Generation of a wavelength-tunable laser oscillation in a wave-guiding gain medium based on passive mode lock

A fiber laser, comprising:

• a pump light source which includes a semiconductor light source to produce a pump beam at a pump wavelength;
• first and second reflective elements disposed relative to each other to form an optical resonator having a plurality of longitudinal modes;
• a fiber gain medium having optical transitions operable to absorb photons at said pump wavelength and to emit photons at a laser wavelength within a spectral gain profile that is different from said pump wavelength, said fiber gain medium configured to maintain light polarization in a specified direction perpendicular to an optic axis of said fiber gain medium;
• a semiconductor absorber disposed in said optical resonator and configured to exhibit a saturable intensity-dependent absorption and to have a bandgap equal to or less than a photon energy corresponding to said laser wavelength, said semiconductor absorber operable to lock a plurality of oscillating longitudinal modes in phase to produce optical pulses at said laser wavelength and configured to exhibit a slow saturation process with a low saturation intensity to initiate said optical pulses and a fast saturation process with a high saturation intensity to shorten a temporal width of said pulses;
• an optical coupler, disposed relative to said fiber gain medium to couple said pump beam into said fiber gain medium;
• and
• a first polarization-maintaining fiber segment disposed to transmit light between said first reflective element and said fiber gain medium;
• and
• a second polarization-maintaining fiber segment disposed to transmit light between said fiber gain medium and said second reflective element, wherein each of said first and said second fiber segments has a principal polarization axis aligned with said specified direction defined by said fiber gain medium.