Patent Publication Number: US-2023140294-A1

Title: Tunable light projector

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of and claims the priority benefit of U.S. application Ser. No. 16/836,939, filed on Apr. 1, 2020. The priori U.S. application Ser. No. 16/836,939 is a continuation-in-part application of and claims the priority benefit of U.S. application Ser. No. 16/371,127, filed on Apr. 1, 2019. The prior U.S. application Ser. No. 16/371,127 is a continuation-in-part application of and claims the priority benefit of U.S. application Ser. No. 16/044,484, filed on Jul. 24, 2018, which claims the priority benefit of U.S. provisional application Ser. No. 62/566,538, filed on Oct. 2, 2017. The prior U.S. application Ser. No. 16/371,127 also claims the priority benefit of U.S. provisional application Ser. No. 62/804,757, filed on Feb. 13, 2019. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     Technical Field 
     The invention generally relates to a sensing device and a light projector, and, in particular, to an optical sensing device, a structured light projector, and a tunable light projector. 
     Description of Related Art 
     At present, the mainstream technology in the field of 3-dimension (3D) sensing is divided into time of flight (TOF) and structured illumination. The TOF technology uses pulsed laser and complementary metal-oxide-semiconductor (CMOS) sensor to calculate the distance based on a measured reflection time. Due to the structure and costs, TOF 3D sensing is generally more suitable for resolving objects at long distance. In structured illumination, infrared source projects IR light onto a diffractive optical element (DOE) to produce 2D diffraction patterns, while a sensor is used to collect the reflected light. The distance of an object in 3-dimension can then be calculated using triangulation method. Structured illumination is limited by having projection lens with fixed focal length, which limits the distance that a clear and focused diffraction pattern are able to form, ultimately limiting the distance of an object that is resolvable to be within a small range. 
     To solve the foregoing problem of structured illumination, adding apodized lens to the lens group in order to produce a multifocal system was proposed. However, such a method comes at the expense of light efficiency, 2D diffraction pattern points and resolution. 
     Moreover, in the 3D face recognition of a mobile device, both a flood light system and a structured light system are used to achieve 3D face recognition. The flood light system is first used to determine whether an approaching object is a human face. If the approaching object is a human face, the structured light system is then started and used to determine whether the detected human face is the face of a user of the mobile device. However, adopting two systems, i.e. the flood light system and the structured light system, in a mobile device may occupy large space and be costly. 
     SUMMARY 
     The invention provides an optical sensing device which uses liquid crystal to control the focus of a structured light. 
     The invention provides a structured light projector which uses liquid crystal to control the focus of a structured light. 
     The invention provides a tunable light projector which uses a tunable liquid crystal panel to switch the light beam between a structured light and a flood light. 
     According to an embodiment of the invention, an optical sensing device adapted to detect an object or features of the object is provided. The optical sensing device includes a structured light projector and a sensor. The structured light projector is configured to project a structured light to the object. The structured light projector includes a light source, a diffractive optical element (DOE), and a liquid crystal lens module. The light source is configured to emit a light beam. The diffractive optical element is disposed on a path of the light beam and configured to generate diffraction patterns so as to form the structured light. The liquid crystal lens module is disposed on at least one of the path of the light beam and a path of the structured light and capable of controlling between at least two focusing state. The sensor is disposed adjacent to the structured light projector and configured to sense a reflected light. The reflected light is reflection of the structured light from the object. 
     According to an embodiment of the invention, a structured light projector is provided. The structured light projector includes a light source, a diffractive optical element, and a liquid crystal lens module. The light source is configured to emit a light beam. The diffractive optical element is disposed on a path of the light beam and configured to generate diffraction patterns so as to form the structured light. The liquid crystal lens module is disposed on at least one of the path of the light beam and a path of the structured light and capable of controlling between at least two focusing state. 
     According to an embodiment of the invention, a tunable light projector including a light source, a fixed optical phase modulator, a tunable liquid crystal panel, and a driver is provided. The light source is configured to emit a light beam. The fixed optical phase modulator is disposed on a path of the light beam and configured to modulate phases of the light beam. The tunable liquid crystal panel is disposed on the path of the light beam from the fixed optical phase modulator and configured to switch the light beam between a structured light and a flood light. The tunable liquid crystal panel includes a first substrate, a second substrate, a liquid crystal layer, a first electrode layer, and a second electrode layer. The liquid crystal layer is disposed between the first substrate and the second substrate. At least one of the first electrode layer and the second electrode layer is a patterned layer. The first electrode layer and the second electrode are both disposed on one of the first substrate and the second substrate, or are respectively disposed on the first substrate and the second substrate. The driver is electrically connected to the first electrode layer and the second electrode layer and configured to change a voltage difference between the first electrode layer and the second electrode layer, so as to switch the light beam between the structured light and the flood light. 
     According to an embodiment of the invention, a tunable light projector including a light source, a fixed optical phase modulator, and a tunable liquid crystal panel is provided. The light source is configured to emit a light beam, and the fixed optical phase modulator is disposed on a path of the light beam and configured to modulate phases of the light beam. The tunable liquid crystal panel is disposed on the path of the light beam and configured to be switched between a plurality of states, wherein the plurality of states include a lens array state in which the tunable liquid crystal panel comprises a lens array. 
     Base on the above, the structured light projector according to some embodiments includes at least one liquid crystal lens module with variable focal length. Having the liquid crystal lens module with variable focal length in the structured light projector increase the range of projected structured being in focus. Furthermore, a small optical sensor using the above structured light projector may be obtained. In the tunable light projector according to the embodiment of the invention, a tunable liquid crystal panel is adopted to switch a light beam between a structured light and a flood light, so that the embodiment of the invention integrates a flood light system and a structured light system into a single system, which reduces the cost and the volume of an electronic device having structured light and flood light functions. 
     To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG.  1    is a schematic diagram of an optical sensing device according to an embodiment of the invention. 
         FIG.  2    is a schematic cross-sectional view of a structured light projector of  FIG.  1   . 
         FIGS.  3 A- 3 C  are schematic cross-sectional views of another structured light projector according to at least one embodiment of the invention. 
         FIGS.  4 A- 4 B  are schematic cross-sectional views of various liquid crystal lens modules of  FIG.  2    under two different states according to at least one embodiment of the invention. 
         FIGS.  5 - 8    are schematic cross-sectional views of various liquid crystal lens modules of  FIG.  2    according to at least one embodiment of the invention. 
         FIG.  9    is a schematic diagram of a liquid crystal layer from a top view, in accordance with at least one embodiment of the invention. 
         FIGS.  10 A- 10 B  are schematic cross-sectional diagrams of another liquid crystal lens modules under two different states according to at least one embodiment of the invention. 
         FIG.  11 A  and  FIG.  11 B  are schematic cross-sectional views of a tunable light projector respectively in a structured light mode and a flood light mode according to an embodiment of the invention. 
         FIG.  12 A ,  FIG.  12 B , and  FIG.  12 C  are schematic top views of the first electrode layer in  FIG.  11 A  and  FIG.  11 B  respectively according to three embodiments in the invention. 
         FIG.  13 A ,  FIG.  13 B , and  FIG.  13 C  are schematic top views of other three variations of the first electrode layer in  FIG.  12 A . 
         FIG.  14 A  is a schematic cross-sectional view of the tunable liquid crystal panel in FIG.  11 A. 
         FIG.  14 B  and  FIG.  14 C  are other two variations of the tunable liquid crystal panel in  FIG.  14 A . 
         FIG.  15 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  15 B  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  15 C  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  16 A  shows the alignment direction of the first alignment layer or the second alignment layer in  FIG.  15 A  or  FIG.  15 C  according to an embodiment of the invention. 
         FIG.  16 B  shows the alignment directions of another variation of the first alignment layer or the second alignment layer in  FIG.  15 A  or  FIG.  15 C  according to another embodiment of the invention. 
         FIG.  17 A  is a schematic cross-sectional view of a tunable light projector adopting the alignment layers shown in  FIG.  16 B . 
         FIG.  17 B  shows a schematic top view of a spot area and the alignment layer in  FIG.  17 A . 
         FIG.  18 A ,  FIG.  18 B , and  FIG.  18 C  are schematic cross-sectional views of a tunable liquid crystal panel and the voltage difference applied to the liquid crystal layer in three different modes. 
         FIG.  19 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  19 B  is a schematic top view of the first substrate in  FIG.  19 A . 
         FIG.  20 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  20 B  is a schematic top view of the first substrate in  FIG.  20 A . 
         FIG.  21 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  21 B  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. 
         FIG.  22    is a schematic cross-sectional view of a tunable light projector according to another embodiment of the invention. 
         FIG.  23 A  and  FIG.  23 B  are schematic cross-sectional views of a tunable light projector respectively in a structured light mode and a flood light mode according to another embodiment of the invention. 
         FIG.  24    is a schematic cross-sectional view of a tunable light projector according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Further, spatially relative terms, such as “underlying”, “below”, “lower”, “overlying”, “upper”, “top”, “bottom”, “left”, “right” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
       FIG.  1    is a schematic cross-sectional view of an optical sensing device  10  according to an embodiment of the invention. The optical sensing device  10  shown in  FIG.  1    is a sensing device which uses structured light to detect an object. More specifically, the optical sensing device  10  includes a structured light projector  100  and a sensor  104  disposed adjacent to the structured light projector  100 . The structured light projector  100  is configured to generate a structured light SL towards an object  12 , and a sensor  104  is configured to sense the structured light SL reflected from the object  12 . The structured light may include, but are not limited to, multiple light beams that project a light pattern such as a series of lines, circles, dots or the like, to an object  12 , wherein the lines, circles, dots or the like may or may not be arranged in an ordered manner. The object  12  may be, for example, a hand, a human face or any other objects that have 3D features. When the structured light SL is projected on the object  12 , the light pattern of the structured light SL may deform due to the concave-convex surface of the object  12 . The deformed structured light SL is then reflected from object  12 , the reflected light passes through an opening  106  before reaching sensor  104 . The opening  106  includes, for example, a lens, an aperture, a transparent cover or the like. The sensor  104  senses the deformation of the light pattern on the object  12  so as to calculate the depths of the surface of the object  12 , i.e. distances from points on the object  12  to the sensors  104 . Sensor  104  may be connected to a processor (not shown) to calculate the 3-dimensional feature of the object  12 . 
       FIG.  2    is a cross-sectional diagram of a structured light projector  100  according to an embodiment of the invention. The structured light projector  100  shown includes a light source  110 , a liquid crystal lens module  120  and a diffractive optical element (DOE)  130 . The light source  110  disposed on one end of the structured light projector  100  is configured to emit a light beam LB. The light source  110  may be a light emitting device (LED), laser diode, an edge emitting laser, a vertical-cavity surface-emitting laser (VCSEL) or any other suitable light source capable of emitting a visible or non-visible (e.g. infrared (IR) or ultraviolet (UV)) light beam LB. In some embodiments, the light source  110  may be a single IR laser diode, in some other embodiments the light source  110  may be an array of IR laser diode, the number of light source forming light source  110  is not limited. 
     The structured light projector  100  further includes a liquid crystal lens module  120  disposed on the path of light beam LB. The liquid crystal lens module  120  is capable of controlling the focusing states of the light beam LB and provide at least two focusing state to the structured light projector  100 . Optionally, a polarizer (not shown) may be placed on the path of the light beam LB before the liquid crystal lens module  120  to provide liquid crystal lens module  120  with a polarized (e.g. linear polarized or circular polarized) light beam LB. 
     In  FIG.  2   , the diffractive optical element  130  is shown to be disposed on the path of the light beam LB after liquid crystal lens module  120 , however the order of placement of diffractive optical element  130  and liquid crystal lens module  120  is not limited. In some embodiments, the diffractive optical element  130  may be disposed on the path of the light beam LB before liquid crystal lens module  120 . In some embodiments, the diffractive optical element  130  may even be disposed between elements of liquid crystal lens module  120  on the path of the light beam LB. The diffractive optical element  130  is an optical element configured to generate diffraction patterns in order to generate the structured light SL as described above with reference to  FIG.  1   . For example, the diffractive optical element  130  may contain patterns that splits the light beam LB into multiple dots, or shape the light beam into gridlines, but is not limited thereto. For simplicity, the light beam LB after passing diffractive optical element  130  will henceforth be referred to as structured light SL. Furthermore, for ease of description, mutually orthogonal x-direction and z-direction is provided. For example, in the present embodiment, the z-direction is defined as the direction perpendicular to the light emitting surface of the light source  110 . 
       FIG.  3 A- 3 C  show schematic cross-sectional views of variations of structured light projectors  200   a - 200   c  according to some embodiments of the invention. Structured light projectors  200   a - 200   c  are similar to structured light projector  100  shown in  FIG.  2   . The difference between structured light projectors  200   a - 200   c  and structured light projector  100  lies in that structured light projectors  200   a - 200   c  include a liquid crystal lens cell  122  and a solid lens  124  while omitting liquid crystal lens module  120 . In some embodiment, the combination of liquid crystal lens cell  122  and solid lens  124  may also be regarded as liquid crystal lens module  120  of  FIG.  2   . 
     Referring to  FIG.  3 A , the solid lens  124  is disposed on the path of the light beam LB between the diffractive optical element  130  and the light source  110 , and the liquid crystal lens cell  122  is disposed on the path of the light beam LB between solid lens  124  and diffractive optical element  130 . In  FIG.  3 B , the solid lens  124  is disposed on the path of the light beam LB between the diffractive optical element  130  and the light source  110 , and the liquid crystal lens cell  122  is disposed on the side of diffractive optical element  130  away from the light source. In other words, liquid crystal lens cell  122  is disposed on the path of the structured light SL. In  FIG.  3 C , the solid lens  124  is disposed on the path of the light beam LB between the diffractive optical element  130  and the light source  110 , and the liquid crystal lens cell  122  is disposed on the path of the light beam LB between solid lens  124  and light source  110 . 
     In some embodiments, solid lens  124  may be a single lens or a multiple lens group that determines the primary focal length of the structured light projector  200   a . In some embodiments, solid lens  124  collimates the light beam LB before light beam LB enters liquid crystal lens cell  122  or diffractive optical element. In some embodiments, the liquid crystal lens cell  122  has a variable focal length and includes least one liquid crystal cell layer. The focal length of the liquid crystal lens cell  122  is controlled by controlling the orientation of the liquid crystal molecules (not shown) in the liquid crystal lens cell  122  by application of external electric field. 
       FIG.  4 A- 8    disclose some embodiment of liquid crystal lens module which may be used as liquid crystal lens module  120  of  FIG.  2   . In some embodiments, liquid crystal lens module disclosed in  FIG.  4 A- 8    may be used as liquid crystal lens cell  122  of  FIG.  3 A- 3 C  and the invention is not limited thereto. 
       FIGS.  4 A and  4 B  are schematic cross-sectional views of liquid crystal lens module  220  according to an embodiment of the invention. The liquid crystal lens module  220  includes a first substrate  224   a , a second substrate  224   b , and a liquid crystal layer  222 . The liquid crystal layer  222  is sandwiched between the first substrate  224   a  and the second substrate  224   b  in the vertical z-direction. An effective refractive index of each position on the liquid crystal layer  222  is related to a voltage applied on a first electrode  230   a  and a second electrode  230   b , wherein the first electrode  230   a  is disposed on the first substrate between the liquid crystal layer  222  and first substrate  224   a , the second electrode  230   b  is disposed on second substrate  224   b  between the liquid crystal layer  222  and second substrate  224   b , and the voltage is provided by power source  228 . The liquid crystal lens module  220  further includes alignment layers  232  disposed on first electrode  230   a  and second electrode  230   b  respectively and in contact with two opposing sides of liquid crystal layer  222 . The alignment layers  232   a  and  232   b  are layers having a surface texture to align the liquid crystal molecules  226  to an initial direction by controlling the pretilt angle and the polar angle of the liquid crystal molecules  226 . The pretilt angle is an angle between the long axis of a liquid crystal molecule  226  and a plane perpendicular to the z-direction, the polar angle is an angle between the long axis of a liquid crystal  226  and a fixed axis (e.g. along x-direction) in the plane perpendicular to z-direction. The materials for alignment layer  232  used in the present embodiments may be a polymer such as polyimide, but is not limited thereto. 
     Referring to  FIG.  4 A , the liquid crystal layer  222  of liquid crystal lens module  220  is a layer with non-uniform thickness. As shown in  FIG.  4 A , liquid crystal layer  222  has curved surface and a flat surface, and is thickest in the middle part. The curved surface of the liquid crystal layer  222  corresponds to a curved surface of first substrate  224   a , curved first electrode  230   a  and a curved top alignment layer  232 . Furthermore, in the present embodiment, when disconnected from power source  228 , liquid crystal molecules  226  are aligned to be substantially in the same orientation throughout liquid crystal layer  222 , i.e. all the long axis of liquid crystal molecules  226  are along the horizontal x-direction, wherein the x-direction and z-direction are orthogonal. When the electrodes  230   a  and  230   b  are connected to power source  228 , as shown in  FIG.  4 B , the orientation of liquid crystal molecules  226  is rotated such that the long axis is aligned to the z-direction. 
     In the present embodiment, liquid crystal lens module  220  of  FIG.  4 A- 4 B  can be regarded as a refractive lens. Specifically, when liquid crystal lens module  220  is not connected to power source  228 , the liquid crystal layer  222  has a first effective refractive index such that when combined with the convex shape of the liquid crystal lens module  220 , light entering along the z-direction will be focused to a first focal length F 1 . In  FIG.  4 B , when liquid crystal layer  222  is connected to power source  228 , the alignment of liquid crystal molecules  226  along the z-direction change the effective refractive index of the liquid crystal layer  222  to a second effective refractive index such that when combined with the convex shape of the liquid crystal layer  222 , light entering along the z-direction will be focused to a second focal length F 2 . Therefore, the focal length of liquid crystal lens module  220  can be controlled by switching the power source  228  on or off. 
       FIG.  5    is a schematic cross-sectional view of liquid crystal lens module  320  according to an embodiment of the invention. The liquid crystal lens module  320  includes first substrate  224   a , second substrate  224   b , liquid crystal layer  222 , first electrode  230   a , second electrode  230   b  and alignment layers  232   a  and  232   b  that are arranged similarly to liquid crystal lens module  220 . Referring to  FIG.  5   , the difference between liquid crystal lens module  320  and liquid crystal lens module  220  lies in the first substrate  224   a , the first and second electrodes  230   a  and  230   b , and the shape of first alignment layers  232   a . Specifically, in  FIG.  5   , the first substrate  224   a  is a substrate having uniform thickness in z-direction, the first electrode  230   a  and top alignment layer  232  is planar, and the second electrode  230   b  and second alignment layers  232   b  are stepped. Due second electrode  230   b  and second alignment layers  332  being stepped, the liquid crystal layer  222  is liquid crystal layer having non-uniform thickness that has optical properties of a diffractive lens. The stepped second electrode  230   b  and second alignment layer  232   b  may be designed, for example, in a way that the liquid crystal layer  222  following the shape of the steps may be a Fresnel lens, but the invention is not limited thereto. Similar to liquid crystal lens module  220 , the focal length of liquid crystal lens module  320  may be controlled by applying a voltage across first electrodes  230   a  and second electrodes  230   b.    
       FIG.  6 A  is a schematic cross-sectional view of liquid crystal lens module  420   a  according to an embodiment of the invention. 
     In  FIG.  6 A , the liquid crystal lens module  420   a  includes first substrate  224   a , second substrate  224   b , liquid crystal layer  222 , second electrode  230   b  and alignment layers  232   a  and  232   b  that are arranged similarly to liquid crystal lens module  220 . Referring to FIG.  FIG.  6 A , the difference between liquid crystal lens module  420   a  and liquid crystal lens module  220  lies in the first substrate  224   a , the first electrode  230   a , and the first alignment layers  232   a . Specifically, in  FIG.  6 A , the first substrate  224   a  is a substrate having uniform thickness in z-direction, the first electrode  230   a  is a patterned electrode having a gap or opening in between and disposed on a side of the first substrate  224   a  opposite the liquid crystal layer  222 , and the first alignment layers  232   a  is planar. Accordingly, the liquid crystal layer  222  of the present embodiment has uniform thickness. In some embodiments, the first electrode  230   a  may also be disposed between the first substrate  224   a  and the first alignment layers  232   a , but is not limited thereto. 
     Due to the pattern of the first electrode  230   a , voltage in the liquid crystal layer  222  is unevenly distributed, resulting in liquid crystal molecules having varying orientation when first electrode  230   a  is connected to a power source. In some embodiments, the pattern of the first electrode  230   a  may be any other pattern other than the pattern shown in  FIG.  6 A . The uneven distribution of liquid crystal orientation produces a distributed refractive index. Depending on the distribution of the refractive index, the liquid crystal lens module  420   a  may be a refractive lens or a diffractive lens. 
       FIG.  6 B  is a schematic cross-sectional view of liquid crystal lens module  420   b  according to an embodiment of the invention. Liquid crystal lens module  420   b  is similar to liquid crystal lens module  420   a  except that liquid crystal lens module  420   b  further includes a third electrode  230   c  disposed adjacent to the first electrode  230   a  away from the liquid crystal layer  222 . In this embodiment, the first and second electrode  230   a  and  230   b  may connect to a first power source  428   a  to be provided with voltage V 1 , while the third and second electrode  430   c  and  430   b  may connect a second power source  428   b  to be provided with voltage V 2 . The addition of third electrode  230   c  allows further control of voltage distribution in the liquid crystal layer  222  to provide further fine tuning of the optical properties. Depending on the distribution of the refractive index, the liquid crystal lens module  420   b  may be a refractive lens or a diffractive lens. 
       FIG.  7    is a schematic cross-sectional view of liquid crystal lens module  520  according to an embodiment of the invention. Liquid crystal lens module  520  is a liquid crystal lens module with liquid crystal layer  222  having uniform thickness. Specifically, the liquid crystal lens module  520  includes first substrate  224   a  and second substrate  224   b , liquid crystal layer  222 , second electrode  230   b  and alignment layers  232   a  and  232   b  that are arranged similarly to liquid crystal lens module  420   a . Difference between liquid crystal lens module  520  and liquid crystal lens module  420   a  lies in the position of first electrode  230   a  and structure of second electrode  230   b . Specifically, in  FIG.  7   , the first electrode  230   a  is disposed between the first substrate  224   a  and the first alignment layers  232   a , and the second electrode  230   b  is a pixilated electrode. 
     The second electrode  230   b  includes at least one electrode  530   a  connected to a power source  228  and at least one floating electrode  530   b  disposed adjacent to the electrode  530   a  to form the pixilated structure. The floating electrodes  530   b  are separated by insulators disposed therebetween, such as being separated by part of the first alignment layers  232   b  as shown in  FIG.  7   . In some embodiments, floating electrodes  530   b  can also be disposed on the first substrate  224   a , the second substrate  224   b , or both the first substrate  224   a  and the second substrate  224   b.    
     The voltages across floating electrodes  530   b  of second electrode  230   b  are related to the adjacent electrode  530   a . Floating electrodes  530   b  provides more steps of voltage change to better control orientation of liquid crystal molecules in the liquid crystal layer  222 . Alternatively, some or all of the floating electrodes  530   b  may also be individually connected to other power sources to further control the liquid crystal molecules. Depending on the distribution of the refractive index, the liquid crystal lens module  520  may be a refractive lens or a diffractive lens. 
       FIG.  8    is a schematic cross-sectional view of liquid crystal lens module  620  according to an embodiment of the invention. Liquid crystal lens module  620  is similar to liquid crystal lens module  520  except that liquid crystal lens module  620  has pixilated first electrode  230 , and further includes a high impedance material layer  640  disposed between the pixilated first electrode  230   a  and first alignment layers  232   a . The high impedance material layer  640  provide continuous varying voltage between the electrodes, therefore improving the quality of the image formed. The sheet resistance of the high impedance material layers  640  ranges from 10 9  to 10 14  Ω/sq. The high impedance material layers  640  are made of semiconductor material including a III-V semiconductor compound or a II-VI semiconductor compound, or polymer material including PEDOT (poly(3,4-ethylenedioxythiophene)), for example. Of course, the high impedance material layer  640  may be implemented in any of the liquid crystal lens module described above and may have any other pattern. The invention is not limited thereto. 
       FIG.  9    is a schematic diagram of a liquid crystal layer  222  from a top view, i.e. along z-direction, according to an embodiment of the invention. Specifically,  FIG.  9    is an exemplary arrangement pattern of the liquid crystal molecules in the liquid crystal layer  222  in the x-y plane due to alignment layer control. The y-direction provided in  FIG.  9    is the direction perpendicular to both x and z direction. In  FIG.  9   , the polar angle of liquid crystal molecules are controlled by the alignment layer to form the Pancharatnam-Berry phase liquid crystal lens. Other liquid crystal lens may be formed by having alignment layers with different surface pattern and the invention is not limited thereto. 
       FIGS.  10 A and  10 B  are schematic cross-sectional views of liquid crystal lens module  720  according to an embodiment of the invention. In  FIG.  10   , the liquid crystal lens module  720  includes a liquid crystal cell  722  and an anisotropic lens  724 , wherein the liquid crystal cell  722  is connected to a power source  228 . In liquid crystal lens module  720 , the liquid crystal cell  722  is disposed on a path of a light polarized in the direction perpendicular to x and z direction. The liquid crystal cell  722  is configured to control the polarization of the incoming light. 
     Referring to  FIGS.  10 A and  10 B , when the liquid crystal cell  722  is in an off state (voltage not applied), the polarization of incoming light is not affected, when the liquid crystal cell  722  is in an on state (voltage applied), the polarization of incoming light is rotated 90° to be along the x-direction. In other words, when liquid crystal cell  722  is on, liquid crystal cell acts as a half waveplate to change the polarization of incoming light. The anisotropic lens  724  is disposed on the path of light passing through liquid crystal cell  722 . The anisotropic lens  724  is a lens which has refractive index (hence focal length) that depends on the polarization of light, for example when light is polarized in optical axis A 1  direction of the anisotropic lens, the refractive index is at maximum, when light is polarized orthogonal to optical axis A 1  direction, the refractive index is at minimum. Because the on and off state of the liquid crystal cell  722  changes the polarization of light, the focal length of the anisotropic length is also changed. The liquid crystal lens module  720  is also referred to as a passive liquid crystal lens because the liquid crystal cell does not actively converge or diverge the light. 
     The voltage distribution applied to the electrodes of the liquid crystal lens module, liquid crystal lens cell and to the liquid crystal cell as described above may be controlled by a controller coupled to the electrodes. In some embodiments, the controller is, for example, a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a programmable controller, a programmable logic device (PLD), or other similar devices, or a combination of the said devices, which are not particularly limited by the invention. Further, in some embodiments, each of the functions of the controller may be implemented as a plurality of program codes. These program codes will be stored in a memory or a non-transitory storage medium, so that these program codes may be executed by the controller. Alternatively, in an embodiment, each of the functions of the controller may be implemented as one or more circuits. The invention is not intended to limit whether each of the functions of the controller is implemented by ways of software or hardware. 
     By including a liquid crystal lens having variable focal length into a structured light projector, the focusing range of a structured light projector becomes tunable and is able cover a wider range, allowing features of 3D objects at different distances to be measured. Furthermore, when compared to the traditional voice coil motor (VCM) in a focusing lens, the optical projector using liquid crystal lens has the advantage of being more compact and having low power consumption. Hence, the optical projector of the invention may be easily fitted in mobile electronic devices, providing the feature of 3D sensing to mobile electronic devices. 
       FIG.  11 A  and  FIG.  11 B  are schematic cross-sectional views of a tunable light projector respectively in a structured light mode and a flood light mode according to an embodiment of the invention. Referring to  FIG.  11 A  and  FIG.  11 B , a tunable light projector  800  in this embodiment includes at least one light source  810  (a plurality of light sources  810  are exemplarily shown in  FIG.  11 A  and  FIG.  11 B ), a fixed optical phase modulator  820 , a tunable liquid crystal panel  900 , and a driver  830 . The light sources  810  are configured to emit a plurality of light beams  811  (a light source  810  emitting a light beam  811  is exemplarily shown in  FIG.  11 A  and  FIG.  11 B ). In this embodiment, the light sources  810  are respectively a plurality of light-emitting regions (or light-emitting points) of a VCSEL, a plurality of edge-emitting lasers (EELs), or a plurality of other appropriate laser emitters or laser diodes. 
     The fixed optical phase modulator  820  is disposed on a path of the light beam  811  and configured to modulate phases of the light beam  811 . In this embodiment, the fixed optical phase modulator  820  is a DOE or a lens array which modulates the light beam  811  to a structured light. 
     The tunable liquid crystal panel  900  is disposed on the path of the light beam  811  from the fixed optical phase modulator  820  and configured to switch the light beam  811  between a structured light (as shown in  FIG.  11 A ) and a flood light (as shown in  FIG.  11 B ). The tunable liquid crystal panel  900  includes a first substrate  910 , a second substrate  920 , a liquid crystal layer  930 , a first electrode layer  940 , and a second electrode layer  950 . The liquid crystal layer  930  is disposed between the first substrate  910  and the second substrate  920 . At least one of the first electrode layer  940  and the second electrode layer  950  is a patterned layer.  FIG.  11 A  and  FIG.  11 B  show that the first electrode layer  940  is a patterned layer. However, in other embodiments, the second electrode layer  950  may be a patterned layer, or both the first electrode layer  940  and the second electrode layer  950  may be patterned layers. In this embodiment, the first substrate  910  and the second substrate  920  are transparent substrates, e.g. glass substrates or plastic substrates. The first electrode layer  940  and the second electrode layer  950  may be made of indium tin oxide (ITO), any other transparent conductive metal oxide, or any other transparent conductive material. 
     The first electrode layer  940  and the second electrode  950  are both disposed on one of the first substrate  910  and the second substrate  920 , or are respectively disposed on the first substrate  910  and the second substrate  920 . The driver  830  is electrically connected to the first electrode layer  940  and the second electrode layer  950  and configured to change a voltage difference between the first electrode layer  940  and the second electrode layer  950 , so as to switch the light beam  811  between the structured light and the flood light. Specifically, the optical spatial phase distribution of the liquid crystal layer  930  is changed with the change of the voltage difference, so as to switch the light beam  811  between the structured light and the flood light. 
     For example, in  FIG.  11 A , the voltage difference between the first electrode layer  940  and the second electrode layer  950  is about zero, and the refractive index distribution of the liquid crystal layer  930  is uniform, so that the liquid crystal layer  930  is like a transparent layer. As a result, the structured light from the fixed optical phase modulator  820  passes through the transparent layer and is still a structured light, and the tunable light projector  800  is in a structured light mode. In  FIG.  11 B , the voltage difference between the first electrode layer  940  and the second electrode layer  950  is not equal to zero, and the refractive index distribution of the liquid crystal layer  930  is not uniform, so that the liquid crystal layer  930  is like a lens array. As a result, the structured light from the fixed optical phase modulator  820  is converted to a flood light by the lens array, and the tunable light projector  300  is in a flood light mode. The structured light may irradiate an object and form a light pattern with dots, stripes, or any other suitable pattern on the object. The flood light may uniformly irradiate the object. 
     In the tunable light projector in this embodiment, the tunable liquid crystal panel  900  is adopted to switch the light beam  811  between a structured light and a flood light, so that this embodiment integrates a flood light system and a structured light system into a single system, which reduces the cost and the volume of an electronic device having structured light and flood light functions. 
     In another embodiment, the fixed optical phase modulator  820  is configured to modulate the light beam  811  to a flood light. Moreover, when the voltage difference between the first electrode layer  940  and the second electrode layer  950  is about zero, the flood light from the fixed optical phase modulator  820  passes through the liquid crystal layer  930  being a transparent layer and is then still a flood light. When the voltage difference between the first electrode layer  940  and the second electrode layer  950  is not zero, the flood light from the fixed optical phase modulator is converted into a structured light by the liquid crystal layer  930  being an optical layer like a lens array. 
     In still another embodiment, the fixed optical phase modulator  820  is configured to modulate light beam to a collimated light, and two voltage differences between the first electrode layer  940  and the second electrode layer  950  respectively switch the liquid crystal layer  930  to two refractive index distributions so as to switch the collimated light from the fixed optical phase modulator to a structured light and a flood light, respectively. 
       FIG.  12 A ,  FIG.  12 B , and  FIG.  12 C  are schematic top views of the first electrode layer in  FIG.  11 A  and  FIG.  11 B  respectively according to three embodiments in the invention. Referring to  FIG.  12 A ,  FIG.  12 B , and  FIG.  12 C , the patterned layer (e.g. the first electrode layer  940  or the second electrode layer  950 , and the figures show the first electrode layer  940  as examples) has a plurality of micro-openings  942  having a maximum diameter D less than 1 millimeter. The shapes of the micro-openings  942  includes circles (as shown in  FIG.  12 A ), rectangles (as shown in  FIG.  12 B ), squares, hexagons (as shown in  FIG.  12 C ), other geometric shapes, other irregular shapes, or a combination thereof. 
       FIG.  13 A ,  FIG.  13 B , and  FIG.  13 C  are schematic top views of other three variations of the first electrode layer in  FIG.  12 A . Referring to  FIG.  12 A ,  FIG.  13 A ,  FIG.  13 B , and  FIG.  13 C , sizes and positions of the micro-openings  942  may be regular or irregular. For example, in  FIG.  12 A , the sizes of the micro-openings  942  are equal to one another, and the positions of the micro-openings  942  are regular. In  FIG.  13 A , the sizes of the micro-openings  942  are equal to one another, and the positions of the micro-openings  942  are irregular. In  FIG.  13 B , the micro-openings  942  have different sizes, and the positions of the micro-openings  942  are regular. In  FIG.  13 C , the micro-openings  942  have different sizes, and the positions of the micro-openings  942  are irregular. 
       FIG.  14 A  is a schematic cross-sectional view of the tunable liquid crystal panel in  FIG.  11 A , and  FIG.  14 B  and  FIG.  14 C  are other two variations of the tunable liquid crystal panel in  FIG.  14 A . Referring to  FIG.  14 A , the tunable liquid crystal panel  900  has the liquid crystal layer  930  including polymer network liquid crystals (PNLCs), which includes liquid crystal molecules  932  with a polymer network  934 . Referring to  FIG.  14 B , the tunable liquid crystal panel  900   a  may have a liquid crystal layer  930   a  including nematic liquid crystals. Referring to  FIG.  14 C , the tunable liquid crystal panel  900   b  may have a liquid crystal layer  930   b  including polymer dispersed liquid crystals (PDLCs), which includes liquid crystal molecules  932   b  with a polymer  934   b.    
       FIG.  15 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG.  15 A , the tunable liquid crystal panel  900   c  is similar to the tunable liquid crystal panel  900   a  in  FIG.  14 B , and the main difference therebetween is as follows. In this embodiment, the tunable liquid crystal panel  900   c  further includes a first alignment layer  960  and a second alignment layer  970 . The first alignment layer  960  is disposed between the first substrate  910  and the liquid crystal layer  930   a , and the second alignment layer  970  is disposed between the second substrate  920  and the liquid crystal layer  930   a . In this embodiment, the first alignment layer  960  is disposed between the first electrode layer  940  and the liquid crystal layer  930   a , and the second alignment layer  970  is disposed between the second electrode layer  950  and the liquid crystal layer  930   a . In this embodiment, the first alignment layer  960  and the second alignment layer  970  are parallel alignment layers. 
       FIG.  15 B  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG.  15 B , the tunable liquid crystal panel  900   d  is similar to the tunable liquid crystal panel  900   c , and the main difference therebetween is as follows. In the tunable liquid crystal panel  900   d  according to this embodiment, the first alignment layer  960   d  and the second alignment layer  970   d  are vertical alignment layers. 
       FIG.  15 C  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG.  15 C , the tunable liquid crystal panel  900   e  is similar to the tunable liquid crystal panel  900   c , and the main difference therebetween is as follows. In the tunable liquid crystal panel  900   e  according to this embodiment, the first alignment layer  960  and the second alignment layer  970   d  are a combination of a vertical alignment layer and a parallel alignment layer. For example, the first alignment layer  960  is a parallel alignment layer, and the second alignment layer  970   d  is a vertical alignment layer. 
       FIG.  16 A  shows the alignment direction of the first alignment layer or the second alignment layer in  FIG.  15 A  or  FIG.  15 C  according to an embodiment of the invention. Referring to  FIG.  16 A , in an embodiment, alignment directions L 1  of the first alignment layer  960  and the second alignment layer  670  have uniform spatial distribution. In other words, the azimuthal angles of alignment in different areas of the first alignment layer  960  or the second alignment layer  670  are the same. 
       FIG.  16 B  shows the alignment directions of another variation of the first alignment layer or the second alignment layer in  FIG.  15 A  or  FIG.  15 C  according to another embodiment of the invention. Referring to  FIG.  16 B , in another embodiment, alignment directions L 1  of the first alignment layer  960   a  and the second alignment layer  970   a  have random spatial distribution. In other words, the azimuthal angles of alignment in different areas of the first alignment layer  960   a  or the second alignment layer  970   a  are random. The different alignment directions and the different azimuthal angles may refract or diffract light beams  811  from the light sources  810  with different polarized directions. 
       FIG.  17 A  is a schematic cross-sectional view of a tunable light projector adopting the alignment layers shown in  FIG.  16 B .  FIG.  17 B  shows a schematic top view of a spot area and the alignment layer in  FIG.  17 A . Referring to  FIG.  17 A  and  FIG.  17 B , the tunable light projector  800   c  in this embodiment is similar to the tunable light projector  800  in  FIG.  11 A , and the main difference therebetween is as follows. In the tunable light projector  800   c  according to this embodiment, a locally same alignment direction area R 1  of the random spatial distribution of alignment directions of the first alignment layer  960   a  and the second alignment layer  970   a  is smaller than a spot area R 2  on the tunable liquid crystal panel  900   c  irradiated by the light beam  811  from the fixed optical phase modulator  820 . As a result, various polarized directions of the light beam  811  may all be refracted or diffracted by the liquid crystal layer  900   c.    
       FIG.  18 A ,  FIG.  18 B , and  FIG.  18 C  are schematic cross-sectional views of a tunable liquid crystal panel and the voltage difference applied to the liquid crystal layer in three different modes. Referring to  FIG.  18 A ,  FIG.  18 B , and  FIG.  18 C , the tunable liquid crystal panel  900   f  in this embodiment is similar to the tunable liquid crystal panel  900   b  in  FIG.  14 C , and the main difference therebetween is as follows. The tunable liquid crystal panel  900   f  in this embodiment further includes a high resistive layer  980  (the same as the high impedance material layer  640  in  FIG.  8   ) adjacent to the patterned layer (e.g. the first electrode layer  940 ). In  FIG.  18 A , when the voltage difference between the first electrode layer  940  and the second electrode layer  950  is zero, the voltage difference ΔV applied to the liquid crystal layer  930   b  is zero, and the liquid crystal layer  930   b  is in a scattering mode and is configured to scatter the light beam  811  from the fixed optical phase modulator  820 . 
     In  FIG.  18 B , when the voltage difference between the first electrode layer  940  and the second electrode layer  950  is an alternating current (AC) with a high frequency (e.g. a frequency being greater than 1 kHz and being less than or equal to 60 kHz), the voltage difference ΔV applied to the liquid crystal layer  930  varies gradually with the positions due to the high resistive layer  980 , and the liquid crystal layer  930   b  is in a scattering and light converging mode and is configured to slightly scatter and converge the light beam  811  from the fixed optical phase modulator  820 . 
     In  FIG.  18 C , when the voltage difference between the first electrode layer  940  and the second electrode layer  950  is an alternating current (AC) with a low frequency (e.g. a frequency being greater than or equal to 60 Hz and being less than or equal to 1 kHz), the voltage difference ΔV applied to the liquid crystal layer  930  keeps about constant in various positions, the liquid crystal layer  930   b  is in a transparent mode and like a transparent layer, and the light beam  811  passes through the liquid crystal layer  930   b . Moreover, the aforementioned high frequency is greater than the aforementioned low frequency. 
       FIG.  19 A  is a schematic cross-sectional views of a tunable liquid crystal panel according to another embodiment of the invention, and  FIG.  19 B  is a schematic top view of the first substrate in  FIG.  19 A . Referring to  FIG.  19 A  and  FIG.  19 B , the tunable liquid crystal panel  900   g  in this embodiment is similar to the tunable liquid crystal panel  900   c  in  FIG.  15 A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  900   g  according to this embodiment, the first electrode layer  940   g  and the second electrode layer  950   g  are both disposed on the same substrate, e.g. the first substrate  910 , and are both patterned layers. The first electrode layer  940   g  and the second electrode layer  950   g  has an in-plane switch (IPS) electrode design. Specifically, the first electrode layer  940   g  includes a plurality of conductive micro-patterns  942   g , and the second electrode layer  950   g  includes a plurality of conductive micro-patterns  952   g . The conductive micro-patterns  942   g  and the conductive micro-patterns  952   g  are alternately arranged along a direction (e.g. the right direction in  FIGS.  19 A and  19 B ). The conductive micro-patterns  942   g  and the conductive micro-patterns  952   g  may have a straight shape. For example, each of the conductive micro-patterns  942   g  and the conductive micro-patterns  952   g  may extend along a direction perpendicular to the paper surface of  FIG.  19 A . However, in this embodiment, The conductive micro-patterns  942   g  and the conductive micro-patterns  952   g  may have a zigzag shape as shown in  FIG.  19 B . 
       FIG.  20 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention, and  FIG.  20 B  is a schematic top view of the first substrate in  FIG.  20 A . The tunable liquid crystal panel  900   h  in this embodiment is similar to the tunable liquid crystal panel  900   g  in  FIG.  19 A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  900   h  according to this embodiment, the first electrode layer  940   g  and the second electrode layer  950   h  have a fringe-field switch (FFS) electrode design. The second electrode layer  950   h  is a plane continuous layer between the first electrode layer  940   g  and the substrate  910 , and the first electrode layer  940   g  and the second electrode layer  950  are insulated from each other by an insulating layer  990  disposed therebetween. The first electrode layer  940   g  in  FIG.  20 A  and  FIG.  20 B  is the same as the description of the first electrode layer  940   g  in  FIG.  19 A  and  FIG.  19 B . 
       FIG.  21 A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG.  21 A , the tunable liquid crystal panel  900   j  in this embodiment is similar to the tunable liquid crystal panel  900   a  in  FIG.  14 B , and the main difference therebetween is as follows. In the tunable liquid crystal panel  930   a , the first electrode layer  940  and the second electrode layer  950   j  are two patterned layers disposed on the first substrate  910  and the second substrate  920 , respectively, and patterns of the two patterned layers are the same. However, in other embodiment, patterns of the two patterned layers may be different. 
       FIG.  21 B  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG.  21 B , the tunable liquid crystal panel  900   i  in this embodiment is similar to the tunable liquid crystal panel  900   g  or  900   h  in  FIG.  19 A  or  FIG.  20 A , and the main difference therebetween is as follows. The tunable liquid crystal panel  900   i  in this embodiment includes the first electrode layer  940   g  and the second electrode layer  950   g  as those in  FIG.  19 A  on the first substrate  910 , and includes the first electrode layer  940   g  and the second electrode layer  950   h  as those in  FIG.  20 A  on the second substrate  920 . That is, the first substrate  910  side has an IPS electrode design, and the second substrate  920  side has an FFS electrode design. However, in other embodiments, both the first substrate  910  side and the second substrate  920  side may have the IPS electrode design, or both the first substrate  910  side and the second substrate  920  side may have the FFS electrode design. 
       FIG.  22    is a schematic cross-sectional view of a tunable light projector according to another embodiment of the invention. The tunable light projector  800   k  in this embodiment is similar to the tunable light projector  800  in  FIG.  11 A  and  FIG.  11 B , and the difference therebetween is the arrangement sequence of the fixed optical phase modulator  820  and the tunable liquid crystal panel  900 . In  FIG.  11 A  and  FIG.  11 B , the fixed optical phase modulator  820  is disposed between the light source  810  and the tunable liquid crystal panel  900 . However, in this embodiment, the tunable liquid crystal panel  900  is disposed between the light source  810  and the fixed optical phase modulator  820 ; that is, the fixed optical phase modulator  820  is disposed on the path of the light beam from the tunable liquid crystal panel  900 . In this way, when the tunable liquid crystal panel  900  is switched between different modes as mentioned in the aforementioned embodiment, the light beam after passing through the fixed optical phase modulator  820  then can be switched between the structured light and the flood light. 
       FIG.  23 A  and  FIG.  23 B  are schematic cross-sectional views of a tunable light projector respectively in a structured light mode and a flood light mode according to another embodiment of the invention. Referring to  FIG.  23 A  and  FIG.  23 B , the tunable light projector  800   l  in this embodiment is similar to the tunable light projector  800 , and the main difference therebetween is as follows. In the tunable light projector  800   l  of this embodiment, the tunable liquid crystal panel  900   l  is configured to be switched between a plurality of states (two states are exemplarily shown in  FIG.  23 A  and  FIG.  23 B , respectively), and the plurality of states include a lens array state (as shown in  FIG.  23 B ) in which the tunable liquid crystal panel  900   l  includes a lens array including a plurality of lenses  905  arranged in an array. In this embodiment, the lenses  905  are a plurality of Pancharatnam-Berry phase liquid crystal lenses arranged in an array, the alignment of the liquid crystal molecules of the liquid crystal layer  9301  of the each lens  905  is similar to that shown in  FIG.  9   , and may be achieved by the alignment layers  9601  and  9701 . 
     In the structured light mode, no voltage difference is applied between the electrode layers  940  and  950  of the tunable liquid crystal panel  900   l , and the tunable liquid crystal panel  900   l  is like a transparent plate, so that the structured light from the fixed optical phase modulator  820  is maintained and pass through the tunable liquid crystal panel  900   l . Moreover, in the flood light mode, a voltage difference is applied between the electrode layers  940  and  950  by the driver  830 , and the tunable liquid crystal panel  900   l  is like a lens array and converts the structured light from the fixed optical phase modulator  820  into a flood light. 
     The tunable liquid crystal panel  900   l  may also be used to replace the liquid crystal lens cell  122  in  FIG.  3 A ,  FIG.  3 B , and  FIG.  3 C , so as to change the focal length. 
     Referring to  FIG.  23 A  and  FIG.  23 B  again, in this embodiment, the lens array is distributed all over the tunable liquid crystal panel  900   l . However, in other embodiments, the lens array may be within a region of interest of the tunable liquid crystal panel  900   l , which may be achieved by the pattern designed of at least one the electrode layers  940  and  950  and an appropriate voltage difference distribution applied therebetween. 
     In an embodiment, the driver  830  is configured to change a focal length of each of lenses  905  of the lens array. In an embodiment, the driver  830  is configured to change a position of each of lenses  905  of the lens array. In an embodiment, the driver  830  is configured to change a dimension of each of lenses  905  of the lens array. In an embodiment, the driver  830  is configured to change at least one of a focal length, a position, and a dimension of each of lenses  905  of the lens array. 
     In this embodiment, the tunable liquid crystal panel  900   l  is a transmissive liquid crystal panel, and is disposed on the path of the light beam  811  from the fixed optical phase modulator  820 . However, in other embodiments, the fixed optical phase modulator  820  may be disposed on the path of the light beam  811  from the tunable liquid crystal panel  900   l , similar to that shown in  FIG.  22   . 
       FIG.  24    is a schematic cross-sectional view of a tunable light projector according to another embodiment of the invention. Referring to  FIG.  24   , the tunable light projector  800   m  in this embodiment is similar to the tunable light projector  800   l  in  FIG.  23 A  and  FIG.  23 B , and the main difference therebetween is as follows. In the tunable light projector  800   m  of this embodiment, the tunable liquid crystal panel  900   m  is a reflective liquid crystal panel, which reflect the light beam  811  from the light source  810  to the fixed optical phase modulator  820 . However, in other embodiments, the tunable liquid crystal panel  900   m  may reflect the light beam  811  from the fixed optical phase modulator  820  to the object  12  (as shown in  FIG.  1   ). 
     In this embodiment, the tunable liquid crystal panel  900   m  may include the tunable liquid crystal panel  900   l  and a reflector  906  disposed thereon, so that the light beam  811  may penetrate the liquid crystal layer of the tunable liquid crystal panel  900   m  twice. The reflector  906  may be a reflective film coated on the substrate of the tunable liquid crystal panel  900   l  or a reflective sheet disposed on the substrate of the tunable liquid crystal panel  900   l , and the reflector  906  may be on the inner side or the outer side of the substrate. 
     In this embodiment, since the light beam  811  penetrates through the liquid crystal layer of the tunable liquid crystal panel  900   m  twice, the optical path length of the light beam  811  in the liquid crystal layer is doubled. As a result, the thickness of the liquid crystal layer of the tunable liquid crystal panel  900   m  may be reduced. Generally, the response time of liquid crystal is inversely square proportional to the thickness of the liquid crystal layer, so that the response time of the tunable liquid crystal panel  900   m  may be effectively reduced. 
     In this embodiment, the solid lens  124  is disposed on the path of the light beam  811 . However, in other embodiments, the solid lens  124  may be omitted. 
     In conclusion, in the tunable light projector according to the embodiment of the invention, a tunable liquid crystal panel is adopted to switch a light beam between a structured light and a flood light, so that the embodiment of the invention integrates a flood light system and a structured light system into a single system, which reduces the cost and the volume of an electronic device having structured light and flood light functions. Each of the aforementioned tunable light projectors may replace any one of the aforementioned structured light projectors in the optical sensing device to form an optical sensing device having both a flood light recognition function and a structured light recognition function. In the flood light recognition function, the sensor may sense the object and determine whether the object is a human face. In the structured light recognition function, the sensor may sense the light pattern on the object and determine whether the detected human face is the face of a user of an electronic device. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.