Tunable radio frequency and microwave photonic filters

• US 20050175358A1
• Filed: 01/11/2005
• Published: 08/11/2005
• Est. Priority Date: 01/12/2004
• Status: Active Grant

• Current Assignee: Oewaves Incorporated
• Original Assignee: Oewaves Incorporated
• Inventors: Ilchenko, Vladimir, Maleki, Lutfollah
• Granted Patent: US 7,587,144 B2
• Time in Patent Office: Days
• US Class Current: 398/198
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 2/00 Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light G02F1/35 takes precedence
• CPC Class Codes: G02F 2201/16 series; tandem
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/15 involving resonance effects, e.g. resonantly enhanced interaction
• CPC Class Codes: H03C 7/00 Modulating electromagnetic waves devices or arrangements for the modulation of light G02F1/00
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/60 Receivers

Abstract

RF and microwave devices and techniques are disclosed for processing RF and microwave signals by using (1) photonic or optical components and (2) RF and microwave components. In some implementations, a part of the processing is performed in the RF and microwave domain such as applying a microwave or RF input signal to control an optical modulator ,and another part of the processing is performed in the optical domain such as optical filtering of the modulated optical beam to select desired microwave or RF spectral components. The frequency of a selected spectral component can be tuned by either tuning the frequency of the optical beam that is modulated by the optical modulator or a filter that is used to filter modulated optical beam.

Claims

1. A device, comprising:

an input port to receive an input microwave or RF signal;

a laser to produce a continuous-wave laser beam;

a first optical path to receive a first portion of the laser beam;

a second optical path to receive a second portion of the laser beam, the second optical path comprising;

an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and

a tunable optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component, the tunable optical filter comprising two optical resonators that are optically coupled to produce a filter function of at least a second order;

a tuning control unit to tune at least one of the two optical resonators to change a frequency of the at least one selected spectral component; and

an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component.

2. The device as in claim 1, wherein the two optical resonators exhibit and are tuned via an electro-optic effect.

3. The device as in claim 2, wherein the two optical resonators comprise a lithium niobate material that produces the electro-optic effect.

4. The device as in claim 2, wherein the two optical resonators are whispering gallery mode resonators.

5. The device as in claim 1, wherein the two optical resonators are whispering gallery mode resonators.

6. The device as in claim 1, wherein the two optical resonators are whispering gallery mode resonators and are tunable via an electro-optic effect, the tunable optical filter further comprising a third electro-optic whispering gallery mode resonator optically coupled to one of the two tunable optical resonators and tuned by the tuning control unit to effectuate a third order filter function in the tunable optical filter.

7. The device as in claim 1, wherein the tunable optical filter further comprises:

a first optical waveguide optically coupled to the first and second optical resonators and to receive the modulated optical beam from the optical modulator, and

a second, separate optical waveguide optically coupled to the first and second optical resonators to output the filtered modulated optical beam to the optical detector, wherein the first and second optical resonators are not directly optically coupled to each other and are optically coupled with each other via optical coupling to the first and second waveguides.

8. The device as in claim 7, wherein the frequency of the laser is at between resonance frequencies of the two optical resonators and the filtered modulated optical beam has a linewidth less than a linewidth of each of the two optical resonators.

9. The device as in claim 1, wherein the tunable optical filter further comprises:

a first optical waveguide optically coupled to the first and second optical resonators and to receive the modulated optical beam from the optical modulator and to output the filtered modulated optical beam to the optical detector, and

a second, separate optical waveguide optically coupled to the first and second optical resonators, wherein the first and second optical resonators are directly optically coupled to each other in addition to optical coupling with each other via optical coupling to the first and second waveguides.

10. The device as in claim 9, wherein the frequency of the laser is at between resonance frequencies of the two optical resonators and the filtered modulated optical beam has a third-order filter function.

11. The device as in claim 1, wherein the two optical resonators are first and second optical resonators, respectively, and the tunable optical filter further comprises third and fourth optical resonators,

wherein the first optical resonator receives the modulated optical beam from the optical modulator and the fourth optical resonator outputs the filtered modulated optical beam to the optical detector,

wherein the first, second, third and fourth optical resonators are optically coupled to one another in a configuration that,

the first optical resonator is optically coupled to the second and third optical resonators,

the second optical resonator is further optically coupled to the fourth optical resonator,

the third optical resonator is further optically coupled to the fourth optical resonator, and

the second and third optical resonators are not directly coupled to each other and are indirectly coupled via the first and fourth optical resonators.

12. The device as in claim 11, further comprising:

a first optical coupler optically coupled to the first optical resonator to direct the modulated optical beam to the first optical resonator; and

a second optical coupler optically coupled to the fourth optical resonator to couple light in the fourth optical resonator out as the filtered modulated optical beam.

13. A device, comprising:

an input port to receive an input microwave or RF signal;

a tunable laser to produce a continuous-wave laser beam and to tune a laser frequency of the laser beam;

a first optical path to receive a first portion of the laser beam;

a second optical path to receive a second portion of the laser beam, the second optical path comprising;

an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and

an optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component;

a tuning control unit to tune the laser frequency of the tunable laser to change a frequency of the at least one selected spectral component; and

an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component.

14. The device as in claim 13, wherein the optical filter comprises a fixed-frequency optical filter.

15. The device as in claim 13, wherein the optical fiber comprises a Fabry-Perot resonator filter.

16. The device as in claim 13, wherein the optical filter comprises at least two cascaded optical resonators.

17. The device as in claim 16, wherein the optical resonators comprise whispering gallery mode resonators.

18. The device as in claim 16, wherein the whispering gallery mode resonators are microsphere resonators.

19. The device as in claim 16, wherein the whispering gallery mode resonators are toroidal resonators.

20. The device as in claim 16, wherein the optical resonators are ring resonators that have whispering gallery modes.

21. The device as in claim 13, wherein the optical resonators exhibit an electro-optic effect.

22. The device as in claim 13, wherein the optical filter is tunable in frequency.

23. A method for filtering a signal, comprising:

applying a microwave or RF signal to an optical modulator to control optical modulation of an optical beam and to produce a modulated optical beam that carries the signal;

optically filtering the modulated optical beam to reject undesired signal spectral bands in the modulated optical beam to produce a filtered optical beam that carries at least one selected signal spectral band;

tuning a frequency of the optical beam to select the frequency of the at least one selected signal spectral band;

combining a portion of the optical beam that is not modulated by the optical modulator and the filtered optical beam into a combined beam; and

using an optical detector to convert the combined beam into a filtered microwave or RF signal that carries the at least one selected signal spectral band.

24. The method as in claim 23, further comprising using a fixed frequency optical filter to optically filter the modulated optical beam.

25. The method as in claim 23, further comprising using a Fabry-Perot resonator filter to optically filter the modulated optical beam.

26. The method as in claim 23, further comprising using cascaded whispering gallery mode resonators to optically filter the modulated optical beam.

27. The method as in claim 23, further comprising using an optical filter with a filter function of at least a second order to optically filter the modulated optical beam.

28. The method as in claim 27, further comprising using at least two cascaded optical resonators to produce the filter function of at least a second order.

29. The method as in claim 23, further comprising:

using cascaded optical resonators to optically filter the modulated optical beam; and

tuning the optical resonators to achieve a desired initial filter spectral profile in the filtered optical beam prior to tuning the frequency of the optical beam to select the frequency of the at least one selected signal spectral band.