Method for providing a detection signal for objects to be detected

Abstract

A method for providing a detection-signal for objects to be detected—at least a first and second light-beam including different frequencies being generated with a first optical non-linear 3-wave-process from a light-beam of a light-source including an output-frequency, and the first light-beam including a reference-frequency being detected, and the second light-beam including an object-frequency being emitted and received after reflection on an object, and the light-beam including the output-frequency and the second light-beam including the object-frequency being superposed, and a reference-beam including a reference-frequency being generated with a second optical non-linear 3-wave-process from the two superposed light-beams including the output-frequency and including the object-frequency, and a detection-signal being generated so that the object-distance is determinable due to the aforementioned superposition based on the time-difference between the detection of the first light-beam including the reference-frequency and a detection of a change of the reference-beam including the reference-frequency.

Claims

1. A method for providing a detection signal for an object to be detected, the method comprising: generating at least one first and one second light beam including different frequencies with a first optical non-linear 3-wave process from a light beam of a light source including an output frequency, wherein the first light beam includes a reference frequency being detected, wherein the second light beam includes an object frequency being emitted and being received after reflection on an object, and wherein the light beam includes the output frequency and the second light beam including the object frequency being superposed; generating a reference beam including a reference frequency with a second optical non-linear 3-wave process from the two superposed light beams including the output frequency and including the object frequency; and generating a detection signal so that a distance of the object is determinable due to the aforementioned superposition based on the time difference between the detection of the first light beam including the reference frequency and a detection of a change of the reference beam including the reference frequency.

2. The method of claim 1, wherein the intensity of the reference beam includes the reference frequency changes, in particular, increases due to the aforementioned superposition.

3. A sensor device for providing a detection signal for an object to be detected, comprising: a light source for generating an output beam including at least one output frequency; a first beam generation unit for generating at least one first and one second light beam of different frequency with a first optical non-linear 3-wave process from the output beam; a second beam generation unit for generating a reference beam including reference frequency with a second optical non-linear 3-wave process from a superposition of the second light beam emitted and received after reflection on the object, and the light beam including the output frequency; and a detection unit for detecting light, the detection unit being configured to generate a detection signal so that the distance of the object is determinable due to the aforementioned superposition based on the time difference between the detection of the first light beam including the reference frequency and a detection of a change of the reference beam including the reference frequency.

4. The sensor device of claim 3, wherein the first and/or second beam generation unit includes a non-linear optical crystal, the non-linear optical crystal being manufactured from, in particular, periodically polarized potassium titanyl phosphate, lithium niobate and/or stoichiometric lithium tantalate and/or barium borate, lithium triborate, bismuth borate and/or potassium hydrogen phosphate.

5. The sensor device of claim 3, wherein the first beam generation unit is configured to provide the first optical non-linear 3-wave process with a spontaneous parametric fluorescence.

6. The sensor device of claim 3, wherein the second beam generation unit is configured to provide the second optical non-linear 3-wave process with difference frequency generation.

7. The sensor device of claim 3, further comprising: an absorber, manufactured from black silicon, for absorbing at least light beams from the second beam generation unit.

8. The sensor device of claim 3, further comprising: a receiving unit for receiving light beams reflected by objects, which includes a frequency filter, in particular a bandpass filter, to suppress the first light beam and for transmitting the second light beam.

9. The sensor device of claim 3, further comprising: a time difference measuring unit, which includes a digital counter, in particular controlled by clock sources at a high frequency, and/or a serial connection of multiple digital gates, so that the point in time of a generation of a light pulse and the point in time of the detection of the reflected light form the time difference.

10. The sensor device of claim 3, wherein the detection unit has a non-linear detection characteristic.

11. A LIDAR scanner or a micro-scanner, comprising: at least one sensor device for providing a detection signal for an object to be detected, the sensor device including: a light source for generating an output beam including at least one output frequency; a first beam generation unit for generating at least one first and one second light beam of different frequency with a first optical non-linear 3-wave process from the output beam; a second beam generation unit for generating a reference beam including reference frequency with a second optical non-linear 3-wave process from a superposition of the second light beam emitted and received after reflection on the object, and the light beam including the output frequency; and a detection unit for detecting light, the detection unit being configured to generate a detection signal so that the distance of the object is determinable due to the aforementioned superposition based on the time difference between the detection of the first light beam including the reference frequency and a detection of a change of the reference beam including the reference frequency; and a micromechanical mirror for deflecting a beam of the first beam generation unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a sensor device according to a first specific embodiment of the present invention.

(2) FIG. 2 schematically shows a measuring signal of a detection unit according to a second specific embodiment of the present invention.

(3) FIG. 3 schematically shows a sensor device according to a third specific embodiment of the present invention.

(4) FIG. 4 schematically shows a reference signal of a detection unit according to a fourth specific embodiment of the present invention.

(5) FIG. 5 schematically shows steps of a method according to a fifth specific embodiment of the present invention.

DETAILED DESCRIPTION

(6) FIG. 1 shows a sensor device according to a first specific embodiment of the present invention.

(7) A specific embodiment of a system according to the present invention is shown in FIG. 1.

(8) A laser beam 2 including a frequency f.sub.laser and wavelength λ.sub.0, for example 531 nm, is initially generated with the aid of a laser 10. The power of laser 10 is controlled by a pulse-modulated current source including a continuous level l.sub.1 and pulse level l.sub.2. Laser 10 correspondingly emits a continuous power P.sub.1, for example, 1 mW and a pulse power P.sub.2, for example 50 W. The pulse length is, for example, between 1 ns to 10 ns, which may be between 2 ns and 8 ns, in particular, between 4 ns and 6 ns.

(9) Laser beam 2 is fed to a non-linear crystal 30. The crystal may be manufactured from (periodically polarized) potassium titanyl phosphate, (periodically polarized) lithium niobate, (periodically polarized) stoichiometric lithium tantalite, barium borate, lithium triborate, bismuth borate and/or potassium hydrogen phosphate. There, an object beam 3 including a frequency f.sub.obj and a wavelength λ.sub.1 is formed in a first step with the aid of parametric fluorescence, also referred to as down-conversion, for detecting an object, and a reference beam 4 including a frequency f.sub.ref and a wavelength λ.sub.2, for example, λ.sub.1=1550 nm and λ.sub.2=810 nm, or also any arbitrary wavelength between 700 nm and 1600 nm, the resonance condition f.sub.obj+f.sub.ref=f.sub.laser being met. Object beam and reference beam 3, 4 are identified in this step by the solid line in FIG. 1.

(10) In a second step, object beam and reference beam 3, 4 are spatially separated with the aid of a wavelength-sensitive beam splitter 60, for example, in the form of a dichroitic mirror.

(11) Reference beam 4 is fed to a detector 100 and converted into an electrical signal. Detector 100 may include a photodiode, which detects the intensity of the photon stream and/or an SPAD diode, which responds to individual photons. Alternatively or in addition, an avalanche photodiode may also be used.

(12) Object beam 3 is fed to measuring object 70 with the aid of a transmitting device 68 and/or with the aid of a deflection device. The light of object beam 3 is reflected by measuring object 70—in this case, diffusely—and proportionately received by receiving optical system 67. Receiving optical system 67 includes a wavelength filter 66. The wavelength filter or frequency filter may be a bandpass filter including a high transmission at λ.sub.1−1.5 nm to λ.sub.1+1.5 nm and a low transmission at λ.sub.2. The bandpass filter in this case may be configured for transmitting light of the wavelength of object beam 3 λ.sub.1+/−10 nm, in particular, λ.sub.1+/−5 nm, which may be λ.sub.1+/−2.5 nm, in particular, λ.sub.1+/−1.5 nm and/or which may be λ.sub.1+/−5%, in particular, λ.sub.1+/−2%, which may be λ.sub.1+/−1% and for low transmission at λ.sub.2, which may be in a range λ.sub.2+/−10 nm, in particular, λ.sub.2+/−5 nm, which may be λ.sub.2+/−2.5 nm or λ.sub.2+/−1.5 nm and/or which may be λ.sub.2+/−5%, in particular, λ.sub.2+/−2%.

(13) In the third step, light 5, which has been received by receiving optical system 67, is fed via deflection mirrors 55, 56 and 57 again to the non-linear crystal 30. There, in addition to the parametric fluorescence generated in the first step, a light beam 6 of wavelength λ.sub.2 in turn is formed by the effect of the difference frequency generation as a result of the additional feed of a light beam 5 of wavelength λ.sub.1. This light beam 6 then subsequently strikes beam splitter 60. The portion of beam 6 of wavelength λ.sub.2 is fed to detector 100, as a result of which a measuring signal is generated.

(14) Generated light beams 6, 7 after the difference frequency generation are represented by dashed lines in FIG. 1. Light beams 3, 4, 6, 7, which have been generated by parametric fluorescence on the one hand and by difference frequency generation on the other hand, are not distinguishable in terms of their frequency or wavelength. Light beams 3, 4, 6, 7 may, for example, differ in terms of their polarization depending on the selected technology for phase adaptation of the light beams, also referred to as “phase matching.” This enables a separation of light beams 3, 4, 6, 7 and unneeded light beam 7 from the difference frequency generation including wavelength λ.sub.1 may be fed to an absorber 96. The remaining photons of laser 10 may also be fed to the absorber.

(15) Device 1 described in FIG. 1 is a specific embodiment of a LIDAR system, which provides a detection signal that is depicted in FIG. 2. The base level of laser P.sub.1 results in a detection signal level S.sub.1. The detection signal will rise sharply to level S.sub.2 at the point in time of pulse generation to. It is possible to avoid an overmodulation as a result of a non-linear detector characteristic. Only the intensity of reference beam 4 may be seen on detector 100 in the time span between the emission of a light pulse to and the arrival of light t.sub.TOF reflected by the object. At point in time t.sub.1≈t.sub.TOF of the generation of light beam 4 of wavelength λ.sub.2 via the difference frequency generation in non-linear crystal 30, a change of detection signal λ.sub.2 is to be expected, as shown in FIG. 2.

(16) The time span between the generation of light pulse 3 and the detection of object 70 may be measured with the aid of a time difference measuring unit 110 and converted with the aid of an evaluation unit 120 into the object distance d being sought:
d=½t.sub.TOF*c.sub.0, where c.sub.0=speed of light in a vacuum.

(17) Time span t.sub.TOF may be determined using known methods of electrical time measurement. Digital counters that are incremented by high-frequency clock sources, or the series connection of digital gates, the signal to triggering the measurement and the detection terminating the measurement at t.sub.1, are particularly suited.

(18) FIG. 3 shows a second specific embodiment of the present invention, which is described below.

(19) A laser beam 2 including frequency f.sub.laser and wavelength λ.sub.0, for example 531 nm, is initially generated with the aid of laser 10. The power of laser 10 is controlled by a pulse-modulated current source including continuous level l.sub.2 and pulse level l.sub.2. Laser 10 correspondingly emits a continuous power P.sub.1, for example, 1 mW and a pulse power P.sub.2, for example 50 W. The pulse length is, for example, between 1 ns to 10 ns, which may be between 2 ns and 8 ns, in particular, between 4 ns and 6 ns.

(20) In a second step, laser beam 2 is split in beam splitter 20. Laser beam 2 on optical path A is fed to a non-linear crystal 30a. The crystal may be manufactured from (periodically polarized) potassium titanyl phosphate, (periodically polarized) lithium niobate, (periodically polarized) stoichiometric lithium tantalite, barium borate, lithium triborate, bismuth borate and/or potassium hydrogen phosphate. There, an object beam 3 including a frequency f.sub.obj and a wavelength λ.sub.1 is formed in a first step with the aid of parametric fluorescence, and reference beam 4 including a frequency f.sub.ref and a wavelength λ.sub.2, where, for example, λ.sub.1=1550 nm and λ.sub.2=810 nm, or also any arbitrary wavelength between 700 nm and 1600 nm, the resonance condition f.sub.obj+f.sub.ref=f.sub.laser being met.

(21) In a third step on first optical path A, object beam and reference beam 3, 4 are spatially separated with the aid of a wavelength-selective beam splitter 60, for example, in the form of a dichroitic mirror or the like.

(22) Reference beam 4 is fed to a detector 101 and then converted into an electrical reference signal. Detector 101 may include a photodiode, which detects the intensity of the photon stream, and/or an SPAD diode, which responds to individual photons. The latter enables a reliable detection, even at low light intensity. Alternatively or in addition, an avalanche photodiode may also be used. The reference signal measured in detector 101 is depicted in FIG. 4.

(23) Object beam 3 is fed to measuring object 70. The light of object beam 3 is diffusely reflected by measuring object 70 and proportionately received by receiving optical system 67. Receiving optical system 67 includes a wavelength filter 66. Wavelength filter or frequency filter 66 may be a bandpass filter including a high transmission at λ.sub.1−1.5 nm to λ.sub.1+1.5 nm and a low transmission at λ.sub.2. The bandpass filter in this case may be configured for transmitting light at the wavelength of object beam 3 λ.sub.1+/−10 nm, in particular, λ.sub.1+/−5 nm, which may be λ.sub.1+/−2.5 nm, in particular, λ.sub.1+/−1.5 nm and/or which may be λ.sub.1+/−5%, in particular, λ.sub.1+/−2%, which may be λ.sub.1+/−1% and for low transmission at λ.sub.2, which may be in a range λ.sub.2+/−10 nm, in particular, λ.sub.2+/−5 nm, which may be λ.sub.2+/−2.5 nm or λ.sub.2+/−1.5 nm and/or which may be λ.sub.2+/−5%, in particular, λ.sub.2+/−2%.

(24) In the fourth step, the light, which has been received by receiving optical system 67, is combined by a beam combiner 80 with laser beam 8 passing via optical path B and again fed to a non-linear crystal 30b. There, in addition to the parametric fluorescence passing through laser beam 5 via optical path A, an increase in intensity of laser beam 6 of wavelength λ.sub.2 is formed based on the difference frequency generation as a result of the additional feed of a beam of wavelength λ.sub.1. The portion of laser beam 6 of wavelength λ.sub.2 is fed to detector 100, as a result of which a measuring signal is formed, as depicted in FIG. 2. The portion of laser beam 7 of wavelength λ.sub.1 is no longer needed and may be fed to an absorber 96.

(25) FIG. 5 shows steps of a method according to a fifth specific embodiment of the present invention.

(26) In a first step S1, light of a laser 10 is transmitted into a non-linear optical crystal.

(27) There, an object beam including a frequency f.sub.obj and a reference beam f.sub.ref is formed in a second step S2 with the aid of parametric fluorescence, also referred to as down-conversion, resonance condition f.sub.obj+f.sub.ref=f.sub.laser being met. The wavelengths of the object beam may be in the range of 1550 nm and the wavelengths of the reference beam may be in the range of 810 nm.

(28) The intensity of the reference beam is continuously measured in a third step S3 with a detector 100, for example, with a photodiode.

(29) In a fourth step S4, the detected optical signal is converted into an electrical signal.

(30) The object beam on the other hand is fed in a fifth step S5 to measuring object 70 with the aid of a suitable transmission device, for example, a lens optical system or mirror optical system and optionally including a deflection device, for example, a micro-mirror or a rotating mirror or the like.

(31) The light of the object beam is diffusely reflected by measuring object 70 in a sixth step S6 and proportionately received by a receiving optical system 67.

(32) In a seventh step S7, the received object beam of frequency f.sub.obj is fed together with the laser beam at frequency f.sub.laser again to non-linear crystal 30.

(33) There, a beam including frequency f.sub.ref is formed in an eighth step S8 as a result of the effect of the difference frequency generation.

(34) This beam is superposed with the reference beam in a ninth step S9 and measured with detector 100 described in third step S3. This results in an excessive increase of the intensity of the measuring signal. The time difference between the initial measurement of the reference beam and the measurement of the intensity increase serves as a measuring signal for determining the object distance.

(35) In summary, a compact, cost-efficient and reliable LIDAR sensor system including a high degree of sensitivity and high degree of eye safety is provided by the present invention and, in particular, by at least one of the specific embodiments described. Specifically, an optimization in terms of eye safety and/or maximization of the admissible transmission power, for example, are/is possible in this system by separating the wavelength for the illumination of the object and for the detection, regardless of the implementation of a suitable detector. In addition, a bandwidth of a spectral filter situated in the detection path is no longer noise power dominant and is, in particular, therefore independent of sunlight. Thus, a flat detector may, for example, be used in a biaxial detection path or all the light collected by the receiving optical system may be fed to a single detector with the aid of a suitable structure in the integrated photonic system, and thus a receiving array may be avoided. At the same time, a narrow-band and angle-independent, but complex, wavelength filter may be dispensed with.

(36) Moreover, a high degree of sensitivity is enabled, since a completely different noise power path is used, which allows for a compact LIDAR system including smaller lenses and, if necessary, micro-mirror deflection. The LIDAR system may also be combined with optical phase arrays.

(37) The present invention, although it has been described with reference to t exemplary embodiments, is not limited thereto, but is modifiable in a variety of ways.