Laser sensor module for self-mixing interferometry

Abstract

The present invention relates to a laser sensor module (150). The laser sensor module includes: a first laser source (152) configured to emit modulated laser light; a circuit (159) configured to drive the first laser source with a first modulation drive current to cause it to emit modulated laser light; a detector (156) configured to detect the modulated laser light, the modulated laser light inducing a photocurrent having variations caused by the modulation of the modulated laser light; and a second laser source (154) configured to emit modulated light. The circuit is configured to drive the second laser source with a second modulation drive current to cause it to emit modulated light. The detector is configured to detect the modulated light, and the circuit is configured to adjust the amplitude of the second modulation drive current to induce a contribution to the photocurrent that compensates for variations in the photocurrent induced by the laser of the first laser source. Also described are an apparatus including the laser sensor module, a method for compensating for variations in the photocurrent detected by the detector of the laser sensor module, and a corresponding computer program.

Description

Field of the Invention

[0001] The present invention relates to a laser sensor module having at least two laser sources. The present invention also relates to a device, in particular to a detector device or a mobile communication device comprising such a laser sensor module. The present invention also relates to corresponding methods and corresponding computer programs. Background Art

[0002] Laser devices based on laser diodes are attractive for optical sensing applications. In particular, VCSELs, as a specific type of laser diode, where the laser beam emission is perpendicular to the wafer surface, are even more attractive components when combined with integrated photodiodes (VIPs) because they provide a light source and a detector in one package. Optical sensing applications using laser devices based on VCSELs with integrated photodiodes (VIPs) are, for example, particle sensing, distance sensing, velocity sensing, etc. Laser devices based on VCSELs are advantageous due to low cost, low power consumption, high sensitivity, small size, self-aligned optical paths, etc.

[0003] A known technique for such sensing purposes is self-mixing interferometry, where a detector such as a photodiode is located behind the laser or can be part of the laser structure itself. In a general self-mixing interferometry system, a lens is placed in front of the laser, the laser beam hits an object, for example, whose velocity needs to be determined, and the light reflected from the object interferes in the laser. This results in a change in the intensity detected by the detector.

[0004] For many applications, it is necessary to modulate the laser current because this causes a wavelength change, which is then used to improve the detection of distance and / or absolute velocity.

[0005] However, using a modulated laser current causes some drawbacks because the change in the intensity of the light emitted by the laser source and detected by the detector causes a change in the photocurrent, which is large compared to the amplitude of the self-mixing interference signal. This can lead to several problems, such as clipping of the photodiode signal in the front-end electronics. These problems can be solved by providing special electronics to compensate for these changes in the photocurrent, but these facilities are complex and not easy to implement, and these changes usually cannot be significantly reduced.

[0006] Therefore, there is a need for a laser sensor module that can efficiently handle problems in the detector caused by large intensity changes in the emitted light. Summary of the Invention

[0007] It is an object of the present invention to prevent large intensity changes in the detector of a laser sensor module while still being able to change the wavelength of the measurement beam emitted by the laser source.

[0008] In a first aspect of the present invention, a laser sensor module is provided, comprising:

[0009] A first laser source configured to be capable of emitting modulated laser light,

[0010] A circuit configured to be capable of driving the first laser source with a first modulation drive current so that the first laser source emits modulated laser light, and

[0011] A detector configured to be capable of detecting the modulated laser light, the modulated laser light inducing a photocurrent, the photocurrent having variations caused by the modulation of the modulated laser light,

[0012] Wherein, the laser sensor module further comprises:

[0013] A second laser source configured to be capable of emitting modulated light,

[0014] Wherein, the circuit is configured to be capable of driving the second laser source with a second modulation drive current so that the second laser source emits modulated light, and the detector is configured to be capable of detecting the modulated light,

[0015] The circuit is configured to be capable of adjusting the amplitude of the second modulation drive current to induce a contribution to the photocurrent, the contribution compensating for the variations in the photocurrent induced by the laser of the first laser source.

[0016] In another aspect of the present invention, a device comprising the laser sensor module is proposed. Such a device particularly comprises a detector device or a mobile communication device comprising the laser sensor module.

[0017] In yet another aspect of the present invention, a corresponding method, a computer program, and a non-transitory computer-readable recording medium are provided. The computer program comprises program code. When the computer program is executed on a processor of the laser sensor module or a processor of the device, the program code is used to cause the laser sensor module or the device to execute the steps of the method disclosed herein. A computer program product is stored in the non-transitory computer-readable recording medium, and when the computer program product is executed by a processor, the method disclosed herein is executed.

[0018] Preferred embodiments of the present invention are defined in the dependent claims. It should be understood that the claimed method, computer program, and medium have similar and / or identical preferred embodiments as the claimed laser sensor module, particularly as defined in the dependent claims and disclosed herein.

[0019] The present invention is based on the idea of using not only one laser source and a detector configured to detect the light emitted by the laser source, but also a second laser source, wherein the change in photocurrent of the modulated light from the first laser source is compensated by an additional contribution to the photocurrent induced by the modulated light emitted by the second laser source, and vice versa.

[0020] For this purpose, the circuit adjusts the amplitude of a second modulation drive current (for driving the second laser source) based on the detected modulated laser emitted by the first laser source to induce a contribution to the photocurrent in the detector that compensates for the change in photocurrent caused by the modulated laser emitted by the first laser source.

[0021] It should be understood that the following description is equivalent, i.e., adjusting the first modulation drive current (for driving the first laser source) to induce a contribution to the photocurrent in order to compensate for the change in photocurrent that is induced in the detector based on the detected modulated light emitted by the second laser source.

[0022] It should also be noted that when the first laser source emits laser light, i.e., when the first laser source operates in laser mode, the second laser source does not necessarily have to operate in laser mode. This means that the second laser source can emit laser light by operating in laser mode or can emit incoherent, divergent light by operating in non-laser mode. The said aspect will be further clarified later with reference to other embodiments of the present invention. However, it should be noted that for the present invention, it is essential that at least one laser source operates in laser mode to emit laser light for the purpose of using the present invention for self-mixing interference.

[0023] It should also be understood that the present invention is based on the use of at least two laser sources, and the two laser sources should be considered the minimum possible number of laser sources used. Using more laser sources is certainly a viable option.

[0024] In this specification, the term "laser source" includes a light-emitting element or component, such as the mesa of a VCSEL. The first laser source and the second laser source (two mesas) can be arranged on a common chip. For example, in the case of a VCSEL, the two mesas on the common chip can be represented as two VCSELs in this specification. The laser source can be configured to emit radiation in the spectral range of 700 nm to 1600 nm. Thus, generally, the laser source can be configured to emit electromagnetic radiation in the red or infrared spectral range, which enables the laser sensor module to be used for various applications and is particularly advantageous for applications of distance and / or speed measurement.

[0025] Preferably, the circuit can be configured to determine a first modulation drive current and a second modulation drive current based on the photocurrent measured by the detector. Accordingly, the circuit is electrically connected to the detector and the laser source to adjust the drive current of the laser source based on the photocurrent of the detector.

[0026] According to one embodiment, the circuit can be configured to provide a first modulation drive current (for the first laser source) and a second modulation drive current (for the second laser source), wherein the two drive currents, namely the first and second modulation drive currents, vary over a predetermined period of time according to a waveform.

[0027] Accordingly, the first modulation drive current and the second modulation drive current can be modulated such that these currents have a shape such as a sine or cosine waveform.

[0028] Preferably, the circuit is configured to be able to drive the first laser source and the second laser source with current amplitudes that are opposite in phase relative to each other. Accordingly, the first modulation drive current can be modulated by a first sine wave, and the second modulation drive current can be modulated by a second sine wave that is offset by 180° relative to the first sine wave. Accordingly, the light emitted by the first laser source and the second laser source and the photocurrent induced based on the detection of the modulated light are also modulated accordingly.

[0029] This provides the technical effect that the change in the second photocurrent compensates for the change in the first photocurrent, and vice versa.

[0030] In addition to modulating the current amplitude by trigonometric functions, the current amplitude can also be modulated by triangular laser current modulation. Using this modulation, the triangular photocurrent induced in the detector can be eliminated by the above compensation.

[0031] The first laser source, the second laser source, and the detector can be arranged on a common chip. In the case where the detector is a photodiode and the laser source is a laser diode, such as a VCSEL, the photodiode can also be integrated in at least one laser diode, preferably in two laser diodes. According to this configuration, the photodiode can be arranged outside the optical resonator of at least one laser diode, or the photodiode can be arranged inside the optical resonator of at least one laser diode. If the photodiode is integrated in the laser diode, whether inside or outside the optical resonator of the laser diode, the present invention is particularly advantageous.

[0032] According to one embodiment, the change in the amplitude of the first drive current and the change in the amplitude of the second drive current are in the range of 0.05 mA to 0.5 mA. This range generally allows for appropriate wavelength changes to detect the distance and / or speed of an object. In addition, these changes are not too large and can be efficiently compensated in the detected photocurrent.

[0033] Preferably, the first laser source and the second laser source are operated with drive currents having amplitudes in the range of 0.05 mA to 2 mA. Thus, for example, the first laser diode can be operated with a first DC drive current amplitude of 1.5 mA and an AC amplitude variation of about 0.2 mA, so as to operate the first laser source in the range of 1.4 mA to 1.6 mA. This range is generally higher than the threshold operating current amplitude of typical VCSELs used. Thus, the first laser source can be operated in a laser mode to emit laser light. Then the second laser diode can be operated with a second DC drive current amplitude of about 0.3 mA and an AC amplitude variation of about 0.4 mA to operate the second laser source in the range of 0.1 mA to 0.5 mA, which range is generally lower than the threshold operating current amplitude of typical VCSELs used.

[0034] These values are merely exemplary, but preferably, the variation in the amplitude of the first drive current is substantially the same as the variation in the amplitude of the second drive current. If the difference in the amplitude variations is large, the compensation effect on the photocurrent variation cannot be achieved efficiently. If one of the first laser source and the second laser source is operated with a drive current below the threshold, preferably different DC drive current amplitudes are used for the first laser source and the second laser source, because the slope of the photodiode current below the threshold is significantly lower than the slope of the photodiode current above the threshold.

[0035] Generally, the circuit can also be configured to be able to vary differently the intensity and / or wavelength of the light emitted by the first laser source and the second laser source to obtain different emission wavelengths and different output powers of the two laser sources.

[0036] As described above, it is important for the self-mixing interferometry that at least one laser source is operated in a laser mode. If only one laser source is operated in a laser mode, the concept of compensating for large variations in the photocurrent proposed is also effective. Thus, according to one embodiment, the circuit can be configured to drive the first laser source with a first drive current amplitude greater than the threshold operating current amplitude of the first laser source, and to drive the second laser source with a second laser current amplitude less than the threshold operating current amplitude of the second laser source. However, even though this configuration is a viable option, for many applications, it is more desirable that both laser current amplitudes are greater than the respective threshold operating current amplitudes of the corresponding laser diodes to operate the two laser sources in a laser mode with coherent narrow-beam light emission. For example, this will be accomplished by driving both laser sources with a DC current amplitude of 1.5 mA and an AC amplitude variation of 0.2 mA. The modulation signals on the two laser sources will be in antiphase to achieve compensation.

[0037] It should be understood that the preferred embodiments of the present invention can also be any combination of the dependent claims and the corresponding independent claims.

[0038] Other advantageous embodiments are defined as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] With reference to the embodiments described below, these and other aspects of the present invention will become apparent and be elucidated. In the drawings:

[0040] Figure 1 A schematic cross-section of an embodiment of a laser sensor module according to the present invention including two laser diodes and an integrated photodiode is shown;

[0041] Figure 2 A top view of a laser sensor module formed on a chip according to the present invention is shown;

[0042] Figure 3 Shows Figure 2 A connection scheme of the connections of two laser diodes and a photodiode;

[0043] Figure 4 Is a graph showing the relationship between a typical photodiode current and a laser output power and a laser diode current;

[0044] Figure 5 Is a graph showing the modulation of the output powers of two laser sources operated by modulation drive currents that are in opposite phases to each other;

[0045] Figure 6 Shows a method for compensating for a change in photocurrent of a detector of a laser sensor module as Figures 1-3 Shown, in the form of a flowchart;

[0046] Figure 7 Is a schematic diagram of a configuration for measuring the tilt amount of an object using a lens in front of a laser sensor module according to the present invention; and

[0047] Figure 8 Shows the use of Figure 7 The configuration shown to measure the width of an object. DETAILED DESCRIPTION OF THE INVENTION

[0048] Figure 1 A schematic cross-section of an embodiment of a laser sensor module 150 according to the present invention including two laser diodes 152, 154 and an integrated photodiode 156 is shown.

[0049] Hereinafter, the detector of the present invention is referred to as a "photodiode", and the laser source of the present invention is referred to as a "laser diode".

[0050] The laser sensor module 150 includes a first laser diode 152 and a second laser diode 154. These laser diodes 152, 154 can be configured as vertical cavity surface emitting lasers (VCSELs), respectively. The VCSELs can have mesa structures 53a, 53b known in the art. The VCSELs can be configured to have a common optical resonator 54, which includes a lower distributed Bragg reflector (DBR) 56 and upper DBRs 58a, 58b. The reflectors 56 and 58a, 58b form the respective optical resonators 54 of the first laser diode 152 and the second laser diode 154. According to Figure 1 In the embodiment shown, the lower distributed Bragg reflector 56 is shared by the first laser diode 152 and the second laser diode 154. The laser active quantum well layers 57a, 57b and the current confinement layers 59a, 59b can be arranged between the lower DBR and the upper DBR as known in the art.

[0051] The laser sensor module 150 further includes a photodiode 156. In this embodiment, the photodiode 156 is integrated in the optical resonator 54 of the laser diodes 152, 154. In the present embodiment, the photodiode 156 is integrated in the lower DBR of the laser diode, which further includes upper DBRs 58a, 58b and a laser active medium having quantum wells between the DBRs. Integrating the photodiode 156 into the lower DBR 56 can be accomplished as follows. The lower DBR 56 can consist of three regions: starting from an n-doped layer below the laser active medium, changing to a p-doped layer, and then an intrinsic absorption layer of the photodiode 156 placed around the antinode of the standing wave pattern in order to obtain the maximum response ability and maximum contrast of the stimulated emission and spontaneous emission of the laser diodes 152, 154. The p-i-n structure of the photodiode 156 is completed by an additional n-doped layer. The intracavity contacts 68a, 68b in the central part of the n-doped DBR serve as both the VCSEL cathode and the photodiode anode. According to the shown embodiment, the first intracavity contact 68a is implemented for the first laser diode 152, and the second intracavity contact 68b is implemented for the second laser diode 154.

[0052] It should be noted that Figure 1 the embodiment shown in Figure 1The illustrated embodiment with an internal photodetector is sensitive not only to stimulated emission (laser) of the radiation emitted by the laser diode, but also to spontaneous emission (LED light) of the radiation emitted by the laser diode. Since it is a viable option of the present invention to operate one laser diode in the laser mode and the other laser diode in the non-laser mode, the embodiment of the laser sensor module 150 with an internal photodetector as shown in Figure 1 may be advantageous.

[0053] In addition to Figure 1 the components of the laser sensor module 150 shown, the laser sensor module 150 further includes a circuit that is not shown in Figure 1 and will be explained below with reference to Figure 2 and Figure 3 .

[0054] Figure 2 shows a top view of the laser sensor module 150 formed on a chip according to the present invention, Figure 3 shows Figure 2 the connection scheme of the connection between the two laser diodes and the photodiode. The laser sensor module 150 may be the same as that shown in Figure 1 .

[0055] The laser sensor module 150 includes two laser diodes 152, 154 respectively configured as VCSELs. Each VCSEL has the mesa structure already described with reference to Figure 1 . Therefore, the laser sensor module 150 may also be represented as a laser device with two mesas. The VCSELs 152, 154 are arranged on a common chip 170. The laser sensor module 150 further includes a single photodiode 156 and electrical contacts 158 that are only visible in Figure 2 . The single photodiode 156 may be integrated into the two laser diodes 152, 154, outside or inside the resonator. The photodiode 156 receives radiation from the two laser diodes 152, 154 separately.

[0056] Figure 3A connection scheme showing the electrical connection between two laser diodes 152, 154 and a photodiode 156 is shown. In addition to these components, the laser sensor module 150 further includes a circuit 159. The circuit 159 is configured to be able to control the laser diodes 152, 154 and the photodiode 156, and measure the photodiode current in the photodiode 156 for the drive currents of multiple ones of the laser diodes 152, 154. VPD represents the photodiode voltage between the photodiode cathode 160 and the contact portion 162, and the contact portion 162 is at the same potential as the cathodes of the laser diodes 152, 154. In addition, the contact portion 162 is at the same potential as the cathode of an additional forward-biased diode 157 for contacting the anode layer of the photodiode 156. IPD represents the photodiode current that can be measured by the circuit 159 based on the radiation emitted by the laser diodes 152, 154 and received by the photodiode 156. It should be understood that more than two laser diodes can be integrated in the laser sensor module 150.

[0057] The circuit 159 can be configured to separately and / or alternately set and determine the drive currents of each of the laser diodes 152, 154 by using the measured photodiode current of the common photodiode 156. According to the principles of the present invention, the circuit 159 is configured to be able to drive the first laser diode 152 with a first modulated drive current so that the first laser diode 152 emits modulated laser light. The photodiode 156 is configured to be able to detect the modulated laser light, and the modulated laser light induces a photocurrent having a change caused by the modulation of the modulated laser light. In addition, the circuit 159 is configured to be able to drive the second laser diode 154 with a second modulated drive current so that the second laser diode 154 emits modulated light that is also detected by the photodiode 156. This modulated light of the second laser diode 154 contributes to the photocurrent. According to the principles of the present invention, the circuit 159 adjusts the amplitude of the second modulated drive current to induce such a contribution to the photocurrent by the modulated light of the second laser diode 154, and this contribution can compensate for the change in the photocurrent caused by the modulated laser light emitted by the first laser diode 152. Thus, the change in the photocurrent originating from the first laser diode 152 is compensated by the change in the photocurrent originating from the second laser diode 154.

[0058] Figure 4 is a graph showing the relationship between a typical photodiode current and laser output power and the laser diode current. It can be clearly seen that a larger laser diode drive current results in a larger output power of the emitted light, which induces a larger photocurrent in the photodiode. Modulation of the drive current of the laser diode directly results in modulation of the output power of the emitted light, which induces a photocurrent having a changing value in the photodiode.

[0059] In the case of triangular laser modulation of a laser diode (as also shown in Figure 5 ), the laser current can be reduced, for example, from 2.2 mA to 2.0 mA, as shown by the modulation current arrow in Figure 4 . This results in an undesired reduction in photocurrent of, for example, 0.1 mA. To compensate for this photocurrent change, as shown by the compensation current arrow in Figure 4 , an increased laser drive current, for example, from 0.1 mA to 0.5 mA, can be used for another laser diode. This results in an increase in photocurrent of 0.1 mA, thereby eliminating the undesired photocurrent change. Since the second laser diode is still operating below threshold, this hardly affects the additional laser output power of the second laser source.

[0060] Figure 5 FIG. is a diagram showing modulation of the output powers of two laser sources operated by modulation drive currents that are in antiphase with respect to each other. Exemplarily, the first laser diode and the second laser diode are driven with triangular laser current modulation. As already explained above with reference to Figure 4 , this results in triangular modulation of the output power of the light emitted by the laser diode. Since the output power values of the first laser diode and the second laser diode are in antiphase with respect to each other, a total photocurrent that does not include any variation is induced in the detector.

[0061] Figure 6 FIG. shows a flowchart of a method 100 for compensating for photocurrent variations in a detector 156 of a laser sensor module 150 as described above with reference to Figures 1-3 .

[0062] In step 102, a first laser source 152 is driven with a first modulation drive current to cause the first laser source 152 to emit modulated laser light. In step 104, the modulated laser light is detected by the detector 156 and a photocurrent is induced that has variations caused by the modulation of the modulated laser light. In step 106, a second laser source 154 is driven with a second modulation drive current to cause the second laser source 154 to emit modulated light. In step 108, the modulated light emitted by the second laser source 154 is detected by the detector 156, wherein the amplitude of the second modulation drive current is adjusted to induce a contribution to the photocurrent that compensates for the variation in the photocurrent caused by the laser light emitted by the first laser source 152. Thus, a photocurrent that has no variations, i.e., a current that has only a DC component and no AC component, is preferably obtained. It should be understood that Figure 6 the order of the steps shown is merely exemplary and all of these steps should be considered equivalent.

[0063] Figure 7A schematic diagram showing a configuration in which a lens 190 is used in front of a laser sensor module 150 according to the present invention to measure the tilt amount 201 of an object 200a is shown. This configuration exemplarily shows an SMI application that requires modulating the laser current because the absolute speed and / or distance of an object cannot be measured using a direct current laser current.

[0064] The laser sensor module 150 also includes a VCSEL with an integrated photodiode (VIP), and by placing the lens 190 in front of the laser sensor module 150, the direction of the light emitted by the first laser source 152 is tilted relative to the light emitted by the second laser source 154. It should be understood that the lens 190 can also be directly attached to at least one of the first laser source 152 and the second laser source 154 to tilt the direction of the light emitted by the first laser source 152 relative to the laser emitted by the second laser source 154. This can be achieved by any suitable technique known in the art, such as lithography. To measure the tilt amount 201 of the object 200a as Figure 7 shown, both laser sources 152, 154 operate in a laser mode. Therefore, both the first laser source 152 and the second laser source 154 of the laser sensor module 150 are driven by a modulated drive current greater than the respective operating thresholds of the first laser source 152 and the second laser source 154.

[0065] Both laser beams are incident on the object 200a, and the light reflected from the object 200a interferes in the laser, resulting in the generation of a self-mixing interference (SMI) signal, which is then detected by the detector 156 of the laser sensor module 150. A transimpedance amplifier (TIA) can be used to detect small SMI signals. The typical resistance value of such a TIA is about 1 MΩ. Usually, an attached circuit is required to eliminate the triangular modulation pattern as Figure 5 shown, but due to the elimination method described above with reference to Figure 6 no additional circuit is required. The distances from the first laser source 152 and the second laser source 154 to the object 200a can be derived, and the tilt amount 201 of the object 200a can be measured by comparing the distances.

[0066] If an increased detection range is also required for distance measurement, it is advantageously possible to additionally use two different aperture sizes (not shown) for the first laser source 152 and the second laser source 154. Thus, the dλ / dI parameter (also known as the slope efficiency) can be adjusted, where λ is the respective wavelength of the emitted light of one laser source and I is the intensity of the emitted light. By adjusting this parameter, different Doppler frequencies are detected for the first laser source 152 and the second laser source 154. These different Doppler frequencies can all be detected by the detector 156 of the laser sensor module 150. Due to the different Doppler frequencies, one laser source can be used for nearby objects and the other laser source can be used for more distant objects.

[0067] Figure 8 A schematic diagram is shown using Figure 7 the configuration shown to measure the width 202 of the object 200b. In this case, the laser sensor module is used to check, for example, whether the width 202 of the object 200b has a desired size in a production line. This configuration exemplarily shows another SMI application that requires modulating the laser current. The laser sensor module can be the same as Figure 7 that shown. The first laser source 152 and the second laser source 154 emit laser light. The object can be moved to a plurality of different positions along at least one direction. Depending on the position of the object 200b, two laser beams or only one laser beam or no laser beam emitted by the first laser source 152 and / or the second laser source 154 irradiates the object 200a. The light reflected from the object 200b also interferes in the laser, resulting in the generation of a self-mixing interference (SMI) signal, which is then detected by the detector 156 of the laser sensor module 150. Since two laser beams, one laser beam, or no laser beam is reflected depending on the position of the object 200b, measuring at various different positions allows the width 202 of the object 200b to be evaluated.

[0068] Although the invention has been shown and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, by studying the drawings, the disclosure, and the appended claims.

[0069] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" does not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used advantageously.

[0070] A computer program may be stored / distributed on a suitable non-transitory medium, such as an optical storage medium or a solid state medium provided together with other hardware or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0071] Any reference signs in the claims shall not be construed as limiting the scope.

Claims

1. A laser sensor module (150), comprising: a first laser source (152) configured to emit modulated laser light, a circuit (159) configured to drive the first laser source (152) with a first modulation drive current so that the first laser source (152) emits modulated laser light, and a detector (156) configured to detect the modulated laser light, the modulated laser light inducing a photocurrent having variations caused by the modulation of the modulated laser light, wherein the laser sensor module (150) further comprises: a second laser source (154) configured to emit modulated light, the circuit (159) configured to drive the second laser source (154) with a second modulation drive current so that the second laser source (154) emits modulated light, and the detector (156) configured to detect the modulated light, the circuit (159) configured to adjust the amplitude of the second modulation drive current to induce a contribution to the photocurrent that compensates for variations in the photocurrent induced by the laser of the first laser source (152).

2. The laser sensor module (150) according to claim 1, wherein the circuit (159) is configured to determine the first modulation drive current and the second modulation drive current based on the measured photocurrent of the detector (156).

3. The laser sensor module (150) according to claim 1 or 2, wherein the circuit (159) is configured to provide the first modulation drive current and the second modulation drive current, both of which vary over a predetermined time period according to a waveform.

4. The laser sensor module (150) according to claim 1 or 2, wherein the circuit (159) is configured to drive the first laser source (152) and the second laser source (154) with current amplitudes that are opposite in phase relative to each other.

5. The laser sensor module (150) according to claim 1 or 2, wherein the circuit (159) is configured to drive the first laser source (152) and the second laser source (154) with triangular laser current modulation.

6. The laser sensor module (150) according to claim 1 or 2, wherein the first laser source (152), the second laser source (154), and the detector (156) are arranged on a common chip (170); or the detector (156) is a photodiode, and the laser sources (152, 154) are laser diodes, and the photodiode is integrated in at least one of the laser diodes and arranged outside the optical resonator (54) of the at least one laser diode; or the photodiode is integrated in at least one of the laser diodes and arranged within the optical resonator (54) of the at least one laser diode.

7. The laser sensor module (150) according to claim 1 or 2, wherein the variations in the amplitude of the first drive current and the amplitude of the second drive current are in the range of 0.05 mA to 0.5 mA.

8. The laser sensor module (150) according to claim 1 or 2, wherein, the circuit (159) is configured to be able to differently change the intensity and / or wavelength of the light emitted by the first laser source (152) and the second laser source (154).

9. The laser sensor module (150) according to claim 1 or 2, wherein, the circuit (159) is configured to: be able to drive the first laser source (152) with a first drive current amplitude greater than the threshold operating current amplitude of the first laser source (152) so as to operate the first laser source (152) in a laser mode, and be able to drive the second laser source (154) with a second laser current amplitude less than the threshold operating current amplitude of the second laser source (154) so as to operate the second laser source (154) in a non-laser mode.

10. The laser sensor module (150) according to claim 1 or 2, wherein, the circuit (159) is configured to be able to drive the first laser source (152) and the second laser source (154) with a first laser current amplitude and a second laser current amplitude respectively greater than the corresponding threshold operating current amplitudes of the first laser source (152) and the second laser source (154), so that the first laser source (152) and the second laser source (154) operate in a laser mode.

11. The laser sensor module (150) according to claim 1 or 2, wherein, the laser sensor module (150) further has: different aperture sizes for the first laser source (152) and the second laser source (154) to differently modulate the change of the wavelength of the emitted laser relative to the intensity of the emitted laser for the two laser sources, wherein the detector (156) is configured to be able to detect the modulated laser emitted by the first laser source (152) and the modulated laser emitted by the second laser source (154) to detect different Doppler frequencies caused by different apertures.

12. The laser sensor module according to claim 1 or 2, wherein, the laser sensor module (150) further includes: a lens (190) attached to at least one of the first laser source (152) and the second laser source (154) to tilt the direction of the laser emitted by the first laser source (152) relative to the laser emitted by the second laser source (154) to generate spatially separated light beams for measuring the tilt amount (201) of the object (200) and / or the width (202) of the object (200).

13. An apparatus including the laser sensor module (150) according to any one of claims 1-12.

14. A method (100) for compensating for the change in photocurrent of the detector (156) of a laser sensor module (150), including the following steps: driving a first laser source (152) with a first modulated drive current so that the first laser source (152) emits modulated laser, Detect the modulated laser through a detector (156), the modulated laser inducing a photocurrent having variations caused by the modulation of the modulated laser. Drive a second laser source (154) with a second modulation drive current to cause the second laser source (154) to emit modulated light. Detect the modulated light through the detector (156). Wherein, the amplitude of the second modulation drive current is adjusted to induce a contribution to the photocurrent that compensates for variations in the photocurrent induced by the laser of the first laser source (152).

15. A computer program product comprising program code. Wherein, When the computer program product is executed on a processor of the laser sensor module according to any one of claims 1 to 12 or on a processor of the device according to claim 13, the program code is for causing the laser sensor module or the device to perform the steps of the method according to claim 14.

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