WO2023222481A1

WO2023222481A1 - Laser module with laser and external cavity, and method for producing same

Info

Publication number: WO2023222481A1
Application number: PCT/EP2023/062454
Authority: WO
Inventors: Martin Daniels
Original assignee: Osram Gmbh
Priority date: 2022-05-17
Filing date: 2023-05-10
Publication date: 2023-11-23
Also published as: DE102022204907A1

Abstract

A laser module (1) comprises a laser (90), which is designed to emit a laser beam (8) propagating along an optical axis (O), a collimating lens (40), which collimates the laser beam emitted from an emission facet (96) of the laser (90), and a wavelength-sensitive lattice (60), which partially reflects the collimated laser beam. The collimating lens (40) and wavelength-sensitive lattice (60) are arranged along the optical axis (O) of the laser beam emitted from the laser (90), such that an external cavity is formed by a rear mirror facet of the laser (90) and a reflection plane (62) of the lattice (60) to produce a lo-bandwidth portion of the laser beam transmitted by the wavelength-sensitive lattice (60). The reflection plane (62) of the wavelength-sensitive lattice (60), on which the laser beam collimated by the collimating lens (40) is partially reflected during operation, is inclined with an angular deviation (β) with respect to a plane perpendicular to the optical axis (O) of the laser (90). The collimating lens (40) is configured laterally offset with respect to a position centred on the optical axis (O) of the laser (90) into a position (44, 45) shifted in the direction (X, Y) perpendicular to the optical axis (O), in which the collimating lens (40) collimates the laser beam in a beam direction (7) perpendicular to the inclined reflection plane (62).

Description

LASER MODULE WITH LASER AND EXTERNAL CAVITY AND METHOD FOR PRODUCING THE SAME

DESCRIPTION

The present application claims the priority of German patent application No. 10 2022 204 907.1 dated May 17, 2022, the disclosure content of which is hereby incorporated into the present application by reference.

Technical area

Various exemplary embodiments relate to a laser module with a semiconductor laser, for example a laser, and an external cavity for the purpose of narrow-band and wavelength-stabilized emission. In particular, they also concern laser modules for use in vehicles, especially in head-up displays. Further aspects relate to a method for producing a corresponding laser module.

background

It is known to use laser modules in a variety of ways, including in vehicles. The very high luminance associated with such laser technology allows, for example, further miniaturization in the area of vehicle lighting (e.g. headlights, etc.). However, it also allows the installation of newer technologies such as distance and speed measurement (e.g. with LIDAR) as well as communication between road users through data transmission via optical means.

Another well-known application of laser technology in vehicles is in the area of augmented reality (AR). Here, for example, using a head-up display, information is shown to the driver in two or three dimensions in his field of vision or the field of vision with objects recognized therein is superimposed with this information. This can be done via an in the window (or Holographic optical element (HOE) integrated into a transparent plate placed in front of it, which - also referred to as a so-called combiner - is suitably irradiated by an imaging matrix with a light wave front, to exploit the effects of the hologram implemented in the holographic optical element Highly coherent light is required, which can therefore preferably come from one or more laser modules and is in particular narrow-band and wavelength-stabilized.

In the possible uses of laser modules in vehicles described above, a laser is often used as a standard component, which consists of the actual laser, namely a laser chip, a substrate carrying the laser chip, electrical lines with optional electronic components such as a photodiode, two or three contact tabs or pins, and is formed from a housing with a coupling window that protects these components. The laser chip is usually an edge emitter. The housings with the base formed from the substrate and contact pins are standardized according to size, e.g. they can be TO 38, TO 56 or TO 90 housings, etc. In the present application, “laser” can also be used to refer to the entire component with housing and base and not just the actual laser chip. Furthermore, the present application is not limited to a specific housing shape. Rather, so-called CoS assemblies (chip-on-submount) can also be the subject of the improvements described below, i.e., for example, laser chips without a housing.

Such lasers are often provided with, for example, sleeve-shaped attachments in order to form a general optical system, which is characterized by the laser and a volume Bragg grating (VBG), by means of which external cavities or resonators are realized (ECDL - external cavity diode laser). , whose goal is to achieve an even narrower emission spectrum. For example, a spectrum with a bandwidth of, for example, 0.1 nm or even smaller can be obtained from a spectrum with a bandwidth of a few or several nanometers, for example 2 - 3 nm, of the laser (as a mere resonator in the chip), if a external cavity is set up. In holographic applications, among other things, such narrow bandwidths are required or almost mandatory, for example To avoid color fringes and blurry images etc. or to achieve high image quality or goodness. A narrow band and wavelength stabilization (ie, no wavelength shift with changing temperature) could be particularly relevant for e.g. spectroscopic applications or pump laser applications.

In such an ECDL structure, a collimation lens and a wavelength-sensitive grating, in particular a volume Bragg grating (VBG), can be provided on optical elements in addition to the laser. The resonator is defined by a rear mirror facet of the laser chip and a reflection plane of the Bragg grating defined by the Bragg grating. The emission facet of the laser chip has a very small dimension, for example it includes a strip of 3 or 4 pm x 0.5 - 1.0 pm up to 200 pm or even 400 pm (slow axis) x 0.5 - 1.0 pm (fast axis) in the case of an edge emitter, which is therefore also referred to as a broad strip emitter. However, the laser module presented below is in no way limited in terms of this dimensioning, but the corresponding semiconductor laser can be designed accordingly, for example preferably with widths (slow axis) of 20 pm to 100 pm and heights (fast axis) of 1.0 pm or smaller. The collimation lens collimates the divergent beam after emerging from the emission facet so that it hits the Bragg grating in a parallel direction. This is wavelength-sensitive and only reflects the light with the target wavelength back into the collimation lens, which in the best case focuses it precisely on the small emission facet, so that exactly the light with the resonant target wavelength reaches the active layer of the chip. In this way, the narrow band of the emission spectrum is ensured.

However, the very small emission facet noted above requires an extremely high degree of precision in the spatial alignment of the Bragg grating (and lens) with respect to the optical axis of the laser. Ideally, the optical axis of the laser running through the emission facet and the symmetry axis of the collimating lens coincide exactly and the effective reflection plane of the Bragg grating is perpendicular to both, so that the reflected beam takes the same path as it was emitted. A rough estimate with typical values for the focus of the collimation lens (e.g. 3 mm) and for the height of the facet (1 pm) provides a value for the required adjustment accuracy of the Bragg grating: the reflection plane must be accurate to approximately 0.01 ° in relation to the optical axis vertical plane must be set so that the reflected beam hits the emission facet again.

These accuracies can certainly be achieved in practice, but with a lot of time and money. This is because the Bragg grating at the distal end of the generally sleeve-shaped attachment must be pivoted over two mutually perpendicular angular directions or axes in order to then determine by measurement the angular position at which the bandwidth of the laser beam passing through the grating is satisfactorily low fails. This position must also be adjusted by suitable measures (e.g. external gripping arms) before a holder surrounding the grid can be finally welded, soldered or glued on, or, as is otherwise generally known, joined or fastened in various ways (e.g. also by laser soldering). Additional stresses and distortions caused by this process due to the cooling process must also be taken into account, although compliance with the tolerances must be taken into account.

Consequently, there is a need for a simpler structure, a saving in costs and a reduction in adjustment effort. In addition, it can be a task to improve the adjustment accuracy.

Presentation of various aspects

According to one aspect, such requirements can be taken into account by proposing a laser module which, as described, comprises: a laser which is set up to emit a laser beam propagating along an optical axis, a preferably rotationally symmetrical collimation lens which consists of an emission facet of the Laser's emitted laser beam is collimated, as well as a wavelength-sensitive grating, which can in particular be a volume Bragg grating and which partially reflects the collimated laser beam. The Collimation lens and the wavelength-sensitive grating are arranged along the optical axis of the laser beam emitted by the laser, so that an external cavity is formed by a rear mirror facet of the laser and a reflection plane of the grating to accommodate a part of the laser beam transmitted by the wavelength-sensitive grating to generate low bandwidth.

Furthermore, the reflection plane of the wavelength-sensitive grating, on which the laser beam collimated by the collimating lens is partially reflected during operation, is assumed to be inclined with an angular deviation relative to a plane perpendicular to the optical axis of the laser. It should be noted that the plane referred to here as the “reflection plane” is, strictly speaking, a virtual plane that represents the (Bragg) grid or its inclination. A volume Bragg lattice actually consists of many lattice planes, all arranged parallel to each other (hence the wording "volume" lattice). These parallel planes in the volume Bragg grating, which are extremely close to one another compared to the length of the cavity, are characterized by a refractive index modulation in the substrate in question. The reflection plane so designated in the present application therefore represents the entirety of the interacting individual grid planes of the volume Bragg grating that are parallel to it. In simplified terms, it therefore represents a single inclined, partially reflective plane within the grid substrate.

This can be intended, for example, if in particular there is a tilting of the respective grid plane in the substrate relative to an outer surface of the substrate in which the grid is inscribed during production using known methods in order to create a reflection on the substrate surface - even if it is provided with an anti-reflective coating for anti-reflection is - to be separated from that of the actual grid. In this case, the grating - accepting this tilting - can first be positioned in the beam path in relation to the (mechanically easily detectable) substrate surface, in order to then be compensated for by the features to be described below. A purely exemplary value for such a tilt can be, for example, 0.5°. It should also be noted that a manufacturing tolerance of, for example, 0.3° could have to be taken into account here. In principle, this “slant angle” can be adjusted when the grid is manufactured become. However, its magnitude is not crucial for the proposed aspects and exemplary embodiments.

In particular, the angular deviation can also be unintentional and possibly unavoidable, namely due to the alignment accuracy of the grating in the receptacle in the corresponding attachment (or the like) of the laser module. A fine adjustment as described above is not necessary here, so that this angular deviation can also be significantly larger than the approximately 0.01° mentioned above.

In order to compensate for this intended or unintentional angular deviation relative to the plane perpendicular to the optical axis, which as such would result in the reflected beam not hitting the emission facet again, it is provided according to the present aspect that the collimation lens is opposite one The position centered on the optical axis of the laser is set to be laterally offset in a position shifted in the direction (X, Y) perpendicular to the optical axis, in which the collimation lens collimates the laser beam in an orientation perpendicular to the inclined reflection plane.

The lateral displacement of the collimation lens relative to the optical axis as such leads to the beam orientation (the so-called beam pointing) of the beam or parallelized beam leaving the collimation lens changing and deviating from the optical axis. In the conventional case, referred to as beam pointing error, this beam alignment is brought about intentionally in the present case, in such a way that the beam or parallelized beam of rays hits the reflection plane inclined by the angular deviation exactly perpendicularly. The back and forth beams then overlap each other exactly, so that the emission facet of the laser is also passed through (or hit) with a comparatively high level of accuracy.

This measure now makes it possible, instead of a conventional, complex tilting of the wavelength-sensitive grating across 2 axes of rotation, a linear displacement of the collimation lens in X and/or Y. Direction to achieve a fine adjustment of the laser beam path. If, for example, a spherical shape of the corresponding support ring and a corresponding receptacle in the sleeve-shaped attachment for the laser module are required for the tilting of the grid, these or similar parts can be dispensed with in the present case. In the present case, for example, a device such as a hexapod or another angle adjuster is no longer necessary to carry out the fine adjustment of the grating, because a linear displacement of the collimation lens or the part carrying it is much easier to carry out. Due to the easier access from outside, stronger holding forces can be exerted during the adjustment than in the conventional case, so that the adjustment process can be carried out more safely and more precisely. The use of fewer components and the simpler adjustment process significantly save costs and effort. In any case, it should be emphasized that the adjustment to the final state can or must take place without an angular adjustment of the volume Bragg grating. Additionally, embodiments may provide (see below) that the collimating lens and volume Bragg grating form a mechanical unit (a common subassembly). Furthermore, in this case, a z-adjustment may also be necessary, ie the distance between the laser and the collimation lens, in order to ensure the best possible degree of collimation.

One embodiment provides that the collimation lens is positioned relative to the position centered on the optical axis of the laser in a first direction (X) perpendicular to the optical axis and in a second direction (Y) perpendicular to the optical axis, which is also perpendicular to the first direction (X) is vertical, set in the shifted position. Such an XY positioning can be carried out particularly easily in terms of process technology.

According to a further special development of the laser module, the lateral offset in the direction (X, Y), or in the first direction (X) and/or the second direction (Y), is at least 0.1 pm, preferably at least 0.5 pm, more preferably at least 1 pm, more preferably at least 2 pm. A possible upper limit can be 100 pm purely as an example, but depends in detail on the offset from which the lens geometry becomes noticeable in the beam path, ie, from the special collimation lens, and from which point the inclination of the beam exit relative to the fixed laser module housing geometry is no longer acceptable overall.

Alternatively or additionally, an amount of at least +/-0.005°, preferably +/-0.01°, more preferably +/-0.02° can be specified for the angular deviation of the reflection plane of the grating compared to the plane perpendicular to the optical axis of the laser . However, the lateral offset is generally much easier to determine/measure directly in the XY direction than the tilt angle to be compensated.

According to another aspect, the laser module includes an attachment comprising two or more elements (subassemblies) for enclosing the external cavity. A first attachment element carries or holds the laser, and a second attachment element carries or holds the collimation lens. In this case, the first attachment element and the second attachment element are in particular set up, before a final cohesive fixation (for example by laser welding, soldering or gluing, or other known and suitable joining techniques) against each other in the direction (X, Y), or in the first direction (X) and / or the second direction (Y) to be shifted perpendicular to the optical axis in order to obtain a suitably shifted position of the collimation lens during an adjustment, which, for example, achieves the effects described above.

This aspect also supports the idea of allowing fine adjustment of the laser beam path by lateral offset of the collimation lens before final fixation. An adjustment or tilting of the wavelength-sensitive grating can possibly be dispensed with (but this is not fundamentally excluded by the invention). The grid can preferably be accommodated and held in the second, but also in the first or a third attachment element.

Overall, in this structure proposed here, according to this aspect, the external shape of the laser module remains fundamentally unchanged. However, attachment elements are set up to be laterally displaceable relative to one another, instead of providing a monolithic attachment, which then contains a number of small parts which has fine adjustment and holder. On the other hand, the two attachment elements are easily accessible for adjustment, and the subsequent fixation of these elements can also be easily controlled. The lateral displacement in X and Y can be prepared or set up, for example, by one or more planar sliding surfaces (which extend in the XY plane) with which the two attachment elements face each other.

According to a special development of the laser module, both the collimation lens and the wavelength-sensitive grating are held by the second attachment element and before a final cohesive fixation with the first attachment element, or with a third attachment element connected to the first attachment element

Attachment element, which is not designed to be laterally displaceable with respect to the optical axis, together in a fixed spatial position relative to each other relative to the laser and its optical axis in the direction or in the first direction (X) and / or the second direction (Y) are set up to be displaceable perpendicular to the optical axis.

A particular advantage here arises from the fact that the collimation lens and the grating are arranged in a fixed relationship to one another and the grating therefore follows this movement during the lateral displacement. There is no distortion of the grid alignment due to thermal stresses in or on the attachment element when cooling, for example after laser welding, and the number of parts can also be kept low so that the grid can be easily and directly accommodated in the attachment element.

In the case of the third attachment element, this can have a ring-like structure and can be set up to be displaceable in a third direction (Z) relative to the first attachment element before a final cohesive fixation with it, which is aligned parallel to the optical axis of the laser in order to adjust a focus of the To enable collimation lens in relation to the emission facet of the laser. The provision of the third attachment element offers the further advantage that the general adjustment process can be designed flexibly. This is because, for example, the order of the focus setting (in the Z direction) and the offset setting can be chosen arbitrarily. A fine adjustment in a common positioning device is even conceivable, with iterative positioning in the Z and XY directions.

According to an alternative, special development of the laser module, both the collimation lens and the wavelength-sensitive grating are also held by the second attachment element, thereby achieving the same advantages as described above. Instead of the third attachment element described, a different fourth attachment element is provided here. Before a final cohesive fixation of this fourth attachment element with the first attachment element, it is together with the fourth attachment element and in a fixed spatial position relative to one another relative to the laser and its optical axis in the direction or in the first direction (X) and/or the second Direction (Y) set up to be displaceable perpendicular to the optical axis.

The fourth attachment element, like the third attachment element, can have a ring-like structure and advantageously enclose the second attachment element, so that the second attachment element is set up to be displaceable in a third direction (Z), which is parallel to the fourth attachment element, before a final cohesive fixation with it optical axis of the laser is aligned to enable adjustment of a focus of the collimating lens with respect to the emission facet of the laser.

In this embodiment, the adjustment in the XY direction and in the Z direction can be carried out flexibly in a particularly simple manner. The adjustment is also carried out using components with simple geometric shapes and stable attachment elements made of materials that can be easily welded or glued, such as stainless steel. It should be noted in these embodiments that the grating can also be inserted into a subassembly together with the lens such that the outer surface of the substrate is arranged exactly perpendicular to the optical axis of the lens. This means that the reflection plane can also be arranged to be intentionally inclined, if one takes into account the inclination of the reflection plane relative to the outer surface of the substrate. In any case, such an embodiment is included in the aspects proposed here. It also offers certain process-related advantages, as the grid cannot be accidentally installed incorrectly.

As described, the examples of the mutual cohesive fixation between the respective attachment elements concerned can be a laser welding fixation or an adhesive fixation.

Furthermore, the second attachment element can be designed as a sleeve with a central axis which is arranged essentially parallel to the optical axis of the laser, and wherein the collimation lens and the wavelength-sensitive grating are mounted inside the sleeve. This creates a protected structure for the cavity. Furthermore, with a cylindrical sleeve shape, a positive surface can be offered for displacement in the Z direction (outer surface) as well as in the XY direction (e.g. flat end face).

Furthermore, the wavelength-sensitive grating can be held by the second attachment element in a predetermined grating holder, in such a way that an adjustment by adjusting an angle of inclination of the grating relative to the optical axis in the recorded state of the grating is excluded. This enables a very simple construction of the second attachment element.

Optionally, the laser can be accommodated in a housing, in particular in a TO 38, TO 56 or TO 90 housing, with the first attachment element having a receptacle for fastening the housing or a substrate carrying the housing. The recording can also allow relative displaceability in Z- include direction. However, the invention is by no means limited to encapsulated lasers.

The laser can be formed, for example, by a laser diode, such as a half-elite laser, or by a solid state laser or a solid-state laser. Furthermore, the laser can advantageously be an edge emitter, since the proposed features with regard to the small emission facet are particularly notable here. However, other types of lasers are fundamentally also possible. Instead of an edge emitter, according to exemplary embodiments, surface emitters or VCSEL (Vertical Cavity Surface Emitting Laser) or HCSEL (Horizontal Cavity Surface Emitting Laser) can also be used.

The laser can also be in the form of a single-mode or multi-mode diode laser or laser diode.

Another aspect relates to a method for producing a laser module associated with the laser module. The laser module also includes: a laser that is set up to emit a laser beam that propagates along an optical axis, a collimation lens that collimates the laser beam emitted from an emission facet of the laser, and a wavelength-sensitive grating that partially reflects the collimated laser beam.

The procedure itself includes the following steps:

Arranging the collimation lens and the wavelength-sensitive grating along the optical axis of the laser beam emitted by the laser during operation, so that an external cavity is formed by a rear mirror facet of the laser and a reflection plane of the grating to accommodate a part of the laser beam transmitted by the wavelength-sensitive grating to produce low bandwidth;

Displacing the collimation lens relative to the laser from an original position in at least one direction (X, Y) perpendicular to the optical axis; Determining a bandwidth of an emission spectrum of the laser beam transmitted by the wavelength-sensitive reflector; and

setting a position shifted in the direction (X, Y) depending on the result;

Mechanically fixing the collimating lens relative to the laser at the specified position.

The same advantages arise as those described above. The method steps can lead to the laser module with a laterally offset collimation lens described above in one aspect. Conversely, it is also possible with the method for a laterally offset collimation lens to form the starting point, and for the adjustment process to find exactly the position on the optical axis as the optimal setting - for example because the grating does not initially deviate from the angle perpendicular to the optical axis level had.

Further advantages, features and details of the various aspects emerge from the claims, the following description of preferred embodiments and the drawings. In the figures, the same reference numbers designate the same features and functions.

Brief description of the drawings

Show it:

1 shows a basic structure of a laser module with an external cavity with a schematic representation of a step of fine adjustment of the laser beam according to the prior art;

2 like FIG. 1, but with a schematic representation of a step of fine adjustment of the laser beam according to an exemplary embodiment;

3 shows a schematic representation of the beam path of the laser beam in the cavity with misalignment of the unadjusted grid; Fig. 4 like Fig. 3, but with adjusted grid alignment, according to the prior art;

Fig. 5 like Fig. 3, but with adjusted collimation lens according to an exemplary embodiment of the proposed method;

6A shows a structure with illustrated adjustment step according to the prior art as in FIG. 1, where the functional components are divided into groups of common movement;

Fig. 6B like Fig. 6A, but with an additional focus adjustment step;

7A shows a structure with illustrated adjustment step according to an embodiment as in FIG. 2, where the functional components are divided into groups of common movement;

Fig. 7B like Fig. 7A, but with an additional focus adjustment step; wherein the laser is moved with respect to the collimating lens and the grating, viewed as a unit;

Fig. 7C as Fig. 7A, but with an additional focus adjustment step, where the collimating lens is moved together with the grating with respect to the laser;

8 shows a first exemplary embodiment of a laser module with an attachment;

9 shows a second exemplary embodiment of a laser module with an attachment;

10 shows a third exemplary embodiment of a laser module with an attachment;

11 shows a cross-sectional view of the laser module from FIG. 10 with the collimation lens centered; 12 shows a cross-sectional view of the laser module from FIG. 10 with the laterally shifted alignment of the collimation lens;

13 shows an alternative cross-sectional representation of the laser module from FIG. 10 with the laterally shifted alignment of the collimation lens;

14 shows a flowchart of a method for producing a laser module according to an exemplary embodiment.

Preferred embodiment(s) of the invention

In the following description of preferred embodiments, it should be noted that the present disclosure of the various aspects is not limited to the details of the construction and arrangement of the components as shown in the following description and in the figures. The exemplary embodiments can be put into practice or carried out in various ways. It should be further noted that the language and terminology used herein are used solely for the purpose of specific description and should not be construed as such in a limiting manner by those skilled in the art. Furthermore, in the following description, the same reference numerals in the various exemplary embodiments or figures denote the same or similar features or objects, so that in some cases a repeated detailed description of the same is omitted in order to preserve the compactness and clarity of the representation.

Fig. 1 shows an overview of the relevant functional elements of a laser module 1 without the attachment holding them. The laser module 1 includes a laser in the form of an encapsulated laser diode 90 with a base plate 91, housing 92 and two contact connections 98, of which one contact connection is covered by the front one in perspective. The actual semiconductor chip 95 is located in the housing 92 and can hardly be seen in this illustration. However, an example of such a standard module is shown schematically in Fig. 13. The base 91 and the contact connections 98 or pins form a base on which the housing 92 is attached, which protects the semiconductor chip 95, which forms the actual laser diode with an internal cavity. The mode of operation of the laser diode or the semiconductor chip 95 is that of an edge emitter. If the semiconductor chip 95 is supplied with power via the contact connections 98 via connecting lines (not shown), it emits a narrow-band laser radiation from its emission facet 96, which serves as a coupling surface. The semiconductor chip 95 is, for example, placed vertically on the surface 94 of the substrate 91. Not shown is an optional photodiode, which can be used to regulate the power supply in a known manner so that the luminous flux is as constant as possible. In the case of the photodiode, a third contact terminal (not shown) may be provided. The housing 92 is provided on the surface 94 of the base 91 and protects the semiconductor chip 95 and possibly other components. An opening or window 93 is set up on the front side of the housing 92, through which the laser radiation emitted from the edge surface 96 can emerge. The laser diode 90 can be a component available on the market, for example with a TO 38, TO 56 or TO 90 housing. But other types are just as possible. The semiconductor chip 95 is set up, for example, to emit light in the infrared, visual or ultraviolet wavelength range.

Returning to Fig. 1, the laser module 1 further comprises a collimation lens 40 and a wavelength-sensitive grating 60, which is called a volume Bragg grating (VBG). is trained. The collimation lens 40 collimates the divergent laser beam emitted by the semiconductor chip 95 through the emission facet 96, and the grating 60 is ideally aligned such that the parallelized light of the laser beam is incident perpendicularly onto the respective reflection plane of the grating written in the corresponding substrate of the VBG. As a result, the beam is thrown back or partially reflected in the same way, so that it travels back in a narrow band into the active layer of the semiconductor chip 95 and further supports the formation of narrow-band laser light there. The external cavity is formed by the reflection plane 62 of the VBG and the rear mirror facet of the laser diode 90 (semiconductor chip 95). In order to generate the narrow-band laser light, a high coupling efficiency is required. Accordingly, according to the prior art shown in FIG. 1 with respect to a manufacturing method including the adjustment, the grating 60 is aligned so that the condition of the perpendicularly incident laser beam is guaranteed. For this purpose, as is indicated schematically in FIG. 1 by the two arrows 64, 65, the grid 60 is pivoted over two axes with the aid of external devices (eg hexapod or other angle adjuster, not shown). The fact that the stated condition has been fulfilled can be determined, for example, by detecting the spectrum of the laser beam emitted by the laser module as a whole and measuring its bandwidth. The desired narrow band is achieved precisely when the reflected laser beam again hits at least the emission facet 96 and can thereby couple into the semiconductor chip, so that the coupling efficiency increases.

2 shows a fine adjustment process step that is alternative to that of FIG . In particular, unlike in FIG. 1, no alignment of the grid 60 is carried out. Rather, a linear displacement of the collimation lens 40 is carried out - also by adjusting devices not shown - namely in the X and Y directions perpendicular to the optical axis of the laser 90 (see arrows 44 and 45).

In order to increase the coupling efficiency, the focus of the collimation lens 40 should also be set to the area of the emission facet, but this has been omitted from both FIGS. 1 and 2 for the sake of clarity. In other words, the emission facet is exactly in the object-side focal plane of the collimation lens. Then the beam is ideally collimated after passing through the collimating lens. The volume Bragg grating, in turn, does not necessarily have to be in the focal plane on the image side. 3 to 5 show the comparison of the exemplary embodiment from FIG. 2 with the prior art with regard to the original (not yet adjusted) and the adjusted beam path.

Fig. 3 shows the initial state before the adjustment. The laser 90, the collimating lens 40 and the Bragg grating (grating 60) are to be considered as provided and assembled with the elements of the attachment supporting them, not shown here. In Fig. 3, only the emission facet 96 of the semiconductor chip 95 of the laser is sketched purely schematically as a small box, as are the collimation lens 40 and the reflection plane 62 of the grating 60 as a mere line. As can be seen, the reflection plane 62 has an angular deviation β (exaggerated in the figures) compared to a plane perpendicular to the optical axis O. This can be intentional as described at the beginning or, for example, from only a rough adjustment in the receptacle of the grid 60 in an attachment element not yet shown here, e.g. B. mere insertion. Due to the deviation, the laser beam 8 generated by the laser and running towards the grid 60 does not fall perpendicularly onto the reflection plane 62, which is why the laser beam is reflected back in a different direction (returning laser beam 9) and is focused into a point outside the emission facet 96.

4 illustrates the prior art measure corresponding to FIG. 1: the grid 60 or the reflection plane 62 is pivoted about only one axis in FIG. As a result, the returning laser beam 9 is ideally focused again exactly into the emission facet 96 (assuming ideal focus setting).

The case corresponding to the exemplary embodiment according to FIG. 2 can be seen in FIG. The "misalignment" or angular deviation of the grating 60 (ie, the reflection plane) with respect to the plane perpendicular to the optical axis O is left unchanged and instead the collimation lens 40 is displaced in a direction perpendicular to the optical axis, for example the Y direction 45 , so that the collimating lens is arranged decentered with respect to the optical axis. The position selected by shifting in the Y direction 45 is such that a changed beam alignment 7 (beam pointing) is achieved, which occupies an angle a with the optical axis. As far as the angle a becomes equal to the angle β, the laser beam emitted by the laser falls perpendicularly onto the reflection plane 62 again, so that the laser beams 8 and 9 traveling back and forth in the cavity coincide with one another and the emission facet is hit at least as well as in the case 4 - but with significantly less effort and with the result of higher process stability, as will be explained below.

6A and 6B, similar to FIG. 1, the laser module 1 is shown only with its functional components (laser diode 90, collimation lens 40, Bragg grating 60) and the conventional pivoting mechanism (via 2 axes) for adjustment. Fig. 6B differs from Fig. 6A in that it also takes into account the adjustment, i.e. a shift 43, of the focus in the Z direction. Boxes are drawn around these components in both figures, which designate groups of components that are mechanically combined, i.e. do not have to move against each other during the adjustment. In the case of FIG. 6A, the pivotable grating 60 forms one group G2, and the laser diode 90 together with the collimating lens 40, which cannot be moved in this regard, forms the other group G1. In the case of FIG. 6B, the collimation lens 40 also forms an independent group G3. In practice, the prior art therefore requires a mount to be implemented, e.g. in an attachment (so-called submount) for the laser module, which enables the mobility of three (subassembly) groups G1 - G3 relative to one another, and which also corresponds to two subsequent ones Fixations (gluing or laser welding, soldering or other known and suitable joining techniques, etc.) are required.

7A to 7C show the analogous grouping of the functional components when carrying out the adjustment according to the exemplary embodiment as shown in FIG. 2, FIGS. 7B and 7C show the additional integration of the focus adjustment in contrast to FIG. ie, a displacement 43 of the collimation lens 40 in the Z direction along the optical axis O. The exemplary embodiments of FIGS. 7b and 7C differ from one another in that in the laser module 1 in FIG. 7B, the laser 90, which forms a group G1, is moved in the Z direction with respect to the (fixed) collimation lens 40 to adjust the focus, where the collimation lens 40 together with the Bragg grating 60 forms a unit or group G2, while in Fig. 7C this group G2 is moved in relation to the stationary laser 90 or group G1.

In any case, it is noteworthy that because the grating 60 no longer needs to be pivoted according to the exemplary embodiments, the collimation lens 40 and the Bragg grating 60 can form a movement unit or group G2, so that in comparison with the conventional case according to Prior art (Fig. 6B) a movement group is omitted (only 2 groups G1 and G2 instead of 3 groups G1 to G3) if the focus setting with a shift 43 or 63 in the Z direction is also taken into account (Fig. 7b or 7C). As a result, this also results in a further simplification of the laser module structure or the corresponding attachment.

8 shows a schematic representation of a first exemplary embodiment of a laser module 1 which has an attachment 2. The attachment is in three parts (before the parts are fixed together) and comprises a first attachment element 20, a second attachment element 22 and a third attachment element 24. The first attachment element 20 is annular and has a cylindrical inner surface 201 and a cylindrical outer surface 203. Furthermore a receptacle 202 is provided at a lower end of the inner ring opening, which is dimensioned such that the base 91 of the laser 90 is accommodated therein and secured by gluing (fixation point 31).

The third attachment element 24 is sleeve-shaped and has a cylindrical inner surface 241, the inner diameter of which corresponds to an outer diameter of the first attachment element 20, so that before a fixing step, the cylindrical inner surface 241 of the third attachment element 24 and the cylindrical outer surface 203 of the first attachment element 20 slide on one another and one Mutual displacement 43 is permitted parallel to the optical axis O of the laser beam emitted by the laser. Furthermore, the third attachment element 24 has an inner flange section with an at least partially flat end face 242, which extends perpendicular to the optical axis 0. On this end face 242, an opposite end face 223 of the second attachment element 22 is slidably set up, so that the second attachment element 22 is relative to the third attachment element 24 in a plane perpendicular to the optical axis 0 in an X direction and also a Y direction, both of which Spanning the plane, can be moved (shifts 44, 45). It is also possible for the second attachment element to be designed to be displaceable in only a single direction, for example the X direction, for example by a sliding tongue-and-groove connection or the like. In this case, the ring of the third attachment element 24 can optionally be set up to be rotatable about the optical axis 0 (around the first attachment element 20).

The second attachment element 22 has a sleeve shape and is provided with a cylindrical inner surface 222. A collimation lens 40 is firmly attached therein at the proximal lower end, facing the laser 90. At the upper distal end there is a receptacle 221 for a Bragg grating 60, the inscribed grating structure of which forms a reflection plane 62 and which is also firmly attached to the receptacle of the second attachment element 22.

As can easily be seen in FIG. 8, the collimation lens 40 and the Bragg grating 60 as group G2 are set up to be displaceable together in the X and Y directions as well as in the Z direction relative to the laser 90. The model of FIG. 8 corresponds approximately to the relationship shown in FIG. 7B if one considers the base (first attachment element 20) holding the laser 90 to be stationary. With the laser module 1 shown in FIG. 8, both the focus adjustment and the compensation for the misalignment of the Bragg grating described above can be adjusted using an external device (not shown). After adjustment, fixations can be made at the points marked by arrows 32 and 33 or continuously or symmetrically at points spaced apart by 120° angles, preferably by laser spot welding or gluing, but if necessary also by soldering or other known and suitable joining techniques. be made. 9 shows an alternative embodiment of a laser module 1 compared to FIG. 8. To avoid repetition, only differences will be discussed. The laser module 1 of this second exemplary embodiment does not have a third attachment element. Rather, here (before fixing) the second attachment element 22 slides with its end face 223 directly on a corresponding, at least partially flat end face 204 of the first attachment element 20. As a result, exactly the same effect is achieved as in the first exemplary embodiment. However, the Z displacement missing due to the omission of the third attachment element is brought about by a corresponding pair of sliding surfaces, ie by sliding between the cylindrical outer surface 97 of the base 91 of the laser 90 and the cylindrical inner surface 203 of the receptacle 202 of the first attachment element 20. In this exemplary embodiment, only two fixations at points 31 and 33 are required. The exemplary embodiment corresponds approximately to the relationship shown in FIG. 7C if one considers the base (first attachment element 20) holding the laser 90 to be stationary

A further modification of the first exemplary embodiment is shown in FIG. In order to avoid repetition, only differences will be discussed here. This third exemplary embodiment of a laser module 1 again comprises 3 attachment elements 20, 22, 24. The second attachment element is guided with its cylindrical outer surface 224 in a cylindrical inner surface 243 of the third attachment element, so that a focus adjustment (shift 43) in the Z direction becomes possible. The displacement 44, 45 perpendicular to the optical axis O in the X and Y directions (also possibly only a single direction possible if the ring of the third attachment element is rotatable), which is used to compensate for an angular deviation of the Bragg grating 60 from one to Optical axis O vertical plane is required is made possible by an interaction between an at least partially flat end face 245 of the third attachment element 24 and a corresponding end face 204 of the first attachment element. The example again corresponds to the representation in Fig. 7B. The same effects are achieved as in the previous exemplary embodiments. 11 to 13 show, using the third exemplary embodiment of FIG. 10 (in an exaggerated representation, however), the shifted position of the collimation lens 40 relative to the optical axis 0, with FIG . It can be clearly seen there that the collimation lens with the corresponding attachment element 24 is shifted to the left in the image plane relative to the optical axis 0 of the laser beam. If the direction 100 of the outgoing beam coincides with the optical axis 0 in the case of the still unshifted collimation lens according to FIG. 11, then in the case of FIG. 12 the direction 101 of the outgoing beam is already inclined at an angle other than zero. In Fig. 13, the optical axis 0 of the laser and the optical or symmetry axis P of the collimation lens are shown in the state shifted relative to one another (the laser module in Fig. 13 is rotated by 90 degrees compared to the illustration in Fig. 12).

It should be noted that the attachment or only parts thereof can preferably be made of a weldable material, i.e. preferably a metal, in particular stainless steel.

A method 200 according to an exemplary embodiment for producing a laser module 1 similar to that described above is shown below using a flowchart in FIG. 14.

In a first step 210, a laser 90, which is set up to emit a laser beam propagating along an optical axis O, a collimation lens 40, which collimates the laser beam emitted from an emission facet 96 of the laser 90, and a volume Bragg grating 60, which partially reflects the collimated laser beam, is provided.

In a further step 220, the collimation lens and the volume Bragg grating 60 are arranged along the optical axis of the laser beam emitted by the laser 90 during operation, so that an external cavity is formed by a rear mirror facet of the laser 90 and a reflection plane of the grating to get one to produce the low bandwidth portion of the laser beam transmitted by the volume Bragg grating 60.

In the further step 230, the collimation lens 40 is displaced relative to the laser 90 from an original position in at least one direction X, Y perpendicular to the optical axis 0, see FIGS. 11 and 12 or the axes 0 and P in FIG.

In the further step 240, a bandwidth of an emission spectrum of the laser beam transmitted by the volume Bragg grating 60 is determined, for example with a spectrometer.

In the further step 250, a position shifted in the direction X, Y is determined depending on the result. For example, different positions of the collimation lens 40 can be moved in the

In the further step 260, the collimation lens 40 is fixed relative to the laser 90 at the specified position using the means described above (gluing, welding, soldering or other joining techniques, etc.).

As described, various modifications of the proposed laser module 1 are possible without departing from the scope of protection set forth in the appended claims. For example, the emitted laser beam can be collimated using two cylindrical lenses instead of just one collimation lens in order to equalize the different beam quality in both spatial directions, for example using a FAC and SAC (fast axis collimation lens or slow axis collimation lens). The laser module described can be adjusted in the same way as described above, although both lenses should be arranged between the volume Bragg grating and the laser. However, the version with only one collimation lens is preferred. In principle, in any case, non- Rotationally symmetrical collimation lenses are included in the scope of the attached patent claims.

Likewise, unlike what is shown in the exemplary embodiments, a base and/or housing does not necessarily need to be provided in relation to the semiconductor laser or the laser. The individual attachment elements also need to be set up in this form, in particular not in a sleeve form - for example, the laser, lens and VBG can also be aligned in relation to one another with the help of other mechanical elements or holders.

REFERENCE MARKS LIST:

Laser module

Attachment first attachment element cylindrical inner surface

Holder for laser cylindrical outer surface

End face of second attachment element

Holder for Bragg grating, cylindrical inner surface, end face, cylindrical outer surface, third attachment element, cylindrical inner surface

Front surface (distal) cylindrical outer surface Front surface (proximal) collimating lens

Shift in Z direction

Shift in X direction

Shift in Y direction wavelength-sensitive grating, Bragg grating reflection plane

Shift in Z direction

Shift in X direction

Shift in Y direction 7 Beam alignment (by collimating lens offset)

8 traveling laser beam

9 returning laser beam (reflected)

90 lasers

91 base

92 housing

93 exit opening for laser beam

94 substrate surface

95 semiconductor chip

96 emission facet

97 cylindrical external surface

98 contact connections

100 Direction of outgoing beam (conventional)

101 Direction of the outgoing beam (exemplary embodiment)

G1-G3 subassemblies

P Optical or symmetry axis of the collimation lens

0 optical axis

Claims

Expectations:

1. Laser module (1), comprising: a laser (90) which is set up to emit a laser beam (8) which propagates along an optical axis (0), a collimation lens (40) which consists of an emission facet (96). the laser beam emitted by the laser (90) is collimated, and a wavelength-sensitive grating (60) which partially reflects the collimated laser beam, the collimation lens (40) and the wavelength-sensitive grating (60) being along the optical axis (0) of the laser (90). ) emitted laser beam are arranged, so that an external cavity is formed by a rear mirror facet of the laser (90) and a reflection plane (62) of the grating (60) around a part of the laser beam with a small bandwidth that is transmitted by the wavelength-sensitive grating (60). to generate, the reflection plane (62) of the wavelength-sensitive grating (60), on which the laser beam collimated by the collimating lens (40) is partially reflected during operation, with an angular deviation (ß) compared to the optical axis (0) of the laser (90 ) is inclined to the vertical plane; and wherein the collimation lens (40) is set to be laterally offset from a position centered on the optical axis (0) of the laser (90) to a position (44, 45) shifted in the direction (X, Y) perpendicular to the optical axis (0). , in which the collimation lens (40) collimates the laser beam in a beam orientation (7) perpendicular to the inclined reflection plane (62).

2. Laser module (1) according to claim 1, wherein the collimation lens (40) relative to the position centered on the optical axis (0) of the laser (90) in a first direction (X) perpendicular to the optical axis (0) and in a to the optical axis (0) perpendicular to the second direction (Y), which is also perpendicular to the first direction (X), is set in the shifted position (44, 45).

3. Laser module (1) according to claim 1 or 2, wherein the lateral offset in the direction (X, Y), or in the first direction (X) and/or the second direction (Y), is at least 1 pm, and/or the angular deviation (ß) of the reflection plane of the grating compared to The plane perpendicular to the optical axis (0) of the laser (90) is at least +/-0.01 °.

4. Laser module (1) according to one of claims 1 to 3, further comprising: an attachment (2) comprising two or more elements for enclosing the external cavity, wherein a first attachment element (20) carries the laser (90) and a second attachment element (22) carries the collimation lens (40), and wherein the first attachment element (20) and the second attachment element (22) are set up before a final mutual cohesive fixation against one another in the direction (X, Y), or in the first direction (X) and/or the second direction (Y) perpendicular to the optical axis (0) in order to obtain the shifted position (44, 45) of the collimation lens (40) during an adjustment.

5. Laser module (1) according to claim 4, wherein both the collimation lens and the wavelength-sensitive grating are held by the second attachment element and before a final cohesive fixation with the first attachment element, or with a third attachment element connected to the first attachment element, which is in relation to the optical axis is not set up to be laterally displaceable, together in a fixed spatial position relative to the laser (90) and its optical axis in the direction or in the first direction (X) and / or the second direction (Y) perpendicular to the optical Axis are set up to be movable.

6. Laser module (1) according to claim 5, wherein in the case of the third attachment element this has a ring-like structure and is set up to be displaceable in a third direction (Z) relative to the first attachment element before a final cohesive fixation with it, which is parallel to the optical axis of the Laser (90) is aligned to adjust one To enable the collimation lens to focus in relation to the emission facet of the laser (90).

7. Laser module (1) according to claim 4, wherein both the collimation lens and the wavelength-sensitive grating are held by the second attachment element and before a final cohesive fixation of a fourth attachment element with the first attachment element, together with the fourth attachment element and in a fixed spatial position relative to one another to the laser (90) and its optical axis are designed to be displaceable perpendicular to the optical axis in the direction or in the first direction (X) and / or the second direction (Y).

8. Laser module (1) according to claim 7, wherein in the case of the fourth attachment element, this has a ring-like structure and encloses the second attachment element, so that the second attachment element is opposite the fourth attachment element before a final cohesive fixation with it in a third direction (Z). is displaceable, which is aligned parallel to the optical axis of the laser (90) to enable the adjustment of a focus of the collimating lens with respect to the emission facet of the laser (90).

9. Laser module (1) according to one of claims 4 to 8, wherein the mutual cohesive fixation is a laser welding fixation or an adhesive fixation or a soldering or laser soldering connection.

10. Laser module (1) according to one of claims 4 to 9, wherein the second attachment element is designed as a sleeve with a central axis which is arranged essentially parallel to the optical axis of the laser (90), and wherein the collimation lens and the wavelength-sensitive grating in Mounted inside the sleeve.

11. Laser module (1) according to one of claims 4 to 10, wherein the wavelength-sensitive grating is held by the second attachment element in a predetermined grating receptacle, which allows adjustment by adjusting a Inclination angle of the grating relative to the optical axis in the recorded state of the grating excludes.

12. Laser module (1) according to one of claims 4 to 11, wherein the laser (90) is accommodated in a housing, in particular in a TO 38, TO 56 or TO 90 housing, wherein the first attachment element has a receptacle for fastening of the housing or a substrate carrying the housing.

13. Laser module (1) according to one of claims 4 to 12, wherein the laser (90) is an edge emitter

14. A method for producing a laser module (1), which comprises: a laser (90) which is set up to emit a laser beam propagating along an optical axis, a collimation lens which contains the laser beam emitted from an emission facet of the laser (90). collimated, as well as a wavelength-sensitive grating that partially reflects the collimated laser beam, comprising the steps:

Arranging (220) the collimation lens and the wavelength-sensitive grating along the optical axis of the laser beam emitted by the laser (90) during operation, so that an external cavity is formed by a rear mirror facet of the laser (90) and a reflection plane of the grating, around a to produce a small bandwidth portion of the laser beam transmitted by the wavelength-sensitive grating;

Displacing (230) the collimation lens relative to the laser (90) from an original position in at least one direction (X, Y) perpendicular to the optical axis;

determining (240) a bandwidth of an emission spectrum of the laser beam transmitted by the wavelength-sensitive reflector; and

determining (250) a position shifted in the direction (X, Y) depending on the result;

Mechanically fixing (260) the collimation lens relative to the laser (90) at the specified position.