Optical modulation with vanadium oxide thin films

A substantially lossless switch for switching a modulated light signal between optical fibers comprising:

• an input optical fiber for carrying a modulated infrared signal having a wavelength above the absorption edge of vandium oxide;
• a dielectric substrate positioned in the path of said light signal, said substrate having relatively high transmission and relatively high thermal conductivity;
• a vanadium dioxide thin film disposed on the surface of said substrate, said film having a thickness of between about 5000 A to about 10000 A, said film capable of being switched between semiconductor and metal states, said film transmitting substantially all of the light signal incident thereon in its semiconductor state and reflecting substantially all of the light signal incident thereon in its metal state;
• first and second output optical fibers for selectively receiving light from said input fiber;
• said first output fiber disposed behind said film and oriented relative to said input fiber such that light incident on said film in its semiconductor state is substantially transmitted through said film into said first output fiber;
• said second output fiber oriented relative to said film and to said input fiber such that light incident on said film in its metal state is substantially reflected into said second output fiber;
• a plurality of thermoelectric junctions disposed around the side edges of said substrate in thermal contact with said substrate, said junctions capable of heating or cooling said substrate and said film by directing an electric current into or away from each of said junctions;
• and
• control means for directing a current into or away from each of said junctions for selectively heating and cooling said substrate and said film.

A substantially lossless tap for sampling an optical fiber comprising:

• an input optical fiber carrying a modulated light having a wavelength above the absorption edge of vanadium oxide;
• a vanadium oxide thin film disposed in the path of the signal, said film experiencing a continuous increase in reflectance with increases in temperature near its transition temperature;
• first and second output optical fibers for receiving the light signal from said input fiber;
• said first fiber is disposed behind said film and oriented relative to said input fiber such that said light signal carried by said fiber incident on said film is substantially transmitted through said film into said first output fiber;
• said second output fiber oriented relative to said film and to said input fiber such that a portion of said light signal incident on said film is partially reflected into said second output fiber;
• heating means in thermal contact with said film for maintaining said film at a predetermined constant temperature;
• and
• control means connected to said heating means for selectively controlling the temperature of said film above or below its transition temperature.

A substantially lossless programmable tap for an optical fiber comprising:

• an input optical fiber for carrying a modulated infrared light signal having a wavelength above the absorption edge of vanadium dixoide;
• a dielectric substrate positioned in the path of said light signal, said substrate having relatively high transmission and relatively high thermal conductivity;
• a vanadium dioxide thin film disposed on the surface of said substrate, said film having a thickness of between 5000 A to 10000 A, said film experiencing a continuous increase in reflectance with increases in temperature near its transition temperature;
• first and second output optical fibers for receiving a light signal from said input fiber;
• said first output fiber disposed behind said film and oriented relative to said input fiber such that the light signal incident on and transmitted through said film passes through said substrate into said first output fiber;
• said second output fiber positioned relative to said film and to said input fiber such that a predetermined fraction of said light signal reflected from said film passes into said second output fiber;
• a plurality of thermoelectric junctions disposed around the edge of said substrate in thermal contact with said substrate and said film for maintaining said film at a preselected temperature to reflect a predetermined fraction of said light signal from said film;
• and
• a control means connected to said thermoelectric junctions for selectively supplying current to said junctions to maintain said film at a preselected temperature to reflect a predetermined fraction of said signal to said second output fiber.

A transmit-receive switch for a laser radar for sending an output pulse into the world and detecting a reflected pulse comprising:

• a source of laser light having a wavelength above the absorption edge of vanadium oxide;
• a vanadium oxide thin film disposed in the path of said laser lights capable of transmitting substantially all of the light signal incident thereon when said film is in its semiconductor state and capable of relfecting substantially all of the light signal incident thereon out into the world when said film is in its metal state, said film being switchable between its semiconductor and metal state by varying the temperature thereof above or below its transition temperature;
• switching means capable of selectively raising and lowering the temperature of said film above and below the transition temperature for selectively reflecting said laser pulse into the world by switching said film to its metal state and for selectively receiving a reflected pulse from the world by switching said film to its semiconductor state permitting said pulse to be transmitted through said film;
• timing means connected to said switchng means for switching said film at preselected times;
• and
• sensing means disposed behind said film for sensing a reflected pulse passing through said film in its transparent state.