PATENT DOCUMENT

Publication Number: US-11243686-B2
Application Number: US-202016993120-A
Country: US
Kind Code: B2

Title: Self-mixing interference based sensors for characterizing user input

Abstract:
An earbud includes a housing, a speaker mounted within the housing, a processor mounted within the housing, a user input surface on the housing, and a set of self-mixing interferometry (SMI) sensors mounted within the housing. The set of SMI sensors includes a first SMI sensor configured to emit a first beam of light, and a second SMI sensor configured to emit a second beam of light. The second beam of light passes through the user input surface about an axis that is non-perpendicular to the user input surface. The processor is configured to adjust a parameter of the speaker at least partly in response to a first SMI output of the first SMI sensor and a second SMI output of the second SMI sensor.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a housing having a touch input surface; 
 a first laser light source positioned within the housing and having a first resonant cavity configured to emit a first beam of light, receive a redirection of the first beam of light, and self-mix the first beam of light and the redirection of the first beam of light; 
 a second laser light source positioned within the housing and having a second resonant cavity configured to emit a second beam of light, receive a redirection of the second beam of light, and self-mix the second beam of light and the redirection of the second beam of light; 
 a set of sensors configured to detect a respective property associated with each of a first self-mixed light of the first laser light source and a second self-mixed light of the second laser light source; and 
 a processor configured to detect, at least partly in response to the detected respective properties associated with each of the first self-mixed light and the second self-mixed light, a gesture of a user made on the touch input surface, wherein:
 the housing defines an earbud; 
 a first axis of the first beam of light intersects the touch input surface at a first angle; and 
 a second axis of the second beam of light intersects the touch input surface at a second angle different from the first angle. 
 
 
     
     
       2. The electronic device of  claim 1 , further comprising a speaker is mounted within the housing. 
     
     
       3. The electronic device of  claim 1 , wherein the gesture of the user comprises a swipe gesture. 
     
     
       4. The electronic device of  claim 1 , wherein the processor is configured to:
 detect, at least partly in response to a first detected property associated with the first self-mixed light, a deflection of the touch input surface perpendicular to the touch input surface; and 
 detect, at least partly in response to a second detected property associated with the second self-mixed light, a movement of the user along the touch input surface. 
 
     
     
       5. The electronic device of  claim 4 , wherein the processor is configured to:
 detect the movement of the user along the touch input surface at least partly in response to first detecting the deflection of the touch input surface. 
 
     
     
       6. The electronic device of  claim 1 , wherein:
 the first angle is a perpendicular angle; and 
 the second angle is a non-perpendicular angle. 
 
     
     
       7. The electronic device of  claim 1 , further comprising:
 at least one lens positioned in a path of the second beam of light; wherein, 
 the lens bends the second axis of the second beam of light before the second beam of light intersects the touch input surface at the second angle. 
 
     
     
       8. The electronic device of  claim 7 , wherein the at least one lens tilts the second axis of the second beam of light toward the first axis of the first beam of light. 
     
     
       9. The electronic device of  claim 7 , wherein the at least one lens tilts the second axis of the second beam of light away from the first axis of the first beam of light. 
     
     
       10. The electronic device of  claim 1 , wherein the second laser light source is tilted with respect to the first laser light source. 
     
     
       11. The electronic device of  claim 1 , wherein the detected respective properties associated with each of the first self-mixed light of the first laser light source and the second self-mixed light of the second laser light source comprise at least one of: a junction voltage, a bias current, a power supply voltage, or a power output of a respective laser light source of the first laser light source or the second laser light source. 
     
     
       12. The electronic device of  claim 1 , wherein:
 the first laser light source is integrated with a respective first sensor in the set of sensors; and 
 the second laser light source is integrated with a respective second sensor in the set of sensors. 
 
     
     
       13. The electronic device of  claim 1 , further comprising:
 a reflective material disposed to move in relation to deflection of the touch input surface and positioned in a path of the first beam of light, but not in a second path of the second beam of light. 
 
     
     
       14. The electronic device of  claim 1 , wherein the touch input surface is optically transmissive to at least the second beam of light. 
     
     
       15. The electronic device of  claim 1 , wherein the touch input surface is optically transmissive to the first beam of light and the second beam of light. 
     
     
       16. The electronic device of  claim 1 , wherein the second beam of light has a different wavelength than the first beam of light. 
     
     
       17. An earbud, comprising:
 a housing; 
 a speaker mounted within the housing; 
 a processor mounted within the housing; 
 a user input surface on the housing; and 
 a set of self-mixing interferometry (SMI) sensors including a first SMI sensor configured to emit a first beam of light and a second SMI sensor configured to emit a second beam of light; wherein:
 the second beam of light passes through the user input surface about an axis that is non-perpendicular to the user input surface; and 
 the processor is configured to adjust a parameter of the speaker at least partly in response to a first SMI output of the first SMI sensor and a second SMI output of the second SMI sensor. 
 
 
     
     
       18. The earbud of  claim 17 , wherein the parameter of the speaker comprises a volume of the speaker. 
     
     
       19. The earbud of  claim 17 , wherein the processor is configured to gate use of the second SMI output at least partly in response to a state of the first SMI output. 
     
     
       20. The earbud of  claim 17 , wherein the processor is configured to:
 compare the first SMI output to a deflection threshold; 
 determine at least one parameter of the second SMI output after the first SMI output satisfies the deflection threshold; and 
 adjust a volume of the speaker in response to the at least one parameter of the second SMI output. 
 
     
     
       21. The earbud of  claim 17 , further comprising:
 a reflector disposed to move in relation to deflection of the user input surface; wherein,
 at least a portion of the first beam of light reflects off of the reflector.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 16/383,036, filed on Apr. 12, 2019, which is a nonprovisional of and claims the benefit under 37 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/657,576, filed on Apr. 13, 2018, and U.S. Provisional Patent Application No. 62/702,264, filed on Jul. 23, 2018, the contents of which are incorporated by reference as if fully disclosed herein. 
    
    
     FIELD 
     The present disclosure generally relates to sensing or characterizing user input provided on an electronic device by a user of the electronic device (e.g., gestures made by a finger or stylus on a cover glass positioned over a display of the electronic device, or by a finger on an exterior of a housing). 
     BACKGROUND 
     Electronic devices are commonplace in today&#39;s society. Examples of electronic devices include mobile devices, such as cell phones, tablet or laptop computers, watches, earbuds, and so on, and non-mobile devices, such as electronic kiosks, automated teller machines, desktop computers, and so on. Such electronic devices may include buttons, switches, touch input surfaces, or other components through which a user may provide inputs or commands to the electronic device. 
     Touch screens and other user input surfaces can provide a means to receive user input into an electronic device. In some cases, a user input surface (also referred to as a “touch input surface”) may overlay a display of an electronic device (e.g., a user input surface may overlay a display of virtual buttons or icons, hyperlinks, text, images, and the like). A user may interact with such a display by touching or pressing the user input surface using one or more fingers (or a stylus). The electronic device may detect the touch or press using various types of sensors, such as touch sensors or force sensors. A sensor may detect touch or force using various technologies, and in some cases may employ capacitive sensing, resistive sensing, ultrasonic sensing, or optical sensing. 
     Sensors that employ optical sensing may detect the deflection of a user input surface caused by a user&#39;s press, or may detect a percentage of emitted light reflected by a user&#39;s finger or stylus. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     Disclosed herein are devices, systems, and methods that use lasers to detect user input on a touch screen or other user input surface of an electronic device. Disclosed arrangements of lasers can be used to detect lateral or up and down motion of a user&#39;s finger or stylus on a user input surface. In some embodiments the lasers may include vertical-cavity surface-emitting lasers (VCSELs), edge-emitting lasers, vertical external cavity surface-emitting lasers (VECSELs), or quantum-dot lasers (QDLs). In some embodiments, deflection of a user input surface may be detected and characterized by analyzing an interference signal produced when coherent light generated and emitted by a laser reflects from the user input surface, is received back into the laser, and is coherently mixed with the light generated within the laser cavity. As used herein, “light” will refer not just to visible light frequencies, but will include other frequencies of electromagnetic radiation, such as infrared, ultraviolet, or other frequency ranges. “Laser light” will refer to electromagnetic radiation emitted from an amplified resonant cavity. 
     More specifically, described herein is an electronic device having a user input surface and a set of lasers (e.g., VCSELs). The VCSELs may emit respective beams of coherent light toward the user input surface, or toward another surface or even a photodetector, as explained in the embodiments below. The surface or object toward which the laser&#39;s coherent light is directed will hereinafter be referred to generally as the “target.” Each VCSEL&#39;s beam of coherent light can include a first amount of coherent light generated by the VCSEL and a second amount of coherent light reflected from the user input surface or target into the VCSEL and mixed with the first amount of coherent light inside the laser cavity. A first beam of coherent light emitted by a first VCSEL may intersect the user input surface at a right angle. A second beam of coherent light emitted by a second VCSEL may intersect the user input surface at a first acute angle in a first plane. A third beam of coherent light emitted by a third VCSEL may intersect the user input surface at a second acute angle in a second plane that differs from the first plane. The electronic device also has a set of sensors configured to measure interferometric parameters associated with the beams of coherent light. The measured interferometric parameters can be used to characterize a movement of a user input on the user input surface and a deflection of the user input surface. 
     In related embodiments, the second and third VCSELs may be associated with respective lenses—or another beam shaping surface element with reflective, refractive, or diffractive properties—configured to direct the respective beams of coherent light to intersect the user input surface at the respective acute angle. The interferometric parameters can include a junction voltage of a VCSEL, a change in power of the VCSEL, a variation in the supply voltage for the VCSEL, bias current of a VCSEL, or another interferometric parameter. 
     In related embodiments, the electronic device can include a photodetector corresponding to a VCSEL that is configured to detect reflections of the VCSEL&#39;s beam. Interferometric parameters can be detected from an output of the photodetector, such as a current output or a voltage output. The photodetector may be positioned beneath the VCSEL, i.e., on the side of the VCSEL opposite the surface from which the beam is emitted. In a second configuration, the photodetector is integrated into the VCSEL. In a third alternative, the photodetector can be placed adjacent the VCSEL. Other configurations are discussed in relation to  FIGS. 2A-F . 
     In a first category of embodiments, signals of the interferometric parameters can be analyzed using a spectrum-based analysis, from which a speed and direction of the movement can be inferred. In some embodiments the speed can be calculated from the fundamental harmonic frequency found by the spectrum analysis, and the direction of the movement can be calculated from a phase change in the second harmonic frequency found by the spectrum analysis. Such embodiments are discussed in relation to  FIGS. 7A-B . 
     In a second category of embodiments, signals of the interferometric parameters can be analyzed using a time domain based analysis, from which a speed and direction of the movement may also be inferred. A moving target may create a distorted sinusoidal behavior of an interferometric parameter, whose time domain signal may be measured using, e.g., threshold detectors. Measured properties of the time domain signal may include duty cycle, interference fringes, and times between leading and falling edges of the threshold detectors having inputs of the time domain signal. Such embodiments are discussed in relation to  FIGS. 8A-C . 
     The present disclosure also describes an electronic device having a touch input surface; first, second, and third lasers within the electronic device, which lasers are configured to emit respective coherent light toward the touch input surface; and a set of sensors configured to detect a respective property of each of the first, second, and third emitted coherent light. The second and third lasers may be configured non-collinearly with respect to the first laser. The first detected property of the first coherent light may be used to detect a user-caused deflection of the touch input surface, the deflection being perpendicular to the touch input surface. The second detected property of the second coherent light may be used at least in part to detect a lateral movement or motion of the user-caused deflection of the touch input surface, in a first direction, and a third detected property of the third coherent light emitted may be used at least in part to detect a lateral movement of the user-caused deflection of the touch input surface in a second direction, with the second direction being different from the first direction. 
     In related embodiments, a detected property of any of the coherent light can be an interferometric parameter or property, such as a junction voltage, bias current of a VCSEL, a power supply voltage, or a power output of the respective laser. In embodiments that make use of a photodetector, the interferometric parameter may be an output current, voltage, or power of the photodetector. 
     The electronic device may also include, internally, one or more photodetectors, each photodetector being associated to a respective laser. One or more of the lasers may be a VCSEL. One or more of the coherent lights may be reflected and undergo self-mixing interference within the VCSEL. For electronic devices using more than one laser and/or photodetector pair, the lasers may use time-multiplexing of coherent light emission in order to reduce crosstalk. 
     The lateral motions and the deflection of the touch input surface may be determined using a spectrum analysis of at least one of the detected properties, a time domain analysis of the detected properties, or both. 
     The present disclosure also describes a method of detecting a user input on a touch input surface of an electronic device. The method includes emitting first, second, and third coherent light beams from respective first, second, and third VCSELs that are internal to the electronic device. The method includes applying a sinusoidal modulation to a bias current of at least one of the first, second, and third VCSELs, at a modulation frequency, and measuring a signal of an interferometric parameter associated with the at least one of the first, second, or third VCSELs. The method may also include: determining a first value by demodulating the signal of the interferometric parameter at the modulation frequency; determining a second value by demodulating the signal of the interferometric parameter at twice the modulation frequency; and determining a displacement of the touch input surface using the first value and the second value. 
     In another set of embodiments, an electronic device is described. The electronic device may include a housing having a touch input surface, first and second laser light sources, a set of sensors, and a processor. The first laser light source may be positioned within the housing and have a first resonant cavity configured to emit a first beam of light, receive a redirection of the first beam of light, and self-mix the first beam of light and the redirection of the first beam of light. The second laser light source may be positioned within the housing and have a second resonant cavity configured to emit a second beam of light, receive a redirection of the second beam of light, and self-mix the second beam of light and the redirection of the second beam of light. The set of sensors may be configured to detect a respective property associated with each of a first self-mixed light of the first laser light source and a second self-mixed light of the second laser light source. The processor may be configured to detect, at least partly in response to the detected respective properties associated with each of the first self-mixed light and the second self-mixed light, a gesture of a user made on the touch input surface. A first axis of the first beam of light may intersect the touch input surface at a first angle, and a second axis of the second beam of light may intersect the touch input surface at a second angle different from the first angle. 
     In another set of embodiments, an earbud is described. The earbud may include a housing, a speaker mounted within the housing, a processor mounted within the housing, and a user input surface on the housing. The earbud may also include a set of self-mixing interferometry (SMI) sensors including a first SMI sensor configured to emit a first beam of coherent light and a second SMI sensor configured to emit a second beam of coherent light. The second beam of coherent light may pass through the user input surface about an axis that is non-perpendicular to the user input surface. The processor may be configured to adjust a parameter of the speaker at least partly in response to a first SMI output of the first SMI sensor and a second SMI output of the second SMI sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIGS. 1A-1C  illustrate example electronic devices that may include at least one of the embodiments. 
         FIG. 2A  illustrates a cross section of a transmissive touch input surface of an electronic device. 
         FIG. 2B  illustrates a cross section of an electronic device with a reflective touch input surface capable of deflection. 
         FIG. 2C  illustrates a cross section of a mixed mode touch input surface capable of deflection. 
         FIG. 2D  illustrates a cross section of an electronic device having a rigid input surface atop compressible supports, and a laser system and a photodetector for detecting inputs, according to an embodiment. 
         FIG. 2E  illustrates a cross section of an electronic device with a laser system and a photodetector for detecting inputs on a touch input surface, according to an embodiment. 
         FIG. 2F  illustrates a cross section of an electronic device with a laser system and a photodetector for detecting inputs on a touch input surface, according to another embodiment. 
         FIG. 3A  illustrates part of a laser system that may use a VCSEL for detecting user input on a touch input surface, according to an embodiment. 
         FIG. 3B  illustrates a graph of an example photodetector signal due to a singular displacement of a touch input surface. 
         FIG. 3C  illustrates a graph of an example photodetector signal due to a periodic displacement of a touch input surface. 
         FIG. 4A  illustrates a side view of a VCSEL, according to an embodiment. 
         FIG. 4B  illustrates self-mixing interference in a VCSEL. 
         FIG. 4C  shows a graph relating change in power in coherent light emitted by a VCSEL with length of a feedback cavity. 
         FIG. 4D  shows a graph relating change in power in coherent light emitted by a VCSEL with length of a feedback cavity, in the case that the target is moving. 
         FIG. 5A  illustrates a side view of a configuration of part of a laser system for detecting user input, according to an embodiment. 
         FIG. 5B  illustrates a side view of a configuration of part of a laser system for detecting user input, according to an embodiment. 
         FIG. 5C  illustrates a side view of a configuration of part of a laser system for detecting user input, according to an embodiment. 
         FIG. 5D  illustrates a side view of a configuration of part of a laser system for detecting user input, according to an embodiment. 
         FIG. 6A  illustrates a plan view of lasers in a laser system for detecting user input, according to an embodiment. 
         FIG. 6B  shows a perspective view of lasers in a laser system for detecting user input, according to an embodiment. 
         FIG. 6C  shows time correlated graphs of time-multiplexed signals to lasers, according to an embodiment. 
         FIG. 7A  illustrates self-mixing or interferometric feedback in a VCSEL that emits coherent light toward, and receives reflected coherent light from, a target that is moving. 
         FIG. 7B  shows graphs from spectrum analyses of interferometric parameters of a VCSEL that are measured for moving targets. 
         FIG. 7C  shows time correlated graphs of a laser current, laser wavelength, and a signal of an interferometric parameter that can be used as part of a spectrum analysis. 
         FIG. 7D  is a flow chart of a spectrum analysis method for determining speed and direction of a moving target. 
         FIG. 7E  is a block diagram of a system that implements a spectrum analysis method for determining speed and direction of a moving target. 
         FIG. 8A  shows an example of a circuit that can be used with a time domain determination of a speed and direction of a target. 
         FIG. 8B  shows time correlated graphs for a time domain determination of speed and direction of a moving target. 
         FIG. 8C  shows time correlated graphs of a target velocity and a sampled output of the circuit of  FIG. 8A . 
         FIGS. 9A and 9B  show time correlated graphs for time domain determination of displacement of a target. 
         FIG. 10  shows an example circuit for the time determination of displacement of the target of  FIG. 9 . 
         FIGS. 11A-E  show example cross sections of lenses that can be used with lasers in a system for detecting user input. 
         FIGS. 12A-12D  show various embodiments of an SMI module that can be used to detect click/tap/force-based gestures and/or swipe/scroll gestures on a user input surface of an earbud or other audio device, such as the earbud shown in  FIG. 1C . 
         FIG. 13  shows an example block diagram of components of an electronic device that includes a system for detecting user input. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The embodiments described herein are directed to electronic devices having user input surfaces (e.g., touch input surfaces) that a user may touch or press to interact with the electronic device. Examples of electronic devices with such surfaces include mobile devices such as smartphones, tablet computers, and earbuds, and non-mobile devices such as ATMs and electronic kiosks. Touch input surfaces may in some cases cover displays by which electronic devices present information such as text, icons, or virtual buttons to a user. A user can input commands to such electronic devices by pressing the touch input surface at a location of an icon or other graphical element. The touch or press can be a continuous “drag” input (e.g., a swipe or scroll gesture) in which, for example, a finger of the user maintains a pressure on the touch input surface and moves a lateral distance across the touch input surface. A better user experience for such an electronic device may be obtained when the electronic device is better able to distinguish user input from sources that could cause a false detection of user input. 
     The embodiments described herein include devices, components, and methods of using lasers to detect a user&#39;s touch or press on a touch screen, display screen, touch input surface, or other user input surface. Terms such as touch input surface, touch screen, and user input surface are used equivalently herein to refer to a surface of an electronic device through which a user of the electronic device can interact with the electronic device by applying a touch or press. 
     A particular type of laser that is used in various embodiments is a VCSEL. Many conventional lasers, such as edge-emitting laser diodes, are often fabricated so that the lasing cavity is directed horizontally with respect to the fabrication wafer, making it difficult to test the lasers before dicing and mounting. With VCSELs, the lasing cavity is directed vertically with respect to the fabrication wafer, allowing for on-wafer testing. Further, an advantage to VCSELs for the embodiments described herein is that they can be easily mounted on, for example, a substrate so that the emitted laser light is directed toward a target or user input surface. Reflections of the emitted light can be received back into the lasing cavity to create a phenomenon of self-mixing interference. Some conventional lasers or edge-emitting laser diodes may also be able to receive laser light back into their laser cavity and undergo self-mixing. While this description will for the most part describe the embodiments in terms of laser systems that use VCSELs, the embodiments described herein may also be implemented using edge-emitting laser diodes or other types of lasers capable of undergoing self-mixing interference of generated and received coherent light. 
     Self-mixing interference alters the emitted coherent light beam in at least two ways. First, the wavelength of the emitted coherent light with self-mixing interference is shifted from the wavelength that would be emitted by the VCSEL without the self-mixing interference. Second, the optical power of the emitted coherent light with self-mixing interference can also be changed. 
     Self-mixing interference can alter performance properties or parameters of a VCSEL or its emitted coherent light in ways that can be detected. Such parameters include (but are not limited to) changes in a junction voltage, a bias current, a supply voltage, or a power output. These alterable performance properties or parameters are referred to herein as interferometric parameters associated with the coherent light of the VCSEL. Further, self-mixing interference is dependent on the distance between the target and the lasing cavity, such that the distance may be correlated to the interferometric parameters and/or changes in the interferometric parameters. For purposes of this description, a light source (e.g., a laser light source) that undergoes self-mixing of light within its lasing cavity (or resonant cavity), in combination with a sensor for detecting a parameter of the self-mixing, is sometimes referred to herein as an SMI sensor or SMI module. 
     To detect a press on a user input surface, the user input surface, in one set of embodiments, is able to deflect in response to the press. A laser within an electronic device may be configured to emit a coherent light beam toward the user input surface such that the coherent light beam intersects an interior side of the user input surface. The laser may receive an altered reflected light that, in turn, alters the self-mixing interference. The deflection thus can result in a detectable change in an interferometric parameter, which can then be interpreted by the electronic device (e.g., as a user input, or as a particular type of user input, such as a particular gesture). In another set of embodiments, the user input surface is rigid, but supported on structures that are able to deflect, so that a distance between the VCSEL and the user input surface changes, altering the self-mixing interference. In yet another set of embodiments, the user input surface is transparent, at least partially, so that a user&#39;s finger or stylus impressed on or near the user input surface alters the self-mixing interference. Examples of these sets of embodiments will be explained in relation to  FIGS. 2A-F  below. 
     The electronic device may also include one or more photodetectors (or equivalently “photoreceptor” or “photosensor”), in addition to the lasers, for detection of the user applied pressure on the user input surface. In some embodiments, a photodetector may be placed adjacent to a corresponding laser on a substrate. In still other embodiments, the photodetector may be placed between the substrate and the laser, placed in line with the laser, or integrated with the laser. 
     In some embodiments, further properties of the user-caused deflection may be detectable based on changes in the interferometric parameters. In some embodiments, the motion properties, such as direction and/or speed of the deflection, can be detected. Considering the deflecting surface as a target moving toward or away from the laser emitting the coherent light, the target&#39;s movement can produce a Doppler shift in the wavelength of the reflected light. This shift also affects the self-mixing interference, leading to detectable changes in the interferometric parameters or properties associated with the laser and/or its emitted light. As the target moves toward the laser, the power (or other measurable parameter) undergoes an oscillation. The oscillation can have the form of a sinusoid or a distorted sinusoid, as explained below. For example, in the case of a weakly reflecting target, a change in power is often related to the change in distance from the target by ΔP∝ cos(4πL/λ), where L is the distance target from the laser, and λ is the wavelength of the laser light. For a strongly reflecting target, the power function is a distorted sinusoid, and higher harmonics are present. The higher harmonics can be analyzed to provide information about the position and movement of the target. As a moving deflection may cause L to vary on the scale of μ-meters, and λ is on the scale of 100&#39;s of nanometers, the sinusoid goes through a large number of periods. By sampling the interferometric parameter and performing a spectrum analysis (e.g., using a Fast Fourier Transform (FFT)), the fundamental frequency and its higher harmonics can be obtained. The speed of movement of the target can be obtained from the fundamental frequency. The direction of the movement can be obtained from a phase shift that occurs at the second harmonic. 
     Additionally and/or alternatively, a time domain analysis of the interferometric parameter&#39;s signal may be performed. A circuit containing a pair of comparators may receive the signal. The rising side of the signal&#39;s oscillations can initially exceed a first threshold (causing the first comparator to trigger, or turn “on”) and subsequently exceed the second threshold, (causing the second comparator to turn “on”). During the falling side of the signal&#39;s oscillations, the second comparator turns “off,” followed by the first comparator turning “off.” A difference between the time interval between the turn on times, and the time interval between the two turn off times can be used to infer the motion and direction of the target. 
     The time domain analysis can also be used to detect an initiation of a user input. As the user input surface, or other form of the target, is initially displaced, the velocity of the target increases. The increase in velocity from zero can cause the interferometric parameter&#39;s signal to alternately exceed both comparator thresholds, then fall below both thresholds. Such a change over both thresholds from a quiescent state of the signal can indicate a start of a user input. This can trigger the electronic device to awake from an idle state. 
     Whether by a spectrum analysis or a time domain analysis, the ability to detect speed and direction can be used to detect a user&#39;s drag motion on the touch input surface. In some embodiments, three lasers may be arranged on a substrate in a non-collinear pattern. For example, the three lasers can be positioned to form a right angle between the line formed by a first laser and a second laser, and the line formed between the first laser and a third laser. In other embodiments, the angle between the two lines may be other than a right angle. The first (vertex) laser can be used to detect deflection of the press or touch into (i.e., normal to) the touch input surface, and the second and third lasers can be used to detect lateral movement of the deflection (i.e., a drag motion) across the touch input surface in separate directions. 
     The lasers may have lenses placed on or near the coherent light emitting apertures of the lasers. Such lenses can be used, for example, with at least the second and third lasers in the configuration just discussed. In embodiments in which the lasers are mounted on a substrate so that their emitted coherent light beams are directed perpendicular to the substrate, the lenses can bend the directions of the light beams. This can be used, in part, to determine a direction of movement of the drag motion on the touch input surface. 
     These and other embodiments are discussed below with reference to  FIGS. 1A-13 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1A  illustrates an example electronic device  100  that can incorporate or use components, systems, or methods for detecting user inputs on a touch input surface. The device shown in  FIG. 1A  may be a smartphone, such as an iPhone. Other examples of devices that can make use of the embodiments described herein include a computer mouse or touchpad, and a TV remote. Other examples are possible. The electronic device  100  may include a case  102  that contains internal electronics, such as a power source (e.g., a battery), a processor and associated memory, a radio transceiver, and other components. The electronic device may also have a display surface  104  for presenting information to a user. 
     The display surface  104  may be touch sensitive and function as a user input surface to receive input commands from a user. The user can input commands on the display surface  104  by applying local pressure such as by one or more fingers, a stylus, or other contact device. Associated with the display surface  104  can be a laser system, as explained below, for detecting user touches on the display surface. 
       FIG. 1B  shows a second example of an electronic device  110  that can incorporate or use components, systems, or methods for detecting user inputs on a user input surface. In this example the electronic device  110  may be an electronic watch. The electronic device  110  may include a housing  114  having a display surface  112 . The electronic device  110  can be worn by a user with the wrist band  120  (only partially shown). The electronic device  110  can include one or more buttons  118  and/or a crown  116 . The housing  114  may include the internal electronics of the electronic device  110 , such as a power source (e.g., a battery), a processor and associated memory, a radio transceiver, and other components. 
     The display surface  112  of the electronic device  110  may present information such as text, icons, and the like to a user. The display surface  112  may be touch sensitive and function as a touch input surface for receiving inputs from the user. The display surface  112  may include a cover glass over internal components and systems. The cover glass may be transparent. In some embodiments, the cover glass may deflect upon a press by the user, such as by a finger or a stylus. The applied press may be detected by force sensors. The deflection caused by the applied press may also or alternatively be detected using a laser system, as in the embodiments described herein. 
       FIG. 1C  shows a third example of an electronic device  130  that can incorporate or use components, systems, or methods for detecting user inputs on a user input surface. In this example the electronic device  130  may be an earbud. The electronic device  130  may include a housing  134  having a user input surface  132  (e.g., a touch input surface). The electronic device  130  can be worn by a user by fitting a first portion  136  of the housing  134 , containing a speaker  138  (i.e., a speaker  138  mounted within the housing  134 ), into the user&#39;s ear. A second portion  140  of the housing  134  may take the form of an elongate member (or tube) extending from the first portion  136  of the housing  134 . The user input surface  132  may be provided as part or all of the elongate member of the second portion  140  of the housing  134 . In alternative embodiments, the second portion  140  of the housing  134  may not be provided or take a different form. In some of these alternative embodiments, the user input surface  132  may be provided, for example, on the first portion  136  of the housing  134 , adjacent or opposite the speaker  138 . Alternatively, the user input surface  132  may be provided on other portions of the housing  134 . 
     The housing  134  may house the internal electronics of the electronic device  130 , such as a power source (e.g., a battery), a processor and associated memory, a radio transceiver, and other components. 
     In some embodiments, the user input surface  132  may deflect upon a touch or press by a user, such as by a finger. The applied press may be detected by a force sensor (e.g., a capacitive or resistive force sensor). The deflection caused by the applied press may also or alternatively be detected using a laser system, as in the embodiments described herein. Gestures, such as a swipe gesture, may also be detected using the laser system. 
     Although  FIGS. 1A-1C  show mobile electronic devices, the techniques and structures described below can be used with touch screens or touch input surfaces of non-mobile devices, such as display screens of ATMs, ticket dispensers, and so on. Described below with respect to  FIG. 13  are further components and systems that can be included in an electronic device that includes the embodiments described herein. 
       FIGS. 2A-C  show cross sections of various embodiments of touch input surfaces of electronic devices. For example, the cross sections may be along the cut line A-A of the electronic device shown in  FIG. 1A , or along the cut line B-B of the electronic device shown in  FIG. 1B , or along the cut line C-C of the electronic device shown in  FIG. 1C . These figures also show various respective configurations for lasers (e.g., VCSELs) that may be used within electronic devices to detect a user input on the touch input surface. 
       FIG. 2A  shows a first embodiment in which a laser  210 , supported on a substrate  211 , within an electronic device, is configured to detect a user input on or near a touch input surface  200   a . In this embodiment the touch input surface  200   a  is made from a light transmissive material, such as glass, that allows some or all incident light to pass through it. Coherent light (or just “light”) from laser  210  is directed perpendicularly toward the touch input surface  200   a  and passes through it. When a user&#39;s finger  202  or other input device approaches the touch input surface  200   a , a change may occur in the amount of light reflected back into the electronic device. The reflected light may be detected by internal receiving components, such as by one or more photodetectors. Additionally or alternatively, the reflected light may cause self-mixing interference within the laser  210  and so induce changes in interferometric parameters when the laser  210  is a VCSEL. The changes may be detectable by a photodetector associated with the VCSEL or by monitoring of electrical performance properties of the VCSEL (such as supply power, bias current, or junction voltage). The changes may be interpreted by a processing unit or combinations of processing components as a user input or type of user input. Some embodiments may also be able to detect an approach or proximity of the user&#39;s finger or input device. 
       FIG. 2B  shows a second embodiment in which the laser  210 , supported on a substrate  211 , is configured to detect a user input on a touch input surface  200   b  that includes a reflective component  204 . In this embodiment the touch input surface  200   b  is configured to deflect in response to a touch or force applied by the user. In some embodiments, the deflection of the touch input surface  200   b  may be on the order of 1 to 20 μm, though that is not required. When laser  210  emits its light toward the touch input surface  200   b , the light reflects from the reflective component  204 . When the touch input surface  200   b  has been deflected closer to the laser  210 , there may be detected changes in interferometric parameters due to the laser&#39;s self-mixing interference. The detected changes can be interpreted as a user input or type of user input. 
     As described in more detail below, the detected changes may also enable the distance of the deflection to be determined. Also as described below, the detected changes may be analyzed to determine the speed and direction of the deflection on the touch input surface  200   b.    
       FIG. 2C  shows a third embodiment in which three lasers  212   a ,  212   b , and  212   c  are supported on a substrate  211  and configured to emit coherent light towards touch input surface  200   c  that is both light transmissive (at least on some sections) and can be deflected by a force or applied pressure. The touch input surface  200   c  has a reflective surface  206  configured to reflect light from at least one of the three lasers  212   a ,  212   b , and  212   c . In the embodiment shown, only light emitted from the middle laser can be reflected back into the electronic device. As described for the configuration of  FIG. 2B , the reflected light may be used to determine that a user input has occurred, and may be able to determine a speed and direction of a user&#39;s drag input. 
     In this embodiment, the light emitted from the two lasers  212   a  and  212   c  may be transmitted through the transmissive sections of the touch input surface  200   c , and, as described above for the touch input surface  200   a , may be used for detecting proximity of the user&#39;s finger or input device. 
     In the embodiment shown in  FIG. 2C , the three lasers  212   a ,  212   b , and  212   c  are provided with respective lenses  208   a ,  208   b , and  208   c . The lenses  208   a ,  208   b , and  208   c  can serve to redirect light emitted from the respective lasers at a desired angle. In the case shown, light emitted from lasers  212   a  and  212   b  is redirected from the initial direction (horizontal to the left, as shown) to intersect or impinge on the touch input surface  200   c  at an acute angle (with respect to a vector normal to the touch input surface  200   c ). 
     Additionally and/or alternatively, in all configurations of  FIGS. 2A-C , reflections of the emitted light of the laser(s) may be detected by one or more photodetectors. Changes in the reflected light (e.g., intensity, or reception location on the photodetector) may be detected and analyzed to determine whether the changes are due to a user input or particular type of user input. The photodetectors may be used as a secondary check for a user input detected by the laser(s), or instead of interferometric sensing performed at the laser. Certain embodiments using photodetectors will now be described. 
       FIG. 2D  shows a fourth embodiment in which the user input surface  200   d  is rigid, and does not deflect detectably under pressure applied by a user&#39;s finger  202  or other input source. The embodiment includes a laser system in which a laser  214  and a photodetector  220  are supported on a substrate  211 . The laser  214  emits its coherent light toward the user input surface  200   d . The user input surface  200   d  is supported above the substrate by supports  216   a ,  216   b . The supports  216   a ,  216   b  include respective compressible sections  218   a ,  218   b . Upon application of pressure by a user&#39;s finger  202 , or a stylus, the user input surface  200   d  retains its shape, but is displaced closer to the laser  214  by compression of the compressible sections  218   a ,  218   b . This displacement can be detectable using self-mixing of the laser&#39;s coherent light reflected from the user input surface  200   d  and/or detection of the reflected light by the photodetector  220 . 
       FIG. 2E  shows a fifth embodiment, in which a laser system has a laser  222  that is supported on a substrate  211  within an electronic device, and is oriented to emit its coherent light toward deflectable user input surface  200   e . In this configuration a photodetector  224  is affixed to an interior side of the user input surface  200   e . Deflection or displacement of the user input surface  200   e  by a user&#39;s finger  202  can be detected using self-mixing of the coherent light from laser  222  reflected from the user input surface  200   e  and/or detection of the light by the photodetector  224 . 
       FIG. 2F  shows a sixth embodiment analogous to that of  FIG. 2E . In this embodiment of the laser system, a photodetector  228  is affixed to a substrate  211  within an electronic device. A laser  226  is affixed to an interior side of a user input surface  200   f , and oriented to emit its coherent light toward the photodetector  228 . Deflection or displacement of the user input surface  200   f  by input from a user&#39;s finger  202  can be detected using self-mixing of the coherent light from laser  222  reflected from the substrate and/or detection of the light by the photodetector  224 . 
     The various configurations of lasers, photodetectors, and user input surfaces of  FIGS. 2A-2F , as well as of other configurations, can be implemented to detect both very small static and dynamic displacements of the user input surfaces, as will now be explained in relation to  FIGS. 3A-3C . In some embodiments, the displacements may be on the order of a few wavelengths of the laser light. Such capability may be used, for example, to implement a solid state button on a user input surface of an electronic device. 
       FIG. 3A  illustrates one embodiment of a laser system within an electronic device  300  that uses a laser  302  for detecting user input on a touch input surface  320 . For simplification of explanation, the laser  302  will be assumed to be a VCSEL. 
     The VCSEL  302  may be mounted on a substrate  304  within the electronic device. Details of the VCSEL are explained below with respect to  FIG. 4A . The VCSEL has connected to it associated circuitry  306  that supplies the VCSEL with a supply voltage and/or a signal voltage that causes the VCSEL  302  to lase, i.e., emit a beam of coherent light  314  (or just “emitted light”). In the embodiment shown, the emitted coherent light  314  is directed perpendicularly with respect to the substrate  304 . 
     The emitted coherent light  314  travels from the VCSEL  302  through a cover glass  31  (or other member that is transparent to at least the wavelength of emitted coherent light  314  emitted by the laser). The cover glass  312  may serve to encapsulate the VCSEL  302  and associated electrical circuitry  306  within the electronic device  300 . Above the cover glass  312  is a touch input surface  320  able to undergo a deflection or displacement  322  when a user presses it with sufficient force. The touch input surface  320  may in some embodiments be the top surface of the cover glass  312  itself, which deflects. Alternatively, there may be a gap between the cover glass  312  and the touch input surface  320 , as shown. In still other embodiments in which the cover glass  312  is light transmissive, as in touch input surface  200   a , the touch input surface  320  may instead be just a finger of a user. 
     When a signal is applied through the associated circuitry  306  to cause VCSEL  302  to lase, the emitted light  314  intersects the deflected touch input surface  320  and produces reflected light  316 , which may be scattered in multiple directions. Some of the reflections  318  may be directed back towards VCSEL  302 , enter its lasing cavity, and cause self-mixing interference. The self-mixing interference may produce detectable changes in interferometric parameters that may indicate a user input or particular type of user input. 
     Adjacent to the VCSEL  302  may be a photodetector  308  that is connected to monitoring circuitry  310 . In the embodiment shown, the monitoring circuitry  310  is configured to monitor output current of the photodetector  308 . Some of the reflected light  316  from the deflection of the touch input surface  320  may be reflected as light  319  that impinges on the photodetector  308 . In this embodiment, the output current is produced as a photoelectric current resulting from light  319  impinging on the photodetector  308 . In other embodiments, a photodetector (not shown) may be incorporated or integrated with the VCSEL  302 . 
       FIG. 3B  is a graph  330  showing plots of an example output signal  334  of a measured interferometric parameter resulting from a static displacement  332  of a user input surface in a configuration similar to that of  FIG. 3A . The displacement  332  is maintained at approximately 5 μm from times 0 to 15 msec, at which time the displacement begins to reduce. During the decrease in the displacement to zero, there are changes in a self-mixing of the laser light in the VCSEL producing a detectable oscillation in an interferometric parameter, as explained more fully in relation to  FIGS. 4A-C . Additionally and/or alternatively, there can be detectable changes in an interferometric parameter detected by a photodetector used in conjunction with the VCSEL, such as photodetector  308 . In the experimental results shown in  FIG. 3B , the measured interferometric parameter is a voltage in the millivolt range. As shown, the changes in the static displacement  332  on the order of micrometers can produce a measurable output signal  334 . As explained below, the velocity and direction of movement of the user input surface may be detected from the measured output signal  334  of an interferometric parameter. 
       FIG. 3C  is a graph  340  showing plots of an example output signal  344  of a measured interferometric parameter resulting from a periodic displacement of a user input surface, such as the user input shown in  FIG. 3A . The displacement  342  may be approximately a cosine wave with period of 100 msec. During the times when the displacement is changing most quickly, there may be greater changes in a self-mixing of the laser light in the VCSEL producing a detectable oscillation in an interferometric parameter. Additionally and/or alternatively, there can be detectable changes in an interferometric parameter detected by a photodetector used in conjunction with the VCSEL, such as photodetector  308 . In the particular results shown in  FIG. 3C , the measured interferometric parameter is a voltage in the millivolt range. As shown, the changes in the periodic displacement  342  (on the order of micrometers) can produce a measurable output signal  344 . In other embodiments and/or configurations, the interferometric parameter may be another parameter, such as current or power. The graphs of such other interferometric parameters may differ from the displacement  342  shown in  FIG. 3C . For example, the period of the waveform may differ, or the waveform may be other than one which approximates a cosine wave. As explained below, the velocity and direction of movement of the user input surface may be detected from the measured output signal  344  of an interferometric parameter. 
       FIGS. 4A-C  show examples of basic operations of a laser, such as a VCSEL. The operations may also be valid for other types of lasers that can undergo self-mixing interference. 
       FIG. 4A  shows an example structural diagram of a VCSEL  400 . In any type of laser, an input energy source causes a gain material within a cavity to emit light. Mirrors on ends of the cavity feed the light back into the gain material to cause amplification of the light and to cause the light to become coherent and (mostly) have a single wavelength. An aperture in one of the mirrors allows transmission of the laser light (e.g., transmission toward a touch input surface). 
     In the VCSEL  400 , there are two mirrors  402  and  404  on opposite ends of the cavity. The lasing occurs within the cavity  406 . In the VCSEL  400 , the two mirrors  402  and  404  may be implemented as distributed Bragg reflectors, which are alternating layers with high and low refractive indices. The cavity  406  contains a gain material, which may include multiple doped layers of III-V semiconductors. In one example the gain material may include AlGaAs, InGaAs, and/or GaAs. The emitted laser light  410  can be emitted through the topmost layer or surface of VCSEL  400 . In some VCSELs the coherent light is emitted through the bottom layer. 
       FIG. 4B  shows a functional diagram of self-mixing interference (or also “optical feedback”) with a laser. In  FIG. 4B , the cavity  406  has been reoriented so that emitted laser light  410  is emitted from the cavity  406  to the right. The cavity  406  has a fixed length established at manufacture. The emitted laser light  410  travels away from the cavity  406  until it intersects or impinges on a target, which may be the touch input surface  320  of  FIG. 3 . The gap of distance L from the emission point through the mirror  404  of the emitted laser light  410  to the target is termed the feedback cavity  408 . The length L of the feedback cavity  408  is variable as the target can move with respect to the VCSEL  400 . 
     The emitted laser light  410  is reflected back into the cavity  406  by the target. The reflected light  412  enters the cavity  406  to interact with the original emitted laser light  410 . This results in a combined emitted laser light  414 . The combined emitted laser light  414  may have characteristics (e.g., a wavelength or power) that differ from what the emitted laser light  410  would have in the absence of reflection and self-mixing interference. 
       FIG. 4C  is a graph  420  showing the variation in power of the combined emitted laser light  414  as a function of the length L of the feedback cavity  408 , i.e., the distance from the emission point through the mirror  404  of the emitted laser light  410  to the target. The graph depicts a predominantly sinusoidal variation with a period of λ/2. Theoretical considerations imply that the variation is given by the proportionality relationship: λP∝ cos(4π/λ). This relationship generally holds in the absence of a strong specular reflection. In the case of such strong specular reflection, the cosine becomes distorted, i.e., higher harmonics are present in the relationship. However, the peak-to-peak separation stays at λ/2. For a stationary target, this relationship can be used to determine that a deflection has occurred. In conjunction with other techniques, such as counting of the completed number of periods, the absolute distance of the deflection may also be determined. The case of a non-stationary target, such as during a drag operation of a user press, is explained below in relation to  FIGS. 7A-B . 
       FIG. 4D  shows a graph  421  of the variation in power of the combined emitted laser light  414  as a function of the length L of the feedback cavity  408 , in the case of strong specular reflection. In this case the curve is a distorted cosine. The period of the curve is still approximately λ/2. 
       FIGS. 5A-D  show cross sections of respective configurations  500   a - d  for laser systems within an electronic device for detecting user input on a user input surface, according to various embodiments. Hereinafter, for simplicity of explanation, such laser systems will be presumed to use VCSELs as the laser light source. It will be clear to one of skill in the art how to implement the embodiments using other laser light sources. In the embodiments shown, a user input surface  506  of the electronic device experiences a user touch input. The user input surface  506  may be a cover glass. The user input surface  506  may deflect when pressed. Or, as illustrated in  FIG. 2D , the user input surface may be rigid but may be displaced. The deflection may occur only at or near a top edge, or the entire user input surface  506  may deflect. The thickness of the user input surface  506  may be chosen for ease of detection of an applied user input. Additionally and/or alternatively, the user input surface  506  may allow transmission of light, either entirely or in part. 
     Various embodiments may detect not just a press (force or pressure) from a user at a specific location on the user input surface  506 , but also may be able to track a movement of the user&#39;s finger (or stylus) across the user input surface  506 . 
     In these embodiments, the VCSELs and other components for detecting the deflection of the outer surface of user input surface  506  may be contained in a module  504 . In these embodiments the module  504  may include an aperture that contains a respective lens to redirect the emitted laser light  508  of the various VCSELs. The redirection of the emitted laser light  508  can be used to detect motion of the user input, as explained below in relation to  FIGS. 7A-B . 
     In the embodiment  500   a  of  FIG. 5A , a single VCSEL  502  is connected to one side of the module  504 . The VCSEL  502  is connected to the module  504  so that the emitted laser light  508  is directed toward lens  510   a  mounted in an aperture on another side of module  504 . The lens  510   a  redirects emitted laser light  508  to intersect the user input surface  506  at an acute angle with respect to a vector normal (i.e., perpendicular) to the user input surface  506  at the point of the user input. Reflections from a deflection or displacement may be received back into VCSEL  502  and induce self-mixing interference in VCSEL  502 . The self-mixing interference may produce detectable changes in interferometric parameters to allow for user input detection. 
     In the embodiment  500   b  of  FIG. 5B , a single VCSEL  502  is connected above a photodetector  512  that is connected to one side of the module  504 . As with the embodiment of  FIG. 5A , VCSEL  502  is connected to the module  504  so that the emitted laser light  508  is directed toward lens  510   b  mounted in an aperture on another side of module  504 . The lens  510   b  redirects emitted laser light  508  to intersect the user input surface  506  at an acute angle with respect to a vector normal to the user input surface  506  at the point of the user input. Reflections from a deflection may be received back into VCSEL  502  and induce self-mixing interference in VCSEL  502 . The self-mixing interference may produce detectable changes in interferometric parameters to allow for user input detection. 
     Additionally and/or alternatively, the reflected light may also be detected by the photodetector  512 . Changes in photodetector  512  performance due to received reflected light may also be used determine if a user is applying a force to the user input surface  506 . 
     In the embodiment  500   c  of  FIG. 5C , a single VCSEL  502  is connected to one side of the module  504 . As with the embodiment of  FIG. 5A , VCSEL  502  is connected to the module  504  so that the emitted laser light  508  is directed toward lens  510   c  mounted in an aperture on another side of module  504 . The lens  510   c  redirects emitted laser light  508  to intersect the user input surface  506  at an acute angle with respect to a vector normal to the user input surface  506  at the point of the user input. Some reflections from deflection may induce self-mixing interference in VCSEL  502 . The self-mixing interference may produce detectable changes in interferometric parameters to allow for user input detection. 
     In this embodiment, there may be an additional photodetector  514  connected to the module  504 . The photodetector  514  may be positioned adjacent to the VCSEL  502 . In this embodiment, differently reflected light  509  travels from deflections at the point of user input to be received by the photodetector  514 . Changes in photodetector  514  performance due to received reflected light may also be used to determine if a user is applying a force to the user input surface  506 . 
     In the embodiment  500   d  of  FIG. 5D , two VCSELs  502  and  503  are positioned within the module  504 . The embodiment shown in  FIG. 5D  may be part of further embodiments that use two or more VCSELs, such as those discussed below with respect to  FIGS. 6A-B . In the embodiment of  FIG. 5D , the VCSEL  502  is connected to the module  504  so that the emitted laser light  508  is directed through the lens  510   d  mounted in an aperture on a side of the module  504 . The VCSEL  503  is connected to the module  504  so that its respective emitted laser light  511  is directed through lens  510   e  mounted in the aperture of module  504 . 
     In the embodiment  500   d  of  FIG. 5D , the lens  510   d  redirects emitted laser light  508  to intersect the user input surface  506  at an acute angle with respect to a vector normal to the user input surface  506  at the point of the user input. Reflections from a deflection may be received back into VCSEL  502  and induce self-mixing interference in VCSEL  502 . The emitted laser light  511  may be directed to intersect the user input surface  506  perpendicularly, so that the reflections of the light are relatively more likely to be received back into VCSEL  503  and induce self-mixing interference in VCSEL  503 . The VCSELs  502  and  503  may have the emissions of their laser light time multiplexed (i.e., alternate in time) by a separate controller (not shown). Such time multiplexing can reduce crosstalk interference. A specific case of time multiplexing is shown below in  FIG. 6C , in relation to the configuration of  FIG. 6A . 
     The self-mixing interferences within VCSELs  502  and  503  may produce detectable changes in their respective interferometric parameters. These respective changes may be used together to aid in detection of both a user input and a direction of movement of such a user input. Such multiple VCSEL detection will now be discussed. 
       FIG. 6A  shows a plan view of an arrangement  600  of three VCSELs  604   a ,  604   b , and  604   c  positioned on a substrate  602  within an electronic device. The configuration is directed to detecting motion or movement of a user&#39;s touch or press on a touch input surface. The VCSEL  604   a  is positioned so that it is located at an intersection of an imaginary line connecting VCSEL  604   a  to VCSEL  604   b  and an imaginary line connecting VCSEL  604   a  to VCSEL  604   c . In the embodiment shown, the two lines form a right angle, but in other embodiments the lines may intersect at a different angle. The distance from VCSEL  604   a  to VCSEL  604   b  may be the same as, or different from, the distance from VCSEL  604   a  to VCSEL  604   c . Using three (or more) VCSELs arranged non-collinearly may allow for detection of lateral movement of a user input (such as in a drag motion) in separate directions along a user input surface, as will now be explained. 
       FIG. 6B  shows a perspective view of components of an electronic device for detecting the existence and movement of a user input on a touch input surface. Shown in  FIG. 6B  is a substrate  602  positioned beneath a touch input surface  610 . In the embodiment shown, the substrate  602  and touch input surface  610  are configured as parallel planes. Three VCSELs  604   a ,  604   b , and  604   c , are connected to substrate  602  and positioned as shown in  FIG. 6A . The three VCSELs  604   a ,  604   b , and  604   c  are positioned to emit respective laser lights (which are coherent light beams)  606   a ,  606   b , and  606   c  toward the touch input surface  610 . Lenses may be associated with one or more of the VCSELs  604   a ,  604   b , and  604   c  to redirect the laser light beams. 
     In the embodiment shown, VCSEL  604   a  emits laser light  606   a  perpendicularly toward the touch input surface  610 . Positioned above VCSEL  604   a  is a reflector  608 , so that the emitted laser light  606   a  is likely to be reflected back into VCSEL  604   a  and induce self-mixing interference. Other embodiments may omit the reflector  608 . The reflective material of reflector  608  may be positioned on either the inner side (toward VCSEL  604   a ) or the outer side of touch input surface  610 . In this embodiment, the VCSEL  604   b  emits laser light  606   b  that may be deflected by a lens (not shown) to intersect the touch input surface  610  at a first acute angle. The VCSEL  604   c  emits laser light  606   c  that is deflected by a second lens (not shown) to intersect the touch input surface  610  at a second acute angle. 
     VCSEL  604   a  can be used for detection of a user input (e.g., a press) on the touch input surface  610 . Due to the reflector  608 , the likelihood that reflected light from the emitted laser light  606   a  is received back into VCSEL  604   a  may be increased. Thus, when a user input causes a deflection of the touch input surface  610 , the likelihood of detectable changes in the interferometric parameters corresponding to VCSEL  604   a  may also be increased. In some embodiments, interferometric parameters of VCSEL  604   a  may be given more importance for detection of a user input. 
     The two VCSELs  604   b  and  604   c  may be used for detection of motion or movement of a user input, as well as for an initial determination that there is a user input. The virtual axes  612  provide an orientation. The Z-axis is oriented perpendicularly into the touch input surface  610 . As explained below with respect to  FIGS. 7A-B , speed and direction of motion of a target (e.g., a deflection) toward or away from a VCSEL may also be detectable. 
     In the embodiment shown, the emitted laser light  606   b  is directed from the VCSEL  604   b  both vertically in the Z-axis and along the Y-direction. A lateral movement of a deflection across the touch input surface  610  having a component in the Y-direction may be detectable using an analysis of the interferometric parameters corresponding to VCSEL  604   b . Analogously, the emitted laser light  606   c  is directed from the VCSEL  604   c  both vertically in the Z-axis and along the X-direction. A lateral movement of the deflection across the touch input surface  610  having a component in the X-direction may be detectable using a separate analysis of the interferometric parameters corresponding to VCSEL  604   c.    
       FIG. 6C  shows time correlated graphs of time multiplexed driving inputs  622 ,  624 , and  626  applied to VCSELs  604   a ,  604   b , and  604   c . By time multiplexing their laser light emissions, signals caused by self-mixing interference, or from detection by a photodetector, only arise from one VCSEL source in each time interval. In some embodiments, a small buffer interval of time (not shown) may separate driving inputs  622  and  624 , and driving inputs  624  and  626 . Methods and procedures for detecting user inputs and motion of such inputs on a user input surface will now be explained. 
     Interferometric parameters, or changes in them, induced by self-mixing interference may be used to a determine distance between a laser light source, such as a VCSEL, and the target or reflecting object. The determined distance may be either a change in distance from a known reference distance, or may be an absolute distance. Also, interferometric parameters, or changes in them, induced by self-mixing interference may be used to a determine a velocity of the target or reflecting object. This disclosure now presents three families of embodiments for determining distance and/or velocity using measurements of interferometric parameters. A first family of embodiments is described in relation to  FIGS. 7A-7B . This family may use a modulation of a bias current to a laser diode to modulate the wavelength emitted by the laser diode. An absolute distance to, or velocity of, the target may be obtained by performing a spectrum analysis of samples of an interferometric parameter. A second family of embodiments, described in relation to  FIGS. 8A-8C , uses a time domain analysis without sampling of a measured interferometric parameter. A third family of embodiments, described in relation to  FIGS. 9A-9B , is based on modulating a bias current of a VCSEL and measuring spectral properties (harmonics) of a signal of a photodetector associated with VCSEL. 
       FIG. 7A  shows a diagram  700  of components of a laser capable of self-mixing interference that can produce changes in interferometric parameters. As in such lasers, there are two mirrors  702  and  704  enclosing the lasing material within the laser cavity  706 . In VCSELs, the mirrors may be implemented as distributed Bragg reflectors. In the absence of a target  710  to produce reflection, the emitted laser light  712  would have a wavelength λ. 
     In the embodiment shown, there is a target  710  moving with respect to the laser with a speed (magnitude)  v . The velocity of the movement may be either toward or away from the laser. The target  710  produces a reflected light  714  that, due to Doppler effects of the movement, has an altered wavelength λ+Δλ. The Doppler induced change in wavelength is given by Δλ= v =(2λ/c). The reflected light  714  induces self-mixing interference in the laser, which can produce changes in interferometric parameters associated with the laser light. These changed interferometric parameters can include changes in junction voltage or current, a laser bias current, voltage or supply power, another interferometric parameter, or, for embodiment using a photodetector, a change in an output current, voltage, or power of the photodetector. 
     Using the particular example of power, and recalling from above that in the absence of a strong back reflection (e.g., no specular reflector), the change in power is related to the length L of the optical feedback cavity  708  by ΔP∝ cos(4πL/λ), one sees that movement of the target  710  causes the length L of the optical feedback cavity  708  to change through multiple wavelengths of the emitted laser light  712 . The sinusoidal movement of the target  710  is shown in the plot  722  in the top of correlated graphs  720 . The movement causes the change in power to have the primarily sinusoidal plots  724   a - c  shown in the lower of the correlated graphs  720 . The motion of the target reverses direction at times  726   a  and  726   b . In the case of strong back reflection, as discussed previously in relation to  FIG. 4D , the functional form for the change in power has further harmonics and has a distorted cosine shape. The sinusoidal plots  724   a - c  would then be altered accordingly. 
     Because the movement of the target causes the optical feedback cavity length to change through multiple wavelengths of the emitted laser light, the sinusoidal power signal (or an equivalent sinusoidal signal of another interferometric parameter) is amenable for spectrum analysis, such as with a Fast Fourier Transform (FFT). Embodiments based on such spectrum analyses provide a first family of embodiments of methods and devices for using self-mixing interference for measuring distance and velocity of a target. The bottom graph  730  of  FIG. 7A  shows an amplitude (or “magnitude”) plot from such a spectrum analysis. The spectrum may have been calculated from samples taken within a sampling time interval contained between time  0  and time  726   a , during which the target is moving in a single direction with respect to the laser. 
     In some embodiments, the spectrum analysis may use a sample size of 128 or 256 samples. The spectrum analysis may also apply a filter (such as a triangle filter, a raised cosine filter, or the like) to the samples of the signal of the interferometric parameter being measured (such as the supply power or change therein, or the junction voltage or current, or the laser bias current, among others). 
       FIG. 7A  shows a graph  730  of the magnitude or amplitude spectrum in which there are three pronounced components. There is a DC component  732 , which reflects the fact that the signal of the interferometric parameter often has a steady state value around which the signal oscillates sinusoidally. There is then a first harmonic frequency, or fundamental beat  734 , that is associated with the major or predominant frequency f B  of the sinusoidal signal of the interferometric parameter. It can be shown that in some configurations f B =c×(Δλ/λ 2 ), where Δλ is the Doppler shift in the wavelength due target motion, and is given by Δλ= v ×(2λ/c). In the case of sufficient back reflection into the laser cavity, the signal is rarely a pure sinusoid, so the magnitude spectrum may also show a second harmonic frequency component at frequency 2×f B , and a third harmonic frequency component at frequency 3×f B . Higher harmonic frequency components may exist but are typically reduced. The measured fundamental beat frequency f B  can be used to calculate Δλ, from which  v  can be calculated. Examples of values relating the speed of the target to Δλ and f B  are given in Table 1, for a laser having unmixed emitted light with a wavelength of 940 nm, under a specific environment, refractive index and beam angle: 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Speed  ν   
                 Δλ 
                 f B   
               
               
                   
               
             
            
               
                  1 mm/s 
                 6.3 × 10 −9  nm 
                 2.13 kHz 
               
               
                  10 mm/s 
                 6.3 × 10 −8  nm 
                 21.3 kHz 
               
               
                 100 mm/s 
                 6.3 × 10 −7  nm 
                  213 kHz 
               
               
                   
               
            
           
         
       
     
       FIG. 7B  shows a first combined magnitude and phase graph  740  obtained from, in one embodiment, a spectrum analysis of a junction voltage signal. The top of the combined magnitude and phase graph  740  shows the magnitude of the FFT, while the bottom of phase graph  740  shows the phase. In the phase graph  740 , the target is moving in a first direction with respect to the laser. The movement of the target produces a predominantly but non-ideal sinusoidal form, so that there is more than one harmonic present, as shown in amplitude plot in the top of the combined magnitude and phase graph  740 .  FIG. 7B  also shows a second combined magnitude and phase graph  750  obtained under the same conditions except that the target is moving in the opposite direction (at the same speed). 
     A phase shift at the second harmonic frequency may be used to determine a direction of the motion. The specific example shown in the phase plot of phase graph  740  is from a spectrum analysis performed on a voltage signal induced by the target moving in a first direction with respect to the laser. The direction is obtained by calculating:
 
2×phase{Fundamental Harmonic}−phase{Second Harmonic}.
 
When this value is greater than zero, the target is moving toward the laser, whereas when the value is less than zero, the target is moving away from the laser. Next, the specific example shown in the phase plot of graph  750  is from an example spectrum analysis performed on a voltage signal induced by the target moving in the opposite of the first direction with respect to the laser. The calculation of the above quantity in this case will be less than zero.
 
     To return to the configuration and embodiments described in  FIG. 6B , a drag motion laterally across the touch input surface  610  induces a deflection inwards (i.e., in the Z-direction) that moves similarly in or on the touch input surface  610 . The movement of the deflection has a component along each of the X- and Y-directions. These component motions may be separately detected based on spectrum analyses of changes in interferometric parameters of at least the VCSELs  604   b  and  604   c . These detections are aided by the deflections of the emitted laser lights  606   b  and  606   c . Further details about the lenses that may be used to cause such deflections are given now. 
       FIG. 7C  shows time correlated graphs  760  relating a laser current  762  (also called a modulation current) with the resulting laser wavelength  764  and the resulting signal  766  of the measured interferometric parameter. The graphs are under the condition of a user input. By driving a laser with a modulation current, such as the laser current  762 , the produced laser light has a laser wavelength  764  that similarly varies according to a triangle wave. As a result of the user input on the touch input surface, the self-mixing interference causes the signal  766  of the interferometric parameter to have the form of a sinusoid (or distorted sinusoid) imposed on a triangle wave. One use of applying the modulation current  762  with a triangle wave is to allow for separate spectrum analyses (e.g., FFTs, as explained with respect to  FIG. 7D ) of samples taken during the time intervals of the ascending segment and of the descending segment of the triangle waveform modulation of the laser current  762 . While the graphs  760  are shown for a triangle waveform modulation of laser current  762 , some embodiments may use other alternatingly ascending and descending modulation currents for the laser. Also, while the laser current  762  is shown with equal ascending and descending time intervals, in some embodiments these time intervals may have different durations. 
       FIGS. 7D and 7E  respectively show a flowchart of a spectrum analysis based method  770  and a block diagram of a system  790  to implement a spectrum analysis procedure that can be used as part of detecting user input and drag motions on a touch input surface. The method  770  and the system  790  may drive or modulate a laser, such as one or more of VCSELs  604   a ,  604   b , and  604   c , with a modulation current  762 . The method  770  and the system  790  may also analyze a signal  766  related to an interferometric parameter. For purposes of explanation, in the embodiments of  FIGS. 7D and 7E  it will be assumed that the modulation current  762  has a triangle waveform. One of skill in the art will recognize how the method  770  and the system  790  can be implemented using alternative modulation current waveforms. The method  770  concurrently analyzes the triangle waveform modulation current  762  and the signal  766  of the interferometric parameter. The triangle waveform modulation current  762  and the signal  766  of the interferometric parameter are received at respective receiving circuits. Such receiving circuits may be one or more of the blocks of the system shown in  FIG. 7E  and described below, or may be one or more dedicated processing units such as a graphics processing unit, an ASIC, or an FPGA, or may include a programmed microcomputer, microcontroller, or microprocessor. Various stages of the method may be performed by separate such processing units, or all stages by one (set of) processing units. 
     At the initial stage  772  of the method  770 , an initial signal is generated, such as by a digital or an analog signal generator. At stage  776   a  the generated initial signal is processed as needed to produce the triangle waveform modulation current  762  that is applied to the VCSEL. Stage  776   a  can include, as needed, operations of digital-to-analog conversion (DAC) (such as when the initial signal is an output of a digital step generator), low-pass filtering (such as to remove quantization noise from the DAC), and voltage-to-current conversion. 
     The application of the triangle waveform modulation current  762  to the VCSEL induces a signal  766  in the interferometric parameter. It will be assumed for simplicity of discussion that the signal  766  of the interferometric parameter is from a photodetector, but in other embodiments it may be another signal of an interferometric parameter from another component. At initial stage  774  of the method  770 , the signal  766  is received. At stage  776   b , initial processing of the signal  766  is performed as needed. Stage  776   b  may include high-pass filtering. 
     At stage  778  the processing unit may equalize the received signals, if necessary. For example the signal  766  may include a predominant triangle waveform component matching the triangle waveform modulation current  762 , with a smaller and higher frequency component due to changes in the interferometric parameter. High-pass filtering may be applied to the signal  766  to obtain the component signal related to the interferometric parameter. Also, this stage may involve separating the parts of signal  766  and the triangle waveform modulation current  762  corresponding to the ascending and to the descending time intervals of the triangle waveform modulation current  762 . This stage may include sampling the separated information. 
     At stages  780  and  782 , a separate FFT is first performed on the parts of the processed signal  766  corresponding to the ascending and to the descending time intervals. Then the two FFT spectra are analyzed. 
     At stage  784 , further processing of the FFT spectra can be applied, such as to remove artifacts and reduce noise. Such further processing can include windowing, peak detection, and Gaussian fitting. 
     From the processed FFT spectra data, information regarding the user input can be obtained, including the direction and velocity of the input (such as during a drag motion by the user). A velocity of movement of the touch input surface may be inferred from the average of corresponding peaks (such as the fundamental beat, as shown in  FIG. 7A ), the distance from the difference of the peaks, and the direction of travel from the larger of the peaks. 
       FIG. 7E  shows a block diagram of a system  790  that can implement the spectrum analysis just described in the method  770 . In the exemplary system  790  shown, the system  790  includes generating an initial digital signal and processing it as needed to produce a modulation current  762  as an input to the VCSEL  793 . In an illustrative example, an initial step signal may be produced by a digital generator to approximate a triangle function. The digital output values of the digital generator are used in the digital-to-analog (DAC) converter  792   a . The resulting voltage signal may then be filtered by the low-pass filter  792   b  to remove quantization noise. Alternatively, an analog signal generator can be used to generate an equivalent voltage signal directly. The filtered voltage signal then is an input to a voltage-to-current converter  792   c  to produce the desired modulation current  762  in a form for input to the VCSEL  793 . 
     As described above, deflection (either static, or dynamic such as a finger drag) on a user input surface can cause changes in an interferometric parameter, such as a parameter of the VCSEL  793  or of a photodetector operating in the system. The changes can be measured to produce a signal  766 . In the embodiment shown it will be assumed the signal  766  is measured by a photodetector. For the modulation current  762  having the triangle waveform, the signal  766  may be a triangle wave of similar period combined with a smaller and higher frequency signal related to the interferometric parameter. 
     The signal  766  is first passed into the high-pass filter  795   a , which can effectively convert the major ascending and descending ramp components of the signal  766  to DC offsets. As the signal  766  from a photodetector (or a VCSEL in other embodiments) may typically be a current signal, the transimpedance amplifier  795   b  can produce a corresponding voltage output (with or without amplification) for further processing. 
     The voltage output can then be sampled and quantized by the analog-to-digital conversion (ADC) block  795   c . Before immediately applying a digital FFT to the output of the ADC block  795   c , it can be helpful to apply equalization. The initial digital signal values from the digital generator used to produce the triangle waveform modulation current  762  are used as input to the digital high pass filter  794   a  to produce a digital signal to correlate with the output of the ADC block  795   c . An adjustable gain can be applied by the digital variable gain block  794   b  to the output of the digital high pass filter  794   a.    
     The output of the digital variable gain block  794   b  is used as one input to the digital equalizer and subtractor block  796 . The other input to the digital equalizer and subtractor block  796  is the output of the ADC block  795   c . The two signals are differenced, and used as part of a feedback to adjust the gain provided by the digital variable gain block  794   b.    
     Once an optimal correlation is obtained by the feedback, an FFT, indicated by block  797 , can then be applied to the components of the output of the ADC block  795   c  corresponding to the rising and descending of the triangle wave. From the FFT spectra obtained, movement of the user input surface can be inferred, as discussed above and indicated by block  798 . 
     The method just described, and its variations, involve using sampling of a signal of an interferometric parameter and applying spectrum analyses to the samples of a signal. As will now be explained, a second family of embodiments of methods and devices for determining properties of a user input can be obtained directly from the signal of an interferometric parameter using a time domain based analysis without applying a spectrum analysis. 
       FIG. 8A  shows an example of a circuit  800  that can be used to implement a time domain analysis. A time domain analysis can be used to obtain properties of a user input obtained directly from the signal of an interferometric parameter, without applying a spectrum analysis to that signal. The configuration of the circuit  800  is one example of an embodiment, and in some cases the circuit may be otherwise embodied. 
     The configuration of the circuit  800  includes two sections. The first section  802  includes the laser, in this case the VCSEL  804 , and other biasing circuitry. The circuitry includes an amplifier  806  that accepts a bias voltage input and produces an output that drives a gate of transistor  808  positioned at the cathode of the VCSEL  804 . This input circuitry can be used to apply the triangle waveform modulation current  762  to the VCSEL  804 . Included in section  802  is a sensing resistor. 
     The second section  803  in the configuration of circuit  800  is a circuit to receive and analyze the signal of the interferometric parameter of the VCSEL  804 . In the particular embodiment shown, laser light is received from the VCSEL  804  at a photodiode  810 . In other embodiments, such as those that do not use a photodiode, the signal of the interferometric parameter may be a junction voltage, bias current, power, or other electrical property measured in section  802 . For example, the current across the sensing resistor in section  802 , rather than the shown photodiode current or voltage, may be the input to the amplifier  812 . The amplifier  812  can be used for buffering and/or amplifying the received signal of the interferometric parameter. 
     The output of amplifier  812  is then used as an input to a pair of comparators  814   a  and  814   b . The comparators  814   a  and  814   b  can be set at different trigger threshold voltages, V TH1  and V TH2 , to detect rises and falls of the received signal of the interferometric parameter, as will be explained below. The trigger threshold voltages of the comparators  814   a  and  814   b  can be controlled by a microcontroller  816  (or other processing unit, as described above). In embodiments in which the microcontroller  816  has digital outputs, the digital outputs thereof can adjust the trigger threshold voltages of the comparators  814   a  and  814   b  by first being converted to analog by the digital-to-analog (DAC) converters  818   a  and  818   b.    
       FIG. 8B  shows time correlated graphs  820  of a received signal  822  of the interferometric parameter, together with output signals  824  and  826  of the comparators  814   a  and  814   b . The received signal  822  of the interferometric parameter that results from self-mixing is, in the example shown, a distorted sinusoid, as discussed above. The comparator  814   a  is configured (by the trigger threshold voltage, V TH1 ) to detect when the signal  822  crosses a high threshold, T 1 , and the comparator  814   b  is configured (by the trigger threshold voltage, V TH2 ) to detect when the signal  822  crosses a lower threshold, T 2 . 
     Because the lower threshold T 2  is set lower than the upper threshold T 1 , the (distorted sinusoid) signal  822  exceeds the lower threshold T 2  during a longer time period than the signal  822  exceeds the upper threshold T 1 . The time period during which the signal  822  exceeds the upper threshold T 1  is a subperiod of the time period during which the signal  822  exceeds the lower threshold T 2 . As a consequence, there is a first time interval  828  between when comparator  814   b  triggers ‘on’ until when comparator  814   a  triggers ‘on.’ This is termed the time difference between rising edges. Similarly, there is a second time interval  830  between when comparator  814   a  triggers ‘off’ until when comparator  814   b  triggers ‘off.’ This is termed the time difference between falling edges. 
     The difference in lengths of time of the first time interval  828  (where the first time interval  828  may correspond to the rising edge time of the signal  822 ), and the second time interval  830  (where the second time interval  830  may correspond to the falling edge time of the signal  822 ) can be used to determine properties of the user input. In the example shown, the user input is moving toward the laser, so that the signal  822  has a sinusoidal shape distorted to the right. As result, the rising edge time of the first time interval  828  exceeds the falling edge time of the second time interval  830 . The excess can imply a direction of motion of the user input. Also, the durations of the time periods during which the signal  822  exceeds the lower threshold T 1  and exceeds the upper threshold T 2  may also be used to aid in determining the speed of the user input. 
       FIG. 8C  shows time correlated graphs  840  that show a target velocity  842  can produce detectable changes in a sampled self-mixing signal  844 . In this embodiment, the sampled self-mixing signal  844  can be a direct sampling of the received self-mixing signal that is the output of the amplifier  812 . The sampling period can be chosen to be able to detect rapid changes in the target velocity due to user input. The sampled self-mixing signal  844  shown may, for example, represent samples of the continuous time signal  822 . 
     In the correlated graphs  840 , the target velocity  842  is initially zero (or approximately so), such as may occur under no user input. After initiation of a user input, the target velocity  842  shows an initial increase before stabilizing, such as may occur for a uniform applied pressure of user input. As a result, the sampled self-mixing signal  844  can, as for the continuous self-mixing signal, alternatingly exceed the upper threshold T 1  and then fall back below the lower threshold T 2 . The time interval  846  from exceeding the upper threshold T 1  until being below the lower threshold T 2  can be related to the target velocity. Similarly, a time from a sample being below the lower threshold T 2  until the next sample being above the upper threshold T 1  may also be used to determine the target velocity or other properties of the user input. 
     For detection of a drag motion of the user input, the time domain analysis method just described can be used with the configuration of three VCSELs shown in  FIG. 6B . One (or more) VCSELs can be used to determine motion of a user input in the X-direction and one (or more) VCSELs can be used to determine motion of the user input in the Y-direction, as explained previously. Further, the time domain analysis methods may make use of time-multiplexing of the lasers, as discussed in relation to  FIG. 6C . 
     A third family of embodiments of methods and devices for determining properties of a user input can be obtained directly from the signal of an interferometric parameter and using a different time domain based analysis. This family is described in relation to  FIGS. 9 and 10 . The methods and devices make use of a sinusoidal modulation of a bias current of the laser diode and detects resulting effects in an interferometric parameter of a photodetector associated with the laser diode. 
     In this family of embodiments, a laser light source, such VCSEL  302  of  FIG. 3A , is used to direct laser light at an input surface, such as the touch input surface  320  of  FIG. 3A . For simplicity of explanation only for this family of embodiments, the laser light source(s) will be assumed to be VCSEL(s). In this family of embodiments, there may be one or more photodetectors associated with each VCSEL, at least one of whose output parameters is correlated with a property of the self-mixing of the laser light that arises when some of the laser light emitted from the VCSEL is received back into the VCSEL after reflection from a target. In some embodiments, the photodetector is integrated as part of the VCSEL, such as at the location of the mirror  402  in  FIG. 4B . Instead of, or in addition to, an output of a photodetector, some embodiments may measure an interferometric property of the VCSEL itself, such as a junction voltage. 
     The self-mixing laser light that impinges on the photodetector contains at least two contributions: a first contribution from internal reflections at the light exit surface of the VCSEL and a second contribution from reflections from the target, as indicated in  FIG. 4B . The second contribution enters the laser cavity phase shifted from the first. The radian value of the phase shift can be expressed as Δφ=2π[2L mod λ], or equivalently as 
               2   ⁢           ⁢   π   ⁢           ⁢     (         2   ⁢   L     λ     -     ⌊       2   ⁢   L     λ     ⌋       )       ,         
where λ is the wavelength of the laser light.
 
     The bias current of a VCSEL may be driven by electronics, or other means, to include a superimposed sinusoidal modulation component, to have the form I BIAS ∝1+β sin(ω m t), where β is typically less than 1, and ω m  is the radian modulation frequency. The radian modulation frequency ω m  is much less than the frequency of the laser light. When a VCSEL is driven with such a bias current, the self-mixing laser light is such that Δφ∝a+b sin(ω m t), for constants a and b. The specific forms for constants a and b for some embodiments will be presented below. 
     When the two reflected contributions impinge on the photodetector, the phase shift between them can cause their electric fields to interfere, either destructively or constructively. As a result, an output current of the photodetector can have the form I PD ∝[1+δ cos(Δφ)]. 
     The Fourier series expansion of the function cos(a+b sin(ω m t)) has the form  {cos(a+b sin(ω m t))}=J 0 (b) cos(a)−2J 1 (b) sin(a) sin(ω m t)+2J 2 (b) cos(a) cos(2ω m t)−2J 3 (b) sin(a) sin(3ω m t)+higher order harmonics, where J k  indicates the Bessel function of the first kind of order k. So for the situation above of a sinusoidally modulated bias current of a VCSEL, the photodetector output current has a harmonics of the radian modulation frequency that can be selected by filtering, and the respective coefficient values that can be determined by demodulation, as explained in relation to  FIG. 10  below. 
     For a target that had an initial distance L 0  from the VCSEL, and which has undergone a displacement of ΔL from L 0 , the constants a and b above are given by:
 
 a =[4π( L   0   +ΔL )/λ], and  b =[−4πΔλ( L   0   +ΔL )/λ 2 ].
 
     The specific form of the expansion for I PD  may be given by: 
     
       
         
           
             
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               ⁢ 
               … 
             
           
         
       
     
     By defining a Q-component of I PD  as a low pass filtering and demodulation with respect to the first harmonic, i.e. Q∝Lowpass{I PD ×sin(ω m t)}, and an I-component as a low pass filtering and demodulation with respect to the second harmonic, i.e. I∝Lowpass{I PD ×cos(2ω m t)}, one can obtain a first value 
               Q   ∝     sin   ⁡     (       4   ⁢   π   ⁢   Δ   ⁢   L     λ     )         ,         
and a second value
 
               I   ∝     cos   ⁡     (       4   ⁢   π   ⁢   Δ   ⁢   L     λ     )         .         
Then one can use the unwrapping arctan function (that obtains an angle in any of all four quadrants) to obtain the displacement as
 
     
       
         
           
             
               Δ 
               ⁢ 
               L 
             
             = 
             
               
                 λ 
                 
                   4 
                   ⁢ 
                   π 
                 
               
               ⁢ 
               arc 
               ⁢ 
               
                   
               
               ⁢ 
               tan 
               ⁢ 
               
                   
               
               ⁢ 
               
                 
                   ( 
                   
                     Q 
                     / 
                     I 
                   
                   ) 
                 
                 . 
               
             
           
         
       
     
     In a modification of this implementation of the low pass filtering and demodulation, a Q′-component of I PD  can be defined as a low pass filtering and demodulation with respect to the third harmonic, i.e. Q′∝Lowpass{I PD ×sin(3ω m t)}. This can then be used with the I-component derived by filtering and demodulation at the second harmonic, as above, to obtain a modified first value 
                 Q   ′     ∝     sin   ⁡     (       4   ⁢   π   ⁢   Δ   ⁢   L     λ     )         ,         
and the second value
 
               I   ∝     cos   ⁡     (       4   ⁢   π   ⁢   Δ   ⁢   L     λ     )         .         
Then, as before, one can use the unwrapping arctan function (that obtains an angle in any of all four quadrants) to obtain the displacement as
 
               Δ   ⁢   L     =       λ     4   ⁢   π       ⁢   arc   ⁢           ⁢   tan   ⁢           ⁢       (       Q   ′     /   I     )     .             
This modification makes use of frequency components of I PD  separate from the original modulation frequency applied to the VCSEL bias current I BIAS . This may reduce the need for filtering and/or isolation of I PD  at the original modulation frequency ω m .
 
     In a still further modification, one can use the form of the Baseband Signal (DC signal component) in the expansion above to obtain an alternative I-component derived by filtering and demodulation at the DC component: 
               I   ′     ∝       cos   ⁡     (       4   ⁢   π   ⁢   Δ   ⁢   L     λ     )       .           
This alternative I-component can then be used with the Q-component above to obtain
 
     
       
         
           
             
               Δ 
               ⁢ 
               L 
             
             = 
             
               
                 λ 
                 
                   4 
                   ⁢ 
                   π 
                 
               
               ⁢ 
               arc 
               ⁢ 
               
                   
               
               ⁢ 
               tan 
               ⁢ 
               
                   
               
               ⁢ 
               
                 
                   ( 
                   
                     Q 
                     / 
                     
                       I 
                       ′ 
                     
                   
                   ) 
                 
                 . 
               
             
           
         
       
     
     The low pass filtering and demodulations just discussed can be further explained in relation to  FIGS. 9A-B  and  FIG. 10 . 
       FIGS. 9A-B  show two time correlated graphs:  900 ,  910 . Graph  900  shows a plot  902  of a bias current I BIAS  of a VCSEL modulated by a sine wave at a single frequency. The amplitude of the sinusoidal modulation is only for illustration, and need not correspond to amplitudes in all embodiments. The bias current I NAS  has its sinusoidal variation about a fixed direct current value,  904 . 
     As a result of the sinusoidal modulation, the output current of a photodetector receiving the VCSEL&#39;s self-mixing laser light undergoes a time variation, shown in the plot  912  in the graph  910 . The time axes of graphs  900  and  910  are correlated. The plot  912  illustrates that the output current of the photodetector varies around a fixed direct current value  914 . 
     The sinusoidally modulated bias current I BIAS  and corresponding photodetector current may arise within the circuit shown in  FIG. 10 , as now described. Other circuits may be used to implement the time domain I/Q methods just described, and may produce bias currents and respective photodetector currents having respective plots similar to  902  and  912 . 
       FIG. 10  shows an exemplary circuit block diagram that may be used to implement this third family of embodiments. Other circuits may also be used, as would be clear to one skilled in the art. The circuit block diagram of  FIG. 10  shows the relationship and connections of certain components and sections; other circuits that implement these embodiments may use more or fewer components. As explained in more detail below,  FIG. 10  shows components which generate and apply a sinusoidally modulated bias current to a VCSEL. The sinusoidal bias current can generate in a photodetector  1016  an output current depending on the frequency of the sinusoidal bias and the displacement to the target. In the circuit of  FIG. 10 , the photodetector&#39;s  1016  output current is digitally sampled and then multiplied with a first sinusoid at the frequency of the original sinusoidal modulation of the bias current, and a second sinusoid at double that original frequency. The two separate multiplied outputs are then each low pass filtered and the phase calculated. Thereafter the displacement is determined using at least the phase. 
     The DC voltage generator  1002  is used to generate a constant bias voltage. A sine wave generator  1004  may produce an approximately single frequency sinusoid signal, to be combined with constant voltage. As shown in  FIG. 10 , the sine wave generator  1004  is a digital generator, though in other implementations it may produce an analog sine wave. The low pass filter  1006 A provides filtering of the output of the DC voltage generator  1002  to reduce undesired varying of the constant bias voltage. The bandpass filter  1006 B can be used to reduce distortion and noise in the output of the sine wave generator  1004  to reduce noise, quantization or other distortions, or frequency components of its signal away from its intended modulation frequency, ω m . 
     The circuit adder  1008  combines the low pass filtered constant bias voltage and the bandpass filtered sine wave to produce on link  1009  a combined voltage signal which, in the embodiment of  FIG. 10 , has the form V 0 +V m  sin(ω m t). This voltage signal is used as an input to the voltage-to-current converter  1010  to produce a current to drive the lasing action of the VCSEL  1014 . The current from the voltage-to-current converter  1010  on the line  1013  can have the form I 0 +I m  sin(ω m t). 
     The VCSEL  1014  is thus driven to emit a laser light modulated as described above. Reflections of the modulated laser light may then be received back within the lasing cavity of VCSEL  1014  and cause self-mixing interference. The resulting self-mixing interference light may be detected by photodetector  1016 . As described above, in such cases the photocurrent output of the photodetector  1016  on the link  1015  can have the form:  0 +i m  sin(ω m t)+γ cos(φ 0 +φ m  sin(ω m t)). As the I/Q components to be used in subsequent stages are based on just the third term, the first two terms can be removed or reduced by the differential transimpedance amplifier and anti-aliasing (DTIA/AA) filter  1018 . To do such a removal/reduction, a proportional or scaled value of the first two terms is produced by the voltage divider  1012 . The voltage divider  1012  can use as input the combined voltage signal on the link  1009  produced by the circuit adder  1008 . The output of the voltage divider  1012  on link  1011  can then have the form α (V 0 +V m  sin(ω m t)). The photodetector current and this output of the voltage divider  1012  can be the inputs to the DTIA/AA filter  1018 . The output of the DTIA/AA filter  1018  can then be, at least mostly, proportional to the third term of the photodetector current. 
     The output of the DTIA/AA filter  2018  may then be quantized for subsequent calculation by the analog-to-digital converter (ADC)  1020 . Further, the output of the ADC  1020  may have residual signal component proportional to the sine wave originally generated by the sine wave generator  1004 . To filter this residual signal component, the originally generated sine wave can be scaled (such as by the indicated factor of β) at multiplier block  1024 C, and then subtracted from the output of ADC  1020 . The filtered output on link  2021  may have the form A+B sin(ω m t)+C cos(2ω m t)+ . . . , from the Fourier expansion discussed above. The filtered output can then be used for extraction of the I/Q components by mixing. 
     The digital sine wave originally generated by sine wave generator  1004  onto link  1007  is mixed (multiplied) by the multiplier block  1024 A with the filtered output on link  1007 . This product is then integrated and low pass filtered at block  1028 A to obtain the Q component discussed above. 
     Also, the originally generated digital sine wave is used as input into the squaring/filtering block  1026  to produce a digital cosine wave at a frequency double that of the originally produced digital sine wave. The digital cosine wave is then mixed (multiplied) at the multiplier component  1024 B with the filtered output of the ADC  1020  on link  1021 . This product is then integrated and low pass filtered at component  1028 B to obtain the I component discussed above. 
     The Q and the I components are then used by the phase calculation component  1030  to obtain the phase, from which the displacement of the target can be calculated, as discussed above. 
     One skilled in the art will appreciate that while the embodiment shown in  FIG. 10  makes use of the digital form of the originally generated sine wave produced by sine wave generator  1004  onto link  1007 , in other embodiments the originally generated sine wave may be an analog signal and mixed with an analog output of the DTIA/AA  1018 . 
     The circuit of  FIG. 10  can be adapted to implement the modified I/Q method described above that uses Q′∝Lowpass{I PD ×sin(3ω m t)}. Some such circuit adaptations can include directly generating both mixing signals sin(2ω m t) and sin(3ω m t), and multiplying each with the output of the ADC block  1020 , and then applying respective low pass filtering, such as by the blocks  1028   a,b . The differential TIA and anti-aliasing filter may then be replaced by a filter to remove or greatly reduce the component of I PD  at the original modulation frequency ω m . One skilled in the art will recognize other circuit adaptations for implementing this modified I/Q method. 
     The I/Q time domain based methods just described may be used with the spectral based methods of the first family of embodiments. The spectral methods of the first family can be used at various times to determine the absolute distance to the target, and provide a value of L 0 , after which any of the various I/Q methods just described may be used to determine ΔL. 
     The I/Q time domain based methods may be used to determine a velocity of motion of a user input on a touch input surface by using the three VCSEL configuration of  FIGS. 6A and 6B . For one or more of the three VCSELs, the I/Q method can be used to determine displacements at more than one time instance. From the difference in time and the change in displacement(s), a speed and direction can be obtained. 
     In any of the embodiments described, light emitted by the lasers may be directed by lenses as part of detecting a presence of a user input, or a motion of the user input across the touch input surface. For example, the VCSELs  604   a  and  604   b  may be associated with lenses so that their respective coherent lights are directed with horizontal components. Such lenses will now be described. 
       FIGS. 11A-E  show cross sections  1100 A-E of shapes of lenses that may be positioned on or near the surface through which the coherent light of the laser or VCSEL is emitted, or may be positioned at locations between the laser and the touch input surface. The lenses can serve to redirect the emitted coherent light from a first direction to a second direction. Such a redirection allows the emitted coherent light to intersect or impinge on the touch input surface at an angle that is not perpendicular to the touch input surface, as described above. The lenses may be made from a molded polymer, a silicon hydride, glass, or other optically transmissive material. In the following detailed descriptions like numbers denote like elements. 
     In  FIGS. 11A-E , the laser or VCSEL  1102  is depicted emitting its coherent light horizontally and perpendicularly from a substrate to which it is attached, though this is only for explanation and is not required. In these figures, the emitted light  1107  is shown emerging from a surface of a surrounding material with surface  1106 , then passing through a cover glass  1110  to impinge or intersect with the target  1108 . In some embodiments the surrounding material with surface  1106  may be a solid transmissive material, or may be air or other gas with surface  1106  being a thin transmissive layer above the air. 
       FIG. 11A  shows a cross section  1100   a  of a single-sided freeform lens  1104 . In this embodiment, the lens  1104  has a concave surface  1105  shaped to redirect the coherent laser light at an angle as well as provide focusing. In this embodiment the surface element  1106  is planar layer. 
       FIG. 11B  shows a cross section  1100   b  of a double-sided freeform lens  1112 . In this embodiment the lens  1112  has a concave surface  1113  shaped to redirect the coherent laser light at an angle as well as provide focusing. In this embodiment, the surface element  1106  is shaped with a curve to provide further lensing. 
       FIG. 11C  shows a cross section  1100   c  of a conic lens  1116  with curved surface  1115 . In this embodiment, the surface  1106  is shaped to have multiple linear segments. In this embodiment the segment  1117  of surface  1106  is oriented and/or made of a material so that the coherent light  1107  emerging from the curved surface  1115  of lens  1116  undergoes total internal reflection from the segment  1117  and then emerges from the segment  1118 . 
       FIG. 11D  shows a cross section  1100   d  having a single-sided freeform lens  1122 . In this embodiment, the lens  1122  is positioned to form a gap between itself and the laser  1102 . In this embodiment, the surface  1106  of the lens  1122  includes a convex (i.e., curved towards the laser  1102 ) surface segment  1120  to deflect the light  1107 . 
       FIG. 11E  shows a cross section  1100   e  having a lens  1124  that is positioned to form a gap between itself and the laser  1102 . In this embodiment, the lens  1124  includes diffractive optic grating  1126  positioned on the segment of the surface  1106  that is adjacent to the laser  1102 . In one embodiment, the diffractive optic grating  1126  may be implemented as chromium on glass, or as a phase-etched binary diffractive optic grating. 
     In some cases, an SMI module, such as the module described with reference to  FIG. 5D , may be used to detect user input provided to an electronic device such as the earbud described with reference to  FIG. 1C . In such cases, a first SMI sensor may be used to detect click, tap, or force-based gestures, as might be supported by an earbud or other audio device to provide a “play” or “pause” input to the earbud. A second SMI sensor may be used to detect swipe or scroll gestures, as might be supported by the earbud or other audio device to increase or decrease a volume of the device. The second SMI sensor, in particular, may occupy much less space than a mechanical, capacitive, or resistive-based volume control mechanism. Also, to detect a user&#39;s swipe or scroll gesture, the user need only swipe across a beam of light emitted by the second SMI sensor, and does not need to swipe across an array of capacitive electrodes or the like.  FIGS. 12A-12D  show various embodiments of an SMI module that can be used to detect click/tap/force-based gestures and/or swipe/scroll gestures on a user input surface of an earbud or other audio device, such as the earbud shown in  FIG. 1C . The modules described with reference to  FIGS. 12A-12D  may alternatively be used to detect user input on other surfaces, in other types of electronic devices. 
       FIG. 12A  shows a module  1200  that includes a first SMI sensor  1202   a  and a second SMI sensor  1202   b . The module  1200  may be disposed below (or adjacent) a user input surface  1204 , and in some cases may be abutted to or adhered to the user input surface  1204  (e.g., using an optically transparent adhesive). In alternative embodiments, the first and second SMI sensors  1202   a ,  1202   b  and/or components thereof may be provided in separate modules, or may be positioned within a housing  1206  independently of any module. 
     In some cases, the user input surface  1204  (e.g., a touch input surface) may be part of a housing  1206  of an earbud or other electronic device. In some cases, the user input surface  1204  may be contiguous with one or more other portions of the housing  1206 . In some cases, the housing portion that defines the user input surface  1204  may be formed of a different material than other portions of the housing  1206 . For example, the housing  1206  may include a first portion (or component) formed of plastic or metal, and the user input surface  1204  may include a second portion (or component) formed of a different (e.g., softer) plastic, a piece of glass, or other material. The user input surface  1204  may in some cases be flush with respect to an adjacent housing component or components, or in other cases may be inset or raised with respect to an adjacent housing component or components. 
     As shown, the module  1200  may be attached to a substrate  1208 , which substrate  1208  may be attached to the housing  1206 . Alternatively, the module  1200  may be attached directly to the housing  1206  (e.g., to an interior portion of the housing  1206 , or to an underside of a housing portion that defines the user input surface  1204  (e.g., the module  1200  may be bonded, using an adhesive, to an underside of the housing portion that defines the user input surface  1204 ). 
     The module  1200  may be positioned, aligned, and/or oriented with respect to the user input surface  1204  using an alignment mechanism  1210 . In some cases, the alignment mechanism  1210  may include one or more datums, bosses, walls, or sockets. The alignment mechanism  1210  may be attached to the substrate  1208  as shown, or to the housing  1206  or user input surface  1204 , or to a combination of both. 
     The module  1200  may house or support the first SMI sensor  1202   a  and the second SMI sensor  1202   b . Each of the first and second SMI sensors  1202   a ,  1202   b  may include a light source (e.g., a laser light source) and a sensor (e.g., a photodetector, a voltage measurement circuit configured to measure the junction voltage of a current-driven laser light source, or a current measurement circuit configured to measure the bias current of a voltage-driven laser light source). In some embodiments, a laser light source and photodetector of an SMI sensor  1202   a  or  1202   b  may be integrated or stacked. In other embodiments, a laser light source and photodetector of an SMI sensor may be positioned adjacent each other (e.g., side-by-side). 
     Electrical connections may be made between components of the module  1200  (e.g., the first and second SMI sensors  1202   a ,  1202   b ) and a processor  1212  mounted within the housing  1206 . The electrical connections may be made by means of conductive traces of the substrate  1208 , by means of a flexible printed circuit attached to the substrate  1208  or module  1200 , by means of a socket attached to the substrate  1208  or module  1200 , or by other means. 
     The first SMI sensor  1202   a  (or more particularly, a first laser light source of the first SMI sensor  1202   a ) may have a first resonant cavity (or laser cavity) that is configured to emit a first beam of light  1214   a , receive a redirection (e.g., a reflection or scatter) of the first beam of light  1214   a , and self-mix the first beam of light  1214   a  and the redirection of the first beam of light  1214   a . Similarly, the second SMI sensor  1202   b  (or more particularly, a second laser light source of the second SMI sensor  1202   b ) may have a second resonant cavity that is configured to emit a second beam of light  1214   b , receive a redirection (e.g., a reflection or scatter) of the second beam of light  1214   b , and self-mix the second beam of light  1214   b  and the redirection of the second beam of light  1214   b . A first axis  1216   a  of the first beam of light  1214   a  may intersect the user input surface  1204  at a first angle (e.g., at a perpendicular angle), and a second axis  1216   b  of the second beam of light  1214   b  may intersect the user input surface  1204  at a second angle that differs from the first angle (e.g., at a non-perpendicular angle). 
     A reflective material  1218  (a reflector) may be disposed to move in relation to deflection of the user input surface  1204 , and may be positioned partly or wholly in a path of the first beam of light  1214   a . The reflective material  1218  may be positioned outside a second path of the second beam of light  1214   b . In some cases, the reflective material  1218  may include a reflective film, ink, or other form of material applied to (or mechanically attached to) the underside of the housing portion that defines the user input surface  1204 . When the first and second beams of light  1214   a ,  1214   b  include infrared (IR) light, the reflective material  1218  may include an IR-reflective film or ink. The reflective material  1218  may redirect (e.g., reflect) light in the first beam of light  1214   a  back toward the laser light source of the first SMI sensor  1202   a.    
     The housing portion that defines the user input surface  1204  may be optically transmissive to at least the second beam of light  1214   b , allowing the second beam of light  1214   b  to pass through the user input surface  1204  and reflect off of a finger, stylus, or other object that comes into contact with the user input surface  1204  or is positioned near the user input surface  1204 . When the second beam of light  1214   b  includes IR light, the housing portion that defines the user input surface  1204  may be IR-transparent. The finger, stylus, or other object external to the housing  1206  may cause a portion of the second beam of light  1114   b  to be redirected (e.g., reflected) back toward the laser light source of the second SMI sensor  1202   b.    
     A set of sensors (e.g., photodetectors or measurement circuits of each respective SMI sensor  1202   a ,  1202   b ) may be configured to detect a respective property associated with each of the first self-mixed light of the first laser light source and the second self-mixed light of the second laser light source, as described elsewhere herein. The detected respective property may include, for example, a junction voltage, a bias current, a power supply voltage, or a power output of a respective laser light source. 
     In some embodiments, a first set of one or more lenses  1220   a  may be positioned in a path of (e.g., along the axis  1216   a  of) the first beam of light  1214   a  and/or a second set of one or more lenses  1220   b  may be positioned in a path of (e.g., along the axis  1216   b  of) the second beam of light  1214   b . The first set of one or more lenses  1220   a  may in some cases focus or collimate the first beam of light  1214   a , and/or optimize the amount of light redirected back toward the resonant cavity of the first SMI sensor  1202   a . The second set of one or more lenses  1220   b  may in some cases bend the second axis  1216   b  of the second beam of light  1214   b , before the second beam of light  1214   b  intersects the user input surface  1204 . In some cases, the second set of one or more lenses  1220   b  may tilt the axis  1216   b  of the second beam of light  1214   b  away from the axis  1216   a  of the first beam of light  1214   a . Additionally or alternatively, the second set of one or more lenses  1220   b  may also focus or collimate the second beam of light  1214   b , and/or optimize the amount of light redirected back toward the resonant cavity of the second SMI sensor  1202   b.    
     The first and second SMI sensors  1202   a ,  1202   b  may be operated contemporaneously or sequentially. When operated contemporaneously, the laser light sources of the different SMI sensors  1202   a ,  1202   b  may be configured to emit and sense different coherent (or partially coherent) wavelengths of light. When operated sequentially, the laser light sources of the different SMI sensors  1202   a ,  1202   b  may be configured to emit and sense the same or different coherent (or partially coherent) wavelengths of light. 
     The processor  1212  may be configured to detect a gesture of a user made on the user input surface  1204 . The gesture may be detected at least partly in response to the detected respective properties associated with each of the first self-mixed light of the first laser light source (i.e., at least partly in response to an output of the first SMI sensor  1202   a ) and the second self-mixed light of the second laser light source (i.e., at least partly in response to an output of the second SMI sensor  1202   b ). In some cases, the processor  1212  may be configured to detect a deflection (D) of (or distance to) the user input surface  1204 , which deflection is perpendicular to the user input surface  1204 . The deflection (e.g., a press, click, or other force-based gesture) may be detected at least partly in response to a first detected property associated with the first self-mixed light of the first laser light source, as described elsewhere herein. The processor  1212  may also determine a velocity of the deflection along the axis  1216   a . When the stiffness of the user input surface  1204  is repeatable (i.e., if the user input surface  1204  returns to the same equilibrium position after each user touch), the processor  1212  may use the detected property(ies) of the first self-mixed light to determine an amount of force applied to the user input surface  1204 . 
     The processor  1212  may also or alternatively be configured to detect a movement (M) of a user (or stylus, or other object) along the user input surface  1204 . The movement (e.g., a swipe or scroll gesture) may be detected at least partly in response to a second detected property associated with the second self-mixed light of the second laser light source, as described elsewhere herein. The velocity of the movement (M) may be determined based at least partly on a velocity of the second beam of light  1214   b  (along the axis  1216   b ) and an angle (θ) that the axis  1216   b  forms with the user input surface  1204 . 
     In some cases, the processor  1212  may be configured to detect the movement of the user along the user input surface  1204  at least partly in response to first detecting a deflection of the user input surface  1204 . That is, use of a second SMI output of the second SMI sensor  1202   b  may be gated at least partly in response to a state of a first SMI output of the first SMI sensor  1202   a . This may enable, for example, the second SMI sensor  1202   b  to be operated in a low power state (e.g., a lower power or OFF state) until a deflection of the user input surface  1204  is detected, with the deflection suggesting that 1) a user, stylus, or other object is in physical contact with the user input surface  1204 , and 2) the output of the second SMI sensor  1202   b  is not a result of noise or the detection of movement in the air near the user input surface  1204 . In some embodiments, the processor  1212  may compare the first SMI output to a deflection threshold, then determine at least one parameter of the second SMI output after the first SMI output satisfies the deflection threshold. At least partly in response to the at least one parameter of the second SMI output, the processor  1212  may adjust a parameter of an electronic device (e.g., adjust the volume of a speaker of the electronic device). 
     In some cases, the processor  1212  may be configured to operate the first SMI sensor  1202   a  in a low power state (e.g., a low power or OFF state), and pulse the second SMI sensor  1202   b  at a reduced sample rate. When a disturbance is detected by the second SMI sensor  1202   b  (e.g., an increased SMI output because of a finger or object touching or approaching the user input surface  1204 ), the processor  1212  may fully power or turn ON the first SMI sensor  1202   a , and/or operate both the first and second SMI sensors  1202   a ,  1202   b  at a higher sample rate. 
     In some cases, the processor  1212  may use an SMI output of the first SMI sensor  1202   a  to disambiguate between components of the second SMI sensor&#39;s speed vector that are perpendicular to or parallel to the user input surface  1204 . For example, if the reflective material  1218  is a known distance from the first SMI sensor  1202   a , and the user input surface  1204  is a known distance from the first SMI sensor  1202   a  and reflective material  1218 , a deflection (D) or distance determined from the SMI output of the first SMI sensor  1202   a  may be used to determine a distance to the finger or other object that is touching the user input surface  1204 , and this distance to the finger or other object may be used to disambiguate between perpendicular and parallel components of the second SMI sensor&#39;s speed vector, thus reducing cross-talk between the perpendicular and parallel components. This disambiguation assumes that the axes  1216   a ,  1216   b  of the first and second beams of light  1214   a ,  1214   b  intersect the user input surface at points that are “close enough” relative to the curvature of the finger or other object that touches the user input surface  1204 . 
     The processor  1212  may adjust various parameters of an electronic device (e.g., an earbud) in response to the output of the first and/or second SMI sensor  1202   a ,  1202   b . In the case of an earbud or other audio device, the parameters may be parameters of an audio stream or speaker. 
     In some embodiments, the processor  1212  may interpret a deflection of the user input surface  1204 , that is more than a threshold deflection, as an intended press or click. When the module  1200  is incorporated into an earbud, the processor  1212  may play or pause an audio stream in response to the detected press or click. 
     In some embodiments, the processor  1212  may interpret a detected movement along the user input surface  1204  as an intended swipe or scroll gesture. When the module  1200  is incorporated into an earbud, the processor  1212  may adjust the volume of a speaker in response to the detected swipe or scroll gesture. The processor may determine a direction of the swipe or scroll gesture and associate the direction with an increase or decrease in the volume. The processor may also determine a speed of the swipe or scroll gesture and associate the speed, and/or a length of the swipe or scroll gesture, with a magnitude of the volume increase or decrease. 
     In some embodiments of the module  1200 , the first SMI sensor  1202   a  may be replaced with a capacitive, resistive, or other type of deflection or force sensor. 
       FIG. 12B  shows another module  1230  that includes a first SMI sensor  1202   a  and a second SMI sensor  1202   b . The module  1200  may be configured and positioned similarly to the module  1200 . However, in contrast to the second set of one or more lenses  1220   b  tilting the axis  1216   b  of the second beam of light  1214   b  away from the axis  1216   a  of the first beam of light  1214   a , the second set of one or more lenses  1220   b  tilts the axis  1216   b  of the second beam of light  1214   b  toward the axis  1216   a  of the first beam of light  1214   a . In some cases, the axes  1216   a ,  1216   b  of the first and second beams of light  1214   a ,  1214   b  may intersect at or about the user input surface  1204  when the user input surface  1204  is in its equilibrium state. 
       FIG. 12C  shows another module  1240  that includes a first SMI sensor  1202   a  and a second SMI sensor  1202   b . The module  1200  may be configured and positioned similarly to the module  1200 . However, in contrast to the laser light sources of the first and second SMI sensors  1202   a ,  1202   b , which emit their respective beams of light  1214   a ,  1214   b  along parallel axes, the laser light source of the second SMI sensor  1202   b  is tilted with respect to the laser light source of the first SMI sensor  1202   a  in  FIG. 12C . In some cases, the tilt may be achieved by use of a datum, boss, wedge  1242 , or socket attached to (or formed on) the substrate  1208 . 
       FIG. 12D  shows another module  1250  that includes a first SMI sensor  1202   a  and a second SMI sensor  1202   b . The module  1200  may be configured and positioned similarly to the module  1200 . However, the module  1240  does not include the reflective material  1218  and, thus, the first beam of light  1214   a  may pass through the user input surface  1204  and reflect off of a user, stylus, or other object (or not) instead of reflecting off of the reflective material  1218 . 
     Referring now to  FIG. 13 , there is shown a block diagram of an electronic device that may include a user input surface (e.g., a touch input surface) as described in the embodiments. The electronic device  1300  can include one or more processors or processing unit(s)  1302 , storage or memory components  1304 , a power source  1306 , an optional display  1308  (which in some cases may include the user input surface), input/output interface  1310  (which may include lasers such as VCSELs for detecting user input on the user input surface), one or more sensors  1312  (which may include photodetectors or measurement circuits as discussed in the embodiments above), a network communication interface  1314 , and an optional one or more cameras  1316 , each of which will be discussed in turn below. The user input surface may be a component of the display  1308 , the input/output interface  1310 , or another component of the electronic device. 
     The one or more processors or processing units  1302  can control some or all of the operations of the electronic device  1300 . The processor(s)  1302  can communicate, either directly or indirectly, with substantially all of the components of the electronic device  1300 . In various embodiments the processing units  1302  may receive the signals from photodetectors and/or the electronics of a VCSEL that correspond to the interferometric parameters, and perform the spectrum analyses of the signals discussed above. 
     For example, one or more system buses  1318  or other communication mechanisms can provide communication between the processor(s) or processing units  1302 , the storage or memory components  1304  (or just “memory”), the power source  1306 , the optional display  1308 , the input/output interface  1310 , the sensor(s)  1312 , the network communication interface  1314 , and the optional one or more cameras  1316 . The processor(s) or processing units  1302  can be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, the one or more processors or processing units  1302  can be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of multiple such devices. As described herein, the term “processor” or “processing unit” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. 
     The memory  1304  can store electronic data that can be used by the electronic device  1300 . For example, the memory  1304  can store electrical data or content such as, for example, audio files, document files, timing signals, algorithms, and image data. The memory  1304  can be configured as any type of memory. By way of example only, memory  1304  can be implemented as random access memory, read-only memory, Flash memory, removable memory, or other types of storage elements, in any combination. 
     The power source  1306  can be implemented with any device capable of providing energy to the electronic device  1300 . For example, the power source  1306  can be a battery or a connection cable that connects the electronic device  1300  to another power source such as a wall outlet. 
     The display  1308  may provide an image or video output for the electronic device  1300 , but may not be provided in some types of devices (e.g., an earbud). The display  1308  can be substantially any size and may be positioned substantially anywhere on the electronic device  1300 . In some embodiments, the display  1308  can be a liquid display screen, a plasma screen, or a light emitting diode screen. The display  1308  may also function as a touch input surface, as described in the embodiments, in addition to displaying output from the electronic device  1300 . In these embodiments, a user may press on the display  1308  in order to provide input to the electronic device  1300 . 
     The input/output interface  1310  can receive data from a user or one or more other electronic devices. The I/O interface  1310  can include a display, a user input surface or touch input surface such as a described in the embodiments above, a track pad, one or more buttons, one or more microphones or speakers, one or more ports such as a microphone port, and/or a keyboard. 
     In addition to photodetectors and monitors of VCSEL properties, the one or more sensors  1312  may include other types of sensors. Examples of sensors include, but are not limited to, light sensors such as light emitting sensors and/or light detection sensors, audio sensors (e.g., microphones), gyroscopes, and accelerometers. Example light emitting sensors include but are not limited to the VCSELs described above. Other example light detection sensors include, but are not limited to, sensors that include optical or photodetectors such as photodiodes and photoresistors. The sensor(s)  1312  can be used to provide data to the processor  1302 , which may be used to enhance or vary functions of the electronic device. 
     The network communication interface  1314  can facilitate transmission of data to a user or to other electronic devices. For example, in embodiments where the electronic device  1300  is a smart telephone, the network communication interface  1314  can receive data from a network or send and transmit electronic signals via a wireless or wired connection. Examples of wireless and wired connections include, but are not limited to, cellular, WiFi, Bluetooth, and Ethernet. In one or more embodiments, the network communication interface  1314  supports multiple network or communication mechanisms. For example, the network communication interface  1314  can pair with another device over a Bluetooth network to transfer signals to the other device while simultaneously receiving signals from a WiFi or other wired or wireless connection. 
     The optional one or more cameras  1316  can be used to capture images or video, but may not be provided in a device such as an earbud or watch. Each camera can be implemented as any suitable image sensor, such as a complementary metal-oxide-semiconductor (CMOS) image sensor. The camera(s) include an optical system that is in optical communication with the image sensor. The optical system can include conventional elements such as a lens, a filter, an iris, and/or a shutter. Various elements of the camera  1316 , such as the optical system and/or the image sensor, can be controlled by timing signals or other signals supplied from the processor  1302  and/or the memory  1304 . 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed.

Metadata:
Filing Date: 20200813
Publication Date: 20220208
Grant Date: 20220208
Priority Date: 20180413
Inventors: MCCORD, MICHAEL K.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01B9/02092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03547", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1016", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04883", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R3/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R2430/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04883", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2430/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0423", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0423", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R3/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04883", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R1/1016", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2430/01", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 73456543