An apparatus is provided. The apparatus includes: a first main waveguide, configured to input and output a first optical signal; a first to-be-tested waveguide, configured to couple the first optical signal to generate a second optical signal, and transfer the second optical signal, an optical signal that is reflected by a second fiber Bragg grating, and an optical signal that is reflected by a first fiber Bragg grating. The apparatus also includes the first fiber Bragg grating, configured to totally reflect the optical signal that is reflected by the second fiber Bragg grating; the second fiber Bragg grating, configured to partially transmit and partially reflect the second optical signal and the optical signal that is reflected by the first fiber Bragg grating; and a first photoelectric detector, configured to receive an optical signal that is transmitted by the second fiber Bragg grating of the corresponding first to-be-tested waveguide.