Depth profile of the nonlinear optical susceptibility of ion-implanted KNbO3 waveguides

Abstract

We report on the depth profile of the nonlinear optical susceptibility in ion-implanted potassium niobate (KNbO3) waveguides using reflected second harmonic generation from wedged samples. After irradiation the waveguide layer exhibits partial loss of its optical nonlinearity that can be recovered to better than 90% of its value of the virgin crystal by subsequent annealing and repoling. We propose microscopic depolarization due to ion implantation to be responsible for the observed decrease of the nonlinear optical susceptibility.

Blue-light second-harmonic generation in ion-implanted KNbO3 channel waveguides of new design

“…9 Further work is in progress to anneal and repole these KNbO 3 waveguide samples to reduce the mode attenuation and fully restore the NLO coefficient and to form narrower channel guides with a cross section of 5 m ϫ 5 m in order to increase the normalized conversion efficiency significantly. 13 In summary, we demonstrated phase-matched secondharmonic generation in KNbO 3 channel waveguides which were fabricated by photoresist masks with wedged edges and one single-energy ion implantation. Up to 2.6 mW blue light was generated for an overall conversion efficiency of 3.3% W Ϫ1 .…”

“…Using N ϭN 2 ϭ2.275, ϭ880 nm, d 32 ϭ12.8 pm V Ϫ1 , 12 dϭ1, hϭ1, Qϭ1, and ⌫ϭ0.026 m Ϫ2 , we calculate a normalized conversion efficiency of ϭ140% W Ϫ1 cm Ϫ2 . If we consider ͑i͒ hϭ0.24 due to the waveguide loss coefficients of ␣ 2 ϭ16 dB cm Ϫ1 and ␣ ϭ3 dB cm Ϫ1 , ͑ii͒ dϭ0.7 because these waveguides are not annealed and repoled, 13 and ͑iii͒ Qϭ0.65 because the conversion efficiency of the substrate KNbO 3 crystal is only 2.0% W Ϫ1 cm Ϫ1 compared to the maximum value of 3.1% W Ϫ1 cm Ϫ1 , then we expect a theoretical conversion efficiency of •h•L 2 ϭ5.1% W Ϫ1 (15% W Ϫ1 cm Ϫ2 ) for this channel waveguide. The remaining difference of about 35% between the calculated and measured conversion efficiency is ascribed to the inhomogeneity in the waveguide which is also responsible for the broadening of the wavelength tuning curve mentioned above.…”

Electro-optic and nonlinear optical properties of ion implanted waveguides in organic crystals

“…A fundamental wavelength of λ ω = 1176 nm was chosen so that the second-harmonic generated light at λ 2ω = 588 nm was within the visible absorption band of DAST [14]. Therefore, only the second-harmonic generated light at the sample surface was observed and any substrate contributions were eliminated [11]. The polarization of the fundamental beam was parallel to the A light beam impinging on an interface between a linear and a nonlinear optical active medium will result in a second-harmonic reflected wave.…”

“…To use ion implanted waveguides for active integrated photonic devices, it is of main importance to maintain the high nonlinear optical properties in the waveguide region. In inorganic nonlinear optical active crystals such as KNbO 3 or LiNbO 3 , a reduction of the nonlinear optical properties below 50% of its bulk value was observed upon implantation [11,12]. With thermal annealing and subsequent repoling the optical nonlinearity was recovered to more than 90% of the bulk value [11].…”

“…In inorganic nonlinear optical active crystals such as KNbO 3 or LiNbO 3 , a reduction of the nonlinear optical properties below 50% of its bulk value was observed upon implantation [11,12]. With thermal annealing and subsequent repoling the optical nonlinearity was recovered to more than 90% of the bulk value [11]. In organic nonlinear optical crystals, the origins of the refractive index change by ion implantation are electronic excitations [10], and are therefore essentially different compared to inorganic crystals, in which the refractive index changes are due to ion induced nuclear displacements.…”