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Open Access Publications from the University of California

FPGA-Based Optical Cavity Phase Stabilization for Coherent Pulse Stacking

  • Author(s): Xu, Y
  • Wilcox, R
  • Byrd, J
  • Doolittle, L
  • Du, Q
  • Huang, G
  • Yang, Y
  • Zhou, T
  • Leemans, W
  • Galvanauskas, A
  • Ruppe, J
  • Tang, C
  • Huang, W
  • et al.
Abstract

© 1965-2012 IEEE. Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable, and distributed digital control system with firmware and software integration for algorithms, to support the CPS application. We model CPS as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection algorithm on an field-programmable gate array (FPGA). A two-stage (2+1 cavities) 15-pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5kHz, and stabilized at an individually-prescribed round-trip phase with 0.7deg and 2.1deg rms phase errors for Stages 1 and 2, respectively. Optical cavity phase control with nanometer accuracy ensures 1.2% intensity stability of the stacked pulse over 12 h. The FPGA-based feedback control system can be scaled to large numbers of optical cavities.

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