arXiv subjects

Gregory Moille

Publications and source records attributed to Gregory Moille.

52 records · Page 3Linked to original sources

arXiv2020

A universal frequency engineering tool for microcavity nonlinear optics: multiple selective mode splitting of whispering-gallery resonances

Whispering-gallery microcavities have been used to realize a variety of efficient parametric nonlinear optical processes through the enhanced light-matter interaction brought about by supporting multiple high quality factor and small modal volume resonances. Critical to such studies is the ability to control the relative frequencies of the cavity modes, so that frequency matching is achieved to satisfy energy conservation. Typically this is done by tailoring the resonator cross-section. Doing so modifies the frequencies of all of the cavity modes, that is, the global dispersion profile, which may be undesired, for example, in introducing competing nonlinear processes.Here, we demonstrate a frequency engineering tool, termed multiple selective mode splitting (MSMS), that is independent of the global dispersion and instead allows targeted and independent control of the frequencies of multiple cavity modes. In particular, we show controllable frequency shifts up to 0.8 nm, independent control of the splitting of up to five cavity modes with optical quality factors $\gtrsim 10^5$, and strongly suppressed frequency shifts for untargeted modes. The MSMS technique can be broadly applied to a wide variety of nonlinear optical processes across different material platforms, and can be used to both selectively enhance processes of interestand suppress competing unwanted processes.

physics.optics↗

arXiv2020

Dissipative Kerr Solitons in a III-V Microresonator

We demonstrate stable microresonator Kerr soliton frequency combs in a III-V platform (AlGaAs on SiO$_2$) through quenching of thermorefractive effects by cryogenic cooling to temperatures between 4~K and 20~K. This cooling reduces the resonator's thermorefractive coefficient, whose room-temperature value is an order of magnitude larger than that of other microcomb platforms like Si$_3$N$_4$, SiO$_2$, and AlN, by more than two orders of magnitude, and makes soliton states adiabatically accessible. Realizing such phase-stable soliton operation is critical for applications that fully exploit the ultra-high effective nonlinearity and high optical quality factors exhibited by this platform.

physics.optics↗

arXiv2020

Efficient photo-induced second harmonic generation in silicon photonics

Silicon photonics lacks a second-order nonlinear optical response in general because the typical constituent materials are centro-symmetric and lack inversion symmetry, which prohibits second-order nonlinear processes such as second harmonic generation (SHG). Here, for the first time, we realize efficient SHG in a silicon-based optical microresonator by combining a strong photo-induced effective second-order nonlinearity with resonant enhancement and perfect-phase matching. We show a record-high conversion efficiency of 2,500 %/W, which is 2 to 4 orders of magnitude larger than previous works. In particular, our devices realize mW-level SHG output powers with > 20 % power conversion efficiency. This demonstration is a major breakthrough in realizing efficient second-order nonlinear processes in silicon photonics, and paves the way for integrated self-referencing of Kerr frequency combs for compact optical frequency synthesis and optical clock technologies.

physics.optics↗

arXiv2020

On-chip optical parametric oscillation into the visible: generating red, orange, yellow, and green from a near-infrared pump

Optical parametric oscillation (OPO) in a microresonator is promising as an efficient and scalable approach to on-chip coherent visible light generation. However, so far only red light at < 420 THz (near the edge of the visible band) has been reported. In this work, we demonstrate on-chip OPO covering > 130 THz of the visible spectrum, including red, orange, yellow, and green wavelengths. In particular, using a pump laser that is scanned 5 THz in the near-infrared from 386 THz to 391 THz, the signal is tuned from the near-infrared at 395 THz to the visible at 528 THz, while the idler is tuned from the near-infrared at 378 THz to the infrared at 254 THz. The widest signal-idler separation we demonstrate of 274 THz corresponds to more than an octave span and is the widest demonstrated for a nanophotonic OPO to date. Our work is a clear demonstration of how nonlinear nanophotonics can transform light from readily accessible compact near-infrared lasers to targeted visible wavelengths of interest, which is crucial for field-level deployment of spectroscopy and metrology systems.

physics.optics↗

arXiv2019

Kerr Microresonator Soliton Frequency Combs at Cryogenic Temperatures

We present measurements of silicon nitride nonlinear microresonators and frequency comb generation at cryogenic temperatures as low as 7~K. The resulting two orders of magnitude reduction in the thermo-refractive coefficient relative to room-temperature enables direct access to single bright Kerr soliton states through adiabatic frequency tuning of the pump laser while remaining in thermal equilibrium. Our experimental results, supported by theoretical modeling, show that single solitons are easily accessible at temperatures below 60~K for the microresonator device under study. We further demonstrate that the cryogenic temperature primarily impacts the thermo-refractive coefficient. Other parameters critical to the generation of solitons, such as quality factor, dispersion, and effective nonlinearity, are unaltered. Finally, we discuss the potential improvement in thermo-refractive noise resulting from cryogenic operation. The results of this study open up new directions in advancing chip-scale frequency comb optical clocks and metrology at cryogenic temperatures.

physics.optics↗

arXiv2019

Ultra-efficient frequency comb generation in AlGaAs-on-insulator microresonators

Recent advances in nonlinear optics have revolutionized the area of integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, the state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as Si3N4 and SiO2. While semiconductor materials hold much higher nonlinear coefficients and convenience in active integration, they suffered in the past from high waveguide losses that prevented the realization of highly efficient nonlinear processes on-chip. Here we challenge this status quo and demonstrate an ultra-low loss AlGaAs-on-insulator (AlGaAsOI) platform with anomalous dispersion and quality (Q) factors beyond 1.5*10^6. Such a high quality factor, combined with the high nonlinear coefficient and the small mode volume, enabled us to demonstrate a record low Kerr frequency comb generation threshold of ~36 uW for a resonator with a 1 THz free spectral range (FSR), ~100 times lower compared to that in previous semiconductor platform. Combs with >250 nm broad span have been generated under a pump power lower than the threshold power of state of the art dielectric micro combs. A soliton-step transition has also been observed for the first time from an AlGaAs resonator. This work is an important step towards ultra-efficient semiconductor-based nonlinear photonics and will lead to fully integrated nonlinear photonic integrated circuits (PICs) in near future.

physics.optics↗

arXiv2019

Broadband Resonator-Waveguide Coupling for Efficient Extraction of Octave Spanning Microcombs

Frequency combs spanning over an octave have been successfully demonstrated in Kerr nonlinear microresonators on-chip. These micro-combs rely on both engineered dispersion, to enable generation of frequency components across the octave, and on engineered coupling, to efficiently extract the generated light into an access waveguide while maintaining a close to critically-coupled pump. The latter is challenging as the spatial overlap between the access waveguide and the ring modes decays with frequency. This leads to strong coupling variation across the octave, with poor extraction at short wavelengths. Here, we investigate how a waveguide wrapped around a portion of the resonator, in a pulley scheme, can improve extraction of octave-spanning microcombs, in particular at short wavelengths. We use coupled mode theory to predict the performance of the pulley couplers, and demonstrate good agreement with experimental measurements. Using an optimal pulley coupling design, we demonstrate a 20~dB improvement in extraction at short wavelengths compared to straight waveguide coupling.

physics.optics↗

arXiv2019

Milliwatt-threshold visible-telecom optical parametric oscillation using silicon nanophotonics

The on-chip creation of coherent light at visible wavelengths is crucial to field-level deployment of spectroscopy and metrology systems. Although on-chip lasers have been implemented in specific cases, a general solution that is not restricted by limitations of specific gain media has not been reported. Here, we propose creating visible light from an infrared pump by widely-separated optical parametric oscillation (OPO) using silicon nanophotonics. The OPO creates signal and idler light in the 700 nm and 1300 nm bands, respectively, with a 900 nm pump. It operates at a threshold power of (0.9 +/- 0.1) mW, over 50x smaller than other widely-separated microcavity OPO works, which have only been reported in the infrared. This low threshold enables direct pumping without need of an intermediate optical amplifier. We further show how the device design can be modified to generate 780 nm and 1500 nm light with a similar power efficiency. Our nanophotonic OPO shows distinct advantages in power efficiency, operation stability, and device scalability, and is a major advance towards flexible on-chip generation of coherent visible light.

physics.optics↗

arXiv2019

pyLLE: a Fast and User Friendly Lugiato-Lefever Equation Solver

We present the development of pyLLE, a freely accessible and cross-platform Lugiato-Lefever equation solver programmed in Python and Julia and optimized for the simulation of microresonator frequency combs. Examples illustrating its operation, the simplicity of use, and performance against other programming language are presented. The documentation of the software can be found at https://gregmoille.github.io/pyLLE/

cs.MS↗

arXiv2019

Efficient telecom-to-visible spectral translation through ultra-low power nonlinear nanophotonics

The ability to spectrally translate lightwave signals in a compact, low-power platform is at the heart of the promise of nonlinear nanophotonic technologies. For example, a device to link the telecommunications band with visible and short near-infrared wavelengths can enable a connection between high-performance chip-integrated lasers based on scalable nanofabrication technology with atomic systems used for time and frequency metrology. While second-order nonlinear (χ^(2)) systems are the natural approach for bridging such large spectral gaps, here we show that third-order nonlinear (chi^(3)) systems, despite their typically much weaker nonlinear response, can realize spectral translation with unprecedented performance. By combining resonant enhancement with nanophotonic mode engineering in a silicon nitride microring resonator, we demonstrate efficient spectral translation of a continuous-wave signal from the telecom band (~ 1550 nm) to the visible band (~ 650 nm) through cavity-enhanced four-wave mixing. We achieve such translation over a wide spectral range >250 THz with a translation efficiency of (30.1 +/- 2.8) % and using an ultra-low pump power of (329 +/- 13) uW. The translation efficiency projects to (274 +/- 28) % at 1 mW and is more than an order of magnitude larger than what has been achieved in current nanophotonic devices.

physics.optics↗

arXiv2018

Chip-integrated visible-telecom photon pair sources for quantum communication

Photon pair sources are fundamental building blocks for quantum entanglement and quantum communication. Recent studies in silicon photonics have documented promising characteristics for photon pair sources within the telecommunications band, including sub-milliwatt optical pump power, high spectral brightness, and high photon purity. However, most quantum systems suitable for local operations, such as storage and computation, support optical transitions in the visible or short near-infrared bands. In comparison to telecommunications wavelengths, the significantly higher optical attenuation in silica at such wavelengths limits the length scale over which optical-fiber-based quantum communication between such local nodes can take place. One approach to connect such systems over fiber is through a photon pair source that can bridge the visible and telecom bands, but an appropriate source, which should produce narrow-band photon pairs with a high signal-to-noise ratio, has not yet been developed in an integrated platform. Here, we demonstrate a nanophotonic visible-telecom photon pair source for the first time, using high quality factor silicon nitride resonators to generate bright photon pairs with an unprecedented coincidence-to-accidental ratio (CAR) up to (3800 +/- 200). We further demonstrate dispersion engineering of the microresonators to enable the connection of different species of trapped atoms/ions, defect centers, and quantum dots to the telecommunications bands for future quantum communication systems.

physics.optics↗

arXiv2018

Phased-Locked Two-Color Single Soliton Microcombs in Dispersion-Engineered Si3N4 Resonators

We propose and theoretically investigate a dispersion-engineered Si3N4 microring resonator, based on a cross-section containing a partially-etched trench, that supports phase-locked, two-color soliton microcomb states. These soliton states consist of a single circulating intracavity pulse with a modulated envelope that sits on a continuous wave background. Such temporal waveforms produce a frequency comb whose spectrum is spread over two widely-spaced spectral windows, each exhibiting a squared hyperbolic secant envelope, with the two windows phase-locked to each other via Cherenkov radiation. The first spectral window is centered around the 1550 nm pump, while the second spectral window is tailored based on straightforward geometric control, and can be centered as short as 750 nm and as long as 3000 nm. We numerically analyze the robustness of the design to parameter variation, and consider its implications to self-referencing and visible wavelength comb generation.

physics.optics↗

arXiv2017

Compact High-Q Optical Comb based on a Photonic Harmonic Potential

An effective harmonic potential for photons is achieved in a photonic crystal structure, owing to the balance of the background dispersion and a bichromatic potential. Consequently, ultra-compact resonators with several equi-spaced resonances and high loaded Q factors (0.7 million) are demonstrated. A detailed statistical analysis is carried out by exploiting the complex reflection spectra measured with Optical Coherent Tomography. The log-normal distribution of the intrinsic Q-factors peaks at 3 million. The device is made of $Ga_{0.5}In_{0.5}P$ in order to suppress the two photon absorption in the Telecom spectral range considered here. This is crucial to turn the strong localization of light into ultra-efficient parametric interactions.

physics.optics↗

arXiv2015

Towards Faster InP Photonic Crystal All-Optical-Gates

We demonstrated a two-fold acceleration of the fast time constant characterising the recovery of a P-doped Indium-Phosphide Photonic Crystal all-optical gate. Time-resolved spectral analysis is compared with a three-dimensional drift-diffusion model for the carrier dynamics, demonstrating the transition from the ambipolar to the faster minority carrier dominated diffusion regime. This open the perspective for faster yet efficient nanophotonic all-optical gates.

physics.optics↗

arXiv2015

100GHz Integrated All-Optical Switch Enabled by ALD

The carrier lifetime of a photonic crystal all-optical switch is optimized by controlling the surface of GaAs by Atomic Layer Deposition. We demonstrate an all optical modulation capability up to 100GHz at Telecom wavelengths, with a contrast as high as 7dB. Wavelength conversion has also been demonstrated at a repetition rate of 2.5GHz with average pump power of about 0.5mW

physics.optics↗

arXiv2015

High-performance and power-efficient 2${\times}$2 optical switch on Silicon-on-Insulator

A compact (15μm${\times}$μm) and highly-optimized 2${\times}$2 optical switch is demonstrated on a CMOS-compatible photonic crystal technology. On-chip insertion loss are below 1dB, static and dynamic contrast are 40dB and >20dB respectively. Owing to efficient thermo-optic design, the power consumption is below 3 mW while the switching time is 1 μs.

physics.optics↗