Wavelength locking and multiplexing of high-power semiconductor lasers

Abstract

The disclosure relates to wavelength stabilization and wavelength multiplexing of multiple high-power multi-mode semiconductor lasers. The lasers are wavelength-stabilized in free space using multi-peak output reflectors to wavelength-lock their output at different reflection wavelength in dependence on operating conditions, to reduce output reflectivity required for locking and increase output power. Selecting output reflectors having different non-overlapping sets of reflectivity peaks for different lasers or groups of lasers enables combining their output by wavelength multiplexing.

1 . A multi-laser light source comprising:
 a plurality of multi-mode semiconductor lasers;   beam combining optics for combining multi-mode laser beams emitted by the plurality of multi-mode semiconductor lasers into a single combined multi-mode beam; and   a multi-band partial reflector (MBPR) disposed in an optical path of the combined multi-mode beam for transmitting therethrough at least 80% of an optical power of the combined multi-mode beam,
 the MBPR having at least two distinct reflectivity peaks centered at at least two distinct reflection wavelengths, 
 each reflectivity peak characterized by a peak reflectivity in a range of 1% to 15% for providing an optical feedback to each of the plurality of multi-mode semiconductor lasers at the at least two distinct reflection wavelengths, and 
 wherein the at least two distinct reflection wavelengths and corresponding distinct reflectivity peak, of the at least two distinct reflectivity peaks, are selected:
 based on a determination of an operating wavelength range, which is based on a respective wavelength operating range for each of the plurality of multi-mode semiconductor lasers, of the multi-laser light source for a pre-defined range of operating conditions, 
 based on a selection of reflection wavelengths, within the operating wavelength range of the multi-laser light source, and corresponding peak reflectivity values, of the at least two distinct reflectivity peaks, so that wavelength locking ranges, associated with the at least two distinct reflectivity peaks, cover the operating wavelength range, and 
 to enable wavelength locking of each of the plurality of multi-mode semiconductor lasers at one of the at least two distinct reflection wavelengths at any operating condition within the pre-defined range of operating conditions. 
 
   
     
     
         2 . The multi-laser light source of  claim 1  further comprising:
 a support base having a stepped laser mounting surface comprising a plurality of steps, wherein
 the plurality of multi-mode semiconductor lasers are mounted upon the plurality of steps for producing the multi-mode laser beams, 
 the multi-mode laser beams are spatially offset from each other in a vertical direction that is perpendicular to the stepped laser mounting surface; 
 the beam combining optics align the vertically offset multi-mode laser beams in a same vertical plane so as to form a composite light beam; and 
 the at least two distinct reflection wavelengths and the corresponding distinct reflectivity peak, of the at least two distinct reflectivity peaks, are selected so that each of the plurality of multi-mode semiconductor lasers exhibits an optical gain peak within a wavelength locking range from at least one of the at least two distinct reflection wavelengths over the pre-defined range of operating conditions. 
 
 
     
     
         3 . The multi-laser light source of  claim 1 , wherein
 the pre-defined range of operating conditions comprises pre-defined operating ranges of laser temperature and drive current, and   the at least two distinct reflection wavelengths and the corresponding peak reflectivities are selected so as to enable wavelength locking of each of the plurality of multi-mode semiconductor lasers at one of the at least two distinct reflection wavelengths at any temperature and drive current within the pre-defined operating ranges.   
     
     
         4 . The multi-laser light source of  claim 1 , wherein each of the plurality of multi-mode semiconductor lasers comprises a laser chip of a substantially same layer structure and nominal material composition. 
     
     
         5 . The multi-laser light source of  claim 1 , wherein a quantity of multi-mode semiconductor lasers, of the plurality of multi-mode semiconductor lasers is greater than a quantity of distinct reflectivity peaks of the at least two distinct reflectivity peaks. 
     
     
         6 . The multi-laser light source of  claim 1 , wherein the MBPR comprises at least two volume Bragg gratings (VBG) for reflecting light at a respective distinct reflection wavelength of the at least two distinct reflection wavelengths. 
     
     
         7 . The multi-laser light source of  claim 1 , wherein the MBPR comprises a multi-band VBG having a reflection spectrum comprising the at least two distinct reflectivity peaks. 
     
     
         8 . The multi-laser light source of  claim 1 , wherein each of the at least two distinct reflectivity peaks is characterized by a peak reflectivity between 2% and 15%. 
     
     
         9 . The multi-laser light source of  claim 1 , wherein the at least two reflection wavelengths are spaced apart by at least 2 nm. 
     
     
         10 . The multi-laser light source of  claim 8 , wherein the at least two reflection wavelengths are spaced by a wavelength spacing in a range of 2 nm to 25 nm. 
     
     
         11 . The multi-laser light source of  claim 1 , wherein a quantity of multi-mode semiconductor lasers, of the plurality of multi-mode semiconductor lasers is at least 3, and a quantity of the at least two distinct reflectivity peaks in the at least two distinct reflectivity peaks is at most 3. 
     
     
         12 . The multi-laser light source of  claim 1 , wherein
 the plurality of multi-mode semiconductor lasers comprise:
 a first multi-laser semiconductor light source in accordance with  claim 1  for generating a first composite multi-mode light beam, and 
   the multi-laser light source further comprises:
 a second multi-laser semiconductor light source in accordance with claim h for generating a second composite multi-mode light beam; and 
 an additional MBPR disposed in an optical path of the second composite multi-mode light beam and configured to transmit therethrough at least 80% of an optical power of the second composite multi-mode light beam,
 the additional MBPR comprising two or more distinct reflectivity peaks, wherein each of the two or more distinct reflectivity peaks is characterized by a peak reflectivity in the range of 1% to 15%, so as to provide an optical feedback to each of the multi-mode semiconductor lasers in the second multi-laser semiconductor light source at two or more distinct reflection wavelengths corresponding to the peak reflectivities of the two or more distinct reflectivity peaks, 
 
   the beam combiner optics includes a wavelength multiplexer disposed to receive the first and second composite multi-mode light beams to produce therefrom a single multiplexed beam by means of wavelength division multiplexing, and   the at least two distinct reflection wavelengths of the MBPR of the first multi-laser semiconductor light source differ from the two or more distinct reflection wavelengths of the additional MBPR of the second multi-laser semiconductor light source so as to enable the wavelength division multiplexing thereof by the wavelength multiplexer.   
     
     
         13 - 20 . (canceled)