Nanomaterial‐Incorporated Nonlinear Optical Waveguides Explored With All‐Fiber Multiphoton Polymerization

Multiphoton polymerization (MPP) offers a mask‐less and full three‐dimensional accessibility for photonic integrated circuits (PICs). However, conventional free‐space‐based MPP suffers from poor stability, reconfigurability and process efficiency due to bulky components and complex free‐space alignment. Furthermore, it is typically restricted to linear passive devices constraining the functional scope of PICs. We demonstrate nonlinear polymer waveguides incorporating homogeneously dispersed nonlinear nanomaterials through an all‐fiber‐configured MPP process. Control of the target voxel is achieved by managing in‐line chromatic dispersion along with optimizing the design of lensed optical fibers employed. The nanomaterials, upconversion nanoparticles (UCNPs), simultaneously enable cascaded multiphoton absorption with a telecommunication‐wavelength photon source, and introduce nonlinear saturable absorption allowing the devices to operate in an ultrafast regime. An 880 µm‐long waveguide with a few‐micrometer‐scale cross section is fabricated. The nonlinearity of the resultant UCNP‐dispersed waveguide is verified by demonstrating a mode‐locked fiber ring laser that generates 746 fs pulses at a 1.49 MHz repetition rate. The all‐fiber MPP process provides a compact platform for localized fabrication of nanomaterial‐incorporated nonlinear polymer waveguides.