Engineered phase matching for broad frequency-tunability in terahertz-wave generation from quasi-phase-matched GaP devices

Abstract

A method to obtain broad frequency-tunability in terahertz (THz)-wave generation is proposed using a quasi-phase-matched GaP device that originally has narrow frequency-tunability. In this method, the phase matching curve for the GaP device is engineered via the GaP dispersion relation by shifting the signal frequency to 333.1 THz (0.90 lm) so that a flat part (i.e., a frequencyindependent part) can be formed on the phase matching curve. By selecting an appropriate quasiphase matching (QPM) period K such that QPM occurs at the center of the flat part of the curve, we can obtain a frequency-tunable width of 1.34 THz (37.8 lm) at around a THz-wave frequency of 3.26 THz (92.0 lm). This width is 9.9 times wider than that obtained using a similar quasiphase-matched GaP device at a signal frequency of 193.5 THz (1.55 lm) without the reformed phase matching curve. The advantage of the proposed method is that, unlike a previous method that used a chirped v (2) grating, broad frequency-tunability is obtained without reducing the high conversion efficiency produced by QPM. For comparison, a reduction in the conversion efficiency for the chirped v (2) grating method is demonstrated when a 9.9 times wider frequency-tunable width is achieved. V C 2015 AIP Publishing LLC. [http://dx.