William J Ulrich

US Patent:

20090226186, Sep 10, 2009

Filed:

Mar 5, 2008

Appl. No.:

12/042748

Inventors:

Jose E. ROMAN - Catonsville MD, US
William J. Ulrich - Baltimore MD, US
Shan Zhong - Ellicott City MD, US

International Classification:

H04B 10/06

US Classification:

398202

Abstract:

The present invention provides a method for biasing/controlling an optical demodulator suitable for use in an optical phase-shift-keying (PSK) system, such as an optical differential-phase-shift-keying (DPSK) system or an optical differential-quadrature-phase-shift-keying (DQPSK) system, the method including: receiving a signal from an optical demodulator/balanced receiver pair; full-wave rectifying the signal; passing the full-wave rectified signal through a low-pass filter; monitoring the full-wave rectified signal received from the optical demodulator/balanced receiver pair and passed through the low-pass filter; and providing related feedback to the optical demodulator. Preferably, the signal includes a radio frequency (RF) signal. Full-wave rectifying the signal includes full-wave rectifying the signal using a full-wave rectifying circuit. Optionally, the low-pass filter includes about a 1 GHz bandwidth (BW) low-pass filter. Monitoring the full-wave rectified signal received from the optical demodulator/balanced receiver pair and passed through the low-pass filter includes monitoring the full-wave rectified signal using an RF power meter. The RF signal power monitored is dependent on an optical phase shift of the optical demodulator. Optionally, the method is employed in a high data rate optical transmission system.