Active light sensing system and device

Abstract

An active light sensing system, including: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

Description

[0001] ACTIVE LIGHT SENSING SYSTEM AND DEVICE

[0002] TECHNICAL FIELD

[0003] The present disclosure generally pertains to an active light sensing system and a device.

[0004] TECHNICAL BACKGROUND

[0005] Generally, active light sensing systems are known, for example, time-of-flight (“ToF”) systems which emit a modulated light signal to a scene from which it is thrown back and detect the returning modulated light signal to obtain a distance to the scene, based on a round-trip time or a phase of the modulated light signal.

[0006] However, active light sensing systems are sensitive to ambient light which has an influence on the signal-to-noise ratio (“SNR”) and, thus, on the accuracy of the of the active light sensing system.

[0007] Although there exist techniques for active light sensing systems, it is generally desirable to improve the existing techniques.

[0008] SUMMARY

[0009] According to a first aspect, the disclosure provides an active light sensing system, comprising: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor. According to a second aspect, the disclosure provides a device, comprising an active light sensing system, wherein the active light sensing system includes: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

[0010] Further aspects are set forth in the dependent claims, the drawings and the following description.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments are explained by way of example with respect to the accompanying drawings, in which:

[0013] Fig. 1 schematically illustrates in a block diagram an embodiment of a device which includes an active light sensing system;

[0014] Fig. 2 schematically illustrates in a block diagram an embodiment of a known light detection device;

[0015] Fig. 3 schematically illustrates an angle of incidence dependency of a transmission wavelength range of an optical bandpass filter;

[0016] Fig. 4 schematically illustrates an angle of incidence dependency of a transmission wavelength range of an optical bandpass filter;

[0017] Fig. 5 schematically illustrates a simulation of an angle of incidence dependency of a transmission wavelength range of an optical bandpass filter; Fig. 6 schematically illustrates in a block diagram an embodiment of a light detection device; and

[0018] Fig. 7 schematically illustrates in a block diagram an embodiment of a light detection device.

[0019] DETAILED DESCRIPTION OF EMBODIMENTS

[0020] Before a detailed description of the embodiments under reference of Fig. 6 is given, general explanations are made.

[0021] As mentioned in the outset, generally, active light sensing systems are known, for example, time- of-flight (“ToF”) systems which emit a modulated light signal to a scene from which it is thrown back and detect the returning modulated light signal to obtain a distance to the scene, based on a round-trip time of the modulated light signal in the case of a direct ToF (“dToF”) system or a phase of the modulated light signal in a case of an indirect ToF (“iToF”) system.

[0022] For enhancing the general understanding of the present disclosure, an embodiment of a device 1 which includes an active light sensing system 2 is discussed in the following under reference of Fig. 1, which schematically illustrates the embodiment in a block diagram, and which also applies to other embodiments of the present disclosure.

[0023] In this embodiment, the active light sensing system 2 may be a dToF system or an iToF system (both types of ToF systems are generally known) such that the sensing data generated by the active light sensing system 2 are depth data.

[0024] The device 1 may be any kind of device which includes and processes the sensing data (here depth data) provided by the active light sensing system 2, for example, a vehicle, a robot, a mobile device (e.g., smartphone, tablet or laptop), ahead mounted display or the like.

[0025] The active light sensing system 2 includes a light detection device 3, an active light source 4 and a controller 5 which controls the overall operation of the active light sensing system 2.

[0026] The active light source 4 emits within its field-of-illumination (“FOI”) a modulated light signal to a scene 6 (in other words, the active light source 4 illuminates the scene 6 with a modulated light signal within its FOI) in which an object 7 is present that at least partially throws back or reflects the illumination light. The active light source 4 may illuminate the scene 6 within its FOI by scanning the scene 6 by periodically illuminating different parts of the FOI.

[0027] The modulated light signal is spatially and temporally modulated in intensity.

[0028] The spatial intensity modulation results in high-intensity light areas 8 and low-intensity light areas 9 (“spot dToF” or spot “iToF”), wherein a high-intensity light area 8 may be a spot, a line or the like. The spatial modulation may also result in a single high-intensity light area 8, e.g., in the center of the FOI with a spatial Gaussian light intensity distribution or the like (“flooded illumination”). The spatial radiant intensity can also cover the full field of view of the receiver camera at every measurement, which is commonly known as “full field” illumination.

[0029] The temporal intensity modulation results, in the case of a dToF system, in a train of separate light pulses and, in the case of an iToF system, in a periodic light signal (e.g., sinusoidal, rectangular, triangular, etc.).

[0030] The light detection device 3 detects the modulated light signal thrown back by the object 7 within its field-of-view (“FOV”) and generates depth data which are output via a data bus 10 by the controller 5 to a processor 11 of the device 1 which processes the depth data.

[0031] Returning to the general explanations, however, active light sensing systems are sensitive to ambient light which has an influence on the signal-to-noise ratio (“SNR”) and, thus, on the precision of the active light sensing system. Other factors that influence the SNR include the distance to the scene or the object reflectivity.

[0032] Typically, ambient light mitigation includes the use of optical bandpass filters and high-power active light sources.

[0033] In some known active light sensing systems a monochromatic laser is used as the active light source and a typical bandwidth of the optical bandpass filter is about 40 nm in order to account for different effects such as an angle of incidence dependency of the transmission of the optical bandpass filter, a temperature drift of the wavelength of the emitted light of the active light source of the laser, a temperature drift of the transmission wavelength range of the optical bandpass filter, center wavelength deviation of the filter and laser due to manufacturing tolerances and the laser line width.

[0034] The total bandwidth the optical bandpass filter may have to account for all these effects is given by:

[0035] AZ = AZ \Q[+ AZ[ \\'+ AZ|C\\'+ AFF+ AZ| -| + AZ[ \\"

[0036] Here, AZLCWand AZFCWis the center wavelength variation due to the laser and filter manufacturing to tolerances, respectively, AZLTand AZFTis the wavelength shift due to the temperature variation for the laser and filter, respectively, and AZI Wis the laser linewidth.

[0037] As AZLCWand AZFCWare statistical in nature and typically not correlated, a root sum square may be used to account for both the laser and the filter manufacturing tolerances:

[0038] However, a large bandwidth allows more ambient light to propagate through the optical bandpass filter, thereby increasing the noise level on the optical sensor.

[0039] Assuming a constant spectral irradiance from the sun on the region of the filter bandwidth, the iToF and dToF SNR is proportional to the inverse of the square root of the bandwidth of the optical bandpass filter:

[0040] 1

[0041] SNR - -= V A

[0042] It has been recognized that the reduction of the bandwidth of the optical bandpass filter has the potential of improving the SNR, for example, a reduction to 5 nm bandwidth may approximately, in some embodiments, improve the SNR by a factor of three.

[0043] However, as discussed above, the bandwidth must typically be rather large compared to the line width of the active light source to account for the different effects mentioned above.

[0044] The optical bandpass filter is known to be typically positioned either in front of a lens arrangement of the light detection device or in front of an optical sensor of the light detection device.

[0045] For enhancing the general understanding of the present disclosure, an embodiment of a known light detection device 20 is discussed in the following under reference of Fig. 2, which schematically illustrates the embodiment in a block diagram.

[0046] The light detection device 20 includes a lens arrangement 21, an optical bandpass filter 22 and an optical sensor 23.

[0047] For the sake of illustration only two different angles of incidence of incoming light are shown, which is schematically illustrated by first incoming light rays 25-1 that propagate parallel to the optical axis 24 defined by the lens arrangement 21 and second incoming light rays 26-1 that have the maximum propagation angle with respect to the optical axis that is within the FOV.

[0048] The first incoming light rays 25-1 propagate through the lens arrangement 21 along the optical axis 24 which focuses the first incoming light rays 25-1 on the optical sensor 23, as illustrated by image-side light rays 25-2.

[0049] The lens arrangement 21 focuses the second incoming light rays 26-1 on the optical sensor 23 such that image-side light rays 26-2 are formed. The optical bandpass filter 22, which is here an optical interference filter, may either be positioned in front of the lens arrangement 21 such that the incoming light rays propagate through the optical bandpass filter 22 or in front of the optical sensor 23 such that the image-side light rays propagate through the optical bandpass filter 22. The optical bandpass filter 22 may be a single element or may include one or more separate optical bandpass filter.

[0050] Generally, the transmission wavelength range of the optical bandpass filter 22 that is given for the maximum angle of incidence 0maxon the optical bandpass filter 22 must include the wavelength of the active light (i.e., the wavelength of the emitted light of the active light source of the active light source).

[0051] When the optical bandpass filter 22 is positioned in front of the lens arrangement 21, the maximum angle of incidence 0maxon the optical bandpass filter 22 follows the FOV of the light detection device 20.

[0052] When the optical bandpass filter 22 is positioned in front of the optical sensor 23, the maximum angle of incidence 0maxis defined by the chief ray angle (“CRA”) and the f-number N.

[0053] The f-number should be small (typically 1.3 or lower) since: in ambient light dominated noise conditions.

[0054] In such cases, the maximum angle of incidence 0maxon the optical bandpass filter 22 is typically limited to:

[0055] For N = 1.3, the maximum angle of incidence 0maxmay be in some cases approximately

[0056] 40 degrees. In such cases, the transmission wavelength range may shift about 35 nm to the blue such that the bandwidth of the optical bandpass filter 22 should be larger, since otherwise the amount of active light that propagates through the optical bandpass filter 22 is reduced, thereby decreasing the SNR due to a lower signal level.

[0057] In other words, typically, the SNR is limited either by higher noise levels due to a higher amount of ambient light due to a higher bandwidth of the optical bandpass filter 22 to account for large angles of incidence on the optical bandpass filter 22 or by lower signal levels due to a lower amount of active light that propagates through the optical bandpass filter 22 due to a lower bandwidth and a large a shift of the transmission wavelength range of the optical bandpass filter for large angles of incidences.

[0058] For further enhancing the general understanding of the present disclosure, an angle of incidence dependency of a transmission wavelength range of the optical bandpass filter 22 is discussed under reference of Fig. 3, which schematically illustrates the embodiment. Another embodiment is of the optical bandpass filter 22 is shown in Fig. 4. The embodiments will be discussed in the following together.

[0059] The graph shows a first spectral transmission curve 30 of the optical bandpass filter 22 of Fig. 2 for the first incoming light rays 25-1.

[0060] The first spectral transmission curve 30 defines a transmission wavelength range of the optical bandpass filter 22 in which light having a wavelength within the transmission wavelength range is transmitted through the optical bandpass filter 22. The transmission wavelength range is determined by the center transmission wavelength and the bandwidth of the optical bandpass filter 22.

[0061] For the first spectral transmission curve 30, the center wavelength is given by Xo, which is the center wavelength at normal incidence, since in Fig. 2 the first incoming light rays 25-1 propagates on the optical axis 24 which coincides with the normal vector of the front surface of the optical bandpass filter 22.

[0062] The graph further shows a second spectral transmission curve 31 of the optical bandpass filter 22 of Fig. 2 for the second incoming light rays 26-1.

[0063] As depicted in Fig. 3 or 4, the transmission wavelength range of the second spectral transmission curve 31 is shifted to the blue due to a shift of the center wavelength AXAOI, since the second incoming light rays 26-1 have a higher angle of incidence on the optical bandpass filter 22.

[0064] The amount of the shift of the center wavelength AZOI is given by: wherein 0 is the angle of incidence on the optical bandpass filter 22 and neffis the effective index of refraction of the optical bandpass filter 22. A simulation of AXAOIfor neff= 2.5 is depicted in Fig. 5. In order to reduce the shift of the center wavelength AXAOI, either the effective index of refraction neffof the optical bandpass filter 22 can be increased or the angle of incidence distribution can be reduced.

[0065] The effective index of refraction neffmay be limited by material properties and the angle of incidence is limited by the CRA and the f-number N.

[0066] Assuming that the active light includes a wavelength XALthat corresponds to the center wavelength at normal incidence Xo, the transmission of the active light is at maximum for normal incidence as depicted in Fig. 3 for the first spectral transmission curve 30.

[0067] However, the transmission of the active light is reduced for larger angles of incidence as depicted in Fig. 3 (not in Fig. 4), since the transmission value of the second spectral transmission curve 31 is lower than the transmission value of the first spectral transmission curve 30.

[0068] Typically, the bandwidth of the optical bandpass filter 22 is chosen to be larger than it could be to account for the angle of incidence dependency of the transmission wavelength range.

[0069] Returning to the general explanations, it has thus been recognized that that the reduction of the bandwidth of the optical bandpass filter has the potential of improving the SNR, since more ambient light is rejected and the influence of the ambient light on the measurement is thus reduced.

[0070] It has been recognized that the bandwidth of the optical bandpass filter can be reduced when the maximum angle of incidence on the optical bandpass filter is reduced, since the shift of transmission wavelength range is reduced such that smaller bandwidths are sufficient.

[0071] It has been recognized that the maximum angle of incidence on the optical bandpass filter can be reduced when the optical bandpass filter is positioned inside the lens arrangement, wherein the lens arrangement has an internal plane where the light rays incident angles are minimized.

[0072] It has been recognized that the lens arrangement should be split into two parts such that the optical bandpass filter can be positioned between the two parts inside the lens arrangement.

[0073] Hence, some embodiments pertain to an active light sensing system, wherein the active light sensing system includes: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

[0074] Some embodiments pertain to a device, wherein the device includes an active light sensing system, wherein the active light sensing system includes: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

[0075] The active light sensing system may be a dToF system, an iToF system, a camera, a light scanner, or the like. The active light sensing system may thus generate sensing data which may be depth data or image data. The device may be any kind of device which includes the active light sensing system and processes the sensing data provided by the active light sensing system, for example, the device may be a vehicle, a robot, a mobile device (e.g., smartphone, tablet or laptop), head mounted display or the like.

[0076] The active light source may include one or more LEDs (“Light Emitting Diode”) or one or more lasers such as a semiconductor laser, e.g., a VCSEL (“Vertical-Cavity Surface-Emitting Laser”) or an edge emitting laser.

[0077] The active light source is configured to emit light. In other words, the active light source is configured to illuminate a scene within its FOI.

[0078] In some embodiments, the emitted light is a modulated light signal. In other words, in some embodiments, the active light source illuminates a scene with a modulated light signal within its FOI.

[0079] The modulated light signal may be spatially and temporally modulated in intensity.

[0080] The spatial modulation may result in high-intensity light areas and low-intensity light areas (e.g., for “spot dToF” or “spot iToF”), wherein a high-intensity light area may be a spot, a line or the like.

[0081] The temporal intensity modulation may result, e.g. in the case of a dToF system, in a train of separate light pulses and, e.g. in the case of an iToF system, in a periodic light signal (e.g., sinusoidal, rectangular, triangular, etc.).

[0082] In some embodiments, the wavelength of the emitted light of the active light source is in the near-infrared spectral region.

[0083] In some embodiments, the near-infrared spectral region covers 750 nm (nanometer) to 3000 nm, in particular, 750 nm to 1600 nm.

[0084] The optical sensor may include one or more light detection pixels.

[0085] A light detection pixel may include or may be a photodiode, an active pixel (which may also be referred to as CMOS (“Complementary Metal-Oxide-Semiconductor”) pixel), a single-photon avalanche diode (“SPAD”), an avalanche photodiode (“APD”), a current-assisted photonic demodulator (“CAPD”) or the like or a combination thereof.

[0086] In some embodiments, the optical sensor includes a plurality of light detection pixels arranged in rows and columns, each light detection pixel being configured to perform photoelectric conversion on incident light. The first and the second lens arrangement may include or may be one or more lenses arranged and configured to achieve the functions as described herein.

[0087] In some embodiments, the optical bandpass filter is an optical interference filter.

[0088] As generally known, an optical interference filter, also known as a dichroic filter or thin-film filter, is an optical filter that reflects some wavelengths of light and transmits others, with almost no absorption for all wavelengths of interest.

[0089] The optical interference filter may include multiple thin layers (typically on a glass substrate) of dielectric material having different refractive indices. There may also be metallic layers. The principle of operation is similar to a Fabry -Perot etalon.

[0090] The optical interference filter may be a Fabry-Perot etalon, which may also be referred to as free space Fabry-Perot optical bandpass filter. As generally known, a Fabry-Perot etalon is an optical cavity made from two parallel reflecting surfaces (e.g., thin mirrors).

[0091] Optical interference filters are wavelength-selective by virtue of the interference effects that take place between the incident and reflected waves at the thin-film boundaries. They can be configured as optical bandpass filters. By controlling the thickness and number of the layers, the transmission wavelength range of the optical interference filter can be tuned and made as wide or narrow as desired.

[0092] As discussed above, the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement.

[0093] In some embodiments, the propagation angle of the light ray that has propagated through the first lens arrangement is less than 5 degrees with respect to the optical axis.

[0094] Thereby, the bandwidth of the optical bandpass filter can be chosen smaller than in some conventional light detection devices.

[0095] In some embodiments, the first lens arrangement includes a first plurality of lenses which includes a mixture of negative and positive lenses, in particular, wherein the first lens arrangement includes a fish-eye lens, and wherein the second lens arrangement includes a second plurality of positive lenses.

[0096] In some embodiments, the transmission wavelength range of the optical bandpass filter has a bandwidth of less than 5 nm. It has further been recognized that the split of the lens arrangement into two parts allows the usage of a tunable optical bandpass filter.

[0097] Thus, it has been recognized that the other effects leading to a large required bandwidth of the optical bandpass filter can be addressed by a tunable optical bandpass filter, since the center wavelength of the optical bandpass filter can be shifted in accordance with thermal drifts such that the bandwidth of the optical bandpass filter can be chosen even more narrow.

[0098] The other effects pertain to a temperature drift of the wavelength of the emitted light of the active light source of the laser, a temperature drift of the transmission wavelength range of the optical bandpass filter and manufacturing tolerances.

[0099] Hence, in some embodiments, the optical bandpass filter is a tunable optical bandpass filter.

[0100] In some embodiments, the tunable optical bandpass filter is a tunable free space Fabry-Perot optical bandpass filter. In such embodiments, one of the reflecting surfaces of the optical cavity may be movable (e.g., by a piezo actuator) to vary the resonance condition for varying the transmission wavelength range.

[0101] Returning to Fig. 6, there is schematically illustrated in a block diagram an embodiment of the light detection device 3 of Fig. 1, which is discussed in the following.

[0102] The light detection device 3 includes a first lens arrangement 41, the optical bandpass filter 22, a second lens arrangement and the optical sensor 23.

[0103] The optical bandpass filter 22 is positioned between the first lens arrangement 41 and the second lens arrangement 42. The lens arrangement 21 of Fig. 2 is thus split into two parts with different functions.

[0104] For the sake of illustration only two different angles of incidence of incoming light are shown, which is schematically illustrated by first incoming light rays 45-1 that propagates along the optical axis 43 defined by the first lens arrangement 41 and the second lens arrangement 42, and second incoming light rays 46-1 that have the maximum propagation angle with respect to the optical axis 43 that is within the FOV of the light detection device 3.

[0105] The first incoming light rays 45-1 propagate through the first lens arrangement 41 to form intermediate light rays 45-2, the optical bandpass filter 22 and the second lens arrangement 42 to form image-side light rays 45-3 along the optical axis 43 until they are incident on the optical sensor 23. The incoming second light rays 46-1 propagate with a higher propagation angle with respect to the optical axis 43 than intermediate light rays 46-2 that has propagated through the first lens arrangement 41.

[0106] In other words, the first lens arrangement 41 is configured to reduce a propagation angle of an incoming light ray - for example incoming light rays 45-1 and 46-1 - with respect to the optical axis 43 as defined by the first lens arrangement 41 and the second lens arrangement 42.

[0107] The first lens arrangement 41 includes a first plurality of lenses which includes a mixture of negative or diverging lenses and positive or converging lenses. The first plurality of lenses may include a fish-eye lens.

[0108] The first lens arrangement 41 thus generates a low angle of incidence plane for the optical bandpass filter 22 within the optical lens stack of the light detection device 3.

[0109] As the optical bandpass filter 22 is positioned between the first lens arrangement 41 and the second lens arrangement 42 in the optical path of the light rays that has propagated through the first lens arrangement, i.e. the intermediate light rays 45-2 and 46-2, where the low angle of incidence plane is generated by the first lens arrangement 41, the bandwidth of the optical bandpass filter 22 can be chosen lower than in other configurations. In particular, configurations in which the optical bandpass filter 22 is positioned in front of the lens arrangement 21 or the first lens arrangement 41 or in front of the optical sensor 23.

[0110] The intermediate light rays 45-2 and 46-2 then propagate through the optical bandpass filter 22 and then through the second lens arrangement 42 which generates output light rays 45-3 and 46-3, respectively, which propagate such that they are focused on the optical sensor 23.

[0111] In other words, the second lens arrangement 42 is configured to focus the light rays - for example the intermediate light rays 45-2 and 46-2 - that has propagated through the first lens arrangement 41 and the optical bandpass filter 22 on the optical sensor 23.

[0112] The second lens arrangement 42 includes a second plurality of lenses which includes positive or converging lenses.

[0113] The lens arrangement 21 of Fig. 2 is thus split into two parts with different functions: the first lens arrangement 41 reduces a propagation angle to generate a low angle of incidence plane for the optical bandpass filter and the second lens arrangement 42 focuses the transmitted light on the optical sensor 23.

[0114] An embodiment of the light detection device 3 of Fig. 1 and Fig. 6 is schematically illustrated in a block diagram in Fig. 7, which is discussed in the following. The first lens arrangement 41 includes in order from left - where the incoming light rays enter the light detection device 3 - to right: a first negative meniscus lens, a second negative meniscus lens, an aperture, a plano-concave lens, a first positive meniscus lens and a second positive meniscus lens or a plano-convex lens.

[0115] The second lens arrangement 42 includes in order from left - where the light rays that has propagated through the optical bandpass filter 22 enter the second lens arrangement 42 - to right: a first positive meniscus lens, a second positive meniscus lens and a third positive meniscus lens.

[0116] The light rays depicted in Fig. 7 represent a simulated optical path of the light rays through the light detection device 3, in particular through the first lens arrangement 41, the optical bandpass filter 22 and the second lens arrangement 42. Depicted are incoming light rays with maximum angle of incidence within the FOV of the light detection device 3.

[0117] As depicted in Fig. 7, the propagation angle of the incoming light rays is reduced by the first lens arrangement 41 such that a low angle of incidence plane is generated for the optical bandpass filter between the first lens arrangement 41 and the second lens arrangement 42.

[0118] In this embodiment, a f-number (N) of 1.3 is targeted which translates to a CRA of more than 22.6 degrees (and, thus, the maximum angle of incidence is twice this value).

[0119] Assuming an effective refractive index of 2.5 and a center wavelength of the laser of 940 nm, the wavelength shift of the transmission wavelength range of the optical bandpass filter 22 of the conventional light detection device of Fig. 2 is estimated to be about 35.1 nm.

[0120] However, with the embodiment of Fig. 7, the maximum angle of incidence on the optical bandpass filter is about 10 degrees such that the wavelength shift of the transmission wavelength range of the optical bandpass filter 22 is estimated to be about only 2.2 nm.

[0121] Considering the other effects:

[0122] In some cases, a manufacturing tolerance may be AXLCW ± 7 nm and AXFCW ± 5 nm, resulting a total manufacturing tolerance of AXTOL ± 8.6 nm.

[0123] The temperature shift of the optical bandpass filter 22 may be neglected since it may be close to zero depending on the substrate.

[0124] The active laser source may have a thermal shift of around 0.07 nm / degree C. For automotive applications, for example, with temperature ranges of -40 degree C to 105 degree C (AEC-Q100 grade 2), the laser thermal shift may be about 10.2 nm. For the conventional light detection device of Fig. 2 this adds up to a total wavelength shift of the transmission wavelength range of the optical bandpass filter 22 of 56.4 nm, while for the embodiment of Fig. 7 the total wavelength shift of the transmission wavelength range of the optical bandpass filter 22 is about 23.5 nm.

[0125] Hence, a relative SNR gain of about 1.55 is achieved.

[0126] Returning to the general explanations, summarizing some aspects of some embodiments:

[0127] The splitting of the lens arrangement into two parts allows to position the optical bandpass filter inside the lens arrangement by positioning it between the two parts.

[0128] The first lens arrangement reduces the maximum angle of incidence on the optical bandpass filter such that the optical bandpass filter can have a lower bandwidth.

[0129] The lower bandwidth allows a higher rejection of ambient light such that the SNR is improved.

[0130] The SNR may thus be improved, e.g., in ToF systems (in both dToF and iToF) by reducing the influence of ambient light.

[0131] As discussed above, the ambient light rejection is improved by creating a low incidence angle plane inside the camera objective lens stack, where the optical bandpass filter is placed, allowing for the use of an optical bandpass filter with a lower bandwidth.

[0132] The optical bandpass filter may be tunable to account for a temperature drift of the wavelength of the emitted light of the active light source of the laser, a temperature drift of the transmission wavelength range of the optical bandpass filter and manufacturing tolerances.

[0133] Note that the present technology can also be configured as described below.

[0134] (1) An active light sensing system, including: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

[0135] (2) The active light sensing system of (1), wherein the optical bandpass filter is an optical interference filter.

[0136] (3) The active light sensing system of (1) or (2), wherein the first lens arrangement includes a first plurality of lenses which includes a mixture of negative and positive lenses, in particular, wherein the first lens arrangement includes a fish-eye lens, and wherein the second lens arrangement includes a second plurality of positive lenses.

[0137] (4) The active light sensing system of (1) or (2), wherein the transmission wavelength range of the optical bandpass filter has a bandwidth of less than 5 nm.

[0138] (5) The active light sensing system of anyone of (1) to (4), wherein the propagation angle of the light ray that has propagated through the first lens arrangement is less than 5 degrees with respect to the optical axis.

[0139] (6) The active light sensing system of anyone of (1) to (5), wherein the optical bandpass filter is a tunable optical bandpass filter.

[0140] (7) The active light sensing system of (6), wherein the tunable optical bandpass filter is a tunable free space Fabry-Perot optical bandpass filter.

[0141] (8) The active light sensing system of anyone of (1) to (7), wherein the active light source includes a laser.

[0142] (9) The active light sensing system of anyone of (1) to (8), wherein the wavelength of the emitted light of the active light source is in the near-infrared spectral region.

[0143] (10) The active light sensing system of anyone of (1) to (9), wherein the active light sensing system is a direct time-of-flight system.

[0144] (11) The active light sensing system of anyone of (1) to (9), wherein the active light sensing system is an indirect time-of-flight system. (12) The active light sensing system of anyone of (1) to (11), wherein the optical sensor includes a plurality of light detection pixels arranged in rows and columns, each light detection pixel being configured to perform photoelectric conversion on incident light.

[0145] (13) A device, including an active light sensing system, wherein the active light sensing system includes: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

[0146] (14) The device of (13), wherein the optical bandpass filter is an optical interference filter.

[0147] (15) The device of (13) or (14), wherein the first lens arrangement includes a first plurality of lenses which includes a mixture of negative and positive lenses, in particular, wherein the first lens arrangement includes a fish-eye lens, and wherein the second lens arrangement includes a second plurality of positive lenses.

[0148] (16) The device of (13) or (14), wherein the transmission wavelength range of the optical bandpass filter has a bandwidth of less than 5 nm.

[0149] (17) The device of anyone of (13) to (16), wherein the propagation angle of the light ray that has propagated through the first lens arrangement is less than 5 degrees with respect to the optical axis.

[0150] (18) The device of anyone of (13) to (17), wherein the optical bandpass filter is a tunable optical bandpass filter. (19) The device of (18), wherein the tunable optical bandpass filter is a tunable free space Fabry-Perot optical bandpass filter.

[0151] (20) The device of anyone of (13) to (19), wherein the active light sensing system is a direct or an indirect time-of-flight system.

Claims

CLAIMS1. An active light sensing system, comprising: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

2. The active light sensing system of claim 1, wherein the optical bandpass filter is an optical interference filter.

3. The active light sensing system of claim 1, wherein the first lens arrangement includes a first plurality of lenses which includes a mixture of negative and positive lenses, in particular, wherein the first lens arrangement includes a fish-eye lens, and wherein the second lens arrangement includes a second plurality of positive lenses.

4. The active light sensing system of claim 1, wherein the transmission wavelength range of the optical bandpass filter has a bandwidth of less than 5 nm.

5. The active light sensing system of claim 1, wherein the propagation angle of the light ray that has propagated through the first lens arrangement is less than 5 degrees with respect to the optical axis.

6. The active light sensing system of claim 1, wherein the optical bandpass filter is a tunable optical bandpass filter.

7. The active light sensing system of claim 6, wherein the tunable optical bandpass filter is a tunable free space Fabry-Perot optical bandpass filter.

8. The active light sensing system of claim 1, wherein the active light source includes a laser.

9. The active light sensing system of claim 1, wherein the wavelength of the emitted light of the active light source is in the near-infrared spectral region.

10. The active light sensing system of claim 1, wherein the active light sensing system is a direct time-of-flight system.

11. The active light sensing system of claim 1 , wherein the active light sensing system is an indirect time-of-flight system.

12. The active light sensing system of claim 1, wherein the optical sensor includes a plurality of light detection pixels arranged in rows and columns, each light detection pixel being configured to perform photoelectric conversion on incident light.

13. A device, comprising an active light sensing system, wherein the active light sensing system includes: an active light source configured to emit light; and a light detection device, including: an optical sensor configured to perform photoelectric conversion on incident light; an optical bandpass filter having a transmission wavelength range which includes a wavelength of the emitted light of the active light source; and a first lens arrangement and a second lens arrangement; wherein: the first lens arrangement is configured to reduce a propagation angle of an incoming light ray with respect to the optical axis as defined by the first lens arrangement and the second lens arrangement, the optical bandpass filter is positioned between the first and the second lens arrangement in the optical path of the light ray that has propagated through the first lens arrangement, and the second lens arrangement is configured to focus the light ray that has propagated through the first lens arrangement and the optical bandpass filter on the optical sensor.

14. The device of claim 13, wherein the optical bandpass filter is an optical interference filter.

15. The device of claim 13, wherein the first lens arrangement includes a first plurality of lenses which includes a mixture of negative and positive lenses, in particular, wherein the first lens arrangement includes a fish-eye lens, and wherein the second lens arrangement includes a second plurality of positive lenses.

16. The device of claim 13, wherein the transmission wavelength range of the optical bandpass filter has a bandwidth of less than 5 nm.

17. The device of claim 13, wherein the propagation angle of the light ray that has propagated through the first lens arrangement is less than 5degrees with respect to the optical axis.

18. The device of claim 13, wherein the optical bandpass filter is a tunable optical bandpass filter.

19. The device of claim 18, wherein the tunable optical bandpass filter is a tunable free space Fabry-Perot optical bandpass filter.

20. The device of claim 13, wherein the active light sensing system is a direct or an indirect time-of-flight system.

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