PATENT DOCUMENT

Publication Number: US-11906303-B2
Application Number: US-202217894571-A
Country: US
Kind Code: B2

Title: Wearable skin vibration or silent gesture detector

Abstract:
Disclosed herein are wearable devices, their configurations, and methods of operation that use self-mixing interferometry signals of a self-mixing interferometry sensor to recognize user inputs. The user inputs may include voiced commands or silent gesture commands. The devices may be wearable on the user&#39;s head, with the self-mixing interferometry sensor configured to direct a beam of light toward a location on the user&#39;s head. Skin deformations or vibrations at the location may be caused by the user&#39;s speech or the user&#39;s silent gestures and recognized using the self-mixing interferometry signal. The self-mixing interferometry signals may be used for bioauthentication and/or audio conditioning of received sound or voice inputs to a microphone.

Claims:
What is claimed is: 
     
       1. A wearable device, comprising:
 a frame configured to attach the wearable device to a user and to direct a beam of light toward a skin portion of the user; 
 a self-mixing interferometry sensor mounted to the frame and configured to emit the beam of light; and 
 an interpreter configured to:
 receive a self-mixing interferometry signal from the self-mixing interferometry sensor; 
 detect skin vibration information in the self-mixing interferometry signal; and 
 transmit one or more signals responsive to a detection of the skin vibration information in the self-mixing interferometry signal. 
 
 
     
     
       2. The wearable device of  claim 1 , wherein:
 the frame defines an earbud; 
 the wearable device further comprises:
 a microphone; and 
 an in-ear speaker; 
 
 the frame directs the beam of light toward a location in an ear of the user; and 
 the interpreter identifies a voiced command of the user using the skin vibration information. 
 
     
     
       3. The wearable device of  claim 1 , wherein:
 the frame defines an eyeglass set including an arm; 
 the self-mixing interferometry sensor is mounted to the arm; 
 the arm directs the beam of light toward a location proximate to a temporal bone of the user; and 
 the interpreter identifies a voiced command of the user based on the skin vibration information. 
 
     
     
       4. The wearable device of  claim 1 , wherein interpreter is further configured to:
 detect temporomandibular joint movement information corresponding to the skin vibration information in the self-mixing interferometry signal. 
 
     
     
       5. The wearable device of  claim 4 , wherein interpreter is further configured to:
 identify the temporomandibular joint movement information as a silent gesture command of the user. 
 
     
     
       6. The wearable device of  claim 1 , wherein:
 the beam of light is a first beam of light; 
 the wearable device directs a second beam of light toward the skin portion of the user; and 
 the interpreter is configured to receive a second self-mixing interferometry signal based at least in part on the second beam of light. 
 
     
     
       7. The wearable device of  claim 1 , wherein:
 the beam of light is a laser light beam emitted by a laser diode; 
 a bias current of the laser diode is modulated with a sine wave; and 
 the interpreter is configured to use a time domain I/O analysis to detect the skin vibration information in the self-mixing interferometry signal. 
 
     
     
       8. The wearable device of  claim 1 , wherein:
 the beam of light is a laser light emitted by a laser diode; 
 a bias current of the laser diode is modulated with a triangle wave; and 
 the interpreter is configured to use a spectrum analysis to detect the skin vibration information in the self-mixing interferometry signal. 
 
     
     
       9. The wearable device of  claim 1 , wherein the interpreter is a command interpreter configured to identify a voiced command encoded in the skin vibration information. 
     
     
       10. A device, comprising:
 a frame configured to be worn by a user; 
 a self-mixing interferometry sensor mounted to the frame and configured to emit a beam of light toward a location on a skin portion of the user; and 
 an interpreter configured to:
 receive a self-mixing interferometry signal from the self-mixing interferometry sensor; 
 detect a first skin vibration information in the self-mixing interferometry signal; 
 detect a second skin vibration information in the self-mixing interferometry signal, wherein the second skin vibration information includes vibration information different from the first skin vibration information; and 
 transmit one or more signals responsive to a detection of the second skin vibration information in the self-mixing interferometry signal, the one or more signals indicating a movement unrelated to a voiced command. 
 
 
     
     
       11. The device of  claim 10 , further comprising:
 a microphone; wherein: 
 the interpreter is configured to:
 receive an output of the microphone; 
 determine the first skin vibration information in the self-mixing interferometry signal based at least in part on a voiced command from the output of the microphone; and 
 send one more second signals indicating a movement related to the voiced command. 
 
 
     
     
       12. The device of  claim 11 , the interpreter is configured to:
 detect a correlation of the voiced command of the user with a voice pattern detected in the first skin vibration information. 
 
     
     
       13. The device of  claim 11 , further comprising:
 a bioauthentication circuit configured to:
 authenticate the voiced command using a self-mixing interferometry signal of the self-mixing interferometry sensor; wherein: 
 
 the self-mixing interferometry signal includes the first skin vibration information. 
 
     
     
       14. The device of  claim 13 , the bioauthentication circuit is configured to:
 determine that the user was speaking during a time interval of the received output of the microphone based at least in part on the first skin vibration information; and 
 authenticate the voiced command using a detection that the user was speaking during the time interval. 
 
     
     
       15. The device of  claim 10 , wherein:
 the frame is a head-mountable frame; and 
 the location on the skin portion of the user is proximate to at least one of a temporal bone and a parietal bone. 
 
     
     
       16. A device, comprising:
 a frame configured to be worn by a user; 
 a self-mixing interferometry sensor mounted to the frame and configured to emit a beam of light toward skin of the user; and 
 an audio conditioning circuit configured to:
 receive a self-mixing interferometry signal from the self-mixing interferometry sensor; 
 detect skin vibration information in the self-mixing interferometry signal; and 
 determine time intervals of non-speech of the user based at least in part on a detection of the skin vibration information. 
 
 
     
     
       17. The device of  claim 16 , further comprising:
 a microphone configured to produce an audio signal; wherein the audio conditioning circuit is configured to: 
 modify the audio signal using the self-mixing interferometry signal of the self-mixing interferometry sensor based at least in part on a determination of the time intervals of non-speech of the user. 
 
     
     
       18. The device of  claim 17 , wherein the audio conditioning circuit is configured to modify the audio signal is further configure to:
 suppress background noise during a time segment in the determined time intervals of non-speech of the user modify the audio signal. 
 
     
     
       19. The device of  claim 16 , further comprising:
 a microphone configured to produce an audio signal; wherein the audio conditioning circuit is configured to: 
 determine time intervals of speech of the user based at least in part on the detection of the skin vibration information; and 
 refrain from modifying the audio signal based at least in part on a determination of the time intervals of speech of the user. 
 
     
     
       20. The device of  claim 16 , wherein:
 the beam of light is a laser light beam emitted by a laser diode; and 
 the audio conditioning circuit is configured to modify an audio signal using at least one of: 
 a time domain I/O analysis of the self-mixing interferometry signal when a sine wave modulation is applied to a bias current of the laser diode, and 
 a spectrum analysis of the self-mixing interferometry signal when a triangle wave modulation is applied to the bias current of the laser diode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/849,826, filed Apr. 15, 2020, entitled “Wearable Voice-Induced Vibration or Silent Gesture Sensor,” which is a nonprovisional and claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/852,481, filed May 24, 2019, entitled “SMI-Based Wearable Voice-Induced Vibration and Silent Gesture Sensor,” the contents of which are incorporated herein by reference as if fully disclosed herein. 
    
    
     FIELD 
     The present disclosure generally relates to wearable electronic devices. The wearable electronic devices are equipped with self-mixing interferometry sensors for detection of user inputs and/or user input commands. The self-mixing interferometry sensors may detect the user inputs by detecting skin deformations or skin vibrations at one or more locations on a user&#39;s head. The skin deformations or skin vibrations may be caused by a user&#39;s voiced or silent speech or head motion. 
     BACKGROUND 
     Wearable electronic devices, such as smart watches or headphones, are often configured to receive user inputs or commands by detecting a user&#39;s voice, or a user&#39;s press at a button or on an input screen. The voiced input command may be received by a microphone of the wearable electronic device. 
     Each of these input processes has potential limitations. Voice recognition software must distinguish the user&#39;s or wearer&#39;s voice from background noise or voices of others, and press or force inputs require a user&#39;s hands to be free. Also, a user may be unable to input a command to the wearable electronic device without being heard. 
     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 wearable electronic devices and user input detection systems for wearable electronic devices. The wearable electronic devices (or “wearable devices”, or “devices”) may be equipped with one or more self-mixing interferometry sensors operable to detect a user input or user command by detecting skin deformation or skin vibrations at a location on the user, such as on the head of the user. 
     More specifically, described herein is a wearable device that includes: a frame configured to attach the wearable device to a user; a self-mixing interferometry sensor mounted to the frame and configured to emit a beam of light; and a command interpreter configured to receive a self-mixing interferometry signal from the self-mixing interferometry sensor. The frame may be configured to direct the beam of light toward the head of the user. The self-mixing interferometry signal may include skin deformation information. The command interpreter may be configured to identify a command encoded in the skin deformation information. 
     In additional and/or alternative embodiments, the skin deformation information may include skin vibration information. The device may be configured as an earbud that also includes a microphone and an in-ear speaker. The self-mixing interferometry sensor may direct the beam of light toward a location in an ear of the user, and the command interpreter may be operable to identify a voiced command of the user using the skin vibration information. 
     In additional and/or alternative embodiments, the skin deformation information may include skin vibration information. The device may be configured as an eyeglasses set, with the self-mixing interferometry sensor mounted to an arm of the eyeglasses set. The self-mixing interferometry sensor may direct the beam of light toward a location proximate to the temporal bone of the user. The command interpreter may be operable to identify a voiced command of the user based on the skin vibration information. 
     In additional and/or alternative embodiments, skin deformation information may include temporomandibular joint movement information. The device may be configured as a headphone, with at least one self-mixing interferometry sensor mounted on the headphone to direct the beam of light toward a location on the user&#39;s head proximate to the temporomandibular joint of the user. The command interpreter may be operable to identify the temporomandibular joint movement information as a silent gesture command of the user. 
     In additional and/or alternative embodiments, the skin deformation information may include temporomandibular joint movement information. The device may be configured as a visual display headset, with at least a first and a second self-mixing interferometry sensor. The first self-mixing interferometry sensor may direct its beam of light toward a location on the user&#39;s head proximate to a temporomandibular joint of the user, and the second self-mixing interferometry sensor may direct its beam of light toward a location on the user&#39;s head proximate to the parietal bone. The command interpreter may be configured to receive respective first and second self-mixing interferometry signals from the first and second self-mixing interferometry sensors. The command interpreter may be configured to detect a silent gesture command of the user using the first self-mixing interferometry signal and to detect a voiced command of the user using the second self-mixing interferometry signal. 
     Also described herein is a device that may include: a head-mountable frame that is configured to be worn by a user; a self-mixing interferometry sensor mounted to the head-mountable frame and operable to emit a beam of light toward a location on the user&#39;s head; a microphone; a command interpreter configured to receive an output of the microphone and recognize a voiced command of the user; and a bioauthentication circuit configured to authenticate the voiced command using a self-mixing interferometry signal of the self-mixing interferometry sensor. 
     In additional and/or alternative embodiments, the self-mixing interferometry signal may include skin deformation information. The bioauthentication circuit may be operable to detect, using at least the skin deformation information, that the user was speaking during a time interval of the received output of the microphone and authenticate the voiced command using the detection. The authentication of the voiced command may include detecting a correlation between the voiced command of the user and a voice pattern of the user detected in the skin deformation information. 
     In some embodiments, the device may be an earbud that includes an in-ear speaker and a radio transmitter. The device may transmit the voiced command using the radio transmitter upon authentication of the voiced command. 
     In some embodiments, the device may be a headphone, and the location on the user&#39;s head may be proximate to at least one of a temporal bone and the parietal bone of the user. The device may transmit the voiced command using the radio transmitter upon authentication of the voiced command. 
     Also described herein is a device that may include: a head-mountable frame configured to be worn by a user; a self-mixing interferometry sensor mounted to the head-mountable frame and operable to emit a beam of light toward a location on the user&#39;s head; a microphone configured to produce an audio signal; and an audio conditioning circuit configured to modify the audio signal using a self-mixing interferometry signal of the self-mixing interferometry sensor. 
     In any or all of these various embodiments, the beam of light may be produced by a laser diode. The various embodiments may use a time-domain I/Q analysis of the self-mixing interferometry signal. Such a time-domain I/Q analysis includes applying a sine wave modulation to the laser diode&#39;s bias current. Alternatively or in conjunction, the various embodiments may use a spectrum analysis of the self-mixing interferometry signal when a triangle wave modulation is applied to the laser diode&#39;s bias current. In yet another implementation, a constant (D.C.) driving of the laser diode&#39;s bias current may also be used. 
    
    
     
       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. 
         FIG.  1    illustrates a self-mixing interferometry sensor emitting a coherent light beam at a location on a head of a user, according to an embodiment. 
         FIG.  2 A  illustrates a block diagram of the components of a wearable device, in relation to part of a user&#39;s head, according to an embodiment. 
         FIG.  2 B  illustrates a block diagram of the components of another wearable device, in relation to part of a user&#39;s head, according to an embodiment. 
         FIG.  2 C  illustrates a block diagram of the components of a third wearable device, in relation to part of a user&#39;s head, according to an embodiment. 
         FIG.  3 A  illustrates an ear bud that may use skin deformation or skin vibration detection, according to an embodiment. 
         FIG.  3 B  illustrates a headphone apparatus with a component for detecting skin deformation, or skin vibration or movement, according to an embodiment. 
         FIG.  4 A  illustrates a VCSEL diode with an integrated intra-cavity photodetector, according to an embodiment. 
         FIG.  4 B  illustrates a VCSEL diode associated with a separate photodetector, according to an embodiment. 
         FIG.  4 C  illustrates a VCSEL diode with an extrinsic, on-chip photodetector, according to an embodiment. 
         FIG.  4 D  illustrates a VCSEL diode with an extrinsic, off-chip photodetector, according to an embodiment. 
         FIG.  5    shows time-correlated graphs of a self-mixing interferometry signal and a corresponding short-time Fourier transform during voiced speech, according to an embodiment. 
         FIG.  6    shows time-correlated graphs of a self-mixing interferometry signal and a corresponding short-time Fourier transform during silent jaw motion, according to an embodiment. 
         FIG.  7 A  illustrates a schematic for a self-mixing interferometry light source, according to an embodiment. 
         FIG.  7 B  illustrates self-mixing of laser light, according to an embodiment. 
         FIG.  7 C  illustrates a variation in an interferometric parameter due to self-mixing, according to an embodiment. 
         FIG.  8 A  is a flow chart of a spectrum analysis method for determining distances from a light source to an object using self-mixing interferometry, according to an embodiment. 
         FIG.  8 B  shows time-correlated graphs of signals that may occur in a self-mixing interferometry sensor, according to an embodiment. 
         FIG.  8 C  illustrates a block diagram of a circuit operable to implement the spectrum analysis method for determining distances from a light source to an object using self-mixing interferometry, according to an embodiment. 
         FIG.  9 A  is a flow chart of a time domain method for determining distances from a light source to an object using self-mixing interferometry, according to an embodiment. 
         FIGS.  9 B-C  show time-correlated graphs of signals that may occur in a self-mixing interferometry sensor, according to an embodiment. 
         FIG.  10    illustrates a block diagram of a circuit operable to implement the time domain method for determining distances from a light source to an object using self-mixing interferometry, according to an embodiment. 
         FIG.  11    illustrates a block diagram of an electronic device that is configured to detect user input, according to an embodiment. 
     
    
    
     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 description is 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 wearable devices that can detect and respond to user inputs. The user inputs may include either or both of voiced (audible) commands or silent (inaudible) gesture commands of a user. As used herein, a “command,” whether voiced or a silent gesture, is to be understood as any of: a user instruction to the device to change the device&#39;s operation, an input of data or other information to the device by the user, or another user input to affect the state of the wearable device itself or of an associated electronic device. The embodiments described herein may also be used to record audible or inaudible communications other than commands. The wearable device may include a self-mixing interferometry sensor that uses self-mixing interferometry to detect the voiced or silent gesture commands, or other voiced or silent communications. 
     In self-mixing interferometry, a beam of light (visible or invisible) is emitted by a light source of the self-mixing interferometry sensor toward an object. Reflections or backscatters of the emitted beam of light from an object may be received in the light source and cause the light source to enter an altered steady state in which the emitted light is different from light emitted without received reflections. As the distance or displacement of the object from the self-mixing interferometry sensor varies, corresponding variations in the altered state of the self-mixing interferometry sensor are induced. These induced alterations produce detectable variations in a signal of the self-mixing interferometry sensor that allow the distance, displacement, motion, velocity, or other parameters of the object to be determined. 
     In various embodiments described herein, the wearable device may be worn or attached to a user, such as on the user&#39;s head. The user&#39;s voiced or silent gesture commands may induce skin deformations, such as skin vibrations. For example, audible speech by the user may induce skin vibrations at one or more locations on the scalp or head of the user. A silent gesture of the user, such as inaudibly forming a word with the jaw and tongue without exhaling, may induce skin deformations at one or more locations on the scalp or head of the user. The skin deformations may be detected by a self-mixing interferometry sensor mounted on a frame of the wearable device. 
     Specific embodiments described in further detail below include a microphone equipped earbud, in which the self-mixing interferometry sensor detects the user&#39;s speech or voice based on skin vibrations at a location in the user&#39;s ear. In a variation, the earbud may not have a conventional microphone. Instead, the self-mixing interferometry sensor may function for detecting sound inputs. In a second embodiment, an over the ear(s) headphone may include one or multiple self-mixing interferometry sensors that may detect the user&#39;s voiced commands or silent gestures from skin deformations at locations proximate to the parietal bone, one of the temporal bones, one of the temporomandibular joints, or another location on the user&#39;s head. In a third embodiment, an eyeglass frame may include a self-mixing interferometry sensor that may detect skin deformations proximate to the temporal bone. A fourth embodiment relates to a visual display headset, such as may be used by a mixed reality, an augmented reality, or virtual reality (AR/VR) user headset. The AR/VR headset may include multiple self-mixing interferometry sensors that may detect the user&#39;s voiced commands or silent gestures from skin deformations at locations proximate to the parietal bone, one of the temporal bones, one of the temporomandibular joints, or another location on the user&#39;s head. These embodiments are listed as examples, and are not intended to limit the embodiments of this disclosure. 
     Detected skin deformations may be used in various ways. One use is to recognize or identify a command, whether it be input to the wearable device as a voiced command or as a silent gesture command. Skin deformations such as skin vibrations from voiced commands may be correlated with a known voice pattern of the user. This can allow the voiced command to be recognized and accepted by the device even when the voiced command is not accurately detected by a microphone (such as may occur in the presence of background noise). 
     Another use is for bioauthentication of received commands. As an example, a self-mixing interferometry sensor may detect skin vibrations when the user is speaking, and so allow the device to accept the command as it is heard by a microphone of the wearable device. If the self-mixing interferometry sensor does not detect skin deformations or skin vibrations above a threshold, the device may ignore an audible input detected by its microphone. In this way, the device can disregard unwanted voiced commands not made by the actual user. 
     In still another use, a self-mixing interferometry signal may be used for audio conditioning. For example, a user&#39;s speech recorded by a microphone may contain background noise. A self-mixing interferometry signal may allow the device to determine the intended voiced command, and can transmit (such as to another person or device) a reduced noise version of the voiced command. 
     These and other embodiments are discussed below with reference to  FIGS.  1 - 11   . 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.  1    illustrates a block diagram of a system  100  by which a wearable electronic device may operate to detect user inputs by detecting or measuring skin deflections or deformations at a location on a user&#39;s body. The block diagram of the system  100  is representational only, and does not imply any information regarding dimensions or shape of the features shown. Examples of such electronic devices include, but are not limited to, an earbud, a headphone, an eyeglass frame, or a mixed reality, an augmented reality or virtual reality (AR/VR) headset. These exemplary wearable electronic devices will be explained in further detail below in relation to  FIGS.  3 A-B . The skin deformation may be caused by voiced or silent commands issued by the user to affect operation of a wearable electronic device. 
     The wearable electronic device may include a self-mixing interferometry sensor  102 . The self-mixing interferometry sensor  102  is configured to emit an outgoing beam of light  106  directed toward a location on a user&#39;s head  110 . The outgoing beam of light  106  may pass through an optional collimating or other lens  104  for focusing and/or filtering prior to impinging on a location of the user&#39;s head  110 . Reflections or backscatter  108  of the outgoing beam of light  106  from the user&#39;s head  110  may reflect back into the light source within the self-mixing interferometry sensor  102  and alter a property of the outgoing emitted beam of light  106 . 
     In some embodiments, the light source within the self-mixing interferometry sensor  102  may be a laser diode in which the received reflections  108  of the beam of light  106  induce self-mixing interference within the laser diode&#39;s lasing cavity. The self-mixing interference produces an altered steady state of operation of the laser diode from a state of operation that would occur in the absence of received reflections  108 . For example, the emitted optical power of the beam of light or emitted wavelength may be altered. Such an alteration may be detectable as a change in an operational parameter (or “interferometric parameter”) of the source of the beam of light  106 , or of an associated electrical component of the electronic device. A particular type of laser diode that may be used in a self-mixing interferometry sensor is a vertical cavity, surface emitting laser (VCSEL) diode. Structural and operational details regarding VCSELs are described below. One skilled in the art will recognize that other types of laser diodes or light sources may be used in the self-mixing interferometry sensors described herein. 
     Motion of the location on the user&#39;s head  110  may be caused by the user&#39;s speech, such as a voiced command, or by a silent gesture of the user. Examples of locations on the user&#39;s head  110  include the skin or scalp proximate to temporomandibular joints, the temporal bones, the parietal bone, or another location. As an example, speech by the user may cause vibrations in the temporal bones, which in turn may cause vibrations in the skin proximate to the temporal bones. The skin vibrations may be detected by the self-mixing interferometry sensor  102  of the device. 
       FIGS.  2 A-C  show various block diagrams of configurations for wearable electronic devices. The configurations shown in the block diagrams are representational only, and do not imply any information regarding dimensions or shape of the features shown. 
       FIG.  2 A  is a block diagram of a configuration  200  by which a wearable electronic device  202  may have an attachment  204  to a part of a user&#39;s head  206  in order to receive inputs from the user by detecting skin deformations. The skin deformations may be caused by the user audibly or inaudibly making a voiced command or a silent gesture, or by another cause related to a user input to the wearable electronic device. 
     The device  202  may include a self-mixing interferometry (SMI) sensor  210  that emits an outgoing beam of light  208   a  toward a location on the user&#39;s head  206 , and receives reflections  208   b  of the outgoing beam of light  208   a . The reflections  208   b  may cause self-mixing interference in a light source, such as a laser diode, of the SMI sensor  210 . The self-mixing interference may be observed in a self-mixing interferometry signal, and may be associated or correlated with motion of the user&#39;s head  206 . 
     The device  202  may include a command interpreter  212 , that may analyze the self-mixing interferometry signal, such as by the methods described below in relation to  FIGS.  7 A- 10   . The command interpreter  212  may include processors and/or other processing circuits to detect skin deformation information, such as distance, displacement, motion or velocity of the skin at the location on the user&#39;s head  206 . From the skin deformation information, the command interpreter  212  may be able to recognize a command of the user, whether it be voiced or a silent gesture. 
     The command interpreter  212  may send instructions or other signals to affect the state of the device  202 , or of an associated device. For example, in the case that the device  202  is an earbud speaker/microphone combination, the instructions may cause the device  202  to reduce a volume produced by the speaker, or may instruct a cellphone linked with the earbud to dial a person. 
       FIG.  2 B  shows a block diagram of an additional and/or alternative configuration  220  that may extend the configuration  200  of  FIG.  2 A . The configuration  220  includes a wearable device  222  that can attach to a user&#39;s head  226  by means of a connection component  224 . Particular devices making use of the configuration  200  will be described below, with two exemplary devices shown in  FIGS.  3 A-B . As in the configuration  200  of  FIG.  2 A , the device  222  includes a self-mixing interferometry (SMI) sensor  240 , as described above, configured to emit a beam of light  228   a  toward a location on the user&#39;s head  226 , and receive reflections  228   b  from the location that may cause a light source in the SMI sensor  240  to undergo self-mixing interference. The self-mixing interference may be detected in a self-mixing interferometry signal of the self-mixing interferometry sensor  240 . 
     The device  222  further includes a microphone  232  configured to receive sound input  230 . The sound input  230  may be a voiced command of the user, or originate from another sound source, such as another person, a music source, or from background noise. The microphone  232  may perform an initial filtering or signal conditioning on the received sound input  230 , and may produce a corresponding output signal having an alternate format, such as a digital encoded format. The microphone  232  allows the device  222  to use sensor fusion, in which both the output signal of the microphone  232  and the self-mixing interferometry signal from the SMI sensor  240  are both used to detect a user input. 
     The device  222  includes a command interpreter  234  configured to receive a signal output from the microphone  232  and associated with the sound input  230 . The command interpreter  234  may optionally receive a self-mixing interferometry signal from the SMI sensor  240 . The command interpreter  234  may analyze the microphone&#39;s sound signal and apply a voice recognition algorithm to decide if the sound input  230  originated from a person&#39;s voice, such as the user&#39;s voice. The command interpreter  234  may also make a decision about the content in the sound input  230 , and determine if they represent a voiced command. 
     The command interpreter  234  may optionally be configured to analyze the self-mixing interferometry signal from the SMI sensor  240  to determine if the user was speaking during the time interval in which the sound input  230  was received. The command interpreter  234  may also make a decision, based on skin deformation information in the self-mixing interferometry signal, about whether the user made either a voiced command or a silent gesture command during the time interval when the microphone received the sound input  230 . 
     The device  222  further includes a bioauthentication circuit  236  configured to authenticate whether a voiced command or a silent gesture command arose from the user. The bioauthentication circuit  236  may be part of, or work in conjunction with, a processor  238  included in the device  222 . 
     One such authentication may be to accept a voiced command recognized in the microphone&#39;s output signal only if the analysis of the self-mixing interferometry signal confirms that the user was speaking when the microphone received the sound input  230 . In another type of authentication, a voiced command recognized in the microphone&#39;s output signal is accepted only when it agrees with a voiced command recognized in skin deformation information of the self-mixing interferometry signal. These two types of authentication can reduce improper command entry to the device  222 , such as from a recording of the user&#39;s voice, or from another person&#39;s voice. 
     In still another authentication, a silent gesture command recognized in skin deformation information of the self-mixing interferometry signal may be accepted as valid if the sound input  230  occurring concurrently with the skin deformation is below a volume threshold, such as when the user is not speaking and the background noise is low. 
     The bioauthentication circuit  236 , and/or its associated processor  238 , may store voice patterns from the user for recognizing and/or authenticating voiced commands. The voice patterns of the user may have been entered into the device  222  during an initial training session, or may be obtained during usage of the device  222  by use of learning algorithms. A voice signal recognized in the microphone&#39;s output signal may only be accepted as a valid input command to the device  222  when it is found to match a stored voice pattern of the user. 
       FIG.  2 C  shows a block diagram of an additional and/or alternative configuration  250  that may extend the configuration  200  of  FIG.  2 A or  2 B . The configuration  250  includes a wearable device  252  that can attach to a user&#39;s head  256  by means of a connection component  254 . Particular devices that may make use of the configuration  250  will be described below, with two examples shown in  FIGS.  3 A-B . As in the configuration  200  of  FIG.  2 A , the device  252  includes a self-mixing interferometry (SMI) sensor  262 , as described above, configured to emit a beam of light  258   a  toward a location on the user&#39;s head  256 , and receive reflections  258   b  from the location. The reflections  258   b  may cause a light source in the SMI sensor  262  to undergo self-mixing interference. The self-mixing interference may be detected in a self-mixing interferometry signal of the SMI sensor  262 . 
     As with the device  222 , the device  252  includes a microphone  264  operable to detect sound input  260 , which may be a voiced command of the user, or originate from another sound source, such as another person, a music source, or from background noise. The microphone  264  may perform an initial filtering or signal conditioning on the received sound input  260 , and may produce a corresponding output signal having an alternate format, such as a digital encoded format. The microphone  264  allows the device  252  to use sensor fusion, in which both an output signal of the microphone  264  and the self-mixing interferometry signal from the SMI sensor  262  are both used to detect a user input. 
     The device  252  includes an audio conditioning circuit  266  configured to receive both the output signal of the microphone  264  and the self-mixing interferometry signal from the SMI sensor  262 . The audio conditioning circuit  266  may be part of the processor  268 , or may work in conjunction with the processor  268  to analyze the output signal of the microphone  264  and the self-mixing interferometry signal from the SMI sensor  262 . The audio conditioning circuit  266  may perform bioauthentication operations, such any of those described above. 
     The audio conditioning circuit  266  may be configured to perform various operations using the combination of the self-mixing interferometry signal and the output signal of the microphone  264 . In one such operation, the audio conditioning circuit  266  and/or its associated processor  268  may have stored various voiced commands of the user. The audio conditioning circuit  266  may use the self-mixing interferometry signal and a concurrently received output signal to determine an intended voiced command from among the stored voiced commands of the user. The matched voiced command may then be transmitted by the audio conditioning circuit  266  and/or its associated processor  268  to an electronic device associated with the device  252 . For example, the device  252  may be the earbud  300  described below, and may be linked by a Bluetooth connection with a cellphone. By transmitting the matched voiced command, noise in the received sound input  260  would not be further transmitted. 
     In a second operation, the audio conditioning circuit  266  may determine that the output signal from the microphone  264  is below an amplitude or volume threshold. However, the audio conditioning circuit  266  may detect that the user was making a silent gesture command based on the self-mixing interferometry signal. The silent gesture command may be matched with a stored voiced command of the user, and that stored voiced command may be transmitted to an associated electronic device. For example, the device  252  may be the earbud  300  below. A user may inaudibly form words with jaw motions, such the words or numbers of a passcode, to maintain privacy. While only background noise may be detected by the microphone  264  in the sound input  260 , the audio conditioning circuit  266  may detect the formed words in the skin deformation information in the self-mixing interferometry signal. Then the stored voiced command may be transmitted to a cellphone linked with the earbud. 
     In a third operation, the audio conditioning circuit  266  may use signal processing algorithms, such as weighted averaging, applied to a concurrently received sound input  260  and a self-mixing interferometry signal. The signal processing may remove noise, strengthen or interpolate for inaudible sections in the received sound input  260 , or perform other operations. 
     The audio conditioning circuit  266  may perform other or alternative operations in addition to or instead of the operations described. 
     Details of four specific examples of wearable devices that may implement the configurations described above are now presented, along with further processes or operations they may perform. However, it is to be understood that other wearable devices are within the scope of this disclosure. 
       FIGS.  3 A-B  show two exemplary wearable electronic devices that may be configured to detect and receive user inputs or commands. The user inputs may be voiced commands or silent gestures. 
       FIG.  3 A  illustrates a wearable earbud device (or just “earbud”)  300  positioned within a user&#39;s ear  302 . The earbud  300  may include a microphone  304  contained in a tubular housing extending from the user&#39;s ear toward the user&#39;s mouth (along a portion of the user&#39;s face). The microphone  304  may use any sufficiently compact technology, such as a piezoelectric or other technology, to be contained within an earbud and be operable to detect and receive voice and audio sounds. The earbud  300  may include a middle section  305  configured to lodge in the opening of the user&#39;s ear canal. The middle section  305  may include an in-ear speaker configured to direct sound into a user&#39;s ear canal. The middle section  305  may also include a radio transmitter/receiver operable to transmit voice or audio signals to another device, such as the user&#39;s cellphone. The radio transmitter/receiver may also receive electromagnetic signals (such as Bluetooth or another radio frequency transmission technology) modulated to carry voice or audio signals, and cause the in-ear speaker to produce such voice or audio signals. 
     The earbud  300  may also contain a self-mixing interferometry sensor  306  configured so that when the earbud  300  is worn, the self-mixing interferometry sensor  306  is positioned to direct a beam of light toward a location  308  in the ear of the user. In some embodiments, the location  308  is such that there is minimal tissue between the self-mixing interferometry sensor and the user&#39;s skull. The positioning of the self-mixing interferometry sensor  306  on the earbud  300  may be adjustable by the user to improve detection by the self-mixing interferometry sensor  306  of skin deformation, which may include skin vibrations. 
     In such embodiments, when a user speaks, voice-induced vibrations may occur in the skull of the user, which may cause corresponding skin vibrations at the location  308 . Skin vibrations may be detected at location  308  by the self-mixing interferometry sensor  306  based on self-mixing interference, induced by the skin vibrations, in a beam of light emitted by the self-mixing interferometry sensor  306 . 
     As the skin vibrations at the location  308  may include vibrations induced by other sources than the user&#39;s speech, the detected skin vibrations may be analyzed by a processing circuitry (not shown) in the earbud  300  to detect information in the skin vibrations that are induced by the user&#39;s speech. Such an analysis may include comparisons of the skin vibrations to one or more voice patterns or stored voiced commands of the user. Such voice patterns may include those of common voiced commands. 
     The earbud  300  may implement any of the bioauthentication operations described above. The earbud  300  may additionally and/or alternatively implement any of the audio conditioning operations described above. The middle section  305  may include such electronic circuits as needed to perform such operations, and may contain a battery to supply power to the microphone  304  and such other electronic circuits. 
       FIG.  3 B  shows a second embodiment of a wearable device  320  that may use self-mixing interferometry sensors as part of detecting user inputs. The wearable device  320  is a headphone device  320  that may fit on a user&#39;s head  322 . The headphone device  320  includes at least one over-ear speaker cup  326 . The headphone device  320  is attached to the user&#39;s head  322  by a flexible band  328 . 
     The headphone device  320  may include multiple self-mixing interferometry sensors  324   a - d  to detect skin deformations at multiple locations on the user&#39;s head  322 . Multiple self-mixing interferometry sensors may allow for correlation of their respective self-mixing interferometry signals during a user&#39;s voiced commands or silent gesture commands. The particular configuration of the self-mixing interferometry sensors  324   a - d  is exemplary, and is not to be construed as limiting. 
     The flexible band  328  includes the self-mixing interferometry sensor  324   a , and is configured to direct a light beam emitted by the self-mixing interferometry sensor  324   a  toward a portion of the scalp or skin of the user  322  that is proximate to the parietal bone of the skull of the user  322 . Audible speech by the user  322  may cause vibrations in the user&#39;s skull that travel to the parietal bone, which may in turn induce skin vibrations at the location at which the self-mixing interferometry sensor  324   a  directs its beam of light. 
     The self-mixing interferometry sensor  324   b  may be located in the over-ear speaker cup  326  and be positioned so that its emitted beam of light is directed to skin proximate to the temporomandibular joint (TMJ). The user  322  may use jaw and tongue motions to form speech, either audibly by exhaling, or inaudibly by not exhaling, during the jaw and tongue motions. In either case, a corresponding motion at the TMJ can cause a skin deformation that can be detected by the self-mixing interferometry sensor  324   b . Thus the signal of self-mixing interferometry sensor  324   b  may be used in detection of both or either of voiced commands and silent gesture user inputs. Further, a user&#39;s particular jaw motions that are not related to a speech or human sound may be used as a source of inputs. For example, jaw motions to the right or left, or up or down, may be detectable and interpretable as specific inputs. 
     The self-mixing interferometry sensor  324   c  may be located in the over-ear speaker cup  326  and be positioned so that its emitted beam of light is directed to skin proximate to the temporal bone of the user  322 . Audible speech by the user  322  may cause vibrations in the user&#39;s skull that travel to the temporal bone, which may in turn induce skin vibrations at the location at which the self-mixing interferometry sensor  324   c  directs its beam of light. 
     The self-mixing interferometry sensor  324   d  may be located in the over-ear speaker cup  326 , and may be positioned so that its emitted beam of light is directed to a location in the ear of the user  322 , such as the location  308  in the ear described above in relation to the earbud  300 . As described above, audible speech by a user may induce skin vibrations at that location which may be detected by the self-mixing interferometry sensor  324   d.    
     The headphone device  320  may make use of any combination of self-mixing interferometry signals of the self-mixing interferometry sensors  324   a - d . The headphone device  320  may contain a command interpreter and at least one of a bioauthentication circuit and an audio conditioning circuit, as described previously. 
     Though only the right side over-ear speaker cup  326  is described, one skilled in the art will recognize that the headphone device  320  may include a similar over-ear speaker cup for the user&#39;s left side. The left side over-ear speaker cup may have the same, more, or fewer self-mixing interferometry sensors than the four shown for the right side over-ear speaker cup  326 . Also, one skilled in the art will also recognize the right side over-ear speaker cup  326  may itself have more or fewer than the four self-mixing interferometry sensors  324   a - d  shown and described. 
     The headphone device  320  may detect the user&#39;s voiced commands from skin deformation information in the signals of the four self-mixing interferometry sensors  324   a - d . The headphone device  320  may contain transmitter circuitry that allows the headphone device  320  to send the voiced commands to another device. Thus the headphone device may not need to include a dedicated microphone. 
     A third embodiment of a wearable device that may use self-mixing interferometry sensors as part of detecting user inputs is an eyeglass frame. A self-mixing interferometry sensor may be located on an arm of the eyeglass frame and be positioned to emit its beam of light toward a location on a user&#39;s head proximate to the temporal bone. As already described, audible speech by the user may induce skin vibrations at the location that may be detectable by the self-mixing interferometry sensor. 
     As described above, information in the detected skin vibration may be used by a command interpreter to determine a voiced command user input. The self-mixing interferometry sensor may be part of a configuration that includes a command interpreter and a transmitting circuit, such as in the configurations described in relation to  FIGS.  2 A-C . The eyeglass frame may also include at least one of a bioauthentication circuit and an audio conditioning circuit, as previously described. 
     In a variation of this third embodiment, the eyeglass frame may include a self-mixing interferometry sensor located on the bridge connecting the two lenses, and positioned to direct its light toward the location on the skin over the frontal bone of the user. Voiced speech by the user may cause skin vibrations at the location that may be detected by the self-mixing interferometry sensor. The self-mixing interferometry sensor on the bridge may be in lieu of the self-mixing interferometry sensor on the arm, or in addition to it. 
     A fourth embodiment of a wearable device that may use self-mixing interferometry sensors as part of detecting user inputs, such as voiced commands or silent gesture user inputs, is an augmented reality/virtual reality (AR/VR) headset. Such an AR/VR headset may include visual display goggles positioned in front of the user&#39;s eyes. The AR/VR headset may include one or two over-ear speaker cups, as shown in  FIG.  3 B , to provide voice and audio input the user. Alternatively, the AR/VR headset may include an earbud component, such as the earbud  300  of  FIG.  3 A  to provide voice and audio input to the user. 
     The AR/VR headset may include multiple self-mixing interferometry sensors. One self-mixing interferometry sensor may be positioned on the visual display goggles to direct its beam of light toward the skin of the user&#39;s head overlying the frontal bone. 
     Another self-mixing interferometry sensor may be located in a flexible strap that extends over the top of the user&#39;s head, and be positioned to direct its beam of light toward a location on the user&#39;s head proximate to the parietal bone. For example, this self-mixing interferometry sensor may be positioned as shown for self-mixing interferometry sensor  324   a  in  FIG.  3 B . 
     The AR/VR headset may have a flexible strap that extends horizontally around the user&#39;s head and attaches to the visual display goggles. Another self-mixing interferometry sensor may be positioned on such a horizontal flexible strap so that its beam of light is directed toward a location on the user&#39;s head proximate to the temporal bone. 
     In embodiments of AR/VR headsets that use earbuds similar to earbud device  300  for voice and audio input to the user, the earbud may include a self-mixing interferometry sensor similarly positioned and operable as the self-mixing interferometry sensor  306  in  FIG.  3 A . The earbud may also be equipped with a microphone, such as microphone  304  of  FIG.  3 A . 
     In embodiments of AR/VR headsets that use at least one over-ear speaker cup similar to over-ear speaker cup  326 , the over-ear speaker cup may include self-mixing interferometry sensors similarly positioned and operable as self-mixing interferometry sensors  324   b - d . The over-ear speaker cup may have more or fewer than three self-mixing interferometry sensors. 
     The self-mixing interferometry sensors of the various embodiments may make use of laser diodes to produce laser light as the emitted beam of light. The reflections of the beam of light may induce self-mixing interference in the lasing cavity. The self-mixing interferometry signal arising from the self-mixing interference may be of an electrical or optical parameter of the laser diode itself, or may be of a photodiode (PD) associated with, or part of, the laser diode. Specific details about, and configurations of, vertical cavity, surface emitting laser (VCSEL) diodes will be presented below in relation to  FIGS.  4 A-D . However, other types of laser diodes may be used in a self-mixing interferometry sensor, such as edge emitting lasers, quantum cascade lasers, quantum dot lasers, or another type. While the exemplary embodiments for detecting user input are described below as including both laser diodes and associated PDs, other embodiments may not include an PD. In such other embodiments, the measured interferometric parameter used to determine distance or displacement may be a parameter of the laser diode itself, such as a junction voltage or current, a power level, or another parameter. 
       FIGS.  4 A-D  show exemplary configurations or structures of VCSEL diodes and associated photodetectors (PDs) that may be included in the self-mixing interferometry sensors of various embodiments of wearable devices. Such self-mixing interferometry sensors may be used as the source of the beam of light emitted by a self-mixing interferometry sensor in a wearable electronic device, such as the four particular embodiments of wearable devices described above. These configurations are exemplary, and should not be construed as limiting. 
       FIG.  4 A  shows a structure  400  for a VCSEL diode with an intrinsic (or “integrated”) intra-cavity PD. The structure  400  can be formed in a single semiconductor wafer, and includes a VCSEL diode having an active gain region  404 . At forward bias, a bias current  402  I BIAS  flows through the VCSEL diode to cause it to emit laser light  406  from its top surface. A photodetector  410  can be embedded in the bottom distributed Bragg reflector mirror of the VCSEL diode to detect the laser light, including laser light that has undergone self-mixing interference (SMI). The photodetector (PD)  410  may be implemented as a resonant cavity photodetector (RCPD) with a resonance wavelength that is matched to the emission wavelength of the laser. There may be an etch stop layer  408  forming a boundary between the VCSEL diode lasing cavity and the PD  410 . During emission of laser light  406 , in the case that the PD  410  is a resonant cavity photodetector, the PD  410  is reversed biased so that a photodetector current  412  I PD  flows from the resonant cavity PD  410 . 
     During emission of the laser light  406 , SMI may occur due to reception in the cavity of reflections of the laser light  406 . The SMI may cause variations in the photodetector current  412  I PD  that correlate with distance or displacement to the location on a user&#39;s head at which the reflections arise. 
       FIG.  4 B  shows a structure  420  for part of a self-mixing interferometry sensor in which VCSEL diode  422  is used in conjunction with an extrinsic PD  430  located on a separate chip within a self-mixing interferometry sensor. The VCSEL diode  422  emits a beam of laser light  426   a . The emitted beam of laser light  426   a  may traverse a beam splitter and be directed by components of a focusing system toward location on the user&#39;s head. Reflections of the emitted beam of laser light  426   a  from the location may be received back into the VCSEL diode  422  and cause SMI. The SMI alters a property of the emitted beam of laser light  426   a , such as the optical power, to a new steady state value. 
     Some of the altered beam of emitted beam of laser light  426   a  is diverted by the beam splitter  424  to become the diverted beam of laser light  426   b  that is received by the PD  430 . The distance between the VCSEL diode  422  and the beam splitter  424  may be on the order of 100 to 250 μm, though this is not required. The PD  430  may include a bandpass filter  428  to eliminate light at wavelengths different from that of the diverted beam of laser light  426   b . An interferometric parameter, such as current, of the PD  430  may be monitored, and variations therein used by other components or circuits of the self-mixing interferometry sensor to determine distances from the self-mixing interferometry sensor to a reflection source, such as a location on a head of a user of the wearable electronic device. 
       FIG.  4 C  shows a structure  440  for part of a self-mixing interferometry sensor having VCSEL diode  442  and an extrinsic, on-chip PD  456 . The PD  456  may be a RCPD as described above. The RCPD  456  may form an annular disk around the VCSEL diode  442 . In the structure  440 , the RCPD  456  may be positioned over associated reverse biased VCSEL diode  450  having a quantum wells at layer  452  in order to make the fabrication process easier. In other embodiments, reverse biased VCSELs may not exist and the RCPD could be in direct contact with the substrate on which the VCSEL is located. 
     In operation, the VCSEL diode  442  is forward biased so that it emits laser light beam  446 , and bias current, I BIAS ,  444  flows through it. The associated VCSEL diode  450  is reverse biased to prevent it from lasing. The laser light beam  446  may be directed toward a location on the user&#39;s head. The laser beam of light may be reflected from the location on the user&#39;s head during the emission, and cause SMI in the VCSEL diode  442  that alters the optical power of the emitted laser light beam  446 . Reflections of the altered emitted laser light beam  446  may be diverted by the beam splitter  448  and received by the RCPD  456 . During emission of the laser light, the RCPD  456  is reverse biased and produces photodiode current, I PD ,  454 . The photodiode current  454  is generated in response to the laser light  446  partially reflected from the beam splitter  448 . The photodiode current  454  may vary due to the SMI and such variation may be used to determine distances to a reflection source, such as a location on a head of a user of the wearable electronic device. 
       FIG.  4 D  shows a structure  460  for part of a self-mixing interferometry sensor having dual emitting VCSEL diode  462  and an extrinsic, off-chip PD  470 . During forward bias, a bias current, I BIAS    464 , flows and the dual emitting VCSEL diode  462  emits a beam of laser light  466  from its top surface, which can be directed by components or circuits of a self-mixing interferometry sensor toward a location on a user&#39;s head during emission. The dual emitting VCSEL diode  462  also emits a second beam of laser light  468  from a bottom surface toward a PD  470 . The dual emitting VCSEL diode  462  may be formed in a first semiconductor chip and joined to another chip in which the PD  470  is formed, with the joining such that the second beam of laser light  468  enters the PD  470 . A connecting layer  472  between the two chips may allow the second beam of laser light  468  to be transmitted to the PD  470 . 
     As in the previous structures, the first beam of laser light  466  may be reflected from the location on the user&#39;s head, with the reflections causing SMI in the VCSEL diode  462 . The SMI may alter both the first beam of laser light  466  and the second beam of laser light  468 . The alteration may cause a correlated change in an interferometric parameter of the structure  460 , such as the photodetector current, I PD ,  474  in the PD  470 . Distances or displacements to the location on the user&#39;s head may be determined using the correlated changes, such as described in relation to  FIGS.  7 A- 10    below. 
       FIGS.  5  and  6    each show a pair of respective time-correlated graphs between a self-mixing interferometry signal and a corresponding short-time Fourier transform (STFT) of that signal. These figures illustrate how the wearable devices that make use of self-mixing interferometry sensors can detect time intervals during which the user is likely to be making a voiced command or a silent gesture input. Detecting such time intervals is useful in both bioauthentication operations and for audio conditioning operations, as described above. 
       FIG.  5    shows two exemplary time-correlated graphs  500  related to a self-mixing interferometry signal produced when a user is speaking. The top graph  502  shows an electronic output of the SMI signal itself, which may be photodetector output current or voltage, or an interferometric parameter of a laser diode, such as an optical power or bias current. The SMI signal includes voice pattern components that extend above approximately 10 mV. The SMI signal also includes a time interval  504  during which the user does not speak, so that the SMI signal only includes a background noise floor. On each side of the time interval  504  are representative speech events, shown in boxes. 
     The bottom graph  508  shows an amplitude plot of a short-time Fourier transform (STFT) of the SMI signal. During the time interval  504 , the amplitude is below a noise threshold  505 , whereas during the representative speech events the amplitude exceeds the noise threshold  505 . 
     As described above in relation to  FIGS.  2 A-C , time intervals during which the user is speaking or silent are used in bioauthentication operations and audio conditioning operations. Such operations may thus apply a STFT to an SMI signal as part of determining that the user is giving a voiced command. 
       FIG.  6    shows two exemplary time-correlated graphs  600  related to a self-mixing interferometry signal produced by skin deformations due to jaw motion, such as at a TMJ. The top graph  602  shows an electronic output of the SMI signal itself, which may be photodetector output current or voltage, or an interferometric parameter of a laser diode, such as an optical power or bias current. The SMI signal includes pronounced spikes in amplitude at jaw motion events, such as jaw motion event  603   a.    
     The bottom graph  604  shows an amplitude plot of a STFT of the SMI signal. During the jaw motion event  603   a , the STFT shows a pronounced peak  603   b  that extends above a noise floor  605  so a user&#39;s jaw motion events may be distinguished from background noise. Bioauthentication and/or audio conditioning operations may apply a STFT to the SMI as part of determining silent gesture commands made by jaw motion of the user. 
       FIGS.  7 A-C  illustrate properties of self-mixing interference of coherent light emitted from a light source. The explanations are intended only to describe certain aspects of self-mixing interference needed to understand the disclosed embodiments. Other aspects of self-mixing interference will be clear to one skilled in the art. 
       FIG.  7 A  illustrates an exemplary configuration of a laser light source  700 , specifically a VCSEL diode  700 , that may be used as part of a self-mixing interferometry sensor. In any type of laser, an input energy source causes a gain material within a cavity to emit coherent 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 location on the surface of a user&#39;s head). 
     In the VCSEL  700 , there are two mirrors  702  and  704  on opposite ends of a cavity  706 . The lasing occurs within the cavity  706 . In the VCSEL diode  700 , the two mirrors  702  and  704  may be implemented as distributed Bragg reflectors, which are alternating layers with high and low refractive indices. The cavity  706  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  710  can be emitted through the topmost layer or surface of VCSEL diode  700 . In some VCSEL diodes, the coherent light is emitted through the bottom layer. 
       FIG.  7 B  shows a functional diagram of self-mixing interference (or also “optical feedback”) with a laser. In  FIG.  7 B , the cavity  706  has been reoriented so that emitted laser light  710  is emitted from the cavity  706  to the right. The cavity  706  has a fixed length established at manufacture. The emitted laser light  710  travels away from the cavity  706  until it intersects or impinges on a target, which may be a location on a user&#39;s head, as in the embodiments described in relation to  FIGS.  3 A-B . The gap of distance L from the emission point through the mirror  704  of the emitted laser light  710  to the target is termed the feedback cavity  708 . The length L of the feedback cavity  708  is variable as the target can move with respect to the VCSEL diode  700 . 
     The emitted laser light  710  is reflected back into the cavity  706  by the target  716 . The reflected light  712  enters the cavity  706  to coherently interact with the original emitted laser light  710 . This results in a new steady state illustrated with the new emitted laser light  714 . The emitted laser light  714  at the new steady state may have characteristics (e.g., a wavelength or power) that differ from what the emitted laser light  710  would have in the absence of reflection and self-mixing interference. 
       FIG.  7 C  is a graph  720  showing the variation in power of the combined emitted laser light  714  as a function of the length L of the feedback cavity  708 , i.e., the distance from the emission point through the mirror  704  of the emitted laser light  710  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: ΔP∝cos(4πL/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 an initially 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 range of the deflection may also be determined. 
     Though the graph  720  shows the variation in power of the combined emitted laser light  714  as a function of the length L of the feedback cavity  708 , similar results and/or graphs may hold for other interferometric properties of a VCSEL diode or other type laser diode that are measured by a self-mixing interferometry sensor. 
     Measurements of one or more interferometric parameters by a self-mixing interferometry sensor can be used to infer distances and/or displacements of the target  716  from the VCSEL  700 . These distance or displacement measurements can then be used to detect skin deformations or skin vibrations, as in the embodiments described above. A first family of embodiments uses a spectrum analysis of a signal of an interferometric parameter. A variation in the interferometric parameter is produced when an input signal (e.g., a bias current) of the laser diode is modulated with a triangle wave about a constant current value. The first family of embodiments is described in relation to  FIGS.  8 A-C . 
     A second family of embodiments uses time domain filtering and demodulation of a signal of an interferometric parameter. A variation in the interferometric parameter is produced when a bias current of the laser diode is modulated with a sine wave about a constant current value. The second family of embodiments is described in relation to  FIGS.  9 A-C  and  10 . 
     In regard to the first family of embodiments,  FIG.  8 A  is a flowchart of a spectrum analysis method  800  for determining distances from an self-mixing interferometry sensor to a location on a user&#39;s head. The spectrum analysis method  800  involves applying a triangle wave modulation to a bias current of a laser diode, and applying separate spectrum analyses to the signal of an interferometric parameter obtained during the rising time interval of the triangle wave modulation and to the signal of the interferometric parameter obtained during the falling time interval of the triangle wave modulation. The signal of the interferometric property may be an output signal of a photodetector, such as an output current or voltage, or it may be a signal of an interferometric parameter of the VCSEL itself. 
       FIG.  8 B  shows three time correlated graphs  860  relating a triangle modulated laser bias current  862  with the resulting laser wavelength  864  and the resulting signal  866  of the measured interferometric parameter. The graphs  860  in  FIG.  8 B  correspond to a stationary target. While the laser bias current  862  is shown with equal ascending and descending time intervals, in some embodiments these time intervals may have different durations. The spectrum analysis methods may make use of both the laser bias current  862  and the signal  866  of the measured interferometric parameter. In the case of a non-stationary target, the observed frequencies in the resulting signal  866  would differ during the rising and falling time intervals of the bias current  862 . Distance and velocity can be obtained by a comparison of the two frequency values. 
     Returning to  FIG.  8 A , at stage  802  of the spectrum analysis method  800 , an initial signal is generated, such as by a digital or an analog signal generator. At stage  806   a  the generated initial signal is processed as needed to produce the triangle modulated laser bias current  862  that is applied to the VCSEL. The operations of stage  806   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 modulated laser bias current  862  to the VCSEL induces a signal  866  in the interferometric parameter. It will be assumed for simplicity of discussion that the signal  866  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  804  of the spectrum analysis method  800 , the signal  866  is received. At stage  806   b , initial processing of the signal  866  is performed as needed. Stage  806   b  may include high-pass filtering. 
     At stage  808  the processing unit may equalize the received signals, if necessary. For example the signal  866  may include a predominant triangle waveform component matching the triangle modulated laser bias current  862 , with a smaller and higher frequency component due to changes in the interferometric parameter. High-pass filtering may be applied to the signal  866  to obtain the component signal related to the interferometric parameter. Also, this stage may involve separating the parts of signal  866  and the triangle modulated laser bias current  862  corresponding to the ascending and to the descending time intervals of the triangle modulated laser bias current  862 . The operations may include sampling the separated information. 
     At stages  808  and  810 , a separate FFT is first performed on the parts of the processed form of signal  866  corresponding to the ascending and to the descending time intervals. Then the two FFT spectra are analyzed at stage  812 . 
     At stage  814 , 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. 
     At stage  816 , from the processed FFT spectra data, information regarding the skin deformation can be obtained, including an absolute distance, and/or a direction and velocity of the skin deformation or vibration at the location on the user&#39;s head. More specifically, the velocity is detected in the direction of the laser light. 
       FIG.  8 C  shows a block diagram of a system  890  that can implement the spectrum analysis just described in the spectrum analysis method  800 . In the exemplary system  890  shown, the system  890  includes generating an initial digital signal and processing it as needed to produce a triangle modulated laser bias current  862  as an input to a bias current of a VCSEL diode  893 . In an illustrative example, an initial step signal (not shown) 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  892   a . The resulting voltage signal may then be filtered by the low-pass filter  892   b  to remove quantization noise. Alternatively, an analog signal generator can be used to generate an equivalent triangle voltage signal directly. The filtered voltage signal then is an input to a voltage-to-current converter  892   c  to produce the desired triangle modulated laser bias current  862  in a form for input to the VCSEL diode  893 . 
     As described above, reflections from the location on the user&#39;s head can cause SMI in the VCSEL diode  893  that alter an interferometric parameter of the VCSEL diode  893 . This alteration in the interferometric parameter may be measured or inferred, either from a parameter of the VCSEL diode  893  itself or from a parameter of an associated photodetector. The changes can be measured to produce a signal  866 . In the system  890  shown it will be assumed the signal  866  is measured by a photodetector. For the triangle modulated laser bias current  862 , the signal  866  may be a triangle wave of similar period combined with a smaller and higher frequency signal related to the changes in the interferometric parameter. 
     The signal  866  is first passed into the high-pass filter  895   a , which can effectively convert the major ascending and descending ramp components of the signal  866  to DC offsets. As the signal  866  from a photodetector may be a current signal, the transimpedance amplifier  895   b  can produce a corresponding voltage output for further processing. 
     The voltage output can then be sampled and quantized by the analog-to-digital conversion (ADC) block  895   c . Before immediately applying a digital FFT to the output of the ADC block  895   c , it can be helpful to apply equalization in order to clear remaining residue of the triangle signal received by the photodiode, and thus isolate the interferometric signal. The initial digital signal values from the digital generator used to produce the triangle modulated laser bias current  862  are used as input to the digital high pass filter  894   a  to produce a digital signal to correlate with the output of the ADC block  895   c . An adjustable gain can be applied by the digital variable gain block  894   b  to the output of the digital high pass filter  894   a.    
     The output of the digital variable gain block  894   b  is used as one input to the digital equalizer and subtractor block  896 . The other input to the digital equalizer and subtractor block  896  is the output of the ADC block  895   c . The two signals are differenced, and used as part of a feedback to adjust the gain provided by the digital variable gain block  894   ba.    
     Once an optimal correlation is obtained by the feedback, an FFT, indicated by block  897 , can then be applied to the components of the output of the ADC block  895   c  corresponding to the rising and descending of the triangle wave. From the FFT spectra obtained, movement of the location on the user&#39;s head can be inferred, as discussed above and indicated by block  898 . 
     The second family of embodiments of devices and methods for recognizing a user input or command based on skin deformation or skin vibration directly obtains distance or displacement measurements from the signal of an interferometric parameter and using a time domain based analysis. This family is described in relation to  FIGS.  9 A-C  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 second family of embodiments, a laser light source, such any of the VCSELs described in  FIGS.  4 A-D , is used to direct laser light toward the location on the user&#39;s head. For simplicity of explanation only for this family of embodiments, the laser light source(s) will be assumed to be VCSEL(s). One skilled in the art will recognize how the embodiments may make use of other types of lasers or light sources that undergo self-mixing interference. In this second 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 diode is received back into the VCSEL diode after reflection from a target. In some embodiments, the photodetector is integrated as part of the VCSEL, such as in  FIG.  4 A . In other embodiments, the photodetector may be separate from the VCSEL, as in  FIG.  4 B . Instead of, or in addition to, an output of such a photodetector, some embodiments may measure another interferometric property of the VCSEL diode, such as a junction voltage. 
     The self-mixing interference effect contains at least two contributions: a first contribution from internal an electric field existing within the VCSEL diode and a second contribution from reflections from the target coupled back into the VCSEL diode, as indicated in  FIG.  4 B . 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 diode 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 diode is driven with such a bias current, the phase of the optical feedback light returning from the target upon reflection is such that Δφ∝a+b sin(ω m t), for constants a and b. Certain specific forms for constants a and b for some embodiments will be presented below. 
     When the two contributions coherently interfere inside the laser cavity, 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)] in response to the similarly evolving optical output power of the VCSEL diode. 
     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  FIGS.  9 A-C  and  10  below. 
     For a target that had an initial distance L 0  from the VCSEL diode, and which has undergone a displacement of ΔL from L 0 , the constants a and b above in some cases are given by:
 
 a =[4π( L   0   +ΔL )/λ], and  b =[−4πΔλ( L   0   +ΔL )/λ 2 ].
 
     Certain specific forms of the expansion for I PD  may thus be given by: 
     
       
         
           
             
               I 
               PD 
             
             ∝ 
             
               
                 Baseband 
                 ⁢ 
                     
                 Signal 
               
               - 
               
                 2 
                 ⁢ 
                 
                   
                     J 
                     1 
                   
                   [ 
                   
                     
                       
                         
                           - 
                           4 
                         
                         ⁢ 
                         πΔ 
                         ⁢ 
                         λ 
                         ⁢ 
                         
                           L 
                           0 
                         
                       
                       
                         λ 
                         2 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             Δ 
                             ⁢ 
                             L 
                           
                           
                             L 
                             0 
                           
                         
                       
                       ) 
                     
                   
                   ] 
                 
                 ⁢ 
                 
                   sin 
                   ⁡ 
                   ( 
                   
                     
                       4 
                       ⁢ 
                       π 
                       ⁢ 
                       Δ 
                       ⁢ 
                       L 
                     
                     λ 
                   
                   ) 
                 
                 ⁢ 
                 
                   sin 
                   ⁡ 
                   ( 
                   
                     
                       ω 
                       m 
                     
                     ⁢ 
                     t 
                   
                   ) 
                 
               
               + 
               
                 2 
                 ⁢ 
                 
                   
                     J 
                     2 
                   
                   [ 
                   
                     
                       
                         
                           - 
                           4 
                         
                         ⁢ 
                         π 
                         ⁢ 
                         Δ 
                         ⁢ 
                         λ 
                         ⁢ 
                         
                           L 
                           0 
                         
                       
                       
                         λ 
                         2 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             Δ 
                             ⁢ 
                             L 
                           
                           
                             L 
                             0 
                           
                         
                       
                       ) 
                     
                   
                   ] 
                 
                 ⁢ 
                 
                   cos 
                   ⁡ 
                   ( 
                   
                     
                       4 
                       ⁢ 
                       π 
                       ⁢ 
                       Δ 
                       ⁢ 
                       L 
                     
                     λ 
                   
                   ) 
                 
                 ⁢ 
                 
                   cos 
                   ⁡ 
                   ( 
                   
                     2 
                     ⁢ 
                     
                       ω 
                       m 
                     
                     ⁢ 
                     t 
                   
                   ) 
                 
               
               - 
               
                 2 
                 ⁢ 
                 
                   
                     J 
                     3 
                   
                   [ 
                   
                     
                       
                         
                           - 
                           4 
                         
                         ⁢ 
                         π 
                         ⁢ 
                         Δ 
                         ⁢ 
                         λ 
                         ⁢ 
                         
                           L 
                           0 
                         
                       
                       
                         λ 
                         2 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             Δ 
                             ⁢ 
                             L 
                           
                           
                             L 
                             0 
                           
                         
                       
                       ) 
                     
                   
                   ] 
                 
                 ⁢ 
                 
                   sin 
                   ⁡ 
                   ( 
                   
                     
                       4 
                       ⁢ 
                       π 
                       ⁢ 
                       Δ 
                       ⁢ 
                       L 
                     
                     λ 
                   
                   ) 
                 
                 ⁢ 
                 
                   sin 
                   ⁡ 
                   ( 
                   
                     3 
                     ⁢ 
                     
                       ω 
                       m 
                     
                     ⁢ 
                     t 
                   
                   ) 
                 
               
               + 
               … 
             
           
         
       
     
     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(βω 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 ω m  applied to the VCSEL diode 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.  9 A-C  and  FIG.  10   .  FIG.  9 A  is a flow chart of a method  900  for detecting skin deformation and/or skin vibration surface, using distance or displacement measurements. 
     At block  902 , the modulation waveform for the bias current to the VCSEL diode is generated. The generation may involve separately generating a direct current (DC) input signal and a sine wave current input signal with desired modulation frequency ω m  (in radians), and then summing the two signals to produce I BIAS . The two input signals can be generated either by current sources, or from voltage sources that produce I BIAS . The generation of the two input signals may initially begin using one or more digital generators, such as digital-to-analog (DAC) converters. 
     At block  904 , the generated modulation waveform may be filtered to reduce signal frequency components not at the desired modulation frequency ω m . Such filtering may be a digital filtering applied to a digital sine wave source, or an analog filtering of an analog sine wave current input signal. Filtering may also be applied to the DC signal source before being summed with the sine wave current input signal. 
     The generated modulation waveform is applied to I BIAS , modifying the VCSEL diode&#39;s emitted laser light accordingly. Self-mixing interference then may occur due to reflections from the location on the user&#39;s head. 
     At block  906 , a photodetector receives the VCSEL diode&#39;s laser light, and a corresponding signal produced. The signal may be a photodetector current, a voltage of the photodetector, or another interferometric property. Further, as explained above, the photodetector may be integrated with the VCSEL diode itself. 
     Because the bias current of the VCSEL diode was modulated at desired modulation frequency ωm, it may well be that the received photodetector signal also has a frequency component at ω m . At block  908 , a scaled version of the modulated form of I BIAS  and received photodetector signal may be differenced in a differential filtering to reduce cross-talk or other interferences. The result may be a differenced signal that correlates with the self-mixing interference in the VCSEL diode&#39;s laser light. 
     At block  910 , an I and a Q component of the filtered form of the photodetector signal are then extracted. These extractions may be performed by separate mixing (multiplying) of the filtered form of the photodetector signal with separately generated sinusoidal signals at respective frequencies ω m  and 2ω m , as discussed above. Alternatively, the modifications discussed above based on using either Q′ or I′ may be used. The mixed signals are then separately low pass filtered. 
     At block  912 , the phase of the I and Q components may be calculated using unwrapping arctan function, as described above. An alternative method of obtaining the phase may also be used. At block  914 , the displacement is determined based on the phase, as described above. 
       FIGS.  9 B-C  show two time correlated graphs:  920 ,  930 . Graph  920  shows a plot  922  of a bias current I BIAS  of a VCSEL diode 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 used in all embodiments. The bias current I BIAS  has its sinusoidal variation about a fixed direct current value,  924 . 
     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  932  in the graph  930 . The time axes of graphs  926  and  936  are correlated. The plot  932  illustrates that the output current of the photodetector varies around a fixed direct current value  934 . 
     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 as described, and may produce bias currents and respective photodetector currents having respective plots similar to  922  and  932 . 
       FIG.  10    shows an exemplary circuit block diagram that may be used to implement the third family 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 relationships 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 diode  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 diode  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 diode  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: i PD =i 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) block  1020 . Further, the output of the ADC block  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 block  1020 . The filtered output on link  1021  may have the form A+B sin(ω m t)+C cos(2ω m t)+D sin(3ω 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 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 block  1020  on link  1021 . This product is then 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 entire 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. 
     In additional and/or alternative embodiments, the I/Q time domain based methods just described may be used with the spectrum based methods of the first family of embodiments. The spectrum methods of the first family can be used at certain times to determine the absolute distance to the target, and provide a value of L 0 . Thereafter, during subsequent time intervals, any of the various I/Q methods just described may be used to determine ΔL. 
     In additional and/or alternative embodiments, the spectrum methods based on triangle wave modulation of a bias current of a VCSEL may be used as a guide for the I/Q time domain methods. The I/Q methods operate optimally in the case that J 1 (b)=J 2 (b), so that the I and Q components have the same amplitude. However, b depends on the distance L. An embodiment may apply a triangle wave modulation to the VCSEL&#39;s bias current to determine a distance to a point of interest. Then this distance is used find the optimal peak-to-peak sinusoidal modulation of the bias current to use in an I/Q approach. Such a dual method approach may provide improved signal-to-noise ratio and displacement accuracy obtained from the I/Q method. 
     Referring now to  FIG.  11   , there is shown an exemplary structural block diagram of components of an electronic device  1100 , such as the embodiments described above. The block diagram is exemplary only; various embodiments described above may be implemented using other structural components and configurations. The electronic device  1100  can include one or more processors or processing unit(s)  1102 , storage or memory components  1104 , a power source  1106 , a display  1108  (which may display or indicate an operating status, or display the image being projected in an AR/VR system), an input/output interface  1110 , one or more sensors such as microphones, a network communication interface  1114 , and one or more self-mixing interferometry (SMI) sensors  1112 , as described above. Either of the display  1108  or the input/output interface  1110  may include input touch screens, buttons, sliders, indicator lights, etc., by which a user can control operation of the electronic device  1100 . These various components will now be discussed in turn below. 
     The one or more processors or processing units  1102  can control some or all of the operations of the electronic device  1100 . The processor(s)  1102  can communicate, either directly or indirectly, with substantially all of the components of the electronic device  1100 . In various embodiments, the processing units  1102  may receive the self-mixing interferometry signals from the SMI sensors  1112 , such as self-mixing interferometry signals from any or all of the photodetectors, VCSELs, and other electronics of the imaging and SMI sensors  1112 . Such signals may include those that correspond to the interferometric parameters, and perform any of the methods, or parts of the methods, discussed above. 
     For example, one or more system buses  1118  or other communication mechanisms can provide communication between the processor(s) or processing units  1102 , the storage or memory components  1104  (or just “memory”), the power source  1106 , the display  1108 , the input/output interface  1110 , the SMI sensor(s)  1112 , the network communication interface  1114 , and the microphone(s)  1116 . The processor(s) or processing units  1102  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  1102  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  1104  can store electronic data that can be used by the electronic device  1100 . For example, the memory  1104  can store electrical data or content such as, for example, audio files, document files, timing signals, algorithms, and image data. The memory  1104  can be configured as any type of memory. By way of example only, memory  1104  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  1106  can be implemented with any device capable of providing energy to the electronic device  1100 . For the wearable electronic devices described above, the power source  1106  can be a battery, such as a lithium, alkali, or other type. 
     The display  1108  may provide an image or video output for certain of the electronic devices  1100 , such as the AR/VR systems described above. The display  1108  can be any appropriate size for a wearable electronic device. The display  1108  may also function as a user touch input surface, in addition to displaying output from the electronic device  1100 . In these embodiments, a user may press on the display  1108  or gesture toward a portion of the image projected in the AR/VR system in order to provide user input to the electronic device  1100 . Such user inputs may be in addition to the user inputs based on the detection skin deformations and skin vibrations described above. 
     The input/output interface  1110  can be configured to allow a user to provide settings or other inputs to the various embodiments described above. For example, the electronic device  1100  may include one or more user settable switches or buttons, such as to adjust a volume. The input/output interface  1110  may also be configured with one or more indicator lights to provide a user with information related to operational status of the electronic device. 
     In addition to the SMI sensors  1112 , the electronic device  1100  may include one or more microphones  1116 , as described in relation to  FIGS.  2 B-C . Examples of microphones include, but are not limited to, piezoelectric, condenser, ribbon, and other technologies known to one skilled in the art. 
     The network communication interface  1114  can facilitate transmission of data to a user or to other electronic devices. For example, the network communication interface  1114  can receive data from a network or send and transmit electronic signals via a wireless connection. Examples of wireless connections include, but are not limited to, Bluetooth, WiFi, or another technology. In one or more embodiments, the network communication interface  1114  supports multiple network or communication mechanisms. For example, the network communication interface  1114  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. 
     Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. As used herein, the phrase “at least one of” preceding a series of items, with the term “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list. The phrase “at least one of” does not require selection of at least one of each item listed; rather, the phrase allows a meaning that includes at a minimum one of any of the items, and/or at a minimum one of any combination of the items, and/or at a minimum one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or one or more of each of A, B, and C. Similarly, it may be appreciated that an order of elements presented for a conjunctive or disjunctive list provided herein should not be construed as limiting the disclosure to only that order provided. Further, the term “exemplary” does not mean that the described example is preferred or better than other examples. 
     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. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20220824
Publication Date: 20240220
Grant Date: 20240220
Priority Date: 20190524
Inventors: Mutlu, Mehmet
CIHAN, AHMET FATIH
Assignee: APPLE INC
CPC Classifications: [{"code": "G01B9/02092", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/017", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/167", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R1/1091", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/13", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01B11/161", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01B9/02092", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04R5/033", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/011", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/012", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/017", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/167", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/017", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R2460/13", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R1/1091", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/167", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 73456712