Low phase noise K-band signal generation using polarization diverse single-soliton integrated microcombs

Frequency microcombs with microwave and millimeter-wave repetition rates provide a compact solution for coherent communication and information processing.The implementation of these microcombs using a CMOS-compatible platform further paves the way for large-scale photonic integration and modularity.Here,we demonstrate free-running soliton microcombs with K-band repetition rates with very low phase noise over a 4 GHz pump detuning range reaching−117(−123)dBc/Hz at 10 kHz offset for a 19.7(10)GHz carrier without active pump stabilization,exceeding commercial electronic microwave oscillators at frequency offsets above 40 kHz.The minimum laser noise to soliton microwave signal transduction factor observed is−73dB.This noise performance is achieved using a hybridized dual-mode for soliton generation to achieve passive thermal stabilization and minimal soliton spectrum shift from prior Raman scattering and dispersive wave formation.We further examine the locking of the repetition rate to an external ultrastable photonic oscillator to illustrate the feasibility of phase noise suppression below the thermorefractive noise limits of microresonator frequency combs.

Towards optimum Franson interference recurrence in mode-locked singly-filtered biphoton frequency combs

Mode-locked biphoton frequency combs exhibit multiple discrete comblike temporal correlations from the Fourier transform of its phase-coherent frequency spectrum.Both temporal correlation and Franson interferometry are valuable tools for analyzing the joint properties of biphoton frequency combs,and the latter has proven to be essential for testing the fundamental quantum nature,the time-energy entanglement distribution,and the large-alphabet quantum key distributions.However,the Franson recurrence interference visibility in biphoton frequency combs unavoidably experiences a falloff that deteriorates the quality of time-energy entanglement and channel capacity for longer cavity round trips.In this paper,we provide a new method to address this problem towards optimum Franson interference recurrence.We first observe mode-locked temporal oscillations in a5.03 GHz free-spectral range singly filtered biphoton frequency comb using only commercial detectors.Then,we observe similar falloff trend of time-energy entanglement in 15.15 GHz and 5.03 GHz free-spectral range singly filtered biphoton frequency combs,whereas,the optimum central time-bin accidental-subtracted visibility over 97%for both cavities.Here,we find that by increasing the cavity finesse F,we can enhance the detection probability in temporal correlations and towards optimum Franson interference recurrence in our singly filtered biphoton frequency combs.For the first time,via a higher cavity finesse F of 45.92 with a 15.11 GHz free-spectral range singly filtered biphoton frequency comb,we present an experimental≈3.13-fold improvement of the Franson visibility compared to the Franson visibility with a cavity finesse F of 11.14 at the sixth time bin.Near optimum Franson interference recurrence and a time-bin Schmidt number near 16 effective modes in similar free-spectral range cavity are predicted with a finesse F of 200.Our configuration is versatile and robust against changes in cavity parameters that can be designed for various quantum applications,such as high-dimensional time-energy entanglement distributions,high-dimensional quantum key distributions,and wavelength-multiplexed quantum networks.

Soliton bursts and deterministic dissipative Kerr soliton generation in auxiliary-assisted microcavities

Dissipative Kerr solitons in resonant frequency combs offer a promising route for ultrafast mode-locking,precision spectroscopy and time-frequency standards.The dynamics for the dissipative soliton generation,however,are intrinsically intertwined with thermal nonlinearities,limiting the soliton generation parameter map and statistical success probabilities of the solitary state.Here,via use of an auxiliary laser heating approach to suppress thermal dragging dynamics in dissipative soliton comb formation,we demonstrate stable Kerr soliton singlet formation and soliton bursts.First,we access a new soliton existence range with an inverse-sloped Kerr soliton evolution—diminishing soliton energy with increasing pump detuning.Second,we achieve deterministic transitions from Turinglike comb patterns directly into the dissipative Kerr soliton singlet pulse bypassing the chaotic states.This is achieved by avoiding subcomb overlaps at lower pump power,with near-identical singlet soliton comb generation over twenty instances.Third,with the red-detuned pump entrance route enabled,we uncover unique spontaneous soliton bursts in the direct formation of low-noise optical frequency combs from continuum background noise.The burst dynamics are due to the rapid entry and mutual attraction of the pump laser into the cavity mode,aided by the auxiliary laser and matching well with our numerical simulations.Enabled by the auxiliary-assisted frequency comb dynamics,we demonstrate an application of automatic soliton comb recovery and long-term stabilization against strong external perturbations.Our findings hold potential to expand the parameter space for ultrafast nonlinear dynamics and precision optical frequency comb stabilization.

Biochemical sensing in graphene-enhanced microfiber resonators with individual molecule sensitivity and selectivity

Photonic sensors that are able to detect and track biochemical molecules offer powerful tools for information acquisition in applications ranging from environmental analysis to medical diagnosis.The ultimate aim of biochemical sensing is to achieve both quantitative sensitivity and selectivity.As atomically thick films with remarkable optoelectronic tunability,graphene and its derived materials have shown unique potential as a chemically tunable platform for sensing,thus enabling significant performance enhancement,versatile functionalization and flexible device integration.Here,we demonstrate a partially reduced graphene oxide(prGO)inner-coated and fiber-calibrated Fabry-Perot dye resonator for biochemical detection.Versatile functionalization in the prGO film enables the intracavity fluorescent resonance energy transfer(FRET)to be chemically selective in the visible band.Moreover,by measuring the intermode interference via noise canceled beat notes and locked-in heterodyne detection with Hz-level precision,we achieved individual molecule sensitivity for dopamine,nicotine and single-strand DNA detection.This work combines atomic-layer nanoscience and high-resolution optoelectronics,providing a way toward high-performance biochemical sensors and systems.

Real-time transition dynamics and stability of chipscale dispersion-managed frequency microcombs

Femtosecond mode-locked laser frequency combs have served as the cornerstone in precision spectroscopy,alloptical atomic clocks,and measurements of ultrafast dynamics.Recently frequency microcombs based on nonlinear microresonators have been examined,exhibiting remarkable precision approaching that of laser frequency combs,on a solid-state chip-scale platform and from a fundamentally different physical origin.Despite recent successes,to date,the real-time dynamical origins and high-power stabilities of such frequency microcombs have not been fully addressed.Here,we unravel the transitional dynamics of frequency microcombs from chaotic background routes to femtosecond mode-locking in real time,enabled by our ultrafast temporal magnifier metrology and improved stability of dispersion-managed dissipative solitons.Through our dispersion-managed oscillator,we further report a stability zone that is more than an order-of-magnitude larger than its prior static homogeneous counterparts,providing a novel platform for understanding ultrafast dissipative dynamics and offering a new path towards high-power frequency microcombs.

Probing 10μK stability and residual drifts in the cross-polarized dual-mode stabilization of single-crystal ultrahigh-Q optical resonators

The thermal stability of monolithic optical microresonators is essential for many mesoscopic photonic applications such as ultrastable laser oscillators,photonic microwave clocks,and precision navigation and sensing.Their fundamental performance is largely bounded by thermal instability.Sensitive thermal monitoring can be achieved by utilizing cross-polarized dual-mode beat frequency metrology,determined by the polarization-dependent thermorefractivity of a single-crystal microresonator,wherein the heterodyne radio-frequency beat pins down the optical mode volume temperature for precision stabilization.Here,we investigate the correlation between the dualmode beat frequency and the resonator temperature with time and the associated spectral noise of the dual-mode beat frequency in a single-crystal ultrahigh-Q MgF_(2) resonator to illustrate that dual-mode frequency metrology can potentially be utilized for resonator temperature stabilization reaching the fundamental thermal noise limit in a realistic system.We show a resonator long-term temperature stability of 8.53μK after stabilization and unveil various sources that hinder the stability from reaching sub-μK in the current system,an important step towards compact precision navigation,sensing,and frequency reference architectures.

Real-time dynamics and cross-correlation gating spectroscopy of free-carrier Drude slow-light solitons

Optical solitons—stable waves balancing delicately between nonlinearities and dispersive effects—have advanced the field of ultrafast optics and dynamics,with contributions spanning from supercontinuum generation to soliton fission,optical event horizons,Hawking radiation and optical rogue waves,among others.Here,we investigate picojoule soliton dynamics in silicon slow-light,photonic-bandgap waveguides under the influence of Drude-modeled,free-carrier-induced nonlinear effects.Using real-time and single-shot amplified dispersive Fourier transform spectroscopy simultaneously with high-fidelity cross-correlation frequency resolved optical gating at femtojoule sensitivity and femtosecond resolution,we examine the soliton stability limits,the soliton dynamics including free-carrier quartic slow-light scaling and acceleration,and the Drude electron–hole plasma-induced perturbations in the Cherenkov radiation and modulation instability.Our real-time single-shot and time-averaged cross-correlation measurements are matched with our detailed theoretical modeling,examining the reduced group velocity free-carrier kinetics on solitons at the picojoule scale.

Hydrodynamical self-interference of a scattered polariton quanta

Researchers have observed the free-propagation of a single microcavity polariton directly and its self-interference when scattering upon a defect.These experimental observations of quantum hydrodynamics in the single polariton limit test the wave-particle duality and aid in the development of polariton-based photonic circuits in quantum information processing.

Measurement of sub-fm/Hz^(1/2) displacement spectral densities in ultrahigh-Q single-crystal microcavities with hertz-level lasers

Tracing a resonance frequency of a high quality factor(Q)optical cavity facilitates subpicometer displacement measurements of the optical cavity via Pound-Drever-Hall(PDH)locking scheme,tightly synchronizing a laser frequency to the optical cavity.Here we present observations of subfemtometer displacements on a ultrahigh-Q single-crystal MgF_(2)whispering-gallery-mode microcavity by frequency synchronization between a 1 Hz cavity-stabilized laser and a resonance of the MgF_(2) cavity using PDH laser-cavity locking.We characterize not only the displacement spectral density of the microcavity with a sensitivity of 1.5×10^(-16) m/Hz^(1/2) over the Fourier offset frequency ranging from 15 mHz to 100 kHz but also a 1.77 nm displacement fluctuation of the microcavity over 4500 s.Such measurement capability not only supports the analysis of integrated thermodynamical and technical cavity noise but allows for minute displacement measurements using laser-cavity locking for ultraprecise positioning,metrology,and sensing.

Stimulated generation of deterministic platicon frequency microcombs

Dissipative Kerr soliton generation in chip-scale nonlinear resonators has recently observed remarkable advances,spanning from massively parallel communications, to self-referenced oscillators, and to dual-comb spectroscopy.Often working in the anomalous dispersion regime, unique driving protocols and dispersion in these nonlinear resonators have been examined to achieve the soliton and soliton-like temporal pulse shapes and coherent frequency comb generation. The normal dispersion regime provides a complementary approach to bridge the nonlinear dynamical studies, including the possibility of square pulse formation with flattop plateaus, or platicons.Here we report observations of square pulse formation in chip-scale frequency combs through stimulated pumping at one free spectral range and in silicon nitride rings with +55 fs~2∕mm normal group velocity dispersion.Tuning of the platicon frequency comb via a varied sideband modulation frequency is examined in both spectral and temporal measurements. Determined by second-harmonic autocorrelation and cross correlation, we observe bright square platicon pulse of 17 ps pulse width on a 19 GHz flat frequency comb. With auxiliary-laser-assisted thermal stabilization, we surpass the thermal bistable dragging and extend the mode-locking access to narrower 2 ps platicon pulse states, supported by nonlinear dynamical modeling and boundary limit discussions.