Fiber coupling enhancement via external feedback

An apparatus for coupling a multi-mode diode laser to a double-clad fiber, comprising:

• a. a multi-mode diode laser having an output of electromagnetic radiation wherein the output has brightness, wavelength, and lower order and higher order spatial modes;
• b. a double-clad fiber comprising an outer cladding, an inner cladding with a dopant that is substantially photoexcited by the output from the multi-mode diode laser, and an inner core substantially transparent to the output of the multi-mode diode laser, and further comprising an end whereby electromagnetic radiation can be directed into the core and cladding, and;
• c. a focusing objective, wherein:
• i. the multi-mode diode laser, focusing objective and double-clad fiber are aligned, such that the output from the multi-mode laser is substantially directed through the focusing objective to the end of the double-clad fiber;
• and,
• ii. a Bragg grating having a reflectivity is fabricated within the core of the double-clad fiber at the wavelength of the multi-mode diode laser so that output from the multi-mode diode laser is reflected back to the multi-mode diode laser such that the lower order spatial modes of the diode laser are enhanced and, thereby, the brightness of the multi-mode diode laser output that is coupled back into the core and inner cladding of the double-clad fiber is also enhanced.