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The aluminum gallium arsenide-on-insulator (AlGaAsOI) platform exhibiting high nonlinearity, strong light confinement, and negligible two-photon absorption (TPA) has motivated research in realizing highly efficient nonlinear devices. Resonator structures can push nonlinear efficiency to unprecedented levels by significantly enhancing the cavity field. In recent years, multimode microring resonators, with lower scattering loss than single-mode designs, have garnered increasing attention for chip-based nonlinear photonics applications. However, the intermodal coupling will degrade the Q and introduce avoided mode crossing (AMX), causing changes in local dispersion. The perturbed dispersion significantly influences the phase-matching condition, making AMX management crucial for multimode resonator design. This paper introduces a fabrication-tolerant tapered waveguide design to achieve selective-mode coupling, enabling single-mode excitation in the bus-ring coupling region and eliminating the unwanted higher-order mode of the multimode waveguide. Leveraging the multimode microring resonators in the AlGaAsOI platform, we demonstrate dark-pulse comb generation through TE00-TE10 mode coupling, and we obtain a large dark pulse existence range of 89 GHz by backward tuning. Moreover, we achieve a widely separated (45 THz) optical parametric oscillation (OPO) with the assistance of higher-order dispersion.

The exploration of physical degrees of freedom of light with infinite dimensionality, such as orbital angular momentum (OAM) and frequency, has profoundly reshaped the landscape of modern optics, with representative photonic functional devices including optical vortex emitters and frequency combs. In nanophotonics, whispering gallery mode microresonators naturally support applications based on the OAM of light and have been employed as on-chip emitters of monochromatic optical vortices. On the other hand, whispering gallery mode microresonators can serve as a highly efficient non-linear optical platform for producing light at different frequencies, that is, microcombs. Here we combine optical vortices and microcombs by demonstrating an optical vortex comb on a III–V integrated non-linear ring microresonator. The angular grating-dressed non-linear microring simultaneously emits spatiotemporal light springs consisting of 50 OAM modes, with each frequency of the microcomb carrying a distinct OAM value. We also experimentally generate optical pulses with time-varying OAM by carefully endowing the spatiotemporal light springs with a specific intermodal phase relation. We expect our work to favour the development of integrated non-linear and quantum photonics for exploring fundamental optical physics and advancing photonic quantum technology.

We consider Jackiw–Teitelboim gravity with a massless matter field and turn on bulk excitations leading to a nontrivial vev of the corresponding dual boundary operator. To leading order, we realize the corresponding deformation of thermofield double state by explicitly identifying their Hilbert space. The deformed state can be prepared with an operator insertion at the mid-point of the Euclidean time evolution in the context of Hartle–Hawking construction. We show that the inserted operators form an SL(2,R) representation. We construct a specific orthonormal basis that is directly related to the operator basis of the vev deformations. If we include the higher order corrections, the bulk geometry is no longer left-right symmetric. We argue that, classically, the mode coefficients in the bulk deformation cannot be fully recovered from the data collected along the boundary cutoff trajectories. Then the bulk seems to contain more information than the cutoff boundary, and this might be responsible for nontrivial behind-horizon degrees of freedom.

Microresonator-based optical frequency combs enable many potential applications, from frequency metrology to optical communication. Soliton comb generation relies on dispersion control. For bright soliton generation, it is required to have anomalous group velocity dispersion. However, the avoided mode crossing in the microresonator can disturb the local dispersion and may prevent the soliton formation. Although the avoided mode crossing may enable dark soliton generation, the unintended avoided mode crossing distorts the comb spectrum. Here, we present a robust multimode waveguide design against intermodal coupling to suppress unintended avoided mode crossing. By engineering the waveguide dimension, the phase mismatch between coupling modes can be increased, which will significantly reduce the modal coupling strength. We experimentally demonstrated the avoided mode crossing-suppressed microresonators in the AlGaAs-on-insulator platform.

Recent advances in integrated nonlinear material platforms and low-loss optical microresonators enabled a broad range of chip-scale optical applications, such as optical frequency combs, quantum photonics, and optical signal processing. The aluminum gallium arsenide-on-insulator (AlGaAsOI) platform exhibiting high nonlinearity, strong light confinement, and negligible two-photon absorption has motivated research in realizing highly efficient nonlinear components. Low loss and dispersion engineering are essential for nonlinear processes in waveguides as the former allows for a long nonlinear interaction distance while the latter ensures good phase matching. Constructing waveguides into microresonators can bring the nonlinear efficiency of the device to an unprecedented level but also requires extra considerations concerning the excess losses induced by waveguide bend and coupler, and the dispersion perturbation induced by intermodal coupling. This paper presents the fabrication process and its critical aspects for high Q AlGaAsOI microresonators. We report the highest Q for high-confinement III-V microring resonators that are fabricated using an electron-beam lithography-based patterning process. We also present an efficient coupler that simplifies the post-processing step for fiber-chip coupling. Moreover, we present generic design methods to suppress the avoided mode crossing (AMX) or dispersion defects in microresonators and demonstrate AMX-free AlGaAsOI microresonators.

Nonlinear optical signal processing (NOSP) has the potential to significantly improve the throughput, flexibility, and cost-efficiency of optical communication networks by exploiting the intrinsically ultrafast optical nonlinear wave mixing. It can support digital signal processing speeds of up to terabits per second, far exceeding the line rate of the electronic counterpart. In NOSP, high-intensity light fields are used to generate nonlinear optical responses, which can be used to process optical signals. Great efforts have been devoted to developing new materials and structures for NOSP. However, one of the challenges in implementing NOSP is the requirement of high-intensity light fields, which is difficult to generate and maintain. This has been a major roadblock to realize practical NOSP systems for high-speed, high-capacity optical communications. Here, we propose using a parity-time (PT) symmetric microresonator system to significantly enhance the light intensity and support high-speed operation by relieving the bandwidth-efficiency limit imposed on conventional single resonator systems. The design concept is the co-existence of a PT symmetry broken regime for a narrow-linewidth pump wave and near-exceptional point operation for broadband signal and idler waves. This enables us to achieve a new NOSP system with two orders of magnitude improvement in efficiency compared to a single resonator. With a highly nonlinear AlGaAs-on-Insulator platform, we demonstrate an NOSP at a data rate approaching 40 gigabits per second with a record low pump power of one milliwatt. These findings pave the way for the development of fully chip-scale NOSP devices with pump light sources integrated together, potentially leading to a wide range of applications in optical communication networks and classical or quantum computation. The combination of PT symmetry and NOSP may also open up opportunities for amplification, detection, and sensing, where response speed and efficiency are equally important.

Kerr frequency comb generation in microresonators is enabled by notable developments in fabrication technology and novel nonlinear material platforms. However, even in a low loss and highly nonlinear microresonator, the avoided resonance crossing may hamper reliable frequency comb generation. We present a method to suppress the avoided resonance crossing induced by polarization mode coupling. Our approach employs a filter waveguide coupled to a microring resonator for selective filtering of the TM_00 mode while keeping the operational TE_00 mode with low loss. We experimentally demonstrate an avoided-crossing-suppressed microresonator in the AlGaAs-on-insulator platform.

We study a Toda-type equation with two scalar fields which is not integrable and construct two families of exact solutions which are expressed in terms of rational functions. The equation appears in U(1) Chern-Simons theories coupled to two nonrelativistic matter fields with opposite charges. One family of solutions is a trivial embedding of Liouville-type solutions. The other family is obtained by transforming the equation into the Taubes vortex equation on the hyperbolic space. Though the Taubes equation is not integrable, a trivial vacuum solution provides nontrivial solutions to the original Toda-type equation.

In 2+1 dimensional nonrelativistic Chern-Simons gauge theories on S2which has a global SU(M) symmetry, the semilocal Popov vortex equations are obtained as Bogomolny equations by minimizing the energy in the presence of a uniform external magnetic field. We study the equations with many flavors and find several families of exact solutions. The equations are transformed to the semilocal Liouville equations for which some exact solutions are known. In this paper, we find new exact solutions of the semilocal Liouville equations. Using these solutions, we construct solutions to the semilocal Popov equations. The solutions are expressed in terms of one or more arbitrary rational functions on S2. Some simple solutions reduce to CPM−1lump configurations.

We report an ultrafast web inspector that operates at a 1000 times higher scan rate than conventional methods. This system is based on a hybrid dispersion laser scanner that performs line scans at nearly 100 MHz. Specifically, we demonstrate web inspection with detectable resolution of 48.6  μm/pixel (scan direction) ×  23  μm (web flow direction) within a width of view of 6 mm at a record high scan rate of 90.9 MHz. We demonstrate the identification and evaluation of particles on silicon wafers. This method holds great promise for speeding up quality control and hence reducing manufacturing costs.

The field-theoretic one-loop effective action in a static scalar background depending nontrivially on a single spatial coordinate is related, in the proper-time formalism, to the trace of the evolution kernel (or heat kernel) for an appropriate, one-dimensional, quantum-mechanical Hamiltonian. We describe a recursive procedure applicable to these traces for shape-invariant Hamiltonians, resolving subtleties from the continuum mode contributions by utilizing the expression for the regularized Witten index. For some cases which include those of domain-wall-type scalar backgrounds, our recursive procedure yields the full expression for the scalar or fermion one-loop effective action in both 1+1 and 3+1 dimensions.

Reflection amplitudes are defined as two-point functions of certain class of conformal field theories where primary fields are given by vertex operators with real couplings. Among these, we consider (Super-) Liouville theory and simply and non-simply laced Toda theories. In this paper we show how to compute the scaling functions of effective central charge for the models perturbed by some primary fields which maintains integrability. This new derivation of the scaling functions are compared with the results from conventional TBA approach and confirms our approach along with other non-perturbative results such as exact expressions of the on-shell masses in terms of the parameters in the action, exact free energies. Another important application of the reflection amplitudes is a computation of one-point functions for the integrable models. Introducing functional relations between the one-point functions in terms of the reflection amplitudes, we obtain explicit expressions for simply-laced and non-simply-laced affine Toda theories. These nonperturbative results are confirmed numerically by comparing the free energies from the scaling functions with exact expressions we obtain from the one-point functions.