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

We report on the fabrication of nonlinear KTiOPO 4 (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. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)