An optical signal routing device comprising: a first lens positioned for receiving an optical signal; a second lens ; a wavelength division multiplexing, WDM, filter positioned between the first and second lenses, the WDM filter configured to reflect a signal of a first wavelength (λ i ) with at least a first attenuation and pass the signal of the first wavelength attenuated by at most a second attenuation to the second lens, the first attenuation exceeding the second attenuation by at least a first predetermined amount, the WDM filter being further configured to reflect a signal of a second wavelength (λ k ) different than the first wavelength with at most a third attenuation, the first attenuation exceeding the third attenuation by at least a second predetermined amount; and a reflector positioned to reflect the signal of the first wavelength reflected by the WDM filter toward the WDM filter with at least a fourth attenuation, the fourth attenuation exceeding the second attenuation by at least a third predetermined amount, the reflector is configured to reflect the signal of the second wavelength toward the WDM filter with at most a fifth attenuation, the first attenuation exceeding the fifth attenuation by at least a fourth predetermined amount, wherein the signal of the first wavelength and the signal of the second wavelength are routed from the first lens to the WDM filter along a first optical path , the signal of the first wavelength and the signal of the second wavelength are routed from the WDM filter to the reflector along a second optical , and the signal of the first wavelength and the signal of the second wavelength are routed from the reflector to the WDM filter along the second optical path, the second optical path being different from the first optical path. a first lens positioned for receiving an optical signal; a second lens ; a wavelength division multiplexing, WDM, filter positioned between the first and second lenses, the WDM filter configured to reflect a signal of a first wavelength (λ i ) with at least a first attenuation and pass the signal of the first wavelength attenuated by at most a second attenuation to the second lens, the first attenuation exceeding the second attenuation by at least a first predetermined amount, the WDM filter being further configured to reflect a signal of a second wavelength (λ k ) different than the first wavelength with at most a third attenuation, the first attenuation exceeding the third attenuation by at least a second predetermined amount; and a reflector positioned to reflect the signal of the first wavelength reflected by the WDM filter toward the WDM filter with at least a fourth attenuation, the fourth attenuation exceeding the second attenuation by at least a third predetermined amount, the reflector is configured to reflect the signal of the second wavelength toward the WDM filter with at most a fifth attenuation, the first attenuation exceeding the fifth attenuation by at least a fourth predetermined amount, wherein the signal of the first wavelength and the signal of the second wavelength are routed from the first lens to the WDM filter along a first optical path , the signal of the first wavelength and the signal of the second wavelength are routed from the WDM filter to the reflector along a second optical , and the signal of the first wavelength and the signal of the second wavelength are routed from the reflector to the WDM filter along the second optical path, the second optical path being different from the first optical path. <EOS>