arXiv subjects

Hong X. Tang

Publications and source records attributed to Hong X. Tang.

At least 109 records · Page 6Linked to original sources

arXiv2017

Efficient visible frequency comb generation via Cherenkov radiation from a Kerr microcomb

Optical frequency combs enable state-of-the-art applications including frequency metrology, optical clocks, astronomical measurements, and sensing. Recent demonstrations of microresonator-based Kerr frequency combs or microcombs pave the way to scalable and stable comb sources on a photonic chip. Generating microcombs in the visible wavelength range, however, has been limited by large material dispersion and optical loss. Here we demonstrate a scheme for efficiently generating visible microcomb in a high Q aluminum nitride microring resonator. Enhanced Pockels effect strongly couples infrared and visible modes into hybrid mode pairs, which participate in the Kerr microcomb generation process and lead to strong Cherenkov radiation in the visible band of an octave apart. A surprisingly high conversion efficiency of 22% is achieved from the pump laser to the visible comb. We further demonstrate a robust frequency tuning of the visible comb by more than one free spectral range and apply it to the absorption spectroscopy of a water-based dye molecule solution. Our work marks the first step towards high-efficiency visible microcomb generation and its utilization, and it also provides insights on the significance of Pockels effect and its strong coupling with Kerr nonlinearity in a single microcavity device.

physics.optics↗

arXiv2017

Ultrabroadband supercontinuum generation and frequency-comb stabilization using on-chip waveguides with both cubic and quadratic nonlinearities

Using aluminum-nitride photonic-chip waveguides, we generate optical-frequency-comb supercontinuum spanning from 500 nm to 4000 nm with a 0.8 nJ seed pulse, and show that the spectrum can be tailored by changing the waveguide geometry. Since aluminum nitride exhibits both quadratic and cubic nonlinearities, the spectra feature simultaneous contributions from numerous nonlinear mechanisms: supercontinuum generation, difference-frequency generation, second-harmonic generation, and third-harmonic generation. As one application of integrating multiple nonlinear processes, we measure and stabilize the carrier-envelope-offset frequency of a laser comb by direct photodetection of the output light. Additionally, we generate ~0.3 mW in the 3000 nm to 4000 nm region, which is potentially useful for molecular spectroscopy. The combination of broadband light generation from the visible through the mid-infrared, combined with simplified self-referencing, provides a path towards robust comb systems for spectroscopy and metrology in the field.

physics.optics↗

arXiv2016

Large-Area Superconducting Nanowire Single-Photon Detector with Double-Stage Avalanche Structure

We propose a novel design of superconducting nanowire avalanche photodetectors (SNAPs), which combines the advantages of multi-stage avalanche SNAPs to lower the avalanche current I_AV and that of series-SNAPs to reduce the reset time. As proof of principle, we fabricated 800 devices with large detection area (15 um * 15 um) and five different designs on a single silicon chip for comparison, which include standard SNSPDs, series-3-SNAPs and our modified series-SNAPs with double-stage avalanche structure 2*2-SNAPs, 2*3-SNAPs, and 3*3-SNAPs. The former three types of the detectors demonstrate fully-saturated device detection efficiencies of ~20% while the latter two types are latching at larger bias currents. In addition, the I_AV of 2*2-SNAPs is only 64% of the switching current I_SW that is lower than series-3-SNAPs (74%) and well below that of 4-SNAPs (84%) reported elsewhere. We also measure that the exponential decay times of the detectors are proportional to (1/n)^2 due to the lack of external choke inductors. In particular, the decay time of 3*3-SNAPs is only 0.89 ns compared to the standard SNSPDs' 63.2 ns, showing the potential to attain GHz counting rates.

physics.ins-det↗

arXiv2016

Broadband frequency conversion via adiabatically tapered $χ^{(2)}$ waveguide in photonic integrated circuits

We propose to use the integrated aluminum nitride waveguide with engineered width variation to achieve optical frequency conversion based on $χ^{(2)}$ nonlinear effect on a photonic chip. We show that in an adiabatically tapered waveguide, the frequency conversion has a much broader bandwidth and the efficiency within the bandwidth is almost constant, which is favorable for short pulses. We demonstrate both analytically and numerically an "area law" for the frequency conversion, i.e. the product of bandwidth and efficiency is conserved as long as peak conversion efficiency does not saturate. The adiabatic structure shows higher saturation thresholds in pump power or interaction length, outperforming the conventional uniform waveguide design. With our approach, high-efficiency and wavefront-keeping conversion for short pulses is possible on a photonic chip, which will surely find applications for scalable on-chip information processing.

quant-ph↗

arXiv2016

Coupled Spin-Light dynamics in Cavity Optomagnonics

Experiments during the past two years have shown strong resonant photon-magnon coupling in microwave cavities, while coupling in the optical regime was demonstrated very recently for the first time. Unlike with microwaves, the coupling in optical cavities is parametric, akin to optomechanical systems. This line of research promises to evolve into a new field of optomagnonics, aimed at the coherent manipulation of elementary magnetic excitations by optical means. In this work we derive the microscopic optomagnonic Hamiltonian. In the linear regime the system reduces to the well-known optomechanical case, with remarkably large coupling. Going beyond that, we study the optically induced nonlinear classical dynamics of a macrospin. In the fast cavity regime we obtain an effective equation of motion for the spin and show that the light field induces a dissipative term reminiscent of Gilbert damping. The induced dissipation coefficient however can change sign on the Bloch sphere, giving rise to self-sustained oscillations. When the full dynamics of the system is considered, the system can enter a chaotic regime by successive period doubling of the oscillations.

cond-mat.mes-hall↗

arXiv2016

Characterization of optical quantum circuits using resonant phase shifts

We demonstrate that important information about linear optical circuits can be obtained through the phase shift induced by integrated optical resonators. As a proof of principle, the phase of an unbalanced Mach-Zehnder interferometer is determined. Then the method is applied to a complex optical circuit designed for linear optical quantum computation. In this controlled-NOT gate with qubit initialization and tomography stages, the relative phases are determined as well as the coupling ratios of its directional couplers.

physics.optics↗

arXiv2016

Low loss spin wave resonances in organic-based ferrimagnet vanadium tetracyanoethylene thin films

We experimentally demonstrate high quality factor spin wave resonances in an encapsulated thin film of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]$_\textit{x~2}$) coated on an a-plane sapphire substrate by low temperature chemical vapor deposition. The thickness standing wave modes are observed in a broad frequency range (1 GHz ~ 5 GHz) with high quality factor exceeding 3,200 in ambient air at room temperature, rivaling those of inorganic magnetic materials. The exchange constant of V[TCNE]$_\textit{x~2}$, a crucial material parameter for future study and device design of the V[TCNE]$_\textit{x~2}$, is extracted from the measurement with a value of $(4.61\pm 0.35)\times 10^{-16} \mathrm{\: m^{2}}$. Our result establishes the feasibility of using organic-based materials for building hybrid magnonic devices and circuits.

cond-mat.mes-hall↗

arXiv2016

Noise-free quantum optical frequency shifting driven by mechanics

The ability to manipulate single photons is of critical importance for fundamental quantum optics studies and practical implementations of quantum communications. While extraordinary progresses have been made in controlling spatial, temporal, spin and orbit angular momentum degrees of freedom, frequency-domain control of single photons so far relies on nonlinear optical effects, which have faced obstacles such as noise photons, narrow bandwidth and demanding optical filtering. Here we demonstrate the first integrated near-unity efficiency frequency manipulation of single photons, by stretching and compressing a waveguide at 8.3 billion cycles per second. Frequency shift up to 150 GHz at telecom wavelength is realized without measurable added noise and the preservation of quantum coherence is verified through quantum interference between twin photons of different colors. This single photon frequency control approach will be invaluable for increasing the channel capacity of quantum communications and compensating frequency mismatch between quantum systems, paving the road toward hybrid quantum network.

physics.optics↗

arXiv2016

Cavity piezomechanical strong coupling and frequency conversion on an aluminum nitride chip

Schemes to achieve strong coupling between mechanical modes of aluminum nitride microstructures and microwave cavity modes due to the piezoelectric effect are proposed. We show that the strong coupling regime is feasible for an on-chip aluminum nitride device that is either enclosed by a three-dimensional microwave cavity or integrated with a superconducting coplanar resonator. Combining with optomechanics, the piezomechanical strong coupling permits coherent conversion between microwave and optical modes with high efficiency. Hence, the piezomechanical system will be an efficient transducer for applications in hybrid quantum systems.

physics.optics↗

arXiv2016

Multimode Strong Coupling in Superconducting Cavity Piezo-electromechanics

High frequency mechanical resonators subjected to low thermal phonon occupancy are easier to be prepared to the ground state by direct cryogenic cooling. Their extreme stiffness, however, poses a significant challenge for external interrogations. Here we demonstrate a superconducting cavity piezo-electromechanical system in which multiple modes of a bulk acoustic resonator oscillating at $10\,\textrm{GHz}$ are coupled to a planar microwave superconducting resonator with a cooperativity exceeding $2\times10^{3}$, deep in the strong coupling regime. By implementation of the non-contact coupling scheme to reduce mechanical dissipation, the system exhibits excellent coherence characterized by a frequency-quality factor product of $7.5\times10^{15}\,\textrm{Hz}$. Interesting dynamics of temporal oscillations of the microwave energy is observed, implying the coherent conversion between phonons and photons. The demonstrated high frequency cavity piezo-electromechanics is compatible with superconducting qubits, representing an important step towards hybrid quantum systems.

physics.optics↗

arXiv2016

Parametric down-conversion photon pair source on a nanophotonic chip

Quantum photonic chips, which integrate quantum light sources alongside active and passive optical elements, as well as single photon detectors, show great potential for photonic quantum information processing and quantum technology. Mature semiconductor nanofabrication processes allow for scaling such photonic integrated circuits to on-chip networks of increasing complexity. Second order nonlinear materials are the method of choice for generating photonic quantum states in the overwhelming part of linear optic experiments using bulk components but integration with waveguide circuitry on a nanophotonic chip proved to be challenging. Here we demonstrate such an on-chip parametric down-conversion source of photon pairs based on second order nonlinearity in an Aluminum nitride microring resonator. We show the potential of our source for quantum information processing by measuring high-visibility antibunching of heralded single photons with nearly ideal state purity. Our down conversion source operates with high brightness and low noise, yielding pairs of correlated photons at MHz-rates with high coincidence-to-accidental ratio. The generated photon pairs are spectrally far separated from the pump field, providing good potential for realizing sufficient on-chip filtering and monolithic integration of quantum light sources, waveguide circuits and single photon detectors.

quant-ph↗

arXiv2016

Design and characterization of integrated components for SiN photonic quantum circuits

The design, fabrication, and detailed calibration of essential building blocks towards fully integrated linear-optics quantum computation are discussed. Photonic devices are made from silicon nitride rib waveguides, where measurements on ring resonators show small propagation losses. Directional couplers are designed to be insensitive to fabrication variations. Their offset and coupling lengths are measured, as well as the phase difference between the transmitted and reflected light. With careful calibrations, the insertion loss of the directional couplers is found to be small. Finally, an integrated controlled-NOT circuit is characterized by measuring the transmission through different combinations of inputs and outputs. The gate fidelity for the CNOT operation with this circuit is estimated to be 99.81% after post selection. This high fidelity is due to our robust design, good fabrication reproducibility, and extensive characterizations.

quant-ph↗

arXiv2016

Self-aligned multi-channel superconducting nanowire avalanche photodetector

We describe a micromachining process to allow the coupling of an array of single-mode telecommunication fibers to individual superconducting nanowire single photon detectors (SNSPDs). As proof of principle, we show the integration of four detectors on the same silicon chip, including two standard single-section nanowire detectors and two superconducting nanowire avalanche photodetectors (SNAPs) with modified series structure without external inductor, and their performances are compared. The SNAP shows saturated system detection efficiency of 16% while the dark count rate is less than 20 Hz, without the use of photon-recycling reflectors. The SNAP also demonstrates doubled signal-to-noise ratio, reduced reset time (~ 4.9 ns decay time) and improved timing jitter (62 ps FWHM) compared to standard SNSPDs.

physics.ins-det↗

arXiv2015

Non-reciprocal nonlinear optic induced transparency and frequency conversion on a chip

Developments in photonic chips have spurred photon based classical and quantum information processing, attributing to the high stability and scalability of integrated photonic devices [1, 2]. Optical nonlinearity [3] is indispensable in these complex photonic circuits, because it allows for classical and quantum light sources, all-optical switch, modulation, and non-reciprocity in ambient environments. It is commonly known that nonlinear interactions are often greatly enhanced in the microcavities [4]. However, the manifestations of coherent photon-photon interaction in a cavity, analogous to the electromagnetically induced transparency [5], have never been reported on an integrated platform. Here, we present an experimental demonstration of the coherent photon-photon interaction induced by second order optical nonlinearity (χ^{(2)} ) on an aluminum nitride photonic chip. The non-reciprocal nonlinear optic induced transparency is demonstrated as a result of the coherent interference between photons with different colors: ones in the visible wavelength band and ones in the telecom wavelength band. Furthermore, a wide-band frequency conversion with an almost unit internal (0.14 external) efficiency and a bandwidth up to 0.76\,\mathrm{GHz} is demonstrated.

quant-ph↗

arXiv2015

Quantum interference in heterogeneous superconducting-photonic circuits on a silicon chip

Quantum information processing holds great promise for communicating and computing data efficiently. However, scaling current photonic implementation approaches to larger system size remains an outstanding challenge for realizing disruptive quantum technology. Two main ingredients of quantum information processors are quantum interference and single-photon detectors. Here we develop a hybrid superconducting-photonic circuit system to show how these elements can be combined in a scalable fashion on a silicon chip. We demonstrate the suitability of this approach for integrated quantum optics by interfering and detecting photon pairs directly on the chip with waveguide-coupled single-photon detectors. Using a directional coupler implemented with silicon nitride nanophotonic waveguides, we observe 97% interference visibility when measuring photon statistics with two monolithically integrated superconducting single photon detectors. The photonic circuit and detector fabrication processes are compatible with standard semiconductor thin-film technology, making it possible to implement more complex and larger scale quantum photonic circuits on silicon chips.

quant-ph↗

arXiv2015

Cavity magnomechanics

A dielectric body couples with electromagnetic fields through radiation pressure and electrostrictive forces, which mediate phonon-photon coupling in cavity optomechanics. In a magnetic medium, according to Korteweg-Helmholtz formula, magnetostrictive forces should arise and lead to phonon-magnon interaction. Here we report such a coupled phonon-magnon system based on ferrimagnetic spheres, which we term as cavity magnomechanics, by analogy to cavity optomechanics. Coherent phonon-magnon interactions, including electromagnetically induced transparency and absorption, are demonstrated. Excitingly, due to strong hybridization of magnon and microwave photon modes and their high tunability, our platform exhibits new features including parametric amplification of magnons and phonons, triply resonant photon-magnon-phonon coupling and phonon lasing. Our work demonstrates the fundamental principle of cavity magnomechanics and its application as a new information transduction platform based on coherent coupling between photons, phonons and magnons.

quant-ph↗

arXiv2015

In-resonator variation of waveguide cross-sections for dispersion control of aluminum nitride micro-rings

We propose and demonstrate a dispersion control technique by combination of different waveguide cross sections in an aluminum nitride micro-ring resonator. Narrow and wide waveguides with normal and anomalous dispersion, respectively, are linked with tapering waveguides and enclosed in a ring resonator to produce a total dispersion near zero. The mode-coupling in multimoded waveguides is also effectively suppressed. This technique provides new degrees of freedom and enhanced flexibility in engineering the dispersion of microcomb resonators.

physics.optics↗

arXiv2015

Optomagnonic whispering gallery microresonators

Magnons in ferrimagnetic insulators such as yttrium iron garnet (YIG) have recently emerged as promising candidates for coherent information processing in microwave circuits. Here we demonstrate optical whispering gallery modes of a YIG sphere interrogated by a silicon nitride photonic waveguide, with quality factors approaching $10^6$ in the telecom c-band after surface treatments. Moreover, in contrast to conventional Faraday setup, this implementation allows input photon polarized colinearly to the magnetization to be scattered to a sideband mode of orthogonal polarization. This Brillouin scattering process is enhanced through triply resonant magnon, pump and signal photon modes - all of whispering gallery nature - within an "optomagnonic cavity". Our results show the potential use of magnons for mediating microwave-to-optical carrier conversion.

cond-mat.mes-hall↗