Fig. 1: Integration of μFP cavity with PICs.
From: Harnessing micro-Fabry–Pérot reference cavities in photonic integrated circuits
a, Survey of the resonator thermal noise limit at 10 kHz and Q factor for on-chip ring cavity, whispering-gallery-mode (WGM) cavity and vacuum FP cavity. Ring resonator data are obtained from refs. 13,24,30,31,32; WGM resonator data, from refs. 7,33,34; and vacuum FP resonator data, from this work and refs. 1,2. Note that our cavity has more than 104 times smaller form factor than that in other work1 and does not require a vacuum enclosure. b, Schematic of the in-vacuum-bonded μFP cavity (i). ROC, radius of curvature. Photograph of the μFP cavity (ii). c, Optical ring-down measurement of the μFP cavity, yielding a Q factor of 4.26 billion. d, Schematic of the integration architecture. An RTC is required to transform mirror-like reflection to the response desired by the application. For SIL, a resonant optical feedback is required. For other applications, like PDH locking, a complete reflection suppression is required. e, Schematic of the mode-matching approach from PIC to μFP with an end-fire (i) and a grating (ii) coupler.
