Patent Publication Number: US-2021191143-A1

Title: Structured light generation device and diffractive optical element thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. patent application Ser. No. 16/161,258, filed Oct. 16, 2018, which is a continuation-in-part application of U.S. patent application Ser. No. 14/706,401, field May 7, 2015, and hereby incorporates the content of these applications by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an optical device, and more particularly to a structured light generation device. 
     BACKGROUND OF THE INVENTION 
     In current days mobile devices such as smart phones are essential electronic devices for most people in the modern societies. The use of mobile phone is no more limited to voice communication between two persons. In nowadays, smart phone generally contains large panel which is used as the media of input and output simultaneously, i.e., touch panel and display are combined together. As the trends of designing touch panels are toward the large-size touch panels, mobile devices have sufficient spaces to accommodate requisite components. However, in addition to the large-size touch panels, the trends of designing mobile devices are also toward light weightiness and slimness. Consequently, if some components of the mobile device have to be installed in the mobile device in a specified fashion because of the required functions or other factors, the thicknesses and the sizes of these components are directly related to the thickness of the mobile device. For example, in most commercially-available smart phones, the thickness of the lens module is larger than the thickness of the smart phone. Consequently, after the lens module is accommodated within the smart phone, the position of the lens module is usually protruded over the case of the smart phone. Under this circumstance, the smart phone is not aesthetically pleasing. 
     Historically, the introduction of camera/lens module to mobile phone was not essential in the beginning Since then, in less than 10-15 years, camera has been a standard equipment in mobile phone. Furthermore, multiple camera modules are even equipped in one mobile phone to enhance the imaging quality, such as depth of field, different zooming effects, wide-angle viewing and even stereo vision. To proceed more different capabilities of sensing and imaging, additional components of light emitters and sensors are required together with existing camera or even new-functional camera. Examples include LED flash light, ambient light source and sensor, diffusers for time of flight (TOF) and structured light module. Among the examples, the structured light module is mainly used to project a special light pattern in space for object recognition, e.g., facial recognition, and/or 3D information extraction, e.g., distance, range, and surface identifications. 
     As mentioned above, the smart phone is equipped with the lens module. In addition, the trend of designing the smart phone is toward the integration of a component having a projecting function and a 3D information acquiring function, in which structured light module plays a critical role.  FIG. 1  is a schematic side view illustrating a conventional light generation device, which is capable to produce a structured light. As shown in  FIG. 1 , the light generation device  1  comprises a light source module  12 , a collimator  14  and a diffractive optical element (DOE)  16 . For example, the light source module  12  is a laser light source module for generating a divergent beam  13 . After the divergent beam  13  is received by a collimator  14 , the divergent beam  13  is collimated as a collimated light beam  15  by the collimator  14 . After the collimated light beam  15  is received by the diffractive optical element  16 , the collimated light beam  15  is diffracted by the diffractive optical element  16 . Consequently, a diffracted light beam  17  with a specified beam diffusion angle θ′ and/or a specified structured light pattern is outputted from the diffractive optical element  16 . Typical value of θ′ is 30 to 45 degrees which means the projected range (FOV) is 60-90 degrees and typically it is projected with a rectangular form. 
     For most DOEs that used in structured light module, for reducing the occurrence of the diffraction error, the light beam to be received by the diffractive optical element (DOE)  16  has to be collimated as the collimated light beam  15 . In other words, it is necessary to install the collimator  14  in the light generation device  1  to collimate the divergent beam  13  as the collimated light beam  15 . For achieving good collimating efficacy, the collimator  14  needs to have a larger effective focal length, a smaller numerical aperture (NA) or a larger F/# (f-number). Under this circumstance, the overall length (OAL) of the light generation device  1  or the total track length (TTL) cannot be effectively reduced. Consequently, it is difficult to reduce the weightiness and the thickness of the mobile device. In such a circumstance, it is micro-lens array (MLA) to be used to replace the collimating lens as a solution such that the OAL as well as TTL can be reduced. However, the design and the fabrication of MLA is complicated, and the yield is low which is also caused by the alignment issue in assembly. 
     Therefore, it is important to introduce a novel architecture to reduce the weightiness and the thickness of the mobile device. For example, a new structure of the light generation device and a new structure of the diffractive optical element are provided. If the smaller diffraction error and the higher diffraction efficiency are obtained when the divergent beam (i.e., the non-collimated light beam) is received by the diffractive optical element, the possibility of producing a slim-type light generation device is increased. 
     SUMMARY OF THE INVENTION 
     For overcoming the drawbacks of the conventional technologies, the present invention provides a structured light generation device. A diffractive optical element of the structured light generation device receives a non-collimated light beam. Since the structured light generation device is not equipped with a collimator, the reduction percentage of the overall thickness of the structured light generation device is more than 20%. Since the material cost and the assembling cost of the overall structured light generation device are both reduced, the structured light generation device is suitably applied to a slim-type mobile device or a wearable device. 
     In accordance with an aspect of the present invention, there is provided a structured light generation device. The structured light generation device includes a laser light source module and a diffractive optical element. The laser light source module includes a light source. The light source emits a non-collimated light beam. The diffractive optical element includes a diffraction layer. After the non-collimated light beam from the laser light source module is received by the diffraction layer, the non-collimated light beam is modulated as an optical information-bearing light. The structured light generation device satisfies at least one of mathematical relationships (1) and (2): 
     
       
         
           
             
               
                 
                   
                     
                       W 
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                     ≥ 
                     
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                         θ 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
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                     1 
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                     W 
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                     7 
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     wherein θ is a half angle of beam diffusion of the non-collimated light beam, φ is a beam diameter of the non-collimated light beam when projected to the diffraction layer, and W d  is a working distance between the light source and the diffraction layer. 
     In an embodiment, the optical information-bearing light is a coded structured light. 
     In an embodiment, the structured light generation device further includes a casing. The laser light source module and the diffractive optical element are accommodated within the casing. The optical information-bearing light is outputted from the structured light generation device through at least one light output zone of the casing. 
     In an embodiment, the diffractive optical element further includes a light-transmissible substrate. The diffraction layer is disposed on a first surface of the light-transmissible substrate. 
     In an embodiment, the diffraction layer comprises plural microstructures. 
     In an embodiment, the first surface and a second surface of the light-transmissible substrate are concentric surfaces. The first surface of the light-transmissible substrate is arranged between the laser light source module and the second surface of the light-transmissible substrate, or the second surface of the light-transmissible substrate is arranged between the laser light source module and the first surface of the light-transmissible substrate. 
     In an embodiment, the first surface of the light-transmissible substrate is a flat surface or a curvy surface. 
     In an embodiment, the diffraction layer is distributed over a part or an entire of the first surface of the light-transmissible substrate. 
     In an embodiment, the diffraction layer is located at an outer side of the first surface of the light-transmissible substrate and exposed outside the first surface of the light-transmissible substrate, or the diffraction layer is located at an inner side of the first surface of the light-transmissible substrate. 
     In an embodiment, the first surface of the light-transmissible substrate faces the laser light source module or faces an external side of the structured light generation device. 
     In an embodiment, the diffractive optical element further includes a beam-expandable functional structure. The beam-expandable functional structure is formed on or disposed on a second surface of the light-transmissible substrate. The non-collimated light beam is transmitted through the beam-expandable functional structure. 
     In an embodiment, the beam-expandable functional structure includes a concave lens structure with a geometric optical surface. The concave lens structure is produced by a semiconductor production process or a precise machining process. 
     In an embodiment, the first surface of the light-transmissible substrate is arranged between the laser light source module and the second surface of the light-transmissible substrate, or the second surface of the light-transmissible substrate is arranged between the laser light source module and the first surface of the light-transmissible substrate. 
     In an embodiment, the diffractive optical element further includes an additional diffraction layer. The additional diffraction layer is disposed on a second surface of the light-transmissible substrate. The second surface of the light-transmissible substrate is arranged between the laser light source module and the first surface of the light-transmissible substrate. After the non-collimated light beam from the light source is transmitted through the additional diffraction layer, the non-collimated light beam is subjected to a beam-expanding action. The beam-expanded non-collimated light beam is modulated as the optical information-bearing light by the diffraction layer on the first surface of the light-transmissible substrate. 
     In an embodiment, a thickness of the light-transmissible substrate is smaller than 1 mm. 
     In an embodiment, there is a spacing distance between the laser light source module and the light-transmissible substrate, and the spacing distance is in a range between 0 mm and 4 mm. 
     In an embodiment, a numerical aperture (NA) of the diffractive optical element is in a range between 0.1 and 0.64. 
     In an embodiment, a non-air medium is filled between the light source and the diffractive optical element, and the non-collimated light beam is transmitted through the non-air medium. 
     In an embodiment, the non-air medium is made of a silicone resin, an epoxy resin or a polymer compound. 
     In an embodiment, a numerical aperture (NA) of the diffractive optical element is in a range between 0.2 and 0.96. 
     In an embodiment, a thickness of the diffraction layer is smaller than 0.1 mm. 
     In an embodiment, the laser light source module outputs a dot-like light pattern, a stripe-like light pattern, a multi-stripe light pattern, a randomly-distributed dot array light pattern or a regularly-distributed dot array light pattern. 
     In an embodiment, the laser light source module further includes an additional light source, and the diffractive optical element includes a first modulation unit corresponding to the light source and a second modulation unit corresponding to the additional light source. After the non-collimated light beam from the light source is transmitted through the first modulation unit, the optical information-bearing light is generated. After an additional non-collimated light beam from the additional light source is transmitted through the second modulation unit, an additional optical information-bearing light is generated. 
     In an embodiment, the non-collimated light beam from the light source and the additional non-collimated light beam from the additional light source are outputted according to different time sequences, or the non-collimated light beam from the light source and the additional non-collimated light beam from the additional light source are outputted according to the same time sequence. 
     In accordance with another aspect of the present invention, there is provided a diffractive optical element. The diffractive optical element includes a light-transmissible substrate and a diffraction layer. The diffraction layer is disposed on the light-transmissible substrate. After a non-collimated light beam from a light source is received by the diffraction layer, the non-collimated light beam is modulated as an optical information-bearing light. The diffractive optical element satisfies at least one of mathematical relationships (1) and (2): 
     
       
         
           
             
               
                 
                   
                     
                       W 
                       d 
                     
                     ≥ 
                     
                       ϕ 
                       
                         
                           2 
                           · 
                           tan 
                         
                          
                         
                             
                         
                          
                         θ 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     1 
                      
                     
                         
                     
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                     7 
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                   2 
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     wherein θ is a half angle of beam diffusion of the non-collimated light beam, φ is a beam diameter of the non-collimated light beam when projected to the diffraction layer, and W d  is a working distance between the light source and the diffraction layer. 
     In an embodiment, the diffraction layer is disposed on a first surface of the light-transmissible substrate. 
     In an embodiment, the diffraction layer includes plural microstructures. 
     In an embodiment, the first surface and a second surface of the light-transmissible substrate are concentric surfaces. The first surface of the light-transmissible substrate is arranged between the light source and the second surface of the light-transmissible substrate, or the second surface of the light-transmissible substrate is arranged between the light source and the first surface of the light-transmissible substrate. 
     In an embodiment, the first surface of the light-transmissible substrate is a flat surface or a curvy surface. 
     In an embodiment, the diffraction layer is distributed over a part or an entire of the first surface of the light-transmissible substrate. 
     In an embodiment, the diffraction layer is located at an outer side of the first surface of the light-transmissible substrate and exposed outside the first surface of the light-transmissible substrate, or the diffraction layer is located at an inner side of the first surface of the light-transmissible substrate. 
     In an embodiment, the diffractive optical element further includes a beam-expandable functional structure. The beam-expandable functional structure is formed on or disposed on a second surface of the light-transmissible substrate. 
     In an embodiment, the beam-expandable functional structure includes a concave lens structure, and the concave lens structure is distributed over a part or an entire of the second surface of the light-transmissible substrate. 
     In an embodiment, the diffractive optical element further includes an additional diffraction layer. The additional diffraction layer is disposed on a second surface of the light-transmissible substrate. The second surface of the light-transmissible substrate is arranged between the light source and the first surface of the light-transmissible substrate. After the non-collimated light beam from the light source is transmitted through the additional diffraction layer, the non-collimated light beam is subjected to a beam-expanding action. The beam-expanded non-collimated light beam is modulated as the optical information-bearing light by the diffraction layer on the first surface of the light-transmissible substrate. 
     In an embodiment, a thickness of the light-transmissible substrate is smaller than 1 mm. 
     In an embodiment, a thickness of the diffraction layer is smaller than 0.1 mm. 
     In an embodiment, a numerical aperture (NA) of the diffractive optical element is in a range between 0.1 and 0.64. 
     In an embodiment, a non-air medium is filled between the light source and the diffractive optical element, and the non-collimated light beam is transmitted through the non-air medium. 
     In an embodiment, the non-air medium is made of a silicone resin, an epoxy resin or a polymer compound. 
     In an embodiment, a numerical aperture (NA) of the diffractive optical element is in a range between 0.2 and 0.96. 
     In accordance with a further aspect of the present invention, there is provided a structured light generation device. The structured light generation device includes a laser light source module and a diffractive optical element. The laser light source module includes a light source. The light source emits a non-collimated light beam. The diffractive optical element includes a diffraction layer. After the non-collimated light beam from the laser light source module is received by the diffraction layer, the non-collimated light beam is modulated as an optical information-bearing light. An optical axis of the light source and the diffractive optical element is non-linear. 
     In an embodiment, the structured light generation device further includes a reflective mirror. After the non-collimated light beam from the laser light source module is projected to the reflective mirror, the non-collimated light beam is reflected to the diffractive optical element by the reflective mirror. 
     In an embodiment, there is a first distance between the light source and the reflective mirror along the optical axis, and there is a second distance between the reflective mirror and the diffractive optical element along the optical axis. A total distance of the first distance and the second distance is in a range between 0 mm and 7 mm. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view illustrating a conventional light generation device; 
         FIG. 2A  schematically illustrates a dot-like light pattern outputted from a laser light source module; 
         FIG. 2B  schematically illustrates a stripe-like light pattern outputted from the laser light source module; 
         FIG. 2C  schematically illustrates a regularly-distributed dot array light pattern outputted from the laser light source module; 
         FIG. 2D  schematically illustrates a randomly-distributed dot array light pattern outputted from the laser light source module; 
         FIG. 3  is a schematic side view illustrating the architecture of a structured light generation device according to a first embodiment of the present invention; 
         FIG. 4  is a schematic enlarged side view illustrating the diffractive optical element of the structured light generation device as shown in  FIG. 3 ; 
         FIG. 5  is a schematic side view illustrating a portion of a structured light generation device according to a second embodiment of the present invention; 
         FIG. 6  is a schematic enlarged side view illustrating a diffractive optical element of a structured light generation device according to a third embodiment of the present invention; 
         FIG. 7  is a schematic side view illustrating a portion of a structured light generation device according to a fourth embodiment of the present invention; 
         FIG. 8A  is a schematic enlarged side view illustrating a diffractive optical element of a structured light generation device according to a fifth embodiment of the present invention; 
         FIG. 8B  schematically illustrates the optical path of the structured light generation device according to the fifth embodiment of the present invention; 
         FIG. 9A  is a schematic enlarged side view illustrating a diffractive optical element of a structured light generation device according to a sixth embodiment of the present invention; 
         FIG. 9B  schematically illustrates the optical path of the structured light generation device according to the sixth embodiment of the present invention; 
         FIG. 10  is a schematic side view illustrating a portion of a structured light generation device according to a seventh embodiment of the present invention; 
         FIG. 11A  schematically illustrates a first optical information-bearing light which is generated after the non-collimated light beam from the first light source of the structured light generation device of  FIG. 10  is transmitted through the diffractive optical element; 
         FIG. 11B  schematically illustrates a second optical information-bearing light which is generated after the non-collimated light beam from the second light source of the structured light generation device of  FIG. 10  is transmitted through the diffractive optical element; 
         FIG. 11C  schematically illustrates a third optical information-bearing light which is generated after the non-collimated light beam from the third light source of the structured light generation device of  FIG. 10  is transmitted through the diffractive optical element; and 
         FIG. 12  is a schematic side view illustrating a structured light generation device according to an eighth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a structured light generation device. The structured light generation device is suitably applied to a mobile device such as a smart phone. In case that the laser light source module of the conventional light generation device  1  has a TO-CAN package structure, the size is 6×6×7 mm (length×width×thickness). In accordance with a feature of the present invention, the structured light generation device is not equipped with the optical element for collimating the light beam. Consequently, the size is reduced to 4×6×4 mm or less. Since the thickness of the structured light generation device of the present invention is reduced to 4 mm or less, the thickness reduction of the present structured light generation device is larger than 20% (i.e., 7 mm-4 mm/7 mm=42.85%) when compared with the conventional light generation device. In case that the package structure of the present structured light generation device uses a surface mount device (SMD) laser light source module, the thickness of the structured light generation device can be reduced to 2 mm. When compared with the conventional light generation device, the thickness reduction of the present structured light generation device is larger than 50% (i.e., 7 mm-2 mm/7 mm=71.42%). Consequently, the structured light generation device is suitably applied to the handheld device. Moreover, the laser chip of the laser light source module can be directly printed on a printed circuit board (PCB) and fabricated by the conventional mounting process. 
     As known, the laser beam emitted by the general laser light source module is a non-collimated light beam. Conventionally, a collimator is used to collimate the non-collimated light beam into a parallel light beam. Then, the parallel light beam is introduced into another optical element (such as a diffractive optical element), and thus a structured light is generated. Typically, the beam divergence angle (full angle) from laser source can be ranged from 10, 20, and 40 or even 60 degrees, depending the characteristics of light emission and the beam divergence angle may be not uniform. Consequently, the collimator can be spherical, aspherical and even bi-conic to correct the wavefront for the DOE efficiently. In this context, the term “non-collimated light beam” indicates the laser beam emitted by the general laser light source module. Moreover, before the non-collimated light beam is introduced into the diffractive optical element of the present invention, the non-collimated light beam is not subjected to any collimating process. Consequently, the non-collimated light beam has a beam divergence that is not equal to zero degree. 
     Preferably but not exclusively, the laser light source module for emitting the non-collimated light beam includes an edge emitting laser light source module, a vertical cavity surface emitting laser (VCSEL) light source module or any other appropriate laser light source module. The size of emitter can be ranged from a few to a few hundred μm (1 μm=1 mm/1000) for a single point-like source to a few mm for a VCSEL array. In case of edge emitting laser source, the source size is generally a stripe with a scale of a few μm×a few hundred μm (height×width). 
     Please refer to  FIGS. 2A, 2B, 2C and 2D .  FIG. 2A  schematically illustrates a dot-like light pattern outputted from a laser light source module.  FIG. 2B  schematically illustrates a stripe-like light pattern outputted from the laser light source module.  FIG. 2C  schematically illustrates a regularly-distributed dot array light pattern outputted from the laser light source module.  FIG. 2D  schematically illustrates a randomly-distributed dot array light pattern outputted from the laser light source module. It is noted that the light patterns outputted from the laser light source module are not restricted to the light patterns of  FIGS. 2A, 2B, 2C and 2D . For example, in another embodiment, the laser light source module outputs a multi-stripe light pattern. 
     In case that the type of the laser light source module is different, the type of the non-collimated light beam from the laser light source module is different. Preferably, the non-collimated light beam is a Gaussian beam. In case that the laser light source module is a Fabry-Perot type laser light source module, the outputted non-collimated light beam is an elliptic Gaussian beam. In case laser light source module is a vertical cavity surface emitting laser light source array (VCSEL array), the outputted non-collimated light beam is a TEM01 mode beam, a TEM10 mode beam or a higher-order TEM mode donut beam. 
     In case the types of the laser light source modules are different, the non-collimated light beams from the laser light source modules have different wavefronts and are obviously distinguished. In an embodiment, a diffraction layer of the diffractive optical element is designed according to the wavefront of the non-collimated light beam. Regardless of the type of the diffraction layer of the diffractive optical element, the thickness is smaller than 0.1 mm. 
       FIG. 3  is a schematic side view illustrating the architecture of a structured light generation device according to a first embodiment of the present invention. The structured light generation device  2  comprises a laser light source module  22  and a diffractive optical element  24 . The structured light generation device  2  may further comprise a casing  23 . The laser light source module  22  and the diffractive optical element  24  are accommodated within the casing  23 . In this embodiment, the laser light source module  22  comprises a light source  220  for outputting a non-collimated light beam  25 . Preferably but not exclusively, the light source  220  is a laser chip. The non-collimated light beam  25  is outputted from a window  221  of the laser light source module  22 . In an embodiment, the window  221  is an opening of the laser light source module  22 . Optionally, an additional component (not shown) without the collimating function is located at the opening. For example, the additional component is a dustproof transparent protective sheet or glue. In some other embodiments, the laser light source module  22  provides a lighting surface or a vertical cavity surface emitting laser light source array (VCSEL array) for emitting plural non-collimated light beams  25 . 
     The diffractive optical element  24  is located in front of the laser light source module  22 . The non-collimated light beam  25  is directed to the diffractive optical element  24 . In accordance with the present invention, no additional optical element or structure with the collimating function is included in the laser light source module  22  or interposed between the laser light source module  22  and the diffractive optical element  24 . Moreover, there is a spacing distance L between the diffractive optical element  24  and the laser light source module  22 . The spacing distance L is in the range between 0 mm and 4 mm. If the heat dissipation efficacy is not impaired, the diffractive optical element  24  may be completely attached on the laser light source module  22 . Alternatively, the diffractive optical element  24  and the laser light source module  22  are separated from each other by a specified distance. If the diffractive optical element  24  of the present invention is completely attached on the laser light source module  22 , the total length T of the diffractive optical element  24  and the laser light source module  22  (i.e., the overall length along the optical axis X 1 ) can be largely reduced. In case that the laser light source module  22  has a TO-CAN package structure, the thickness U of the casing  23  is reduced to 4 mm or less. In case that the laser light source module  22  has a surface mount device (SMD) package structure, the thickness U of the casing  23  is reduced to 2 mm or less. 
     The diffractive optical element  24  comprises a light-transmissible substrate  241  and a diffraction layer  242 . The diffraction layer  242  is disposed on the light-transmissible substrate  241  or disposed within the light-transmissible substrate  241 . In an embodiment, the light-transmissible substrate  241  is made of a light-transmissible material. The diffraction layer  242  comprises plural microstructures that are formed on at least one surface of the light-transmissible substrate  241  and have diffractive textures or patterns. After the non-collimated light beam  25  is directed to the diffractive optical element  24  and diffracted by the diffractive optical element  24 , an optical information-bearing light  27  with two dimensions or more than two dimensions is generated. The optical information-bearing light  27  is outputted to the outside of the structured light generation device  2  through a light output zone  231  of the casing  23  and projected to any appropriate light-receiving surface or space in order to perform various operations (e.g., a 3D information acquiring operation or an object identifying operation). 
     Preferably but not exclusively, the optical information-bearing light is a coded structured light. Moreover, the optical information-bearing light has a structured pattern with plural regular dots, a structured pattern with plural random dots, or a structured pattern with plural stripes. Moreover, since the optical information-bearing light  27  is modulated by the diffractive optical element  24 , the brightness of the optical information can be uniform or have a gray level change according to the practical requirements. That is, there are no unexpected light spots beyond the designing condition. In addition to the optical information with the higher brightness, the optical information-bearing light  27  may also contain the background light with the lower brightness. In case that the optical information-bearing light  27  contains the background light, the brightness is uniform or slowly changed. 
     For determining the minimum volume of the structured light generation device  2 , the structured light generation device  2  satisfies at least one of the mathematical relationships (1) and (2): 
     
       
         
           
             
               
                 
                   
                     
                       W 
                       d 
                     
                     ≥ 
                     
                       ϕ 
                       
                         
                           2 
                           · 
                           tan 
                         
                          
                         
                             
                         
                          
                         θ 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     1 
                      
                     
                         
                     
                      
                     mm 
                   
                   &lt; 
                   
                     W 
                     d 
                   
                   &lt; 
                   
                     7 
                      
                     
                         
                     
                      
                     mm 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     wherein θ is a half angle of beam diffusion of the non-collimated light beam  25 , φ is a beam diameter of the non-collimated light beam  25  when projected to the diffraction layer  242 , and W d  is a working distance between the light source  220  and the diffraction layer  242 . 
     In an embodiment, the half angle of beam diffusion (θ) of the non-collimated light beam  25  is 20 degree, and the beam diameter φ of the non-collimated light beam  25  when projected to the diffraction layer  242  is at least 1 mm. That is, if the optical information-bearing light  27  is generated after the non-collimated light beam  25  is transmitted through the diffraction layer  242 , the beam diameter φ of the non-collimated light beam  25  when projected to the diffraction layer  242  is at least 1 mm. According to the above mathematical relationship (1), the working distance W d  between the light source  220  and the diffraction layer  242  is at least one 1.37 mm. 
     After the type of the laser light source module  22  of the structured light generation device  2  is selected and the half angle of beam diffusion (θ) of the non-collimated light beam  25  and the beam diameter φ of the non-collimated light beam  25  are obtained, the working distance W d  between the light source  220  and the diffraction layer  242 . Consequently, the minimum volume of the structured light generation device  2  can be determined. 
       FIG. 4  is a schematic enlarged side view illustrating the diffractive optical element of the structured light generation device as shown in  FIG. 3 . A first surface  2411  of the light-transmissible substrate  241  faces the laser light source module  22 . The optical information-bearing light  27  is outputted from a second surface  2412  of the light-transmissible substrate  241 . The diffraction layer  242  is formed on the first surface  2411  of the light-transmissible substrate  241 . The second surface  2412  of the light-transmissible substrate  241  is not equipped with the diffraction layer  242 . In an embodiment, the diffraction layer  242  comprises plural microstructures that are formed on and exposed to the first surface  2411  of the light-transmissible substrate  241  through a UV curable adhesive layer. In another embodiment, the diffraction layer  242  comprises plural microstructures that are formed on an outer side of the first surface  2411  of the light-transmissible substrate  241  through a textured layer by an etching process. The first surface  2411  and the second surface  2412  of the light-transmissible substrate  241  are in parallel with each other. The thickness of the light-transmissible substrate  241  is about 0.3 mm. The way of forming the diffraction layer  242  and the type and thickness of the light-transmissible substrate  241  are not restricted. 
       FIG. 5  is a schematic side view illustrating a portion of a structured light generation device according to a second embodiment of the present invention. The structures of the components of the structured light generation device which are identical to those of the first embodiment are not redundantly described herein. In the first embodiment, there is no filling material between the light source  220  and the diffractive optical element  24  and air is a medium for travelling the non-collimated light beam  25 . In this embodiment, a non-air medium  29  is filled between the light source  320  of the laser light source module  32  and the diffractive optical element  34 . The non-collimated light beam from the light source  320  is transmitted through the non-air medium  29 . Due to the non-air medium  29 , the structured light generation device can be fixed easily and fabricated quickly. Preferably but not exclusively, the non-air medium  29  is made of a silicone resin, an epoxy resin or a polymer compound. 
       FIG. 6  is a schematic enlarged side view illustrating a diffractive optical element of a structured light generation device according to a third embodiment of the present invention. The structures of the components of the structured light generation device which are identical to those of the first embodiment are not redundantly described herein. In this embodiment, the first surface  4411  of the light-transmissible substrate  441  facing the laser light source module does not have the diffracting function. The second surface  4412  of the light-transmissible substrate  441  is equipped with a diffraction layer  442  for receiving the non-collimated light beam and modulating the non-collimated light beam as the optical information-bearing light. In this embodiment, the first surface  4411  and the second surface  4412  of the light-transmissible substrate  441  are concentric surfaces. That is, the first surface  4411  and the second surface  4412  of the light-transmissible substrate  441  have the same center O. The drawing of  FIG. 6  gives a reference of location for the center O is only for illustration. To be specific, the center location is more away from the DOE surface such that the cross section and hence, the dimension of width is smaller. This design has some benefits. After the non-collimated light beam is transmitted through the first surface  4411  of the light-transmissible substrate  441 , the non-collimated light beam is directed to the second surface  4412  of the light-transmissible substrate  441  in a better incidence direction. Consequently, the diffractive optical element  44  has smaller diffraction error and the higher diffraction efficiency. In this embodiment, the diffractive optical element  44  has a proper numerical aperture (NA). Consequently, the first surface  4411  of the light-transmissible substrate  441  has sufficient collection power for the non-collimated light beam. Preferably but not exclusively, the numerical aperture (NA) of the diffractive optical element  44  is in the range between 0.1 and 0.64. 
       FIG. 7  is a schematic side view illustrating a portion of a structured light generation device according to a fourth embodiment of the present invention. The structures of the components of the structured light generation device which are identical to those of the third embodiment are not redundantly described herein. In the third embodiment, there is no filling material between the light source (not shown) and the diffractive optical element  44  and air is a medium for travelling the non-collimated light beam. In this embodiment, a non-air medium  59  is filled between the light source  520  of the laser light source module  52  and the diffractive optical element  54 . The non-collimated light beam from the light source  520  is transmitted through the non-air medium  59 . Due to the non-air medium  59 , the structured light generation device can be fixed easily and fabricated quickly. Preferably but not exclusively, the non-air medium  59  is made of a silicone resin, an epoxy resin or a polymer compound. 
     In this embodiment, the diffractive optical element  54  has a proper numerical aperture (NA). Consequently, the diffractive optical element  54  has sufficient collection power for the non-collimated light beam. Preferably but not exclusively, the numerical aperture (NA) of the diffractive optical element  54  is in the range between 0.2 and 0.96. 
     Please refer to  FIGS. 8A and 8B .  FIG. 8A  is a schematic enlarged side view illustrating a diffractive optical element of a structured light generation device according to a fifth embodiment of the present invention.  FIG. 8B  schematically illustrates the optical path of the structured light generation device according to the fifth embodiment of the present invention. The structures of the components of the structured light generation device which are identical to those of the first embodiment are not redundantly described herein. In this embodiment, a diffraction layer  642   a  is formed on the first surface  6411  of the light-transmissible substrate  641 , and a diffraction layer  642   b  is formed on the second surface  6412  of the light-transmissible substrate  641 . After the non-collimated light beam  65  from the light source  620  is transmitted through the diffraction layer  642   a , the non-collimated light beam  65  is subjected to a beam-expanding action and thus a beam-expanded non-collimated light beam  65 ′ is generated. In this embodiment, the laser wavelength is 850 nm and with a full beam diffusion angle 20 degrees. The corresponding object numerical aperture is 0.1 and effectively the f-number for the DOE is f/1.37. After the non-collimated light beam  65 ′ is received by the diffraction layer  642   b , the non-collimated light beam  65 ′ is modulated as an optical information-bearing light. In this embodiment, the thickness of the light-transmissible substrate  641  is 1 mm. Preferably but not exclusively, the thicknesses of the diffraction layer  642   a  and the diffraction layer  642   b  are not larger than 0.3 mm. The functions of the diffraction layers  642   a  and  642   b , the thicknesses of the diffraction layers  642   a  and  642   b  and the thickness of the light-transmissible substrate  641  may be varied according to the practical requirements. 
     The above examples are presented herein for purpose of illustration and description only. According to the practical requirements, the first surface or the second surface of the light-transmissible substrate of the diffractive optical element may be a flat surface or a curvy surface with a radian or a curvature. Moreover, the diffraction layer may be distributed over or formed on a part or an entire of the surface of the light-transmissible substrate. In the above embodiments, the diffraction layer is exposed outside the first surface or the second surface of the light-transmissible substrate. That is, the diffraction layer is located at an outer side of the first surface or second surface of the light-transmissible substrate. In some other embodiments, the diffraction layer is located at an inner side of the first surface or second surface of the light-transmissible substrate. 
     In addition to the above structure, the diffractive optical element of the present invention may have a functional surface for providing another function. Please refer to  FIGS. 9A and 9B .  FIG. 9A  is a schematic enlarged side view illustrating a diffractive optical element of a structured light generation device according to a sixth embodiment of the present invention.  FIG. 9B  schematically illustrates the optical path of the structured light generation device according to the sixth embodiment of the present invention. In the embodiment, the lasing wavelength is 850 nm and the full beam diffusion angle is 20 degrees. The structures of the components of the structured light generation device which are identical to those of the first embodiment are not redundantly described herein. In comparison with the first embodiment, the first surface  7411  of the light-transmissible substrate  741  of the diffractive optical element  74  facing the light source  720  has or comprises a beam-expandable structure or shape  744 . For example, the beam-expandable structure or shape  744  is a concave lens structure. Here the concave lens structure is with a radius of curvature is about −0.6596 mm. In this embodiment, the corresponding object numerical aperture is 0.1 and effectively the corresponding (working) f-umber is about f/1.44. 
     The concave lens structure has a geometric optical surface produced by a DOE semiconductor production process or a precise machining process. The second surface  7412  of the light-transmissible substrate  741  is equipped with the diffraction layer  742 . After the non-collimated light beam  75  is transmitted through the first surface  7411  of the light-transmissible substrate  741 , the size of the non-collimated light beam is expanded. Since the light beam  75 ′ to be projected to the diffraction layer  742  has a larger light-receiving area to acquire more wavefront modulation data, the projected image is more exquisite. It is noted that the beam-expandable structure or shape may be distributed over or formed on a part or an entire of the surface of the light-transmissible substrate. In this embodiment, the thickness of the light-transmissible substrate  741  is 1 mm. Preferably but not exclusively, the central thickness of the light-transmissible substrate  741  is not larger than 0.3 mm. 
     Please refer to  FIGS. 10, 11A, 11B and 11C .  FIG. 10  is a schematic side view illustrating a portion of a structured light generation device according to a seventh embodiment of the present invention.  FIG. 11A  schematically illustrates a first optical information-bearing light which is generated after the non-collimated light beam from the first light source of the structured light generation device of  FIG. 10  is transmitted through the diffractive optical element.  FIG. 11B  schematically illustrates a second optical information-bearing light which is generated after the non-collimated light beam from the second light source of the structured light generation device of  FIG. 10  is transmitted through the diffractive optical element.  FIG. 11C  schematically illustrates a third optical information-bearing light which is generated after the non-collimated light beam from the third light source of the structured light generation device of  FIG. 10  is transmitted through the diffractive optical element. 
     The structures of the components of the structured light generation device which are identical to those of the above embodiments are not redundantly described herein. In comparison with the above embodiments, the laser light source module  82  of the structured light generation device of this embodiment comprises a first light source  820   a , a second light source  820   b  and a third light source  820   c . The diffractive optical element  84  comprises a first modulation unit  843   a , a second modulation unit  843   b  and a third modulation unit  843   c  corresponding to the first light source  820   a , the second light source  820   b  and the third light source  820   c , respectively. After the non-collimated light beam from the first light source  820   a  is transmitted through the first modulation unit  843   a  of the diffractive optical element  84 , a first optical information-bearing light is generated. The structured light pattern  87   a  of the first optical information-bearing light is shown in  FIG. 11A . After the non-collimated light beam from the second light source  820   b  is transmitted through the second modulation unit  843   b  of the diffractive optical element  84 , a second optical information-bearing light is generated. The structured light pattern  87   b  of the second optical information-bearing light is shown in  FIG. 11B . After the non-collimated light beam from the third light source  820   c  is transmitted through the third modulation unit  843   c  of the diffractive optical element  84 , a third optical information-bearing light is generated. The structured light pattern  87   c  of the third optical information-bearing light is shown in  FIG. 11C . Preferably but not exclusively, the non-collimated light beams are outputted from the first light source  820   a , the second light source  820   b  and the third light source  820   c  in different time sequences. Under this circumstance, the structured light patterns  87   a ,  87   b  and  87   c  are shown according to different time sequences. According to the time sequences of outputting the non-collimated light beams from the first light source  820   a , the second light source  820   b  and the third light source  820   c , any two of the structured light patterns  87   a ,  87   b  and  87   c  are individually shown or overlapped with each other. 
       FIG. 12  is a schematic side view illustrating a structured light generation device according to an eighth embodiment of the present invention. The structures of the components of the structured light generation device which are identical to those of the above embodiments are not redundantly described herein. In this embodiment, the optical axis X 2  corresponding to the light source  920  of the laser light source module  92  and the diffractive optical element  94  is non-linear. The structured light generation device of this embodiment further comprises a reflective mirror  98 . The reflective mirror  98  is arranged between the laser light source module  92  and the diffractive optical element  94 . After the non-collimated light beam  95  from the light source  920  is projected to the reflective mirror  98 , the non-collimated light beam  95  is reflected to the diffractive optical element  94 . The reflected non-collimated light beam  95 ′ is received by the diffraction layer  942  of the diffractive optical element  94  and modulated as an optical information-bearing light  97 . The distance between the light source  920  and the reflective mirror  98  along the optical axis X 2  is L 1 . The distance between the reflective mirror  98  and the diffractive optical element  94  along the optical axis X 2  is L 2 . Preferably but not exclusively, the total distance of the distance L 1  and the distance L 2  is in the range between 0 mm and 7 mm. 
     From the above descriptions, the present invention provides a structured light generation device. In comparison with the conventional technology, the structured light generation device of the present invention is not equipped with the collimator between the laser light source module and the diffractive optical element. More especially, if the diffractive optical element is attached on the laser light source module, the total length of the structured light generation device of the present invention along the optical axis can be largely reduced. Under this circumstance, the material cost and the assembling cost of the overall structured light generation device are both reduced. Consequently, the structured light generation device is suitably applied to a slim-type mobile device or a wearable device. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.