FMCW LIDAR laser system and operating method for laser system

Abstract

In one embodiment, the laser system (1) comprises a semiconductor laser (2) which is designed to emit light in continuous wave operation at angular frequencies w which are different from one another. n The laser system (1) further comprises a tuning device (3) configured to periodically vary the angular frequency w n , so that the change (Δw) of each angular frequency in angular frequency wn is the value of the related adjacent angular frequency w n The detector (4) has an upper frequency limit, which is at most one-tenth of the smallest mode spacing in the mode spacing (D). The beam splitter (5) is designed to guide the M modes to the detector (4) on the one hand and to the object (6) on the other hand, so that the detector (4) is also designed to detect, for each of the M modes, the portion of the laser radiation (R) reflected by the object (6) and also the portion of the laser radiation (R) optically directly coming from the semiconductor laser (3).

Description

Technical Field

[0001] A laser system is specified. Furthermore, an operating method for a laser system is specified. Background Art

[0002] Publications US 2018 / 0210068 A1, US 2019 / 0302268 A1 and US 2019 / 0317219 A1 relate to FMCW lidar systems. FMCW stands for Frequency Modulated Continuous Wave, i.e. frequency modulated continuous wave operation. Lidar stands for Light Detection and Ranging, i.e. optical distance measurement and speed measurement. Summary of the invention

[0003] The object to be achieved is to provide a laser system having a high optical output power.

[0004] The object is achieved, inter alia, by a laser system and by an operating method having the features according to exemplary embodiments of the invention. Advantageous developments are the subject matter of exemplary embodiments of the invention.

[0005] According to at least one embodiment, the laser system comprises one or more semiconductor lasers. At least one semiconductor laser is configured to emit laser radiation. The semiconductor laser is in particular a continuous wave laser. The term “continuous wave laser” in this context does not exclude that the laser is switched off for a specified short time, for example between individual frequency ramps.

[0006] According to at least one embodiment, the semiconductor laser emits laser radiation in M ​​modes. The M modes have angular frequencies w that are different from one another in pairs. n and thus have different wavelengths. The number of modes M is at least two. The parameter n can assume any integer value between 1 and M, including the boundary values.

[0007] According to at least one embodiment, the laser system comprises a tuning device. The tuning device is configured to vary the angular frequency w preferably periodically. n That is, the angular frequency w n Each angular frequency in is variable. Preferably, all M modes and thus all angular frequencies w n change together and in parallel with each other. n The change in the adjacent angular frequency w is preferably related to n The mode spacing between them is at most 2 or 5 or 10 or 50 times smaller. That is, the angular frequency w n The change in is small relative to the associated mode spacing.

[0008] According to at least one embodiment, the laser system comprises one or more detectors. The at least one detector is in particular a detector diode, for example a photodiode. The detector can be single-channel or also multi-channel.

[0009] According to at least one embodiment, the upper frequency limit of the detector is the angular frequency w n The minimum mode spacing among the mode spacings is at most 5 or 10 or 100 or 500 times smaller than that of the minimum mode spacing. That is, the detector is relatively slow and has a relatively small bandwidth.

[0010] According to at least one embodiment, the laser system comprises a beam splitter. The beam splitter is designed to guide the M modes of the laser radiation, on the one hand, to the detector and on the other hand to the object to be detected. The detector is thereby also designed to detect, for each of the M modes, the portion of the laser radiation reflected by the object and also the portion of the laser radiation optically directly coming from the at least one semiconductor laser. The object is not a component of the laser system. For example, the object is a traffic participant such as a motor vehicle or a pedestrian.

[0011] Optically directly from a semiconductor laser means, for example, that the relevant portion of the laser radiation does not undergo a wavelength change and is processed in particular only with optically passive components such as beam splitters, mirrors and / or lenses, or optionally with a tuning device arranged in the relevant beam path as the only optically active component.

[0012] In at least one embodiment, the laser system comprises a semiconductor laser which is designed to emit light in continuous wave operation at angular frequencies w which are different from one another. n The laser radiation is emitted in M ​​modes, where 2≤M and where Furthermore, the laser system comprises a tuning device which is designed to vary the angular frequency w n , where the angular frequency w n The change in each angular frequency is related to the adjacent angular frequency w n The detector of the laser system has an upper frequency limit, which is at most one tenth of the smallest mode spacing of the mode spacings. The beam splitter of the laser system is designed to guide the M modes of the laser radiation to the detector on the one hand and to the object on the other hand, so that the detector is also designed to detect, for each of the M modes, the proportion of the laser radiation reflected by the object and also the proportion of the laser radiation optically directly coming from the semiconductor laser.

[0013] Typically, FMCW lidar systems with single-mode lasers as light sources require optical output powers of several hundred milliwatts (mW), depending on the targeted distance, for example at a distance of about 200 m. Such single-mode laser diodes are not available today, since typical DFB laser diodes and DBR laser diodes in ECL implementations only emit about 100 mW. DFB stands for distributed feedback, DBR stands for distributed reflector and ECL stands for external cavity laser. In contrast, solutions based on fiber lasers are very expensive compared to individual laser diodes. This applies in particular to EDFA and SOA. Here, EDFA stands for erbium-doped fiber amplifier and SOA stands for semiconductor-based optical amplifier.

[0014] The laser system described here provides a cost-effective solution for using multimode lasers with high efficiency in FMCW lidar systems, wherein the number of emitted longitudinal modes is at least two. This means, for example, that higher-order gratings can be used, which are more cost-effective to produce due to the required lower structural resolution, and / or that complex temperature control can be omitted. In addition, such multimode laser diodes are more efficient and can also be operated in parallel in a single system.

[0015] Therefore, a laser diode is proposed in a laser system, which emits in a plurality of longitudinal modes, i.e. at different angular frequencies. The laser system does not require a grating which is complex to produce, such as is required, for example, for a DFB laser or a DBR laser. Alternatively, a higher-order grating with a larger structural size can be used, since such a grating is more cost-effective.

[0016] Such multimode laser diodes are scalable in their length in order to achieve the desired coherence. For example, with laser diode lengths between 5 mm and 10 mm, coherence lengths of less than 1 MHz or less than 500 kHz are achieved for each individual mode, compared to a comparable DFB-ECL, while the total power is higher. A frequency change of the wavelength is preferably applied simultaneously to all M longitudinal modes. In a coherent detector, the different modes do not mix here, since the spacing of the different modes relative to one another is greater than the maximum frequency modulation. For example, the frequency modulation is at a maximum of 1 GHz and the spacing between the modes is more than 10 GHz in each case.

[0017] With the laser system described here, by using the semiconductor laser described here, high optical powers of much more than 100 mW can be achieved without additional amplifiers, making it possible to realize efficient FMCW lidar systems. The construction of the laser described here involves a solid-state construction, which does not require a cost-intensive fiber laser. Since no grating is required or only a higher-order grating is required, the manufacturing costs can be reduced.

[0018] Because the optical losses at the grating are eliminated or at least significantly reduced, the semiconductor laser and thus the laser system can operate more efficiently. In addition, the laser system can be used in a wide temperature range. Therefore, in general, an efficient light source can be achieved by the semiconductor laser in the FMCW laser radar system.

[0019] According to at least one embodiment, the laser system is a frequency-modulated continuous wave lidar system, so that the detector is set up to detect angular frequency shifts according to M modes, wherein the angular frequency shifts occur when the laser radiation is reflected at the moving object. As a result, the distance and / or radial velocity of the object relative to the laser system can be determined.

[0020] According to at least one embodiment, the resonator of the semiconductor laser has a geometric resonator length of at least 4 mm or 5 mm or 6 mm. Alternatively or additionally, the geometric resonator length is at most 12 mm or 10 mm. The optical resonator length is obtained by multiplying the geometric resonator length by the relevant refractive index. In the case of semiconductor lasers based on the material system GaAs, the refractive index is about 3.2 in the relevant wavelength range of about 1 μm to 1.5 μm.

[0021] According to at least one embodiment, the geometric resonator length of the semiconductor laser is defined by the edges of the semiconductor laser. The resonator formed by the semiconductor laser itself is in particular the only resonator in the laser system. If a plurality of semiconductor lasers are present in the laser system, each semiconductor body of the semiconductor laser preferably forms its own resonator without any further resonators.

[0022] According to at least one embodiment, the laser system comprises a mode limiting device. The mode limiting device is designed to limit M to at most 10 or at most 5. That is to say, the following applies: 2≤M≤5 or 2≤M≤10.

[0023] According to at least one embodiment, the mode confinement device is formed by a higher-order diffraction grating and / or by an optically narrowband-effective coating. The diffraction grating is in particular a second-order, third-order or fourth-order grating. A second-order grating means, for example, that the grating itself is designed for a first-order wavelength of 1800 nm, wherein the laser radiation is approximately 900 nm.

[0024] According to at least one embodiment, the mode limiting device is integrated in or at the semiconductor laser. That is, the semiconductor laser and the mode limiting device are constructed in one piece. The semiconductor laser is, for example, a DFB laser with a higher-order grating structure. It is also possible that the edges of the semiconductor laser are provided with an optical coating or multiple coatings that correspondingly play a mode limiting role. That is, there is no external cavity or resonator path outside the semiconductor laser that can accommodate a mode limiting device such as a grating.

[0025] According to at least one embodiment, the semiconductor laser or the laser system has no mode limiting device. That is, in the resonator for the laser radiation, in the semiconductor laser or also outside the semiconductor laser, no mode limiting device is installed. In this case, it is particularly suitable that there are at least six or 11 modes in the mode. Alternatively or additionally, the number of modes M is at most 30 or 20 or 15. That is, for example, 6≤M≤20 or 11≤M≤30 applies.

[0026] According to at least one embodiment, the tuning device is partially or completely integrated in the semiconductor laser. In this case, the tuning device is designed in particular to change the operating current intensity. n The required change in the operating current intensity of at most 1% or at most 0.2% is sufficient. That is, with an already moderate change in the operating current intensity, it is possible to achieve all angular frequencies w n The required amount of change.

[0027] According to at least one embodiment, the tuning device is completely outside the semiconductor laser. In this case, the tuning device is implemented, for example, by an acousto-optical modulator, AOM for short, or by a Mach-Zehnder structure.

[0028] According to at least one embodiment, the mode spacing is at least 5 GHz or 10 GHz or 20 GHz, respectively. Alternatively or additionally, the mode spacing is less than 0.9 THz or 0.7 THz or 0.5 THz.

[0029] According to at least one embodiment, the angular frequency w n The variation of each angular frequency in is at least 0.2 GHz or 0.4 GHz, respectively. Alternatively or additionally, the variation is at most 4 GHz or 2 GHz or 1 GHz.

[0030] According to at least one embodiment, the M modes each have a mode width of at most 5 MHz or 1 MHz or 0.6 MHz. That is, the M modes are relatively narrow in terms of frequency spectrum. It is possible that the mode width is at least 10 kHz or 100 kHz or 0.2 MHz, respectively.

[0031] According to at least one embodiment, the intermediate wavelength of the laser radiation is at least 850 nm or 905 nm. Alternatively or additionally, the intermediate wavelength is at most 1600 nm or 1550 nm. In particular, the intermediate wavelength is between 905 nm and 970 nm, inclusive, or in the range of 1500 nm to 1550 nm, inclusive.

[0032] According to at least one embodiment, the temporal variation of the intermediate wavelength is the angular frequency w caused by the tuning device. n The maximum change over time is 10 3 or 10 4 or 10 6 This means that the wavelength drift of the intermediate wavelength is significantly smaller than a targeted tuning by means of a tuning device. Therefore, the relatively slow drift of the intermediate wavelength does not affect or does not significantly affect the measurement accuracy of the laser system, in particular the measurement accuracy with regard to the velocity measurement of objects that partially reflect the laser radiation.

[0033] According to at least one embodiment, the relative strengths of the M modes relative to one another fluctuate during a tuning cycle of the tuning device by at most 10% or 5% or 1% or 0.2%. That is, during the tuning cycle, the strengths of the M modes relative to one another are approximately constant. Thereby, in particular, fluctuations in the strengths of the M modes relative to one another do not have an influence or a significant influence on the speed measurement of the object.

[0034] According to at least one embodiment, the semiconductor laser comprises a semiconductor layer sequence. The semiconductor layer sequence is preferably based on a III-V compound semiconductor material. The semiconductor material is, for example, a nitride compound semiconductor material such as Al n In 1-n-m Ga m N or phosphide compound semiconductor materials such as Al n In 1-n-m Ga m P or also involves arsenide compound semiconductor materials such as Al n In 1-n-m Ga m As or Al n Ga m In 1-n-m As k P 1-k, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n + m ≤ 1 respectively, and 0 ≤ k < 1. For example, here 0 < n ≤ 0.8, 0.4 ≤ m < 1, n + m ≤ 0.95 and / or 0 < k ≤ 0.5 apply to at least one layer or to all layers of the semiconductor layer sequence. Here, the semiconductor layer sequence can have doping materials and additional components. For simplicity, however, only the main components of the crystal grating of the semiconductor layer sequence are indicated, namely Al, As, Ga, In, N or P, even if the main components can be partially replaced and / or supplemented by a small amount of other materials. Preferably, the semiconductor layer sequence is based on the material system AlInGaAs.

[0035] Furthermore, the semiconductor layer sequence preferably has exactly one active region which is configured to generate laser radiation, in particular by means of electroluminescence. The active layer particularly includes a multi-quantum well structure, abbreviated as MQW.

[0036] Overall, the laser radiation preferably has a spectral width of preferably at most 1 nm or 5 nm or 0.2 nm, in particular as the full width at half maximum, abbreviated as FWHM, over all M modes.

[0037] According to at least one embodiment, the laser system does not have an additional optical amplification component which is configured to re-amplify the laser radiation emitted by the semiconductor laser. That is, as an optically active component, the laser system preferably only has a semiconductor laser, a tuning device and a detector and does not have other intensity-changing or wavelength-changing active components. Thereby, the laser system can be constructed compactly and cost-effectively.

[0038] According to at least one embodiment, the laser system does not have active thermal stabilization. It is not excluded that the laser system is placed on a heat sink or that the laser system is roughly temperature-controlled. Rough temperature control means, for example, that the temperature of the semiconductor laser and / or the laser system is stabilized to 5° or higher or to 10° or higher and is not stabilized to 1 / 10° as is partly common for DFB lasers.

[0039] According to at least one embodiment, the laser system further includes optical focusing optics. The optical focusing optics is configured to focus the fraction of the laser radiation of the M modes that is reflected back towards the laser system at the object and to guide it to the detector. Here, the optical focusing optics is configured to process all M modes identically. That is, the optical focusing optics does not have wavelength-selective optical elements such as diffraction gratings or prisms.

[0040] Furthermore, a method for operating a laser system is proposed. In particular, the laser system is operated using the method as described in conjunction with one or more of the above embodiments. Features of the operating method are therefore also disclosed for the laser system, and vice versa.

[0041] In at least one embodiment, the operating method comprises at least the following steps, in particular in the order described:

[0042] - Provide laser systems, and

[0043] - operating the semiconductor laser, in particular energizing the semiconductor laser, so that in continuous wave operation the M modes of the laser radiation are each guided by the beam splitter on the one hand to the detector and on the other hand to the object, so that the detector receives for each of the M modes the portion of the laser radiation reflected by the object and also the portion of the laser radiation optically directly coming from the semiconductor laser. In this case, operating the semiconductor laser or energizing the semiconductor laser particularly preferably takes place in continuous wave mode.

[0044] According to at least one embodiment, for all M modes, the portion of the laser radiation reflected by the object has an intensity I n,R And the optical fraction coming directly from the semiconductor laser has an intensity I n , where n takes any integer value between 1 and M, including the boundary values. n and I n,R In this case, they are preferably respectively related to one another.

[0045] For the detector signal S at the detector as a function of time preferably applies:

[0046]

[0047] In this case, x denotes the angular frequency shift caused by the tuning device, ie the frequency difference between the local oscillator and the signal reflected by the object.

[0048] In the above formula, the Doppler shift is not taken into account. Optionally, the Doppler shift can also be detected as an additional term. For particularly simple distance measurements, and optionally speed measurements derived therefrom, however, the Doppler shift is preferably not taken into account.

[0049] The laser system described here is used, for example, as a laser radar in a vehicle such as an automobile. Correspondingly, as described in conjunction with one or more of the above embodiments, the invention described here also relates to a vehicle, in particular an automobile, comprising a laser system. The features of the laser system are therefore also disclosed for the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The laser system described here and the operating method described here are explained in detail below based on exemplary embodiments with reference to the drawings. The same reference numerals here describe the same elements in the individual figures. However, the relationships that are in proportion are not shown here, but rather the individual elements may be shown exaggeratedly for a better understanding.

[0051] The accompanying drawings show:

[0052] Figure 1 A schematic diagram showing an exemplary embodiment of an operating method described herein for a laser system described herein,

[0053] Figure 2 A schematic diagram showing the time profile of the wavelength for the operating method described here,

[0054] Figure 3 and Figure 4 A schematic cross-sectional view of a semiconductor laser for use in an embodiment of a laser system described herein,

[0055] Figure 5 shows a schematic wavelength dependency of the reflectivity of a cladding of a semiconductor laser for the laser system described here,

[0056] Figures 6 to 9 a diagram showing intensity versus wavelength for an exemplary emission spectrum of a semiconductor laser for use in the laser system described herein, and

[0057] Fig.10 Schematic diagram showing the time dependence of the signal at a detector for the laser system described herein. DETAILED DESCRIPTION

[0058] exist Figure 1 The operating method for a laser system 1 is illustrated in FIG. In the laser system, a semiconductor laser 2 is used as a source for laser radiation R. The laser radiation R comprises a plurality of modes of different wavelengths emitted simultaneously. That is, the laser radiation R consists of different angular frequencies w n of radiation composition.

[0059] A beam splitter 5 is arranged downstream of the semiconductor laser 2. A major portion of the laser radiation R passes through the beam splitter 5. The laser radiation R passing through the beam splitter 5 is guided to an object 6 and a relatively small portion is reflected by the object 6 back toward the laser system.

[0060] The reflected radiation is collimated by means of a light converging optical device 8, for example formed by a lens system. The reflected radiation component is guided to the detector 4 via a mirror 92 and a lens 91. The detector 4 is preferably a detector diode, in particular a photodiode. The detector 4 is preferably single-channel, but can also be multi-channel.

[0061] Likewise, a significantly smaller portion of the laser radiation R reflected at the beam splitter 5 and likewise guided via a plurality of mirrors 92 and lenses 91 reaches the detector 4 . This radiation portion thus reaches the detector 4 optically directly from the semiconductor laser 2 .

[0062] according to Figure 1 A tuning device 3 is arranged outside the semiconductor laser 2 and downstream of the beam splitter 5. By means of the tuning device 3, the modal periodicity of the laser radiation R can be easily changed in terms of its frequency. Figure 1 In contrast to the illustration of FIG. 2 , the tuning device 3 can also be integrated monolithically in the semiconductor laser 2 .

[0063] exist Figure 1 The beam paths in the laser system 1 illustrated in FIG. 1 are purely exemplary. For example, it is possible that the portion of the laser radiation R reflected by the beam splitter 5 is a larger radiation portion and is directed to the object 6 and that no radiation portion is directed through the beam splitter 5. Furthermore, the tuning device 3 can also be arranged upstream of the beam splitter 5 if it is not integrated in the semiconductor laser 2.

[0064] The laser radiation R reflected and focused by the object 6 is mixed at the detector 4 with the radiation optically coming directly from the semiconductor laser 2. This results in a signal S at the detector 4, the time profile of which can provide information about the distance of the object 6 relative to the laser system 1. An exemplary profile of the signal S over time t is shown in Fig.10 It is explained in.

[0065] In particular, if the Doppler frequency shift is additionally detected when the laser radiation is reflected at the object 6, the relative speed of the object 6 relative to the laser system 1 can be determined. However, the relative speed can also be calculated from two short-time successive distance measurements.

[0066] The laser radiation R, after having passed through the tuning device 3, therefore has a frequency f PO , which is equal to the frequency f of the laser radiation emitted by the semiconductor laser 2 LO and due to the tuning device 3 called f OFFSET The sum of the frequency changes: f PO =f LO +f OFFSET The frequency of the reflected light is f a The result is f a =f LO +f OFFSET +Δf, where Δf is the frequency change due to the motion of the object 6.

[0067] With the semiconductor laser 2 described here, an FMCW laser radar system with a range of more than 200 m with respect to the focused beam can be realized. For this purpose, an optical power in the range of more than 100 mW to about 1 W is required. However, common single-mode lasers, in particular edge emitters such as DFB lasers, DBR lasers and ECLs are usually limited to a few tens of mW to 100 mW. In contrast, alternative solutions with higher output lasers such as fiber lasers, in particular EDFA lasers, are relatively costly.

[0068] Compared to conventional ECL single-mode lasers with a corresponding coherence length and a low optical power of only a few tens of mW, a longitudinal multimode operating semiconductor laser 2 is therefore currently used. The semiconductor laser 2 preferably does not have a complex DFB grating structure or DBR grating structure or in any case has a higher-order grating that can be produced more cost-effectively, selects only a few modes and can be realized more simply.

[0069] Here, the longitudinal mode spacing is much greater than the frequency modulation of the FMCW system. For a semiconductor laser 2 based on the material system GaAs, this means that, with a frequency spacing D=C0 / (2L0 / N) of the modes relative to one another (where L0 / N is equal to the effective resonator length of the laser diode) and for a system with a wavelength variation Δw of about 1 GHz and assuming that the mode spacing D is much greater than 5 GHz, the maximum geometrical cavity length of the semiconductor laser 2 is less than about 10 mm at a refractive index N of about 3.2. With such a cavity length, high amplification and small line width per mode in the sub-MHz range can already be achieved.

[0070] By dispensing with the high-precision grating, the laser can be manufactured more cost-effectively. The lower losses due to the absence of the grating allow for a higher laser output power and thus the optional dispensing with additional optical amplifier components that may still be included in the laser system.

[0071] In this case, either the laser is directly frequency modulated, which affects all modes identically. Alternatively, as in Figure 1 As explained in , indirect frequency modulation is performed by means of an external tuning device 3. This modulation also applies equally to all modes. In this case, the frequency modulation Δw is much smaller than the mode spacing D.

[0072] The following mixing occurs in the detector 4, calculated for the example of only two laser modes, ie M=2:

[0073] In the following, w1 represents the frequency of the first mode and w2 represents the frequency of the second mode. x represents the shift of the frequency due to the frequency modulation. E1 and E3 are the powers of the modes in the detector 4, i.e. the power on the direct path or the power of the local oscillator. E2 and E4 are the powers of the modes reflected by the object 6.

[0074] For the signal S at the detector 4 we have:

[0075] S~[E1sin(w1t)+E2sin((w1+x)t)+E3sin(w2t)+E4sin((w2+x)t)] 2

[0076] In this case, E1 and E2 on the one hand and E3 and E4 on the other hand are usually related to one another. In this case, E1 and E2 are usually independent of E3 and E4.

[0077] This gives the signal S as a dependent term:

[0078] - squared and total frequencies, ie high THz or nm, are not detected in the preferably slow detector and thus provide a proportion of 0;

[0079] -S~E1E2cos(xt)+E3E4cos(xt), where the mixed products between E1-E3, E1-E4, E2-E3 and E2-E4 are also too fast for the detector because the difference corresponds approximately to the mode spacing D, which is much larger than the bandwidth of the detector 4.

[0080] In contrast to systems with a longitudinal signal mode of S~E1E2cos(xt), additional signal strengths can be achieved with the semiconductor lasers described here, in particular because lossy mounting of mode-selective gratings is not required. Furthermore, no thermal stabilization is required.

[0081] Furthermore, laser diodes can be used in a wide wavelength range, in particular GaAs semiconductor lasers are available in the entire wavelength range, in particular the range of approximately 900 nm to 1000 nm.

[0082] exist Figure 2 The variation of the wavelength λ of the mode over the time t is schematically illustrated in FIG. 1 , see the solid line for the laser radiation R as emitted by the laser system 1 and see the dashed line for the reflected laser radiation returned by the object. It can be seen that the wavelength variation Δw due to the tuning device 3 is performed periodically. No additional small angular frequency shift Δf is performed due to the movement of the object 6.

[0083] Replace as in Figure 2The ramp-shaped frequency modulation with small transmission pauses explained by way of example in the example may also be a continuous sinusoidal or triangular frequency modulation.

[0084] exist Figure 3 2 is an example of a semiconductor laser 2 for the laser system 1 described here. The semiconductor laser 2 comprises a semiconductor layer sequence 21, in which an active region 22 is present. A mode confinement device 7 is installed at or in the semiconductor layer sequence 21. The mode confinement device 7 is a higher-order grating, which can be produced more cost-effectively, since only relatively large structures are produced.

[0085] As in Figure 4 The exemplary semiconductor laser 2 illustrated in FIG. 1 also has a semiconductor layer sequence 21 in which an active region (not shown) is present. The geometric length of the semiconductor layer sequence 21 along the resonator and thus along the emission direction is in the range of about 8 mm. For the change of the emission wavelength, an electrode 94 is installed on the semiconductor layer sequence 21. Via the electrode 94, the operating current is variable, so that the change Δw of the wavelength of the running mode is achieved.

[0086] Optionally, it is possible that an optically effective coating 93 is present at the edges of the semiconductor layer sequence 21. The coating 93 can provide different curves of the reflectivity r as a function of the wavelength λ, see Figure 5 Via this optional coating, a mode confined device can be realized.

[0087] In addition Figure 4 It is stated that the semiconductor laser 2 is mounted on a carrier 95 , wherein the carrier 95 is a heat sink or a relatively imprecisely thermally regulated carrier.

[0088] Alternatively, as also in all other exemplary embodiments, the semiconductor laser 2 itself can act as a beam splitter 5, as in Figure 4 That is, the laser radiation R can be emitted at two edges of the semiconductor layer sequence 21 with different intensities. The side that emits the most radiation component is directed toward the object 6 and the much smaller component is directed toward the detector 4. Figure 4 Not drawn in.

[0089] exist Figures 6 to 9 , different exemplary spectra of laser radiation R as generated by a semiconductor laser 2 are shown. The laser radiation R is composed of a plurality of modes. The M modes have angular frequencies w1 to w M The mode spacing D is, for example, higher than 10 GHz, since the wavelength variation Δw of the tuning device 3 is, for example, in the range around 1 GHz.

[0090] exist Figure 6As can be seen from FIG. 1 , the laser radiation R has only two modes. The two modes preferably have similar intensities. Correspondingly, according to Figure 7 There are four modes. The intensity of the mode can be optionally changed.

[0091] exist Figure 8 and Fig. 9 , wherein the intensity of the individual modes changes over time in subranges. The subranges are marked by dashed lines. Such intensity fluctuations occur in particular if there is no mode limiting device and if there is a relatively large number M of modes. However, the accuracy of the laser system 1 is not impaired or is only slightly impaired by the intensity fluctuations, provided that such fluctuations in the intensity relationship occur on a relatively large time scale and thus proceed slowly, in particular with respect to the wavelength change Δw due to the tuning device 3.

[0092] Unless otherwise stated, the components shown in the figures are preferably in the order described relative to one another, in particular directly one after the other. Components not involved in the figures are preferably spaced apart from one another. If the lines are drawn parallel to one another, the associated surfaces are preferably also oriented parallel to one another. Furthermore, unless otherwise stated, the relative positions of the drawn components relative to one another are correctly presented in the figures.

[0093] The invention described here is not restricted to the description based on the exemplary embodiments. Rather, the invention comprises any novel feature and any combination of features, which in particular includes any combination of features in the claims, even if the feature or the combination itself is not explicitly specified in the claims or exemplary embodiments.

[0094] The claims claim priority from German patent application 102020104385.6, the disclosure content of which is hereby incorporated herein by reference.

[0095] Reference numerals list

[0096] 1 Laser system

[0097] 2 Semiconductor Laser

[0098] 21 Semiconductor layer sequence

[0099] 22 Active area

[0100] 3 Tuning equipment

[0101] 4 Detector

[0102] 5 Beam splitter

[0103] 6 Objects

[0104] 7-Mode Restricted Devices

[0105] 8 Light Converging Optics

[0106] 91 Lens

[0107] 92 Reflector

[0108] 93 Coating

[0109] 94 Electrodes

[0110] 95 bearing parts

[0111] D mode spacing (frequency spacing)

[0112] I. Intensity

[0113] L Resonator length

[0114] λ Wavelength

[0115] r Reflectivity

[0116] R Laser Radiation

[0117] S Signal at the detector

[0118] t time

[0119] w n Angular frequency of the mode of laser radiation

[0120] Δw The wavelength change through the tuning device

[0121] Δf is the angular frequency shift of the object

Claims

1. A laser system (1), comprising: - a semiconductor laser (2) which is designed to emit light in continuous-wave operation at angular frequencies w which are different from one another n The laser radiation (R) is emitted in the case of M modes, where 2≤M and where - a tuning device (3) designed to periodically vary the angular frequency w n , so that the angular frequency w n The change in each angular frequency (Δw) is related to the adjacent angular frequency w n at most one-half of the pattern spacing (D) between - a detector (4) having an upper limit frequency of at most one tenth of the smallest mode spacing among the mode spacings (D), and - a beam splitter (5) which is designed to guide the M modes of the laser radiation (R) on the one hand to the detector (4) and on the other hand to the object (6), so that the detector (4) is also designed to detect, for each of the M modes, the portion of the laser radiation (R) reflected by the object (6) and also the portion of the laser radiation (R) optically directly coming from the semiconductor laser (2).

2. The laser system (1) according to claim 1, The laser system is a frequency-modulated continuous-wave lidar system, so that the detector (4) is designed to detect an angular frequency shift (Δf) based on the M modes in order to determine the distance and / or radial velocity of the object (6) relative to the laser system (1), the angular frequency shift occurring when the laser radiation (R) is reflected from the object (6).

3. The laser system (1) according to claim 1 or 2, The resonator of the semiconductor laser (2) has a geometrical resonator length (L) of between 5 mm and 10 mm inclusive, The geometric resonator length (L) is defined by the edges of the semiconductor laser (2).

4. The laser system (1) according to claim 1 or 2, The laser system further comprises a mode confinement device (7) which is configured to confine M to at most 5, such that: 2≤M≤5 applies.

5. The laser system (1) according to claim 4, wherein the mode confinement device (7) comprises or is a higher order diffraction grating, The mode confinement device (7) is integrated into the semiconductor laser (2).

6. The laser system (1) according to claim 1 or 2, The semiconductor laser (2) does not have a mode confinement device (7), so that: 6≤M≤20 applies.

7. The laser system (1) according to claim 1 or 2, The tuning device (3) is at least partially integrated in or at the semiconductor laser.

8. The laser system (1) according to claim 7, The tuning device (3) is designed to change the operating current intensity of the semiconductor laser (2).

9. The laser system (1) according to claim 1 or 2, The tuning device (3) is located completely outside the semiconductor laser (2) and / or is spaced apart from the semiconductor laser (2).

10. The laser system (1) according to claim 1 or 2, in - the mode spacing (D) is respectively greater than 5 GHz and less than 0.9 THz, - the angular frequency w n Each angular frequency in is respectively between 0.2 GHz and 4 GHz, including the boundary value, due to the variation (Δw) of the tuning device (3), - the mode widths of the M modes are respectively less than 1 MHz, - the median wavelength of the laser radiation (R) is between 850 nm and 1600 nm, limit values ​​included, and - The variation of the intermediate wavelength over time is the angular frequency w n The variation of the variation (Δw) caused by the tuning device (3) over time is at most 10 3 One percent.

11. The laser system (1) according to claim 1 or 2, The relative strengths of the M modes with respect to each other fluctuate by at most 1% during a tuning cycle of the tuning device (3).

12. The laser system (1) according to claim 1 or 2, The semiconductor layer sequence (21) of the semiconductor laser (2) comprises exactly one active region (22).

13. The laser system (1) according to claim 1 or 2, The laser system has no additional optical amplification components which are designed to re-amplify the laser radiation (R) emitted by the semiconductor laser (2), and The laser system has no active thermal stabilization.

14. The laser system (1) according to claim 1 or 2, The laser system further comprises a light converging optical device (8) for the portion of the laser radiation (R) in the M modes that is reflected at the object (6) back to the laser system (1), The light concentrating optics (8) are configured to process all M modes identically.

15. An operating method for a laser system (1) according to any one of claims 1 to 14, the operating method comprising the following steps: - providing the laser system (1), - the semiconductor laser (2) is energized so that the beam splitter (5) in continuous wave operation guides the M modes of the laser radiation (R) on the one hand to the detector (4) and on the other hand to the object (6), so that the detector (4) receives for each of the M modes the portion of the laser radiation (R) reflected by the object (6) and also the portion of the laser radiation (R) optically directly coming from the semiconductor laser (2).

16. The method according to claim 15, For all The portion of the laser radiation (R) reflected by the object (6) has an intensity I n,R and the optical component directly coming from the semiconductor laser (2) has an intensity I n And the intensity I n and I n,R They are related to each other, where for the detector signal S at the detector (4) as a function of time t: Here x represents the angular frequency shift due to the tuning device (3).

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