Periodically Poled Nonlinear Photonic Crystal KTa_0.51Nb_0.49O₃ Combining Wide Transparent Range and Large Quadratic Coefficient

Abstract

coefficients, which have been utilized for obtaining the generation of broadband light at new frequencies and its control. [1,2] In parametric conversion processes, phase matching (PM) condition is the prerequisite for highly efficient energy conversion, corresponding to the conservation of momentum in the nonlinear optical interaction. In order to overcome the limitations of traditional angular PM by optical birefringence, several applicable PM strategies have been proposed, comprising quasi-phase-matching (QPM), [3,4] Fresnel phase-matching (FPM), [5] additional periodic phase (APP), [6] random quasi-phasematching (RQPM), [7] etc. Among them, periodically poled engineered crystals, especially lithium niobate waveguides on insulators (LNOI), [8][9][10] have been extensively developed as a unique platform for integrated photonic applications on quantum information, [11] smart chips, [12] remote communications, [13] to name just a few examples. [14][15][16] The periodically poling technique is mainly applied in ferroelectric materials, thus producing designed domain inversion and reciprocal lattice vectors (RLVs) to compensate for the phase mismatch. Compared with angular birefringent phase-matching (BPM), the QPM technique has two apparent advantages. [10] First, it can utilize the largest nonlinear tensor element d ij . For example, the effective d 33 (27-34 pm V −1 ) in periodically poled LiNbO 3 (PPLN) is three times larger than d 31 (4.5 pm V −1 ) that is utilized in the BPM technique. Second, in principle, QPM allows efficient nonlinear interactions at any frequencies in the transparent range of the ferroelectric materials, including inaccessible wavelength by the BPM technique. Therefore, finding new QPM ferroelectric crystals with large d ij and wide transparency simultaneously is an urgent but a challenging task.KTa 1-x Nb x O 3 (KTN) perovskite is a mixed crystal of KTaO 3 and KNbO 3 . It is a typical displacement-type ferroelectric crystal with a tunable Curie temperature T c by adjusting Ta/Nb ratio. [17] In as-grown KTN crystals, both 90° and 180° domains are randomly arranged throughout the crystal, thus providing rich RLVs to support three-dimensional QPM conditions. [18][19][20][21][22] However, these natural random domains are difficult to Since the first proposal of quasi-phase-matching (QPM) in 1962, finding new nonlinear photonic crystals has been an attractive topic in nonlinear optics fields. However, combining high conversion efficiency and wide operation range concurrently into one single crystal remains a great challenge. Herein, a periodically poled KTa 0.51 Nb 0.49 O 3 (PPKTN) is fabricated as a one-dimensional nonlinear photonic crystal for the first time, to the authors' best knowledge. Benefitting from the large quadratic nonlinear coefficient, the QPM second harmonic generation (SHG) at 1030 nm is realized with a high conversion efficiency of up to 39%. More importantly, KTN crystal possesses wider midinfrared spectral transparency (0.4-8.0 µm) than commercialized LiNbO 3 and KTiOPO ...

Anomalous Optical Properties of KTN:Li Ferroelectric Supercrystals

“…Recent studies in bulk KTN show how ferroelectric domain distribution can considerably affect spectroscopic response in the visible and near-infrared spectrum [25]. To test the role of domains in the anomalous optical response, we measured SHG for a wide range of signal wavelengths [7,[26][27][28][29].…”