LASER DIODE AND METHOD FOR PRODUCING LASER RADIATION OF AT LEAST TWO FREQUENCIES

Abstract

The invention relates to laser diode for generating laser radiation of at least two frequencies, comprising: a semiconductor body having a ridge waveguide; a DFB structure or DBR structure in the ridge waveguide; and a piezoelectric element for producing mechanical stress in the ridge waveguide, which piezoelectric element is arranged on the ridge waveguide. The invention further relates to a method for producing laser radiation of at least two frequencies by means of the laser diode.

Claims

1. A laser diode for generating laser radiation of at least two frequencies, comprising a semiconductor body with a ridge waveguide, a DFB structure or DBR structure in the ridge waveguide, and a piezoelectric element disposed on the ridge waveguide for generating a mechanical stress in the ridge waveguide.

2. The laser diode according to claim 1, wherein the mechanical stress causes the ridge waveguide to have a birefringent property in the region of the piezoelectric element.

3. The laser diode according to claim 1, wherein the laser diode is adapted to simultaneously emit a first laser radiation of a first frequency and a second laser radiation of a second frequency different from the first frequency when an electric voltage is applied to the piezoelectric element.

4. The laser diode according to claim 3, wherein the electrical voltage is a DC voltage.

5. The laser diode according to claim 3, wherein the absolute value of the electrical voltage is between 0.1 V and 300 V.

6. The laser diode according to claim 5, wherein the absolute value of the electrical voltage is between 10 V and 300 V.

7. The laser diode according to claim 1, wherein a frequency difference between the first frequency and the second frequency is between 1 kHz and 1 THz.

8. The laser diode according to claim 1, wherein the piezoelectric element comprises AlN, ZnO, PZT, LiNbO.sub.3, KNbO.sub.3 or LiTaO.sub.3.

9. The laser diode according to claim 1, wherein the semiconductor body is based on an arsenide compound semiconductor.

10. A method for generating laser radiation of at least two frequencies with a laser diode comprising a semiconductor body having a ridge waveguide, a DFB structure or DBR structure in the ridge waveguide, and a piezoelectric element arranged on the ridge waveguide, wherein an electrical voltage is applied to the piezoelectric element to generate a mechanical stress in the ridge waveguide, and wherein the laser diode simultaneously emits a first laser radiation of a first frequency and a second laser radiation of a second frequency different from the first frequency.

11. The method according to claim 10, wherein the first laser radiation and the second laser radiation are emitted simultaneously from a laser facet of the laser diode.

12. The method according to claim 10, wherein a frequency difference between the first frequency and the second frequency is controllable by the electric voltage applied to the piezoelectric element.

13. The method according to claim 10, wherein the electrical voltage is a DC voltage having an absolute value between 0.1 V and 300 V.

14. The method according to claim 10, wherein the mechanical voltage causes the ridge waveguide to have a birefringent property in the region of the piezoelectric element.

15. The method according to claim 10, wherein a frequency difference between the first frequency and the second frequency is between 1 MHz and 1 THz.

16. The method according to claim 10, wherein the piezoelectric element comprises AlN, ZnO, PZT, LiNbO.sub.3, KNbO.sub.3 or LiTaO.sub.3.

17. A laser diode for generating laser radiation of at least two frequencies, comprising: a semiconductor body with a ridge waveguide; a DFB structure or DBR structure in the ridge waveguide; and a piezoelectric element disposed on the ridge waveguide for generating a mechanical stress in the ridge waveguide, wherein the mechanical stress causes the ridge waveguide to have a birefringent property in the region of the piezoelectric element, the laser diode is adapted to simultaneously emit a first laser radiation of a first frequency and a second laser radiation of a second frequency different from the first frequency when an electric voltage is applied to the piezoelectric element, and the first laser radiation and the second laser radiation have different polarization directions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention is explained in more detail below by means of an exemplary embodiment in connection with FIG. 1.

[0027] FIG. 1 shows a schematic perspective view of an exemplary embodiment of the laser diode.

[0028] The components shown as well as the proportions of the components among each other are not to be regarded as true to scale.

DETAILED DESCRIPTION

[0029] The laser diode 10 shown schematically in FIG. 1 comprises a semiconductor body 1. The semiconductor body 1 contains a semiconductor layer sequence which comprises, in particular, an n-type semiconductor region, an active layer and a p-type semiconductor region. Furthermore, the semiconductor body 1 comprises a p-type contact and an n-type contact for electrically contacting the semiconductor layer sequence. The individual layers of the semiconductor layer sequence and their contacts are not shown here for simplicity. The semiconductor layer sequence may be based on an arsenide compound semiconductor, for example.

[0030] A ridge waveguide 2 is formed at the upper side of the semiconductor body 1. The ridge waveguide 2 is formed by a ridge, which may be produced by an etching process into the p-type semiconductor region, for example. The ridge waveguide 2 extends in the direction of the resonator axis of the laser diode 10 between a first laser facet 11 and a second laser facet 12. The length of the laser resonator, i.e., the distance between the first laser facet 11 and the second laser facet 12, is between 0.5 mm and 5 mm, for example.

[0031] A DFB structure 3 is formed at the surface of the ridge waveguide 2. In particular, the DFB structure 3 is formed by a sequence of elevations and depressions in the ridge waveguide 2 and can be produced, for example, by an etching process in the ridge waveguide 2. The elevations and depressions are formed in particular in the p-type semiconductor region of the laser diode 10. In particular, the DFB structure is periodic at least in regions. As can be seen in FIG. 1, the periodicity can be interrupted, for example, in the middle of the laser resonator in order to generate a phase jump there. On the upper side of the laser diode 10, an electrically insulating layer and above it a p-contact may be arranged, wherein the electrically insulating layer comprises an opening at the upper side of the ridge waveguide 2, so that the p-contact contacts only the upper side of the ridge waveguide. The electrically insulating layer and the p-contact are not shown in FIG. 1, so that the DFB structure 3 is visible. The n-contact, which is also not shown, can be arranged on a back side of the laser diode 10. Alternatively to a DFB structure 3, the laser diode may comprise a DBR structure.

[0032] A piezoelectric element 4 is arranged on the ridge waveguide 2 having the DFB structure 3 in the laser diode 10.

[0033] The piezoelectric element 4 covers only a portion of the ridge waveguide 2, which is preferably arranged in the vicinity of the second laser facet 12 provided for coupling out radiation. In the longitudinal direction of the ridge waveguide 2, for example, the piezoelectric element 4 may comprise an extension between 50 μm and 1 mm, preferably between 100 μm and 200 μm. In the direction transverse to the ridge waveguide 2, the piezoelectric element 4 covers the ridge waveguide 2, its side flanks and at least partially also the surface of the laser diode 10 next to the ridge waveguide 2.

[0034] The laser diode 10 is preferably not electrically contacted in the region of the piezoelectric element 4, in particular the p-contact of the laser diode 10 is preferably arranged only outside the piezoelectric element 4. The area of the laser resonator located below the piezoelectric element 4 is thus not electrically pumped.

[0035] The piezoelectric element 4 comprises a first electrode 41, a second electrode 42 and a layer 43 of a piezoelectric material arranged between the first electrode 41 and the second electrode 42. In particular, the layer 43 may comprise a ceramic having piezoelectric properties. For example, the layer 43 may comprise AlN, ZnO, PZT, LiNbO.sub.3, KNbO.sub.3 or LiTaO.sub.3. By applying an electrical voltage to the electrodes 41, 42, a mechanical stress can advantageously be generated in the ridge waveguide 2 in the laser diode 10. The mechanical stress generated in this way causes the ridge waveguide 2 to have a birefringent property in the region of the piezoelectric element 4. The electrical voltage is, for example, a DC voltage with an absolute value in the range from 0.1 V to 300 V, and particularly preferably in the range from 10 V to 100 V.

[0036] By means of the birefringent property of the ridge waveguide 2 generated in this way, it can be achieved that two laser modes with two different frequencies propagate in the laser resonator between the first laser facet 11 and the second laser facet 12. The two laser modes differ from each other in their polarization and frequency.

[0037] Therefore, the laser diode 10 emits from the second laser facet 12, which is the output facet in the exemplary embodiment, simultaneously a first laser radiation 21 with a first frequency f1 and a second laser radiation 22 with a second frequency f2. Advantageously, the difference between the first frequency f1 and the second frequency f2 can be selectively adjusted by the electrical voltage applied to the electrodes 41, 42. For example, the frequency difference Δf between the first frequency f1 and the second frequency f2 may be between 1 kHz and 1 THz, preferably in the range of 1 MHz to 1 GHz.

[0038] In particular, an advantage of the laser diode 10 is that the laser radiation 21, 22 of two different frequencies f1, f2 is generated directly in the laser diode 10 without the need for further optical elements outside the laser diode 10. The laser diode 10 described herein therefore provides a laser light source that is particularly suitable for applications in which laser radiation of two different frequencies is to be used in a compact setup. Therefore, one possible application of the laser diode 10 is sensors that require a laser light source of two different frequencies as a light source.

[0039] The invention is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses any new feature as well as any combination of features, which in particular includes any combination of features in the patent claims, even if that feature or combination itself is not explicitly specified in the patent claims or exemplary embodiments.