We simulate a coupled Lugiato–Lefever model on a 12 × 12 AQHE ring lattice to compute Lyapunov exponents that reveal transitions from stable edge states to chaos. This demonstrates operational regimes for robust topological frequency-comb generation.

We solve the on-chip microcomb CEO detection bottleneck by generating a comb between two octave-separated pumps and self-aligning to both. We demonstrate this architectural inversion on foundry-fabricated chips, robustly achieving up- and downstream frequency metrology.

We derive the equations governing the motion of Kerr solitons in pair waveforms. Recent experiments in microresonators have studied a variety of interaction effects in multisoliton waveforms, including collisions and formation of soliton molecules and crystals. Here we analyze the effective interaction that arises from the coupling of soliton-tail overlap nonlinearity with global soliton variables associated with the breaking of translation symmetry. The interaction is either purely repulsive, or alternates between attraction and repulsion, according to whether the decay of soliton tails is monotone or oscillatory. In the latter case, stable fixed points of the effective dynamical system signify stable soliton molecule configuration, but the exponential weakening of the interaction with increasing inter-soliton separation may prevent the molecule from forming in experimentally accessible time scales. Our theory becomes asymptotically exact in the large-separation limit, and we verify the theoretical calculations using soliton trajectories extracted from direct numerical solutions of the wave equation.

Frequency comb generation in normal dispersion microresonators has become increasingly more competitive due to advances that take advantage of mode splitting. Examples include the use of injection locking to induce a mode split, coupling of multiple resonators, and the use of photonic crystal resonators (PhCR) in which a grating is inscribed on the inner or outer wall of the resonator. When the split mode is pumped, complex dark pulses often called platicons can form. In this work, we examine the stability of platicons in the pump-power and pump-detuning parameter space in a PhCR with different mode splittings. We show that regions of bistability can occur in which two platicon solutions are stable. We also show that broad regions of stability exist in which the bistability can be avoided.

We demonstrate an in situ detection technique to track the effective cavity-pump detuning without any active perturbation of the pump laser that is generating soliton microcombs in the cavity. The technique utilizes a narrow band notch filter to isolate the pump from the cavity output, a commonly used technique to avoid the saturation of the photodetector in the detection circuitry of the microcomb repetition frequency, and measures the effective detuning by detecting the peak of the resonant profile, corresponding to the hot cavity resonance, present at the isolated pump. The technique is applicable to determine the effective detuning regardless of the existence of soliton states in the cavity.

Dissipative Kerr solitons (DKSs) have emerged as the preferred solution for on-chip integrated optical frequency comb (OFC) generation in metrology. A multi-pumped DKS enables either all-optical trapping in the Kerr-induced synchronization regime, or a multi-component OFC with a locked repetition rate yet with constant frequency offsets between the components in the multi-color DKS regime. The multi-color DKS regime is of particular interest since nonlinear mixing between the DKS and the secondary pumped component generates idler waves at different frequencies that are useful for the spectral extension of the DKS comb. Here, we explore multi-color idler generation at frequencies in which the resonator free spectral range matches that at the DKS. We demonstrate theoretically and experimentally that without phase matching, the idler forms a bright pulse fundamentally bound to the bright DKS through parametric interaction, despite occurring in normal dispersion. Our work can enable new applications in metrology and spectroscopy of quantum systems toward visible wavelengths, as the parametric nature of our bright-bright state eliminates dependence on dispersion regime or visible wavelength pumping.

Frequency combs generated in microresonators by nonlinear states, such as soliton crystals, with crystalline defects can provide a rich optical spectrum that is useful for RF applications. In this paper, we report on the existence of a novel soliton glass solution to a modified Lugiato-Lefever equation, which we then show can be theoretically stable for Fabry-Perot microresonators. Soliton glasses are unique compared to previously reported soliton crystals and molecules in that soliton glasses produce a spectral line spacing that equals the inverse of the repetition time of the waveform in the cavity, accompanied by a stable aperiodic temporal spacing between soliton pulses in the resonator. Like a material glass, the soliton glass is characterized by short-range order and long-range disorder. We show that there are transition regions to access the soliton glass that go through spatio-temporal chaos. We computationally verify the stability of the glass over time scales equal to 2000 photon lifetimes using conventional evolutionary simulations in the presence of substantial noise. We also demonstrate the linear stability of the glass solutions by showing that any perturbations decay on a time scale that is on the order of the photon lifetime.

Integrated frequency comb sources are a key enabling technology for frequency metrology applications. Their on-chip integration promises to bring metrology capacity outside of the lab, particularly since they can operate at low continuous-wave pump laser power in the dissipative Kerr soliton (DKS) regime. Yet, such small foot-print and low power comes at a cost: higher noise and overall lower comb power. In particular, this translates to highly challenging detection and locking of the carrier-envelope offset, necessary for complete stabilization of the comb. Recently, Kerr-induced synchronization (KIS) of a DKS to a reference laser has been demonstrated as a tool for passive all-optical stabilization of DKS microcombs, with fundamental modification to the DKS and microcomb properties. Here, we demonstrate that the combination of additional power from the reference laser (now part of the DKS) and the KIS phase locking that pins the repetition rate together fundamentally alter the DKS, forcing an energy redistribution to maintain its center of mass. We demonstrate this self-balancing effect theoretically, which in a pure quadratic dispersion resonator leads to reference-dependent recoil. With higher-order dispersion through which the DKS yields phase-matched dispersive waves (DWs), we demonstrate that self-balancing increases the DW radiation, experimentally showing a 22 dB increase of comb teeth at 780 nm in an octave-spanning microcomb for efficient deployable carrier-envelope offset detection.

Optical frequency combs (OFCs) are frequency rulers essential for precision metrology, next generation navigation, and testing of fundamental physics. Despite intense efforts, chip-integrated OFCs remain laboratory-bound, unable to fulfill their promise of compact and cost-effective deployment. While improvement in fabrication and integration are important, a conceptual limitation has fundamentally stymied progress: on-chip OFC architectures have aimed to miniaturize their table-top counterparts and relied on cascading outward from (i.e., spectrally broadening) a single pump. In integrated platforms, this approach does not readily allow for the generation of strong and low-noise octave-spaced signals that are crucially needed for robust zero-frequency offset detection. Here, we overcome this limitation via an architectural inversion where an optical microcomb forms by filling the spectrum between two octave-separated pump lasers. The two pumps generate a parametrically driven cavity soliton (PDCS) in an integrated χ^(3) resonator, which robustly self-aligns to (i.e., synchronizes with) the pump lasers across multiple foundry-fabricated devices and operating configurations. This produces a single octave-spanning comb extending from telecom to visible wavelengths, whose zero-frequency offset is completely defined by the two harmonically-related pump lasers, and can therefore be reliably detected and stabilized. We showcase our platform's capabilities by executing all of the three core tasks of OFC metrology: optical frequency synthesis, low-noise millimeter-wave generation, and integrated optical clock readout, using the same self-aligned microcomb with only its input locks changed.

The transverse mode instability (TMI) is a nonlinear phenomenon that leads to coupling between the fundamental and higher-order modes (HOMs) in high-power fiber amplifiers when the pump power exceeds a threshold. This mode instability diminishes beam quality. Bending of the gain fiber has been shown to be an effective technique for suppressing TMI. We use the phase-matched model to simulate TMI within bent fibers using a co-propagating pump. We separately include the contributions of leakage loss and the mode deformation due to bending. Our results indicate that while both effects contribute to the suppression process, the bending loss plays a more important role. We also find that it is advantageous to only bend the initial part of the fiber near the input, which maximizes suppression of the HOMs while minimizing loss of the fundamental mode. We then numerically optimize the bend radius and the length of the bent portion of the fiber to maximize TMI suppression. Using the counter-propagating pump, the TMI threshold is less sensitive to the location of the bend portion of the gain fiber, as compared with the co-propagating pump. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

We demonstrate a microwave injection locking (MIL) technique to stabilize the phase of the repetition frequency of a broadband free-running single soliton comb. MIL is achieved by applying amplitude modulation to the pump laser, that generates the soliton in a high-Q Si3N4 microresonator and by locking the free-running soliton comb to the third-order modulation sidebands. We obtain a single sideband phase-noise suppression of 35 dB at a 1-kHz offset from the carrier and an injection locking bandwidth of 60 kHz.

Synchronization of oscillators is ubiquitous in nature. Often, the synchronized oscillators couple directly, yet in some cases synchronization can arise from their parametric interactions. Here, we theoretically predict and experimentally demonstrate the parametric synchronization of a dissipative Kerr soliton frequency comb. We specifically show that the parametric interaction between the soliton and two auxiliary lasers permits the entrainment of the frequency comb repetition rate. Besides representing the first prediction and demonstration of parametric synchronization of soliton frequency combs, our scheme offers significant flexibility for all-optical metrological-scale stabilization of the comb.

We begin by reviewing three optical technologies (the worldwide optical network, integrated photonics, and frequency combs) that are poised to revolutionize land-based positioning, navigation and timing (PNT) by greatly reducing our dependence on the global position system (GPS) and other global navigation satellite systems (GNSS). To achieve this revolution a holdover clock with sufficient resolution must be developed. We describe the required elements in a holdover clock and an architecture that was proposed by colleagues at the Army Research Laboratory (ARL) in Adelphi, MD with collaborators at the University of Maryland Baltimore County (UMBC). Microresonator frequency combs are a key element in a holdover clock. We then describe work being carried out at UMBC in collaboration with scientists at other institutions including AIM-Photonics to advance the state-of-the-art in microresonator frequency combs for PNT applications.

We present an easy-to-implement numerical method for analyzing electromagnetic wave propagation in dielectric rings. Our approach employs a finite-difference-based solver in cylindrical coordinates, solving a mixed electric-magnetic field formulation to accurately enforce boundary conditions and compute resonant modes. The method avoids geometric transformations; instead, it directly discretizes the Helmholtz wave equation in cylindrical coordinates and solves the resulting generalized eigenvalue problem. We validate our model against commercial solvers for various structures, including a Si3N4 ring embedded in SiO2, a ring on a thin-film-coated substrate, and a torus, achieving agreement in effective refractive indices within 0.3

SummaryPound-Drever-Hall (PDH) stabilization typically requires an external modulator and RF source, so it is challenging to fabricate as a photonic integrated circuit (PIC). We introduce COMPACT laser stabilization, which is modulation-free while still allowing heterodyne photodetection and while retaining similar sensitivity to PDH. We experimentally measured its error signal.

We calculate the phase noise for the first 100 comb line frequencies of two modified uni-traveling-carrier (MUTC) photodetectors. The frequency comb is generated by one-picosecond pulses with a 2-GHz repetition frequency. We observe a non-monotonic increase in the phase noise and investigate its origins. Our model identifies the interplay among the space charge effect, the heterostructure design, and the nonlinear relationship between the electric field and the electron drift current that leads to a complex variation of the phase noise as a function of the comb line frequency. Based on the findings, we present ways to reduce the phase noise of the photodetectors. While the optimal design depends on the desired frequency range of operation, we find a design that can reduce the phase noise over a wide range of comb-line frequencies.

We demonstrate all-optical parametric synchronization and disciplining of an octave-spanning integrated frequency comb without direct comb tooth capture, thanks to four-wave mixing that triply pins the microcomb repetition rate. © 2025 The Author(s)