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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. With the development of electric field poling 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. 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., QC 20220928

The propagation front of a crack generates large strain gradients and it is therefore a strong source of gradient-induced polarization (flexoelectricity). Herein, we demonstrate that, in piezoelectric materials, a consequence of flexoelectricity is that crack propagation is helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. The discovery of crack propagation asymmetry proves that fracture physics cannot be assumed to be symmetric in polar materials, and indicates that flexoelectricity should be incorporated in any realistic model., QC 20190424

Scanning electron microscopy was used to study the mobility of domain walls in vapor-transport equilibrated stoichiometric LiTaO3. By using low-acceleration voltage, switching occurs solely for polarization pointing up domains, resulting in fast domain-wall motion. When the incoming electron beam was more energetic with larger penetration depth, the switching instead occurred for polarization pointing down domains. Our results are discussed in terms of the interaction of the scanning electron beam with the polarization-screening charges at the crystal surface., QC 20190923

The propagation front of a crack generates large strain gradients and it is therefore a strong source of gradient-induced polarization (flexoelectricity). Herein, we demonstrate that, in piezoelectric materials, a consequence of flexoelectricity is that crack propagation is helped or hindered depending on whether it is parallel or antiparallel to the piezoelectric polar axis. The discovery of crack propagation asymmetry proves that fracture physics cannot be assumed to be symmetric in polar materials, and indicates that flexoelectricity should be incorporated in any realistic model.

A 10.8 mu m wide ridge waveguide was fabricated by diamond-blade dicing in an ion-exchanged periodically poled Rb-doped KTiOPO4 sample. The waveguide was used to generate blue second harmonic light at 468.8 nm in the TM(00 )mode through first order Type I quasi-phase matching, exploiting the large d(33) coefficient of the crystal. It was evaluated using a cw Ti:Sapphire laser, and 6.7 mu W of blue light was generated with 5.8 mW of fundamental radiation at 933.8 nm coupled through the waveguide. The results presented here pave the way for efficient nonlinear processes in a waveguide format. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement, QC 20190119

QC 20240715

A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO4. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-mu m features are to be domain engineered, which otherwise is incompatible with conventional photolithography. A non-negligible domain broadening was seen and attributed to a low nucleation rate using this type of electrode. However, under the appropriate poling conditions, this could be exploited to obtain a QPM grating with a short pitch (2 mu m), equal to half of the electrode period., QC 20150312. Updated from accepted to published.

Periodically poled LiTaO3 has a shorter cut-off wavelength than KTP and LiNbO3, which makes this material attractive for UV generation. However, the standard congruent material suffers strongly from photorefractive damage which has limited its use in the UV. It is expected that stoichiometric LiTaO3 (SLT) would make a superior material in this context, as the defect concentration, which directly relates to the damage, is strongly reduced. Close to perfectly stoichiometric crystals can be obtained by post growth diffusion of Li2O into the crystal at high temperatures to compensate the Li2O deficiency, so called vapour transport equilibrated (VTE) SLT [1]. The coercive field is drastically reduced for SLT which facilitates the way for fabricating QPM devices [2]. However lower defects and reduced coercive field might cause instability for charged domain walls (DW) or walls that are not in their lowest energy state. Since the stability mechanism for VTE SLT is not very well known, its investigation would lead to improvement in device fabrication with short period and also helps to understand the DW dynamics. In this work, we study the impact of chemical etching after poling on domain stability of SLT. We show that chemical etching right after poling induced DW movement without any external field. We demonstrate that when the original DW configuration is head-to-head (HH) or tail-to-tail (TT), the DW movement results in backswitching or merging with neighboring domians, respectively. Our finding are monitored by in situ SHG during etching followed by characterization of the domain structure with optical microscopy. We also show that this behavior is independent of the domain orientation with respect the crystallographic axes., QC 20170109

QC 20200911

NQC 2015

NQC 201602

Part of proceedings: ISBN 978-1-4799-0594-2Duplicate record in Scopus 2-s2.0-84898712869QC 20140619