Coupled systems with multiple interacting degrees of freedom provide a fertile ground for emergent dynamics, which is otherwise inaccessible in their solitary counterparts. Particularly, nonlinearity and non-equilibrium dynamics enable new opportunities in coupled photonic systems that are not present in their linear and equilibrium counterparts that can have profound consequences in sensing and computing. In this talk, I will overview recent experimental progress on accessing such dynamics in time-multiplexed networks of nonlinear resonators towards computing and sensing applications. I will present demonstrations of topological dissipation, non-equilibrium spectral phase transitions, topological mode-locked lasers, non-Hermitian topologically enhanced sensing, and photonic elementary cellular automata. I will also overview the progress on integrated optical parametric oscillators (OPOs) and their networks in lithium niobate (LN) nanophotonics for classical and quantum information processing applications.
Coupled systems with multiple interacting degrees of freedom provide a fertile ground for emergent dynamics, which is otherwise inaccessible in their solitary counterparts. Particularly, nonlinearity and non-equilibrium dynamics enable new opportunities in coupled photonic systems that are not present in their linear and equilibrium counterparts that can have profound consequences in sensing and computing. In this talk, I will overview recent experimental progress on accessing such dynamics in time-multiplexed networks of nonlinear resonators towards computing and sensing applications. I will present demonstrations of topological dissipation, non-equilibrium spectral phase transitions, topological mode-locked lasers, non-Hermitian topologically enhanced sensing, and photonic elementary cellular automata. I will also overview the progress on integrated optical parametric oscillators (OPOs) and their networks in lithium niobate (LN) nanophotonics for classical and quantum information processing applications.
Entangled photon pairs generated by a low-power continuous-wave laser could replicate pulsed laser-based tabletop spectroscopy by taking advantage of the inherent quantum correlations between the photons. Much of the current work in the thin-film lithium niobate platform has focused on infrared wavelengths, leaving shorter wavelengths still a largely unexplored space, particularly for spectroscopy. In this work, we have fabricated periodically poled lithium niobate nanophotonic waveguides for entangled photon generation through spontaneous parametric downconversion with a visible pump (406 nm). Characterization of the waveguided pair source confirms the spectral and temporal correlations of energy-time entangled photons with an on-chip pair generation efficiency of (2.3 ± 0.5) × 1011 pairs/s/mW, brightness of (1.6 ± 0.3) × 109 pairs/s/mW/nm, and two-photon interference visibility greater than 99%. With the same material platform, we have also demonstrated second harmonic generation with on-chip powers up to 30 μW and wavelengths as low as 355 nm, demonstrating lithium niobate’s potential for ultraviolet nonlinear photonics and frequency doubling in the UV-A spectral region. Through design of larger cross-section waveguides, we have also explored how variations in the lithium niobate thin film thickness can affect quasi-phase matching. To date, this is the first reported demonstration of periodically poled lithium niobate nanophotonic waveguides for spontaneous parametric downconversion at a fully visible pump wavelength (406 nm) as well as second harmonic generation in the UV (355 nm). Future work towards fully on-chip spectroscopy will explore integrating an on-chip Mach-Zehnder interferometer with the entangled photon source.
Evident from more than 50 years of table-top nonlinear optics, utilizing strong quadratic nonlinearities in integrated photonics can significantly expand the potentials of photonics for applications ranging from sensing to computing, especially in the ultra-short-pulse regime. In the past few years, nanophotonic lithium niobate (LN) has emerged as one of the most promising integrated photonic platforms with strong quadratic nonlinearity. In this talk we present some of our recent experimental results on realization and utilizing of dispersion-engineered and quasi-phase-matched devices in nanophotonic LN for intense optical parametric amplification, ultrafast ultra-low-energy all-optical switching, and few-cycle vacuum squeezing. We show a path for realization of large-scale ultrafast nanophotonic circuits in the classical and quantum regimes and discuss how networks of such resonators can lead to topological and non-Hermitian dynamics, and all-optical quantum information processors.
A plethora of applications have recently motivated extensive efforts on the generation of low noise Kerr solitons and coherent frequency combs in various platforms ranging from fiber to whispering gallery and integrated microscale resonators. However, the Kerr (cubic) nonlinearity is inherently weak, and in contrast, strong quadratic nonlinearity in optical resonators is expected to provide an alternative means for soliton formation with promising potential. In this talk we overview recent experimental results on formation of two types of dissipative quadratic solitons in optical parametric oscillators, namely temporal simultons in the mid-infrared and temporal walk-off induced solitons. Unlike Kerr solitons, these quadratic solitons occur in low-finesse resonators and can provide substantial pulse compression and high conversion efficiencies. We present a route to significantly improve the performance of these demonstrated quadratic solitons when extended to an integrated platform.
Evident from more than 50 years of table-top nonlinear optics, utilizing strong quadratic nonlinearities in integrated photonics can significantly expand the potentials of photonics for applications ranging from sensing to computing. In the past few years, nanophotonic lithium niobate (LN) has emerged as one of the most promising integrated photonic platforms with strong quadratic nonlinearity. In this talk we present some of our recent experimental results on realization and utilizing of dispersion-engineered and quasi-phase-matched devices in nanophotonic LN for intense optical parametric amplification, ultrafast ultra-low-energy all-optical switching, and ultra-low-energy broadband sources in the mid-infrared. We also present some recent experimental and numerical results on how resonators with only strong quadratic nonlinearities exhibit phase transitions in the spectral domain, and pulse compression. We show a path for realization of such nonlinear resonators at the wavelength-scale and discuss how networks of such resonators can lead to topological and non-Hermitian dynamics in the classical and quantum regimes.
We present experimental evidence of a 64th order exceptional point realized on a time-multiplexed photonic resonator network. Our highly scalable implementation uses a unidirectionally coupled one-dimensional lattice to achieve higher order exceptional points that are robust to variation in nearest neighbor couplings. Moreover, the non-reciprocal couplings of our network allow for the possibility to exceed the signal to noise limits that restrict other exceptional point implementations.
Half-harmonic generation is the inverse of second-harmonic generation. This talk overviews the concept, and how it is used for mid-IR frequency combs for molecular spectroscopy, and optical Ising machines, which can enable special-purpose nonclassical computing.
We propose and demonstrate low-refractive-index particles with all-dielectric metamaterial shell which lead to formation of high intensity photonic nanojets. We show that the extra degree of freedom because of the anisotropy of the shell gives rise to an increase in the photonic jet intensity inside the metamaterial shell without a need to increase the size of the particle. The anisotropy of the shell can also control the spectral and spatial location of the Mie-type multipolar resonances to achieve the desired scattering. In experiments, the metamaterial shell is composed of strong nonlinear materials leading to enhanced nonlinear wavelength conversion at nanoscale.
The coherent Ising machine (CIM) is a network of optical parametric oscillators (OPOs) that solves for the ground state of Ising problems through OPO bifurcation dynamics. Here, we present experimental results comparing the performance of the CIM to quantum annealers (QAs) on two classes of NP-hard optimization problems: ground state calculation of the Sherrington-Kirkpatrick (SK) model and MAX-CUT. While the two machines perform comparably on sparsely-connected problems such as cubic MAX-CUT, on problems with dense connectivity, the QA shows an exponential performance penalty relative to CIMs. We attribute this to the embedding overhead required to map dense problems onto the sparse hardware architecture of the QA, a problem that can be overcome in photonic architectures such as the CIM.
KEYWORDS: Sum-frequency generation, Frequency conversion, Current controlled current source, Optical parametric oscillators, Mid-IR, Frequency combs, Femtosecond phenomena, Nonlinear dynamics, Harmonic generation, Femtosecond frequency combs
Half-harmonic generation is the reverse of second harmonic generation that happens in optical parametric oscillators (OPOs) at degeneracy. It is an intrinsically phase-locked down-conversion process, which can be used to efficiently transfer well-developed near-IR frequency combs to the mid-IR.
We overview recent experimental progress in cascading multiple stages of half-harmonic generation of femtosecond frequency combs starting from a 1-μm pump. We have achieved stable operation with efficiencies as high as ~64%, pulses as short as three optical cycles at 4 μm, and output powers as high as 2.6 W at 2 μm. Our recent numerical and analytical studies of nonlinear dynamics and different operation regimes of femtosecond OPOs indicate a path toward achieving even higher efficiencies and shorter pulses.
We have performed intracavity molecular spectroscopy of water vapor, isotopic carbon dioxide, methane, acetylene,
carbon monoxide, formaldehyde and other gases using broadband mid-IR sync-pumped OPO sources (PPLN-based OPO pumped by a femtosecond Er-fiber laser, or OP-GaAs-based OPO pumped by a femtosecond Tm-fiber laser) operating near degeneracy, with up to 2.5–6.1 μm instantaneous bandwidth. We found that the measured spectral line shapes may show dispersive features. The measured spectra were compared to a simple model, based on the intracavity round-trip dispersion, and excellent agreement between theory and measurements was found. Detection limits in the ppb-range were demonstrated.
We generate broadband mid-infrared frequency combs via degenerate optical parametric oscillation in a subharmonic
OPO. This technique efficiently transfers the desirable properties of shorter wavelength mode-locked sources to the mid-
IR. Our OPO resonator is a 3m or 4m ring cavity composed of one pair of concave mirrors with R=50mm and four flat
mirrors, all but one of which are gold coated with > 99% reflection. A single dielectric mirror is used to introduce the
pump (2.05 micron from IMRA America, 75 MHz, 80 fs, 600mW or 1.55 micron from Menlo Systems C-fiber, 100
MHz, 70 fs, 350 mW or 1.56 micron from Toptica Photonics FemtoFiber Pro, 80 MHz, 85 fs, 380 mW). The dielectric
mirror is transmissive for the pump and reflective in a 2.5- 4 micron or 3- 6 micron (for 2 micron pump) range.
Broadband parametric gain around the 3.1-micron subharmonic is provided by short (0.2-0.5mm) periodically poled
lithium niobate (MgO:PPLN) at Brewster angle. Crystals were cut from Crystal Technology Inc. material having QPM
period of 34.8 microns for type 0 (e=e+e) phase matching at t=32 deg. C. With the 2-micron pump, orientation patterned
gallium arsenide from BAE systems is used as the non-linear material In both systems, the enormous acceptance
bandwidth at degeneracy, typical for OPOs with type 0 (or type I) phase-matching, gives broad bandwidth and makes
temperature tuning insignificant. Broadband oscillation is achieved when signal/idler are brought into degenerate
resonance by fine-tuning the cavity length with a mirror on a piezo stage. Using an 8% reflective pellicle, we outcouple a
frequency comb of more than 1000nm bandwidth, centered around 3.1 microns from the Er/PPLN system. A 1mm or
2.5mm thick ZnSe plate at Brewster angle provides 2nd-order group velocity dispersion compensation, improving the
OPO bandwidth. The OPO threshold was measured to be < 30mW. When locked, the OPO outputs 60 mW of average
power centered at 3.1 microns. With the Tm/OP-GaAs system we achieve octave-spanning output from 3- 6 micron
using a mix of YAG and CaF for dispersion compensation and output powers over 30 mW.
We implement a new approach for generating broadband mid-infrared frequency combs via degenerate optical
parametric oscillation. This technique efficiently transfers the desirable properties of shorter wavelength mode-locked
sources to the mid-IR. Our OPO resonator is a 3m ring cavity composed of one pair of concave mirrors with R=50mm
and four flat mirrors, all but one of which are gold coated with > 99% reflection. A single dielectric mirror is used to
introduce the 1560nm pump (Menlo Systems C-fiber, 100 MHz, 70 fs, 350 mW or Toptica Photonics FemtoFiber Pro, 80
MHz, 85 fs, 380 mW). The dielectric mirror is transmissive for the pump and reflective in the 2.5- 4 micron range.
Broadband parametric gain around 3.1-micron subharmonic is provided by short (0.2-0.5mm) periodically poled lithium
niobate (MgO:PPLN) at Brewster angle. Crystals were cut from Crystal Technology Inc. material having QPM period of
34.8 microns for type 0 (e=e+e) phase matching at t=32 deg. C. The enormous acceptance bandwidth at degeneracy,
typical for OPOs with type 0 (or type I) phase-matching, gives broad bandwidth and makes temperature tuning
insignificant. Broadband oscillation is achieved when signal/idler are brought into degenerate resonance by fine-tuning
the cavity length with a mirror on a piezo stage. Using an 8% reflective pellicle, we outcouple a frequency comb of more
than 1000nm bandwidth, centered around 3.1 microns. A 1mm or 2.5mm thick ZnSe plate at Brewster angle provides
2nd-order group velocity dispersion compensation, improving the OPO bandwidth. The OPO threshold was measured to
be < 30mW. When locked, the OPO outputs 60 mW of average power centered at 3.1 microns. With proper intracavity
dispersion management including chirped mirrors, we expect to extend the spectral width to an octave or more.
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