Method for quadrature phase angle correction in a coherent...

Details Method for quadrature phase angle correction in a coherent... Method for quadrature phase angle correction in a coherent...

2005-07-12

2005-07-12

Pyo, Kevin (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C250S2140LS, C250S225000, C332S103000, C342S194000

Reexamination Certificate

active

06917031

ABSTRACT:
A method is provided for correcting a quadrature angle error that exists in the coherent receiver hardware of a dual-polarization optical transport system. The receiver hardware that causes the quadrature angle error is a 90 degree optical hybrid mixing device. The method involves generating an estimate of the quadrature angle error and compensating for the quadrature angle error by multiplying the first and second detected baseband signals by coefficients that are a function of the estimate of the quadrature angle error. The method is robust to severe channel distortion encountered within an optical fiber transmission channel as well as temperature effects and ageing of the 90 degree optical hybrid. The method is suited for a digital signal processing implementation in the coherent receiver when a modulation scheme used on a transmitted signal is quadriphase-shift keying (QPSK). In other embodiments, the method can be used to correct for quadrature angle error in modulation schemes such as binary PSK, M-ary PSK where M>4, or Quadrature Amplitude Modulation (QAM). The method can be implemented by an application-specific integrated circuit(ASIC).

REFERENCES:
patent: 2004/0121741 (2004-06-01), Rashev et al.
“Secure Optical Communications Utilizing PSK Modulation, Polarization Multiplexing and Coherent Digital Homodyne Detection with Wavelength and Polarization Agility”, A. Salamon, G. Levy-Yurista, M. Tseytlin, P.S. Cho, and I. Schpantzer, Celight Inc., http://www.celight.com/images/pdfs/Polarization_Presentation_OFC_2003.pdf.
“Digital, endless polarization control for polarization multiplexed fiber-optic communications”, M. Tseytlin, O. Ritterbush, J. Schwarzwalder, and A. Salamon, Celight Inc., 2003, http://www.celight.com/images/pdfs/Celight_Coherent_Communications.pdf.

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