Optical power meter for safe operation of optical wireless power systems

Abstract

To provide a system for measuring the power of a laser beam.SOLUTION: A system comprises an opaque enclosure, from which the laser beam is directed through an exit aperture. The enclosure contains: a beam splitter configured to transmit the major part of the laser beam through the exit aperture, and to reflect the minor part of the laser beam; a diffuser element positioned such that the reflected minor part 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 the diffused light of the minor part of the laser beam impinging thereon; and an absorber element positioned such that a part of light entering the enclosure through the exit aperture and reflected by the beam splitter impinges on the absorber element and is essentially absorbed.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention provides an accurate power meter for a laser-based charging system, and thus relates to the field of safety systems for remote charging of mobile devices, which are used in particular to prevent excessive exposure to lasers.

Background Art

[0002] In recent years, many battery-driven mobile systems have been developed, and their batteries typically have a capacity of about 1 to 60 Wh, and such batteries can operate for several hours to several weeks before recharging is required. The charging time of such mobile systems is typically less than 12 hours, and thus the charger needs to supply about 1 to 5 W of power to charge the battery within that time frame. For such mobile systems, remote laser charging systems have been developed, which eliminate the need to connect the mobile device to a power source by wires during charging. Considering the conversion efficiency between optical power and electrical power, the optical power of the transport beam of the optical charging system is typically several watts.

[0003] In a laser-based remote charging system, ensuring safety is essential. The accessible emission limit (AEL) of a Class I laser is defined in the United States by Federal Regulations 21 CFR ~ 1040 and other documents. Class 1 lasers are safe under normal operating conditions. This means that when viewing the laser with the naked eye or with a common magnifying optical device (such as a telescope or microscope), the maximum permissible exposure (MPE) cannot be exceeded. When the time is longer than the allowable time If there is human exposure to power above the limit or acceptable power limit, the system is not permitted to be classified as a Class I laser, and such a laser is not suitable for general public use.

[0004] According to the above rules, the allowable exposure time of a beam with a power of several watts is short, on the order of microseconds for a 7 mm Gaussian beam of 1 W at 1060 nm, so an efficient active safety system is required to facilitate automatic beam stop before the exposure time to the laser exceeds the allowable time. In such a safety system, it is necessary to accurately measure the optical power radiated from the transmitter to ensure safe operation.

[0005] Most current laser power transmission systems either do not include a power meter or include a power meter that is not suitable for providing accurate results for long-term operation of the device. Such prior art systems may not take into account changes in beam shape, wavelength, or optical characteristics of the system itself that occur naturally over time. Therefore, they are not reliable enough to guarantee safe operation over a long period of time.

[0006] For example, the system described in US2007 / 0019693 about "Wireless power beaming to common electronic devices" by D.S. Graham uses a photodiode (28) to measure the retroreflection from the lens. This method uses only the light that would otherwise be wasted because the light does not reach the receiver and is not converted to power at the receiver, so the power efficiency The rate is high. However, a photodiode is sensitive to misalignment of the lens, dust, and wavelength changes (since lenses generally have a dielectric coating, such coatings are known to be sensitive to wavelength changes), and without recalibration, it does not provide reliable measurements over time. Also, it is highly sensitive to irradiation of the photodiode from an external light source.

[0007] US2014 / 0126603 by Della-Pergola has the same inventors as this application and is co-owned by the applicant, and uses a leaky mirror to direct a beam at a single photodiode. This design is particularly susceptible to dust, misalignment, and changes in the beam shape since lenses are used as part of these configurations. US9, 312,701 regarding "System for Optical Wireless Power Supply" has the same inventors as this application and proposes detecting an object within a beam based on detecting power loss within the beam. US2014 / 0092929 also has the same inventors and is co-owned by the applicant, and proposes monitoring the power and shape of the beam to ensure safety.

[0008] Many safety systems rely on measuring the laser power radiated from a transmitter. Current technology proposes using a power meter to measure the laser power and may specify using a "leaky" mirror or reflection from the lens surface to couple a portion of the light to a photodiode, but cannot provide a system that can maintain accurate calibration of the power meter over a long period of time, and therefore requires frequent recalibration to enable safe operation.

[0009] Therefore, a remote optical charging system that overcomes at least some of the drawbacks of prior art systems and methods To ensure the safety of the optical charging system, a long-term, accurate, and reliable power meter is required.

[0010] The disclosure of each publication described in this item and other items of the specification is hereby incorporated by reference in its entirety into this specification. SUMMARY OF THE INVENTION

[0011] The present disclosure provides a safety system for a laser-based wireless power transmission system that guarantees highly reliable accurate optical power measurement over a long period of time without the need for recalibration and / or cleaning, thereby ensuring safe operation over a long period of time with minimal power loss. operation over a long period of time with minimal power loss.

[0012] The power measurement system described in the present disclosure provides longer-term reliability, safety, and maintenance-free operation compared to conventional approaches that favor high efficiency and low cost. What makes this system different from conventional systems is that instead of placing the detector in a direction and position where both the reflected laser light and stray light from the environment can easily collide, the detector is placed near the exit aperture of the laser, but faces the laser such that external light incident on the housing is absorbed by the housing wall and does not collide with the detector. Furthermore, the power meter of the present disclosure provides stability in power measurement with low power loss to the main beam and no loss in range. A number of factors are explained. These factors include changes in beam mode, wavelength, temperature, optical configuration Deterioration of components, and changes in transmittance and reflectance, dust accumulation on optical and electronic surfaces, bias in measurements due to internal reflections ("ghosts") from the main beam, and bias in measurements due to external illumination is included.

[0013] Thus, according to an exemplary implementation of the apparatus described in the present disclosure, a system for measuring the power of a laser beam is provided, the system comprising a substantially opaque housing from which the laser beam is directed to pass through an exit aperture, the housing comprising (i) a beam splitter configured to transmit a majority of the laser beam through the exit aperture and reflect a minor portion of the laser beam, (ii) a diffuser element arranged such that the minor reflected portion of the laser beam impinges thereon, (iii) at least one detector element in optical communication with the diffuser element, the detector element providing a signal in response to the diffused light of the minor portion of the laser beam impinging thereon, and (iv) an absorber element arranged such that a portion of the light that enters the housing through the exit aperture and is reflected by the beam splitter impinges on and is substantially absorbed by the absorber element.

[0014] In such a system, the laser may be disposed within the housing or outside the housing and its beam directed into the housing.

[0015] Furthermore, the optical coupling efficiency of the detector to the laser may be substantially greater than the optical coupling of the detector to any other location outside the housing.

[0016] Furthermore, the shape of the wavefront of the majority of the beam transmitted by the beam splitter Is not substantially affected by passing through the splitter.

[0017] In any of the systems described above, when the wavelength of the beam varies from its average value by up to 3 nm the ratio of the power transmitted by the laser beam to the power received by the detector element can be substantially constant. Further, when the polarization of the beam varies from its average value the ratio of the power transmitted by the laser beam to the power received by the detector element can be substantially constant. Further, when the beam profile of the beam varies from its average value the ratio of the power transmitted by the laser beam to the power received by the detector element can be substantially constant. In any of these systems, the beam splitter may comprise a transparent front face and an anti-reflective back face. Further, the diffuser element may be configured to equalize the signal from the beam across the entire beam profile. The diffuser element may have a concave shape adapted to uniformly illuminate the detector element

[0018] Regarding the detector element, it may comprise an adjacent pair of detectors, and the pair of detectors may be arranged such that the detected beam impinges on both of them. In such a case, when the laser beam is generated by a laser diode, the pair of detectors may be arranged such that the fast axis of the laser beam is parallel to the line connecting the centers of the detectors.

[0019] Finally, in all of these systems, the majority of the laser beam transmitted from the exit aperture may be larger than 80% of the source laser beam.

[0020]

Brief Description of the Drawings

[0021] The invention described in the claims of this application will be more fully understood from the following detailed description together with the following drawings. will be understood.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0022] Referring first to Figure 1, this graph shows the maximum allowable exposure time for a beam with a wavelength of 1050 nm and a diameter of 7 mm, showing the decrease in allowable exposure time as a function of beam power. is shown.

[0023] Next, referring to Figure 2A, a prior art beam transmission system is shown, where a small portion of the emitted laser beam is reflected in a direction opposite to its propagation direction and towards the detector, To provide a signal estimated to be proportional to the output power, an example of how a beam splitter is used is shown. Typically, about 98% of the beam is transmitted and 2% of the laser light is reflected backward and impinges on the detector. However, since the detector is oriented towards an aperture through which most of the laser light is transmitted, incident light from the environment entering the aperture also impinges on the detector and can thus distort the measured values obtained. Many prior art systems suffer from design problems that are susceptible to interference from external illumination and place the power measurement sensor in a direction known as the opposite or backward direction rather than the forward direction. The so-called "backward direction of the laser" is 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 wavelengths at which the power meter has sensitivity. The so-called "forward direction of the laser" is defined as the direction in which the transmission efficiency from the laser to the power meter or photodiode is greater than the transmission efficiency from any point outside the transmitter for wavelengths at which the power meter has sensitivity. Therefore, in the backward direction, the coupling of light incident on the detector 25B from outside the system is greater than the coupling of the reflected laser 21A to the detector. For example, a leaky rear mirror is often used for power measurement. The rear mirror of the laser is designed to have a high reflectivity for a specific laser wavelength and typically reflects most of the light incident from the outside.

[0024] Typically, about 98% of the beam is transmitted and 2% of the laser light is reflected backward and impinges on the detector. However, since the detector is oriented towards an aperture through which most of the laser light is transmitted, incident light from the environment entering the aperture also impinges on the detector and can thus distort the measured values obtained. Many prior art systems suffer from design problems that are susceptible to interference from external illumination and place the power measurement sensor in a direction known as the opposite or backward direction rather than the forward direction. The so-called "backward direction of the laser" is 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 wavelengths at which the power meter has sensitivity.

[0025] The so-called "forward direction of the laser" is defined as the direction in which the transmission efficiency from the laser to the power meter or photodiode is greater than the transmission efficiency from any point outside the transmitter for wavelengths at which the power meter has sensitivity. Therefore, in the backward direction, the coupling of light incident on the detector 25B from outside the system is greater than the coupling of the reflected laser 21A to the detector. For example, a leaky rear mirror is often used for power measurement. The rear mirror of the laser is designed to have a high reflectivity for a specific laser wavelength and typically reflects most of the light incident from the outside. The so-called "backward direction of the laser" is 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 wavelengths at which the power meter has sensitivity.

[0026] The so-called "forward direction of the laser" is defined as the direction in which the transmission efficiency from the laser to the power meter or photodiode is greater than the transmission efficiency from any point outside the transmitter for wavelengths at which the power meter has sensitivity. Therefore, in the backward direction, the coupling of light incident on the detector 25B from outside the system is greater than the coupling of the reflected laser 21A to the detector. For example, a leaky rear mirror is often used for power measurement. The rear mirror of the laser is designed to have a high reflectivity for a specific laser wavelength and typically reflects most of the light incident from the outside. The so-called "backward direction of the laser" is 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 wavelengths at which the power meter has sensitivity.

[0027] Therefore, in the backward direction, the coupling of light incident on the detector 25B from outside the system is greater than the coupling of the reflected laser 21A to the detector. For example, a leaky rear mirror is often used for power measurement. The rear mirror of the laser is designed to have a high reflectivity for a specific laser wavelength and typically reflects most of the light incident from the outside. The so-called "forward direction of the laser" is defined as the direction in which the transmission efficiency from the laser to the power meter or photodiode is greater than the transmission efficiency from any point outside the transmitter for wavelengths at which the power meter has sensitivity. Therefore, in the backward direction, the coupling of light incident on the detector 25B from outside the system is greater than the coupling of the reflected laser 21A to the detector. For example, a leaky rear mirror is often used for power measurement. The rear mirror of the laser is designed to have a high reflectivity for a specific laser wavelength and typically reflects most of the light incident from the outside. The so-called "backward direction of the laser" is 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 wavelengths at which the power meter has sensitivity. The power meter is transparent to other wavelengths, which can skew the power measurement. When placed behind the detector, about 0.1% of the laser light is coupled into the detector, while As much as 5% can be coupled into the laser. To measure the power of the laser, a small portion of the beam is The split light is then directed to a power meter or detector. Both the angle of the detector and the distance between the detector and the detector affect the accuracy of the detector. The 9693 uses the back surface of the lens as a splitter to measure the back reflection from the lens surface. In US2014 / 0126603, Della Pergola (Also in the "reverse" direction) using the rear mirror of the laser as a coupler for power measurement. In this case the laser back mirror is the beam splitter.

[0028] FIG. 2A shows a detector 25A arranged according to the previously used technique, with the detector 25A facing backward. A power meter is shown. The laser beam 22A is split by a splitter and the beam A small percentage of the laser beam 24A is reflected back to reach the detector 25A, while the majority of the laser beam The beam splitter 23A is positioned so that the light emitted from the exit aperture is In addition, stray light 26A entering from the outside passes through the exit aperture and reaches the detector 25A. This affects the measurement and reduces accuracy. , that is, facing away from the laser and towards the outside world.

[0029] FIG. 2B illustrates an exemplary optical fiber array constructed in accordance with a novel solution to the problem of interference of incident background light. In this configuration, the detector 25B is located near the exit aperture. The laser is irradiated forward, i.e., facing the laser and away from the outside world. Therefore, stray light entering the housing does not strike the detector, and the laser power In this implementation, the beam splitter also splits the beam It may be that 98% is transmitted and 2% is reflected towards the detector. In this configuration, detector 25B detects that 2% of laser beam 24B strikes splitter 23B. After that, it is deflected and reaches the detector 25B, but almost no power comes from the stray beam 26B. positioned so as not to be reached.

[0030] The laser is shown in Figure 2B as being housed in an opaque housing, but the power meter It can also be configured as a separate device for measuring an externally generated laser beam. It should be understood that in this case the housing has an opening through which the beam enters. To reduce the incidence of extraneous light, the laser must be positioned so that For convenience, it should be placed as close as possible to the opening or even in contact with the enclosure wall that contains the opening. should be done.

[0031] Referring now to FIG. 3, a laser 21 travels in a forward direction 22 toward a power detector 27. Used in power meter modules designed to isolate small portions of a laser beam A beam splitter 26 is shown diagrammatically. The beam splitter 26 is arranged to receive the light beam coming from the rear direction 24. The light is redirected towards a loss element 25, typically a component that absorbs wavelengths within the range of the beam. This prevents a significant portion of the rear beam from being reflected further towards the detector. As shown in Figure 2B, these components The element is optically sealed, especially to prevent dust accumulation on the splitter 23 and the loss element 25, inside an opaque housing.

[0032] Laser beams, especially multimode diode laser beams, often have a changing beam shape. Next, FIG. 4 shows an image of a typical beam shape, which shows a laser beam profile 32 marked with the fast axis 33 and the slow axis 3 4. The so-called "hot spot" indicated by the diagonal line 35, like the shape of the entire beam 32, often changes in shape, position, and intensity during normal operation of the laser. To avoid such dynamic fluctuations in the beam shape from changing the power measurement results, the entire beam must be sampled with uniform efficiency, which has generally been achieved by focusing the entire beam onto a detector. However, such a configuration is highly sensitive to the alignment of the focusing element with respect to the beam and the detector, tends to drift over time, and requires realignment or recalibration. with respect to the beam and the detector, tends to drift over time, and requires realignment or recalibration. recalibration.

[0033] Next, referring to FIG. 5, another perspective of the axis of the diode laser beam is schematically shown. The beam 42 is emitted from a diode laser 41 that is either a single longitudinal mode diode laser or a multi-longitudinal mode diode laser. The beam 42 from such a diode laser typically has two different orthogonal axes 43, 44 that behave differently, a so-called fast axis 43 that spreads from the diode emitter at about 25° to 50°, and a slow axis 44 that spreads from the diode emitter at 5° to 20°. The modes across the slow axis 44 are typically less coherent and less stable compared to the modes across the fast axis. The modes across the slow axis 44 are typically less coherent and less stable compared to the modes across the fast axis. The modes across the slow axis 44 are typically less coherent and less stable compared to the modes across the fast axis. Yes. Therefore, the cross-section of the beam in the direction of the fast axis 43 is usually close to the Gaussian shape 45 and does not change significantly over time.

[0034] Due to the lack of consistency in the power profile at the slow axis 44, the sampler needs to sample the entire slow axis 44 of the beam with a uniform efficiency. Sampling of the fast axis 43 is less sensitive because the power profile in that direction is more stable and sampling at any given cross-section remains representative of the entire beam profile in that direction. As a result , in some cases, non-uniform sampling of a part of the fast axis 43 in space may be sufficient.

[0035] Next, referring to FIGS. 6A and 6B, a solution for ensuring accurate measurement of the beam power is schematically shown. In some cases, focusing the entire beam onto a detector power meter may not be practical or possible. In such cases, uniform sampling of the split beam is achieved by colliding the beam with diffusers 56, 57, from which the diffused light collides with detectors 50, 59 respectively. The purpose of the diffuser is to ensure that the light collected by the diffuser equally represents each part of the beam incident on the diffuser so that the sampling ratio is the same for each part of the beam. When the optical path length of the power meter between such diffusers 5 6, 57 and the power detectors 50, 59 is substantially longer than the beam diameter at the slow axis respectively where the coefficient of the beam path length is considered sufficient to be 30 times the beam diameter and a simple diffuser can be used to obtain substantially uniform sampling of the entire beam by the power meter. For a system with a short optical length of the power meter ​​​​​In this system, non-uniform sampling occurs due to differences in distance between different points on the diffuser and the power meter. This can lead to high sensitivity to changes in the beam shape. In FIG. 6A, beams from different sides of diffuser 56 are shown impinging on detector 50. In the example shown, the light from the left side of the beam is more intense than the light from the right side of the beam. It is clear that the α-threshold is closer to the detector and generates a larger signal in the detector. applies to the slow axis of the diode laser emission in a system with a path length shorter than but the beam profile varies at any given position across the profile. When showing intensity, this creates an excessive dependency on changes in the beam profile.

[0036] In many cases, such a long optical path of 30 times the beam diameter is undesirable for practical reasons. Therefore, three alternative solutions were implemented, either separately or together: First, a lens, focusing mirror, or telescope (not shown in FIGS. 6A and 6B ), etc. Using the optical system of FIG. 1, the closest point in the beam sampled by the diffuser and the diffused while keeping the difference between the farthest point sampled by the instrument as short as possible. Second, the optical path can be compressed to fit into a small space. A diffuser 56 with a planned variable reflectance or transmittance can be used to illuminate different positions in the beam. Third, as shown in FIG. 6B, the different distances and angles between the beams can be compensated for. The slow axis is typically concave in the direction of light incidence so that the optical path length between the points is more uniform. A shaped diffuser 57 may be used that is either convex or concave with respect to both axes. When detectors 50 and 59 are arranged near the center of curvature of the diffuser, the distance from each point in the diffuser to the detector is the same. Typically, a slight deviation from a perfect circular aperture allows for uniform off-axis illumination of the diffuser by the beam. These three solutions may be used together or separately. An optical designer skilled in the art will know how to design and construct such a system and its combinations. Thus, the implementation of the combination of these three features achieves resilience to changes in the beam mode. As shown in Figure 6B, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. The implementation of the diffuser-based detection method generally utilizes only a small portion of the total solid angle to collect light by a photodetector, as light diffuses away from the diffuser in many directions. Therefore, an extension to any of these configurations can be obtained by implementing a number of such detectors within the diffused beam and providing multiple simultaneous power indication signals. All of these

[0037] An optical designer skilled in the art will know how to design and construct such a system and its combinations. Thus, the implementation of the combination of these three features achieves resilience to changes in the beam mode. As shown in Figure 6B, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. The implementation of the diffuser-based detection method generally utilizes only a small portion of the total solid angle to collect light by a photodetector, as light diffuses away from the diffuser in many directions. Therefore, an extension to any of these configurations can be obtained by implementing a number of such detectors within the diffused beam and providing multiple simultaneous power indication signals. All of these

[0038] As shown in Figure 6B, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. As shown in Figure 6B, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. As shown in Figure 6B, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. As shown in Figure 6B, it is advantageous to use a pair of detectors 50 and 59 instead of a single detector element. The detectors are arranged such that the line connecting them is optically parallel to the fast axis direction of the laser diode. Thus, the two detectors generate similar signals even if they are slightly offset from the center of the diffused beam. This is shown more clearly in Figure 7. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician. These similar signals may be used to give a warning when the system is out of calibration, as the two signals start to differ, thereby enabling the execution of corrective actions to prevent dangerous operations such as a decrease in power level, end of the beam, and / or call to the technician.

[0039] The implementation of the diffuser-based detection method generally utilizes only a small portion of the total solid angle to collect light by a photodetector, as light diffuses away from the diffuser in many directions. Therefore, an extension to any of these configurations can be obtained by implementing a number of such detectors within the diffused beam and providing multiple simultaneous power indication signals. All of these The implementation of the diffuser-based detection method generally utilizes only a small portion of the total solid angle to collect light by a photodetector, as light diffuses away from the diffuser in many directions. Therefore, an extension to any of these configurations can be obtained by implementing a number of such detectors within the diffused beam and providing multiple simultaneous power indication signals. All of these The implementation of the diffuser-based detection method generally utilizes only a small portion of the total solid angle to collect light by a photodetector, as light diffuses away from the diffuser in many directions. Therefore, an extension to any of these configurations can be obtained by implementing a number of such detectors within the diffused beam and providing multiple simultaneous power indication signals. All of these The implementation of the diffuser-based detection method generally utilizes only a small portion of the total solid angle to collect light by a photodetector, as light diffuses away from the diffuser in many directions. Therefore, an extension to any of these configurations can be obtained by implementing a number of such detectors within the diffused beam and providing multiple simultaneous power indication signals. All of these Since these signals do not depend on the characteristics of the original beam other than power, these signals are mutually only need to be calibrated once, and this calibration is ensured to be maintained regardless of fluctuations in the beam profile. Specifically, in the case of a cylindrical diffuser, a plurality of detectors can be arranged along the cylindrical axis.

[0040] Another typical aspect of this system, as shown in FIG. 6B, lies in the importance of sealing from dust. When dust accumulates on the sampler and other elements in the path of the beam, the sampling ratio may change, and the measurement of the beam power may become inaccurate. To avoid such dust problems, the system is sealed, for example, by a dust housing 58 or by extending and complicating the air passage between the outside and the inside using a labyrinth air passage, preventing dust from reaching the sampling system. The diffuser 57 and the detectors 50, 59 may be further sealed within a light-shielding housing 55 so that the influence of any random light incident on the module on the accuracy of the sampling measurement is reduced.

[0041] Referring now to FIG. 7, in this exemplary configuration, an exemplary scheme for tracking the power of the optical beam 610 incident from a laser source 621 disposed outside the housing 615 of the power meter is schematically shown, and the beam enters through the entrance aperture 602. However, as shown in the exemplary system of FIG. 2B, the laser may be disposed within the housing. Similar to the above implementation, a beam splitter 607 is used to deflect a portion of the incident beam towards the detectors 601, 609. In this module 600, the beam 610 is The printer 607 directs the main beam 6 towards the receiver from the exit aperture 603 into a smaller sampled portion 612 that constitutes a known small portion of the entire laser beam and 11. The beam sample 612 enters the light-shielding housing 616, where it collides with the diffuser element 608. The diffuser element 608 may be spherical, cylindrical, or of another shape that facilitates scrambling of the wavefront of the colliding beam, such that the direction of each photon is random or substantially random with respect to other photons . A portion of the scattered beam collides with a pair of detectors 601, 609 such that the fast axis of the beam 617 is parallel to the line connecting the centers of the two detectors and 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, thereby equally covering any possible noisy random variations in the beam profile along that direction, while the more stable Gaussian profile along the fast axis can be partially covered by each detector since each portion remains reasonably stable over time .

[0042] The cylindrical diffuser functions best, for example, when using a multimode edge-emitting diode laser, when the spatial distribution of the original beam is asymmetric along the two axes of the incident beam . The curved axis of the diffuser, as indicated by reference numeral 57 in FIG. 6, is aligned with the axis of the beam characterized by stronger spatial variations .

[0043] In FIGS. 3 and 4, this is the slow axis 34, 44 of the laser, respectively. Next, both detectors convert the optical signal into an electrical signal and provide a measured value of the power of the signal. This information is then used for safety determination .

[0044] ​​​​​​ FIG. 7 shows that a part of the main optical beam 611 is reflected toward the power meter and this light 613 enters the system from the outside through the aperture 603. The aperture 603 The spurious light incident on may be ambient light from a light source other than the reflection of the laser beam . This incident light 613 impinges on the beam splitter 607, and a part of the impinging light is reflected as beam 61 4 and impinges on the beam absorber 605. The beam absorber 605 prevents the reflected beam 614 from being further reflected within the housing 615 that surrounds and encloses the components of the system 600 .

[0045] Using a configuration as shown in FIG. 7 results in an electrical signal provided to the pair of detectors 601, 609 that is hardly affected by the characteristics of the original beam other than its power. Such other characteristics include, but are not limited to, polarization, wavelength, and spatial distribution. Solutions proposed in the prior art for measuring power typically suggest using a low coupling coefficient at the splitter . Typical coupling coefficient values of less than 0.5% or even less than 0.2% of the power are possible using a dielectric coating to decouple the light at the splitter and additional losses typically occur, especially at the diffuser and in other parts. Dielectric splitters can be used, but they have some drawbacks . Lasers, especially diode lasers, have longitudinal mode hops and changes in the type of wavelength, resulting in small shifts in wavelength and / or bandwidth over time. Dielectric coatings are highly sensitive to changes in wavelength, and thus using a dielectric coating has these

[0046] results in these result in a system that can be highly sensitive to wavelength changes and thus become unsafe. Wavelength-resistant dielectric coatings are available but are more expensive.

[0047] On the other hand, Fresnel reflection from a metal surface is typically much less sensitive to wavelength changes. In the systems described herein, it is more advantageous to use a splitter based on metal surface reflection or Fresnel reflection instead of a conventional dielectric coating splitter. In some implementations, the surface of the splitter on the opposite side where the output beam is split may be coated with an anti-reflection coating. In some implementations, a polka dot metal coating may be used, especially for use with high-power or large beams.

[0048] The first preferred sampler uses Fresnel reflection from the front facet of the typically transparent optical surface of the splitter 607, i.e., the facet facing the laser beam. The rear facet is typically coated with an anti-reflection coating to prevent reflection therefrom, although embodiments that reflect from both surfaces may be advantageous in some situations, especially when the sampler is thin and its surfaces are slightly non-parallel. The sampler is spatially consistent across the entire area covered by the beam and thus reduces sensitivity to changes in beam shape.

[0049] Such a structure is well-suited for sampling a fixed polarization beam having a fixed wavelength.

[0050] The sampling angle is such that Fresnel reflection samples a small portion of the beam 610. ​​is selected. Typically, small angles from 0% to 75% of the Brewster angle have the advantage of being independent of polarization. Large angles from 75% to 120% of the Brewster angle are more sensitive to polarization, but allow for higher transmission (especially for "P" polarization), and thus higher efficiency. Angles close to 45° typically allow for the most compact structure, which can be advantageous when a compact system is desired. In an advantageous embodiment, the main polarization is set as "P" polarization along the sampler axis, and thus the sampling ratio at an incident angle of about 45 ° is small (about 1 - 1.3%) compared to sampling at an angle close to 0° where the sampling ratio is typically 3 - 5%. In this way, elasticity to changes in wavelength and polarization is achieved. Accordingly, the detection device of the present invention includes a diffuser element 608 and subsequent photodetectors 601,

[0051] 609, which collects light from only a portion of the solid angle of the diffused beam. The diffuser element can be transmissive where the diffusion distribution is generated along the original direction of the beam, or reflective where the distribution is generated by reflection from a diffused facet tor. The latter case is shown in FIG. 7. A perfect diffuser generates a universal Lambertian distribution that is independent of the polarization or wavelength of the sampled beam. The fixed solid angle of this distribution is collected by the photodetector and converted into a power indication signal, so this indication signal is also insensitive to the polarization and wavelength of the sampled beam. A practical diffuser is selected such that the residual dependence on polarization and wavelength is negligible with respect to the required accuracy of the power tracking system.

[0052] ​​​In one embodiment, the photodetectors 601, 609 are placed at a sufficiently large distance from the diffuser such that the entire diffuser region shares substantially the same distance and angle with respect to the detectors. This kind of arrangement ensures that all coordinates of the diffuser contribute equally to the power indication signal, and thus this signal is not affected by the spatial distribution of the original beam. In practice, for a given lateral range of the sampled beam, the detection distance is selected such that the residual geometric differences result in a sensitivity where they can be ignored with respect to the required accuracy of the power tracking system. The amount of light collected by the photodetector, and thus the magnitude of the associated power indication signal, is determined by the collection solid angle, which depends on the detection distance and the detector area. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In yet another embodiment, the unintentional photosensitivity is characterized as part of the expected signal.

[0053] In yet another implementation, the sampled beam is focused onto the diffuser, thus significantly reducing its lateral spread. Such a design allows for a reduction in the detection distance and thus results in a more compact system without sacrificing the immunity of the power indication signal to the spatial distribution of the original beam. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In another embodiment, the detector area is determined by a pinhole aperture placed directly above a slightly larger photodetector. Such a design masks the area of the detector that is accidentally photosensitive and thus provides an active area of the correct size. A typical diameter of such a pinhole can be, but is not limited to, 300 μm. In another implementation, the detector area is large enough so that the influence of unintentional accidental photosensitivity does not affect the accuracy of the power tracking system. In yet another embodiment, the unintentional photosensitivity is characterized as part of the expected signal. In yet another embodiment, the unintentional photosensitivity is characterized as part of the expected signal.

[0054] In yet another implementation, the sampled beam is focused onto the diffuser, thus significantly reducing its lateral spread. Such a design allows for a reduction in the detection distance and thus results in a more compact system without sacrificing the immunity of the power indication signal to the spatial distribution of the original beam. In yet another implementation, the sampled beam is focused onto the diffuser, thus significantly reducing its lateral spread. Such a design allows for a reduction in the detection distance and thus results in a more compact system without sacrificing the immunity of the power indication signal to the spatial distribution of the original beam. In yet another implementation, the sampled beam is focused onto the diffuser, thus significantly reducing its lateral spread. Such a design allows for a reduction in the detection distance and thus results in a more compact system without sacrificing the immunity of the power indication signal to the spatial distribution of the original beam. In yet another implementation, the sampled beam is focused onto the diffuser, thus significantly reducing its lateral spread. Such a design allows for a reduction in the detection distance and thus results in a more compact system without sacrificing the immunity of the power indication signal to the spatial distribution of the original beam.

[0055] In yet another implementation, the diffuser has a spherical profile.

[0056] A simple implementation of such an element is a spherical diffusive reflector. Placing a photodetector at the origin of this sphere results in all diffuser points sharing the same distance to the detector, regardless of the detection distance, which in this case is the sphere radius. Thus, the lack of dependence on the spatial distribution of the original beam is guaranteed for any detection distance.

[0057] The detector / sensor is optimally placed at a position away from the focus of the curved diffuser (cylindrical or spherical), which is typically found at 1 / 2 of the radius of curvature from the surface of the diffuser . Depending on the mechanical design, the broad beam generated by the diffuser can hit certain mechanical elements and be reflected specularly or diffusely towards the optical detector. This contribution increases the power indication signal beyond the value expected by direct collection only. 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, a plurality of baffles are placed to impede the indirect collection path . These are shutters whose own reflections do not reach the detector. In yet another embodiment, the associated mechanical elements are coated with an absorbing material to minimize their contribution to the power indication signal. Such a coating may be, for example, Metal Velvet(TM) available from Acktar Advanced Coatings of Kiryat Gat, Israel

[0058] . These are shutters whose own reflections do not reach the detector. In yet another embodiment, the associated mechanical elements are coated with an absorbing material to minimize their contribution to the power indication signal. Such a coating may be, for example, Metal Velvet(TM) available from Acktar Advanced Coatings of Kiryat Gat, Israel

[0059] ​​​​​​​Those skilled in the art will understand that the present invention is not limited to what has been particularly shown and described above. Rather, the scope of the present invention includes combinations and sub - combinations of the various features described above, as well as modifications and variations thereof that are not found in the prior art and that may be made by those skilled in the art upon reading the above description. Both these modifications and variations are included.

Claims

1. 1. A system for measuring the power of a laser beam, comprising: a substantially opaque housing through which the laser beam is directed through an exit aperture; The housing includes: at least one detector element disposed in an optical path of the reflected fraction of the laser beam, the detector element providing a signal in response to the fraction of the laser beam impinging on the detector element; a beam splitter configured to transmit a majority of the laser beam through the exit aperture and reflect a minor portion of the laser beam towards the detector element; an absorber element positioned such that light passing through the exit aperture, entering the housing, and reflected by the beam splitter impinges on and is substantially absorbed by the absorber element; Equipped with the detector element is positioned in a direction optically oriented toward the laser but not in optical communication with the exit aperture such that stray light entering the housing does not impinge on a front surface of the detector element.

2. The system described in claim 1, wherein the optical coupling efficiency of the detector element to the laser beam is substantially greater than the optical coupling efficiency with light incident from outside the opaque housing.

3. A system as described in claim 1 or 2, further comprising a diffuser element positioned so that a reflected small portion of the laser beam impinges on it.

4. The system described in claim 1, wherein a laser is disposed within the housing.

5. The system described in claim 1, wherein a laser is positioned outside the housing and directs its beam into the housing.

6. A system described in any one of claims 1 to 5, wherein the shape of the wavefront of the majority of the laser beam transmitted by the beam splitter is substantially unaffected by passing through the beam splitter.

7. A system described in any one of claims 1 to 6, wherein the ratio of the power transmitted by the laser beam to the power received by the detector element is substantially constant when the wavelength of the laser beam varies from its average value by up to 3 nm.

8. A system described in any one of claims 1 to 7, wherein when the polarization of the laser beam changes from its average value, the ratio of the power transmitted by the laser beam to the power received by the detector element is substantially constant.

9. A system described in any one of claims 1 to 8, wherein when the beam profile of the laser beam changes from its average value, the ratio of the power transmitted by the laser beam to the power received by the detector element is substantially constant.

10. A system described in any one of claims 1 to 9, wherein the beam splitter has a transparent front surface and an anti-reflective back surface.

11. The system described in claim 3, wherein the diffuser element is configured to equalize the signal from the laser beam across the entire beam profile.

12. The system described in claim 3, wherein the diffuser element has a concave shape adapted to uniformly illuminate the detector element.

13. A system described in any one of claims 1 to 12, wherein the detector element comprises a pair of adjacent detectors, the pair of detectors being positioned so that the detected beam impinges on both of them.

14. The system described in claim 13, wherein the laser beam is generated by a laser diode and the pair of detectors are positioned so that the fast axis of the laser beam is parallel to a line connecting the centers of the pair of detectors.

15. A system described in any one of claims 1 to 14, wherein the majority of the laser beam transmitted through the exit opening is greater than 80% of the source laser beam.

16. A system described in any one of claims 1 to 15, wherein the optical communication is line of sight, allowing light to impinge on the front surface of the power meter.

Images