Ion-exchanged waveguides in periodically poled Rb-doped KTiOPO4 for efficient second harmonic generation.

Patrick Mutter,Cristine C Kores,Andrius Zukauskas,Max Widarsson,Fredrik Laurell,Carlota Canalias

doi:10.1364/oe.410773

Abstract

An ion-exchange process has been developed for periodically poled Rb-doped KTiOPO4 (RKTP) which warrants high efficiency and low loss channel waveguides. The domain stability was investigated, and it was found that domain gratings with uncharged walls could stand the ion-exchange process without deterioration. 3.1 mW of blue second harmonic light was generated from 74 mW of radiation at 940.2 nm coupled into an 8 µm wide and 7 mm long waveguide, corresponding to a normalized conversion efficiency of 115%/Wcm2. Waveguides in PPRKTP open the possibility for stable operation at high optical powers, as well as generating entangled photons at low optical powers, and enable the investigation of novel nonlinear processes such as counter-propagating interactions in a waveguide format.

Highlights

Nonlinear interactions can be tailored with quasi-phase matching (QPM) to generate coherent light at desired wavelengths [1], and these can be efficient in waveguides as a high intensity is maintained over a long interaction length [2]
In this work we present the fabrication of channel waveguides in PPRKTP crystals with a QPM grating with a period of 5.82 μm
We have developed a method to fabricate low-loss channel waveguides in PPRKTP using ion-exchange in a melt containing Rb+, Ba2+ and K+

Summary

Introduction

Nonlinear interactions can be tailored with quasi-phase matching (QPM) to generate coherent light at desired wavelengths [1], and these can be efficient in waveguides as a high intensity is maintained over a long interaction length [2]. For traditional titanium-diffused and annealed-proton-exchanged waveguides the fundamental modes are elliptical which leads to poor mode-matching with optical fibers It should be pointed out, that MgO doped LN (MgOLN) can be used to reduce GRIIRA [8], and with the novel thin film LN on insulator platform it has been possible to fabricate short and even sub-μm period QPM gratings [10,11]. It is difficult to efficiently butt-couple to such waveguides with optical fibers and it might require grating assisted in- and out-coupling [13] In this context is KTiOPO4 (KTP) an interesting alternative platform to LN and MgOLN as it can be periodically poled with short periods for use in first order (m=1) QPM [14] and it does not experience photorefraction and is much less sensitive to GRIIRA and BLIIRA [15,16]. These results could pave the way for counter-propagating nonlinear interactions [31] in waveguide format

Waveguide fabrication and domain structure

Optical experiments

Findings

Conclusion