Spin-vcsel apparatus and method of operation

Abstract

The present disclosure relates to optical communications using a spin vertical-cavity surface- emitting laser (VCSEL). The disclosure provides a laser apparatus comprising the spin VCSEL, which comprises a cavity structure. The cavity structure comprises one or more controllable optical properties, comprising a birefringence rate and / or an effective dichroism rate. The spin VCSEL is configured to receive an electrical current signal comprising an amplitude modulation. The spin VCSEL generates a first laser signal by converting the received electrical current signal in the cavity structure (102) with the one or more controllable optical properties, wherein the first laser signal comprises a circular polarization modulation. The circular polarization modulation of the first laser signal correlates with the amplitude modulation of the electrical current signal.

Description

[0001] SPIN-VCSEL APPARATUS AND METHOD OF OPERATION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a spin vertical-cavity surface-emitting laser (VCSEL) with one or more controllable optical properties. The disclosure also presents a laser apparatus that comprises the spin VCSEL. The spin VCSEL comprises a cavity structure, which comprises the one or more controllable optical properties. A method for operating the laser apparatus is also provided in this disclosure.

[0004] BACKGROUND

[0005] Optical communication technology for short-haul optical communication, for example in data centers, is mainly based on intensity modulation of laser light in fully-integrated VCSELs or in some cases (e.g., in some hyperscale data centers) based on external modulators. These conventional optical devices are used for converting information carriers in the electrical domain into the optical domain.

[0006] An exemplary spin VCSEL for ultrafast short-range communication relies on an additional pump laser and passive optical elements to couple the carrier-density dynamics and the carrierspin dynamics in a second VCSEL to achieve electrical modulation of the polarization state of its laser emission.

[0007] In view of this exemplary spin VCSEL, it would be desirable to achieve the coupling of the carrier-density dynamics and the carrier-spin dynamics without the need of optical spininjection and an additional pumping laser.

[0008] SUMMARY

[0009] This disclosure accordingly aims to improve conventional optical devices, for example, VCSELs or laser devices comprising a spin VCSEL, which are used for converting information from the electrical domain into the optical domain. An objective is to achieve an increased modulation bandwidth only by design of the device and the point of operation, which goes beyond that of a conventional intensity-modulated VCSEL. Another objective is to avoid optical spin-injection and an additional pumping laser.

[0010] This and other objectives are achieved by the concept of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0011] A first aspect of this disclosure provides a laser apparatus comprising a spin vertical-cavity surface-emitting laser, spin VCSEL, comprising a cavity structure, wherein the cavity structure comprises one or more controllable optical properties. The optical properties comprise a birefringence rate and / or an effective dichroism rate. The spin VCSEL is configured to: receive an electrical current signal comprising an amplitude modulation; and generate a first laser signal by converting the received electrical current signal in the cavity structure with the one or more controllable optical properties, the first laser signal comprising a circular polarization modulation. The circular polarization modulation of the first laser signal correlates with the amplitude modulation of the electrical current signal.

[0012] A spin VCSELs is a VCSEL with a majority of, for example, spin-up or spin-down charge carriers during recombination and generation of its laser signal. Due to the conservation of angular momentum, the emitted (first) laser signal carries a spin angular momentum as well, e.g., it is circularly polarized. To be more precise, the circular polarization degree (CPD) may evolve in time.

[0013] The bandwidth of a conventional intensity-modulated VCSEL is limited by the dynamics, which govern the interactions between the carriers in the active region of the VCSEL and the photons, which are created there whenever carriers recombine and generate laser light, in other words, the carrier-photon dynamics. Spin dynamics describe the temporal evolution of spin states of carriers and photons in the active region of the spin VCSEL, at least in the case of a majority and minority of spin states (due to an optical pumping with light with non-zero CPD). The speed of the spin dynamics of the carriers and photons in spin VCSEL (e.g., a cavity of the spin VCSEL) is limited by usually very short spin-relaxation times for the spin-polarized charge carriers and the optical birefringence in the laser cavity. Compared to the carrier-photon dynamics in the conventional VCSEL, the spin dynamics in the spin VCSEL may be much faster, as they may occur on much shorter time scales. Typically, carrier-photon dynamics and spin dynamics do not influence each other. The concept of this disclosure enables a coupling of these two systems together via the control of the one or more optical properties (e.g., the birefringence rate and / or an effective dichroism rate) of the VCSEL cavity only.

[0014] Further, by the controllable birefringence and / or dichroism of the cavity structure, the laser apparatus can be operated in or close to a special point of the laser dynamics, for example a so- called polarization switching point, in which the spin VCSEL is capable to inherently couple spin and intensity dynamics. Thereby, additional hardware components to achieve spin injection are not needed.

[0015] In an implementation form of the first aspect, an absolute value of the birefringence rate comprises any value between 25 GHz and 2000 GHz.

[0016] In an implementation form of the first aspect, an absolute value of the dichroism rate comprises any value between 0 and 10 per nanosecond.

[0017] With these ranges for the optical properties of the cavity structure, the desired operating point can be ensured.

[0018] In an implementation form of the first aspect, the electrical current signal further comprises a constant offset. Additionally, the absolute value of the effective dichroism rate is obtained based on the constant offset.

[0019] This enables to control the desired dichroism rate in an efficient and simple manner.

[0020] In an implementation form of the first aspect, the amplitude modulation of the electrical current signal comprises at least a higher current amplitude and a lower current amplitude.

[0021] Thus, information may be encoded into the electrical current signal, and may be transferred to the first laser signal by the spin VCSEL.

[0022] In an implementation form of the first aspect, a change of the current amplitude of the electrical current signal correlates with a change of a CPD of the first laser signal. The change of the CPD may be used to encode information in the first laser signal, wherein this information may correspond to the information encoded into the electrical current signal by means of the changing current amplitude.

[0023] In an implementation form of the first aspect, the first laser signal further comprises an intensity modulation that correlates with the amplitude modulation of the electrical current signal.

[0024] In an implementation form of the first aspect, the laser apparatus further comprises one or more optical components configured to convert the first laser signal into a second laser signal comprising an intensity modulation, wherein the intensity modulation of the second laser signal correlates with the circular polarization modulation of the first laser signal.

[0025] The second laser signal enables the use of a standard receiver. The receiver may convert the second laser signal back into an electrical signal, for example, using a photodiode with a high enough bandwidth.

[0026] In an implementation form of the first aspect, the laser apparatus further comprises an optical fiber configured to receive the first laser signal or the second laser signal for transmitting it to a receiver.

[0027] The first laser signal may be directly coupled into the optical fiber. Thus, no optical components for converting the first laser signal are required at the laser apparatus of the first aspect.

[0028] In an implementation form of the first aspect, the laser apparatus further comprises a receiver configured to receive the first laser signal or the second laser signal, and to convert the first laser signal or the second laser signal into an electrical signal.

[0029] The receiver may be a conventional receiver, as it may be used in a communication systems that includes a conventional intensity-modulated VCSEL.

[0030] In an implementation form of the first aspect, the cavity structure comprises a surface grating.

[0031] This enables to control the optical properties, e.g., the birefringence rate and / or the dichroism rate, of the cavity structure so that the desired operating point can be achieved. Further, this enables a completely integrated and compact approach, without the need for additional pumping.

[0032] In an implementation form of the first aspect, the cavity structure has a non-circular symmetric shape.

[0033] The shape of the cavity structure influences its optical properties. Thus, the non-circular symmetric cavity enables to control the birefringence rate and / or the dichroism so that the desired operating point can be achieved.

[0034] Further, this enables a completely integrated and compact approach, without the need for additional pumping.

[0035] In an implementation form of the first aspect, the laser apparatus is further configured to receive the electrical current signal through an aperture, wherein the aperture has a non-circular symmetric shape.

[0036] This enables to control the optical properties of the cavity structure, e.g., the birefringence rate and / or the dichroism rate, so that the desired operating point can be achieved.

[0037] In an implementation form of the first aspect, the cavity structure comprises the surface grating and has a non-circular symmetric shape.

[0038] Thereby, the effect of both the surface grating and the shape of the cavity can be combined to achieve a better control of the birefringence rate and / or the dichroism rate, so that the desired operation point for the laser apparatus is reached.

[0039] A second aspect of this disclosure provides a method for operating a laser apparatus comprising a spin VCSEL, the spin VCSEL comprising a cavity structure that comprises one or more controllable optical properties, and the optical properties comprise a birefringence rate and / or an effective dichroism rate. The method comprises: providing an electrical current signal comprising an amplitude modulation to the spin VCSEL; and generating a first laser signal having a circular polarization modulation by converting the electrical current signal in the cavity structure with the one or more controllable optical properties; wherein the circular polarization modulation of the first laser signal correlates with the amplitude modulation of the electrical current signal.

[0040] In an implementation form of the second aspect, an absolute value of the birefringence rate comprises any value between 25 GHz and 2000 GHz.

[0041] In an implementation form of the second aspect, an absolute value of the dichroism rate comprises any value between 0 and 10 per nanosecond.

[0042] With these ranges for the optical properties of the cavity structure, the desired operating point can be ensured.

[0043] In an implementation form of the second aspect, the electrical current signal further comprises a constant offset. Additionally, the absolute value of the dichroism rate is obtained based on the constant offset.

[0044] This enables to control the desired dichroism rate in an efficient and simple manner.

[0045] In an implementation form of the second aspect, the amplitude modulation of the electrical current signal comprises at least a higher current amplitude and a lower current amplitude.

[0046] Thus, information may be encoded into the electrical current signal, and may be transferred to the first laser signal by the spin VCSEL.

[0047] In an implementation form of the second aspect, a change of the current amplitude of the electrical current signal correlates with a change of a CPD of the first laser signal.

[0048] The change of the CPD may be used to encode information in the first laser signal, wherein this information may correspond to the information encoded into the electrical current signal by means of the changing current amplitude. In an implementation form of the second aspect, the first laser signal further comprises an intensity modulation that correlates with the amplitude modulation of the electrical current signal.

[0049] In an implementation form of the second aspect, the method further comprises converting, with one or more optical components, the first laser signal into a second laser signal comprising an intensity modulation, wherein the intensity modulation of the second laser signal correlates with the circular polarization modulation of the first laser signal.

[0050] The second laser signal enables the use of a standard receiver. The receiver may convert the second laser signal back into an electrical signal, for example, using a photodiode with a high enough bandwidth.

[0051] In an implementation form of the second aspect, the method further comprises receiving, with an optical fiber, the first laser signal or the second laser signal for transmitting it to a receiver.

[0052] The first laser signal may be directly coupled into the optical fiber. Thus, no optical components for converting the first laser signal are required at the laser apparatus of the second aspect.

[0053] In an implementation form of the second aspect, the method further comprises receiving, with a receiver, the first laser signal or the second laser signal, and converting, with the receiver, the first laser signal or the second laser signal into an electrical signal.

[0054] The receiver may be a conventional receiver, as it may be used in a communication systems that includes a conventional intensity-modulated VCSEL.

[0055] In an implementation form of the second aspect, the cavity structure comprises a surface grating.

[0056] This enables to control the optical properties, e.g., the birefringence rate and / or the dichroism rate, of the cavity structure so that the desired operating point can be achieved.

[0057] Further, this enables a completely integrated and compact approach, without the need for additional pumping. In an implementation form of the second aspect, the cavity structure has a non-circular symmetric shape.

[0058] The shape of the cavity structure influences its optical properties. Thus, the non-circular symmetric cavity enables to control the birefringence rate and / or the dichroism so that the desired operating point can be achieved.

[0059] Further, this enables a completely integrated and compact approach, without the need for additional pumping.

[0060] In an implementation form of the second aspect, method further comprises receiving the electrical current signal through an aperture, wherein the aperture has a non-circular symmetric shape.

[0061] This enables to control the optical properties of the cavity structure, e.g., the birefringence rate and / or the dichroism rate, so that the desired operating point can be achieved.

[0062] In an implementation form of the second aspect, the cavity structure comprises the surface grating and has a non-circular symmetric shape.

[0063] Thereby, the effect of both the surface grating and the shape of the cavity can be combined to achieve a better control of the birefringence rate and / or the dichroism rate, so that the desired operation point for the laser apparatus is reached.

[0064] The method of the second aspect may have implementation forms according to the implementation forms of the laser apparatus of the first aspect. The method may operate a laser apparatus according to any implementation form of the first aspect. The method of the second aspect achieves the same advantages as described above for the laser apparatus of the first aspect.

[0065] In summary, an idea of this disclosure is to couple carrier-photon dynamics to spin dynamics in a VCSEL. Typically, these two are not coupled, hence, no interaction between the two systems occurs conventionally. However, according to the concept of this disclosure, the two are directly coupled to each other, when the spin VCSEL converts the received electrical current signal in the cavity structure with the one or more controllable optical properties. Owing to the faster spin dynamics, the coupling increases the bandwidth, with which the first laser signal can be modulated, going beyond the modulation bandwidth of a conventional intensity-modulated VCSEL.

[0066] It has to be noted that certain devices, elements, units and means described in the present disclosure could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities could be implemented in respective software or hardware elements, or any kind of combination thereof.

[0067] BRIEF DESCRIPTION OF DRAWINGS

[0068] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings (input and output signals are only for illustrative purposes, and do not necessarily correspond to a physical field or signal), in which

[0069] FIG. 1 shows a laser apparatus according to this disclosure.

[0070] FIG. 2a)-b) show simulation results of modulations using random bit sequences for a conventional laser apparatus and for the laser apparatus according to this disclosure, respectively.

[0071] FIG. 3a)-b) show simulation results for a random bit sequence transmitted with the laser apparatus according to this disclosure. FIG. 4 shows an exemplary laser apparatus according to this disclosure, wherein a first laser signal of the spin VCSEL is converted into a second laser signal.

[0072] FIG. 5 shows an exemplary laser apparatus according to this disclosure.

[0073] FIG. 6 shows an exemplary laser apparatus according to this disclosure, wherein the cavity structure has a non-circular symmetric shape.

[0074] FIG. 7 shows an exemplary laser apparatus according to this disclosure, wherein the cavity structure comprises a surface grating.

[0075] FIG. 8 shows an exemplary laser apparatus according to this disclosure, wherein the cavity structure comprises the surface grating and has a non-circular symmetric shape.

[0076] FIG. 9 shows a method for operating a laser apparatus, according to this disclosure.

[0077] DETAILED DESCRIPTION OF EMBODIMENTS

[0078] FIG. 1 shows an exemplary embodiment of a laser apparatus 100 according to this disclosure. The laser apparatus 100 is suitable for optical communications, in particular, communications using a modulated laser signal to transmit information.

[0079] The laser apparatus 100 comprises a spin VCSEL 101 comprising a cavity structure 102. The cavity structure 102 comprises one or more controllable optical properties.

[0080] The optical properties comprise, for example and not as a limitation, a birefringence rate additionally or alternatively an effective dichroism rate.

[0081] The cavity structure 102 may comprise, or be formed by, one or more stacked components (not shown).

[0082] The spin VCSEL 101 is configured to receive an electrical current signal 103 comprising an amplitude modulation. The current amplitude modulation may comprise one or more time periods of a higher current amplitude and one or more time periods of a lower current amplitude. In this way, information may be encoded into the electrical current signal 103.

[0083] When the spin VCSEL 101 receives the electrical current signal 103 in the cavity structure 102 with the one or more controllable optical properties, the spin VCSEL 101 is configured to output a first laser signal 104.

[0084] The first laser signal 104 comprises a circular polarization modulation, which correlates with the amplitude modulation of the electrical current signal 103. In particular, a change of the current amplitude of the electrical current signal 103 may correlate with a change of a CPD of the first laser signal 104.

[0085] In addition, the first laser signal 104 may also comprise an intensity modulation that correlates with the amplitude modulation of the electrical current signal 103. Information encoded into the electrical current signal 103 can be encoded into the first laser signal 104 in this way, wherein a modulation bandwidth is increased over a conventional intensity-modulated VCSEL.

[0086] The one or more optical properties of the cavity structure 102 may be controlled to have specific value ranges.

[0087] In the above-described laser apparatus 100, an absolute value of the birefringence rate comprises any value between 25 GHz and 2000 GHz, and an absolute value of the dichroism rate comprises any value between 0 and 10 per nanosecond.

[0088] The absolute value of the birefringence rate may be higher than the conventional intensity resonance frequency of the device, but at least 25 GHz. It is noted that the absolute value of the birefringence rate is limited to realistic values that can be addressed with a typical spin-flip rate, which is 2000 GHz.

[0089] Thereby, the laser apparatus 100 can be operated close to a special operation point of the laser dynamics, for example and not as a limitation the polarization switching point. Said special type of operation point exhibits nonlinear dynamics and is not desired in the conventional operation of a laser, in particular in VCSELs. That is, conventional VCSELs are designed such that they can be operated far away from these special operating points. Thus, the spin-VCSEL 101 according to this disclosure can be tailored by controlling the optical properties of the cavity structure 102 (e.g., the birefringence rate and / or the dichroism rate) in the aforementioned ranges, such that at least one of these specific dynamic points is actually within the operating range of the laser apparatus 101.

[0090] In a preferred embodiment, the electrical current signal 103 further comprises a constant offset, and the absolute value of the dichroism rate is obtained based on the constant offset.

[0091] Further, in an embodiment, the optical properties of the cavity structure 102 can be controlled to achieve the desired range values for the birefringence rate and / or the effective dichroism rate so that the operating point of the laser apparatus 100 is obtained. To that end, the laser apparatus 101 is further configured to receive the electrical current signal 103 through an aperture, where the aperture comprises a non-circular symmetric shape.

[0092] The above-described components of the laser apparatus 100 can be considered as transmitterside components of the laser apparatus 100. The laser apparatus 100 may further comprise one or more receiver-side components, for example, the laser apparatus 100 may further comprise a receiver configured to receive the first laser signal 104, and to convert the first laser signal 104 back into an electrical signal.

[0093] The range of values for the one or more optical properties of the cavity structure 102 that achieve the desired operating point (or operating range) of the laser apparatus 100 have been determined in a multi-objective optimization approach according to this disclosure.

[0094] FIG. 2a) shows simulation results of modulations using random bit sequences for a conventional spin laser apparatus, which includes optical pumping for spin injection. The spin laser was modelled quantitatively by using the so-called spin-flip model. With this, it was shown that the polarization response offers a higher bandwidth than the intensity-modulation response when spin injection via continuous-wave pumping with a circularly polarized laser is applied.

[0095] The results of FIG. 2a), show a clearly opened eye in the eye diagram and confirms the possibility of data transmission. In the figure, the CPD label on the vertical axis describes the circular polarization degree. These results demonstrated that continuous-wave pumping injects spin-polarized carriers into the VCSEL, which finally enables the coupling between the current carrying the data and the polarization of the laser signal. Hence, it was implicitly assumed that a pump laser is required.

[0096] In the present disclosure, the multi-objective optimization algorithm may be applied to the spinflip model. The algorithm optimizes the vertical and horizontal eye opening, marked V and H in FIG. 2b), while minimizing the absolute value of continuous-wave pumping (hereinafter denoted as cwpol). The algorithm is enabled to vary the design parameters of the spin-flip model within a realistic value range for the laser apparatus 101 in order to achieve this. These parameters include for example one or more of

[0097] • Linear dichroism

[0098] • Photon-decay rate

[0099] • Spin-decay rate

[0100] • Linewidth enhancement factor

[0101] • Linear birefringence (to be maximized)

[0102] • Bias point (to be minimized)

[0103] • Spin-injection degree cwpol (to be minimized)

[0104] By using the multi-objective optimization algorithm according to this disclosure, it is noted that that there is a parameter range in which intensity and polarization dynamics are coupled. This parameter range is located close to a polarization- switching point of a VCSEL in a region of bistable polarization behavior.

[0105] This allows the operation of the VCSEL as a spin-VCSEL 101 with an accompanying extension of the modulation bandwidth, even without additional spin-injection (e.g., with cwpol = 0). Thus, the bandwidth extension occurs due to an optimal VCSEL design and not due to external pumping as in conventional spin-VCSELs.

[0106] FIG. 3a) and FIG. 3b) show simulation results in which a random bit sequence was "transmitted" with a laser of a particular parameter set, where the combination of spin-injection (e.g., cwpol), a bias current of the spin laser (denoted as Ibias, in multiples of a threshold) and the birefringence rate was varied with the optimization goals of a large eye opening, a low bias (Ibias low) and a low spin-injection (cwpol low).

[0107] For an appropriate combination of birefringence rate and bias, the spin-injection cwpol can be omitted and data transmission is still feasible (e.g. the eye was still open, where negative values for the eye opening are best values, which results from a fitness function design of an automated result evaluation).

[0108] FIG. 3a) and FIG. 3b) show the result space. Each dot represents a random bit sequence transmission and eye analysis of the polarization signal with the corresponding parameters, where grey dots with negative eye-opening values did result in error free data transmission. Grey dots with positive eye-opening values did result in very low bit error rate data transmission. Black dots did not represent an optimal combination of the design parameters and might not result in error-free data transmission in the polarization of the laser, respectively. The results in FIG. 3a) and FIG. 3b) reveal that there is error-free data-transmission at cwpol=0. As the fitness function analyzes polarization only, the coupling between intensity and polarization dynamics is thus proven even without spin-injection for a particular but not narrow parameter range.

[0109] Conventional VCSELs are typically not operated in this regime and, hence, are not optimized or even useable as spin lasers without optical spin-injection and an additional pumping laser.

[0110] FIG. 4 shows an exemplary embodiment for a laser apparatus 100 according to this disclosure, which builds on the laser apparatus 100 shown in FIG. 1. Same elements are labelled with the same reference signs.

[0111] Hereinafter, only the differences between Fig. 1 and Fig. 4 are explained. In the embodiment of FIG. 4, the laser apparatus further comprises one or more optical components 401. The one or more optical components are configured to convert the first laser signal 104 into a second laser signal 402, which comprises an intensity modulation.

[0112] The one or more optical components 401 may be, for example, passive optical elements.

[0113] The intensity modulation of the second laser signal 402 correlates with the circular polarization modulation of the first laser signal 104. At the spin VCSEL 101, due to the coupling of the carrier-photon dynamics and the spin dynamics achieved by the one or more optical properties of the cavity structure 102 and by the received electrical current signal 103, polarization modulations of the emitted first laser light 104 are achieved. These polarization modulations have a higher bandwidth than conventional intensity-modulated VCSELs, owing to the fast spin dynamics. In this embodiment, thus, the polarization modulations are converted into intensity modulations of the second laser signal 402 with the one or more optical components 401.

[0114] FIG. 5 shows an exemplary laser apparatus 100 according to this disclosure, which builds on that of FIG. 4. Same elements are labelled with the same reference signs. Hereinafter, only the differences between Fig. 4 and Fig. 5 are explained.

[0115] In the embodiment according to Fig. 5, the laser apparatus 100 further comprises an optical fiber 501. The optical fiber is configured to receive the second laser signal 402 for transmitting it to a receiver.

[0116] The second laser signal 402 may be transmitted to a receiver via the optical fiber 501. This is analogous to a short-haul optical communication system with conventional VCSELs.

[0117] Thereby, a possible application scenario of the laser apparatus 100 of FIG. 5 is short-haul optical communication in data centers, e.g., for server-to- server communication. The laser apparatus 100 may in this case comprise three main components: the spin VCSEL 101 at the transmitter side, an optical fiber for transmission, and a receiver at the receiver side, e.g., a fast photodiode.

[0118] FIG. 6 shows an exemplary laser apparatus 100 according to this disclosure, which builds on that of FIG. 4. Same elements are labelled with the same reference signs. Hereinafter, only the differences between Fig. 4 and Fig. 6 are explained.

[0119] In the laser apparatus 100 according to FIG. 6, the cavity structure 102 comprises a non-circular symmetric shape. This is depicted in the inset of FIG. 6, where a top view of the cavity structure 102 is shown. For example and not as a limitation, the cavity structure 102 shown FIG. 6 has an elliptic shape, where a dimension of the cavity structure 102 in an x direction is different than a dimension in a y direction. Other non-symmetrical and non-circular shapes (in the top view) can be comprised.

[0120] The aforementioned non-circular shape refers to a top view of the cavity structure 102, e.g., its shape in two dimensions (2D). In three dimensions (3D) the cavity structure 102, thus, comprises a non-cylindrical shape.

[0121] The shape of the cavity structure 102 influences the optical properties of the entire cavity structure 102. The parameters range in the desired operation point of the laser apparatus 100, in particular the birefringence rate and / or the effective dichroism rate, can be controlled in the respective ranges disclosed above by choosing the shape of the cavity structure 102.

[0122] FIG. 6 depicts an exemplary implementation for the cavity structure 102. By way of example and not as a limitation, the cavity structure 102 may comprise two Bragg mirrors 603, 605 forming a cavity with embedded active zone 604, which provides the gain for lasing operation, e.g., via one or more quantum wells. Optionally, one or more additional layers 602 can be placed on top of the upper Bragg mirror 603, e.g., for the purpose of phase matching.

[0123] The exemplary embodiment of FIG. 6 enables to address the laser apparatus 100 parameters using a manufacturing technique that is well known and is thus easily adaptable. Further, this embodiment enables a completely integrated and compact approach, without the need for additional pumping.

[0124] FIG. 7 shows an exemplary laser apparatus 100 according to this disclosure, which builds on that of FIG. 4. Same elements are labelled with the same reference signs. Hereinafter, only the differences between Fig. 4 and Fig. 7 are explained.

[0125] In the embodiment of FIG. 7, the cavity structure 102 comprises a surface grating 601. The surface grating 601 enables to control the birefringence rate and / or the dichroism rate of the cavity structure 102. Further, other effective laser properties of the laser apparatus 100 can be controlled by means of the surface grating 601. The cavity structure 102 may further comprise one or more components, exemplary the components 602-605. In this embodiment, the surface grating 601 can be placed on top of the upper Bragg mirror 603 and, optionally, one or more additional layers 602 can be placed in between.

[0126] Thereby, the VCSEL 101 properties (and accordingly the laser apparatus 100 properties) can be tuned in a way that the previously described range of operation is addressed.

[0127] Model simulations of the entire cavity structure 102 including the surface grating 601 can be performed by modifying the physical properties of the surface grating 601 (for example period length, duty cycle, valley depth) whilst taking into account the material parameters of each of the components 602 to 605 of the cavity structure 102. The modification is performed by the optimizing algorithm according to this disclosure and explained above, until the desired properties (values) of the birefringence rate and / or the dichroism rate are obtained.

[0128] The laser apparatus 100 according to FIG. 7 may further comprise the optical fiber 501 (not shown).

[0129] This embodiment enables to address the laser apparatus 100 parameters using a manufacturing technique that is well known and is thus easily adaptable. Further, this embodiment enables a completely integrated and compact approach, without the need for additional pumping.

[0130] FIG. 8 shows an exemplary laser apparatus 100 according to this disclosure, which builds on that of FIG. 6 and FIG. 7. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 6, FIG. 7 and FIG. 8 are explained.

[0131] In the embodiment of FIG. 8, the cavity structure 102 comprises the surface grating 601 and further comprises a non-circular (in 2D) symmetric shape, as depicted in the inset of FIG. 8.

[0132] Thereby, the surface grating 601 and the shape of the cavity structure 102 are combined to achieve a better control of the birefringence rate and / or the dichroism rate of the cavity structure 102. Further, other effective laser properties of the laser apparatus 100 can be controlled by means of the surface grating 601 and the shape of the cavity structure 102. The laser apparatus 100 according to FIG. 8 may further comprise the optical fiber 501 (not shown).

[0133] This embodiment enables to address the laser apparatus 100 parameters using a manufacturing technique that is well known and is thus easily adaptable. Further, a completely integrated and compact approach can be achieved, without the need for additional pumping.

[0134] FIG. 9 shows a method 900 for operating a laser apparatus 100 according to this disclosure. As described above, the laser apparatus 100 comprises a spin VCSEL 101 comprising a cavity structure 102. The cavity structure 102 comprises one or more controllable optical properties, the optical properties comprising a birefringence rate and / or an effective dichroism rate.

[0135] The method 900 comprises a step 901 of providing an electrical current signal 103 comprising an amplitude modulation to the spin VCSEL 101.

[0136] The method 900 further comprises a step 902 of generating, with the spin VCSEL 101, a first laser signal 104 comprising a circular polarization modulation by converting the electrical current signal 103 in the cavity structure 102 with the one or more controllable optical properties, wherein the circular polarization modulation of the first laser signal 105 correlates with the amplitude modulation of the electrical current signal 104.

[0137] With the solutions of this disclosure, the following main advantages can be achieved:

[0138] • Three desirable properties of modulators are combined into a single system: (1) a very high modulation bandwidth (»100 GHz), (2) a fully integrated system (e.g. compact, cheap, and easy to manufacture), and (3) full electrical control of the modulation.

[0139] • Higher bandwidth of polarization modulations in a spin VCSEL 101, to be used for data transfer in optical short-haul communication, compared to standard intensity-modulated VCSELs. The polarization modulations show higher bandwidth than conventional intensity modulations, due to a higher resonance frequency for the spin-dynamics. This resonance frequency can be controlled solely via the optical properties of the cavity structure, namely the birefringence rate and the dichroism rate. Standard contact technology for the electrical contacts of the spin VCSEL 101 and roomtemperature operations are possible.

[0140] • Short-haul optical communication, e.g., in data centers for data transmission between servers / server blades, can be achieved replacing conventional VCSELs.

[0141] • Depending on the power of the spin VCSELs, the use in metropolitan networks, last-mile application / passive optical networks can also be envisaged. The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A laser apparatus (100) comprising: a spin vertical- cavity surface-emitting laser, spin VCSEL, (101) comprising a cavity structure (102); wherein the cavity structure (102) comprises one or more controllable optical properties, the optical properties comprising a birefringence rate and / or an effective dichroism rate; wherein the spin VCSEL (101) is configured to: receive an electrical current signal (103) comprising an amplitude modulation; and generate a first laser signal (104) by converting the received electrical current signal (103) in the cavity structure (102) with the one or more controllable optical properties, the first laser signal (104) comprising a circular polarization modulation; and wherein the circular polarization modulation of the first laser signal (104) correlates with the amplitude modulation of the electrical current signal (103).

2. The laser apparatus (100) according to claim 1, wherein an absolute value of the birefringence rate comprises any value between 25 GHz and 2000 GHz.

3. The laser apparatus (100) according to claims 1 or 2, wherein an absolute value of the dichroism rate comprises any value between 0 and 10 per nanosecond.

4. The laser apparatus (100) according to one of the preceding claims, wherein the electrical current signal (103) further comprises a constant offset; and wherein the absolute value of the dichroism rate is obtained based on the constant offset.

5. The laser apparatus (100) according to one of the preceding claims, wherein the amplitude modulation of the electrical current signal (103) comprises at least a higher current amplitude and a lower current amplitude.

6. The laser apparatus (100) according to claim 5, wherein a change of the amplitude of the electrical current signal (103) correlates with a change of a circular polarization degree of the first laser signal (104).

7. The laser apparatus (100) according to one of the preceding claims, wherein the first laser signal (104) further comprises an intensity modulation that correlates with the amplitude modulation of the electrical current signal (103).

8. The laser apparatus (100) according to one of the preceding claims, further comprising: one or more optical components (401) configured to convert the first laser signal (104) into a second laser signal (402) comprising an intensity modulation, wherein the intensity modulation of the second laser signal (402) correlates with the circular polarization modulation of the first laser signal (104).

9. The laser apparatus (100) according to one of the preceding claims, further comprising an optical fiber (501) configured to receive the first laser signal (104) or the second laser signal (402) for transmitting it to a receiver.

10. The laser apparatus (100) according to one of the preceding claims, further comprising a receiver configured to receive the first laser signal (104) or the second laser signal (402), and to convert the first laser signal (104) or the second laser signal (402) into an electrical signal.

11. The laser apparatus (100) according to one of the claims 1 to 10, wherein the cavity structure (102) comprises a surface grating (601).

12. The laser apparatus (100) according to one of the claims 1 to 10, wherein the cavity structure (102) has a non-circular symmetric shape.

13. The laser apparatus (100) according to one of the claims 1 to 10, further configured to receive the electrical current signal (103) through an aperture, wherein the aperture has a noncircular symmetric shape.

14. The laser apparatus (100) according to one of the claims 1 to 13, wherein the cavity structure (102) comprises the surface grating (601) and has a non-circular symmetric shape.

15. A method (800) for operating a laser apparatus (100) comprising a spin vertical-cavity surface-emitting laser, spin VCSEL, the spin VCSEL (101) comprising a cavity structure (102)comprising one or more controllable optical properties, the optical properties comprising a birefringence rate and / or an effective dichroism rate, and the method comprising: providing (801) an electrical current signal (103) comprising an amplitude modulation to the spin VCSEL (101); and generating (802) a first laser signal (104) having a circular polarization modulation by converting the electrical current signal (103) in the cavity structure (102) with the one or more controllable optical properties; wherein the circular polarization modulation of the first laser signal (104) correlates with the amplitude modulation of the electrical current signal (103).

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