Wide-band RF photonic receivers and other devices using two optical modes of different quality factors
This document provides techniques, apparatus and designs for using electro-optic WGM resonators that support two different families of optical WGM modes with different quality factors in various applications. A radio frequency (RF) resonator is formed on the optical resonator and structured to supply an RF field and spatially overlaps the RF field of the RF resonator with the first and second optical whispering gallery modes to cause RF energy in the RF field at a first RF carrier frequency to couple with the first optical whispering gallery mode and RF energy in the RF field at a second RF carrier frequency to couple with the second optical whispering gallery mode.
1. A method for operating a radio frequency (RF) photonic receiver that has an optical resonator formed of an electro-optic material and shaped to support at least one high quality factor optical mode having a narrow bandwidth, and at least one low quality factor optical mode with a broader bandwidth than the narrow bandwidth of the high quality factor optical mode, comprising:
coupling external laser light into the optical resonator in the high quality factor optical mode into the narrow bandwidth to optically energize the optical resonator;
applying a spatially inhomogeneous RF field to the electro-optical material in a region of the optical resonator where the high quality factor and low quality factor optical modes are localized to cause optical coupling that transfers optical energy from the high quality factor optical mode to the low quality factor optical mode;
applying an RF signal modulation in the RF field to cause an electro-optic modulation of the light in the low quality factor optical whispering gallery mode to produce modulated light in the low quality factor optical mode that carries the RF signal modulation in the broader bandwidth than the narrow bandwidth of the high quality factor optical mode;
and effectuating an increase in the bandwidth of the RF photonic receiver beyond what is permitted by the narrow bandwidth of the high quality factor optical mode of the optical resonator by converting the modulated light in the low quality factor optical mode into an RF output signal that carries RF signal modulation.
2. The method as in claim 1 , comprising:
operating a feedback control circuit to use the RF output signal to produce a feedback control signal; and
including the feedback control signal as part of the RF field that is applied to the electro-optical material to enable a closed opto-electrical loop to cause a signal oscillation in the RF photonic receiver.
3. The method as in claim 1 , wherein the optical resonator is a conically shaped whispering gallery mode resonator, and the high quality factor optical mode and the low quality factor optical mode are whispering gallery modes.
4. The method as in claim 1 , wherein the optical resonator is a whispering gallery mode resonator, and the high quality factor optical mode and the low quality factor optical mode are whispering gallery modes.