Lithium niobate (LN) has excellent physical effects such as nonlinearity, electro-optics, acousto-optics, piezoelectricity as well as photoelasticity, and it is a popular material in the field of optical research. With the successful development of commercial lithium niobate thin films (LNOI), lithium niobate has become a research hotspot in the field of optoelectronic integration in recent years. Researchers at home and abroad have developed integrated optoelectronic devices such as frequency doublers, modulators and filters with excellent performance on lithium niobate films. For a complete lithium niobate optoelectronic integrated chip, the on-chip communication band light source is an indispensable part, so the development of lasers on lithium niobate thin films has become an urgent need.

As we all know, the rare earth erbium ion energy level system meets the conditions of laser radiation in the communication band. Doping the lithium niobate film with erbium ions, combining the whispering gallery mode microdisk cavity with small size and high quality factor, and choosing an appropriate pump source, are expected to realize an on-chip integrated lithium niobate microlaser.

The researchers chose to dope with erbium ions during the growth of lithium niobate bulk crystal, and used the smart-cut process to make the crystals into thin films. Then the researchers used a focused ion beam (FIB) milling method to fabricate a microdisk resonator on a 600nm-thick Z-cut erbium-doped lithium niobate film.

The pump source in the 980-nm band and the 1480-nm band were used respectively, coupled through a tapered fiber. And the laser output in the 1550-nm band was obtained. The following figure shows the wavelength, threshold and slope efficiency of the output laser.
This research has realized the development of an integrated light source on a lithium niobate chip. And it is of extraordinary significance to the efficient integration of the light source and various functional devices on lithium niobate thin film.

Figure 1. (a) Setups; (b) Transmission; (c) Quality factor; (d) Energy levels of erbium ion; (e) Lasers at visible wavelength.

Figure 2. (a, b) The laser wavelength, threshold and slope efficiency of pump at 974nm; (c, d) The laser wavelength, threshold and slope efficiency of pump at 1460nm.

Link:
https://engine.scichina.com/publisher/scp/journal/SCPMA/64/3/10.1007/s11433-020-1625-9?slug=fulltext
https://doi.org/10.1007/s11433-020-1625-9