LIDAR measuring device

Abstract

A LIDAR measuring device and a method for determining the speed of particles in a measuring volume includes a narrowband continuous wave laser light source (1), which emits light which is coupled into a measuring branch (3) and a reference branch (4). The light coupled into the measuring branch (3) is at least partially emitted by a transmitting device in the direction of the measuring volume such that the emitted light is at least partially scattered and/or reflected by the particles in the measuring volume. A part of the scattered and/or reflected light is then received by a receiver device and is coherently superimposed with the light leaving the reference branch (4), and the resulting light beam is directed onto a detector (6) to generate a detector signal characteristic for the resulting light beam. Finally, the speed of the particles in the measuring volume is determined in an evaluation unit (11) by taking into account the detector signal.

Claims

1. A LIDAR measuring device for determining the speed of particles in a measuring volume, comprising: a narrowband continuous wave laser light source (1) that emits light that is coupled into a measuring branch (3) and a reference branch (4); a transmitting device, wherein the light coupled into the measuring branch (3) is at least partially emitted by the transmitting device in a direction of the measuring volume in such a way that the emitted light is at least partially scattered and/or reflected by the particles in the measuring volume; a receiver device, wherein at least a part of the scattered and/or reflected light is received by the receiver device and is coherently superimposed with the light leaving the reference branch (4) to form a resulting light beam; a detector (6) to receive the resulting light beam and to generate a detector signal characteristic for the resulting light beam; an evaluation unit (11) to determine a speed of the particles in the measuring volume by taking into account the detector signal; a control device (13) to vary the frequency of the light emitted by the laser light source (1), wherein the evaluation unit (11) is configured to determine the speed of the particles in at least one measuring region of the measuring volume on the basis of a spectral analysis of the detector signal by taking into account a predefined frequency modulation, wherein the variation of the frequency of the light emitted by the laser light source (1) takes place based on a control signal generated by the control device (13), said control signal corresponding to a pseudo-noise signal caused by a predefined frequency function.

2. The LIDAR measuring device according to claim 1, wherein the control device (13) changes a current strength of the supply current for the laser light source (1) in order to vary the frequency of the emitted light.

3. The LIDAR measuring device according to claim 1, wherein the laser light source (1) has a laser diode (9), wherein an injection current of the laser diode (9) is modified in order to vary the frequency of the emitted light.

4. The LIDAR measuring device according to claim 1, wherein the frequency modulation is selected in such a way that the laser light source (1) emits light with a coherence length of from 0.1 to 100 m.

5. The LIDAR measuring device according to claim 1, wherein the laser light source (1) emits light with a coherence length of from 1 to 50 m.

6. The LIDAR measuring device according to claim 1, the control device (13) of the laser light source impresses an additional signal in such a way that an additional time-linear portion is added to the frequency of the emitted light.

7. The LIDAR measuring device according to claim 6, wherein the time-linear change in the frequency of the emitted light is selected to be large enough that the sign of the difference does not change despite a Doppler shift of the frequency of the received light as compared to the transmitting frequency, said shift being caused by movement of the particles.

8. The LIDAR measuring device according to claim 1, wherein the control device (13) changes the current strength such that the frequency of the light emitted by the laser light source (1) is varied linearly upward and downward.

9. The LIDAR measuring device according to claim 1, wherein the control device (13) is configured such that the emitted light is pulsed, wherein pulse lengths are selected such that they are longer than what corresponds to the desired spatial resolution, such that the spatial resolution continues to be determined by the frequency modulation of the laser light source.

10. The LIDAR measuring device according to claim 1, wherein an optical switch is arranged in the measuring branch (3).

11. The LIDAR measuring device according to claim 10, wherein the optical switch is an acoustico-optical modulator.

12. The LIDAR measuring device according to claim 1, wherein at least one element polarizing the light is arranged in the reference branch (4).

13. A use of a LIDAR measuring device according to claim 1 to record a wind speed and/or a wind direction on the windward side of a wind turbine.

14. A use of a LIDAR measuring device according to claim 1 to record a wind speed and/or a wind direction on the windward side of a wind turbine, wherein the measuring device is attached to a spinner of the wind turbine.

15. A method for determining the speed of particles in a measuring volume, comprising: transmitting light with a narrowband continuous wave laser light source (1) and coupling the transmitted light into a measuring branch (3) and a reference branch (4); at least partially emitting the light coupled into the measuring branch (3) by a transmitting device in the direction of the measuring volume in such a way that the emitted light is at least partially scattered and/or reflected by the particles in the measuring volume; receiving by a receiver device at least a part of the scattered and/or reflected light and coherently superimposing the at least a part of the scattered and/or reflected light with the light leaving the reference branch (4) to form a resulting light beam; directing the resulting light beam onto a detector (6) to generate a detector signal characteristic for the resulting light beam; determining a speed of the particles in the measuring volume in an evaluation unit (11) by taking into account the detector signal, wherein the frequency of the light emitted by the laser light source (1) is varied with a control device (13) and a spectral analysis of the detector signal is carried out in the evaluation unit (11) in order to calculate the speed of the particles in at least one measuring region of the measuring volume, by taking into account a predefined frequency modulation, wherein the variation of the frequency of the light emitted by the laser light source (1) takes place based on a control signal generated by the control device (13), said control signal corresponding to a pseudo-noise signal caused by a predefined frequency function.

16. The method according to claim 15, wherein the variation of the frequency of the light emitted by the laser light source (1) takes place based on a control signal generated by the control device (13), said control signal containing a time-linear portion.

Description

(1) In the following, the invention is explained in greater detail by means of exemplary embodiments with reference to the figures, without limiting the general concept of the invention. The following is shown:

BRIEF DESCRIPTION OF THE DRAWINGS

(2) FIG. 1: principle structure of a LIDAR measuring device designed according to the invention;

(3) FIG. 2: curve of the electrical power spectral density as a function of the frequency;

(4) FIG. 3: curve of a modulated frequency over a section of time;

(5) FIG. 4: curve of the modulated injection current over a section of time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) FIG. 1 schematically shows a LIDAR measuring device designed according to the invention. The LIDAR measuring device has a continuous wave laser light source 1 with an output power of 10 mW, which emits light with a wavelength of 1550 nm. The light emitted by the laser light source 1 is coupled, on one hand, into an at least partially fiber-optically defined measuring branch 3 and, on the other hand, into a completely fiber-optically defined reference branch 4 with the help of a fiber-optic coupler, which takes on the function of a beam splitter 2.

(7) The optic fibers used are preferably single mode fibers with low damping and a field radius of advantageous 5 μm. Polarization-maintaining fibers, so-called PM fibers, are preferably used.

(8) A further fiber-optic coupler 5 is arranged at the end of the measuring branch 3 and the reference branch 4 for combining the light from the measuring branch 3 and from the reference branch 4. The light leaving the reference branch 4 is coherently superimposed with the received light and the resulting light beam is routed to the detector 6. According to this exemplary embodiment, the detector has two separate photodetectors, which are preferably designed as InGaAs detectors. Characteristic signals are generated for the detected beam with the help of the detector 6, wherein the two signals are subtracted from one another in a subtraction element 14 in order to eliminate faults. The difference signal is then supplied to an evaluation unit 11, in which the different signal is evaluated to detect the presence and/or movement of particles, by means of an analog-digital converter 12.

(9) If no PM fibers are being used, an adjustable, fiber-optic polarization regulator and a diverting path, for example in the form of a wound section of the fiber, are provided in the reference branch 4.

(10) The measuring branch has an erbium-doped fiber amplifier with a preferred output power of 1 W and an optic circulator 7, arranged sequentially, as the amplifier 8.

(11) From the circulator 7, the light coupled into the measuring branch 3 is routed to a transmitting and receiving lens 10, with a focal length of 250 mm for example, and from there focused in the direction of the measuring volume to be measured and/or the respective measuring region.

(12) The beam scattered and/or reflected in particles in the measuring volume then reaches, at least to a certain extent, the transmitting and receiving lens 10 of the LIDAR measuring device. In the exemplary embodiment shown here, the transmitting and receiver device are combined in the transmitting and receiving lens 10. The scattered and/or reflected light hereby received is subsequently coupled into the remaining fiber-bonded section of the measuring branch 3 via the circulator 7.

(13) The continuous wave laser light source 1 has a laser diode 9 and is coupled to a control device 13, which varies the injection current of the laser diode 9 in a suitable manner such that the frequency of the light emitted from the laser diode is also changed. A frequency function is stored in the control device 13 as a function of the desired spatial resolution such that the light emitted by the laser light source 1 is changed, particularly broadened and deformed, as compared to the light typically emitted by the laser diode 9 by means of the modulation as a function of the frequency function in the optical power spectral density. With the help of the control device 13, the frequency of the emitted light is thus changed based on a suitable frequency function defining a pseudo-noise signal. Due to the consideration of various time-shifting values during the evaluation by the evaluation unit, the detection of particles and the movement thereof can be carried out separately in a spatially resolved manner, in purely mathematical terms, for various measuring regions remote from the lens 10 at different distances, without changing the described setup.

(14) Essential for the invention is that the frequency of the light emitted by a laser light source 1 is precisely varied such that no phase modulator is required for the laser light source and furthermore no acoustico-optical modulator (AOM) is required, in contrast to the technical solutions known from the prior art.

(15) In order to achieve a suitable frequency modulation such that the phase modulator used according to the prior art can be dispensed with and a modulation of the frequency of the emitted light is still achieved, which achieves the same effect as with the phase modulation Θ(t) used with known measuring systems, the current frequency of the laser diode according to

(16) $f_{\mathrm{mom}}\left(t\right)=\frac{1}{2\pi }.Math.\frac{d\Theta \left(t\right)}{\mathrm{dt}}$

(17) must be changed, wherein Θ(t) corresponds to the respective phase. To do this, a modulation of the injection current of

(18) $\delta i_{\mathrm{mod}}\left(t\right)=\frac{1}{{\gamma }_{\mathrm{tun}}}{f}_{\mathrm{mom}}\left(t\right)=\frac{1}{2\pi {\gamma }_{\mathrm{tun}}}.Math.\frac{d\Theta \left(t\right)}{\mathrm{dt}}$

(19) is necessary.

(20) However, this leads to an undesired modulation of the laser output power

(21) $\delta P_{0,\mathrm{mod}}\left(t\right)=\beta .Math.\delta i_{\mathrm{mod}}\left(t\right)=\frac{\beta }{2{\mathrm{\pi \gamma }}_{\mathrm{tun}}}.\frac{d\Theta \left(t\right)}{\mathrm{dt}}$

(22) wherein β=dP.sub.0/di characterizes the slope efficiency, for which 0.2 mW/mA can be assumed as a reference value.

(23) From the laser output power P.sub.0+δP.sub.0,mod, a part ρ is coupled into the LO branch, wherein the modulation-based variation of the transmitting power is insignificant:

(24) $P_{LO}+\delta P_{LO}\left(t\right)=\rho \left(P_0+\delta P_{0,mod}\left(t\right)\right)=\rho P_0+\mathrm{\rho \beta }.Math.\delta i_{mod}\left(t\right)=\rho P_0+\frac{\rho .Math.\beta }{2\pi {\gamma }_{\mathrm{tun}}}.Math.\frac{d\Theta \left(t\right)}{\mathrm{dt}}$

(25) With an ideal, balanced reception, the variation of the LO power is not noticeable. With a real, balanced reception, an AC signal of

(26) $\delta i_{\mathrm{Det}}=\epsilon .Math.ℛ.Math.\delta P_{\mathrm{LO}}\left(t\right)=\frac{\epsilon .Math.ℛ.Math.P_{\mathrm{LO}}.Math.\beta }{2{\mathrm{\pi \gamma }}_{\mathrm{tun}}.Math.P_0}.Math.\frac{d\Theta \left(t\right)}{dt}$

(27) with the photodiode response sensitivity R=1 A/W is received. As a comparison, a detector current results for a (corrected) useful signal of power P.sub.signal with the root mean square

(28) $i_{\mathrm{signal},\mathrm{eff}}=ℛ.Math.\frac{1}{\sqrt{2}}\sqrt{P_{\mathrm{signal}}.Math.P_{\mathrm{LO}}}$

(29) For a rough comparison, the root mean square of f.sub.mom(t), where
f.sub.mom.sup.2(t)=½f.sub.max.sup.2

(30) is estimated. This results in

(31) $\frac{\stackrel{\_}{{\left(\delta i_{\mathrm{Det}}\right)}^2}}{\stackrel{\_}{{\left(i_{\mathrm{signal},\mathrm{eff}}\right)}^2}}\cong {\left(\frac{\mathrm{\epsilon ℛ}{P}_{Lo}\beta .Math.f_{\max }}{{\gamma }_{\mathrm{tun}}.Math.P_0}\right)}^2.Math.\frac{1}{{ℛ}^2.Math.P_{\mathrm{signal}}.Math.P_{LO}}={\left(\frac{\mathrm{\epsilon \beta }.Math.f_{\max }}{{\gamma }_{\mathrm{tun}}.Math.P_0}\right)}^2.Math.\frac{P_{\mathrm{LO}}}{P_{\mathrm{signal}}}$

(32) Where

(33) ε=0.01; β=0.2 mW/mA; γ.sub.tun=100 MHz/mA; P.sub.0=20 mW; f.sub.max=10 MHz; P.sub.LO=100 μW, this results in

(34) $\frac{\stackrel{\_}{{\left(\delta i_{\mathrm{Det}}\right)}^2}}{\stackrel{\_}{{\left(i_{\mathrm{signal},\mathrm{eff}}\right)}^2}}\cong \frac{10^{-14}W}{P_{\mathrm{signal}}}$

(35) This comparison makes it clear that the modulation-based noise background does not need to be considered with such a root mean square. In addition, it should be considered that the signal is narrowband, for example 100 kHz, while the modulation-based noise is broadband and is concentrated on the low-frequency frequency domain, as is shown in FIG. 2.

(36) With the phase modulation known in the prior art with the electro-optical phase modulator, the predefined phase Θ(t) is used for correction. The phase modulator is actuated with a signal proportional to the phase. This can result in a scaling error such that the phase impressed on the optical signal is {tilde over (Θ)}(t)=η.sub.scale.Math.Θ(t). In this context, it is known that values of η.sub.scale=0.9 to 1.1 are non-critical.

(37) With the direct modulation, provided according to the invention, of the laser light source with the help of a suitable frequency function, a modulation signal according to

(38) $\delta i_{mod}\left(t\right)=\frac{1}{{\gamma }_{\mathrm{tun}}}{f}_{\mathrm{mom}}\left(t\right)=\frac{1}{2\pi {\gamma }_{\mathrm{tun}}}.Math.\frac{d\Theta \left(t\right)}{dt}$

(39) is impressed on the injection current. If a scaling error occurs in this case as well, to which the following applies

(40) 0$\delta {\tilde{i}}_{\mathrm{mod}}\left(t\right)={\eta }_{\mathrm{scale}}.Math.\frac{1}{2{\mathrm{\pi \gamma }}_{\mathrm{tun}}}\frac{d\Theta \left(t\right)}{dt}=\frac{1}{2\pi {\gamma }_{\mathrm{tun}}}.\frac{d\left({\eta }_{\mathrm{scale}}\Theta \left(t\right)\right)}{dt}$

(41) the effects are thus the same. This directly means that the LIDAR measuring device according to the invention, with which a frequency modulation is carried out directly on the laser light source, is implementable such that the previously used phase modulator can be omitted.

(42) As shown already with the previous statements, it is known from the prior art to subject the optical wave emitted by a laser light source to a predefined phase modulation Θ(t) with the help of a phase modulator and to shift the optical frequency in an interferometer arm by f.sub.AOM by means of an acoustico-optical modulator (AOM). A fixed target at a distance z then provides a detector signal

(43) $\begin{array}{cc}u\left(t\right)\propto \exp \left\{j\left[2\pi f_{\mathrm{AOM}}t+\Theta \left(t-\frac{2z}{c}\right)-\Theta \left(r\right)\right]\right\}& \left(1\right)\end{array}$

(44) If the target moves at speed v in the +z direction, a Doppler shift

(45) $f_{\mathrm{Doppler}}=-\frac{2}{\lambda }v$
also occurs:

(46) $\begin{array}{cc}u\left(t\right)\propto \exp \left\{j\left[2\pi f_{\mathrm{AOM}}t+2\pi f_{\mathrm{Doppler}}t+\Theta \left(t-\frac{2z}{c}\right)-\Theta \left(t\right)\right]\right\}& \left(2\right)\end{array}$

(47) For correction, this signal can be multiplied by the known function

(48) $\begin{array}{cc}h\left(t;z\right)\propto \exp \left\{-j\left[\Theta \left(t-\frac{2z}{c}\right)-\Theta \left\{t\right)\right]\right\}& \left(3\right)\end{array}$

(49) The corrected signal for position z is then purely sinusoidal:
u.sub.cnt(t)=u(t).Math.h(t;z)∝exp{j└2πf.sub.AOMt+2πf.sub.Dopplert┘}  (4)

(50) In the spectrum, it provides a narrow line for f.sub.AOM+f.sub.Doppler.

(51) If this correction function h(t;z) is used, the target is at locations

(52) $z_1<z-\frac{\Delta z_{\mathrm{LC}}}{2}\mathrm{or}{z}_2>z+\frac{\Delta z_{\mathrm{LC}}}{2},$
thus the electrical power spectral density is broad. The width depends on Θ(t). Likewise, the variable Δz.sub.LC depends on the phase pattern Θ(t) and is characterized as the spatial resolution, constrained by the modulation-based low coherence. Corresponding phase patterns, e.g. for Δz.sub.LC=5 m, 10 m, 15 m, can be found numerically by means of a special iteration process. Targets within range

(53) $\begin{array}{cc}\left[z-\frac{\Delta z_{\mathrm{LC}}}{2},z+\frac{\Delta z_{\mathrm{LC}}}{2}\right]& \left(5\right)\end{array}$

(54) thus provide approximately a narrow spectrum for the frequency f.sub.AOM+f.sub.Doppler having a width

(55) $\delta f=\frac{q}{T},$
which is essentially provided by the measuring time T. Outside of this range, a broad spectrum is obtained.

(56) According to a further embodiment of the invention, the frequency of the light emitted by the laser light source, particularly a laser diode, is changed into two types. In this context, there is a stochastic modulation of the frequency and, in addition, the frequency of the light emitted by the laser light source is changed in a time-linear manner. The following applies:
f.sub.laser=f.sub.laser,0+Γ.Math.t  (6)

(57) Thus a detector signal is obtained according to

(58) $\begin{array}{cc}u\left(t\right)\propto \exp \left\{j\left[2\pi \Gamma .Math.\frac{2z}{c}.Math.t+2\pi f_{\mathrm{Doppler}}t+\Theta \left(t-\frac{2z}{c}\right)-\alpha \left(t\right)\right]\right\}& \left(7\right)\end{array}$

(59) In contrast to equation (2), the location-dependent, chirp-based frequency

(60) $f_{\mathrm{chirp}}\left(z\right)=\Gamma .Math.\frac{2z}{c}$
then occurs here in place of the constant frequency f.sub.AOM.

(61) If there is a correction where h(t;z) according to eq. (3), a result according to eq. (4) is obtained:

(62) 0$\begin{array}{cc}{u}_{\mathrm{ent}}\left(t\right)=u\left(t\right).Math.h\left(t;z\right)\propto \exp \left\{j\left[2\pi \Gamma .Math.\frac{2z}{c}.Math.t+2\pi f_{\mathrm{Doppler}}t\right]\right\}& \left(8\right)\end{array}$

(63) Because the chirp rate Γ and the location z are defined and thus are known, the Doppler frequency f.sub.Doppler can be determined therefrom.

(64) If the location of the target is then changed, but the correction function h(t;z) is retained, modified chirp-based frequencies as follows are thus obtained at the edges

(65) $z\pm \frac{\Delta z_{\mathrm{LC}}}{2}$
of the spatial resolution

(66) $\begin{array}{cc}{f}_{\mathrm{chirp}}\left(z\pm \frac{\Delta z_{\mathrm{LC}}}{2}\right)=\Gamma .Math.\frac{2z}{c}\pm \Gamma .Math.\frac{\Delta z_{\mathrm{LC}}}{c}=f_{\mathrm{chirp}}\left(z\right)\pm \frac{\delta f_{\mathrm{chirp}}}{2}& \left(9\right)\end{array}$

(67) Within the interval

(68) $\left[z-\frac{\Delta z_{\mathrm{LC}}}{2},z+\frac{\Delta z_{\mathrm{LC}}}{2}\right],$
the frequency in the spectrum is thus smeared by δf.sub.chirp. To ensure that the Doppler resolution is not substantially worsened as compared to the solution known from the prior art which uses an acoustico-optical modulator (AOM), the following must apply
δf.sub.chirp≤δf  (10)

(69) This results in

(70) $\begin{array}{cc}\Gamma .Math.\frac{2\Delta z_{\mathrm{LC}}}{c}\le \delta f\Gamma \le \frac{c}{2\Delta z_{\mathrm{LC}}}.Math.\delta f& \left(11\right)\end{array}$

(71) If the largest-possible

(72) $\Gamma =\frac{c}{2\Delta z_{\mathrm{LC}}}.Math.\delta f$
Γ is selected and measurements where Γ=|Γ| and Γ=−|Γ⊕ are carried out, which correspond to a triangular frequency modulation, spectral lines after correction are obtained with the frequencies

(73) $\begin{array}{cc}{f}_{+}=.Math..Math.\Gamma .Math..Math.\frac{2z}{c}-f_{\mathrm{Doppler}}.Math.=.Math.\frac{z}{\Delta z_{\mathrm{LC}}}.Math.\delta f-f_{\mathrm{Doppl}}\mathrm{and}f=.Math.-.Math.\Gamma .Math..Math.\frac{2z}{c}-f_{\mathrm{Doppler}}.Math.=.Math.\frac{z}{\Delta z_{\mathrm{LC}}}.Math.\delta f-f_L& \left(12\right)\end{array}$

(74) For the Doppler frequency, the following thus applies:

(75) $\begin{array}{cc}{f}_{\mathrm{Doppler}}=-\frac{f_1^2-f^2}{4.Math.\frac{z}{\Delta z_{\mathrm{LC}}}.Math.\delta f}& \left(13\right)\end{array}$

(76) If one of the frequencies is f.sub.±<δf and thus not determinable, it again applies that f.sub.Doppler can also be determined from the other one:

(77) $\begin{array}{cc}\mathrm{If}{f}_{-}>f_{+},\mathrm{then}{f}_{\mathrm{Doppler}}>0.fwdarw.︀f_{\mathrm{Doppler}}=f_{-}-\frac{z}{\Delta z_{\mathrm{LC}}}.Math.\delta f& \left(14a\right)\end{array}$$\begin{array}{cc}\mathrm{If}{f}_{-}<f_{+},\mathrm{then}{f}_{\mathrm{Doppler}}<0.fwdarw.︀f_{\mathrm{Doppler}}=\frac{z}{\Delta z_{\mathrm{LC}}}.Math.\delta f-f_{+}& \left(14b\right)\end{array}$

(78) A few specific calculation examples are shown in the following:

(79) $\begin{array}{cc}\Delta z_{\mathrm{LC}}=10m,\delta f=0.5\mathrm{MHz},q=2T=4\mathrm{\mu s},\Gamma =7.5.Math.{10}^{12}\mathrm{Hz}/s=7.5\mathrm{MHz}/\mathrm{\mu s},\Gamma .Math.T=30\mathrm{MHz},\Delta i_{\mathrm{tot}}=\Gamma .Math.T/{\gamma }_{\mathrm{tun}}=37.5\mathrm{\mu A}\left(i\right)z=10m,f_{\mathrm{Doppler}}=10\mathrm{MHz}f_1=9.5\mathrm{MHz},f=10.5\mathrm{MHz}\left(\mathrm{ii}\right)z=50m,f_{\mathrm{Doppler}}=10\mathrm{MHz}f_{-}=7.5\mathrm{MHz},f_{-}=12.5\mathrm{MHz}\left(\mathrm{iii}\right)z=100m,f_{\mathrm{Doppler}}=10\mathrm{MHz}f_{-}=5\mathrm{MHz},f_{-}=15\mathrm{MHz}\left(\mathrm{iv}\right)z=20m,f_{\mathrm{Doppler}}=1\mathrm{MHz}f_1=0\mathrm{MHz},f=2\mathrm{MHz}& \left(15\right)\end{array}$

(80) For the frequency modulation of the current supply of the laser light source, particularly of the injection current of a laser diode, the following considerations are significant. In this manner, a suitable frequency modulation and the linear frequency chirp can be implemented.

(81) With a predefined phase pattern Θ(t) in order to implement a spatial resolution Δz.sub.LC and a desired linear frequency chirp (chirp rate Γ), the total phase modulation of the optical wave must be
Θ.sub.tot(t)=Θ(t)+½2πΓ.Math.t.sup.2

(82) and the corresponding frequency modulation and current modulation

(83) 0$f_{\mathrm{tot}}\left(t\right)=\frac{1}{2\pi }.Math.\frac{d{\Theta }_{\mathrm{tot}}\left(t\right)}{\mathrm{dt}}=\frac{1}{2\pi }.Math.\frac{d\Theta \left(t\right)}{\mathrm{dt}}+\Gamma .Math.t\delta i_{\mathrm{mod}}\left(t\right)=\frac{1}{{\gamma }_{\mathrm{tun}}}{f}_{\mathrm{tot}}\left(t\right)=\frac{1}{2\pi {\gamma }_{\mathrm{tun}}}\frac{d\Theta \left(t\right)}{\mathrm{dt}}+\frac{\Gamma }{{\gamma }_{\mathrm{tun}}}.Math.t$

(84) FIGS. 3 and 4 each show exemplary measurements, which prove the previous calculations. FIG. 3 in this case shows the curve of the frequency f.sub.tot in MHz and FIG. 4 shows the modulated injection current δi.sub.mod in μA, each over a timeframe of 4 μs (Γ=7.5 MHz/μs, γ.sub.tun=800 MHz/mA)

(85) The specification incorporates by reference the disclosure PCT/EP2018/057050, filed Mar. 20, 2018 and DE 10 2017 106 226.2, filed Mar. 22, 2017.

(86) The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.

LIST OF REFERENCE NUMERALS

(87) 1 Laser light source

(88) 2 Beam splitter

(89) 3 Measuring branch

(90) 4 Reference branch

(91) 5 Fiber-optic coupler

(92) 6 Detector

(93) 7 Circulator

(94) 8 Amplifier

(95) 9 Laser diode

(96) 10 Lens

(97) 11 Evaluation unit

(98) 12 Analog-digital converter

(99) 13 Control device

(100) 14 Subtraction element