Active Mode Locking: Quantum Oscillator vs. Classical Coupled Oscillators

Mode expansion approach is proposed to simulate the active mode locked laser. In this method, electric fields of optical modes in the laser cavity are treated as free classical oscillators. The optical modulator provides the coupling among the modes or oscillators. It is found that the eigenvalue of this coupled system is corresponding to the threshold optical gain and normal mode or eigenfunction is corresponding to optical field of each mode. The simulation results obtained by mode expansion method agree with those calculated by the well- known Master equation, which provides an analytical solution with a function similar to the quantum harmonic oscillator. However, since the proposed method focuses on the individual mode and its coupling with the other modes instead of mode profile in general, it gives more information than Master equation. To show the capability of the new method, several applications are explored where Master equation fails to solve the problems. It is believed that the proposed method helps design the devices such as optical pulse generator, multi-wavelength laser and therefore have great application in optical signal generation and processing