Compact, coherent, high brightness light sources for the mid and far ir

Abstract

Compact high brightness light sources for the mid and far IR spectral region, and exemplary applications are disclosed based on passively mode locked Tm fiber comb lasers. In at least one embodiment the coherence of the comb sources is increased in a system utilizing an amplified single-frequency laser to pump the Tm fiber comb laser. The optical bandwidth generated by the passively mode locked Tm fiber comb laser is further decreased by using simultaneous 2 nd and 3 rd order dispersion compensation using either appropriate chirped fiber Bragg gratings for dispersion compensation, or fibers with appropriately selected values of 2 nd and 3 rd order dispersion. Fibers with large anomalous values of third order dispersion, or fibers with large numerical apertures, for example fibers having air-holes formed in the fiber cladding may be utilized.

What is claimed is: 
     
         1 . A fiber-laser based system, comprising;
 a passively mode locked fiber oscillator operating at or near a wavelength of 2000 nm, said oscillator comprising a plurality of fiber sections, each section having at least one length of fiber, wherein:   a first fiber section has a positive dispersion value,D21,   a second fiber section has a negative dispersion value,D22,   said first fiber section has a negative third order dispersion value,D31,   said second fiber section has a positive third order dispersion value,D32, and said dispersion values approximately satisfy the relation:
   0.2<( D 21 /D 31)/( D 22 /D 32)<5, 
   
       wherein said dispersion values provide overall cavity dispersion in a range of about ±20,000 fs2 per meter intra-cavity fiber length; and
 a pump source to pump said passively mode locked fiber oscillator. 
 
     
     
         2 . The fiber-laser based system according to  claim 1 , wherein said dispersion values approximately satisfy the relation:
   0.5<( D 21 /D 31)/( D 22 /D 32)<2.   
     
     
         3 . The fiber-laser based system according to  claim 1 , wherein said dispersion values approximately satisfy the relation:
   0.7<( D 21 /D 31)/( D 22 /D 32)<1.3.   
     
     
         4 . The fiber-laser based system according to  claim 1 , wherein said passively mode locked fiber oscillator operates in the wavelength range from about 1700 nm to about 2500 nm. 
     
     
         5 . The fiber-laser based system according to  claim 1 , wherein said passively mode locked fiber oscillator comprises a Tm, a Tm:Ho, or a Ho doped fiber. 
     
     
         6 . The fiber-laser based system according to  claim 1 , further comprising a continuum fiber for super continuum generation. 
     
     
         7 . The fiber-laser based system according to  claim 6 , further comprising a fiber amplifier inserted between said oscillator and said continuum fiber. 
     
     
         8 . The fiber-laser based system according to  claim 7 , wherein said fiber amplifier is capable of higher order soliton compression, nonlinear compression, Raman soliton generation or chirped pulse amplification. 
     
     
         9 . The fiber-laser based system according to  claim 7 , wherein said fiber amplifier is core pumped or cladding pumped. 
     
     
         10 . The fiber-laser based system according to  claim 9 , wherein said fiber amplifier is core pumped with an Er fiber amplifier. 
     
     
         11 . The fiber-laser based system according to  claim 7 , further comprising a highly nonlinear silica fiber spliced directly to the output of said oscillator. 
     
     
         12 . The fiber-laser based system according to  claim 7 , further comprising a highly nonlinear silica fiber spliced directly to the output of said fiber amplifier. 
     
     
         13 . The fiber-laser based system according to  claim 1 , wherein said oscillator is core pumped, and said pump source comprises: a single-frequency laser; and an Er fiber amplifier amplifying an output of said single-frequency laser. 
     
     
         14 . The fiber-laser based system according to  claim 1 , wherein said system is operably arranged as a frequency comb system for the mid and far IR spectral region, said system, further comprising a modulator to vary an output power of said pump source in such a way as to control a carrier envelope offset frequency within said oscillator. 
     
     
         15 . The fiber-laser based system according to  claim 1 , wherein said oscillator comprises a saturable absorber. 
     
     
         16 . The fiber-laser based system according to  claim 1 , wherein said oscillator is configured as a ring oscillator. 
     
     
         17 . The fiber-laser based system according to  claim 1 , wherein said system is operably arranged as a frequency comb system for the mid and far IR spectral region, said system, further comprising an extra-cavity acousto-optic frequency shifter for carrier envelope phase control. 
     
     
         18 . The fiber-laser based system according to  claim 6 , further comprising an f-2f interferometer for carrier phase measurements. 
     
     
         19 . The fiber-laser based system according to  claim 18 , wherein said f-2f interferometer is configured for carrier phase control of said oscillator. 
     
     
         20 . An optical sub-surface micromachining apparatus comprising:
 A fiber-laser based system generating pulses having pulse widths less than about 100 ps, in a wavelength range from about 1700 to 2500 nm.   
     
     
         21 . The optical sub-surface micromachining apparatus according to  claim 20 , wherein said micro-machining apparatus is configured for machining of silicon. 
     
     
         22 . A fiber-laser based system comprising: negative dispersion gain fiber and positive dispersion undoped fiber, wherein the core size of the gain fiber is larger than the core size of the undoped fiber, and wherein said system produces pulses with an approximately parabolic pulse spectrum.