Aberration-type retroreflector for wireless power applications

Abstract

A wireless optical power transmission system comprising a transmitter that outputs an optical power beam through an optical aperture, the transmitter comprising: (a) a laser that generates the optical power beam, (b) a deflection module for directing the optical power beam, and (c) a controller adapted to adjust the deflection module. The system also has a receiver, the receiver comprising a retroreflector having a cat-eye configuration adapted to return a retroreflected beam from at least a portion of the optical power beam incident thereon back toward the transmitter optical aperture. The cat-eye retroreflector should have an optical performance level that introduces aberrations into the retroreflected beam, the level of aberrations being such that the retroreflected beam has a divergence that is sufficiently large that the 1 / e 2 diameter of the retroreflected beam at the optical aperture is greater than the diameter of the optical aperture.

Description

Technical Field

[0001] This disclosure describes techniques related to the field of wireless power transmission using optical power beams, and in particular relates to the need for retroreflectors, which are used by many such systems to ensure accurate location and tracking of the receiver of the transmitted power. Background Technology

[0002] A key feature of optical wireless power transmission systems is that the system needs to be able to locate, track, and control the incident light beam of transmitted power onto an element in the receiver that absorbs the transmitted power beam; this element is typically a photovoltaic cell or photovoltaic array. This feature has many important functions in such optical power transmission systems.

[0003] First, this feature is used to determine when a receiver has been detected and when the beam is preferably centered on the absorbing element, or at least when the majority of the beam power strikes the power absorbing element. This task is an essential safety procedure and is typically performed using beam-guiding devices (e.g., scanning mirrors or MEMS-based scanning devices) by scanning the area where a receiver is expected to be found by transmitting a power beam in a safe, low-power mode. This feature can be used to ensure that the beam has been directed to the receiver power absorber before the system is allowed to increase the beam power to a level capable of delivering useful power to the receiver; higher levels of transmission are typically secured through more advanced mechanisms.

[0004] Furthermore, after the control system has enabled wireless power beam locking onto the receiver absorber, the beam aiming device can be controlled to follow the receiver's movement throughout the area covered by the power transmitter, or to reduce the beam power or turn it off completely if the receiver has moved out of the system's service area, in order to maintain power transmission and maintain system security.

[0005] The contents of all publications mentioned in this section and in other sections of this specification are hereby incorporated by reference, with each publication incorporated in its entirety. Summary of the Invention

[0006] This disclosure seeks to provide novel systems and methods for using retroreflectors to track the incidence of an optical power beam on a receiver absorber element, overcoming at least some of the drawbacks of existing systems and methods.

[0007] A common method for enabling a wireless power system to lock a beam onto a receiver absorber and follow the receiver's movement throughout the area covered by the power transmitter, or to reduce or shut down the beam for safety if the receiver has moved out of the system's service area, is to utilize a retroreflector mounted on the receiver. When the transmitted beam strikes the retroreflector, it reflects the beam back towards the transmitter, substantially collinear with the incident beam but in the opposite direction. This retroreflected beam is received at the transmitter's optical aperture and used to provide input to a control system that determines characteristics such as the direction along which the incident power beam should be aimed and the power that the transmitter is allowed to send to the receiver. Because the retroreflector should be located at or near the center of the power receiving aperture to accurately determine when the transmitted power beam strikes the receiver's power absorber element, the retroreflector should have an area significantly smaller than the input aperture of the power receiving element so that the majority of the incident power beam is absorbed by the power receiving element to perform its primary function of transmitting power to the receiver. Only a small portion of the incident beam is back-reflected towards the transmitter. Such an arrangement is illustrated, for example, in a PCT international patent application, WO 2016 / 125156, entitled "Distributed Optical Resonator with Thin Receiver Unit," jointly owned by the applicants and co-inventors. In that reference, Figure 5 A to Figure 5 D illustrates such a retroreflector that covers only a small portion of the input aperture of the photovoltaic absorber cell. Typically, the area of ​​the retroreflector is such that it covers between 5% and 40% of the area of ​​the power absorption input aperture, although applications with even smaller or larger percentages can be effectively deployed.

[0008] Due to the small size of retroreflectors, the beam reflected back towards the transmitter input aperture is very narrow, and for an incident power beam with a diameter of about one centimeter or larger, the diameter of the reflected beam can be as small as 1 mm or less. For this reason, retroreflectors typically used have high optical quality and the lowest possible level of optical aberrations to keep the retroreflected beam as collimated as possible. To keep the complexity and cost of retroreflectors within the limits required for consumer products (such as wireless charging systems for mobile devices like cell phones or laptops), simple spherical cat's-eye retroreflectors known in the prior art are typically used as the retroreflector base. Using such a cat's-eye retroreflector with low aberrations appears to allow for optimal control of the size and divergence of the retroreflected signal beam, thereby improving aiming accuracy. Therefore, for example, some problems to be addressed when using beams with aberrations are described in International Patent Publication WO 2012 / 172541, co-owned by the applicant, entitled "Spatially Distributed Laser Resonator". Therefore, in existing transmission systems, beam aberration is considered an unwanted hindrance to the operation of laser power transmission systems.

[0009] However, in practice, it has been found that optical wireless power transmission systems with low-aberration retroreflectors (such as those using cat-eye retroreflectors) do not function well enough to locate and track receivers with the desired high precision, nor can they accurately meet the security requirements of such systems. Unlike the wide-beam illumination of RF-powered systems, optical wireless power systems illuminate the absorber target (typically a photovoltaic cell) on the receiver using a very narrow beam emitted from a transmitting lens in the optical exit aperture of the transmitter unit. The portion of the incident beam reflected by the optical wireless power system's retroreflector (which is typically a narrower beam than the incident power beam) is collected by the transmitter to enable the system to determine the precise angular position of the receiver absorbing the photovoltaic cell. In some cases, this also assists in laser formation and wavelength tuning, and provides a safety indication in events where an object enters the beam path, causing a change in the reflected optical signal, as described below. This feature of keeping the power beam centered on the power absorption device in the receiver makes it possible to measure the difference between (i) the beam power emitted from the transmitter and (ii) the beam power returned to the transmitter after being retroreflected from the receiver, providing information about whether any object has intruded into the beam path (which would indicate a serious beam hazard). Such measurements are only of any reliable significance if the control system is able to maintain the incident beam in a fairly constant spatial position on the absorber device.

[0010] While the receiver orientation can be determined at the transmitter using a different lens than the one used to transmit the incident power beam, it is best to implement a safety feature to verify the absence of objects in the beam path by using the same lens, specifically the same aperture portion of the lens used for both the outgoing and incoming beams, to collect the retroreflected light. This can be achieved by using a beam splitter behind the transmitter's beam aperture to redirect the returning retroreflected beam to a power meter (where the beam's power level can be monitored) and then to a position detector behind the pinhole to determine where the retroreflected beam is striking. The control system adjusts the beam directional mirror until the retroreflected beam is at its predetermined center position. This predetermined center position then also enables accurate detection of beam intrusion, as the retroreflected beam always strikes the same location on the transmitter's input aperture.

[0011] It is speculated that the use of retroreflectors with low optical aberrations and high beam quality (producing narrow and nearly collimated retroreflected beams) may be the cause of some problems in previously available optical wireless power transmission systems. Such problems stem from the fact that retroreflected beams are relatively prone to missing into the input aperture of the transmitter lens due to factors such as beam deviation or vibration of the receiver containing the retroreflector, or small or rapid movements (as expected in handheld devices). To overcome these problems, such previously described systems require the use of relatively large transmitter optical apertures to receive the retroreflected beams within the aperture, even if the retroreflected beams are not incident on the optical axis of the aperture due to potential beam deviations.

[0012] The optical wireless power transmission system described here differs from previously available systems in that the retroreflector used to return the retroreflected position-indicating beam to the detector within the transmitter's optical aperture is either or both of the following: (i) an intentionally defocused retroreflector; or (ii) a retroreflector with an intentionally increased level of optical aberrations, exceeding the optical aberrations of retroreflectors with optimal optical quality (as is commonly used in currently available power transmission systems). The increased aberration level can advantageously be an increased level of spherical aberration, but the addition of any higher-order rotationally symmetric aberrations can also be used to degrade the optical quality of the retroreflector. Any such degradation of the retroreflector results in a retroreflected beam with increased divergence, rather than a beam returned from a previously preferred retroreflector with optical characteristics optimized to provide the best possible beam collimation. Therefore, the reflected beam has a larger area when it reaches the transmitter entrance aperture, and movement or vibration of the retroreflected beam does not prevent the detector in the transmitter's optical aperture from detecting such a larger beam. After at least a portion of the retroreflected beam is incident within the transmitter's optical aperture, capturing the axial position of the retroreflected beam becomes possible, and a position detector (e.g., a four-quadrant detector behind a pinhole extending beyond the beam aperture) provides a control signal to the beam-emitting scanning device to center the beam at the receiver's input aperture, thus tracking the receiver's position as it moves. Such a pinhole position sensor is only a simplified version of the position-tracking configuration, and more complex optical systems can also be used. As an alternative to using a pinhole to select a small portion of the retroreflected beam for position tracking, a beam splitter can be used to deflect a small portion of the retroreflected beam to the position detector.

[0013] Using a suboptimally designed retroreflector results in a more divergent retroreflected beam, meaning an increased size of the retroreflected beam at the transmitter. This allows for the use of a smaller transmitter optical aperture, as the larger edge of the divergent beam diameter, even if the retroreflected beam is off-axis relative to the input aperture, will ensure that at least a portion of the beam can be detected. Furthermore, this can be achieved using a smaller diameter optical aperture. Existing systems with narrow retroreflected beams emitted at the same angle off the transmitter beam axis as the more divergent beam would require a larger input aperture to be detected. The currently described system using a more divergent beam allows for the use of smaller diameter optics for both beam emission and detection, resulting in significant cost savings. The optimal degree of planned divergence of the retroreflected beam depends on factors such as the system's range, the sensitivity of the detector used to detect the returning beam, and the level of stray light projected onto the detector. This stray light may be due to radiation from an external source (such as the sun), but primarily due to internal reflections of the laser beam within the transmitter. The system's range is understood as the maximum distance over which the system is expected to provide a power beam to the receiver.

[0014] A common cat's-eye retroreflector structure, with a positive lens placed in front of a concave mirror, is most easily achieved by using a glass sphere or two combined hemispherical glass elements with a reflective rear surface, such that the focal point of the lens and the focal point of the concave mirror are confocal. Spherical aberration of the retroreflector can be adjusted by using a slightly aspherical form of the incident lens surface, or by using an aspherical reflective rear surface of the retroreflector, or by using an optical material with a refractive index slightly different from that required to provide optimal optical performance, or by using a slightly different radius of one of the hemispherical elements constituting the cat's-eye retroreflector, or a combination of more than one of these methods. Regardless of the method used, it is important to keep aspherical aberration as low as possible to ensure ease and reliability in tracking the position of the retroreflected beam. In this context, using corner prism retroreflectors in the currently described system is disadvantageous because they introduce higher levels of aspherical symmetry phase and position aberrations.

[0015] Therefore, according to exemplary embodiments of the systems and devices described in this disclosure, a wireless optical power transmission system is provided, the wireless optical power transmission system comprising: (i) A transmitter that outputs an optical power beam through an optical aperture, the transmitter comprising: (a) A laser that generates an optical power beam. (b) A deflection module for guiding the optical power beam. (c) A controller suitable for adjusting the deflection module, and (ii) A receiver comprising a retroreflector having a cat's-eye configuration, the retroreflector being adapted to return at least a portion of the retroreflected beam from the incident optical power beam toward the transmitter optical aperture, wherein: The cat's-eye retroreflector has an optical performance level that introduces aberrations into the retroreflected beam, such that the retroreflected beam has a sufficiently large divergence to achieve a 1 / e divergence at the optical aperture. 2 The diameter is larger than the optical aperture diameter.

[0016] In any such wireless optical power transmission system, the retroreflected beam's 1 / e 2 The diameter should be at least 1.5 times the diameter of the optical aperture. Alternatively, it should be at least twice the diameter of the optical aperture.

[0017] Furthermore, the main components of aberrations may include radially symmetric aberrations or defocus, and the main components of aberrations may be spherical aberrations.

[0018] In any such wireless optical power transmission system, the cat's eye retroreflector may include a transparent sphere having a refractive index configured as 1 + n, where n is the refractive index of the medium from which the optical power beam is incident, and the sphere having a reflective coating on a surface opposite to the surface from which the optical power beam strikes. In such a system, if the medium from which the optical power beam is incident is air, the refractive index of the transparent sphere should be 2.

[0019] In any of the aforementioned wireless optical power transmission systems, excluding those including a transparent sphere, a cat's-eye retroreflector may include a pair of separate optical elements, one of which, upon which the optical power beam strikes, has a positive focal length, and the second element has a reflective surface located at the focal plane of the first element. In such a system, the cat's-eye retroreflector may include a pair of hemispherical spheres optically contacted in their planes, each hemisphere having a different radius. In such a system, the hemisphere upon which the optical power beam strikes should have a smaller radius than the hemisphere opposite to it, the radius ratio being equal to n - 1, where n is the refractive index of the hemispherical material.

[0020] Furthermore, in any of the aforementioned wireless optical power transmission systems, the aberrations introduced into the retroreflected beam can make the retroreflected beam have a sufficiently large divergence such that the optical aperture captures at least a portion of the retroreflected beam, even in cases where the retroreflector already has optimal minimum aberrations and no portion of the retroreflected beam is captured by the optical aperture.

[0021] Furthermore, the optical performance level of the retroreflector should be lower than that of the retroreflector with the optimal minimum aberration level.

[0022] Furthermore, in any of the aforementioned wireless optical power transmission systems, the retroreflector is the only retroreflector on the receiver.

[0023] According to another exemplary implementation of the systems and devices described in this disclosure, a cat's eye retroreflector for a wireless power transmission system is also provided, adapted to be illuminated by a first beam emitted through a transmitter aperture and configured to retroreflect a second beam substantially back toward the aperture, wherein the retroreflector has an aberration that imparts an aberration level to the second beam including at least 65% radial asymmetric aberration or defocus, such that 1 / e of the second beam at the transmitter... 2 The diameter is larger than the aperture of the transmitter. The aberration level of the retroreflector can be intentionally selected for this purpose.

[0024] According to another exemplary implementation of the system disclosed herein, a cat's eye retroreflector for a wireless optical power transmission system is also provided, which is adapted to be illuminated by a transmitter via a first beam emitted through an optical aperture of the transmitter, and to retroreflect a second beam substantially back toward said aperture. Specifically, when the cat's-eye retroreflector deviates from the optical axis of the first beam, the retroreflected second beam does not completely overlap with the first beam and only partially passes through the optical aperture of the transmitter. The degree of overlap depends at least in part on the level of aberrations induced in the retroreflected beam by the cat's-eye retroreflector, and The cat-eye retroreflector has a larger aberration level than the second retroreflector, which will produce the best collimated retroreflected beam, such that the transmitter's optical aperture will capture the second retroreflected beam from the cat-eye retroreflector at a greater off-axis distance than for the best collimated retroreflected beam of the second retroreflector.

[0025] Using such a cat's-eye retroreflector, for the same off-axis distance of the cat's-eye retroreflector as the second retroreflector that produces the optimal collimated retroreflected beam, the aperture size of the transmitter can be made smaller than the aperture size of the system using the second retroreflector that produces the optimal collimated retroreflected beam.

[0026] Further inventions that can be implemented in the systems or apparatus described in this disclosure may include at least some of the following: An retroreflector for a wireless power transmission system, when illuminated by an off-axis position of a first beam emitted from a source aperture, retroreflects a second beam back toward the source aperture, wherein the aberration induced by the retroreflector to the retroreflected beam is such that: when the diameter of the retroreflector is less than 50% of 1 / e2 of the diameter of the first beam, the retroreflected beam can still be detected at the source even if the retroreflector is located at a position deviating from the axis of the first beam by at least one retroreflector diameter but not more than four retroreflector diameters.

[0027] An retroreflector for a wireless power transmission system, when illuminated by an off-axis position of a first beam emitted from a source aperture, causes a second beam to retroreflect back toward the source aperture in a direction not opposite to the propagation of the first beam, wherein the aberration induced by the retroreflector to the retroreflected beam is such that: when the diameter of the retroreflector is less than 50% of 1 / e2 of the diameter of the first beam, the retroreflected beam can still be detected at the source even if the retroreflector is located at a position deviating from the axis of the first beam by at least one retroreflector diameter but not more than four retroreflector diameters.

[0028] In such a retroreflector, the source aperture and the emitted beam have dimensions such that the aperture transmits less than 98% of the source beam incident upon it.

[0029] An retroreflector for use with a wireless power transmission system, which, when illuminated by a first beam emitted through the source aperture of a transmitter, causes a second beam to retroreflect toward the source aperture of the first beam, wherein the retroreflector is an aberration-type element that introduces at least one of radial symmetry aberration and defocus into the second beam.

[0030] An retroreflector for use with a wireless power transmission system, which, when illuminated by a first beam emitted through a source aperture of the transmitter at less than 98% of the beam, causes a second beam to retroreflect toward the source aperture of the first beam, wherein the retroreflector is an aberration-type element that introduces at least one of radial symmetry aberration and defocus into the second beam.

[0031] An antireflector for a wireless power transmission system is illuminated by a first beam through an aperture that transmits less than 98% of the source beam incident thereon, and causes a second beam to be retroreflected toward the source of the first beam, wherein the second beam does not completely overlap with the first beam and is transmitted only partially through the aperture.

[0032] In such a retroreflector, at least 1% of the second beam is transmitted through the aperture.

[0033] In such a retroreflector, at least 10% of the second beam is transmitted through the aperture.

[0034] A detector for a retroreflected beam in a wireless power transmission system, the system transmitting a laser beam through an aperture that allows less than 98% of the beam power to pass through, the laser beam being directed toward a remote point at a predetermined longitudinal distance from the transmitter where a receiver with a retroreflector may be located, wherein the laser axis does not directly strike the retroreflector, but only the edge of the laser beam strikes the retroreflector, which has a defocusing effect on its retroreflected beam, and wherein the retroreflected beam passes through the aperture, at which the retroreflected beam is detected by a detector configured to detect a signal retroreflected from the defocused retroreflector when the defocused retroreflector is located at a position at least 0.25*r from the laser beam axis, where r is 1 / e of the laser beam leaving the transmitter. 2 The radius, but the detector is configured to adjust, reduce or terminate the power of the laser beam when the retroreflector is 2.5*r or more from the laser beam axis.

[0035] A detector for a retroreflected beam in a wireless power transmission system, the system transmitting a laser beam through an aperture that allows less than 98% of the beam power to pass through, the laser beam being directed toward a remote point at a predetermined longitudinal distance from the transmitter where a receiver with a retroreflector may be located, wherein the laser axis does not directly strike the retroreflector, but only the edge of the laser beam strikes the retroreflector, the retroreflector having a defocusing effect on its retroreflected beam, and wherein the retroreflected beam passes through the aperture, at which the retroreflected beam is detected by a detector configured to detect a signal retroreflected from the defocused retroreflector when the defocused retroreflector is located at a position at least 0.25*r from the laser beam axis, where r is 1 / e of the laser beam leaving the transmitter. 2 The radius, where the detection of retroreflected signals enables wireless power transmission systems to improve the aiming of the laser beam onto the receiver. Attached Figure Description

[0036] The invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the accompanying drawings, in which: Figure 1A The illustration schematically depicts a prior art laser-based wireless power transmission system in which a well-collimated incident beam from the transmitter is shown striking a photovoltaic cell and a retroreflector in the receiver. Figure 1B It shows the relationship with Figure 1A The same system, but includes a pinhole located behind the transmitter output lens that samples the retroreflected beam and uses a position detector to provide information about the spatial orientation of the receiver and its retroreflector; Figure 2A and Figure 2B The illustration shows an optical wireless transmission system retroreflecting a beam from an incident optical power beam that converges toward the beam waist and then diverges beyond the beam waist. Figure 2A The image shows the receiver positioned behind the waistband, and Figure 2B This shows the receiver positioned in front of the corset; Figure 3A The prior art retroreflector is shown, which produces a well-collimated retroreflected beam. As a result, when the beam axis deviates from the retroreflector, a large transmitter operating aperture with a large diameter lens is required in the transmitter to increase the possibility of capturing the retroreflected beam. Figure 3B It shows the relationship with Figure 3A The same situation, but using a smaller diameter lens, because of the use of a smaller diameter lens, Figure 3A The retroreflected beam was not captured; Figure 3C This illustrates a case where using a retroreflective beam with more aberrations enables the capture of a larger diameter of a more divergent retroreflective beam using a lens system with a smaller input aperture and therefore a lower cost. Figure 4 illustrates a prior art retroreflector without intentionally generated defocusing effect, which has a front sphere with the focus generated on the reflective rear surface of the rear sphere. Figure 5 A schematic diagram illustrates a plot of the percentage of light power transmitted by the lens as a function of the lens's relative area; and Figure 6 The illustration shows a graphical example of the use of a spherical retroreflector positioned off-axis from the transmitter beam. The figure shows the degree to which the retroreflected beam spot deviates from the center of the transmitter aperture as a function of the distance of the retroreflector along the beam path, as well as the size of the retroreflected beam spot. Detailed Implementation

[0037] First refer to Figure 1AThe illustration schematically depicts a prior art laser-based wireless power transmission system, in which a well-collimated incident beam 11 from transmitter 10 is shown striking a photovoltaic cell 12 and a retroreflector 13 in a receiver. Retroreflector 13 can be positioned at the edge of the incident power beam impact area such that a retroreflected beam 14 (which is reflected generally parallel to but not overlapping the incident power beam, and is much weaker than the incident beam) can be close to the edge of the transmitter's optical aperture, such that a portion of the retroreflected beam is truncated and lost for a position detector behind the optical aperture. Furthermore, any small movement of the receiver could cause the retroreflected beam to completely miss the transmitter's input aperture, resulting in an interruption of power transmission to the receiver, necessitating a transmitter beam guiding system to search for the receiver again with a reduced-power scanning beam.

[0038] Figure 1B It shows the relationship with Figure 1A The same system, but includes a pinhole 16 located behind the transmitter output lens, which samples the retroreflected beam 14 and transmits the signal to a position detector 17, which provides information to a controller 15 about the spatial orientation of the receiver 12 and its retroreflector 13. The controller then inputs a direction control signal to a beam scanning mirror 19 to guide the power beam to the receiver position determined by the position detector. Figure 1B A concave form 18 is also shown, the waveform of the transmitted beam can exhibit said concave form, depending on whether the receiver is before or after the waist of the transmitted beam, as combined Figure 2A and Figure 2B Further explanation.

[0039] Now for reference Figure 2A and Figure 2B These illustrations schematically depict this effect in a system with a single, optically good retroreflector used to retroreflect signals from a conventional collimated beam having a diameter that converges toward the beam waist and then diverges beyond the waist. If the retroreflector is not centered relative to the incident beam axis (a common occurrence due to vibration or movement of receiver 21), the retroreflector may not send the retroreflected signal back to the transmitter because the retroreflected wave will be guided back along a direction perpendicular to the portion of the wavefront that falls on the retroreflector, rather than perpendicular to the entire beam axis. In this case, the retroreflector effectively “samples” only a small lateral portion of the beam and retroreflects that portion of the beam along a direction perpendicular to that portion of the wavefront. If the sampled portion is not at the center of the original beam (i.e., not on the axis), the reflected beam along the direction perpendicular to the sampled portion of the wavefront is not parallel to the incident beam axis.

[0040] Now for reference Figure 2A The details are shown, schematically illustrating the output lens 28 of the transmitter 20 emitting a forward beam 23 that converges through a beam waist 26 (which is the narrowest part of the focused beam) and then diverges toward a receiver 21 having a spherical retroreflector 22. The wavefront profile 25 of the incident optical power beam 23 is shown, which is concave toward the receiver 21 before the beam waist 26 and then concave toward the transmitter 20 after the beam waist.

[0041] Receiver 21 includes a single retroreflector 22 for sending a retroreflected beam back to transmitter 20, indicating the impact of the forward laser beam 23 on the retroreflector. This returned beam serves as feedback input to control the aiming of beam 23 at retroreflector 22 and as feedback for safety interlocking. Figure 2A As shown, it is assumed that the retroreflector 22 is not located at the waist of the incident beam 23, but rather within the beamwidth transverse limit at another point along the beam length. Figure 2A If the beam is located behind the beam waist, it samples only a small portion of the wavefront 25 of the beam 23 falling on it and retroreflects a beam 24 whose axis is perpendicular to the small amount of wavefront 25 sampled near the retroreflector 22. Since the small amount of wavefront 25 sampled is not perpendicular to the axial direction of the forward-emitting beam 23, the retroreflected beam 24 is guided in a direction perpendicular to the wavefront 25, which is not coaxial with the forward-emitting beam 23, and, as shown in the example of Figure 2, even if it has the expected slight divergence of the retroreflected incident wave, it may completely miss the optical aperture 28 of the transmitter, thus rendering its entire function of providing system control and safety feedback ineffective.

[0042] The extent to which the retroreflected beam partially or completely misses the transmitter's aperture depends on whether the receiver is closer to the transmitter than the focal waist of the incident power beam, or farther away from the transmitter than the focal waist of the incident power beam. If the retroreflector is closer to the transmitter than the focal waist of the beam, the failure to capture all or part of the retroreflected beam increases; and if the retroreflector is farther away from the focal waist of the beam (from the transmitter), the failure decreases. Observation Figure 2A In the example shown, where receiver 21 is located behind beam waist 26, it is clear that as the retroreflector moves to the right (R), a portion of the wavefront of the incident beam striking the retroreflector reflects back toward the transmitter in a direction perpendicular to the wavefront at the retroreflector, and due to the concave shape of the wavefront behind the beam waist, the retroreflection direction has an inclination toward the left-hand side (L) of the beam axis. In other words, as the receiver moves to the right away from the beam axis and the transmitter aperture, the retroreflected beam moves to the left, thereby at least partially compensating for the right-hand (side) movement of the retroreflector.

[0043] On the other hand, now refer to Figure 2B The receiver 21 is shown positioned before the waist of the beam. The curvature of the wavefront before the waist diameter causes the retroreflected beam to also move to the right (R) when the receiver moves to the right, thus increasing the likelihood that the retroreflected beam will miss hitting the lens in the transmitter aperture 28. This situation is more... Figure 2A The situation is more difficult to correct because when the receiver moves off-axis, the retroreflected beam deviates even more from the axis of the transmitter beam aperture and in the same direction as the receiver's movement. In practice, this increased deviation of the retroreflected beam in the region before the beam waist can be compensated in the control system by applying a negative 1 digital multiplication to the image processing beam position detection stage, so that the deviated beam image can be processed by the detection system.

[0044] In summary, this effect means that the retroreflected beam will only return directly to the transmitter's aperture when the receiver is positioned such that the retroreflector is precisely aligned with the axis of the transmitted incident beam. If the receiver moves and the retroreflector is no longer on the axis, the retroreflected beam will no longer strike the center of the transmitter's aperture; the degree of deviation depends on whether the receiver is positioned before or after the beam axis. With relatively small receiver movements, the retroreflected beam from a well-collimated incident beam will completely miss the transmitter's aperture, causing the system to lose track of the receiver's position. This necessitates the transmitter's beam scanning mechanism restarting the search for the receiver and locking onto its position once found again.

[0045] To reduce the occurrence of this situation, existing systems with well-collimated retroreflective beams therefore require a sufficiently large aperture to maintain tracking of the retroreflective beam for a predetermined deviation of the receiver from the incident beam axis (up to the level of deviation expected due to receiver movement). On the other hand, if, according to currently proposed methods and systems, the retroreflective beam is intentionally produced with an aberration level exceeding that of the optimally collimated retroreflective beam, the retroreflective beam will diverge sufficiently, increasing the likelihood that at least the outer portion of the retroreflective beam will enter the transmitter aperture. To take advantage of this phenomenon, the transmitter aperture can then be made smaller than that of a system with an optimally collimated retroreflective beam, while still maintaining the same probability of capturing the retroreflective beam as in the well-collimated case. Generating a retroreflective beam with higher divergence is most conveniently achieved by using a retroreflector with a controlled defocus level (i.e., a spherical aberration level or higher). Spherical aberration is preferred because it maintains the rotational symmetry of the beam. Aberrations that fail to maintain a reasonable level of spherical symmetry can cause retroreflected beams to acquire shapes that are far from reasonable circular (e.g., elongated ellipses), making it difficult for the system to provide meaningful beam tracking.

[0046] Using a more divergent retroreflective beam means that the beam can be detected over a wider lateral range from the axis of the emitted beam compared to systems using retroreflectors with optimal optical quality. Therefore, instead of using large optical apertures to capture the low-divergence retroreflective beams of previous systems, it becomes possible to use smaller optical apertures to capture the wider divergent retroreflective beams of the currently described system, accompanied by reductions in system cost and size.

[0047] This feature of the system and method of this application is in Figures 3A to 3C The image in the middle shows... Figure 3A The illustration shows the situation at the transmitter's optical exit / incident aperture 30, which uses a prior art retroreflector to generate a well-collimated retroreflected beam from the transmitted beam 31. Because retroreflectors themselves are typically small to avoid using too much received transmitted power, the retroreflected beam is also small, and even considering the expected divergence even when well-collimated, and the natural diffraction effect of the beam from a very small source, it will also be small when it returns to the transmitter's exit / incident aperture. Therefore, when the beam axis deviates from the retroreflector due to, for example, movement of the receiver, a well-collimated retroreflected beam with a relatively small coverage area 33 at the aperture may deviate significantly from the aperture center, requiring a large transmitter operating aperture 30 with a larger diameter lens to increase the likelihood of capturing a well-collimated retroreflected beam 33. A large operating aperture 30 must simultaneously accommodate both the transmitted power beam 31 and the retroreflected return beam 33, thus requiring more expensive lenses. The transmit beam 31 itself requires an aperture 32 that is only slightly larger than the diameter of the transmit beam 31. Figure 3A In the above, the lateral deviation of the retroreflected beam at the transmitter exit / incident aperture is given by the distance between the centers of beams 31 and 33, and this deviation is also used for the following Figure 3B and Figure 3C In the examples, so that these cases can be compared. For Figure 3A In the case shown, with the large entrance aperture 30, the retroreflected beam 33 was well detected, even at the edge of the entrance aperture.

[0048] Figure 3B The effect of attempting to use a smaller emitter entrance aperture of 36 is now shown. Using a smaller emitter entrance aperture is typically done to allow for the use of smaller and lower-cost lenses. In this case, for... Figure 3A Retroreflection collimated beams of the same size, and with the same... Figure 3AWith the same lateral deviation from the center of the exit / incident aperture, the retroreflected beam is shown to have completely missed entering the exit / incident aperture 36 of the transmitter, causing the transmitter to lose detection of the beam and thus lose tracking of the receiver due to the movement of the receiver. This situation illustrates a problem in prior art systems using well-collimated retroreflected beams, a problem that the systems and methods of this disclosure attempt to solve.

[0049] on the other hand, Figure 3C The situation is now illustrated when the less well-collimated retroreflective beam of this disclosure is used in the system. Because the more divergent retroreflective beam 37 has a larger diameter, the same level of handling certain receiver displacements can be achieved using a smaller input aperture and therefore a less expensive lens system. Figure 3C In this context, for the same transmitted beam 31, a smaller lens diameter 36 can be used, while simultaneously... Figure 3A and Figure 3B The same optical axis offset distance shown still captures the edge of the more divergent retroreflected beam 37. As in Figure 3C What I saw in the middle, and Figure 3B As shown in the diagram, a portion of the collimated beam 37 with greater divergence does indeed enter the incident aperture 36, and this can continue to be tracked by the system. The overall effect of using retroreflectors with a larger aberration level compared to the aberration level of a beam with well-corrected aberration levels, as described currently, is that a smaller and therefore less expensive transmitter aperture optics 36 can be used while achieving the same effect as the larger aperture optics 30 in prior art systems.

[0050] Component Selection In order to realize a laser power transmission system with an aberration-enhanced retroreflective beam as described in this disclosure, several features are proposed to assist in calculating the values ​​of components that will enable such an implementation.

[0051] Retroreflector design Figure 4A The illustration shows a prior art cat's-eye retroreflector without intentionally generated defocusing effects. This retroreflector has a precise front hemisphere 40 with a radius such that it produces a focal point 41 on the reflective rear surface of the rear sphere 42. Achieving retroreflection requires two distinct radii. The radii of the two hemispheres can be calculated using conventional geometric optics lens maker equations, yielding the following expression: r2 = r1 / (n - 1) in r1 is the radius of the hemisphere that serves as the input lens for the retroreflector beam, and r2 is the radius of the hemisphere that serves as the beam reflector, and n is the refractive index of the hemispherical material.

[0052] The equation above assumes that the refractive index of the air at the location of the retroreflector is 1. Using a more precise form, the value of the refractive index should take this difference into account.

[0053] Typically, some corrections are needed to the results of this equation because the numerical aperture is usually high in these applications.

[0054] Using the same refractive index for both hemispheres is advantageous to avoid the need for an anti-reflective coating between the two components, but it is also possible to use different refractive indices for the two components. The desired aberration level of the retroreflective beam can be achieved by slightly modifying either or both of the radii or refractive indices of one or both hemispheres.

[0055] Based on the equations above, note that when n = 2, r1 = r2, which means that the cat's eye retroreflector can be formed from a single sphere, which is simpler and more practical than gluing two hemispheres together. Figure 4B A single-sphere cat's-eye retroreflector 43 is shown, having a refractive index as close as possible to 2, and a radius that produces a focal point 44 on the reflective rear surface 45 of the sphere.

[0056] Glass with a refractive index of exactly 2 may not be readily available, and therefore, even with the best possible aberration correction using readily available glass with a refractive index of approximately 2, existing techniques may still result in very small residual aberrations. However, deviations from the precise refractive index value of 2 can be used in the retroreflector described herein to adjust the degree to which the retroreflector's aberrations deviate from the optimal achievable aberration level, thereby providing a retroreflector with the aberration characteristics required according to the invention.

[0057] Furthermore, it should be noted that the value of n - 1 in the above equation is only an approximation, because the value 1 is intended to be the refractive index of the medium surrounding the retroreflector (air in this case), and if the refractive index of air differs from the value 1, then the equation and the resulting recommendations for the retroreflector of this disclosure should be modified accordingly, even if very slightly. Since such modifications are typically very small, they are omitted in this specification. However, this effect is noted for clarification, and the value of "-" referred to in the claims when describing the refractive index of the cat's-eye retroreflector material is understood to be an approximation of the true refractive index of the air surrounding the retroreflector.

[0058] Transmitter beam optics In a typical optical wireless power transmission system used in a home environment, the transmitted beam is emitted from an aperture with a diameter of several centimeters (typically up to 2 cm). The beam needs to be projected over a distance of more than ten meters, approximately 1000 times the size of the output aperture. This means that beam focusing at the farthest point of the beam's range can only be achieved using lenses with a numerical aperture of approximately 0.001, while this task becomes virtually impossible with lenses having a numerical aperture greater than 0.01.

[0059] To achieve commercial acceptability, it is typically necessary to reduce the overall size of the transmitter, and especially the size of the optical system, the cost of which depends heavily on its diameter. In practice, the aperture of the optical system should be chosen to be at least about 90% of the transmitted power beam, or even slightly more, up to about 98%, but requiring close to 100% of the transmitted beam has proven to be a diminishing returns task.

[0060] To illustrate this point, see now for reference. Figure 5 The diagram schematically illustrates a plot of the percentage of optical power transmitted by a lens as a function of the lens's relative area. As can be observed from the graph, the lens area required to transmit 99% of a Gaussian profile beam is twice that required to transmit 90% of the same beam, and to transmit 99.99% of the power, a lens with four times the area of ​​a 90% lens and typically eight times the weight (due to the need for a larger lens thickness) and therefore significantly higher cost would be required. Thus, the need to use transmission levels exceeding approximately 90% or slightly higher leads to an excessive increase in the size and cost of the optical system without a significant increase in the transmitted power level.

[0061] However, although the power gain from increasing the aperture size is very small, safety requirements dictate that the retroreflected beam from the receiver must be collected through the same aperture to ensure that the system can detect no object in the line of sight between the transmitter and the receiver.

[0062] When the incident power beam is indeed centered on the retroreflector, this alignment is achieved automatically, and the retroreflected beam propagates directly into the transmitter's optical aperture in opposite directions to the transmitted beam. However, due to beam deviation, system vibration, receiver movement, and other factors, the alignment of the beam with the retroreflector cannot always be perfect. Therefore, when the incident power beam is not perfectly pointed at the retroreflector, the beam may not return to the finite diameter beam aperture and may be completely missed for collection. This creates a conflict between maintaining the lens diameter and thus keeping the lens cost low, while simultaneously maintaining a sufficiently large aperture to allow the returned retroreflected beam to enter without compromising the safety requirements for transmitting the incident beam through the same lens and receiving the retroreflected beam. Therefore, existing systems typically use transmitting lenses with apertures larger than required to transmit an acceptable percentage of laser power.

[0063] The spot size d produced by the focused emission beam is approximated by a well-known expression: d = 1.22 * λ / NA Where λ is the wavelength of the light beam, and NA is the numerical aperture of the focusing lens.

[0064] Using a beam with a wavelength of approximately 1µm, and with small-angle approximations using sine and tangent functions, NA is given by the following equation: Substituting the approximate values ​​given above, we can see that the spot size is approximately 2500 * λ, which is roughly equal to half the aperture diameter in several centimeters (the values ​​used above to describe a typical home installation). Figure 3A As illustrated in the diagram, the aperture used in such prior art systems is typically slightly larger to increase the permissible level of receiver motion without “losing” the retroreflected beam.

[0065] Now for reference Figure 6 The figure illustrates a graphical example of the results of a spherical retroreflector located 4 mm from the axis of the transmitting beam. The figure shows the degree to which the retroreflected beam spot deviates from the center of the transmitter aperture and the size of the retroreflected beam spot as a function of the distance of the retroreflector along the beam path for a beam focused to have its waist diameter at a distance of 7 m.

[0066] The retroreflected beam spot size increases continuously with the downward travel distance of the retroreflector, as shown by the solid line, which indicates the retroreflected signal spot size on or at least near the transmitter beam aperture. On the other hand, the distance from the center of the returning beam spot to the optical center of the aperture is... Figure 6The dashed lines in the diagram illustrate this. It can be seen that for retroreflectors positioned before the beam waist, the beam can be offset from the transmitter center by up to approximately 5 mm, while for retroreflectors positioned after the beam waist... Figure 2A The self-compensation effect described in the previous description begins to take effect, causing the offset to decrease as the retroreflector travels further down the range. However, for most of the system's useful range, a well-collimated retroreflector will cause the retroreflected beam to miss the aperture, and the system will therefore lose tracking of the receiver. This is precisely the problem addressed by using a less well-collimated retroreflected beam in the system and method of this application, which, even when deviating from the central axis of the aperture, still allows at least the peripheral portion of the intentionally broadened beam to enter the aperture and correct the beam aiming direction to maintain tracking of the receiver. Another alternative result of the system disclosed herein is that it maintains the same beam detection criteria as the best-focused retroreflected beams in the prior art, but achieves this using significantly smaller optics in the transmitter, thereby reducing the cost of the transmitter.

[0067] To provide some exemplary quantitative estimates, although the lens area required to transmit 95% of the laser power beam toward a receiver with a numerical aperture of 0.001 is approximately 3 mm². 2 However, in order to capture the returning beam, the lens needs to have a diameter of at least 2 * (5mm offset + 4mm reflected beam radius), which is approximately 18mm. Such a lens would have a diameter exceeding 250mm. 2 This would significantly increase the area of ​​the transmitter's optical system and the size and cost. If a smaller aperture, just large enough to transmit the beam, is used, the retroreflected signal will not be able to enter the lens aperture, resulting in a loss of tracking of the receiver.

[0068] These quantitative estimates provide the basis for the solutions disclosed in this application, allowing the use of defocused retroreflectors instead of retroreflectors with optimal optical design, or retroreflectors with intentionally increased spherical aberration, or a combination of both. In addition to using increased spherical aberration (i.e., using retroreflectors with suboptimal focal lengths), other rotationally symmetric aberrations can also be used to achieve the desired deviation of the retroreflected beam.

[0069] Example embodiments are provided so that this disclosure will be thorough and fully convey the scope to those skilled in the art. To provide a thorough understanding of embodiments of this disclosure, numerous specific details, such as examples of particular components, devices, and methods, have been set forth. It will be apparent to those skilled in the art that these specific details are not necessarily adopted, example embodiments may be embodied in many different forms, and should not be construed as limiting the scope of this disclosure. Furthermore, those skilled in the art will understand that the invention is not limited to what has been specifically shown and described above. Rather, the scope of the invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications of these features that would occur to those skilled in the art upon reading the foregoing description and which are not present in the prior art.

Claims

1. A wireless optical power transmission system, comprising: A transmitter that outputs an optical power beam through an optical aperture, the transmitter comprising: A laser that generates an optical power beam; Deflection module used to guide optical power beams; A controller adapted to adjust the deflection module; and A receiver, comprising a retroreflector having a cat's-eye configuration, the retroreflector being adapted to return at least a portion of the retroreflected beam from an incident optical power beam back toward the transmitter optical aperture, wherein: The cat-eye retroreflector has an optical performance level that introduces aberrations into the retroreflected beam, such that the retroreflected beam has a sufficiently large divergence that at the optical aperture, 1 / e of the retroreflected beam... 2 The diameter is larger than the optical aperture diameter.

2. The wireless optical power transmission system according to claim 1, wherein, The 1 / e of the retroreflected beam 2 The diameter is at least 1.5 times the diameter of the optical aperture.

3. The wireless optical power transmission system according to claim 1, wherein, The 1 / e of the retroreflected beam 2 The diameter is at least twice the diameter of the optical aperture.

4. The wireless optical power transmission system according to any one of the preceding claims, wherein, The main components of the aberrations include radially symmetric aberrations or defocus.

5. The wireless optical power transmission system according to any one of the preceding claims, wherein, The main component of the aberrations is spherical aberration.

6. The wireless optical power transmission system according to any one of the preceding claims, wherein, The cat-eye retroreflector includes a transparent sphere having a refractive index configured as 1 + n, where n is the refractive index of the medium from which the optical power beam is incident, and the sphere having a reflective coating on a surface opposite to the surface on which the optical power beam is struck.

7. The wireless optical power transmission system according to claim 6, wherein, The medium from which the optical power beam is incident is air, so the refractive index of the transparent sphere should be 2.

8. The wireless optical power transmission system according to any one of claims 1 to 5, wherein, The cat-eye retroreflector includes a pair of separate optical elements, wherein the optical power beam strikes the elements having a positive focal length, and the second element has a reflective surface located at the focal plane of the first element.

9. The wireless optical power transmission system according to any one of claims 1 to 5, wherein, The cat-eye retroreflector comprises a pair of hemispherical spheres optically in contact on their planes, each of the hemispheres having a different radius.

10. The wireless optical power transmission system according to claim 8 or 9, wherein, The hemisphere struck by the optical power beam has a smaller radius than the hemisphere opposite to it, and the radius ratio of the hemispheres is equal to n - 1, where n is the refractive index of the material of the hemispheres.

11. The wireless optical power transmission system according to any one of the preceding claims, wherein, The aberrations introduced into the retroreflected beam cause the retroreflected beam to have a sufficiently large divergence such that the optical aperture captures at least a portion of the retroreflected beam, even in cases where the retroreflector already has optimal minimum aberrations and no portion of the retroreflected beam is captured by the optical aperture.

12. The wireless power transmission system according to any one of the preceding claims, wherein, The optical performance level of the retroreflector is lower than that of the retroreflector with the optimal minimum aberration level.

13. The wireless power transmission system according to any one of the preceding claims, wherein, The retroreflector is the only retroreflector on the receiver.

14. A cat's eye retroreflector for a wireless power transmission system, adapted to be illuminated by a first beam emitted through a transmitter aperture, and configured to retroreflect a second beam substantially back toward said aperture, wherein, The retroreflector has an aberration that imparts an aberration level to the second beam including at least 65% radial asymmetric aberration or defocus, such that 1 / e of the second beam at the transmitter... 2 The diameter is larger than the aperture of the transmitter.

15. The cat's eye retroreflector according to claim 14, wherein, The aberration level of the retroreflector is intentionally selected.

16. A cat's eye retroreflector for a wireless optical power transmission system, adapted to be illuminated by a transmitter via a first beam emitted through an optical aperture of the transmitter, and to cause a second beam to be retroreflected substantially back toward the aperture. in, When the cat's-eye retroreflector deviates from the axis of the first beam, the retroreflected second beam does not completely overlap with the first beam and only partially transmits through the optical aperture of the transmitter. The degree of overlap depends at least in part on the level of aberrations induced in the retroreflected beam by the cat's eye retroreflector, and The cat-eye retroreflector has a larger aberration level than the second retroreflector that will produce the optimal collimated retroreflected beam, such that the optical aperture of the transmitter will capture the second retroreflected beam from the cat-eye retroreflector at a greater off-axis distance than for the optimal collimated retroreflected beam of the second retroreflector.

17. The retroreflector according to claim 16, wherein, For the same cat's-eye retroreflector off-axis distance as the second retroreflector that produces the optimal collimated retroreflected beam, the aperture size of the transmitter can be made smaller than that of a system using the second retroreflector that will produce the optimal collimated retroreflected beam.

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