Optical-fibre passively mode locked laser generator with non-linear polarization switching

A method of generating passively-mode-locked stimulated pulses in an optical-fibre laser generator having an active optical fibre doped with a fluorescent dopant, means for feeding luminous pumping energy to the active fibre to excite the fluorescent dopant to a laser emission state, said dopant decaying from said laser emission state to a base state to generate a luminous emission signal at a predetermined wavelength, a polarization control means for orienting the polarization of said emission signal in a predetermined plane, feedback means optically connected to ends of said active fibre for passing at least a portion of said emission signal between said ends, at least one optical component with transmissiveness depending on polarization, and means for extracting said emission signal from said active fibre, at least the active fibre, polarization control means, feedback means and optical component with transmissiveness depending on polarization comprising of an optical fibre path, in which said emission signal propagate and in which at least one portion of the emission signal present at one end of the active fibre is sent back to the interior of said fibre, comprising the steps of:

• (1) adjusting said polarization control means to a configuration causing an absence of an emission signal coming out of said extracting means in a linear propagation condition of the emission signal within said optical path;
• and
• (2) supplying said active fibre with a pumping power corresponding to the stimulated emission in the active fibre of an emission signal having a luminous power higher than a predetermined value corresponding to non-linear luminous-propagation conditions of the emission signal in the optical path, while keeping the configuration of the polarization control means constant.

A method of generating passively-mode-locked stimulated pulses in an optical-fibre laser generator having an active optical fibre doped with a fluorescent dopant, means for feeding luminous pumping energy to the active fibre to excite the fluorescent dopant to a laser emission state, said dopant decaying from said laser emission state to a base state and generating a luminous emission signal at a predetermined wavelength, a polarization control means for orienting the polarization of said emission signal in a predetermined plane, feedback means optically connected to ends of said active fibre for passing at least a portion of said emission signal between said ends, at least one optical component with transmissiveness depending on polarization, and means for extracting said emission signal from said active fibre, at least the active fibre, polarization control means, feedback means and optical component with transmissiveness depending on polarization comprising of an optical fibre path, in which said emission signal propagate and in which at least one portion of the emission signal present at one end of the active fibre is sent back to the interior of said fibre, comprising the steps of:

• (1) supplying said active fibre with a pumping power corresponding to the stimulated emission in the active fibre of an emission signal having a luminous power lower than a predetermined value corresponding to linear luminous-propagation conditions of the emission signal in the optical path;
• (2) controlling the presence of said emission signal coming out of said extraction means;
• (3) adjusting said polarization control means in a configuration causing an absence of an emission signal coming out of said extraction means;
• and
• (4) increasing the pumping power supplied to said active fibre as far to overcome a second predetermined value, which value corresponds to non-linear luminous-propagation conditions of the emission signal in the optical path in which the polarization of the emission signal is rotated at right angles to that in said linear propagation conditions, while keeping the configuration of the polarization control means constant.