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.
Highlights
Properties for the laser[15], have more advantages for the applications of monolithically integrated optical heterodyne systems and wavelength division multiplexing in the optical networks[20]
Femtosecond laser writing is applied for the fabrication of the splitter structure with designed geometries owing to its flexibility and conveniences, providing the possibility of simultaneous second harmonic generation (SHG) and tailoring of guided light beams
1 × 4 beam splitting capable of light tailoring and efficient SHG has been implemented in a nonlinear KTP crystal, which paves a solid way for a wide variety of applications in many disciplines
Summary
Properties for the laser[15], have more advantages for the applications of monolithically integrated optical heterodyne systems and wavelength division multiplexing in the optical networks[20]. For the positive refractive index changes (Δn > 0) such as induced in glasses[33], it is easy to control the splitter geometries of the waveguide structures as a result of the guiding core located in the femtosecond laser modification regions. The hexagonal optical-lattice-like microstructure, in which a guiding core is surrounded by periodically arrayed laser-induced tracks with negative index modifications, has been realized for the first time in the Nd:YAG laser crystal[40]. Monolithic 3D optical-lattice-like cladding waveguide beam splitters have been experimentally implementation, in which unmodified cores are surrounded by hexagonal or dual-hexagonal lattices of tracks (Δn < 0) with induced defects capable of efficient light confinement in a wide spectral range. The SHG performance at ~532 nm has been realized in the structure regions under the pump of continuous wave (cw) fundamental waves at wavelength of ~1064 nm, which is compared between the waveguide splitters and corresponding straight channel waveguides
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