Patent Publication Number: US-2022231482-A1

Title: Infrared-Laser Source Device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to United Kingdom Patent Application Number 2100638.2, filed Jan. 18, 2021, the disclosure of which is hereby incorporated by reference in its entirety herein. 
     BACKGROUND 
     Today, laser diodes are used in a wide variety of sectors such as medicine, telecommunications, and entertainment for example. However, one of the preferred applications to which the present disclosure refer is the field of optical detection for monitoring purposes. Among the different types of laser sources there is the vertical-cavity surface-emitting laser, or VCSEL, that is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers. With 940 nm emission wavelength, or similar wavelength in the near-infrared (NIR), such laser sources are at the cutting edge of the lighting technology. The main advantages are the small size, narrow infrared (IR) emission bandwidth, resulting in a high sunlight immunity, high output power and good efficiency. As prices are getting more and more attractive, VCSELs are planned to be used for many upcoming driver and in-cabin monitoring camera projects. 
     Unfortunately, the high power combined with the small size, creates very high intensities on the light emitting surface. When looking at the source from the front, this creates retinal projections in the human eye with high intensities leading to a perceptibility of IR-light that is visible as dark-red-glow, whereas the IR-light is supposed to be invisible for the human eye. Such a dark-red-glow may disturb or dazzle the driver which has his face in the field of lighting. This issue is not limited to VCSELs but may occur with other types of laser diodes providing beams in the NIR range. 
     Existing laser sources typically used e.g. for in-cabin monitoring drivers behaviors of motor vehicles, are provided with a single diffusing element playing the role of light distributing element of the laser beam that is initially emitted in a single direction. A micro lens array is usually used to distribute the laser light across the scene, i.e. towards the face of the drivers according to the aforementioned example. 
     There is a need to overcome the aforementioned issues and drawbacks at least partially, especially to improve safety and comfort of any person present in a light field illuminated by an infrared-laser source. 
     SUMMARY 
     The present disclosure relates to the field of laser source devices, especially infrared-laser source devices that are typically used for illuminating a scene that need to be observed by a monitoring camera. Such infrared-laser source devices are particularly efficient to illuminate a dark or nocturnal scene. More specifically, the beams provided by such infrared-laser source devices are directed, or likely to be oriented, towards a human face which must not be blinded or dazzled for safety or comfort reasons. The present disclosure also relates to a lighting device, e.g. for a monitoring camera, which comprises such an infrared-laser source device, as well as a vehicle, especially a motor vehicle, equipped with such a lighting device. 
     Due to the infrared-laser source device of the present disclosure, the radiance of the laser exiting surface at the light output interface of the device can be reduced while maintaining the desired angular distribution and power of the light on the target surface of the illuminated scene. In other words, the problem caused by high light intensities at the output interface is solved by increasing the size of the light emitting area that is visible to the human eye if it looks at the exiting surface of the external housing of the infrared-laser source device. Advantageously, the present disclosure does not reduce the light power provided by the laser source onto the illuminated scene. Furthermore, the light distribution, provided by the angular exit distribution of the light, on the target surface of the scene may also be maintained. In addition, these technical effects and the aforementioned advantages can be obtained without significantly increasing the height of the external housing of the infrared-laser source device. 
     According to one embodiment, the IR-laser beam emitted by the infrared-laser source is in a near-infrared range. For example, the IR-laser beam may comprise 940 nm emission wavelength. 
     According to a preferred embodiment, the infrared-laser source is a vertical-cavity surface-emitting laser (VCSEL). 
     In one embodiment, at least one of the first light distributing element and the second light distributing element is made of at least one of a micro-lens array, a translucent material, a grained surface, a free-form lens or an advanced beam shaper capable of homogenizing an input beam while shaping the output intensity profile and the way light is distributed in space. 
     In another embodiment, the distance between the first light distributing element and the second light distributing element is made variable by an adjusting means. 
     According to one embodiment, the second light distributing element is located at a distance comprised between 2 and 5 mm from the first light distributing element. 
     In a further embodiment, the infrared-laser source is made of a single element and the second light distributing element is substantially located halfway between the infrared-laser source and the first light distributing element. 
     In a different embodiment, the infrared-laser source is made of a plurality of separated elements and the second light distributing element is made of a micro-lens arranged onto each of said elements. Preferably, the second light distributing element is located at a distance which is substantially greater than the spacing between the separated elements of the second light distributing element. 
     According to one embodiment, the first light distributing element  15  further widens the IR-laser beam that exits the second light distributing element and/or corrects the distribution of at least one portion of said IR-laser beam. 
     According to one embodiment, the infrared-laser source and the second light distributing element are arranged within an internal housing which is located inside the external housing. The external housing is preferably an add-on with respect to the internal housing. 
     In another embodiment, at least one of the external housing and the internal housing comprises a translucent material, preferably plastic or glass, acting as light output interface. 
     In a further embodiment, at least one of the first light distributing element and the second light distributing element is integrated to or arranged against the external housing, respectively the internal housing. 
     The present disclosure also relates to a lighting device, preferably a lighting device for a monitoring camera, which comprises the infrared-laser source device according to any of its embodiment or according to any possible combination of its embodiments. 
     The present disclosure further relates to a vehicle, preferably a motor vehicle, comprising the lighting device mentioned above. 
     Other embodiments and advantages will be disclosed hereafter in the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure and the embodiments suggested in the present disclosure should be taken as non-limitative examples and will be better understood with reference to the attached Figures in which: 
         FIG. 1  is a schematic representation of a laser source device according to the prior art, 
         FIG. 2  is a schematic representation of the infrared-laser source device according to a first main embodiment of the present disclosure, 
         FIG. 3  shows, more specifically, a schematic representation of the IR-laser beam within the device of  FIG. 2 , so as to better illustrate one of the technical effects provided by the present disclosure, 
         FIG. 4  provides a graph comparison of the effects provided by the prior art, shown on the left side, with respect to the present disclosure, shown on the right side, when looking the laser beam as it appears on the light output interface from outside of the device, on the upper part of the figure, and when looking the laser beam as it appears on a target surface, on the bottom of the figure, 
         FIG. 5  is a schematic representation of a second main embodiment of the present disclosure, 
         FIG. 6  is a schematic representation of a third main embodiment of the present disclosure, 
         FIGS. 7A to 7C  show, as variants of any embodiments of the present disclosure, details regarding the front part of the external housing, and/or the internal housing if any, 
         FIG. 8  schematically depicts a lighting device provided with the infrared-laser source device of the present disclosure, and 
         FIG. 9  is a schematic illustration of a motor vehicle including the lighting device of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     In some previous examples, a light source device including a plurality of light emitters and a projection optical system configured to a magnification of the light emission amount per unit area in the light emission region. In still other previous examples, a VCSEL assembly including a plurality of individually addressable infrared-emitting VCSELs arranged in a VCSEL array; a controller arranged to address individual VCSELs of the VCSEL array; and a plurality of primary optics elements arranged in a primary optics array. This assembly allows to adjust the illuminance over relatively small scene regions, e.g. regions as small as the arm and chest or eyes and nose of a person in such a scene. 
     Another previous example relates to a laser arrangement including a laser array and especially a Vertical Cavity Surface Emitting Laser (VCSEL) array provided with a diffusor, a lighting device including a laser or VCSEL array and a time-of-flight camera including such a laser arrangement. One of the main goals of this document is to provide an arrangement with reduced building height. 
     In yet another example relates to a laser device with configurable intensity distribution. The main object disclosed in this document is to provide a laser device which allows a generation of a desired intensity distribution in the working plane without the need of an optics specially designed for this intensity distribution or beam profile. 
     None of these prior examples can overcome the issue resulting from the aforementioned dark-red-glow. Accordingly, there is a need to overcome the aforementioned issues and drawbacks at least partially, especially to improve safety and comfort of any person present in a light field illuminated by an infrared-laser source. 
     As general matter, it should be noted that the sizes and the ratios of the elements shown in the appended figures are not respected but have been greatly exaggerated so as to privilege the general principle of the device&#39;s operation and device&#39;s layout. This is why these figures are mainly qualified as being schematic representations. 
       FIG. 1  provides a schematic illustration of a laser source device  1  according to the prior art. Such a device typically includes an external housing  11  that may be mounted onto a printed circuit board  20 . The housing  11  includes, in its front part F, a light output interface  12  that may consist of a transparent or translucent portion arranged within the housing  11  such as a laser light permeable window. 
     The external housing  11  further includes, in its rear part R, an infrared-laser source  14  that is able to emit an IR-laser beam B. At the output of the source  14 , the laser beam B is, as any laser beam, pointing toward a single direction and made of a single wavelength. As a result, the laser beam B is originally a parallel beam as schematically depicted in  FIG. 1 . The size of the laser beam B mainly depends on the size of the infrared-laser source  14 . Actually, the source  14  may be made up of a plurality of micro-laser sources arranged in an array for example. The IR-laser beam B emitted by the infrared-laser source  14  further provides a first emitting area C 1  at the light output interface  12 , or substantially at the light output interface  12 . 
     Finally, the external housing  11  of  FIG. 1  also includes a light distributing element  15  aiming to diverge the light at the light output interface  12 . Accordingly, the light provided by the emitting area C 1  towards the outside of the housing  11  is no longer a parallel beam but a divergent beam that is thus more suitable to illuminate a target object, person or surface within a monitoring scene for example. 
     As schematically depicted in  FIG. 1 , as well as in some other figures, the light output interface  12  can preferably be regarded as including the light distributing element  15  given that the thickness of such an element is much smaller than depicted in the schematic representation provided by the appended figures. In addition, it should be also noted that the emitting area C 1  has been schematically represented in the middle of the thickness of the light distributing element  15 , so as to comply with the optical scheme showing the change in cross-sectional area within the laser beam B caused by the light distributing element  15 . However, since the light distributing element  15  is located against the front part F of the external housing  11 , or even integrated therein, and since the thickness of the optical element is much smaller than depicted in the figures, one can consider that the emitting area C 1  corresponds to the coverage provided by the laser beam B on the external face of the housing  11 , as it would appear for a person looking at the infrared-laser source device  1  from the front. 
     The main issue of the laser source device  1  of  FIG. 1  lies in the fact that a person looking at the infrared-laser source device  1  from the front can be disturbed or dazzled by a dark-red glow caused by the radiance of the IR-laser beam B. Indeed, due to the high light power of the infrared-laser source  14  and the small coverage provided by the emitting area C 1  at the light output interface  12 , the IR-light becomes visible for the human eye, especially within the near-infrared (NIR) spectra, while IR-light (including NIR-light) is supposed to be invisible for the human eye. As a result, prevention of eye safety limits or eye confusion are harder to reach with the needed system performance, in particular in the case where illuminating device, such as that of  FIG. 1 , is used for monitoring human behaviors, e.g. using in-cabin monitoring camera pointed towards human faces. 
     The present disclosure intends to solve such a concern by suppressing or at least drastically reducing the aforementioned red-glow effect. To this end,  FIG. 2  shows, as first embodiment of the present disclosure, an infrared-laser source device  10  provided with an external housing  11 . The external housing  11  basically includes the same elements as those described in connection with  FIG. 1 , namely:
         a light output interface  12  arranged in a front part F of the external housing,   at least one infrared-laser source  14  arranged in a rear part R of the external housing  11 , the infrared-laser source  14  being able to emit an IR-laser beam B which provides a first emitting area C 1  at the light output interface  12 , and   a first light distributing element  15  that diverges light at the light output interface  12 .       

     Contrary to  FIG. 1 , the infrared-laser source device  10  of the present disclosure further includes a second light distributing element  16  separated from the first light distributing element  15  and providing, at the light output interface  12 , a second emitting area C 2  larger than the first emitting area C 1 . 
     Due to the infrared-laser source device  10 , the light emitting surface C 2 , as it appears for a person looking thereto, is increased relative to the first emitting area C 1  due to the second light distributing element  16 . This effect is schematically depicted in  FIG. 3  which shows that the IR-laser beam B, issued from the infrared laser source  14 , is successively enlarged by the first and second light distributing elements  15 ,  16 , so as to provide the first and second emitting areas C 1 , C 2  respectively. The second emitting area C 2  is clearly larger than the first emitting area C 1 . As a result, the radiance of the second emitting area C 2  is advantageously reduced while maintaining the other main parameters of the laser beam B, namely the power of the light and the desired angular distribution on the target surface. 
       FIG. 4  is a pattern comparison showing the benefit provided by the present disclosure (on the right side of the figure) with respect to the prior art shown (on the left part of the figure). The upper part of the figure shows two black square zones, each having a side of a little more than 8 mm. Within each of these black square zones is represented the emitting area at the light output interface  12  as it appears, on the one hand, for the laser source device  1  of the prior art (on the left side) and, on the other hand, for the infrared-laser source device  10  of the present disclosure (on the right side). Each of the emitting area C 2  is located at the exit surface of the external housing  11  of the related laser source device  1 ,  10 . Accordingly, the exit surface has been schematically marked by a pictogram showing an opened window. One can note that the emitting area of the prior art is very small (the pattern is about 2×2 mm) thus providing a concentrated radiance, while the emitting area of the present disclosure (which corresponds to the second emitting area C 2 ) is much larger (the pattern is about 5×4 mm) thus providing a reduced radiance. 
     The same power has been used for energizing the infrared laser source  14  providing the IR-laser beam B. Accordingly, one can note that the same power used for illuminating a larger surface leads to lower the intensity. Therefore, any person looking at the second emitting area C 2  provided by the infrared-laser source device  10  will no longer be disturbed or much less disturbed by the dark-red-glow. Accordingly, the present disclosure provides key-advantages including, among others, relaxed eye-safety conditions, no or much lower perceptibility of the IR-light and no longer or reduced laser speckles (i.e. small spots or patches of colors). 
     At the bottom of  FIG. 4 , the two lower squares represent the light distribution provided by the corresponding emitting area on a target surface. Accordingly, the lower row of squares has been schematically marked by a pictogram which represents a target. One can see that the light distribution on the target surface is the same or substantially the same for the device  1  of the prior art as for the device  10  of the present disclosure. More specifically, the target surface covered by the laser beam B has an aperture of about 60°, both on the horizontal axis and on the vertical axis, and the intensity of the light within the target surface is the same, or almost the same, for the device  1  of the prior art as that of the present disclosure. This means that the emitting areas of the exit surfaces as they appear on the device  1  of the prior art and on the device  10  of the present disclosure provide both the same light distribution on a monitored target. However, the infrared-laser source device  10  of  FIG. 2  has the advantage of providing a much lower radiance on the emitting surface C 2  at the light output interface  12 . 
     As another advantage, it should be noted that with the double-spreading of the light, as well as shown in  FIG. 3 , large light output areas can be obtained without massively increasing the high of the infrared-laser source device  10 . Since the size of such a device  10  may be critical, especially when it is to be located inside other apparatus such as monitoring camera for example, it is important to keep an infrared-laser source device  10  having a good compactness. 
     The IR-laser beam B emitted by the infrared-laser source  14  is preferably in a near-infrared range. The near infrared (NIR) includes radiations in the non-visible spectrum for the human eye which extend from 780-3000 nm. In this range, laser light emits radiations in the safe portion of the electromagnetic spectrum for the human eye, provided that the radiance of the emitting area at the light output interface  12  is small enough. In such a wavelength range and for a moderate radiance, the light is mainly absorbed by the cornea and by the lens, thus preventing the light to reach the retina. Preferably, the NIR-range of the IR-laser beam emitted by the infrared laser source  14  is between 780-3000 nm, in particular between 780-1300 nm and still preferably includes 940 nm emission wavelength. 
     According to a preferred embodiment, the infrared-laser source  14  is a vertical cavity surface laser (VCSEL). VCSEL is a type of semiconductor laser diode with a laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers which emit from surfaces formed by cleaving the individual chip out of a wafer. A typical size of VCSEL die is about 1 mm 2  (1×1 mm). The VCSEL laser diode or VCSEL chip has several advantages, especially in terms of production where the yield can be controlled to a more predictable outcome. Accordingly, there is a significant interest in using the technology provided by the VCSEL. 
     Reverting to the light distributing elements  15 ,  16 , they can be regarded as diffusing elements to spread the light received by each of them. These elements  15 ,  16  are preferably similar in design but not identical. At least one of the light distributing elements  15 ,  16  is made of at least one of a micro-lens array, a translucent material, a grained surface, a free-form lens or an advanced beam shaper capable of homogenizing an input beam while shaping the output intensity profile and the way light is distributed in space. 
     It should be noted that the light apertures provided by the light distributing elements  15 ,  16  are not necessarily the same. Accordingly, the spreading angle provided by one of the light distributing elements  15 ,  16  can differ from that of the other element. In addition, any of the light distributing elements  15 ,  16  may provide a symmetrical or an asymmetrical light distribution. Due to an asymmetrical light distribution, it may be possible to optimize the target surface that is e.g. to be illuminated, in particular if the infrared-laser source device  10  is off-axis with respect to the target surface. 
     According to one embodiment, the distance between the first light distributing element  15  and the second light distributing element  16  is made variable by an adjusting means. Such an adjusting means may be e.g. a tuning screw or a lockable sliding system able to slide the external housing  11  with respect to an internal housing  17  that will be disclosed in connection with  FIG. 6 . The goal of such an adjusting means may be regarded as providing the infrared-laser source device  10  adjustable, preferably once, e.g. during factory assembly. Accordingly, it may be adapted to several requirements or needs, especially in terms of field width. As a result, the distance between the infrared-laser source device  10  and the target becomes advantageously less critical. 
     As shown in the example of  FIG. 2 , the second light distributing element  16  is located between the infrared-laser source  14  and the first light distributing element  15 . According to one embodiment, the second light distributing element  16  is substantially located halfway between the infrared-laser source  14  and the first light distributing element  15 . 
     In another embodiment, the second light distributing element  16  is located at a distance between 2 and 5 mm from the first light distributing element  15 . Such values give a good idea of the compactness of the infrared-laser source device  10 . The distance between the two light distributing elements  15 ,  16  may be such that the emitting areas C 1  and C 2  are within a ratio equal to a factor of approximately 10, preferably between 7 and 15. For example, if the second light distributing element  16  has ±20° spread, i.e. an aperture angle of 40°, the distance between the first and second light distributing elements  15 ,  16  should be 3.5 mm. With such values, a typical VCSEL providing a first emitting area C 1  of 1 mm 2  should be used with a second light distributing element  16  able to provide a second emitting area C 2  of 12.6 mm 2 , so that the second emitting area C 2  may be a square area equivalent to 3.55×3.55 mm. 
       FIG. 5  illustrates a second main embodiment of the infrared-laser source device  10 . According to this embodiment, the infrared-laser source  14  is made of a plurality of separated elements. In addition, the second light distributing element  16  is preferably made of a micro-lens arranged onto each of these elements. In other words, a micro-lens array may be integrated into an infrared-laser source die. For example, the aforementioned plurality of elements of the infrared-laser source  14  may be a VCSEL die and the second light distributing element  16  may be an integrated diffusing element arranged on the VCSEL die. This embodiment provides a very compact result which is particularly appropriate to achieve the infrared-laser source device  10 . 
     As shown in the embodiment of  FIG. 5 , the second light distributing element  16  is located at a distance which is substantially greater than the spacing between the separated elements of the infrared-laser source  14 . 
     According to another embodiment, the first light distributing element  15  further widens the IR-laser beam B exiting the second light distributing element  16  and/or corrects the distribution of at least one portion of the IR-laser beam B. Correcting the distribution of a portion of the beam B could lead to get an asymmetric beam, e.g. in view to obtain an atypical distribution of the target lighting. 
       FIG. 6  shows another main embodiment in which the infrared-laser source  14  and the second light distributing element  16  are arranged within an internal housing  17  which, in turn, is located inside the external housing  11 . The external housing  11 , together with the first light distributing element  15 , could be regarded as a cover to be put onto the internal housing  17 , or designed to surround the internal housing  17 . Due to this embodiment, it becomes possible to enhance existing laser source devices  1  since the internal housing  17 , together with the infrared-laser source  14  and the second light distributing element  16  may correspond to the infrared-laser source device  1  of  FIG. 1 , and since the external housing  11 , together with the first light distributing element  17 , may be considered as an added module mounted onto the infrared-laser source device  1 . Accordingly, this embodiment appears to be an especially cost-effective solution. 
     The distance between the first and second light distributing elements  15 ,  16  may be easily set by adapting the height of the external housing  11 . The internal and external housings  17 ,  11  may be rigidly attached to each other or may be bound via an adjusting means enabling the aforementioned distance to be adjusted. Preferably, the external housing  11  is an add-on with respect to the internal housing  17 . Still preferably, both the internal and external housings  17 ,  11  are secured onto a printed circuit board  20 , as shown in  FIG. 6 . In one embodiment, the internal housing  17  is fitted to the external housing  11 , and the external housing  11  is mounted onto the printed circuit board  20  using any fastening means, including soldering. 
     According to a further embodiment, at least one of the external housing  11  and the internal housing  17  includes a translucent material, such as plastic or glass, acting as light output interface  12 . The translucent material may be a portion of the housings  11 ,  17  arranged in their front part F, or may be used as base material for the entire housings, more specifically for the entire of at least one of these housings. 
     As shown in  FIGS. 7A-7C , preferably at least one of the first light distributing element  15  and the second light distributing element  16  is integrated to or arranged against the external housing  11 , respectively the internal housing  17 . Although  FIGS. 7A-7C  show a portion of the external housing  11 , in particular the front part F of the housing provided with the first light distributing element  15  at the light output interface  12 , it should be noted that the same layouts could be applied to the internal housing  17  for example. According to  FIGS. 7A-7C , the light output interface  12  is made of a translucent material portion of the external housing  11 . 
     According to the variant shown in  FIG. 7A , the first light distributing element  15  is arranged against the front part F of the external housing  11 , in particular against the internal face of the external housing  11  at the output interface  12 . For example, in the variant of  FIG. 7A , the first light distributing element  15  may be a separate part glued to the translucent window of the external housing  11 . 
     According to the variant of  FIG. 7B , the first distributing element  15  is, at the light output interface  12 , integrated within the front part F of the external housing  11 , more specifically within the thickness of the external housing  11 , while being protected by a translucent window acting as at least a portion of the light output interface  12 . For example, the first light distributing element  15  may be embossed during a molding process of the external housing  11  or at least of the window of the external housing  11 . Alternatively, the window part of the external housing  11  may be machined to form a recess into which the light distributing element  15  may be glued for instance. 
     The third variant of  FIG. 7C  shows another embodiment in which the first light distributing element  15  is also integrated within the thickness of the external housing  11  which may act as a cover for the other elements of the infrared-laser source device  10 . In this variant, the translucent material portion (used as window for the IR-laser beam B) and the first light distributing element  15  have their own recess within the external housing  11 . Each of them may be glued to the housing, for example. 
     As schematically depicted in  FIG. 8 , the present disclosure also relates to a lighting device  30  for a camera  40 , preferably a monitoring camera. The lighting device  30  includes the infrared-laser source  10  according to any of its embodiments, or any possible combination of its embodiments previously disclosed. The lighting device  30  may be appended to the camera  40  or it may be embedded within the camera as illustrated in  FIG. 8 . As variant, the present disclosure may also relate to a camera  40 , preferably a monitoring camera, including the infrared-laser source  10  according to any of its embodiments, or any possible combination of its embodiments. The monitoring camera may monitor in-cabin of a vehicle for example. 
     As schematically depicted in  FIG. 9 , the present disclosure also relates to a vehicle  50 , preferably a motor vehicle, including the aforementioned lighting device  30  or camera  40  which is preferably a monitoring camera as that mentioned above. 
     The present disclosure further relates to a printed circuit board  20  including the infrared-laser source  10  according to any of its embodiments, or any possible combination of its embodiments. 
     Although an overview of the inventive subject matter has been described with reference to specific example embodiments, various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of embodiments of the disclosure disclosed in the present description.