Graphene-based bolometer

Abstract

A bolometer. In one embodiment a graphene sheet is configured to absorb electromagnetic waves. The graphene sheet has two contacts connected to an amplifier, and a power detector connected to the amplifier. Electromagnetic power in the evanescent electromagnetic waves is absorbed in the graphene sheet, heating the graphene sheet. The power of Johnson noise generated at the contacts is proportional to the temperature of the graphene sheet. The Johnson noise is amplified and the power in the Johnson noise is used as a measure of the temperature of the graphene sheet, and of the amount of electromagnetic wave power absorbed by the graphene sheet.

What is claimed is: 
     
         1 . A bolometer comprising:
 a graphene sheet having a first pair of contacts and configured:
 to be coupled to received electromagnetic waves; 
 to have a temperature, when electromagnetic power in the received electromagnetic waves is absorbed by the graphene sheet, corresponding to the amount of electromagnetic power absorbed by the graphene sheet; and 
 to generate thermal noise at the first pair of contacts at a level corresponding to the temperature 
   a Fabry-Perot resonator comprising two mirrors, the graphene sheet being between the two mirrors; and   a circuit connected to the first pair of contacts, the circuit configured to measure the thermal noise level.   
     
     
         2 . The bolometer of  claim 1 , further comprising a refrigerator configured to cool the graphene sheet to a temperature below 4 K. 
     
     
         3 . The bolometer of  claim 2 , wherein the refrigerator is a pulse tube refrigerator. 
     
     
         4 . The bolometer of  claim 2 , wherein the refrigerator is a Gifford-McMahon cooler. 
     
     
         5 . The bolometer of  claim 1 , wherein the graphene sheet substantially has the shape of a rectangle, the rectangle having a length and a width, the length being greater than or equal to the width. 
     
     
         6 . The bolometer of  claim 5 , wherein the length of the rectangle is less than 20 microns. 
     
     
         7 . The bolometer of  claim 5 , wherein the product of the length of the rectangle and the width of the rectangle is less than 1000 square microns. 
     
     
         8 . The bolometer of  claim 5 , wherein the graphene sheet has an electron mobility of more than 100,000 cm 2 /V/s. 
     
     
         9 . The bolometer of  claim 1 , comprising a first layer of hexagonal boron nitride immediately adjacent to a first surface of the graphene sheet, and a second layer of hexagonal boron nitride immediately adjacent to a second surface of the graphene sheet. 
     
     
         10 . The bolometer of  claim 9 , wherein each of the first layer of hexagonal boron nitride and the second layer of hexagonal boron nitride has a thickness greater than 4 nm and less than 40 nm. 
     
     
         11 . The bolometer of  claim 1 , wherein the circuit comprises an amplifier connected to the first pair of contacts. 
     
     
         12 . The bolometer of  claim 11 , further comprising a matching circuit connected between the first pair of contacts and the amplifier. 
     
     
         13 . The bolometer of  claim 11 , further comprising a power detector connected to the amplifier. 
     
     
         14 . The bolometer of  claim 1 , wherein the graphene sheet consists of a single atomic layer of graphene. 
     
     
         15 . The bolometer of  claim 1 , wherein the graphene sheet comprises two atomic layers of graphene. 
     
     
         16 . An imaging system comprising:
 an array of bolometers, each of the bolometers of the array being a bolometer according to  claim 1  and having an electromagnetic wave input, the electromagnetic wave inputs forming an array of electromagnetic wave inputs; and   an imaging system configured to project an image onto the array of electromagnetic wave inputs.   
     
     
         17 . A bolometer comprising:
 a graphene sheet having a first pair of contacts and a second pair of contacts and being configured:
 to be coupled to received electromagnetic waves; 
 to have a temperature, when electromagnetic power in the received electromagnetic waves is absorbed by the graphene sheet, corresponding to the amount of electromagnetic power absorbed by the graphene sheet; and 
 to generate thermal noise at the first pair of contacts at a level corresponding to the temperature; and 
   a circuit connected to the first pair of contacts, the circuit configured to measure the thermal noise level,   wherein
 a first contact of the second pair of contacts, 
 the graphene sheet, and 
 a second contact of the second pair of contacts together form a part of a microstrip transmission line. 
   
     
     
         18 . The bolometer of  claim 17 , wherein:
 a first end of the microstrip transmission line is coupled to an antenna, and:
 a second end of the microstrip transmission line is coupled to ground, or 
 a portion of the microstrip transmission line, including a second end of the microstrip transmission line, forms a quarter-wave open stub connected to the graphene sheet. 
   
     
     
         19 . A bolometer comprising:
 a graphene sheet having a first pair of contacts and a second pair of contacts and being configured:
 to be coupled to received electromagnetic waves; 
 to have a temperature, when electromagnetic power in the received electromagnetic waves is absorbed by the graphene sheet, corresponding to the amount of electromagnetic power absorbed by the graphene sheet; and 
 to generate thermal noise at the first pair of contacts at a level corresponding to the temperature; and 
   a circuit connected to the first pair of contacts, the circuit configured to measure the thermal noise level,   wherein each contact of the second pair of contacts is connected to a respective conductor of a pair of conductors of a log periodic antenna.