Method and device having a saturable absorber for filtering

An optical circuit comprising:

• a demultiplexer disposed to receive an input light beam for spatially dispersing the input light beam into a plurality of sub-beams, dependent on wavelengths;
• and,
• a saturably-absorbing circuit disposed to receive the plurality of sub-beams for forming an output beam, comprising:
• a saturable absorber, wherein the saturable absorber becomes saturated dependent on intensity of light, at least for light having wavelength within a particular range, so that a coefficient of absorption for any sub-beam with intensity within a first interval of intensities is at least four times less than a coefficient of absorption for any sub-beam with intensity within a second interval of intensities, wherein the first interval is above the saturation threshold and the second interval is below the saturation threshold, and
• either a reflector for reflecting the plurality of sub-beams back along their optical paths, wherein the demultiplexer combines the plurality of sub-beams reflected by the reflector into the output beam, or a multiplexer disposed to receive the plurality of sub-beams for combining the plurality of sub-beams.