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.

Femtosecond Laser Written Depressed-Cladding Waveguide 2 × 2, 1 × 2 and 3 × 3 Directional Couplers in Tm3+:YAG Crystal

“…The circularly shaped depressed cladding waveguides in Nd:YAG [58] and LiNbO 3 [59] were adopted to inscribing 2D 1×2 Y-splitter and 3D 1×2 Y-splitter respectively. The lattice microstructured cladding waveguide 3D 1×3 beam splitter in LiNbO 3 [60] and 1×4 beam splitter in KTP [61] were demonstrated. Recently, conventional 2×2 reconfigurable weakly coupled directional beamsplitter in LiNbO 3 was demonstrated [62].…”

Passive Q-switch laser operation of circular, buried depressed-cladding waveguides realized by direct fs-laser beam writing in Nd:YAG/Cr^4+:YAG composite media

“…Cladding waveguides realized by direct writing with an fs-laser beam can be used in other integrated components, such as for beam manipulation [19] or for generation of visible light [20]. Very attractive is the possibility to obtain laser pulses with high-peak power by passive Q-switch and to integrate such a laser device for nonlinear conversion applications.…”

Room-temperature subnanosecond waveguide lasers in Nd:YVO4 Q-switched by phase-change VO2: A comparison with 2D materials

“…As a powerful 3D micro-nano fabrication technique, femtosecond laser writing/inscription has been widely applied to produce various photonic devices or components in optical materials1516171819. Femtosecond laser written dielectric waveguide laser systems have been realized in a number of active glasses, ceramics and crystals, offering broadband laser operations from visible to mid-infrared (MIR) wavelength regimes20212223. Additionally, the advantage of laser inscription technology for direct-write 3D waveguide fabrication enables designed laser beam tailoring at direct optical pump, which shows superior features on the laser shaping to non-direct-write waveguide laser systems101122.…”

“…Femtosecond laser written dielectric waveguide laser systems have been realized in a number of active glasses, ceramics and crystals, offering broadband laser operations from visible to mid-infrared (MIR) wavelength regimes20212223. Additionally, the advantage of laser inscription technology for direct-write 3D waveguide fabrication enables designed laser beam tailoring at direct optical pump, which shows superior features on the laser shaping to non-direct-write waveguide laser systems101122. Lasing in waveguides, similar to the bulk systems, can be realized in continuous wave (CW) as well as pulsed operation regimes.…”