Phase-lock Optical Singal Recovery

 

Phase-locked Optical Signal Recovery

Martyn Fice and Alwyn Seeds

Sponsors

Air Force Office of Scientific Research 

Description
 

Phase-locked receivers have long been used for the recovery of signals in low signal to noise ratio (SNR) environments, such as space applications.  The implementation of such techniques for optical signals is difficult, because the wide (MHz) line widths of these signals require correspondingly wide loop bandwidths.  The short feedback propagation delay required to achieve the necessary bandwidth cannot be achieved using conventional fibre optic components.

 

At University College London (UCL), we have developed the Optical Injection Phase Lock Loop (OIPLL) to overcome these limitations.  In this technique, a narrow bandwidth optical phase lock loop (OPLL) is used to control the free-running frequency of an optically injection locked laser to compensate for thermal drift, drift in the frequency of the incoming signal, and low-frequency noise.  Such loops have been shown to maintain stable lock over wide temperature ranges (>10 K).

 

Optical Injection Phase Lock Loop

 

In this project, we are investigating the application of the OIPLL to the recovery of optical signals in low SNR environments.  Carrier recovery from high data rate (10 Gb/s) modulated signals has been demonstrated in the presence of amplified spontaneous emission noise from erbium doped fibre amplifiers using a heterodyne OIPLL.  The next phase of the project will focus on using the recovered optical carrier to synchronously demodulate the optical data signal.  It is expected that this will open the way for the application of the technique to schemes using more complex optical modulation schemes (i.e. those utilising phase modulation), which offer enhanced sensitivity or increased capacity.

 

RF spectrum for beating between CW master and slave lasers
with and without phase locking using heterodyne OIPLL