Back Cover: Efficient second harmonic generation by birefringent phase matching in femtosecond‐laser‐inscribed KTP cladding waveguides (Phys. Status Solidi RRL 7/2012)

Abstract

KTiOPO4 (KTP) is a widely used nonlinear crystal for frequency conversion. Nonlinear optical waveguides play significant roles in the promising micro photonic devices owing to the combination of nonlinear features of bulks and waveguide compact geometries. Femtosecond laser inscription has become a unique and powerful technique to fabricate waveguides in many optical materials. In the Letter on pp. 306–308, Dong et al. report on a novel nonlinear KTP waveguide structure by using femtosecond laser writing. Different from the well investigated stress-induced “double-line” waveguides, the fabricated KTP waveguide is confined in the circular core region surrounded by the fs-laser-induced low-refractive-index tracks. Such a cladding waveguide supports the guidance of two transverse polarizations well, and the large diameter (∼100 μm) of the cross section of the waveguide matches the scale of the optical fiber. Efficient guided-wave phase-matched second harmonic generation (SHG) at 532 nm has been realized under a pulsed 1064 nm laser pump, reaching a conversion efficiency as high as 45.6%, showing SHG performance superior to the stress-induced KTP waveguide. This work offers a new approach to build efficient nonlinear waveguides in optical crystals by using femtosecond laser inscription.