Photovoltaic cell for laser beam power detection

A safety system for a wireless optical power transmission system comprising a transmitter, a receiver and a control unit, wherein:

• (i) said transmitter comprises:
• a laser adapted to emit a beam;
• and
• a scanning mirror adapted for steering said beam towards said receiver;
• (ii) said receiver comprises:
• a photovoltaic cell having a plurality of conductors on a surface adapted to receive said laser beam, said photovoltaic cell having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV;
• and
• a cover layer disposed upon said photovoltaic cell, said cover layer comprising a material adapted to restrict by either absorption or reflection, illumination having wavelengths outside of the range of the wavelength of said laser beam, and to transmit said laser beam towards said photovoltaic cell;
• and
• (iii) said control unit is adapted to receive first data representing the position of said scanning mirror, and to receive second data from said transmitter representing the power of said beam emitted by said laser, and to determine from said first and second data, the expected power incident on said photovoltaic cell, and to compare said expected power with said power of said laser beam impinging upon said receiver, as measured by said photovoltaic cell, and to indicate a potential safety problem if said expected power deviates from said measured power by more than a predetermined level.

A wireless optical power transmission system comprising a transmitter and receiver, said transmitter comprising:

• a laser adapted to emit a beam;
• a scanning mirror adapted for steering said beam towards said receiver;
• and
• a control unit adapted to receive signals from a detection unit on said receiver, and to control at least one of (i) the power of said beam emitted by said laser and (ii) a position of said scanning mirror:
• said receiver comprising:
• a photovoltaic cell having a plurality of conductors on a surface adapted to receive said laser beam, said photovoltaic cell having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, said photovoltaic cell adapted to detect said power of said laser beam reaching said photovoltaic cell;
• wherein:
• said receiver comprises a cover layer disposed upon said photovoltaic cell, said cover layer comprising a material adapted to absorb or reflect illumination having wavelengths outside of the range of the wavelength of said laser beam, and to transmit said laser beam towards said photovoltaic cell;
• and at least one of:
• (i) a first anti-reflective coating disposed upon the surface of said cover layer remote from said photovoltaic cell, said first anti-reflective coating adapted to reflect illumination having wavelengths outside of the range of the wavelength of said laser beam, and to transmit said laser beam into said cover layer;
• and
• (ii) a second anti-reflective coating disposed between the surface of said photovoltaic cell and said cover layer, said second anti-reflective coating adapted to reflect illumination having wavelengths outside of the range of the wavelength of said laser beam, and to transmit said laser beam into said photovoltaic cell;
• wherein, said detection unit generates a signal representing the power of said laser beam impinging upon said receiver, independent of illuminations of other wavelengths other than that of said laser beam, and said control unit is adapted to control at least one of (i) said beam and (ii) said position of said scanning mirror in order to maintain said power impinging on said receiver.

A power converting device for converting optical power into electrical power adapted for optical wireless power transmission using a laser beam, comprising:

• a power converting device having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, and having an external layer through which laser light is transmitted towards said at least one junction, said external layer being configured to transmit at least a first wavelength into said at least one junction with at least 80% efficiency when illuminated through said external layer from any direction between ±20° to the normal to the surface of said external layer;
• wherein at least one of:
• the conversion efficiency of said power converting device for said first wavelength being at least 30%, said first wavelength being a near infra-red wavelength between 700 nm and 1500 nm;
• said power converting device external layer being configured to reflect or absorb a portion of incident illumination at a second wavelength between 550 nm and 700 nm, so that less than 60% of the illumination at said second wavelength reaches the at least one junction when illuminated through said external layers from any direction between ±20° to the normal to the surface of said external layer(s) and said power converting device conversion efficiency for said second wavelength is at below 20%;
• said power converting device external layer being configured to absorb or reflect at least a third wavelength between 300 nm and 550 nm, so that at least 50% of the power of said third wavelength is absorbed before reaching said at least one junction, when illuminated through said external layer from any direction between ±20° to the normal to the surface of said external layer, and said power converting device conversion efficiency for said third wavelength being less than 10%;
• and
• said power converting device conversion efficiency for a fourth wavelength between 1500 nm and 2000 nm being below 5%.

A power converting device for converting optical power beam to electrical power comprising:

• a semiconductor device having a p-n junction adapted to absorb said optical power beam,
• top and bottom conductors in electrical contact with said semiconductor device, said top conductor covering a portion of a top surface of said semiconductor device;
• and an optical layer disposed on said top surface of said semiconductor device, said optical layer comprising a top volume and a bottom volume, said bottom volume being in optical contact with said top surface of said semiconductor device, and with said top conductor of said semiconductor device, and said top volume being in optical contact with air;
• wherein:
• said top conductor is adapted to reflect at least 30% of the light impinging upon it;
• said optical layer has an optical density for said optical power beam of less than 2;
• and
• said top conductor is adapted to direct at least 25% of the light reflected by it into angles greater than sin−1(1/the refractive index of said bottom volume).

A power converting device for converting optical power into electrical power adapted for optical wireless power transmission using a laser beam, said power converting device comprising:

• a photovoltaic cell having a plurality of conductors on a surface adapted to receive said laser beam, said photovoltaic cell having at least one junction having a bandgap energy between 0.75 eV and 1.2 eV, and having a cover layer disposed upon it;
• wherein:
• said cover layer comprises a material adapted to at least one of absorb or reflect illumination having wavelengths within the range of 550 nm to 700 nm, and to transmit said laser beam towards said photovoltaic cell, and said laser beam having a wavelength between 700 nm and 1500 nm;
• and
• the transmission of said cover layer for said wavelength of said laser beam being at least 50% higher than its transmission for wavelengths within the range of 550 nm to 700 nm,
• such that said power converting device has an efficiency of conversion to electrical power at said wavelength of said laser beam at least 2.5 times greater than its efficiency at a wavelength of 550 nm.