A laser, an optical module, and an apparatus are provided. The laser includes a gain region waveguide, a feedback waveguide, a first end face, and a second end face. The gain region waveguide and the feedback waveguide are located between the first end face and the second end face, an end of the gain region waveguide is connected to an end of the feedback waveguide, and the feedback waveguide) is located on a side that is of the gain region waveguide and that is close to the second end face. The first end face and the second end face are configured to transmit light in the gain region waveguide and the feedback waveguide, and the first end face is configured to transmit laser light.

A method of stimulating emission of light comprising using a single-mode sapphire optical waveguide as a gain medium, and a sapphire optical device comprising an optical gain medium comprising a single-mode sapphire optical waveguide.