Michele Giunta

Photonic microwave signals with zeptosecond-level absolute timing noise

Ultralow-noise microwave signals are generated at 12 GHz by a low-noise fibre-based frequency comb and cutting-edge photodetection techniques. The microwave signals have a fractional frequency stability below 6.5 × 10–16 at 1 s and a timing noise floor below 41 zs Hz–1/2. Photonic synthesis of radiofrequency (RF) waveforms revived the quest for unrivalled microwave purity because of its ability to convey the benefits of optics to the microwave world1,2,3,4,5,6,7,8,9,10,11. In this work, we perform a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fibre-based frequency comb and cutting-edge photodetection techniques. We demonstrate the generation of the purest microwave signal with a fractional frequency stability below 6.5 × 10−16 at 1 s and a timing noise floor below 41 zs Hz−1/2 (phase noise below −173 dBc Hz−1 for a 12 GHz carrier). This outperforms existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with the lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems12, telecommunications13 and time–frequency metrology2,14. The measurement methods developed here can benefit the characterization of a broad range of signals.

Space-borne frequency comb metrology

Precision time references in space are of major importance to satellite-based fundamental science, global satellite navigation, earth observation, and satellite formation flying. Here we report on the operation of a compact, rugged, and automated optical frequency comb setup on a sounding rocket in space under microgravity. The experiment compared two clocks, one based on the optical D2 transition in Rb, and another on hyperfine splitting in Cs. This represents the first frequency comb based optical clock operation in space, which is an important milestone for future satellite-based precision metrology. Based on the approach demonstrated here, future space-based precision metrology can be improved by orders of magnitude when referencing to state-of-the-art optical clock transitions.

Ultra-low noise microwave signal generation with an optical frequency comb

Photonic synthesis of radio frequency waveforms revived the quest for unrivalled microwave purity by its seducing ability to convey the benefits of the optics to the microwave world. In this contribution, we will present a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fiber-based frequency comb and cutting-edge photo-detection techniques. We will show the generation of the purest microwave signal with a fractional frequency stability below 6.5×10-16 at 1 s and a timing noise floor below 41 zs Hz-1/2 (phase noise below -173 dBc Hz-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurements methods developed here can benefit the characterization of a broad range of signals.

Rapid electro-optic control of the carrier-envelope-offset frequency for ultra-low noise frequency combs

We report on a novel electro-optic modulator that acts on the carrier-envelope-offset frequency of a femtosecond pulsed laser with negligible cross-talk to the position of the optical carrier modes. The fast response on the nanosecond time scale allows to stabilize the carrier-envelope-offset frequency with a bandwidth in excess of 1 MHz while not perturbing a potential independent stabilization of a carrier mode to an optical reference. Out-of-loop verification of both optical and CEO frequency suggests a sub-Hz stability for all (partially virtual) spectral comb lines between 0 Hz and 400 THz.

Simultaneous spectral purity transfer at three optical clock transitions using an ultra-low noise Er:Fiber frequency comb

We have performed a multi-branch Er:fiber-based frequency comb comparison for simultaneously address the stability at different spectral regions. The optical beats are synchronously realized for three relevant wavelengths, corresponding to half the Sr, Yb and Hg lattice clock transition frequencies, showing an integrated phase noise below 55 mrad (1 Hz–1 MHz) and modified ADEV of ∼6×10⁻¹⁸ at 1 s, averaging below 1×10⁻¹⁸ in <20 s (Lambda-mode, 1 s gate time).

Ultra-short optical pulses leading to ultra-stable photonic microwave generation

Microwave signals can be generated by photo-detecting ultra-short optical pulse trains. We demonstrate that the pulse duration, although shorter than the impulse response of photodiode, can greatly limit the phase noise of generated microwave signal.

Compact Low-Noise Photonic Microwave Generation From Commercial Low-Noise Lasers

We demonstrate how phase-locking a whispering gallery mode-stabilized semiconductor laser to a high-stability Erbium-based distributed feedback fiber laser makes an outstanding optical reference for photonic microwave generation using an optical frequency comb. Using only commercially available compact lasers, it allows generation of a 12-GHz microwave signal with absolute levels of phase noise below −47 dBc/Hz at 1 Hz and −170 dBc/Hz at 50 kHz from the carrier.

Ultra-low phase noise frequency-comb-based microwave generation and characterization

We report on the generation of ultra-low phase noise microwave signals at 12GHz by photodetecting the pulse train of an Erbium-doped fiber-based optical frequency comb phase locked to a ultra-narrow linewidth ultra-stable laser at With advanced photodetection techniques and homemade phase noise measurement apparatus, our experiment demonstrates generation of a microwave source with absolute phase noise below -170dBc/Hz at 10kHz and above, and below -100dBc/Hz at 1Hz from a 12GHz carrier, which pushes even further the best results reported so far.