Narrow-band light emitting laser device and method

Abstract

The invention concerns a laser device with at least one laser diode, in particular with an optical resonator, wherein the semiconductor laser device is configured to emit laser light in a first spectral wavelength range comprising a first wavelength, and a reflector element optically and in particular mechanically coupled to the at least one laser diode and configured to reflect a portion of the light of the first wavelength back into the at least one laser diode in order to adapt the resonance wavelength of the at least one laser diode to the first wavelength. The reflector element comprises a carrier substrate coupled to a front surface of the at least one laser diode and arranged within the beam path of the light emitted by the at least one laser diode and the reflector element comprises a first meta surface comprising a plurality of nano- structures that is arranged on the carrier substrate within the beam path of the light emitted by the at least one laser diode. The first meta surface is configured to reflect the portion of the light of the first wavelength back into the semiconductor laser device.

Description

[0001] NARROW-BAND LIGHT EMITTING LASER DEVICE AND METHOD

[0002] The present application claims priority from German patent application DE 10 2024 114 941 . 8 filed on May 28 , 2024 , the disclosure of which is incorporated by way for reference in its entirety .

[0003] The present invention relates to a laser device , in particular a laser device comprising a self-aligning feedback for stabilizing a laser light emitted by the laser device , and to a method for operating the laser device .

[0004] BACKGROUND

[0005] Laser emitters , such as for example used in laser beam proj ectors , must be operated with a current in order to emit laser light . Laser operation begins at a characteristic current in the direction of flow, the threshold current . Below this current , the laser emitter emits noncoherent radiation, similar to a light-emitting diode , but no laser light . Above the threshold current , the optical output power of the laser emitter is proportional to the impressed current . The wavelength of the light emitted by the laser emitter depends , among other things , on the material or material system used for the laser emitter , the impressed current and the temperature , in particular the transition temperature , in the laser emitter .

[0006] For various applications , it is advantageous to provide a laser emitter that is designed to generate particularly narrow-band light , also known as wavelength-stable light . This can be achieved, for example , by a suitable design of the laser emitter or the use of suitable materials , or it can be achieved by placing a filter downstream of the laser emitter , for example a bandpass filter , which reduces the light generated by the laser emitter with a broader wavelength range to a desired narrow wavelength range .

[0007] However , for some applications it can be advantageous to provide a laser emitter that provides such narrowband light , which is difficult or impossible to achieve with a suitable laser emitter design, the use of suitable materials or the use of filters .

[0008] Another possibility to reduce a light generated within the laser emitter with a broader wavelength range to a desired narrow wavelength range , i . e . to stabilize the wavelength of the laser emitter, is to feedback the light generated by the laser emitter using a resonator, e . g . a ring resonator or micro-ring . However, the problem here is that the resonance wavelength of the laser emitter does not match the resonance wavelength of the resonator per se due to manufacturing tolerances . In a laboratory environment , this can be brought into line by targeted tuning of the laser emitter or the resonator, but for an economical product realization this tuning poses a maj or problem.

[0009] It is therefore an obj ect of the present invention to provide a laser device and a method for operating the laser device which counteracts at least one of the aforementioned problems .

[0010] SUMMARY OF THE INVENTION

[0011] This and other obj ects are addressed by the subj ect matter of the independent claims . Features and further aspects of the proposed principles are outlined in the dependent claims .

[0012] Self-inj ection locking is a dynamic phenomenon, which provides passive stabilization of a laser emission frequency via resonant optical feedback . The stabilization coefficient depends on the level of the feedback and quality factor of an external resonant structure creating the feedback . The inventors now propose to use a meta surface with a high-quality factor as an external resonator to create optical feedback into an edge emitter laser ( EEL ) .

[0013] A meta surface can be integrated directly onto the top surface of a VCSEL . This integration is facilitated by the planar geometry of a top surface of VCSELs , which emit perpendicular to this surface namely in the growth direction of the laser . Contrarily, EELs emit light parallel to the wafer surf ace / perpendicular to the growth direction of the laser , making it more challenging to integrate a meta surface directly on an emission facet of the laser . A realization of a meta surface directly on the emission facet of EEL is in general possible , but it is very challenging and expensive because it is not possible to make it on wafer level .

[0014] In addition, the laser spot of an EEL is not circular ( like VCSEL ) but it comprises an elliptical beam shape . Therefore , there is a constructional difference between a meta surface that can be used for EEL to that that can be used for a VCSEL .

[0015] The inventors therefore propose to provided the meta surface on a surface of a transparent substrate ( at laser wavelength) which is optically and in particular mechanically attached to the laser . The meta surface can for example be provided on the surface of the substrate in form of precise subwavelength nano-structures that are made in such a way that the meta surface reflects the laser light emitted from the laser at a specific frequency with a large reflectivity amplitude ( for example reflectivity R > 0 . 99 ) . The reflected light is inj ected into the laser and locks the laser at this specific frequency or in other words adapts the resonant frequency of the laser to the frequency of the back reflected laser light .

[0016] In particular the inventors propose to provide a reflector element comprising a meta surface coupled to a laser diode that enables the laser diode to emit laser light in a narrow spectral wavelength range . The concept utilizes a meta surface by means of which a specific chosen wavelength, in particular a part of the laser light having the specific chosen wavelength is reflected back into the laser diode . If the feedback now interferes constructively with the laser light emitted by the laser diode , the threshold value for this selected and back reflected chosen wavelength is lowered . Thus , emission of laser light occurs predominantly in the chosen wavelength rage , in particular at least with a higher optical output power .

[0017] A separation of the meta surface from the laser facet gives possibilities such as : One can realize the meta surface by using completely different material system compared to laser technology and then assemble them;

[0018] It is possible to measure and test the meta surface and even binning them (based on wavelength ) and then use the most proper meta surface for each laser;

[0019] Adding an antireflecting coat (ARC ) on meta surface or on laser is possible ;

[0020] Adding some index-matching material between laser facet and meta surface is possible .

[0021] Advantages that can result from such a configuration of laser device are :

[0022] Cost-effective : A simple and cost-effective way for manufacturing narrowband lasers out of conventional EELs .

[0023] Compact : Very compact in size due to a direct attachment of the meta surface or a meta surface substrate on the laser facet of a laser diode .

[0024] Well-defined phase matching : A precise distance between the laser facet and the meta surface is guaranteed through the thickness of a meta surface substrate . This can be important because the phase of the inj ected light is defined by this thickness . In comparison in micro ring resonator solutions , one must adj ust the PIC at a well-defined distance to the laser facet , which is done by active alignment processes .

[0025] Easy alignment : When using PIC and ring resonator , one must couple the laser to the waveguide ( of PIC ) at a very precise distance which is a challenging task . This is eliminated by attaching the meta surface / meta surface substrate directly on laser facet . The distance will be automatically defined, via thickness of metasurface and there is no high sensitivity to the planar positioning of metasurface on laser facet .

[0026] Better performance : The area of the meta surface can be designed depending on the laser beam convergence , the distance between the meta surface and the laser facet and the desired intensity of inj ection . These flexibilities lead to an improvement of the laser performance which is difficult if one uses a PIC concept . Flexibility : By means of the proposed solution it is possible to provide narrowband lasers at different frequencies by means of the same broadband laser emitter but different meta surface optics . This will allow a flexible use of the product with little effort and cost . This is possible by using meta surface optics with nanostructures with different dimensions .

[0027] More functionality : The meta surface substrate can be used for several tasks , namely for laser stabilization and other purposes such as for example for beam collimation, beam shape correction, and / or polarization of the laser light .

[0028] Better divergence angle : A frequency stabilization of a laser usually improves its divergence angle and can improve the shape of the emitted laser spot in the far field for example from oval to round .

[0029] According to a first aspect , a laser device is provided . The laser device comprises at least one laser diode , in particular with an optical resonator . The at least one laser diode is configured to emit laser light in a first spectral wavelength range comprising a first wavelength . For example , the semiconductor laser device can be referred to as a broad band laser, which is configured to emit laser light with a comparable broad / large spectral wavelength range .

[0030] The optoelectronic device further comprises a reflector element optically and in particular mechanically coupled to the at least one laser diode . The reflector element is configured to reflect a portion of the laser light of the first wavelength back into the at least one laser diode in order to adapt the resonance wavelength of the at least one laser diode to the first wavelength . The reflector element therefore comprises a carrier substrate coupled to a front surface of the at least one laser diode , which is arranged within the beam path of the laser light emitted by the at least one laser diode . Further the reflector element comprises a first meta surface comprising a plurality of nano-structures , wherein the first meta surface is arranged on the carrier substrate within the beam path of the laser light emitted by the at least one laser diode , and wherein the first meta surface is configured to reflect the portion of the laser light of the first wavelength back into the semiconductor laser device .

[0031] Due to the feedback or reflection of laser light of the first wavelength back into the at least one laser diode , the at least one laser diode will inherently favor laser emission with the first wavelength, since the feedback interferes constructively with the at least one laser diode . By this the at least one laser diode configured to emit a broader band light can be operated such that it emits laser light with a narrower spectral wavelength range , and in particular with substantially only laser light of the first wavelength . In contrast to a laser diode which, due to its configuration, is configured to emit broad band laser light with a more diverged optical output power over the emitted spectral range , a laser device according to some of the proposed aspects can be used to provide a device configured to emit laser light in a narrow spectral wavelength range which can emit laser light with the first wavelength with high optical output power .

[0032] For example , the at least one laser diode can be formed by an edgeemitting laser chip which has an optical resonator at one end of which a laser light emission surface is located . The optical resonator can be formed between the laser light emission surface and an end opposite the laser light emission surface . For example , the laser light emission surface can be configured to be partially reflective and the end opposite the laser light emission surface can be mirrored, so that an optical resonator is formed . The at least one laser diode can comprise one or more laser ridge ( s ) , which is / are formed in the at least one laser diode and provide a current confinement within the at least one laser diode . Alternatively, current confinement can also be achieved by applying thin / narrow contact layer ( s ) , such as in a current / gain guided laser .

[0033] According to some aspects , the reflector element is configured to reflect a portion of the laser light of the first wavelength back into the at least one laser diode to adapt the resonance wavelength of the at least one laser diode to the first wavelength such that the at least one laser diode emits laser light in a second spectral wavelength range which is narrower than the first spectral wavelength range and comprises the first wavelength . In turn, according to some aspects , the laser device is , when excited by the reflected laser light of the first wavelength, configured to emit laser light substantially only of a second spectral wavelength range which is narrower than the first spectral wavelength range and comprises the first wavelength .

[0034] According to some aspects the second spectral wavelength range comprises wavelengths which deviate substantially at most ±5 nm, ±2 nm, or ±1 nm from the first wavelength . For example , the laser device is configured to emit laser light substantially only of the first wavelength when excited by the reflected laser light of the first wavelength . This can be achieved in particular by the fact that excited by the reflected laser light of the first wavelength, a so-called "collapse" results in the at least one laser diode , which entails an emission of substantially only laser light of the first wavelength . In the following , this can also be referred to as "narrow band light" of the laser device .

[0035] In particular, the first wavelength may be the peak wavelengths of a desired narrow spectral wavelength range of the laser device to be emitted by the laser device . In particular, the at least one laser diode can be configured to emit light with a spectral wavelength range which has the first wavelength, and the laser device in particular due to the reflector element can be configured to reduce the initially emitted spectral wavelength range emitted by the at least laser diode to a narrower spectral wavelength range with the first wavelength as the peak wavelength . Accordingly, the laser device can be configured to emit a laser light with a narrower second spectral wavelength range that is stabilized with respect to the first wavelength compared to the laser light initially emitted by the at least laser diode with a first spectral wavelength range .

[0036] According to some aspects , the reflector element and in particular the first meta surface is configured and arranged such that at least 80% , at least 90% , at least 95 % , at least 98% , at least 99% , or at least 99 . 9% of the laser light of the first wavelength generated in the at least one laser diode and emitted onto the first meta surface are reflected back into the at least one laser diode .

[0037] According to some aspects , the first meta surface is configured in a similar way as a laser light emission surface for coupling out a laser light generated by the at least one laser diode and may extend a resonator of the at least one laser diode by the distance between the laser light emission surface and the first meta surface forming a "new" light emission surface on a side of the first meta surface opposite the at least one laser diode . In such a case , the laser light emission surface of the at least one laser diode can be designed in such a way that it is less reflective as it would be without the reflector element attached to the front surface of the at least one laser diode .

[0038] According to some aspects the first meta surface is generated directly on a surface of the carrier substrate , and / or scribed into a surface of the carrier substrate . According to some aspects the carrier substrate is attached to front surface of the at least one laser diode for example by means of a transparent glue or if needed with a refractive index matching material for better optical coupling .

[0039] According to some aspects , the carrier substrate is spaced from a laser light emission surface for coupling out a laser light generated by the at least one laser diode . This is , the carrier substrate can comprise regions , which are set back with regard to the front surface of the at least one laser diode such that a cavity / gap can be formed between the front surface of the at least one laser diode and regions of the carrier substrate . However , the carrier substrate can also cover the whole front surface of the at least one laser diode and be in contact with the whole front surface of the at least one laser diode .

[0040] According to some aspects , the first meta surface is arranged on a first surface of the carrier substrate opposite the front surface of the at least one laser diode , or the first meta surface can be arranged on a second surface of the carrier substrate facing the front surface of the at least one laser diode . The first meta surface can thus be arranged on two different sides of the carrier substrate . According to some aspects , the reflector element comprises a second meta surface arranged on the carrier substrate , wherein the second meta surface is configured to collimate or focus the laser light generated by the at least one laser diode at least in one spatial direction . In particular, by means of the second meta surface the shape of the laser light spot emitted from the at least one laser diode can be improved, for example from an oval shape to a round shape . In particular by means of the second meta surface the fast axis of the emitted laser light can be collimated to make the laser light spot round . The second meta surface can however also be configured to change the laser light spot emitted from the laser device in a different way such as for example focus the light on a desired focus point , or change the shape of the laser light spot to a line shape ( collimate the light in one spatial direction and diverge it in a perpendicular spatial direction ) .

[0041] According to some aspects , the reflector element comprises a second meta surface arranged on the carrier substrate , wherein the second meta surface is configured to polarize the laser light generated by the at least one laser diode . In particular by means of the second meta surface the shape of the laser light emitted from the at least one laser diode can be polarized in a desired direction, for example to be later used in combination with a polarization filter or the like .

[0042] According to some aspects , the reflector element comprises an aperture arranged between the front surface and the first meta surface , wherein the aperture comprises an opening having substantially the same size as a laser light emission surface for coupling out a laser light generated by the at least one laser diode , and wherein the opening is arranged within the beam path of the laser light emitted by the at least one laser diode . By means of the aperture , on the one hand the laser light spot emitted from the at least one laser diode is shaped before impinging on the first meta surface and on the other hand the reflected back laser light spot reflected from the first meta surface impinging on the laser light emission surface is shaped . This is a way of spatial mode matching of reflected laser light into the laser light emission surface . In addition, by means of the aperture the size and shape of the laser light spot on the first meta surface can be controlled, which can be helpful for designing and the manufacture of the first meta surface in terms of size and position . The optical aperture can for example be in form of a metallization of one side of the carrier substrate comprising a respective opening .

[0043] According to some aspects , the reflector element comprises an actuator arranged on and / or integrated into the carrier substrate , wherein the actuator is configured to change at least one property of the first meta surface . In particular, by means of the actuator ( electrically switchable , mechanically switchable , optically excitable , thermally excitable and / or chemically excitable ) a tuneable first meta surface can be provided of which at least one property can be changed by means of activating the actuator . By means of this for example the first meta surface can be tuned to comprise a desired different property or can be tuned for the purpose of compensation of instabilities . For example by means of the actuator a strain can be applied to the first meta surface and / or the carrier substrate such that a property, in particular optical property, ( shape , thickness , stiffness , distance between nano-structures , ...) of the first meta surface can be changed or such that the position of the first meta surface can be changed with regard to a laser light emission surface for coupling out a laser light generated by the at least one laser diode . By this for example an optical property of the first meta surface can be changed, such as for example the reflectivity wavelength of the first meta surface , and / or the collimation / f ocusing behavior of the first meta surface , and / or by this a positioning due to a misalignment of the first meta surface compared to the laser light emission surface of the at least one laser diode can be conducted . By this , a feedback loop can be provided, which due to for example temperature fluctuations , mechanical vibration and so on, can compensate the first meta surface ' s resonance frequency if there is a change of the resonance frequency in some part of the system due to aforementioned reasons .

[0044] According to some aspects , the actuator can be formed by a piezoelectric material , a first electrode and a second electrode opposite the first electrode . The piezoelectric material is arranged between the first and the second electrode , and the first electrode , the second electrode and the piezoelectric material in particular form a piezoelectric capacitor . To control the piezoelectric capacitor , and in particular to achieve tensioning or relaxation of the coupling element in the desired manner, the first electrode is coupled to an actuating and / or control output . Depending on requirements , the piezoelectric capacitor can be charged, discharged or the voltage of the piezoelectric capacitor can be kept constant so that the carrier substrate and thus the first meta surface can be tensioned, relaxed or held "in position" to for example match its resonance wavelength to the first wavelength .

[0045] According to some aspects , the reflector element comprises a cover material covering the first and / or second meta surface . By means of this , an encapsulation can be provided to protect the first and / or second meta surface from physical damage . In case of the cover element being the outermost layer / material of the reflector element , in particular the last element of the reflector element within the beam path of laser light emitted from the at least one laser diode , the cover can for example be of a lower index material ( e . g . Si02 ) than the elements / layers in front of the cover material .

[0046] According to some aspects , the first meta surface comprises a material with a higher refractive index than the carrier substrate . By this in conj unction with the nanostructures of the first meta surface the desired function of the reflector element , and in particular of the first meta surface , can be provided in a respective way .

[0047] According to some aspects , the first meta surface is configured to reflect the portion of the laser light of the first wavelength back into the at least one laser diode in a focused way, in particular focused on a laser light emission surface for coupling out a laser light generated by the at least one laser diode . In particular the nano-structures of the first meta surface can be designed in such a way that the reflected laser light is not diverged when being reflected but the laser light is reflected and converged at the same time . In particular, the first meta surface can be designed such that there is a mode matching of the first meta surface with the laser mode profile of the laser light emitted from the at least one laser diode . By this it can for example be provided that most of the reflected laser light is inj ected into a laser light emission surface for coupling out a laser light generated by the at least one laser diode the laser ridge with very small scattering losses not impinging directly onto the laser light emission surface . This can for example be realized by the nanostructures of the first meta surface in a central region of the first meta surface being larger , in particular wider / thicker , than in an outer region surrounding the central region . Hence the first meta surface can comprise a specific pattern which provides the desired functionality . In particular a pitch of the nano-structures of the first meta surface in a central region of the first meta surface is larger than in an outer region surrounding the central region .

[0048] According to a further aspect , a method for operating a laser device is provided, wherein the laser device is configured to emit narrow band laser light . In particular , the method may be a method for operating a laser device according to at least some of the aforementioned aspects . Thus , all aspects already described for the laser device can be applied to the method in the same way .

[0049] The method comprises the following steps :

[0050] Operating at least one laser diode in such a way that it emits laser light in a first spectral wavelength range comprising a first wavelength;

[0051] Reflecting a portion of the laser light of the first wavelength back into the at least one laser diode by means of a reflector element optically and mechanically coupled to the at least one laser diode ; and

[0052] Adapting the resonance wavelength of the at least one laser diode to the first wavelength such that the at least one laser diode emits laser light in a second spectral wavelength range which is narrower than the first spectral wavelength range and comprises the first wavelength; wherein the reflector element comprises a carrier substrate coupled to a front surface of the at least one laser diode and arranged within the beam path of the laser light emitted by the at least one laser diode ; and wherein the reflector element comprises a first meta surface comprising a plurality of nano-structures , the first meta surface being arranged on the carrier substrate within the beam path of the laser light emitted by the at least one laser diode .

[0053] In particular, the feedback or back reflection into the at least one laser diode selectively amplifies the first wavelength in the at least one laser diode or simultaneously attenuates the other wavelengths in the at least one laser diode relative thereto .

[0054] SHORT DESCRIPTION OF THE DRAWINGS

[0055] Further aspects and embodiments in accordance with the proposed principle will become apparent in relation to the various embodiments and examples described in detail in connection with the accompanying drawings in which

[0056] Figs . 1A to 1C show a front view of a laser diode , a front view of a reflector element and a front view of a laser device according to some aspects of the proposed principle ;

[0057] Fig . 2 shows a side view including a detailed view of an embodiment of a laser device according to some aspects of the proposed principle ;

[0058] Fig . 3A and 3B show a side view of a further embodiment of a laser device and a detailed view of a reflector element according to some aspects of the proposed principle ;

[0059] Fig . 4A and 4B show a side view of a further embodiment of a laser device and a detailed view of a reflector element according to some aspects of the proposed principle ; and Figs . 5 to 9 show each a side view of a further embodiment of a laser device according to some aspects of the proposed principle .

[0060] DETAILED DESCRIPTION

[0061] The following embodiments and examples disclose various aspects and their combinations according to the proposed principle . The embodiments and examples are not always to scale . Likewise , different elements can be displayed enlarged or reduced in size to emphasize individual aspects . It goes without saying that the individual aspects of the embodiments and examples shown in the figures can be combined with each other without further ado , without this contradicting the principle according to the invention . Some aspects show a regular structure or form. It should be noted that in practice slight differences and deviations from the ideal form may occur without , however, contradicting the inventive idea .

[0062] In addition, the individual figures and aspects are not necessarily shown in the correct size , nor do the proportions between individual elements have to be essentially correct . Some aspects are highlighted by showing them enlarged . However , terms such as "above" , "over" , "below" , "under" "larger" , "smaller" and the like are correctly represented with regard to the elements in the figures . So it is possible to deduce such relations between the elements based on the figures .

[0063] Figures 1A to 1C show a front view of a laser diode 2 , a front view of a reflector element 4 and a front view of a laser device 1 according to some aspects of the proposed principle . Further Figure 2 shows a side view including a detailed view of the laser device 1 according to some aspects of the proposed principle . The laser diode 2 is in form of an edge-emitting laser chip which has an optical resonator 17 at one end of which a laser light emission surface 3 is located . The optical resonator 17 can be formed between the laser light emission surface 3 and an end mirror 18 opposite the laser light emission surface 3 . The laser light emission surface 3 is configured to be partially reflective and the end mirror 18 opposite the laser light emission surface 3 is mirrored, so that an optical resonator 17 is formed . In the embodiment shown, the laser diode 2 comprises a laser ridge , which is formed in the laser diode 2 to provide a current confinement within the laser diode 2 .

[0064] The laser diode 2 is configured to emit laser light L when electrically powered with a current above a threshold current of the laser diode 2 . The laser diode 2 is configured to emit laser light in a first wavelength range with the first wavelength range comprising a first wavelength XI . In particular the laser diode can be a broad band light emitting laser diode including the first wavelength XI .

[0065] The laser device 1 further comprises a reflector element 4 that is optically as well as mechanically attached to a front surface 8 of the laser diode 2 . The reflector element 4 comprises a carrier substrate 5 on which a first meta surface 6 is arranged / integrated . The first meta surface 6 comprises nano-structures 9 arranged / integrated on / into the carrier substrate 5 . The nano-structures 9 are made of high index materials ( e . g . Ti02 or Nb2O5 ) arranged on al lower index material of the carrier substrate 5 ( e . g . Si02 ) and a Q-factor of the first meta surface can be tuned by the asymmetry parameter of the nano-structures 9 .

[0066] The reflector element 4 and in particular the first meta surface 6 is configured to reflect laser light LR having the first wavelength XI . Thus , in the arrangement of the reflector element 4 being attached to the front surface 8 of the laser diode 2 , a portion of the laser light of the first wavelength XI emitted from the laser diode 2 is reflected back to and in particular into the laser diode 2 . By this , the resonance wavelength of the laser diode 2 is changed to the first wavelength XI , such that after reflection of the laser light of the first wavelength XI the laser diode 2 will inherently favor laser emission with the first wavelength XI , since the feedback interferes constructively with the laser diode 2 . By this the laser diode 2 configured to initially emit a broader band light can be operated such that it emits laser light with a narrower spectral wavelength range , and in particular with substantially only laser light of the first wavelength XI .

[0067] In the embodiment shown, the first meta surface is integrated into a first surface 10a of the carrier substrate 5 opposite the laser light emission surface 3 of the laser diode 2 . The carrier substrate 5 can therefore comprise a cavity in which the first meta surface 6 is integrated, or the first meta surface 6 can be scribed / etched into the first surface 10a of the carrier substrate 5 .

[0068] The carrier substrate 5 is directly attached to the whole front surface

[0069] 8 of the laser diode 2 by means of for example a transparent glue or if needed with a refractive index matching material for better optical coupling . The laser light L emitted from the laser diode 2 passes through the carrier substrate 5 with a well-defined thickness and on the other side of the carrier substrate 5 reaches the nano-structures

[0070] 9 of the first meta surface . At this plane , a portion of the laser light L , in particular light at a first wavelength XI , is reflected back into the laser diode with a defined phase and intensity . The reflected laser light LR has enough power to force the laser diode 2 to then emit laser light at substantially only the first wavelength XI and self-inj ection locking happens . By means of the thickness of the carrier substrate a distance d between the laser light emission surface 3 and the first meta surface 6 can be adj usted to harmonize the laser diode 2 with the first meta surface 6 and to achieve a desired result of the emission profile of the laser device 1 as well as to increase the coupling efficiency of the reflected laser light LR into the laser diode 2 . In addition, the size of the first meta surface 6 is preferably larger than the laser light emitted by the laser diode , to ensure all light passes the first meta surface 6 and is thus processed in the same way .

[0071] Figures 3A and 3B show a side view of a further embodiment of a laser device 1 and a detailed view of a reflector element 4 according to some aspects of the proposed principle . In the embodiment shown, the first meta surface 6 is arranged on the first surface 10a of the carrier substrate 5 in form of regularly distributed nano-structures 9 in form of regular cubes / pillars / dies . The nano-structures 9 can also be called metaatoms ( unit cells ) which are made of high index materials ( e . g . , TiO2 or Nb2O5 ) . The resonance frequency Xres of the first meta surface 6 is dependent on the pitch P of the nano structures 9 . Hence the pitch P can roughly be calculated by Xres / n, wherein n is an integer natural number . Hence the pitch P roughly equals to for example the half-wave , or quarter-wave of the desired resonance frequency Xres . In case of laser light that is to be emitted with the laser device 1 of a wavelength with its peak wavelength at 430 nm, a pitch P of fore example 215 nm can be chosen .

[0072] Figures 4A and 4B show a side view of a further embodiment of a laser device 1 and a detailed view of a reflector element 4 according to some aspects of the proposed principle . In the embodiment shown, the first meta surface 6 is arranged on the first surface 10a of the carrier substrate 5 in form of regularly distributed nano-structures 9 in form of regular cubes / pillars / dies that are however arranged / conf igured with a different pitch Pl , P2 in a central region 15a compared to an outer region 15b . The nano-structures 9 of the first meta surface 6 are in particular designed in such a way that the reflected laser light LR is not diverged ( like embodiment shown in Fig . 3A and 3B ) but the laser light is reflected and gets converged at the same time / f ocussed on the laser light emission surface 3 of the laser diode 2 . In other words , the first meta surface 6 is designed such that there is a mode matching with the laser mode profile of the laser light emitted from the laser diode 2 . As a result , most of the reflected laser light LR is inj ected into the laser light emission surface 3 of the laser diode 2 with very small scattering losses .

[0073] Figure 5 shows a side view of a further embodiment of a laser device 1 according to some aspects of the proposed principle . As it is illustrated in Fig . 5 , another approach is to provide the nanostructures 9 of the first meta surface 6 in a cavity 16 of the carrier substrate 5 on a second surface 15b of the carrier substrate 5 facing the laser light emission surface 3 of the laser diode 2 . For this , a cavity 16 with a defined depth in the carrier substrate 5 is provided . Then the first meta surface 6 is provided inside the cavity 16 . The reflector element 4 is then attached on the front surface 8 of the laser diode 2 . By this approach the laser light emission surface 3 of the laser diode 2 can be protected from mechanical contact with the reflector element 4 . Further also the first meta surface 6 is protected from external influences within the cavity 16 . In addition, the cavity 16 can be realized via an etch process which allows a very precise depth of it , which is important for defining the distance between the first meta surface 6 and the laser light emission surface 3 and thus the phase of the reflected laser light LR .

[0074] Figure 6 shows a side view of a further embodiment of a laser device 1 according to some aspects of the proposed principle . In the embodiment shown, a second meta surface 7 is provided on the first surface 15a of the carrier substrate 5 , wherein the second meta surface 7 can in one embodiment be configured to collimate the laser light L in at least one spatial direction, for example the fast axis of the laser light L to change the laser spot from elliptical to round . In another embodiment , or in addition, the second meta surface 7 can be used for polarization purpose ad thus polarize the laser light L .

[0075] Figure 7 shows a side view of a further embodiment of a laser device 1 according to some aspects of the proposed principle . In the embodiment shown, the reflector element 4 comprises an aperture 11 arranged within the cavity 16 on the second surface 10b of the carrier substrate 5 . By means of the aperture 11 and in particular the size of an opening 13 of the aperture 11 , the size and shape of laser light spot on the first meta surface 6 can be tuned as well the reflected laser light spot ( laser light emission surface 3 of the laser diode 2 ) is shaped . This is a way of spatial mode matching of the reflected laser light LR into the laser light emission surface 3 of the laser diode 2 . The optical aperture 11 can for example be provided by metallization of the second surface 15b of the carrier substrate 5 .

[0076] Figure 8 shows a side view of a further embodiment of a laser device 1 according to some aspects of the proposed principle . In the embodiment shown, the reflector element 4 comprises an actuator 13 that is configured to make the first meta surface 6 tuneable . This is for example a possibility for a more robust stabilization of the laser device . A tuneable first meta surface 6 can be realized by means of an electrically, mechanically, thermally etc . actuator . If for any reason, for example temperature fluctuations , mechanical vibration and so on, cause a change of the resonance frequency in any part of the laser device , a feedback loop can restabilized by the actuator to be able to adj ust the first meta surface ' s resonance frequency .

[0077] For example the actuator 13 can be formed by a piezoelectric material , a first electrode 19a and a second electrode 19b opposite the first electrode 19a . The piezoelectric material is arranged between the first and the second electrode , and the first electrode , the second electrode and the piezoelectric material in particular form a piezoelectric capacitor . To control the piezoelectric capacitor , and in particular to achieve tensioning or relaxation of the coupling element in the desired manner, the first electrode is coupled to an actuating and / or control output . Depending on requirements , the piezoelectric capacitor can be charged, discharged or the voltage of the piezoelectric capacitor can be kept constant so that the carrier substrate 5 and thus the first meta surface 6 can be tensioned, relaxed or held "in position" to for example match its resonance wavelength to the first wavelength XI .

[0078] Figure 9 shows a side view of a further embodiment of a laser device 1 according to some aspects of the proposed principle . In the embodiment shown, a cover material 14 with for example a lower index material ( e . g . Si02 ) is used to protect the first meta surface 6 from physical damage . It is however to be understood that the cover material 14 can also be used to protect the second meta surface 7 as shown in Figure 6 from physical damage . LIST OF REFERENCES

[0079] 1 laser device

[0080] 2 laser diode

[0081] 3 laser light emission surface

[0082] 4 reflector element

[0083] 5 carrier substrate

[0084] 6 first meta surface

[0085] 7 second meta surface

[0086] 8 front surface

[0087] 9 nano-structures

[0088] 10a , 10b surface of carrier

[0089] 11 aperture

[0090] 12 opening

[0091] 13 actuator

[0092] 14 cover material

[0093] 15a , 15b region

[0094] 16 cavity

[0095] 17 resonator

[0096] 18 end mirror

[0097] 19a , 19b electrode

[0098] Xi first wavelength

[0099] L laser light

[0100] LR reflected laser light d distance

[0101] P, Pi , Pi pitch

Claims

CLAIMS1. A laser device (1) with at least one laser diode (2) , in particular with an optical resonator, wherein the semiconductor laser device (2) is configured to emit laser light in a first spectral wavelength range comprising a first wavelength (Xi) ; and a reflector element (4) optically and in particular mechanically coupled to the at least one laser diode (2) and configured to reflect a portion of the laser light of the first wavelength (Xi) back into the at least one laser diode (2) in order to adapt the resonance wavelength of the at least one laser diode (2) to the first wavelength (Xi) ; wherein the reflector element (4) comprises a carrier substrate(5) coupled to a front surface (8) of the at least one laser diode (2) and arranged within the beam path of the laser light emitted by the at least one laser diode (2) ; and wherein the reflector element (4) comprises a first meta surface(6) comprising a plurality of nano-structures (9) , the first meta surface (6) being arranged on the carrier substrate (5) within the beam path of the laser light emitted by the at least one laser diode (2) , and the first meta surface (6) being configured to reflect the portion of the laser light of the first wavelength (Xi) back into the semiconductor laser device (2) .

2. Laser device according to claim 1, wherein the reflector element (4) is configured to reflect a portion of the laser light of the first wavelength (Xi) back into the at least one laser diode (2) to adapt the resonance wavelength of the at least one laser diode (2) to the first wavelength (Xi) such that the at least one laser diode (2) emits laser light in a second spectral wavelength range which is narrower than the first spectral wavelength range and comprises the first wavelength (Xi) .

3. Laser device according to claim 2,wherein the second spectral wavelength range comprises wavelengths which deviate substantially at most +-2nm from the first wavelength (Xi) .

4. Laser device according to any one of the preceding claims, wherein the carrier substrate (5) is spaced from a laser light emission surface (3) for coupling out a laser light generated by the at least one laser diode (2) .

5. Laser device according to any one of the preceding claims, wherein the first meta surface (6) is arranged on a first surface (10a) of the carrier substrate (5) opposite the front surface (8) of the at least one laser diode (2) .

6. Laser device according to any one of claims 1 to 4 , wherein the first meta surface (6) is arranged on a second surface (10b) of the carrier substrate (5) facing the front surface (8) of the at least one laser diode (2) .

7. Laser device according to any one of the preceding claims, wherein the reflector element (4) comprises a second meta surface (7) arranged on the carrier substrate (5) , wherein the second meta surface (7) is configured to collimate or focus the laser light generated by the at least one laser diode (2) at least in one spatial direction.

8. Laser device according to any one of the preceding claims, wherein the reflector element (4) comprises a second meta surface (7) arranged on the carrier substrate (5) , wherein the second meta surface (7) is configured to polarize the laser light generated by the at least one laser diode (2) .

9. Laser device according to any one of the preceding claims, wherein the reflector element (4) comprises an aperture (11) arranged between the front surface (8) and the first meta surface (6) ,wherein the aperture (11) comprises an opening (12) having substantially the same size as a laser light emission surface (3) for coupling out a laser light generated by the at least one laser diode ( 2 ) , and wherein the opening (12) is arranged within the beam path of the laser light emitted by the at least one laser diode (2) .

10. Laser device according to any one of the preceding claims, wherein the reflector element (4) comprises an actuator (13) arranged on and / or integrated into the carrier substrate (5) , wherein the actuator (13) is configured to change the properties of the first meta surface (6) .

11. Laser device according to claim 10, wherein the actuator (13) is configured to change the position of the first meta surface (6) compared to a laser light emission surface (3) for coupling out a laser light generated by the at least one laser diode (2) , and / or wherein the actuator (13) is configured to change the optical properties of the first meta surface (6) , in particular the reflectivity wavelength of the first meta surface (6) .

12. Laser device according to any one of the preceding claims, wherein the reflector element (4) comprises a cover material (14) covering the first and / or second meta surface (6, 7) .

13. Laser device according to any one of the preceding claims, wherein the first meta surface (6) comprises a material with a higher refractive index than the carrier substrate (5) .

14. Laser device according to any one of the preceding claims, wherein the first meta surface (6) is configured to reflect the portion of the laser light of the first wavelength (Xi) back into the at least one laser diode (2) in a focused way, in particular focused on a laser light emission surface (3) for coupling out a laser light generated by the at least one laser diode (2) .

15. Laser device according to any one of the preceding claims, wherein the first meta surface (6) is mode matched with the laser light generated by the at least one laser diode (2) .

16. Laser device according to any one of the preceding claims, wherein a pitch (Pl, P2 ) of the nano-structures (9) of the first meta surface (6) in a central region (15a) of the first meta surface (6) is larger than in an outer region (15b) surrounding the central region ( 15a ) .

17. Laser device according to any one of the preceding claims, wherein, when excited by the reflected laser light of the first wavelength (Xi) , the laser device (1) is configured to emit laser light substantially only of a second spectral wavelength range which is narrower than the first spectral wavelength range and comprises the first wavelength (Xi) .

18. A method for operating a laser device (1) , in particular laser device according to any one of the preceding claims, comprising the steps :Operating at least one laser diode (2) in such a way that it emits laser light in a first spectral wavelength range comprising a first wavelength (Xi) ;Reflecting a portion of the laser light of the first wavelength (Xi) back into the at least one laser diode (2) by means of a reflector element (4) optically and mechanically coupled to the at least one laser diode (2) ; andAdapting the resonance wavelength of the at least one laser diode (2) to the first wavelength (Xi) such that the at least one laser diode (2) emits laser light in a second spectral wavelength range which is narrower than the first spectral wavelength range and comprises the first wavelength (Xi) ; wherein the reflector element (4) comprises a carrier substrate (5) coupled to a front surface (8) of the at least one laser diode (2) and arranged within the beam path of the laser light emitted by the at least one laser diode (2) ; andwherein the reflector element (4) comprises a first meta surface (6) comprising a plurality of nano-structures (9) , the first meta surface (6) being arranged on the carrier substrate (5) within the beam path of the laser light emitted by the at least one laser diode ( 2 ) .

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