Patent Publication Number: US-2021173291-A1

Title: Tunable light projector

Description:
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 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, a tunable light projector is provided. The tunable light projector includes a light source configured to emit a light beam; a fixed optical phase modulator disposed on a path of the light beam and configured to modulate phases of the light beam; a tunable liquid crystal panel disposed on the path of the light beam and a partial region of the tunable liquid crystal panel is configured to electrically switch the light beam between a structured light and a flood light, the tunable liquid crystal panel comprising: a first substrate; a second substrate, wherein the first substrate is closer to the light source than the second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; a first electrode layer; and a second electrode layer, wherein 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; and a driver electrically connected to light source and the tunable liquid crystal panel and configured to control the light source and control the tunable liquid crystal panel to switch the light beam between the structured light and the flood light. 
     According to an embodiment of the invention, a tunable light detector is provided. The tunable light detector includes: a tunable light projector, comprising: a light source configured to emit a light beam; a fixed optical phase modulator disposed on a path of the light beam and configured to modulate phases of the light beam; a tunable liquid crystal panel disposed on the path of the light beam wherein a partial region of the tunable liquid crystal panel is configured to electrically switch the light beam between a structured light and a flood light, the tunable liquid crystal panel comprising: a first substrate; a second substrate, wherein the first substrate is closer to the light source than the second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; a first electrode layer; and a second electrode layer, wherein 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; and a driver electrically connected to the light source and the tunable liquid crystal panel and configured to control the light source and control the tunable liquid crystal panel to switch the light beam between the structured light and the flood light; and a sensor, detecting the reflected structure light or the reflected flood light emitted by the tunable light projector. 
     In the tunable light projector according to the embodiment of the invention, a partial region of 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 the liquid crystal panel, 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. 1A  is a schematic cross-sectional view of a tunable light projector according to some embodiments of the invention. 
         FIG. 1B  is a schematic top view of a liquid crystal panel according to some embodiments of the invention. 
         FIGS. 2A, 2B, 2C and 2D  are schematic cross-sectional views of a tunable light projector respectively in a structured light mode and a flood light mode according to some embodiments of the invention. 
         FIGS. 3A-3D  are schematic cross-sectional views of a tunable liquid crystal panel according to some embodiments of the invention. 
         FIGS. 4A-4D  are schematic top views of the first electrode layer according to some embodiments in the invention. 
         FIGS. 5A and 5B  are schematic cross-sectional views of a tunable liquid crystal panel according to some embodiments of the invention. 
         FIGS. 6A-6C  are schematic top views of some different variations of the first electrode layer in  FIG. 4D . 
         FIGS. 7A-7D  are schematic cross-sectional views of a tunable liquid crystal panel according to some embodiments of the invention. 
         FIGS. 8A and 8B  are schematic top views of a liquid crystal layer according to some embodiments of the invention. 
         FIG. 9  is a schematic cross-sectional view of the tunable liquid crystal panel according to some embodiments. 
     
    
    
     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. 1A  is a schematic cross-sectional view of a tunable light projector. Referring to  FIG. 1A , a tunable light projector  200  in this embodiment includes at least one light source  210  (a plurality of light sources  210  are exemplarily shown in  FIG. 1A ), a fixed optical phase modulator  220 , a tunable liquid crystal panel  100 , and a driver  230 . The light sources  210  are configured to emit a plurality of light beams  211  (a light source  210  emitting a light beam  211  is exemplarily shown in  FIG. 1A ). In this embodiment, the light sources  210  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. In some embodiments, the light sources  210  emits the infrared (IR) lights. 
     The fixed optical phase modulator  220  is disposed on a path of the light beam  211  and configured to modulate phases of the light beam  211 . In this embodiment, the fixed optical phase modulator  220  is a diffractive optical element (DOE) or a micro lens array which modulates the light beam  211  to a structured light or a flood light. 
     The tunable liquid crystal panel  100  is disposed on the path of the light beam  211  from the fixed optical phase modulator  220  and configured to switch the light beam  211  between a structured light and a flood light. In some embodiments, the tunable liquid crystal panel  100  switches a structured light to a flood light. In some embodiments, the tunable liquid crystal panel  100  switches a flood light to a structured light. 
     The tunable liquid crystal panel  100  includes a first substrate  110 , a second substrate  112 , a liquid crystal layer  130 , a first electrode layer  120  and a second electrode layer  122 . 
     The liquid crystal layer  130  is disposed between the first substrate  110  and the second substrate  112 , wherein the first substrate is at the side closer to the light source and the second substrate is at the side away from the light source. In this embodiment, the first substrate  110  and the second substrate  112  are transparent substrates, e.g. glass substrates or plastic substrates. The first electrode layer  120  and the second electrode layer  122  may be made of indium tin oxide (ITO), any other transparent conductive metal oxide, or any other transparent conductive material. 
       FIG. 1A  shows that the first electrode layer  120  is a patterned layer. However, in other embodiments, the second electrode layer  122  may be an unpatterned layer, a patterned layer, or both the first electrode layer  120  and the second electrode layer  122  may be patterned layers. In some embodiments, at least one of the first electrode layer  120  and the second electrode layer  122  is a patterned layer. In some embodiments, both the first electrode layer  120  and the second electrode layer  122  are unpatterned layers. 
     The first electrode layer  120  and the second electrode  122  are both disposed on one of the first substrate  110  and the second substrate  112 , or are respectively disposed on the first substrate  110  and the second substrate  112 . The driver  230  is electrically connected to the light source  210  and the tunable liquid crystal panel  100 . More specifically, the driver  230  is electrically connected to the first electrode layer  120  and the second electrode layer  122  and configured to change a voltage difference between the first electrode layer  120  and the second electrode layer  122 , so as to switch the light beam  211  from the structured light to the flood light or from the flood light to the structured light. Specifically, the optical spatial phase distribution of the liquid crystal layer  130  is changed with the change of the voltage difference, so as to switch the light beam  211  between the structured light and the flood light. 
     The tunable liquid crystal panel  100  further comprises the color filter  140 , the first polarizer  150 , the second polarizer  152  and the backlight layer  160 . The first polarizer  150  is between the first substrate  110  and the backlight layer  160 . The color filter  140  is between the second substrate  112  and the second polarizer  152 . 
     When the color filter  140  received the visible light emitted by the backlight layer  160 , the color filter  140  filters the light to generate a plurality of colors such as red, green and blue. The first and second polarizers  150  and  152  are used to polarize the visible light generated by the backlight layer  160 . 
     The backlight layer  160  does not cover a partial region of the tunable liquid crystal panel  100 , wherein this partial region is above the tunable light projector  200  and the area of the partial region of the tunable liquid crystal panel  100  is substantially the same as the area of the tunable light projector  200 . Therefore, the light beam emitted by the light source  210  is able to penetrate the tunable liquid crystal panel  100 , without being blocked by the color filter  140 , the first polarizer  150  and the second polarizer  152 . In some embodiments, the color filter  140 , the first polarizer  150  and the second polarizer  152  are infrared penetrable. Also, the metal wirings and the thin film transistor of the tunable liquid crystal panel  100  (not shown) also do not cover the partial region of the tunable liquid crystal panel  100 , so the light beam emitted by the light source  210  is able to penetrate the tunable liquid crystal panel  100 . In other words, the materials of tunable liquid crystal panel  100  in front of the tunable light projector is reduced as much as possible to enhance the structure light or the flood light emitted by the light source  210 . 
     For the area other than the partial region of the tunable liquid crystal panel  100 , it is used as a normal liquid crystal display. 
     In some embodiments, in order to switch the structure light to the flood light or to switch the flood light to the structure light, the orientations of the liquid crystal molecules in the partial region of the tunable liquid crystal panel  100  is different from the liquid crystal molecules of the rest of the tunable liquid crystal panel  100 . 
       FIG. 1B  is a schematic top view of a liquid crystal panel according to some embodiments of the invention. The electronic device  10  includes the liquid crystal panel  100 . The tunable light projector  200  is occupies a partial region of the liquid crystal panel  100 . A sensor  300  is disposed near the tunable light projector  200  and is outside of the liquid crystal panel  100 . When the tunable light projector  200  emits the structure light or the flood light to object to be detected, the sensor is used to detect the structure light or the flood light reflected by the object to be detected. The position of the sensor  300  is not limited thereto. In some embodiments, the sensor  300  may be within the liquid crystal panel  100 . 
       FIGS. 2A, 2B, 2C and 2D  are schematic cross-sectional views of a tunable light projector respectively in a structured light mode and a flood light mode according to some embodiments of the invention. In some embodiments, the fixed optical phase modulator  220  is configured to modulate the light beam  211  to a structure light. In some embodiments, for example, in  FIG. 2A , the voltage difference between the first electrode layer  120  and the second electrode layer  122  is about zero, and the refractive index distribution of the liquid crystal layer  130  is uniform, so that the liquid crystal layer  130  is like a transparent layer. As a result, the structured light from the fixed optical phase modulator  220  passes through the transparent layer and is still a structured light, and the tunable light projector  200  is in a structured light mode. In  FIG. 2B , the voltage difference between the first electrode layer  120  and the second electrode layer  122  is not equal to zero, and the refractive index distribution of the liquid crystal layer  130  is not uniform, so that the liquid crystal layer  130  is like a lens array. As a result, the structured light from the fixed optical phase modulator  220  is converted to a flood light by the lens array, and the tunable light projector  100  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 some embodiments, the fixed optical phase modulator  220  is configured to modulate the light beam  211  to a flood light. In some embodiments, for example, in  FIG. 2C , the voltage difference between the first electrode layer  120  and the second electrode layer  122  is about zero, and the refractive index distribution of the liquid crystal layer  130  is uniform, so that the liquid crystal layer  130  is like a transparent layer. As a result, the flood light from the fixed optical phase modulator  220  passes through the transparent layer and is still a flood light, and the tunable light projector  200  is in a flood light mode. In  FIG. 2D , the voltage difference between the first electrode layer  120  and the second electrode layer  122  is not equal to zero, and the refractive index distribution of the liquid crystal layer  130  is not uniform, so that the liquid crystal layer  130  is like a lens array. As a result, the structured light from the fixed optical phase modulator  220  is converted to a structure light by the lens array, and the tunable light projector  100  is in a structure light mode. 
     In this embodiment, the tunable liquid crystal panel  100  is adopted to switch the light beam  211  from a structured light to a flood light or to switch the light beam  211  from a flood light to a structured 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. 
       FIG. 3A  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG. 3A , the tunable liquid crystal panel  100   a  is similar to the tunable liquid crystal panel  100  in  FIG. 1A , and the main difference therebetween is as follows. In this embodiment, the tunable liquid crystal panel  100   a  further includes a first alignment layer  170  and a second alignment layer  172 . The first alignment layer  170  is disposed between the first substrate  110  and the liquid crystal layer  130   a , and the second alignment layer  172  is disposed between the second substrate  112  and the liquid crystal layer  130   a . In this embodiment, the first alignment layer  170  is disposed between the first electrode layer  120  and the liquid crystal layer  130   a , and the second alignment layer  172  is disposed between the second electrode layer  122  and the liquid crystal layer  130   a . In this embodiment, the first alignment layer  170  and the second alignment layer  172  are anti-parallel alignment layers. In other words, the alignment direction of the first alignment layer  170  and the second alignment layer  172  are opposite from each other. 
       FIG. 3B  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG. 3B , the tunable liquid crystal panel  100   b  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  100   b  according to this embodiment, the first alignment layer  170   d  and the second alignment layer  172   d  are vertical alignment layers. 
       FIG. 3C  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG. 3C , the tunable liquid crystal panel  100   c  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  100   c  according to this embodiment, the first alignment layer  170  and the second alignment layer  172   d  are a combination of a vertical alignment layer and a parallel alignment layer. For example, the first alignment layer  170  is a parallel alignment layer, and the second alignment layer  172   d  is a vertical alignment layer. 
       FIG. 3D  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention. Referring to  FIG. 3D , the tunable liquid crystal panel  100   c  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  100   c  according to this embodiment, the first alignment layer  170  and the second alignment layer  172   d  are parallel alignment layers and the alignment direction of the first alignment layer  170  and the alignment direction of the second alignment layer  172  are perpendicular to each other. In this embodiment, the first alignment layer  170  and the second alignment layer  172  are parallel alignment layers with their alignment perpendicular to each other. 
     With different alignment combination of the first alignment layer  170  and the second alignment layer  172 , the liquid crystal molecules in the liquid crystal layer  130  can have different orientations, which generates different optical phases, when there is about zero voltage between the first electrode  120  and the second electrode  122 . 
       FIGS. 4A-4D  are schematic top views of the first electrode layer according to some embodiments in the invention. 
     In  FIGS. 4A and 4B , the first electrode layer  120   g  and the second electrode layer  122   g  are both disposed on the same substrate, e.g. the first substrate  110 , and are both patterned layers. The first electrode layer  120   g  and the second electrode layer  122   g  has an in-plane switch (IPS) electrode design. Specifically, the first electrode layer  120   g  includes a plurality of conductive micro-patterns  120   g , and the second electrode layer  122   g  includes a plurality of conductive micro-patterns  122   g . The conductive micro-patterns  120   g  and the conductive micro-patterns  122   g  are alternately arranged along a direction (e.g. the right direction in  FIGS. 4A and 4B ). The conductive micro-patterns  120   g  and the conductive micro-patterns  122   g  may have a straight shape as shown in  FIG. 4A , which is also known as ITO slit design. In some embodiments, each of the conductive micro-patterns  120   g  and the conductive micro-patterns  122   g  may extend along a direction perpendicular to the paper surface of  FIG. 4A . In some embodiments, the conductive micro-patterns  120   g  and the conductive micro-patterns  122   g  may have a zigzag shape as shown in  FIG. 4B . In some embodiments, e.g.  FIGS. 4A and 4B , the width of the electrodes or a pitch between the electrodes of the patterned ITO layers in the partial region of the tunable liquid crystal panel is different from the rest of the tunable liquid crystal panel. In some embodiments, e.g.  FIGS. 4A and 4B , the width of the electrodes or a pitch between the electrodes of the patterned ITO layers in the partial region of the tunable liquid crystal panel is the same as the rest of the tunable liquid crystal panel. 
     In  FIG. 4C , the first electrode layer  120   g  and the second electrode layer  122   g  have a fringe-field switch (FFS) electrode design. The second electrode layer  122   g  is a plane continuous layer between the first electrode layer  120   g  and the substrate  110 , and the first electrode layer  120   g  and the second electrode layer  122  are insulated from each other by an insulating layer  110   a  disposed therebetween. The first electrode layer  120   g  in  FIG. 4C  is the same as the description of the first electrode layer  120   g  in  FIG. 4A  and  FIG. 4B . 
     In  FIG. 4D , the first electrode layer  120   g  has a hole patterned electrode design. The second electrode layer  122   g  is a plane continuous layer between the first electrode layer  120   g  and the substrate  110 , and the first electrode layer  120   g  and the second electrode layer  122  are insulated from each other by an insulating layer  110   a  disposed therebetween. The first electrode layer  120   g  has a plurality of micro-openings, such as circles, as shown in  FIG. 4D , which is also known as a hole pattern design. 
     With the first electrode layer  120  and the second electrode layer  122  being patterned, when the voltage between the first electrode layer  120  and the second electrode layer  122  is not zero, the liquid crystal molecules in the liquid crystal layer  130  will be arranged according to the electric field between the first electrode layer  120  and the second electrode layer  122 . Therefore, the refractive index distribution of the liquid crystal layer  130  is non-uniform, which may diffract the light into a desired pattern. 
       FIG. 5A  is a schematic cross-sectional views of a tunable liquid crystal panel according to some embodiment of the invention, such as  FIGS. 4A and 4B . Referring to  FIG. 5A , the tunable liquid crystal panel  100   d  in this embodiment is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  100   d  according to this embodiment, the first electrode layer  120   g  and the second electrode layer  122   g  are both disposed on the same substrate, e.g. the first substrate  110 , and are both patterned layers. The first electrode layer  120   g  and the second electrode layer  122   g  has an in-plane switch (IPS) electrode design. Specifically, the first electrode layer  120   g  includes a plurality of conductive micro-patterns  120   g , and the second electrode layer  122   g  includes a plurality of conductive micro-patterns  122   g . The conductive micro-patterns  120   g  and the conductive micro-patterns  122   g  are alternately arranged along a direction (e.g. the right direction in  FIG. 5A ). 
       FIG. 5B  is a schematic cross-sectional view of a tunable liquid crystal panel according to another embodiment of the invention, such as  FIGS. 4C and 4D . The tunable liquid crystal panel  100   e  in this embodiment is similar to the tunable liquid crystal panel  100   d  in  FIG. 5A , and the main difference therebetween is as follows. In the tunable liquid crystal panel  100   e  according to this embodiment, the first electrode layer  120   g  and the second electrode layer  122   h  have a fringe-field switch (FFS) electrode design. The second electrode layer  122   g  is a plane continuous layer between the first electrode layer  120   g  and the substrate  910 , and the first electrode layer  120   g  and the second electrode layer  122   g  are insulated from each other by an insulating layer  100   a  disposed therebetween. The first electrode layer  120   g  in  FIG. 5B  is the same as the description of the first electrode layer  120   g  in  FIG. 5A . 
       FIGS. 6A-6C  are schematic top views of some different variations of the first electrode layer in  FIG. 4D  and  FIG. 5B  respectively according to three embodiments in the invention. Referring to  FIG. 6A ,  FIG. 6B , and  FIG. 6C , the patterned layer (e.g. the first electrode layer  120  and the figures show the first electrode layer  120  as examples) has a plurality of micro-openings  120   a  having a maximum diameter of the opening less than 1 millimeter. The shapes of the micro-openings  120   a  includes circles (as shown in  FIG. 6A ), rectangles (as shown in  FIG. 6B ), squares, hexagons (as shown in  FIG. 6C ), other regular shapes, other irregular shapes, or a combination thereof. 
       FIGS. 7A-7D  are schematic cross-sectional views of a tunable liquid crystal panel according to some embodiments of the invention. Referring to  FIG. 7A , the tunable liquid crystal panel  100   e  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In this embodiment, the tunable liquid crystal panel  100   e  has the first electrode  120   g  on the first substrate  110 , and the second electrode  122   g  also on the first substrate  110 . In some embodiment, the tunable liquid crystal panel  100   e  has both the first electrode  120   g  and the second electrode  122   g  on the second substrate  112 . Since the first electrode  120   g  and the second electrode  122   g  are both on the first substrate  110 , which is the same side of the tunable liquid crystal panel  100   e , the first electrode  120   g  and the second electrode  122   g  may form an in-plane switch (IPS) electrode design, which are arranged in a pattern similar to  FIG. 4A  or  FIG. 4B . In this IPS design, that the first electrode  120   g  and the second electrode  122   g  form two conductive micro-patterns, which are driven by two different voltages separately. As a result, the electric field generated by the first electrode  120   g  and the second electrode  122   g  will not be uniform within the tunable liquid crystal panel  100   e.    
     Referring to  FIG. 7B , the tunable liquid crystal panel  100   f  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In this embodiment, the tunable liquid crystal panel  100   f  has both the first electrode  120  and the second electrode  122 . The first electrode  120  is a patterned electrode while the second electrode  122  is an unpatterned electrode. In some embodiments, the first electrode  120  is an unpatterned electrode while the second electrode  122  is a patterned electrode. 
     Referring to  FIG. 7C , the tunable liquid crystal panel  100   g  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In this embodiment, the tunable liquid crystal panel  100   g  has both the first electrode  120  and the second electrode  122 , and both the first electrode  120  and the second electrode  122  are patterned electrode. 
     Referring to  FIG. 7D , the tunable liquid crystal panel  100   h  is similar to the tunable liquid crystal panel  100   a  in  FIG. 3A , and the main difference therebetween is as follows. In this embodiment, the tunable liquid crystal panel  100   h  has both the first electrode  120  and the second electrode  122 , and both the first electrode  120  and the second electrode  122  are unpatterned electrode. 
       FIGS. 8A and 8B  are schematic top views of a liquid crystal layer according to some embodiments of the invention.  FIG. 8A  and  FIG. 8B  are schematic diagram of a liquid crystal layer  130  from a top view, i.e. along z-direction, according to an embodiment of the invention. In some embodiments, e.g.  FIG. 7D , both the first electrode  120  and the second electrode  122  are unpatterned electrode. However, the liquid crystal molecules  130   a  of the liquid crystal layer  130  may be arranged in a pre-determined pattern, as shown in  FIGS. 8A and 8B , due to the alignment layers  170  and  172 . When there is no voltage difference between the first electrode  110  and the second electrode  112 , the liquid crystal molecules  130   a  are laying in a pre-determined pattern according to alignment layers  170  and  172 . When the voltage difference between the first electrode  110  and the second electrode  112  is not equal to zero, the liquid crystal molecules  130   a  are aligned in a vertical direction. And the light  211  emitted from the light source  210  may be switched from a structure light to a flood light from a flood light to a structure light. 
     In  FIG. 8A , the liquid crystal molecules  130   a  are controlled by the alignment layers  170  and  172  to form a diffractive optical element with liquid crystal molecules aligned in two orientations. Other diffractive optical elements may be formed by having alignment layers with different surface pattern and the invention is not limited thereto. 
     In  FIG. 8B , the polar angle of liquid crystal molecules is controlled by the alignment layers  170  and  172  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. 
       FIG. 9  is a schematic cross-sectional view of the tunable liquid crystal panel according to some embodiments. Referring to  FIG. 9 , the tunable liquid crystal panel  100  has the liquid crystal layer  130  including polymer network liquid crystals (PNLCs), which includes liquid crystal molecules  130   a  with a polymer network  132 . 
     When the voltage between the first electrode  110  and the second electrode  112  is about zero, the liquid crystal molecules  130   a  in the liquid crystal layer are aligned vertically, so the refractive index distribution of the liquid crystal layer  130  is uniform, so that the liquid crystal layer  130  is like a transparent layer. As a result, the structure light passes the liquid crystal layer is still a structure light, and the tunable liquid crystal panel is in a structure light mode. 
     When the voltage between the first electrode  110  and the second electrode  112  is not zero, the liquid crystal molecules  130   a  orientated along the direction of the electric field between the first electrode  110  and the second electric field  112 . However, due to the presence of the polymer network  132 , the orientation of the liquid crystal molecules  130   a  are randomly oriented in the liquid crystal layer. As a result, the refractive index distribution of the liquid crystal layer  130  is non-uniform. As a result, the structure light passes through the liquid crystal layer  130  becomes a flood light, and the tunable liquid crystal panel is in a flood light mode. 
     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.