Efficient second harmonic generation by birefringent phase matching in femtosecond-laser-inscribed KTP cladding waveguides

Abstract

We report on the fabrication of nonlinear KTiOPO4 (KTP) cladding waveguides by using femtosecond-laser direct inscription. The produced guiding structures with a circular cross section of ∼100 μm diameter support good light confinement both for the visible and infrared, for TE and TM polarization. Under the 1064 nm pulsed fundamental pump beam, guided-wave second harmonic generation (SHG) at 532 nm has been realized with an optical conversion efficiency as high as 45.6% (∼0.076% W–1 cm–2), which is three times the magnitude of the normalized efficiency obtained for “double-line” KTP waveguides (fabricated with the aim of comparison), thus showing an intriguing potential as integrated frequency converters