PATENT DOCUMENT

Publication Number: US-11614806-B1
Application Number: US-202117319010-A
Country: US
Kind Code: B1

Title: Input device with self-mixing interferometry sensors

Abstract:
Self-mixing interferometry (SMI) sensors can be used for generation of content using an input device without requiring a touch-sensitive surface. In some examples, the SMI sensors can be used to detect characteristics of the input device including position, orientation, and/or motion of the input device and/or force applied by the input device (e.g., force applied by a stylus tip). In some examples, some or all of the characteristics of the input device can be used in processing to generate content, including textual character input and three-dimensional objects. In some examples, the generation of content can use information from one or more additional sensors for the input device and/or from additional devices in combination with the characteristics of the input device based on the SMI sensors for generation of content.

Claims:
The invention claimed is: 
     
       1. A stylus comprising:
 a housing; 
 a plurality of self-mixing interferometry (SMI) sensors configured to emit light to and detect light from one or more surfaces, wherein the plurality of SMI sensors includes a first SMI sensor, a second SMI sensor and a third SMI sensor, wherein the first SMI sensor, the second SMI sensor and the third SMI sensor generate beams with 120 degree separation when projected on a non-touch sensitive external surface; 
 processing circuitry coupled to the plurality of SMI sensors, the processing circuitry configured to compute one or more distances to one or more surfaces and one or more directional velocities; and 
 wireless communication circuitry configured to transmit information from the stylus to an external device configured to use the information from the stylus as input, wherein the information includes the one or more distances, the one or more directional velocities, or other information derived from the one or more distances or the one or more directional velocities. 
 
     
     
       2. The stylus of  claim 1 , wherein using the information from the stylus as input comprises rendering writing or drawing strokes of the stylus on the non-touch sensitive external surface. 
     
     
       3. The stylus of  claim 1 , wherein the processing circuitry is further configured to:
 compute, using the one or more distances and the one or more directional velocities, a first displacement along a first axis, a second displacement along a second axis orthogonal to the first axis, a third displacement along a third axis orthogonal to the first axis and the second axis, a tilt angle, an orientation angle, or an axial angle. 
 
     
     
       4. The stylus of  claim 1 , first SMI sensor and the second SMI sensor are configured to generate orthogonal light beams to measure planar displacement. 
     
     
       5. The stylus of  claim 1 , wherein a tip of the stylus is formed from opaque material and the tip includes a plurality of windows for beams from the one or more SMI sensors to exit and return to stylus. 
     
     
       6. The stylus of  claim 1 , wherein a tip of the stylus is formed from an optically transparent or translucent material. 
     
     
       7. The stylus of  claim 6 , wherein the tip includes one or more lenses to increase beam power for one or more of the plurality of SMI sensors or improve symmetry of a plurality of beams for the plurality of SMI sensors. 
     
     
       8. The stylus of  claim 1 , further comprising:
 a mechanical component disposed at least partially within the housing and configured to be displaced in response to contact between the stylus and a surface of the one or more surfaces. 
 
     
     
       9. The stylus of  claim 8 , wherein the mechanical component comprises a compliant rod. 
     
     
       10. The stylus of  claim 9 , wherein the plurality of SMI sensors includes three or more SMI sensors configured to measure displacement of the compliant rod in three dimensions in response to a force applied to a tip of the stylus. 
     
     
       11. The stylus of  claim 1 , wherein a first respective beam exiting the stylus housing generated by the first SMI sensor is oriented away from an axis extending parallel to the housing of the stylus. 
     
     
       12. A system comprising:
 a first device comprising:
 a plurality of first sensors configured to track displacement of the first device in contact with a non-touch sensitive surface, wherein the plurality of first sensors comprises a plurality of self-mixing interferometry (SMI) sensors, wherein the plurality of SMI sensors includes a first SMI sensor, a second SMI sensor and a third SMI sensor, wherein the first SMI sensor, the second SMI sensor and the third SMI sensor generate beams with 120 degree separation when projected on an external surface; and 
 first communication circuitry coupled to the plurality of first sensors and configured to transmit information from the plurality of first sensors to a second device; and 
 
 the second device comprising:
 one or more second sensors configured to track a position of the first device with respect to the non-touch sensitive surface; 
 second communication circuitry configured to receive the information from the plurality of first sensors; 
 processing circuitry configured to generate content using the position of the first device with respect to the non-touch sensitive surface and using the displacement of the first device in contact with the non-touch sensitive surface; and 
 a display configured to display the content generated by the processing circuitry on the non-touch sensitive surface. 
 
 
     
     
       13. The system of  claim 12 , wherein the first device is a stylus and the second device is a head-mounted display device. 
     
     
       14. The system of  claim 12 , wherein the one or more second sensors comprises a camera and wherein the second device tracks the position of the first device by detecting light emitted by the first device. 
     
     
       15. The system of  claim 12 , wherein the one or more sensors comprises a magnetic sensor or an audio sensor or an electromagnetic sensor configured to track the position of the first device with respect to the non-touch sensitive surface using changes in magnetic field, acoustic field, or electromagnetic field. 
     
     
       16. The system of  claim 12 , wherein the first device comprises a camera and the second device comprises a light emitter, wherein the system is configured to track the position of the first device or the displacement of the first device based on a pattern of light emitted by the second device and detected by the camera of the first device. 
     
     
       17. The system of  claim 12 , wherein generating content using the position of the first device with respect to the non-touch sensitive surface and using the displacement of the first device in contact with the non-touch sensitive surface comprises matching an absolute initial position of the first device as the position of the first device in contact with the non-touch sensitive surface at a first time, and generating a stroke relative to the absolute initial position using on relative motion of the first device from the first time to a second time derived from the displacement of the first device from the absolute initial position. 
     
     
       18. The system of  claim 12 , wherein tracking the displacement of the first device is augmented using one or more additional sensors including an accelerometer in the first device, a gyroscope in the first device, and inertial measurement unit in the first device, or a camera in the second device. 
     
     
       19. The system of  claim 12 , wherein the one or more second sensors comprises a camera configured to detect the first device or a hand, and the system is configured to activate the plurality of first sensors in response to detecting the first device or the hand meeting one or more activation criteria. 
     
     
       20. The system of  claim 12 , wherein the plurality of first sensors are further configured to track a distance of the first device from the non-touch sensitive surface and wherein the system detects the contact of the first device with the non-touch sensitive surface based on the distance. 
     
     
       21. The system of  claim 12 , wherein the plurality of first sensors are further configured to track a distance of the first device from the non-touch sensitive surface and wherein the system detects a break in the contact of the first device with the non-touch sensitive surface based on the distance. 
     
     
       22. The system of  claim 12 , wherein the system determines an amount of force applied by the first device to the non-touch sensitive surface using displacement of the first device.

Description:
FIELD OF THE DISCLOSURE 
     This relates generally to input devices, and more particularly to input devices including self-mixing interferometry sensors. 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch panels, touch screens and the like. Touch-sensitive devices, and touch screens in particular, are quite popular because of their ease and versatility of operation as well as their affordable prices. A touch-sensitive device can include a touch panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. The touch-sensitive device can allow a user to perform various functions by touching or hovering over the touch panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, the touch-sensitive device can recognize a touch or hover event and the position of the event on the touch panel, and the computing system can then interpret the event in accordance with the display appearing at the time of the event, and thereafter can perform one or more actions based on the event. 
     Styli have become popular input devices for touch-sensitive devices. In particular, use of an active stylus capable of generating stylus stimulation signals that can be sensed by the touch-sensitive device can improve the precision of stylus input. However, such styli require a touch-sensitive surface in order to generate content. 
     SUMMARY OF THE DISCLOSURE 
     This relates to an input device including self-mixing interferometry (SMI) sensors that can be used for generation of content using the input device without requiring a touch-sensitive surface. In some examples, the SMI sensors can be used to detect characteristics of the input device including position, orientation, and/or motion of the input device and/or force applied by the input device (e.g., force applied by a stylus tip). In some examples, some or all of the characteristics of the input device can be used in processing to generate content, including textual character input and three-dimensional objects. In some examples, the generation of content can use information from one or more additional sensors for the input device and/or from additional devices in combination with the characteristics of the input device based on the SMI sensors for generation of content. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 E  illustrate example systems that can include a touch screen according to examples of the disclosure. 
         FIG.  2    illustrates a block diagram of an example system including an example computing system and an example input device according to examples of the disclosure. 
         FIG.  3    illustrates an example process for generating content with an input device on a non-touch sensitive surface according to examples of the disclosure. 
         FIG.  4    illustrates an example process for generating content with more one or more input devices on a non-touch sensitive surface according to some examples of the disclosure. 
         FIG.  5    illustrates a system comprising an input device and a computing system according to examples of the disclosure. 
         FIG.  6    illustrates an exemplary system comprising an input device and a computing system according to examples of the disclosure. 
         FIGS.  7 A- 7 C  illustrate an example input device configuration with two SMI sensors according to examples of the disclosure. 
         FIGS.  8 A- 8 D  illustrate an example input device configuration with three SMI sensors according to examples of the disclosure. 
         FIGS.  9 A- 9 B  illustrate an example input device configuration with three SMI sensors according to examples of the disclosure. 
         FIG.  10    illustrates an example stylus input device configuration with a plurality of SMI sensors and a rod formed from compliant materials according to examples of the disclosure. 
         FIGS.  11 A- 11 B  illustrate an example stylus input device configuration with an SMI sensor and a rigid rod according to examples of the disclosure. 
         FIGS.  12 A- 12 B  illustrate an example stylus input device configuration with multiple SMI sensors and a rigid rod according to examples of the disclosure. 
         FIG.  13    illustrates an example stylus input device configuration comprising multiple SMI sensors and a trackball according to examples of the disclosure. 
         FIGS.  14 A- 14 D  illustrate example SMI sensors according to examples of the disclosure. 
         FIGS.  15 A- 15 D  illustrate example different beam-shaping or beam-steering optics that can be used with the SMI sensors according to examples of the disclosure. 
         FIG.  16    illustrates a triangular bias process for determining velocity and distance of a surface using self-mixing interferometry according to examples of the disclosure. 
         FIG.  17    illustrates a block diagram of a system that can implement the spectrum analysis for self-mixing interferometry signals according to examples of the disclosure. 
         FIG.  18    illustrates a sinusoidal bias process for determining displacement of a surface using quadrature demodulation with self-mixing interferometry according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples. 
     This relates to an input device including self-mixing interferometry (SMI) sensors that can be used for generation of content using the input device without requiring a touch-sensitive surface. In some examples, the SMI sensors can be used to detect characteristics of the input device including position, orientation, and/or motion of the input device and/or force applied by the input device (e.g., force applied by a stylus tip). In some examples, some or all of the characteristics of the input device can be used in processing to generate content, including textual character input and three-dimensional objects. In some examples, the generation of content can use information from one or more additional sensors for the input device and/or from additional devices in combination with the characteristics of the input device based on the SMI sensors for generation of content. 
       FIGS.  1 A- 1 E  illustrate examples of systems with touch screens that can accept input from an input device  100 , such as an active stylus, via a touch-sensitive surface and/or via a non-touch-sensitive surface according to examples of the disclosure.  FIG.  1 A  illustrates an exemplary mobile telephone  136  that includes a touch screen  124  that can accept input from an input device, such as an active stylus, via a touch-sensitive surface (e.g., touch screen  124 ) and/or via a non-touch-sensitive surface according to examples of the disclosure.  FIG.  1 B  illustrates an example digital media player  140  that includes a touch screen  126  that can accept input from an input device, such as an active stylus, via a touch-sensitive surface (e.g., touch screen  126 ) and/or via a non-touch-sensitive surface according to examples of the disclosure.  FIG.  1 C  illustrates an example personal computer  144  that includes a touch screen  128  that can accept input from an input device, such as an active stylus, via a touch-sensitive surface (e.g., touch screen  128 ) and/or via a non-touch-sensitive surface according to examples of the disclosure.  FIG.  1 D  illustrates an example tablet computing device  148  that includes a touch screen  130  that can accept input from an input device, such as an active stylus, via a touch-sensitive surface (e.g., touch screen  130 ) and/or via a non-touch-sensitive surface according to examples of the disclosure.  FIG.  1 E  illustrates an example wearable device  150  (e.g., a watch) that includes a touch screen  152  that can accept input from an input device, such as an active stylus, via a touch-sensitive surface (e.g., touch screen  152 ) and/or via a non-touch-sensitive surface according to examples of the disclosure. Wearable device  150  can be coupled to a user via strap  154  or any other suitable fastener. It should be understood that the example devices illustrated in  FIGS.  1 A- 1 E  are provided by way of example, and other devices can accept input from an input device, such as an active stylus, via a touch-sensitive surface and/or via a non-touch-sensitive surface according to examples of the disclosure. Additionally, although the devices illustrated in  FIGS.  1 A- 1 E  include touch screens, in some examples, the devices may have a non-touch sensitive display. As described in more detail below, the input device and computing device can include additional input/output (TO) capabilities to enable input from the input device via a non-touch-sensitive surface. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130  and  150  can be can be based on self-capacitance. A self-capacitance based touch system can include a matrix of small, individual plates of conductive material or groups of individual plates of conductive material forming larger conductive regions that can be referred to as touch electrodes or as touch node electrodes. For example, a touch screen can include a plurality of individual touch electrodes, each touch electrode identifying or representing a unique location (e.g., a touch node) on the touch screen at which touch or proximity is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch screen/panel. Such a touch screen can be referred to as a pixelated self-capacitance touch screen, though it is understood that in some examples, the touch node electrodes on the touch screen can be used to perform scans other than self-capacitance scans on the touch screen (e.g., mutual capacitance scans). During operation, a touch node electrode can be stimulated with an alternating current (AC) waveform, and the self-capacitance to ground of the touch node electrode can be measured. As an object approaches the touch node electrode, the self-capacitance to ground of the touch node electrode can change (e.g., increase). This change in the self-capacitance of the touch node electrode can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. In some examples, the touch node electrodes of a self-capacitance based touch system can be formed from rows and columns of conductive material, and changes in the self-capacitance to ground of the rows and columns can be detected, similar to above. In some examples, a touch screen can be multi-touch, single touch, projection scan, full-imaging multi-touch, capacitive touch, etc. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130  and  152  can be based on mutual capacitance. A mutual capacitance based touch system can include electrodes arranged as drive and sense lines that may cross over each other on different layers (in a double-sided configuration), or may be adjacent to each other on the same layer. The crossing or adjacent locations can form touch nodes. During operation, the drive line can be stimulated with an AC waveform and the mutual capacitance of the touch node can be measured. As an object approaches the touch node, the mutual capacitance of the touch node can change (e.g., decrease). This change in the mutual capacitance of the touch node can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. As described herein, in some examples, a mutual capacitance based touch system can form touch nodes from a matrix of small, individual plates of conductive material. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130  and  152  can be based on mutual capacitance and/or self-capacitance. The electrodes can be arrange as a matrix of small, individual plates of conductive material or as drive lines and sense lines, or in another pattern. The electrodes can be configurable for mutual capacitance or self-capacitance sensing or a combination of mutual and self-capacitance sensing. For example, in one mode of operation electrodes can be configured to sense mutual capacitance between electrodes and in a different mode of operation electrodes can be configured to sense self-capacitance of electrodes. In some examples, some of the electrodes can be configured to sense mutual capacitance therebetween and some of the electrodes can be configured to sense self-capacitance thereof. 
       FIG.  2    illustrates a block diagram of an example system including an example computing system  200  and an example input device  230  according to examples of the disclosure. Computing system  200  can receive input from input device  230 , such as an active stylus, and render content for display generated using the input device, such as writing or drawing by a stylus. Computing system  200  can be included in, for example, mobile telephone  124 , digital media player  140 , personal computer  128 , tablet computing device  130 , wearable device  150 , or any mobile or non-mobile computing device that includes a display. In some examples, wearable device  150  can be an AR/VR system with head-mounted display. 
     In some examples, computing system  200  can include an integrated touch screen  204  to display images and to detect touch and/or proximity (e.g., hover) events from an object (e.g. active or passive stylus or finger) at or proximate to the surface of the touch screen  204 . In some examples, touch screen  204  can be configured to display content generated using input device  230  (e.g., writing or drawings on a non-touch sensitive surface, or on the touch sensitive surface of touch screen  204 ). In some examples, computing system  200  can include a non-touch sensitive display configured to display content generated using the input device (e.g., writing or drawings on a non-touch sensitive surface). 
     In some examples, computer system  200  can include a power source  201  (e.g., energy storage device such as a battery), host processor  202 , program storage device  206  and/or memory  208 , wireless communication circuitry  210 , and sensor device(s)  212 . Host processor  202  can control some or all of the operations of computer system  200 . Host processor  202  can communicate, either directly or indirectly, with some or all of the other components of the computer system  200 . For example, a system bus or other communication mechanism can provide communication between power source  201 , the host processor  202 , touch screen or display  204 , program storage device  206 , memory  208 , wireless communication circuitry  210 , and sensor device(s)  212 . 
     Host processor  202  can be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions, whether such data or instructions is in the form of software or firmware or otherwise encoded. For example, the host processor  202  can include a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a controller, or a combination of such devices. As described herein, the term “processor” or “processing circuitry” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. In some cases, host processor  202  can provide part or all of the processing systems or processors described with reference to any of  FIGS.  3 - 18   . 
     Host processor  202  can receiving touch input to touch screen  204  or other input devices and performing actions based on the outputs. For example, host processor  202  can be connected to program storage  206  (and/or memory  208 ) and a display controller/driver to generate images on the display screen. The display screen includes, but is not limited to, Liquid Crystal Display (LCD) displays, Light-Emitting Diode (LED) displays, including Organic LED (OLED), Active-Matrix Organic LED (AMOLED), Passive-Matrix Organic LED (PMOLED) displays, a projector, a holographic projector, a retinal projector, or other suitable display. In some examples, the display driver can provide voltages on select (e.g., gate) lines to each pixel transistor and can provide data signals along data lines to these same transistors to control the pixel display image for touch screen  204 . 
     Host processor  202  can cause a display image on touch screen  204 , such as a display image of a user interface (UI) or display image of content generated using input device  230 , and can use touch processor and/or touch controller to detect a touch on or near touch screen  204 , such as a touch input to the displayed UI when computing system  200  includes a touch screen. The touch input can be used by computer programs stored in program storage  206  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  202  can also perform additional functions that may not be related to touch processing. 
     Note that one or more of the functions described in this disclosure can be performed by firmware stored in memory  208  and/or stored in program storage  206  and executed by host processor  202  or other processing circuitry of computing device  200 . The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding signals) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. In some examples, program storage  206  and/or memory  208  can be a non-transitory computer readable storage medium. The non-transitory computer readable storage medium (or multiple thereof) can have stored therein instructions, which when executed by host processor  202  or other processing circuitry, can cause the device including computing system  200  to perform one or more functions and methods of one or more examples of this disclosure. The computer-readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic or infrared wired or wireless propagation medium. 
     The power source  201  can be implemented with any device capable of providing energy to computing system  200 . For example, the power source  201  can include one or more batteries or rechargeable batteries. Additionally or alternatively, the power source  201  can include a power connector or power cord that connects computing system  200  to another power source, such as a wall outlet. 
     Memory  208  can store electronic data that can be used by computing system  200 . For example, memory  208  can store electrical data or content such as, for example, audio and video files, documents and applications, device settings and user preferences, timing signals, control signals, and data structures or databases. Memory  208  can include any type of memory. By way of example only, memory  208  can include random access memory, read-only memory, Flash memory, removable memory, other types of storage elements, or combinations of such memory types. 
     Sensing device(s)  212  can include sensors circuitry configured to sense one or more types of parameters, such as but not limited to, vibration; light; touch; force; heat; movement; relative motion; biometric data (e.g., biological parameters) of a user; air quality; proximity; position; connectedness; and so on. In some examples, sensing device(s)  212  can include an image sensor such as an outward facing camera  214 , a radiofrequency sensor (and/or transmitter)  216 , an infrared sensor (and/or transmitter)  218 , a magnetic sensor (and/or generator)  220  (e.g., a magnetometer), an ultrasonic sensor (and/or transmitter)  222 , and/or an inertial measurement unit  224 . It should be understood the  FIG.  2    illustrates some example sensors of sensing device(s)  212 , but that the sensors are not so limited. In some examples, the sensing device(s)  212  can further include other sensor(s) including a heat sensor, a position sensor, a light or optical sensor, an accelerometer, a pressure transducer, a gyroscope, an acoustic sensor, a health monitoring sensor, and/or an air quality sensor, among other possibilities. Additionally, the one or more sensors o sensing device( 2 )  212  can utilize any suitable sensing technology, including, but not limited to, interferometric, magnetic, capacitive, ultrasonic, resistive, optical, acoustic, piezoelectric, or thermal technologies. 
     Wireless communication circuitry  212  can transmit or receive data from another electronic device, such as from input device  230 . Although wireless communication circuitry  22212  is illustrated and described, it is understood that other wired communication interfaces may be used. In some examples, the wireless and/or wired communications interfaces can include, but are not limited to, cellular, Bluetooth, and/or Wi-Fi communications interfaces. Although not shown, computing system  200  can also include other input/output mechanisms including one or more touch sensing input surfaces, a crown, one or more physical buttons, one or more microphones or speakers, one or more ports such as a microphone port, and/or a keyboard. Additionally or alternatively, 
     Input device  230  can including a housing. In some examples, the housing of a stylus input device can include a cylindrical body  232  (referred to herein as a stylus body  232 ) with a tip portion (referred to herein a stylus tip  234  or tip portion) at the distal end. In some examples, the tip portion  234  can be part of a unibody housing and in some examples, the tip portion  234  can be removable from the cylindrical body  232 . The housing can include an ergonomic depression  258  (or multiple ergonomic depressions) as a guide for placement of one of a user&#39;s fingers (e.g., thumb or index finger). The ergonomic depression  258  (also referred to herein as a notch or guide) can result in the orientation of the input device in a range of positions with respect to a user&#39;s hand and finger gestures. The circuitry of the input device  230  can be disposed in the housing. For example, the circuitry can include, a power source  231  (e.g., battery), processing circuitry (e.g., processor  260 ), memory  264 , wireless communication circuitry  262  and various sensors. The sensors can include, SMI sensors  242 , among other possible sensors. In some examples, input device  230  can include an outward facing camera  236 , a beacon transmitter  238  (e.g., using any electromagnetic signals), an ultrasonic sensor (and/or transmitter)  244 , a force sensor  246  (e.g., such as a strain gauge, capacitive gap force sensor, a piezoelectric sensor  240 ), an IMU  248  (and/or other motion or orientation device such as an accelerometer or gyroscope), a capacitive electrode or other capacitive sensor  250 , a radiofrequency sensor (and/or transmitter)  252 , infrared sensor (and/or transmitter)  254 , a magnetic sensor (and/or generator)  220 , among other suitable sensors. Processor  260  can communicate, either directly or indirectly, with some or all of the other components of input device  230 . For example, a system bus or other communication mechanism can provide communication between the various components of input device  230 . 
     As described herein, in some examples, motion and/or position of input device  230  can be tracked to generate input for computing system  200 . In some examples, position and/or motion of input device  230  can be tracked using SMI sensors  242 . For example, input device  230  can include a plurality of SMI sensors  242 . In some examples, input device  230  can be a stylus and the plurality of SMI sensors  242  can be disposed in the distal end of the stylus, such as in proximity the stylus tip  234 . The SMI sensors  242  can be configured to both transmit and receive light (e.g., emitting and receiving a laser beam), which can provide data about the position and movement of the stylus tip  234  relative to a non-touch-sensitive surface. 
     In some examples, tracking the position and/or motion of input device  230  using the SMI sensors  242  can be augmented with additional sensors. For example, the sensor device(s)  212  and or the various sensors of input device  230  can track information about the input device  230  (e.g. position, motion, orientation, force, etc. of the input device) and the information can be transferred from the one or more sensor device(s)  212  to the host processor  202 . The information from the input device (e.g., received via wireless communication circuitry  210 ,  262 ) and the one or more sensor device(s)  212  can be stored in memory  208 , in some examples. The information can be processed by host processor  202  to render and/or display content on the display  204  from the input device  230  (e.g., rendering writing or drawing by a stylus input device on non-touch sensitive surfaces on the display). In some examples, the information about the input device can be gathered by, transferred to, processed by and/or stored on the stylus. For example, one or more sensing modalities within the input device can provide additional information about input device force, orientation, motion, and/or position. The combined information from the SMI sensors and the one or more sensing modalities can then be transferred to, processed by, and/or stored on a computing device to render and/or display content on the display according to examples of the disclosure. In some examples, a computing device can render content in three-dimensional environment based on position and/or motion of an input device. For example, system  200  can be a head-mounted augmented and/or virtual reality headset that can render and overlay content over a real-world environment or a representation of a real-world environment captured by outward facing cameras  214 . 
     It should be apparent that the architecture shown in  FIG.  2    is only one example architecture of computing system  200  and input device  230 , and that the system could have more or fewer components than shown, or a different configuration of components. The various components shown in  FIG.  2    can be implemented in hardware, software, firmware or any combination thereof, including one or more signal processing and/or application specific integrated circuits. 
     As described herein, in some examples, an input device including SMI sensors can be used for input on a non-touch sensitive surface.  FIG.  3    illustrates an example process  300  for generating content with an input device on a non-touch sensitive surface according to examples of the disclosure. At  305 , one or more parameters associated with the input device can be detected and/or tracked. In some examples, the parameters associated with the input device can detected and/or tracked at least partially using SMI sensors. In some examples, the one or more parameters can include a position of the input device, motion of the input device, orientation of the input device, and force information, among other parameters. In some examples, the SMI sensors can be used to track motion of a stylus tip  234  relative to a non-touch sensitive surface to determine two-dimensional or three-dimensional displacement and distance of the stylus tip relative to the non-touch sensitive surface. In some examples, force information can represent contact between the input device (e.g., stylus tip  234 ), measured using force sensor  246 . In some examples, the force data can be represented as variable force measurements, such as raw data representative of the force applied to the stylus tip  234 . In some examples, the force data can be represented as a binary measurement, in which a force measurement above a first threshold can result in a report of a contact and a force measurement below a second threshold can result in a break of contact with the surface. In some examples, the first and second thresholds can be the same. In some examples, the first and second thresholds can be different to provide a level of hysteresis and avoid high frequency transitions between detecting an initiation or break in contact. 
     At  310 , the parameters associated with the input device—optionally including position, motion, and/or orientation of the input device—can be transmitted to processing means. At  315 , the parameters associated with the input device can be processed by the processing means. In some examples, the processing means can include processor  260  which can be configured to process the parameters from the SMI sensors into processed parameters. For example, the parameters associated with the input device that are detected and/or tracked by the SMI sensors of the input device can include a velocity and distance measurement for each SMI sensor, and the processor  260  can convert these velocity and distance measurements into two-dimensional, three-dimensional, four-dimensional, five-dimensional, or six dimensional displacement parameters (e.g., x, y, and z relative displacement, tilt, orientation and/or axial rotation). In some examples, the parameters tracked by the SMI sensors can be processed along with other parameters associated with the input device that are detected and/or tracked by other sensors of the input device to generate processed parameters. In some examples, the processing means can include processor  260  and/or host processor  202 , which can be configured to process the parameters from the SMI sensors into processed parameters. For example, the parameters associated with the input device that are detected and/or tracked by the SMI sensors of the input device (optionally processed in part by processor  260 ) can be transmitted to host processor  202  for processing by a different computing device (e.g., computing system  200 ) to generate processed parameters. In some examples, the processing circuitry of the different computing device (e.g., host processor  202 ) can be configured to process the parameters associated with the input device that are received from the input device and the parameters detected and/or tracked by sensor device(s) of the computing device. 
     At  320 , processed parameters associated with the input device can be stored in memory in one or both of the input device and a different computing device (e.g., in memory  208  or  264 ). For example, the results of processing by processor  260  can be stored in memory  264  and/or transmitted to computing system  200  for storage, rendering and/or display of input device content (e.g., writing or drawing) based on the tracked and processed parameters of the input device. Additionally or alternatively, in some examples, the parameters can be transferred between the input device and the computing device (e.g., using wired or wireless communication circuitry). The tracked input device parameters can be stored and/or processed to generate content at the computing device that can be rendered on the display. 
     In some examples, the detection and/or tracking of one or more parameters can be performed when the input device is not touching or proximate to a touch-sensitive surface of a computing device (e.g., disabled when over or touching a touch screen  204 ). In some examples, the detection and/or tracking of one or more parameters can be performed when the different computing device detects the input device in proximity with a non-touch sensitive surface and/or when the different computing device detects a hand holding the input device in a pose and/or with an orientation indicative of intended input by the user of the input device. 
     As described herein, in some examples, a system including an input device with SMI sensors and a computing device including a display (e.g., a head-mounted display device) can be used for rendering content on the display based on input from the input device on a non-touch sensitive surface.  FIG.  4    illustrates an example process  400  for generating content with more one or more input devices on a non-touch sensitive surface according to some examples of the disclosure. At  405 , the input device can be activated (woken up) in accordance with satisfying one or more activation criteria. In some examples, activating or waking-up the input device can cause the SMI sensors to be powered on to measure parameters of the input device, can cause an input device processor to be powered on to process the data from the SMI sensors and/or power on the communication circuitry to transmit data from the input device to a different computing device. In some examples, activating or waking-up the input device can refer to configuring the SMI sensor scans to run at a different scan rate (e.g., more frequently) or at a different (e.g., higher) resolution of SMI scan, configuring the wireless communication circuitry to operate at a different power level or rate (e.g., increasing the power and/or rate of communication), and/or configuring the processing circuitry to operate at a different power level or rate (e.g., increasing the power and/or processing rate), among other possibilities. 
     In some examples, the one or more activation criteria can be based on detecting and/or tracking one or more parameters associated with the input device indicative of a change in an operating state of input device. In some examples, the activation criteria can be related to one or more sensors of the input device. For example, as discussed previously, the input device can include a force sensor (e.g., force sensor  240 , piezoelectric sensor  246 ) configured to detect force above a threshold indicative of a user holding the input device (e.g., a force-based activation criterion that is satisfied when the amount of force is above a threshold, and not satisfied when the force threshold is below the threshold). In some examples, the force sensor can be a strain gauge or piezoelectric sensor (e.g., corresponding to piezoelectric sensor  246 ). In some examples, the force sensor can be disposed beneath ergonomic depression  252  in the stylus body  232 . In some examples, the force sensor can be disposed in other regions around the stylus body  232 . Additionally or alternatively, in some examples, one or more SMI sensors can also be configured as a force sensor. The one or more SMI sensors can also be configured to measure force in combination with one or more force sensors (e.g. force sensor  240 , piezoelectric sensor  246 ). As another example, the input device can include a motion sensor (e.g., IMU  248 ) configured to detect motion of the input device. In some examples, a specific orientation of the input device and/or a pattern of movement of the input device can be indicative of a user picking up the input device and/or holding the input device in a pose ready for user input. In such examples, the one or more activation criteria can include a motion and/or orientation based activation criterion that is satisfied when the motion and/or orientation indicate a user picking up the input device or holding the input device in a pose for input, and not satisfied when the motion and/or orientation indicate otherwise. 
     Additionally or alternatively, in some examples, the activation criteria can relate to one or more sensors of a computing device different from the input device. For example, an image sensor of a computing device (e.g., outward facing camera(s)  214 ) can be used. In some examples, the activation criteria can include a criterion that the input device is within the field of view of the outward facing camera(s)  214 . In some examples, the activation criteria can include a criterion that the input device is within a threshold distance of a writing surface (e.g., a wall, a table, a pad of paper, a floor). In some examples, the activation criteria can include a criterion that the input device is held within a hand based on detection of a pose of the hand holding the input device and/or based on a pattern of occlusion of the input device by a hand of the user. 
     At  410 , input device can detect contact between the input device and a surface (e.g., a non-touch sensitive surface or a touch-sensitive surface). In some examples, contact between the input device and the surface can indicate an input from the input device (e.g., an initiation of writing or drawing input). In some examples, the contact can be based on one or more sensors of the input device. In some examples, the SMI sensors (e.g., optionally activated when the activation criteria are satisfied) can be used to track distance between the stylus tip  234  and the surface, and a contact can be detected when the distance to the surface is less than a threshold (e.g., zero or within a threshold of zero based on the distance between the SMI sensor and the stylus tip point). Additionally or alternatively, the contact can be detected based on force applied to the stylus tip  234  (e.g., using force sensor  246 ) or based on motion (e.g., using an accelerometer or IMU  248 ) that are indicative of contact between the input device and the surface. 
     At  415 , the system can localize the input device to determine one or more spatial relationships between the input device and the computing device or between the input device and the surface within a three-dimensional space. As described herein, localizing the input device can enable the tracking and generation of content using relative movement detected by the SMI sensors of the input device. In some examples, a spatial relationship between the input device (e.g., stylus tip) and a non-touch-sensitive surface can be determined. In some examples, a variety of sensors and/or wireless communication circuitry can be used to determine the stylus position and/or motion with respect to the surface. For example, SMI sensors can be used to determine parameters including, but not limited to, angle (e.g., azimuth, radial, orientation/tilt), movement, and position in relation to the surface. In some examples, the input device can be localized using the sensors of the system. For example, the computing device (e.g., a head mounted display) can use outward facing camera(s)  214  to detect the input device with respect to the three-dimensional surface. In some examples, the computing device can generate information including, but not limited to, the position and/or movement of the outward facing camera with respect to a non-touch sensitive surface. In some examples, a head mounted display comprising an outward facing camera can capture information about the position and/or movement of the outward facing camera with respect to the input device. In some examples, the system can additionally or alternatively use one or more infrared sensors (e.g., using infrared sensor (and/or transmitter)  218 ,  254 ), magnetic sensors (e.g., magnetic sensor (and/or generator)  220 ,  256 ), radiofrequency sensors (radiofrequency sensor (and/or transmitter)  216 ,  252 ), etc. to localize the input device relative to the surface. In some examples, the input device can comprise one or more infrared (IR) or near IR wavelength light-emitting diodes and the computing system can include one or more cameras configured to detect 2D/3D position of IR or near IR light (e.g., to detect a pattern of IR or near IR light and/or a sequence of positions or patterns of IR or near IR light). In some examples, the input device can comprise active or passive magnetic components and/or RF components configured to operate in an ultra-low power mode or without a power supply and the computing system can include a magnetometer or RF receivers to triangulate three-dimensional position of the input device. 
     In some examples, the localization can match and lock the input device self-orientation (e.g., azimuth and radial angle) with the three-dimensional writing surface orientation, so that writing or drawing input from the input device can be displayed accurately along with the surface or a representation of the surface in a three-dimensional environment. 
     At  420 , the parameters of the input device can be tracked and used to render content on the three-dimensional environment displayed by the display. For example, the head mounted display can be used in conjunction with the input device to display writing or drawings on a non-touch sensitive surface in the real-world environment. The rendering can be based on relative motion by the input device and based on the spatial relationships from the localization at  415 . For example, as described above with respect to  FIG.  3   , one or more parameters associated with the input device can be detected and/or tracked. The one or more parameters can include position, orientation, and/or movement of the one or more input devices. In some examples, the one or more parameters can include a displacement of the stylus tip  234  tracked using the SMI sensors, including angle-corrected lateral velocity and displacement. In some examples, the computing device of the system (e.g., a head mounted display) can present the three-dimensional environment or a representation of the three-dimensional environment and render writing or drawing by the input device using the one or more parameters tracked at least partially using the SMI sensors in the three-dimensional environment. As described above with respect to  FIG.  3   , the tracking of the one or more parameters can include tracking additional complimentary, or redundant information from the SMI sensors or additional sensors (e.g., IMU of the input device, force of the force sensors, SMI distance from the surface, etc.) to augment the tracking of the input device motion, orientation and force to render the input device content. 
     At  425 , input device can detect a break in contact between the input device and the surface (e.g., a non-touch sensitive surface or a touch-sensitive surface). In some examples, break in contact between the input device and the surface can indicate a temporary end of an input from the input device (e.g., an initiation of a break in writing or drawing input between strokes). These breaks can be used to avoid digital inking using the input device between strokes. In some examples, the break in contact can be based on one or more sensors of the input device. In some examples, the SMI sensors can be used to track distance between the stylus tip  234  and the surface, and a break in contact can be detected when the distance to the surface is greater than a threshold (e.g., zero or more than a threshold of zero based on the distance between the SMI sensor and the stylus tip point). Additionally or alternatively, the break in contact can be detected based on force applied to the stylus tip  234  (e.g., using force sensor  246 ) or based on motion (e.g., using an accelerometer or IMU  248 ) that are indicative of a break in contact between the input device and the surface. 
     At  430 , the input device can be deactivated (sleep) in accordance with satisfying one or more deactivation criteria. In some examples, deactivating or sleeping the input device can cause the SMI sensors to be powered down (put in a low-power mode), causing the input device processor to be powered down (put in a low-power mode) and/or power down (put in a low-power mode) the communication circuitry. In some examples, deactivating or sleeping the input device can refer to configuring the SMI sensor scans to run at a different scan rate (e.g., less frequently) or at a different (e.g., lower) resolution of SMI scan, configuring the wireless communication circuitry to operate at a different power level or rate (e.g., decreasing the power and/or rate of communication), and/or configuring the processing circuitry to operate at a different power level or rate (e.g., decreasing the power and/or processing rate), among other possibilities. The one or more sleep criteria can include one or more of detecting a user is no longer holding the input device or no longer using the input device for input (e.g., force threshold is below a threshold, motion indicative of a user putting down the input device and/or holding the input device outside a pose ready for user input, a writing surface is not detected in the field of view of the outward facing camera(s)  214 , the input device is outside a threshold distance of a writing surface, and/or a visual indication that the input device is not held within a hand). 
     Localization can be performed in a number of contexts, including, but not limited to, when the stylus enters a wake-up condition, when the stylus comes within a threshold distance of a non-touch sensitive writing surface, when the stylus begins and/or stops writing as described by step  425 , when the stylus is placed on a surface, when the stylus is moved across a surface, intermittently while the stylus is at rest  430 , etc. 
     It is understood that process  400  illustrated in  FIG.  4    is not limited to the operation as presented, but can include, fewer, additional, and/or simultaneous operations according to various examples. For example, the input device may remain in an activation state at all times or be manually activated rather than activating or deactivating the input device at  405  and  430 . Additionally or alternatively, the system can localize and re-localize the input device relative to the computing device and/or real-world surface multiple times before, during, and after contact, tracking parameters of the input device, or break in contact. In some examples, writing or drawing input from the input device can be used without rendering the content on the display at the localized region within the three-dimensional environment. For example, the tracking of the input device position can be used to identify specific relative motions indicative of corresponding inputs. For example, input writing letters can be used to render text input to an active text input user interface on the display without the writing being rendered as handwriting at the location of the input device within the three-dimensional space. As another example, movement corresponding to a check mark can be detected as a selection or confirmation input rather than as writing or drawing input localized to the surface within the three-dimensional environment. 
     As described herein, computing system  200  can be implemented to localize and/or track stylus movement according to examples of the disclosure.  FIG.  5    illustrates a system comprising an input device  530  (e.g., a stylus corresponding to input device  230 ) and a computing system  500  (e.g., corresponding to computing system  200 ). The computing system can comprise one or more outward facing cameras  514  (e.g., corresponding to outward facing camera(s)  214 ) that can capture input device  530  and a non-touch-sensitive surface  576  in its field of view. The input device  530  can comprise one or more SMI sensors and/or can include any appropriate combination of the one or more sensors described according to the examples of the disclosure. In some examples, input device  530  can make contact with non-touch-sensitive-surface  576  at point  570 , draw a stroke  574  on non-touch-sensitive-surface  576  (e.g., a line) between points  570  and  572 , and break contact with non-touch-sensitive-surface  576  at point  572 . The input device  530  movement and/or position information can be collected by sensors within stylus  530  (e.g., relative displacement using SMI sensors). Stroke  574  can be rendered on writing surface  504  using the display (e.g., corresponding to display  204 ) of computing system  500  as a line between points  570  and  572 , however the computing system  500  can render a corresponding straight line  505   c  on the display with the correct orientation and position with respect to writing surface  504  as the input stroke using input device  530  on the real-world writing surface  576 . The correct position and/or orientation can be achieved using the spatial relationship between the input device  530  and the real-world writing surface  576  using localization. Without localization, the relative motion of stroke  504  could be used to generate other lines with different orientations and positions (or less accurate positions/orientations) with respect to the real-world environment as represented by line  505   a  or line  505   b , each of which can correspond to the relative line motion rendered of stroke  574 . Thus, the user experience can be improved by the system computing system  500  and/or input device  530  include a one or more sensor components to collect information about the absolute position of input device  530  and non-touch sensitive surface  576  and/or spatial relationships between the input device and the surface. In some examples, outward facing camera(s)  514  can collect information that identifies input device  530  and its absolute position/spatial relationship with respect to non-touch-sensitive surface  576 . 
     The localization described with respect to  FIG.  5    relies on the camera of computing device  500 , but in some examples, the localization can involve components of both the input device and the computing device.  FIG.  6    illustrates an exemplary system comprising an input device  630  (e.g., corresponding to input device  230 ) and a computing system  600  (e.g., corresponding to computing system  200 ) according to examples of the disclosure. In some examples, the computing system can comprise one or more light emitting components  618  (e.g., one or more infrared transmitters  218 ) configured to emit light (e.g., infrared light), including towards a non-touch-sensitive surface  676 . In some examples, the light emitting components  618  can be configured to emit structured light (e.g., light having a pattern array) onto the non-touch-sensitive surface that can be detected by a light detector such as outward facing camera  636 . In some examples, the structured light can change the intensity, dimensions, or density of projected light beams that can be identified using camera sensors or other light detector(s) and used to provide information about the spatial relationship between the input device, surface, and computing system. In some examples, outward facing camera  636  can be disposed in or near the tip of the input device  630  (e.g., stylus tip  234 ) to image the surface in proximity or contact with the input device tip. Additionally, as described herein, input device  630  can comprise one or more SMI sensors among other sensors to detect and/or track input device  630  making contact with non-touch-sensitive-surface  676  at point  670 , relative motion of a stroke  674  on non-touch-sensitive-surface  676  (e.g., a line) between points  670  and  672 , and a break in contact with non-touch-sensitive-surface  676  at point  672 . Stroke  674  can be rendered on the writing surface using the display of computing system  600  as a line between points  670  and  672 , in a similar manner as describe with respect of  FIG.  5   , but using the absolute position/spatial relationship(s) between the input device  630 , non-touch sensitive surface  676  and/or computing system  600  and the relative motion of input device  630  with respect to non-touch sensitive surface  676  to render the content. In some examples, light emitter and detector configuration can be reversed such that the input device can emit light and the computing system can detect light to determine a spatial relationship between the input device and the computing system. 
     As described herein, SMI sensors can be used to track distance to a surface and/or relative motion of the input device with respect to a surface. In some examples, the SMI sensors can be configured to emit two or more beams to a surface external to the input device as described with reference to  FIGS.  7 A- 9 B . In some examples, one or more SMI sensors can be configured to emit light toward a component at least partially internal to the input device as described with reference to  FIGS.  10 - 12   . 
       FIGS.  7 A- 7 C  illustrate an example input device configuration with two SMI sensors according to examples of the disclosure. Input device  730  can be a stylus including a tip  734  formed at least partially from a partially or completely optically transparent material (e.g., represented by cover glass  784 ), and SMI sensors  742  including a first SMI sensor  742   a  and a second SMI sensor  742   b  that can be configured to track displacement in two-dimensions (e.g., in an x-y plane). In some examples, SMI sensors  742  can be arranged and the materials of the tip  734  can be designed to provide an improved or optimal refraction angle for the beams of the SMI sensors. For example, as shown in the top view of a cross-section of the stylus tip in  FIG.  7 B , a first SMI sensor  742   a  and a second SMI sensor  742   b  can be arranged mutually orthogonal and orthogonal to a third dimension relative to the plane of surface  776 . In some examples, optical components can be disposed between the tip  734  and SMI sensors  742  to properly orient beams of light emitted and/or received by the SMI sensors. For example, the optical components can comprise a lens  782  and one or more translucent or transparent materials  780  (e.g., a total internal reflection surface) configured to refract light in a desired (or optimal) refraction angle. Lens materials can comprise translucent or transparent material, including, but not limited to, a lens substrate, glass, optical polyester (e.g., OKP-1), organic materials, etc. The lens can be shaped to refract and/or reflect light as required to achieve a desired signal-to-noise ratio (SNR), system speed, and/or accuracy. For example, the lens can be shaped to focus and/or collimate the light. Although optical components are shown for one SMI sensor in  FIG.  7 C , it is understood that similar components could be used for each SMI sensor. 
     As described herein, SMI sensors can be configured to measure information including velocity, distance and displacement by transmitting and receiving light. The transmitted light can reflect off non-touch-sensitive surface  776 , the reflected light can pass through the transparent tip and be detected by SMI sensors  742   a  and  742   b . In some examples, the sensors can be driven with waveform configurations according to examples of the disclosure. For example, the sensors can be driven with a triangular current waveform. In other examples, the sensors can be driven with a sinusoidal input. When driven by a sinusoidal input, the received signals can be demodulated. For example, a in-phase/quadrature (I/Q) demodulation scheme can implemented. 
       FIGS.  8 A- 8 D  illustrate an example input device configuration with three SMI sensors according to examples of the disclosure. Input device  830  can be a stylus including a tip  834  formed at least partially from a partially or completely optically transparent material (e.g., represented by cover glass  884 ), and SMI sensors  842  including a first SMI sensor  842   a , a second SMI sensor  842   b , and a third SMI sensor  842   c , that can be configured to track displacement in three-dimensions (e.g., x, y and z axes). In some examples, SMI sensors  842  can be arranged and the materials of the tip  834  can be designed to provide an improved or optimal refraction angle for the beams of the SMI sensors. For example, as shown in the top view of a cross-section of the stylus tip in  FIG.  8 B , a first SMI sensor  842   a , a second SMI sensor  842   b , and a third SMI sensor  842   c  can be arranged such that beams of light emitted from any pair of sensors upon exiting the tip  834  are mutually orthogonal (or within a threshold angle such that the beams are approximately orthogonal). In some examples, optical components  880  can be disposed between the tip  834  and SMI sensors  842  to properly orient the path of beams of light emitted and received by the SMI sensors. For example, as shown in the side profile and perspective views of  FIGS.  8 C and  8 D , the optical components  880  can include one or more lenses  882   a - 882   c  and/or TIR surfaces  870   a - 870   c  similar to those described with reference to  FIG.  7 C  and not repeated here for brevity. 
       FIGS.  9 A- 9 B  illustrate an example input device configuration with three SMI sensors according to examples of the disclosure. Input device  930  can be a stylus including a tip  934  and three SMI sensors  942  arranged 120 degrees apart (or within a threshold angle of 120 degrees apart) along the circumference of the stylus and oriented such that beams of light emitted by each sensor are mutually orthogonal as shown by the beams  943   a - c  emitted by SMI sensors  942   a - c . For example, as shown in the top view of a cross-section of the stylus tip in  FIG.  9 B  and projected onto the plane of the surface, a first SMI sensor  942   a , a second SMI sensor  942   b , and a third SMI sensor  942   c  can be arranged such that beams of light emitted from any pair of sensors upon exiting the tip  934  have approximately 120 degrees of separation when projected into the plane of the surface. The stylus housing can include transparent or translucent windows configured to allow light from the SMI sensors to exit the stylus housing and return to the SMI sensors. Additionally, the SMI sensors  942  can be disposed at a different, greater distance from the point of the stylus tip as compared with input devices  730  and  830 . The SMI sensors  942  can be configured to measure displacement based on light reflected off a surface including, but not limited to, micron-scale changes in three-dimensional position. Stylus movement with respect to the surface, therefore, can be captured with a high degree of resolution. 
     In some examples, SMI sensors  942   a - c  can measure distance (e.g., from non-touch sensitive surface  976 ) and velocity information for three-axes that can be used to determine stylus position, orientation and/or movement. For example, the input device can capture distance and velocity measurements for each of the three SMI sensor. Based on the relative position and motion, the processing circuitry of the input device and/or computing system can calculate displacement within a 3-dimensional space. In some examples, the processing can include calculating movement information including, but not limited to, stylus tilt with respect to the non-touch sensitive surface, yaw of stylus about an axis extending from a line along a first dimension of the stylus body, and orientation of the stylus with respect to a surface. In some examples, the system can contextualize information gathered before, during and/or after a stylus is moved to extrapolate stylus position and/or motion when SMI sensor data may be incomplete. For example, a stylus can be held in a transient position including, but not limited to, held orthogonal to the surface or held parallel to the surface such that one or more SMI beams may not be incident on the surface, or otherwise held at a distance outside of a focusing range of the SMI sensors. As a result, the SMI sensors may not receive a retroreflective signal from the surface, or may not receive a complete retroreflective signal (e.g., missing a lateral beam vector component corresponding to lateral velocity). To determine three-dimensional position and/or movement of the stylus, the system can extrapolate from information that precedes or follows the previously mentioned transient positions. Integrating movement and/or position data prior to the transient position can allow for an estimate the movement and/or position of the stylus during the transient state. For example, the velocity measured by one or three or more SMI sensors can be used to calculate information about stylus movement and/or position when the stylus is held orthogonal or parallel to a non-touch-sensitive surface. 
     In some examples, as described herein the arrangement of three or more SMI sensors can provide information that informs how the system renders strokes on a display. For example, stylus tilt can be determined and vary properties of strokes rendered on the display. Stylus tilt can be calculated using the input of three or more SMI sensors with respect to the non-touch-sensitive surface. For example, while writing, the stylus end opposite from the tip can be lowered towards the non-touch-sensitive surface. The system can be configured to emulate the experience of writing with a pen or pencil such that, when the stylus is lowered towards the non-touch-sensitive surface, a line width rendered on the display can increase. In further examples, while writing, the stylus end opposite from the tip can be raised away from the non-touch-sensitive surface, towards a position wherein the stylus is orthogonal to the surface. The system can be configured to narrow line width rendered on the display in response to detecting the stylus movement. 
     In some examples, to improve estimation of stylus yaw and more accurately process and render strokes, the computing system (e.g., computing system  200 ) can use information from one or more sensing devices  212  and from the stylus (e.g., input device  230 / 930 ) to store a multi-dimensional map of the non-touch sensitive surface  976 . Prior to rendering strokes on the display, information from three or more SMI sensors can be used by the one more processors to correct any skew in the surface coordinate system that may result from stylus rotation in the hand of the user. Using the addition of information from SMI sensors to calculate stylus yaw can be used to reduce algorithmic complexity, thus reducing processing power and/or increasing processing speed, according to some examples of the disclosure. 
     In some examples, input device  930  can include an opaque tip that can provide for a broader range of tip materials, which may be better for user experience. For example, the material of the tip may be selected to provide a physical feedback of friction that may be similar to the friction between a writing surface and a tip of an ink or lead pen or pencil. The friction provided by the tip can prevent erroneous marks on the paper and provide more accurate input using a stylus. To emulate the sensation, tip  934  can be formed from materials that provide a similar writing experience while allowing SMI sensors to receive reflections from a non-touch-sensitive surface. For example, the tip can be formed from a plastic material that when moved across a non-touch sensitive surface can provide frictional drag, thus emulating the sensation of writing with a pen or pencil. Additionally, the tip material can be selected to avoid damaging surface, to improve durability and/or to resist wear of the stylus tip. 
     In some examples, the stylus can write on a curved (non-planar), non-touch-sensitive surface. For example, SMI sensors  942   a - c  can be arranged such that beams  943   a - c  transmitted from each SMI sensor can be incident on the non-touch sensitive surface  976  and provide displacement and velocity information from points sufficiently far apart to allow for detection of surface curvature. Beams can be directed, for example, between 0.5-2 mm apart as projected on the surface. In some examples, the beams can be separated by approximately one millimeter. The information from the SMI sensors can be processed by the processing circuitry of the computing system and/or input device to understand the planarity of the surface, using the calculated surface planarity to render lines corresponding to stylus strokes on the surfaces in the three-dimensional environment while reducing or eliminating influence from curvature of the non-touch sensitive surface. 
     As described herein, in some examples, the SMI sensors can be configured to measure displacement of internal components of an input devices, such as by tracking displacement of a rod or trackball at least partially disposed in the housing of the input device. 
       FIG.  10    illustrates an example stylus input device configuration with a plurality of SMI sensors and a rod formed from compliant materials according to examples of the disclosure. As illustrated in  FIG.  10   , the compliant rod  1092  can be disposed at partially within the housing of stylus  1030 . In some examples, the compliant rod  1092  can be partially integrated with the stylus tip  1034 . When writing on surface  1076 , force applied to the stylus tip  1034  can couple to compliant rod  1092 , causing displacement of the rod within the stylus housing (e.g., within the cavity of the housing). In some examples, one or more SMI sensors can be configured to track movement of compliant rod  1092 . For example, one or more SMI sensors  1042   a  can be arranged to emit light towards the end of the compliant rod to measure axial displacement. A sensor positioned to track movement of the end of the compliant rod can provide information about strokes generated by the stylus while in contact with the non-touch-sensitive surface according to examples of the disclosure. For example, contact and applied force vectors between the surface and the stylus can move the compliant rod towards SMI sensor  1042   a . Displacement and velocity of the compliant rod with respect to SMI sensor(s)  1042   a  can then be used to understand the force applied to the stylus. Information about force vectors applied to the stylus tip can be used to vary properties of content generated on a display including, but not limited to, traces and directions of stroke vectors from surface lateral movement tracking, stroke line width and its changes from surface-normal force detection, stroke textures from surface friction/roughness detection. Additionally or alternatively, in some examples, one or more additional SMI sensors  1042   b  can be arranged circumferentially around the rod, optionally at a non-orthogonal angle with respect to the axis of the rod. For example, a number of SMI sensors  1042   b  can be used in conjunction to capture deflections of the compliant rod  1092  in two or three dimensions and these deflections of the compliant rod can be used to detect the relative motion and/or position of the stylus. Because the SMI sensor beams target the compliant rod internal to the stylus, such an implementation removes a requirement for transparent or translucent materials for the housing. In some examples, the rod can be formed at least partially of rigid materials, including, but not limited to, plastics that can reflect light from the SMI sensors. Rod materials can provide writing detection on surfaces independent of optical properties of the writing surfaces with which the stylus is used. In some examples, as the portion of rod  1092  that contacts surface  1076  vibrates in response to surface roughness, the stylus can include one or more sensors configured to capture vibration. For example, one or more IMU and/or force sensors can be used to collect information about vibration. System  200  can then process information about vibration to account for surface roughness, varying properties of rendered lines on a display. It is understood that although SMI sensors provide benefits such as high resolution positioning, tracking of stylus tilt, and translation of the rod, alternative sensing modalities can be implemented. Additionally or alternatively, sensing types including, but not limited to, capacitive and piezoelectric sensors. In some examples, pencil rotation can be detected through integration with one or more components including, but not limited to, an external camera, magnetic sensing, calibrated IMUs, or an ergonomic depression formed on the housing to enforce a rotation angle when the stylus is held. In some examples, pencil rotation can be corrected. For example, the system can guide a user through a calibration process wherein the stylus is held or moved in specific positions and/or orientations. 
       FIGS.  11 A- 11 B  illustrate an example stylus input device configuration with an SMI sensor and a rigid rod according to examples of the disclosure. Stylus  1130  can comprise a tip  1134  coupled to rigid rod  1192 , with the rod enclosed within the stylus housing. In some examples, the compliance of the tip can be provided by a wave spring  1194  between the housing and a guide tube for the stylus tip. In some examples, a single SMI sensor  1142  can configured to emit a beam toward the rod and capture the axial displacement of the compliant tip  1134  and rod  1192 . As force is applied to the tip by pressing against a surface  1176 , the rigid rod moves in response due to compression of the wave spring  1194 . The change in axial displacement can be processed to detect force and used by the system (e.g., by computing device  200  and/or input device  230 ). 
     In some examples, the stylus can include multiple (e.g., three or more SMI sensors  1242 ) configured to monitor displacement of a target in multiple dimensions rather than simply axial force.  FIGS.  12 A- 12 B  illustrate an example stylus input device configuration with multiple SMI sensors and a rigid rod according to examples of the disclosure. Stylus  1230  can include a tip  1234 , a rod  1292  and a wave spring  1294  like stylus  1130 . However, unlike in stylus  1130  rod  1292  can include a cap or head  1296  such that the cross-sectional area of the cap is greater than the circumference of a cross-section of the rod. Together the rod  1292  and head  1296  can provide a T-shaped target when viewed from an axial cross-section. Additionally, stylus  1230  can include multiple SMI sensors aimed toward head  1296 . As force is applied to tip  1234 , the tip  1234  and the target including the rod  1292  and head  1296  can be displaced (using the compliance of wave spring  1294  or other suitable component to provide compliance) as shown in  FIG.  12 B . The displacement of the tip can be measured by the multiple SMI beams from SMI sensors  1242  that are incident on the head  1296 . For example, as the tip  1234  moves, the beams emitted by the three or more SMI sensors  1242  can reflect off the head  1296  and return to the SMI sensors. In some examples, the SMI sensors  1242  can include at least three sensors and can measure axial displacement as well as circumferential displacement. In some examples, the SMI sensors can provide additional information about stylus movement and/or position. For example, the combination of measurements from three or more SMI sensors can be used to resolve a vector of force applied to tip  1234 . Combining information from the three or more SMI sensors can provide a differential displacement. Information about the force applied to the stylus can be used, for example, to vary properties of lines rendered on a display including, but not limited to, line width. Additionally or alternatively, force information can be used as a threshold to enable user interaction, such as selecting an icon and/or modifying gestures interpreted by the system. 
       FIG.  13    illustrates an example stylus input device configuration comprising multiple SMI sensors and a trackball according to examples of the disclosure. In some examples, the stylus  1330  can include a trackball  1398  according to examples of the disclosure. In some examples, the stylus  1330  can including SMI sensors  1342  configured to track the trackball as the stylus is moved across a non-touch-sensitive surface  1376 . In some examples, the SMI sensors  1342  can include at least two SMI sensors to track two-dimensional movement. In some examples, the SMI sensors  1342  can include at least three SMI sensors to track three-dimensional movement. The SMI sensors can be configured to track the orthogonal displacement of trackball, thus giving an indication of the displacement of the stylus that can be used for tracking relative displacement of the input device. 
     An SMI sensor is defined herein as a sensor configured to generate electromagnetic radiation (e.g., light), emit the electromagnetic radiation from a resonant cavity (e.g., a resonant optical cavity), receive a reflection or backscatter of the electromagnetic radiation (e.g., electromagnetic radiation reflected or backscattered from a surface, or an object having a surface (collectively referred to herein as a surface) back into the resonant cavity, coherently or partially coherently self-mix the generated and reflected/backscattered electromagnetic radiation within the resonant cavity, and produce an output indicative of the self-mixing (i.e., an SMI signal). The generated, emitted, and received electromagnetic radiation can be coherent or partially coherent. In some examples, the electromagnetic radiation emitted by an SMI sensor can be generated by an electromagnetic radiation source such as a vertical-cavity surface-emitting laser (VCSEL), a vertical external-cavity surface-emitting laser (VECSEL), an edge-emitting laser (EEL), a horizontal cavity surface emitting laser (HCSEL), a quantum-dot laser (QDL), a quantum cascade laser (QCL), or a light-emitting diode (LED) (e.g., an organic LED (OLED), a resonantcavity LED (RC-LED), a micro LED (mLED), a superluminescent LED (SLED), or an edge emitting LED), and so on. The generated, emitted, and received electromagnetic radiation can include, for example, visible or invisible light (e.g., green light, infrared (IR) light, ultraviolet (UV) light, and so on). The output of an SMI sensor (i.e., the SMI signal) may include a photocurrent produced by a photodetector (e.g., a photodiode), which photodetector is integrated with, or positioned under, above, or next to, the sensor&#39;s electromagnetic radiation source. Alternatively or additionally, the output of an SMI sensor may include a measurement of the current or junction voltage of the SMI sensor&#39;s electromagnetic radiation source. In some examples, the output of the SMI sensors can be converted to a distance or velocity measurement using processing circuitry described herein. A system using an input device with SMI sensors, such as one of the systems described with reference to  FIGS.  1 - 13   , may in some cases be used to provide input to an augmented, virtual or mixed reality application. 
       FIGS.  14 A- 14 D  illustrate example SMI sensors according to examples of the disclosure.  FIG.  14 A  shows a first example SMI sensor  1400  that can include a VCSEL  402  with an integrated resonant cavity (or intra-cavity) photodetector (RCPD)  1404 .  FIG.  14 B  shows a second example SMI sensor  1410  that can include a VCSEL  1412  with an extrinsic on-chip RCPD  1414 . In some examples, the RCPD  1414  may form a disc around the VCSEL  1412 .  FIG.  14 C  shows a third example SMI sensor  1420  that can include a VCSEL  1422  with an extrinsic off-chip photodetector  1424 .  FIG.  14 D  shows a fourth example SMI sensor  1430  that can include a dual-emitting VCSEL  1432  with an extrinsic off-chip photodetector  1434 . In some examples, the top emission may be emitted towards optics and/or another target and the bottom emission may be provided to the extrinsic off-chip photodetector  1434 . 
       FIGS.  15 A- 15 D  illustrate example different beam-shaping or beam-steering optics that can be used with the SMI sensors according to examples of the disclosure.  FIG.  15 A  shows beam-shaping optics  1500  (e.g., a lens or collimator) that can collimate the beam of electromagnetic radiation  1502  emitted by an SMI sensor  1504 . A collimated beam can be useful when the range supported by a device is relatively greater (e.g., when a device has a range of approximately ten centimeters).  FIG.  15 B  shows beam-shaping optics  1510  (e.g., a lens) that can focus the beam of electromagnetic radiation  1512  emitted by an SMI sensor  1514 . Focusing beams of electromagnetic radiation may be useful when the range supported by a device is limited (for example, to a few centimeters or less).  FIG.  15 C  shows beam-steering optics  1520  (e.g., a lens or set of lenses) that can direct the beams of electromagnetic radiation  1522  emitted by a plurality of SMI sensors  1524  such that the beams  1522  converge. Alternatively, the SMI sensors  1524  can be configured or oriented such that their beams converge without the optics  1520 . In some examples, the beam-steering optics  1520  can include or be associated with beam-shaping optics, such as the beam-shaping optics described with reference to  FIG.  15 A or  15 B .  FIG.  15 D  shows beam-steering optics  1530  (e.g., a lens or set of lenses) that directs the beams of electromagnetic radiation  1532  emitted by a plurality of SMI sensors  1534  such that the beams  1532  diverge. Alternatively, the SMI sensors  1534  can be configured or oriented such that their beams diverge without the optics  1530 . In some examples, the beam-steering optics  1530  can include or be associated with beam-shaping optics, such as the beam-shaping optics described with reference to  FIG.  15 A or  15 B . 
       FIG.  16    illustrates a triangular bias process  1600  for determining velocity and distance of a surface using self-mixing interferometry. Process  1600  can be used by one or more of the systems or devices described with reference to  FIGS.  1 - 13    to modulate an SMI sensor using a triangular waveform. At  1602 , an initial signal can be generated, such as by a digital or analog signal generator. At  1606 - 1 , the generated initial signal can processed to produce the triangle waveform modulation current  1702  that can be applied to a VCSEL as shown in  FIG.  17   . In some examples, producing the triangle waveform can refer to operations of a digital-to-analog converter (DAC) 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  1702  to the VCSEL can induce an SMI output  1718  (i.e., a change in an interferometric property of the VCSEL). It will be assumed for simplicity of discussion that the SMI output  1718  is from a photodetector, but in other examples it may be from another sensor. 
     At  1604 , the SMI output  1718  can be received and at  1606 - 2 , the SMI output  1718  can be initially processed, as needed. The initial processing can include high-pass filtering or digital subtraction. At  1608 , a processor can 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 SMI output  1718  can be a predominant triangle waveform component being matched to the modulation current  1702 , with a smaller and higher frequency component due to changes in the interferometric property. High-pass filtering can be applied to the SMI output  1718  to obtain the component signal related to the interferometric property. In some examples, at  1608 , the processor can further separate and/or subtract the parts of the SMI output  1718  and the modulation current  1702  corresponding to the ascending and to the descending time intervals of the modulation current  1702 . In some examples, at  1608 , the processor can further sample the separated information. 
     At  1610  and  1612 , a separate fast Fourier transform (FFT) can be first performed on the parts of the processed SMI output  1718  corresponding to the ascending and to the descending time intervals. The two FFT spectra may be analyzed at  1614 . At stage  1616 , the FFT spectra can be further processed, 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  1618 . 
       FIG.  17    illustrates a block diagram of a system (e.g., part or all of the processing system described with reference to  FIGS.  1 - 13   ) that can implement the spectrum analysis described in the process described above with respect to  FIG.  16   . In the exemplary system shown, the system includes generating an initial digital signal and processing it as needed to produce a modulation current  1702  as an input to the VCSEL  1710 . In an illustrative example, an initial step signal can be produced by a digital generator to approximate a triangle function. The digital output values of the digital generator can be used in the DAC  1704 . The resulting voltage signal can then be filtered by the low-pass filter  1706  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 can be an input to a voltage-to-current converter  1708  to produce the desired modulation current  1702  in a form for input to the VCSEL  1710 . 
     As described above, movement of a target can cause changes in an interferometric parameter, such as a parameter of the VCSEL  1710  or of a photodetector operating in the system. The changes can be measured to produce an SMI output  1718 . In the example shown, it will be assumed the SMI output  1718  is measured by a photodetector. For the modulation current  1702  having the triangle waveform, the SMI output  1718  can be a triangle wave of a similar period combined with a smaller and higher frequency signal related to the interferometric property. In some examples, the SMI output  1718  may not be perfectly linear, even though the modulation current  1702  may be linear. This can be a result of the bias current verses light output curve of the VCSEL  1710  being non-linear (e.g., due to non-idealities, such as self-heating effects). 
     The SMI output  1718  can be first passed into the high-pass filter  1720 , which can effectively convert the major ascending and descending ramp components of the SMI output  1718  to DC offsets. As the SMI output  1718  can be a current, the transimpedance amplifier  1722  can produce a corresponding voltage output (with or without amplification) for further processing. The voltage output can then be sampled and quantized by the ADC block  1724 . Before immediately applying a digital FFT to the output of the ADC block  1724 , it can be helpful to apply equalization. The initial digital signal values from the digital generator used to produce the modulation current  1702  can be used as input to the digital high-pass filter  1712  to produce a digital signal to correlate with the output of the ADC block  1724 . An adjustable gain can be applied by the digital variable gain block  1714  to the output of the digital high-pass filter  1712 . 
     The output of the digital variable gain block  1714  can be used as one input to the digital equalizer and subtractor block  1716 . The other input to the digital equalizer and subtractor block  1716  can be the output of the ADC block  1724 . The two signals can be differenced, and used as part of a feedback to adjust the gain provided by the digital variable gain block  1714 . Equalization and subtraction can be used to clean up any remaining artifacts from the triangle waveform that may be present in the SMI output  1718 . For example, a slope error or nonlinearity in the SMI output  1718  can result in artifacts from the triangle waveform after digital high-pass filter  1712 . In such a situation, these artifacts may show up as low frequency components after the FFT and make the peak detection more challenging for nearby objects. Applying equalization and subtraction can partially or fully remove these artifacts. 
     After obtaining an improved or optimal correlation by the feedback, an FFT, indicated by block  1728 , can then be applied to the components of the output of the ADC block  1724  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  1726 . 
     Although the above description of the process involves applying a spectrum analysis to an SMI output, it is understood that this is an example, and that in other implementations, alternate methods for determining absolute distances may be obtained directly from a time domain SMI output, without applying a spectrum analysis. Various configurations are possible and contemplated without departing from the scope of the present disclosure. 
       FIG.  18    illustrates a sinusoidal bias process  1800  for determining displacement of a surface using quadrature demodulation with self-mixing interferometry. Process  1800  can be used by one or more of the systems or devices described with reference to  FIGS.  1 - 13   , to modulate an SMI sensor using a sinusoidal waveform. 
     As explained in more detail below,  FIG.  18    shows components which generate and apply a sinusoidally modulated bias current to a VCSEL. The sinusoidal bias current can generate in a photodetector  1816  an output current depending on the frequency of the sinusoidal bias and the displacement to the structural component of the device. In the circuit of  FIG.  18   , the photodetector&#39;s  1816  output current can be 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 can each be low-pass filtered and the phase of the interferometric parameter can be calculated. Thereafter the displacement can be determined using at least the phase. 
     The DC voltage generator  1802  can be used to generate a constant bias voltage. A sine wave generator  1804  can produce an approximately single frequency sinusoid signal, to be combined with constant voltage. As shown in  FIG.  18   , the sine wave generator  1804  can be a digital generator, though in other implementations it can produce an analog sine wave. The low-pass filter  1806 - 1  can provide filtering of the output of the DC voltage generator  1802  to reduce undesired varying of the constant bias voltage. The bandpass filter  1806 - 2  can be used to reduce distortion and noise in the output of the sine wave generator  1804  to reduce noise, quantization or other distortions, or frequency components of its signal away from its intended modulation frequency, ω m . 
     The adder circuit  1808  can combine the low-pass filtered constant bias voltage and the bandpass filtered sine wave to produce on link  1809  a combined voltage signal which, in the example of  FIG.  18   , can have the form V 0 +V m  sin(ω mt ). This voltage signal can be used as an input to the voltage-to-current converter  1810  to produce a current to drive the lasing action of the VCSEL  1814 . The current from the voltage-to-current converter  1810  on the line  1813  can have the form I 0 +I m  sin(ω mt ). 
     The VCSEL  1814  can thus be driven to emit a laser light modulated as described above. Reflections of the modulated laser light can then be received back within the lasing cavity of VCSEL  1814  and cause self-mixing interference. The resulting emitted optical power of the VCSEL  1814  can be modified due to self-mixing interference, and this modification can be detected by the photodetector  1816 . As described above, in such cases the photocurrent output of the photodetector  1816  on the link  1815  can have the form: i PD =i 0 +i m  sin(ω mt )+γ cos(ψ 0 +ψ m  sin(ω mt )). The I/Q components to be used in subsequent processing can be based on the third term, and as a result, the first two terms can be removed or reduced by the differential transimpedance amplifier and anti-aliasing (DTIA/AA) filter  1818 . To do such a removal/reduction, a proportional or scaled value of the first two terms can be produced by the voltage divider  1812 . The voltage divider  1812  can use as input the combined voltage signal on the link  1809  produced by the adder circuit  1808 . The output of the voltage divider  1812  on link  1811  can then have the form: α(V 0 +V m  sin(ω mt )). The photodetector current and this output of the voltage divider  1812  can be the inputs to the DTIA/AA filter  1818 . The output of the DTIA/AA filter  1818  can then be, at least mostly, proportional to the third term of the photodetector current. 
     The output of the DTIA/AA filter  1818  can then be quantized for subsequent calculation by the ADC block  1820 . Further, the output of the ADC block  1820  can have a residual signal component proportional to the sine wave originally generated by the sine wave generator  1804 . 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  1824 - 3 , and then subtracted from the output of ADC block  1820  at subtraction block  1822 . The filtered output on link  1821  can have the form: A+B sin(ω mt )+C cos(2ω mt )+D sin(3ω mt )+ . . . , from the Fourier expansion of the γ cos(ψ 0 +ψ m  sin(ω mt )) term 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  1804  onto link  1807  can be mixed (multiplied) by the multiplier block  1824 - 1  with the filtered output on link  1821 . This product can then be low-pass filtered at block  1828 - 1  to obtain the Q component discussed above, possibly after scaling with a number that can be related to the amount of frequency modulation of the laser light and distance to the target. Additionally, the originally generated digital sine wave can be used as input to the squaring/filtering block  1826  to produce a digital cosine wave at a frequency double that of the originally produced digital sine wave. The digital cosine wave can then be mixed (multiplied) at the multiplier block  1824 - 2  with the filtered output of the ADC block  1820  on link  1821 . This product can then be low-pass filtered at block  1828 - 2  to obtain the I component discussed above, possibly after scaling with a number that can be related to the amount of frequency modulation of the laser light and distance to the target. The I and the Q components can then be used by the phase calculation component  1830  to obtain the phase from which the displacement of the target can be calculated. 
     It is understood that although the example shown in  FIG.  18    uses the digital form of the originally generated sine wave produced by sine wave generator  1804  on link  1807 , that in other examples the originally generated sine wave may be an analog signal and mixed with an analog output of the DTIA/AA filter  1818 . In other examples, the voltage divider  1812  can be a variable voltage divider. In other examples, the voltage divider  1812  can be omitted and the DTIA/AA filter  1818  can be a single-ended DTIA/AA filter. In such examples, subtraction may be performed digitally at subtraction block  1822 . In other examples, the subtraction block  1822  can be omitted and no subtraction of the modulation current may be performed. 
     The circuit of  FIG.  18    can be adapted to implement the modified I/Q process described above that uses Q′∝Lowpass{I PD  sin(3ω mt )}. Some such circuit adaptations can include directly generating both mixing signals sin(2 ω mt ) and sin(3 ω mt ), and multiplying each with the output of the output of the ADC block  1220 , and then applying respective low-pass filtering, such as by the blocks  1828 - 1 ,  1828 - 2 . The DTIA/AA filter  1818  can 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 process. For example, the signal sin(3 ω mt ) can be generated by multiplying link  1807  and the output of squaring/filtering block  1826 , and subsequently performing bandpass filtering to reject frequency components other than sin(3 ω mt ). 
     Additional or alternatively, in some examples, the I/Q time domain based processes and spectrum based processes can both be used. The spectrum based processes can be used at certain times to determine the absolute distance to the target (e.g., distance from the input device to a writing surface), and provide a value of L 0 . Thereafter, during subsequent time intervals, any of the various I/Q processes can be used to determine ΔL. Additional or alternatively, in some examples, the spectrum based processes using triangle wave modulation of a bias current of a VCSEL can be used as a guide for the I/Q time domain processes. The I/Q processes can operate optimally in the case that J 1 (b)=J 2 (b), so that the I and Q components can have the same amplitude. However, b can depend on the distance L. In some examples, a triangle wave modulation can be applied to the VCSEL&#39;s bias current to determine a distance to a point of interest. Then this distance can be 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 can provide improved signal-to-noise ratio and displacement accuracy obtained from the I/Q method. 
     Therefore, according to the above, some examples of the disclosure are directed to a stylus. The stylus can comprise a housing; a plurality of self-mixing interferometry (SMI) sensors configured to emit light to and detect light from one or more surfaces; processing circuitry coupled to the plurality of SMI sensors, the processing circuitry configured to compute one or more distances to one or more surfaces and one or more directional velocities; and wireless communication circuitry configured to transmit information from the stylus to an external device configured use the information from the stylus as input. The information can include the one or more distances, the one or more directional velocities, or other information derived from the one or more distances or the one or more directional velocities. Additionally or alternatively to one or more of the examples disclosed above, in some examples, using the information from the stylus as input can comprise rendering writing or drawing strokes of the stylus on a non-touch sensitive surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the processing circuitry can be further configured to: compute, using the one or more distances and the one or more directional velocities, a displacement along a first axis, a displacement along a second axis orthogonal to the first axis, a displacement along a third axis orthogonal to the first axis and the second axis, a tilt angle, an orientation angle, and/or an axial angle. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of SMI sensors can include a first SMI sensor and a second SMI sensor configured to generate orthogonal light beams to measure planar displacement. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the housing of the stylus can include one or more notches. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of SMI sensors can include a first SMI sensor, a second SMI sensor and a third SMI sensor to measure three-dimensional displacement. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first SMI sensor, the second SMI sensor and the third SMI sensor can generate beams with 120 degree separation when projected on an external surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a tip of the stylus can be formed from opaque material and the tip can include a plurality of windows for beams from the one or more SMI sensors to exit and return to stylus. Additionally or alternatively to one or more of the examples disclosed above, in some examples, a tip of the stylus can be formed from an optically transparent or translucent material. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the tip can include one or more lenses to increase beam power for one or more of the plurality of SMI sensors or improve symmetry of a plurality of beams for the plurality of SMI sensors. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the stylus can further comprise a mechanical component disposed at least partially within the housing and configured to be displaced in response to contact between the stylus and a surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the mechanical component can comprise a compliant rod. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of SMI sensors can include a first SMI sensor and a second SMI sensor configured to measure orthogonal displacement of the compliant rod. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of SMI sensors can include one SMI sensor to configured to measure axial displacement of the compliant rod in response to force applied to a tip of the stylus. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the mechanical component can further comprise a head for the compliant rod. An area of the head can be greater than an area of the compliant rod in a plane orthogonal to the axial direction of the compliant rod. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of SMI sensors can include three or more SMI sensors configured to measure displacement of the compliant rod in three dimensions in response to a force applied to a tip of the stylus. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the mechanical component can comprises a trackball and the plurality of SMI sensors can include a first SMI sensor and a second SMI sensor configured to measure orthogonal rotation of the trackball. Some examples of the disclosure are directed to a method of operating the stylus described herein or a non-transitory computer readable storage medium storing instructions configured to be executed by one or more processors of the stylus to cause the processor(s) to perform any of the above operations of the stylus. 
     Some examples of the disclosure are directed to a system. The system can comprise: a first device comprising: a plurality of first sensors configured to track displacement of the first device in contact with a non-touch sensitive surface, the plurality of first sensors comprising a plurality of self-mixing interferometry (SMI) sensors; and first communication circuitry coupled to the plurality of first sensors and configured to transmit information from the plurality of first sensors to a second device. The system can comprise the second device, the second device comprising: one or more second sensors configured to track a position of the first device with respect to the non-touch sensitive surface; second communication circuitry configured to receive the information from the plurality of first sensors; processing circuitry configured to generate content using the position of the first device with respect to the non-touch sensitive surface and using the displacement of the first device in contact with the non-touch sensitive surface; and a display configured to display the content generated by the processing circuitry on the non-touch sensitive surface. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first device can be a stylus and the second device can be a head-mounted display device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more second sensors can comprise a camera and the second device can track the position of the first device by detecting light emitted by the first device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more sensors can comprise a magnetic sensor or an audio sensor or an electromagnetic sensor configured to track the position of the first device with respect to the non-touch sensitive surface using changes in magnetic field, acoustic field, or electromagnetic field. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the first device can comprise a camera and the second device comprises a light emitter. The system can further track the position of the first device or the displacement of the first device based on a pattern of light emitted by the second device and detected by the camera of the first device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, generating content using the position of the first device with respect to the non-touch sensitive surface and using the displacement of the first device in contact with the non-touch sensitive surface can comprise matching an absolute initial position of the first device as the position of the device in contact with the non-touch sensitive at a first time and generating a stroke relative to the absolute initial position using on relative motion of the first device from the first time to a second time derived from the displacement of the first device from the absolute initial position. Additionally or alternatively to one or more of the examples disclosed above, in some examples, tracking the displacement of the first device can be augmented using one or more additional sensors including an accelerometer in the first device, a gyroscope in the first device, and inertial measurement unit in the first device, or a camera in the second device. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the one or more second sensors can include a camera configured to detect the first device or a hand, and the system can be configured to activate the plurality of first sensors in response to detecting the first device and the hand meeting one or more activation criteria. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of first sensors can be further configured to track a distance of the first device from the non-touch sensitive surface and the system can detect the contact of the first device with the non-touch sensitive surface based on the distance. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the plurality of first sensors can be further configured to track a distance of the first device from the non-touch sensitive surface and the system can detect a break in the contact of the first device with the non-touch sensitive surface based on the distance. Additionally or alternatively to one or more of the examples disclosed above, in some examples, the system can determine an amount of force applied by the first device to the non-touch sensitive surface using displacement of the first device. Some examples of the disclosure are directed to a method of operating the system described herein or a non-transitory computer readable storage medium storing instructions configured to be executed by one or more processors of the system to cause the processor(s) to perform any of the above operations of the system. 
     Although examples of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of examples of this disclosure as defined by the appended claims.

Metadata:
Filing Date: 20210512
Publication Date: 20230328
Grant Date: 20230328
Priority Date: 20210512
Inventors: CIHAN, AHMET FATIH
HARB, ADRIAN Z.
HUANG, MENGSHU
DEY, STEPHEN ERIC
PAN, Yuhao
Mutlu, Mehmet
CHEN, TONG
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/046", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04162", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0383", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/038", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/03545", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/03542", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0317", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0308", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04883", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04162", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0317", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03542", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/046", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/04883", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/046", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04101", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/043", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/03542", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/04162", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0317", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04883", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 85722620