SINGLE MODE SEMICONDUCTOR LASER WITH PHASE CONTROL

Abstract

The invention relates to a method for producing a semiconductor laser comprising the method steps: generating a lateral structure layer, at least in the material abrasion areas, a basic selection of the laser modes amplified or amplifiable through stimulated emission taking place via the lateral structure layer; and generating an optical element for defining the phasing of the amplified or amplifiable laser modes, the optical element being generated in such a manner that it has a distance d to an end of the lateral structure layer in the longitudinal direction of the waveguide ridge, distance d fulfilling the condition

[00001]$\min .Math.d-m.Math.\frac{{\lambda }_{eff}}{2}.Math.\le \frac{{\lambda }_{eff}}{4},$

being a natural number (m∈) and λ.sub.eff being the effective wavelength in the material.

Claims

1. A method for producing a semi-conductor laser comprising the method steps: applying a multilayer structure on a semiconductor substrate, the layers of the multilayer structure extending parallel to a layer extension plane defined by a surface of the semiconductor substrate and the application of the multilayer structure including at least the generation of an active region; abrading of material of the multilayer structure in at least two material abrasion areas separated from one another, the material being abraded essentially perpendicular to the layer extension plane, whereby a waveguide ridge is formed; generating an insulation layer on at least the material abrasion areas; generating a lateral structure layer, at least in the material abrasion areas, a selection of the laser modes amplified or amplifiable through stimulated emission taking place via the lateral structure layer; generating facet layer structures which serve for reflecting and/or decoupling laser radiation and are disposed on a cavity end or on two opposite cavity ends perpendicular to the layer extension plane in the longitudinal direction of the waveguide ridge, generating an optical element for defining the phasing of the amplified or amplifiable laser modes, the optical element being generated in such a manner that it has a distance d to an end of the lateral structure layer in the longitudinal direction of the waveguide ridge, distance d fulfilling the condition min|d−m.Math.λ_eff/2|≤λ_eff/4, m being a natural number (m∈N) and λeff being the effective wavelength in the material.

2. The method according to claim 1, wherein the optical element is generated simultaneously with the formation of the facet layer structure or on the facet layer structure in subsequence to the formation of said facet layer structure.

3. The method according to claim 1, wherein the generation of the optical element includes the formation of meta-optical metal structures.

4. The method according to claim 1, wherein the generation of the optical element includes the formation of metallic or organic three-dimensional structures, which are hardened selectively from a liquid or viscous precursor.

5. The method according to claim 1, wherein the generation of the optical element includes the formation of dielectric layer structures or mirror layer structures while taking into consideration the influencing of the phasing of the amplified or amplifiable laser modes.

6. The method according to claim 1, wherein the optical element is formed in the area of the multilayer structure.

7. The method according to claim 6, wherein the optical element is formed by ion implantation in the multilayer structure or by generating photonic crystals in the multilayer structure or by generating photonically integrated circuits.

8. The method according to claim 1, wherein a plurality of semiconductor lasers are realized to be adjacent to one another or to abut against one another on a shared semiconductor substrate and that the semiconductor lasers are separated in subsequence to the formation.

9. A semiconductor laser, comprising: a multilayer structure comprising at least one waveguide ridge and material abrasion areas laterally abutting against the waveguide ridge, the multilayer structure being disposed on a semiconductor substrate and a layer extension plane being defined by a surface of the semiconductor substrate, the multilayer structure having at least one active region, the active region having a layer structure and/or material structure for forming a laser layer based on the principle of stimulated emission, a lateral structure layer being provided at least in the material abrasion areas, a selection of the laser modes amplified or amplifiable via stimulated emission taking place via the lateral structure layer, and facet layer structures, which serve for reflecting and/or decoupling laser radiation, being formed on a cavity end or on two opposite cavity ends perpendicular to the layer extension plane in the longitudinal direction of the waveguide ridge, wherein the semiconductor laser has an optical element for defining the phasing of the amplified or amplifiable laser modes, the optical element having a distance d to an end of the lateral structure layer in the longitudinal direction of the waveguide ridge, distance d fulfilling the condition min|d−m.Math.λ_eff/2|≤λ_eff/4, m being a natural number (m∈N) and λeff being the effective wavelength in the material.

10. The semiconductor laser according to claim 9, wherein the optical element is embedded in the facet layer structure or is disposed on the facet layer structure.

11. The semiconductor laser according to claim 9, wherein the optical element has meta-optical metal structures.

12. The semiconductor laser according to claim 9, wherein the optical element has metallic and/or organic three-dimensional structures, which are hardened selectively from a liquid or a viscous precursor.

13. The semiconductor laser according to claim, wherein the optical element has dielectric layer structures and/or mirror layer structures.

14. The semiconductor laser according to claim 9, wherein the optical element is formed in the area of the multilayer structure.

15. The semiconductor laser according to claim 14, wherein the optical element is realized as an ion implantation area of the multilayer structure or as an area of the multilayer structure having photonic crystals or as a component of a photonically integrated circuit.

Description

[0055] Examples and advantageous embodiments of the invention at hand can be taken from the enclosed, purely schematic drawings:

[0056] FIG. 1 shows a schematic illustration of the functioning of the semiconductor laser according to the invention;

[0057] FIG. 2 shows a schematic exemplary illustration of a semiconductor according to the invention in a perspective view;

[0058] FIG. 3 shows a schematic illustration of the electric field of the light mode of a semiconductor laser according to the invention.

[0059] In a top view of a layer extension plane, FIG. 1 shows the general functioning or the general position of optical element 2 according to the invention with respect to a lateral structure layer 1. Lateral structure layer 1 (only hinted at) can be formed from parallel ridges, e.g., a metallic material, as a so-called DFB structure or distributed feedback structure, only corresponding dashes for symbolizing the ridges being marked in the illustration of FIG. 1. According to recent findings, a lateral structure layer which does not consist of parallel ridges but is optimized in two spatial directions can just as easily improve properties of a semiconductor laser.

[0060] Ergo, the lateral structure layer is not meant to be exclusively understood as an arrangement of parallel, preferably metallic ridges having an equal distance for generating a periodic grating but in general as structure layers which enable at least a basic selection of a large amount of laser modes amplifiable in a laser cavity.

[0061] In FIG. 1, two rows of ridges of lateral structure layer 1 are hinted at. Between these, a waveguide ridge (not illustrated in FIG. 1) could be disposed. Optical element 2 according to the invention is located having a distance d to the end of lateral structure layer 1, distance d being at most half of the effective wavelength of the desired laser radiation. This leads to the optical element acting in a length-defining manner on the laser cavity. Furthermore, the generation and amplification of overlapping frequency fluctuation modes are effectively suppressed via precisely set distance d. Moreover, the suitable formation of the optical element at distance d, namely, by setting the effective refractive index of the entire laser cavity while taking into consideration optical element 2, defines a precise phasing of the amplifiable laser modes so that effectively, only one individual laser mode is amplified and decoupled and thus a single mode operation type of the laser is made possible.

[0062] In the example of FIG. 1, an optical element 2 is disposed at each of two ends of lateral structure layer 1. While such an arrangement can be advantageous, it need not necessarily be realized, however. For instance, an individual optical element 2 can suffice for determining the phasing of the amplified laser mode and for suppressing or preventing overlapping frequency fluctuation modes.

[0063] FIG. 2 shows a perspective view of an embodiment of a semiconductor according to the invention in an exemplary and schematic manner. The semiconductor comprises a substrate 3, on which a layer structure or multilayer structure 4-9 suitable for generating and decoupling laser radiation is applied epitaxially.

[0064] For instance, multilayer structure 4-9 can serve for forming a semiconductor laser, for example an interband cascade laser or a quantum cascade laser. Multilayer structure 4-8 comprises an active zone 6 surrounded by an upper and a lower waveguide layer 5, 7, which in turn are embedded in an upper and a lower cladding layer 4, 8, 9. A waveguide ridge 9 is formed from upper cladding layer 8, 9 in the area of material abrasion areas 10 via a material abrasion method. Contact layers 11, 12 serve for injecting current.

[0065] In addition to waveguide ridge 9, optical element 2 according to the invention is formed by the material abrasion method. In the example of FIG. 2, this takes place in the form of a mirror layer structure, namely in the form of a distributed Bragg reflector, which on the one hand has the arrangement already schematically illustrated in FIG. 1, in particular distance d illustrated in FIG. 1 to the end of lateral structure layer 1 and moreover defines the phasing of the amplified or amplifiable laser modes and thus contributes to the further mode selection, up to precisely one a laser mode. Optical element 2 is disposed in the area of multilayer structure 4 to 8 and 9 in the example of FIG. 2, that is in the longitudinal direction of waveguide ridge 9 between an end of waveguide ridge 9 and an end of the laser cavity.

[0066] Alternatively or additionally thereto, it can be provided for optical element 2 to be disposed in the area of a facet 13. For this purpose, it can be provided for optical element 2 to be either embedded in a facet layer structure (not illustrated in FIG. 2 itself) or to be applied on the outside of the facet layer structure in the longitudinal direction of waveguide ridge 9. As can be discerned on the right-hand end of the laser cavity according to FIG. 2, lateral structure layer 1 can be guided towards or can be formed on the cavity end without difficulty, so that distance d of the desired laser mode according to the invention can be easily maintained when forming optical element 2 in the area of the facet of the semiconductor laser, in particular on a facet layer structure or within a facet layer structure. For the facet layer structure, which is otherwise intended for optimizing or setting the laser threshold and/or the output power, in general has an overall thickness of only a few tens of nanometers up to several hundreds of nanometers. Particularly preferably, it can thus even be provided for optical element 2 to be introduced, in particular integrated, into the facet layer structure in such a manner that the otherwise provided layers of the facet layer structure are only adjusted regarding their properties and/or regarding their sequence, meaning the method steps for forming the facet layer structure can also be carried out for simultaneously forming optical element 2 according to the invention.

[0067] FIG. 3 shows a schematic illustration of electric field E of the light mode of a semiconductor laser according to the invention. The arrows represent field strength E and the direction of the electric field of the light mode at a set point in time. Distance d between the end 14 of the wavelength-selective element or lateral structure layer 1 and the beginning 15 of an optical element 2 according to the invention in the form of a DBR mirror, which is determined via the first transition from the left from a higher to a lower refractive medium, ideally is an integral multiple of half the wavelength in the medium according to the invention. The example shows four half wavelengths. According to the invention, the phasing between the wavelength-selective element or lateral structure layer 1 and the DBR segment or optical element 2 is adjusted in such a manner that both elements are phased for the desired wavelength. This is sufficiently ensured by the required specificity of the condition according to the invention

[00009]$\min .Math.d-m.Math.\frac{{\lambda }_{\mathrm{eff}}}{2}.Math.\le \frac{{\lambda }_{\mathrm{eff}}}{4}.$