Introduction
Fabrication of nonlinear photonic crystals
Fig.1 Experimental schematic of fabrication methods of nonlinear photonic crystals. (a) Electric field poling method with electrolyte; (b) electric field poling method with Al electrode [2]; (c) femtosecond direct laser writing technique [15]. The inset outlines the inscription routine in which the black lines indicate the switch of the laser is turned off |
Quasi-phase matching and nonlinear diffraction harmonic generation
Fig.2 All the types of phase-matching condition during processes. (a)Birefringent phase matching (BPM) and quasi-phase matching (QPM) processes [22]†; (b) spontaneously longitudinal phase matching generates nonlinear Čerenkov radiation (NCR) without reciprocal vectors compensation; (c) transverse phase matching compensated by reciprocal vectors generates nonlinear Raman-Nath diffraction (NRND); (d) nonlinear Bragg diffraction (NBD) generated by both transverse and longitudinal phase matching |
Development of various superlattice structures
One-dimensional superlattices
Fig.3 Experimental schematic and observed second harmonic diffraction patterns of nonlinear Raman-Nath diffraction in one-dimensional single-period structure. (a) Experimental schematic with structured nonlinear photonic crystal [28]†; (b) nonlinear diffraction pattern of structured nonlinear photonic crystal [28]; (c) holograms loaded on spatial light modulator representing the phase structure of the fundamental wave [29]†; (d) nonlinear diffraction pattern of structured fundamental wave [29] |
Tab.1 Experimental parameters of quasi-phase matching harmonic generation in one-dimensional superlattices |
Ref. | superlattice structure | ferroelectric crystal | fundamental wavelength/mm | nonlinear effect | harmonic wavelength/mm | conversion efficiency | bandwith /nm |
---|---|---|---|---|---|---|---|
[3] | Fibonacci | LiTaO3 | 0.9726, 1.0846, 1.2834, 1.3650, 1.5699 | SHG | 0.4863, 0.5423, 0.6417, 0.6825, 0.7845 | 7.5%, 17.5%, 9.1%, 6.7%, 20.4% | 0.3, 0.4, 0.85, 1.1, 2.5 |
LiTaO3 | 1.570 | THG | 0.523 | 23% | 5 | ||
[27] | single-period | LiNbO3 | 1.064 | SHG | 0.532 | 42% | − |
[30] | cascaded (dual-period + 7 channels) | LiTaO3 | 1.064, 1.342 | SHG+ THG | 447, 532, 671 quasi-white-light | 3% | − |
[31] | chirped | LiNbO3 | 1.37−1.47 | SHG | 0.69−0.74 | 30% | 98 |
LiNbO3 | 1.38−1.45 | THG | 0.46−0.48 | 2% | 74 | ||
[32] | short-range ordered | LiNbO3 | 1.50 | SHG | 0.75 | 0.23% | 60 |
Notes: SHG: second harmonic generation; THG: third harmonic generation |
Two-dimensional superlattices
Fig.5 Schematic diagrams of the structural geometry in two-dimensional superlattices. (a) Hexagonal superlattice [6]; (b) annular superlattice [40]†; (c) brick-like superlattice [41]; (d) ellipse superlattice [42]; (e) octagonal superlattice [43]; (f) H-fractal superlattice [44]; (g) sunflower spiral superlattice [12]†; (h) short-range ordered superlattice [13]; (i) radial superlattice [10] |
Three-dimensional superlattices
Fig.8 Patterns of quasi-phase matching harmonics and schematic diagrams of the structural geometry in three-dimensional superlattices. (a) Patterns of harmonics generated from naturally grown Ba0.77Ca0.23TiO3 [20]; (b) tetragonal LiNbO3 fabricated by femtosecond laser engineering [60]; (c) tetragonal Ba0.77Ca0.23TiO3 fabricated by tightly focused infrared femtosecond laser pulses [61]; (d) cylindrical and cubical structures simulated by computer [62]† |