Optical Free-Space Time and Frequency Transfer: Doppler-Tolerant Synchronization
Abstract
The overall objective of this seedling research project is to explore the signal processing aspects of high-precision time and frequency transfer, from the design of algorithms to the implementation in a real-time system based on field-programmable gate arrays. Specific objectives of the proposed research include the development of high-performance algorithms to extract timing signals from interference signals generated by optical frequency combs in a time transfer experiment, despite significant Doppler shifts due to relative motion of the two transceiver sites. The overall proposed approach is to use optical laser frequency combs to provide unambigous discrimination of time signals. However, the bandwidth required is orders of magnitude above achievable bandwidths from electronics. In the proposed approach, the receiver is implemented using a linear optical sampling technique, where a second local frequency comb is used to sample the incoming pulses on a photodiode, yielding the required input bandwidth. Further, linear optical sampling is combined with equivalent time sampling to provide a series of interference signals for discrimination. This particular sampling scheme allows detection of epochs with femtosecond precision or better when there is no relative motion between the two sources. However, this scheme, when used with a proposed high carrier frequency of 200 THz containing non-idealities of the experiment (Doppler shift due to relative motion and dispersion of optical signals paths) still results in significant degradations of the precision of the timing extraction. This degradation is dependent on the exact wavefom1 used to define the epoch and on the processing algorithms used to extract the timing signals, and can be reduced by algorithmic techniques proposed to be explored here. For example, pulse shaping techniques can be used to pre-compensate air dispersion or even provide a combined dual-slope dispersive pulse waveform, allowing disentangling the effect of the Doppler shift on the extracted epochs. These techniques will be explored here to preserve the precision of timing extraction.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1510649
Entities
People
- Jean-daniel Deschenes
Organizations
- Army Contracting Command
- Defense Advanced Research Projects Agency
- Laval University