Abstract: The present application is directed to an optical apparatus including an optical waveguide configured to receive an optical signal at an input wavelength. The apparatus also includes one or more optical pump sources connected to transmit pump light to the optical gain medium for the optical gain medium to amplify the optical signal. The apparatus also includes an optical feedback loop for a protection wavelength that includes the optical gain medium and at least a portion of the optical waveguide. A round-trip optical gain of the optical feedback loop is higher at an optical wavelength of the pump light than at the input wavelength less than unity in the presence of the optical signal. In addition, the round-trip gain of the optical feedback loop is greater than or equal to unity in the absence of the optical signal.

Abstract: An apparatus comprising apparatus, comprising an optical waveguide configured to receive an optical signal at an input wavelength, the optical waveguide including an optical gain medium. The apparatus also comprises one or more optical pump sources connected to transmit pump light to the optical gain medium such that the optical gain medium is able to amplify the optical signal. The apparatus also comprises an optical feedback loop that includes the optical gain medium and at least a portion of the optical waveguide, wherein a round-trip optical gain of the optical feedback loop is higher at an optical wavelength of the pump light than at the input wavelength.