Patent Publication Number: US-2021165085-A1

Title: Sensor with cross talk suppression

Description:
BACKGROUND 
     Technical Field 
     The present disclosure is directed to a sensor that reduces cross talk within the sensor. 
     Description of the Related Art 
     Proximity sensors, sometimes referred to as ranging sensors, are often used to detect a distance to a target object. Generally, proximity sensors include a transmitter that transmits a light signal at the target object, and a receiver that receives the light signal reflected from the target object back to the sensor. The distance from the sensor to the target object is then calculated based on the received light signal. 
     The light signal received by the receiver of the proximity sensor is often degraded or masked by light signals from unwanted paths in the proximity sensor and surrounding structures. For example, light signals reflected off of components within the proximity sensor itself and/or light signals transmitted directly from the transmitter of the proximity sensor may overpower and reduce the signal to noise ratio of the light signal received by the receiver. This phenomenon is sometimes referred to as cross talk. 
     Degradation of the light signal received by the receiver often cause inaccurate proximity calculation results. Thus, proximity sensors often include various solutions to minimize or reduce the amount of cross talk between the transmitter and the receiver of the proximity sensor. For example, some proximity sensors include physical structures to block light signals from external sources that may degrade or interfere with the light signal received by the receiver. 
     BRIEF SUMMARY 
     The present disclosure is directed to a sensor that detects a distance between the sensor and a target object. The sensor includes, in part, a transmission optical structure and a light source. The transmission optical structure includes a functional layer that provides one or more optical functions, such as a beam shaping function or a collimating function, and a polarizing layer that provides a polarizing function. The polarizing layer has a corralling property to convert or impose polarization of unpolarized light transmitted through the transmission optical structure to have mostly or all P-polarization. In addition, the light source emits a light signal that has mostly or all P-polarization. As the transmission optical structure and the light source both maximize P-polarization and minimize S-polarization of light within the sensor, cross talk within the sensor is reduced. As a result, detection results of the sensor are improved. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar features or elements. The size and relative positions of features in the drawings are not necessarily drawn to scale. 
         FIG. 1A  is a diagram of a sensor according to an embodiment disclosed herein. 
         FIG. 1B  is a diagram of a sensor without the light source and the transmission optical structure of the sensor of  FIG. 1A . 
         FIG. 2  is a diagram of a light signal transmitted by the sensor of  FIG. 1B . 
         FIG. 3  is a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 4  is a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 5  is a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 6  is a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 7  illustrates a polarizing layer for a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 8  illustrates a polarizing layer for a transmission optical structure according to an embodiment disclosed herein. 
         FIGS. 9A, 9B, 9C, and 9D  are cross-sectional views illustrating subsequent stages of fabricating a polarizing layer for a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 10  is a flow diagram illustrating a process for designing a polarizing layer for a transmission optical structure according to an embodiment disclosed herein. 
         FIG. 11  is a side view of a light source according to an embodiment disclosed herein. 
         FIG. 12  is a top view of the light source of  FIG. 11  according to an embodiment disclosed herein. 
         FIG. 13  is a top view of the light source of  FIG. 11  according to an embodiment disclosed herein. 
         FIG. 14  is a top view of the light source of  FIG. 11  according to an embodiment disclosed herein. 
         FIG. 15  is a top view of the light source of  FIG. 11  according to an embodiment disclosed herein. 
         FIG. 16  is a top view of the light source of  FIG. 11  according to an embodiment disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various aspects of the disclosed subject matter. However, the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and methods of manufacturing electronic devices, optical lenses, and sensors have not been described in detail to avoid obscuring the descriptions of other aspects of the present disclosure. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprise” and variations thereof, such as “comprises” and “comprising,” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.” 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same aspect. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more aspects of the present disclosure. 
     Reference throughout the specification to integrated circuits is generally intended to include integrated circuit components built on semiconducting or glass substrates, whether or not the components are coupled together into a circuit or able to be interconnected. Throughout the specification, the term “layer” is used in its broadest sense to include a thin film, a cap, or the like, and one layer may be composed of multiple sub-layers. 
     It is noted that the dimensions set forth herein are provided as examples. Other dimensions are envisioned for this embodiment and all other embodiments of this application. 
     As discussed above, light signals received by a proximity sensor may be degraded due to cross talk. For example, light signals received by the proximity sensor may be degraded or masked by light signals from unwanted paths in the proximity sensor and surrounding structures, such as light signals reflected off of components within the proximity sensor itself and light signals transmitted directly from the transmitter of the proximity sensor. Consequently, proximity calculation results of proximity sensors may sometimes be inaccurate. 
     The present disclosure is directed to a sensor that reduces or removes cross talk within the sensor, and, thus, has improved detection results.  FIG. 1A  is a diagram of a sensor  10  according to an embodiment disclosed herein. The sensor  10  determines a distance between the sensor  10  and a target object external to the sensor  10 . In one embodiment, the sensor  10  is a time-of-flight sensor. Operation of the sensor  10  will be discussed in further detail below. 
     The sensor  10  may be included in various electronic devices, such as mobile handsets, cameras, tablets, laptops, and computers, for a variety of different applications. For example, the sensor  10  may be incorporated into a mobile handset and used in conjunction with a camera to adjust a focus or a flash of the camera. 
     The sensor  10  includes a substrate  12 , a body  14 , a light source  16 , a transmission optical structure  18 , a detector  20 , a reception optical structure  22 , and a cover  24 . 
     The substrate  12  provides a support platform for the sensor  10 . The body  14 , the light source  16 , the transmission optical structure  18 , the detector  20 , and the reception optical structure  22  are positioned on the substrate  12 . The substrate may be any type of rigid material, such as plastic, metal, glass, and semiconductor material. In one embodiment, the substrate  12  is a printed circuit board that includes one or more electrical components (e.g., capacitors, transistors, processors, etc.). 
     The body  14  is positioned on the substrate  12 . The substrate  12  and the body  14 , together, form an enclosure or package that contains the light source  16 , the transmission optical structure  18 , the detector  20 , and the reception optical structure  22 . The substrate  12  and the body  14  protect the light source  16 , the transmission optical structure  18 , the detector  20 , and the reception optical structure  22  from an external environment. The body  14  includes an output aperture  26  and a detection aperture  28 . 
     The output aperture  26  directly overlies and is aligned with the light source  16  and the transmission optical structure  18 . The output aperture  26  provides a hole for a light signal  30  to pass through. The light signal  30  is a light signal or photons emitted from the light source  16  and directed to the target object in which a distance between the target object and the sensor  10  is being determined. 
     The detection aperture  28  directly overlies and is aligned with the detector  20  and the reception optical structure  22 . The detection aperture  28  provides a hole for a light signal  32  to pass through. The light signal  32  is the light signal  30  reflected off of the target object. 
     The light source  16  is positioned on the substrate  12 . The light source  16  directly underlies and is aligned with the transmission optical structure  18  and the output aperture  26 . 
     The light source  16  emits the light signal  30  through the transmission optical structure  18  and the output aperture  26 . In one embodiment, the light source  16  is an infrared or near infrared light source, such as a vertical-cavity surface-emitting laser (VCSEL). As will be discussed in further detail below, the light source  16  maximizes a first type of polarization (P-polarization) and minimizes a second type of polarization (S-polarization) of the light signal  30  to reduce or remove cross talk within the sensor  10 . 
     The transmission optical structure  18  directly overlies the light source  16  and is aligned with the light source  16  and the output aperture  26 . In one embodiment, the transmission optical structure  18  covers the entire output aperture  26 . In one embodiment, the transmission optical structure  18  is physically coupled to the body  14 . 
     The transmission optical structure  18  has one or more optical functions. In one embodiment, the transmission optical structure  18  has a beam shaping function, an imaging function, a collimating function, a diffusing function, a beam splitting function, a wavefront coding function, or a combination thereof. In addition, the transmission optical structure  18  maximizes the first type of polarization (P-polarization) and minimizes the second type of polarization (S-polarization) of the light signal  30  to reduce or remove cross talk within the sensor  10 . The transmission optical structure  18  will be discussed in further detail below. 
     In one embodiment, the transmission optical structure  18  is made of one or more transparent materials. For example, in one embodiment, the transmission optical structure  18  is made of one or more of the following: silicon (Si), silicon dioxide, (SiO2), zinc sulphide (ZnS), galium nitride (GaN), zinc selenide (ZnSe), titanium dioxide (TiO2), silicon carbide (SiC), gallium phosphide (GaP), gallium arsenide (GaAs), and hydrogenated silicon (Si:H). Fabrication of the transmission optical structure  18  will be discussed in further detail below. 
     The detector  20  is positioned on the substrate  12 . The detector  20  directly underlies and is aligned with the reception optical structure  22  and the detection aperture  28 . In one embodiment, as shown in  FIG. 1A , the detector  20  is integrated into a semiconductor substrate  34 . The substrate  34  may include various electrical components (e.g., transistors, capacitors, resistors, processors, etc.) and devices (e.g., a reference sensor array). 
     The detector  20  receives the light signal  32 , which is the light signal  30  reflected off of the target object and passes through the reception optical structure  22  and the detection aperture  28 . The detector  20  includes a plurality of photodetectors that sense or measure the light signal  32 . The detector  20  may be any type of sensors that measure light signals. In one embodiment, the detector  20  is a single-photon avalanche diode (SPAD) array. 
     The reception optical structure  22  directly overlies the detector  20  and is aligned with the detector  20  and the detection aperture  28 . In one embodiment, the reception optical structure  22  covers the entire detection aperture  28 . In one embodiment, the reception optical structure  22  is physically coupled to the body  14 . 
     In one embodiment, the reception optical structure  22  has one or more optical functions. For example, in one embodiment, the reception optical structure  22  has a beam shaping function, an imaging function, a collimating function, a diffusing function, a polarizing function, a beam splitting function, a wavefront coding function, or a combination thereof. 
     In one embodiment, the reception optical structure  22  is made of a single transparent material (i.e., monolithic). In one embodiment, the reception optical structure  22  is made of one or more transparent materials. For example, the reception optical structure  22  may include one or more of the following: silicon (Si), silicon dioxide, (SiO2), zinc sulphide (ZnS), galium nitride (GaN), zinc selenide (ZnSe), titanium dioxide (TiO2), silicon carbide (SiC), gallium phosphide (GaP), gallium arsenide (GaAs), and hydrogenated silicon (Si:H). 
     The cover  24  directly overlies and is aligned with the sensor  10 . The cover  24  protects the sensor  10  from a surrounding environment. In one embodiment, the cover  24  is a component of the electronic device in which the sensor  10  is included. For example, the cover  24  may be a protective layer of glass of a mobile handset. 
     In one embodiment, the cover  24  is made of one or more transparent materials. For example, the cover  24  may include one or more of the following: glass, plastic, silicon (Si), silicon dioxide, (SiO2), zinc sulphide (ZnS), galium nitride (GaN), zinc selenide (ZnSe), titanium dioxide (TiO2), silicon carbide (SiC), gallium phosphide (GaP), gallium arsenide (GaAs), and hydrogenated silicon (Si:H). 
     The sensor  10  determines a distance between the sensor  10  and the target object in a surrounding environment. The light source  16  transmits the light signal  30  through the transmission optical structure  18  and the output aperture  26 , and at the target object. The detector  20  receives and measures the light signal  32 , which is the light signal  30  that hits the target object and is reflected back through the reception optical structure  22  and the detection aperture  28 . In one embodiment, the sensor  10  uses the light signal  30  and the light signal  32  to determine the time of flight of the light signal  30  to travel from the light source  16 , to the target object, and back to the detector  20 . A distance between the sensor  10  and the target object is determined based on the time of flight. In one embodiment, the sensor  10  uses an indirect time of flight method in which the light signal  30  is a modulated signal, and the sensor  10  determines a distance between the sensor  10  and the target object based on the relative phase of the light signal  30  and the light signal  32 . In one embodiment, the distance between the sensor  10  and the target object is determined based on the relative intensities of the light signal  30  and the light signal  32 . Other methods are also possible. 
     As discussed above, the light source  16  and the transmission optical structure  18  maximize a first type of polarization (P-polarization) and minimize a second type of polarization (S-polarization) of the light signal  30  to reduce or remove cross talk within the sensor  10 . If the sensor  10  did not include the light source  16  and the transmission optical structure  18 , the light signal  32 , which is the light signal  30  reflected off of the target object and received by the detector  20 , may potentially become degraded or interfered with by light signals or photons from other sources, such as the light signal  30  reflected off of other surfaces of the sensor  10 . Stated differently, the detector  20  may detect light signals or photons reflected off of, for example, the body  14  instead of the target object, and, thus, may give erroneous ranging errors. This phenomenon is sometimes referred to as cross talk. For example,  FIG. 1B  is a sensor  11  without the light source  16  and the transmission optical structure  18  of the sensor  10 . The sensor  11  includes the same components as the sensor  10 , except that the light source  16  is replaced with a light source  17  and the transmission optical structure  18  is replaced with a transmission optical structure lens  19 . 
     In contrast to the light source  16  and the transmission optical structure  18 , the light source  17  and the transmission optical structure  19  do not maximize a first type of polarization (P-polarization) and minimize a second type of polarization (S-polarization) of the light signal  30 . Consequently, referring to  FIG. 1B , one or more of a light signal  38 , a light signal  40 , and a light signal  42  may reduce the signal to noise ration of the light signal  32 . The light signal  38  is a portion of the light signal  30  that is reflected off of the body  14  and a lower surface  44  of the cover  24 , and to the detector  20 . The light signal  40  is a portion of the light signal  30  that is reflected off of an upper surface  46  of the cover  24 , and to the detector  20 . The light signal  42  is a portion of the light signal  30  that is reflected off of the lower surface  44  and the upper surface  46  of the cover  24 , and to the detector  20 . Cross talk within the sensor  11  will often limit the accuracy of the sensor  11  when the light signal  32  is sufficiently small. 
     The magnitude of light reflected off of surfaces of the sensor  11  (e.g., the light signal  38 , the light signal  40 , and the light signal  42 ) is dependent on the polarization content of the incident light. Generally, the reflection of S-polarized light is stronger than the reflection of P-polarized light. Thus, the amount of reflected light within the sensor  11  (i.e., cross talk) may be reduced by minimizing S-polarization and maximizing P-polarization of light between the output aperture  26  and the detection aperture  28  of the sensor  11 . For example,  FIG. 2  is a diagram of the light signal  30  signal transmitted by the sensor  11 .  FIG. 2  illustrates an example of reflection of S-polarized light and P-polarized light of the light signal  30 . 
     A cross talk plane  48  extends across both the output aperture  26  and the detection aperture  28 , and is parallel to (or in the same plane as) a plane including the light signal  30  and the light signal  32 . The cross talk plane  48  is sometimes referred to as a plane of incidence. S-polarized light  50  is the transverse-electric component of the light signal  30  that extends in a direction perpendicular to the cross talk plane  48 . P-polarized light  52  is the transverse-magnetic component of the light signal  30  that extends in a direction parallel to the cross talk plane  48 . 
     Initially, as shown in the example of  FIG. 2 , the light signal  30  transmitted out of the output aperture  26  includes the S-polarized light  50  and P-polarized light  52 . However, as the reflection of S-polarized light is stronger than the reflection of P-polarized light, the light signal  40 , which is a portion of the light signal  30  that is reflected off of the upper surface  46  of the cover  24 , includes mostly the S-polarized light  50 . The S-polarized light  50  is detected by the detector  20  and may cause erroneous ranging errors. In contrast, as the reflection of P-polarized light is weaker than the reflection of S-polarized light, the light signal  30 , which continues through the cover  24 , includes mostly the P-polarized light  52 . Thus, in the example shown in  FIG. 2 , cross talk may be reduced by minimizing S-polarized light  50  and maximizing the P-polarized light  52 . 
     One possible solution to minimize S-polarized light and maximize P-polarized light is to use polarization filters, such as metal gratings. For example, a polarization filter may be positioned in the path of the light signal  30 , and be configured to remove S-polarized light and transmit P-polarized light. Unfortunately, the use of polarization filters are not ideal as polarization filters often reduce efficiency (e.g., reduce the magnitude) of light used to detect a target object. In addition, such filters will often confine light inside the sensor package, and, thus, increase the intra-package cross-talk amplitude 
     Instead of polarization filters, the sensor  10  includes an optical structure and a light source to minimize S-polarized light (e.g., the S-polarized light  50 ) and maximize P-polarized light (e.g., the P-polarized light  52 ) within the sensor  10 . Namely, the transmission optical structure  18  of the sensor  10  maintains or increases P-polarization components of the light signal  30  by converting S-polarization components of the light signal  30  to P-polarization components, and the light source  16  of the sensor  10  transmits light that has mostly or all P-polarization components. As a result, in contrast to the sensor  11  shown in  FIG. 1B , the light signal  38 , the light signal  40 , and the light signal  42  are minimized or non-existent within the sensor  10  shown in  FIG. 1A . 
     As discussed above, referring to  FIG. 1A , the transmission optical structure  18  directly overlies the light source  16 , and is aligned with the light source  16  and the output aperture  26 . The transmission optical structure  18  maximizes P-polarization and minimizes S-polarization of the light signal  30  to reduce or remove cross talk within the sensor  10 , and may include one or more additional optical functions. 
       FIG. 3  is the transmission optical structure  18  according to an embodiment disclosed herein. In the embodiment shown in  FIG. 3 , the transmission optical structure  18  includes a first optical structure  54  and a second optical structure  56 . Referring to  FIG. 1A , in one embodiment, the first optical structure  54  and the second optical structure  56  are physically coupled to the body  14 . 
     The first optical structure  54  includes a substrate  58 , a functional layer  60  on the substrate  58 , and a protective layer  62  on the functional layer  60 . The functional layer  60  is positioned between the substrate  58  and the protective layer  62 . Referring to  FIG. 1A , in one embodiment, the protective layer  62  faces the cover  24 . Stated differently, the protective layer  62  is positioned between the cover  24  and the functional layer  60 . 
     The substrate  58  provides a platform for the functional layer  60  and the protective layer  62 . In one embodiment, the substrate  58  is made of a rigid, transparent material for a particular wavelength of operation. For example, the substrate  58  may include one or more of silicon dioxide, borosilicate glass, amorphous silicon, polycrystalline silicon, and monocrystalline silicon. 
     The functional layer  60  has one or more optical functions. In one embodiment, the transmission optical structure  18  has a beam shaping function, an imaging function, a collimating function, a diffusing function, a beam splitting function, a wavefront coding function, or a combination thereof. The functional layer  60  includes a plurality of microstructures with various dimensions to implement the one or more optical functions. In one embodiment, functional layer  60  includes a layer of material covering the microstructures. The layer of material covering the microstructures and the microstructures are made of different materials to create a change in refractive index at the interface of the layer of material and the microstructures and provide the one or more optical functions described above. In one embodiment, the layer of material and the protective layer  62  are made of different materials. In one embodiment, the layer of material is made of the same material as the protective layer  62 . In one embodiment, the layer of material is not included in the functional layer  60 , and the protective layer  62  instead covers the microstructures. In this embodiment, the microstructures and the protective layer  62  create a change in refractive index at the interface of the protective layer  62  and the microstructures and provide the one or more optical functions described above. In one embodiment, the functional layer  60  is made of two or more of amorphous silicon, polycrystalline silicon, and monocrystalline silicon. 
     The protective layer  62  encapsulates the functional layer  60  to prevent damage and contamination to the plurality of microstructures of the functional layer  60 . In addition, the protective layer  62  provides a robust surface that may be easily cleaned without risk of damaging the functional layer  60 . The protective layer  38  may be made of a variety of materials, such as silicon dioxide, silicon nitride, aluminum oxide, or epoxy. In one embodiment, the protective layer  62  is made of the same material as the substrate  58 . In one embodiment, the protective layer  62  includes multiple layers having different thicknesses so that transmission of light at particular wavelengths can be optimized. 
     It is noted that the lower surface of the substrate  58  and the upper surface of the protective layer  62  provide flat, planar surfaces. Thus, one or more additional layers of material, such as an anti-reflective coating or a filter layer, may be formed on the lower surface of the substrate  58  and/or the upper surface of the protective layer  62 . 
     The second optical structure  56  is similar to the first optical structure  54  except that the second optical structure  56  maintains or increases P-polarization of the light signal  30  by converting S-polarization of the light signal  30  to P-polarization. The second optical structure  56  includes a substrate  64 , a polarizing layer  66  on the substrate  64 , and a protective layer  68  on the polarizing layer  66 . The polarizing layer  66  is positioned between the substrate  64  and the protective layer  68 . Referring to  FIG. 1A , in one embodiment, the protective layer  68  faces the cover  24 . Stated differently, the protective layer  68  is positioned between the cover  24  and the polarizing layer  66 . 
     Similar to the substrate  58 , the substrate  64  provides a platform for the polarizing layer  66  and the protective layer  68 . In one embodiment, the substrate  64  is made of a rigid, transparent material for a particular wavelength of operation. For example, the substrate  64  may include one or more of silicon dioxide, borosilicate glass, amorphous silicon, polycrystalline silicon, and monocrystalline silicon. 
     The polarizing layer  66  maximizes P-polarization and minimizes S-polarization. For example, referring to  FIG. 2 , the polarizing layer  66  minimizes the S-polarized light  50  and maximizes the P-polarized light  52 . Stated differently, the polarizing layer  66  re-orientates S-polarization components into P-polarization components to convert or impose polarization of unpolarized light to have mostly or all P-polarization. It is noted that the polarizing layer  66  is not a polarization filter, and does not filter or block S-polarized light. Thus, the polarizing layer  66  has better efficiency compared to polarization filters. The polarizing layer  66  includes a plurality of microstructures with various dimensions to implement polarization of unpolarized light. The structure and the fabrication of the polarizing layer  66  will be discussed in further detail below. 
     Similar to the protective layer  62 , the protecting layer  68  encapsulates the polarizing layer  66  to prevent damage and contamination to the plurality of microstructures of the polarizing layer  66 . In addition, the protective layer  68  provides a robust surface that may be easily cleaned without risk of damaging the polarizing layer  66 . The protective layer  68  may be made of a variety of materials, such as silicon dioxide, silicon nitride, aluminum oxide, or epoxy. In one embodiment, the protective layer  68  is made of the same material as the substrate  64 . In one embodiment, the protective layer  68  includes multiple layers having different thicknesses so that transmission of light at particular wavelengths can be optimized. 
     It is noted that the lower surface of the substrate  64  and the upper surface of the protective layer  68  provide flat, planar surfaces. Thus, one or more additional layers of material, such as an anti-reflective coating or a filter layer, may be formed on the lower surface of the substrate  64  and/or the upper surface of the protective layer  68 . 
     In one embodiment, as shown in  FIG. 3 , the first optical structure  54  is positioned above the second optical structure  56 . Stated differently, referring to  FIG. 1A , the first optical structure  54  is positioned closer to the cover  24  than the second optical structure  56 . In one embodiment, the second optical structure  56  is positioned above the first optical structure  54 . 
     In one embodiment, as shown in  FIG. 3 , the first optical structure  54  and the second optical structure  56  are spaced from each other by a distance  70 . In one embodiment, the distance  70  is between 100 and 500 micrometers. In one embodiment, the first optical structure  54  and the second optical structure  56  are in direct contact with each other. For example, in one embodiment, the substrate  58  of the first optical structure  54  is in direct contact with the protective layer  68  of the second optical structure  56 . 
     In one embodiment, the transmission optical structure  18  includes the second optical structure  56 , but does not include the first optical structure  54 . In this embodiment, the transmission optical structure  18  includes the polarization function of the second optical structure  56 , but does not include the one or more optical functions of the first optical structure  54 . 
     In one embodiment, the first optical structure  54  does not include the protective layer  62 , and the second optical structure  56  does not include the protective layer  68 . In this embodiment, the functional layer  60  and the polarizing layer  66  are exposed to a surrounding environment, such as air. 
     Other configurations for the transmission optical structure  18  are also possible.  FIG. 4 ,  FIG. 5 , and  FIG. 6  illustrate other possible configurations of the transmission optical structure  18 . 
       FIG. 4  is the transmission optical structure  18  according to an embodiment disclosed herein. In contrast to the embodiment shown in  FIG. 3 , in the embodiment shown in  FIG. 4 , the functional layer  60  and the polarizing layer  66  are combined into a single layer. The transmission optical structure  18  shown in  FIG. 4  includes the substrate  58 , a polarizing and functional layer  72  on the substrate  58 , and the protective layer  62  on the polarizing and functional layer  72 . The polarizing and functional layer  72  is positioned between the substrate  58  and the protective layer  62 . The substrate  58  and the protective layer  62  have been described above. 
     The polarizing and functional layer  72  is a single layer that provides the functionality of both the functional layer  60  and the polarizing layer  66 . Stated differently, the polarizing and functional layer  72  concurrently provides one or more optical functions similar to that of the functional layer  60 , and polarization similar to that of the polarizing layer  66 . In one embodiment, the polarizing and functional layer  72  maximizes P-polarization and minimizes S-polarization; and provides a beam shaping function, an imaging function, a collimating function, a diffusing function, a polarizing function, a beam splitting function, a wavefront coding function, or a combination thereof. 
     In one embodiment, the transmission optical structure  18  shown in  FIG. 4  does not include the protective layer  62 . In this embodiment, the polarizing and functional layer  72  is exposed to a surrounding environment, such as air. 
       FIG. 5  is the transmission optical structure  18  according to an embodiment disclosed herein. In contrast to the embodiment shown in  FIG. 3 , in the embodiment shown in  FIG. 5 , the functional layer  60  and the polarizing layer  66  are positioned on the same substrate. The transmission optical structure  18  shown in  FIG. 5  includes the substrate  58 , the polarizing layer  66  on the substrate  58 , the functional layer  60  on the polarizing layer  66 , and the protective layer  62  on the functional layer  60 . The substrate  58 , the polarizing layer  66 , the functional layer  60 , and the protective layer  62  have been described above. 
     In one embodiment, as shown in  FIG. 5 , the functional layer  60  is positioned above the polarizing layer  66 . Stated differently, referring to  FIG. 1A , the functional layer  60  is positioned closer to the cover  24  than the polarizing layer  66 . In one embodiment, the polarizing layer  66  is positioned above the functional layer  60 . 
     In one embodiment, the transmission optical structure  18  shown in  FIG. 5  does not include the protective layer  62 . In this embodiment, the functional layer  60  is exposed to a surrounding environment, such as air. 
       FIG. 6  is the transmission optical structure  18  according to an embodiment disclosed herein. In contrast to the embodiment shown in  FIG. 3 , in the embodiment shown in  FIG. 6 , the functional layer  60  and the polarizing layer  66  are positioned on opposite sides of the same substrate. The transmission optical structure  18  shown in  FIG. 6  includes the substrate  58 , the polarizing layer  66  on a first surface  74  of the substrate  58 , the functional layer  60  on a second surface  76  of the substrate  58 , the protective layer  62  on the functional layer  60 , and the protective layer  68  on the polarizing layer  66 . The substrate  58 , the polarizing layer  66 , the functional layer  60 , the protective layer  62 , and the protective layer  68  have been described above. 
     The first surface  74  and the second surface  76  of the substrate  58  face in opposite directions. In one embodiment, referring to  FIG. 1A , the first surface  74  faces the cover  24  and the second surface  76  faces the substrate  12 . In one embodiment, the first surface  74  faces the substrate  12  and the second surface  76  faces the cover  24 . 
     In one embodiment, the transmission optical structure  18  shown in  FIG. 6  does not include the protective layer  62  and the protective layer  68 . In this embodiment, the functional layer  60  and the polarizing layer  66  are exposed to a surrounding environment, such as air. 
     In one embodiment, the polarization function of the transmission optical structure  18  is implemented by a microstructure layer. For example, the polarizing layer  66  in  FIG. 3 , the polarizing and functional layer  72  in  FIG. 4 , the polarizing layer  66  in  FIG. 5 , and the polarizing layer  66  in  FIG. 6  may each be a microstructure layer including a plurality of microstructures. 
       FIGS. 7 and 8  illustrate two different microstructure layers having a polarizing function. In the embodiments shown in  FIGS. 7 and 8 , the polarizing layer  66  of  FIG. 3  is used for exemplary purposes. In particular, the microstructure layers in  FIG. 7  and  FIG. 8  correspond to the polarizing layer  66  in the second optical structure  56  of  FIG. 3 . However, the microstructure layers shown in  FIG. 7  and  FIG. 8  may be used for any of the embodiments disclosed herein. 
       FIG. 7  illustrates the polarizing layer  66  for the transmission optical structure  18  according to an embodiment disclosed herein. As discussed above with respect to  FIG. 3 , the polarizing layer  66  is on the substrate  64 , and the protective layer  68  is on the polarizing layer  66 . The polarizing layer  66  maximizes P-polarization and minimizes S-polarization. 
     The polarizing layer  66  includes a microstructure layer  77  having a plurality of microstructures  78 . The microstructures  78  have various heights and widths. The heights and widths of the microstructures  78  are selected to provide the polarization properties of the polarizing layer  66 . Stated differently, the heights and widths of the microstructures  78  are selected to have a corralling property to convert or impose polarization of unpolarized light transmitted through the microstructure layer  77  to have mostly or all P-polarization. The selection of the dimensions of the microstructures will be discussed in further detail below. 
     In one embodiment, the microstructures  78  have near wavelength scale features. Namely, the dimensions of the heights and widths of the microstructures  78  are within a predetermined range of the wavelength of light transmitted by the light source  16 . For example, in one embodiment, the light source  16  transmits an infrared or near infrared light, which has a wavelength between 700 nanometers and 1 millimeter. In this embodiment, the dimensions of the heights and widths of each of the microstructures  78  are between 700 nanometers and 1 millimeter. For example, a height  82  and a width  84  of a microstructure  86  may be between 700 nanometers and 1 millimeter. In one embodiment, as shown in  FIG. 7 , the microstructures  78  include microstructures having at least three different heights. In one embodiment, the microstructures  78  include microstructures having the same width. 
     In one embodiment, one or more of the microstructures  78  are spaced from each other on the substrate  64 . For example, a microstructure  88  is separated from a microstructure  90  by an upper layer (e.g., a layer of material  79 , which will be described below, or the protective layer  68 ) such that there is a space or gap  80  that exposes the substrate  64  to the upper layer. In one embodiment, some or all of the microstructures  78  are physically coupled to each other. For example, a microstructure  92  is attached to a microstructure  94  such that there is no space or gap that exposes the substrate  64  to the upper layer. 
     In one embodiment, the microstructure layer  77  provides one or more optical functions (e.g., a beam shaping function, an imaging function, a collimating function, a diffusing function, a beam splitting function, a wavefront coding function, or a combination thereof) in addition to polarization. For example, in one embodiment, the microstructures  78  of the microstructure layer  77  are used to implement the polarizing and functional layer  72  in the embodiment shown in  FIG. 4 . In this embodiment, the microstructure layer  77  concurrently provides one or more optical functions similar to that of the functional layer  60 , and polarization similar to that of the polarizing layer  66 . 
     In one embodiment, the polarizing layer  66  includes the layer of material  79  that covers the microstructure layer  77  and fills spaces or gaps  80  between the microstructures  78 . The layer of material  79  separates the microstructure layer  77  from the protective layer  68 . The layer of material  79  and the microstructures  78  are made of different materials to create a change in refractive index at the interface of the layer of material  79  and the microstructures  78  and provide the one or more optical functions described above. In one embodiment, the layer of material  79  and the protective layer  68  are made of different materials. In one embodiment, the layer of material  79  is made of the same material as the protective layer  68 . In one embodiment, the layer of material  79  is not included in the polarizing layer  66  and the protective layer  66  instead covers the microstructure layer  77  and fills the space or gaps  80  between the microstructures  78 . In this embodiment, the microstructures  78  and the protective layer  66  create a change in refractive index at the interface of the protective layer  66  and the microstructures  78  and provide the one or more optical functions described above. 
       FIG. 8  illustrates the polarizing layer  66  for the transmission optical structure  18  according to an embodiment disclosed herein. As discussed above with respect to  FIG. 3 , the polarizing layer  66  is on the substrate  64 , and the protective layer  68  is on the polarizing layer  66 . The polarizing layer  66  maximizes P-polarization and minimizes S-polarization. 
     The polarizing layer  66  includes a microstructure layer  96  having a plurality of microstructures  98 . In contrast to the microstructures  78  in the embodiment shown in  FIG. 7 , the microstructures  98  have a grating pattern. Namely, the microstructures  98  have various widths but the same height. The widths and the height of the microstructures  98  are selected to provide the polarization properties of the polarizing layer  66 . Stated differently, the widths and the height of the microstructures  98  are selected to have a corralling property to convert or impose polarization of unpolarized light transmitted through the microstructure layer  96  to have mostly or all P-polarization. The selection of the dimensions of the microstructures will be discussed in further detail below. 
     In one embodiment, the microstructures  98  have sub-wavelength scale features. Namely, the dimensions of the heights and widths of the microstructures  78  are outside of a predetermined range of the wavelength of light transmitted by the light source  16 . For example, in one embodiment, the light source  16  transmits an infrared or near infrared light, which has a wavelength between 700 nanometers and 1 millimeter. In this embodiment, the dimensions of the heights and widths of each of the microstructures  78  are less than 700 nanometers. For example, a width  100  of a microstructure  102  may be less than 700 nanometers, and a height  104  of all of the microstructures  98  may be less than 700 nanometers. In one embodiment, as shown in  FIG. 7 , the microstructures  98  include microstructures having at least three different widths. In one embodiment, the microstructures  98  include microstructures having the same width. 
     In one embodiment, one or more of the microstructures  98  are spaced from each other on the substrate  64 . For example, a microstructure  106  is separated from a microstructure  108  by an upper layer (e.g., a layer of material  99 , which will be described below, or the protective layer  68 ) such that there is a space or gap  110  that exposes the substrate  64  to the upper layer. 
     In one embodiment, the microstructure layer  96  provides one or more optical functions (e.g., a beam shaping function, an imaging function, a collimating function, a diffusing function, a beam splitting function, a wavefront coding function, or a combination thereof) in addition to polarization. For example, in one embodiment, the microstructures  98  of the microstructure layer  96  are used to implement the polarizing and functional layer  72  in the embodiment shown in  FIG. 4 . In this embodiment, the microstructure layer  96  concurrently provides one or more optical functions similar to that of the functional layer  60 , and polarization similar to that of the polarizing layer  66 . 
     In one embodiment, the polarizing layer  66  includes the layer of material  99  that covers the microstructure layer  96  and fills spaces or gaps  110  between the microstructures  98 . The layer of material  99  separates the microstructure layer  96  from the protective layer  68 . The layer of material  99  and the microstructures  98  are made of different materials to create a change in refractive index at the interface of the layer of material  99  and the microstructures  98  and provide the one or more optical functions described above. In one embodiment, the layer of material  99  and the protective layer  68  are made of different materials. In one embodiment, the layer of material  99  is made of the same material as the protective layer  68 . In one embodiment, the layer of material  79  is not included in the polarizing layer  66  and the protective layer  66  instead covers the microstructure layer  96  and fills the space or gaps  110  between the microstructures  98 . In this embodiment, the microstructures  98  and the protective layer  66  create a change in refractive index at the interface of the protective layer  66  and the microstructures  98  and provide the one or more optical functions described above. 
     A variety of semiconductor processing techniques may be used to form the microstructure layer  77  and the microstructure layer  96 . For example, a single thick layer can be formed and then etched to form the different microstructures using a plurality of different masks. Alternatively, a microstructure layer may be formed from a plurality of layers that are formed and etched consecutively. 
       FIGS. 9A, 9B, 9C, and 9D  are cross-sectional views illustrating subsequent stages of fabricating a polarizing layer, such as the polarizing layer  66  and the polarizing and functional layer  72 , for the transmission optical structure  18 , according to an embodiment disclosed herein. In the embodiment shown in  FIGS. 9A, 9B, 9C, and 9D , the polarizing layer  66  of  FIG. 8  is used for exemplary purposes. In particular, the fabricated microstructure layer in  FIGS. 9A, 9B, 9C, and 9D  corresponds to the microstructure layer  96  of  FIG. 8 , albeit having different dimensions. However, the stages of fabricating a polarizing layer shown in  FIGS. 9A, 9B, 9C, and 9D  may be used for any of the embodiments disclosed herein. 
     In  FIG. 9A , a first layer  114  of material is formed on the substrate  64 . The first layer  114  is used to form the microstructure layer  96  for the polarizing layer  66  of  FIG. 8 . The first layer  114  may be formed using various semiconductor processing techniques, such as sputtering, chemical vapor deposition, or plasma vapor deposition. This allows a manufacturer to use existing semiconductor processing machines for forming the transmission optical structure  18 . 
     In one embodiment, the layer  114  of material is made of one or more of the following: silicon (Si), silicon dioxide, (SiO2), zinc sulphide (ZnS), galium nitride (GaN), zinc selenide (ZnSe), titanium dioxide (TiO2), silicon carbide (SiC), gallium phosphide (GaP), gallium arsenide (GaAs), and hydrogenated silicon (Si:H). 
     In one embodiment, as discussed above, the substrate  64  is made of a transparent, rigid material. For example, the substrate  64  may include one or more of silicon dioxide, borosilicate glass, amorphous silicon, polycrystalline silicon, and monocrystalline silicon. 
     In  FIG. 9B , the layer  114  of material is patterned and etched to form the microstructure layer  96  of the polarizing layer  66 . Namely, portions of the layer  114  are removed to expose the substrate  64  and form openings  118 . The openings  118  may be formed using masking techniques or other standard semiconductor processing techniques for masking and removing materials. For example, portions of the layer  114  may be removed by chemical etching. As discussed above, the microstructure layer  96  includes a grating pattern having microstructures with various widths but the same height. The selection of the dimensions of the microstructures will be discussed in further detail below. 
     In an alternative embodiment, the layer  114  of the microstructure layer  96  as shown in  FIG. 9B  is formed by using a pattern deposition. This may be achieved with a photoresist deposition process. Positive or negative photolithography may be used for masking techniques. 
     In  FIG. 9C , a layer  120  of material is formed on the layer  114  of the microstructure layer  96 , in the openings  118 , and on the exposed surface of the substrate  64 . The layer  120  is used to form the protective layer  68  of  FIG. 8 . The layer  120  may be formed using various semiconductor processing techniques, such as sputtering, chemical vapor deposition, or plasma vapor deposition. The layer  120  may be made of a variety of materials, such as silicon dioxide, silicon nitride, aluminum oxide, or epoxy. 
     As shown in  FIG. 9C , once the layer  120  is formed, an upper surface  122  may be uneven (i.e., not planar). The uneven surface of the upper surface  122  may reduce or inhibit the polarization properties of the microstructure layer  96 . To avoid this, in  FIG. 9D , the upper surface  122  of the layer  120  is planarized to smooth, planar upper surface. The upper surface  122  may be planarized using various semiconductor processing techniques, such as chemical-mechanical polishing. 
     Although  FIGS. 9A, 9B, 9C, and 9D  illustrate subsequent stages of fabricating the polarizing layer  66  of  FIG. 8 , the fabrication steps shown in  FIGS. 9A, 9B, 9C, and 9D  may be applied to any of the embodiments disclosed herein. For example, in order to fabricate the microstructure layer  77 , which includes various heights and widths, shown in  FIG. 7 , the fabrication steps shown in  FIGS. 9A, 9B, 9C, and 9D  may be repeated to form additional layers for the microstructures  78 . Stated differently, a plurality of layers of material (e.g., the layer  114 ) may be formed and etched consecutively until the microstructure layer  77  is obtained. 
     As discussed above, each of the polarizing layer  66  and the polarizing and functional layer  72  includes a microstructure layer having a plurality of microstructures. The microstructures have various heights and/or widths to provide the polarization properties. In one embodiment, a global search algorithm is used to select the heights and/or widths of the microstructures to have a corralling property to convert or impose polarization of unpolarized light to have mostly or all P-polarization. For example,  FIG. 10  is a flow diagram illustrating a process  123  for designing a polarizing layer, such as the polarizing layer  66  and the polarizing and functional layer  72 , for the transmission optical structure  18  according to an embodiment disclosed herein. 
     In block  124 , an initial design of the transmission optical structure  18  is created. This includes selecting initial dimensions for the various layers in the transmission optical structure  18 . For instance, the thickness of each of the layers (e.g., the substrate  58 , the functional layer  60 , the protective layer  62 , the substrate  64 , the polarizing layer  66 , and the protective layer  68  of the embodiment shown in  FIG. 3 ), and the heights and/or widths of the microstructures of the polarizing and functional layers (e.g., the functional layer  60  and the polarizing layer  66  of the embodiment shown in  FIG. 3 ) may be selected. 
     In block  126 , the initial design of the transmission optical structure  18  is simulated. The initial design of the transmission optical structure  18  may be simulated using various simulation techniques, such as computer, mathematical, or visual simulation techniques. 
     In block  128 , the initial design of the transmission optical structure  18  is evaluated based on the simulation performed in the block  126 . For example, the performance of the polarizing layer (e.g., the polarizing layer  66  of the embodiment shown in  FIG. 3 ) may be evaluated based on the simulation to determine whether the various heights and/or widths of the microstructures provide mostly or all P-polarization. As another example, the performance of the functional layer (e.g., the functional layer  60  of the embodiment shown in  FIG. 3 ) may be evaluated based on the simulation to determine whether the various heights and/or widths of the microstructures provide the proper optical function (e.g., a beam shaping function, an imaging function, a collimating function, a diffusing function, a polarizing function, a beam splitting function, a wavefront coding function, or a combination thereof). 
     If the initial design is acceptable, the process  123  proceeds to block  130 . If the initial design is unacceptable, the process  123  proceeds to block  132 . 
     In block  130 , the initial design of the transmission optical structure  18  is finalized. Once finalized, the transmission optical structure  18  may then be fabricated using, for example, the process described with respect to  FIGS. 9A, 9B, 9C, and 9D . 
     In block  132 , the initial design of the transmission optical structure  18  is modified. For example, the initial dimensions for the various layers in the transmission optical structure  18  may be modified. For instance, the thickness of each of the layers (e.g., the substrate  58 , the functional layer  60 , the protective layer  62 , the substrate  64 , the polarizing layer  66 , and the protective layer  68  of the embodiment shown in  FIG. 3 ), and the heights and/or widths of the microstructures of the polarizing and functional layers (e.g., the functional layer  60  and the polarizing layer  66  of the embodiment shown in  FIG. 3 ) may be modified. Subsequently, the process  123  returns to block  126 , where the modified design of the transmission optical structure  18  is simulated. 
     In addition to the transmission optical structure  18 , the light source  16  is also configured to minimize S-polarized light (e.g., the S-polarized light  50 ) and maximize P-polarized light (e.g., the P-polarized light  52 ) within the sensor  10 . Namely, the light source  16  emits light (e.g., the light signal  30 ) that has mostly or all P-polarization. 
     As discussed above, the light source  16  is positioned on the substrate  12 , and directly underlies the transmission optical structure  18  and the output aperture  26 . The light source  16  emits the light signal  30  through the transmission optical structure  18  and the output aperture  26 . In one embodiment, the light source  16  is an infrared or near infrared light source, such as a vertical-cavity surface-emitting laser (VCSEL). 
       FIG. 11  is a side view of the light source  16  according to an embodiment disclosed herein.  FIG. 12  is a top view of the light source  16  according to an embodiment disclosed herein. It is beneficial to review  FIGS. 11 and 12  together. The light source  16  includes a substrate  134  on the substrate  12 , a first mirror  136  on the substrate  134 , an active layer  138  on the first mirror  136 , a second mirror  140  on the active layer  138 , a conductive contact  142  on the second mirror  140 , and emitters  144  on or in the second mirror  140 . 
     The substrate  134  of the light source  16  is positioned on the substrate  12  of the sensor  10 . In one embodiment, the substrate  134  is a semiconductor substrate. 
     The first mirror  136  and the second mirror  140  are highly reflective mirrors. In one embodiment, each of the first mirror  136  and the second mirror  140  has reflectivity between 99 and 99.9%. In one embodiment, the first mirror  136  has a higher reflectivity than the second mirror  140 . In one embodiment, the first mirror  136  and the second mirror  140  are distributed Bragg reflectors. 
     The active layer  138  is positioned between the first mirror  136  and the second mirror  140 . The active layer  138  includes one or more laser cavities. In one embodiment, the active layer  138  includes one or more quantum wells. The active layer  138  generates light when an electrical signal is applied to the active layer  138 . 
     In one embodiment, the first mirror  136  and the second mirror  140  are oppositely doped from each other such that the first mirror  136 , the active layer  138 , and the second mirror  140  forms a p-i-n junction. For example, in one embodiment, the first mirror  136  has an n-type conductivity type and the second mirror  140  has a p-type conductivity type. Conversely, in another embodiment, the first mirror  136  has a p-type conductivity type and the second mirror  140  has an n-type conductivity type. In one embodiment, the substrate  134  has the same conductivity type as the first mirror  136 . 
     The conductive contact  142  is formed on an upper surface  146  of the second mirror  140 . The conductive contact  142  is made of a conductive material, such as gold. The conductive contact  142  receives an electrical signal (e.g., voltage or current signal) from a driver circuit positioned on, for example, the substrate  12 . Although not shown in  FIG. 11 , the light source  16  may include another conductive contact to receive an electrical signal. For example, in one embodiment, the light source  16  includes a conductive contact formed between the substrate  12  and the substrate  134 . As will be discussed in further detail below, the conductive contact  142  surrounds one side of the emitters  144 . 
     The emitters  144  are formed on or in the second mirror  140 . The emitters  144  provide windows for light generated by the active layer  138  to be emitted from. In one embodiment, the shape of the emitters  144  are formed by one or more blocking layers formed within the light source  16 . For example, as shown in  FIG. 12 , the emitters  144  may be windows (i.e., through holes) formed in an oxide layer  148 . The oxide layer  148  may be positioned between the active layer  138  and the second mirror  140 , between the active layer  138  and the first mirror  136 , between the substrate  134  and the first mirror  136 , and/or on the upper surface  146  of the second mirror  140 . Although six emitters are shown in  FIG. 12 , the light source  16  may include any number of emitters. As will be discussed in further detail below, the emitters  144  are asymmetric. 
     In operation, the conductive contact  142  receives an electrical signal (e.g., voltage or current signal) from a driver circuit positioned on, for example, the substrate  12 . In response, photons are generated by the quantum well of the active layer  138 . As the first mirror  136  and the second mirror  140  are highly reflective, the photons bounce between the first mirror  136  and the second mirror  140 , and are emitted from the emitters  144  and out of the upper surface  146  of the second mirror  140  as a concentrated light signal. 
     The light source  16  is configured to minimize S-polarized light (e.g., the S-polarized light  50 ) and maximize P-polarized light (e.g., the P-polarized light  52 ) of the light signal emitted from the light source  16 . Stated differently, the light signal emitted from the light source  16  has mostly or all P-polarization. The polarization of the light emitted by the light source  16  is manipulated by controlling the direction of charge carrier motion in the lasing cavity (e.g., the active layer  138 ) of the light source  16 , and controlling the spatial modes available for lasing. 
     The direction of charge carrier motion in the lasing cavity of the light source  16  is controlled by the shape of the conductive contact  142 . Namely, the conductive contact  142  is shaped such that charge injection is performed from a single side of the emitters  144 . For example, as shown in  FIG. 12 , the conductive contact  142  includes a contact portion  150  and an emitter portion  152 . The contact portion  150  is positioned laterally to the emitters  144  and receives the electrical signal from the driver circuit. The emitter portion  152  extends from the contract portion  150  and is positioned on a single side (sides  154 ) of the emitters  144 . The emitter portion  152  is not positioned on the opposite side (sides  156 ) of the emitters  144 . Stated differently, the contact portion  150  partially surrounds and is immediately adjacent to the emitters  144 . In one embodiment, the contact portion  150  surrounds less than  50  percent of the outer edge or border of each of the emitters  144 . In one embodiment, as shown in  FIG. 12 , the emitter portion  152  extends between two columns of emitters  144 . In one embodiment, the emitter portion  152  has a smaller surface area than the contact portion  150 . The configuration of the conductive contact  142  allows charge injection from one side of the emitters  144 , and polarizes the light signal emitted from the light source  16  to have mostly or all P-polarization. 
     The spatial modes available for lasing are controlled by the shape of the emitters  144 . Namely, the emitters  144  are shaped to be asymmetrical about at least one axis. For example, as shown in  FIG. 12 , the emitters  144  are oval shaped and are asymmetrical about at least one axis. In one embodiment, the emitters  144  do not have a circular or square shape. The asymmetric shape of the emitters  144  polarizes the light signal emitted from the light source  16  to have mostly or all P-polarization. Although the emitters  144  are oval shaped in  FIG. 12 , other asymmetrical shapes are possible. For example, the emitter  144  may have a triangular shape or a polygonal shape. 
     Other possible configurations for the conductive contact and the emitter are possible.  FIGS. 13 and 14  show other configurations in which the conductive contact is positioned on one side of the emitters, and the emitters have an asymmetrical shape. 
       FIG. 13  is a top view of the light source  16  according to an embodiment disclosed herein. Similar to the embodiment shown in  FIG. 12 , the conductive contact  142  is shaped such that charge injection is performed from a single side of the emitters  144 , and the emitters  144  are asymmetric about at least one axis. However, in contrast to the embodiment shown in  FIG. 12 , the contact portion  150  and the emitter portion  152  of the conductive contact  142  are positioned on a single side of the emitters  144 . In one embodiment, the emitter portion  152  has a smaller surface area than the contact portion  150 . In one embodiment, as shown in  FIG. 13 , the emitter portion  152  includes openings  158  positioned between each of the emitters  144 . 
       FIG. 14  is a top view of the light source  16  according to an embodiment disclosed herein. Similar to the embodiment shown in  FIG. 12 , the conductive contact  142  is shaped such that charge injection is performed from a single side of the emitter  144 , and the emitter  144  is asymmetric about at least one axis. However, in contrast to the embodiment shown in  FIG. 12 , the contact portion  150  of the conductive contact  142  is L-shaped. Stated differently, the contact portion  150  extends in a first direction and a second direction transverse to the first direction. Further, the light source  16  includes a single emitter. In one embodiment, the emitter portion  152  has a smaller surface area than the contact portion  150 . 
     In one embodiment, the conductive contact  142  is shaped such that charge injection is performed from two sides of the emitters  144  that are positioned along the same axis. This configuration of the conductive contact  142  allows charge injection of the emitters  144  along a single axis, and polarizes the light signal emitted from the light source  16  to have mostly or all P-polarization.  FIGS. 15 and 16  show configurations in which the conductive contact is positioned on two sides of the emitters that are positioned along the same axis. 
       FIG. 15  is a top view of the light source  16  according to an embodiment disclosed herein. Similar to the embodiment shown in  FIG. 12 , the emitter  144  is asymmetric about at least one axis. However, in contrast to the embodiment shown in  FIG. 12 , the conductive contact  142  is shaped such that charge injection is performed from two opposite sides of the emitter  144  that are aligned with each other. Stated differently, the conductive contact  142  includes two emitter portions  152  that surround a first side  153  of the emitter  144  and a second side  155 , opposite to the first side  153 , of the emitter  144 . The remaining portions of the emitter  144  are not surrounded and do not contact the two emitter portions  152 . This configuration of the conductive contact  142  allows charge injection of the emitter  144  along a single axis, and polarizes the light signal emitted from the light source  16  to have mostly or all P-polarization. 
       FIG. 16  is a top view of the light source  16  according to an embodiment disclosed herein. Similar to the embodiment shown in  FIG. 15 , the emitter  144  is asymmetric about at least one axis, and the conductive contact  142  is shaped such that charge injection is performed from two opposite sides  153 ,  155  of the emitter  144 . However, in contrast to the embodiment shown in  FIG. 15 , the remaining portions of the emitter  144  are surrounded by the conductive contract  142 . Namely, the conductive contact  12  includes a portion  163  and a portion  165  that surround the lower and upper sides of the emitter  144 , respectively. The portion  163  has a width  159 , and the portion  165  has a width  157 . The widths  157 ,  159  are smaller than a width  161  of the emitter portions  152 . This configuration of the conductive contact  142  allows charge injection of the emitter  144  along a single axis, and polarizes the light signal emitted from the light source  16  to have mostly or all P-polarization. 
     As described above, the transmission optical structure  18  and the light source  16  are configured to minimize S-polarized light (e.g., the S-polarized light  50 ) and maximize P-polarized light (e.g., the P-polarized light  52 ) within the sensor  10 . As a result, the light signal  38 , the light signal  40 , and the light signal  42  is minimized or non-existent in the sensor  10 . In another embodiment, either the transmission optical structure  18  or the light source  16  is configured to minimize S-polarized light and maximize P-polarized light within the sensor  10 . For example, if the transmission optical structure  18  is configured to polarize light and the light source  16  is not configured to polarize light, the light source  16  may emit unpolarized light. As another example, if the transmission optical structure  18  is not configured to polarize light and the light source  16  is configured to polarize light, the transmission optical structure  18  may not include a polarizing layer. 
     The various embodiment disclosed herein provide a sensor that determines a distance between the sensor and a target object external to the sensor. The sensor includes a transmission optical structure and/or a light source that are configured to minimize S-polarized light and maximize P-polarized light within the sensor. As a result, cross talk within the sensor is reduced or removed, and detection results of the sensor are improved. 
     The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.