Mode-locked multi-mode fiber laser pulse source

Abstract

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

What is claimed is: 
     
         1 . A laser system comprising:
 a length of multi-mode optical fiber capable of propagating a fundamental mode, the length of multi-mode optical fiber comprising a multi-mode core and a cladding, the multi-mode core comprising a gain medium, the length of multi-mode optical fiber comprising a bent portion;   a length of single mode optical fiber optically coupled to the length of multi-mode optical fiber, the length of single mode optical fiber configured to confine light amplified by the length of multi-mode optical fiber to preferentially the fundamental mode;   reflectors disposed to form a laser cavity, the laser cavity comprising the lengths of multi-mode and single mode optical fiber; and   a pump source optically coupled to the cladding of the length of multi-mode optical fiber and configured to excite the gain medium by cladding pumping.   
     
     
         2 . The laser system of  claim 1 , where the bent portion comprises a coil of multi-mode optical fiber. 
     
     
         3 . The laser system of  claim 1 , wherein the bent portion has a bend diameter greater than or equal to 1.5 cm. 
     
     
         4 . The laser system of  claim 1 , further comprising a splice between the multi-mode optical fiber and the single mode optical fiber. 
     
     
         5 . The laser system of  claim 4 , wherein the multi-mode optical fiber, the single mode optical fiber, or both the multi-mode optical fiber and the single mode optical fiber are tapered at the splice. 
     
     
         6 . The laser system of  claim 1 , wherein the single mode optical fiber is arranged with respect to the multi-mode optical fiber such that a single mode of the single mode optical fiber is matched to the fundamental mode of the multi-mode optical fiber. 
     
     
         7 . The laser system of  claim 1 , wherein a numerical aperture of said cladding of said multi-mode optical fiber exceeds a numerical aperture of the multi-mode core. 
     
     
         8 . The laser system of  claim 1 , wherein at least a portion of said multi-mode optical fiber comprises polarization-maintaining multi-mode optical fiber. 
     
     
         9 . A laser system comprising:
 a multi-mode optical fiber comprising a core and a cladding, the core doped with gain material for amplifying optical energy;   a laser cavity comprising said multi-mode optical fiber; and   a pump source arranged to pump the cladding of the multi-mode optical fiber,   wherein the multi-mode optical fiber comprises a tapered portion to confine the optical energy amplified by the multi-mode optical fiber to substantially the fundamental mode of the multi-mode optical fiber.   
     
     
         10 . The laser system of  claim 9 , further comprising a splice that joins the tapered portion of multi-mode optical fiber to a single mode optical fiber. 
     
     
         11 . The laser system of  claim 10 , wherein the single mode optical fiber is configured to confine optical energy amplified by the multi-mode optical fiber to preferentially a fundamental mode of the multi-mode optical fiber. 
     
     
         12 . The laser system of  claim 9 , wherein the multi-mode optical fiber comprises a bent portion. 
     
     
         13 . The laser system of  claim 9 , wherein the multi-mode optical fiber comprises polarization-maintaining multi-mode optical fiber. 
     
     
         14 . A laser system comprising:
 a polarization maintaining multi-mode optical fiber capable of propagating a fundamental mode, the polarization maintaining multi-mode optical fiber comprising a multi-mode core and a cladding, the multi-mode core comprising a gain medium;   a single mode optical fiber optically coupled to the polarization maintaining multi-mode optical fiber, the single mode optical fiber configured to confine light amplified by the polarization maintaining multi-mode optical fiber to preferentially the fundamental mode of the multi-mode optical fiber;   a laser cavity comprising the polarization maintaining multi-mode optical fiber and the single mode optical fiber; and   a pump source optically coupled to the cladding of the polarization maintaining multi-mode optical fiber and configured to excite the gain medium by cladding pumping.   
     
     
         15 . The laser system of  claim 14 , wherein the polarization maintaining multi-mode optical fiber comprises an elliptical core. 
     
     
         16 . The laser system of  claim 14 , wherein the polarization maintaining multi-mode optical fiber comprises stress-producing regions. 
     
     
         17 . The laser system of  claim 14 , wherein the polarization maintaining multi-mode optical fiber comprises a bent portion. 
     
     
         18 . The laser system of  claim 14 , further comprising a splice that joins the polarization maintaining multi-mode optical fiber to the single mode optical fiber. 
     
     
         19 . The laser system of  claim 18 , wherein the polarization maintaining multi-mode optical fiber, the single mode optical fiber, or both the polarization maintaining multi-mode optical fiber and the single mode optical fiber are tapered at the splice.