arXiv subjects

Tobias J. Kippenberg

Publications and source records attributed to Tobias J. Kippenberg.

At least 91 records · Page 5Linked to original sources

arXiv2022

A photonic integrated circuit based erbium-doped amplifier

Erbium-doped fiber amplifiers have revolutionized long-haul optical communications and laser technology. Erbium ions could equally provide a basis for efficient optical amplification in photonic integrated circuits. However, this approach has thus far remained impractical due to insufficient output power. Here, we demonstrate a photonic integrated circuit based erbium amplifier reaching 145 mW output power and more than 30 dB small-signal gain -- on par with commercial fiber amplifiers and beyond state-of-the-art III-V heterogeneously integrated semiconductor amplifiers. We achieve this by applying ion implantation to recently emerged ultralow-loss Si3N4 photonic integrated circuits with meter-scale-length waveguides. We utilize the device to increase by 100-fold the output power of soliton microcombs, required for low-noise photonic microwave generation or as a source for wavelength-division multiplexed optical communications. Endowing Si3N4 photonic integrated circuits with gain enables the miniaturization of a wide range of fiber-based devices such as high-pulse-energy femtosecond mode-locked lasers.

physics.optics↗

arXiv2022

Reduced Material Loss in Thin-film Lithium Niobate Waveguides

Thin-film lithium niobate has shown promise for scalable applications ranging from single-photon sources to high-bandwidth data communication systems. Realization of the next generation high-performance classical and quantum devices, however, requires much lower optical losses than the current state of the art ($\sim$10 million). Unfortunately, material limitations of ion-sliced thin-film lithium niobate have not been explored, and therefore it is unclear how high-quality factor can be achieved in this platform. Here we evaluate the material limited quality factor of thin-film lithium niobate photonic platform can be as high as $Q\approx 1.8\times10^{8}$ at telecommunication wavelengths, corresponding to a propagation loss of 0.2 dB/m.

physics.optics↗

arXiv2022

Photo-induced cascaded harmonic and comb generation in silicon nitride microresonators

Silicon nitride (Si$_3$N$_4$) is an ever-maturing integrated platform for nonlinear optics. Yet, due to the absence of second-order ($χ^{(2)}$) nonlinearity, Si$_3$N$_4$ is mostly considered for third-order ($χ^{(3)}$) nonlinear interactions. Recently, this limitation was overcome by optical poling in both Si$_3$N$_4$ waveguides and microresonators via the photogalvanic effect, resulting in the inscription of quasi-phase-matched $χ^{(2)}$ gratings. Here, we report cascaded nonlinear effects in a normal dispersion Si$_3$N$_4$ microresonator with combined $χ^{(2)}$ and $χ^{(3)}$ nonlinearities. We demonstrate that the photo-induced $χ^{(2)}$ grating also provides phase-matching for the sum-frequency generation process, enabling the initiation and successive switching of primary combs at pump wavelength. Additionally, the doubly resonant pump and second-harmonic fields allow for cascaded third-harmonic generation, where a secondary optically written $χ^{(2)}$ grating is identified. Finally, we reach a low-noise, broadband microcomb state evolved from the sum-frequency coupled primary comb. These results expand the scope of cascaded effects in $χ^{(2)}$ and $χ^{(3)}$ microresonators.

physics.optics↗

arXiv2022

Near ultraviolet photonic integrated lasers based on silicon nitride

Low phase noise lasers based on the combination of III-V semiconductors and silicon photonics are well established in the near-infrared spectral regime. Recent advances in the development of low-loss silicon nitride-based photonic integrated resonators have allowed to outperform bulk external diode and fiber lasers in both phase noise and frequency agility in the 1550 nm-telecommunication window. Here, we demonstrate for the first time a hybrid integrated laser composed of a gallium nitride (GaN) based laser diode and a silicon nitride photonic chip-based microresonator operating at record low wavelengths as low as 410 nm in the near-ultraviolet wavelength region suitable for addressing atomic transitions of atoms and ions used in atomic clocks, quantum computing, or for underwater LiDAR. Using self-injection locking to a high Q (0.4 $\times$ 10$^6$) photonic integrated microresonator we observe a phase noise reduction of the Fabry-Pérot laser at 461 nm by a factor greater than 100$\times$, limited by the device quality factor and back-reflection.

physics.optics↗

arXiv2022

Hierarchical tensile structures with ultralow mechanical dissipation

Structural hierarchy is found in myriad biological systems and has improved man-made structures ranging from the Eiffel tower to optical cavities. Hierarchical metamaterials utilize structure at multiple size scales to realize new and highly desirable properties which can be strikingly different from those of the constituent materials. In mechanical resonators whose rigidity is provided by static tension, structural hierarchy can reduce the dissipation of the fundamental mode to ultralow levels due to an unconventional form of soft clamping. Here, we apply hierarchical design to silicon nitride nanomechanical resonators and realize binary tree-shaped resonators with quality factors as high as $10^9$ at 107 kHz frequency, reaching the parameter regime of levitated particles. The resonators' thermal-noise-limited force sensitivities reach $740\ \mathrm{zN/\sqrt{Hz}}$ at room temperature and $\mathrm{90\ zN/\sqrt{Hz}}$ at 6 K, surpassing state-of-the-art cantilevers currently used for force microscopy. We also find that the self-similar structure of binary tree resonators results in fractional spectral dimensions, which is characteristic of fractal geometries. Moreover, we show that the hierarchical design principles can be extended to 2D trampoline membranes, and we fabricate ultralow dissipation membranes suitable for interferometric position measurements in Fabry-Pérot cavities. Hierarchical nanomechanical resonators open new avenues in force sensing, signal transduction and quantum optomechanics, where low dissipation is paramount and operation with the fundamental mode is often advantageous.

cond-mat.mes-hall↗

arXiv2022

Bayesian tomography of high-dimensional on-chip biphoton frequency combs with randomized measurements

Owing in large part to the advent of integrated biphoton frequency combs (BFCs), recent years have witnessed increased attention to quantum information processing in the frequency domain for its inherent high dimensionality and entanglement compatible with fiber-optic networks. Quantum state tomography (QST) of such states, however, has required complex and precise engineering of active frequency mixing operations, which are difficult to scale. To address these limitations, we propose a novel solution that employs a pulse shaper and electro-optic phase modulator (EOM) to perform random operations instead of mixing in a prescribed manner. We successfully verify the entanglement and reconstruct the full density matrix of BFCs generated from an on-chip Si$_{3}$N$_{4}$ microring resonator(MRR) in up to an $8\times8$-dimensional two-qudit Hilbert space, the highest dimension to date for frequency bins. More generally, our employed Bayesian statistical model can be tailored to a variety of quantum systems with restricted measurement capabilities, forming an opportunistic tomographic framework that utilizes all available data in an optimal way.

quant-ph↗

arXiv2021

Nanomechanical resonators with ultra-high-$Q$ perimeter modes

Systems with low mechanical dissipation are extensively used in precision measurements such as gravitational wave detection, atomic force microscopy and quantum control of mechanical oscillators via opto- and electromechanics. The mechanical quality factor ($Q$) of these systems determines the thermomechanical force noise and the thermal decoherence rate of mechanical quantum states. While the dissipation rate is typically set by the bulk acoustic properties of the material, by exploiting dissipation dilution, mechanical $Q$ can be engineered through geometry and increased by many orders of magnitude. Recently, soft clamping in combination with strain engineering has enabled room temperature quality factors approaching one billion ($10^9$) in millimeter-scale resonators. Here we demonstrate a new approach to soft clamping which exploits vibrations in the perimeter of polygon-shaped resonators tethered at their vertices. In contrast to previous approaches, which rely on cascaded elements to achieve soft clamping, perimeter modes are soft clamped due to symmetry and the boundary conditions at the polygon vertices. Perimeter modes reach $Q$ of 3.6 billion at room temperature while spanning only two acoustic wavelengths -- a 4-fold improvement over the state-of-the-art mechanical $Q$ with 10-fold smaller devices. The small size of our devices makes them well-suited for near-field integration with microcavities for quantum optomechanical experiments. Moreover, their compactness allows the realization of phononic lattices. We demonstrate a one-dimensional Su-Schrieffer-Heeger chain of high-$Q$ perimeter modes coupled via nearest-neighbour interaction and characterize the localized edge modes.

physics.app-ph↗

arXiv2021

Probing material absorption and optical nonlinearity of integrated photonic materials

Optical microresonators with high quality ($Q$) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator $Q$ factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of $Q$, the ultimate attainable $Q$, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited $Q$ factors in several photonic material platforms. High-$Q$ microresonators are fabricated from thin films of SiO$_2$, Si$_3$N$_4$, Al$_{0.2}$Ga$_{0.8}$As and Ta$_2$O$_5$. By using cavity-enhanced photothermal spectroscopy, the material-limited $Q$ is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate $Q$ vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.

physics.optics↗

arXiv2021

Quantum coherent microwave-optical transduction using high overtone bulk acoustic resonances

A device capable of converting single quanta of the microwave field to the optical domain is an outstanding endeavour in the context of quantum interconnects between distant superconducting qubits, but likewise can have applications in other fields, such as radio astronomy or, in the classical realm, microwave photonics. A variety of transduction approaches, based on optomechanical or electro-optical interactions, have been proposed and realized, yet the required vanishing added noises and an efficiency approaching unity, have not yet been attained. Here we present a new transduction scheme that could in theory satisfy the requirements for quantum coherent bidirectional transduction. Our scheme relies on an intermediary mechanical mode, a high overtone bulk acoustic resonance (HBAR), to coherently couple microwave and optical photons through the piezoelectric and strain-optical effects. Its efficiency results from the combination of integrated Si3N4 photonic circuits with ultra low loss sustaining high intracavity photon numbers with the highly efficient microwave to mechanical transduction offered by piezoelectrically coupled HBAR. We develop a quantum theory for this multipartite system by first introducing a quantization method for the piezoelectric interaction between the microwave mode and the mechanical mode from first principles (which to our knowledge has not been presented in this form), and link the latter to the conventional Butterworth-Van Dyke model. The HBAR is subsequently coupled to a pair of hybridized optical modes from coupled optical ring cavities via the strain-optical effect. We analyze the conversion capabilities of the proposed device using signal flow graphs, and demonstrate that near quantum coherent transduction is possible, with realistic experimental parameters.

quant-ph↗

arXiv2021

Dual chirped micro-comb based parallel ranging at megapixel-line rates

Laser based ranging (LiDAR) - already ubiquitously used in industrial monitoring, atmospheric dynamics, or geodesy - is key sensor technology. Coherent laser ranging, in contrast to time-of-flight approaches, is immune to ambient light, operates continuous wave allowing higher average powers, and yields simultaneous velocity and distance information. State-of-the-art coherent single laser-detector architectures reach hundreds of kilopixel per second rates. While emerging applications such as autonomous driving, robotics, and augmented reality mandate megapixel per second point sampling to support real-time video-rate imaging. Yet, such rates of coherent LiDAR have not been demonstrated. Here we report a swept dual-soliton microcomb technique enabling coherent ranging and velocimetry at megapixel per second line scan measurement rates with up to 64 spectrally dispersed optical channels. It is based on recent advances in photonic chip-based microcombs that offer a solution to reduce complexity both on the transmitter and receiver sides. Multi-heterodyning two synchronously frequency-modulated microcombs yields distance and velocity information of all individual ranging channels on a single receiver alleviating the need for individual separation, detection, and digitization. The reported LiDAR implementation is hardware-efficient, compatible with photonic integration, and demonstrates the significant advantages of acquisition speed afforded by the convergence of optical telecommunication and metrology technologies. We anticipate our research will motivate further investigation of frequency swept microresonator dual-comb approach in the neighboring fields of linear and nonlinear spectroscopy, optical coherence tomography.

physics.optics↗

arXiv2021

Compact, spatial-mode-interaction-free, ultralow-loss, nonlinear photonic integrated circuits

Nonlinear photonics based on integrated circuits has enabled applications such as parametric amplifiers, soliton frequency combs, supercontinua, and non-reciprocal devices. Ultralow optical loss and the capability for dispersion engineering are essential, which necessitate the use of multi-mode waveguides. Despite that rich interaction among different spatial waveguide eigenmodes can give rise to novel nonlinear phenomena, spatial mode interaction is typically undesired as it increases optical loss, perturbs local dispersion profile, and impedes soliton formation. Adiabatic bends, such as Euler bends whose curvature varies linearly with their path length, have been favoured to suppress spatial mode interaction. Adiabatic bends can essentially connect any two waveguide segments with adiabatic mode conversion, thus efficiently avoid mode mixing due to mode mismatch. However, previous works lack quantitative measurement data and analysis to fairly evaluate the adiabaticity, and are not based on photonic integrated circuits with tight optical confinement and optical losses of few dB/m. Here, we adapt, optimize, and implement Euler bends to build compact racetrack microresonators based on ultralow-loss, multi-mode, silicon nitride photonic integrated circuits. The racetrack microresonators feature a small footprint of only 0.21 mm^2 for 19.8 GHz FSR. We quantitatively investigate the suppression of spatial mode interaction in the racetrack microresonators with Euler bends. We show that the optical loss rate (15.5 MHz) is preserved, on par with the mode interaction strength (25 MHz). This results in an unperturbed microresonator dispersion profile. We further demonstrate single soliton of 19.8 GHz repetition rate. The optimized Euler bends and racetrack microresonators can be key building blocks for integrated nonlinear photonic systems, programmable processors and photonic quantum computing.

physics.optics↗

arXiv2021

Platicon microcomb generation using laser self-injection locking

The past decade has witnessed major advances in the development of microresonator-based frequency combs (microcombs) that are broadband optical frequency combs with repetition rates in the millimeter-wave to microwave domain. Integrated microcombs can be manufactured using wafer-scale process and have been applied in numerous applications. Most of these advances are based on the harnessing of dissipative Kerr solitons (DKS) in optical microresonators with anomalous group velocity dispersion (GVD). However, microcombs can also be generated with normal GVD using dissipative localized structures that are referred to as "dark pulse", "switching wave" or "platicon". Importantly, as most materials feature intrinsic normal GVD, the requirement of dispersion engineering is significantly relaxed for platicon generation. Therefore while DKS microcombs require particular designs and fabrication processes, platicon microcombs can be readily built using standard CMOS-compatible platforms such as thin-film (i.e. typically below 300 nm) Si3N4. Yet laser self-injection locking that has been recently used to create highly compact integrated DKS microcomb modules has not been demonstrated for platicons. Here we report the first fully integrated platicon microcomb operating at a microwave-K-band repetition rate. Using laser self-injection locking of a DFB laser edge-coupled to a Si3N4 microresonator, platicons are electrically initiated and stably maintained, enabling a compact microcomb module without any complex control. We further characterize the phase noise of the platicon repetition rate and the pumping laser. The observation of self-injection-locked platicons facilitates future wide adoption of microcombs as a build-in block in standard photonic integrated architectures via commercial foundry service.

physics.optics↗

arXiv2021

Photonic chip-based continuous-travelling-wave parametric amplifier

The ability to amplify optical signals is of pivotal importance across science and technology. The development of optical amplifiers has revolutionized optical communications, which are today pervasively used in virtually all sensing and communication applications of coherent laser sources. In the telecommunication bands, optical amplifiers typically utilize gain media based on III-V semiconductors or rare-earth-doped fibers. Another way to amplify optical signals is to utilize the Kerr nonlinearity of optical fibers or waveguides via parametric processes. Such parametric amplifiers of travelling continuous wave have been originally developed in the microwave domain, and enable quantum-limited signal amplification with high peak gain, broadband gain spectrum tailored via dispersion control, and ability to enable phase sensitive amplification. Despite these advantages, optical amplifiers based on parametric gain have proven impractical in silica fibers due to the low Kerr nonlinearity. Recent advances in photonic integrated circuits have revived interest in parametric amplifiers due to the significantly increased nonlinearity in various integrated platforms. Yet, despite major progress, continuous-wave-pumped parametric amplifiers built on photonic chips have to date remained out of reach. Here we demonstrate a chip-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, meter-long, silicon nitride photonic integrated circuits that are tightly coiled on a photonic chip, we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fiber-chip-fiber coupling losses in the optical C-band.

physics.optics↗

arXiv2021

Ultralow-noise frequency-agile photonic integrated lasers

Low-noise lasers are of central importance in a wide variety of applications, including high spectral-efficiency coherent communication protocols, distributed fibre sensing, and long distance coherent LiDAR. In addition to low phase noise, frequency agility, that is, the ability to achieve high-bandwidth actuation of the laser frequency, is imperative for triangular chirping in frequency-modulated continuous-wave (FMCW) based ranging or any optical phase locking as routinely used in metrology. While integrated silicon-based lasers have experienced major advances and are now employed on a commercial scale in data centers, integrated lasers with sub-100 Hz-level intrinsic linewidth are based on optical feedback from photonic circuits that lack frequency agility. Here, we demonstrate a wafer-scale-manufacturing-compatible hybrid photonic integrated laser that exhibits ultralow intrinsic linewidth of 25 Hz while offering unsurpassed megahertz actuation bandwidth, with a tuning range larger than 1 GHz. Our approach uses ultralow-loss (1 dB/m) Si$_3$N$_4$ photonic microresonators, combined with aluminium nitride (AlN) or lead zirconium titanate (PZT) microelectromechanical systems (MEMS) based stress-optic actuation. Electrically driven low-phase noise lasing is attained by self-injection locking of an Indium Phosphide (InP) laser chip and only limited by fundamental thermo-refractive noise. By utilizing difference drive and apodization of the photonic chip, a flat actuation response up to 10 MHz is achieved. We leverage this capability to demonstrate a compact coherent LiDAR engine that can generate up to 800 kHz FMCW triangular optical chirp signals, requiring neither any active linearization nor predistortion compensation, and perform a 10 m optical ranging experiment, with a resolution of 12.5 cm.

physics.optics↗

arXiv2021

Continuous-Wave Frequency Upconversion with a Molecular Optomechanical Nanocavity

Frequency upconversion is a cornerstone of electromagnetic signal processing, analysis and detection. It is used to transfer energy and information from one frequency domain to another where transmission, modulation or detection is technically easier or more efficient. Optomechanical transduction is emerging as a flexible approach to coherent frequency upconversion; it has been successfully demonstrated for conversion from radio- and microwaves (kHz to GHz) to optical fields. Nevertheless, optomechanical transduction of multi-THz and mid-infrared signals remains an open challenge. Here, we utilize molecular cavity optomechanics to demonstrate upconversion of sub-microwatt continuous-wave signals at $\sim$32~THz into the visible domain at ambient conditions. The device consists in a plasmonic nanocavity hosting a small number of molecules. The incoming field resonantly drives a collective molecular vibration, which imprints an optomechanical modulation on a visible pump laser and results in Stokes and anti-Stokes upconverted Raman sidebands with sub-natural linewidth, indicating a coherent process. The nanocavity offers 13 orders of magnitude enhancement of upconversion efficiency per molecule compared to free space, with a measured phonon-to-photon internal conversion efficiency larger than $10^{-4}$ per milliwatt of pump power. Our results establish a flexible paradigm for optomechanical frequency conversion using molecular oscillators coupled to plasmonic nanocavities, whose vibrational and electromagnetic properties can be tailored at will using chemical engineering and nanofabrication.

physics.optics↗

arXiv2021

Coherent terahertz-to-microwave link using electro-optic-modulated Turing rolls

Arising from modulation instability, Turing rolls in optical Kerr microresonators have been used in the generation of optical frequency combs and the synthesis of microwave and terahertz frequencies. In this work, by applying electro-optic modulation on terahertz-frequency Turing rolls, we implement electro-optic frequency division with a microcomb to synthesize variable low-noise microwave signals. We also actively stabilize the terahertz oscillations to a microwave reference via intracavity power modulation, obtaining fractional frequency instabilities that are better than those of the free-running situation by up to six orders of magnitude. This study not only highlights the extraordinary spectral purity of Turing roll oscillations but also opens the way for bidirectional terahertz-to-microwave links with hybrid optical frequency comb techniques.

physics.optics↗

arXiv2021

Strained crystalline nanomechanical resonators with ultralow dissipation

In strained mechanical resonators, the concurrence of tensile stress and geometric nonlinearity dramatically reduces dissipation. This phenomenon, dissipation dilution, is employed in mirror suspensions of gravitational wave interferometers and at the nanoscale, where soft-clamping and strain engineering have allowed extremely high quality factors. However, these techniques have so far only been applied in amorphous materials, specifically silicon nitride. Crystalline materials exhibit significantly lower intrinsic damping at cryogenic temperatures, due to the absence of two level systems in the bulk, as exploited in Weber bars and silicon optomechanical cavities. Applying dissipation dilution engineering to strained crystalline materials could therefore enable extremely low loss nanomechanical resonators, due to the combination of reduced internal friction, high intrinsic strain, and high yield strength. Pioneering work has not yet fully exploited this potential. Here, we demonstrate that single crystal strained silicon, a material developed for high mobility transistors, can be used to realize mechanical resonators with ultralow dissipation. We observe that high aspect ratio ($>10^5$) strained silicon nanostrings support MHz mechanical modes with quality factors exceeding $10^{10}$ at 7 K, a tenfold improvement over values reported in silicon nitride. At 7 K, the thermal noise-limited force sensitivity is approximately $45\ \mathrm{{zN}/{\sqrt{Hz}}}$ - approaching that of carbon nanotubes - and the heating rate is only 60 quanta-per-second. Our nanomechanical resonators exhibit lower dissipation than the most pristine macroscopic oscillators and their low mass makes them particularly promising for quantum sensing and transduction.

cond-mat.mes-hall↗

arXiv2021

Microwave-to-optical conversion with a gallium phosphide photonic crystal cavity

Electrically actuated optomechanical resonators provide a route to quantum-coherent, bidirectional conversion of microwave and optical photons. Such devices could enable optical interconnection of quantum computers based on qubits operating at microwave frequencies. Here we present a novel platform for microwave-to-optical conversion comprising a photonic crystal cavity made of single-crystal, piezoelectric gallium phosphide integrated on pre-fabricated niobium circuits on an intrinsic silicon substrate. The devices exploit spatially extended, sideband-resolved mechanical breathing modes at $\sim$ 3.2 GHz, with vacuum optomechanical coupling rates of up to $g_0/2π\approx$ 300 kHz. The mechanical modes are driven by integrated microwave electrodes via the inverse piezoelectric effect. We estimate that the system could achieve an electromechanical coupling rate to a superconducting transmon qubit of $\sim$ 200 kHz. Our work represents a decisive step towards integration of piezoelectro-optomechanical interfaces with superconducting quantum processors.

physics.optics↗