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Generation and Coherent Control of Pulsed Quantum Frequency Combs
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Coherent correlator and equalizer using a reconfigurable all-optical tapped delay line.

Mohammad Reza Chitgarha1, Salman Khaleghi, Omer F Yilmaz

  • 1Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA. chitgarh@usc.edu

Optics Letters
|July 2, 2013
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This study shows a reconfigurable optical tapped delay line can find multiple patterns in Quadrature Phase Shift Keying (QPSK) signals and equalize various high-speed optical signals, even with dispersion.

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Area of Science:

  • Optical communications
  • Signal processing
  • Photonics

Background:

  • Advanced modulation formats like Quadrature Phase Shift Keying (QPSK), 8 Phase Shift Keying (8 PSK), and 16 Quadrature Amplitude Modulation (16 QAM) are crucial for high-capacity optical networks.
  • Dispersion and noise degrade signal quality, necessitating effective equalization techniques.

Purpose of the Study:

  • To demonstrate a reconfigurable optical tapped delay line (OTDL) for pattern searching and signal equalization.
  • To evaluate the performance of the OTDL system with various modulation formats and data rates.

Main Methods:

  • Experimental setup utilizing a reconfigurable OTDL with coherent detection.
  • Testing with 20 Gbaud Quadrature Phase Shift Keying (QPSK) signals for pattern searching.
  • Equalization tests on 20/31 Gbaud QPSK, 20 Gbaud 8 PSK, and 16 QAM signals over 25 km of SMF-28 fiber.

Main Results:

  • Successful identification of multiple patterns within QPSK signals, confirmed by correlation peaks.
  • Effective equalization of QPSK, 8 PSK, and 16 QAM signals with low average Error Vector Magnitudes (EVMs) of 8.3%, 8.9%, and 7.8%, respectively.
  • Achieved an optical signal-to-noise penalty of less than 1 dB for a 20 Gbaud QPSK signal with up to 400 ps/nm dispersion.

Conclusions:

  • The reconfigurable OTDL combined with coherent detection is a viable solution for advanced optical signal processing.
  • The demonstrated system offers robust performance in pattern searching and equalization for high-speed optical communication systems, even under challenging conditions like chromatic dispersion.