BACKGROUND:  Coherent optical link systems operate with a transmitter laser using a transmitter oscillator, and a receiver laser using a local oscillator. Random phase fluctuations of the local oscillator, relative to the transmitter oscillator, cause optical distortion in the form of laser phase noise. The power spectral density and variance of the laser phase noise strongly depend on the laser linewidth, requiring high quality narrow linewidth lasers to reduce optical distortion. However, narrow linewidth lasers are very expensive, significantly increasing the costs of coherent optical systems.

INNOVATION:  The adaptive phase noise reduction method enables the use of affordable, large linewidth lasers by significantly relaxing the laser linewidth requirements. Thus, expensive, high quality, narrow linewidth lasers are not necessary, which allows for economic savings in all coherent optical systems.

POTENTIAL APPLICATIONS 

• Coherent optical communications.
• Optically noisy systems.

ADVANTAGES

• Compensates for laser phase noise optical impairments by using digital signal processing adaptive filtering.
• Reduces costs for coherent optical systems by allowing economical use of large linewidth lasers while still achieving target performance.
• Reduces bit error rate floor without needing a training sequence or the associated transmission overhead.
• Scales down size and power requirements by utilizing very large scale integration (VLSI) technology.

DEVELOPMENT-TO-DATE:  The method has been successfully modeled and simulated.

Reference: UCLA Case No. 2006-272