Optical power meter for safe operation of an optical wireless power system

Abstract

A system for measuring power of a laser beam includes a substantially opaque housing from which the laser beam is directed through an exit aperture. The housing contains a beam splitter configured to transmit a major portion of the laser beam through the exit aperture and reflect a minor portion of the laser beam, a diffuser element positioned such that the reflected minor portion of the laser beam impinges thereon, at least one detector element in optical communication with the diffuser element, the detector element providing a signal in response to diffused light of the minor portion of the laser beam impinging thereon, and an absorber element positioned such that any portion of light that enters the housing through the exit aperture and is reflected by the beam splitter impinges on the absorber element and is substantially absorbed.

Description

Technical Field

[0001] This invention relates to the field of safety systems for remotely charging mobile devices (particularly for preventing excessive exposure to lasers) by providing an accurate power meter for a laser-based charging system. Background Technology

[0002] In recent years, numerous battery-powered mobile systems have been developed, with batteries typically ranging from approximately 1 to 60 Wh in capacity. This allows these devices to operate for hours to weeks before needing a recharge. Charging times for such mobile systems are generally less than 12 hours, thus requiring chargers to provide approximately 1-5 W of power within that timeframe. Remote laser charging systems have been developed for these mobile systems, converting light energy into electrical energy without requiring the mobile device to be wired to a power source during charging. Considering the conversion efficiency between optical and electrical power, the optical power of the beam carried by the laser charging system is typically a few watts.

[0003] Ensuring safety is a requirement for remote, laser-based charging systems. The achievable emission limit (AEL) for Class I lasers is defined in the United States by Federal Regulations 21 CFR-1040 and other documents. Class I lasers are safe under all normal use conditions. This means that the maximum permissible exposure (MPE) must not be exceeded when observing the laser with the naked eye or with the aid of typical magnifying optics such as a telescope or microscope. Human exposure to power exceeding acceptable durations or power limits will not classify the system as a Class I laser, thus making it unsuitable for general public use.

[0004] Because the permitted exposure time for beams with power of a few watts is very short according to the aforementioned regulations—approximately microseconds for a 1W 7mm Gaussian beam at 1060nm—an effective active safety system is needed to facilitate automatic beam shut-off before the laser exposure time exceeds the permissible duration. Any such safety system requires accurate measurement of the optical power emitted by the transmitter to ensure safe operation.

[0005] Most current laser power transmission systems either do not include a power meter or include one that may not be suitable for providing accurate results during extended operation of the equipment. Such prior art systems may not account for changes in beam shape, wavelength, or the optical properties of the system itself that occur naturally over time. Therefore, their reliability is insufficient to ensure safe operation over long periods.

[0006] For example, the system described in DS Graham's US2007 / 0019693 "Wireless power beaming to common electronic devices" uses a photodiode (28) to measure back reflection from a lens. This method is energy-efficient because it uses only light that would otherwise be wasted, as it does not reach the receiver and is not converted into electrical energy at the receiver. However, photodiodes are sensitive to lens misalignment, dust, and wavelength variations (because lenses typically have a dielectric coating, which is known to be sensitive to wavelength variations), and cannot provide reliable measurements over time without recalibration. It is also highly sensitive to illumination of the photodiode from an external light source.

[0007] US2014 / 0126603 by Della-Pergola, co-inventor of this application and jointly owned by the applicant, also uses a light leak mirror to guide the beam to a single photodiode. This design can also be susceptible to dust, misalignment, and beam shape variations, especially since lenses are used in some of these configurations. US 9,312,701, "System for optical wireless power supply," co-inventor of this application, proposes detecting objects in a beam based on detecting power loss in the beam. US2014 / 0092929, also co-inventor of this application and jointly owned by the applicant, proposes monitoring the power and shape of the beam to ensure safety.

[0008] Many safety systems rely on measuring the power of the laser emitted from the transmitter. Current technology recommends using a power meter to measure laser power and sometimes specifies the use of a "leakage" mirror or the reflection of a lens surface to couple some light to a photodiode, but it fails to provide a system that can maintain accurate calibration of the power meter over long periods of time, thus requiring frequent recalibration to ensure safe operation.

[0009] Therefore, a long-term, accurate and reliable power meter is needed to ensure the safety of remote optical charging systems that overcome at least some of the shortcomings of existing technology systems and methods.

[0010] The contents of each publication mentioned in this section and other sections of the specification are incorporated herein by reference in their entirety. Summary of the Invention

[0011] This invention discloses a security system for a laser-based wireless power transmission system. The system ensures safe operation over long periods of time with minimal power loss by using a power measurement module that ensures reliable and accurate measurement of optical power over long periods of time without the need for recalibration and / or cleaning.

[0012] The power measurement system described in the current disclosure offers long-term reliability, safety, and maintenance-free operation, superior to more traditional methods that prefer higher efficiency and lower cost. This system differs from previous systems in that, instead of positioning the detector in a direction and location where reflected laser light and stray light from the environment can easily strike it, the detector is placed near the laser's exit aperture, but facing the laser, so that incoming light entering the housing is absorbed by the housing walls without striking the detector. Furthermore, the power meter described in the current disclosure describes numerous factors that provide stability for power measurements, with low power loss of the main beam and no range loss. These factors include resilience to variations in beam mode, wavelength, temperature, degradation of optical elements and variations in transmittance and reflectivity, dust accumulation on optical and electronic surfaces, measurement bias caused by internal reflections (“ghosting”) from the main beam, and measurement bias caused by external illumination.

[0013] Therefore, an exemplary implementation of the device described in this disclosure provides a system for measuring the power of a laser beam, comprising: a substantially opaque housing from which the laser beam is guided through an exit aperture, the housing comprising:

[0014] (i) A beam splitter configured to transmit the main portion of the laser beam through an exit aperture and reflect the secondary portion of the laser beam;

[0015] (ii) A diffuser element, which is positioned such that a secondary portion of the reflected laser beam strikes it;

[0016] (iii) At least one detector element optically communicates with a diffuser element, the detector element providing a signal in response to diffuse light from a secondary portion of a laser beam striking it; and

[0017] (iv) An absorber element, which is positioned such that any portion of light that enters the housing through the exit hole and is reflected by the beam splitter strikes the absorber element and is substantially absorbed.

[0018] In such a system, the laser is either housed inside the housing or located outside the housing and its beam is directed into the housing.

[0019] Furthermore, the optical coupling efficiency from the detector to the laser may be substantially greater than that from the detector to any other location outside the housing.

[0020] In addition, the wavefront shape of the main part of the beam transmitted by the beam splitter should be substantially unaffected by the channel passing through the beam splitter.

[0021] In any of the above systems, when the wavelength of the beam changes by up to 3 nm from its average value, the ratio of the power emitted by the laser beam to the power received by the detector element remains essentially constant. Furthermore, when the polarization of the beam changes from its average value, the ratio of the power emitted by the laser beam to the power received by the detector element remains essentially constant. Additionally, when the beam distribution changes from its average value, the ratio of the power emitted by the laser beam to the power received by the detector element remains essentially constant.

[0022] In any of these systems, the beam splitter may include a transparent front surface and an anti-reflective rear surface. Additionally, the diffuser element is configured to equalize the signal distribution across the beam. The diffuser element may have a concave shape suitable for uniformly illuminating the detector element.

[0023] Regarding the detector elements, a pair of adjacent detectors may be included, which are positioned such that the detected beam strikes both of them. In this case, if the laser beam is generated by a laser diode, the pair of detectors should be arranged such that the fast axis of the laser beam is parallel to the line connecting the centers of the detectors.

[0024] Finally, in all these systems, the majority of the laser beam transmitted through the exit aperture may be greater than 80% of the source laser beam. Attached Figure Description

[0025] The present invention, as described in the following detailed description in conjunction with the accompanying drawings, will be more fully understood and appreciated.

[0026] Figure 1 This shows how the maximum permissible exposure time decreases with power for a beam with a wavelength of 1050 nm and a diameter of 7 mm;

[0027] Figure 2A and Figure 2B Some differences between the beam splitter and detector disclosed in the present description are shown;

[0028] Figure 3 An exemplary system is shown for accurately measuring the power of an optical charging system over a long period of time without the need for recalibration;

[0029] Figure 4 A typical beam distribution of a diode laser with variable power across its long and short axes is shown, in which hot spots are identified;

[0030] Figure 5 An exemplary laser is shown, illustrating the power variation across the long and short axes;

[0031] Figure 6A and Figure 6BAdditional structural components for improving the accuracy of power meter measurements are shown; and

[0032] Figure 7 The components of a power meter in an exemplary implementation are shown. Detailed Implementation

[0033] First refer to Figure 1 The figure shows the maximum permissible exposure time for a beam with a wavelength of 1050 nm and a diameter of 7 mm, and illustrates the decrease in permissible exposure time as the beam power decreases.

[0034] Referring now to Figure 2A, which illustrates a prior art beam transmission system, this demonstrates how a beam splitter reflects a small portion of the emitted laser beam in the opposite direction to its propagation and toward a detector to provide a signal supposedly proportional to the output power. Typically, approximately 98% of the beam is transmitted, and 2% of the laser is reflected back to strike the detector. However, since the detector faces an aperture through which most of the laser transmission passes, incident light entering the aperture from the environment will also strike the detector, and may therefore potentially tamper with the obtained measurements.

[0035] Many existing technology systems suffer from design problems that make them susceptible to interference from external lighting because they place power measurement sensors in what is called the rearward or backward direction instead of the forward direction.

[0036] The term "rearward direction of the laser" refers to any direction in which the transmission efficiency from the laser to the power meter or photodiode is less than the transmission efficiency from at least one point outside the transmitter, for the wavelength to which the power meter is sensitive.

[0037] The so-called "forward direction of the laser" is defined as: the direction in which the transmission efficiency from the laser 21B to the power meter or photodiode is greater than the transmission efficiency from any point outside the transmitter, for the wavelength to which the power meter is sensitive.

[0038] Therefore, in the rearward direction, the coupling of light from outside the system to detector 25B is greater than the coupling of light reflected from laser 21A to detector. For example, a leaky rearview mirror is commonly used for power measurement. The laser's rearview mirror is designed to have high reflectivity for a specific laser wavelength and is generally transmissive to other wavelengths, which can tamper with the power measurement when other wavelengths originate from outside. With the power meter placed behind the laser's rearview mirror, approximately 0.1% of the laser light may couple to the detector, while up to 5% of light from outside may couple to the laser. To measure the laser's power, a small portion of the beam is split and directed to either the power meter or detector. Both the detector's configuration relative to the laser and the angle of the beam splitter affect the detector's accuracy. Graham's US 2007 / 0019693 uses the rear surface of a lens as a beam splitter to measure back reflections from the lens surface. In US 2014 / 0126603, Della Pergola uses the laser's rearview mirror as a coupler for power measurement (also in the "rearward" direction). In this case, the laser rearview mirror is the beam splitter.

[0039] Figure 2A shows a power meter constructed according to previously used technology, wherein detector 25A is in a rearward orientation. Beam splitter 23A is positioned such that laser beam 22A is split by the beam splitter, and a small percentage of beam 24A is reflected rearward and reaches detector 25A, with the main portion of the laser beam emitted from the exit aperture. However, stray light 26A from the outside also reaches detector 25A through the exit aperture, affecting the measurement and reducing its accuracy. This is because the detector is facing rearward relative to the laser, i.e., in its direction away from the laser and towards the outside world.

[0040] exist Figure 2B The image shows an exemplary power meter constructed based on a novel solution to the problem of interference from incident background light. In this configuration, detector 25B is placed near the exit aperture but facing forward relative to the laser, i.e., facing the laser and with its back to the outside world. Therefore, stray light entering the housing will not strike the detector and thus will not affect the laser power reading. In this implementation, the beam splitter can again ensure that 98% of the beam is transmitted and 2% of the beam is reflected toward the detector. In this configuration, detector 25B is positioned such that 2% of the laser beam 24B is deflected and reaches detector 25B after striking beam splitter 23B, but almost no power from stray beam 26B reaches detector 25B.

[0041] Although lasers are Figure 1While the power meter is considered to be contained within an opaque housing in section -2, it is understood that it could also be constructed as a separate device for measuring externally generated laser beams. In this case, the housing would need to have an opening, and the laser would be positioned such that the beam could enter through that opening. To minimize the entry of external light, it is most advantageous to position the laser as close as possible to the opening, or even to contact the housing wall containing the opening.

[0042] Now for reference Figure 3 The diagram schematically illustrates a beam splitter 26 used in this power meter module, designed to separate a small portion of the laser beam traveling from the laser 21 in the forward direction 22 toward the power detector 27. The beam splitter 26 also redirects light from the backward direction 24 to a lossy element 25, which is typically a component that absorbs wavelengths within the beam's range, absorbing most of the reflected light to prevent any significant portion of the backward beam from being further reflected to the detector. Figure 2B As shown, these components are sealed in an opaque housing to prevent dust accumulation, particularly on the beam splitter 23 and the loss element 25.

[0043] Laser beams (especially multimode diode laser beams) often undergo beam shape changes. Figure 4 An image showing a typical beam shape is now presented, illustrating the laser beam distribution 32, with the fast axis 33 and slow axis 34 marked. The so-called "hot spots," shown by diagonal 35, frequently change shape, position, and intensity during normal laser operation, as does the shape of the entire beam 32. To avoid this dynamic change in beam shape based on varying power measurements, the entire beam must be sampled with uniform efficiency, typically achieved by focusing the entire beam onto a detector. However, this configuration is sensitive to the alignment of the focusing element with the beam and detector and tends to drift over time, requiring realignment or recalibration.

[0044] Now for reference Figure 5 The diagram schematically illustrates another view of the axis of a diode laser beam. Beam 42 is emitted from a diode laser 41, which can be a single-mode or multi-mode diode laser. Beam 42 from such a diode laser typically has two distinct orthogonal axes 43 and 44, exhibiting different behavior. The so-called fast axis 43 diverges from the diode emitter at approximately 25–50°, while the slow axis 44 diverges from the diode emitter at 5–20°. The mode across the slow axis 44 is generally less uniform and less stable compared to the mode across the fast axis. Therefore, the cross-section of the beam in the direction of the fast axis 43 is typically close to a Gaussian shape 45 and does not substantially change over time.

[0045] Because of the lack of power distribution uniformity along the slow axis 44, the sampler needs to sample the entire slow axis 44 of the beam with uniform efficiency. Sampling along the fast axis 43 is less sensitive because the power distribution in this direction is more stable, and sampling at any given point will maintain representativeness of the entire beam distribution in that direction. Therefore, in some cases, non-uniform sampling of a portion of the fast axis 43 in space is sufficient.

[0046] Now for reference Figure 6A and Figure 6B These diagrams schematically illustrate solutions for ensuring accurate measurement of beam power. In some cases, focusing the entire beam onto the detector power meter is impractical or impossible. In such cases, uniform sampling of the split beam is achieved by striking the beam against diffusers 56 and 57, from which diffused light strikes detectors 50 and 59, respectively. The purpose of the diffusers is to ensure that the light collected by the detectors is equally representative of each portion of the beam falling onto the diffusers, thus ensuring a uniform sampling rate for each portion of the beam. If the optical path length of the power meter between such diffusers 56 and 57 and the power detectors 50 and 59 is substantially longer than the beam diameter on the slow axis, where a factor of 30 times the beam diameter is considered sufficient, then a simple diffuser can be used to sample the entire beam almost uniformly through the power meter. In systems with short power meter optical path lengths, distance differences between different points on the diffusers and the power meter can lead to non-uniform sampling, which in turn can result in sensitivity to changes in beam shape. This is evident in… Figure 6A The illustration shows beams from different sides of diffuser 56 striking detector 50, and it is clear that in the example shown, light from the left side of the beam will approach the detector closer than light from the right side of the beam, generating a larger signal in the detector. If the beam distribution exhibits varying intensity at any given location in its distribution, like the slow axis of a diode laser emission, this will generate an over-reliance on variations in the beam distribution in systems with path lengths shorter than those described above.

[0047] In many cases, such a long optical path (30 times the beam diameter) is undesirable for practical reasons, and therefore three alternative solutions can be implemented individually or together. First, tools such as lenses, focusing lenses, or telescopes can be used. Figure 6A and Figure 6B Optical arrangements such as (not shown) are used to compress the optical path so that it can fit in a shorter space while keeping the difference between the nearest point and the farthest point sampled by the diffuser in the beam as small as possible. Second, a diffuser 56 with planned variable reflectivity or transmittance can be used to compensate for different distances and angles between different positions in the beam, thereby making the sampling uniform. Third, asFigure 6B As shown, a shaped diffuser 57 can be used, which is typically recessed along the direction of light incidence along the slow axis, or recessed for both axes, thereby making the optical path length more uniform between different points in the beam. If detectors 50, 59 are placed close to the center of curvature of the diffuser, then the distance from each point in the diffuser to the detector will be the same. Typically, a small deviation from a perfectly circular aperture will allow the beam to uniformly illuminate the diffuser off-axis. These three solutions can be used together or individually; those with ordinary skill in the field of optical design will know how to design and build such systems and their combinations. Thus, the combined implementation of these three features achieves flexibility in response to changes in beam pattern.

[0048] like Figure 6B As shown, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are positioned such that the line connecting them is optically parallel to the fast axis of the laser diode. Therefore, the two detectors will generate similar signals even if they are slightly off-center from the diffuse beam. Figure 7 This is illustrated more clearly. If the system goes out of calibration range, these similar signals can be used to provide a warning because the two signals will start to differ, thereby enabling corrective measures to be taken to prevent dangerous operations, such as reducing the power level, terminating the beam, and / or calling a technician.

[0049] Detection schemes based on diffusers typically utilize only a small fraction of the total solid angle to collect light via optical detectors, as light propagates in many directions away from the diffuser. Therefore, by implementing multiple such detectors within the diffuse beam, providing multiple simultaneous power indication signals, extensions can be obtained for any of these configurations. All these signals are independent of the characteristics of the original beam (except for power), ensuring that these signals only need to be calibrated relative to each other once, and that this calibration remains effective even if the beam distribution changes. Specifically, in the case of a cylindrical diffuser, multiple detectors can be positioned along the axis of the cylinder.

[0050] Another key aspect of this system is the importance of dustproof sealing, such as... Figure 6B As shown. Dust accumulation on the sampler and other components in the beam path can cause changes in the sampling rate, leading to inaccurate beam power measurements. To avoid such dust problems, the system can be sealed, for example, by a dustproof housing 58, or by extending and complicating the air path between the outside and inside using a labyrinthine air path to prevent dust from reaching the sampling system. The diffuser 57 and detectors 50, 59 can also be enclosed within a light-blocking housing 55, so that any random light entering the module will have a degrading effect on the accuracy of the sampling measurements.

[0051] Now for referenceFigure 7 This schematically illustrates an exemplary scheme for tracking the power of a beam 610 from a laser source 621 located outside the power meter housing 615 in this exemplary arrangement, with the beam entering through an inlet aperture 602. However, the laser could be located inside the housing, such as... Figure 2B An exemplary system is shown in the example. As in a previous implementation, a beam splitter 607 is used to deflect a portion of the incident beam toward detectors 601, 609. In this module 600, beam 610 is split by beam splitter 607 into a main beam 611 that exits through exit aperture 603 and is directed toward the receiver, and a smaller sample portion 612 that constitutes a known small portion of the total laser beam. Beam sample 612 enters light-blocking housing 616, where it strikes diffuser element 608. Diffuser element 608 may be spherical, cylindrical, or other shapes that help to disrupt the wavefront of the striking beam, such that the orientation of each photon relative to other photons is random, or nearly random. A portion of the scattered beam strikes a pair of detectors 601, 609 in such a way that the fast axis of beam 617 is parallel to the line connecting the centers of the two detectors, while the slow axis is along the direction in which the detectors are adjacent to each other. In this configuration, both detectors cover the entire length of the slow axis, so that both detectors also cover the possible random noise variations in the beam distribution along that direction, while the more stable Gaussian distribution along the fast axis can be partially covered by each detector, since each part remains reasonably stable over time.

[0052] If the spatial distribution of the original beam is asymmetrical along the two axes of the incident beam, such as when using a multimode side-emitting diode laser, a cylindrical diffuser works best. As shown in Figure 6, the diffuser's curved axis is aligned with the axis of the beam characterized by stronger spatial variation; in situations like... Figure 3 and Figure 4 In the diagram, these are the slow axes 34 and 44 of the laser, respectively. Both detectors then convert the optical signal into an electrical signal and provide a measurement of the signal power. This information is then used for security determination.

[0053] exist Figure 7 The diagram shows a portion of the main beam 611 reflected back to the power meter, and this light 613 entering the system from the outside through aperture 603. Stray light entering aperture 603 could also be ambient light from a source other than the laser beam. This incident light 613 strikes beam splitter 607, and a portion of the striking light is reflected as beam 614, which then strikes beam absorber 605. Beam absorber 605 prevents the reflected beam 614 from being further reflected within the housing 615 that surrounds and encloses the components of system 600.

[0054] Use, for example, Figure 7The configuration shown indicates that the electrical signals generated at detectors 601 and 609 are largely insensitive to the characteristics of the original beam (except for its power). These other characteristics include, but are not limited to, polarization, wavelength, and spatial distribution. Existing solutions for power measurement typically suggest using low coupling coefficients in the beam splitter. Using dielectric coatings to couple light at the beam splitter, typical coupling coefficient values ​​of less than 0.5% or even less than 0.2% of the power are possible, and additional losses are often incurred, especially in the diffuser and in other parts. While dielectric beam splitters are available, they do have several drawbacks: lasers (especially diode lasers) experience longitudinal mode hopping and wavelength type changes, which cause their wavelength and / or bandwidth to drift slightly over time. Dielectric coatings are sensitive to wavelength changes, and therefore, using dielectric coatings can make the system potentially unsafe due to these wavelength variations. Wavelength-resistant dielectric coatings can be used, but they are more expensive.

[0055] On the other hand, Fresnel reflections from metallic surfaces are generally less sensitive to wavelength variations. In the system described herein, it is more advantageous to use a beamsplitter based on Fresnel reflection or metallic surface reflection instead of a conventional dielectric-coated beamsplitter. In some implementations, the surface of the beamsplitter opposite the surface on which the output beam is split can be coated with an anti-reflection coating. Dotted metallic coatings can also be used in some implementations, particularly for higher power or large beams.

[0056] The first preferred sampler uses Fresnel reflection from the front side of the generally transparent optical surface of the beam splitter 607, i.e., the side facing the laser beam. The back side is typically coated with an anti-reflective coating to prevent reflections from it, but embodiments reflecting from both surfaces may be advantageous in some cases, particularly if the sampler is thin and its surfaces are slightly non-parallel. The sampler maintains spatial consistency over the area covered by the beam, thereby reducing sensitivity to changes in beam shape; this configuration is well-suited for sampling fixed-polarization beams with a fixed wavelength.

[0057] Choosing the sampling angle allows the Fresnel reflection to sample a small fraction of the beam 610. Small angles (typically between 0% and 75% of the Brewster angle) offer the advantage of being independent of polarization. Larger angles (between 75% and 120% of the Brewster angle) are more sensitive to polarization but allow for higher transmittance (especially for “P” polarization), thus providing higher efficiency. Angles close to 45° typically allow for the most compact configuration, which can be advantageous when a compact system is required. In an advantageous embodiment, the primary polarization is set to “P” polarization on the sampler axis, so the sampling rate at an incident angle of approximately 45° is smaller (approximately 1-1.3%) compared to sampling at angles close to 0°, where the sampling rate is typically between 3-5%. In this way, flexibility is achieved against variations in wavelength and polarization.

[0058] The detection device in this invention therefore includes a diffuse element 608, followed by optical detectors 601 and 609, which collect only a portion of the solid angle of the diffuse beam. The diffuse element can be transmissive, wherein the diffuse distribution is generated along the original direction of the beam, or reflective, wherein the distribution is generated by reflection from the diffuse surface. Figure 7 The latter case is illustrated. A perfect diffuser generates a universal Lambertian distribution that is independent of the polarization or wavelength of the sampled beam. Since the fixed solid angle of this distribution is collected by an optical detector and converted into a power indication signal, this indication signal is also insensitive to the polarization and wavelength of the sampled beam. A practical diffuser is chosen such that the remaining dependence on polarization and wavelength is negligible relative to the accuracy required by the power tracking system.

[0059] In one embodiment, optical detectors 601 and 609 are positioned at a sufficiently large distance from the diffuser such that the entire diffuser region shares substantially the same distance and angle relative to the detectors. This geometry ensures that all coordinates of the diffuser contribute equally to the power indication signal, and therefore the signal is insensitive to the spatial distribution of the original beam. In practice, for a given lateral range of the sampled beam, the detection distance is chosen such that the remaining geometric differences have negligible sensitivity relative to the accuracy required by the power tracking system.

[0060] The amount of light collected by the optical detector, and thus the magnitude of the associated power indication signal, is determined by the collection solid angle, which in turn depends on the detection distance and the detector area. In another embodiment, the detector area is defined by a pinhole placed directly above a slightly larger photodetector. This design masks areas of unintentional photosensitivity of the detector, thus providing an effective area of ​​accurate size. A typical diameter of this pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough that the effects of unintentional incidental photosensitivity do not affect the accuracy of the power tracking system. In yet another embodiment, unintentional photosensitivity is characterized as part of the intended signal.

[0061] In another implementation, the sampled beam is focused onto a diffuser, thereby substantially reducing its lateral range. Such a design allows for a reduction in detection distance, resulting in a more compact system without sacrificing the power indication signal's immunity to the spatial distribution of the original beam.

[0062] In another implementation, the diffusers have a spherical distribution; a simple implementation of this element is a spherical diffuser. When the optical detector is placed at the origin of this sphere, all diffuser points share the same distance relative to the detector, regardless of the detection distance (in this case, the radius of the sphere). Therefore, for any detection distance, the spatial distribution of the original beam can be guaranteed to be independent.

[0063] The detector / sensor is preferably positioned away from the focal point of the curved diffuser (cylindrical or spherical), which is typically located at half the radius of curvature of the diffuser surface. Depending on the mechanical design, the broad beam generated by the diffuser may strike some mechanical components and be specularly or diffusely reflected back to the optical detector. This contribution increases the power indication signal beyond what would be expected by direct collection alone. In a preferred embodiment, all potential mechanical reflectors are placed at a distance such that their contribution to the power indication signal is negligible. In another embodiment, baffles are placed to block indirect collection paths; these are louvers that their own reflections cannot reach the detector. In yet another embodiment, the associated mechanical components are coated with an absorbing material to minimize their contribution to the power indication signal. This coating can be, for example, Metal Velvet, available from Acktar Advanced Coatings Ltd., Kiryat Gat, Israel. TM .

[0064] Those skilled in the art should understand that this invention is not limited to the specific details shown and described above. Rather, the scope of this invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications that would occur to those skilled in the art after reading the above description and which are not part of the prior art.

Claims

1. A system for measuring the power of a laser beam, comprising: A substantially opaque housing from which the laser beam is guided through an exit aperture open to the external environment; the housing comprises: A beam splitter is configured to transmit the main portion of the laser beam through the exit aperture and reflect the secondary portion of the laser beam. A diffuser element, which is positioned such that a secondary portion of the reflected laser beam strikes it; At least one detector element, optically communicating with the diffuser element, the at least one detector element providing a signal in response to diffuse light from a secondary portion of the laser beam impacting it; and An absorber element is positioned such that light entering the housing through the outlet hole and reflected by the beam splitter strikes the absorber element and is substantially absorbed, wherein: The at least one detector element is positioned optically toward the laser emitting the laser beam; The at least one detector element is aligned such that reflected laser light entering the substantially opaque housing from the external environment through the exit hole is prevented from striking the front surface of the at least one detector element; and The at least one detector element is aligned such that stray light from any point in the external environment entering the substantially opaque housing through the exit hole is prevented from striking the front surface of the at least one detector element.

2. The system according to claim 1, wherein, The laser is housed within the housing.

3. The system according to claim 1, wherein, The laser is positioned outside the housing and its beam is directed into the housing.

4. The system according to any one of the preceding claims, wherein, The optical coupling efficiency of the at least one detector element to the laser is substantially greater than the optical coupling of the at least one detector element to any other location outside the housing.

5. The system according to any one of the preceding claims, wherein, The wavefront form of the main portion of the beam transmitted by the beam splitter is substantially unaffected by the channel passing through the beam splitter.

6. The system according to any one of the preceding claims, wherein, When the wavelength of the beam changes by up to 3 nm from its average value, the ratio of the power emitted by the laser beam to the power received by the at least one detector element remains essentially constant.

7. The system according to any one of the preceding claims, wherein, When the polarization of the beam changes from its average value, the ratio of the power emitted by the laser beam to the power received by the at least one detector element remains substantially constant.

8. The system according to any one of the preceding claims, wherein, When the beam distribution of the laser beam changes from its average value, the ratio of the power emitted by the laser beam to the power received by the at least one detector element remains substantially constant.

9. The system according to any one of the preceding claims, wherein, The beam splitter includes a transparent front surface and an anti-reflective rear surface.

10. The system according to any one of the preceding claims, wherein, The diffuser element is configured to distribute the signal from the beam evenly across the beam.

11. The system according to any one of the preceding claims, wherein, The diffuser element includes a concave shape adapted to uniformly illuminate the at least one detector element.

12. The system according to any one of the preceding claims, wherein, The at least one detector element includes a pair of adjacent detectors, which are positioned such that the detected light beam strikes both of them.

13. The system according to claim 12, wherein, The laser beam is generated by a laser diode that emits a laser beam with a fast axis, and the pair of adjacent detectors are arranged such that the fast axis of the laser beam is perpendicular to the boundary line between the pair of adjacent detectors.

14. The system according to any one of the preceding claims, wherein, The main portion of the laser beam transmitted through the exit aperture is greater than 80% of the source laser beam.

15. The system according to any one of the preceding claims, wherein, The at least one detector element is positioned in a direction that is not optically connected to the exit aperture.

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