title: Efficient Second Harmonic Generation in 3D Nonlinear Optical-Lattice-Like Cladding Waveguide Splitters by Femtosecond Laser Inscription.
abstract: Integrated photonic devices with beam splitting function are intriguing for a broad range of photonic applications. Through optical-lattice-like cladding waveguide structures fabricated by direct femtosecond laser writing, the light propagation can be engineered via the track-confined refractive index profiles, achieving tailored output beam distributions. In this work, we report on the fabrication of 3D laser-written optical-lattice-like structures in a nonlinear KTP crystal to implement 1 × 4 beam splitting. Second harmonic generation (SHG) of green light through these nonlinear waveguide beam splitter structures provides the capability for the compact visible laser emitting devices. With Type II phase matching of the fundamental wavelength (@ 1064 nm) to second harmonic waves (@ 532 nm), the frequency doubling has been achieved through this three-dimensional beam splitter. Under 1064-nm continuous-wave fundamental-wavelength pump beam, guided-wave SHG at 532 nm are measured with the maximum power of 0.65 mW and 0.48 mW for waveguide splitters (0.67 mW and 0.51 mW for corresponding straight channel waveguides), corresponding to a SH conversion efficiency of approximately ~14.3%/W and 13.9%/W (11.2%/W, 11.3%/W for corresponding straight channel waveguides), respectively. This work paves a way to fabricate compact integrated nonlinear photonic devices in a single chip with beam dividing functions.
authors.affiliation: School of Physics, State Key Laboratory of Crystal Materials, and Key Laboratory of Particle Physics and Particle Irradiation (Ministry of Education), Shandong University, 250100 Jinan, Shandong, China.
authors.forename: Weijie
authors.initials: W
authors.lastname: Nie
authors.affiliation: Laboratory for Optical Systems, Department of Microsystems Engineering-IMTEK, University of Freiburg, 79110 Freiburg, Germany.
authors.forename: Yuechen
authors.initials: Y
authors.lastname: Jia
authors.affiliation: Laser Microprocessing Group, Universidad de Salamanca, 37008 Salamanca, Spain.
authors.forename: Javier R
authors.initials: JR
authors.lastname: Vázquez de Aldana
authors.affiliation: School of Physics, State Key Laboratory of Crystal Materials, and Key Laboratory of Particle Physics and Particle Irradiation (Ministry of Education), Shandong University, 250100 Jinan, Shandong, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Chen