Tunable single-mode laser on thin film lithium niobate.

The erbium-doped lithium niobate on insulator (LNOI) laser plays an important role in the complete photonic integrated circuits (PICs). Here, we demonstrate an integrated tunable whispering gallery single-mode laser (WGSML) by making use of a coupled microdisk and microring on LNOI. A 974 nm single-mode pump light can have an excellent resonance in the designed microdisk, which is beneficial to the whispering gallery mode (WGM) laser generation. The WGSML at 1560.40 nm with a maximum 31.4 dB side mode suppression ratio (SMSR) has been achieved. By regulating the temperature, the output power of the WGSML increases, and the central wavelength can be changed from 1560.30 to 1560.40 nm. Furthermore, 1560.60 and 1565.00 nm WGSMLs have been achieved by changing the coupling gap width between the microdisk and microring. We can also use the electro-optic effect of LNOI to obtain more accurate adjustable WGSMLs in further research.