots presents very significant technological challenges to enable essential functions, such as mobility and communication, given the small size and limited power generation capability. The research presented here has been focused on developing a communications system that has the potential for providing ultra-low power communications for robots such as these.;The communication system is a variant of photon-counting based communications. Instead of counting individual photons the system only counts the arrival of time coincident sets of photons that have distinct correlations. The utilization of sets of photons significantly decreases the bit error rate because they are highly identifiable in the presence of ambient light. The sets of photons can be generated in two ways. Quantum Entangled photons are one such set that can be generated through Spontaneous Parametric Down Conversion. This process is not energy efficient, but Quantum Entangled photons have an effective range that is hundreds of times greater than for photon sets that are not entangled. This is due to the highly correlated momenta for entangled photons, which translates into positional correlation in the transmitted beam. A transmitter based on quantum entangled photons was built and tested. A one bit value was coded by sending photons of like polarization and a zero bit value was coded by sending photons with orthogonal polarizations. The system successfully transmitted data at a remarkably low power level, a received optical power of 1 Pico joule per bit, in the presence of significant background noise.;The second way to generate sets of photons is to utilize multiple sources that are pulsed simultaneously. This has the benefit of being much more energy efficient than a Quantum Entangled photon source. A transmitter utilizing this concept was built for evaluation. The components used in this system were chosen so that they could in the future be integrated into a cubic centimeter device. The experimental system was able to achieve a Bit Error Rate of 10 -3 while transmitting data at a rate of 100 Kbits/sec over a distance of 70 meters with a background level that was above the signal level (received Signal to Noise Ratio was -0.7 dB) using only 760 pW of transmitted power. Even with very low electrical to optical energy efficiency ∼1%, an optimized optical system utilizing this technique would still use only 76 nw of electrical power. This is a power level that can be sustained by a power scavenging micro robot. The operating characteristics of this system have been modeled and used to extrapolate future performance improvements that can be achieved utilizing improved components that can be readily built.