Microcontroller based feedforward digital controller for laser frequency locking for wide band WDM communication systems

Abstract:
In this paper, feed forward controller model based on the laser’s inverse model is
proposed. An enhanced digital control algorithm for 3rd, 5th, and 7th and possibly
higher harmonics for laser frequency locking is developed. A generic diagram for the
digital implementation of the proposed controller is presented. Digital implementation
of the control algorithm modules is proposed and discussed. Hardware realization based
on microcontrollers for the proposed digital controller is introduced and described for
He-Ne laser systems. Simulation results of the full system showed that using higher
harmonics in laser frequency locking yields better performance in regard to the
frequency shifts, improved noise performance, and hence better reproducibility. It also
showed that the frequency difference between lasers locked with higher order harmonic
locking using the digital realization is better than that locked with lower order harmonic
locking. The measurement results using the lab version of the realized controller and
He-Ne laser system is presented and found in a very good agreement with the
simulation results which assure that the proposed digital controller can be accurately
used for transmitting multiple users’ data over WDM communication systems with
acceptable stability.