Efficient wavelength combining of multiple laser arrays
View Patent ↗Light beams from multiple emitters, such as lasers, arranged in two or more arrays are combined by beam-superposition using a dispersive element, such as a diffraction grating, to provide a combined output beam with increased power. Each emitter produces light of a controlled wavelength that is incident upon the diffraction grating at a corresponding selected incidence angle to produce a diffracted wave that propagates in an output direction and forms a component of the combined output beam. First and second arrays are located on opposing sides of the combined output beam and are arranged such that light from all of the emitters overlaps to form the combined output beam. The wavelengths may be controlled by an external resonator, for example. As many as four arrays may be combined using a two-dimensional diffraction grating.
1. An apparatus for combining a plurality of emitters to provide a combined output beam propagating in an output direction, the apparatus comprising:
a dispersive element;
a first plurality of emitters arranged in a first array and configured to provide first components of the combined output beam;
a second plurality of emitters arranged in a second array and configured to provide second components of the combined output beam;
a third plurality of emitters arranged in a third array and configured to provide third components of the combined output beam; and
a fourth plurality of emitters arranged in a fourth array and configured to provide fourth components of the combined output beam;
where each emitter of the first, second, third and fourth pluralities of emitters produces light of a controlled wavelength that is incident upon the dispersive element at an incidence angle to the dispersive element, where the controlled wavelength of the light and incidence angle are related such that a diffracted wave is produced that propagates in the output direction and forms a component of the combined output beam,
where the first array and the second array are located on opposing sides of the combined output beam, and
where the third array and the fourth array are located on opposing sides of the combined output beam;
where the first, and second, third and fourth components of the combined output beam overlap.
2. The apparatus of claim 1 , where the first, second, third and fourth arrays are linear arrays.
3. The apparatus of claim 2 , where the dispersive element comprises a diffraction grating comprising a first plurality of parallel lines having a first line spacing.
4. The apparatus of claim 3 , further comprising:
a first lens configured to focus light from the first plurality of emitters onto the diffraction grating; and
a second lens configured to focus light from the second plurality of emitters onto the diffraction grating.
5. The apparatus of claim 3 , where the first lens has a first line of focus on the diffraction grating, where the second lens has a second line of focus on the diffraction grating, and where the first and second lines of focus are parallel to the first plurality of parallel lines of the diffraction grating.
6. The apparatus of claim 3 , where the first array is located in a focal plane of the first lens and the second array is located in a focal plane of the second lens.
7. The apparatus of claim 3 , where a linewidth Δλ of an emitter of the first array and a spacing s between adjacent emitters of the first array are configured such that
Δλ
cos
θ
′
⪡
b
,
where b=sd/f is the wavelength separation of adjacent emitters, the first plurality of parallel lines has a first line spacing d, the output direction is at an angle θ′ to a direction normal to the diffraction grating, and the first lens has a focal length f.
8. The apparatus of claim 3 , where the first and second arrays are oriented at different incidence angles to the diffraction grating such that specular reflection of light emitted from the first array of emitters is not incident upon the second array of emitters and specular reflection of light emitted from the second array of emitters is not incident upon the first array of emitters.
9. The apparatus of claim 3 , where the diffraction grating comprises a transmissive diffraction grating or a reflective diffraction grating.
10. The apparatus of claim 3 , where first, second, third and fourth plurality of emitters and the diffraction grating are configured such that only a single diffracted wave is produced.
11. The apparatus of claim 1 , where:
the first plurality of lines is orientated in an x-direction and the second plurality of lines are orientated in a y-direction,
light from an emitter n of the first array is incident at an angle to α n the x-direction and an angle β n to the y-direction and has wavelength λ n ,
light from an emitter n of the second array in a second quadrant is incident at an angle approximately π-α n to the x-direction and an angle β n to the y-direction and has wavelength λ n ,
light from an emitter n of the third array in a third quadrant is incident at an angle approximately π-α n to the x-direction and approximately an angle π-β n to the y-direction and has wavelength λ n ,
light from an emitter n of the fourth array is incident at an angle to the x-direction and an angle approximately to the y-direction and has wavelength λ n ,
where
cos
α
n
=
cos
α
′
±
λ
n
d
x
and
cos
β
n
=
cos
β
′
±
λ
n
d
y
,
in which d x denotes the first line spacing, d y denotes the second line spacing, and α′ and β′ denote the angles between the combined output beam and the x- and y-directions, respectively and where the combined beam propagates in a direction that is normal to or nearly normal to the dispersive element.
12. The apparatus of claim 1 , where the first, second, third and fourth pluralities of emitters utilize a master oscillator power amplifier (MOPA) architecture for controlling the wavelengths of light from the emitters.
13. The apparatus of claim 1 , where the difference between the controlled wavelengths of light from adjacent emitters is larger than the spectral linewidths of the adjacent emitters, so as to avoid cross-talk between adjacent emitters.
14. The apparatus of claim 1 , where the dispersive element comprises a prism.
15. An apparatus for combining light of controlled wavelengths to provide a combined output beam propagating in an output direction, the apparatus comprising:
a first diffraction grating comprising a first plurality of parallel lines having a first line spacing;
an array of low power master oscillators;
an external resonator, comprising a lens, a second diffraction grating and a mirror, where the lens focuses light from the low power master oscillators onto the second diffraction grating to be diffracted onto the mirror that controls the wavelengths of the low power master oscillators;
a first power amplifier array that receives light from the array of low power master oscillators and produces light of the controlled wavelengths that is incident upon the first diffraction grating at first incidence angles corresponding to the controlled wavelengths;
a second power amplifier array that receives light from the array of low power master oscillators and produces light of the controlled wavelengths that is incident upon the first diffraction grating at second incidence angles corresponding to the controlled wavelengths;
a third power amplifier array that receives light from the array of low power master oscillators and produces light of the controlled wavelengths that is incident upon the first diffraction grating at third incidence angles corresponding to the controlled wavelengths; and
a fourth power amplifier array that receives light from the array of low power master oscillators and produces light of the controlled wavelengths that is incident upon the first diffraction grating at fourth incidence angles corresponding to the controlled wavelengths;
where light from the first, second, third, and fourth power amplifier arrays is diffracted from the first diffraction grating and overlaps to form the combined output beam, and where the first and second power amplifier arrays are located on opposing sides of the combined output beam, and the third and fourth power amplifier arrays are located on opposing sides of the combined output beam.
16. The apparatus of claim 15 , further comprising:
a first lens configured to focus light from the first power amplifier array onto the first diffraction grating;
a second lens configured to focus light from the second power amplifier array onto the first diffraction grating;
a third lens configured to focus light from the third power amplifier array onto the first diffraction grating; and
a fourth lens configured to focus light from the fourth power amplifier array onto the first diffraction grating.
17. The apparatus of claim 16 where the first lens has a first line of focus on the first diffraction grating, where the second lens has a second line of focus on the first diffraction grating, where the third lens has a third line of focus on the first diffraction grating, where the fourth lens has a fourth line of focus on the first diffraction grating and where the first, second, third, and fourth lines of focus are parallel to the first plurality of parallel lines of the first diffraction grating.
18. The apparatus of claim 16 , where the first array is located in a focal plane of the first lens, the second array is located in a focal plane of the second lens, and the third array is located in a focal plane of the third lens, and the fourth array is located in a focal plane of the fourth lens.
19. A method for combining light from a plurality of emitters to provide a combined output beam propagating in an output direction from a diffraction grating having a first plurality of parallel lines, the method comprising:
for each emitter of a first plurality of emitters arranged in a first array, of a second plurality of emitters arranged in a second array, of a third plurality of emitters arranged in a third array, and of a fourth plurality of emitters arranged in a fourth array:
producing light of a controlled wavelength;
directing the produced light onto the diffraction grating, the directed light incident on the diffraction grating at an incidence angle corresponding to the controlled wavelength; and
diffracting the directed light by the diffraction grating to form a component of the combined output beam;
where the first and second arrays are located on opposing sides of the combined output beam,
where the third and fourth arrays are located on opposing sides of the combined output beam, and
where the first, second, third and fourth arrays are positioned such that diffracted directed light from the first, second, third and fourth pluralities of emitters overlap to form the combined output beam.
20. The method of claim 19 ,
where directing the light produced by the first plurality of emitters onto the diffraction grating comprises passing the produced light through a first lens having a first line of focus on the diffraction grating;
where directing the light produced by the second plurality of emitters onto the diffraction grating comprises passing the produced light through a second lens having a second line of focus on the diffraction grating; and
where the first and second lines of focus are parallel to the first plurality of parallel lines of the diffraction grating.
21. The method of claim 20 , where a linewidth Δλ of an emitter of the first array and a spacing s between adjacent emitters of the first array are configured such that
Δλ
cos
θ
′
•
b
=
d
f
s
,
where b is the wavelength separation of adjacent emitters, the first plurality of lines has a first line spacing d, the output direction is at an angle θ′ to a direction normal to the diffraction grating, and the first lens has a focal length f.
22. The method of claim 19 , where the first plurality of lines has a first line spacing d, and the output direction is at an angle θ′ to a direction normal to the diffraction grating, and where the method further comprises:
controlling the selected angle θ n , a corresponding wavelength λ n of light emitted from the n th emitter of the first array, or a combination thereof, such that
sin
θ
n
=
sin
θ
′
+
λ
n
d
for the first array; and
controlling the selected angle {tilde over (θ)} n , a corresponding wavelength {tilde over (λ)} n of light emitted from the n th emitter of the second array, or a combination thereof, such that
sin
θ
~
n
=
sin
θ
′
-
λ
n
~
d
for the second array,
where the wavelengths λ n and {tilde over (λ)} n fall within the gain bandwidth of an amplifying medium of their respective emitters.
23. The method of claim 19 , where the first plurality of emitters comprises a first power amplifier array and the second plurality of emitters comprises a second power amplifier array, the method further comprising:
generating light at the controlled wavelengths in a master oscillator array;
controlling the wavelengths of the generated light using an external optical resonator;
coupling light from the master oscillator array the first power amplifier array; and
coupling light from the master oscillator array the second power amplifier array.
24. The method of claim 19 , where the diffraction grating has a second plurality of parallel lines orthogonal to the first plurality of parallel lines, the method further comprising:
emitting light from the third plurality of emitters to produce a diffracted wave, diffracted by the second plurality of parallel lines of the diffraction grating, that propagates in the output direction and forms a third component of the combined output wave; and
emitting light from the fourth plurality of emitters to produce a diffracted wave, diffracted by the second plurality of parallel lines of the diffraction grating, that propagates in the output direction and forms a fourth component of the combined output wave.
25. The method of claim 19 , where first and second plurality of emitters and the diffraction grating are configured such that only first order diffracted waves are produced.
26. The method of claim 19 , further comprising controlling the difference between the controlled wavelengths of adjacent emitters to be larger than the spectral linewidths of the adjacent emitters so as to avoid cross-talk between adjacent emitters.