The Micro Loop-Gap Resonator: A Novel Miniaturized Microwave Cavity for Double-Resonance Rubidium Atomic Clocks

Nowadays mobile and battery-powered applications push the need for radically miniaturized and low-power frequency standards that surpass the stability achievable with quartz oscillators. For the miniaturization of double-resonance rubidium ( 87 Rb) atomic clocks, the size reduction of the microwave cavity or resonator (MWR) to well below the wavelength of the atomic transition (6.835 GHz for 87 Rb) is of high interest. Here, we present a novel miniaturized MWR, the μ-LGR, for use in a miniature DR atomic clock and designed to apply a well-defined microwave field to a microfabricated Rb cell that provides the reference signal for the clock. This μ-LGR consists of a loop-gap resonator-based cavity with very compact dimensions (<;0.9 cm 3 ). The μ-LGR meets the requirements of the application and its fabrication and assembly can be performed using repeatable and low-cost techniques. The concept of the proposed device was proven through simulations, and prototypes were successfully tested. Experimental spectroscopic evaluation shows that the μ-LGR is well-suited for use in an atomic clock. In particular, a clock short-term stability of 7 × 10 -12 τ -1/2 was measured, which is better than for other clocks using microfabricated cells and competitive with stabilities of compact Rb clocks using conventional glass-blown cells.