Radiation-Emitting Laser Diode, Method for Choosing Refractive Indices of a Waveguide Layer Sequence for a Radiation-Emitting Laser Diode and Method for Producing a Radiation-Emitting Laser Diode

Abstract

In an embodiment a radiation-emitting laser diode includes a waveguide layer sequence having an active region configured to generate electromagnetic radiation with a preferred polarization direction, a first waveguide layer of a first doping type and a second waveguide layer of a second doping type, wherein the active region is arranged between the first waveguide layer and the second waveguide layer, wherein refractive indices of the waveguide layer sequence form a first effective refractive index for a transverse electric (TE) mode with its electric field oscillating in a first transverse direction and a second effective refractive index for a transverse magnetic (TM) mode with its electric field oscillating in a second transverse direction, and wherein an effective refractive index difference of the first effective refractive index and the second effective refractive index is at least 4.Math.10.sup.4.

Claims

1-14. (canceled)

15. A radiation-emitting laser diode comprising: a waveguide layer sequence comprising: an active region configured to generate electromagnetic radiation with a preferred polarization direction; a first waveguide layer of a first doping type; and a second waveguide layer of a second doping type, wherein the active region is arranged between the first waveguide layer and the second waveguide layer, wherein refractive indices of the waveguide layer sequence form a first effective refractive index for a transverse electric (TE) mode with its electric field oscillating in a first transverse direction and a second effective refractive index for a transverse magnetic (TM) mode with its electric field oscillating in a second transverse direction, and wherein an effective refractive index difference of the first effective refractive index and the second effective refractive index is at least 4.Math.10.sup.4.

16. The radiation-emitting laser diode according to claim 15, wherein refractive indices of the active region, the first waveguide layer and the second waveguide layer differ from one another, and/or wherein thicknesses of the active region, the first waveguide layer and the second waveguide layer differ from one another.

17. The radiation-emitting laser diode according to claim 15, wherein a length of the waveguide layer sequence is at least 500 m and at most 6 mm.

18. The radiation-emitting laser diode according to claim 15, further comprising: a first cladding layer of the first doping type arranged on the waveguide layer sequence on a first main surface and a second cladding layer of the second doping type arranged on the waveguide layer sequence on a second main surface.

19. The radiation-emitting laser diode according to claim 18, further comprising a metallic contact layer arranged on the second cladding layer in an electrically and thermally conductive manner.

20. The radiation-emitting laser diode according to claim 18, further comprising a substrate arranged on the first cladding layer, wherein the first cladding layer comprises a mode spoiler.

21. A method for choosing refractive indices of a waveguide layer sequence for a radiation-emitting laser diode, the method comprising: providing initial refractive indices for the waveguide layer sequence comprising an active region for generating electromagnetic radiation, a first waveguide layer of a first doping type, and a second waveguide layer of a second doping type; considering a coupling of a transverse electric (TE) mode in a first transverse direction and a transverse magnetic (TM) mode in a second transverse direction in the waveguide layer sequence as a function of the initial refractive indices; and choosing the refractive indices of the waveguide layer sequence by adjusting the initial refractive indices depending on a threshold value of the coupling.

22. The method according to claim 21, wherein the coupling is dependent on an effective refractive index difference of a first effective refractive index for the TE mode and a second effective refractive index for the TM mode, and wherein an effective refractive index is dependent on the initial refractive indices and/or the refractive indices of the waveguide layer sequence.

23. The method according to claim 22, wherein the threshold value corresponds to the effective refractive index difference, and wherein the refractive indices of the waveguide layer sequence are determined when the effective refractive index difference is at least 4.Math.10.sup.4, otherwise the coupling is again determined as a function of the adjusted refractive indices.

24. The method according to claim 21, wherein a polarization intensity ratio is dependent on an effective refractive index difference.

25. The method according to claim 21, wherein the coupling of the TE mode and the TM mode is dependent on an extension of the TM mode in the second transverse direction.

26. The method according to claim 21, wherein the coupling of the TE mode and the TM mode is dependent on a length of the waveguide layer sequence.

27. The method according to claim 21, wherein the coupling of the TE mode and the TM mode is dependent on a thickness of each of the layers of the waveguide layer sequence.

28. A method for producing the radiation-emitting laser diode, wherein the method for producing the radiation-emitting laser diode comprises producing the waveguide layer sequence having the refractive indices chosen by the method according to claim 21.

29. A radiation-emitting laser diode comprising: a waveguide layer sequence comprising: an active region configured to generate electromagnetic radiation of a preferred polarization direction; a first waveguide layer of a first doping type; and a second waveguide layer of a second doping type, wherein the active region is arranged between the first waveguide layer and the second waveguide layer, wherein refractive indices of the waveguide layer sequence form a first effective refractive index for a transverse electric (TE) mode with its electric field oscillating in a first transverse direction and a second effective refractive index for a transverse magnetic (TM) mode with its electric field oscillating in a second transverse direction, and wherein an effective refractive index difference of the first effective refractive index and the second effective refractive index is at least 4.Math.10.sup.4 and at most 5.Math.10.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The radiation-emitting laser diode and the method for choosing refractive indices of the waveguide layer sequence for the radiation-emitting laser diode described herein are explained in greater detail below with reference to exemplary embodiments and the associated figures.

[0067] FIG. 1 shows a schematic representation of a radiation-emitting laser diode according to an exemplary embodiment;

[0068] FIGS. 2 and 3 each exemplarily show a spatial profile of a real part of the refractive index of layers of a radiation-emitting laser diode according to an exemplary embodiment; and

[0069] FIG. 4 exemplarily shows a measurement of the polarization intensity ratio and the calculated effective refractive index difference of different radiation-emitting laser diodes.

[0070] Identical, similar or identically acting elements are provided with the same reference signs in the figures. The figures and the size ratios of the elements represented in the figures among one another are not drawn to scale. Rather, individual elements, in particular layer thicknesses, can be represented exaggeratedly large for better illustration and/or for better comprehension.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0071] The radiation-emitting laser diode 1 according to the exemplary embodiment of FIG. 1 comprises a waveguide layer sequence 2. The waveguide layer sequence 2 comprises an active region 3 configured to generate electromagnetic radiation. Furthermore, the waveguide layer sequence 2 comprises a first waveguide layer 4 of a first doping type, and a second waveguide layer 5 of a second doping type. The active region 3 is arranged between the first waveguide layer 4 and the second waveguide layer 5.

[0072] A first cladding layer 6 of the first doping type is arranged on the waveguide layer sequence 2 on a first main surface. The first main surface is formed by an outer surface facing away from the active region of the first waveguide layer 4. Furthermore, a second cladding layer 7 of the second doping type is arranged on the waveguide layer sequence 2 on a second main surface. The second main surface is formed by an outer surface facing away from the active region of the second waveguide layer 5. The first cladding layer 6 is in direct contact to the first waveguide layer 4 and the second cladding layer 7 is in direct contact to the second waveguide layer 5.

[0073] Furthermore, a metallic contact layer 10 is arranged on the second cladding layer 7 in an electrically and thermally conductive manner. The metallic contact layer 10 is in direct contact to the second cladding.

[0074] The first cladding layer 6, the first waveguide layer 4, the active region 3, the second waveguide layer 5, the second cladding layer 7 and the metallic contact layer 10 are arranged above one another in the order indicated.

[0075] The first doping type is different from the second doping type. For example, the first doping type is n-type and thus, the first cladding layer 6 and the first waveguide layer 4 are at least partially n-doped. It is possible that parts of the waveguide layer 4 are undoped and/or comprise p-type dopants. Since the doping types are different, the second doping type is p-type and thus, the second cladding layer 7 and the second waveguide layer 5 are p-doped.

[0076] The layers of the wave guide layer sequence 2, the first cladding layer 6 and the second cladding layer 7 each extend parallel to a main extension plane. Furthermore, the layers of the wave guide layer sequence 2, the first cladding layer 6 and the second cladding layer 7 each extend in a main extension direction.

[0077] During operation of the radiation-emitting laser diode 1, the electromagnetic radiation generated in the active region 3 is predominantly emitted as electromagnetic radiation into the waveguide layer sequence 2.

[0078] Due to different boundary conditions within the waveguide layer sequence 2, the electromagnetic radiation comprises two transverse modes, namely a transverse electric, TE, mode and a transverse magnetic, TM, mode. An electric field of the TE mode oscillates along a first transverse direction 8 and an electric field of the TM mode oscillates along a second transverse direction 9. The first transverse direction 8 and the second transverse direction 9 are aligned in a plane being perpendicular to the main extension direction. The main extension direction is parallel to a propagation direction of the electromagnetic radiation. Furthermore, the first transverse direction 8 and the second transverse direction 9 are aligned perpendicular to one another within the plane being perpendicular to the main extension direction.

[0079] Due to polarization dependent boundary conditions between adjacent layers of the waveguide layer sequence 2, the first cladding layer 6 and the second cladding layer 7, the TE mode and the TM mode feature different effective refractive indices. Also, the TE mode has a different overlap with the waveguide layer sequence 2, the first cladding layer 6 and the second cladding layer 7 than the TM mode.

[0080] Due to the different boundary conditions, the TE mode features a first effective refractive index for oscillation of its electrical field along the first transverse direction and the TM mode features a second effective refractive index for oscillation of its electrical field along the second transverse direction.

[0081] The refractive indices of the waveguide layer sequence 2, the first cladding layer 6 and the second cladding layer 7 are configured in such a way that an effective refractive index difference of the first effective refractive index and the second effective refractive index is at least 4.Math.10.sup.4, in particular at least 5.Math.10.sup.4. Having such an effective refractive index difference, a polarization intensity ratio of the electromagnetic radiation emitted from the radiation-emitting laser diode 1 is at least 90%, in particular at least 93%.

[0082] The diagrams according to FIGS. 2 and 3 show on the left y-axis a real part of a refractive index Re(n) of the layers of the radiation-emitting laser diode 1. On the right y-axis a normalized intensity I in arbitrary units of the TE mode and the TM mode is shown. On the x-axis a position z in m in vertical direction, i.e. a stacking direction of the layers of the radiation-emitting laser diode 1, is shown.

[0083] According to FIG. 2, the radiation-emitting laser diode 1 within this exemplary embodiment of FIG. 2 comprises, in addition to the radiation-emitting laser diode 1 of FIG. 1, a substrate 11. The substrate 11 is arranged on the first cladding layer 6. The first cladding layer 6 has a thickness of about 2 m. The first waveguide layer 4 has a thickness of about 1.3 m and the second waveguide layer 5 has a thickness of about 500 nm. The active region 3 sandwiched between the first waveguide layer 4 and the second waveguide layer 5 has a thickness of about 100 nm. The second cladding layer 7 has a thickness of about 1.2 m.

[0084] Within such a radiation-emitting laser diode 1, the first effective refractive index, in particular the real part of the first effective refractive index, for the TE mode is 3.40258 and the second effective refractive index, in particular the real part of the second effective refractive index, for the TM mode is 3.40215. Therefore, the effective refractive index difference is 3.30.Math.10.sup.4.

[0085] According to FIG. 3, the first cladding layer 6 has a thickness of about 2.1 m. The first waveguide layer 4 has a thickness of about 750 nm and the second waveguide layer 5 has a thickness of about 250 nm. The active region 3 sandwiched between the first waveguide layer 4 and the second waveguide layer 5 has a thickness of about 100 nm. The second cladding layer 7 has a thickness of about 1.1 m.

[0086] Within a radiation-emitting laser diode 1 according to FIG. 3, the first effective refractive index, in particular the real part of the first effective refractive index, for the TE mode is 3.35245 and the second effective refractive index, in particular the real part of the second effective refractive index, for the TM mode is 3.35149. Therefore, the effective refractive index difference is 9.6.Math.10.sup.4.

[0087] In the diagram according to FIG. 4, a polarization intensity ratio PR is depicted in percent on the y-axis. On the x-axis, an effective refractive index difference n.sub.eff of a first effective refractive index of a TE mode and a second effective refractive index of a TM mode of different radiation-emitting laser diodes 1 is shown. The radiation-emitting laser diodes 1 are mounted via a metallic contact layer 10 to a carrier.

[0088] The polarization intensity ratio of each radiation-emitting laser diode 1 is measured via an optical experiment.

[0089] A coupling of the TE mode and the TM mode is dependent on an effective refractive index difference. In particular, by reducing the coupling of the TE mode and the TM mode, the polarization intensity ratio can be increased.

[0090] If a polarization intensity ratio of at least 96% is desired, an effective refractive index difference of at least 6.7.Math.10.sup.4 has to be achieved. This can be achieved by designing refractive indices of a waveguide layer sequence 2 including the first cladding layer 6 and the second cladding layer 7 for a radiation-emitting laser diode 1 as a function of the coupling of the TE mode and the TM mode.

[0091] Initially, within a method for choosing such refractive indices, initial refractive indices are provided for a waveguide layer sequence 2 of a radiation-emitting laser diode 1. The initial refractive indices are represented, for example, by the refractive indices of the layers of a radiation-emitting laser diode 1.

[0092] In a next step the coupling of the TE mode and the TM mode is considered. For example, the refractive index difference is determined by a simulation, e.g., by solving the Eigenvalue equations of the wave guide layer sequence. If the coupling is below a threshold value, i.e. if the effective refractive index difference is below 4.Math.10.sup.4, the refractive indices of the layers of the radiation-emitting laser diode 1 are adjusted.

[0093] Subsequently, the coupling of the radiation-emitting laser diode 1 with the adjusted refractive indices is chosen accordingly.

[0094] The features and exemplary examples described in connection with the Figures can be combined with one another according to further exemplary examples, even if not all combinations are explicitly described. Furthermore, the exemplary examples described in connection with the Figures can alternatively or additionally have further features as described in the general part of the description.

[0095] The invention is not limited to the exemplary examples by the description based on the exemplary examples. Rather, the invention comprises any new feature as well as any combination of features, which includes in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary examples.