Laser light system with wavelength attenuation

An optical wavelength division multiplex (WDM) network system with wavelength attenuation, comprising:

• a transmitter comprising:
• a laser light source;
• and
• a wavelength multiplexer;
• a fiber transmission line;
• a optical cross connect comprising an optical switch;
• and
• a receiver comprising:
• a wavelength demultiplexer;
• and a photodetector,
• wherein the laser light source further comprises:
• an inner ring comprising:
• a semiconductor optical amplifier (SOA);
• a pair of optical circulators;
• a first optical filter;
• a variable optical attenuator;
• and
• a first optical waveguide optically connecting other elements of the inner ring in series, with the SOA aligned between the pair of optical circulators, to form the inner ring;
• and
• an outer ring comprising:
• the SOA;
• the pair of optical circulators;
• a second optical filter;
• an output port;
• and
• a second optical waveguide optically connecting elements of the outer ring in series to form the outer ring, except for a portion of the inner ring between the pair of optical circulators, the portion shared with the outer ring,
• wherein,
• the pair of optical circulators are configured to limit a direction of light propagation in the SOA
• a) to a first direction for a light circulating the inner ring, and
• b) to a second direction opposite to the first direction for a light circulating the outer ring,
• and wherein,
• the inner ring is configured to operate as a gain-clamped SOA with a feedback control light under an operating condition with a designed injection current and at a designed ambient temperature, wherein a peak wavelength of the feedback control light is configured to be defined by a passband of the first optical filter,
• and wherein further,
• the outer ring is configured to generate from the output port a laser output within a wavelength region corresponding to a gain region of the gain-clamped SOA under the operating condition, wherein the laser output is comprising a peak wavelength of the laser output defined by a passband of the second optical filter,
• wherein the first optical filter is configured to locate the peak wavelength of the feedback control light in a proximity of a shorter wavelength end of a 3-dB amplified spontaneous emission (ASE) gain band of the SOA under the operating condition and without the feedback control light, and
• wherein the second optical filter is comprising a comb filter configured to exhibit passbands with a designed free spectral range and with a 3 dB bandwidth of each of the passbands not larger than 0.03 nm, and an operation wavelength range covering a gain region of the gain-clamped SOA under the operating condition.