Laser diode with distributed feedback and method for producing
Laser diode comprises an active layer; a waveguiding region at least partially surrounding the active layer; a rear facet; a front facet designed for outcoupling laser radiation, wherein the active layer extends at least partially along a first axis (X) between the rear facet and the front facet; and a grating operatively connected to the waveguiding region, wherein the grating comprises a plurality of bridges and trenches designed such that an average increase of a coupling parameter P for the plurality of trenches along the grating is non-zero, wherein the coupling parameter P of a trench is defined by the equation, wherein d res is a distance of the trench to the active layer, w is a width of the trench and Δn is the refractive index difference between a refractive index of the trench and a refractive index of a material surrounding the trench.
1. Laser diode ( 100 ) comprising:
an active layer ( 10 );
a waveguiding region ( 12 ) at least partially surrounding the active layer ( 10 );
a rear facet ( 14 );
a front facet ( 16 ) designed for outcoupling laser radiation, wherein the active layer ( 10 ) extends at least partially along a first axis (X) between the rear facet ( 14 ) and the front facet ( 16 ); and
a grating ( 18 ) operatively connected to the waveguiding region ( 12 ), wherein the grating ( 18 ) comprises a plurality of ridges ( 22 ) and trenches ( 24 ), wherein the grating ( 18 ) is a surface grating with the order of the grating ( 18 ) in the range between 10 and 100,
wherein
the plurality of trenches ( 24 ) is designed such that an average increase of a coupling parameter P for the plurality of trenches ( 24 ) along the grating ( 18 ) is non-zero, wherein the coupling parameter P of a trench ( 24 ) is defined by the equation (1)
P
=
Δ
n
wd
res
,
(
1
)
wherein d res is a distance of the trench ( 24 ) to the active layer ( 10 ), w is a width of the trench ( 24 ), and Δn is a refractive index difference between a refractive index of the trench ( 24 ) and a refractive index of a material surrounding the trench ( 24 ).
2. Laser diode ( 100 ) according to claim 1 , wherein the grating ( 18 ) has an apodization measure A P of greater than or equal to 1.1 in relation to the coupling parameter P, wherein the apodization measure A P according to equation (2)
A
P
=
Maximum
{
P
}
Minimum
{
P
}
(
2
)
results from the ratio between a maximum and a minimum value for the coupling parameter P of the plurality of trenches ( 24 ) of the grating ( 18 ).
3. Laser diode ( 100 ) according to claim 1 , wherein the grating ( 18 ) has an apodization measure A R of greater than or equal to 1.1 in relation to the local reflectance R(x), wherein the apodization measure A R according to equation (3)
A
R
=
Maximum
{
R
(
x
)
}
Minimum
{
R
(
x
)
}
(
3
)
results from the ratio between a maximum and a minimum value for the local reflectance R (x) of the grating ( 18 ).
4. Laser diode ( 100 ) according to claim 1 , wherein the grating has a dimension value of apodization A κL greater than or equal to 1.1 in relation to the local coupling factor length product κ L , wherein the apodization measure A κL according to equation (4)
A
κ
L
=
Maximum
{
κ
L
(
x
)
}
Minimum
{
κ
L
(
x
)
}
(
4
)
results from the ratio between a maximum and a minimum value for the local coupling factor length product κ L (x) of the grating ( 18 ).
5. Laser diode ( 100 ) according to claim 1 , wherein the coupling parameter P of the individual trenches ( 24 ) is adapted to the power density of the wave ( 26 ) guided in the waveguiding region ( 12 ), wherein the coupling parameter P is decreased in the areas of high power density compared to the coupling parameter P in the areas of low power density.
6. Laser diode ( 100 ) according to claim 1 , wherein the functional relationship of the coupling parameter P along the grating ( 18 ) is arbitrary, monotonically increasing or decreasing, linearly increasing or decreasing, quadratically increasing or decreasing, or exponentially increasing or decreasing.
7. Laser diode ( 100 ) according to claim 1 , wherein a variation V dres resulting from the ratio between a maximum and a minimum value for the distance d res of the individual trenches ( 24 ) to the active layer ( 10 ) according to equation (5)
V
dres
=
Maximum
{
d
res
}
Minimum
{
d
res
}
,
(
5
)
is greater than or equal to 1.1.
8. Laser diode ( 100 ) according to claim 1 , wherein a variation V w resulting from the ratio between a maximum and a minimum value for the width w of the individual trenches ( 24 ) according to equation (6)
V
w
=
Maximum
{
w
}
Minimum
{
w
}
(
6
)
is greater than or equal to 1.1.
9. Laser diode ( 100 ) according to claim 1 , wherein a variation VΔn
V Δn resulting from the ratio between a maximum and a minimum value for the refractive index difference Δn between the respective refractive index of an individual trench ( 24 ) and the refractive index of the material enclosing the trench ( 24 ) according to equation (7)
V
Δ
n
=
Maximum
{
Δ
n
}
Minimum
{
Δ
n
}
(
7
)
is greater than or equal to 1.1.
10. Laser diode ( 100 ) according to claim 1 , wherein the length L of the grating ( 18 ) is greater than or equal to 100 μm or corresponds to at least 10% of the distance between the rear facet ( 14 ) and the front facet ( 16 ) along the first axis (X).
11. Laser diode ( 100 ) according to claim 1 , wherein the grating extends over the complete resonator length or is divided into at least two sub-gratings, wherein the at least two sub-gratings between the rear facet ( 14 ) and the front facet ( 16 ) along the first axis (X) are distributed arbitrarily.
12. Laser diode ( 100 ) according to claim 11 , wherein the trenches ( 24 ) of the grating ( 18 ) are located completely or partially in areas of optical gain or no optical gain.
13. Laser diode ( 100 ) according to claim 1 , wherein the plurality of trenches ( 24 ) is equidistant spaced.
14. Laser diode ( 100 ) according to claim 1 , wherein at at least one of the trenches ( 24 ) a width w of the trench ( 24 ) tapers in the direction of the active layer ( 10 ).
15. Laser diode ( 100 ) according to claim 1 , wherein the walls of the trenches ( 24 ) have different profiles.
16. Method for producing a laser diode ( 100 ) comprising:
providing an active layer ( 10 ) and a waveguiding region ( 12 ) at least partially surrounding the active layer ( 10 );
forming a rear facet ( 14 ) and a front facet ( 16 ) adapted for coupling out laser radiation, wherein the active layer ( 10 ) extends at least partially along a first axis (X) between the rear facet ( 14 ) and the front facet ( 16 ); and
forming a grating ( 18 ) with a plurality of ridges ( 22 ) and trenches ( 24 ) such that the grating ( 18 ) is operatively connected to the waveguiding region ( 12 ), wherein the grating ( 18 ) is a surface grating with the order of the grating ( 18 ) in the range between 10 and 100,
wherein
the plurality of trenches ( 24 ) is designed such that at least one dimension value of apodization A for the plurality of trenches ( 24 ) is greater than or equal to 1.1.
17. Method for producing a laser diode ( 100 ) according to claim 16 , further comprising:
applying an etching mask ( 30 ) with a plurality of openings ( 32 ) to the waveguiding region ( 12 ), wherein the width of the openings ( 32 ) varies locally along a first axis (X) and/or a second axis (Y); and
patterning the masked waveguiding region ( 12 ) by an etching process.
18. Method for producing a laser diode ( 100 ) according to claim 16 , wherein the etching process is anisotropic reactive ion etching.
19. Laser Diode ( 100 ) comprising:
an active layer ( 10 );
a waveguiding region ( 12 ) at least partially surrounding the active layer ( 10 );
a rear facet ( 14 );
a front facet ( 16 ) designed for outcoupling laser radiation, wherein the active layer ( 10 ) extends at least partially along a first axis (X) between the rear facet ( 14 ) and the front facet ( 16 ); and
a grating ( 18 ) operatively connected to the waveguiding region ( 12 ), wherein the grating ( 18 ) comprises a plurality of ridges ( 22 ) and trenches ( 24 ),
wherein
the plurality of trenches ( 24 ) is designed such that an average increase of a coupling parameter P for the plurality of trenches ( 24 ) along the grating ( 18 ) is non-zero, wherein the coupling parameter P of a trench ( 24 ) is defined by the equation (8)
P
=
Δ
n
wd
res
(
8
)
wherein d res is a distance of the trench ( 24 ) to the active layer ( 10 ), w is a width of the trench ( 24 ), and Δn is a refractive index difference between a refractive index of the trench ( 24 ) and a refractive index of a material surrounding the trench ( 24 ), wherein the variation of the grating strength along the longitudinal axis is a quadratic increase, and wherein the grating ( 18 ) has an apodization measure A of greater than or equal to 3 in relation to the local reflectance R(x) or the local coupling factor length product κ L (x), wherein the apodization measure A according to equations (9) and (10)
A
R
=
Maximum
{
R
(
x
)
}
Minimum
{
R
(
x
)
}
(
9
)
A
κ
L
=
Maximum
{
κ
L
(
x
)
}
Minimum
{
κ
L
(
x
)
}
(
10
)
results from the ratio between a maximum and a minimum value for the local reflectance R(x) of the grating ( 18 ) or from the ratio between a maximum and a minimum value for the local coupling factor length product κ L (x) of the grating ( 18 ), respectively.
20. Laser diode ( 100 ) comprising:
an active layer ( 10 );
a waveguiding region ( 12 ) at least partially surrounding the active layer ( 10 );
a rear facet ( 14 );
a front facet ( 16 ) designed for outcoupling laser radiation, wherein the active layer ( 10 ) extends at least partially along a first axis (X) between the rear facet ( 14 ) and the front facet ( 16 ); and
a grating ( 18 ) operatively connected to the waveguiding region ( 12 ), wherein the grating ( 18 ) comprises a plurality of ridges ( 22 ) and trenches ( 24 ),
wherein
the plurality of trenches ( 24 ) is designed such that an average increase of a coupling parameter P for the plurality of trenches ( 24 ) along the grating ( 18 ) is non-zero, wherein the coupling parameter P of a trench ( 24 ) is defined by the equation (11)
P
=
Δ
n
wd
res
(
11
)
wherein d res is a distance of the trench ( 24 ) to the active layer ( 10 ), w is a width of the trench ( 24 ), and Δn is a refractive index difference between a refractive index of the trench ( 24 ) and a refractive index of a material surrounding the trench ( 24 ), wherein the coupling parameter P of the individual trenches ( 24 ) along a second axis (Y) extending perpendicular to the first axis (X) is location-dependent and the location-dependent coupling parameter P of a trench ( 24 ) is adapted to the power density of the wave ( 26 ) guided in the waveguiding region ( 12 ), and wherein the value of the location-dependent coupling parameter P of the trench ( 24 ) is decreased in the areas of high power density compared to the value of the location-dependent coupling parameter P of the trench ( 24 ) in the areas of low power density.