Studies on the effect of duty cycle variation in Fibonacci-based quasi-phase matching devices

Abstract

We have studied the effect of duty cycle variation in the Fibonacci optical superlattice (FOS) structure by analysing the second harmonic generation (SHG) spectrum. Unlike periodic quasi-phase matching (QPM) device, the variation in duty cycle changes the SHG spectrum asymmetrically. The higher intensity and other multiple peaks in the spectrum change asymmetrically when the duty ratio varies away from 0.5. As a result, the SHG spectrum of lower and higher duty ratios from the ideal FOS device generates multiple dissimilar peaks as it was observed from entirely different QPM devices. However, the main phase matching peak shows symmetric nature, irrespective of the duty cycle variation like the periodic one. Further, we have analysed the correlation spectrum to prove the asymmetric nature of the FOS SHG spectrum. Although FOS device exhibits asymmetric spectral nature in duty cycle variation, it shows the same optical interaction regardless of the pump direction.