Fresnel reflection-based optical pick-off element for laser-based systems

Abstract

A laser projection system [200] is provided that includes at least one pick-off element [306] or pick-off interface [540] that redirects a portion of the input laser light toward one or more photodetectors [310], such as for laser power monitoring. A given pick-off element interface or a given pick-off interface redirects the input laser light using Fresnel reflection. Fresnel reflection occurs due to a difference in refractive index between two materials that contact and form an interface. In some embodiments, the pick-off element is disposed in an optical path between a beam combiner and an optical scanner of the system. The pick-off element can be a plate beam splitter, a cube beam splitter, or a prism. In some embodiments, at least one pick-off interface is provided between two or more substrates of the beam combiner [316].

Description

Background Art

[0001] Background A projector is an optical device for projecting or irradiating a pattern of light onto another object (e.g., on the surface of another object such as a projection screen) to display an image or video on that other object. A laser projector is a projector in which the light source includes at least one laser, and the laser is temporarily modulated to provide a pattern of laser light, and the pattern of laser light is then spatially dispersed over a display area of another object (e.g., a screen or a lens) to display an image or video. In order to more appropriately control the performance of a laser projector, it may be advantageous to monitor the laser output of the laser projector. For example, by accurately monitoring the laser output of a laser projector, the laser projector can control the laser output to adjust the white point and / or brightness of the display.

Summary of the Invention

[0002] By referring to the accompanying drawings, the present disclosure can be better understood, and many of its features and advantages can become apparent to those skilled in the art. The use of the same reference numerals in different drawings indicates similar or identical items.

Brief Description of the Drawings

[0003] [Figure 1] It is a diagram showing a display system having an integrated laser projection system according to some embodiments. [Figure 2] It is a diagram showing a laser projection system having an optical scanner including an optical relay disposed between two scanning mirrors according to some embodiments. [Figure 3] It is a perspective view of a laser projector including an individual pick-off component for redirecting a portion of the laser light to a photodetector via Fresnel reflection according to some embodiments. [Figure 4]This figure shows an example of Fresnel reflection deflection of a portion of light from one or more laser beams passing through individual pick-off components, according to some embodiments. [Figure 5] This is a perspective view of a laser projector having a beam combiner including a secondary indexing substrate interposed between two primary indexing substrates, according to one embodiment, where each primary indexing substrate has a first refractive index and the secondary indexing substrate has a second refractive index, and the difference between the first and second refractive indices causes the laser light beam to be partially reflected toward a photodetector at the interface between the primary and secondary indexing substrates. [Figure 6] Figure 5 shows an example of a secondary index substrate thickness in which, according to several embodiments, the first and second sets of laser light beams reflected at the input and output interfaces of the secondary index substrate do not overlap. [Figure 7] Figure 5 shows an example in which the thickness of the secondary index substrate is such that, according to several embodiments, the first and second sets of laser light beams reflected at the input and output interfaces of the secondary index substrate partially overlap. [Figure 8] This is a perspective view of a laser projector having a beam combiner, which includes a secondary index substrate interposed between two primary index substrates, according to one embodiment, and a mirror positioned on the first side of the beam combiner to deflect the laser light beam toward a photodetector located on the second side of the beam combiner. [Figure 9] The figure shows a perspective view of a laser projector having a beam combiner including a secondary index substrate interposed between two primary index substrates, according to one of several embodiments, wherein a first mirror is positioned on the first side of the beam combiner to deflect the laser light beam toward a photodetector, and a second mirror is positioned on the second side of the beam combiner to deflect the laser light beam toward a photodetector. [Figure 10]This chart shows the wavelength response of photodetectors, such as the photodetector shown in Figures 8 and 9, according to several embodiments, as well as the wavelength-tunable reflectance profiles of the first and second partial reflection mirrors. [Figure 11] This chart shows the first weighted wavelength response of a coupling between a first partial reflection mirror and a photodetector, and the second weighted wavelength response of a coupling between a second partial reflection mirror and a photodetector, according to several embodiments. [Figure 12] This is a perspective view of a laser projector having a beam combiner including a secondary index substrate interposed between two primary index substrates, according to some embodiments, wherein a first beam splitter is located on the first side of the beam combiner to deflect the laser beam toward a first photodetector located on the second side of the beam combiner, and to allow a portion of the laser beam to pass through the first beam splitter toward a second photodetector located on the first side of the beam combiner. [Figure 13] This is a perspective view of a laser projector having a beam combiner that includes a secondary index substrate positioned adjacent to a primary index substrate at the end of the beam combiner, according to some embodiments, wherein a pick-off interface between the primary index substrate and the secondary index substrate deflects a portion of the laser light beam incident on the interface toward a photodetector. [Figure 14] This is a perspective view of a laser projector having a beam combiner including alternating primary and secondary index substrates, according to several embodiments, wherein each pick-off interface between the primary and secondary index substrates deflects a portion of the laser beam incident on the pick-off interface toward the respective photodetector aligned with the pick-off interface. [Figure 15] This is a perspective view of a laser projector having a beam combiner and a prism according to several embodiments, where the prism is separate from the beam combiner, and Fresnel reflection of the laser beam at the input interface of the prism deflects a portion of the laser beam toward a photodetector. [Figure 16]This is a perspective view of a laser projector having a beam combiner and a prism according to some embodiments, where the prism is separate from the beam combiner, and Fresnel reflection of the laser beam at the output interface of the prism deflects a portion of the laser beam toward a photodetector. [Modes for carrying out the invention]

[0004] Detailed explanation Figures 1 to 16 illustrate embodiments for compactly arranging a near-eye display system (e.g., a wearable head-up display (WHUD)) or another display system. Using the techniques described herein, one or more portions of one or more laser inputs (sometimes referred to herein as “laser beams”) of the laser projection system of such a display system are redirected to one or more photodetectors via Fresnel reflection, which occurs when one or more laser inputs strike an interface between two materials having different refractive indices. Materials that can form such an interface between them include, but are not limited to, any combination of N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, and air. By using Fresnel reflection to redirect a portion of a given laser beam to a photodetector, rather than a conventional coating-based approach, a narrower transmission tolerance is obtained, resulting in a more consistent and desirable amount of light from the laser beam directed to the photodetector. By improving the consistency of the amount of light redirected to the photodetector in this way, problems associated with insufficient photodetector sensitivity and supersaturation can be mitigated.

[0005] As illustrated, monitoring the laser output of a laser projector can be advantageous for better control of the projector's performance. For example, accurately monitoring the laser output of a laser projector allows the projector to control its output to adjust the white point and / or brightness of the display, thereby improving the user experience. Conventional laser projection systems sample or "pick off" laser light using a pick-off optical system with a dielectric coating that redirects a portion of the laser light to a sensor. However, pick-off optical systems with reflective dielectric coatings are generally narrowband and have undesirably large tolerances (e.g., transmittance tolerance or reflectance tolerance) for the amount of light redirected to the sensor, resulting in inconsistent amounts of light being redirected to the sensor, potentially leading to oversaturation of the sensor due to too much light being redirected, or insufficient light being redirected, preventing reliable detection by the sensor. The systems and techniques described herein redirect light via a pick-off element having one or more interfaces between two materials having different refractive indices, resulting in Fresnel reflection. In some embodiments, “Fresnel reflection” refers to the reflection of a portion of incident light at a discontinuous interface between two media having different refractive indices. By deflecting a portion of the laser light within a given laser projection system via Fresnel reflection at such an interface, the proportion of incident light deflected by the pick-off element or pick-off interface of the embodiments described herein (e.g., toward a photodetector for laser power determination) is more consistent than in conventional systems that rely on dielectric coating-based pick-off optics, thereby making the amount of light deflected toward the photodetector for laser power determination and corresponding display adjustment more consistent, resulting in an improved user experience.

[0006] In some embodiments, the display system includes a laser projection system having a pick-off element positioned between a beam combiner and an optical scanner, the pick-off element deflecting a portion of the input light toward a photodetector. During operation, modulable laser sources of the laser projection system supply laser beams of different wavelengths to the beam combiner, which combines the laser beams into a concentrated laser beam. The beam combiner outputs the concentrated laser beam toward the optical scanner along an optical path passing through the pick-off element.

[0007] In some embodiments, the pick-off element is a plate beam splitter or a prism beam splitter. In some such embodiments, one or more optical surfaces of the pick-off element (i.e., the plane through which the laser light passes) are uncoated. The interface between a given optical surface of the pick-off element and air causes Fresnel reflection of the input focused laser beam, resulting in a portion of the input focused laser beam being deflected toward the photodetector. It should be noted that this Fresnel reflection can be achieved without dielectric coating on a given optical surface of the pick-off element.

[0008] In some embodiments, the pick-off element is a cubic beam splitter comprising a first prism made of a first material having a first refractive index and a second prism made of a second material having a second refractive index different from the first refractive index, thereby causing Fresnel reflection of the input concentrated laser beam at the interface between the first and second prisms, and consequently deflecting a portion of the input concentrated laser beam toward a photodetector.

[0009] In some embodiments, the display system includes a laser projection system having a beam combiner that incorporates one or more pick-off interfaces that use Fresnel reflection to deflect a portion of the input light toward a photodetector. Hereinafter, “pick-off interface” is considered a type of pick-off element. During operation, modulable laser sources of the laser projection system supply laser beams of different wavelengths to the beam combiner, which combines the laser beams into a concentrated laser beam. The beam combiner outputs the concentrated laser beam toward an optical scanner along an optical path passing through the pick-off interfaces. Each pick-off interface of the beam combiner uses Fresnel reflection to deflect a portion of one or more laser beams or the concentrated laser beam toward a photodetector.

[0010] In some embodiments, the beam combiner includes a secondary indexing substrate positioned between a first primary indexing substrate and a second primary indexing substrate, thereby positioning a first pick-off interface between the first primary indexing substrate and the secondary indexing substrate, and a second pick-off interface between the second primary indexing substrate and the secondary indexing substrate. Each primary indexing substrate is made of a first material having a first refractive index, while the secondary indexing substrate is made of a second material having a second refractive index different from the first. The difference between the first and second refractive indices causes light incident on the first and second pick-off interfaces to be deflected toward a photodetector via Fresnel reflection. In this example, a first portion of the concentrated laser beam, when reflected by the first pick-off interface, travels along a first optical path, and a second portion of the concentrated laser beam, when reflected by the second pick-off interface, travels along a second optical path. In some embodiments, the width of the secondary indexing substrate causes the first optical path to overlap with the second optical path at least partially. In some embodiments, the width of the secondary index substrate prevents the first optical path from overlapping with the second optical path.

[0011] In some embodiments, mirrors are positioned in the first and second optical paths of the reflected first and second portions of the concentrated laser beam, and are configured to reflect some or all of the first and second portions of the concentrated laser beam back through the beam combiner to the first photodetector. In some embodiments, the mirrors are fully reflective (i.e., no light passes through the mirror; all or substantially all light is reflected by the mirror toward the photodetector). In some embodiments, the mirrors are only partially reflective (and therefore at least partially transparent), and the second photodetector is positioned to receive first fragments of the first and second portions of the concentrated laser beam passing through the partially transparent mirror, while second fragments of the first and second portions are reflected toward the first photodetector. For example, the first and second photodetectors may be positioned on opposite sides of the beam combiner, respectively. In some embodiments, the mirrors are configured with a tunable reflectance profile selected based on the wavelength response of the first photodetector. In some embodiments, the tunable reflectance profile of the mirror causes the weighted wavelength response of the mirror-first photodetector combination to be substantially flat (e.g., equal or substantially equal response for all wavelengths of light, or at least with respect to the wavelengths of light contained in the concentrated laser beam).

[0012] In some embodiments, the primary and secondary indexing substrates of the beam combiner are arranged together to form a single pick-off interface that deflects a portion of the concentrated laser beam toward a photodetector via Fresnel reflection. In some such embodiments, the secondary indexing substrate is located at the end of the beam combiner, through which the concentrated laser beam exits the beam combiner.

[0013] In some embodiments, the beam combiner includes alternating primary and secondary index substrates, thereby forming a plurality of pick-off interfaces between the primary and secondary index substrates, each pick-off interface deflecting the laser beam to a different photodetector via Fresnel reflection. In some such embodiments, at least one of the plurality of pick-off interfaces combines at least two laser beams output by a modulable laser source as part of the formation of a concentrated laser beam, and deflects a portion of at least one of the laser beams via Fresnel reflection to a photodetector associated with that pick-off interface (e.g., aligned).

[0014] While some embodiments of this disclosure are described and illustrated with reference to specific examples of near-eye display systems in the form of wearable head-up displays (WHUDs), it should be noted that the devices and techniques of this disclosure are not limited to these specific examples and can instead be implemented in any of the various display systems using the guidelines provided herein.

[0015] Figure 1 shows an example of a display system 100 using a scanning-based optical system according to several embodiments, having a support structure 102 including an arm 104, which houses a laser projection system configured to project an image toward the user's eye, thereby allowing the user to perceive the projected image as displayed within the field of view (FOV) area 106 of the display in one or both of the lens elements 108, 110. In the illustrated embodiment, the display system 100 is a near-eye display system in the form of a WHUD, in which the support structure 102 is configured to be worn on the user's head and has the general shape and appearance (i.e., form factor) of a spectacle (e.g., sunglasses) frame. The support structure 102 houses, or otherwise includes, various components to facilitate the projection of such an image toward the user's eye, such as a laser projector, optical scanner, waveguide, etc. In some embodiments, the support structure 102 further includes various sensors such as one or more front cameras, rear cameras, other light sensors, motion sensors, accelerometers, etc. The support structure 102 may further include one or more radio frequency (RF) interfaces, or other radio interfaces such as a Bluetooth® interface, a WiFi interface, etc. Furthermore, in some embodiments, the support structure 102 may further include one or more batteries or other portable power sources for supplying power to the electrical components of the display system 100. In some embodiments, some or all of these components of the display system 100 are housed entirely or partially within the internal volume of the support structure 102, such as within the arms 104 of region 112 of the support structure 102. While exemplary form factors are shown, it should be understood that in other embodiments, the display system 100 may have a different shape and appearance from the spectacle frame shown in Figure 1. The use of the term “or” as used herein should be understood to refer to the non-exclusive definition of “or” unless otherwise specified. For example, the phrase “X or Y” as used herein means “either X or Y, or both.”

[0016] One or both of the lens elements 108, 110 can be used by the display system 100 to provide an augmented reality (AR) display that can overlay the rendered graphic content or, alternatively, can be provided in conjunction with the view of the real world perceived by the user through the lens elements 108, 110. For example, the laser light used to form a perceptible image or series of images can be projected onto the user's eye by the laser projector of the display system 100 through a series of optical elements such as, for example, a corresponding lens element, one or more scanning mirrors, and a waveguide that is at least partially formed within one or more optical relays. Thus, one or both of the lens elements 108, 110 includes at least a portion of the waveguide that routes the display light received by the waveguide's incoupler to the waveguide's outcoupler, and the waveguide's outcoupler outputs the display light toward the user's eye of the display system 100. The display light is modulated and scanned over the user's eye so that the user perceives the display light as an image. Additionally, each of the lens elements 108, 110 is sufficiently transparent so that the user can see through the lens element, and can provide a field of view of the user's real-world environment such that an image appears overlaid across at least a portion of the real-world environment.

[0017] In some embodiments, the laser projector is a digital light processing-based projector, a scanning laser projector, or any combination of a modulated light source such as a laser or one or more light-emitting diodes (LEDs) and a dynamic reflector mechanism such as one or more dynamic scanners or digital light processors. In some embodiments, the laser projector includes a plurality of laser diodes (e.g., red laser diodes, green laser diodes, and blue laser diodes) and at least one scanning mirror (e.g., two one-dimensional scanning mirrors, which may be micro-electromechanical system (MEMS) based or piezoelectric based). The laser projector is communicatively coupled to a controller and a non-temporary processor-readable storage medium or memory, which stores processor-executable instructions and other data that, when executed by the controller, cause the controller to control the operation of the projector. In some embodiments, the controller is communicatively coupled to a processor (not shown) that controls the scanning area size and scanning area position for the projector and generates content to be displayed on the display system 100. The laser projector scans light across the display system 100, specifically the FOV area 106 and a designated variable area. The scanning area size corresponds to the size of the FOV area 106, and the scanning area position corresponds to one of the lens elements 108, 110 in which the FOV area 106 is visible to the user. Generally, it is desirable for a display to have a wide FOV to accommodate light extraction over a wide range of angles. In this specification, the range of different user eye positions from which the display can be viewed is referred to as the display's eyebox.

[0018] In some embodiments, the display system includes an optical scanner that routes light to a waveguide disposed at an output of a second scanning mirror via a first and a second scanning mirror and an optical relay disposed between the first and second scanning mirrors. In some embodiments, at least a portion of an outcoupler of the waveguide may overlap with the FOV region 106. These aspects are described in more detail below.

[0019] FIG. 2 shows a simplified block diagram of a laser projection system 200 (sometimes also referred to as a “laser projector”) that projects an image directly onto a user's eye via laser light. The laser projection system 200 includes an optical engine 202, an optical scanner 204, and a waveguide 205. The optical scanner 204 includes a first scanning mirror 206, a second scanning mirror 208, and an optical relay 210. The waveguide 205 includes an incoupler 212 and an outcoupler 214, and in this example, the outcoupler 214 is optically aligned with the user's eye 216. In some embodiments, the laser projection system 200 is implemented in another display system such as a wearable heads-up display or the display system 100 of FIG. 1.

[0020] The optical engine 202 includes one or more laser light sources configured to generate and output laser light 218 (e.g., visible laser light such as red, blue, and green laser light, and in some embodiments, non-visible laser light such as infrared laser light). In some embodiments, the optical engine 202 is coupled to a driver or other controller (not shown), and the driver or other controller controls the timing of the emission of the laser light from the laser light sources of the optical engine 202 according to instructions received by the controller or driver from a computer processor coupled thereto, and modulates the laser light 218 so that it is perceived as an image when output to the retina of the user's eye 216.

[0021] For example, during the operation of the laser projection system 200, multiple laser beams, each having a different wavelength, are output by the laser light source of the optical engine 202 and then combined via a beam combiner (not shown) before being directed towards the user's eye 216. The optical engine 202 modulates the intensity of each laser beam so that the combined laser light reflects a set of pixels in the image, and the specific intensity of each laser beam at any given time contributes to the amount of corresponding color content and the brightness of the pixels represented by the combined laser light at that time.

[0022] In some embodiments, one or both of the first and second scanning mirrors, 206 and 208, of the optical scanner 204 are MEMS mirrors. For example, the first scanning mirror 206 and the second scanning mirror 208 are MEMS mirrors that are driven and vibrated by their respective operating voltages during the active operation of the laser projection system 200, causing the first and second scanning mirrors, 206 and 208, to scan the laser beam 218. The vibration of the first scanning mirror 206 causes the laser beam 218 output by the optical engine 202 to be scanned across the surface of the second scanning mirror 208 through the optical relay 210. The second scanning mirror 208 scans the laser beam 218 received from the first scanning mirror 206 toward the in-coupler 212 of the waveguide 205. In some embodiments, the first scanning mirror 206 vibrates or rotates around the first axis 219, thereby scanning the laser beam 218 in only one dimension (i.e., in a line) across the surface of the second scanning mirror 208. In some embodiments, the second scanning mirror 208 vibrates or rotates around the second axis 221. In some embodiments, the first axis 219 is tilted with respect to the second axis 221.

[0023] In some embodiments, the in-coupler 212 has a substantially rectangular shape and is configured to receive the laser beam 218 and guide the laser beam 218 into the waveguide 205. The in-coupler 212 is defined by a smaller dimension (i.e., width) and a larger orthogonal dimension (i.e., length). In one embodiment, the optical relay 210 is a line-scanning optical relay that receives the laser beam 218 scanned by a first scanning mirror 206 by a first dimension (e.g., a first dimension corresponding to the smaller dimension of the in-coupler 212), routes the laser beam 218 to a second scanning mirror 208, and introduces the convergence (e.g., via collimation) of the laser beam 218 by the first dimension to the exit pupil plane of the optical relay 210 beyond the second scanning mirror 208. In this specification, “pupil plane” refers to a location along the optical path of the laser beam through the optical system where the laser beam converges to an aperture along one or more dimensions. For example, the optical relay 210 may be associated with one or more entrance pupil planes located along the optical path of the laser light through an optical system that converges to a virtual aperture before the laser light enters the optical relay 210. For example, the optical relay 210 may be associated with one or more exit pupil planes located along the optical path of the laser light through an optical system that converges to a virtual aperture along one or more dimensions after the laser light leaves the optical relay 210.

[0024] According to various embodiments, the optical relay 210 includes one or more spherical, aspherical, parabolic, or free-form lenses that shape and relay the laser beam 218 on a second scanning mirror 208, or includes two or more optical surfaces including, but not limited to, spherical, aspherical, parabolic, or free-form lenses or reflectors (sometimes referred to herein as “reflecting surfaces”) that shape and direct the laser beam 218 onto the second scanning mirror 208. The second scanning mirror 208 receives the laser beam 218 and scans the laser beam 218 by a second dimension, the second dimension corresponding to the long dimension of the in-coupler 212 of the waveguide 205. In some embodiments, the second scanning mirror 208 sweeps the exit pupil surface of the laser beam 218 along a line along the second dimension. In some embodiments, the in-coupler 212 is located downstream of or near the second scanning mirror 208 in a swept line, such that the second scanning mirror 208 scans the laser beam 218 as a line or column across the in-coupler 212.

[0025] In some embodiments, the optical engine 202 includes an end-emitting laser (EEL) that emits laser light 218 having a substantially elliptical, non-circular cross-section, and the optical relay 210 magnifies or minimizes the laser light 218 along one or both of a first direction (e.g., the semi-major axis of the beam profile of the laser light 218) or a second direction (e.g., the semi-minor axis of the beam profile of the laser light 218), and reshapes (e.g., circularizes) the laser light 218 before focusing it onto the second scanning mirror 208. In some such embodiments, the surface of the mirror plate of the first scanning mirror 206 is elliptical and non-circular (e.g., its shape and size are similar to the cross-sectional area of ​​the laser light 218). In other such embodiments, the surface of the mirror plate of the first scanning mirror 206 is circular.

[0026] The waveguide 205 of the laser projection system 200 includes an in-coupler 212 and an out-coupler 214. As used herein, the term “waveguide” is understood to mean a combiner that transmits light from an in-coupler (such as in-coupler 212) to an out-coupler (such as out-coupler 214) using one or more of total internal reflection (TIR), special filters, or reflective surfaces. In some display applications, the light is a parallel image, and the waveguide transmits and replicates the parallel image to the eye. Generally, the terms “in-coupler” and “out-coupler” are understood to refer to any type of optical grating structure, including but not limited to diffraction gratings, holograms, holographic optical elements (e.g., optical elements using one or more holograms), volume diffraction gratings, volume holograms, surface relief diffraction gratings, or surface relief holograms. In some embodiments, a given in-coupler or out-coupler is configured as a transmission grating (e.g., a transmission diffraction grating or a transmission holographic grating) that transmits light through the in-coupler or out-coupler and applies the designed optical function to the light during transmission. In some embodiments, a given in-coupler or out-coupler is a reflection grating (e.g., a reflection diffraction grating or a reflection holographic grating) that reflects light through the in-coupler or out-coupler and applies the designed optical function to the light during reflection. In this example, the laser beam 218 received at the in-coupler 212 is relayed to the out-coupler 214 via the waveguide 205 using TIR. The laser beam 218 is then output to the user's eye 216 via the out-coupler 214. As described above, in some embodiments, the waveguide 205 is implemented as part of a spectacle lens, such as lens 108 or lens 110 (Figure 1) of a display system having the form factor of eyeglasses and using a laser projection system 200.

[0027] Although not shown in the example in Figure 2, in some embodiments, additional optical components are included in any of the optical paths between the optical engine 202 and the first scanning mirror 206, between the first scanning mirror 206 and the optical relay 210, between the optical relay 210 and the second scanning mirror 208, between the second scanning mirror 208 and the in-coupler 212, between the in-coupler 212 and the out-coupler 214, or between the out-coupler 214 and the eye 216 (for example, to shape the laser beam so that it is visible to the user's eye 216). In some embodiments, a prism is used to direct the light from the second scanning mirror 208 towards the in-coupler 212 so that the light is coupled to the in-coupler 212 at an appropriate angle to facilitate the propagation of light in the waveguide 205 by TIR. In some embodiments, an exit pupil magnifier, such as a fold grating, is positioned between the in-coupler 212 and the out-coupler 214 to receive light coupled to the waveguide 205 by the in-coupler 212, magnify the light, and redirect the light towards the out-coupler 214, in which case the out-coupler 214 couples the laser light from the waveguide 205 (for example, towards the user's eye 216). In some embodiments, a pick Figure 3 shows an exemplary block diagram of a laser projector 300 that uses a pick-off element 306 (shown here as a plate beam splitter, but in alternative embodiments a cubic beam splitter may be used instead) to redirect the laser beam to a photodetector (PD) 310 via Fresnel reflection. In this example, similar reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0028] The laser projector 300 includes an optical engine 202 containing blue (B), green (G), and red (R) lasers, and laser sources 312-1, 312-2, and 312-3 that output their respective laser beams 314. The laser beams 314 are collimated by a collimation lens 320 and then combined by a beam combiner 316 to form a concentrated laser beam 318. The beam combiner 316 comprises a first substrate 324, a second substrate 326, and a third substrate 328. In some embodiments, each of the first substrate 324, the second substrate 326, and the third substrate 328 is formed at least partially from N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, or another applicable light-transmitting material.

[0029] The first interface 330 is located at the first end of the beam combiner 316. In some embodiments, the first coating is applied to the first interface 330 (for example, applied to the surface of the first substrate 324 which serves as the first end of the beam combiner 316). In some embodiments, the first coating is reflective or substantially reflective to all wavelengths of light. In some embodiments, the first coating (e.g., a first dichroic reflector coating or thin film) reflects or substantially reflects only the blue wavelengths of light, including the wavelength of the laser light beam 314 output by the blue laser source 312-1, and transmits or substantially transmits the other wavelengths of light. In some embodiments, the first coating is a broadband reflective coating configured to reflect a broad spectrum of light (e.g., including one or more of the blue, green, and red wavelengths of light output by the blue laser source 312-1, the green laser source 312-2, and the red laser source 312-3). In some embodiments, the first interface 330 is uncoated and reflects light via TIR. The first interface 330 receives the laser light beam 314 output by the blue laser source 312-1 and reflects it along the length of the beam combiner 316 toward the second end of the beam combiner 316 and toward the optical scanner 204.

[0030] The second interface 332 is the interface between the first substrate 324 and the second substrate 326. In some embodiments, a second coating is applied to the second interface 332 between the first substrate 324 and the second substrate 326. In some embodiments, the second coating (e.g., a second dichroic reflector coating or thin film) reflects or substantially reflects only the green wavelengths of light, including the wavelength of the laser beam 314 output by the green laser source 312-2, and transmits or substantially transmits other wavelengths of light, including the blue wavelength of the laser beam 314 output by the blue laser source 312-1. The second interface 332 receives the laser beam 314 output by the green laser source 312-2 and reflects it along the length of the beam combiner 316 toward the second end of the beam combiner 316 and toward the optical scanner 204. The second interface 332 also receives the laser beam 314 emitted by the blue laser source 312-1, which has already been reflected at the first interface 330, and allows it to pass through without reflection.

[0031] The third interface 334 is the interface between the second substrate 326 and the third substrate 328. In some embodiments, a third coating is applied to the third interface 334 between the second substrate 326 and the third substrate 328. In some embodiments, the third coating (e.g., a third dichroic reflector coating or thin film) reflects or substantially reflects only red wavelengths of light, including the wavelength of the laser beam 314 output by the red laser source 312-3, and transmits or substantially transmits other wavelengths of light, including the blue wavelength of the laser beam 314 output by the blue laser source 312-1 and the green wavelength of the laser beam 314 output by the green laser source 312-2. The third interface 334 receives the laser beam 314 output by the red laser source 312-3 and reflects it along the length of the beam combiner 316 toward the second end of the beam combiner 316 and toward the optical scanner 204. The third interface 334 also receives the laser beam 314 output by the blue laser source 312-1 and the laser beam 314 output by the green laser source 312-2, which have already been reflected at the first interface 330, and allows both of them to pass through without reflection.

[0032] In some embodiments, one or more waveplates 322 are placed at one or more inputs of a beam combiner 316 in one or more optical paths of one or more laser light beams 314. The waveplates 322 change the polarization of light, such as the laser light beams 314, passing through the waveplates. For example, the waveplates can change the polarization state of the laser light beams 314 to an S-polarized state or a P-polarized state.

[0033] After the laser beam 314 is combined via the beam combiner 316, the concentrated laser beam 318 is directed to the optical scanner 204, which scans the concentrated laser beam 318 into a waveguide (for example, the waveguide 205 embodiment in Figure 2) for subsequent projection. For example, the waveguide can project the concentrated laser beam onto a display area of ​​an object such as the lens of the WHUD, or directly towards the user's eyes, so that the user can view the image or video represented by the concentrated laser beam 318.

[0034] The concentrated laser beam 318, after being output by the beam combiner 316, passes through the pick-off element 306. That is, the pick-off element 306 is positioned in the optical path of the concentrated laser beam 318 between the beam combiner 316 and the optical scanner. The pick-off element 306 deflects the light 308 (sometimes referred to herein as “bent light 308”), which is part of the concentrated laser beam 318, to a photodetector 310, which measures the intensity of the bent laser light 308. The measured light intensity is then used to calculate and monitor the laser output of the optical engine 202. In some embodiments, the pick-off element 306 includes first and second surfaces through which the concentrated laser beam 318 passes, each of which is uncoated and planar or substantially planar. In some embodiments, the pick-off element 306 includes a first surface that is uncoated and planar or substantially planar, and a second surface that is planar or substantially planar and includes an anti-reflective coating, and the concentrated laser beam 318 passes through each of the first and second surfaces. According to various embodiments, some or all of the optical engine 202, optical scanner 204, pick-off element 306, and photodetector 310 are arranged on a substrate 301, which may be, for example, a printed circuit board (PCB).

[0035] As mentioned earlier, conventionally, laser light in a given system is sampled or "picked off" using a pick-off optical system with a dielectric coating to redirect a portion of the laser light to the sensor. However, such conventional approaches that rely on pick-off optical systems with reflective dielectric coatings are typically narrowband and have an undesirably large tolerance for the amount of light redirected to the sensor. For example, in some cases, the transmittance tolerance of a dielectric coating-based pick-off optical system is in the range of 97% to 99.5% transmittance, so that the amount of light redirected to the sensor is 0.5% to 3% of the total light. That is, in such cases, the maximum intensity of the portion of laser light redirected to the sensor is about six times the minimum intensity of the portion of laser light redirected to the sensor. Such a wide range between the maximum and minimum intensity of the laser light received by the sensor presents problems in ensuring sufficient sensor sensitivity at the minimum intensity and avoiding sensor oversaturation at the maximum intensity.

[0036] Instead of applying a specific dielectric coating to an optical surface to pick off a portion of the laser beam, the systems and techniques described herein deflect light via Fresnel reflection at the interface between two materials having different refractive indices. For example, considering the interface between air and a substantially flat optical surface (e.g., a planar optical surface) of a pick-off element 306 formed from N-BK7 borosilicate crown glass, the proportion of the concentrated laser beam 318 deflected via Fresnel reflection as deflected light 308 is shown in Table 1 below.

[0037] [Table 1]

[0038] N-BK7 borosilicate crown glass typically has an average refractive index "n" of approximately 1.5168, with a typical tolerance of approximately + / -0.0005. In this example, we assume that this typical tolerance defines the upper and lower limits of the possible refractive index of N-BK7 borosilicate crown glass. Table 1 shows the percentage of concentrated laser beam 318 deflected toward the photodetector 310 as deflected light 308 for the average (n=1.5168), upper limit (n=1.5173), and lower limit (n=1.5163) refractive indices of N-BK7 borosilicate crown glass for both S-polarization and P-polarization. As shown, the difference in the percentage of deflected light for both S-polarization and P-polarization is relatively small compared to the difference in the dielectric coating-based pick-off optics described above. Furthermore, the ratio of the lowest proportion of fluctuated light (i.e., the lower limit of the refractive index) to the highest proportion of fluctuated light (i.e., the upper limit of the refractive index) in this example is approximately 1.0025 for S-polarized light and approximately 1.0044 for P-polarized light. Therefore, even considering the typical variation in the refractive index of the N-BK7 borosilicate crown glass, the proportion of input light fluctuated by the interface between the N-BK7 borosilicate crown glass via Fresnel reflection is more consistent than the proportion of input light fluctuated using conventional dielectric coating-based pick-off optics. This improved consistency of the proportion of input light (focused laser beam 318 in this example) fluctuated to the photodetector 310 mitigates the problems associated with ensuring sufficient photodetector sensitivity at the lower limit and avoiding photodetector oversaturation at the upper limit compared to conventional methods. In this example, an embodiment of the pick-off element 306 including an interface between air and N-BK7 borosilicate crown glass is considered, but it should be noted that the consistency in the range of the percentage of light deflected by the interface between air and other materials, or between two other materials with different refractive indices, is expected to be better than that generally achievable with conventional dielectric coating-based pick-off optics. Examples of such other materials include fused silica, crown glass, and flint glass, sapphire, diamond, barium fluoride, and calcium fluoride.According to various alternative embodiments, the pick-off element 306 may include or be made entirely from any of the other materials listed above.

[0039] Figure 4 is a perspective view of one embodiment of the pick-off element 306 of Figure 3, showing how light is deflected via Fresnel reflection on the first and second surfaces of the pick-off element 306. In this example, the same reference numerals are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0040] As shown in the figure, the incident focused laser beam 318, shown here by a single dashed line, includes three or more coupled laser beams, such as the laser beam 314 in Figure 3, but is incident on the first surface 402. A first portion 406 of the focused laser beam 318 is deflected as part of the deflected laser beam 308 by a first Fresnel reflection occurring at the interface of the first surface 402 between the material of the pick-off element 306 and the air. The first Fresnel reflection is caused by the difference between the refractive indices of the air and the material of the pick-off element 306 at the first surface 402. The remainder of the focused laser beam 318 continues to pass through the pick-off element 306. When the focused laser beam 318 passes through the second surface 404 of the pick-off element 306, a second Fresnel reflection occurs due to the difference between the refractive indices of the air and the material of the pick-off element 306 at the second surface 404. This second Fresnel reflection causes a second portion 408 of the concentrated laser beam 318 to be redirected back to the pick-off element 306 and exit through the first surface 402 as part of the redirected light 308. The remainder of the concentrated laser beam 318 then exits the pick-off element 306 (and subsequently proceeds toward, for example, the optical scanner 204). In some embodiments, the first or second Fresnel reflection is prevented by applying an anti-reflective coating to either the first surface 402 or the second surface 404 of the pick-off element 306. Otherwise, neither the first nor the second surface, 402 and 404 of the pick-off element 306 is coated.

[0041] In some embodiments, instead of using individual pick-off elements such as the pick-off element 306 in Figure 3 to deflect the laser light toward a photodetector, a modified beam combiner is provided having one or more interfaces between different indexed materials (i.e., materials having different refractive indices), resulting in Fresnel reflection of a portion of the incident laser beam at such interfaces, which deflects a portion of the incident laser beam toward one or more photodetectors. Figure 5 shows an exemplary block diagram of a laser projector 500, which includes a beam combiner having first and second pick-off interfaces, 540 and 542 between first and second primary indexed substrates, 528 and 538 and a secondary indexed substrate 536. Each of the first and second primary indexed substrates, 528 and 538, is at least partially formed from a first material having a first refractive index, while the secondary indexed substrate 536 is formed from a second material having a second refractive index different from the first refractive index. The first pick-off interface 540 and the second pick-off interface 542 each deflect a portion of the concentrated laser beam 318 toward a photodetector 510 located on the first side of the beam combiner 516. In this example, the same reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0042] In this example, the secondary index substrate 536 is positioned to be interposed between the first and second primary index substrates, 528 and 538, resulting in a first pick-off interface 540, which is the interface between the first primary index substrate 528 and the secondary index substrate 536, and a second pick-off interface 542, which is the interface between the second primary index substrate 538 and the secondary index substrate 536. When the focused laser beam 318 passes through the first pick-off interface 540, a first Fresnel reflection occurs due to the difference in refractive index between the first primary index substrate 528 and the secondary index substrate 536, thereby deflecting a portion of the focused laser beam 318 toward the photodetector 510. When the focused laser beam 318 passes through the second pick-off interface 542, a second Fresnel reflection occurs due to the difference in refractive index between the second primary index substrate 538 and the secondary index substrate 536, thereby deflecting a portion of the focused laser beam 318 toward the photodetector 510. It should be noted that the first Fresnel reflection can be considered as effectively three separate Fresnel reflections, one for each of the three laser beams 314 that constitute the concentrated laser beam 318. As shown in Table 2 below, the proportion of light deflected by one of the first and second pick-off interfaces, 540 and 542, varies based on the refractive indices of the first and second materials forming the given interface.

[0043] [Table 2]

[0044] The example in Table 2 gives the percentage of input light deflected by one of the given first pick-off interfaces 540 and second pick-off interfaces 542, in which case the first and second primary index substrates, 528 and 538, are formed from N-BK7 borosilicate crown glass, and the secondary index substrate 536 is formed from one of the enumerated materials (fused silica, crown glass, flint glass, sapphire) corresponding to each entry. The refractive index of N-BK7 borosilicate crown glass is assumed to be n=1.5168 in Table 2. As shown in Table 2, the amount of light deflected via Fresnel reflection at a given interface between two materials having different refractive indices is proportional to the difference between the refractive indices of the two materials.

[0045] As can be seen by comparing Table 1 and Table 2, the difference in refractive index between air and N-BK7 borosilicate crown glass (or, more precisely, any of the materials listed in Table 2) is relatively larger than the difference in refractive index between N-BK7 borosilicate crown glass and any of the materials listed in Table 2. Therefore, in some alternative embodiments, the beam combiner 516 contains a void instead of the secondary index substrate 536, thereby deflecting a relatively large proportion of the focused laser beam 318 to the photodetector 510 as part of the deflected light 308, regardless of whether the focused laser beam 318 is P-polarized or S-polarized. This example involves deflecting light via Fresnel reflection between substrates having different refractive indices, but it should be understood that in alternative embodiments, one or more optical adhesive layers may be placed at either or both of the first and second pick-off interfaces, 540 and 542, where the optical adhesive layers have different refractive indices from the first and second refractive indices of the primary and secondary index substrates 528, 538, and 536, respectively, thereby causing Fresnel reflection between any of the optical adhesive layers of the primary and secondary index substrates 528, 538, and 536 that are in physical contact with the optical adhesive layer.

[0046] Figures 6 and 7 show that the width of the secondary indexing substrate 536 (i.e., the width extending from the first primary indexing substrate 528 to the second primary indexing substrate 538) determines whether a portion of the concentrated laser beam 318 deflected by the first pick-off interface 540 (i.e., the "first portion") overlaps with a portion of the concentrated laser beam 318 deflected by the second pick-off interface 542 (i.e., the "second portion").

[0047] Figure 6 shows a partial perspective view 600 of one embodiment of the beam combiner 516 of Figure 5, which includes a secondary indexing substrate 536 having a width W1. In this example, similar reference numerals are used to refer to similar elements introduced in any of the preceding examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0048] As shown in the figure, the width W1 of the secondary index substrate 536 is large enough so that the first portion 308-1 of the deflected light 308 deflected by the first pick-off interface 540 travels along the first optical path, and the second portion 308-2 of the deflected light 308 deflected by the second pick-off interface 542 travels along the second optical path, and the first optical path does not overlap with the second optical path. In some applications, it is undesirable for the first portion 308-1 and the second portion 308-2 to overlap. This is because it results in additional effects regarding how the light intensities of the first portion 308-1 and the second portion 308-2 are detected by the photodetector (e.g., photodetector 510). In other words, in a given region where overlapping light from the first portion 308-1 and the second portion 308-2 is incident on the photodetector, the photodetector detects the light intensity which is a combination of the light intensities of the overlapping first portion 308-1 and the second portion 308-2. By providing a secondary index substrate 536 having a sufficiently large width such as width W1, the first optical path of the first portion 308-1 and the second optical path of the second portion 308-2 do not overlap, and the additional effects associated with the aforementioned overlap are avoided.

[0049] Figure 7 shows a partial perspective view 700 of one embodiment of the beam combiner 516 of Figure 5, which includes a secondary indexing substrate 536 having a width W2. In this example, similar reference numerals are used to refer to similar elements introduced in any of the preceding examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0050] As shown in the figure, the width W2 of the secondary index substrate 536 is large enough so that the first portion 308-1 of the deflected light 308 deflected by the first pick-off interface 540 travels along the first optical path, and the second portion 308-2 of the deflected light 308 deflected by the second pick-off interface 542 travels along the second optical path, with the first optical path partially overlapping the second optical path. In some applications, it is desirable for the first portion 308-1 and the second portion 308-2 to overlap in order to increase the intensity of the light supplied to the photodetector (e.g., photodetector 510) in the region where the overlapping light from the first and second portions, 308-1 and 308-2, is incident. This is because the overlap produces the additional effects described above. By providing a secondary index substrate 536 having a sufficiently small width such as width W2, the first optical path of the first portion 308-1 and the second optical path of the second portion 308-2 overlap at least partially, and the intensity of light received by the photodetector increases due to the aforementioned additional effects associated with such overlap.

[0051] Figure 8 shows an exemplary block diagram of the laser projector 800, which includes a mirror 802 located on the first side of the beam combiner 516 to receive the deflected light 308 by Fresnel reflection from the first and second pick-off interfaces, 540 and 542, and to reflect the deflected light 308 back through the beam combiner 516 toward a photodetector 810 located opposite the second side of the beam combiner 516, opposite to the first side of the beam combiner 516. It should be noted that, except for the inclusion of the mirror 802 and the photodetector 810, and the removal of the photodetector 510, the embodiment of the laser projector 800 is structurally similar to the embodiment of the laser projector 500 in Figure 5. In this example, similar reference numerals are used to refer to similar elements introduced in any of the aforementioned examples, and for brevity, some aspects or functions of such elements may not be repeated here.

[0052] In some embodiments, the mirror 802 is a reflective coating applied to a first surface of the beam combiner 516, positioned on the first side of the beam combiner 516. According to various embodiments, the mirror 802 is a separate optical element mounted, touching, or adjacent to the first surface of the beam combiner 516 in the optical path of the deflected light 308. In some embodiments, the mirror 802 is planar. In some embodiments, the mirror 802 is curved. In some embodiments, in addition to reflection, the mirror 802 performs one or more optical functions of the received light (such optical functions are the result of one or more diffusing elements, gratings, metasurfaces, etc., included in the mirror 802). Using such optical functions, a specific reflectivity profile of the mirror 802 can be achieved, and the way in which a certain wavelength of light is deflected toward the photodetector 810 can be modified, for example, to adapt to the response profile of the photodetector 810.

[0053] The deflected light 308, deflected from the concentrated laser beam 318 via Fresnel reflection from the first and second pick-off interfaces, 540 and 542, is incident on the mirror 802, then reflected back through the beam combiner 516 (e.g., passing through some or all of the first primary indexing substrate 528, the second primary indexing substrate 538, and the secondary indexing substrate 536), exits the second surface of the beam combiner 516 (located on the second side of the beam combiner 516), and is subsequently received by the photodetector 810. Placing the photodetector 810 opposite the second side of the beam combiner 516 allows for a favorable reduction in the form factor of the laser projector 800 compared to placing such a photodetector opposite the first side of the beam combiner 516.

[0054] In some embodiments, the mirror 802 is fully reflective (i.e., no portion of the deflected light 308 passes through the mirror 802). In some embodiments, the mirror 802 is only partially reflective, and its reflectivity varies depending on the wavelength of the reflected light, as will be described in more detail below (characterized by the "wavelength-dependent reflectivity profile" of the mirror 802).

[0055] Figure 9 shows a perspective view 900 of one embodiment of the laser projector 800 of Figure 8, in which the photodetector 810 is oriented in a first direction such that the optical path of the deflected light 308 after reflection by the mirror 802 is non-orthogonal to the surface of the photodetector 810. In this example, the same reference numerals are used to refer to similar elements introduced in any of the above examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0056] In this example, the mirror 902 is positioned in the optical path of the deflected light 308 on the second side of the beam combiner 516. The mirror 902 is positioned so that the deflected light 308 is reflected toward the surface of the photodetector 810. In some embodiments, the photodetector 810 is positioned such that its surface lies in a plane substantially parallel to the surface of the substrate 301 on which the photodetector 810 is placed. Such an orientation of the photodetector 810 can reduce the complexity of the electrical connections between the photodetector 810 and the substrate 301. By including the mirror 902, the illustrated orientation of the photodetector 810 can be accommodated, and advantageously, the complexity of the electrical connections between the photodetector 810 and the substrate 301 can be reduced.

[0057] Figure 10 shows an exemplary response profile of one embodiment of the photodetector 810 in Figure 8, and an exemplary wavelength-dependent reflectance profile of one embodiment of the mirror 802 in Figure 8, in exemplary chart 1000. In this example, similar reference numbers are used to refer to similar elements introduced in any of the above examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0058] As shown in the figure, in this example, the photodetector 810 has a response profile 1002 such that higher wavelength light is more easily detected by the photodetector 810 than lower wavelength light. That is, in the embodiment characterized by the response profile 1002, higher wavelength light elicits a greater response from the photodetector 810 than lower wavelength light. In this example, the blue wavelength (approximately 441 nm) of the laser beam 314 emitted by the blue laser source 312-1 is indicated by the first line 1004 relative to the response profile 1002, the green wavelength (approximately 550 nm) of the laser beam 314 emitted by the green laser source 312-2 is indicated by the second line 1006 relative to the response profile 1002, and the red wavelength (approximately 638 nm) of the laser beam 314 emitted by the red laser source 312-3 is indicated by the third line 1008 relative to the response profile 1002. While examples of blue, green, and red wavelengths are given in this example, it should be understood that this embodiment is applicable to other wavelengths of light not listed herein, including infrared and ultraviolet wavelengths.

[0059] A first embodiment of the mirror 802 has a first wavelength-dependent reflectance profile 1010 that gives a reflectance of about 100% for the blue wavelength of light, about 35% for the green wavelength of light, and about 15% for the red wavelength of light. A second embodiment of the mirror 802 has a second wavelength-dependent reflectance profile 1012 that gives a reflectance of about 75% for the blue wavelength of light, about 50% for the green wavelength of light, and about 10% for the red wavelength of light.

[0060] As shown in the figure, each of the first and second wavelength-dependent reflectance profiles, 1010 and 1012, causes a larger proportion of blue wavelengths of light to be reflected toward the photodetector 810 compared to the proportion of green and red wavelengths of the reflected light. Each of the first and second wavelength-dependent reflectance profiles, 1010 and 1012, also causes a smaller proportion of red wavelengths of light to be reflected toward the photodetector 810 compared to the proportion of blue and green wavelengths of the reflected light. In this way, an embodiment of the mirror 802 having either the first or second wavelength-dependent reflectance profile, 1010 and 1012, at least partially adapts to the non-uniform response profile 1002 of the photodetector 810, effectively weighting the response of the photodetector 810 to give a more uniform response to the deflected light 308.

[0061] Figure 11 shows an exemplary chart 1100 illustrating an example of weighted response profiles for an embodiment of the photodetector 810 in Figure 8, each weighted by reflecting the deflected light 308 using embodiments of mirror 802, each having a different wavelength-dependent reflectance profile. In this example, similar reference numbers are used to refer to similar elements introduced in any of the preceding examples, and for brevity, some aspects or functions of such elements may not be repeated here.

[0062] As a first example, the first weighted response of an embodiment of the photodetector 810, combined with a first wavelength-dependent reflectance profile of an embodiment of the mirror 802, is defined by a first weighted response profile 1112. In this example, the combination of a first response profile of an embodiment of the photodetector 810 (not shown) and a first wavelength-dependent reflectance profile of an embodiment of the mirror 802 (not shown) results in a combination of the photodetector 810 and the mirror 802 having a substantially flat response across each of the blue, green, and red wavelengths of light, shown here through lines 1104, 1106, and 1108, respectively (shown here to correspond to about 50% of the intensity of light input to the mirror 802). That is, the combination of the first response profile and the first wavelength-dependent reflectance profile yields a first weighted response profile 1112 that corresponds to a substantially normalized response across the blue, green, and red wavelengths of light. By providing embodiments of the mirror 802 and photodetector 810 having a combined first weighted response profile 1112, a system including a corresponding embodiment of the laser projector 800 can perform fewer subsequent calculations, if any, to account for the non-uniform wavelength response due to the first response profile of the photodetector 810 (for example, when calculating the laser output of the laser projector 800).

[0063] As a second example, the second weighted response of the embodiment of the photodetector 810, combined with a second wavelength-dependent reflectance profile of the mirror 802 embodiment, is defined by a second weighted response profile 1110. The weighted response profile 1110 causes the photodetector 810 to primarily detect the blue wavelength of the deflected light 308. By weighting the response of the photodetector 810 using the wavelength-dependent reflectance profile of the mirror 802 in this way, the system including the laser projector 800 can determine, or at least approximate, the laser output of a specific laser source (e.g., a blue laser source 312-1 in this example) of the optical engine 202 based on the light intensity detected by the photodetector 810. In some embodiments, the weighted response profile of the combination of the photodetector 810 and the mirror 802 corresponds to a photopic brightness function corresponding to the perceived brightness sensitivity of the human eye.

[0064] Figure 12 shows an exemplary block diagram of the laser projector 1200 including a mirror 1202, which is located on the first side of the beam combiner 516 and receives the bent light by Fresnel reflection from the first and second pick-off interfaces, 540 and 542, and reflects back the first bent light 1208-1 through the beam combiner 516 toward the first photodetector 1210-1 located opposite the second side of the beam combiner 516, and passes the second bent light 1208-2 toward the second photodetector 1210-2 located opposite the first side of the beam combiner 516. It should be noted that the embodiment of the laser projector 1200 is structurally similar to some embodiments of the laser projector 800 in Figure 8, except for the inclusion of the second photodetector 1210-2. In this example, the same reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0065] In this example, since mirror 1202 is partially transparent and partially reflective, a first portion of the deflected light received by mirror 1202 is reflected as the first deflected light 1208-1, and a second portion of the deflected light received by mirror 1202 passes through mirror 1202 to a second photodetector 1210-2 located on the first side of the beam combiner 516. In some embodiments, mirror 1202 has a non-uniform wavelength-dependent reflectance profile, such as either of the wavelength-dependent reflectance profiles, 1010 and 1012, in Figure 10, which effectively weights the response profiles of the first and second photodetectors, 1210-1 and 1210-2, respectively. By including the second photodetector 1210-2 on the first side of the beam combiner 516, incident light transmitted rather than reflected by mirror 1202 can be detected.

[0066] In some embodiments, the mirror 1202 is configured to completely or substantially reflect at least one wavelength of light contained in the concentrated laser beam 318 and completely or substantially transmit at least one other wavelength of light contained in the concentrated laser beam 318. In one example, the mirror 1202 substantially reflects the red and green wavelengths of light corresponding to the wavelengths of the laser beam 314 produced by the green laser source 312-2 and the red laser source 312-3, respectively, and substantially transmits the blue wavelength of light corresponding to the wavelength of the laser beam 314 produced by the blue laser source 312-1, such that the first deflection 1208-1 contains the red and green wavelengths of light and the second deflection 1208-2 contains the blue wavelength of light. In this way, the first photodetector 1210-1 detects only the intensities of the red and green light output by the optical engine 202, and the second photodetector 1210-2 detects only the intensity of the blue light output by the optical engine 202, thereby allowing independent measurement of the intensity of each of the specific wavelengths of light. In other words, in this example, the combined laser output of the green laser source 312-2 and the red laser source 312-3 is determined based on the light intensity detected by the first photodetector 1210-1, and the laser output of the blue laser source 312-1 is determined individually based on the light intensity detected by the second photodetector 1210-2.

[0067] Figure 13 shows an exemplary block diagram of a laser projector 1300 including a beam combiner 1316, the beam combiner 1316 having a secondary indexing substrate 1338 located at a second end of the beam combiner 1316 (opposite the first end where the first interface 330 is located), the secondary indexing substrate abutting against the primary indexing substrate 528 to form a pick-off interface 1340. It should be noted that the embodiment of laser projector 1300 differs from the embodiment of laser projector 500 in Figure 5 in that, instead of including a secondary indexing substrate interposed between two primary indexing substrates to form first and second pick-off interfaces, the secondary indexing substrate 1338 is located at the second end of the beam combiner 1316 and together with the primary indexing substrate 528 to form only a single pick-off interface 1340. The embodiment of laser projector 1300 is otherwise structurally similar to several embodiments of laser projector 500 in Figure 5. In this example, the same reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0068] In this example, the concentrated laser beam 318 is incident on the pick-off interface 1340 and, via Fresnel reflection, is deflected as deflected light 308 toward a photodetector 310 located opposite the first side of the beam combiner 1316. The primary index substrate 528 is formed from a first material having a first refractive index, while the secondary index substrate 1338 is formed from a second material having a second refractive index different from the first refractive index. According to various embodiments, the first and second materials are two different materials, each selected from N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, or another applicable light-transmitting material.

[0069] In this example, the photodetector 310 is shown as being located on the first side of the beam combiner 1316, but it should be noted that in other embodiments, the photodetector 310 may instead be located on the second side of the beam combiner 1316, and a mirror may be placed on the first side of the beam combiner to reflect the deflected light 308 toward the photodetector 310 (similar to, for example, the arrangement of mirror 802 and photodetector 810 shown in the example of Figure 8).

[0070] This example involves deflecting light via Fresnel reflection between substrates having different refractive indices, but it should be understood that in alternative embodiments, one or more optical adhesive layers may be placed at the pick-off interface 1340, in which case the optical adhesive layers each have a refractive index different from the first and second refractive indices of the primary and secondary index substrates, 528 and 1338, respectively, thereby causing Fresnel reflection between any of the optical adhesive layers of the primary and secondary index substrates, 528 and 1338 that are in physical contact with the optical adhesive layer.

[0071] Figure 14 shows an exemplary block diagram of a laser projector 1400 including a beam combiner 1416 having substrates of alternating refractive indices, where the interfaces between these substrates redirect a portion of the received laser beam to its respective photodetector, and some of these interfaces also couple the incoming laser beam. In this example, similar reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0072] In this example, the beam combiner 1416 includes a first secondary index substrate 1424 disposed at the first end of the beam combiner 1416, a first primary index substrate 1426 disposed adjacent to the first secondary index substrate 1424, a second secondary index substrate 1428 disposed adjacent to the first primary index substrate 1426, and a second primary index substrate 1438 disposed adjacent to the second secondary index substrate 1428. The first primary index substrate 1426 is interposed between the first secondary index substrate 1424 and the second secondary index substrate 1428 to form a first pick-off interface 1432 and a second pick-off interface 1434, respectively. The second secondary index substrate 1428 is interposed between the first primary index substrate 1426 and the second primary index substrate 1438 to form a second pick-off interface 1434 and a third pick-off interface 1440, respectively. In this example, the first and second primary index substrates, 1426 and 1438, are formed from or include a first material having a first refractive index, while the first and second secondary index substrates, 1424 and 1428, are formed from or include a second material having a second refractive index, the first refractive index being different from the second refractive index. According to various embodiments, the first and second materials are selected from N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, or other applicable light-transmitting materials.

[0073] The first interface 1430 is located at the first end of the beam combiner 1416. In some embodiments, a first coating is applied to the first interface 1430 (for example, applied to the surface of the first substrate 1424 which serves as the first end of the beam combiner 1416). In some embodiments, the first coating reflects or substantially reflects all wavelengths of light. In some embodiments, the first coating (for example, a first dichroic reflector coating or thin film) reflects or substantially reflects only the blue wavelengths of light, including the wavelength of the laser beam 314 output by the blue laser source 312-1, and transmits or substantially transmits the other wavelengths of light. In some embodiments, the first interface 1430 is not coated, and the reflection of the laser beam 314 output by the blue laser source 312-1 by the first interface 1430 is achieved via TIR. The first interface 1430 receives the laser light beam 314 output by the blue laser source 312-1 and reflects it along the length of the beam combiner 1416 toward the second end of the beam combiner 1416 and toward the optical scanner 204.

[0074] The first pick-off interface 1432 is the interface between the first secondary index substrate 1424 and the first primary index substrate 1426. In some embodiments, a second coating is applied to the first pick-off interface 1432 between the first secondary index substrate 1424 and the first primary index substrate 1426. In some embodiments, the second coating (e.g., a second dichroic reflector coating or thin film) reflects or substantially reflects only the green wavelengths of light, including the wavelength of the laser beam 314 output by the green laser source 312-2, and transmits or substantially transmits other wavelengths of light, including the blue wavelength of the laser beam 314 output by the blue laser source 312-1. The first pick-off interface 1432 receives the laser beam 314 output by the green laser source 312-2 and reflects it along the length of the beam combiner 1416 toward the second end of the beam combiner 1416 and toward the optical scanner 204. The first pick-off interface 1432 also receives the laser beam 314 output by the blue laser source 312-1, which has already been reflected at the first interface 1430, and allows it to pass through without reflection. The first pick-off interface 1432 further causes Fresnel reflection of the laser beam 314 output by the blue laser source 1312-1, deflecting a portion of the laser beam 314 output by the blue laser source 1312-1 towards the first photodetector 1410-1 as the first deflected light 1408-1. This Fresnel reflection is caused by the difference in refractive index between the first secondary index substrate 1424 and the first primary index substrate 1426.

[0075] The second pick-off interface 1434 is the interface between the first primary index substrate 1426 and the second primary index substrate 1428. In some embodiments, a third coating is applied to the second pick-off interface 1434 between the first primary index substrate 1426 and the second primary index substrate 1428. In some embodiments, the third coating (e.g., a third dichroic reflector coating or thin film) reflects or substantially reflects only the red wavelengths of light, including the wavelength of the laser beam 314 output by the red laser source 312-3, and transmits or substantially transmits other wavelengths of light, including the blue wavelength of the laser beam 314 output by the blue laser source 312-1 and the green wavelength of the laser beam 314 output by the green laser source 312-2. The second pick-off interface 1434 receives the laser beam 314 output by the red laser source 312-3 and reflects it along the length of the beam combiner 1416 toward the second end of the beam combiner 1416 and toward the optical scanner 204. The second pick-off interface 1434 also receives the laser beam 314 output by the blue laser source 312-1 and the laser beam 314 output by the green laser source 312-2, which have already been reflected at the first interface 1430, and allows both to pass through without reflection. The second pick-off interface 1434 effectively outputs the concentrated laser beam 318. The second pick-off interface 1434 further... source 3 Laser beam 314 and green laser output by 12-1 source 3 Fresnel reflection is induced in the laser beam 314 output by 12-2, and a portion of these laser beams is deflected toward the second photodetector 1410-2 as a second deflected beam 1408-2. This Fresnel reflection is caused by the difference in refractive index between the first primary index substrate 1426 and the second secondary index substrate 1428.

[0076] The third pick-off interface 1440 is the interface between the second secondary index substrate 1428 and the second primary index substrate 1438. The third pick-off interface 1440 causes Fresnel reflection of the concentrated laser beam 318, deflecting a portion of it toward the third photodetector 1410-3 as third deflected light 1408-3. This Fresnel reflection is caused by the difference in refractive index between the second secondary index substrate 1428 and the second primary index substrate 1438.

[0077] By receiving the first deflection light 1408-1, the first photodetector 1410-1 detects the intensity of a portion of the laser light beam 314 output by the blue laser source 312-1, and based on this, the laser output of the blue laser source 312-1 can be calculated by a system including the laser projector 1400 (e.g., one or more of its computer processors).

[0078] By receiving the second deflection light 1408-2, the second photodetector 1410-2 detects the intensity of a portion of the laser light beam 314 output by the blue laser source 312-1 and the green laser source 312-2, and based on this, the combined laser output of the blue laser source 312-1 and the green laser source 312-2 can be calculated by the system. The output of the green laser source 312-2 alone can then be calculated by the system as the difference between the combined laser output of both the blue laser source 312-1 and the green laser source 312-2 (calculated based on the light intensity detected by the second photodetector 1410-2) and the laser output of the blue laser source 312-1 (calculated based on the light intensity detected by the first photodetector 1410-1).

[0079] By receiving the third deflection light 1408-3, the third photodetector 1410-3 detects the intensity of a portion of the laser beam 314 output by the blue laser source 312-1, the green laser source 312-2, and the red laser source 312-3, and based on this, the system can calculate the combined laser output of the blue laser source 312-1, the green laser source 312-2, and the red laser source 312-3. The output of the red laser source 312-2 alone can then be calculated by the system as the difference between the combined laser output of each of the blue laser source 312-1, the green laser source 312-2, and the red laser source 312-3 (calculated based on the light intensity detected by the third photodetector 1410-3) and the combined laser output of both the blue laser source 312-1 and the green laser source 312-2 (calculated based on the light intensity detected by the second photodetector 1410-2).

[0080] In this way, the respective laser outputs of the blue, green, and red laser sources 312-1, 312-2, and 312-3 can be determined by the system, at least in part, due to the arrangement of the beam combiner 1416 and the first, second, and third photodetectors, 1410-1, 1410-2, and 1410-3 in this example.

[0081] This example involves deflecting light via Fresnel reflection between substrates having different refractive indices, but it should be understood that in alternative embodiments, one or more optical adhesive layers may be placed at any or all of the first, second, and third pick-off interfaces 1430, 1434, and 1440, in which case the optical adhesive layers each have a refractive index different from the first and second refractive indices of the primary and secondary index substrates 1426, 1438, 1424, and 1428, respectively, thereby causing Fresnel reflection between any of the optical adhesive layers of the primary and secondary index substrates 1426, 1438, 1424, and 1428 that are in physical contact with the optical adhesive layer.

[0082] Figure 15 shows an exemplary block diagram of a laser projector 1500 that utilizes a prism 1536 as a pick-off element to redirect laser light to a photodetector 310 via Fresnel reflection. In this example, the same reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0083] In this example, the input interface 1540 of the prism 1536 (i.e., the interface where the prism 1536 receives the focused laser beam 318) causes Fresnel reflection of the focused laser beam 318, resulting in a portion of the focused laser beam 318 being deflected towards the photodetector 310 as part of the deflected light 308. For example, Fresnel reflection can be caused by the difference between the refractive index of air and the refractive index of the first material that (at least partially) forms the prism 1536. According to various embodiments, the first material includes N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, or another applicable light-transmitting material.

[0084] It should be noted that the embodiment of laser projector 1500 differs from some embodiments of laser projector 300 in Figure 3 with respect to the arrangement of the photodetector 310 and the use of a prism 1536 instead of a pick-off element 306. Otherwise, the embodiment of laser projector 1500 is structurally similar to some embodiments of laser projector 300 in Figure 3.

[0085] Figure 16 shows an exemplary block diagram of a laser projector 1500 that utilizes a prism 1636 as a pick-off element to redirect laser light to a photodetector 310 via Fresnel reflection. In this example, the same reference numbers are used to refer to similar elements introduced in any of the previous examples, and for the sake of brevity, some aspects or functions of such elements may not be repeated here.

[0086] In this example, the output interface 1640 of the prism 1636 (i.e., the interface through which the prism 1636 outputs the focused laser beam 318 toward the optical scanner 204) causes Fresnel reflection of the focused laser beam 318, resulting in a portion of the focused laser beam 318 being deflected toward the photodetector 310 as part of the deflected light 308 (first passing through a portion of the prism 1636 and returning, as shown in the figure). For example, Fresnel reflection can be caused by the difference between the refractive index of air and the refractive index of the first material that (at least partially) forms the prism 1636. According to various embodiments, the first material includes N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, or another applicable light-transmitting material.

[0087] It should be noted that the embodiment of laser projector 1600 differs from some embodiments of laser projector 300 in Figure 3 with respect to the arrangement of the photodetector 310 and optical scanner 204, and the use of a prism 1636 instead of a pick-off element 306. Otherwise, the embodiment of laser projector 1600 is structurally similar to some embodiments of laser projector 300 in Figure 3.

[0088] While the aforementioned examples utilize an optical engine having red, green, and blue laser sources, it should be understood that embodiments of laser projectors described herein may also include, in addition to or instead, other types of laser sources, including infrared laser sources, ultraviolet laser sources, or both.

[0089] As disclosed herein, in some embodiments, the laser projection system includes a photodetector and a pick-off element including a first surface, the pick-off element being configured to deflect a first portion of the received light toward the photodetector via a first Fresnel reflection. In one embodiment, the pick-off element includes a first interface on a first surface between a first material having a first refractive index and a second material having a second refractive index, the first refractive index being different from the second refractive index, and the first portion of the received light is deflected from the first interface toward the photodetector via a first Fresnel reflection. In another embodiment, the first material includes at least one of N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, or calcium fluoride, and the second material includes air.

[0090] In one embodiment, the pick-off element includes a second surface opposite to a first surface and a second interface on the second surface between the first and second materials, and the pick-off element is configured to deflect a second portion of the received light from the second interface toward a photodetector via a second Fresnel reflection. In another embodiment, the pick-off element includes a second surface opposite to a first surface and an anti-reflective coating disposed on the second surface. In yet another embodiment, the pick-off element is a prism, and the first surface is the input surface of the prism that receives the received light. In yet another embodiment, the pick-off element is a prism, and the first surface is the output surface of the prism that outputs the received light. In another embodiment, the laser projection system includes an optical engine comprising a plurality of laser sources configured to generate a plurality of laser light beams, and a beam combiner configured to combine the plurality of laser light beams into a concentrated laser light beam and to output the concentrated laser light beam, the light received comprising the concentrated laser light beam, and the laser projection system is configured to determine the laser output of one or more of the plurality of laser sources of the optical engine, and further includes an optical scanner configured to receive the concentrated laser light beam from the beam combiner after the concentrated laser light beam has passed a pick-off element and to scan the concentrated laser light beam, and a waveguide configured to receive the scanned concentrated laser light beam from the optical scanner and to project the scanned concentrated laser light beam.

[0091] In some embodiments, the laser projection system includes a first photodetector and a first laser beam MuThe beam combiner includes a beam combiner configured to receive a first and second laser beam and to combine the first and second laser beams into a concentrated laser beam, the beam combiner including a first pick-off interface configured to deflect a first portion of the concentrated laser beam toward a first photodetector via a first Fresnel reflection. In one embodiment, the beam combiner further includes a first primary indexing substrate comprising a first material having a first refractive index and a first secondary indexing substrate comprising a second material having a second refractive index different from the first refractive index, the first pick-off interface being directly located between the first primary indexing substrate and the first secondary indexing substrate. In another embodiment, the first and second materials each comprise different materials selected from the group consisting of N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, calcium fluoride, and air.

[0092] In one embodiment, the beam combiner further includes a second primary indexing substrate comprising a first material having a first refractive index, and a second pick-off interface directly positioned between the first secondary indexing substrate and the second primary indexing substrate, wherein the second pick-off interface is configured to deflect a second portion of the concentrated laser beam toward a first photodetector via a second Fresnel reflection. In another embodiment, the first optical path of the first portion of the concentrated laser beam deflected by the first pick-off interface is separated from the second optical path of the second portion of the concentrated laser beam deflected by the second pick-off interface. In yet another embodiment, the first optical path of the first portion of the concentrated laser beam deflected by the first pick-off interface at least partially overlaps with the second optical path of the second portion of the concentrated laser beam deflected by the second pick-off interface.

[0093] In one embodiment, the laser projection system includes a mirror positioned on a first side of the beam combiner, which reflects at least portions of the first and second portions of the concentrated laser beam toward a first photodetector, the first photodetector being positioned on a second side opposite to the first side of the beam combiner. In another embodiment, the laser projection system includes an additional mirror positioned on a second side of the beam combiner, which receives the first and second portions of the concentrated laser beam from the mirror, and the first and second portions of the concentrated laser beam toward the first photodetector Towards It reflects. In yet another embodiment, the mirror completely reflects the first and second portions of the concentrated laser beam. In yet another embodiment, the mirror partially reflects only the first and second portions of the concentrated laser beam, thereby reflecting a first portion of the first and second portions of the concentrated laser beam toward the first photodetector and a second portion of the first and second portions of the concentrated laser beam passing through the mirror.

[0094] In one embodiment, the mirror is configured to have a wavelength-dependent reflectance profile that normalizes the non-uniform response profile of the first photodetector to light reflected from the mirror onto the first photodetector. In another embodiment, the laser projection system includes a second photodetector positioned on the first side of the beam combiner and configured to receive a second fragment of the first and second portions of the concentrated laser beam passing through the mirror. In yet another embodiment, a first secondary indexing substrate is positioned at the first end of the beam combiner, and the concentrated laser beam exits the beam combiner through the first end. In another embodiment, the beam combiner further includes a second photodetector, a third photodetector, a second primary indexing substrate comprising a first material, a second secondary indexing substrate comprising a second material, and a second pick-off interface disposed between the first secondary indexing substrate and the second primary indexing substrate, wherein the second pick-off interface is configured to deflect only the first and second laser beams toward the second photodetector via a second Fresnel reflection, and further includes a third pick-off interface disposed between the second primary indexing substrate and the second secondary indexing substrate, wherein the third pick-off interface is First laser beam and second laser beam Only the first laser beam is configured to be deflected towards the third photodetector via a third Fresnel reflection.

[0095] In some embodiments, the method includes deflecting a portion of the received light toward a photodetector via Fresnel reflection at the interface between a first material having a first refractive index and a second material having a second refractive index, and detecting the intensity of the deflected portion of the received light using the photodetector.

[0096] It should be noted that not all of the activities or elements described above are necessary in the general description, that some of the activities or devices may not be necessary, and that one or more additional activities may be performed, or that additional elements may be included in addition to those described. Furthermore, the order in which the activities are listed is not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, as those skilled in the art will see, various modifications and changes can be made without departing from the scope of this disclosure as set forth in the appended claims. Accordingly, this specification and the drawings should be considered illustrative rather than restrictive, and all such modifications are intended to be within the scope of this disclosure.

[0097] Benefits, other advantages, and solutions to problems are described above with respect to specific embodiments. However, benefits, advantages, solutions to problems, and any features that may produce or make more prominent any benefit, advantage, or solution should not be construed as essential, required, or necessary features of any or all claims. Furthermore, the specific embodiments disclosed above are merely illustrative, and the subject matter of the disclosure can be modified and implemented in different but equivalent ways that will be obvious to those skilled in the art who benefit from the teachings herein. Except as set out in the appended claims, no limitation is intended on the structural or design details shown herein. It is therefore obvious that the specific embodiments disclosed above may be modified or altered, and all such variations are deemed to be within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set out in the appended claims.

Claims

1. Photodetector and, A pick-off element having a first surface and a second surface opposite to the first surface. Equipped with, The aforementioned pick-off element is, A first interface is formed on the first surface between a first material having a first refractive index and a second material having a second refractive index, The second interface on the second surface between the first material and the second material, Furthermore, The first refractive index differs from the second refractive index, A laser projection system in which the pick-off element is configured to deflect a first portion of the received light from the first interface toward the photodetector via a first Fresnel reflection, and deflect a second portion of the received light from the second interface toward a second photodetector or optical scanner via a second Fresnel reflection.

2. The laser projection system according to claim 1, wherein the first material comprises at least one of N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, or calcium fluoride, and the second material comprises air.

3. The laser projection system according to claim 1, wherein the pick-off element is a prism, the first surface is the input surface of the prism, and the prism receives the received light at the input surface.

4. The laser projection system according to claim 1, wherein the pick-off element is a prism, the first surface is the output surface of the prism, and the prism outputs the received light through the output surface.

5. The laser projection system is An optical engine including multiple laser sources configured to generate multiple laser beams, The system further includes a beam combiner configured to combine the plurality of laser beams into a concentrated laser beam and to output the concentrated laser beam. The received light includes the concentrated laser beam, and the laser projection system is configured to determine the laser output of one or more of the plurality of laser sources of the optical engine. The laser projection system is The optical scanner is configured to receive the concentrated laser beam from the beam combiner after the concentrated laser beam has passed through the pick-off element, and to scan the concentrated laser beam. The laser projection system according to claim 1, further comprising: a waveguide configured to receive the scanned concentrated laser beam from the optical scanner and to project the scanned concentrated laser beam.

6. The first photodetector and A beam combiner configured to receive a first laser beam and a second laser beam, and to combine the first laser beam and the second laser beam into a concentrated laser beam. The beam combiner is equipped with, A first pick-off interface configured to deflect a first portion of the concentrated laser beam toward the first photodetector via a first Fresnel reflection, A first primary index substrate comprising a first material having a first refractive index, A first secondary index substrate comprising a second material having a second refractive index different from the first refractive index, and Equipped with, The first pick-off interface is a laser projection system positioned between the first primary index substrate and the first secondary index substrate.

7. The laser projection system according to claim 6, wherein the first material and the second material each comprise different materials selected from the group consisting of N-BK7 borosilicate crown glass, fused silica, crown glass, flint glass, sapphire, diamond, barium fluoride, and calcium fluoride.

8. The aforementioned beam combiner is A second primary index substrate comprising the first material having the first refractive index, A second pick-off interface is disposed between the first secondary index substrate and the second primary index substrate. Furthermore, The second pick-off interface is configured to deflect a second portion of the concentrated laser beam toward the first photodetector via a second Fresnel reflection. The laser projection system according to claim 7.

9. The laser projection system according to claim 8, wherein the first optical path of the first portion of the concentrated laser beam deflected by the first pick-off interface is separate from the second optical path of the second portion of the concentrated laser beam deflected by the second pick-off interface.

10. The laser projection system according to claim 8, wherein the first optical path of the first portion of the concentrated laser beam deflected by the first pick-off interface at least partially overlaps with the second optical path of the second portion of the concentrated laser beam deflected by the second pick-off interface.

11. The beam combiner further comprises a mirror positioned on the first side, The laser projection system according to claim 8, wherein the mirror reflects at least a portion of the first and second portions of the concentrated laser beam toward the first photodetector, and the first photodetector is located on the second side of the beam combiner opposite the first side.

12. The beam combiner further comprises an additional mirror positioned on the second side, The laser projection system according to claim 11, wherein the additional mirror receives the first and second portions of the concentrated laser beam from the mirror and reflects the first and second portions of the concentrated laser beam toward the first photodetector.

13. The laser projection system according to claim 11, wherein the mirror completely reflects the first portion and the second portion of the concentrated laser beam.

14. The laser projection system according to claim 11, wherein the mirror partially reflects only the first portion and the second portion of the concentrated laser beam, thereby reflecting a first fragment of the first portion and the second portion of the concentrated laser beam toward the first photodetector, and passing a second fragment of the first portion and the second portion of the concentrated laser beam through the mirror.

15. The laser projection system according to claim 14, wherein the mirror is configured to have a wavelength-dependent reflectance profile that normalizes the non-uniform response profile of the first photodetector with respect to light reflected from the mirror onto the first photodetector.

16. The laser projection system according to claim 14, further comprising a second photodetector positioned on the first side of the beam combiner and configured to receive the second fragment of the first and second portions of the concentrated laser beam passing through the mirror.

17. The laser projection system according to claim 7, wherein the first secondary index substrate is located at the first end of the beam combiner, and the concentrated laser beam exits the beam combiner through the first end.

18. The aforementioned beam combiner is The second photodetector, A third photodetector, A second primary index substrate containing the first material, A second secondary index substrate containing the second material, The present invention further comprises a second pick-off interface disposed between the first secondary index substrate and the second primary index substrate, wherein the second pick-off interface is configured to deflect only the first laser beam and the second laser beam toward the second photodetector via a second Fresnel reflection. The laser projection system according to claim 7, further comprising a third pick-off interface disposed between the second primary index substrate and the second secondary index substrate, wherein the third pick-off interface is configured to deflect only the first laser beam from the first and second laser beams toward the third photodetector via a third Fresnel reflection.

19. The first portion of the received light is deflected toward the photodetector via a first Fresnel reflection at the first interface between a first material having a first refractive index and a second material having a second refractive index, The second portion of the received light is redirected toward a second photodetector or optical scanner via a second Fresnel reflection at the second interface between the first material and the second material. The intensity of the first modified portion of the received light is detected by the photodetector. Methods that include...

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