Power and brightness scaling in fiber coupled diode lasers using diodes with optimized beam dimensions

Abstract

A number of beams that can be coupled into an optical fiber can be increased using emitted beams having greater divergence, thus providing increased beam power. Alternatively, with a fixed number of emitters, total optical power can be maintained with fewer beams in an output beam with a smaller numerical aperture.

We claim: 
     
         1 . A method, comprising:
 based on a predetermined step height of a laser diode mount, selecting at least one of an emitted beam fast axis divergence, an emitted beam fast axis size, a fast axis waveguide thickness so as to couple emitted beams from a selected number of laser diodes into an optical fiber;   situating the selected number of laser diodes at the predetermined height;   situating slow axis and fast axis collimation lenses so as to produce collimated beams from emitted beams from each of the laser diodes; and   situating a fast axis telescope and an objective lens so at to direct the collimated beams into the optical fiber.   
     
     
         2 . The method of  claim 1 , wherein at least one of the emitted beam fast axis divergence, the emitted beam fast axis size, and the fast axis waveguide thickness is selected based on a numerical aperture of the optical fiber. 
     
     
         3 . The method of  claim 1 , wherein the step height is between 200 μm and 1,000 μm and a magnification of the fast axis telescope is less than one. 
     
     
         4 . The method of  claim 1 , further comprising selecting a fast axis magnification of the emitted beam based on a core diameter of the optical fiber. 
     
     
         5 . The method of  claim 1 , wherein each of the laser diodes emits in a wavelength range of 800 nm to 1,000 nm, and the selected number of laser diodes consists of either 1) two sets of seven laser diodes that couple a total optical power of at least 160 W into the optical fiber, 2) two sets of nine laser diodes that couple a total optical power of at least 200 W in a beam of numerical aperture less than 0.15 into the optical fiber, wherein the optical fiber has a core diameter of 105 μm, 3) two sets of 15 laser diodes that couple a total optical power of at least 360 W in a beam of numerical aperture less than 0.18 into the optical fiber, wherein the optical fiber has a core diameter of 105 μm, or 4) two sets of 24 laser diodes that couple at least 800 W in a beam of numerical aperture less than 0.18 into the optical fiber, wherein the optical fiber has a core diameter of 200 μm. 
     
     
         6 . A method, comprising:
 based on fixed separations along fast axis directions and a number of laser diodes, selecting at least one of an emitted beam fast axis divergence, an emitted beam fast axis size, or a fast axis waveguide thickness so as to couple a combined beam having a selected power, a selected numerical aperture, or both into an optical fiber; and   situating the number of laser diodes at the fixed separations and directing emitted beams from each of the laser diodes to the optical fiber with corresponding fast and slow axis collimators, a fast axis telescope, and an objective lens.   
     
     
         7 . The method of  claim 6 , wherein the emitted beam fast axis size is less than 1.60 μm or the fast axis beam divergence is greater than 48 degrees. 
     
     
         8 . The method of  claim 6 , further comprising selecting a slow axis dimension so that a slow axis BPP is less than a maximum allowable fiber BPP. 
     
     
         9 . The method of  claim 8 , wherein the slow axis dimension is selected based on a threshold associated with optical damage one or more of the laser diodes. 
     
     
         10 . The method of  claim 6 , wherein each of the laser diodes emits in a wavelength range of 800 nm to 1,000 nm, and the number of laser diodes consists of either 1) two sets of seven laser diodes that couple a total optical power of at least 160 W into the optical fiber, 2) two sets of nine laser diodes that couple a total optical power of at least 200 W in a beam of numerical aperture less than 0.15 into the optical fiber, wherein the optical fiber has a core diameter of 105 μm, 3) two sets of 15 laser diodes that couple a total optical power of at least 360 W in a beam of numerical aperture less than 0.18 into the optical fiber, wherein the optical fiber has a core diameter of 105 μm, or 4) two sets of 24 laser diodes that couple at least 800 W in a beam of numerical aperture less than 0.18 into the optical fiber, wherein the optical fiber has a core diameter of 200 μm. 
     
     
         11 . A method, comprising:
 selecting a step height along a common fast axis direction;   based on the selected step height, selecting a common fast axis beam diameter and a common fast axis beam divergence; and   shaping beams from each of a set of laser diodes spaced apart by the step height and having the common fast axis beam diameter and the common fast axis beam divergence along the common fast axis direction with respective fast axis collimators, a fast axis telescope, and an objective lens so as to produce a combined beam having a combined beam fast axis beam diameter and beam divergence corresponding to an output fiber core diameter and numerical aperture, and shaping beams from each of the set of laser diodes along a slow axis direction with respective slow axis collimators and the objective lens so that the combined beam has a combined beam slow axis beam diameter and beam divergence corresponding to the output fiber core diameter and numerical aperture.   
     
     
         12 . The method of  claim 11 , wherein the beams of the set of laser diodes are combined so as to fill a portion of an aperture of the objective lens. 
     
     
         13 . The method of  claim 11 , wherein the step height is between 200 μm and 1,000 μm, and a magnification of the fast axis telescope is less than one. 
     
     
         14 . The method of  claim 11 , wherein the laser diodes are distributed along a slow axis direction so as to have a fixed slow axis spacing. 
     
     
         15 . The method of  claim 11 , wherein each of the diodes of the set of laser diodes emits in a wavelength range of 800 nm to 1,000 nm, and the set of laser diodes consists of either 1) two sets of seven laser diodes that couple a total optical power of at least 160 W into the optical fiber, 2) two sets of nine laser diodes that couple a total optical power of at least 200 W in a beam of numerical aperture less than 0.15 into the optical fiber, wherein the optical fiber has a core diameter of 105 μm, 3) two sets of 15 laser diodes that couple a total optical power of at least 360 W in a beam of numerical aperture less than 0.18 into the optical fiber, wherein the optical fiber has a core diameter of 105 μm, or 4) two sets of 24 laser diodes that couple at least 800 W in a beam of numerical aperture less than 0.18 into the optical fiber, wherein the optical fiber has a core diameter of 200 μm. 
     
     
         16 . The method of  claim 11 , wherein for each laser diode, the beam is directed to the objective lens with a respective reflector. 
     
     
         17 . The method of  claim 16 , wherein the slow axis collimators are situated to direct fast axis and slow axis collimated beams to the respective reflectors. 
     
     
         18 . The method of  claim 11 , wherein a focal length of the fast axis collimators is between 200 μm and 400 μm and a focal length of the objective lens is between 5 mm and 12 mm. 
     
     
         19 . The method of  claim 11 , wherein the output fiber has a core diameter of 105 μm or 200 μm. 
     
     
         20 . The method of  claim 11 , wherein the laser diodes are flared laser diodes.