arXiv subjects

Alireza Marandi

Publications and source records attributed to Alireza Marandi.

At least 19 recordsLinked to original sources

arXiv2026

Laser electro-optic frequency comb in lithium niobate nanophotonics

Optical frequency combs have revolutionized precision science and technology, yet their nanophotonic implementations have failed to simultaneously achieve high efficiency, power, and coherence. Optically driven microcombs provide broad and stable spectra but low usable power, whereas active comb generators, including mode-locked lasers, can be efficient yet offer less control over coherence. We introduce the laser electro-optic (LEO) frequency comb, a comb-generation mechanism in which coherent continuous-wave injection drives a phase-modulated laser cavity above threshold into a distinct operating regime. Unlike other coherently driven integrated comb sources, the LEO comb generates comb powers that exceed the injected continuous-wave power by an order of magnitude. We realize the LEO comb in a hybrid lithium niobate/III-V nanophotonic circuit and demonstrate milliwatt-level power per comb line, 1.76-ps pulses, a 4.7-nm background-free spectrum, and linewidths as narrow as 19.6 kHz. By unifying high efficiency, power, and coherence, this architecture establishes a definitive route to chip-scale frequency comb sources that deliver on the promise of scalable, high-performance coherent optical technologies.

physics.optics↗

arXiv2026

Frequency resolved optical gating using parametric amplification for characterizing ultrafast temporally multimode squeezed states

Temporally multimode squeezed states have been a topic of recent interest due to their applications in quantum communication, information processing, and sensing. Characterizing the mode shapes is crucial for effectively manipulating these states, but current mode shape and state characterization techniques necessitate constraining assumptions and complicated experimental setups. Here, we propose a characterization technique that simultaneously recovers the complex temporal mode shapes and quadrature variances of ultrafast multimode squeezed states based on frequency resolved optical gating (FROG) using an optical parametric amplifier (OPA). FROG is a promising tool for quantum state characterization due to its flexibility of implementation and high temporal resolution. Using an OPA as the nonlinear process in FROG has the benefit of amplifying weak quantum states to a detectable level while preserving quantum information. Numerical simulations demonstrate the recovery of the mode shapes and levels of squeezing and anti-squeezing of ultrafast multimode squeezed states. This scheme offers a practical experimental approach to measuring arbitrary temporal mode shapes and characterizing large-scale multimode ultrafast Gaussian quantum states.

quant-ph↗

arXiv2026

Quantum Frequency Resolved Optical Gating of Few-Cycle Squeezed Vacuum

Offering terahertz of bandwidths and femtosecond timescales, ultrafast optics is enabling both the study of fundamental quantum optical phenomena and the advancement of quantum-enhanced applications. However, unlocking the full potential of ultrafast quantum optics requires accessing the temporal characteristics of ultrashort quantum pulses across ultrabroad bandwidths. This is particularly important in the near-infrared and visible range of the optical spectrum, which, unlike the terahertz and long-wave infrared, has remained beyond the reach of current techniques. Here, we break this barrier by translating frequency-resolved optical gating (FROG), a widely used technique for ultrafast classical pulse characterization, to the quantum regime. We show how such a quantum FROG can measure complex temporal modes and sub-optical-cycle quadrature covariances in the near-infrared, enabling complete characterization of microscopic Gaussian states. We experimentally use the quantum-FROG to report the measurement of quadrature correlations, complex temporal modes, and squeezing levels of multimode ultrafast squeezed vacuum states generated on a nanophotonic chip. We access multimode squeezing levels of a femtosecond quantum pulse approaching 7 dB and demonstrate FROG-based measurement bandwidths exceeding 100 THz. Quantum FROG enables measurement of previously inaccessible quantum features of ultrashort pulses at the sub-optical-cycle regime and highlights a practical path to accessing terahertz of bandwidths in quantum optics for applications in computing, sensing, and imaging.

physics.optics↗

arXiv2026

Visible dual-comb spectroscopy across more than 100 THz with lithium niobate nanophotonic waveguides

Broadband and high-resolution spectroscopy in the visible and ultraviolet is central to advances in multiple fields, including fundamental quantum physics, biology, atmospheric science and astronomy. Traditionally, these measurements are performed with grating or Fourier-transform spectrometers using incoherent light sources. Leveraging coherent light enables powerful frequency-comb-based techniques, but is limited by the technical complexity of efficiently generating broad spectral bandwidths from relatively narrowband and spectrally distant laser sources. Current visible dual-comb spectrometers require implicit compromises between optical bandwidth, experimental simplicity, and acquisition speed. In this work, we introduce a simple and efficient dual-comb spectrometer that converts robust Er:fiber frequency combs from the near-infrared to the ultraviolet and visible with thin-film lithium niobate (TFLN) nanophotonic waveguides. Using real-time signal processing, we retrieve coherently averaged dual-comb spectra over nearly 120 THz of simultaneous bandwidth in the visible with 100 MHz spectral resolution. With these capabilities, we measure the broadband absorption spectrum of molecular iodine (I2), demonstrating the broadest visible spectral coverage of a dual-comb spectrometer to date. Additional measurements of NO2, atomic rubidium, and atomic sodium further illustrate the achievable combination of spectroscopic bandwidth, resolution, and intrinsic frequency accuracy. Our results demonstrate the powerful integration of low-power frequency combs, nonlinear nanophotonics, and digital signal processing to enable a compact, efficient and versatile approach to high-resolution mapping of complex absorption spectra across 500 THz in the UV-visible and near-infrared spectral regions for multiple applications beyond the research lab

physics.optics↗

arXiv2025

Directional atomic layer etching of MgO-doped lithium niobate using Br-based plasma

Lithium niobate (LiNbO$_3$, LN) is a nonlinear optical material of high interest for integrated photonics with applications ranging from optical communications to quantum information processing. The performance of on-chip devices based on thin-film lithium niobate (TFLN) is presently limited by fabrication imperfections such as sidewall surface roughness and geometry inhomogeneities over the chip. Atomic layer etching (ALE) could potentially be used to overcome these difficulties. Although an isotropic ALE process for LN has been reported, performing LN fabrication completely with ALE faces several challenges, including the lack of a directional ALE process for pattern transfer and the redeposition of involatile compounds. Here, we report a directional ALE process for LN consisting of sequential exposures of HBr/BCl$_3$/Ar plasma for surface modification and Ar plasma for removal. The HBr chemistry is found to decrease redeposition compared to F- and Cl-based plasmas, which we attribute to the higher vapor pressures of Br-based products. A grating pattern etched entirely by the process (total etch depth of 220 nm) exhibits no aspect ratio dependent etching (ARDE) down to the smallest tested gap of 150 nm, in contrast to ion milling in which ARDE manifests even at 300 nm gaps for the same etch depth. The HBr plasma chemistry is also found to support an isotropic process consisting of sequential exposures of H$_2$ plasma and HBr/BCl$_3$/Ar plasma. These processes could be used together to perform the complete fabrication process for TFLN devices, eliminating imperfections arising from ion milling.

cond-mat.mtrl-sci↗

arXiv2025

Topological Soliton Frequency Comb in Nanophotonic Lithium Niobate

Frequency combs have revolutionized metrology, ranging, and optical clocks, which have motivated substantial efforts on the development of chip-scale comb sources. The on-chip comb sources are currently based on electro-optic modulation, mode-locked lasers, quantum cascade lasers, or soliton formation via Kerr nonlinearity. However, the widespread deployment of on-chip comb sources has remained elusive as they still require RF sources, high-Q resonators, or complex stabilization schemes while facing efficiency challenges. Here, we demonstrate an on-chip source of frequency comb based on the integration of a lithium niobate nanophotonic circuit with a semiconductor laser that can alleviate these challenges. For the first time, we show the formation of temporal topological solitons in a on-chip nanophotonic parametric oscillator with quadratic nonlinearity and low finesse. These solitons, independent of the dispersion regime, consist of phase defects separating two $\pi$-out-of-phase continuous wave solutions at the signal frequency, which is at half the input pump frequency. We use on-chip cross-correlation for temporal measurements and confirm formation of topological solitons as short as 60 fs around 2 $\mu$m, in agreement with a generalized parametrically forced Ginzburg-Landau theory. Moreover, we demonstrate a proof-of-concept turn-key operation of a hybrid-integrated source of topological frequency comb. Topological solitons offer a new paradigm for integrated comb sources, which are dispersion-sign agnostic and do not require high-Q resonators or high-speed modulators and can provide access to hard-to-access spectral regions, including mid-infrared.

physics.optics↗

arXiv2025

Quadratic Supercontinuum Generation from UV to Mid-IR in Lithium Niobate Nanophotonics

Supercontinuum light sources are widely used for applications ranging from imaging to sensing and frequency comb stabilization. The most common mechanisms for their generation rely on cubic nonlinearities, for instance in crystals, optical fibers, and integrated photonics. However, quadratic supercontinuum generation (QSCG) offers potential for enhanced energy efficiency and broader spectral coverage because of the typically much stronger nonlinearity and ability to achieve both coherent up- and down-conversion via three-wave mixing processes. Despite such potentials, demonstrations of QSCG in integrated photonic waveguides have been sparse and have barely surpassed their cubic counterparts in terms of spectral coverage and energy-efficiency. Here, we introduce a new dispersion engineering principle and experimentally demonstrate purely quadratic supercontinuum generation in lithium niobate nano-waveguides substantially outperforming previous demonstrations in integrated photonics. In one device, by engineering a near-zero dispersion profile and using a single poling period for quasi-phase matched saturated second-harmonic generation, we achieve robust and energy efficient multi-octave QSCG with only femtojoules of pump pulse energy. In another device, we use a flat dispersion profile with two distant zero crossings of group velocity dispersion (GVD) to achieve broadband difference-frequency generation (DFG) for extending the spectral coverage further into the mid-IR and cover the entire transparency window of lithium niobate from 350 nm to 5000 nm. Our results showcase how DFG-assisted QSCG can access hard-to-access spectral regions in an energy-efficient fashion by properly utilizing dispersion engineering and quasi-phase matching.

physics.optics↗

arXiv2025

Ultrafast All-Optical Measurement of Squeezed Vacuum in a Lithium Niobate Nanophotonic Circuit

Squeezed vacuum, a fundamental resource for continuous-variable quantum information processing, has been used to demonstrate quantum advantages in sensing, communication, and computation. While most experiments use homodyne detection to characterize squeezing and are therefore limited to electronic bandwidths, recent experiments have shown optical parametric amplification (OPA) to be a viable measurement strategy. Here, we realize OPA-based quantum state tomography in integrated photonics and demonstrate the generation and all-optical Wigner tomography of squeezed vacuum in a nanophotonic circuit. We employ dispersion-engineering to enable the distortion-free propagation of femtosecond pulses and achieve ultrabroad operation bandwidths, effectively lifting the speed restrictions imposed by traditional electronics on quantum measurements with a theoretical maximum clock speed of 6.5 THz. We implement our circuit on thin-film lithium niobate, a platform compatible with a wide variety of active and passive photonic components. Our results chart a course for realizing all-optical ultrafast quantum information processing in an integrated room-temperature platform.

quant-ph↗

arXiv2025

Ultrafast neuromorphic computing with nanophotonic optical parametric oscillators

Over the past decade, artificial intelligence (AI) has led to disruptive advancements in fundamental sciences and everyday technologies. Among various machine learning algorithms, deep neural networks have become instrumental in revealing complex patterns in large datasets with key applications in computer vision, natural language processing, and predictive analytics. On-chip photonic neural networks offer a promising platform that leverage high bandwidths and low propagation losses associated with optical signals to perform analog computations for deep learning. However, nanophotonic circuits are yet to achieve the required linear and nonlinear operations simultaneously in an all-optical and ultrafast fashion. Here, we report an ultrafast nanophotonic neuromorphic processor using an optical parametric oscillator (OPO) fabricated on thin-film lithium niobate (TFLN). The input data is used to modulate the optical pulses synchronously pumping the OPO. The consequent signal pulses generated by the OPO are coupled to one another via the nonlinear delayed dynamics of the OPO, thus forming the internal nodes of a deep recurrent neural network. We use such a nonlinearly coupled OPO network for chaotic time series prediction, nonlinear error correction in a noisy communication channel, as well as noisy waveform classification and achieve accuracies exceeding 93% at an operating clock rate of ~ 10 GHz. Our OPO network is capable of achieving sub-nanosecond latencies, a timescale comparable to a single clock cycle in state-of-the-art digital electronic processors. By circumventing the need for optical-electronic-optical (OEO) conversions, our ultrafast nanophotonic neural network paves the way for the next generation of compact all-optical neuromorphic processors with ultralow latencies and high energy efficiencies.

physics.optics↗

arXiv2025

Two-optical-cycle pulses from nanophotonic two-color soliton compression

Few- and single-cycle optical pulses and their associated ultra-broadband spectra have been crucial in the progress of ultrafast science and technology. Moreover, multi-color waveforms composed of independently manipulable ultrashort pulses in distinct spectral bands offer unique advantages in pulse synthesis and attosecond science. However, the generation and control of ultrashort pulses has required bulky and expensive optical systems at the tabletop scale and has so far been beyond the reach of integrated photonics. Here, we break these limitations and demonstrate two-optical-cycle pulse compression using quadratic two-color soliton dynamics in lithium niobate nanophotonics. By leveraging dispersion engineering and operation near phase matching, we achieve extreme compression, energy-efficient operation, and strong conversion of pump to the second harmonic. We experimentally demonstrate generation of $\sim$13-fs pulses at 2 $\mu$m using only $\sim$3 pJ of input energy. We further illustrate how the demonstrated scheme can be readily extended to on-chip single-cycle pulse synthesis with sub-cycle control. Our results provide a path towards realization of single-cycle ultrafast systems in nanophotonic circuits.

physics.optics↗

arXiv2025

Energy-Efficient Ultrashort-Pulse Characterization using Nanophotonic Parametric Amplification

The growth of ultrafast nanophotonic circuits necessitates the development of energy-efficient on-chip pulse characterization techniques. Nanophotonic realizations of Frequency Resolved Optical Gating, a common pulse characterization technique in bulk optics, have been challenging due to their non-collinear nature and the lack of efficient nonlinear optical processes in the integrated platform. Here, we experimentally demonstrate a novel FROG-based technique compatible with the nanophotonic platform that leverages the high gain-bandwidth of a dispersion-engineered degenerate optical parametric amplifier for energy-efficient ultrashort pulse characterization. We demonstrate on-chip pulse characterization of sub-80-fs, ~1-fJ pulses using just ~60-fJ of gate pulse energy, which is several orders of magnitude lower than the gate pulse energy required for characterizing similar pulses in the bulk counterpart. In the future, we anticipate our work will enable the characterization of ultraweak-ultrashort pulses with energies at the single photon level.

physics.optics↗

arXiv2025

Roadmap on Neuromorphic Photonics

This roadmap consolidates recent advances while exploring emerging applications, reflecting the remarkable diversity of hardware platforms, neuromorphic concepts, and implementation philosophies reported in the field. It emphasizes the critical role of cross-disciplinary collaboration in this rapidly evolving field.

cs.ET↗

arXiv2025

Turing-Completeness and Undecidability in Coupled Nonlinear Optical Resonators

Networks of coupled nonlinear optical resonators have emerged as an important class of systems in ultrafast optical science, enabling richer and more complex nonlinear dynamics compared to their single-resonator or travelling-wave counterparts. In recent years, these coupled nonlinear optical resonators have been applied as application-specific hardware accelerators for computing applications including combinatorial optimization and artificial intelligence. In this work, we rigorously prove a fundamental result showing that coupled nonlinear optical resonators are Turing-complete computers, which endows them with much greater computational power than previously thought. Furthermore, we show that the minimum threshold of hardware complexity needed for Turing-completeness is surprisingly low, which has profound physical consequences. In particular, we show that several problems of interest in the study of coupled nonlinear optical resonators are formally undecidable. These theoretical findings can serve as the foundation for better understanding the promise of next-generation, ultrafast all-optical computers.

physics.optics↗

arXiv2025

All-optical computing with beyond 100-GHz clock rates

A computer's clock rate ultimately determines the minimum time between sequential operations or instructions. Despite exponential advances in electronic computer performance owing to Moore's Law and increasingly parallel system architectures, computer clock rates have remained stagnant at $\sim5~\mathrm{GHz}$ for almost two decades. This poses an intractable problem for applications requiring real-time processing or control of ultrafast information systems. Here we break this barrier by proposing and experimentally demonstrating computing based on an end-to-end and all-optical recurrent neural network harnessing the ultrafast nature of linear and nonlinear optical operations while avoiding electronic operations. The all-optical computer realizes linear operations, nonlinear functions, and memory entirely in the optical domain with $>100~\mathrm{GHz}$ clock rates. We experimentally demonstrate a prototypical task of noisy waveform classification as well as perform ultrafast in-situ analysis of the soliton states from integrated optical microresonators. We further illustrate the application of the architecture for generative artificial intelligence based on quantum fluctuations to generate images even in the absence of input optical signals. Our results highlight the potential of all-optical computing beyond what can be achieved with digital electronics by utilizing ultrafast linear, nonlinear, and memory functions and quantum fluctuations.

physics.optics↗

arXiv2025

Optimizing for a Near Single-Mode Type-0 Optical Parametric Amplifier in Nanophotonics

Thin-film lithium niobate (TFLN) has recently emerged as a promising platform for integrated nonlinear photonics, enabling the use of optical parametric amplifiers (OPAs) for applications in quantum information processing, precision metrology, and ultrafast optical signal processing. However, OPA waveguide designs have not yet achieved the phase-matching conditions for type-0 operation in a single spectro-temporal mode, limiting their use. We optimize the waveguide dimensions, poling pattern, pump wavelength, and pump pulse duration for high spectral purity, a metric for single-mode fidelity. We numerically demonstrate a nanophotonic OPA with a spectral purity of 0.982 in a TFLN waveguide. Through semi-classical simulations, we further demonstrate that in the optical parametric regime, where vacuum fluctuations at the input of the OPA can saturate the gain and deplete the pump, the macroscopic output of such a single-mode OPA can be utilized for an ultra-fast quantum random number generator. These results demonstrate a promising direction for integrated OPAs in a wide range of ultrafast quantum nanophotonics applications.

physics.optics↗

arXiv2024

Ultrafast single-photon detection using nanophotonic parametric amplifiers

Integrated photonic quantum information processing (QIP) has advanced rapidly due to progress in various nanophotonic platforms. Single photon detectors have been the subject of intense study due to their ubiquity in QIP systems, yet many state-of-the art detectors operate at cryogenic temperatures under vacuum and suffer from long dead times. We propose and demonstrate a single photon detection scheme based on optical parametric amplification in nanophotonic lithium niobate (LN) combined with a classical photodetector. We use quantum detector tomography and experimentally demonstrate an efficiency of 26.5% with a 2.2% dark count rate. We show that by improving the nonlinearity-to-loss ratio in nanophotonics and using homodyne detection on a squeezed pump, the detector can achieve 69% efficiency with 0.9% dark count rate. The detector operates at room temperature, has no intrinsic dead time, and is readily integrated in LN nanophotonics, in which many other components of photonic QIP are available. Our results represent a step towards all-optical ultrafast photon detection for scalable nanophotonic QIP.

physics.optics↗

arXiv2024

Isotropic atomic layer etching of MgO-doped lithium niobate using sequential exposures of H$_2$ and SF$_6$ plasmas

Lithium niobate (LiNbO$_3$, LN) is a ferroelectric crystal of interest for integrated photonics owing to its large second-order optical nonlinearity and the ability to impart periodic poling via an external electric field. However, on-chip device performance based on thin-film lithium niobate (TFLN) is presently limited by propagation losses arising from surface roughness and corrugations. Atomic layer etching (ALE) could potentially smooth these features and thereby increase photonic performance, but no ALE process has been reported for LN. Here, we report an isotropic ALE process for $x$-cut MgO-doped LN using sequential exposures of H$_2$ and SF$_6$/Ar plasmas. We observe an etch rate of $1.59 \pm 0.02$ nm/cycle with a synergy of $96.9$%. We also demonstrate ALE can be achieved with SF$_6$/O$_2$ or Cl$_2$/BCl$_3$ plasma exposures in place of the SF$_6$/Ar plasma step with synergies of $99.5$% and $91.5$% respectively. The process is found to decrease the sidewall surface roughness of TFLN waveguides etched by physical Ar$^+$ milling by 30% without additional wet processing. Our ALE process could be used to smooth sidewall surfaces of TFLN waveguides as a post-processing treatment, thereby increasing the performance of TFLN nanophotonic devices and enabling new integrated photonic device capabilities.

cond-mat.mes-hall↗

arXiv2024

0.7 MW Yb:YAG pumped degenerate optical parametric oscillator at 2.06 μm

Frequency comb and field-resolved broadband absorption spectroscopy are promising techniques for rapid, precise, and sensitive detection of short-lived atmospheric pollutants on-site. Enhancing detection sensitivity in absorption spectroscopy hinges on bright sources that cover molecular resonances and fast signal modulation techniques to implement lock-in detection schemes efficiently. Yb:YAG thin-disk lasers, combined with optical parametric oscillators (OPO), present a compelling solution to fulfill these requirements. In this work, we report on a bright OPO pumped by a Yb:YAG thin-disk Kerr-lens mode-locked oscillator delivering 2.8 W, 114 fs pulses at 2.06 μm with an averaged energy of 90 nJ. The OPO cavity operates at 30.9 MHz pulse repetition rates, the second harmonic of the pump cavity, allowing for broadband, efficient, and dispersion-free modulation of the OPO output pulses at 15.45 MHz rate. With 13% optical-to-optical conversion efficiency and a high-frequency intra-cavity modulation, this scalable scheme holds promise to advance the detection sensitivity and frontiers of field-resolved spectroscopic techniques.

physics.optics↗