Systems and methods to detect a wavelength of interest (λRX) amongst one or more wavelengths (λ1, λ2, . . . , λN) include receiving the one or more wavelengths (λ1, λ2, . . . , λN); using a portion of a transmitted wavelength (λTX) as a Local Oscillator (LO) signal to perform performing coherent detection with the one or more wavelengths, wherein the transmitted wavelength (λTX) and the wavelength of interest (λRX) are a bi-directional communication link; and determining a presence of the wavelength of interest (λRX) based on the coherent detection.