Publication

Submitted
Alexander D. White, Logan Su, Daniel I. Shahar, Ki Youl Yang, Geun Ho Ahn, Jinhie Skarda, Siddharth Ramachandran, and Jelena Vučković. Submitted. “Gradient-Based Optimization of Optical Vortex Beam Emitters.” arXiv:2202.09490.Abstract
Vortex beams are stable solutions of Maxwell's equations that carry phase singularities and orbital angular momentum, unique properties that give rise to many applications in the basic sciences, optical communications, and quantum technologies. Scalable integration and fabrication of vortex beam emitters will allow these applications to flourish and enable new applications not possible with traditional optics. Here we present a general framework to generate integrated vortex beam emitters using photonic inverse design. We experimentally demonstrate generation of vortex beams with angular momentum spanning -3ℏ to 3ℏ. We show the generality of this design procedure by designing a vortex beam multiplexer capable of exciting a custom vortex beam fiber. Finally, we produce foundry-fabricated beam emitters with wide-bandwidths and high-efficiencies that take advantage of a multi-layer heterogeneous integration.
Alexander D. White, Geun Ho Ahn, Kasper Van Gasse, Ki Youl Yang, Lin Chang, John E. Bowers, and Jelena Vučković. Submitted. “Integrated Passive Nonlinear Optical Isolators.” arXiv:2206.01173.Abstract
Fiber and bulk-optical isolators are widely used to stabilize laser cavities by preventing unwanted feedback. However, their integrated counterparts have been slow to be adopted. While several strategies for on-chip optical isolation have been realized, these rely on either integration of magneto-optic materials or high frequency modulation with acousto-optic or electro-optic modulators. Here, we demonstrate an integrated approach for passively isolating a continuous wave laser using the intrinsically non-reciprocal Kerr nonlinearity in ring resonators. Using silicon nitride as a model platform, we achieve single ring isolation of 17-23dB with 1.8-5.5dB insertion loss, and a cascaded ring isolation of 35dB with 5dB insertion loss. Employing these devices, we demonstrate hybrid integration and isolation with a semi-conductor laser chip.
Ki Youl Yang, Alexander D. White, Farshid Ashtiani, Chinmay Shirpurkar, Srinivas V. Pericherla, Lin Chang, Hao Song, Kaiheng Zou, Huibin Zhou, Kai Pang, Joshua Yang, Melissa A. Guidry, Daniil M. Lukin, Han Hao, Lawrence Trask, Geun Ho Ahn, Andy Netherton, Travis C. Briles, Jordan R. Stone, Lior Rechtman, Jeffery S. Stone, Kasper Van Gasse, Jinhie L. Skarda, Logan Su, Dries Vercruysse, Jean-Philippe W. Maclean, Shahriar Aghaeimeibodi, Ming-Jun Li, David A. B. Miller, Dan Marom, Scott B. Papp, Alan E. Willner, John E. Bowers, Peter J. Delfyett, Firooz Aflatouni, and Jelena Vučković. Submitted. “Inverse-designed multi-dimensional silicon photonic transmitters.” arXiv:2103.14139.Abstract
Modern microelectronic processors have migrated towards parallel computing architectures with many-core processors. However, such expansion comes with diminishing returns exacted by the high cost of data movement between individual processors. The use of optical interconnects has burgeoned as a promising technology that can address the limits of this data transfer. While recent pushes to enhance optical communication have focused on developing wavelength-division multiplexing technology, this approach will eventually saturate the usable bandwidth, and new dimensions of data transfer will be paramount to fulfill the ever-growing need for speed. Here we demonstrate an integrated intra- and inter-chip multi-dimensional communication scheme enabled by photonic inverse design. Using inverse-designed mode-division multiplexers, we combine wavelength- and mode- multiplexing and send massively parallel data through nano-photonic waveguides and optical fibres. Crucially, as we take advantage of an orthogonal optical basis, our approach is inherently scalable to a multiplicative enhancement over the current state of the art.
2022
Avik Dutt, Luqi Yuan, Ki Youl Yang, Kai Wang, Siddharth Buddhiraju, Jelena Vučković, and Shanhui Fan. 2022. “Creating boundaries along a synthetic frequency dimension.” Nature Communications, 13, 1, Pp. 3377. Publisher's VersionAbstract
Synthetic dimensions have garnered widespread interest for implementing high dimensional classical and quantum dynamics on low-dimensional geometries. Synthetic frequency dimensions, in particular, have been used to experimentally realize a plethora of bulk physics effects. However, in synthetic frequency dimension there has not been a demonstration of a boundary which is of paramount importance in topological physics due to the bulk-edge correspondence. Here we construct boundaries in the frequency dimension of dynamically modulated ring resonators by strongly coupling an auxiliary ring. We explore various effects associated with such boundaries, including confinement of the spectrum of light, discretization of the band structure, and the interaction of boundaries with one-way chiral modes in a quantum Hall ladder, which exhibits topologically robust spectral transport. Our demonstration of sharp boundaries fundamentally expands the capability of exploring topological physics, and has applications in classical and quantum information processing in synthetic frequency dimensions.
C. Shirpurkar, J. Zang, K. Y. Yang, D. Carlson, S. P Yu, E. Lucas, S. V. Pericherla, J. Yang, M.Guidry, D.Lukin, G.H.Ahn, J. Lu, L. Trask, F. Aflatouni, J.Vučković, S. B. Papp, and P. J. Delfyett. 2022. “Photonic crystal resonators for inverse-designed multi-dimensional optical interconnects.” Optics Letters, 47, 12, Pp. 3063–3066. Publisher's VersionAbstract
We experimentally demonstrate a 400 Gbit/s optical communication link utilizing wavelength-division multiplexing and mode-division multiplexing for a total of 40 channels. This link utilizes a novel, to the best of our knowledge, 400 GHz frequency comb source based on a chip-scale photonic crystal resonator. Silicon-on-insulator photonic inverse-designed 4 × 4 mode-division multiplexer structures enable a fourfold increase in data capacity. We show less than -10 dBm of optical receiver power for error-free data transmission in 34 out of a total of 40 channels using a PRBS31 pattern.
Geun Ho Ahn, Ki Youl Yang, Rahul Trivedi, Alexander D. White, Logan Su, Jinhie Skarda, and Jelena Vučković. 2022. “Photonic Inverse Design of On-Chip Microresonators.” ACS Photonics, 9, 6, Pp. 1875-1881. Publisher's VersionAbstract
The automation of device design enabled by optimization and machine learning techniques has been transformative for photonics. While this automation has been successful for nonresonant devices, automated photonic design has remained elusive for resonant devices, key elements for on-chip communication technologies of biosensing and quantum optics, due to their highly nonconvex optimization landscapes. We propose a framework that solves this problem by mapping the design of photonic resonators to a set of nonresonant design problems. We theoretically and experimentally demonstrate this framework and show flexible dispersion engineering, a quality factor beyond 2 million on silicon-on-insulator with single-mode operation, and selective wavelength-band operation.
Melissa A Guidry, Daniil M Lukin, Ki Youl Yang, Rahul Trivedi, and Jelena Vučković. 2022. “Quantum optics of soliton microcombs.” Nature Photonics, 16, 1, Pp. 52–58. Publisher's VersionAbstract
Soliton microcombs–-phase-locked microcavity frequency combs–-have become the foundation of several classical technologies in integrated photonics, including spectroscopy, LiDAR and optical computing. Despite the predicted multimode entanglement across the comb, experimental study of the quantum optics of the soliton microcomb has been elusive. In this work we use second-order photon correlations to study the underlying quantum processes of soliton microcombs in an integrated silicon carbide microresonator. We show that a stable temporal lattice of solitons can isolate a multimode below-threshold Gaussian state from any admixture of coherent light, and predict that all-to-all entanglement can be realized for the state. Our work opens a pathway toward a soliton-based multimode quantum resource.
2021
Kai Wang, Avik Dutt, Ki Youl Yang, Casey C. Wojcik, Jelena Vučković, and Shanhui Fan. 2021. “Generating arbitrary topological windings of a non-Hermitian band.” Science, 371, 6535, Pp. 1240-1245. Publisher's VersionAbstract
Controlling the topology of a system provides a route to develop devices that are robust against defects. Whereas earlier developments of topological band theory focused on Hermitian (closed) systems, recent efforts have been toward non-Hermitian (open) systems. K. Wang et al. report on the measurement and control of topologically nontrivial windings of a non-Hermitian energy band. By implementing non-Hermitian lattice Hamiltonians along a frequency synthetic dimension formed by optical frequency modes in a modulated ring-resonator, they directly visualized the nontrivial topological band winding and showed that the winding can be controlled. Such control provides a route for the experimental synthesis, characterization, and control of topologically nontrivial phases in open physical systems. Science, this issue p. 1240 Control of the topological properties of an open system is demonstrated in an optical ring resonator. The nontrivial topological features in the energy band of non-Hermitian systems provide promising pathways to achieve robust physical behaviors in classical or quantum open systems. A key topological feature of non-Hermitian systems is the nontrivial winding of the energy band in the complex energy plane. We provide experimental demonstrations of such nontrivial winding by implementing non-Hermitian lattice Hamiltonians along a frequency synthetic dimension formed in a ring resonator undergoing simultaneous phase and amplitude modulations, and by directly characterizing the complex band structures. Moreover, we show that the topological winding can be controlled by changing the modulation waveform. Our results allow for the synthesis and characterization of topologically nontrivial phases in nonconservative systems.
Dries Vercruysse, Neil V. Sapra, Ki Youl Yang, and Jelena Vučković. 2021. “Inverse-Designed Photonic Crystal Circuits for Optical Beam Steering.” ACS Photonics, 8, 10, Pp. 3085-3093. Publisher's VersionAbstract
The ability of photonic crystal waveguides (PCWs) to confine and slow down light makes them an ideal component to enhance the performance of various photonic devices, such as optical modulators or sensors. However, the integration of PCWs in photonic applications poses design challenges, most notably, engineering the PCW mode dispersion and creating efficient coupling devices. Here, we solve these challenges with photonic inverse design and experimentally demonstrate a slow-light PCW optical phased array (OPA) with a wide steering range. Even and odd mode PCWs are engineered for a group index of 25, over a bandwidth of 20 and 12 nm, respectively. Additionally, for both PCW designs, we create strip waveguide couplers and free-space vertical couplers. Finally, also relying on inverse design, the radiative losses of the PCW are engineered, allowing us to construct OPAs with a 20° steering range in a 20 nm bandwidth.
2020
Neil V. Sapra, Ki Youl Yang, Dries Vercruysse, Kenneth J. Leedle, Dylan S. Black, R. Joel England, Logan Su, Rahul Trivedi, Yu Miao, Olav Solgaard, Robert L. Byer, and Jelena Vučković. 2020. “On-chip integrated laser-driven particle accelerator.” Science, 367, 6473, Pp. 79-83. Publisher's VersionAbstract
Particle accelerators are usually associated with large national facilities. Because photons are able to impart momentum to electrons, there are also efforts to develop laser-based particle accelerators. Sapra et al. developed an integrated particle accelerator using photonic inverse design methods to optimize the interaction between the light and the electrons. They show that an additional kick of around 0.9 kilo–electron volts (keV) can be given to a bunch of 80-keV electrons along just 30 micrometers of a specially designed channel. Such miniaturized dielectric laser accelerators could open up particle physics to a number of scientific disciplines. Science, this issue p. 79 A photonic inverse design approach is used to create a miniaturized on-chip particle accelerator. Particle accelerators represent an indispensable tool in science and industry. However, the size and cost of conventional radio-frequency accelerators limit the utility and reach of this technology. Dielectric laser accelerators (DLAs) provide a compact and cost-effective solution to this problem by driving accelerator nanostructures with visible or near-infrared pulsed lasers, resulting in a 104 reduction of scale. Current implementations of DLAs rely on free-space lasers directly incident on the accelerating structures, limiting the scalability and integrability of this technology. We present an experimental demonstration of a waveguide-integrated DLA that was designed using a photonic inverse-design approach. By comparing the measured electron energy spectra with particle-tracking simulations, we infer a maximum energy gain of 0.915 kilo–electron volts over 30 micrometers, corresponding to an acceleration gradient of 30.5 mega–electron volts per meter. On-chip acceleration provides the possibility for a completely integrated mega–electron volt-scale DLA.
Daniil M Lukin, Constantin Dory, Melissa A Guidry, Ki Youl Yang, Sattwik Deb Mishra, Rahul Trivedi, Marina Radulaski, Shuo Sun, Dries Vercruysse, Geun Ho Ahn, and Jelena Vučković. 2020. “4H-silicon-carbide-on-insulator for integrated quantum and nonlinear photonics.” Nature Photonics, 14, 5, Pp. 330–334. Publisher's VersionAbstract
Optical quantum information processing will require highly efficient photonic circuits to connect quantum nodes on-chip and across long distances. This entails the efficient integration of optically addressable qubits into photonic circuits, as well as quantum frequency conversion to the telecommunications band. 4H-silicon carbide (4H-SiC) offers unique potential for on-chip quantum photonics, as it hosts a variety of promising colour centres and has a strong second-order optical nonlinearity. Here, we demonstrate within a single, monolithic platform the strong enhancement of emission from a colour centre and efficient optical frequency conversion. We develop a fabrication process for thin films of 4H-SiC, which are compatible with industry-standard, CMOS nanofabrication. This work provides a viable route towards industry-compatible, scalable colour-centre-based quantum technologies, including the monolithic generation and frequency conversion of quantum light on-chip.
Yu-Hung Lai, Myoung-Gyun Suh, Yu-Kun Lu, Boqiang Shen, Qi-Fan Yang, Heming Wang, Jiang Li, Seung Hoon Lee, Ki Youl Yang, and Kerry Vahala. 2020. “Earth rotation measured by a chip-scale ring laser gyroscope.” Nature Photonics, 14, 6, Pp. 345–349. Publisher's Version
Ki Youl Yang, Jinhie Skarda, Michele Cotrufo, Avik Dutt, Geun Ho Ahn, Mahmoud Sawaby, Dries Vercruysse, Amin Arbabian, Shanhui Fan, Andrea Alù, and Jelena Vučković. 2020. “Inverse-designed non-reciprocal pulse router for chip-based LiDAR.” Nature Photonics, 14, 6, Pp. 369–374. Publisher's Version
Melissa A. Guidry, Ki Youl Yang, Daniil M. Lukin, Ashot Markosyan, Joshua Yang, Martin M. Fejer, and Jelena Vučković. 2020. “Optical parametric oscillation in silicon carbide nanophotonics.” Optica, 7, 9, Pp. 1139–1142. Publisher's VersionAbstract
Silicon carbide (SiC) is rapidly emerging as a leading platform for the implementation of nonlinear and quantum photonics. Here, we find that commercial SiC, which hosts a variety of spin qubits, possesses low optical absorption that can enable SiC integrated photonics with quality factors exceeding 107. We fabricate multimode microring resonators with quality factors as high as 1.1 million, and observe low-threshold (8.5±0.5mW) optical parametric oscillation using the fundamental mode as well as optical microcombs spanning 200 nm using a higher-order mode. Our demonstration is an essential milestone in the development of photonic devices that harness the unique optical properties of SiC, paving the way toward the monolithic integration of nonlinear photonics with spin-based quantum technologies.
2019
Zachary L. Newman, Vincent Maurice, Tara Drake, Jordan R. Stone, Travis C. Briles, Daryl T. Spencer, Connor Fredrick, Qing Li, Daron Westly, B. R. Ilic, Boqiang Shen, Myoung-Gyun Suh, Ki Youl Yang, Cort Johnson, David M. S. Johnson, Leo Hollberg, Kerry J. Vahala, Kartik Srinivasan, Scott A. Diddams, John Kitching, Scott B. Papp, and Matthew T. Hummon. 2019. “Architecture for the photonic integration of an optical atomic clock.” Optica, 6, 5, Pp. 680–685. Publisher's VersionAbstract
Laboratory optical atomic clocks achieve remarkable accuracy (now counted to 18 digits or more), opening possibilities for exploring fundamental physics and enabling new measurements. However, their size and the use of bulk components prevent them from being more widely adopted in applications that require precision timing. By leveraging silicon-chip photonics for integration and to reduce component size and complexity, we demonstrate a compact optical-clock architecture. Here a semiconductor laser is stabilized to an optical transition in a microfabricated rubidium vapor cell, and a pair of interlocked Kerr-microresonator frequency combs provide fully coherent optical division of the clock laser to generate an electronic 22&\#x00A0;GHz clock signal with a fractional frequency instability of one part in 1013. These results demonstrate key concepts of how to use silicon-chip devices in future portable and ultraprecise optical clocks.
Qi-Fan Yang, Boqiang Shen, Heming Wang, Minh Tran, Zhewei Zhang, Ki Youl Yang, Lue Wu, Chengying Bao, John Bowers, Amnon Yariv, and Kerry Vahala. 2019. “Vernier spectrometer using counterpropagating soliton microcombs.” Science, 363, 6430, Pp. 965-968. Publisher's VersionAbstract
When measuring length, we learn in school that a vernier scale that uses two rulers, slightly offset, can reduce human estimation error and improve the resolution of a measurement. Yang et al. apply the same vernier principle with optical combs to develop a spectrometer that can determine the wavelength of light with high accuracy and precision. Two phase-locked counterpropagating optical microcombs generated in a miniature microresonator provided the rulers. Matching up of the “teeth” of the combs was then used to measure the wavelength of the optical light sources. Science, this issue p. 965 Counterpropagating optical microcombs can be used as a vernier spectrometer to determine the wavelength of light. Determination of laser frequency with high resolution under continuous and abrupt tuning conditions is important for sensing, spectroscopy, and communications. We show that a single microresonator provides rapid and broadband measurement of optical frequencies with a relative frequency precision comparable to that of conventional dual-frequency comb systems. Dual-locked counterpropagating solitons having slightly different repetition rates were used to implement a vernier spectrometer, which enabled characterization of laser tuning rates as high as 10 terahertz per second, broadly step-tuned lasers, multiline laser spectra, and molecular absorption lines. Besides providing a considerable technical simplification through the dual-locked solitons and enhanced capability for measurement of arbitrarily tuned sources, our results reveal possibilities for chip-scale spectrometers that exceed the performance of tabletop grating and interferometer-based devices.
Uwe Niedermayer, A Adelmann, S Bettoni, M Calvi, M Dehler, E Ferrari, F Frei, D Hauenstein, B Hermann, N Hiller, R Ischebeck, C Lombosi, E Prat, S Reiche, L Rivkin, R Aßmann, U Dorda, I Hartl, W Kuropka, F Lemery, B Marchetti, F Mayet, H Xuan, J. Zhu, DS Black, PN Broaddus, RL Byer, A Ceballos, H Deng, S Fan, J Harris, T Hirano, TW Hughes, Y Jiang, T Langenstein, K Leedle, Y Miao, A Ody, A Pigott, N Sapra, O Solgaard, L Su, S Tan, J Vuckovic, K.Yang, Z Zhao, O Boine-Frankenheim, T Egenolf, E Skär, D Cesar, P Musumeci, B Naranjo, J Rosenzweig, X Shen, B Cowan, RJ England, Z Huang, H Cankaya, M Fakhari, A Fallahi, FX Kärtner, T Feurer, P Hommelhoff, J Illmer, A. Li, A Mittelbach, J McNeur, N Schönenberger, R Shiloh, A Tafel, P Yousefi, M Kozak, M Qi, YJ Lee, Y-C Huang, and E Simakov. 2019. “Challenges in simulating beam dynamics of dielectric laser acceleration.” Int. J. Mod. Phys. A, 34, 36, Pp. 1942031. Publisher's VersionAbstract
Dielectric Laser Acceleration (DLA) achieves the highest gradients among structure-based electron accelerators. The use of dielectrics increases the breakdown field limit, and thus the achievable gradient, by a factor of at least 10 in comparison to metals. Experimental demonstrations of DLA in 2013 led to the Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation. In ACHIP, our main goal is to build an accelerator on a silicon chip, which can accelerate electrons from below 100 keV to above 1 MeV with a gradient of at least 100 MeV/m. For stable acceleration on the chip, magnet-only focusing techniques are insufficient to compensate the strong acceleration defocusing. Thus, spatial harmonic and Alternating Phase Focusing (APF) laser-based focusing techniques have been developed. We have also developed the simplified symplectic tracking code DLAtrack6D, which makes use of the periodicity and applies only one kick per DLA cell, which is calculated by the Fourier coefficient of the synchronous spatial harmonic. Due to coupling, the Fourier coefficients of neighboring cells are not entirely independent and a field flatness optimization (similarly as in multi-cell cavities) needs to be performed. The simulation of the entire accelerator on a chip by a Particle In Cell (PIC) code is possible, but impractical for optimization purposes. Finally, we have also outlined the treatment of wake field effects in attosecond bunches in the grating within DLAtrack6D, where the wake function is computed by an external solver.
Neil V Sapra, Dries Vercruysse, Logan Su, Ki Youl Yang, Jinhie Skarda, Alexander Y Piggott, and Jelena Vuckovic. 2019. “Inverse design and demonstration of broadband grating couplers.” IEEE J. Sel. Top. Quantum Electron., 25, 3, Pp. 1–7. Publisher's Version
Constantin Dory, Dries Vercruysse, Ki Youl Yang, Neil V Sapra, Alison E Rugar, Shuo Sun, Daniil M Lukin, Alexander Y Piggott, Jingyuan L Zhang, Marina Radulaski, Konstantinos G Lagoudakis, Logan Su, and Jelena Vučković. 2019. “Inverse-designed diamond photonics.” Nature Communications, 10, 1, Pp. 3309. Publisher's VersionAbstract
Diamond hosts optically active color centers with great promise in quantum computation, networking, and sensing. Realization of such applications is contingent upon the integration of color centers into photonic circuits. However, current diamond quantum optics experiments are restricted to single devices and few quantum emitters because fabrication constraints limit device functionalities, thus precluding color center integrated photonic circuits. In this work, we utilize inverse design methods to overcome constraints of cutting-edge diamond nanofabrication methods and fabricate compact and robust diamond devices with unique specifications. Our design method leverages advanced optimization techniques to search the full parameter space for fabricable device designs. We experimentally demonstrate inverse-designed photonic free-space interfaces as well as their scalable integration with two vastly different devices: classical photonic crystal cavities and inverse-designed waveguide-splitters. The multi-device integration capability and performance of our inverse-designed diamond platform represents a critical advancement toward integrated diamond quantum optical circuits.
2018
Daniel C. Cole, Jordan R. Stone, Miro Erkintalo, Ki Youl Yang, Xu Yi, Kerry J. Vahala, and Scott B. Papp. 2018. “Kerr-microresonator solitons from a chirped background.” Optica, 5, 10, Pp. 1304–1310. Publisher's VersionAbstract
Optical frequency combs based on solitons in nonlinear microresonators open up new regimes for optical metrology and signal processing across a range of expanding and emerging applications. In this work, we advance these combs toward applications by demonstrating protected single-soliton formation and operation in a Kerr-nonlinear microresonator using a phase-modulated pump laser. Phase modulation gives rise to spatially/temporally varying effective loss and detuning parameters, leading to an operation regime in which multi-soliton degeneracy is lifted and a single soliton is the only observable behavior. We achieve direct, on-demand excitation of single solitons as indicated by reversal of the characteristic &\#x201C;soliton step.&\#x201D; Phase modulation also enables precise, high bandwidth control of the soliton pulse train&\#x2019;s properties, and we measure dynamics that agree closely with simulations. We show that the technique can be extended to high-repetition-frequency Kerr solitons through subharmonic phase modulation. These results will facilitate straightforward generation and control of Kerr-soliton microcombs for integrated photonics systems.

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