Passively mode-locked fiber lasers

A fiber laser with a linear optical resonator, comprising:

• first and second reflective elements disposed relative to each other to form a linear optical resonator having a plurality of longitudinal modes;
• a fiber gain medium having optical transitions operable to absorb photons at a pump wavelength in a specified wavelength range and to emit photons at a laser wavelength 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 of said laser wavelength at a pulse repetition rate;
• an optical coupler, disposed relative to said fiber gain medium and configured to couple a pump beam at said pump wavelength to said fiber gain medium;
• and
• a plurality of polarization-maintaining fiber segments having a principle axis aligned with said specified direction defined by said fiber gain medium, said fiber segments disposed in said optical resonator to provide an optical conduit between said first and second reflective elements.

A fiber laser with a linear optical resonator, comprising:

• an optical resonator having a reflective grating positioned as a first end of said resonator and configured to selectively reflect light of certain wavelengths, and an optical reflector positioned as a second end of said resonator to provide optical feedback and to have a high reflectivity at a laser wavelength;
• a fiber gain medium having optical transitions operable to absorb photons at a pump wavelength in a specified wavelength range and to emit photons at said laser wavelength, said fiber gain medium configured to maintain light polarization in a specified polarization 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 of said laser wavelength at a pulse repetition rate;
• an optical coupler, disposed relative to said fiber gain medium and configured to couple a pump beam at said pump wavelength to said fiber gain medium;
• and
• a plurality of polarization-maintaining fiber segments having a principle axis aligned with said specified polarization direction defined by said fiber gain medium, said fiber segments disposed in said optical resonator to provide an optical conduit between said first and second reflective elements.

A method of constructing and operating a fiber laser, comprising:

• forming a linear optical resonator by using two reflective elements;
• disposing a fiber gain medium in an optical path linking said two reflective elements to provide a gain equal to or greater than a total optical loss in said resonator, wherein said fiber gain medium is formed of polarization-maintaining fiber;
• using a saturable absorber in said resonator to mode lock multiple oscillating longitudinal modes to produce optical pulses;
• and
• configuring a linear absorption of said saturable absorber and a total group velocity dispersion inside said resonator to make said optical pulses as soliton pulses.

A method, comprising:

• forming a linear optical resonator by using two reflective elements;
• disposing a fiber gain medium in an optical path linking said two reflective elements to provide a gain equal to or greater than a total optical loss in said resonator, wherein said fiber gain medium is formed of polarization-maintaining fiber;
• using a saturable absorber in said resonator to mode lock multiple oscillating longitudinal modes to produce optical pulses, wherein said satuarable absorber has a slow saturation process with a low saturation intensity and a fast saturation process with a high saturation intensity;
• coupling a pump beam into said resonator at a location between said saturable absorber and said fiber gain medium to direct said pump beam towards said fiber gain medium and to excite said fiber gain medium;
• using said slow saturation process to initiate said optical pulses;
• and
• using said fast saturation process to modify a property of said optical pulses.