Type I Quasi-Phase Matching in a Periodically Poled Rb-Doped KTiOPO4 Ridge Waveguide

Nonlinear optics in waveguides provide means for efficient nonlinear interactions as this platform permits high confinement over long interaction lengths, and it has been a field of intense research since the early days of nonlinear optics [1]. With the development of electric field poling [2] and novel waveguide fabrication methods, waveguide devices have become of interest again and exploited in several contemporary applications like spectroscopy, metrology, sensing and quantum optics. The challenge that drives the field in the present days is the development of waveguides with small modal cross section, high transverse overlap between interacting modes, and low propagation loss. Rubidium-doped KTP (RKTP) is an attractive material as it has high nonlinear coefficients, strong resistance to optical damage, and a wide transparency range. Furthermore, it presents lower ionic conductivity, compared with its isomorph KTP, allowing fabrication of high quality ferroelectric domain gratings [3]. Waveguide fabrication techniques combined with periodically poled structures allows to obtain quasi-phase matching (QPM) of Type I for RKTP so the strong d 33 coefficient can be exploited [4].