WIRELESS LASER POWER TRANSMITTER

• US 20100320362A1
• Filed: 01/04/2009
• Published: 12/23/2010
• Est. Priority Date: 01/03/2008
• Status: Active Grant

• Current Assignee: Wi-Charge Ltd.
• Original Assignee: Wi-Charge Ltd.
• Inventors: Alpert, Ortal, Paschotta, Rudiger
• Granted Patent: US 8,525,097 B2
• Time in Patent Office: Days
• US Class Current: 250/200
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 3/0604 in the form of a plate or disc
• CPC Class Codes: H01S 3/0805 by apertures, e.g. pin-holes or knife-edges
• CPC Class Codes: H01S 3/08059 Constructional details of the reflector, e.g. shape mirrors in general G02B5/08; mountings for mirrors G02B7/18
• CPC Class Codes: H01S 3/08072 Thermal lensing or thermally induced birefringence; Compensation thereof
• CPC Class Codes: H01S 3/083 Ring lasers fibre ring lasers H01S3/06791
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 5/041 Optical pumping
• CPC Class Codes: H01S 5/10 Construction or shape of the optical resonator , e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region H01S5/20 takes precedence
• CPC Class Codes: H01S 5/14 External cavity lasers H01S5/18 takes precedence; mode locking H01S5/065
• CPC Class Codes: H01S 5/183 having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
• CPC Class Codes: H02J 50/30 using light, e.g. lasers
• CPC Class Codes: H04B 10/114 Indoor or close-range type systems
• CPC Class Codes: H04B 10/807 Optical power feeding, i.e. transmitting power using an optical signal
• CPC Class Codes: H04B 2001/0416 having gain or transmission power control

Abstract

An optical power beam transmission systems, with a directional light transmitter and receiver. The transmitter contains an amplifying laser medium, and this together with a retroreflector in the receiver, forms a laser resonator. When lasing sets in, the receiver can extract optical power through an output coupler and convert it to electrical power. The gain medium may be a disc having a thickness substantially smaller than its lateral dimensions. The laser resonator is operated as a stable resonator to ensure safe operation. This is achieved by use of an adaptive optical element, for reducing the diameter of the energy beam impinging on the gain medium, thereby increasing the overlap between the energy beam and the gain medium. As the transmitter-receiver distance is changed, such as by movement of the receiver, the adaptive optical element focal length changes to ensure that the cavity remains within its stability zone.

Claims

1. A free-space lasing system for generating a laser beam, said system comprising:

a power transmitting unit comprising a first retroreflector, and having an angular field of view;

at least one power receiver unit comprising a second retroreflector, and remotely located relative to said power transmitting unit;

a gain medium disposed between said first and second retroreflectors, in proximity to said first retroreflector of said power transmitting unit; and

an element for extracting energy from said beam,

wherein said gain medium has a geometric form such that said lasing is maintained even when said beam is aligned over essentially said entire field of view.

3. A free-space lasing system according to claim 1 wherein said field of view is at least ±

15 degrees.

5. A free-space lasing system according to claim 1 wherein said gain medium has a thickness between the surfaces between which said beam traverses substantially smaller than its lateral dimensions.

6. A free-space lasing system according to claim 1, wherein said gain medium has an anti-reflection coating on at least one of its surfaces adapted to reduce reflection from said at least one surface such that said lasing is maintained even when said beam is aligned over essentially said entire field of view.

7. A free-space lasing system according to claim 1, wherein the thickness of the gain medium is substantially smaller than its lateral dimension, such that the gain profile of said gain medium is substantially independent of said beam alignment over essentially said entire field of view.

8. A free-space lasing system according to claim 1, said system further comprising at least one adaptive optical element for modifying the properties of said lasing system such that stable resonator modes are obtained.

9. A free-space lasing system according to claim 8 wherein said at least one adaptive optical element is such as to reduce the diameter of said laser beam impinging on said gain medium, thereby increasing the overlap between said laser beam and said gain medium

10. A free-space lasing system according to claim 8 wherein at least one of said adaptive optical element and said gain medium has sufficiently low birefringence that the generation of spurious birefracted beams is significantly reduced.

11. A free-space lasing system according to claim 8, wherein said adaptive optical element comprises any one of a thermal lens;

a lens mechanically deformable according to an applied control signal;

a mirror mechanically deformable according to an applied control signal; and

a pixelated liquid crystal array disposed such that the phase shift of light passing through a region of said element can be changed in accordance with a control signal applied to at least one pixel adjacent said region.

14. A free-space lasing system according to claim 11, wherein said applied control signal is related to a characteristic of the laser beam of said lasing system.

15. A free-space lasing system according to the thermal lens recitation of claim 11, wherein said thermal lens is generated by a partially absorbing layer on the surface of said adaptive optical element.

17. A free-space lasing system according to the thermal lens recitation of claim 11, wherein said thermal lens comprises a material having a value of dn/dT/κ

such as to reduce the optical power required to create the focusing power of said thermal lens, where dn/dT is the temperature differential of the refractive index of said material, and κ

is the thermal conductivity of said material.

19. A free-space lasing system according to the thermal lens recitation of claim 11, wherein said thermal lens comprises a heating element for generating the thermal profile required to create said thermal lens.

20. A free-space lasing system according to claim 8, wherein the optical form of said adaptive optical element is determined by feedback from a characteristic of said beam.

21. A free-space lasing system according to claim 20, wherein said characteristic is derived from the level of the output power of said laser beam.

22. A free-space lasing system according to claim 9, wherein said overlap is maximized by adjusting the focusing power of said adaptive optical element, such that said laser beam does not experience significant additional angular shift as a result of said focusing power adjustment.

24. A free-space lasing system according to claim 1, wherein said gain medium is adapted to emit a laser beam essentially parallel to a laser beam incident upon it.

25. A free-space lasing system according to claim 1, wherein the optical thickness profile across the width of said gain medium when said laser beam is traversing it is such that said laser beam emerges from said gain medium in a direction essentially parallel to the direction in which said laser beam impinges on said gain medium.

26. A free-space lasing system according to claim 25, wherein said optical thickness profile across the width of said gain medium is controlled by means of a temperature profile generated across said width.

27. A free-space lasing system according to claim 25, further comprising an additional optical element adapted to compensate for the change in the optical thickness profile of the gain medium arising from said lasing.

28. A free-space lasing system according to claim 1, further comprising an optical diffusing element adjacent to said element for extracting energy, such that said extracted energy is spatially dispersed before impingement on a photoelectric device used for converting said extracted energy.

29. A free-space lasing system according to claim 1, wherein the lateral dimension of said gain medium is selected such that the Rayleigh length of the laser beam is at least a significant fraction of the distance between said transmitting unit and said receiver unit.

31. A free-space lasing system according to claim 29, wherein said lateral dimension of said gain medium is sufficiently small that the power threshold for lasing is no more than an order of magnitude larger than the power of said transmitted beam.

32. A free space lasing system according to claim 1, wherein said gain medium optical thickness for different polarizations of the laser beam is substantially small compared to the diameter of the gain medium, so that transmitted beams of different polarizations substantially overlap.

35. A free space lasing system according to claim 1 further comprising an optical detector disposed such that it detects objects within the beam path by monitoring for changes in any one of said beam power and the transmission of a probe beam of light between said transmitting unit and said receiver unit.

36. A free space lasing system according to claim 1 wherein said optical detector is capable of detecting opaque and transparent objects.

37. A free space lasing system according to claim 35, wherein said objects are detected optically by monitoring for changes in any one of said beam power and the transmission of a probe beam of light between said transmitting unit and said receiver unit.

38. A free space lasing system according to claim 35, wherein said objects are detected by either one of monitoring the transmission of said probe beam where a signal is transmitted from the transmitter and is reflected back to the transmitter by the receiver and monitoring the transmission of said probe beam where a signal is transmitted from the receiver and is reflected back to the receiver by the transmitter.

40. A free space lasing system according to claim 35, wherein said objects are detected by transmission of light of said probe beam having at least one wavelength selected to be absorbed by common transparent materials such as glasses and plastics.

69. A free-space lasing system according to claim 1, said system further comprising an automatic focusing element for modifying the properties of said lasing system such that stable resonator modes are obtained.

70. A free-space lasing system according to claim 69, wherein said automatic focusing element comprises at least one adaptive optical element.

2. (canceled)

4. (canceled)

12-13. -13. (canceled)

16. (canceled)

18. (canceled)

23. (canceled)

30. (canceled)

33-34. -34. (canceled)

39. (canceled)

41. (canceled)

42. A wireless power receiver for receiving a beam of optical power;

said receiver comprising;

a retroreflector for reflecting a major part of said beam;

an adaptive optical element inserted in the path of said beam, adapted to focus said beam; and

a light coupler capable of extracting optical power from said beam,

wherein said receiver is adapted to receive power wirelessly from a remote transmitter unit.

43. A wireless power receiver according to claim 42, wherein said adaptive optical element is adapted to image the retroreflected beam at a plane at least as far as said remote transmitter unit.

44. A wireless power receiver according to claim 42, wherein said remote transmitter unit from which said receiver is adapted to receive power wirelessly, comprises a second retroreflector, such that said transmitter and said receiver units constitute a resonator, and said adaptive optical element is adapted to maintain said resonator within its stability limit.

45. A wireless power receiver according to claim 42, wherein said adaptive optical element includes any one of a thermal lens, a lens mechanically deformable according to an applied control signal, and a pixelated liquid crystal array disposed such that the phase shift of light passing through a region of said element can be changed in accordance with a control signal applied to at least one pixel adjacent said region.

48. A wireless power receiver according to claim 42, wherein said adaptive optical element has a sufficiently large lateral dimension that said retroreflected beam does not extend beyond said lateral dimension for a wide range of angles of incidence of said beam.

49. A wireless power receiver according to claim 44, wherein said remote transmitter unit from which said receiver is adapted to receive power wirelessly, further comprises a gain medium, said gain medium having a lateral dimension such that the Rayleigh length of said beam of optical power is at least a significant fraction of the distance between said transmitter unit and said receiver.

52. A wireless power receiver according to claim 42, further comprising an energy converter for converting part of said beam into electrical power.

53. A wireless power receiver according to claim 42, further comprising a wireless data transceiver capable of transmitting and receiving signals to and from said transmitter unit.

55. A wireless power receiver according to claim 53, wherein said transceiver is capable of receiving a signal instruction for initiating said adaptive optical element.

56. A wireless power receiver according to claim 55, further comprising a power source capable of supplying power to initiate said adaptive optical element.

46-47. -47. (canceled)

50-51. -51. (canceled)

54. (canceled)

57. A method for operating a free space laser, said laser comprising:

a first retroreflector having a gain medium juxtaposed thereto;

a remotely located second retroreflector;

an adaptive optical element juxtaposed to either of said first and said second retroreflectors; and

an element for extracting energy from a laser beam reflected between said retro reflectors,

said method comprising the sequential steps of;

applying an input impulse to said adaptive optical element to provide it with an initial focusing power; and

exciting said gain medium to induce lasing.

58. A method according to claim 57, further comprising the step of removing said input impulse to said adaptive optical element when said lasing has commenced.

59. A method according to claim 57, wherein

said first retroreflector having a gain medium juxtaposed thereto comprises a transmitter, and

said remotely located second retroreflector and said element for extracting energy from said laser beam comprise a receiver,

said method further comprising the step of transmitting a signal between said transmitter and said receiver in either direction, said signal providing information indicating parameters relating to said laser.

60. A method according to claim 59, wherein said information includes at least one of beam power, wavelength, pulse duration and availability for operation, identification of at least one of said transmitter and said receiver.

62. A method according to claim 59, wherein said signal is used to indicate that safe operation is achieved.

63. The method according to claim 62, further comprising the step of stopping lasing when said signal indicates that lasing is unsafe, or in the absence of a signal indicating safe operation.

64. The method according to claim 62, further comprising the step of providing external detectors indicating safe operation of said laser.

61. (canceled)

65. A free space laser, comprising:

a first retroreflector having a gain medium;

a remotely located second retroreflector having juxtaposed thereto, an element for extracting energy from a laser beam reflected between said retroreflectors; and

an adaptive optical element juxtaposed to either of said first and said second retroreflectors;

wherein said adaptive optical element is dynamically configured to modify the resonator properties of said laser such that stable resonator modes are obtained.

66. A free space laser according to claim 65, wherein said adaptive optical element is dynamically configured in accordance with changes in a characteristic of said laser beam.

67. A free space laser according to claim 65, wherein said gain medium has a thickness between the surfaces between which said beam traverses, substantially smaller than its lateral dimensions.

68. A free space laser according to claim 67, wherein said gain medium is such that its gain is substantially unchanged when the angle of incidence of said beam is varied over a range of at least ±

30°

.