PATENT DOCUMENT

Publication Number: US-11422638-B2
Application Number: US-202016883390-A
Country: US
Kind Code: B2

Title: Input devices that use self-mixing interferometry to determine movement within an enclosure

Abstract:
An input device includes an enclosure defining a three-dimensional input space and one or more self-mixing interferometry sensors coupled to the enclosure and configured to produce a self-mixing interferometry signal resulting from reflection of backscatter of emitted light by a body part in the three-dimensional input space. In various examples, movement of the body part may be determined using the self-mixing interferometry signal, which may in turn be used to determine an input. In some examples, a body part displacement or a body part speed and an absolute distance to the body part may be determined using the self-mixing interferometry signal and used to determine an input. In a number of examples, multiple self-mixing interferometry sensors may be used and the movement may be determined by analyzing differences between the respective produced self-mixing interferometry signals.

Claims:
What is claimed is: 
     
       1. An input device, comprising:
 an enclosure defining a three-dimensional input space; 
 a self-mixing interferometry sensor coupled to the enclosure and configured to emit a beam of coherent light from an optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a reflection or backscatter of the beam into the optical resonant cavity, and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity; and 
 a processor configured to: 
 determine a body part displacement or a body part speed and an absolute distance to the body part using the self-mixing interferometry signal; 
 determine an input using the body part displacement or the body part speed and the absolute distance, the input corresponding to a touch of the body part to an object; and 
 estimate an amount of force exerted on the object by the body part. 
 
     
     
       2. The input device of  claim 1 , wherein the body part is a finger or a thumb. 
     
     
       3. The input device of  claim 1 , wherein the input corresponds to a virtual keyboard. 
     
     
       4. The input device of  claim 1 , wherein the self-mixing interferometry sensor is configured to emit the beam at an oblique angle with respect to a wall of the enclosure. 
     
     
       5. The input device of  claim 1 , wherein the self-mixing interferometry sensor is configured to emit the beam normal with respect to a wall of the enclosure. 
     
     
       6. The input device of  claim 1 , wherein the enclosure is configured to be mounted on the body part. 
     
     
       7. The input device of  claim 1 , wherein the enclosure is configured to provide a gap between the self-mixing interferometry sensor and the body part. 
     
     
       8. An input device, comprising:
 an enclosure defining a three-dimensional input space; 
 a first self-mixing interferometry sensor coupled to the enclosure and configured to emit a first coherent light beam from a first optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a first reflection or backscatter of the first coherent light beam into the first optical resonant cavity, and produce a first self-mixing interferometry signal; 
 a second self-mixing interferometry sensor coupled to the enclosure and configured to emit a second coherent light beam from a second optical resonant cavity to illuminate the body part in the three-dimensional input space, receive a second reflection or backscatter of the second coherent light beam into the second optical resonant cavity, and produce a second self-mixing interferometry signal; and 
 a processor configured to: 
 determine movement of the body part by analyzing differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal; 
 screen out a false input using the differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal; and 
 determine an input using the movement. 
 
     
     
       9. The input device of  claim 8 , wherein the first self-mixing interferometry sensor and the second self-mixing interferometry sensor are positioned on opposing sides of the three-dimensional input space. 
     
     
       10. The input device of  claim 9 , wherein the movement comprises lateral movement of the body part between the first self-mixing interferometry sensor and the second self-mixing interferometry sensor. 
     
     
       11. The input device of  claim 8 , wherein the input corresponds to a force applied to a surface. 
     
     
       12. The input device of  claim 8 , wherein the first self-mixing interferometry sensor includes an optical component configured to tilt the first coherent light beam. 
     
     
       13. The input device of  claim 8 , wherein the movement corresponds to withdrawal of the body part from the enclosure. 
     
     
       14. An input device, comprising:
 an enclosure defining a three-dimensional input space; 
 a first self-mixing interferometry sensor coupled to the enclosure and configured to emit a first coherent light beam from a first optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a first reflection or backscatter of the first coherent light beam into the first optical resonant cavity, and produce a first self-mixing interferometry signal; 
 a second self-mixing interferometry sensor coupled to the enclosure and configured to emit a second coherent light beam from a second optical resonant cavity to illuminate the body part in the three-dimensional input space, receive a second reflection or backscatter of the second coherent light beam into the second optical resonant cavity, and produce a second self-mixing interferometry signal; and 
 a processor configured to: 
 determine movement of the body part by analyzing differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal; and 
 determine an input using the movement, the movement of the body part comprising deformation of a fingernail. 
 
     
     
       15. An input system, comprising:
 an enclosure defining a three-dimensional input space; 
 a self-mixing interferometry sensor coupled to the enclosure and configured to emit a beam of coherent light from an optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a reflection or backscatter of the beam into the optical resonant cavity, and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity; and 
 a processor configured to: 
 determine movement of the body part using the self-mixing interferometry signal; 
 determine an input using the movement, the input comprising selection of a virtual key of a virtual keyboard, the input corresponding to a touch of the body part to an object; and 
 estimate an amount of force exerted on the object by the body part. 
 
     
     
       16. The input system of  claim 15 , wherein:
 the self-mixing interferometry sensor is a component of a first electronic device; and 
 the processor is a component of a second electronic device that communicates with the first electronic device. 
 
     
     
       17. The input system of  claim 15 , wherein the processor:
 is a component of a first electronic device; and 
 transmits the input to a second electronic device. 
 
     
     
       18. The input system of  claim 15 , wherein the input comprises a press. 
     
     
       19. The input system of  claim 15 , wherein the movement comprises at least one of an expansion of the body part or a contraction of the body part. 
     
     
       20. The input system of  claim 15 , wherein the input corresponds to the movement of the body part along a surface.

Description:
This application is a nonprovisional of and claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 62/871,357, filed Jul. 8, 2019, the contents of which are incorporated herein by reference as if fully disclosed herein. 
    
    
     FIELD 
     The described embodiments relate generally to input devices. More particularly, the present embodiments relate to input devices that use self-mixing interferometry to determine movement within an enclosure. 
     BACKGROUND 
     Electronic devices use a variety of different input devices to obtain input from users. Examples of such input devices include keyboards, computer mice, track pads, touch screens, force sensors, touch sensors, track balls, microphones, buttons, dials, switches, sliders, cameras, and so on. 
     Different input devices are suited to different applications. For example, keyboards may not be suitable to use with portable devices. Many input devices may involve a user touching a surface that is configured to receive input, such as a touch screen. Such an input device may be less suited to applications where a user may be touching another surface. 
     SUMMARY 
     The present disclosure relates to an input device including an enclosure defining a three-dimensional input space and one or more self-mixing interferometry sensors coupled to the enclosure and configured to produce a self-mixing interferometry signal resulting from reflection of backscatter of emitted light by a body part in the three-dimensional input space. In various examples, movement of the body part may be determined using the self-mixing interferometry signal, which may in turn be used to determine an input. In some examples, a body part displacement or a body part speed and an absolute distance to the body part may be determined using the self-mixing interferometry signal and used to determine an input. In a number of examples, multiple self-mixing interferometry sensors may be used and the movement may be determined by analyzing differences between the respective produced self-mixing interferometry signals. 
     In various embodiments, an input device includes an enclosure defining a three-dimensional input space; a self-mixing interferometry sensor coupled to the enclosure and configured to emit a beam of coherent light from an optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a reflection or backscatter of the beam into the optical resonant cavity, and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity; and a processor. The processor is configured to determine a body part displacement or a body part speed and an absolute distance to the body part using the self-mixing interferometry signal, and determine an input using the body part displacement or the body part speed and the absolute distance. 
     In some examples, the input corresponds to a touch of the body part to an object. In various implementations of such examples, the processor estimates an amount of force exerted on the object by the body part. 
     In a number of examples, the self-mixing interferometry sensor is configured to emit the beam at an oblique angle with respect to a wall of the enclosure. In some examples, the self-mixing interferometry sensor is configured to emit the beam normal with respect to a wall of the enclosure. In a number of examples, the enclosure is configured to be mounted on the body part. In various examples, the enclosure is configured to provide a gap between the self-mixing interferometry sensor and the body part. 
     In some embodiments, an input device includes an enclosure defining a three-dimensional input space; a first self-mixing interferometry sensor coupled to the enclosure and configured to emit a first coherent light beam from a first optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a first reflection or backscatter of the first coherent light beam into the first optical resonant cavity, and produce a first self-mixing interferometry signal; a second self-mixing interferometry sensor coupled to the enclosure and configured to emit a second coherent light beam from a second optical resonant cavity to illuminate the body part in the three-dimensional input space, receive a second reflection or backscatter of the second coherent light beam into the second optical resonant cavity, and produce a second self-mixing interferometry signal; and a processor. The processor is configured to determine movement of the body part by analyzing differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal and determine an input using the movement. 
     In various examples, the first self-mixing interferometry sensor and the second self-mixing interferometry sensor are positioned on opposing sides of the three-dimensional input space. In some implementations of such examples, the movement is lateral movement of the body part between the first self-mixing interferometry sensor and the second self-mixing interferometry sensor. 
     In a number of examples, the processor screens out a false input using differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal. In various examples, the movement of the body part is deformation of a fingernail. In a number of examples, the first self-mixing interferometry sensor includes an optical component configured to tilt the first beam. In some examples, the movement corresponds to withdrawal of the body part from the enclosure. 
     In a number of embodiments, an input system includes an enclosure defining a three-dimensional input space; a self-mixing interferometry sensor coupled to the enclosure and configured to emit a beam of coherent light from an optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a reflection or backscatter of the beam into the optical resonant cavity, and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity; and a processor. The processor is configured to determine movement of the body part using the self-mixing interferometry signal and determine an input using the movement. 
     In some examples, the self-mixing interferometry sensor is a component of a first electronic device and the processor is a component of a second electronic device that communicates with the first electronic device. In various examples, the processor is a component of a first electronic device and transmits the input to a second electronic device. 
     In a number of examples, the input is selection of a virtual key of a virtual keyboard. In various examples, the movement is at least one of an expansion of the body part or a contraction of the body part. In some examples, the input corresponds to movement of the body part along a surface. 
    
    
     
       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. 1A  depicts a first example of an input device that uses self-mixing interferometry to determine movement within an enclosure. 
         FIG. 1B  depicts a top view of the input device of  FIG. 1A . 
         FIG. 1C  depicts an example configuration of a self-mixing interferometry sensor assembly that may be used in the input device of  FIG. 1A . 
         FIG. 1D  depicts an example block diagram illustrating example functional relationships between example components that may be used in the input device of  FIG. 1A . 
         FIG. 2A  depicts a second example of an input device that uses self-mixing interferometry to determine movement within an enclosure. 
         FIG. 2B  depicts a top view of the input device of  FIG. 2A . 
         FIG. 2C  depicts an example configuration of a self-mixing interferometry sensor assembly that may be used in the input device of  FIG. 2A . 
         FIG. 3  depicts a third example of an input device that uses self-mixing interferometry to determine movement within an enclosure. 
         FIG. 4A  depicts a speed profile of a press that may be measured by one or more of the input devices of  FIG. 1A, 2A , or  3  using self-mixing interferometry. 
         FIG. 4B  depicts a displacement profile of a press that may be measured by one or more of the input devices of  FIG. 1A, 2A , or  3  using self-mixing interferometry. 
         FIG. 4C  depicts a heart rate that may be measured by one or more of the input devices of  FIG. 1A, 2A , or  3  using self-mixing interferometry. 
         FIG. 5A  depicts a first example self-mixing interferometry sensor that may be used in one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 5B  depicts a second example self-mixing interferometry sensor that may be used in one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 5C  depicts a third example self-mixing interferometry sensor that may be used in one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 5D  depicts a fourth example self-mixing interferometry sensor that may be used in one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 6  depicts a direct current bias procedure for determining speed of an object using self-mixing interferometry. This procedure may be used by one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 7  depicts a first triangular bias procedure for determining velocity and absolute distance of an object using self-mixing interferometry. This procedure may be used by one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 8  depicts a second triangular bias procedure for determining velocity and absolute distance of an object using self-mixing interferometry. This procedure may be used by one or more of the input devices of  FIG. 1A, 2A , or  3 . 
         FIG. 9  depicts a sinusoidal bias procedure for determining displacement of an object using quadrature modulation with self-mixing interferometry. This procedure may be used by one or more of the input devices of  FIG. 1A, 2A , or  3 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The description that follows includes sample systems, methods, and computer program products that embody various elements of the present disclosure. However, it should be understood that the described disclosure may be practiced in a variety of forms in addition to those described herein. 
     An electronic device may use one or more sensors to detect movement of a body part (such as a finger, hand, and so on) and/or other object in order to determine input using that input. For example, the movement may correspond to one or more gestures, presses on a surface, force applied to a surface, sliding along a surface, and so on. Sensors used to detect such movement may include strain gauges, piezoelectric sensors, capacitive sensors, magnetic hall sensors, intensity-based optical sensors, and so on. However, many of these sensors may involve component configurations that are limiting for some applications. 
     For example, the above sensors may be challenging to use in implementations where input corresponds to movement of a finger, hand, and/or other body part that does not involve the body part contacting an input surface such as a physical key, a touch screen, and so on. By way of illustration, such an implementation may involve movement of a body part to interact with a virtual keyboard that is presented on a heads up display but is not physically present. Use of the above sensors in such an implementation may involve gloves or other cumbersome apparatuses that may prevent and/or impair a user&#39;s tactile interaction with the user&#39;s environment. 
     Further, strain gauges and/or piezoelectric sensors may not be able to operate without contact with the body part. In some cases, strain gauge and/or piezoelectric sensor implementations may involve tight contact with the body part. Capacitive sensors may not provide a linear response with varying sensor/target distance, may involve calibration, and may be subject to electromagnetic interference such that extensive shielding may be used. Magnetic hall sensors may be vulnerable to external magnetic fields. Intensity-based optical sensors may be influenced by background light and/or reflective properties of the body part (such as skin tone). Further, intensity-based optical sensors may use separate transmission and receiving paths and may not be able to provide a linear response and stable signal to noise ratio with varying distance. 
     Input devices that use one or more self-mixing interferometry sensors coupled to an enclosure to detect the movement of a body part within a three-dimensional input space defined by the enclosure may overcome the limitations of the above sensor implementations. In self-mixing interferometry, one or more beams of coherent or partially coherent light emitted by one or more stimulated emission sources (such as one or more vertical-cavity surface-emitting lasers or VCSELs, other lasers, and/or other coherent or partially coherent light sources) may be reflected or backscattered from an object and recoupled into the resonant cavity of the light source that emitted the coherent or partially coherent light. This recoupling may modify one or more interferometric parameters, such as a measurable phase-sensitive change in the resonant cavity electric field, carrier distribution, and/or other changes in the optical gain profile, lasing threshold, and so on of a laser to create a measurable change in the voltage on the laser junction (if the laser is being driven with a current source), a bias current on the laser (if the laser is being driven with a voltage source), and/or the optical power emitted by the laser. 
     The self-mixing interferometry signal may be analyzed in various ways to determine movement of the body part within the three-dimensional input space. For example, direct current laser bias and spectral analysis of the self-mixing interferometry signal that contains the Doppler shift of the reflected or backscattered light may be used to determine a body part speed without information on the direction of motion. By way of another example, triangular bias and spectral analysis of the subtracted self-mixing interferometry signal that contains the Doppler shift of the reflected or backscattered light may be used to determine the body part speed and absolute distance of the body part. By way of yet another example, sinusoidal bias current modulation and quadrature demodulation of the self-mixing interferometry signal that contains sine and cosine of the interferometric phase may be used to determine displacement. The input device may thus determine a variety of different inputs corresponding to different movement of the body part (such as movement within three-dimensional space, one or more gestures, presses to a surface, force applied to a surface, sliding along a surface, and so on) using the self-mixing interferometry signal. 
     Further, unlike strain gauges and/or piezoelectric sensors, the self-mixing interferometry sensor may be able to operate without tight or any contact with the body part. Unlike capacitive sensors, the self-mixing interferometry sensor may be capable of providing a linear response with varying sensor/target distance, may not require calibration, and may be immune to electromagnetic interference and thus not need extensive shielding. Unlike magnetic hall sensors, the self-mixing interferometry sensor may be immune to external magnetic fields. Unlike intensity-based optical sensors, the self-mixing interferometry sensor may not be influenced by background light, may not require separate transmission and receiving paths, may be independent of reflective properties of the body part, and may have a linear response and stable signal to noise ratio with varying distance. 
     As such, the input device may be configured with an enclosure and attached self-mixing interferometry sensor in more comfortable and convenient ways while allowing for detection of a wide variety of inputs. This may allow configurations where a user may directly touch objects within the user&#39;s environment, avoid constrictive apparatuses such as gloves, and so on while still enabling gathering of the data indicating the input. 
     The following disclosure relates to an input device including an enclosure defining a three-dimensional input space and one or more self-mixing interferometry sensors coupled to the enclosure and configured to produce a self-mixing interferometry signal resulting from reflection of backscatter of emitted light by a body part in the three-dimensional input space. In various examples, movement of the body part may be determined using the self-mixing interferometry signal, which may in turn be used to determine an input. In some examples, a body part displacement or a body part speed and an absolute distance to the body part may be determined using the self-mixing interferometry signal and used to determine an input. In a number of examples, multiple self-mixing interferometry sensors may be used and the movement may be determined by analyzing differences between the respective produced self-mixing interferometry signals. 
     These and other embodiments are discussed below with reference to  FIGS. 1A-9 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1A  depicts a first example of an input device  100  that uses self-mixing interferometry to determine movement within an enclosure  101 . The input device  100  may include the enclosure  101 , which may define a three-dimensional input space within which a body part  102  may move (e.g., the area shown between the enclosure  101  and the object  105  within which the body part  102  is positioned). The input device  100  may also include one or more self-mixing interferometry sensor assemblies  103 A,  103 B that may be coupled to the enclosure  101  across one or more gaps from the body part  102 . The self-mixing interferometry sensor assemblies  103 A,  103 B may each be configured to emit a beam of coherent light  104 A,  104 B to illuminate the body part  102  in the three-dimensional input space and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light. The input device  100  may determine movement of the body part  102  using the self-mixing interferometry signal and determine an input using the movement. 
     In this example, the self-mixing interferometry sensor assemblies  103 A,  103 B are coupled to the enclosure  101  on opposite sides of the three-dimensional input space and the body part  102  from each other. This arrangement may enable the input device  100  to distinguish between movements of the body part  102  that change the position of both sides similarly from movements of the body part  102  that change positions differently, allow differential comparison of measurements from multiple sensors, and so on. However, it is understood that this is an example. In various examples, a different number of sensors (such as one, four, and so on) may be used in different configurations (such as sensors positioned adjacent each other, along an axis defined by the enclosure  101 , and so on) without departing from the scope of the present disclosure. Various configurations are possible and contemplated. 
       FIG. 1B  depicts a top view of the input device of  FIG. 1A .  FIG. 1B  illustrates that the self-mixing interferometry sensor assemblies  103 A,  103 B shown in  FIG. 1A  may be configured so that the beams of coherent light  104 A,  104 B are emitted at a tilt with respect to the body part  102  rather than being configured to emit the beams of coherent light  104 A,  104 B directly at the body part  102  surface normal to the self-mixing interferometry sensor assemblies  103 A,  103 B. Tilted beams of coherent light  104 A,  104 B may enable more accurate determination of absolute distance (discussed below), but may involve a larger area between the self-mixing interferometry sensor assemblies  103 A,  103 B and the body part  102 . 
     How the input device  100  may use the self-mixing interferometry sensor assemblies  103 A,  103 B to determine inputs will now be described with respect to  FIGS. 1A and 1B . The input device  100  (and/or another device to which the input device  100  transmits data) may analyze the self-mixing interferometry signal in various ways to determine movement of the body part  102  within the three-dimensional input space. For example, direct current laser bias and spectral analysis of the self-mixing interferometry signal that contains the Doppler shift of the reflected or backscattered light (discussed in more detail below) may be used to determine a body part speed without information on the direction of motion. By way of another example, triangular bias and spectral analysis of the subtracted self-mixing interferometry signal that contains the Doppler shift of the reflected or backscattered light (discussed in more detail below) may be used to determine the body part velocity with information on the direction of motion and absolute distance of the body part. By way of yet another example, sinusoidal bias and quadrature demodulation of the self-mixing interferometry signal that contains sine and cosine of the interferometric phase (discussed in more detail below) may be used to determine displacement. The input device may thus determine a variety of different inputs corresponding to different movement of the body part  102  (such as movement within three-dimensional space, one or more gestures, presses to an object  105 , force applied to the object  105 , sliding along the object  105 , and so on) using the self-mixing interferometry signal. 
     For example, the body part  102  may expand (or squish) upon contacting an object  105 . The body part  102  may then contract when the contact ceases. Both expansion and contraction may cause the body part  102  to change proximity to the self-mixing interferometry sensor assemblies  103 A,  103 B. As such, touch of the body part  102  to an object  105  may be determined by determining a body part speed of the body part  102  moving toward and/or away from one or more of the self-mixing interferometry sensor assemblies  103 A,  103 B. 
     Movement towards both of the self-mixing interferometry sensor assemblies  103 A,  103 B may indicate expansion whereas movement away from both of the self-mixing interferometry sensor assemblies  103 A,  103 B may indicate contraction. Movement towards one of the self-mixing interferometry sensor assemblies  103 A,  103 B but away from the other could indicate lateral movement of the body part  102  between the self-mixing interferometry sensor assemblies  103 A,  103 B as opposed to expansion or contraction. If a signed body part velocity (velocity with information on the direction of motion) is determined using the self-mixing interferometry signal from one of the self-mixing interferometry sensor assemblies  103 A,  103 B, the input device  100  may be able to determine the direction of movement according to the sign, such as positive for movement towards and negative for movement away. However, if a body part speed without information on the direction of motion is determined from one of the self-mixing interferometry sensor assemblies  103 A,  103 B, the input device  100  may not be able to determine the direction of movement absent other data, such as absolute distance where a decrease in absolute distance indicates movement towards and an increase in absolute distance indicates movement away. In some examples, the direction of the movement may be determined by comparing the differences between the body part velocities determined using the self-mixing interferometry signals from each the self-mixing interferometry sensor assemblies  103 A,  103 B. In various examples, determination of a first body part speed followed by a corresponding second body part speed could indicate that expansion followed by contraction has occurred without having to determine the sign of the speed as the two movements would likely be proportional (contraction typically following an expansion of the same magnitude in a short period of time whereas expansion less typically follows a contraction of the same magnitude in a short period of time) and the movement could thus be determined by looking at speed changes over a period of time. 
     In other implementations, such as a DC bias implementation, a gyroscope and an accelerometer may be used to disambiguate expansion from contraction. The gyroscope may provide the orientation of the body part  102  and the accelerometer may provide the direction of acceleration. When speed is non-zero: expansion may be indicated by gyroscope data that the body part  102  faces downwards and accelerometer data indicating downward motion; contraction may be indicated by gyroscope data that the body part  102  faces downwards and accelerometer data indicating upward motion; expansion may be indicated by gyroscope data that the body part  102  faces upwards and accelerometer data indicating upward motion; contraction may be indicated by gyroscope data that the body part  102  faces upwards and accelerometer data indicating downward motion; and so on. This combined use of a gyroscope and an accelerometer may be expanded to any orientation of the body part  102  and/or the object  105 . 
     Further, the input device  100  may use detection of expansion followed shortly by contraction to distinguish a “press” (e.g., a touch to the object  105 ) from a “tap” (e.g., a short touch of the body part  102  to the object  105  that is quickly withdrawn). Additionally, the body part  102  may expand in proportion to the amount of force applied by the body part  102  to the object  105 . The amount of expansion may be obtained by integrating the measured speed or velocity in time. As such, the input device  100  may use the amount of expansion detected to estimate an amount of force applied within a range of force amounts. This may vary for different body parts  102  and the input device  100  may thus calibrate estimated force amounts according to different body parts  102 . Moreover, the sides of the body part  102  may expand and/or contract differently when the body part  102  is twisted (e.g., sheared) and/or slid along the object  105 . As such, these different expansions and/or contractions may be determined and correlated to such twisting of the body part  102  and/or sliding of the body part  102  along the object  105 . In this way, the input device  100  may use the movements detectable using the self-mixing interferometry sensor assemblies  103 A,  103 B to determine a wide variety of inputs. 
     Additionally, different portions of the body part  102  may have different dimensions. As such, the input device  100  may be able to detect movement of the body part  102  and/or portions thereof in three-dimensional space (such as vertically with respect to the self-mixing interferometry sensor assemblies  103 A,  103 B, forward or backwards horizontally as illustrated in  FIG. 1A  with respect to the self-mixing interferometry sensor assemblies  103 A,  103 B, movement in various directions between the self-mixing interferometry sensor assemblies  103 A,  103 B, and so on) and correlate such movement to one or more gestures and/or other inputs. 
     Moreover, the input device  100  may use the self-mixing interferometry sensor assemblies  103 A,  103 B to determine when the body part  102  is being withdrawn from the three-dimensional input space. For example, a determination of the absolute distance between one or more of the self-mixing interferometry sensor assemblies  103 A,  103 B and the body part  102  that increases to the size of the three-dimensional input space may indicate that the body part  102  has been withdrawn from the input area entirely. Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
     Additionally, the input device  100  may use the self-mixing interferometry sensor assemblies  103 A,  103 B to determine when the body part  102  is bending. For example, bending of the body part  102  may change the absolute distance between the body part  102  and one or more of the self-mixing interferometry sensor assemblies  103 A,  103 B in a way that does not agree with the time integration of the measured velocity. This may be used to detect bending. Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
     In various implementations, the input device  100  may operate in a “low power” or “low frame rate” mode where the self-mixing interferometry sensor assemblies  103 A,  103 B may be operated in a low power mode when the body part  102  is not present. Upon detection of the body part  102 , the input device  100  may switch the self-mixing interferometry sensor assemblies  103 A,  103 B to a “high power,” “high frame rate”, “high accuracy” mode. Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
     Further, the input device  100  may use the self-mixing interferometry sensor assemblies  103 A,  103 B to determine movements of the body part  102  that correspond to a pulse and/or heart rate. This may enable the input device to determine such a pulse and/or heart rate based on the movements, distinguish such pulse and/or heart rate from other movements related to input, and so on. 
     As discussed above, the body part  102  may move in two or more ways that cause the same movement of a first part of the body part  102  (such as one illuminated by the beam of coherent light  104 A) but different movement of a second part and/or other parts of the body part  102  (such as one illuminated by the beam of coherent light  104 B). As such, differential measurement using the self-mixing interferometry sensor assemblies  103 A,  103 B may allow the input device  100  to screen out false positives (e.g., false inputs) by distinguishing between the two kinds of movement. For example, this may enable the input device  100  to differentiate between a touch to an object  105  and lateral movement of the body part  102  between the self-mixing interferometry sensor assemblies  103 A,  103 B. By way of another example, this may enable the input device  100  to differentiate between a press on an object  105  and shaking and/or bending of the body part  102 . Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
     In some examples, additional self-mixing interferometry sensor assemblies  103 A,  103 B may enable increased differentiation and thus increased ability of the input device  100  to distinguish different kinds of motion of the body part  102 . This may allow the input device  100  to more accurately reject false positives of inputs for which the input device  100  is monitoring. Such additional self-mixing interferometry sensor assemblies  103 A,  103 B may be positioned at different areas of the enclosure  101  around the body part  102 , different areas along the length of the body part  102 , and so on. 
     For example, the body part  102  may be a finger and different self-mixing interferometry sensor assemblies  103 A,  103 B may be configured with respect to a fingernail of such a finger, a tip of the finger, a top of the finger, a central region of the finger, one or more knuckles of the finger, and so on. Various configurations are possible and contemplated with respect to the present disclosure. 
     In various examples, the self-mixing interferometry sensor assemblies  103 A,  103 B may each include one or more vertical-cavity surface-emitting lasers (VCSELs), other lasers, and/or other coherent or partially coherent light sources with incorporated and/or separate photodetectors and/or other light sensors. The VCSELs may emit a beam of coherent light  104 A,  104 B from an optical resonant cavity to illuminate the body part  102  in the three-dimensional input space, receive a reflection or backscatter of the beam of coherent light  104 A,  104 B into the optical resonant cavity, and produce the self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity (and/or use an integrated and/or separate photodetector and/or other light sensor to do so). Examples of the self-mixing interferometry sensor assemblies  103 A,  103 B will be discussed in more detail below. 
     In a number of examples, the enclosure  101  may be coupled to the body part  102 . For example, the enclosure  101  may be a component of an apparatus that is mounted on the body part  102 . In other examples, the enclosure  101  may be separate from the body part  102  but configured such that the body part  102  may be inserted into and moved within the three-dimensional input space defined by the body part  102 . Various configurations are possible and contemplated with respect to the present disclosure. 
     Although the enclosure  101  is described as defining a three-dimensional input space, the three-dimensional input space defined by the enclosure  101  may not be completely surrounded and/or enclosed by the enclosure  101  and/or other components. For example, as shown, the enclosure  101  may surround three sides of the three-dimensional input space. Various configurations are possible and contemplated with respect to the present disclosure. 
     Although the above illustrates and describes the input device  100  monitoring motion of the body part  102 , it is understood that this is an example. In various implementations, the input device  100  may monitor motion of any kind of object (such as a stylus, a tire, and so on) without departing from the scope of the present disclosure. Various configurations are possible and contemplated. 
       FIG. 1C  depicts an example configuration of a self-mixing interferometry sensor assembly  103 A that may be used in the input device  100  of  FIG. 1A . The self-mixing interferometry sensor assembly  103 A may include a VCSEL  110  and/or other laser, and/or other coherent or partially coherent light source with an incorporated and/or separate photodetector and/or other light sensor. The VCSEL  110  may emit coherent light  111  through a lens  112  of a lens substrate  113  and/or other optical element. The lens  112 , lens substrate  113 , and/or other optical element may collimate or focus the coherent light  111  into the beam of coherent light  104 A. As shown, the lens  112 , lens substrate  113 , and/or other optical element may also function to tilt the beam of coherent light  104 A with respect to the VCSEL  110 . 
       FIG. 1D  depicts an example block diagram illustrating example functional relationships between example components that may be used in the input device  100  of  FIG. 1A . The input device  100  may include one or more processors  120  and/or other processing units and/or controllers; one or more self-mixing interferometry sensor assemblies  103 A,  103 B; one or more non-transitory storage media  121  (which may take the form of, but is not limited to, a magnetic storage medium; optical storage medium; magneto-optical storage medium; read only memory; random access memory; erasable programmable memory; flash memory; and so on); and/or other components (such as one or more communication units, output components, and so on). The processor  120  may execute instructions stored in the storage medium  121  to perform various input device functions, such as controlling the self-mixing interferometry sensor assemblies  103 A,  103 B; receiving one or more self-mixing interferometry signals from the self-mixing interferometry sensor assemblies  103 A,  103 B; determining movement of a body part or other object using one or more received self-mixing interferometry signals; determining one or more inputs based on one or more determined movements; communicating with one or more other electronic devices; and so on. 
     The input device  100  may be any kind of electronic device, such as a laptop computing device, a desktop computing device, a mobile computing device, a smart phone, a wearable device, an electronic watch, a kitchen appliance, a display, a printer, an automobile, a tablet computing device, and so on. Alternatively, the input device  100  may be a device that gathers data regarding movement of one or more objects and wired and/or wirelessly transmits such data to an electronic device (such as those detailed above). In some implementations of such examples, the input device may transmit one or more self-mixing interferometry signals, one or more movements determined from such self-mixing interferometry signals, one or more inputs determined from such movements, and so on. Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
     By way of illustration, the input device  100  may be used to receive input for interacting with a virtual keyboard presented on a heads up display. As such, the input device  100  may detect movement and transmit data about the movement to the heads up display and/or a device that controls the heads up display to present the virtual keyboard. 
       FIG. 2A  depicts a second example of an input device  200  that uses self-mixing interferometry to determine movement within an enclosure  201 .  FIG. 2B  depicts a top view of the input device  200  of  FIG. 2A . With respect to  FIGS. 2A and 2B , the input device  200  may include the enclosure  201 , which may define a three-dimensional input space within which a body part  202  may move. Like the input device  100  in  FIGS. 1A-1B , the input device  200  may include one or more self-mixing interferometry sensor assemblies  203 A,  203 B that may each be configured to emit a beam of coherent light  204 A,  204 B to illuminate the body part  202  in the three-dimensional input space and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light. Further similarly, the input device  200  may determine movement of the body part  202  using the self-mixing interferometry signal and determine an input using the movement. 
     By way of contrast with the input device  100  in  FIGS. 1A-1B , the self-mixing interferometry sensor assemblies  203 A,  203 B may be configured to emit the beams of coherent light  204 A,  204 B directly at the body part  202  surface normal to the self-mixing interferometry sensor assemblies  203 A,  203 B rather than being emitted at a tilt with respect to the body part  202 . This may involve less area between the self-mixing interferometry sensor assemblies  203 A,  203 B and the body part  202  than tilted beam implementations. Further, this may allow the self-mixing interferometry sensor assemblies  203 A,  203 B to omit beam tilting optics and/or other beam tilting components. 
       FIG. 2C  depicts an example configuration of a self-mixing interferometry sensor assembly  203 A that may be used in the input device of  FIG. 2A . Similar to the self-mixing interferometry sensor assembly  103 A of  FIG. 1C , the self-mixing interferometry sensor assembly  203 A may include a VCSEL  210  and/or other laser, and/or coherent or partially coherent light source with an incorporated and/or separate photodetector and/or other light sensor. The VCSEL  210  may emit coherent light  211  through a lens  212  of a lens substrate  213  and/or other optical element. The lens  212 , lens substrate  213 , and/or other optical element may collimate or focus the coherent light  211  into the beam of coherent light  204 A. Unlike the self-mixing interferometry sensor assembly  103 A of  FIG. 1C , the lens  212 , lens substrate  213 , and/or other optical element may not be configured to tilt the beam of coherent light  204 A with respect to the VCSEL  210 . 
       FIG. 3  depicts a third example of an input device  300  that uses self-mixing interferometry to determine movement within an enclosure  301 . Similar to the input device  100  in  FIGS. 1A-1B  and/or the input device  200  in  FIGS. 2A-2B , the input device  200  may include one or more self-mixing interferometry sensor assemblies  303 A,  303 B,  303 C that may each be configured to emit a beam of coherent light  304 A,  304 B,  303 C to illuminate a body part  302  in a three-dimensional input space and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light. Further similarly, the input device  300  may determine movement of the body part  302  using the self-mixing interferometry signal and determine an input using the movement. By way of contrast, the input device  300  may include three rather than two self-mixing interferometry sensor assemblies  303 A,  303 B,  303 C. 
     In this example, the body part  302  may be a finger and the self-mixing interferometry sensor assemblies  303 A,  303 B,  303 C may be configured to emit the beam of coherent light  304 A,  304 B,  303 C to illuminate a fingernail  330  of the finger. The fingernail  330  may deform in different ways depending on the movement of the finger, such as when the finger presses against an object  305 , shears against the object  305 , slides along the object  305 , and so on. The input device  300  may use the self-mixing interferometry signals to determine the deformation and thus the movement of the finger and/or an associated input. 
     In some examples, fingernail polish and/or other substances on the fingernail  330  may affect deformation. In such examples, the input device  300  may detect the presence of such a substance and adjust determinations accordingly. The input device  300  may detect the presence of the substance by comparing the self-mixing interferometry signals to expected values, data from other sensors (such as measuring reflection using an optical sensor), and so on. 
       FIG. 4A  depicts a speed profile of a press that may be measured by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3  using self-mixing interferometry. The speed profile correlates speed of movement over time. The speed profile illustrates a peak at a time 0.4 second that is significantly higher in speed than surrounding measurements. This peak may correlate to the press. 
       FIG. 4B  depicts a displacement profile of a press that may be measured by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3  using self-mixing interferometry.  FIG. 4B  may not correspond to the same event to which  FIG. 4A  corresponds.  FIGS. 4A and 4B  may be at different times. The displacement profile illustrates measured relative displacement over time. The displacement profile illustrates a trough at a time 0.4 second that is significantly lower than surrounding measurements. This trough may correlate to the press. 
       FIG. 4C  depicts a heart rate that may be measured by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3  using self-mixing interferometry.  FIG. 4C  correlates speed over time. As shown, a number of similar peaks are present at times 0.5, 1, and 1.75. Due to the regularity and similarity, these peaks may be determined to relate to movement corresponding to a heart rate. As also shown, there are a number of irregular and different peaks between 2.25 and 3.75. Due to the irregularity and differences, these peaks may be determined to relate to movement other than a heart rate. 
       FIG. 5A  depicts a first example self-mixing interferometry sensor that may be used in one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . In this example, the self-mixing interferometry sensor may be a VCSEL  591 A with an integrated resonant cavity (or intra-cavity) photodetector (RCPD)  592 A. 
       FIG. 5B  depicts a second example self-mixing interferometry sensor that may be used in one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . In this example, the self-mixing interferometry sensor may be a VCSEL  591 B with an extrinsic on-chip photodetector. As shown, an RCPD  592 B may form a disc around the VCSEL  591 B. 
       FIG. 5C  depicts a third example self-mixing interferometry sensor that may be used in one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . In this example, the self-mixing interferometry sensor may be a VCSEL  591 C with an extrinsic off-chip photodetector  592 C. 
       FIG. 5D  depicts a fourth example self-mixing interferometry sensor that may be used in one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . In this example, the self-mixing interferometry sensor may be a dual-emitting VCSEL  591 D with an extrinsic off-chip photodetector  592 D. For example, the top emission may be emitted towards optics and/or another target and the bottom emission may be provided to an extrinsic photodetector  592 D. 
       FIG. 6  depicts a direct current bias procedure  600  for determining speed of an object using self-mixing interferometry. This procedure  600  may be used by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . 
     The procedure includes generating an initial digital signal and processing it to produce a current  610  as an input to a VCSEL  691 . For DC bias, a digital signal may not be necessary. As the current  610  may be constant, a fixed analog voltage may be applied to voltage-to-current converter. In alternative implementations, a digital signal may be used. As described above, movement of a target can cause changes in an interferometric parameter, such as a parameter of the VCSEL  691  or of a photodetector  692  operating in the system. The changes can be measured to produce a signal. In the embodiment shown it will be assumed the signal is measured by a photodetector  692 . The signal may first be passed into a high-pass filter  620 . As the signal from a photodetector (or a VCSEL in other embodiments) may typically be a current signal, a transimpedance amplifier  630  can produce a corresponding voltage output (with or without amplification) for further processing. The voltage output can then be sampled and quantized by an analog-to-digital conversion block  640 . The output may be used to generate a spectrogram  650  by means of a spectral analysis procedure (e.g., a fast Fourier transform), from which an unsigned speed (or speed)  660  may be determined. 
       FIGS. 7 and 8  respectively show a flow chart of a method and a block diagram of a system to implement a spectrum analysis procedure that can be used as part of determining and/or estimating an absolute distance. The method and the system may drive or modulate a laser, such as one or more VCSELs, with a modulation current  802 . The method and the system may also analyze a signal  818  related to an interferometric parameter. For purposes of explanation, in the embodiments of  FIGS. 7 and 8  it will be assumed that the modulation current  802  has a triangle waveform. One of skill in the art will recognize how the method and the system can be implemented using alternative modulation current waveforms. The spectrum analysis method concurrently analyzes the modulation current  802  and the signal  818  of the interferometric parameter. The modulation current  802  and the signal  818  of the interferometric parameter are received at respective receiving circuits. Such receiving circuits may be one or more of the blocks of the system shown in  FIG. 8  and described below, or may be one or more dedicated processing units such as a graphics processing unit, an ASIC, or an FPGA, or may be a programmed microcomputer, microcontroller, or microprocessor. Various stages of the method may be performed by separate such processing units, or all stages by one (set of) processing unit(s). 
       FIG. 7  depicts a first triangular bias procedure  700  for determining velocity and absolute distance of an object using self-mixing interferometry. This procedure  700  may be used by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . 
     At the initial stage  702 , an initial signal is generated, such as by a digital or an analog signal generator. At stage  706   a  the generated initial signal is processed as needed to produce the triangle waveform modulation current  802  that is applied to the VCSEL. Stage  706   a  can be, 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 modulation current  802  to the VCSEL induces a signal  818  in the interferometric property. It will be assumed for simplicity of discussion that the signal  818  of the interferometric property is from a photodetector, but in other embodiments it may be another signal of an interferometric property from another component. At initial stage  704 , the signal  818  is received. At stage  706   b , initial processing of the signal  818  is performed as needed. Stage  706   b  may be high-pass filtering or a digital subtraction. 
     At stage  708  the processing unit may equalize the received signals in order to match their peak-to-peak values, mean values, root-mean-square values, or any other characteristic values, if necessary. For example the signal  818  may be a predominant triangle waveform component being matched to the modulation current  802 , with a smaller and higher frequency component due to changes in the interferometric property. High-pass filtering may be applied to the signal  818  to obtain the component signal related to the interferometric property. Also this stage may involve separating and/or subtracting the parts of the signal  818  and the modulation current  802  corresponding to the ascending and to the descending time intervals of the modulation current  802 . This stage may include sampling the separated information. 
     At stages  710  and  712 , a separate FFT is first performed on the parts of the processed signal  818  corresponding to the ascending and to the descending time intervals. Then the two FFT spectra are analyzed at stage  714 . 
     At stage  716 , further processing of the FFT spectra can be applied, such as to remove artifacts and reduce noise. Such further processing can include peak detection and Gaussian fitting around the detected peak for increased frequency precision. From the processed FFT spectra data, information regarding the absolute distance can be obtained at stage  718 . 
       FIG. 8  depicts a second triangular bias procedure  800  for determining velocity and absolute distance of an object using self-mixing interferometry. This procedure  800  may be used by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . 
       FIG. 8  shows a block diagram of a system that may implement the spectrum analysis described in the method described above with respect to  FIG. 7 . In the exemplary system shown, the system includes generating an initial digital signal and processing it as needed to produce a modulation current  802  as an input to the VCSEL  810 . In an illustrative example, an initial step signal may be produced by a digital generator to approximate a triangle function. The digital output values of the digital generator are used in the digital-to-analog (DAC) converter  804 . The resulting voltage signal may then be filtered by the low-pass filter  806  to remove quantization noise. Alternatively, an analog signal generator based on an integrator can be used to generate an equivalent voltage signal directly. The filtered voltage signal then is an input to a voltage-to-current converter  808  to produce the desired modulation current  802  in a form for input to the VCSEL  810 . 
     As described above, movement of a target can cause changes in an interferometric parameter, such as a parameter of the VCSEL  810  or of a photodetector operating in the system. The changes can be measured to produce a signal  818 . In the embodiment shown it will be assumed the signal  818  is measured by a photodetector. For the modulation current  802  having the triangle waveform, the signal  818  may be a triangle wave of a similar period combined with a smaller and higher frequency signal related to the interferometric property. The signal  818  may not be perfectly linear even though the modulation current  802  may be. This may be because bias-current versus light-output of the curve of the VCSEL  810  may be non-linear due to non-idealities, such as self-heating effects. 
     The signal  818  is first passed into the high-pass filter  820 , which can effectively convert the major ascending and descending ramp components of the signal  818  to DC offsets. As the signal  818  from a photodetector (or a VCSEL in other embodiments) may typically be a current signal, the transimpedance amplifier  822  can produce a corresponding voltage output (with or without amplification) for further processing. 
     The voltage output can then be sampled and quantized by the analog-to-digital conversion (ADC) block  824 . Before immediately applying a digital FFT to the output of the ADC block  824 , it can be helpful to apply equalization. The initial digital signal values from the digital generator used to produce the modulation current  802  are used as input to the digital high-pass filter  812  to produce a digital signal to correlate with the output of the ADC block  824 . An adjustable gain can be applied by the digital variable gain block  814  to the output of the digital high-pass filter  812 . 
     The output of the digital variable gain block  814  is used as one input to the digital equalizer and subtractor block  816 . The other input to the digital equalizer and subtractor block  816  is the output of the ADC block  824 . The two signals are differenced, and used as part of a feedback to adjust the gain provided by the digital variable gain block  814 . 
     Equalization and subtraction may be used to clean up any remaining artifacts from the triangle that may be present in the signal  818 . For example, if there is a slope error or nonlinearity in the signal  818 , the digital high-pass filter  812  may not fully eliminate the triangle and artifacts may remain. In such a situation, these artifacts may show up as low frequency components after the FFT and make the peak detection difficult for nearby objects. Applying equalization and subtraction may partially or fully remove these artifacts. 
     Once an optimal correlation is obtained by the feedback, an FFT, indicated by block  830 , can then be applied to the components of the output of the ADC block  824  corresponding to the rising and descending side of the triangle wave. From the FFT spectra obtained, absolute distance and/or directional velocity may be inferred using the detected peak frequencies on the rising and descending sides, as discussed above and indicated by block  826 . 
     The method just described, and its variations, involve applying a spectrum analysis to an interferometric parameter. However, it is understood that this is an example. In other implementations, alternate methods for determining absolute distances may be obtained directly from the time domain signal of an interferometric parameter, without applying a spectrum analysis. Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
       FIG. 9  depicts a sinusoidal bias procedure  900  for determining displacement of an object using quadrature modulation with self-mixing interferometry. This procedure  900  may be used by one or more of the input devices  100 ,  200 ,  300  of  FIG. 1A, 2A , or  3 . 
     As explained in more detail below,  FIG. 9  shows components which generate and apply a sinusoidally modulated bias current to a VCSEL. The sinusoidal bias current can generate in a photodetector  916  an output current depending on the frequency of the sinusoidal bias and the displacement to the target. In the circuit of  FIG. 9 , the photodetector&#39;s  916  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 of the interferometric parameter is calculated. Thereafter the displacement is determined using at least the phase. 
     The DC voltage generator  902  is used to generate a constant bias voltage. A sine wave generator  904  may produce an approximately single frequency sinusoid signal, to be combined with constant voltage. As shown in  FIG. 9 , the sine wave generator  904  is a digital generator, though in other implementations it may produce an analog sine wave. The low-pass filter  906   a  provides filtering of the output of the DC voltage generator  902  to reduce undesired varying of the constant bias voltage. The bandpass filter  906   b  can be used to reduce distortion and noise in the output of the sine wave generator  904  to reduce noise, quantization or other distortions, or frequency components of its signal away from its intended modulation frequency, ω m . 
     The circuit adder  908  combines the low-pass filtered constant bias voltage and the bandpass filtered sine wave to produce on link  909  a combined voltage signal which, in the embodiment of  FIG. 9 , 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  910  to produce a current to drive the lasing action of the VCSEL diode  914 . The current from the voltage-to-current converter  910  on the line  913  can have the form I 0 +I m  sin(ω m t). 
     The VCSEL diode  914  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  914  and cause self-mixing interference. The resulting self-mixing interference light may be detected by photodetector  916 . As described above, in such cases the photocurrent output of the photodetector  916  on the link  915  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  918 . To do such a removal/reduction, a proportional or scaled value of the first two terms is produced by the voltage divider  912 . The voltage divider  912  can use as input the combined voltage signal on the link  909  produced by the circuit adder  908 . The output of the voltage divider  912  on link  911  can then have the form: α(V 0 +V m  sin(ω m t)). The photodetector current and this output of the voltage divider  912  can be the inputs to the DTIA/AA filter  918 . The output of the DTIA/AA filter  918  can then be, at least mostly, proportional to the third term of the photodetector current. 
     The output of the DTIA/AA filter  918  may then be quantized for subsequent calculation by the analog-to-digital converter (ADC) block  920 . Further, the output of the ADC block  920  may have a residual signal component proportional to the sine wave originally generated by the sine wave generator  904 . 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  924 C, and then subtracted from the output of ADC block  920 . The filtered output on link  921  may have the form: A+B sin(ω m t)+C cos(2ω m t)+D sin(3ω m t)+ . . . , from the Fourier expansion γ cos(φ 0 +φ m  sin(ω m t)) 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  904  onto link  907  is mixed (multiplied) by the multiplier block  924   a  with the filtered output on link  907 . This product is then low-pass filtered at block  928   a  to obtain the Q component discussed above, possibly after scaling with a number that is related to the amount of frequency modulation of the laser light and distance of the target. 
     Also, the originally generated digital sine wave is used as input into the squaring/filtering block  926  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  924   b  with the filtered output of the ADC block  920  on link  921 . This product is then low-pass filtered at component  928   b  to obtain the I component discussed above, possibly after scaling with a number that is related to the amount of frequency modulation of the laser light and distance of the target. 
     The Q and the I components are then used by the phase calculation component  930  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. 9  makes use of the digital form of the originally generated sine wave produced by sine wave generator  904  onto link  907 , in other embodiments the originally generated sine wave may be an analog signal and mixed with an analog output of the DTIA/AA filter  918 . In other implementations, the voltage divider  912  may be a variable voltage divider. In still other implementations, the voltage divider  912  may be omitted and the differential TIA and anti-aliasing filter  918  may be a single-ended differential TIA and anti-aliasing filter  918 . In such an implementation, subtraction may be done only digitally by  922 . In yet other implementations,  922  may be omitted and no subtraction of the modulation current may be performed. 
     The circuit of  FIG. 9  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  920 , and then applying respective low-pass filtering, such as by the blocks  928   a,b . The differential TIA and anti-aliasing filter  918  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. For example, the signal sin(3ω m t) may be generated by multiplying link  907  and the output of squaring/filtering block  926  and subsequently performing bandpass filtering to reject frequency components other than 3ω m t. 
     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 to 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. 
     A DC bias mode, such as is illustrated in  FIG. 6 , may provide unsigned speed. A triangular mode, such as is illustrated in  FIGS. 7 and 8 , may provide velocity and absolute distance. A sinusoidal I/Q mode, such as illustrated in  FIG. 9 , may provide only displacement. DC bias mode may be used to estimate object motion (such as press/release of an object to another), but there may be ambiguities since the direction of motion may not be known. Triangular mode may obtain both speed and direction of motion. Velocity may then be integrated to obtain displacement. This integration result may also be coupled with absolute distance information for higher accuracy. However, as it is spectral domain analysis, it may be difficult to track slow movements (such as speeds bellow millimeters per second speeds). Sinusoidal I/Q mode may obtain displacement directly without integration and may also function when target motion is slow. However, this mode may require a higher signal-to-noise ration as a result of being a time-domain measurement technique. 
     In various implementations, an input device may include an enclosure defining a three-dimensional input space; a self-mixing interferometry sensor coupled to the enclosure and configured to emit a beam of coherent light from an optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a reflection or backscatter of the beam into the optical resonant cavity, and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity; and a processor. The processor may be configured to determine a body part displacement or a body part speed and an absolute distance to the body part using the self-mixing interferometry signal, and determine an input using the body part displacement or the body part speed and the absolute distance. 
     In some examples, the input may correspond to a touch of the body part to an object. In various such examples, the processor may estimate an amount of force exerted on the object by the body part. 
     In a number of examples, the self-mixing interferometry sensor may be configured to emit the beam at an oblique angle with respect to a wall of the enclosure. In some examples, the self-mixing interferometry sensor may be configured to emit the beam normal with respect to a wall of the enclosure. In a number of examples, the enclosure may be configured to be mounted on the body part. In various examples, the enclosure may be configured to provide a gap between the self-mixing interferometry sensor and the body part. 
     In some implementations, an input device may include an enclosure defining a three-dimensional input space; a first self-mixing interferometry sensor coupled to the enclosure and configured to emit a first coherent light beam from a first optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a first reflection or backscatter of the first coherent light beam into the first optical resonant cavity, and produce a first self-mixing interferometry signal; a second self-mixing interferometry sensor coupled to the enclosure and configured to emit a second coherent light beam from a second optical resonant cavity to illuminate the body part in the three-dimensional input space, receive a second reflection or backscatter of the second coherent light beam into the second optical resonant cavity, and produce a second self-mixing interferometry signal; and a processor. The processor may be configured to determine movement of the body part by analyzing differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal and determine an input using the movement. 
     In various examples, the first self-mixing interferometry sensor and the second self-mixing interferometry sensor may be positioned on opposing sides of the three-dimensional input space. In some such examples, the movement may be lateral movement of the body part between the first self-mixing interferometry sensor and the second self-mixing interferometry sensor. 
     In a number of examples, the processor may screen out a false input using differences between the first self-mixing interferometry signal and the second self-mixing interferometry signal. In various examples, the movement of the body part may be deformation of a fingernail. In a number of examples, the first self-mixing interferometry sensor may include an optical component configured to tilt the first beam. In some examples, the movement may correspond to withdrawal of the body part from the enclosure. 
     In a number of embodiments, an input system may include an enclosure defining a three-dimensional input space; a self-mixing interferometry sensor coupled to the enclosure and configured to emit a beam of coherent light from an optical resonant cavity to illuminate a body part in the three-dimensional input space, receive a reflection or backscatter of the beam into the optical resonant cavity, and produce a self-mixing interferometry signal resulting from self-mixing of the coherent light within the optical resonant cavity; and a processor. The processor may be configured to determine movement of the body part using the self-mixing interferometry signal and determine an input using the movement. 
     In some examples, the self-mixing interferometry sensor may be a component of a first electronic device and the processor may be a component of a second electronic device that communicates with the first electronic device. In various examples, the processor may be a component of a first electronic device and transmit the input to a second electronic device. 
     In a number of examples, the input may be selection of a virtual key of a virtual keyboard. In various examples, the movement may be at least one of an expansion of the body part or a contraction of the body part. In some examples, the input may correspond to movement of the body part along a surface. 
     As described above and illustrated in the accompanying figures, the present disclosure relates to an input device including an enclosure defining a three-dimensional input space and one or more self-mixing interferometry sensors coupled to the enclosure and configured to produce a self-mixing interferometry signal resulting from reflection of backscatter of emitted light by a body part in the three-dimensional input space. In various examples, movement of the body part may be determined using the self-mixing interferometry signal, which may in turn be used to determine an input. In some examples, a body part displacement or a body part speed and an absolute distance to the body part may be determined using the self-mixing interferometry signal and used to determine an input. In a number of examples, multiple self-mixing interferometry sensors may be used and the movement may be determined by analyzing differences between the respective produced self-mixing interferometry signals. 
     In the present disclosure, the methods disclosed may be implemented as sets of instructions or software readable by a device. Further, it is understood that the specific order or hierarchy of steps in the methods disclosed are examples of sample approaches. In other embodiments, the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter. The accompanying method claims present elements of the various steps in a sample order, and are not necessarily meant to be limited to the specific order or hierarchy presented. 
     The described disclosure may be provided as a computer program product, or software, that may include a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A non-transitory machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The non-transitory machine-readable medium may take the form of, but is not limited to, a magnetic storage medium (e.g., floppy diskette, video cassette, and so on); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; and so on. 
     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: 20200526
Publication Date: 20220823
Grant Date: 20220823
Priority Date: 20190708
Inventors: Mutlu, Mehmet
PAN, Yuhao
Dey, Stephen E.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01L1/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01P13/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01P13/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/011", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0304", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/017", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01P13/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0304", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01L1/24", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 74101688