Optical wireless power supply system

Abstract

System for optical wireless transmission of power to a power receiving device, typically located in a mobile electronic device. The transmitter has an optical resonator with end reflectors and a gain medium between them, producing a beam. The frequency of the beam is chosen so that it is absorbed by almost all commonly used transparent organic materials. A beam steering unit on the transmitter can direct the beam in any of a plurality of directions, and on the receiver the beam is absorbed through a low reflective surface by means of a photovoltaic power converter. The bandgap of this power converter is chosen to be smaller than the gain medium. The receiver has a voltage converter comprising an inductor, a storage device and a switch. A beam steering controller ensures that the beam is projected on the receiver.

Description

[0001] This application is a divisional application of patent application no. 201680053601.6, filed on July 14, 2016, entitled "Optical Wireless Power Supply System". TECHNICAL FIELD

[0002] The present invention relates to the field of wireless power transfer, and in particular to the application of laser-based transmission systems to transfer optical power to mobile electronic devices in a home environment. BACKGROUND

[0003] There has been a long-standing need to transfer power to remote locations without the need for physical wired connections. This need has become important in the last few decades with the proliferation of portable electronic devices that operate through batteries that need to be recharged periodically. These mobile applications include mobile phones, laptops, small cars, toys, wearable devices and hearing aids. Currently, the capacity of state-of-the-art batteries and the typical battery application of intensively used smartphones make it possible that the battery needs to be charged more than once a day, and the need for long-range wireless battery recharging is important.

[0004] Battery technology has a long history and is still evolving. Benjamin Franklin described the first battery made of a Leyden jar in 1748, the first power source resembling a cannon battery (hence the name battery). Later, Volta invented the copper-zinc battery in 1800, which was significantly more portable. Gaston Planté invented the first rechargeable battery in 1859, the lead-acid battery. Since then, the energy density of rechargeable batteries has increased by less than 8 times, as shown in Figure 1

[0005] Almost a century after the invention of the battery, in the period between 1870 and 1910, Tesla tried to transfer power over distances using electromagnetic waves. Since then, many attempts have been made to safely transfer power to remote locations, characterized by distances significantly greater than the transmission device or the receiving device. The range goes from NASA, which implemented the SHARP (Stationary High Altitude Relay Platform) program in the 1980s, to Marin Soljacic, who experimented with a system similar to Tesla's in 2007.

[0006] So far, only three commercially available technologies allow the safe delivery of power to mobile devices without wires, namely

[0007] ​Magnetic induction - which is typically limited to a range of only a few mm;

[0008] Photovoltaic cells - which when illuminated with sunlight or with artificial lighting at levels achievable in a typically (safe) lit room, cannot produce more than 0.1 Watt in relation to the size of a mobile phone;

[0009] Energy harvesting technology - converting RF waves into usable energy, but in any current practical case cannot operate at more than 0.01 W because RF signal transmission is limited due to health and FCC regulations.

[0010] At the same time, typical batteries of portable electronic devices have a capacity of 1 to 100 Watt*hour and typically require charging every day, thus requiring significantly higher power delivery over significantly longer ranges.

[0011] Therefore, the need to safely deliver electrical power over a range larger than a few meters to portable electronic devices typically equipped with rechargeable batteries has not been met.

[0012] Several attempts have been made to deliver power using collimated or substantially collimated electromagnetic waves within a residential environment. However, commercial availability of such products to the mass market is currently still limited.

[0013] Several issues need to be addressed before such commercial systems can be deployed:

[0014] A safe system should be developed.

[0015] A cost effective system should be developed.

[0016] A system should be developed that can withstand the following hazards of a normal home environment, including contamination such as dust and fingerprints or liquid spills, vibration, beam blockage, non-professional installation and periodic dropping on the floor.

[0017] Currently allowed public exposure to transmitted laser power levels are not sufficient to provide a usable amount of power without using complex safety systems. For example, the United States Code of Federal Regulations Title 21, Volume 8, Revision 4, April 2014, Chapter I, Subchapter J, Part 1040, Section J1040.01, pertains to performance standards for light emitting products, including laser products. For wavelengths outside the visible range, there are Class I, Class III-b, and Class IV lasers (Class II, Ila, and Ilia lasers are between 400 nm and 710 nm, e.g. visible light lasers). Among lasers outside the visible range, Class 1 is considered safe for general public use, while Class III-b and IV are considered unsafe.

[0018] Reference is now made to Figure 2which is a graph showing the MPE (Maximum Permitted Exposure) for a pupil diameter of 7 mm for exposure times of 0.1 to 60 seconds for a class I laser according to the above cited "21 CFR § 8". From the above graph it can be seen that:

[0019] (i) the maximum permissible exposure level generally (but not always) increases with wavelength, and

[0020] (ii) even if the laser is turned off for several 0.1 seconds after a person enters the beam to meet the requirements specified in "21 CFR § 8", it is possible to transmit not more than 1.25 W of light at wavelengths greater than 2.5 μιη, while at shorter wavelengths the limit is orders of magnitude less.

[0021] Thus, without using certain kinds of safety systems, only a few milliwatts of laser power are allowed to be transmitted, even if fully converted back into electrical power, the power supplied is significantly less than that required to charge most portable electronic devices. A portable phone, depending on the model, requires for example 1 to 12 W while charging.

[0022] In order to transmit power above the MPE of a class I laser, a safety system is required. To the best of the applicant's knowledge, no safety system has been commercialized to transmit significant power levels within a residential environment accessible to untrained personnel.

[0023] It is difficult to build a robust safety system. It is well known in the prior art that fingerprints and dust scatter laser light, and transparent surfaces reflect or scatter laser light. If high power is to be delivered, then class IV (or class IIIb) lasers are required, which require a reliable safety system. For class IV lasers, even the irradiance scattered by the main beam is dangerous. According to the April 2014 revision of "21 CFR § 8", Chapter I, Section J, Part 1040, a laser emitting between 400 nm and 1400 nm with a beam radiation of more than 0.5 W is generally considered a class IV laser for exposure times exceeding 0.5 seconds, and even the irradiance scattered by such a laser can be dangerous. Such lasers are required to have a lockout key and warning labels similar to those shown in Figure 3 , where it is noted that the warning relates to "scattered irradiance", the user of the laser is generally required to wear safety goggles, and typically is a trained professional, all of which are very different from the acceptable conditions of use for a home-usable laser power transmission system for charging mobile electronic devices.

[0024] The prior art typically uses anti-reflective (AR) coatings on the surfaces to prevent such reflections, along with carefully arranged beam blocking structures to block such reflections, but reflections still occur. However, the AR coating schemes used in the prior art are prone to failure due to dust or spilled liquid deposited on their surfaces, or due to wear of the coating, for example due to improper cleaning procedures. Additionally, the beam blocking schemes typically severely limit the field of view of the system, and are bulky compared to the size of modern portable electronic devices.

[0025] Thus the prior art lacks reliable and "footprint small" mechanisms to prevent scattering and reflections of the power beam in undesired directions. Such scattering and reflections can be caused by transparent surfaces inadvertently placed between the transmitter and the receiver, and by the optical properties of the transparent surfaces that can be produced by a large variety of different transparent materials, or by liquid spills and fingerprints that can be deposited on the outer surfaces of the system, typically on the front face of the receiver.

[0026] A third problem with the proposed solutions in the prior art is that such safety systems generally require mechanisms to ensure that the power beam system and the safety system are well aligned, so that the two systems are aligned on the same axis, until the power beam is sufficiently divergent or sufficiently attenuated (or a combination of these factors with any other factors), so that the safety limits are no longer exceeded. This is extremely difficult to achieve for collimated IV or IIIb class laser beams, which typically expand very little with distance, and thus exceed the safety limits at very long distances.

[0027] One operational principle of the prior art for building such safety systems is to optically probe the transparent surfaces that can be located in the path of the beam. However, the transparent surfaces that can enter the path of the beam can be made of a large variety of different transparent materials, can be AR coated, or can be at an angle close to the Brewster angle, and thus are almost invisible to optical systems unless they absorb the beam. However, because the light absorption level of each material is different, and can even be negligible, and because optical systems built to rely on optical absorption are highly material specific, and because the number of available materials is extremely large, such systems are likely to be complex, bulky and expensive, and unless properly designed, are likely to be unreliable, especially when considering that they are intended to be critical safety systems. It is also problematic to rely on reflections to provide a detectable attenuation of the beam, because the surfaces can be coated with anti-reflective coatings or be at an angle close to the Brewster angle with respect to the beam, and thus the reflection can be minimal in the special locations of the surfaces.

[0028] There is therefore a need for a laser power transmission system with embedded safety features that overcomes at least some of the disadvantages of the systems and methods of the prior art.

[0029] The disclosures of each of the various publications mentioned in this section and in other sections of this specification are hereby incorporated by reference in their entirety. SUMMARY

[0030] Because many of the reflecting materials in home applications are plastics, the present invention attempts to provide a system for detecting the insertion of a presumably transparent plastic object into a beam of light used to power a remote device. This should be applicable even for plastic materials that are substantially transparent at some wavelengths. To accomplish this, a laser power delivery system is obtained that is well protected from inadvertent reflection due to the insertion of a presumably transparent plastic object into the beam.

[0031] It is not possible to measure the absorption / transmission spectrum of all transparent materials to determine their optical properties because there are too many materials, many of which do not have readily available absorption spectra in the literature that can be used for evaluation. A more theoretical systematic approach is therefore required.

[0032] Non-transparent or even partially non-transparent materials can be easily detected by measuring the attenuation of the beam when placed in the beam. However, some materials are transparent or nearly transparent, and such transparent materials are significantly more difficult to detect. There are two large groups of solid transparent materials, organic and inorganic. The number of inorganic transparent solid materials that are available to the general public is quite limited, consisting mainly of glasses, some common use semiconductor materials, quartz, and some naturally occurring minerals such as diamond, ruby, and calcite. Therefore, a detection system for reflections from inorganic transparent materials can be constructed that covers all possible cases.

[0033] On the other hand, the availability of different organic transparent materials to the general public is enormous, with new types of transparent materials being added to the list all the time. This is a significant problem because it is virtually impossible to optically characterize this group.

[0034] Polymers are a large group of transparent organic materials that are used as a sample group to help explain the way the present invention operates. Polymers are typically composed of long chains of monomers, where the backbone of such polymers is typically composed of carbon or silicon. Figures 4 to 9 The chemical structure of some commonly used transparent polymers is shown. Figure 4 The structure of a polymethyl methacrylate (PMMA) chain is shown. Figure 5 The structure of a polycarbonate is shown. Figure 6 The structure of a polystyrene is shown. Figure 7 Nylon 6,6 is shown. Figure 8 A polypropylene chain is shown. Figure 9 The structure of a polyethylene chain is shown.

[0035] It can be observed that the chemical structure of the shown samples polymers is very different and that the absorption spectrum of these polymers depends on many factors, including material density, traces of reactants and chain length. It is also observed that all the above transparent polymers have some chemical bonds in common, especially C-C and C-H bonds. This is especially true for commercially available polymers, which are almost all based on organic materials, which will be detected by the system of the present application, or semi-organic silicon based on polymers, such as polysiloxanes, polysilanes, polygermanes and poly stannanes, or polyphospahazenes, which will also be detected by the system of the present application.

[0036] In addition to this, the number of transparent materials available to the general public, which are not based on carbon chemistry systems, is quite limited and consists mainly of various glasses, most of which have readily available data on their transmission spectrum.

[0037] If the system is designed so that the laser excites the vibrating C-H bonds in the polymer, or possibly also the C-C bonds, then it is easy to detect when a polymer of this kind is located in the beam by monitoring the power drop caused by the polymer. This assumes that there is always an absorption of C-H or C-C bonds and that the wavelength is always calibrated to the laser wavelength. Rotational peaks can also be used for this purpose, but can be unreliable in polymers, so the vibrating C-H (or C-C) absorption is better suited for this purpose.

[0038] Reference is made to Figure 10 which shows a graph of typical absorption regions of different polymer bonds. It is observed that the C-H stretching vibration occurs in the region of 2900 to 3200 cm -1 nearby in almost all of the shown polymers. It can therefore be used as an absorption mechanism trigger for a security system, where the change in transmission power resulting from the absorption band is used. However, these absorption bands have two problems, which make them less useful for this purpose.

[0039] (i) The C-H vibration absorption line is typically very sharp, with an exact frequency that differs significantly from one polymer to another, so that the laser can excite one polymer but not another. Thus, unless the laser is precisely tuned to the specific C-H vibration line of the polymer, it will not be absorbed.

[0040] (ii) This C-H vibration peak is generally a medium absorption peak, which means that the beam attenuation due to a few mm thick section of material is 20 to 50% (i.e. allowing detection of even trace amounts of material in small containers), whereas medium (20 to 70% attenuation per cm of material) and strong (>70% attenuation per cm) absorption peaks are generally significantly easier to detect, which cannot be used to build a robust system.

[0041] Fingerprints are a common problem in commercial systems designed for consumer environments. In normal operation, the system should not simply fail when a fingerprint is deposited on it; instead, the system should stop transmission when there is a risk of exceeding a safety limit. To this end, the system should detect an obstruction of the beam, but should not stop transmission due to any fingerprint deposited on the receiver. If a strong or medium absorption peak is used, a fingerprint or some other contaminant should be deposited on the external optical surface of the receiver or transmitter that would significantly absorb the beam, causing the power transmission to fail. This is because fingerprints also contain organic compounds that absorb the beam, causing uncontrolled system failure. In order to allow the system to operate in an environment where organic material such as fingerprints can be deposited on the surface of its typical external optical components, a system needs to be constructed that successfully traverses a fingerprint with the laser beam, while a safety system detects a dangerous transparent object that can be inserted in the beam. If the safety system, on the other hand, utilizes a weak absorption band instead of a medium or strong absorption band, the system should continue to operate with a fingerprint, possibly shutting down based on an electronic decision rather than in an uncontrolled manner.

[0042] Turning to the absorption spectrum of 800 cm -1 to 1300 cm -1 The C-C absorption band is stretched, and the width of the band is such that a narrowband laser almost certainly misses a narrowband absorption peak in this region because its typical width is very small when the peak can lie in the range of 800 cm -1 to 1300 cm -1 Additional, as can be seen below in Figure 11 , the band disappears in some polymers, there is no visible absorption peak between 800 and 1300 cm -1 , and there can be some polymers in which the C-C bond does not exist and is replaced by an aromatic carbon-carbon bond or by a C=C bond and a C-O-C bond.

[0043] An additional problem arises from the absorption intensity of the C-C line. In symmetric compounds such as polyethylene, it can be almost undetectable, while in other compounds, its intensity can cause even a weak fingerprint on the surface of the receiver to render the system inoperable because a significant portion of the power can be absorbed by the fingerprint, causing the device to be unusable. In order to enable a system in which a fingerprint can be deposited on its optical surface to operate, a weak but not overly weak absorption line is needed that does not change significantly between different polymers and is found in most organic polymers, the laser is adjusted to the peak that should be used, along with a system that operates in the vicinity of this peak. As can be seen, this peak does not exist in commonly used polymers and in the absorption spectrum shown. Figure 10

[0044] ​According to one exemplary embodiment of the system described in this specification, there is provided a system for optically wireless transmission of power to a power receiving device, comprising:

[0045] (a) an optical resonator cavity having an end reflector and adapted to emit a light beam,

[0046] (b) a gain medium located inside the optical resonator cavity and having a first bandgap energy, the gain medium being thermally attached to a cooling system and configured to amplify light passing therethrough,

[0047] (c) a driver supplying power to the gain medium and controlling a small signal gain of the gain medium,

[0048] (d) a beam steering device configured to direct the light beam in at least one of a plurality of directions,

[0049] (e) a photovoltaic power converter configured to convert the light beam into electrical power having a voltage, the photovoltaic power converter having a second bandgap energy,

[0050] (f) a voltage converter adapted to convert the voltage of the electrical power produced by the photovoltaic power converter to a different voltage, the photovoltaic power converter comprising an inductor, an energy storage device and a switch,

[0051] (g) at least one surface associated with the photovoltaic power converter and optically arranged between the gain medium and the photovoltaic power converter,

[0052] (h) a detector configured to provide a signal indicative of the light beam impinging on the photovoltaic power converter, and

[0053] (i) a controller adapted to control at least one of the state of the beam steering device and the driver, the controller receiving a control input signal from at least the detector,

[0054] wherein:

[0055] (j) the at least one surface is such that it reflects a small fraction of the light impinging on it in a manner that is (i) diffuse, or (ii) such that the reflected light has a virtual focal point located away from the optical resonator cavity with respect to the surface, or (iii) such that the reflected light has a real focal point located at least 1 cm in the direction of the optical resonator cavity with respect to the surface,

[0056] (k) the controller is configured to respond to control input signals received by the detector by at least one of: (i) causing the driver to change a small signal gain of the gain medium, (ii) changing a radiant intensity of the beam, (iii) changing a power supplied by the driver, (iv) changing a scan speed of a beam steering device, (v) changing a scan position of a beam steering device, and (vi) recording a scan position that determines a position of the photovoltaic power converter,

[0057] (l) the gain medium is a semiconductor device or a solid host doped with Nd ions and includes a filter that attenuates radiation at at least one frequency having a wave number in the range of 8,300 cm -1 to 12,500 cm -1 ,

[0058] (m) the second bandgap energy is less than the first bandgap energy,

[0059] (n) the first bandgap energy is 0.8 eV to 1.1 eV,

[0060] (o) the closing series resistance of the switch is less than R

[0061]

[0062] wherein

[0063] R is measured in ohms,

[0064] E gain is the first bandgap energy measured in joules, and

[0065] P laser driver is the power supplied by the laser driver to the gain medium measured in watts, and

[0066] (p) the beam has a radiant intensity of at least 8 kW / m 2 / degree of sphericalness, and a frequency between a first harmonic of a C-H absorption at about 6940 cm -1 and a second harmonic of a C-H absorption at about 8130 cm -1 .

[0067] In any such system, the different voltage can be a voltage higher than a voltage generated by the photovoltaic converter. Further, the state of the beam steering device can be one or both of a pointing direction and a scan speed of the beam steering device.

[0068] Further, in any of the above systems, the radiant intensity of the beam can be at least 800 kW / m 2 / degree of sphericalness.

[0069] Another exemplary embodiment can involve any of the above systems, wherein

[0070] Each of the end reflectors of the resonant cavity is (i) a dielectric mirror, (ii) a Bragg mirror, (iii) a Fresnel reflector, or (iv) a mirror composed of alternating layers of dielectric or semiconductor materials with different refractive indices. Additionally, the gain medium can be a transparent solid host material doped with Nd ions or a semiconductor. In this case, the system can further include a filter for extracting radiation with a wave number greater than 8300 cm -1 -1. In the case where the gain medium is a semiconductor, it can advantageously be a quantum dot gain medium.

[0071] In other exemplary embodiments of the above systems, the cooling system can be at least one of a heat sink, a Peltier diode, and a liquid cooling plate. It can also be equipped with a fan. Additionally, the gain medium can be attached to the cooling system using a layer of solder having a thermal resistance of less than 200° Kelvin / Watt. In any case, the cooling system can be such that the thermal resistance between the gain medium and the surrounding air is less than 200° Kelvin / Watt.

[0072] In alternative embodiments of any of the above systems, the opto-electric power converter can be a photovoltaic cell. In this case, the photovoltaic cell can be a III-V device. In any case, the series resistance of the opto-electric power converter can be less than 1 Ohm.

[0073] According to other embodiments of the above systems, the series resistance of the inductor measured in Ohms should be less than the square of the first bandgap energy measured in Joules divided by 2*10 -40 times the driver power measured in Watts.

[0074] In other embodiments, the energy storage device can be a capacitor or a rechargeable battery.

[0075] Additionally, any of the above systems can further include a back reflector. Thus, the gain medium can be pumped electrically or optically by the driver. Moreover, the second bandgap energy can be greater than 50% of the first bandgap energy.

[0076] Other embodiments implement a method of transmitting power from a transmitter to a receiver, comprising:

[0077] (a) converting a first electrical power into electromagnetic waves having a frequency between a first harmonic of a C-H absorption located at about 6940 cm -1 -1 and a second harmonic of a C-H absorption located at about 8130 cm -1 -1, the electromagnetic waves having at least 8 kW / m2 radiant intensity of the spherical degree, by using an optical resonator having an end reflector and a gain medium connected to a laser driver receiving a first electric power, the gain medium having a first bandgap energy of 0.8 eV to 1.1 eV, being located inside the optical resonator, being thermally attached to a cooling system, and being configured to amplify electromagnetic waves passing therethrough,

[0078] (b) directing the electromagnetic waves in at least one of a plurality of directions using a beam steering device controlled by the control unit,

[0079] (c) detecting the beam projected on the target object having a partially transparent surface associated therewith, whereby the control unit can use the information about the projection to effect at least one of the following: (i) causing a small signal gain change of the gain medium, (ii) causing a change in the radiant intensity of the electromagnetic beam, (iii) causing a change in the first electric power, (iv) changing a scanning speed of the beam steering device, (v) changing a scanning position of the beam steering device, and (vi) recording the scanning position determining the position of the target object,

[0080] (d) converting the electromagnetic waves into a second electric power having a voltage by using a photovoltaic power converter having a second bandgap energy smaller than the first bandgap energy,

[0081] (e) converting the voltage into a different voltage using a voltage converter comprising an inductor, an energy storage device, and a switch, the closing of the switch having a series resistance smaller than R

[0082]

[0083] wherein

[0084] R is measured in Ohm,

[0085] E gain is the first bandgap energy measured in Joule,

[0086] P laser_driver is the first electric power measured in Watt,

[0087] wherein

[0088] (f) the surface is designed such that it reflects a small portion of the electromagnetic waves incident thereon in a way that (i) in a diffuse manner, or (ii) such that the reflected light rays have a virtual focal point located away from the optical resonator with respect to the surface, or (iii) such that the reflected light rays have a real focal point located at least 1 cm in the direction of the optical resonator with respect to the surface, and

[0089] (g) the gain medium is a semiconductor device or a solid matrix doped with Nd ions, comprising a wave number of 8,300 cm-1 at least one frequency in the range of 12,500 cm -1 a filter that attenuates irradiance at at least one frequency in the range of 12,500 cm

[0090] In the method, the switch is capable of switching operation at a frequency determined by

[0091]

[0092]

[0093] wherein

[0094] f is the switching frequency measured in Hz,

[0095] E gain is the bandgap of the gain medium measured in Joules,

[0096] V output is the output voltage from the voltage transformer measured in Volts,

[0097] P laser driver is the power pumped to the gain medium by the laser driver measured in Watts.

[0098] Additionally, the beam projected on the target can be detected by detecting the illumination back-reflected by the target in the transmitter, or by detecting the illumination of the target using a receiver sensor.

[0099] Further, in any of the above methods, the second bandgap energy can be greater than 50% of the first bandgap energy. BRIEF DESCRIPTION OF DRAWINGS

[0100] The present application can be more fully understood and appreciated by reading the following detailed description together with the accompanying drawings, in which:

[0101] Figure 1 Energy densities are shown for various different battery chemistries;

[0102] Figure 2 Maximum permissible exposure values for lasers at different exposure times are shown, according to 21 Code of Federal Regulations Part 8, Section I, Subpart J, Section 1040, Revision of April 2014;

[0103] Figure 3 Examples of warning labels for Class IV laser products are shown;

[0104] Figures 4 to 9 Examples of chemical compositions for various different commonly used transparent polymers are shown;

[0105] Figure 4Poly(methyl methacrylate) (PMMA) chain is shown;

[0106] Figure 5 Polycarbonate structure is shown;

[0107] Figure 6 Polystyrene structure is shown;

[0108] Figure 7 Nylon 6,6 structure is shown;

[0109] Figure 8 Polypropylene chain structure is shown;

[0110] Figure 9 Polyethylene chain structure is shown;

[0111] Figure 10 IR absorption bands of some common organic chemical bonds are shown;

[0112] Figure 11 IR absorption spectrum of polyethylene is shown;

[0113] Figure 12 Harmonic absorption bands of some common organic chemical bonds are shown;

[0114] Figures 13a and 13b show different electronic wiring ways to convert the output voltage of a photovoltaic cell into different voltages;

[0115] Figure 14 Reflected power per square meter as a function of numerical aperture when a beam with a radiant intensity of 8 kW / m2 / sr is focused on it by a mirror; 2

[0116] Figures 15A to 15C Schematic view of an exemplary device according to the present application for avoiding unsafe reflections from the front face of the receiver by the illumination of the transmitter of the present application is shown;

[0117] Figure 16 Schematic view showing a more detailed description of the complete optical wireless power supply system of the present application is shown;

[0118] Figure 17 Graph showing the change of the power transmission of the system of Figure 16 as a function of the tilt angle of the beam steering mirror; and

[0119] Figure 18 Schematic view of the cooling system of the gain medium of the system of Figure 16 is shown. DETAILED DESCRIPTION

[0120] ​In view of the above considerations, one exemplary embodiment of the present optical wireless power supply system can be a system tuned to operate between the first harmonic of the C-H absorption at 6940 cm -1 and the second harmonic of the C-H absorption at 8130 cm -1 The harmonic spectral bands are less known spectral bands, containing significantly less chemical information, are caused by essentially forbidden quantum mechanical transitions, and are only allowed due to complex mechanisms. Thus, they provide a wide weak absorption band, which is exactly preferred for the present application, but is significantly less found for analytical chemistry. The wide nature of the band allows the probing of various different polymer compositions, while the weak absorption allows the system to continue operating even in the vicinity of organic dirt and fingerprints. This makes these lines significantly less used for typical applications of absorption measurements, but ideal for the purpose of the present application. Another advantage of these lines is that there are no ordinary absorption lines directly at the same frequencies, so changing the chemical composition of the material does not strongly change the measurement results. In the graph of Fig. 1 many such harmonic spectral bands are shown. Figure 12

[0121] Electro-optical components operating in the spectral band are rare and difficult to obtain, possibly because diode lasers and diode-pumped solid state (DPSS) lasers are significantly less efficient at these frequencies, and currently only lower power lasers are commercially available. Since lasers with the desired parameters at the preferred frequencies are currently not available, a laser suitable for this use must be designed from scratch. The resonator and the gain medium must be designed. A laser with the selected frequency and radiance value must be constructed, which is sufficient to facilitate a roughly collimated or almost collimated beam. To achieve a well collimated beam, a radiance of at least 8 kW / m 2 / steradian is required, and for higher power systems for efficient power transmission even 800 kW / m 2 / steradian can be required. In the case of small systems operating at long distances, significantly higher radiance (up to 10 GW / m 2 / steradian) can be designed in the future according to similar principles. The receiver used with a radiance less than the level described would need to be excessively large, making the system very bulky.

[0122] ​Different mirror arrangements have been used for the resonator, metallic mirrors made of gold, silver or aluminum with particularly good quality. It was found that they significantly reduce the efficiency of the laser light emission. Significantly better results are achieved with dielectric mirrors. Alternatively, one advantage of a Fresnel mirror is its low cost. Other mirrors that can be used are Bragg mirrors (which can be dielectric). The mirrors need to be positioned in such a way that a stable or almost stable resonator is formed, or a resonator is formed in which the photons are confined in space by a potential well inside the laser (for example in a fiber laser or a diode laser) and the gain medium should be located in the resonator between the mirrors in a position that allows the gain medium to amplify the beam that is resonating inside the resonator, so that it has a radiation brightness of at least 8 kW / m2 / sr 2 / degree of spherical aberration.

[0123] If the gain medium is capable of emitting laser light at more than one wavelength, the dielectric mirrors can be selected to confine the wavelengths to a specific value. Alternatively, filters can be used to fix the frequency of the laser light emission.

[0124] In particular, it is more advantageous if the mirrors have a high reflectivity for at least one wavelength between the first harmonic of the C-H absorption at 6940 cm -1 -1 and the second harmonic of the C-H absorption at 8130 cm -1 -1.

[0125] Three different approaches can be taken for the gain medium.

[0126] 1. DPSS design

[0127] In the DPSS design, the gain medium can be a Nd-doped YAG crystal, although YVO4 crystals, GGG crystals and glasses are also clean options. Neodymium is best suited for operation between the first harmonic of the C-H band and the second harmonic of the C-H band, because Nd has a transition near ~7450 cm -1 -1. The Nd ions need to be excited by absorption of irradiation typically from an 808 nm laser diode, although other wavelengths can be used. Nd-based gain media tend to emit laser light at significantly higher frequencies, unless a filter is added to the resonator to block the transition near 9400 cm -1 -1, or unless otherwise unwanted irradiation from the resonator is induced. When such a filter is added, laser light emission starts at 7440 to 7480 cm -1 -1. The action of such a filter can be achieved using a prism or a grating instead of a filter, or by appropriate color design of the laser resonator.

[0128] 2. Semiconductor laser

[0129] As an alternative, a semiconductor-based design can be suggested. The wavelength of a semiconductor laser can be adjusted by changing the bandgap of the semiconductor used to emit the laser light. Semiconductors, especially III-V semiconductors and even more especially quantum dot semiconductors with a bandgap of the order of 1 eV, emit light at a desired frequency of 6900 cm -1 to 8200 cm -1 Particularly good results are obtained with a bandgap of 0.8 eV to 1.1 eV, which is at least partially absorbed by substantially all commonly used polymers.

[0130] 3. Various alternative designs can also be used in the system described in the present application, such as Nd-doped fiber lasers, which can contain Bragg mirrors and / or fiber ring mirrors. Alternatively, Raman-shifted fiber lasers can also be used.

[0131] During operation, the gain medium heats up and should be cooled to prevent wavelength drift and efficiency loss. If the gain medium is properly cooled, the pump power or current can be increased until a beam with a radiant intensity of at least 8 kW / m 2 / degree of sphericalness at a frequency of 6900 cm -1 to 8200 cm -1 Such a beam can be almost collimated and is attenuated by most organic materials, including polymers, that allow detection. However, it is not strongly absorbed by contaminants such as fingerprints.

[0132] Laser gain media are typically configured to operate at temperatures below 150 degrees Celsius. If their temperature exceeds a certain level, typically about 250 degrees Celsius, a number of problems can occur.

[0133] First, the light emission efficiency can decrease significantly due to the population of lower-level excited states, especially in level 3 and 4 lasers, and due to the thermal recombination of charge carriers in the semiconductor.

[0134] Second, if such a thermal attachment method is used, the soldering of the gain medium can be damaged.

[0135] Third, thermal aberrations can occur, which can lead to beam loss.

[0136] Fourth, the thermal expansion of the laser gain medium can differ from that of its surroundings, which can lead to mechanical stress or even warping and breaking of the gain medium.

[0137] For these reasons, the gain medium, especially, must be attached thermally to the cooling system. The gain medium is typically 1 mm 2 to 40 mm 2The surface of the cooling system emits 0.1 to 100 W of heat. In order to keep the temperature of the gain medium at less than 150 degrees, the cooling system of the gain medium needs to have a thermal resistance of less than 200 Kelvin per Watt, while for systems transmitting higher powers, typically due to more than 10 W of electrical power input, the thermal resistance should be significantly lower, in many cases the thermal resistance needs to be lower than 0.05 Kelvin / Watt.

[0138] Typically a third material, such as solder or adhesive, is used, whose expansion coefficient must be adapted both to the expansion coefficient of the gain medium itself and to the expansion coefficient of the front face of the cooling system, so as to attach the surface of the cooling system to the gain medium.

[0139] The cooling system can typically be a passive heat sink, a heat sink with a fan, a Peltier element connected to a heat sink with or without a fan, or a liquid cooled cooling system. Alternatively, a stand-alone liquid circulating cooling system can be used, either with an active circulation based on a circulating pump, or with a passive circulation based on a heat pipe.

[0140] If the cooling system consists of a heat sink with a fan, its thermal resistance should be less than 0.1 ° Kelvin per Watt.

[0141] If the cooling system is a passive heat sink, its thermal resistance should be less than 0.3 ° Kelvin per Watt.

[0142] If the cooling system is a Peltier element, it is necessary to generate a temperature difference ΔΤ of at least 5 degrees.

[0143] If the cooling system is an active liquid cooled cooling system, it should be able to cover the entire thermal resistance span described herein.

[0144] In systems designed for low cost and quiet operation, passive heat sinks are preferred, while for high power systems, liquid cooled systems are preferred. Heat sinks with fans or fluid pumps are used for systems typically with more than 1 W electrical output and transmitters with small volume, for example less than about 1 liter.

[0145] The gain medium is typically driven by a driver, which supplies power to it, which can be provided as electrical power as is the case for some semiconductor gain media, or optically as is the case for other semiconductor gain media or DPSS systems, or chemically or other forms of energy. The amount of power supplied by the driver determines the small signal gain achieved, which determines the operating conditions and emission of the laser, while the saturation gain of the gain medium is typically a function of the material chosen for the gain medium, although not always in a simple linear fashion, and ultimately a function of the radiant intensity emitted by the laser. Such a laser driver can have two or more operating states, one for power delivery and the other for other functions of the system, such as target acquisition, setup and information transfer. It is important that the laser driver stably emit (with respect to power and beam parameters) in both operating conditions, although stable operation during power delivery is more important.

[0146] To reconvert the beam into electrical power, to deliver the available power, a photovoltaic power converter, typically a photovoltaic cell, should be used. As with the laser, a suitable photovoltaic cell tailored to the frequency of the beam used is not commercially available as an off-the-shelf component, but needs to be custom built. The bandgap of the photovoltaic semiconductor should be slightly smaller than the bandgap of the gain medium used, so that the beam frequency is efficiently absorbed by the semiconductor. If not, the conversion efficiency will be very poor. On the other hand, if the bandgap used is too small, an inefficient system is obtained. The wires on the photovoltaic cell also need to be tailored to the radiant intensity of the beam used - the higher the radiant intensity, the thicker the wires needed.

[0147] Because the bandgap of the laser gain medium should be in the range of 0.8 to 1.1 eV, and the bandgap of the photovoltaic cell used must be lower, and because a single-junction photovoltaic cell typically produces a voltage of about 60 to 80% of the bandgap energy divided by the electronic charge, a single-junction cell tailored to the frequency of the laser obtains a very low voltage, typically 0.3 to 0.8 V, and a typically high current, assuming an output power of a few watts, as required for a practical system. The wires on the semiconductor need to be thick enough to carry the current produced without causing significant losses (e.g. > 5%). The series resistance of the wires typically needs to be less than 1 ohm, or even better, less than 0.1 ohm, and the heat generated by the photovoltaic cell should be efficiently extracted, because its efficiency typically decreases with temperature.

[0148] This combination of low voltage together with high power cannot be easily converted to the higher voltage required to charge portable devices, typically 3.3 or 5V. In addition, some systems, such as communication systems, can require voltages such as -48V, 12V or 3.8V. The systems require a stable voltage to be supplied and at a level higher than the output voltage expected from the photovoltaic cells. A typical method to raise the voltage of photovoltaic cells is to connect them in series, as described in US Patent No. 3,370,986 to M.F. Amsterdam et al. "Photovoltaic Series Array comprising P / N and N / P Cells", which shows a typical wiring method to obtain higher voltage, using almost the same amount of semiconductor and without using extra components, and is therefore the typically chosen solution.

[0149] However this solution is not suitable for systems such as the one described in this application, where lasers with radiant intensity up to 8kW / m 2 / steradian are used, especially because such lasers typically do not have a beam with a uniform shape. In addition, their beam shape can be variable in time and the pointing accuracy can be less than the value desired for optimum. In this case, it is practically impossible to design a compact and efficient system that illuminates all the cells uniformly. If the series connected photovoltaic cells are not illuminated uniformly, they cannot generate equal currents. In this case, the voltage is indeed raised to the desired level, but the current drops to the value generated by the cell that is usually the least illuminated, the cell that generates the least current. In this case, the efficiency is very poor. Therefore, an improved alternative method is needed to raise the voltage.

[0150] A method to raise the voltage of a single cell can be by charging capacitors in parallel and then discharging them in series. This method gives good results for low currents, but when the current is raised above a certain level, the switching time becomes the main factor affecting the efficiency, which decreases as the switching time increases.

[0151] If the energy is converted to AC using fast low resistance switching mechanisms, the AC current can be amplified using a coupled inductor and then reconverted to DC. The raised voltage AC can be converted to DC using a diode bridge and energy storage devices such as capacitors or batteries. Such a system is advantageous when the voltage needs to be raised more than twenty times the photovoltaic cell voltage. Another advantage of such a system is that the lasers can be switched by the transmitter, thus saving the receiver cost and complexity. Such a system is not advantageous when the voltage needs to be raised less than ten times or when size and volume constraints are critical in this application.

[0152] Reference is now made to Figure 13Awhich shows a highly efficient and simple voltage conversion method. In Figure 13A In the wiring scheme of Fig. 2, a simple inductor can be used together with a low resistance switching mechanism and an energy storage device to step up the voltage of the photovoltaic cell. In Figure 13A In Fig. 2, the left block is the photovoltaic cell, the switch S is a low resistance switch such as a MOSFET, JFET, BJT, IGBT or pHEMT, the inductor L is connected to the output of the photovoltaic cell, and the capacitor C acts as an energy storage device.

[0153] The following description assumes for simplicity the use of components with zero resistance. Taking into account the resistance losses would complicate the calculations and is explained later in this description. The switching mechanism cycles the inductor between two basic operating phases: the charging phase and the discharging phase. In the charging phase, the inductor is connected in parallel to the photovoltaic cell by closing the switch S. In this phase, the inductor is charged with the energy converted by the photovoltaic cell. The amount of inductor energy increase is given by:

[0154] ΔE L_CH = Vpv * I L * T CH ,

[0155] where

[0156] Vpv is the output voltage of the photovoltaic cell,

[0157] I L is the average inductor current, and

[0158] T CH is the duration of the charging phase.

[0159] In the discharging phase, the inductor is connected between the photovoltaic cell and the load by opening the switch S. In this phase, the energy transferred by the inductor to the output energy storage device is given by the amount of inductor energy decrease:

[0160] ΔE C = Vo * I L * T DIS ,

[0161] where

[0162] Vo is the voltage of the energy storage device, which is typically very close to the desired output voltage of the device, and thus can be approximated as the output voltage of the system,

[0163] I L is the average inductor current, and

[0164] T DIS is the duration of the discharging phase.

[0165] The energy transferred by the photovoltaic cell to the inductor in this phase is given by

[0166] ΔE L_DIS = Vpv * I L * T DIS .

[0167] The change in inductor energy in this phase is the difference between the input and output energy:

[0168] ΔE L_DIS = Vpv * I L * T DIS - Vo * I L * T DIS .

[0169] In steady state operation, the inductor energy returns to the same value at the end of the cycle as it was at the beginning of the cycle, obtaining

[0170] ΔE L_CH = - ΔE L_DIS ,

[0171] Substituting, we obtain:

[0172] Vo = Vpv * (1 + T CH / T DIS ).

[0173] Thus the voltage at the energy storage device is determined by the photovoltaic cell voltage and the ratio of the durations of the charge and discharge phases.

[0174] However, in the system of the present invention, the parasitic characteristics of the components and other aspects can significantly affect the conversion operation and efficiency, and care should be taken to select and use the right components to allow the system to operate effectively. These elements are now considered one by one:

[0175] Inductor

[0176] 1. The inductance of an inductor is defined as the rate of change of inductor current due to an applied voltage, given by dI / dt = V / L, where dI / dt is the rate of change of current, V is the voltage applied across the inductor, and L is the inductance. In the context of the present system, V is determined by the gain medium in the transmitter. The choice of different gain media results in a change in the photon energy, which therefore requires a change in the photovoltaic bandgap, and hence a change in the photovoltaic voltage. This in turn requires the selection of a different inductor and / or switching frequency. The switching rate must be fast enough to allow the inductor current to respond to changes in the power input by the transmitter through the photovoltaic power converter, and slow enough to avoid large current ripple, which contributes to power loss, input voltage ripple, and output voltage ripple. The optimum value of the inductor should produce a ripple current between 20% and 40% of the maximum expected input current, but the system can operate between 10% and 60%. A precise analysis of the circuit parameters shows that, in order to achieve this, the inductor must have a value L measured in henries within the following limits:

[0177]

[0178]

[0179] where

[0180] f is the switching frequency measured in Hz,

[0181] E gain is the bandgap of the gain medium measured in joules,

[0182] V output is the output voltage from the voltage converter measured in volts, and

[0183] P laser_driver is the power pumped through the laser driver to the gain medium measured in watts.

[0184] In order to successfully integrate an inductor into a mobile client, the inductance should typically be less than 10 mH, since an inductor suitable for the current required to charge by a mobile client and having a volume limit suitable for portable applications is typically far below this value. An inductor with too small an inductance, for example 10 nH, also requires a switching frequency which is so high that it severely limits the availability of other components in the system, for example switches, and the switching losses caused by such a high frequency can be higher than the amount of power delivered by the photovoltaic cell.

[0185] 2. The series resistance R of the inductor parasitic should be as low as possible to minimise conduction power losses: a value is typically chosen which achieves less than 10% efficiency degradation: the series resistance of the inductor measured in ohms should be less than

[0186]

[0187] wherein

[0188] E gain is the bandgap of the gain medium measured in Joules,

[0189] P laser_driver is the power in Watts pumped through the laser driver to the gain medium.

[0190] 3. In a typical system, the inductor has a series resistance less than 10 Ω. The saturation current of the inductor is usually chosen to be higher than the expected peak inductor current, given by:

[0191] I SAT >I PEAK = Im+ Vpv*(l-Vpv / Vo) / (2*L*f).

[0192] In order to extract more than 10 mW of power from a single junction photovoltaic cell, the saturation current must be higher than 10 mW / 0.8v = 12.5 mA.

[0193] 4. In order to operate reliably, the inductor should be rated at a current higher than the expected maximum input current. In order to extract more than 10 mW of power from a single junction photovoltaic cell, the inductor current rating must be higher than 10 mW / 0.8v = 12.5 mA.

[0194] Switching mechanism

[0195] 1. The switching mechanism is usually made of two or more devices. The first device, the main switch, is turned on to put the inductor into the charging phase. The second device can be a diode (as shown in Figure 13A ) or a switch, whose function is to connect the inductor to the load or output energy storage device during the discharging phase and to disconnect it from the load during the charging phase.

[0196] 2. The switching mechanism should have a low switching node capacitance to minimize switching losses:

[0197] P SW2 = 0.5*Csw*Vo 2 *f.

[0198] In order to extract more than 50% of the laser power, the switching node capacitance should be less than

[0199]

[0200] 3. In a typical system, the switching node capacitance is less than 100 nF and greater than 10 pF.

[0201] 4. The main switch in the switch node that connects the inductor to ground or the opto-power converter to the inductor should have a series resistance less than

[0202]

[0203] In a typical system, the switch series resistance is less than 10 Ω.

[0204] Energy storage device

[0205] 1. The energy storage device can be a capacitor or a battery or both.

[0206] 2. The energy storage device is required to maintain the output voltage during the charging phase when the inductor is disconnected from the output. The capacitance of the energy storage device is chosen based on the switching frequency, the laser power and the desired output voltage ripple:

[0207] C OUT > P LASER DRIVER / (f * Vo * ΔVo)

[0208] where ΔVo is the desired output voltage ripple.

[0209] 3. The energy storage device can also supply power to the load during the temporary interruption of the optical path. In order to supply power uninterrupted, the energy storage device should be able to store at least the amount of energy equal to the minimum operating output power (P OUT_MIN ) times the interruption time interval (T INT ):

[0210] E OUT_MIN ≥ P OUT_MIN * T INT .

[0211] If a capacitor is used as the energy storage device, the capacitance should be greater than:

[0212] C OUT ≥ 2 * E OUT / V OUT 2 .

[0213] In order to operate uninterrupted with a minimum operating output power of greater than 10 mW and an interruption time interval of greater than 100 ms, the stored energy must be greater than 1 mJ and the capacitance greater than 80 μF (assuming V OUT = 5 V).

[0214] In some cases, the capacitor can be used as an energy storage device for the user application. In this case, the user application can be designed without any secondary energy storage device (typically a battery installed in the mobile device) and the energy storage device of the system presently described must store enough energy to supply the power needs of the user device until the next charging event. In this case, a supercapacitor with a capacitance of at least 0.5 F and even more than 10 F can be used. In other cases where the power needs of the user device are low, or when it has an independent energy storage device such as a battery installed inside the device, or if the device does not need to run without supplied power, the capacitor used is typically much more than 1 F. If a rechargeable battery is used as an energy storage device, similar to the logic described above for the capacitor, if the battery is used only as a device to regulate the voltage, but not as a device to keep supplying power to the user device between charging events, the energy capacity of the battery can advantageously be up to 100 times the energy supplied in 100 cycles of the switch (typically less than 0.1 Wh), a level determined by the volume budget and cost effectiveness of the battery. On the other hand, if the battery is also used to provide power to the user device between charging events, its capacity should be at least large enough to store the energy required by the user device between charging events, typically more than 0.1 Wh in the case of a portable phone. The battery also has a volume limit depending on the product to which it is to be applied. Thus, a product battery with a volume V, if introduced externally to the device, is typically limited to a volume of the device of up to a few times, i.e. 3V. As an example of this rule of thumb, a battery used to provide power for a portable phone with a volume of 100 cc is typically limited to a volume of less than 300 cc. Due to the above-mentioned limits, such a battery typically has a capacity of less than 300 Wh.

[0215] Figure 13A The circuit in Figure 13B shows a different design that can achieve similar performance characteristics. Figure 13B The role, limitations and expected values of the components of Figure 13A are the same as listed for the circuit in The main difference is that the positive and negative terminals of the output voltage are reversed.

[0216] In some applications, the energy storage device can preferably be located inside the device that is to use the received power. In other applications, particularly those that are expected to run for short periods and do not require a regulated voltage, the energy storage device can even be eliminated.

[0217] The regulation point

[0218] The power output of a photovoltaic cell depends on the input optical power and the load applied to it. The optimum load condition is obtained by the photovoltaic cell for maximum output power, so the control mechanism of the voltage converter must adjust the load point. The control mechanism can be designed to maintain a constant voltage between the cell terminals, which is known to be the maximum power operating point (MPP) for most conditions, or it can track the maximum power operating point by measuring the cell output power and finding the optimum cell voltage at any operating condition. The first approach is simpler; the second approach is more power efficient.

[0219] The generated laser beam needs to be directed towards the receiver. In order to direct the beam towards the receiver, a beam steering device should be used. Some beam steering subsystems that can be used include moving mirrors, moving lenses, electro-optic modulators, magneto-optic modulators, a set of engines moving the entire transmitter system in one or more directions, or any other suitable beam steering device.

[0220] The beam steering device should be controlled by a controller, most conveniently the same controller used to control the laser driver.

[0221] The beam steering device is configured to direct a beam of >8 kW / m 2 / sr of spherical content in any of a plurality of directions.

[0222] The damage threshold of the beam steering device needs to be able to withstand the radiance of the beam.

[0223] For example, if a focusing mechanism with a numerical aperture of 0.5 is used to focus the beam on a mirror, the mirror needs to withstand a power density of at least 6.7 kW / m 2 if the beam has a spherical content of 8 kW / m 2 . If a beam with a higher radiance is used, the mirror should be chosen so that it has a correspondingly higher damage threshold.

[0224] Figure 14 The power reflected per square meter by a mirror as a function of the numerical aperture when a beam of 8 kW / m 2 / sr is focused on it by the mirror is shown.

[0225] If a beam with a higher radiance is used, the power reflected by the mirror increases correspondingly in a linear fashion.

[0226] Since the beam can be far from uniform, "hot spots" can be created that sometimes have 10x the irradiance compared to the average of the beam.

[0227] Therefore, the mirror should have a damage threshold of at least up to and preferably at least 10X the irradiance of the beam, as Figure 14The actual beam irradiance and numerical aperture of the focusing mechanism on the mirror are scaled up by the ratio.

[0228] The receiver typically has an optical front face, located near the photovoltaic cell and between the photovoltaic cell and the transmitter, through which the beam enters the receiver, and a typically delicate structure that protects the photovoltaic cell from scratches, in many cases to match the external design of the device in which the power receiver is integrated. The front face can have a coating that protects it from scratches, such as Corning Gorilla Glass® or similar can be treated to make it more scratch resistant. It can also be treated to reduce the level of contaminants such as fingerprints and dust that can be left on it, or to reduce their optical effect, or it can be coated with an anti-reflective coating to reduce the level of light reflected by it. The front face of the photovoltaic cell can also be coated. In some cases, the front face is part of the photovoltaic cell structure itself or is coated on the photovoltaic cell.

[0229] In some cases, however, by choosing an anti-reflective coating that is very low reflecting, the amount of reflection by the surface can be reduced below a safety threshold, a liquid or a fingerprint contamination or covering that should be spilled on it, such an anti-reflective coating is ineffective in reducing the amount of reflection, and typically 3 to 4% of the incident light is reflected in uncontrolled directions. If such reflections are reflected in a diverging manner, their power density drops rapidly to safe levels. However, if the reflections should be focused, the power density can increase to unsafe levels. Therefore, it is important that the ROC (radius of curvature) of such a surface at any point on it should not be smaller than a predetermined value. In general, the reflection from a surface is intentionally only a small fraction of the incident light, thereby reducing the risk of any significant beam reflection, regardless of the nature or shape of the surface curvature. The level of reflected light can be variable, since if a layer of foreign contaminant material on the surface creates an increased reflectivity, it can even increase the ~4% reflection from an untreated glass surface. However, it is expected that the reflection will not exceed 20%, and generally will be significantly smaller than the 4% of untreated glass, for example in the case of AR coated glass, where the reflectivity is typically 0.1% or even less. Therefore, the surface described in this specification and thus claimed has the property of reflecting a small fraction of the incident light, this specification is used to mean less than 20% of the incident light, typically less than 4% of untreated glass.

[0230] Reference is now made to Figures 15A to 15C which schematically illustrates a method of avoiding the above unsafe reflections, even for a small fraction of the incident light that can be reflected by the surface. Figure 15A is shown to be the case where the surface is a concave surface, Figure 15B is shown to be the case where the surface is a convex surface, Figure 15CThe surface is shown to be a diffusive surface. In Figure 15A the incident beam 110, having a radiance of at least 8 kW / m 2 / solid angle, is directed towards the photovoltaic cell 112, through the front face 111, which can be the front face of the photovoltaic cell. The front face 111 reflects a portion of the beam 110, creating a focused beam 113, having a focal point 114 at a certain distance from the surface. To ensure that the focal point 114 does not present any risk for the eye or the skin or other objects, the radius of curvature (ROC) of the surface 111 must be such that the beam is focused with a low numerical aperture, as shown in Figure 15A , or such that it is defocused, as shown in Figure 15B , or such that it is diffused, as shown in Figure 15C . To achieve these limitations, if the surface is concave in shape towards the photovoltaic cell, as shown in Figure 15A , its ROC must be greater than 1 cm, and if a system with greater power is used, typically more than 0.5 W of light, it should be greater than 5 cm. Alternatively, the surface ROC can be negative, as shown in Figure 15B , but the ROC cannot be in the range 0 to 1 cm. These limitations ensure that the reflected beam has a virtual focal point, i.e. associated with a diverging reflected beam, or a focal point at least 1 cm in front of the surface, thus significantly reducing the risk created by focusing. The surface can also have many regions with a smaller curvature, creating a diffusive surface, as shown in Figure 15C , which significantly helps to reduce the risk of dangerous focal points. In this case, the radius of curvature of each subsection of the surface can be less than 1 cm, not creating a focal point. Furthermore, if the surface is divided into blocks, each block can have a smaller curvature.

[0231] For safe operation, the system also needs to be able to direct the power beam to the photovoltaic cell, to be blocked by it, and not to certain unsafe areas. To achieve this, detectors should be positioned to provide an indication of the beam projection on the receiver. Such detectors should typically be located in the receiver, but arrangements of such detectors in the sender are also possible, in which case the detectors should respond to phenomena resulting from the beam projection on the receiver. Such sender-associated systems can include image acquisition and processing of optical information received by the receiver, for example reflections of the beam from a barcode printed on the receiver, so that the sender can detect the illumination pattern of the barcode. Reflections from one or more retro-reflectors or arrays or patterns thereof can be positioned on the receiver, and such reflections can be detected in the sender by image processing, by measuring the retro-reflections, or by measuring the coherence effects of the reflections. The detectors can be current or voltage sensors located in the receiver, photodiodes in the receiver or in the sender, or imaging devices that can be in the sender or in the receiver. Retro-reflectors near the photovoltaic cell can also be used, together with additional detectors in the sender, to detect the light reflected by the retro-reflectors.

[0232] The detectors send signals to the system controller accordingly when they detect a beam projected on the photovoltaic cell. If the detectors are in the receiver, a communication channel can be used to send the signals wirelessly, which can be RF, IR, visible light, UV, modulated beam, TCP / IP or sound. The system controller is usually located in the sender, but can also be located in a main control unit, which can even be in a computer network from the sender. Upon receiving the signals, the controller responds by implementing at least one of the following:

[0233] (a) changing the state of the laser driver,

[0234] (b) changing the operational properties of the beam steering device, for example its direction of directing the beam, or the speed of changing the direction.

[0235] Reference is now made to Figure 16 which is a schematic illustration showing a detailed description of the complete system. The system includes a sender 21 and a receiver 22. In general, the sender and the receiver are far from each other, but are shown close to each other in Figure 16 for convenience. The beam 15 delivers power from the sender 21 to the receiver 22.

[0236] On the receiver 22, the front face 7 reflects a small portion of the incoming beam 15 as a reflected beam 16, while diffusing it, or creating a virtual focus behind the front face 7, or a real focus at least 1 cm in front of the surface 7. After transmission through the at least partially transparent surface 7, the beam 15 impinges on the opto-electric power converter 1.

[0237] The opto-electric power converter 1 can be contained in an outer package, which can have a front window, which can be the surface 7 or a separate window. It can also be coated to have an outer surface suitable for playing the role of an interface with air, either an adhesive or glass surrounding it. In a typical arrangement, the opto-electric power converter 1 can be a junction of semiconductor layers, typically with wires deposited on it. In many embodiments, the surface 7 is the outer surface of one of these semiconductor layers or is it.

[0238] The signaling probe 8 indicates that the beam 15 impinges on the photovoltaic cell 1 and transmits this information to the controller 13, which in this exemplary system is located in the sender 21. A control signal is transmitted through the connection 23 to the probe 24 on the sender.

[0239] The electric power converter 1 has a band gap E8 and typically obtains a voltage of 0.35 to 1.1 V, although higher voltages can be obtained using multi-junction photovoltaic cells. The power is drained from the photovoltaic cell 1 through the wires 2a and 2b, which have low resistance, into the inductor 3, which stores a portion of the energy flowing through it in a magnetic field.

[0240] The automatic switch 4 is typically a MOSFET transistor connected to a control circuit (not shown in Figure 16 which switches between alternative states, allowing current to flow through the inductor 3 to ground for a first fraction of time, and allowing the inductor to emit its stored magnetic energy as current at a higher voltage than the photovoltaic cell, through the diode 5 to the load 6, which can then use the power.

[0241] The automatic switch 4 can operate at a fixed frequency or at a variable frequency and / or duty cycle and / or waveform, which can be controlled by the sender, or by the user load, or based on the current, voltage or temperature at the load, or based on the current, voltage or temperature at the automatic switch 4, or based on the current, voltage or temperature emitted by the opto-electric power converter 1, or based on some other indication of the state of the system.

[0242] The receiver can be connected directly to the load 6, as Figure 16As shown in the middle, or the load 6 can be located outside the receiver, or it can even be a separate device, such as a portable phone or other power consuming device, which can use a socket connection, such as USB / Micro USB / Lightning / USB type C.

[0243] In most cases, there is also an energy storage device, such as a capacitor or battery, connected in parallel to the load 6, or the load 6 can contain an energy storage device, such as a capacitor or battery.

[0244] The transmitter 21 generates and directs a beam 15 to the receiver 22. In a first mode of operation, the transmitter 21 finds the presence of the receiver 22 in such a way that it uses a scanning beam, or it probes the receiver by using a communication means such as RF, light, IR light, UV light or sound, or it probes the receiver by using a camera to detect visual indicator information of a retro-reflector, or a retro-reflective structure, a barcode, a high-contrast pattern or other visual indicator information. Upon finding a coarse position, the beam 15 typically scans at low power around the general area of the receiver 22. In this scan, the beam 15 is projected on the photovoltaic cell 1. Upon the beam 15 being projected on the photovoltaic cell 1, the detector 8 detects it, and the controller 13 signals accordingly.

[0245] The controller 13 responds to such a signal by commanding the laser driver 12 to change the power P in the input gain medium 11, or by commanding the mirror 14 to change its scanning speed or the direction of the beam, or to keep its position, change the scanning step speed, by one or both of the following ways. Upon the gain medium 11 receiving a different power P from the laser driver 12, its small signal gain changes, i.e. the gain experienced by a single photon as it traverses the gain medium, while no other photon traverses the gain medium. Upon the photon being directed through the gain medium 11 in the direction between the back mirror 10 and the output coupler 9, more photons are emitted in the same direction as the beam 15, and an optical resonance is created between the back mirror 10 and the output coupler 9.

[0246] The output coupler 9 is a partially transmitting mirror with a reflectivity R, operating at the first harmonic of the C-H absorption at 6940 cm -1 -1 ​The spectrum between at least a portion of the second harmonic absorbed by CH is typically a multilayer dielectric or semiconductor coating, wherein alternating layers of materials with different refractive indices are deposited on a substrate, typically glass, plastic, or the surface of the gain medium 11. Alternatively, Fresnel reflections can be used, provided that the gain medium provides a sufficiently small signal gain or has a sufficiently large refractive index, or regular metal mirrors can be used. Bragg reflectors can also be used, where the gain medium should be a semiconductor or fiber amplifier. The output coupler 9 can also consist of a high-reflectivity mirror along with a beam-out device, such as a semi-transparent optical component that transmits a portion of the light and draws out another portion of the light within the resonant cavity by a forward-propagating wave, but typically a third portion is also drawn out within the resonant cavity by a backward-propagating wave.

[0247] The rear reflector 10 should be a high-reflectivity mirror, although a small amount of light may leak from its back, and can be used for monitoring or other purposes, operating at 6940 cm. -1 The first harmonic absorbed by CH is located at 8130 cm⁻¹ -1 The spectrum of at least a portion of the second harmonic absorbed by CH is represented. It can typically consist of alternating layers of materials with different refractive indices deposited on a substrate, usually glass, metal, or plastic. Alternatively, Fresnel reflectors can be used, provided the gain medium provides a sufficiently small signal gain, or regular metal mirrors can be used. Bragg reflectors can also be used, where the gain medium should be a semiconductor or fiber amplifier.

[0248] Gain medium 11 amplification at 6940cm -1 The first harmonic absorbed by CH is located at 8130 cm⁻¹ -1 The irradiation between the second harmonics absorbed by CH, although not necessarily spanning the entire spectral range. When pumped by laser driver 12 with power P, the small signal gain that can be transmitted is greater than the loss caused by output coupler 9. Its area, field of view, and damage threshold should be large enough to maintain at least 8 kW / m². 2 The beam is of sphericity / (1-R), where R is the reflectivity of the output coupler 9. It can be made of a semiconductor material with a bandgap of 0.8 to 1.1 eV, or of a transparent matrix material doped with Nd ions, or of other structures capable of stimulated emission within the said spectral range. The gain medium 11 is located along the optical aiming line from the back reflector 10 to the output coupler 9, thus allowing the radiation reflected by the back reflector 10 to resonate through the gain medium 11 between the back reflector 10 and the output coupler 9.

[0249] For exemplary embodiments in which the gain medium 11 is a semiconductor having a bandgap of 0.8 to 1.1 eV, it should preferably be attached to a heat extraction device and can be pumped electrically or optically by the laser driver 12.

[0250] In exemplary embodiments in which the gain medium 11 is a transparent host doped with Nd ions such as YAG, YVO4, GGG or a glass or ceramic, then the gain medium 11 should preferably also be in optical communication with a filter for drawing the irradiance at 9400 cm"1 -1 nearby resulting from the resonance created between the back mirror 10 and the output coupler 9.

[0251] The beam steering device 14 shown is controlled by the controller 13. It can steer the beam 15 in a plurality of directions. Its area should be large enough so that it contains substantially most of the beam 15 even in the case of tilting to its maximum operating tilt angle. In the case of a 2D oversimplification, if the beam 15 is collimated as a Gaussian beam of 5 mm diameter (1 / e 2 diameter) and the beam steering device is a single-wheel gimbal mirror with its center in the center of the beam, and if the maximum tilt required of the mirror is 30 degrees, and assuming that the beam steering device 14 has no other apertures, then if the mirror has a 5 mm diameter as the beam, it has about 13% loss at normal incidence of the beam, but about 60% loss at a 60 degree tilt angle. This can severely impair the performance of the system. In Figure 17 The power loss is shown in the graph of Fig.

[0252] At the beginning of the operation, the controller 13 commands the laser driver 12 and the mirror 14 to implement a search operation. This can be done by aiming the beam 15 in a general direction in which the receiver 22 is likely to be found, using the laser driver 12 operating in a first state. For example, in the case of a transmitter installed in a corner of a room's ceiling, scanning downward between two adjacent walls of the room. If the beam 15 is to be projected onto the receiver 22 containing the opto-electric power converter 1, the detector 8 will likewise signal the controller 13. As long as no such signal is received, the controller 13 commands the beam steering 14 to continue directing the beam 15 in other directions, searching for the receiver. If such a signal is received from the detector 8, the controller 13 can command the beam steering 14 to stop or slow down its scanning to lock onto the receiver, and instruct the laser driver 12 to increase its power emission. Alternatively, the controller 13 can record the location of the receiver 22 and return to it at a later stage.

[0253] As the laser driver 12 increases its power emission, the small signal gain of the gain medium 11 increases, and thus the beam 15 carries more power, initiating power transfer. If the probe 8 should detect a power loss greater than a threshold, which can be predetermined or dynamically set, and typically at a level representing a significant fraction of the maximum allowed exposure level, and also typically greater than the system noise figure, these conditions imply that the beam 15 is no longer properly aimed at the photovoltaic power converter 1, or that some object has entered the beam's path, or that a malfunction has occurred, and the controller 13 should normally command the laser driver 12 to change its state, by reducing the power to maintain the required safety level. If there are other indications of safe operation, such as indications from the user regarding the safety of the transfer, which can be given by a user interface or API, or safety of operation indications from a second safety system, then the controller can command the laser to increase the power to compensate for the power loss. The controller 13 can also command the beam steering assembly 14 to re-implement the seek operation.

[0254] There can be two different phases in the seek operation. First, a coarse search is implemented using a camera, which can search for visual patterns, retro-reflectors, high-contrast images, response from the signal of the receiver or other indications, or by using the scanning feature of the beam steering 14. This can result in a list of potential locations where the receiver can be found. The second phase is a fine seek, in which the beam steering mirror 14 directs the beam 15 over a smaller area until the probe 8 signals that the beam 15 is projected on the photovoltaic power converter 1.

[0255] Reference is now made to Figure 18 which shows an exemplary cooling system for the gain medium 11 of the system of Figure 16 Although the reflectors 9, 10 are shown as separate optical elements, it should be understood that one or both of them can be directly coated on the gain medium end faces, to simplify the system. The gain medium 11 converts the power received from the laser driver 12 into heat and photons, and typically the system performance is impaired if the gain medium is heated above a certain temperature.

[0256] Therefore, the gain medium 11 is attached to a heat sink 34, using an adhesive 33, which is preferably a thermally conductive solder with low thermal resistance. The adhesive 33 can also be a conductive adhesive. The adhesive 33 can have a coefficient of thermal expansion between the gain medium 11 and the heat sink 34. The heat sink 34 can typically be a low thermal resistance heat sink made of metal, which can be fitted with fins or an external fluid pumping system, such as a fan or liquid pump 35, for increasing its surface area.

[0257] Those skilled in the art will appreciate that the application described is not limited to the details of the foregoing, since the scope of the application is defined by the appended claims. Rather, the scope of the application includes various combinations and sub-combinations of the various features described above, as well as modifications and alterations thereto that occur to those skilled in the art upon reading the foregoing description, which modifications and alterations are intended to fall within the scope of the application.

Claims

1. A system for laser power transmission between a transmitter and a receiver, the transmitter comprising: a III-V semiconductor laser diode with a bandgap of 0.8 eV to 1.1 eV; and a laser driver supplying electrical power to the laser diode; wherein the system is adapted for operation with a receiver comprising: a photovoltaic cell producing a first output voltage of 0.3 to 0.8 V per junction; and a voltage transformer adapted to convert the voltage of the electrical power produced by the photovoltaic cell to a higher voltage, the voltage transformer comprising an inductor, an energy storage device and a switch, the inductor having a resistance of less than 10 ohms, wherein a switch node capacitance C of the switch sw such that: wherein C sw is the farad of the switch node capacitance of the switch, P laser driver is the power in Watts supplied by the laser driver to the gain medium, V o is the output voltage of the voltage transformer in Volts, and f is the switching frequency.

2. The system of claim 1, wherein the switching node has a capacitance of less than 100 nF and more than 10 pF.

3. The system of claim 1, wherein the series resistance R of the main switch in the switching node is such that: wherein E gain is the bandgap of the gain medium measured in Joules, where the switch either grounds the inductor or connects the photovoltaic cell to the inductor.

4. A system for wireless transmission of power from a transmitter to at least one remotely located receiver, the receiver being electronically attached to a power consuming electronic device, the system comprising: a beam generator adapted to generate a laser beam having a frequency in a frequency band between a first harmonic of a C-H absorption located at about 6940 cm -1 and a second harmonic of a C-H absorption located at about 8130 cm -1 and in said frequency band, a weak optical absorption line of an organic material having C-H bonds, said optical absorption line being such that said laser beam has an optical absorption per cm in said organic material of less than 20%, such that due to a layer of organic contamination on a beam projection area of said receiver, said level of optical absorption does not attenuate the power level of the laser beam received by at least one receiver by more than a predetermined amount. a beam steering device adapted to direct the laser beam towards at least one remotely located receiver; a detector configured to detect whether the laser beam is projected on a remotely located receiver and, if so, to detect whether there is a power loss between the transmitter and the receiver that exceeds a predetermined threshold or a dynamically set threshold; and a controller adapted to respond to the detection of a power loss between the transmitter and the receiver by at least one of (a) reducing the power of the laser beam, or (b) diverting the direction in which the beam steering device directs the laser beam.

5. The system of claim 4, wherein the detection of a power loss is indicative of the presence of at least one organic material object located in the transmission path between the transmitter and at least one remotely located receiver, or the system is malfunctioning.

6. The system of one of claims 4 and 5, wherein the layer of organic contaminants on the beam projection area of the receiver is caused by at least one of organic dirt or fingerprints on the beam projection area of the receiver.

7. The system of one of claims 4 to 6, wherein the weak optical absorption line is sufficiently wide so that it can be used to detect a variety of different polymeric materials.

8. The system of one of claims 4 to 7, wherein the weak optical absorption line is sufficiently weak so that it enables the system to continue operating even in the presence of organic dirt and fingerprints.

9. The system of one of claims 4 to 8, adapted to power a receiver comprising a photovoltaic converter having a bandgap.

10. The system of claim 9, wherein the bandgap of the beam generator is larger than the bandgap of the photovoltaic converter of the receiver.

11. The system of claim 9, wherein the bandgap of the beam generator is 0.8 eV to 1.1 eV.

12. The system of one of claims 4 to 11, wherein the laser beam produced by the beam generator has a radiant intensity of at least 10 GW / m2 / sr. 2 / spherical degree.

13. The system of claim 4, wherein the controller checks the state of the beam steering device after receiving a signal from the detector.

14. The system of claim 4, wherein the controller causes the state of the beam steering device to change after receiving a signal from the detector.

15. A system for laser-based wireless power transmission to at least one receiver, the system comprising: (a) a transmitter comprising: (i) a diode laser selected so that its emission wavelength is 6900 cm -1 to 8200 cm -1 and its radiant intensity is greater than 800 kW / m 2 / spherical degree, and its gain medium comprises a III-V semiconductor with a bandgap of 0.8 eV to 1.1 eV; and (ii) a beam steering device adapted to scan the beam over a field of view; (b) a receiver-based detector that detects when the beam impinges on at least one receiver, the receiver-based detector comprising: (i) a partially transparent surface for receiving the beam; (ii) a III-V photovoltaic cell having at least one junction with a bandgap that is less than the bandgap of the gain medium but more than 50% of the bandgap of the gain medium, the III-V photovoltaic cell producing an output voltage of 0.3 to 0.8 V; and (iii) a voltage conversion circuit comprising an inductor and at least one semiconductor switch with a resistance of less than 10 ohms; and (c) a controller wirelessly connected to the receiver-based detector through a communication channel and configured to, upon receiving a signal from the receiver-based detector, cause at least one of: (i) a change in the small signal gain of the gain medium, (ii) a change in the radiance of the beam, (iii) a change in the scan position of the beam steering device, (iv) a change in the scan speed of the beam steering device, and (v) recording the scan position defining the location of at least one receiver.

16. The system of claim 15, wherein the semiconductor switch is any one of a MOSFET, a JFET, a BJT, an IGBT, or a pHEMT switch.

17. A system for wirelessly transmitting power to at least one remotely located receiver, the receiver electronically attached to a power-consuming electronic device, the system comprising: a beam generator adapted to generate an electro-optical beam having a frequency; a beam steering device adapted to direct the electro-optical beam toward at least one receiver; a detector configured to detect whether the electro-optical beam impinges on any of the receivers and to send a signal to a controller accordingly, the controller configured to detect at least one object having an optical absorption of less than 20% attenuation per cm located on a transmission path between the system and one of the receivers and adapted to control the beam generator and the beam steering device accordingly, wherein The frequency of the electro-optical beam is between the first harmonic of a C-H absorption located at about 6940 cm -1 -1 and the second harmonic of a C-H absorption located at about 8130 cm -1 -1. the signal generated by the detector is adapted to cause the controller to implement at least one of (a) reducing the power of the electro-optical beam, (b) diverting the direction in which the beam steering device directs the electro-optical beam, and (c) reducing the radiance of the electro-optical beam upon detecting that the beam impinges on the receiver, and The frequency of the electro-optical beam is chosen so that it falls on an absorption line which is weak enough that the level of contaminants on the beam projection area of the receiver does not affect the power of the unattenuated beam received by the receiver beyond a predetermined level.

18. The system of claim 17, wherein the contaminants are due to the presence of at least one of fingerprints and dust.

19. The system of one of claims 17 and 18, wherein the change in the beam projected on at least one receiver is a reduction in power beyond a predetermined threshold.

20. The system of one of claims 17 to 19, wherein the beam generator is a laser.

21. The system of one of claims 17 to 20, wherein the system is adapted to power a receiver comprising a photoelectric transducer having a bandgap.

22. The system of claim 21, wherein the bandgap of the beam generator is greater than the bandgap of the photoelectric transducer of the receiver.

23. The system of claim 22, wherein the bandgap of the beam generator is greater than 0.8 eV.

24. The system of claim 22, wherein the bandgap of the beam generator is less than 1.1 eV.

25. The system of one of claims 17 to 24, wherein the beam generated by the beam generator has a radiance of at least 10 GW / m2 / sr. 2 / spherical degrees.

26. The system of one of claims 17 to 25, wherein the beam steering device is adapted to electronically report its status.

27. The system of claim 26, wherein the controller checks the status of the beam steering device upon receiving a signal from the probe.

28. The system of claim 26, wherein the controller causes the status of the beam steering device to change upon receiving a signal from the probe.

29. A laser-based transmission system for transmitting optical power to a mobile electronic device in a home environment; the system comprising: a laser generator adapted to generate a laser beam having a frequency; a beam steering device adapted to direct the laser beam toward the mobile electronic device; a probe configured to probe whether the laser beam is projected on the mobile electronic device, to indicate that a power loss generated between the laser generator and the mobile electronic device exceeds a predetermined threshold or a dynamically set threshold, and to generate a signal accordingly; and a controller adapted to respond to the signal from the probe and to control at least one of the laser generator and the beam steering device to reduce the danger due to the intrusion of a transparent object into the beam, wherein the frequency of the laser generator is selected to be between the first harmonic of the C-H absorption at about 6940 cm -1 and the second harmonic of the C-H absorption at about 8130 cm -1 and further selected so that it falls in an absorption line which is weak enough so that: (i) the level of expected home contaminants on the beam projection area of the mobile electronic device does not cause a power loss between the laser generator and the probe sufficient for the controller to respond to the expected home contaminants, and (ii) an object located between the laser generator and the mobile electronic device causes a power loss sufficient for the controller to respond to the presence of the object, the object having a predetermined minimum thickness and an optical absorption per cm at the frequency of less than 20%.

30. A laser-based transmission system for transmitting optical power to a mobile electronic device in a home environment; the system comprising: a laser generator adapted to generate a laser beam having a frequency; a beam steering device adapted to direct the laser beam toward the mobile electronic device; a probe configured to probe whether the laser beam is projected on the mobile electronic device, to indicate that a power loss generated between the laser generator and the mobile electronic device exceeds a predetermined threshold or a dynamically set threshold, and to generate a signal accordingly; and a controller adapted to respond to the signal from the probe and to control at least one of the laser generator and the beam steering device to reduce the danger due to the intrusion of a transparent object into the beam, (i) the level of expected home contaminants on the beam projection area of the mobile electronic device does not cause a power loss between the laser generator and the probe sufficient for the controller to respond to the expected home contaminants, and (ii) an object located between the laser generator and the mobile electronic device causes a power loss sufficient for the controller to respond to the presence of the object, the object having a predetermined minimum thickness and an optical absorption per cm at the frequency of less than 20%.

30. The laser-based transmission system of claim 29, wherein detection of a power loss is used to indicate that at least one object of organic material is positioned on the transmission path between the laser generator and the mobile electronic device, or that the system is malfunctioning.

31. The laser-based transmission system of one of claims 29 and 30, wherein the level of home contaminants expected on the beam projection area of the mobile electronic device is caused by at least one of organic smudges or fingerprints.

32. The laser-based transmission system of one of claims 29 to 31, wherein the absorption line is sufficiently wide so that it can be used to probe a variety of different polymeric materials.

33. The laser-based transmission system of one of claims 29 to 32, wherein the weak optical absorption line is sufficiently weak so that it can enable the system to continue to operate even in the presence of organic smudges and fingerprints.

34. The laser-based transmission system of one of claims 29 to 33, wherein control of at least one of the laser generator and the beam steering device includes at least one of (a) reducing the power of the laser beam, and (b) shifting the direction in which the beam steering device directs the laser beam.

35. The laser-based transmission system of one of claims 29 to 34, adapted to power a receiver that includes a photovoltaic transducer having a bandgap.

36. The laser-based transmission system of claim 35, wherein the bandgap of the laser generator is greater than the bandgap of the photovoltaic transducer of the receiver.

37. The laser-based transmission system of claim 35, wherein the bandgap of the laser generator is 0.8 eV to 1.1 eV.

38. The laser-based delivery system of one of claims 29 to 37, wherein the laser beam produced by the laser generator has a radiant intensity of at least 10 GW / m2 / sr. 2 / spherical degrees.

39. The laser-based transmission system of claim 29, wherein the controller checks the state of the beam steering device after receiving a signal from the probe.

40. The laser-based transmission system of claim 29, wherein the controller causes a change in the state of the beam steering device after receiving a signal from the probe.

41. A safety system responsive to beam intrusion in a laser-based wireless power transmission system, the system comprising: a transmitter including a laser emitting a beam, a controller controlling the power of the laser, and a power monitor using backside leakage from a back mirror of the laser; and a receiver including a photovoltaic cell and a received power probe, the beam emitted by the laser being directed to the receiver by a beam steering device, the receiver being adapted to wirelessly transmit a measure of the received power to the controller in the transmitter, enabling detection of the probability of beam intrusion by evaluating a power loss of the beam projected on the receiver, wherein the controller is configured so that upon the power loss exceeding a predetermined threshold, the controller implements at least one of: (i) reducing a small signal gain of the laser, (ii) changing a radiance of the beam, (iii) changing a direction of the beam, and (iv) changing a polarization of the beam. (iii) changing a scan position of the beam steering device, (iv) changing a scan speed of the beam steering device, and (v) recording a scan position defining a location of the receiver, wherein the predetermined threshold is selected to make a lower response to an external optical surface of the photovoltaic cell having a desired level of household organic contaminants relative to a response to the beam intrusion.

42. The security system of claim 41, wherein the desired level of household organic contaminants includes at least one of organic smudges or fingerprints.

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