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Managing signal sampling rates is essential in digital signal processing to maintain signal integrity. A decimated signal, characterized by a reduced frequency range due to its lower sampling rate, can be upsampled by inserting zeros between each sample. This upsampling process expands the original spectrum and introduces repeated spectral replicas at intervals dictated by the new Nyquist frequency. To refine this zero-inserted sequence, it is passed through a lowpass filter with a cutoff...
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Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
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Parametric down-conversion with nonideal and random quasi-phase-matching.

Chun-Yao Yang1, Chun Lin1, Charlotte Liljestrand2

  • 1Department of Physics and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan.

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|May 14, 2016
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Summary
This summary is machine-generated.

Nonideal quasi-phase-matching (QPM) gratings in parametric down-conversion (PDC) unexpectedly generate biphotons via noncritical birefringent-phasematching and alter their spectrum. These findings offer new avenues for biphoton engineering.

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Area of Science:

  • Quantum optics
  • Nonlinear optics
  • Materials science

Background:

  • Quasi-phase-matching (QPM) is crucial for generating biphotons via parametric down-conversion (PDC).
  • The impact of QPM grating imperfections on biphoton properties remains largely unexplored.
  • Understanding these effects is vital for advancing fundamental tests and applications of quantum optics.

Purpose of the Study:

  • To investigate the effects of nonideal and random QPM structures on biphoton generation in PDC.
  • To explore the interplay between PDC and imperfections in nonlinear crystals.
  • To provide new insights for engineering biphotons using QPM.

Main Methods:

  • Experimental and theoretical studies of PDC using periodically poled nonlinear crystals with short periodicity.
  • Investigating the influence of nonideal duty cycles and random domain length errors in QPM gratings.
  • Analyzing the generated biphoton properties, including spectral characteristics and phase-matching conditions.

Main Results:

  • Observed biphoton generation through noncritical birefringent-phasematching, a phenomenon not seen with ideal QPM gratings.
  • Demonstrated that the biphoton spectrum is significantly influenced by the specific nonidealities and randomness in the QPM structure.
  • Reported a diminished strength of QPM biphotons due to grating imperfections.
  • Validated experimental observations through theoretical modeling.

Conclusions:

  • Nonideal QPM gratings introduce novel phase-matching mechanisms in PDC.
  • The spectral properties of generated biphotons are directly tunable by QPM imperfections.
  • This research opens new possibilities for tailored biphoton generation and quantum applications.