Guided wave opto-acoustic device
The various technologies presented herein relate to various hybrid phononic-photonic waveguide structures that can exhibit nonlinear behavior associated with traveling-wave forward stimulated Brillouin scattering (forward-SBS). The various structures can simultaneously guide photons and phonons in a suspended membrane. By utilizing a suspended membrane, a substrate pathway can be eliminated for loss of phonons that suppresses SBS in conventional silicon-on-insulator (SOI) waveguides. Consequently, forward-SBS nonlinear susceptibilities are achievable at about 3000 times greater than achievable with a conventional waveguide system. Owing to the strong phonon-photon coupling achievable with the various embodiments, potential application for the various embodiments presented herein cover a range of radiofrequency (RF) and photonic signal processing applications. Further, the various embodiments presented herein are applicable to applications operating over a wide bandwidth, e.g. 100 MHz to 50 GHz or more.
1. Apparatus comprising:
a suspended membrane;
at least one optical waveguiding member included in the membrane and at least partially extensive in a longitudinal optical propagation direction; and
at least one phononic resonator defined in the membrane, extensive in said longitudinal direction, and traversed by the optical waveguiding member.
2. The apparatus of claim 1 , wherein each phononic resonator comprises at least one acoustically reflective feature.
3. The apparatus of claim 2 , wherein the acoustically reflective feature is a slot.
4. The apparatus of claim 2 , wherein the acoustically reflective feature is a phononic crystal.
5. The apparatus of claim 2 , wherein the acoustically reflective feature is a Bragg grating.
6. The apparatus of claim 2 , wherein each phononic resonator comprises at least one pair of acoustically reflective features disposed on opposite sides of the optical waveguide.
7. The apparatus of claim 1 , wherein the optical waveguiding member traverses two or more phononic resonators.
8. The apparatus of claim 1 , wherein the membrane has a composition that is substantially silicon nitride and the optical waveguiding member has a composition that is substantially silicon.
9. The apparatus of claim 1 , wherein the membrane and the at least one phononic resonator are conformed to support the propagation of phonons having at least some frequencies in the range 100 MHz-50 GHz on a path that traverses the at least one phononic resonator.
10. The apparatus of claim 1 , wherein the membrane is supported, and offset from a silicon substrate, by a patterned layer of silicon dioxide.
11. The apparatus of claim 1 , further comprising:
a modulator arranged to modulate pump light received from a pump source in response to a radiofrequency waveform received from a radiofrequency generator;
an input combiner arranged to combine an optical input signal with the modulated pump light and to inject the combined light into the optical waveguiding member; and
an output coupling element arranged to extract an output optical signal from the optical waveguiding member.
12. A method, comprising:
injecting pump light and probe light into a waveguide core supported on a membrane in which at least one phononic resonator having a phononic resonance is defined;
extracting the probe light after the probe light has traversed the membrane in a longitudinal optical propagation direction; and
recovering an optical signal from the extracted probe light;
wherein the pump light is modulated at a frequency related to a said phononic resonance;
and wherein the injecting of light into the waveguide core generates phonons that propagate within the membrane in a direction transverse to the longitudinal optical propagation direction.
13. The method of claim 12 , wherein the waveguide core is silicon and the membrane layer is silicon nitride.
14. The method of claim 12 , wherein the phonons have a frequency in the range 100 MHz-50 GHz.
15. The method of claim 12 , wherein the phonons are incident upon a reflector surface that redirects the phonons in a direction substantially toward the waveguide core.