A method includes monitoring a power value of output light of the laser and a power value of reflected light, obtaining an insertion loss value according to the power value of the output light, the power value of the reflected light, and a parameter of a Faraday rotation reflector, obtaining a bias current value according to the insertion loss value, and adjusting the power value of the output light of the laser using the bias current value. The insertion loss value is obtained by detecting the power value of the reflected light obtained after the output light of the laser is reflected. Because the insertion loss value is a power loss value, of the output light of the laser, on a one-way link between the laser and the Faraday rotation mirror.