Environmentally stable passively modelocked fiber laser pulse source
The present invention is directed to providing an environmentally stable, ultra-short pulse source. Exemplary embodiments relate to passively modelocked ultra-short fiber lasers which are insensitive to temperature variations and which possess only negligible sensitivity to pressure variations. Further, exemplary embodiments can be implemented in a cost-effective manner which render them commercially practical in unlimited applications. Arbitrary fiber lengths (e.g., on the order of 1 millimeter to 1 kilometer, or greater) can be used to provide an ultra-short pulse with a cost-effective architecture which is commercially practical.
1. A passively modelocked laser comprising:
a laser energy generator having a cavity which includes:
a fiber gain medium for amplifying energy in the cavity, wherein said cavity comprises multiple sections of fiber having different magnitudes of group-velocity dispersion, said multiple sections of fiber, in combination, providing for increased energy of oscillating pulses;
a pair of reflectors which define an optical axis which passes through the fiber gain medium and supports a plurality of longitudinal modes;
a mode-locking mechanism that locks said longitudinal modes in phase to produce optical pulses at said laser, wherein said modelocking mechanism comprises a semiconductor saturable absorber in said cavity arranged to at least initiate mode locking; and
an output for laser energy generated within said cavity, said output generating ultra-short pulses.
2. The passively modelocked laser according to claim 1 , wherein said gain medium comprises a section of highly-birefringent doped fiber.
3. The passively modelocked laser according to claim 2 , wherein said modelocking mechanism operates with a non-linear phase delay and is arranged in such a way that a non-linear phase difference between polarization states is determined by the relative power between said polarization states.
4. The passively modelocked laser according to claim 1 , wherein said passively modelocked laser is capable of generating output pulses at GHz repetition rates.
5. The passively modelocked laser according to claim 1 , wherein a total length of said multiple sections of fiber is on the order of 1 mm to 1 km.
6. The passively modelocked laser according to claim 2 , wherein said gain medium comprises a section of low-birefringent fiber.
7. The passively modelocked laser according to claim 6 , wherein a total length of the low-birefringent fiber is on the order of eight to ten times shorter than a total length of the highly-birefringent fiber.
8. The passively modelocked laser according to claim 1 , further comprising a tuning element located in said cavity and configured to change either an optical length of said cavity or a wavelength of the laser energy generated within said cavity.
9. The passively modelocked laser according to claim 8 , wherein said tuning element comprises a fiber stretcher located in said cavity that is operable to change a repetition rate of said ultra-short pulses.
10. The passively modelocked laser according to claim 1 , further comprising a compensator which reduces the effects of linear phase drifts of the gain medium.
11. The passively modelocked laser according to claim 10 , wherein said compensator comprises at least one Faraday rotator mirror.
12. The passively modelocked laser according to claim 1 , further comprising a pump light source configured to optically excite said fiber gain medium.