Experimental Realization of Second Harmonic Generation in a Fibonacci Optical Superlattice of LiTaO3

Abstract

We have designed and fabricated a novel nonlinear optical superlattice of LiTaO 3 in which two antiparallel 180 ± domains building blocks A and B were arranged as a Fibonacci sequence. We measured the quasi-phase-matched second-harmonic spectrum of the superlattice. The second-harmonic blue, green, red, and infrared light generation, with energy conversion efficiencies of ϳ5% 20%, was demonstrated experimentally, which efficiencies are comparable with those of a periodic superlattice. Destruction of self-similarity and extinction phenomenon have also been observed in the spectrum. The experiment results are in good agreement with theory. [S0031-9007(97)02784-1] PACS numbers: 42.65. Ky, 77.80.Dj, An important development in condensed-matter physics is the discovery of quasicrystalline structure [1]. Much effort has been devoted to the studies of structure and physical properties of quasicrystal [2,3]. A quasiperiodic superlattice is an analog of one-dimensional quasicrystal. The first quasiperiodic semiconductor superlattice was fabricated by Merlin et al. by molecular-beam epitaxy in 1985 [4]. Since then metallic and dielectric Fibonacci superlattices have been produced by various techniques [5][6][7]. These superlattices have shown many unusual physical properties depending on their composition and layer thickness.In dielectric crystals, the most important physical processes are the excitation and the propagation of classical waves, including optical waves and acoustic waves. Ultrasonic excitation and propagation in the quasiperiodic acoustic superlattices have been studied both theoretically and experimentally [8]. More recently, the localization of optical waves in a quasiperiodic optical superlattice (QPOS) of SiO 2 and TiO 2 has been reported [9]. For second-order nonlinear optical effects of the QPOS, some preliminary theoretical work has been carried out [10]. It has been discovered that the second harmonic spectrum of a QPOS is different from that of a periodic optical superlattics (POS) due to its lower space-group symmetry. According to the theory of quasiphase-matching (QPM) proposed by Armstrong et al. [11], the phase matching condition in the second harmonic process of a QPOS can be written intowhere k 2v , k v are the wave vectors of the second harmonic and fundamental waves, respectively, G m,n is the reciprocal vector (called the "grating wave vector" in nonlinear optics) which depends on the structure parameter of a QPOS. In a Fibonacci system, two incommensurate periods with ratio t are superimposed. The indexing of G m,n requires two integers m, n, which is different from the POS's reciprocal vector G n indexed with only one integer. Therefore, a QPOS can provide more reciprocal vectors to the QPM optical parametric process, which results in the second harmonic spectrum of a QPOS showing more plentiful spectrum structure than that of a POS. This characteristic of the QPOS may be used in multiwavelength laser frequency conversion application. However, up to now, this has not been experimentally ...

Slowly varying amplitude approximation appraised by transfer-matrix approach

“…The concept of Quasi-phase-matching 4,7,8 has been realized in such periodic and quasi-periodic superlattices to achieve harmonic generations and other nonlinear processes with high efficiency. [8][9][10][11][12][13][14][15][16][17][18] The schematic configuration of superlattice is displayed in Fig. 1.…”

Combinatorial Frequency Generation in Quasi-Periodic Stacks of Nonlinear Dielectric Layers

“…Both periodic and quasi-periodic nonlinear structures have been studied primarily with the aim of improving harmonic generation efficiency. QPSs with additional degrees of freedom due to the higher order group symmetry are particularly attractive for creating higher density of states that can facilitate harmonic generation [36][37][38]. It has been observed in [25] that the efficiency of second-harmonic generation (SHG) in QPS is higher than in random medium, but still remains lower than in regular periodic structures.…”

Exploiting quasiperiodic order in the design of optical devices

“…In fact, a QP multilayer can provide more reciprocal vectors to the quasi-phase-matching optical process, and this ultimately results in a more plentiful spectrum structure than that of a periodic multilayer. 29 The importance of the role played by the quasiperiodicity of the substrate is further highlighted when considering third-harmonic generation, where it has been shown that the conversion efficiency in a QP multilayer is increased by a factor of 8 in comparison with the two-step process required for a third-harmonic generator constructed by two periodic superlattices. 30 Quite interestingly, the possibility of designing Fibonacci-based structures able to simultaneously phase match any two nonlinear interactions by introducing a QP modulation of the nonlinear coefficient in ferroelectric devices has been recently discussed.…”

“…[22][23][24][25][26] This interest has motivated several theoretical works aimed to understand the interplay between the optical properties and the underlying aperiodic order of the system through the study of exciton optical absorption 27 and fluorescence decay in aperiodic lattices. 28 At the same time, new insights into the optical capabilities of aperiodically ordered systems have been recently demonstrated by a number of experimental achievements, involving second- 29 and third-harmonic generation, 30 as well as the possible localization of light waves in FDM's. 31,32 Underlying all these theoretical and experimental efforts a crucial fundamental question remains concerning whether quasiperiodically ordered devices would achieve better performance than usual periodic ones for some specific applications.…”