Quasi-optical transceiver having an antenna with time varying voltage

• US 6,348,683 B1
• Filed: 05/04/1998
• Issued: 02/19/2002
• Est. Priority Date: 05/04/1998
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Verghese, Simon, McIntosh, K. Alexander
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/072,362
• Time in Patent Office: 1,387 Days
• Field of Search: 260/214.1, 260/227.19, 260/227.23, 260/227.24, 260/227.27, 343/742, 343/743, 359/152, 359/154, 359/151, 356/346-349
• US Class Current: 250/214.1
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation
• CPC Class Codes: H01L 31/10 characterised by potential barriers, e.g. phototransistors

Abstract

A transceiver for transmitting and receiving high frequency radiation is described. The transceiver includes a first light source that generates radiation at a first frequency and a second light source that generates radiation at a second frequency. The first and the second light source have a difference frequency that is approximately equal to the difference between the first and the second frequencies. The transceiver also includes a transmitter that comprises a first photomixer that is optically coupled to the first and the second light source. A first antenna that radiates a signal at the difference frequency is electrically coupled to the first photomixer. The transceiver also includes a receiver that comprises a second antenna positioned to receive the signal radiated by the first antenna. The second antenna generates a time varying voltage in response to the signal. A second photomixer is electrically coupled to the second antenna and optically coupled to the first and the second light source. The second photomixer generates a current signal in response to the time varying voltage generated by the second antenna.

Claims

1. A transceiver comprising:

a) a first light source generating radiation at a first frequency;

b) a second light source generating radiation at a second frequency, the first and the second light source having a difference frequency approximately equal to the difference between the first and the second frequencies;

c) a transmitter comprising;

i) a first photomixer optically coupled to the first light source and the second light source; and

ii) a first antenna electrically coupled to the first photomixer, the first antenna radiating a signal having a frequency substantially equal to the difference frequency; and

d) a receiver comprising;

i) a second antenna positioned to receive the signal radiated by the first antenna, the second antenna generating a time varying voltage in response to the signal; and

ii) a second photomixer electrically coupled to the second antenna and optically coupled to the first and the second light source, the second photomixer generating a current signal in response to the time varying voltage generated by the second antenna.

2. The transceiver of claim 1 wherein a conductance of the first and second photomixer is modulated at the difference frequency in response to the first and the second light source.

3. The transceiver of claim 1 further comprising a voltage source coupled to the first photomixer, the voltage source biasing the first photomixer to generate a current having a frequency approximately equal to the difference frequency.

4. The transceiver of claim 1 further comprising a transimpedance amplifier electrically coupled to the second photomixer that generates a DC voltage in response to the current signal generated by the second photomixer.

5. The transceiver of claim 1 wherein at least one of the first or the second photomixers comprises a low-temperature-grown GaAs.

6. The transceiver of claim 1 wherein the first and the second photomixer are embedded into a transmission line.

7. The transceiver of claim 6 wherein the transmission line is a co-planar waveguide.

8. The transceiver of claim 1 wherein at least one of the first or the second light source comprises a distributed-Bragg-reflector diode laser or a distributed-feedback diode laser.

9. The transceiver of claim 1 wherein at least one of the first and second antenna comprises a spiral antenna.

10. The transceiver of claim 1 wherein at least one of the first and the second antenna comprises a planar antenna or a horn antenna.

11. The transceiver of claim 1 further comprising a lens coupled to at least one of the first and the second antenna, the lens directing the signal radiated by the first antenna.

12. The transceiver of claim 1 further comprising a processor in communications with the second photomixer, the processor processing the current signal generated by the second photomixer.

13. The transceiver of claim 1 further comprising an intermediate frequency amplifier electrically coupled to the second photomixer that amplifies intermediate frequencies generated by the second photomixer.

14. A method of transmitting and receiving radiation, the method comprising:

a) providing a first light source that generates a first beam of light at a first frequency;

b) providing a second light source that generates a second beam of light at a second frequency;

c) modulating a conductance of a first photomixer at a difference frequency approximately equal to the difference between the first and the second frequencies in response to the first and the second light beam to generate a signal having the difference frequency;

d) transmitting the signal;

e) receiving the signal transmitted;

f) generating a time varying voltage in response to the signal received;

g) modulating a conductance of a second photomixer at the difference frequency in response to the first and the second light beam; and

h) generating a current signal in response to the time varying signal received by the second antenna and the modulated conductance of the second photomixer.

15. The method of claim 14 wherein the current signal generated in step g) comprises a time-varying term having approximately twice the difference frequency and a DC term.

16. The method of claim 14 further comprising the step of detecting a DC voltage in response to the current signal generated in step g).

17. The method of claim 14 further comprising the step of changing at least one of the first or the second frequency and repeating steps c) through h).

18. The method of claim 17 wherein the step of changing at least one of the first or the second frequency comprises changing the operating temperature of at least one of the first or the second light source.

19. The method of claim 14 further comprising the step of measuring a Doppler shift in the time varying voltage generated in step e).

20. A method of performing real time spectroscopy comprising:

a) providing a first light source that generates a first beam of light at a first frequency;

b) providing a second light source that generates a second beam of light at a second frequency;

c) modulating a conductance of a first photomixer at a difference frequency approximately equal to the difference between the first and the second frequencies in response to the first and the second light beam to generate a signal having the difference frequency;

d) transmitting the signal through a medium to be analyzed;

e) receiving the signal;

f) generating a time varying voltage in response to the signal;

g) modulating a conductance of a second photomixer at the difference frequency in response to the first and the second light beam;

h) generating a current signal in response to the time varying signal received by the second antenna and the modulated conductance of the second photomixer;

i) measuring at least one of amplitude or phase of the current signal; and

j) determining at least one of absorption or dispersion characteristics of the medium from the amplitude or phase measurement.

21. The method of claim 20 wherein the medium is a gas.

22. The method of claim 20 further comprising the step of determining a presence of a particular medium from the absorption or dispersion characteristics.

23. The method of claim 20 further comprising the step of changing at least one of the first or the second frequency and repeating steps c) through j).

24. The method of claim 20 wherein the step of determining at least one of absorption or dispersion characteristics of the medium comprises measuring a frequency chirp in the current signal.

25. A method of imaging, an object, the method comprising:

a) providing a first light source that generates a first beam of light at a first frequency;

b) providing a second light source that generates a second beam of light at a second frequency;

c) modulating a conductance of a first photomixer at a difference frequency approximately equal to the difference between the first and the second frequencies in response to the first and the second light beam to generate a signal having the difference frequency;

d) transmitting the signal through an object to be imaged;

e) receiving the signal transmitted;

f) generating a time varying voltage in response to the signal;

g) modulating a conductance of a second photomixer at the difference frequency in response to the first and the second light beam;

h) generating a current signal in response to the time varying signal received by the second antenna and the modulated conductance of the second photomixer;

i) measuring at least one of amplitude or phase of the current signal; and

j) processing at least one of the amplitude or phase of the current signal to form an image of the object.

26. The method of claim 25 further comprising the step of converting the current signal into digital data.

27. The method of claim 25 further comprising the step of down converting the current signal.

28. The method of claim 25 wherein the step of transmitting the signal through the object comprises imaging the signal to a predetermined position on the object.

29. The method of claim 25 wherein the step of receiving the signal transmitted through the object comprises imaging the signal to a detector.

30. A method of network analysis comprising:

a) providing a first light source that generates a first beam of light at a first frequency;

b) providing a second light source that generates a second beam of light at a second frequency;

c) modulating a conductance of a first photomixer at a difference frequency approximately equal to the difference between the first and the second frequencies in response to the first and the second light beam to generate a signal having the difference frequency;

d) transmitting the signal to a network to be analyzed;

e) receiving the signal;

f) generating a time varying voltage in response to the signal;

g) modulating a conductance of a second photomixer at the difference frequency in response to the first and the second light beam;

h) generating a current signal in response to the modulated conductance of the second photomixer;

i) measuring at least one of amplitude or phase of the current signal; and

j) processing at least one of the amplitude or phase of the current signal to determine at least one of a transmission or a reflection parameter of the network.

31. The method of claim 30 wherein the step of receiving the signal transmitted from the network comprises receiving the signal reflected from the network.

32. The method of claim 30 wherein the step of receiving the signal transmitted from the network comprises receiving the signal transmitted through the network.

33. The method of claim 30 wherein the at least one of a transmission or a reflection parameter comprises a scattering parameter.