Tunable optical local oscillator

• US 6,907,052 B2
• Filed: 02/19/2003
• Issued: 06/14/2005
• Est. Priority Date: 02/19/2003
• Status: Expired

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Hurrell, John P., Kozlowski, David A.
• Primary Examiner(s): Harvey, MinSun Oh
• Assistant Examiner(s): Jackson, Cornelius H.
• Application Number:
  US10/368,962
• Publication Number:
  US 20040161250A1
• Time in Patent Office: 846 Days
• Field of Search: 372/20, 372/26, 372/29.01, 372/29.011, 250/227.11, 250/205, 398/85, 398/183, 398/185
• US Class Current: 372/29.011
• CPC Class Codes: H04B 10/60 Receivers
• CPC Class Codes: H04B 10/6151 comprising a polarization controller at the receiver's input stage
• CPC Class Codes: H04B 10/64 Heterodyne , i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained

Abstract

A tunable optical local oscillator is used for optical heterodyne signal detection using an electrooptic Mach-Zehnder modulator to produce a rapidly tunable optical signal from a tunable RF frequency generator. A combination of the Mach-Zehnder modulator and optical fibers for providing stimulated Brillouin scattering are used to suppress unwanted signals for providing a spectrally pure optical local oscillator waveform. Suppression of unwanted optical signals, up to 50 dB, generated by the Mach-Zehnder modulator is obtained, resulting in high spectral purity of the optical local oscillator waveform with an extended tuning range of the tunable optical oscillator equal to the operating bandwidth of up to 60 GHz of the Mach-Zehnder modulators.

Claims

1. A tunable optical local oscillator for providing an optical local oscillator signal, the tunable optical local oscillator comprising,

a laser for providing an optical carrier having a carrier frequency,

a Mach-Zehnder modulator for providing a double sideband signal having first wavelength signal at a first frequency and a second wavelength signal at a second frequency,

an asymmetric means for asymmetric filtering of the double sideband signal for increasing the intensity of the first wavelength signal over the second wavelength signal for providing power asymmetry between the first wavelength signal and the second wavelength signal, and

a laser ring for providing a backward traveling wave and a forward traveling wave of the first wavelength signal for feeding back the first wavelength signal, the backscattering serving to cancel the first wave length signal for passing the second wavelength signal as the optical local oscillator signal.

2. The tunable optical local oscillator of claim 1 further comprising,

a tunable RF local oscillator for providing a modulation signal at a modulation frequency for tuning the Mach-Zehnder modulator to the double sideband signal.

3. The tunable optical local oscillator of claim 1 further comprising,

a bias source for biasing the Mach-Zehnder modulator for suppressing the optical carrier of the double sideband signal.

4. The tunable optical local oscillator of claim 1 further comprising,

a tunable RF local oscillator for providing a modulation signal at a modulation frequency for tuning the Mach-Zehnder modulator to the double sideband signal, and

a bias source for biasing the Mach-Zehnder modulator for suppressing the optical carrier.

5. The tunable optical local oscillator of claim 1 further comprising,

a tunable RF local oscillator for providing a modulation signal at a modulation frequency for tuning the Mach-Zehnder modulator to the double sideband signal, and

a bias source for biasing the Mach-Zehnder modulator for suppressing the optical carrier, the first frequency being displaced below the carrier frequency by the modulation frequency, and the second frequency being displaced above the carrier frequency by the modulation frequency, the first wavelength signal being a longer wavelength signal having a long wavelength, the second wavelength signal being a shorter wavelength signal having a short wavelength shorter than the longer wavelength.

6. The tunable optical local oscillator of claim 1 wherein,

the first wavelength signal has a first power intensity greater than a second power intensity of the second wavelength signal.

7. The tunable optical local oscillator of claim 1, wherein the asymmetric means comprises,

a first erbium doped optical fiber amplifier for amplifying the double sideband signal into an amplified double sideband signal, the first wavelength signal is an amplified first wavelength signal having a first power intensity greater than a second power intensity of the second wavelength signal being an amplified second wavelength signal.

8. The tunable optical local oscillator of claim 1, wherein the asymmetric means comprises,

a tunable Fabry-Perot filter centered on the first frequency for passing the first wavelength signal and for attenuating the second wavelength signal, the second wavelength signal having a low power intensity lower than a high power intensity of the first wavelength signal.

9. The tunable optical local oscillator of claim 1, wherein the asymmetric means comprises,

an erbium doped optical fiber amplifier for amplifying the double sideband signal into an amplified double sideband signal, the first wavelength signal is an amplified first wavelength signal having a first power intensity greater than a second power intensity of the second wavelength signal being an amplified second wavelength signal, and

a tunable Fabry-Perot filter centered on the first frequency for passing the amplified first wavelength signal and for attenuating the amplified second wavelength signal, the amplified second wavelength signal having a low power intensity lower than a high power intensity of the amplified first wavelength signal.

10. The tunable optical local oscillator of claim 1 wherein the laser ring comprises,

a nonlinear optical waveguide for backscattering the first wavelength signal having an intensity above a threshold value for producing a backward traveling optical signal and for forward propagating the second wavelength signal, and

a feedback circulator for feeding back the backward traveling optical signal to the nonlinear optical waveguide for canceling the first wavelength signal.

11. The tunable optical local oscillator of claim 1 wherein the laser ring comprises,

a nonlinear optical waveguide for backscattering the first wavelength signal having an intensity above a threshold value into a backward traveling optical signal and for forward propagating the first wavelength signal and the second wavelength signal, and

a feedback circulator for feeding back the backward traveling optical signal as a fedback backward traveling optical signal to the nonlinear optical waveguide for canceling the first wavelength signal.

12. The tunable optical local oscillator of claim 1 wherein,

the laser ring is a Brillouin fiber laser ring.

13. The tunable optical local oscillator of claim 1 wherein,

the laser provides stimulated Brillouin backscattering generating the backward traveling wave as a Stokes shifted wave.

14. The tunable optical local oscillator of claim 1 wherein the laser ring comprises,

a nonlinear optical waveguide for backscattering the first wavelength signal having an intensity above a threshold value into a backward traveling optical signal and for forward propagating the first wavelength signal and the second wavelength signal,

a feedback circulator for feeding back the backward traveling optical signal as a fedback backward traveling optical signal,

an amplifier for amplifying the fedback backward traveling optical signal as an amplified backward traveling optical signal, the amplified backward traveling signal, and

an output circulator for communicating the amplified backward traveling optical signal to the nonlinear optical waveguide and for passing the second wavelength as the optical local oscillator signal.

15. The tunable optical local oscillator of claim 1 wherein the laser ring comprises,

a nonlinear optical waveguide for backscattering the first wavelength signal having an intensity above a threshold value into a backward traveling optical signal and for forward propagating the first wavelength signal and the second wavelength signal,

a feedback circulator for feeding back the backward traveling optical signal as a fedback backward traveling optical signal, and

an amplifier for amplifying the fedback backward traveling optical signal as an amplified backward traveling optical signal, the amplified backward traveling signal being fed to the nonlinear optical waveguide for canceling the first wavelength signal.

16. The tunable optical local oscillator of claim 15 wherein,

the amplifier is a erbium doped optical fiber amplifier.