On-chip photonic-phononic emitter-receiver apparatus

1. Apparatus comprising:

a membrane in which a two-dimensionally periodic phononic crystal (PnC) structure is patterned; and

at least a first optical waveguide embedded in the membrane;

wherein at least a first line-defect region interrupts the PnC structure and the first optical waveguide is embedded within the line-defect region;

wherein a photoelastically excitable vibrational mode of the line-defect region has a frequency that lies within a phononic bandgap of the PnC structure;

and wherein the first optical waveguide embedded in the membrane comprises an optical cavity configured to receive an optical input carrier wave and an optical local oscillator wave.

2. The apparatus of claim 1 , wherein the membrane is supported on a silicon-on-insulator (SOI) substrate.

3. The apparatus of claim 1 , wherein the PnC structure is defined by a two-dimensional lattice of holes, and wherein the line-defect region lacks holes.

4. The apparatus of claim 1 , wherein at least the first optical waveguide is a silicon waveguide.

5. The apparatus of claim 1 , wherein the membrane is a silicon nitride membrane.

6. The apparatus of claim 1 , wherein:

at least a second optical waveguide is embedded in the membrane within a line-defect region that interrupts the PnC structure;

the first and second optical waveguides are parallel to each other but have no substantial optical coupling to each other;

a central region of the PnC structure lies between the first and second optical waveguides;

the PnC structure is defined by a two-dimensional lattice of holes having a width of N C lattice periods between the first and second optical waveguides and a width of N lattice periods on the side of the first optical waveguide distal the second optical waveguide and on the side of the second optical waveguide distal the first optical waveguide;

each line-defect region has a width W; and

N, N C , and W are selected to produce a symmetric phononic supermode and a corresponding antisymmetric phononic supermode of the line defect regions in which the respective first and second optical waveguides are embedded.

7. The apparatus of claim 6 , wherein an input end of the first optical waveguide is optically coupled to a path for an optical input signal, and wherein an output end of the second optical waveguide is optically coupled to a path for an output signal.

8. The apparatus of claim 6 , wherein:

an input end of the first optical waveguide is optically coupled to a path for an optical input signal and an optical pump wave;

an input end of the second optical waveguide is optically coupled to a path for an optical probe wave; and

an output end of the second optical waveguide is optically coupled to a path for an output signal.

9. The apparatus of claim 6 , wherein at least one further line-defect region interrupts the PnC structure between the first optical waveguide and the second optical waveguide.

10. The apparatus of claim 6 , further comprising a signal source optically coupled to the first waveguide and a probe source optically coupled to the second waveguide.

11. The apparatus of claim 10 , wherein said apparatus is configured as a frequency filter for radio-frequency (RF) signals modulated onto an optical input wave from the signal source.

12. The apparatus of claim 10 , wherein said apparatus is configured as a wavelength converter for transferring radio-frequency (RF) signals from an optical carrier signal of a first carrier wavelength propagating in the first optical waveguide to an optical carrier of a second carrier wavelength propagating in the second optical waveguide.

13. The apparatus of claim 10 , wherein said apparatus is configured as an amplifier for transferring radio-frequency (RF) signals from an optical carrier signal of a first intensity propagating in the first optical waveguide to an optical carrier of a second intensity propagating in the second optical waveguide.

14. The apparatus of claim 10 , wherein said apparatus is configured as a time-delay element.

15. The apparatus of claim 10 , adapted to couple an optical carrier wave and an optical local oscillator wave into the first waveguide, wherein the apparatus further comprises a radio-frequency (RF) modulator arranged to modulate an RF signal onto the optical carrier wave.

16. The apparatus of claim 1 , wherein the optical cavity is a Fabry-Perot resonator cavity.

17. The apparatus of claim 1 , wherein the optical cavity is a distributed Bragg reflector cavity.

18. The apparatus of claim 17 , wherein the distributed Bragg reflector cavity is defined by width variations in the first optical waveguide.

19. A method for processing an input radio-frequency (RF) signal to produce an output RF signal, comprising:

modulating the input RF signal onto an optical input carrier wave;

injecting the optical input carrier wave into a first optical waveguide embedded in a membrane in which a two-dimensionally periodic phononic crystal (PnC) structure is patterned, wherein the optical waveguide is embedded within a line-defect region of the PnC structure and comprises an optical cavity;

injecting a local oscillator wave having a local oscillator frequency into the first optical waveguide concurrently with the optical input carrier wave so as to create a beat tone between said carrier and local oscillator waves, whereby phonons are launched into the membrane, wherein the launched phonons correspond to a photoelastically excitable vibrational mode of the line-defect region and have a frequency that lies within a phononic bandgap of the PnC structure;

tuning a center frequency of the launched phonons by varying the local oscillator frequency;

injecting an optical probe wave into the first optical waveguide embedded in the membrane, or into a further optical waveguide embedded in the membrane, within a range of the launched phonons, whereby the optical probe wave is modulated by the launched phonons;

extracting the phonon-modulated optical probe wave from its optical waveguide; and

demodulating extracted phonon-modulated optical probe wave, thereby to obtain the output RF signal.

20. The method of claim 19 , wherein the optical input carrier wave, the local oscillator wave, and the optical probe wave are all injected into the same waveguide.

21. The method of claim 19 , wherein:

the optical input carrier wave and the local oscillator wave are injected into a first optical waveguide;

at least a second optical waveguide is embedded in the membrane within a line-defect region that interrupts the PnC structure;

the first and second optical waveguides are parallel to each other but have no substantial optical coupling to each other;

a central region of the PnC structure lies between the first and second optical waveguides; and

the optical probe wave is injected into the second optical waveguide.

22. The method of claim 21 carried out to perform a filtering operation, wherein the filtering comprises propagating the launched phonons through at least one further line-defect region that lies between the first and second waveguides.

23. The method of claim 19 , wherein:

a first optical carrier wave and a second optical carrier wave are concurrently injected into the first optical waveguide;

the first optical carrier wave is spaced near enough in frequency to the local oscillator wave to create a beat tone able to launch phonons into the membrane;

the local oscillator wave is closer in frequency to the first optical carrier wave than to the second optical carrier wave;

the input RF signal is modulated onto the second optical carrier wave; and

the modulation of the input RF signal onto the second optical carrier wave produces at least one sideband that is separated from the first optical carrier wave by a frequency separation that is less than the frequency separation between the first optical carrier wave and the optical probe wave.