PATENT DOCUMENT

Publication Number: US-11909171-B2
Application Number: US-202117219744-A
Country: US
Kind Code: B2

Title: Laser-integrated balance detection for self-mixing interferometry

Abstract:
An optical sensor system includes a set of epitaxial layers formed on a semiconductor substrate. The set of epitaxial layers defines a semiconductor laser having a first multiple quantum well (MQW) structure. Electromagnetic radiation is generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure. The set of epitaxial layers also defines a second MQW structure operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser, and a third MQW structure operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser. The optical sensor system also includes a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent.

Claims:
What is claimed is: 
     
       1. An optical sensor system, comprising:
 a semiconductor substrate; 
 a set of epitaxial layers formed on the semiconductor substrate and defining,
 a semiconductor laser having a first multiple quantum well (MQW) structure, wherein electromagnetic radiation is generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure; 
 a second MQW structure, positioned on a first side of the first MQW structure and operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser; and 
 a third MQW structure, positioned on a second side of the first MQW structure and operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser, the second side opposite the first side; and 
 
 a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent. 
 
     
     
       2. The optical sensor system of  claim 1 , wherein the first MQW structure, the second MQW structure, and the third MQW structure are disposed along an emission axis of the semiconductor laser. 
     
     
       3. The optical sensor system of  claim 1 , wherein:
 the semiconductor laser is a vertical cavity surface-emitting laser (VCSEL); and 
 the VCSEL comprises a distributed Bragg reflector (DBR) in which the first MQW structure and the second MQW structure are formed. 
 
     
     
       4. An optical sensor system, comprising:
 a semiconductor substrate; 
 a set of epitaxial layers formed on the semiconductor substrate and defining,
 a semiconductor laser having a first multiple quantum well (MQW) structure, wherein electromagnetic radiation is generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure; 
 a second MQW structure operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser; and 
 a third MQW structure operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser; and 
 
 a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent; wherein, 
 the second MQW structure and the third MQW structure share a same set of one or more epitaxial layers. 
 
     
     
       5. The optical sensor system of  claim 1 , wherein the circuit comprises:
 a first transimpedance amplifier (TIA) configured to receive the first photocurrent; 
 a second TIA configured to receive the second photocurrent; and 
 a set of one or more circuit components configured to combine a first output of the first TIA and a second output of the second TIA. 
 
     
     
       6. The optical sensor system of  claim 1 , wherein the second MQW structure is alternatively operable to,
 generate the first photocurrent; or 
 generate electromagnetic radiation contemporaneously with the first MQW structure. 
 
     
     
       7. The optical sensor system of  claim 1 , wherein the first MQW structure and the second MQW structure are phase-matched. 
     
     
       8. An optical sensor system, comprising:
 a substrate; 
 a first photodetector on the substrate; 
 a second photodetector on the substrate, laterally offset from the first photodetector; 
 an epitaxial stack; 
 a semiconductor laser formed in an epitaxial stack, the epitaxial stack attached to the substrate, the semiconductor laser aligned with the first photodetector and configured to make a first emission of electromagnetic radiation toward the first photodetector, the semiconductor laser having a resonant cavity in which emitted electromagnetic radiation and returned electromagnetic radiation is self-mixed; 
 an optical subsystem configured to,
 receive a second emission of the semiconductor laser; and 
 redirect a portion of the second emission toward the second photodetector; and 
 
 a noise-mitigating self-mixing interferometry (SMI) signal channel configured to combine a first photocurrent from the first photodetector and a second photocurrent from the second photodetector; wherein, 
 the first photodetector is outside of the epitaxial stack. 
 
     
     
       9. The optical sensor system of  claim 8 , wherein a set of epitaxial layers in the epitaxial stack extends over the second photodetector. 
     
     
       10. The optical sensor system of  claim 8 , wherein the optical subsystem comprises at least one grating that helps redirect the portion of the second emission toward the second photodetector. 
     
     
       11. The optical sensor system of  claim 8 , wherein:
 the substrate is a first substrate; 
 the semiconductor laser is formed on a second substrate, with the first substrate positioned on a first side of the semiconductor laser and the second substrate positioned on a second side of the semiconductor laser; and 
 at least a part of the optical subsystem is formed on the second substrate. 
 
     
     
       12. An optical sensor system, comprising:
 a semiconductor substrate; 
 a set of epitaxial layers formed on the substrate and defining,
 a semiconductor laser having a resonant cavity parallel to the semiconductor substrate and parallel or orthogonal to a primary electromagnetic radiation emission axis of the semiconductor laser; 
 a first photodetector positioned adjacent a first end of the resonant cavity and configured to receive a secondary electromagnetic radiation emission of the semiconductor laser; and 
 a second photodetector positioned adjacent a second end of the resonant cavity and configured to receive a tertiary electromagnetic radiation emission of the semiconductor laser; and 
 
 a circuit configured to generate an SMI signal by combining a first photocurrent generated by the first photodetector and a second photocurrent generated by the second photodetector; wherein, 
 the first photocurrent and the second photocurrent have opposite SMI excess phases. 
 
     
     
       13. The optical sensor system of  claim 12 , wherein:
 the resonant cavity is a first resonant cavity; and 
 the set of epitaxial layers comprises a multiple quantum well structure, subdivided between,
 the first resonant cavity of the semiconductor laser; 
 a second resonant cavity of the first photodetector; and 
 a third resonant cavity of the second photodetector. 
 
 
     
     
       14. The optical sensor system of  claim 12 , wherein:
 the first photodetector is separated from the semiconductor laser by a trench extending through at least a subset of epitaxial layers in the set of epitaxial layers. 
 
     
     
       15. The optical sensor system of  claim 14 , further comprising:
 at least one of a coating, a fill material, or a surface treatment within the trench; wherein, 
 the first photodetector is resonance-coupled to the semiconductor laser. 
 
     
     
       16. The optical sensor system of  claim 12 , wherein the semiconductor laser is a distributed feedback laser. 
     
     
       17. The optical sensor system of  claim 16 , wherein the resonant cavity of the distributed feedback laser has periodic changes in refractive index that regulate secondary electromagnetic radiation emission received by the first photodetector. 
     
     
       18. The optical sensor system of  claim 4 , wherein:
 the second MQW structure is disposed along an emission axis of the semiconductor laser; and 
 the third MQW structure does not intersect the emission axis of the semiconductor laser. 
 
     
     
       19. The optical sensor system of  claim 4 , wherein the circuit comprises:
 a first transimpedance amplifier (TIA) configured to receive the first photocurrent; 
 a second TIA configured to receive the second photocurrent; and 
 a set of one or more circuit components configured to combine a first output of the first TIA and a second output of the second TIA. 
 
     
     
       20. An optical sensor system, comprising:
 a substrate; 
 a first photodetector on the substrate; 
 a second photodetector on the substrate, laterally offset from the first photodetector; 
 a semiconductor laser attached to the substrate, the semiconductor laser aligned with the first photodetector and configured to make a first emission of electromagnetic radiation toward the first photodetector, the semiconductor laser having a resonant cavity in which emitted electromagnetic radiation and returned electromagnetic radiation is self-mixed; 
 an optical subsystem comprising at least one grating and configured to,
 receive a second emission of the semiconductor laser; and 
 redirect a portion of the second emission toward the second photodetector, the redirection occurring at least in part because of the at least one grating; and 
 
 a noise-mitigating self-mixing interferometry (SMI) signal channel configured to combine a first photocurrent from the first photodetector and a second photocurrent from the second photodetector.

Description:
FIELD 
     The described embodiments generally relate to optical sensing and, more particularly, to optical sensing based on self-mixing interferometry (SMI). 
     BACKGROUND 
     Coherent optical sensing, including Doppler velocimetry and heterodyning, can be used to obtain spatial information for a target. Example targets include objects, surfaces, particles, and so on. Example spatial information includes presence, distance, velocity, size, surface properties, particle count, and so on. Coherent optical sensing can sometimes be used to obtain spatial information for a target with optical wavelength resolution, at quantum limit signal levels, and with considerably lower photon energy than time-of-flight optical sensing methods. Coherent optical sensing can also limit interference from external aggressors such as ambient light or light generated by light sources of other optical sensing systems. 
     Semiconductor lasers (e.g., edge-emitting lasers (EELs), vertical cavity surface-emitting lasers (VCSELs), or horizontal cavity surface-emitting lasers (HCSELs)) integrated with wafer-level or wafer-bonded photodetectors enable coherent optical sensing using a monolithic sensor structure. For example, a semiconductor laser may generate and emit electromagnetic radiation from a resonant cavity of the semiconductor laser, receive returned (e.g., reflected or scattered) electromagnetic radiation back into the resonant cavity, self-mix the generated and returned electromagnetic radiation within the resonant cavity, and produce an SMI signal that can be detected by an integrated photodetector (e.g., an intra-cavity, stacked, or adjacent photodetector) and used to determine spatial information for a target. 
     To provide the best SMI sensing, noise may need to be identified and suppressed. Noise that affects SMI sensing may include, for example, ambient noise, laser/photodetector nonlinearity noise, driver noise, laser relative intensity noise (RIN), optical sensor system noise (e.g., application-specific integrated circuit (ASIC) noise), quantum limit noise (shot noise), and so on. 
     SUMMARY 
     Embodiments of the systems, devices, methods, and apparatus described in the present disclosure use laser-integrated balance detection to reduce (or remove) noise from the SMI output of an SMI sensor. The noise that can be reduced (or removed) includes noise such as ambient noise, laser/photodetector nonlinearity noise (e.g., thermal noise), driver noise, laser RIN, and optical sensor system noise (e.g., ASIC noise). Balance detection is facilitated by integrating a pair of photodetectors with a laser, extracting photocurrents having opposite SMI excess phases from the photodetectors, and combining (e.g., subtracting) the photocurrents to remove common-mode noise. In various embodiments, the photodetectors may be integrated into a same epitaxial stack as the laser (e.g., on opposite sides of a VCSEL or HCSEL&#39;s resonant cavity), or formed adjacent each other within an epitaxial stack that includes the laser, or on a substrate. 
     In a first aspect, the present disclosure describes an optical sensor system. The optical sensor system may include a semiconductor substrate, and a set of epitaxial layers formed on the substrate. The set of epitaxial layers may define a semiconductor laser having a first multiple quantum well (MQW) structure. Electromagnetic radiation may be generated by the first MQW structure, emitted from the first MQW structure, and self-mixed with a portion of the emitted electromagnetic radiation that is returned to the first MQW structure. The set of epitaxial layers may also define a second MQW structure operable to generate a first photocurrent responsive to detecting a first emission of the semiconductor laser, and a third MQW structure operable to generate a second photocurrent responsive to detecting a second emission of the semiconductor laser. The optical sensor system may also include a circuit configured to generate a self-mixing interferometry (SMI) signal by combining the first photocurrent and the second photocurrent. The combining of the first photocurrent and the second photocurrent may remove, from the SMI signal, noise common to the first photocurrent and the second photocurrent. 
     In a second aspect, the present disclosure describes another optical sensor system. The optical sensor system may include a substrate; a first photodetector on the substrate; and a second photodetector on the substrate, laterally offset from the first photodetector. The optical sensor system may also include a semiconductor laser that is attached to the substrate, aligned with the first photodetector, and configured to make a first emission of electromagnetic radiation toward the first photodetector. The semiconductor laser may have a resonant cavity in which emitted electromagnetic radiation and returned electromagnetic radiation is self-mixed. The optical sensor system may also include an optical subsystem configured to receive a second emission of the semiconductor laser and redirect a portion of the second emission toward the second photodetector, and a noise-mitigating SMI signal channel configured to combine a first photocurrent from the first photodetector and a second photocurrent from the second photodetector. 
     In a third aspect, the present disclosure describes another optical sensor system. The optical sensor system may include a semiconductor substrate, and a set of epitaxial layers formed on the substrate. The set of epitaxial layers may define a semiconductor laser, a first photodetector, and a second photodetector. The semiconductor laser may have a resonant cavity parallel to the semiconductor substrate and parallel or orthogonal to a primary electromagnetic radiation emission axis of the semiconductor laser. The first photodetector may be positioned adjacent a first end of the resonant cavity and configured to receive a secondary electromagnetic radiation emission of the semiconductor laser. The second photodetector may be positioned adjacent a second end of the resonant cavity and configured to receive a tertiary electromagnetic radiation emission of the semiconductor laser. The optical sensor system may also include a circuit configured to generate an SMI signal by combining a first photocurrent generated by the first photodetector and a second photocurrent generated by the second photodetector. The first photocurrent and the second photocurrent may have opposite SMI excess phases. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG.  1 A  shows an example of an optical sensor system that includes a semiconductor laser integrated with a photodetector; 
         FIG.  1 B  shows an example graph of the photocurrent output by the transimpedance amplifier (TIA) shown in  FIG.  1 A , and a graph of the frequency response of an SMI signal extracted from the photo current; 
         FIG.  1 C  shows an example graph of interference that may make it difficult to detect the lower frequency components of the SMI signal described with reference to  FIGS.  1 A and  1 B ; 
         FIG.  2 A  shows an example of an optical sensor system that includes a semiconductor laser integrated with a pair of photodetectors; 
         FIG.  2 B  shows example graphs of the photocurrents output by the TIAs shown in  FIG.  2 A , a graph of the combined photocurrents, and a graph of the frequency response of an SMI signal extracted from the combined photocurrents; 
         FIG.  2 C  shows an example graph of interference that may interfere with the SMI signal described with reference to  FIGS.  2 A and  2 B ; 
         FIG.  3 A  shows an example of an optical sensor system that includes a semiconductor laser integrated with a pair of in-plane photodetectors, both of which are formed in a set of epitaxial layers; 
         FIG.  3 B  shows an example of an optical sensor system that includes a semiconductor laser integrated with a pair of in-plane photodetectors, both of which are formed apart from an epitaxial stack that includes the semiconductor laser; 
         FIGS.  4 A and  4 B  show examples of optical sensor systems that include a semiconductor laser integrated with a pair of in-plane photodetectors, both of which are laterally offset from the semiconductor laser; 
         FIGS.  5 A and  5 B  show an example of a device that may include any of the optical sensor systems described with reference to  FIG.  1 A,  2 A,  3 A,  3 B,  4 A , or  4 B; 
         FIGS.  6 A and  6 B  show another example of a device that may include any of the optical sensor systems described with reference to  FIG.  1 A,  2 A,  3 A,  3 B,  4 A , or  4 B; and 
         FIG.  7    shows an example block diagram of an electronic device that may include any of the optical sensor systems described with reference to  FIG.  1 A,  2 A,  3 A,  3 B,  4 A , or  4 B. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     Balanced detection of an optical signal is one of the most efficient ways to reduce or remove noise from an optical signal. In a classical heterodyning detection scheme, the optical signal to be detected is coupled with a local oscillator signal and tapped to a two photon mixer. A 2×2 tap optical coupler then splits the detected optical signal into two phases. Subtracting the two phases amplifies (doubles) the optical signal and cancels the noise that is common to the two phases (i.e., the common-mode noise). Unfortunately, in an SMI-based optical sensor system, generated and returned electromagnetic radiation is self-mixed monolithically, within a laser&#39;s resonant cavity, before any phase-conjugate splitting of the optical signal to be detected (i.e., the SMI signal) can occur. 
     The following description relates to optical sensor systems that provide balanced detection for SMI sensors. In the described optical sensor systems, all of the active semiconductor devices of the SMI sensor may be formed on (or attached to) a common substrate. In some embodiments, a semiconductor laser and pair of photodetectors may be formed in a shared epitaxial stack, using a shared process, with each of the photodetectors being disposed along an emission axis of the semiconductor laser. In some embodiments, a semiconductor laser and a pair of photodetectors may be formed in a shared epitaxial stack, using a shared process, with a first of the photodetectors being disposed along an emission axis of the semiconductor laser and a second of the photodetectors being positioned adjacent the first photodetector (e.g., in a same one or more epitaxial layers). In some embodiments, the photodetectors may be formed on a same substrate, and an epitaxial stack including a semiconductor laser may be attached to the substrate such that the semiconductor laser is aligned with one of the photodetectors. In some embodiments, a semiconductor laser and pair of photodetectors may be formed in a shared epitaxial stack, using a shared process, with the semiconductor laser being formed as a HCSEL, and with the photodetectors being formed at opposite ends of a horizontal resonant cavity of the HCSEL. 
     The described optical sensor systems provide common-mode noise suppression for SMI sensors and reduce signal distortion. The described optical sensor systems also provide balance detection for a monolithic device and enable an SMI-based monolithic device to generate an SMI signal that is closer to the quantum limit of coherent detection. 
     These and other systems, devices, methods, and apparatus are described with reference to  FIGS.  1 A- 7   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
     Directional terminology, such as “top”, “bottom”, “upper”, “lower”, “front”, “back”, “over”, “under”, “above”, “below”, “left”, “right”, etc. is used with reference to the orientation of some of the components in some of the figures described below. Because components in various embodiments can be positioned in a number of different orientations, directional terminology is used for purposes of illustration only and is in no way limiting. The directional terminology is intended to be construed broadly, and therefore should not be interpreted to preclude components being oriented in different ways. Also, as used herein, the phrase “at least one of” preceding a series of items, with the term “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list. The phrase “at least one of” does not require selection of at least one of each item listed; rather, the phrase allows a meaning that includes at a minimum one of any of the items, and/or at a minimum one of any combination of the items, and/or at a minimum one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or one or more of each of A, B, and C. Similarly, it may be appreciated that an order of elements presented for a conjunctive or disjunctive list provided herein should not be construed as limiting the disclosure to only that order provided. 
       FIG.  1 A  shows a first example of an optical sensor system  100 . The optical sensor system  100  includes a semiconductor substrate  102  on which a set of epitaxial layers  104  is formed. The set of epitaxial layers  104  defines a semiconductor laser  106  having a first multiple quantum well (MQW) structure  108 . In some cases, the semiconductor laser  106  may be configured as a VCSEL. The set of epitaxial layers  104  also defines a second MQW structure  110 . The first and second MQW structures  108 ,  110  may be formed within a distributed Bragg reflector (DBR) defined by the set of epitaxial layers  104 . The DBR may include first, second, and third portions  112 ,  114 ,  116 . The first MQW structure  108  may be formed between the first and second portions  112 ,  114  of the DBR, and the second MQW structure  110  may be formed between the second and third portions  114 ,  116  of the DBR. The first portion  112  of the DBR and/or the second and third portions  114 ,  116  of the DBR may be partially transmissive, or have an aperture, to allow electromagnetic radiation generated by the semiconductor laser  106  to escape from the set of epitaxial layers  104 . 
     The first MQW structure  108 , together with the DBR portions  112 ,  114 ,  116 , may form a first resonant cavity, and in some cases may form a VCSEL. The second MQW structure  110 , in combination with its neighboring DBR portions (e.g.,  114 / 116 ) may form a second cavity, and in some cases may function as a resonant cavity photodetector (RCPD). 
     Optionally, a grating  118  or lens may be formed or deposited on an emission surface of the semiconductor laser  106  (or a coating or a surface treatment may be applied to the emission surface). 
     The first MQW structure  108  may be disposed between first and second electrodes  120 ,  122 , such as a first electrode  120  disposed on a first (or upper) epitaxial layer in the set of epitaxial layers  104 , and a second electrode  122  disposed on a second epitaxial layer in the set of epitaxial layers  104  (e.g., an epitaxial layer disposed between the first and second MQW structures  108 ,  110 ). 
     The second MQW structure  110  may be disposed between the second electrode  122  and a third electrode  124 . The third electrode  124  may be formed on a side of the semiconductor substrate  102  opposite a side of the semiconductor substrate  102  on which the set of epitaxial layers  104  is formed. 
     In operation, the first MQW structure  108  may be forward-biased by a fixed or modulated drive current applied to the first electrode  120 , and may be caused to generate electromagnetic radiation (i.e., lase). The second electrode  122  may be grounded or held at a fixed potential. The generated electromagnetic radiation may be emitted from the first MQW structure  108 . If the emitted electromagnetic radiation  126  reflects or scatters off of a target (e.g., a surface, object, or particle), a portion of the reflected or scattered electromagnetic radiation may be reflected or scattered toward the semiconductor laser  106 , and may be received back into (or returned to) the first MQW structure  108 . When this occurs, the returned portion of the emitted electromagnetic radiation  126  may self-mix with the electromagnetic radiation that is generated by the first MQW structure  108 . The self-mixing leads to changes in the emitted electromagnetic radiation  126 , which changes can be detected by reverse-biasing the second MQW structure  110  with a fixed voltage bias (i.e., the second MQW structure  110  may be reverse-biased and operated as a photodetector (PD)); sensing a photocurrent generated by the second MQW structure  110  (e.g., a photocurrent generated at the third electrode  122 ); and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a transimpedance amplifier (TIA)  128 , and the output of the TIA  128  may be converted to a digital value by an analog-to-digital converter (ADC). In some cases, the output of the TIA  128  may be additionally amplified, filtered, or otherwise processed prior to being converted to a digital value. 
       FIG.  1 B  shows an example of the photocurrent (I_pd) output by the TIA  128 . In particular,  FIG.  1 B  shows a graph  130  of the photocurrent  132  output by the TIA  128  over time, and a graph  134  of the frequency response  136  of an SMI signal extracted from the photocurrent. As shown in the graph  134 , noise  138  may interfere with the low frequency response of the SMI signal. 
       FIG.  1 C  shows an example graph  140  of interference that may make it difficult to detect the lower frequency components  142  of the SMI signal. The interference may include laser/PD nonlinearity noise  144 , driver noise  146 , laser RIN  148 , optical sensor system noise  150  (e.g., ASIC noise), and quantum limit noise  152  (shot noise). As shown, the cumulative noise  144 - 152  may be higher than the noise floor defined by the signal-to-noise ratio (SNR) budget  154  of the SMI signal at lower frequencies. 
       FIG.  2 A  shows a second example of an optical sensor system  200 . The optical sensor system  200  includes a semiconductor substrate  202  on which a set of epitaxial layers  204  is formed. The set of epitaxial layers  204  defines a semiconductor laser  206  having a first MQW structure  208 . In some cases, the semiconductor laser  206  may be configured as a VCSEL. The set of epitaxial layers  204  also defines a second MQW structure  210  and a third MQW structure  212 . The first, second, and third MQW structures  208 ,  210 ,  212  may be disposed along an emission axis  266  of the semiconductor laser  206 , with the second MQW structure  210  being positioned on a first side of the first MQW structure  208 , and with the third MQW structure  212  being positioned on a second side of the first MQW structure  208  (with the second side being opposite the first side). 
     The first, second, and third MQW structures  208 ,  210 ,  212  may be formed within a DBR defined by the set of epitaxial layers  204 . The DBR may include first, second, third, and fourth portions  214 ,  216 ,  218 ,  220 . The first MQW structure  208  may be formed between the second and third portions  216 ,  218  of the DBR. The second MQW structure  210  may be formed between the third and fourth portions  218 ,  220  of the DBR. The third MQW structure  212  may be formed between the first and second portions  214 ,  216  of the DBR. The first, second, third, and fourth portions  214 ,  216 ,  218 ,  220  of the DBR may be partially transmissive, or have an aperture, to allow electromagnetic radiation generated by the semiconductor laser  206  to escape from the set of epitaxial layers  204  in first and second emissions of electromagnetic radiation. 
     The first MQW structure  208 , together with the DBR portions  214 ,  216 ,  218 ,  220 , may form a first resonant cavity, and in some cases may form a VCSEL. The second and third MQW structures  210 ,  212 , in combination with their neighboring DBR portions (e.g.,  214 / 216 , or  218 / 220 ) may form second and third cavities, and in some cases may function as RCPDs. 
     Optionally, a grating  222  or lens may be formed or deposited on an emission surface of the semiconductor laser  206  (or a coating or a surface treatment may be applied to the emission surface). 
     The first MQW structure  208  may be disposed between first and second electrodes  224 ,  226 , such as a first electrode  224  disposed on a first epitaxial layer in the set of epitaxial layers  204  (e.g., an epitaxial layer disposed between the first and second MQW structures  208 ,  210 ), and a second electrode  226  disposed on a second epitaxial layer in the set of epitaxial layers  204  (e.g., an epitaxial layer disposed between the first and third MQW structures  208 ,  212 ). 
     The second MQW structure  210  may be disposed between the first electrode  224  and a third electrode  228 , with the first electrode  224  being disposed between the second and third electrodes  226 ,  228 . The third electrode  228  may be formed on a side of the semiconductor substrate  202  opposite a side of the semiconductor substrate  202  on which the set of epitaxial layers  204  is formed. 
     The third MQW structure  212  may be disposed between the second electrode  226  and a fourth electrode  230 . The fourth electrode  230  may be disposed on a first (or upper) epitaxial layer in the set of epitaxial layers  204 , with the second electrode  226  being disposed between the first and fourth electrodes  224 ,  230 . A forward junction may be formed between the second MQW structure  210  and the second electrode  226 , and/or between the third MQW structure  212  and the first electrode  224 , to provide electrical isolation and proper contact polarity. 
     In operation, the third electrode  228  may be grounded or held at a fixed potential, and the first MQW structure  208  may be forward-biased by a fixed or modulated drive current applied to the second electrode  226 . Forward-biasing the first MQW structure  208  may cause the first MQW structure  208  to generate electromagnetic radiation (i.e., lase). The generated electromagnetic radiation may be emitted from the first MQW structure  208 . If the emitted electromagnetic radiation  232  reflects or scatters off of a target (e.g., a surface, object, or particle), a portion of the reflected or scattered electromagnetic radiation may be reflected or scattered toward the semiconductor laser  206 , and may be received back into (or returned to) the first MQW structure  208 . When this occurs, the returned portion of the emitted electromagnetic radiation  232  may self-mix with the electromagnetic radiation that is generated within the first MQW structure  208 . The self-mixing leads to changes in the emitted electromagnetic radiation  232 . 
     The changes in the emitted electromagnetic radiation  232  may be detected with a first SMI excess phase, from mixing with a first emission direction of the semiconductor laser  206 , by reverse-biasing the second MQW structure  210  with a fixed voltage bias (i.e., the second MQW structure  210  may be reverse-biased and operated as an RCPD); sensing a photocurrent (a first photocurrent) generated by the second MQW structure  210  (e.g., a photocurrent generated at the first electrode  224 ); and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a TIA  234 . 
     The changes in the emitted electromagnetic radiation  232  may also be detected with a second SMI excess phase, from mixing with a second emission direction of the semiconductor laser  206 , by reverse-biasing the third MQW structure  212  with a fixed voltage bias (i.e., the third MQW structure  212  may be reverse-biased and operated as a second RCPD); sensing a photocurrent (a second photocurrent) generated by the third MQW structure  212  (e.g., a photocurrent generated at the fourth electrode  230 ); and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a TIA  236 . 
     The optical sensor system  200  may be designed such that the first and second photocurrents have opposite SMI excess phases. Outputs of the TIAs  234 ,  236  may be combined (e.g., subtracted) by a set of one or more circuit components  238  (e.g., a summing node or other structure) to generate an SMI signal having less noise than the SMI signal extracted from the singular PD described with reference to  FIG.  1 A . The output of the set of one or more circuit components  238  may be converted to a digital value by a ADC. In some cases, the output of the set of one or more circuit components  238  may be additionally amplified, filtered, or otherwise processed prior to being converted to a digital value. The TIAs  234 ,  236 , in combination with the set of one or more circuit components  238 , are one example of a noise-mitigating SMI signal channel. 
     By combining first and second photocurrents having different phases, the TIAs  234 ,  236  and set of one or more circuit components  238  remove, from the SMI signal, noise that is common to the first and second photocurrents (i.e., common-mode noise). In an ideal system, all of the common-mode noise is removed. In a non-ideal system, some or most of the common-mode noise is removed. The TIAs  234 ,  236  and set of one or more circuit components  238  may therefore function as a noise-mitigating SMI signal channel Having a separate TIA  234 ,  236  for processing each photocurrent enables the TIAs  234 ,  236  to be separately tuned (during manufacture or, in some cases, in the field), providing more flexibility in phase and/or amplitude matching the outputs of the TIAs  234 ,  236 . Tuning may be needed, for example, as a result of process variation, different doping, different thickness, or different electrical field power for the different MQW structures  208 ,  210 . Such tuning can be performed automatically, when there is zero SMI, or when there is a known SMI (e.g., during a calibration process). 
     To improve the noise mitigation provided by the TIAs  234 ,  236  and set of one or more circuit components  238 , the second and third MQW structures  210 ,  212  may be phase-matched and have similar thermal characteristics. Alternatively, the second MQW structure  210  may be designed to have less photo-absorption, thereby increasing the optical power of the primary emission  232 , and the different characteristics of the second and third MQW structures  210 ,  212  can be accounted for in the designs of the TIAs  234 ,  236 . 
       FIG.  2 B  shows an example of the photocurrents (I_pd_ 1  and I_pd_ 2 ) that are respectively output by the TIAs  234 ,  236 . In particular,  FIG.  2 B  shows a graph  240  of the photocurrent  242  output by the TIA  234  over time, and a graph  244  of the photocurrent  246  output by the TIA  236  over time. Also shown is a graph  248  of the combined photocurrent  250  output by the set of one or more circuit components  238 , and a graph  252  of the frequency response  254  of an SMI signal extracted from the combined photocurrent  250 . As shown by the hashed curve  256  in the graph  252 , the noise described with reference to  FIG.  1 B  may be eliminated or reduced by the optical sensor system  200 , and may no longer interfere, or interfere less, with the low frequency response of the SMI signal. 
       FIG.  2 C  shows an example graph  258  of interference that may interfere with the SMI signal generated by the optical sensor system  200 . The noise may include optical sensor system noise  260  (e.g., ASIC noise) and quantum limit noise  262  (shot noise), but may not include, or may include a reduced amount of, laser/PD nonlinearity noise, driver noise, and laser RIN. As shown, the cumulative noise  260 ,  262  may be lower than the noise floor defined by the SNR budget  264  of the SMI signal at lower frequencies. 
     In some cases, one or both of the second and third MQW structures  210 ,  212  shown in  FIG.  2 A  may be alternatively operable to generate a photocurrent (as described above), or to generate electromagnetic radiation contemporaneously with the first MQW structure  208 . For example, the noise discussed herein may be less of an issue when the first MQW structure  208  is driven with a DC or low frequency drive current. As another example, the noise may be less of an issue when the SMI frequency from target ranging or velocity are high and away from the high noise floor. In these scenarios, the second or third MQW structure  210 ,  212  may be forward-biased and used to generate additional electromagnetic radiation (i.e., to increase the optical power of the optical sensor system  200 ). Alternatively, one of the second or third MQW structures  210 ,  212  and its associated TIA  234  or  236  may be powered down or turned off. 
     In other cases, where SMI sensing does not need to be performed, both of the second and third MQW structures  210 ,  212  may be forward-biased to increase the optical power of the optical sensor system  200 ; or one or both of the second and third MQW structures  210 ,  212  and its associated TIA  234  or  236  may be powered down or turned off. 
       FIG.  2 A  shows an optical sensor system  200  in which the second and third MQW structures  210 ,  212  are positioned along an emission axis  266  of the semiconductor laser  206 . In an alternative arrangement, the third MQW structure  212  may not intersect the emission axis  266 . For example, the third MQW structure  212  may be positioned adjacent, or in-plane, with the second MQW structure  210 , as described with reference to  FIG.  3 A . 
       FIG.  3 A  shows a third example of an optical sensor system  300 . The optical sensor system  300  includes a semiconductor substrate  302  on which a set of epitaxial layers  304  is formed. The set of epitaxial layers  304  defines a semiconductor laser  306  having a first MQW structure  308 . In some cases, the semiconductor laser  306  may be configured as a VCSEL. The set of epitaxial layers  304  also defines a second MQW structure  310  and a third MQW structure  312 . The first and second MQW structures  308 ,  310  may be disposed along an emission axis  322  of the semiconductor laser  306 , with the second MQW structure  310  being positioned between the semiconductor substrate  302  and the first MQW structure  308 . The third MQW structure  312  may not be disposed along the emission axis  322 , and may not intersect the emission axis  322 . Instead, the third MQW structure  312  may be positioned adjacent an epitaxial stack including the first and second MQW structures  308 ,  310 . In some embodiments, and as shown, the third MQW structure  312  may be positioned adjacent or in-plane with the second MQW structure  310 , and may share a same set of epitaxial layers as the second MQW structure  310 . 
     The first and second MQW structures  308 ,  310  may be formed within a DBR defined by the set of epitaxial layers  304 . The DBR may include first, second, and third portions  314 ,  316 ,  318 . The first MQW structure  308  may be formed between the first and second portions  314 ,  316  of the DBR. The second MQW structure  310  may be formed between the second and third portions  316 ,  318  of the DBR. The first, second, and third portions  314 ,  316 ,  318  of the DBR may be partially transmissive, or have an aperture, to allow electromagnetic radiation generated by the semiconductor laser  306  to escape from the set of epitaxial layers  304  in first and second emissions of electromagnetic radiation. In some cases, the third portion  318  of the DBR may extend under the third MQW structure  312 , and the third MQW structure  312  may be formed within a DBR including the third portion  318  and a fourth portion  320 . 
     The first MQW structure  308  may be disposed between first and second electrodes  324 ,  326 , such as a first electrode  324  disposed on a first (or upper) epitaxial layer in the set of epitaxial layers  304 , and a second electrode  326  disposed on a second epitaxial layer in the set of epitaxial layers  304  (e.g., an epitaxial layer disposed between the first and second MQW structures  308 ,  310 ). 
     The second MQW structure  310  may be disposed between the second electrode  326  and a third electrode  328 . The third electrode  328  may be formed on a side of the semiconductor substrate  302  opposite a side of the semiconductor substrate  302  on which the set of epitaxial layers  304  is formed. 
     The third MQW structure  312  may be disposed between the third electrode  328  and a fourth electrode  330 , with the fourth electrode  330  being disposed on a side of the third MQW structure  312  (and on an epitaxial layer) that is on a side of the third MQW structure  312  opposite a side on which the third electrode  328  is disposed. 
     An optical subsystem  332  may be formed over the first, second, and third MQW structures  308 ,  310 ,  312 , opposite a side of the set of epitaxial layers  304  on which the semiconductor substrate  302  is positioned. In some embodiments, the optical subsystem  332  may allow a first portion of the electromagnetic radiation  334  emitted by the semiconductor laser  306  to pass, while redirecting a second portion of the electromagnetic radiation  334  toward the third MQW structure  312 . In some cases, the optical subsystem  332  may include one or more beam-splitting structures, such as one or more gratings  336 ,  338  or other elements that redirect the second portion of the electromagnetic radiation  334  toward the third MQW structure  312 . In some cases, the optical subsystem  332  may include a substrate  340  (e.g., an optically-transmissive cover, which in some cases may be an external cover of a device). In some cases, the one or more gratings  336 ,  338  (or one or more lenses, other optic elements, coatings, and/or surface treatments) may be formed on, attached to, or applied to the substrate  340 . 
     In operation, the third electrode  328  may be grounded or held at a fixed potential, and the first MQW structure  308  may be forward-biased by a fixed or modulated drive current applied to the first electrode  324 . Forward-biasing the first MQW structure  308  may cause the first MQW structure  308  to generate electromagnetic radiation (i.e., lase). The generated electromagnetic radiation may be emitted from the first MQW structure  308 . If the emitted electromagnetic radiation  334  reflects or scatters off of a target (e.g., a surface, object, or particle), a portion of the reflected or scattered electromagnetic radiation may be reflected or scattered toward the semiconductor laser  306 , and may be received back into (or returned to) the first MQW structure  308 . When this occurs, the returned portion of the emitted electromagnetic radiation  334  may self-mix with the electromagnetic radiation that is generated within the first MQW structure  308 . The self-mixing leads to changes in the emitted electromagnetic radiation  334 . 
     The changes in the emitted electromagnetic radiation  334  may be detected with a first SMI excess phase, from mixing with a first emission direction of the semiconductor laser  306 , by reverse-biasing the second MQW structure  310  with a fixed voltage bias (i.e., the second MQW structure  310  may be reverse-biased and operated as a PD); sensing a photocurrent (a first photocurrent) generated by the second MQW structure  310  (e.g., a photocurrent generated at the second electrode  326 ); and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a first TIA, as described with reference to  FIG.  2 A . 
     The changes in the emitted electromagnetic radiation  334  may also be detected with a second SMI excess phase, from mixing with a second emission direction of the semiconductor laser  306 , by reverse-biasing the third MQW structure  312  with a fixed voltage bias (i.e., the third MQW structure  312  may be reverse-biased and operated as a second PD); sensing a photocurrent (a second photocurrent) generated by the third MQW structure  312  (e.g., a photocurrent generated at the fourth electrode  330 ); and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a second TIA, as described with reference to  FIG.  2 A . The first and second TIAs may be coupled to a set of one or more circuit components to generate an SMI signal that includes none (or less) of the noise that is common to the first and second photocurrents, as described with reference to  FIG.  2 A . To improve the noise mitigation provided by the TIAs and set of one or more circuit components, the second and third MQW structures  310 ,  312  may be phase-matched. 
     In some cases, the second and third MQW structures  310 ,  312  may be formed at the same time, in a same set of epitaxial layers, and then a trench  342  may be etched to electrically separate the second and third MQW structures  310 ,  312 . The trench  342  may be open or filled. Alternatively, the second and third MQW structures  310 ,  312  may be electrically separated by ion implantation or other means. 
     In some cases, the second and third MQW structures  310 ,  312  may be formed at different times. For example, after forming the mesa including the first and second MQW structures  308 ,  310  and first, second, and third portions  314 ,  316 ,  318  of the DBR, a set of epitaxial layers may be formed to define the third MQW structure  312  and fourth portion  320  of a DBR. This alternative method of forming the third MQW structure  312  may allow the second and third MQW structures  310 ,  312  to be independently tuned. 
     Regardless of whether the third MQW structure  312  is formed at the same time or at different times with respect to formation of the second MQW structure  310 , a fourth MQW structure that is operable as a semiconductor laser (e.g., a VCSEL) may in some cases be formed on the third MQW structure  312 . When the fourth MQW structure is formed at the same time, and using the same process as, the first MQW structure  308 , the fourth MQW structure, and in some cases the first portion  314  of the DBR, may be removed (e.g., etched away). Alternatively, the fourth MQW structure may be left in place, and may be turned off or reverse-biased when the first MQW structure is forward-biased to generate electromagnetic radiation. In this manner, the third MQW structure  312  may be used to detect an emission of the semiconductor laser  306 . 
     In some cases, one or both of the second and third MQW structures  310 ,  312  may be alternatively operable to generate a photocurrent (as described above), or to generate electromagnetic radiation contemporaneously with the first MQW structure  308 , as described with reference to  FIG.  2 A . 
       FIG.  3 B  shows a fourth example of an optical sensor system  350 . The optical sensor system  350  includes a substrate  352  on which a first photodetector  354  and a second photodetector  356  are formed (or to which the first and second photodetectors  354 ,  356  are attached). The second photodetector  356  is laterally offset from the first photodetector  354 . In some cases, the substrate  352  may be a silicon (Si) substrate, and the first and second photodetectors may be formed using Si, germanium (Ge), gallium arsenide (GaAs), or another photosensitive medium (e.g., a quantum dot/film, organic medium, and so on). 
     A semiconductor laser  358  (e.g., a VCSEL) is attached to the substrate  352 , aligned with the first photodetector  354  (e.g., an emission axis of the semiconductor laser  358  intersects a surface of the first photodetector  354 ). The semiconductor laser  358  may be configured to make a first emission  360  of electromagnetic radiation toward the first photodetector  354 , and make a second emission  362  in an opposite direction. The second emission  362  may be the primary emission of the semiconductor laser  358 . 
     The second emission  362  may be received by an optical subsystem  364 . The optical subsystem  364  may allow a first portion of the second emission to pass, while redirecting a second portion of the second emission  362  toward the second photodetector  356 . In some cases, the optical subsystem  364  may include one or more gratings  366 ,  368  or other elements that redirect the second portion of the electromagnetic radiation  362  toward the third MQW structure  312 . In some cases, the optical subsystem  364  may be formed on a substrate  370  (e.g., an optically-transmissive semiconductor substrate  370 ) on which the semiconductor laser  358  is formed. In some cases, the one or more gratings  366 ,  368  (or one or more lenses, other optic elements, coatings, and/or surface treatments) may be formed on, attached to, or applied to the substrate  370 . 
     The semiconductor laser  358  may in some cases be defined by an epitaxial stack  372  formed on the substrate  370 , and may include a resonant cavity  374  (e.g., an MQW structure) formed within a DBR defined by the epitaxial stack  372 . The DBR may include first and second portions  376 ,  378  formed on opposite sides of the resonant cavity  374 . In some cases, a subset of epitaxial layers in the epitaxial stack  372  (e.g., the second portion  378  of the DBR) may extend over the second photodetector  356 . The first and second portions  376 ,  378  of the DBR may be partially transmissive, or have an aperture, to allow electromagnetic radiation generated by the semiconductor laser  358  to escape from the epitaxial stack  372  in the first and second emissions of electromagnetic radiation  360 ,  362 . In some cases, the semiconductor laser  358  may be configured as a VCSEL. 
     The semiconductor laser  358  may be configured to have a primary emission (i.e., the second emission  362 ) that is a backside emission. In other words, the semiconductor laser  358  may be configured to operate as a backside emission (BE) device, with most of its optical power being delivered via the second emission  362 . However, the semiconductor laser  358  is also configured to operate as a dual emission (DE) device. The substrate  370  and epitaxial stack  372 , with included semiconductor laser  358 , may be flipped upside down and bonded to the substrate  352  using an optically-transmissive adhesive  380 . During the bonding process, an emission axis  382  of the semiconductor laser  358  may be aligned with the first photodetector  354 , with the semiconductor laser  358  positioned between the substrate  352  and the substrate  370 . 
     The resonant cavity  374  may be disposed between first and second electrodes  384 ,  386 . Each of the electrodes  384 ,  386  may be electrically connected to a respective epitaxial layer in the epitaxial stack  372  and a respective conductive trace on the substrate  352 . 
     Each of the first and second photodetectors  354 ,  356  may be electrically coupled to a set of conductive traces formed on or in the substrate  352 . 
     In operation, the first electrode  384  may be grounded or held at a fixed potential, and the resonant cavity  374  may be forward-biased by a fixed or modulated drive current applied to the second electrode  386 . Forward-biasing the resonant cavity  374  may cause the resonant cavity  374  to generate electromagnetic radiation (i.e., lase). The generated electromagnetic radiation may be emitted from the resonant cavity  374  as the first emission  360  and the second emission  362 . If the second emission  362  reflects or scatters off of a target (e.g., a surface, object, or particle), a portion of the reflected or scattered electromagnetic radiation may be reflected or scattered toward the semiconductor laser  358 , and may be received back into (or returned to) the resonant cavity  374 . When this occurs, the returned portion of the emitted electromagnetic radiation  362  may self-mix with the electromagnetic radiation that is generated within the resonant cavity  374 . The self-mixing leads to changes in the emitted electromagnetic radiation  360 ,  362 . 
     The changes in the emitted electromagnetic radiation may be detected with a first SMI excess phase, from mixing with the first emission  360  direction of the semiconductor laser  358 , using the first photodetector  354 ; sensing a photocurrent (a first photocurrent) generated by the first photodetector  354 ; and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a first TIA, as described with reference to  FIG.  2 A . 
     The changes in the emitted electromagnetic radiation may also be detected with a second SMI excess phase, from mixing with the second emission  362  direction of the semiconductor laser  358 , using the second photodetector  356 ; sensing a photocurrent (a second photocurrent) generated by the second photodetector  356 ; and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a second TIA, as described with reference to  FIG.  2 A . The first and second TIAs may be coupled to a set of one or more circuit components to generate an SMI signal that includes none (or less) of the noise that is common to the first and second photocurrents, as described with reference to  FIG.  2 A . To improve the noise mitigation provided by the TIAs and set of one or more circuit components, the first and second photodetectors  354 ,  356  may be phase-matched. 
       FIG.  4 A  shows a fifth example of an optical sensor system  400 . The optical sensor system  400  includes a semiconductor laser  402  integrated with a pair of in-plane photodetectors  404 ,  406 , both of which are laterally offset from the semiconductor laser  402 . More particularly, the optical sensor system  400  includes a semiconductor substrate  408  on which a set of epitaxial layers  410  is formed. The structures of the semiconductor laser  402  and photodetectors  404 ,  406  may in some cases be formed by forming a singular, continuous set of epitaxial layers  410  on the semiconductor substrate  408 , and then etching trenches  412 ,  414  through at least a subset of the epitaxial layers  410  to separate portions of the epitaxial layers  410  that define the semiconductor laser  402  from portions of the epitaxial layers  410  that respectively define the first and second photodetectors  404 ,  406 . 
     In some cases, the set of epitaxial layers  410  may include a resonant cavity that is subdivided, by the trenches  412 ,  414 , to form a first resonant cavity  416  for the semiconductor laser  402 , a second resonant cavity  418  for the first photodetector  404 , and a third resonant cavity  420  for the second photodetector  406 . In some embodiments, the resonant cavities  416 ,  418 ,  420  may include MQW structures. The trenches  412 ,  414  may in some cases include one or more coatings, fill materials, or surface treatments that 1) make at least the vertical sides of the trenches  412 ,  414  partially reflective, and 2) resonance-couple the first and second photodetectors  404 ,  406  to respective ends of the first resonant cavity  416 . 
     A first electrode  422  may be formed on the set of epitaxial layers  410  above the semiconductor laser  402 , a second electrode  424  may be formed on the set of epitaxial layers  410  above the first photodetector  404 , and a third electrode  426  may be formed on the set of epitaxial layers  410  above the second photodetector  406 . A fourth electrode  428 , common to all of the semiconductor devices (e.g., the semiconductor laser  402 , the first photodetector  404 , and the second photodetector  406 ), may be formed on a side of the semiconductor substrate  408  opposite a side of the semiconductor substrate  408  on which the set of epitaxial layers  410  is formed. 
     The semiconductor laser  402  may be configured as a horizontal cavity surface-emitting laser (HCSEL), with a resonant cavity  416  that extends parallel to the semiconductor substrate  408 , and a primary electromagnetic radiation emission axis  430  that is orthogonal to the resonant cavity  416 . In some cases, a diffraction grating  432  or other optic element may be formed or deposited on an emission surface of the semiconductor laser  402 . The diffraction grating  432  may aid in emitting and receiving electromagnetic radiation perpendicularly to the resonant cavity  416 . 
     The first photodetector  404  may be positioned adjacent (e.g., near) a first end of the resonant cavity  416 , and may be configured to receive a secondary electromagnetic radiation emission of the semiconductor laser  402 , which secondary electromagnetic radiation emission leaks through the first end of the resonant cavity  416  because the first end is only partially reflective. The second photodetector  406  may be positioned adjacent (e.g., near) a second end of the resonant cavity  416 , and may be configured to receive a tertiary electromagnetic radiation emission of the semiconductor laser  402 , which tertiary electromagnetic radiation emission leaks through the second end of the resonant cavity  416  because the second end is only partially reflective. Alternatively, the second photodetector  406  may be configured not to fully absorb the tertiary electromagnetic radiation emission from the semiconductor laser  402 , with the tertiary electromagnetic radiation emission emitting out of the outer facet of the second photodetector  406 , in an in-plane direction (e.g., in an edge emission, parallel to the semiconductor substrate  408 ). In these embodiments, the in-plane electromagnetic radiation may be the primary electromagnetic radiation emission, and there may not be an electromagnetic radiation emission orthogonal to the semiconductor substrate  408  (i.e., no emission of electromagnetic radiation orthogonal to the semiconductor substrate). 
     In operation, the fourth electrode  428  may be grounded or held at a fixed potential, and the first resonant cavity  416  may be forward-biased by a fixed or modulated drive current applied to the first electrode  422 . Forward-biasing the first resonant cavity  416  may cause the first resonant cavity  416  to generate electromagnetic radiation (i.e., lase). The generated electromagnetic radiation may be emitted from the first resonant cavity  416  as a primary electromagnetic radiation emission  434 . Some of the generated electromagnetic radiation may also leak through the first and second ends of the first resonant cavity  416  to form secondary and tertiary electromagnetic radiation emissions. If the primary electromagnetic radiation emission  434  reflects or scatters off of a target (e.g., a surface, object, or particle), a portion of the reflected or scattered electromagnetic radiation may be reflected or scattered toward the semiconductor laser  402 , and may be received back into (or returned to) the first resonant cavity  416 . When this occurs, the returned portion of the emitted electromagnetic radiation  434  may self-mix with the electromagnetic radiation that is generated within the first resonant cavity  416 . The self-mixing leads to changes in the emitted electromagnetic radiation. 
     The changes in the emitted electromagnetic radiation may be detected with a first SMI excess phase, from mixing with the secondary electromagnetic radiation emission direction of the semiconductor laser  402 , using the first photodetector  404 ; sensing a photocurrent (a first photocurrent) generated by the first photodetector  404 ; and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a first TIA coupled to the second electrode  424 , as described with reference to  FIG.  2 A . 
     The changes in the emitted electromagnetic radiation may also be detected with a second SMI excess phase, from mixing with the second electromagnetic radiation emission direction of the semiconductor laser  402 , using the second photodetector  406 ; sensing a photocurrent (a second photocurrent) generated by the second photodetector  406 ; and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a second TIA coupled to the third electrode  428 , as described with reference to  FIG.  2 A . The first and second TIAs may be coupled to a set of one or more circuit components to generate an SMI signal that includes none (or less) of the noise that is common to the first and second photocurrents, as described with reference to  FIG.  2 A . To improve the noise mitigation provided by the TIAs and set of one or more circuit components, the first and second photodetectors  404 ,  406  may be phase-matched. 
       FIG.  4 B  shows a sixth example of an optical sensor system  450 . The optical sensor system  450  includes a semiconductor laser  452  integrated with a pair of in-plane photodetectors  454 ,  456 , both of which are laterally offset from the semiconductor laser  452 . More particularly, the optical sensor system  450  includes a semiconductor substrate  458  on which a set of epitaxial layers  460  is formed. The structures of the semiconductor laser  452  and photodetectors  454 ,  456  may in some cases be formed by forming a singular, continuous set of epitaxial layers  460  on the semiconductor substrate  458 , and using a distributed feedback structure within the semiconductor laser  452 , and in some cases ion implantation or trenches, to effectively separate portions of the epitaxial layers  460  that define the semiconductor laser  452 , the first photodetector  454 , and the second photodetector  456 . The distributed feedback structure may have changes in refractive index that regulate secondary and tertiary electromagnetic radiation emissions that the semiconductor laser  452  makes toward the first and second photodetectors  454 ,  456 . 
     In some cases, the set of epitaxial layers  460  may include a singular resonant cavity  462  that is effectively subdivided as a result of the semiconductor laser  452  being a DFB laser. 
     A first electrode  464  may be formed on the set of epitaxial layers  460  above the semiconductor laser  452 , a second electrode  466  may be formed on the set of epitaxial layers  460  above the first photodetector  454 , and a third electrode  468  may be formed on the set of epitaxial layers  460  above the second photodetector  456 . A fourth electrode  470 , common to all of the semiconductor devices (e.g., the semiconductor laser  452 , the first photodetector  454 , and the second photodetector  456 ), may be formed on a side of the semiconductor substrate  458  opposite a side of the semiconductor substrate  458  on which the set of epitaxial layers  460  is formed. 
     The semiconductor laser  452  may be configured as a HCSEL, with a resonant cavity  472  that extends parallel to the semiconductor substrate  458 , and a primary electromagnetic radiation emission axis  478  that is orthogonal to the resonant cavity  472 . Alternatively, the semiconductor laser  452  may be configured as an edge-emitting laser (EEL) if either of the photodetectors  454 ,  456  are configured to be only partially absorbing of the in-plane electromagnetic radiation leakage out of the DFB, and if the outer facet of such photodetector is partially transmissive. In some cases, a diffraction grating  476  or other optic element may be formed or deposited on an emission surface of the semiconductor laser  452 . The diffraction grating  476  may aid in emitting and receiving electromagnetic radiation perpendicularly to the resonant cavity  472 . 
     The first photodetector  454  may be positioned adjacent a first end of the resonant cavity  472 , and may be configured to receive a secondary electromagnetic radiation emission of the semiconductor laser  452 , which secondary electromagnetic radiation emission leaks through the first end of the resonant cavity  472  because the first end is only partially reflective. The second photodetector  456  may be positioned adjacent a second end of the resonant cavity  472 , and may be configured to receive a tertiary electromagnetic radiation emission of the semiconductor laser  452 , which tertiary electromagnetic radiation emission leaks through the second end of the resonant cavity  472  because the second end is only partially reflective. 
     In operation, the fourth electrode  470  may be grounded or held at a fixed potential, and the resonant cavity  472  may be forward-biased by a fixed or modulated drive current applied to the first electrode  464 . Forward-biasing the resonant cavity  472  may cause the resonant cavity  472  to generate electromagnetic radiation (i.e., lase). The generated electromagnetic radiation may be emitted from the resonant cavity  472  as a primary electromagnetic radiation emission  474 . Some of the generated electromagnetic radiation may also leak through the first and second ends of the resonant cavity  472  to form secondary and tertiary electromagnetic radiation emissions. If the primary electromagnetic radiation emission  474  reflects or scatters off of a target (e.g., a surface, object, or particle), a portion of the reflected or scattered electromagnetic radiation may be reflected or scattered toward the semiconductor laser  452 , and may be received back into (or returned to) the resonant cavity  472 . When this occurs, the returned portion of the emitted electromagnetic radiation  474  may self-mix with the electromagnetic radiation that is generated within the resonant cavity  472 . The self-mixing leads to changes in the emitted electromagnetic radiation. 
     The changes in the emitted electromagnetic radiation may be detected with a first SMI excess phase, from mixing with the secondary electromagnetic radiation emission direction of the semiconductor laser  452 , using the first photodetector  454 ; sensing a photocurrent (a first photocurrent) generated by the first photodetector  454 ; and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a first TIA coupled to the second electrode  466 , as described with reference to  FIG.  2 A . 
     The changes in the emitted electromagnetic radiation may also be detected with a second SMI excess phase, from mixing with the second electromagnetic radiation emission direction of the semiconductor laser  452 , using the second photodetector  456 ; sensing a photocurrent (a second photocurrent) generated by the second photodetector  456 ; and extracting an SMI signal from the photocurrent. In some cases, the photocurrent may be received and amplified by a second TIA coupled to the third electrode  468 , as described with reference to  FIG.  2 A . The first and second TIAs may be coupled to a set of one or more circuit components to generate an SMI signal that includes none (or less) of the noise that is common to the first and second photocurrents, as described with reference to  FIG.  2 A . To improve the noise mitigation provided by the TIAs and set of one or more circuit components, the first and second photodetectors  454 ,  456  may be phase-matched. 
       FIGS.  5 A and  5 B  show an example of a device  500  (an electronic device) that may include any of the optical sensor systems described with reference to  FIG.  1 A,  2 A,  3 A,  3 B,  4 A , or  4 B. The device&#39;s dimensions and form factor, and inclusion of a band  504  (e.g., a wrist band), suggest that the device  500  is an electronic watch, fitness monitor, or health diagnostic device. However, the device  500  could alternatively be any type of wearable device, including an earphone, headset, or glasses/goggles.  FIG.  5 A  shows a front isometric view of the device  500 , and  FIG.  5 B  shows a back isometric view of the device  500 . 
     The device  500  may include a body  502  (e.g., a watch body) and a band  504 . The body  502  may include an input or selection device, such as a crown  518  or a button  520 . The band  504  may be attached to a housing  506  of the body  502 , and may be used to attach the body  502  to a body part (e.g., an arm, wrist, leg, ankle, or waist) of a user. The body  502  may include a housing  506  that at least partially surrounds a display  508 . In some embodiments, the housing  506  may include a sidewall  510 , which sidewall  510  may support a front cover  512  ( FIG.  5 A ) and/or a back cover  514  ( FIG.  5 B ). The front cover  512  may be positioned over the display  508 , and may provide a window through which the display  508  may be viewed. In some embodiments, the display  508  may be attached to (or abut) the sidewall  510  and/or the front cover  512 . In alternative embodiments of the device  500 , the display  508  may not be included and/or the housing  506  may have an alternative configuration. 
     The display  508  may include one or more light-emitting elements including, for example, light-emitting elements that define a light-emitting diode (LED) display, organic LED (OLED) display, liquid crystal display (LCD), electroluminescent (EL) display, or other type of display. In some embodiments, the display  508  may include, or be associated with, one or more touch and/or force sensors that are configured to detect a touch and/or a force applied to a surface of the front cover  512 . 
     In some embodiments, the sidewall  510  of the housing  506  may be formed using one or more metals (e.g., aluminum or stainless steel), polymers (e.g., plastics), ceramics, or composites (e.g., carbon fiber). The front cover  512  may be formed, for example, using one or more of glass, a crystal (e.g., sapphire), or a transparent polymer (e.g., plastic) that enables a user to view the display  508  through the front cover  512 . In some cases, a portion of the front cover  512  (e.g., a perimeter portion of the front cover  512 ) may be coated with an opaque ink to obscure components included within the housing  506 . In some cases, all of the exterior components of the housing  506  may be formed from a transparent material, and components within the device  500  may or may not be obscured by an opaque ink or opaque structure within the housing  506 . 
     The back cover  514  may be formed using the same material(s) that are used to form the sidewall  510  or the front cover  512 . In some cases, the back cover  514  may be part of a monolithic element that also forms the sidewall  510 . In other cases, and as shown, the back cover  514  may be a multi-part back cover, such as a back cover having a first back cover portion  514 - 1  attached to the sidewall  510  and a second back cover portion  514 - 2  attached to the first back cover portion  514 - 1 . The second back cover portion  514 - 2  may in some cases have a circular perimeter and an arcuate exterior surface  516  (i.e., an exterior surface  516  having an arcuate profile). 
     The front cover  512 , back cover  514 , or first back cover portion  514 - 1  may be mounted to the sidewall  510  using fasteners, adhesives, seals, gaskets, or other components. The second back cover portion  514 - 2 , when present, may be mounted to the first back cover portion  514 - 1  using fasteners, adhesives, seals, gaskets, or other components. 
     A display stack or device stack (hereafter referred to as a “stack”) including the display  508  may be attached (or abutted) to an interior surface of the front cover  512  and extend into an interior volume of the device  500 . In some cases, the stack may include a touch sensor (e.g., a grid of capacitive, resistive, strain-based, ultrasonic, or other type of touch sensing elements), or other layers of optical, mechanical, electrical, or other types of components. In some cases, the touch sensor (or part of a touch sensor system) may be configured to detect a touch applied to an outer surface of the front cover  512  (e.g., to a display surface of the device  500 ). 
     In some cases, a force sensor (or part of a force sensor system) may be positioned within the interior volume below and/or to the side of the display  508  (and in some cases within the device stack). The force sensor (or force sensor system) may be triggered in response to the touch sensor detecting one or more touches on the front cover  512  (or a location or locations of one or more touches on the front cover  512 ), and may determine an amount of force associated with each touch, or an amount of force associated with the collection of touches as a whole. The force sensor (or force sensor system) may alternatively trigger operation of the touch sensor (or touch sensor system), or may be used independently of the touch sensor (or touch sensor system). 
     The device  500  may include various sensors. In some embodiments, the device  500  may have a port  522  (or set of ports) on a side of the housing  506  (or elsewhere), and an ambient pressure sensor, ambient temperature sensor, internal/external differential pressure sensor, gas sensor, particulate matter concentration sensor, or air quality sensor may be positioned in or near the port(s)  522 . 
     In some cases, one or more skin-facing sensors  526  may be included within the device  500 . The skin-facing sensor(s)  526  may emit or transmit signals through the housing  506  (or back cover  514 ) and/or receive signals or sense conditions through the housing  506  (or back cover  514 ). For example, in some embodiments, one or more such sensors may include a number of electromagnetic radiation emitters (e.g., visible light and/or IR emitters) and/or a number of electromagnetic radiation detectors (e.g., visible light and/or IR detectors, such as any of the electromagnetic radiation detectors described herein). The sensors may be used, for example, to acquire biological information from the wearer or user of the device  500  (e.g., a heart rate, respiration rate, blood pressure, blood flow rate, blood oxygenation, blood glucose level, and so on), or to determine a status of the device  500  (e.g., whether the device  500  is being worn or a tightness of the device  500 ). 
     The device  500  may include circuitry  524  (e.g., a processor and/or other components) configured to determine or extract, at least partly in response to signals received directly or indirectly from one or more of the device&#39;s sensors, and by way of example, biological parameters of the device&#39;s user, an input provided by the user, a status of the device  500  or its environment, and/or a position (or other aspects) of objects, particles, surfaces, or a user. The biological parameters may include, for example, a biometric, heart rate, respiration rate, blood pressure, blood flow rate, blood oxygenation, blood glucose level, and so on. In some embodiments, the circuitry  524  may be configured to convey the determined or extracted parameters, inputs, or statuses via an output device of the device  500 . For example, the circuitry  524  may cause the indication(s) to be displayed on the display  508 , indicated via audio or haptic outputs, transmitted via a wireless communications interface or other communications interface, and so on. The circuitry  524  may also or alternatively maintain or alter one or more settings, functions, or aspects of the device  500 , including, in some cases, what is displayed on the display  508 . 
     In some embodiments, one of the optical sensor systems described herein may be incorporated into the crown  518 , button  520 , skin-facing sensor  526 , or band  504  of the device  500 ; integrated with the display  508  or positioned behind the display  508 ; and so on. The optical sensor system may be used, for example, to determine biological parameters of the device&#39;s user, an input provided by the user, a status of the device  500  or its environment, and/or a position (or other aspects) of objects, particles, surfaces, or a user. 
       FIGS.  6 A and  6 B  show another example of a device  600  (an electronic device) that may include any of the optical sensor systems described with reference to  FIG.  1 A,  2 A,  3 A,  3 B,  4 A , or  4 B. The device&#39;s dimensions and form factor, including the ratio of the length of its long sides to the length of its short sides, suggest that the device  600  is a mobile phone (e.g., a smartphone). However, the device&#39;s dimensions and form factor are arbitrarily chosen, and the device  600  could alternatively be any portable electronic device including, for example, a mobile phone, tablet computer, portable computer, portable music player, portable terminal, vehicle navigation system, robot navigation system, or other portable or mobile device. The device  600  could also be a device that is semi-permanently located (or installed) at a single location (e.g., a door lock, thermostat, refrigerator, or other appliance).  FIG.  6 A  shows a front isometric view of the device  600 , and  FIG.  6 B  shows a rear isometric view of the device  600 . The device  600  may include a housing  602  that at least partially surrounds a display  604 . The housing  602  may include or support a front cover  606  or a rear cover  608 . The front cover  606  may be positioned over the display  604 , and may provide a window through which the display  604  (including images displayed thereon) may be viewed by a user. In some embodiments, the display  604  may be attached to (or abut) the housing  602  and/or the front cover  606 . 
     The display  604  may include one or more light-emitting elements or pixels, and in some cases may be an LED display, an OLED display, an LCD, an EL display, a laser projector, or another type of electronic display. In some embodiments, the display  604  may include, or be associated with, one or more touch and/or force sensors that are configured to detect a touch and/or a force applied to a surface of the front cover  606 . 
     The various components of the housing  602  may be formed from the same or different materials. For example, a sidewall  618  of the housing  602  may be formed using one or more metals (e.g., stainless steel), polymers (e.g., plastics), ceramics, or composites (e.g., carbon fiber). In some cases, the sidewall  618  may be a multi-segment sidewall including a set of antennas. The antennas may form structural components of the sidewall  618 . The antennas may be structurally coupled (to one another or to other components) and electrically isolated (from each other or from other components) by one or more non-conductive segments of the sidewall  618 . The front cover  606  may be formed, for example, using one or more of glass, a crystal (e.g., sapphire), or a transparent polymer (e.g., plastic) that enables a user to view the display  604  through the front cover  606 . In some cases, a portion of the front cover  606  (e.g., a perimeter portion of the front cover  606 ) may be coated with an opaque ink to obscure components included within the housing  602 . The rear cover  608  may be formed using the same material(s) that are used to form the sidewall  618  or the front cover  606 , or may be formed using a different material or materials. In some cases, the rear cover  608  may be part of a monolithic element that also forms the sidewall  618  (or in cases where the sidewall  618  is a multi-segment sidewall, those portions of the sidewall  618  that are non-conductive). In still other embodiments, all of the exterior components of the housing  602  may be formed from a transparent material, and components within the device  600  may or may not be obscured by an opaque ink or opaque structure within the housing  602 . 
     The front cover  606  may be mounted to the sidewall  618  to cover an opening defined by the sidewall  618  (i.e., an opening into an interior volume in which various electronic components of the device  600 , including the display  604 , may be positioned). The front cover  606  may be mounted to the sidewall  618  using fasteners, adhesives, seals, gaskets, or other components. 
     A display stack or device stack (hereafter referred to as a “stack”) including the display  604  (and in some cases the front cover  606 ) may be attached (or abutted) to an interior surface of the front cover  606  and extend into the interior volume of the device  600 . In some cases, the stack may also include a touch sensor (e.g., a grid of capacitive, resistive, strain-based, ultrasonic, or other type of touch sensing elements), or other layers of optical, mechanical, electrical, or other types of components. In some cases, the touch sensor (or part of a touch sensor system) may be configured to detect a touch applied to an outer surface of the front cover  606  (e.g., to a display surface of the device  600 ). 
     The stack may also include one or an array of sensors  616 , with the sensors positioned in front of or behind, or interspersed with, the light-emitting elements of the display  604 . In some cases, an array of sensors  616  may extend across an area equal in size to the area of the display  604 . Alternatively, the array of sensors  616  may extend across an area that is smaller than or greater than the area of the display  604 , or may be positioned entirely adjacent the display  604 . Although the array of sensors  616  is shown to have a rectangular boundary, the array could alternatively have a boundary with a different shape, including, for example, an irregular shape. The array of sensors  616  may be variously configured as an ambient light sensor, a light-emitting element (e.g., OLED) health sensor (e.g., age sensor), a touch sensor, a proximity sensor, a health sensor, a biometric sensor (e.g., a fingerprint sensor or facial recognition sensor), a camera, a depth sensor, and so on. The array of sensors  616  may also or alternatively function as a proximity sensor, for determining whether an object (e.g., a finger, face, or stylus) is proximate to the front cover  606 . In some embodiments, the array of sensors  616  may provide the touch sensing capability (i.e., touch sensor) of the stack. 
     In some cases, a force sensor (or part of a force sensor system) may be positioned within the interior volume below and/or to the side of the display  604  (and in some cases within the stack). The force sensor (or force sensor system) may be triggered in response to the touch sensor detecting one or more touches on the front cover  606  (or indicating a location or locations of one or more touches on the front cover  606 ), and may determine an amount of force associated with each touch, or an amount of force associated with the collection of touches as a whole. 
     As shown primarily in  FIG.  6 A , the device  600  may include various other components. For example, the front of the device  600  may include one or more front-facing cameras  610  (including one or more image sensors), speakers  612 , microphones, or other components  614  (e.g., audio, imaging, and/or sensing components) that are configured to transmit or receive signals to/from the device  600 . In some cases, a front-facing camera  610 , alone or in combination with other sensors, may be configured to operate as a bio-authentication or facial recognition sensor. Additionally or alternatively, the array of sensors  616  may be configured to operate as a front-facing camera  610 , a bio-authentication sensor, or a facial recognition sensor. 
     The device  600  may also include buttons or other input devices positioned along the sidewall  618  and/or on a rear surface of the device  600 . For example, a volume button or multipurpose button  620  may be positioned along the sidewall  618 , and in some cases may extend through an aperture in the sidewall  618 . The sidewall  618  may include one or more ports  622  that allow air, but not liquids, to flow into and out of the device  600 . In some embodiments, one or more sensors may be positioned in or near the port(s)  622 . For example, an ambient pressure sensor, ambient temperature sensor, internal/external differential pressure sensor, gas sensor, particulate matter concentration sensor, or air quality sensor may be positioned in or near a port  622 . 
     In some embodiments, the rear surface of the device  600  may include a rear-facing camera  624 . A flash or light source  626  may also be positioned along the rear of the device  600  (e.g., near the rear-facing camera). In some cases, the rear surface of the device  600  may include multiple rear-facing cameras. 
     In some cases, the sensor(s)  616 , the front-facing camera  610 , the rear-facing camera  624 , the button  620 , and/or other sensors positioned on the front, back, or sides of the device  600  may emit or transmit optical signals through the housing  602  (including the front cover  606 , rear cover  608 , or sidewall  618 ) and/or receive signals or sense conditions through the housing  602 . Optical signals may also be transmitted and received through the button  620 . In some embodiments, the sensor(s)  616 , the front-facing camera  610 , the rear-facing camera  624 , the button  620 , or the display  604  may include, or be integrated with, one of the optical sensor systems described herein. The optical sensor system may be used, for example, to determine biological parameters of the device&#39;s user, an input provided by the user, a status of the device  600  or its environment, and/or a position (or other aspects) of objects, particles, surfaces, or a user. 
     The device  600  may include circuitry  628  (e.g., a processor and/or other components) configured to determine or extract, at least partly in response to signals received directly or indirectly from one or more of the device&#39;s sensors, biological parameters of the device&#39;s user, a status of the device  600 , parameters of an environment of the device  600  (e.g., air quality), or a composition of a target or object, for example. In some embodiments, the circuitry  628  may be configured to convey the determined or extracted parameters or statuses via an output device of the device  600 . For example, the circuitry  628  may cause the indication(s) to be displayed on the display  604 , indicated via audio or haptic outputs, transmitted via a wireless communications interface or other communications interface, and so on. The circuitry  628  may also or alternatively maintain or alter one or more settings, functions, or aspects of the device  600 , including, in some cases, what is displayed on the display  604 . 
       FIG.  7    shows an example block diagram of an electronic device  700 , which in some cases may be the electronic device described with reference to  FIG.  5 A- 5 B or  6 A- 6 B . Electronic device  700  may include an electronic display  702  (e.g., a light-emitting display), a processor  704 , a power source  706 , a memory  708  or storage device, a sensor system  710 , and/or an input/output (I/O) mechanism  712  (e.g., an input/output device, input/output port, or haptic input/output interface). The processor  704  may control some or all of the operations of the electronic device  700 . The processor  704  may communicate, either directly or indirectly, with some or all of the other components of the electronic device  700 . For example, a system bus or other communication mechanism  714  can provide communication between the electronic display  702 , the processor  704 , the power source  706 , the memory  708 , the sensor system  710 , and the I/O mechanism  712 . 
     The processor  704  may 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 processor  704  may include a microprocessor, a central processing unit (CPU), an ASIC, a digital signal processor (DSP), a controller, or a combination of such devices. As described herein, the term “processor” 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, the processor  704  may provide part or all of the processing system or processor described herein. 
     It should be noted that the components of the electronic device  700  can be controlled by multiple processors. For example, select components of the electronic device  700  (e.g., the sensor system  710 ) may be controlled by a first processor and other components of the electronic device  700  (e.g., the electronic display  702 ) may be controlled by a second processor, where the first and second processors may or may not be in communication with each other. 
     The power source  706  can be implemented with any device capable of providing energy to the electronic device  700 . For example, the power source  706  may include one or more batteries or rechargeable batteries. Additionally or alternatively, the power source  706  may include a power connector or power cord that connects the electronic device  700  to another power source, such as a wall outlet. 
     The memory  708  may store electronic data that can be used by the electronic device  700 . For example, the memory  708  may 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, instructions, and/or data structures or databases. The memory  708  may include any type of memory. By way of example only, the memory  708  may include random access memory, read-only memory, Flash memory, removable memory, other types of storage elements, or combinations of such memory types. 
     The electronic device  700  may also include one or more sensor systems  710  positioned almost anywhere on the electronic device  700 . In some cases, the sensor systems  710  may include one or more of the optical sensor systems described herein. The sensor system(s)  710  may be 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; surface quality; and so on. By way of example, the sensor system(s)  710  may include an SMI sensor, a heat sensor, a position sensor, a light or optical sensor, an accelerometer, a pressure transducer, a gyroscope, a magnetometer, a health monitoring sensor, and an air quality sensor, and so on. Additionally, the one or more sensor systems  710  may utilize any suitable sensing technology, including, but not limited to, interferometric, magnetic, capacitive, ultrasonic, resistive, optical, acoustic, piezoelectric, or thermal technologies. 
     The I/O mechanism  712  may transmit or receive data from a user or another electronic device. The I/O mechanism  712  may include the electronic display  702 , a touch sensing input surface, a crown, one or more buttons (e.g., a graphical user interface “home” button), one or more cameras (including an under-display camera), one or more microphones or speakers, one or more ports such as a microphone port, and/or a keyboard. Additionally or alternatively, the I/O mechanism  712  may transmit electronic signals via a communications interface, such as a wireless, wired, and/or optical communications interface. Examples of wireless and wired communications interfaces include, but are not limited to, cellular and Wi-Fi communications interfaces. 
     The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art, after reading this description, that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art, after reading this description, that many modifications and variations are possible in view of the above teachings. 
     As described above, one aspect of the present technology may be the gathering and use of data available from various sources. The present disclosure contemplates that, in some instances, this gathered data may include personal information data that uniquely identifies or can be used to identify, locate, or contact a specific person. Such personal information data can include, for example, biometric data (e.g., fingerprint data), health data, and data linked thereto (e.g., demographic data, location-based data, telephone numbers, email addresses, home addresses, data or records relating to a user&#39;s health or level of fitness (e.g., vital signs measurements, medication information, exercise information), date of birth, or any other identifying or personal information). 
     The present disclosure recognizes that the use of such personal information data, in the present technology, can be used to the benefit of users. For example, the personal information data can be used to authenticate a user to access their device, or gather performance metrics for the user&#39;s interaction with an augmented or virtual world. Further, other uses for personal information data that benefit the user are also contemplated by the present disclosure. For instance, health and fitness data may be used to provide insights into a user&#39;s general wellness, or may be used as positive feedback to individuals using technology to pursue wellness goals. 
     The present disclosure contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. Such policies should be easily accessible by users, and should be updated as the collection and/or use of data changes. Personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection/sharing should occur after receiving the informed consent of the users. Additionally, such entities should consider taking any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices. In addition, policies and practices should be adapted for the particular types of personal information data being collected and/or accessed and adapted to applicable laws and standards, including jurisdiction-specific considerations. For instance, in the US, collection of or access to certain health data may be governed by federal and/or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA); whereas health data in other countries may be subject to other regulations and policies and should be handled accordingly. Hence different privacy practices should be maintained for different personal data types in each country. 
     Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, in the case of advertisement delivery services, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services or anytime thereafter. In another example, users can select not to provide data to targeted content delivery services. In yet another example, users can select to limit the length of time data is maintained or entirely prohibit the development of a baseline profile for the user. In addition to providing “opt in” and “opt out” options, the present disclosure contemplates providing notifications relating to the access or use of personal information. For instance, a user may be notified upon downloading an app that their personal information data will be accessed and then reminded again just before personal information data is accessed by the app. 
     Moreover, it is the intent of the present disclosure that personal information data should be managed and handled in a way to minimize risks of unintentional or unauthorized access or use. Risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and when applicable, including in certain health related applications, data de-identification can be used to protect a user&#39;s privacy. De-identification may be facilitated, when appropriate, by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or specificity of data stored (e.g., collecting location data at a city level rather than at an address level), controlling how data is stored (e.g., aggregating data across users), and/or other methods. 
     Therefore, although the present disclosure broadly covers use of personal information data to implement one or more various disclosed embodiments, the present disclosure also contemplates that the various embodiments can also be implemented without the need for accessing such personal information data. That is, the various embodiments of the present technology are not rendered inoperable due to the lack of all or a portion of such personal information data. For example, content can be selected and delivered to users by inferring preferences based on non-personal information data or a bare minimum amount of personal information, such as the content being requested by the device associated with a user, other non-personal information available to the content delivery services, or publicly available information.

Metadata:
Filing Date: 20210331
Publication Date: 20240220
Grant Date: 20240220
Priority Date: 20210331
Inventors: CHEN, TONG
TAN, FEI
JIN, Mingzhou
Assignee: APPLE INC
CPC Classifications: [{"code": "H10F77/146", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S7/4812", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4913", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4916", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4917", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L31/035236", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/18361", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/0262", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01S5/0262", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01S5/026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01S5/0264", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01S5/183", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S7/4916", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/0656", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01S7/4814", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/58", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4812", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4813", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B9/02092", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B9/02041", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B2290/45", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01S5/18361", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/0656", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/18327", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/58", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4812", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4813", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4814", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4916", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/18361", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4812", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4916", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4917", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4913", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 81581123