PATENT DOCUMENT

Publication Number: US-10908383-B1
Application Number: US-201816180048-A
Country: US
Kind Code: B1

Title: Local control loop for projection system focus adjustment

Abstract:
Optoelectronic apparatus includes a projector, which includes an array of first emitters, which emit respective first beams of optical radiation at a first wavelength, and a second emitter, which emits a second beam of optical radiation at a second wavelength. Projection optics receive the first and second beams of the optical radiation through an entrance face and project the beams through the exit face. An optical window transmits the radiation at the first wavelength and reflects the radiation at the second wavelength, and is positioned adjacent to the exit face of the projection optics so as to reflect the second beam back through the projection optics toward an optical sensor positioned in proximity to the first and second emitters. A controller drives an actuator to adjust a focal setting of the projection optics responsively to a distribution of the optical radiation received and sensed by the optical sensor.

Claims:
The invention claimed is: 
     
       1. Optoelectronic apparatus, comprising:
 a projector, comprising:
 an array of first emitters, which are configured to emit respective first beams of optical radiation at a first wavelength; 
 a second emitter, which is configured to emit a second beam of optical radiation at a second wavelength; 
 an optical sensor positioned in proximity to the first and second emitters; 
 projection optics having an entrance face and an exit face and configured to receive the first and second beams of the optical radiation through the entrance face and to project the beams through the exit face; and 
 an optical window, which is configured to transmit the optical radiation at the first wavelength and to reflect the optical radiation at the second wavelength, and which is positioned adjacent to the exit face of the projection optics so as to reflect the second beam back through the projection optics toward the optical sensor; 
 
 an actuator configured to adjust a focal setting of the projection optics; and 
 a controller, which is coupled to the optical sensor and to the actuator, and which is configured to drive the actuator responsively to a distribution of the optical radiation received and sensed by the optical sensor. 
 
     
     
       2. The optoelectronic apparatus according to  claim 1 , and comprising a semiconductor substrate, wherein the array of first emitters, the second emitter, and the optical sensor are disposed on the semiconductor substrate. 
     
     
       3. The optoelectronic apparatus according to  claim 1 , wherein the controller is configured to monitor a spatial extent of the distribution of the optical radiation received and sensed by the optical sensor, and to drive the actuator so as to minimize the spatial extent. 
     
     
       4. The optoelectronic apparatus according to  claim 1 , wherein the optical sensor comprises a detector array comprising multiple optical detector elements. 
     
     
       5. The optoelectronic apparatus according to  claim 4 , and comprising an astigmatic optical element in an optical path of the second beam, and wherein the controller is configured to drive the actuator so as to drive the distribution of the optical radiation received and sensed by the detector array to a predetermined shape. 
     
     
       6. The optoelectronic apparatus according to  claim 1 , wherein the actuator is configured to adjust a distance between the projection optics and the array of first emitters. 
     
     
       7. The optoelectronic apparatus according to  claim 1 , wherein the projection optics comprise at least one optical element with an adjustable focal length, and wherein the actuator is configured to adjust the focal length of the at least one optical element. 
     
     
       8. The optoelectronic apparatus according to  claim 1 , wherein the optical window is oriented at an angle not normal to an optical axis of the projection optics. 
     
     
       9. The optoelectronic apparatus according to  claim 1 , and comprising a filter positioned in proximity to the optical sensor and configured to prevent the optical radiation at the first wavelength from impinging on the optical sensor. 
     
     
       10. A method for projection, comprising:
 projecting first beams of optical radiation at a first wavelength from an array of first emitters using projection optics, which receive the first beams of the optical radiation through the entrance face and project the beams through the exit face; 
 directing a second beam of optical radiation at a second wavelength through the projection optics; 
 positioning an optical window, which is configured to transmit the optical radiation at the first wavelength and to reflect the optical radiation at the second wavelength, adjacent to the exit face of the projection optics so as to reflect the second beam back through the projection optics toward an optical sensor positioned in proximity to the first and second emitters; and 
 adjusting a focal setting of the projection optics responsively to a distribution of the optical radiation received and sensed by the optical sensor. 
 
     
     
       11. The method according to  claim 10 , wherein the array of first emitters, a second emitter, which emits the second beam, and the optical sensor are all formed on a semiconductor substrate. 
     
     
       12. The method according to  claim 10 , wherein adjusting the focal setting comprises monitoring a spatial extent of the distribution of the optical radiation received and sensed by the optical sensor, and adjusting the focal setting so as to minimize the spatial extent. 
     
     
       13. The method according to  claim 10 , wherein the optical sensor comprises a detector array comprising multiple optical detector elements. 
     
     
       14. The method according to  claim 13 , and comprising positioning an astigmatic optical element in an optical path of the second beam, wherein adjusting the focal setting comprises driving the distribution of the optical radiation received and sensed by the detector array to a predetermined shape. 
     
     
       15. The method according to  claim 10 , wherein adjusting the focal setting comprises setting a distance between the projection optics and the array of first emitters. 
     
     
       16. The method according to  claim 10 , wherein the projection optics comprise at least one optical element with an adjustable focal length, and wherein adjusting the focal setting comprises adjusting the focal length of the at least one optical element. 
     
     
       17. The method according to  claim 10 , wherein positioning the optical window comprises orienting the optical window at an angle not normal to an optical axis of the projection optics. 
     
     
       18. The method according to  claim 10 , and comprising positioning a filter in proximity to the optical sensor, wherein the filter is configured to prevent the optical radiation at the first wavelength from impinging on the optical sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application 62/588,358, filed Nov. 19, 2017, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to optoelectronic systems, and particularly to monitoring focus of an optoelectronic projection system. 
     BACKGROUND 
     Optical modules are very commonly used in consumer electronic devices. For example, almost all current portable telephones and computers include a miniature camera module. Miniature optical projection modules are also expected to come into increasing use in portable consumer devices for a variety of purposes. 
     Such projection modules may be used, for example, to cast a pattern of structured light onto an object for purposes of three-dimensional (3D) mapping (also known as depth mapping). In one example the projection module comprises an array of light emitters and projection optics, wherein the array is positioned at the focal plane of the projection optics. Beams of light emitted by the array are projected by the projection optics so as to form a pattern of illuminated spots on the object. (The terms “optical radiation” and “light” as used in the present description and in the claims refer generally to any and all of visible, infrared, and ultraviolet radiation.) An image capture assembly captures an image of the pattern that is projected onto the object, and a processor processes the image so as to a 3D map of the object. The method of spot projection is also applicable to 3D mapping utilizing a time-of-flight method, wherein the emitters, such as VCSELs (Vertical Cavity Surface Emitting Lasers), are pulsed, and the image capture assembly comprises high-speed detectors, such as SPADs (Single-photon Avalanche Diodes). 
     As another example, U.S. Pat. No. 9,091,413 describes photonics modules that include optoelectronic components and optical elements (refractive and/or patterned) in a single integrated package. According to the inventors, these modules can be produced in large quantities at low cost, while offering good optical quality and high reliability. They are useful as projectors of patterned light, for example in 3D mapping applications as described above, but they may also be used in various other applications that use optical projection and sensing, including free-space optical communications. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved apparatus and methods for optical projection. 
     There is therefore provided, in accordance with an embodiment of the present invention, optoelectronic apparatus, which includes a projector, including an array of first emitters, which are configured to emit respective first beams of optical radiation at a first wavelength, and a second emitter, which is configured to emit a second beam of optical radiation at a second wavelength. An optical sensor is positioned in proximity to the first and second emitters. Projection optics having an entrance face and an exit face are configured to receive the first and second beams of the optical radiation through the entrance face and to project the beams through the exit face. An optical window is configured to transmit the optical radiation at the first wavelength and to reflect the optical radiation at the second wavelength, and is positioned adjacent to the exit face of the projection optics so as to reflect the second beam back through the projection optics toward the optical sensor. An actuator is configured to adjust a focal setting of the projection optics. A controller is coupled to the optical sensor and to the actuator, and which is configured to drive the actuator responsively to a distribution of the optical radiation received and sensed by the optical sensor. 
     In a disclosed embodiment, the apparatus includes a semiconductor substrate, wherein the array of first emitters, the second emitter, and the optical sensor are disposed on the semiconductor substrate. 
     In one embodiment, the controller is configured to monitor a spatial extent of the distribution of the optical radiation received and sensed by the optical sensor, and to drive the actuator so as to minimize the spatial extent. 
     Additionally or alternatively, the optical sensor includes a detector array including multiple optical detector elements. In one embodiment, the apparatus includes an astigmatic optical element in an optical path of the second beam, and the controller is configured to drive the actuator so as to drive the distribution of the optical radiation received and sensed by the detector array to a predetermined shape. 
     In one embodiment, the actuator is configured to adjust a distance between the projection optics and the array of first emitters. Alternatively or additionally, the projection optics include at least one optical element with an adjustable focal length, and the actuator is configured to adjust the focal length of the at least one optical element. 
     In another embodiment, the optical window is oriented at an angle not normal to an optical axis of the projection optics. 
     Additionally or alternatively, the apparatus includes a filter positioned in proximity to the optical sensor and configured to prevent the optical radiation at the first wavelength from impinging on the optical sensor. 
     There is also provided, in accordance with an embodiment of the invention, a method for projection, which includes projecting first beams of optical radiation at a first wavelength from an array of first emitters using projection optics, which receive the first beams of the optical radiation through the entrance face and project the beams through the exit face. A second beam of optical radiation at a second wavelength is directed through the projection optics. An optical window, which is configured to transmit the optical radiation at the first wavelength and to reflect the optical radiation at the second wavelength, is positioned adjacent to the exit face of the projection optics so as to reflect the second beam back through the projection optics toward an optical sensor positioned in proximity to the first and second emitters. A focal setting of the projection optics is adjusted responsively to a distribution of the optical radiation received and sensed by the optical sensor. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional illustration of an optoelectronic apparatus, in accordance with an embodiment of the invention; 
         FIG. 2  is a schematic top view of a substrate on which emitter and detector arrays are formed, in accordance with an embodiment of the invention; and 
         FIGS. 3 and 4  are schematic sectional illustrations of optoelectronic apparatus, in accordance with other embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Mass production of miniaturized optical devices calls for product designs that meet the often-conflicting objectives of high precision and reliability and low manufacturing cost. For example, a miniature projection module may be configured to project a structured light pattern, and images of the pattern captured by a camera module may then be processed for purposes of depth mapping. For accurate depth mapping, it is important that the contrast and geometry of the pattern be consistent and well controlled. For 3D mapping utilizing the time-of-flight method, accurate operation requires well-defined pulsed spots of light, which concentrate the pulse energy in the desired locations on the object. 
     At the same time, consumer devices are expected to function in a wide range of different temperatures and environmental conditions. Temperature variations cause components of the optical modules to expand or contract, and possibly to change their refractive index, leading to changes in focal properties. Thermal swings can particularly change the focal length of the projection optics in a structured light projection module, causing the spots projected on the object to expand and eventually to overlap, thus degrading the parallax-based depth sensing capability of the module. For depth sensing based on time-of-flight, the expansion of the projected spots degrades the strength of the received signal, thus lowering the signal-to-noise ratio. This problem is particularly acute when the optical components of the module include refractive elements made from molded plastic (dictated by the need for mass production at low cost), because such elements are particularly prone to thermal expansion and contraction, as well as to changes of the refractive index as a function of temperature. 
     Methods used for focus control of conventional imaging systems, such as methods based on image contrast or phase-sensitive pixels, cannot readily be applied to the optics of structured illumination projectors. In order to maintain focus, complex and costly passive athermalization techniques may be employed, but they may not suffice to bring the focal length to within required tolerances. 
     Embodiments of the present invention that are described herein address these problems by incorporating into the optoelectronic projector module a focus detector and a focusing actuator controlled by the focus detector. 
     In the disclosed embodiments, the projector module comprises projection optics and an array of first emitters, such as VCSELs or other sorts of laser diodes, positioned at the focal plane of the projection optics. First beams of light emitted by the first emitters at a first wavelength λ 1  are received by the projection optics through an entrance face and are projected through an exit face of the optics, for example to project a desired pattern. 
     The focus detector comprises a second emitter, which emits a second beam of light at a second wavelength λ 2 , wherein λ 2  differs from λ 1 , and which is positioned at the focal plane of the projection optics so that the second beam of light is also projected by the projection optics. For example, λ 1  may be 940 nm, and λ 2  may be 900 nm or 980 nm. The focus detector also comprises an optical sensor in proximity to the array of first emitters and the second emitter. The focus detector further comprises an optical window, which, by utilizing one or more multilayer thin-film coatings deposited on the window, transmits light at λ 1  and reflects light at λ 2 . The window is positioned adjacent to the exit face of the projection optics, typically at an angle normal to the optical axis of the projection optics, so as to transmit the first beams of light towards an object and to reflect the second beam of light back through the projection optics toward the optical sensor. The window may alternatively be tilted with respect to the optical axis of the projection optics in order to increase the distance between the array of the first emitters and the optical sensor. 
     The distance to which the waists of the first beams are projected is determined by the position of the array of first emitters with respect to the rear focal plane of the projection optics. In an embodiment of the present invention, the array is positioned at the focal plane, and the laser beam waists are projected to a far distance, such as tens or hundreds of meters, for example, and the projection optics are said to work at infinite conjugates. In an alternative embodiment, the array of first emitters is positioned at an offset from the focal plane so as to project the laser beam waists to a finite distance from the projector, for example to a distance of 0.5 m, and the projection optics are said to work at finite conjugates. 
     In the embodiment in which the projection optics work at infinite conjugates, both the first beams and the second beam are projected by the projection optics to a distance which is very large as compared to a typical focal length of the projection optics, for example a focal length of 5-10 mm. The second beam is reflected by the window back to the projection optics and, since the beam is received by the projection optics as if it were arriving from a very large distance, it is focused onto the sensor at the focal plane of the optics. 
     In an alternative embodiment, in which the projection optics work at finite conjugates, both the first beams and the second beam are projected to a finite distance from the projection optics. Consequently, the retro-reflected second beam is defocused at the sensor. 
     In a further embodiment of the present invention, the module comprises an astigmatic optical element in the optical path of the second beam. This element causes the focal spot on the sensor to be an astigmatic spot, with a generally elliptical shape. The astigmatic optical element may be used both for infinite and finite conjugates. 
     A controller, coupled to the sensor and to the actuator, monitors the light distribution on the sensor and drives the actuator in response to the distribution in order to maintain an optimal focus. 
     In an embodiment of the present invention, the projector module comprises a semiconductor substrate, such as a silicon (Si) substrate. The array of first emitters, the second emitter and the sensor are formed on the semiconductor substrate using methods that are known in the art in semiconductor fabrication. For example, the emitters may comprise multiple epitaxial layers of III-VI semiconductor materials. 
     Temperature fluctuations may change the refractive index, as well as the dimensions, of the lenses of the projection optics, and thus change their focal lengths. This, in turn, will cause the projector module to drift from its optimal operating point, so that the first beams are no longer projected to their intended, optimal distance. The focal drift reduces the quality of the pattern of spots of the first beams that is projected onto a scene. At the same time, the shape and/or size of the focal spot of the second beam returning through the projection optics onto the sensor is changed. The controller will have stored the distribution of the focal spot at the optimal operating point. The controller monitors the focal spot, and when it senses a deviation of the shape and/or size of the focal spot from the optimal distribution, it sends a feedback signal to the focus actuator to bring the focal spot back to the optimal distribution. This corrects for the drift in the focal length of the projection optics, and returns the first beams to their intended projection distance. 
     In an embodiment of the present invention, the sensor comprises an array of detectors and the controller monitors the distribution of light on the detectors of the array. 
     In an embodiment of the present invention, the focusing actuator operates by changing the distance between the projection optics and the emitter array. 
     In another embodiment of the present invention, the projection optics comprise at least one lens element with an adjustable focal length, and the focusing actuator operates by adjusting this focal length. 
       FIG. 1  is a schematic sectional illustration of an optoelectronic apparatus  20 , in accordance with an embodiment of the invention. Optoelectronic apparatus  20  comprises a semiconductor substrate  22 , such as a Si-wafer substrate, with a top surface  23  on which an emitter array  24  comprising first emitters  26 , a second emitter  28 , and a sensor comprising, in this example, a detector array  30 , which comprises an array of detector elements  32 , are formed. Although emitter array  24  and detector array  30  appear in the sectional illustration as one-dimensional arrays, they typically comprise two-dimensional arrays, as is illustrated in  FIG. 2 . In alternative embodiments, however, other types of sensors (not necessarily arrays) may be used, and the principles of the present invention may similarly be applied in maintaining the focus of a single projected beam, rather than an entire array. 
     Optoelectronic apparatus  20  further comprises projection optics  34 , with a rear focal plane  35 , and an exit optical window  36 . In the illustration, projection optics  34  are shown, for the sake of simplicity, as a single lens, but optics  34  may alternatively comprise multiple lenses. Projection optics  34  and window  36  are attached to a mechanical frame  38 . An actuator  40  attached between substrate  22  and mechanical frame  38 , comprises, for example, a motor, transducers, or other electromechanical element capable of adjusting the distance between projection optics  34  and the substrate. A controller  42 , coupled to detector array  30  and to actuator  40 , drives the actuator in response to the distribution of the optical radiation received and sensed by the detector array, as indicated by an arrow  44 , in order to increase or to decrease the distance between projection optics  34  and substrate  22  and thus maintain optimal focus of the projected beams. 
     In some embodiments, controller  42  comprises a programmable controller, which is programmed in software and/or firmware to carry out the functions that are described herein. Additionally or alternatively, at least some of the functions of controller  42  may be carried out by hardware logic circuits, which may be hard-wired or programmable. In either case, controller has suitable interfaces for receiving and transmitting data and instructions to and from other elements of apparatus  20  as described. 
     First emitters  26  and second emitter  28  comprise lasers, such as laser diodes or VCSELs. Lasers formed from III-VI group of materials may be integrated on substrate  22  using semiconductor processing methods known to those skilled in the art. First emitters  26  emit respective first beams of light at wavelength λ 1 , while second emitter  28  emits a second beam of light at a wavelength λ 2 , wherein λ 2  differs from λ 1 . In an embodiment of the present invention, λ 1  is 940 nm and λ 2  is either 900 nm or 980 nm. Alternatively, other emitters  26  and  28  may operate at other values of λ 1  and λ 2 . In all cases, window  36  is coated, for example with one or more multilayer thin-film coatings, as is known in the art, to transmit light at wavelength λ 1  and to reflect light at wavelength λ 2 . Optionally, an optical filter  47  may be placed above the array of detector elements  32  to block stray light from the first beams from impinging on the array and thus interfering with the light from the retro-reflected second beam, which is focused onto the array. Optical filter  47  is configured to reflect or absorb light at wavelength λ 1  (i.e., to prevent wavelength λ 1  from reaching the detector) and to transmit light at wavelength λ 2 , and can be fabricated using, for example, similar sorts of multilayer thin-film coatings as are used for window  36 . 
     Electronic components, such as laser drivers, may also be integrated on substrate  22 . 
       FIG. 1  illustrates paths for selected optical rays, in accordance with an embodiment of the invention. In the illustrated embodiment, substrate  22  is positioned so that its top surface  23  exactly coincides with focal plane  35  of projection optics  34 . 
     In order to illustrate the functioning of optoelectronic apparatus  20 , one of first emitters  26  is labeled as a first emitter  46 . First emitter  46  emits a first beam of light at wavelength λ 1 , with the beam and its direction of propagation illustrated schematically by optical rays  48  and  50  and arrows  52  and  54 , respectively. Projection optics  34  refract rays  48  and  50  and, working at infinite conjugates, project them towards an object (not shown) at a far distance, typically tens or hundreds of meters, with window  36  transmitting rays  48  and  50  at wavelength λ 1 . Similarly, each first beam of light emitted by each of first emitters  26  of emitter array  24  is projected through window  36 , thus creating a corresponding pattern of spots in the far field of projection optics  34 . The projection angle of each first beam is determined by the focal length of projection optics  34  and by the position of each first emitter  26  in emitter array  24 , as is known in the art. For the sake of clarity, only the beam emitted by emitter  46  is illustrated. 
     Second emitter  28  emits a second beam of light at wavelength λ 2 , with the second beam and its direction of propagation illustrated schematically by optical rays  56  and  58  and arrows  60  and  62 , respectively. Projection optics  34  refract and project rays  56  and  58 , and would project the rays to a far distance towards the object, but in this case window  36  retro-reflects these rays back to projection optics  34 . Projection optics  34  focus the reflected rays  56  and  58  onto detector array  30 , as shown by arrows  64  and  66 , respectively. 
     Optoelectronic apparatus  20  can be used in consumer applications in variable ambient temperatures, which cause corresponding fluctuations in the temperature of optoelectronic apparatus  20 . These temperature fluctuations, in turn, change the focal length of projection optics  34 , especially if the optical elements are fabricated from plastic, where the dimensions, as well as the refractive index, are strongly dependent of the temperature. Due to the change of the focal length, top surface  23  will no longer coincide with focal plane  35 . Therefore, rays  48 ,  50 ,  56 , and  58  will not be projected to a far distance when exiting from projection optics  34 , and rays  56  and  58  will not be focused at detector array  30 . 
     Controller  42  processes signals received from detector array  30  in order to monitor the distribution of the light, represented by rays  56  and  58  and arrows  64  and  66 , received by the detector array. When controller  42  detects that the received light is not focused to a minimal spot on detector array  30  (or to a spot within a certain tolerance of the minimal size), it drives actuator  40  to change the distance between substrate  22  and projection optics  34  so as to re-focus rays  56  and  58  onto the detector array. This re-focusing brings top surface  23  back to focal plane  35 , and rays  48  and  50  are again projected to a far distance by the projection optics. In this way, utilizing the feedback provided by monitoring the distribution of light on detector array  30  and by closing the loop through actuator  40  ensures that the beams emitted by emitters  26  of emitter array  24  are controlled under fluctuating ambient temperatures, and projected into high-quality spots on the object at a far distance. Optionally, when the spot on detector array  30  cannot be refocused to within tolerable limits, controller  42  may take further action, such as issuing an alert or shutting down the emitters. 
     When substrate  22  is positioned so that its top surface  23  is offset from focal plane  35 , projection optics  34  work at finite conjugates, and the reflected second beam on detector array  30  is defocused at the optimal operating point. A change of the focal properties of projection optics  34  due to thermal fluctuations will change the size of the defocused return spot of the second beam on detector array  30 . This change in size is detected by controller  42 , and used for generating a feedback signal to drive actuator  40  and to control the projected beams, as described above in the context of infinite conjugates. 
     Fluctuation of the ambient temperature may also affect the projection of rays  48 ,  50 ,  56 , and  58  due to temperature-induced changes in mechanical framework  38 . The feedback mechanism described above works in a similar fashion to control the projection of the rays  48  and  50  in this case. 
       FIG. 2  is a schematic top view of substrate  22 , in accordance with an embodiment of the invention. The figure illustrates the positioning of emitter array  24  of first emitters  26 , second emitter  28 , and detector array  30  on top surface  23 , previously illustrated in a sectional view in  FIG. 1 . Second emitter  28  emits light from an emitting area  68 , with a typical diameter of 10 μm. For projection optics  34  working at infinite conjugates, the light emitted from emitting area  68  is focused into a focal spot  70  on detector array  30 . The diameter of focal spot  70  is similar to the diameter of emitting area  68  when apparatus  20  is properly focused, so that top surface  23  coincides with focal plane  35 . 
     The distance between detector array  30  and emitter array  24  may be defined by tilting the angle of window  36  with respect to the optical axis of projection optics  34 . 
       FIG. 3  is a schematic sectional illustration of an optoelectronic apparatus  80 , in accordance with another embodiment of the invention. Optoelectronic apparatus  80  is similar to optoelectronic apparatus  20  illustrated in  FIG. 1 , except for an added astigmatic lens  82 . Consequently, the same labels are used in  FIG. 3  as in  FIG. 1  for similar components. 
     Astigmatic lens  82  is positioned in the path of the second beam emitted by second emitter  28 , in a location chosen so as not to interfere with any of the first beams emitted by first emitters  26 . In  FIG. 3  astigmatic lens is positioned in proximity to detector array  30 . Alternatively, astigmatic lens  82  may be positioned in proximity to second emitter  28 . Astigmatic lens  82 , in conjunction with projection optics  34 , generates a finite focal spot  84  on detector array  30 , whose properties can be used in more precisely controlling the focus of apparatus  80 . 
     The focal properties of astigmatic lens  82  are chosen so that when top surface  23  either coincides with focal plane  35  (with projection optics  34  used at infinite conjugates) or is located at a given offset from the focal plane (finite conjugates), focal spot  84  has a given shape, which is stored by controller  42 . When top surface  23  deviates from its optimal position with respect to focal plane  35  (for example, due to thermal fluctuations), the shape of focal spot  84  changes. As an example, for infinite conjugates astigmatic lens  82  may be configured so that at the optimal operating point focal spot  84  has a shape of a line (one of the astigmatic foci), and a deviation from the optimal operating point will cause the focal spot to deviate from that shape. As a second example, for finite conjugates astigmatic lens  82  may be configured so that focal spot  84  has a given elliptical shape at the optimal operating point. A deviation from the optimal operating point will change the ellipticity of focal spot  84 . 
     Controller  42  monitors the spatial distribution of focal spot  84  on detector array  30 . When controller  42  detects a deviation of the shape of focal spot  84  from the stored, optimal shape, it drives actuator  40  to change the distance between substrate  22  and projection optics  34  so as to return the focal spot to its optimal shape. This re-focusing brings top surface  23  back to its optimal position with respect to focal plane  35 , and rays  48  and  50  are again projected by the projection optics to the required distance. 
       FIG. 4  is a schematic sectional illustration of an optoelectronic apparatus  100 , in accordance with yet another embodiment of the invention. Optoelectronic apparatus  100  is similar to optoelectronic apparatus  20  of  FIG. 1 , except that projection optics  34  have been replaced by projection optics  102 , actuator  40  has been replaced by an actuator  104 , and mechanical frame  38  has been replaced by a mechanical frame  106 . For the components and rays of optoelectronic apparatus  100  that are similar to those of optoelectronic apparatus  20 , the same labels are used. 
     Projection optics  102  comprise at least one optical element  108  having an adjustable focal length, for example a liquid-filled lens. Actuator  104  adjusts the focal length of optical element  108 . Projection optics  102 , window  36 , and substrate  22  are attached to mechanical frame  106 . 
     As in the embodiment of  FIG. 1 , controller  42  monitors the distribution of the focal spot on detector array  30 . In apparatus  100 , however, controller  42  utilizes the distribution of the focal spot to drive actuator  104  to adjust the focal length of optical element  108  so as to bring the focal spot on detector array  30  to its optimal distribution. This adjustment returns optoelectronic apparatus  100  to its optimal operating point. 
     An additional embodiment (not shown in the figures) uses a combination of the astigmatic lens of  FIG. 3  with the adjustable focal-length lens of  FIG. 4 . 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Metadata:
Filing Date: 20181105
Publication Date: 20210202
Grant Date: 20210202
Priority Date: 20171119
Inventors: MACKINNON, NEIL
Assignee: APPLE INC
CPC Classifications: [{"code": "G01S7/4815", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/894", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/497", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N13/254", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N13/271", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01B11/2513", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B7/09", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N13/254", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B7/09", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B27/0025", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04N13/254", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B7/09", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 74260985