Highly efficient on-chip erbium-ytterbium co-doped lithium niobate waveguide amplifiers

The ability to amplify optical signals is of paramount importance in photonic integrated circuits (PICs). Recently, lithium niobate on insulator (LNOI) has attracted increasing interests as an emerging PIC platform. However, the shortage of active devices on LNOI platform limits the development of optical amplification. Here, we firstly report an efficient waveguide amplifier based on erbium and ytterbium co-doped LNOI by using electron beam lithography and inductively coupled plasma reactive ion etching process. We have demonstrated that the net internal gain in the communication band is 15.70 dB/cm under the pumping of 974 nm continuous laser. Benefiting from the efficient pumping facilitated by energy transfer between ytterbium and erbium ions, signal amplification can be achieved at a low pump power of 0.1 mW. It is currently the most efficient waveguide amplifier under unidirectional pumping reported on the LNOI platform, with an internal conversion efficiency of 10%. This work proposes a new and efficient active device for LNOI integrated optical systems, which may become an important fundamental component of future lithium niobate photonic integration platforms.