Bachelor of Technology, Indian Institute of Technology, Kharagpur, ECE (2011)
Doctor of Philosophy, Cornell University (2017)
- Nontrivial point-gap topology and non-Hermitian skin effect in photonic crystals PHYSICAL REVIEW B 2021; 104 (12)
- Synthetic frequency dimensions in dynamically modulated ring resonators APL PHOTONICS 2021; 6 (7)
Arbitrary linear transformations for photons in the frequency synthetic dimension.
2021; 12 (1): 2401
Arbitrary linear transformations are of crucial importance in a plethora of photonic applications spanning classical signal processing, communication systems, quantum information processing and machine learning. Here, we present a photonic architecture to achieve arbitrary linear transformations by harnessing the synthetic frequency dimension of photons. Our structure consists of dynamically modulated micro-ring resonators that implement tunable couplings between multiple frequency modes carried by a single waveguide. By inverse design of these short- and long-range couplings using automatic differentiation, we realize arbitrary scattering matrices in synthetic space between the input and output frequency modes with near-unity fidelity and favorable scaling. We show that the same physical structure can be reconfigured to implement a wide variety of manipulations including single-frequency conversion, nonreciprocal frequency translations, and unitary as well as non-unitary transformations. Our approach enables compact, scalable and reconfigurable integrated photonic architectures to achieve arbitrary linear transformations in both the classical and quantum domains using current state-of-the-art technology.
View details for DOI 10.1038/s41467-021-22670-7
View details for PubMedID 33893284
- Nondissipative non-Hermitian dynamics and exceptional points in coupled optical parametric oscillators OPTICA 2021; 8 (3): 415–21
Dynamic band structure measurement in the synthetic space
2021; 7 (2)
Band structure theory plays an essential role in exploring physics in both solid-state systems and photonics. Here, we demonstrate a direct experimental measurement of the dynamic band structure in a synthetic space including the frequency axis of light, realized in a ring resonator under near-resonant dynamic modulation. This synthetic lattice exhibits the physical picture of the evolution of the wave vector reciprocal to the frequency axis in the band structure, analogous to a one-dimensional lattice under an external force. We experimentally measure the trajectories of the dynamic band structure by selectively exciting the band with a continuous wave source with its frequency scanning across the entire energy regime of the band. Our results not only provide a new perspective for exploring the dynamics in fundamental physics of solid-state and photonic systems with the concept of the synthetic dimension but also enable great capability in band structure engineering in photonics.
View details for DOI 10.1126/sciadv.abe4335
View details for Web of Science ID 000606331400044
View details for PubMedID 33524000
View details for PubMedCentralID PMC7793575
Topological complex-energy braiding of non-Hermitian bands.
2021; 598 (7879): 59-64
Effects connected with the mathematical theory of knots1 emerge in many areas of science, from physics2,3 to biology4. Recent theoretical work discovered that the braid group characterizes the topology of non-Hermitian periodic systems5, where the complex band energies can braid in momentum space. However, such braids of complex-energy bands have not been realized or controlled experimentally. Here, we introduce a tight-binding lattice model that can achieve arbitrary elements in the braid group of two strands 𝔹2. We experimentally demonstrate such topological complex-energy braiding of non-Hermitian bands in a synthetic dimension6,7. Our experiments utilize frequency modes in two coupled ring resonators, one of which undergoes simultaneous phase and amplitude modulation. We observe a wide variety of two-band braiding structures that constitute representative instances of links and knots, including the unlink, the unknot, the Hopf link and the trefoil. We also show that the handedness of braids can be changed. Our results provide a direct demonstration of the braid-group characterization of non-Hermitian topology and open a pathway for designing and realizing topologically robust phases in open classical and quantum systems.
View details for DOI 10.1038/s41586-021-03848-x
View details for PubMedID 34616054
Generating arbitrary topological windings of a non-Hermitian band.
Science (New York, N.Y.)
2021; 371 (6535): 1240–45
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.
View details for DOI 10.1126/science.abf6568
View details for PubMedID 33737483
- Integrated Nonreciprocal Photonic Devices With Dynamic Modulation PROCEEDINGS OF THE IEEE 2020; 108 (10): 1759–84
- Creating locally interacting Hamiltonians in the synthetic frequency dimension for photons PHOTONICS RESEARCH 2020; 8 (9): B8–B14
- Inverse-designed non-reciprocal pulse router for chip-based LiDAR NATURE PHOTONICS 2020
Absence of unidirectionally propagating surface plasmon-polaritons at nonreciprocal metal-dielectric interfaces.
2020; 11 (1): 674
In the presence of an external magnetic field, the surface plasmon polariton that exists at the metal-dielectric interface is believed to support a unidirectional frequency range near the surface plasmon frequency, where the surface plasmon polariton propagates along one but not the opposite direction. Recent works have pointed to some of the paradoxical consequences of such a unidirectional range, including in particular the violation of the time-bandwidth product constraint that should otherwise apply in general in static systems. Here we show that such a unidirectional frequency range is nonphysical using both a general thermodynamic argument and a detailed calculation based on a nonlocal hydrodynamic Drude model for the metal permittivity. Our calculation reveals that the surface plasmon-polariton at metal-dielectric interfaces remains bidirectional for all frequencies.
View details for DOI 10.1038/s41467-020-14504-9
View details for PubMedID 32015328
PT-Symmetric Topological Edge-Gain Effect.
Physical review letters
2020; 125 (3): 033603
We demonstrate a non-Hermitian topological effect that is characterized by having complex eigenvalues only in the edge states of a topological material, despite the fact that the material is completely uniform. Such an effect can be constructed in any topological structure formed by two gapped subsystems, e.g., a quantum spin-Hall system, with a suitable non-Hermitian coupling between the spins. The resulting complex-eigenvalued edge state is robust against defects due to the topological protection. In photonics, such an effect can be used for the implementation of topological lasers, in which a uniform pumping provides gain only in the edge lasing state. Furthermore, such a topological lasing model is reciprocal and is thus compatible with standard photonic platforms.
View details for DOI 10.1103/PhysRevLett.125.033603
View details for PubMedID 32745404
Frequency-Domain Quantum Interference with Correlated Photons from an Integrated Microresonator.
Physical review letters
2020; 124 (14): 143601
Frequency encoding of quantum information together with fiber and integrated photonic technologies can significantly reduce the complexity and resource requirements for realizing all-photonic quantum networks. The key challenge for such frequency domain processing of single photons is to realize coherent and selective interactions between quantum optical fields of different frequencies over a range of bandwidths. Here, we report frequency-domain Hong-Ou-Mandel interference with spectrally distinct photons generated from a chip-based microresonator. We use four-wave mixing to implement an active "frequency beam splitter" and achieve interference visibilities of 0.95±0.02. Our work establishes four-wave mixing as a tool for selective high-fidelity two-photon operations in the frequency domain which, combined with integrated single-photon sources, provides a building block for frequency-multiplexed photonic quantum networks.
View details for DOI 10.1103/PhysRevLett.124.143601
View details for PubMedID 32338976
Inverse-designed optical interconnect based on multimode photonics and mode-division multiplexing
View details for Web of Science ID 000612090002022
Topological Behaviors in Networks of Time-Multiplexed Optical Resonators
View details for Web of Science ID 000612090003101
PT -symmetric topological edge-gain effect
View details for Web of Science ID 000612090003124
Higher-order topological insulators in synthetic dimensions.
Light, science & applications
2020; 9: 131
Conventional topological insulators support boundary states with dimension one lower than that of the bulk system that hosts them, and these states are topologically protected due to quantized bulk dipole moments. Recently, higher-order topological insulators have been proposed as a way of realizing topological states with dimensions two or more lower than that of the bulk due to the quantization of bulk quadrupole or octupole moments. However, all these proposals as well as experimental realizations have been restricted to real-space dimensions. Here, we construct photonic higher-order topological insulators (PHOTIs) in synthetic dimensions. We show the emergence of a quadrupole PHOTI supporting topologically protected corner modes in an array of modulated photonic molecules with a synthetic frequency dimension, where each photonic molecule comprises two coupled rings. By changing the phase difference of the modulation between adjacent coupled photonic molecules, we predict a dynamical topological phase transition in the PHOTI. Furthermore, we show that the concept of synthetic dimensions can be exploited to realize even higher-order multipole moments such as a fourth-order hexadecapole (16-pole) insulator supporting 0D corner modes in a 4D hypercubic synthetic lattice that cannot be realized in real-space lattices.
View details for DOI 10.1038/s41377-020-0334-8
View details for PubMedID 32704364
- Large expert-curated database for benchmarking document similarity detection in biomedical literature search DATABASE-THE JOURNAL OF BIOLOGICAL DATABASES AND CURATION 2019
Experimental band structure spectroscopy along a synthetic dimension.
2019; 10 (1): 3122
There has been significant recent interest in synthetic dimensions, where internal degrees of freedom of a particle are coupled to form higher-dimensional lattices in lower-dimensional physical structures. For these systems, the concept of band structure along the synthetic dimension plays a central role in their theoretical description. Here we provide a direct experimental measurement of the band structure along the synthetic dimension. By dynamically modulating a resonator at frequencies commensurate with its mode spacing, we create a periodically driven lattice of coupled modes in the frequency dimension. The strength and range of couplings can be dynamically reconfigured by changing the modulation amplitude and frequency. We show theoretically and demonstrate experimentally that time-resolved transmission measurements of this system provide a direct readout of its band structure. We also realize long-range coupling, gauge potentials and nonreciprocal bands by simply incorporating additional frequency drives, enabling great flexibility in band structure engineering.
View details for DOI 10.1038/s41467-019-11117-9
View details for PubMedID 31311928
- Broadband enhancement of thermal radiation OPTICS EXPRESS 2019; 27 (12): A818–A828
- Loss of polarization of elliptically polarized collapsing beams PHYSICAL REVIEW A 2019; 99 (3)
- Experimental Demonstration of Dynamical Input Isolation in Nonadiabatically Modulated Photonic Cavities ACS PHOTONICS 2019; 6 (1): 162–69
Long-Term Stabilization and Operation of a Soliton Micro-Comb for 9-Days
View details for Web of Science ID 000482226301402
Absence of frequency ranges of undirectional propagation in nonreciprocal plasmonics
View details for Web of Science ID 000482226302198
Experimental Band Structure Spectroscopy along the Synthetic Dimension
View details for Web of Science ID 000482226300311
Pulse shortening in two coupled rings under amplitude modulations with parity-time symmetry
View details for Web of Science ID 000482226302433
A single photonic cavity with two independent physical synthetic dimensions.
Science (New York, N.Y.)
The concept of synthetic dimensions has generated interest in many branches of science ranging from ultracold-atomic physics to photonics, as it provides a versatile platform for realizing effective gauge potentials and topological physics. Previous experiments have augmented the real-space dimensionality by one additional physical synthetic dimension. We endow a single ring resonator with two independent physical synthetic dimensions. Our system consists of a temporally modulated ring resonator with spatial coupling between the clockwise and counterclockwise modes, creating a synthetic Hall ladder along the frequency and pseudospin degrees of freedom for photons propagating in the ring. We observe a wide variety of rich physics, including effective spin-orbit coupling, magnetic fields, spin-momentum locking, a Meissner-to-vortex phase transition, and signatures of topological chiral one-way edge currents, completely in synthetic dimensions. Our experiments demonstrate that higher-dimensional physics can be studied in simple systems by leveraging the concept of multiple simultaneous synthetic dimensions.
View details for DOI 10.1126/science.aaz3071
View details for PubMedID 31780626
- Pulse shortening in an actively mode-locked laser with parity-time symmetry APL PHOTONICS 2018; 3 (8)
On-chip dual-comb source for spectroscopy.
2018; 4 (3): e1701858
Dual-comb spectroscopy is a powerful technique for real-time, broadband optical sampling of molecular spectra, which requires no moving components. Recent developments with microresonator-based platforms have enabled frequency combs at the chip scale. However, the need to precisely match the resonance wavelengths of distinct high quality-factor microcavities has hindered the development of on-chip dual combs. We report the simultaneous generation of two microresonator combs on the same chip from a single laser, drastically reducing experimental complexity. We demonstrate broadband optical spectra spanning 51 THz and low-noise operation of both combs by deterministically tuning into soliton mode-locked states using integrated microheaters, resulting in narrow (<10 kHz) microwave beat notes. We further use one comb as a reference to probe the formation dynamics of the other comb, thus introducing a technique to investigate comb evolution without auxiliary lasers or microwave oscillators. We demonstrate high signal-to-noise ratio absorption spectroscopy spanning 170 nm using the dual-comb source over a 20-μs acquisition time. Our device paves the way for compact and robust spectrometers at nanosecond time scales enabled by large beat-note spacings (>1 GHz).
View details for PubMedID 29511733
View details for PubMedCentralID PMC5834308
Compact narrow-linewidth integrated laser based on a low-loss silicon nitride ring resonator
2017; 42 (21): 4541–44
We design and demonstrate a compact, narrow-linewidth integrated laser based on low-loss silicon nitride waveguides coupled to a III-V gain chip. By using a highly confined optical mode, we simultaneously achieve compact bends and ultra-low loss. We leverage the narrowband backreflection of a high-Q microring resonator to act as a cavity output mirror, a single-mode filter, and a propagation delay all in one. This configuration allows the ring to provide feedback and obtain a laser linewidth of 13 kHz with 1.7 mW output power around 1550 nm. This demonstration realizes a compact sub-millimeter silicon nitride laser cavity with a narrow linewidth.
View details for DOI 10.1364/OL.42.004541
View details for Web of Science ID 000414097200077
View details for PubMedID 29088208
- Ultra-low-loss on-chip resonators with sub-milliwatt parametric oscillation threshold OPTICA 2017; 4 (6): 619–24
Quantum interference between transverse spatial waveguide modes.
2017; 8: 14010
Integrated quantum optics has the potential to markedly reduce the footprint and resource requirements of quantum information processing systems, but its practical implementation demands broader utilization of the available degrees of freedom within the optical field. To date, integrated photonic quantum systems have primarily relied on path encoding. However, in the classical regime, the transverse spatial modes of a multi-mode waveguide have been easily manipulated using the waveguide geometry to densely encode information. Here, we demonstrate quantum interference between the transverse spatial modes within a single multi-mode waveguide using quantum circuit-building blocks. This work shows that spatial modes can be controlled to an unprecedented level and have the potential to enable practical and robust quantum information processing.
View details for PubMedID 28106036
View details for PubMedCentralID PMC5263888
- On-chip broadband ultra-compact optical couplers and polarization splitters based on off-centered and non-symmetric slotted Siwire waveguides JOURNAL OF OPTICS 2016; 18 (10)
Tunable squeezing using coupled ring resonators on a silicon nitride chip
2016; 41 (2): 223–26
We demonstrate continuous tuning of the squeezing-level generated in a double-ring optical parametric oscillator by externally controlling the coupling condition using electrically controlled integrated microheaters. We accomplish this by utilizing the avoided crossing exhibited by a pair of coupled silicon nitride microring resonators. We directly detect a change in the squeezing level from 0.5 dB in the undercoupled regime to 2 dB in the overcoupled regime, which corresponds to a change in the generated on-chip squeezing factor from 0.9 to 3.9 dB. Such wide tunability in the squeezing level can be harnessed for on-chip quantum-enhanced sensing protocols that require an optimal degree of squeezing.
View details for DOI 10.1364/OL.41.000223
View details for Web of Science ID 000369050100008
View details for PubMedID 26766679
Optical nonlinearities in high-confinement silicon carbide waveguides
2015; 40 (17): 4138–41
We demonstrate strong nonlinearities of n2=8.6±1.1×10(-15) cm2 W(-1) in single-crystal silicon carbide (SiC) at a wavelength of 2360 nm. We use a high-confinement SiC waveguide fabricated based on a high-temperature smart-cut process.
View details for DOI 10.1364/OL.40.004138
View details for Web of Science ID 000360810200055
View details for PubMedID 26368731
Tunable frequency combs based on dual microring resonators
2015; 23 (16): 21527–40
In order to achieve efficient parametric frequency comb generation in microresonators, external control of coupling between the cavity and the bus waveguide is necessary. However, for passive monolithically integrated structures, the coupling gap is fixed and cannot be externally controlled, making tuning the coupling inherently challenging. We design a dual-cavity coupled microresonator structure in which tuning one ring resonance frequency induces a change in the overall cavity coupling condition. We demonstrate wide extinction tunability with high efficiency by engineering the ring coupling conditions. Additionally, we note a distinct dispersion tunability resulting from coupling two cavities of slightly different path lengths, and present a new method of modal dispersion engineering. Our fabricated devices consist of two coupled high quality factor silicon nitride microresonators, where the extinction ratio of the resonances can be controlled using integrated microheaters. Using this extinction tunability, we optimize comb generation efficiency as well as provide tunability for avoiding higher-order mode-crossings, known for degrading comb generation. The device is able to provide a 110-fold improvement in the comb generation efficiency. Finally, we demonstrate open eye diagrams using low-noise phase-locked comb lines as a wavelength-division multiplexing channel.
View details for DOI 10.1364/OE.23.021527
View details for Web of Science ID 000361036400122
View details for PubMedID 26367998
- On-Chip Optical Squeezing PHYSICAL REVIEW APPLIED 2015; 3 (4)
Overcoming Si3N4 film stress limitations for high quality factor ring resonators
2013; 21 (19): 22829–33
Silicon nitride (Si₃N₄) ring resonators are critical for a variety of photonic devices. However the intrinsically high film stress of silicon nitride has limited both the optical confinement and quality factor (Q) of ring resonators. We show that stress in Si₃N₄ films can be overcome by introducing mechanical trenches for isolating photonic devices from propagating cracks. We demonstrate a Si₃N₄ ring resonator with an intrinsic quality factor of 7 million, corresponding to a propagation loss of 4.2 dB/m. This is the highest quality factor reported to date for high confinement Si₃N₄ ring resonators in the 1,550 nm wavelength range.
View details for DOI 10.1364/OE.21.022829
View details for Web of Science ID 000325547200104
View details for PubMedID 24104169
- Splitting of degenerate states in one-dimensional quantum mechanics EUROPEAN PHYSICAL JOURNAL PLUS 2012; 127 (3)
- Design of Tunable Couplers Using Magnetic Fluid Filled Three-Core Optical Fibers IEEE PHOTONICS TECHNOLOGY LETTERS 2012; 24 (3): 164–66
Light-assisted templated self assembly using photonic crystal slabs
2011; 19 (12): 11422–28
We explore a technique which we term light-assisted templated self-assembly. We calculate the optical forces on colloidal particles over a photonic crystal slab. We show that exciting a guided resonance mode of the slab yields a resonantly-enhanced, attractive optical force. We calculate the lateral optical forces above the slab and predict that stably trapped periodic patterns of particles are dependent on wavelength and polarization. Tuning the wavelength or polarization of the light source may thus allow the formation and reconfiguration of patterns. We expect that this technique may be used to design all-optically reconfigurable photonic devices.
View details for DOI 10.1364/OE.19.011422
View details for Web of Science ID 000292865500044
View details for PubMedID 21716373
- Capillary optical fibers: design and applications for attaining a large effective mode area JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2011; 28 (6): 1431–38
- Smooth double barriers in quantum mechanics AMERICAN JOURNAL OF PHYSICS 2010; 78 (12): 1352–60