1.53 μm on-chip gain characteristics of 980-nm-pumped Er3+-Yb3+ co-doped LiNbO3-on-insulator photonic wire

Abstract

Based on eight-electronic-level model of Er³⁺-Yb³⁺ system, steady-state rate equations and pump/signal propagation equations, we have studied 1.53 μm on-chip gain characteristics of 980-nm-pumped Er³⁺-Yb³⁺ co-doped LiNbO₃ on insulator(Er:Yb:LNOI) photonic wire(PW). The model considers all possible transitions. We have studied impacts of PW length, pump power, input signal power, Er³⁺ and Yb³⁺ concentrations on the gain characteristics. The results are compared with those of conventional Ti⁴⁺-diffused Er³⁺/Yb³⁺ co-doped LiNbO₃(Ti:Er:Yb:LN) waveguide. The comparison shows that the Er:Yb:LNOI PW exhibits much superior gain performance than the conventional Ti:Er:Yb:LN waveguide, including as much as two orders larger maximal gain and two times larger saturation gain, two orders lower threshold pump power, and much stronger pump power and propagation distance dependences of signal gain due to ultra-compact mode field and large overlapping degree of Er³⁺ population and mode field profiles of Er:Yb:LNOI PW. The role of Yb³⁺ depends on both pump level and Yb³⁺ concentration. In case of lower pump level and Yb³⁺ concentration, the gain performance of Er:Yb:LNOI PW is slightly better than that of Er:LNOI PW. In case of higher pump level and/or Yb³⁺ concentration, the Yb³⁺ plays a negative role in 1.53 μm gain due to small difference of forward and backward energy transfer coefficients between Yb³⁺ and Er³⁺. Based on slight gain exaltation in case of lower Yb³⁺ concentration and pump level, we propose to incorporate Yb³⁺ only at the end of PW to utilize residual pump power to achieve further amplification after maximal gain point.