Search

Recent developments in Kerr microcombs may pave the way to a future with fully stabilized ultralow size, weight, and power consumption (SWaP) frequency combs. Nevertheless, Kerr microcombs are still hindered by a bandwidth/repetition rate trade-off. That is, the octave bandwidth needed for self-referencing is typically realized only with ∼THz repetition rates beyond the range of standard commercial photodetectors. The carrier envelope offset frequency is often likewise too high for detection. Dual-comb techniques for the measurement of THz repetition rates have made exciting progress, but the fCEO detection problem remains largely unaddressed. In this work, utilizing a Vernier dual-comb configuration, we demonstrate simultaneous detection of the electronically divided repetition rate and fCEO carrier envelope offset frequency of an octave-spanning microcomb. This, in turn, could help usher optical atomic clocks, low-noise microwave generators, and optical frequency synthesizers into various real-world applications.

Biphoton frequency combs (BFCs) are promising quantum sources for large-scale and high-dimensional quantum information and networking systems. In this context, the spectral purity of individual frequency bins will be critical for realizing quantum networking protocols like teleportation and entanglement swapping. Measurement of the temporal auto-correlation function of the unheralded signal or idler photons comprising the BFC is a key tool for characterizing their spectral purity and in turn verifying the utility of the biphoton state for networking protocols. Yet the experimentally obtainable precision for measuring BFC correlation functions is often severely limited by detector jitter. The fine temporal features in the correlation function$-$not only of practical value in quantum information, but also of fundamental interest in the study of quantum optics$-$are lost as a result and have remained unexplored. We propose a scheme to circumvent this challenge through electro-optic phase modulation, experimentally demonstrating time-resolved Hanbury Brown-Twiss characterization of BFCs generated from an integrated 40.5 GHz Si$_3$N$_4$ microring, up to a 3$\times$3-dimensional two-qutrit Hilbert space. Through slight detuning of the electro-optic drive frequency from the comb's free spectral range, our approach leverages Vernier principles to magnify temporal features which would otherwise be averaged out by detector jitter. We demonstrate our approach under both continuous-wave and pulsed pumping regimes, finding excellent agreement with theory. Importantly, our method reveals not only the collective statistics of the contributing frequency bins but also their temporal shapes$-$features lost in standard fully integrated auto-correlation measurements.

We utilize the Vernier effect to partially stabilize a pair of high repetition rate, octave-spanning Kerr solitons in silicon nitride microrings fabricated on the same wafer.

We demonstrate the use of a dual comb photonic system for downconversion and disambiguation of RF signals ranging from 4.3 GHz to 17.3 GHz. Our system has future potential for miniaturization, a key for deployment in real-world applications.

Optical frequency combs have established their presence in many fields among which is microwave photonics. Here, we briefly introduce optical frequency comb generators, focusing on high repetition rate combs. Examples of comb-based signal processing are highlighted, including Brillouin mitigation, beamforming, RF-filtering, sub-sampling and RF-channelizers.

By limiting the optical input launch power, stimulated Brillouin scattering imposes detrimental effects on long haul analog optical links. Utilizing Kerr combs generated from an integrated Silicon Nitride microring resonator, we mitigate Brillouin scattering in a 25 Km sampled analog optical link. Such combs offer reduced footprint, high repetition rates and low power consumption, rendering them attractive for next generation integrated analog photonic links. The distribution of the optical carrier power over multiple spectral lines allows launching higher total average powers, significantly improving the link performance. Operating the link in an externally intensity-modulated direct-detection architecture, we compare link metrics using a soliton or a dark pulse as the sampling frequency comb source. An advantageous aspect of the dark pulse is its high pump conversion efficiency. We find that the Kerr comb pump conversion efficiency has a direct effect on the relative intensity noise and the link noise figure. We show that the spurious free dynamic range using Kerr combs can match that of the well-established electro-optic combs.

We demonstrate optical frequency division of an octave-spanning large repetition rate microcomb to an electronically-detectable frequency in an all-silicon nitride dual microcomb platform

We perform full state tomography of frequency-bin entangled qudits generated from a Si3N4 microring, up to record-high frequency-bin dimension of d = 8. Our method combines randomized electro-optic modulation and pulse shaping with Bayesian inference.

Demonstrating continuously tunable photonic quantum walks in the frequency domain with high-dimensionally entangled photon pairs., Control over the duration of a quantum walk is critical to unlocking its full potential for quantum search and the simulation of many-body physics. Here we report quantum walks of biphoton frequency combs where the duration of the walk, or circuit depth, is tunable over a continuous range without any change to the physical footprint of the system—a feature absent from previous photonic implementations. In our platform, entangled photon pairs hop between discrete frequency modes with the coupling between these modes mediated by electro-optic modulation of the waveguide refractive index. Through control of the phase across different modes, we demonstrate a rich variety of behavior: from walks exhibiting enhanced ballistic transport or strong energy confinement, to subspaces featuring scattering centers or local traps. We also explore the role of entanglement dimensionality in the creation of energy bound states, which illustrates the potential for these walks to quantify high-dimensional entanglement.

The Phase Estimation Algorithm (PEA) is an important quantum algorithm used independently or as a key subroutine in other quantum algorithms. Currently most implementations of the PEA are based on qubits, where the computational units in the quantum circuits are two-dimensional states. Performing quantum computing tasks with higher dimensional states -- qudits -- has been proposed, yet a qudit-based PEA has not been realized. Using qudits can reduce the resources needed for achieving a given precision or success probability. Compared to other quantum computing hardware, photonic systems have the advantage of being resilient to noise, but the probabilistic nature of photon-photon interaction makes it difficult to realize two-photon controlled gates that are necessary components in many quantum algorithms. In this work, we report an experimental realization of a qudit-based PEA on a photonic platform, utilizing the high dimensionality in time and frequency degrees of freedom (DoFs) in a single photon. The controlled-unitary gates can be realized in a deterministic fashion, as the control and target registers are now represented by two DoFs in a single photon. This first implementation of a qudit PEA, on any platform, successfully retrieves any arbitrary phase with one ternary digit of precision., 7 pages, 4 figures

We utilize a single soliton generated in a SiN microring resonator for stimulated Brillouin scattering mitigation in a 50 km link. A 9.1 dB increase in threshold power relative to the CW case is obtained. Potential improvements of the results using dark pulses are discussed.

We numerically investigate the effect of stimulated Raman scattering on parametric pumping of microring resonators. Furthermore, we re-derive the LLE for a generalized pump including a FSR mismatch term to determine the locking range.

We demonstrate a Hong-Ou-Mandel interference pattern in the frequency domain with an electro-optic phase modulator and programmable pulse shapers, using energy-time entangled photons.

The Hong-Ou-Mandel (HOM) interference is one of the most fundamental quantum-mechanical effects that reveal a nonclassical behavior of single photons. Two identical photons that are incident on the input ports of an unbiased beam splitter always exit the beam splitter together from the same output port, an effect referred to as photon bunching. In this Letter, we utilize a single electro-optic phase modulator as a probabilistic frequency beam splitter, which we exploit to observe HOM interference between two photons that are in different spectral modes, yet are identical in other characteristics. Our approach enables linear optical quantum information processing protocols using the frequency degree of freedom in photons such as quantum computing techniques with linear optics.

Stimulated Raman scattering (SRS) is a powerful, label-free imaging technique that holds significant potential for medical imaging. To allow chemical specificity and minimize spectral distortion in the imaging of live species, a high-speed multiplex SRS imaging platform is needed. By combining a spectral focusing excitation technique with a rapid acousto-optic delay line, we demonstrate a hyperspectral SRS imaging platform capable of measuring a 3-dB spectral window of ∼200 cmsup-1/supwithin 12.8 μs with a scan rate of 30 KHz. We present hyperspectral images of a mixture of two different microsphere polymers as well as live fungal cells mixed with human blood.

We measure the repetition rate of a 900 GHz octave-spanning soliton micro-comb based on Vernier dual-comb frequency division implemented with two silicon nitride microresonator combs fabricated on the same wafer.

We demonstrate continuous photonic quantum walks with tunable depth in the frequency domain with high-dimensional entangled photon pairs. We generate a biphoton energy bound state by coherently controlling the phase of the input frequency modes.

We generate a biphoton frequency comb from an integrated 40.4 GHz silicon nitride microring and probe the phase coherence through electro-optic mixing of the frequency bins followed by time-resolved detection of the time-correlation function. (c) 2021 The Author(s)