Abstract:
An optical navigation module for receiving control from an object is provided. The optical navigation module includes a module surface above which the object is disposed; a light source located under the module surface and configured to project a first cone of light to the object along a first optical axis through a first optical construction; and a light sensor located under the module surface and configured to detect a second cone of light that is resulted from the first cone of light being reflected by the object along a second optical axis through a second optical construction, and thereby to collect a spatial intensity profile of the reflected light. The intersection of the first optical axis and the second optical axis is below the module surface.

Description:
FIELD OF THE PATENT APPLICATION 
       [0001]    The present patent application relates to an optical navigation module and more particularly to an optical navigation module that has a compact size and a desired small sensing range without sacrificed sensor sensitivity. 
       BACKGROUND 
       [0002]    Optical navigation module is an essential component of consumer electronics requiring user input through a GUI (Graphical User Interface). Existing designs usually have light sensors configured to receive reflected light as much as possible while the sensing range is not in consideration. 
         [0003]    However, in many applications, the sensing range of the optical navigation module has to be taken as a main consideration. In these cases, the sensing range needs to be limited to a usable range. Electrical methods such as reducing the sensor sensitivity have been developed to limit the sensing range. On the other hand, it is desired to have a small sized optical navigation module for which the sensing range can be limited to a usable range simply by optical methods rather than electrical methods so that the sensor sensitivity is not sacrificed. 
       SUMMARY 
       [0004]    The present patent application is directed to an optical navigation module for receiving control from an object. In one aspect, the optical navigation module includes a module surface above which the object is disposed; a light source located under the module surface and configured to project a first cone of light to the object along a first optical axis through a first optical construction; and a light sensor located under the module surface and configured to detect a second cone of light that is resulted from the first cone of light being reflected by the object along a second optical axis through a second optical construction, and thereby to collect a spatial intensity profile of the reflected light. The intersection of the first optical axis and the second optical axis is below the module surface. 
         [0005]    The optical navigation module may further include a data processing unit electrically connected to the light sensor. The data processing unit is configured to convert the subsequent change of the spatial intensity profile collected by the light sensor into information regarding the motion of the object. 
         [0006]    The light source may include a laser that emits coherent light. The laser may be a vertical-cavity surface-emitting laser. The light source may be configured to emit light that has a wavelength of 850 nm. 
         [0007]    The light sensor may include an array of light sensing pixels. The spatial intensity profile may include a speckle pattern. The second optical construction may include an aperture. The second optical construction may include a lens, a prism, a mirror assembly, or a plurality of light guiding structures each independently carrying a spatially separated portion of the reflected light to the light sensor. 
         [0008]    The module surface may be the outermost surface of a window plate that is made of material that selectively transmits the light emitted by the light source. The window plate may only transmit light in the invisible light spectrum. 
         [0009]    In another aspect, the optical navigation module includes a module surface above which the object is disposed; a light source located under the module surface and configured to project a first cone of light to the object along a first optical axis through a first optical construction; a light sensor located under the module surface and configured to detect a second cone of light that is resulted from the first cone of light being reflected by the object along a second optical axis through a second optical construction, and thereby to collect a spatial intensity profile of the reflected light; and a data processing unit electrically connected to the light sensor. The intersection of the first optical axis and the second optical axis is below the module surface. The data processing unit is configured to convert the subsequent change of the spatial intensity profile collected by the light sensor into information regarding the motion of the object. The module surface is the outermost surface of a window plate that is made of material that selectively transmits the light emitted by the light source. 
         [0010]    In yet another aspect, the optical navigation module includes a module surface above which the object is disposed; a light source located under the module surface and configured to project a first cone of light to the object along a first optical axis through a first optical construction; a light sensor located under the module surface and configured to detect a second cone of light that is resulted from the first cone of light being reflected by the object along a second optical axis through a second optical construction, and thereby to collect a spatial intensity profile of the reflected light; and a data processing unit electrically connected to the light sensor. The intersection of the first optical axis and the second optical axis is below the module surface. The data processing unit is configured to convert the subsequent change of the spatial intensity profile collected by the light sensor into information regarding the motion of the object. The second optical construction includes an aperture. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates an optical navigation module according to an embodiment of the present patent application. 
           [0012]      FIG. 2  schematically illustrates the optical navigation module depicted in  FIG. 1  from the perspective of geometrical optics. 
           [0013]      FIG. 3  schematically shows a top view of the optical navigation module in  FIG. 1 . 
           [0014]      FIG. 4  illustrates an optical navigation module according to another embodiment of the present patent application. 
           [0015]      FIG. 5  shows a graph of relative intensity received by the light sensor versus the vertical distance of the object surface from the module surface. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Reference will now be made in detail to a preferred embodiment of the optical navigation module disclosed in the present patent application, examples of which are also provided in the following description. Exemplary embodiments of the optical navigation module disclosed in the present patent application are described in detail, although it will be apparent to those skilled in the relevant art that some features that are not particularly important to an understanding of the optical navigation module may not be shown for the sake of clarity. 
         [0017]    Furthermore, it should be understood that the optical navigation module disclosed in the present patent application is not limited to the precise embodiments described below and that various changes and modifications thereof may be effected by one skilled in the art without departing from the spirit or scope of the protection. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure. 
         [0018]      FIG. 1  illustrates an optical navigation module according to an embodiment of the present patent application. Referring to  FIG. 1 , the optical navigation module  100  is configured to detect the motion of an object. The optical navigation module  100  includes a light source  101  which illuminates the surface of the object  102  positioned above a module surface  108  by a cone of illumination light  103 . In this embodiment, the object  102  is a finger of a user. The surface of the object  102  reflects the illumination light  103 . Part of the reflected light  104  travels through an aperture  105  to a light sensor  106 , which is sensitive to a spectrum including the wavelength of the light emitted by the light source  101 . Reflection by the object surface can be in the form of specular or scattered reflection or both. 
         [0019]    The motion of the object  102  induces a change in the spatial intensity profile of the reflected light projected on the light sensor  106 . The light sensor  106  is a light sensing pixel array configured for capturing the spatial intensity profile of the reflected light. By comparing the current and subsequent spatial intensity profiles, the direction and distance that the object moves on the x-y plane can be determined by a data processing unit electrically connected to the light sensor  106 , which may be optionally included in the optical navigation module. The data processing unit in this embodiment includes a microprocessor. Alternatively, the optical navigation module may not include the data processing unit while the data processing unit is externally connected to the optical navigation module. If the light source  101  is incoherent, the light sensor  106  captures the image of the illuminated surface of the object  102 . Otherwise, if the light source  101  is coherent, the light sensor  106  captures a speckle pattern formed by the reflected light  104  projected on the light sensor array  106 . 
         [0020]    The aperture  105  can be incorporated in a lens or prism disposed along the reflected light path to the light sensor  106  depending on the construction of the light sensing optical system. The aperture  105  may also include a mirror assembly or a number of light guiding structures each independently carrying a spatially separated portion of the reflected light to the light sensor  106 . There may also be lens structures  107  or prism structures disposed along the illumination light path depending on the construction of illumination optics. 
         [0021]    In this embodiment, the module surface  108  is the outermost surface of a window plate that is made of material that selectively transmits the light emitted by the light source  101 . The window plate, preferably only transmits light in the invisible light spectrum. 
         [0022]    The size, orientation and position of the aperture  105  together with the light sensor area determine the geometry of the cone of light that is able to reach the light sensor  106 . This cone of reflected light  104  receivable by light sensor  106  and the cone of illumination light  103  overlap to form a region above the module surface  108  representing the sensing region  109  of the module. The reflected light  104  can reach the light sensor  106  and thus the motion of the object  102  can be detected only when the surface of the object  102  is inside this sensing region  109 . The height  110  of this sensing region  109  from the module surface  108  defines the maximum sensing range of this module. 
         [0023]    Referring to  FIG. 1 , the actual sensing range  111  depends on the threshold sensitivity of the light sensor  106  and the surface properties of the surface of the object  102  to be detected, and should be within the maximum sensing range  110 . For finger navigation applications, the sensing range is generally required to be small, typically less than 0.5 mm, so that the module is only sensitive to the finger motion when the finger is almost in contact with the finger navigation module. 
         [0024]      FIG. 2  schematically illustrates the optical navigation module depicted in  FIG. 1  from the perspective of geometrical optics. Referring to  FIG. 2 , the virtual light source  201  is the virtual image of the real light source while the virtual light sensor  202  is the virtual image of the real light sensor. The virtual light source  201  emits a cone of light beam  203  subtending an angle of φ emit    204  in air (φ emit  is negative if the cone illuminating on the object surface is converging). The illumination chief ray, which runs along the optical axis of illumination  205 , makes an angle θ cr     —     emit    206  with the normal of the module surface  207 . The angle that the upper marginal ray θ up     —     mr     —     emit    208  makes with the normal of the module surface  207  is given by: 
         [0000]    
       
         
           
             
               
                 
                   
                     θ 
                     
                       up_mr 
                        
                       _emit 
                     
                   
                   ≈ 
                   
                     
                       θ 
                       cr_emit 
                     
                     - 
                     
                       
                         
                           φ 
                           emit 
                         
                         2 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0025]    Similarly, the virtual light sensor  202  receives a cone of light  209  subtending an angle of θ refl    210  in air (φ refl  is negative if the cone tracing from the module surface  207  back to the object surface is converging). The chief ray, which runs along the optical axis  211  of this cone of detectable light, makes an angle θ cr     —     refl    212  with the normal of the module surface  207  and it intersects the optical axis of illumination  205  at the position  213 . The angle that the upper marginal ray θ up     —     mr     —     refl    214  makes with the normal of the module surface  207  is given by: 
         [0000]    
       
         
           
             
               
                 
                   
                     θ 
                     
                       up_mr 
                        
                       _refl 
                     
                   
                   ≈ 
                   
                     
                       θ 
                       cr_refl 
                     
                     - 
                     
                       
                         
                           φ 
                           refl 
                         
                         2 
                       
                       . 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0026]      FIG. 3  schematically shows a top view of the optical navigation module in  FIG. 1 . Referring to  FIG. 3 , the light spot  301  of the illumination cone of light, the light spot of the cone of reflected light  302  receivable by the light sensor, the virtual light source  303  and the virtual light sensor  304  projected on the module surface along the x-y plane are illustrated. r up     —     mr     —     rmit    305  and r up     —     mr     —     refl    306  are the radii of light spots at where the upper marginal rays of the cone of illumination and the cone of reflected light intercepting the module surface along the x-axis respectively. d  307  is the displacement of position of the optical axis of the cone of reflected light  308  relative to the position of the optical axis of the cone of illumination  309  on the module surface. If the position of the optical axis of the cone of reflected light  308  projected on the module surface is at between the projected virtual light source position  303  and the projected position of the optical axis of the cone of illumination  309 , the displacement d  307  is negative. 
         [0000]    Then the maximum sensing range can be found by: 
         [0000]    
       
         
           
             
               
                 
                   
                     h 
                     max 
                   
                   = 
                   
                     
                       
                         
                           r 
                           up_emit 
                         
                         + 
                         
                           r 
                           up_refl 
                         
                         + 
                         d 
                       
                       
                         
                           tan 
                            
                           
                               
                           
                            
                           
                             θ 
                             
                               up_mr 
                                
                               _emit 
                             
                           
                         
                         + 
                         
                           tan 
                            
                           
                               
                           
                            
                           
                             θ 
                             
                               up_mr 
                                
                               
                                 _ref 
                                  
                                 l 
                               
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0027]    The actual sensing range can be equal to h max  when the light sensor is able to respond to reflected light no matter how small the optical power is. So in the real case, the actual sensing range will be a fraction of h max  depending on the sensitivity of the light sensor and the object&#39;s surface properties such as reflectivity and diffusiveness. 
         [0028]    In order to have a small value of h max , the denominator of equation (3) have to be large while the numerator have to be kept small. Large θ up     —     mr     —     emit  and θ up     —     mr     —     refl  are not desired because they indicate that the cones of illumination light and reflected light receivable by the light sensor lie at very oblique orientation which forces the optical navigation module to be large in size. For the numerator, since both r up     —     mr     —     emit  and r up     —     mr     —     refl  are positive, the most efficient way to attain a small h max  is to design the module with a negative d (d&lt;0), which corresponds to the intersection point of the optical axis of the cone of illumination and the optical axis of the cone of reflected light receivable by the light sensor is below the module surface. In this way, the illumination part and the light sensing part are brought closer together, which is favorable to small module size. 
         [0029]      FIG. 4  illustrates an optical navigation module according to another embodiment of the present patent application. In this embodiment, the light source  401  is a VCSEL (vertical-cavity surface-emitting laser) and the aperture  402  is simply a slit structure. In this embodiment, the VCSEL is configured to emit light that has a wavelength of 850 nm. The optical axis of the cone of illumination  403  and the optical axis the cone of reflected light  404  intersect at the position  405  below the module surface  406 . 
         [0030]      FIG. 5  shows a graph of relative intensity received by the light sensor versus the vertical distance of the object surface from the module surface, z object-module , for the designs of d=0.2 mm (d&gt;0), d=0 mm and d=−0.2 mm (d&lt;0) for the embodiment shown in  FIG. 4 . Referring to  FIG. 5 , in the case of d=0.2 mm, the intensity received by the light sensor has a local maximum. The intensity drops with the increase of Z object-module  only when z object-module  is greater than the point corresponding to the local maximum intensity. Therefore, h max  will be higher than that in the other cases. In the cases of d=0 mm and d=−0.2 mm, the intensity drops with the increase of z object-module  monotonically and with a steeper slope, which enables a small h max  value. According to equation (3), h max  is found to be 1.2 mm for the case of d=−0.2 mm. The actual experimental sensing range is around 0.5 mm which is within the calculated range. 
         [0031]    Possible applications of the above embodiments can be optical mice, laptop computers, handheld devices, and any other consumer electronics requiring user input through a GUI (Graphical User Interface). The module can take any desired shape according to the appearance requirements, such as a round shape, a rectangular shape, and etc. 
         [0032]    While the present patent application has been shown and described with particular references to a number of embodiments thereof, it should be noted that various other changes or modifications may be made without departing from the scope of the present invention.