All-optical microwave feedback oscillator with atomic cell resonator

Abstract

We report the demonstration of an all-optical self-sustained cell-based microwave feedback oscillator. In this scheme, a microwave resonance, optically induced in a buffer-gas filled vapor cell resonator through coherent population trapping (CPT), is detected by a fast photodiode, amplified, and used to drive back, through a frequency divider, a Mach–Zehnder electro-optic modulator in a sustaining loop configuration. The total gain and phase of the system was measured in an open-loop configuration with a network analyzer. In good agreement with values predicted by the Leeson effect, the CPT feedback oscillator demonstrates an absolute phase noise of −24 dB rad2/Hz at 1 Hz offset frequency, compatible with a fractional frequency stability of 8 × 10−12 at 1 s, and a phase noise floor of −112 dB rad2/Hz, limited by the low microwave power available at the photodiode output. The amplitude noise of the oscillator shows a comparable noise floor and, for offset frequencies lower than 200 Hz, a 1/f dependence, due to the presence of the frequency divider in the loop.

Microwave phase detection of coherent population trapping resonance in a Cs vapor cell

“…This degradation was probably due to temperature variations of the complete setup but also to the fact that the EOM bias point and laser power were not actively stabilized. Short-term stability results reported here are about two orders of magnitude worse than those of state-of-the-art CPT based atomic clocks [10,11,13], using a standard optical transmission detection scheme, and comparable to those predicted from phase noise performances of a self-sustained cell-based microwave feedback oscillator [27]. With the present microwave phase detection scheme, the main challenge will be to reduce the setup residual phase noise.…”

“…In other studies, placing the atomic cell in an electromagnetic cavity can produce an oscillating magnetization responsible for a coherent signal emission observed at the atomic ground state hyperfine transition frequency [8]. Also, the direct detection of microwaves generated through stimulated Raman scattering (SRS) [23], electromagnetically-induced transparency (EIT) or CPT towards the construction of cell-based optoelectronic oscillators [23][24][25][26][27], has been reported. In this paper, we investigate an alternative method for detection of CPT resonance in a Cs vapor cell using a microwave phase A dual-frequency optical field is generated by the combination of a distributed-feedback (DFB) laser and an external fibered Mach-Zehnder electro-optic modulator (EOM).…”