Fiber laser system with mechanism for inducing parasitic lights losses

Abstract

A method of inducing light losses at a parasitic wavelength in a fiber laser system includes providing a wavelength discriminator (WD) spaced from and between feeding and process fibers or from the end output of the feeding fiber so as to induce losses of light at parasitic wavelength. The device implementing the disclosed method is configured with a laser source, the delivery fiber and WD spaced at a distance between the surface to be treated and the end of the delivery fiber, wherein the WD receives the parasitic light over free space and is configured as a dichroic filter inducing losses to the light at the parasitic wavelength.

1 . A device for suppressing light at parasitic wavelength propagating along a path, comprising:
 a dispersive medium guiding laser light at a signal wavelength which has optical intensity sufficient to exceed a threshold for generating light at the parasitic wavelength; and   a wavelength discriminator (WD) being in free space communication with the dispersive medium and configured to suppress propagation of at least a portion of the light at the parasitic light and transmit the light at the signal wavelength.   
     
     
         2 . The device of  claim 1 , further comprising a beam expander between the dispersive medium and WD, the dispersive medium being an optical fiber selected from the group which consists of passive fibers, active fibers and a combination of active and passive fibers. 
     
     
         3 . The device of  2 , wherein the WD is a dichroic film filter coated upon an output surface of the beam expander or a bulk dichroic filter, and reflecting the portion of the light at the parasitic wavelength so that the reflected portion is not coupled into the dispersive medium. 
     
     
         4 . The device of  claim 1 , wherein the light at the signal wavelengths is in a 1060-1080 nm spectral range, and the WD is configured with the coefficient of reflection greater than 99.6% in a 1115-1150 nm range corresponding to a range of the parasitic wavelengths of stimulated Raman scattering. 
     
     
         5 . The device of  claim 1  further comprising a beam switch or fiber-to-fiber coupler, the dispersive medium being an optical fiber, wherein the beam switch or fiber-to-fiber coupler is located between two opposing and spaced apart inner ends of the optical fiber. 
     
     
         6 . The fiber laser system of  claim 5 , wherein the WD is tiltably mounted relative to a plane of light path so as to deflect light at the parasitic wavelength away from the plane, wherein the WD increases an output power of a source corresponding to a threshold of generation of stimulated emission of light at the parasitic wavelength at more than 30% compared to the same fiber laser system without the WD. 
     
     
         7 . A wavelength discriminator comprising a spectral filter receiving light at signal and parasitic wavelengths which propagate over free space, wherein the spectral filter is configured to suppress propagation of the light at the parasitic light and transmit the light at the signal wavelength. 
     
     
         8 . The wavelength discriminator of  claim 7 , wherein the spectral filter is a dichroic film or a bulk dichroic filter, the spectral and reflecting the portion of the light at the parasitic wavelength so that the reflected portion is not coupled into the dispersive medium. 
     
     
         9 . The device of  claim 7 , wherein the light at the signal wavelengths is in a 1060-1080 nm spectral range, and the WD is configured with the coefficient of reflection greater than 99.6% in a 1115-1150 nm range corresponding to a range of the parasitic wavelengths of stimulated Raman scattering.