1.76 μm on-chip gain characteristics of Tm3+ in a rib waveguide based on Tm3+-doped LiNbO3 thin-film on insulator

• Published in: Journal of luminescence 2024-02, Vol.266, p.120279, Article 120279
• Main Authors: Meng, Fan-Song, Yang, Yu-Jing, Chen, Feng, Liu, Jia-Min, Zhang, De-Long
• Format: Article
• Language: English
• Subjects: Optical amplification; Rib waveguide; Tm:LNOI
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/j.jlumin.2023.120279

A theoretical study has been performed on 1.76 μm on-chip amplification characteristics of Tm3+ in a rib waveguide of LiNbO3 on insulator (Tm:LNOI) under 795 nm wavelength pumping. Steady-state rate equations and propagation equations of signal and pump waves are established on the basis of a three-level model of Tm3+ system with the cross relaxation process 3H4→3F4: 3H6→3F4 included. The validity of the three-level model is demonstrated by referencing previously reported experiment result of Er3+-doped LNOI waveguide amplifier and by examining the effect of Tm3+ blue upconversion emissions on the 1.76 μm amplification. Besides the relations of signal gain to propagation length, launched pump power and input signal power, the effects of waveguide cross-section geometry and Tm3+ concentration on the gain characteristics are also studied. The results show that the waveguide cross-section geometry affects definitely the gain performance via its effect on mode field. The Tm3+ concentration affects the signal gain also via its effect on the 3H4→3F4: 3H6→3F4 cross relaxation coefficient, besides the conventional effect that higher active ion concentration yields larger signal gain. A comparison with conventional Ti4+(Zn2+)-diffused Tm3+-doped LN [Ti(Zn):Tm:LN] waveguide shows that the Tm:LNOI waveguide has much better gain performance than the Ti(Zn):Tm:LN waveguide, including much stronger pump power and propagation distance dependences of signal gain, much higher signal gain and much lower threshold pump power. These features are associated with significantly increased Tm3+ population inversion extent due to ultra-compact mode field and larger overlapping factor of mode field and Tm3+ population profiles in the Tm:LNOI waveguide. •1.8 μm amplification in Tm:LNOI waveguide is simulated based on three-level model.•Quantitative relations of signal gain to controllable parameters are established.•Tm:LNOI amplifier is more efficient than Ti(Zn):Tm:LN due to ultra-compact mode.•Waveguide cross-section geometry affects definitely gain via its effect on mode field.•Tm3+ concentration affects gain via its effect on cross relaxation process.