Even-order harmonic cancellation and increased RF gain using dual-output mach-zehnder modulator with two wavelength input

  • US Patent No. 8224188
  • Issued: July 17, 2012
  • Status: Active

A method and system for processing analog optical signals to produce a single RF output free from even-order harmonic distortion. Two analog optical signals of different wavelengths λ1, λ2 are input into a dual-output Mach-Zehnder modulator (MZM), where one wavelength input is high-biased and one wavelength is low-biased. The complementary high- and low-biased wavelengths are output from each arm of the MZM to a multiplexer, which filters out the unwanted high- or low-biased wavelengths from each MZM arm so that both wavelengths are low-biased or high-biased. The signals are passed to a pair of photodiodes, and the photocurrents from the photodiodes are differenced to produce the final RF output. Because of the complementary phase differences between the two low- or high-biased signals generating the photocurrent, all components of the photocurrent except the fundamental and odd-order harmonics cancel each other, resulting in a high-quality RF output free from harmonic distortion.

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