Optical fiber systems for delivering short high power pulses

Abstract

Described is an optical fiber system for delivering ultrashort pulses with minimal distortions due to nonlinearity. The system is based on delivering the optical pulses in a higher order mode (HOM) of a few-moded fiber. The fiber is designed so that the dispersion for the HOM is very large. This results in a dispersion length L D for the delivery fiber that is exceptionally small, preferably less than the non-linear length L NL . Under these conditions the system may be designed so the optical pulses experience minimum non-linear impairment, and short pulse/high peak power levels are reproduced at the output of the delivery fiber.

1 . A method comprising: 
 (a) generating optical pulses, the optical pulses having a pulse width W,    (b) propagating the optical pulses through a pulse stretcher,    (c) converting the propagating mode of the optical pulses to a HOM,    (d) propagating the optical pulses along a length L of optical fiber to an output, where L is chosen such that the pulse width W O  at the output is approximately equal to W.    
   
   
       2 . The method of  claim 1  wherein L is less than 20 meters.  
   
   
       3 . The method of  claim 2  wherein the optical pulses are less than 200 femtoseconds.  
   
   
       4 . An optical device comprising: 
 (a) a source of optical pulses,    (b) a pulse stretcher coupled to the source of optical pulses,    (c) a mode converter coupled to the pulse stretcher,    (d) an optical fiber coupled to the mode converter, the optical fiber supporting a HOM.    
   
   
       5 . The optical device of  claim 4  wherein the optical pulses have a wavelength in the range 700-900 nm.  
   
   
       6 . The optical device of  claim 5  wherein the optical fiber has a dispersion value of less than −150 ps/nm-km.  
   
   
       7 . The optical device of  claim 4  wherein the optical fiber has a dispersion length L D  and a non-linear length L NL , where L D  is less than L NL .  
   
   
       8 . The optical device of  claim 4  wherein the optical fiber has a dispersion length L D  and a non-linear length L NL , where L D  is less than 0.5 L NL .  
   
   
       9 . The optical device of  claim 5  wherein the optical fiber has A eff  less than 50 microns 2 .  
   
   
       10 . The optical device of  claim 4  wherein the source of optical pulses is a short pulse laser.  
   
   
       11 . The optical device of  claim 10  wherein the optical pulses are less than 200 femtoseconds.  
   
   
       12 . The optical device of  claim 11  wherein the short pulse laser is a titanium/sapphire laser.  
   
   
       13 . The optical device of  claim 4  wherein the mode converter comprises a long period grating.  
   
   
       14 . The optical device of  claim 13  wherein the long period grating has a TAP.  
   
   
       15 . The optical device of  claim 4  wherein the pulse stretcher comprises a bulk-optics element.  
   
   
       16 . The optical device of  claim 4  wherein the optical fiber terminates with a collimating element.  
   
   
       17 . The optical device of  claim 4  wherein the optical fiber has a length of less than 20 meters.  
   
   
       18 . An optical fiber supporting a HOM, and having a dispersion length L D  and a non-linear length L NL , where L D  is less than L NL .  
   
   
       19 . The optical fiber of  claim 16  where L D  is less than 0.5 L NL .  
   
   
       20 . The optical fiber of  claim 16  wherein the optical fiber supports LP02.