High-order mode waveguide amplifier with high mode extinction ratio written in an Er<sup>3+</sup>-doped phosphate glass
Xiangyu Sun, Yuying Wang, Lijing Zhong, Daoyuan Chen, Beibei Xu, Zhijun Ma, Xiaofeng Liu, Giuseppe Barillaro, Zhi Chen, Jianrong Qiu
Abstract
Inscription of fiber-compatible active waveguides in high-gain glass, followed by direct interconnection with few-mode fibers, is one of the most promising solutions for all-optical mode-division multiplexing. In this work, based on the femtosecond laser writing technique, we propose a general fabrication scheme for inscribing high-order mode waveguides in glass, by carefully tailoring the cross-section of the waveguides to match the mode intensity distribution via an improved multi-scan approach. Specifically, we design and fabricate two kinds of waveguides, namely, LP 01 -mode waveguide and LP 11 -mode waveguide in a highly Er 3+ -doped phosphate glass, enabling the insertion loss of the waveguides to be as low as 1.88 dB, and the mode extraction factor of the LP 11 -mode waveguide up to ∼24 dB. Importantly, we have successfully achieved optical amplification of the waveguides, with an on-off gain as high as 3.52 dB. This novel high-order mode waveguide amplifier has broad application prospects in monolithic on-chip integrated photonic light sources and optical interconnection with few-mode fiber and/or silicon-based waveguide.