Electro-optic electromagnetic field sensor system with optical bias adjustment

• US 5,963,034 A
• Filed: 11/20/1997
• Issued: 10/05/1999
• Est. Priority Date: 09/19/1996
• Status: Expired due to Fees

• Current Assignee: Viavi Solutions, Inc. (Lumentum Holdings Inc.)
• Original Assignee: Ramar Corp (Lumentum Holdings Inc.)
• Inventors: Stenger, Vincent E., Mahapatra, Amaresh
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US08/975,349
• Time in Patent Office: 684 Days
• Field of Search: 324/95, 324/96, 324/244.1, 324/260, 250/227.11, 250/227.14, 250/227.17, 250/231.1, 356/351, 356/352, 356/345, 356/346
• US Class Current: 324/244.1
• CPC Class Codes: G01R 29/0885 using optical probes, e.g. electro-optical, luminescent, glow discharge, or optical interferometers
• CPC Class Codes: G01R 33/032 using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect

Abstract

An electro-optic electromagnetic field sensor system includes an electro-optic sensor located at an electromagnetic field sensing site for detecting an intensity of an electromagnetic field. The sensor changes an optical measuring signal received from a laser source to an optical sensor signal representative of the electromagnetic field intensity. An optical bias adjust unit optically coupled to the laser source adjusts the bias operating point of the electro-optic sensor responsive to an electrical bias adjust signal which includes a test signal component. A detector optically coupled to the electro-optic sensor converts the optical sensor signal to an electrical sensor signal and detects a feedback signal indicative of the transfer function of the electro-optic sensor operating on the test signal component. A bias control circuit electrically coupled to the optical bias adjust unit generates the bias adjust signal responsive to the feedback signal. An optical input fiber couples the optical measuring signal from the laser source to the electro-optic sensor and an optical output fiber couples the optical sensor signal to the detector.

Claims

1. An electro-optic electromagnetic field sensor system comprising:

a laser source for providing an optical measuring signal;

an electro-optic sensor optically coupled to the laser source for detecting an intensity of an electromagnetic field and for changing the optical measuring signal to an optical sensor signal that is representative of the field intensity;

an optical bias adjust unit optically coupled to the laser source for adjusting the bias operating point of the sensor;

a detector optically coupled to the sensor for converting the optical sensor signal to an electrical sensor signal;

an optical input fiber for coupling the optical measuring signal from the laser source to the sensor;

an optical output fiber for coupling the optical sensor signal to the detector such that the electro-optic sensor is located at a field sensing site and the laser source, optical bias adjust unit, and detector are located remote from the field sensing site.

2. The system of claim 1 wherein the optical bias adjust unit is responsive to an electrical bias control signal having a test signal component and the detector is operative to detect a feedback signal indicative of the transfer function of the sensor operating on the test signal component and wherein the system further comprises a bias control circuit electrically coupled to the optical bias adjust unit for generating the bias control signal responsive to the feedback signal received from the detector.

3. The system of claim 1 wherein the electro-optic sensor comprises a Fabry-Perot resonator.

4. The system of claim 1 wherein the electro-optic sensor comprises a polarization mixing sensor.

5. The system of claim 4 wherein the optical measuring signal comprises first and second polarized optical components which are orthogonal to each other and wherein the polarization mixing sensor comprises:

an antenna section for detecting an intensity of an electromagnetic field and producing an electrical intensity signal having an amplitude proportional to the field intensity;

a phase modulator optically coupled to the laser source and electrically coupled to the antenna section for changing a phase of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section; and

an optical polarization mixer optically coupled to the phase modulator for optically mixing the first and second polarized optical components received from the phase modulator to produce an optical amplitude modulation signal proportional to a phase difference between the first and second polarized optical components.

6. The system of claim 5 wherein the optical polarization mixer comprises an optical polarizing fiber.

7. The system of claim 5 wherein the optical polarization mixer comprises a polarizer plate.

8. The system of claim 5 wherein the antenna section includes a three-dimensional biconical antenna.

9. The system of claim 5 wherein the antenna section includes a two-dimensional bow-tie pattern antenna.

10. The system of claim 1 further comprising an ion exchanged glass waveguide formed at a curve on a glass substrate and coupled to the electro-optic sensor wherein the waveguide couples light from the sensor to a return waveguide formed alongside the sensor such that the sensor is single-ended.

11. An electro-optic electromagnetic field sensor system comprising:

a laser source for providing an optical measuring signal having first and second polarized optical components which are orthogonal to each other;

an antenna section for detecting an intensity of an electromagnetic field and producing an electrical intensity signal having an amplitude proportional to the electromagnetic field intensity;

a phase modulator optically coupled to the laser source and electrically coupled to the antenna section for changing a phase of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section;

an optical polarization mixer optically coupled to the phase modulator for optically mixing the first and second polarized optical components received from the phase modulator to produce an optical amplitude modulation signal proportional to a phase difference between the first and second polarized optical components;

a detector optically coupled to the optical polarization mixer for converting the optical amplitude modulation signal to an electrical amplitude modulation signal;

an optical input polarization-maintaining fiber for coupling the first and second polarized optical components of the optical measuring signal from the laser source to the phase modulator; and

an optical output fiber for coupling the optical amplitude modulation signal to the detector such that the phase modulator and the antenna section are located at an electromagnetic field sensing site and the laser source and detector are located remote from the electromagnetic field sensing site.

12. The system of claim 11 wherein the optical polarization mixer comprises an optical polarizing fiber.

13. The system of claim 11 wherein the optical polarization mixer comprises a polarizer plate.

14. The system of claim 11 further comprising:

a bias control circuit for providing a bias control signal; and

a second phase modulator optically coupled to the laser source at the remote site and electrically coupled to the bias control circuit for changing a phase of one of the first and second polarized optical components of the optical measuring signal responsive to the bias control signal.

15. The system of claim 11 wherein the detector further detects a feedback signal indicative of the transfer function of the phase modulator operating on a test signal and wherein the system further comprises:

an optical bias adjust unit optically coupled to the laser source at the remote site for adjusting the bias operating point of the phase modulator responsive to an electrical bias control signal; and

a bias control circuit electrically coupled to the optical bias adjust unit for generating the bias control signal responsive to the feedback signal received from the detector and for generating the test signal.

16. The system of claim 15 wherein the optical bias adjust unit includes a second phase modulator for changing a phase of one of the first and second polarized optical components of the optical measuring signal responsive to the bias control signal and wherein the second phase modulator is located remote from the electromagnetic field sensing site.

17. The system of claim 11 further comprising:

a splitter for splitting the optical measuring signal; and

a reference waveguide formed on a substrate wherein the phase modulator is located in proximity to the reference waveguide on the substrate, the reference waveguide receiving a portion of the optical measuring signal from the splitter for adjusting for environmental effects on the phase modulator response.

18. An electro-optic electromagnetic field sensor system comprising:

a laser source for providing an optical measuring signal having first and second polarized optical components which are orthogonal to each other;

an antenna section for detecting an intensity of an electromagnetic field and producing an electrical intensity signal having an amplitude proportional to the electromagnetic field intensity;

a resonator coupled to the laser source and electrically coupled to the antenna section for changing the amplitude of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section to produce an optical amplitude modulation signal;

a detector coupled to the resonator for converting the optical amplitude modulation signal to an electrical amplitude modulation signal;

an optical input polarization-maintaining fiber for coupling one of the first and second polarized optical components of the optical measuring signal from the laser source to the resonator; and

an optical output fiber for coupling the optical amplitude modulation signal to the detector such that the resonator and the antenna section are located at an electromagnetic field sensing site and the laser source and detector are located remote from the electromagnetic field sensing site.

19. The system of claim 18 further comprising:

a bias control circuit for providing a bias control signal; and

wherein the laser source includes a tunable narrow-line laser responsive to the bias control signal to adjust the laser source wavelength.

20. The system of claim 18 wherein the detector further detects a feedback signal indicative of the transfer function of the resonator operating on a test signal and wherein the laser source includes a tunable narrow-line laser responsive to a bias control signal to adjust the laser source wavelength and wherein the system further comprises a bias control circuit for generating the bias control signal responsive to the feedback signal and for generating the test signal.

21. The system of claim 18 further comprising:

a splitter for splitting the optical measuring signal; and

a reference waveguide formed on a substrate wherein the resonator is located in proximity to the reference waveguide on the substrate, the reference waveguide receiving a portion of the optical measuring signal from the splitter for adjusting for environmental effects on the resonator response.

22. An electro-optic electromagnetic field sensor system comprising:

a laser source for providing an optical measuring signal;

a splitter for splitting the optical measuring signal, an optical input fiber coupling the optical measuring signal from the laser source to the splitter;

an electro-optic sensor formed on a substrate for detecting an intensity of an electromagnetic field, the sensor receiving a first portion of the optical measuring signal from the splitter to provide an optical sensor signal that is representative of the field intensity;

an optical bias adjust unit coupled to the laser source for adjusting the bias operating point of the sensor responsive to an electrical bias control signal having a test signal component;

a reference waveguide formed on the substrate in proximity to the electro-optic sensor for adjusting for environmental effects on the sensor, the reference waveguide receiving a second portion of the optical measuring signal from the splitter to provide an optical feedback signal indicative of the transfer function of the sensor operating on the test signal component;

a first detector coupled to the sensor for converting the optical sensor signal to an electrical sensor signal;

a second detector coupled to the reference waveguide for converting the optical feedback signal to an electrical feedback signal;

a bias control circuit electrically coupled to the optical bias adjust unit for generating the bias control signal responsive to the feedback signal received from the second detector;

a first optical output fiber for coupling the optical sensor signal to the first detector; and

a second optical output fiber for coupling the optical feedback signal to the second detector.

23. The system of claim 22 wherein the electro-optic sensor comprises a Fabry-Perot resonator.

24. The system of claim 22 wherein the electro-optic sensor comprises a polarization mixing sensor.

25. The system of claim 24 wherein the optical measuring signal comprises first and second polarized optical components which are orthogonal to each other and wherein the polarization mixing sensor comprises:

an antenna section for detecting an intensity of an electromagnetic field and producing an electrical intensity signal having an amplitude proportional to the field intensity;

a phase modulator electrically coupled to the antenna section for changing a phase of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section; and

an optical polarization mixer coupled to the phase modulator for optically mixing the first and second polarized optical components received from the phase modulator to produce an optical amplitude modulation signal proportional to a phase difference between the first and second polarized optical components.

26. The system of claim 25 wherein the optical polarization mixer comprises an optical polarizing fiber.

27. The system of claim 25 wherein the optical polarization mixer comprises a polarizer plate.

28. For use in an electro-optic electromagnetic field sensor system having a laser source for providing an optical measuring signal and a splitter for splitting the optical measuring signal, apparatus comprising:

an electro-optic sensor formed on a substrate for detecting an intensity of an electromagnetic field, the sensor receiving a first portion of the optical measuring signal from the splitter to provide an optical sensor signal that is representative of the field intensity; and

a reference waveguide formed on the substrate in proximity to the electro-optic sensor for adjusting for environmental effects on the sensor, the reference waveguide receiving a second portion of the optical measuring signal from the splitter to provide an optical feedback signal indicative of the transfer function of the sensor.

29. The apparatus of claim 28 wherein the electro-optic sensor comprises a Fabry-Perot resonator.

30. The apparatus of claim 28 wherein the electro-optic sensor comprises a polarization mixing sensor.

31. The apparatus of claim 28 wherein the electro-optic sensor and the reference waveguide are fabricated on a lithium niobate substrate by titanium diffusion.

32. The apparatus of claim 28 wherein the electro-optic sensor and the reference waveguide are fabricated on a lithium niobate substrate by proton exchange.

33. For use in an electro-optic electromagnetic field sensor system having a laser source for providing an optical measuring signal, apparatus comprising:

an electro-optic sensor formed on a lithium niobate substrate for detecting an intensity of an electromagnetic field, the sensor changing the optical measuring signal to an optical sensor signal that is representative of the field intensity;

a return waveguide formed on the lithium niobate substrate in proximity to the sensor; and

an optically transmissive substrate having a curvilinear waveguide formed thereon, the waveguide having one end coupled to the electro-optic sensor and the other end coupled to the return waveguide wherein the waveguide couples the optical sensor signal from the sensor to the return waveguide.

34. The apparatus of claim 33 wherein the optically transmissive substrate comprises glass and the curvilinear waveguide comprises an ion-exchanged glass waveguide.

35. The apparatus of claim 33 wherein the electro-optic sensor comprises a Fabry-Perot resonator.

36. The apparatus of claim 33 wherein the electro-optic sensor comprises a polarization mixing sensor.

37. An electro-optic electromagnetic field sensor comprising:

a three-dimensional biconical antenna section for detecting an intensity of an electromagnetic field and producing an electrical intensity signal having an amplitude proportional to the field intensity; and

an electro-optic section coupled to the antenna section responsive to the electrical intensity signal to change an optical measuring signal to an optical sensor signal which is representative of the field intensity.

38. The electro-optic sensor of claim 37 wherein the electro-optic section comprises:

a phase modulator formed on a lithium niobate substrate comprising an optical input for receiving an optical measuring signal having first and second polarized optical components and a pair of electrodes coupled to the antenna section responsive to the electrical intensity signal to change a phase of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section.

39. The electro-optic sensor of claim 38 further comprising:

an optical polarization mixer optically coupled to the phase modulator for optically mixing the first and second polarized optical components received from the phase modulator to produce an optical amplitude modulation signal proportional to a phase difference between the first and second polarized optical components.

40. The electro-optic sensor of claim 38 further comprising:

a return waveguide formed on the lithium niobate substrate in proximity to the phase modulator; and

an optically transmissive substrate having a curvilinear waveguide formed thereon, the waveguide having one end coupled to the phase modulator and the other end coupled to the return waveguide wherein the waveguide couples the optical sensor signal from the phase modulator to the return waveguide.

41. The electro-optic sensor of claim 40 wherein the optically transmissive substrate comprises glass and the curvilinear waveguide comprises an ion-exchanged waveguide.

42. The electro-optic sensor of claim 37 wherein the electro-optic section comprises:

a resonator formed on a lithium niobate substrate comprising an optical input for receiving an optical measuring signal having first and second polarized optical components and a pair of electrodes coupled to the antenna section responsive to the electrical intensity signal to change the amplitude of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section to produce an optical amplitude modulation signal.

43. An electro-optic electromagnetic field sensor comprising:

a two-dimensional bow-tie pattern antenna section for detecting an intensity of an electromagnetic field and producing an electrical intensity signal having an amplitude proportional to the field intensity; and

an electro-optic section coupled to the antenna section responsive to the electrical intensity signal to change an optical measuring signal to an optical sensor signal which is representative of the field intensity.

44. The electro-optic sensor of claim 43 wherein the electro-optic section comprises:

a phase modulator formed on a lithium niobate substrate comprising an optical input for receiving an optical measuring signal having first and second polarized optical components and a pair of electrodes coupled to the antenna section responsive to the electrical intensity signal to change a phase of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section.

45. The electro-optic sensor of claim 44 further comprising:

an optical polarization mixer optically coupled to the phase modulator for optically mixing the first and second polarized optical components received from the phase modulator to produce an optical amplitude modulation signal proportional to a phase difference between the first and second polarized optical components.

46. The electro-optic sensor of claim 44 further comprising:

a return waveguide formed on the lithium niobate substrate in proximity to the phase modulator; and

a glass substrate having a curvilinear ion-exchanged glass waveguide formed thereon, the glass waveguide having one end coupled to the phase modulator and the other end coupled to the return waveguide wherein the glass waveguide couples the optical sensor signal from the phase modulator to the return waveguide.

47. The electro-optic sensor of claim 43 wherein the electro-optic section comprises:

a resonator formed on a lithium niobate substrate comprising an optical input for receiving an optical measuring signal having first and second polarized optical components and a pair of electrodes coupled to the antenna section responsive to the electrical intensity signal to change the amplitude of one of the first and second polarized optical components of the optical measuring signal in an amount proportional to the amplitude of the electrical intensity signal from the antenna section to produce an optical amplitude modulation signal.