arXiv subjects

Victor Torres-Company

Publications and source records attributed to Victor Torres-Company.

At least 19 recordsLinked to original sources

arXiv2026

Self-stabilization of microcombs

Optical frequency combs form phase-locked spectral lines arranged on an equidistant grid fully defined by two degrees of freedom, i.e., the repetition rate and frequency offset. Stabilizing these parameters to a common frequency reference results in a coherent frequency ruler, central for modern precision metrology. However, extending this level of stability to chip-scale microcombs remains an outstanding challenge. Here, we demonstrate a self-stabilizing mechanism based on self-injection locking of a selected comb line via an external feedback loop. This process establishes a second anchor point in addition to the pump, thereby constraining the comb's frequency noise dynamics. We show that, with an appropriate choice between pump frequency noise and feedback strength, collective fluctuations of the repetition rate are strongly suppressed. The result is a microcomb exhibiting ultralow phase noise and dramatically reduced timing jitter. In a 100 GHz silicon nitride soliton microcomb, we achieve an unprecedented combination of high-conversion efficiency, sub-Hertz intrinsic linewidth across the entire C band, and an integrated timing jitter of 1 fs. This approach enables chip-scale microcombs with remarkable noise performance and fs-level pulse stability, surpassing conventional noise limits and opening new avenues for precision metrology at the chip scale.

physics.optics↗

arXiv2025

Roadmap: Emerging Platforms and Applications of Optical Frequency Combs and Dissipative Solitons

The discovery of optical frequency combs (OFCs) has revolutionised science and technology by bridging electronics and photonics, driving major advances in precision measurements, atomic clocks, spectroscopy, telecommunications, and astronomy. However, current OFC systems still require further development to enable broader adoption in fields such as communication, aerospace, defence, and healthcare. There is a growing need for compact, portable OFCs that deliver high output power, robust self-referencing, and application-specific spectral coverage. On the conceptual side, progress toward such systems is hindered by an incomplete understanding of the fundamental principles governing OFC generation in emerging devices and materials, as well as evolving insights into the interplay between soliton and mode-locking effects. This roadmap presents the vision of a diverse group of academic and industry researchers and educators from Europe, along with their collaborators, on the current status and future directions of OFC science. It highlights a multidisciplinary approach that integrates novel physics, engineering innovation, and advanced researcher training. Topics include advances in soliton science as it relates to OFCs, the extension of OFC spectra into the visible and mid-infrared ranges, metrology applications and noise performance of integrated OFC sources, new fibre-based OFC modules, OFC lasers and OFC applications in astronomy.

physics.optics↗

arXiv2025

Tightly-confined and long Z-cut lithium niobate waveguide with ultralow-loss

Lithium niobate (LN) is a promising material for future complex photonic-electronic circuits, with wide applications in fields like data communications, sensing, optical computation, and quantum optics. There was a great step toward LN photonic integrated circuits (PICs) with the development of dry etching for low-loss LN on insulator (LNOI) waveguides. However, the versatility of the LN waveguide platform for applications like $χ^3$ nonlinear devices and passive phase sensitive components, has not been fully utilized. The main challenges are the difficulty of making highly confined ultralow-loss waveguides and overcoming the strong material birefringence. Here, we developed a fabrication technology for an ultralow-loss, tightly-confined, dispersion-engineered LN waveguide. We demonstrated an ultra-low propagation loss of 5.8 dB/m in a decimeter-long LN spiral waveguide. We focused on Z-cut LN waveguides with TE mode to avoid the material birefringence. Aiming for $χ^3$ nonlinear applications, we demonstrated the first all normal-dispersion (ANDi) based coherent octave-spanning supercontinuum frequency comb in integrated LN waveguide. Our ultralow-loss Z-cut LN long waveguide might be useful in on-chip narrow linewidth lasers, optical delay lines, and parametric amplifiers.

physics.optics↗

arXiv2024

Single-mode Dispersion-engineered Nonlinear Integrated Waveguides for Ultra-broadband Optical Amplification and Wavelength Conversion

Four-wave mixing has extensively been investigated for various applications such as communications, spectroscopy, metrology, quantum computing and bio-imaging. However, there is a clear desire to implement these functionalities in a small footprint nonlinear platform, being capable of efficient operation across a large optical bandwidth. Many such integrated platforms have been explored, but suffer from intrinsic significant performance degradation, because conventional approaches of nonlinear photonic waveguide geometry construction for dispersion engineering focus on waveguide cross section and result in always being multimode as a byproduct. Here we propose and demonstrate a methodology that utilizes not only the impact of the waveguide cross section on the modal and dispersion behavior of the waveguide but also includes the impact of the waveguide bend for cutting off high-order modes. This approach results in simultaneous single-mode operation and dispersion engineering for very broadband operation of four-wave mixing. While we implemented this in silicon nitride waveguides, which has emerged as a promising platform capable of continuous-wave optical parametric amplification, the design approach can be universally used with other platforms as well. By also considering both second- and fourth-order dispersion we achieve unprecedented amplification bandwidths of approximately 300 nm in super-low-loss silicon nitride nonlinear waveguides. In addition, penalty-free all-optical wavelength conversion of 100 Gbit/s data in a single optical carrier over 200 nm is realized, for the first time, without optical amplification of signal or idler waves. These single-mode hyper-dispersion-engineered nonlinear integrated waveguides can become practical building blocks in versatile nonlinear photonic devices and optical networks.

physics.optics↗

arXiv2024

Ultraviolet astronomical spectrograph calibration with laser frequency combs from nanophotonic lithium niobate waveguides

Astronomical precision spectroscopy underpins searches for life beyond Earth, direct observation of the expanding Universe and constraining the potential variability of physical constants across cosmological scales. Laser frequency combs can provide the critically required accurate and precise calibration to the astronomical spectrographs. For cosmological studies, extending the calibration with such astrocombs to the ultraviolet spectral range is highly desirable, however, strong material dispersion and large spectral separation from the established infrared laser oscillators have made this exceedingly challenging. Here, we demonstrate for the first time astronomical spectrograph calibrations with an astrocomb in the ultraviolet spectral range below 400 nm. This is accomplished via chip-integrated highly nonlinear photonics in periodically-poled, nano-fabricated lithium niobate waveguides in conjunction with a robust infrared electro-optic comb generator, as well as a chip-integrated microresonator comb. These results demonstrate a viable route towards astronomical precision spectroscopy in the ultraviolet and may contribute to unlocking the full potential of next generation ground- and future space-based astronomical instruments.

physics.optics↗

arXiv2024

Self-injection-locked optical parametric oscillator based on microcombs

Narrow-linewidth yet tunable laser oscillators are one of the most important tools for precision metrology, optical atomic clocks, sensing and quantum computing. Commonly used tunable coherent oscillators are based on stimulated emission or stimulated Brillouin scattering; as a result, the operating wavelength band is limited by the gain media. Based on nonlinear optical gain, optical parametric oscillators (OPOs) enable coherent signal generation within the whole transparency window of the medium used. However, the demonstration of OPO-based Hertz-level linewidth and tunable oscillators has remained elusive. Here, we present a tunable coherent oscillator based on a multimode coherent OPO in a high-Q microresonator, i.e., a microcomb. Single-mode coherent oscillation is realized through self-injection locking (SIL) of one selected comb line. We achieve coarse tuning up to 20 nm, and an intrinsic linewidth down to sub-Hertz level, which is three orders of magnitude lower than the pump. Furthermore, we demonstrate that this scheme results into repetition rate stabilization of the microcomb. These results open exciting possibilities for generating tunable coherent radiation where stimulated emission materials are difficult to obtain, and the stabilization of microcomb sources beyond the limits imposed by the thermorefractive noise in the cavity.

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arXiv2023

Vernier Microcombs for Integrated Optical Atomic Clocks

CMOS-compatible Kerr microcombs have drawn substantial interest as mass-manufacturable, compact alternatives to bulk frequency combs. This could enable deployment of many comb-reliant applications previously confined to laboratories. Particularly enticing is the prospect of microcombs performing optical frequency division in compact optical atomic clocks. Unfortunately, it is difficult to meet the self-referencing requirement of microcombs in these systems due to the $\sim$THz repetition rates typically required for octave-spanning comb generation. Additionally, it is challenging to spectrally engineer a microcomb system to align a comb mode with an atomic clock transition with sufficient signal-to-noise ratio. Here, we adopt a Vernier dual-microcomb scheme for optical frequency division of a stabilized ultranarrow-linewidth continuous-wave laser at 871 nm to a $\sim$235 MHz output frequency. In addition to enabling measurement of the comb repetition rates, this scheme brings the freedom to pick comb lines from either or both of the combs. We exploit this flexibility to shift an ultra-high-frequency ($\sim$100 GHz) carrier-envelope offset beat down to frequencies where detection is possible and to place a comb line close to the 871 nm laser - tuned so that if frequency-doubled it would fall close to the clock transition in $^{171}$Yb$^+$. Moreover, we introduce a novel scheme which suppresses frequency noise arising from interferometric phase fluctuations in our dual-comb system and reduces the frequency instability down to our measurement limit. Our dual-comb system can potentially combine with an integrated ion trap toward future chip-scale optical atomic clocks.

physics.optics↗

arXiv2023

Superefficient microcombs at the wafer level

Photonic integrated circuits utilize planar waveguides to process light on a chip, encompassing functions like generation, routing, modulation, and detection. Similar to the advancements in the electronics industry, photonics research is steadily transferring an expanding repertoire of functionalities onto integrated platforms. The combination of best-in-class materials at the wafer-level increases versatility and performance, suitable for large-scale markets, such as datacentre interconnects, lidar for autonomous driving or consumer health. These applications require mature integration platforms to sustain the production of millions of devices per year and provide efficient solutions in terms of power consumption and wavelength multiplicity for scalability. Chip-scale frequency combs offer massive wavelength parallelization, holding a transformative potential in photonic system integration, but efficient solutions have only been reported at the die level. Here, we demonstrate a silicon nitride technology on a 100 mm wafer that aids the performance requirements of soliton microcombs in terms of yield, spectral stability, and power efficiency. Soliton microcombs are reported with an average conversion efficiency exceeding 50%, featuring 100 lines at 100 GHz repetition rate. We further illustrate the enabling possibilities of the space multiplicity, i.e., the large wafer-level redundancy, for establishing new sensing applications, and show tri-comb interferometry for broadband phase-sensitive spectroscopy. Combined with heterogeneous integration of lasers, we envision a proliferation of high-performance photonic systems for applications in future navigation systems, data centre interconnects, and ranging.

physics.optics↗

arXiv2023

Compact lithium niobate photonic integrated circuits

Lithium niobate (LN) is a promising material for future complex photonic-electronic circuits, with wide applications in fields like communications, sensing, quantum optics, and computation. LN took a great stride toward compact photonic integrated circuits (PICs) with the development of partially-etched LN on insulator (LNOI) waveguides. However, integration density is still limited for future high-compact PICs due to the partial edge nature of their waveguides. Here, we demonstrate a fully-etched LN PIC platform which, for the first time, simultaneously achieves ultra-low propagation loss and compact circuit size. The tightly-confined fully-etched LN waveguides with smooth sidewalls allow us to bring the bending radius down to 20 $μ$m (corresponds to 1 THz FSR). We have achieved compact high-$Q$ microring resonators with $Q/V$ of 7.1 $\times$ 10$^{4}$ $μ$m$^{-3}$, almost one order of magnitude larger than previous demonstrations. The statistical mean propagation losses of our LN waveguides is 8.5 dB/m (corresponds to mean $Q$-factor of 4.9 $\times$ 10$^{6}$) even with a small bending radius of 40 $μ$m. Our compact and ultra-low-loss LN platform shows great potential in future miniaturized multifunctional integration systems. As complementary evidence to show the utility of our platform, we demonstrate soliton microcombs with an ultra-high repetition rate of 500 GHz in LN.

physics.optics↗

arXiv2023

Hyperparametric oscillation via bound states in the continuum

Optical hyperparametric oscillation based on the third-order nonlinearity is one of the most significant mechanisms to generate coherent electromagnetic radiation and produce quantum states of light. Advances in dispersion-engineered high-$Q$ microresonators allow for generating signal waves far from the pump and decrease the oscillation power threshold to submilliwatt levels. However, the pump-to-signal conversion efficiency and absolute signal power are low, fundamentally limited by parasitic mode competition and attainable cavity intrinsic $Q$ to coupling $Q$ ratio, i.e., $Q_{\rm i}/Q_{\rm c}$. Here, we use Friedrich-Wintgen bound states in the continuum (BICs) to overcome the physical challenges in an integrated microresonator-waveguide system. As a result, on-chip coherent hyperparametric oscillation is generated in BICs with unprecedented conversion efficiency and absolute signal power. This work not only opens a path to generate high-power and efficient continuous-wave electromagnetic radiation in Kerr nonlinear media but also enhances the understanding of microresonator-waveguide system - an elementary unit of modern photonics.

physics.optics↗

arXiv2022

Differential phase reconstruction of microcombs

Measuring microcombs in amplitude and phase provides unique insight into the nonlinear cavity dynamics but spectral phase measurements are experimentally challenging. Here, we report a linear heterodyne technique assisted by electro-optic downconversion that enables differential phase measurement of such spectra with unprecedented sensitivity (-50 dBm) and bandwidth coverage (> 110 nm in the telecommunications range). We validate the technique with a series of measurements, including single cavity and photonic molecule microcombs.

physics.optics↗

arXiv2022

Optical linewidth of soliton microcombs

Soliton microcombs provide a versatile platform for realizing fundamental studies and technological applications. To be utilized as frequency rulers for precision metrology, soliton microcombs must display broadband phase coherence, a parameter characterized by the optical phase or frequency noise of the comb lines and their corresponding optical linewidths. Here, we analyse the optical phase-noise dynamics in soliton microcombs generated in silicon nitride high-Q microresonators and show that, because of the Raman self-frequency shift or dispersive-wave recoil, the Lorentzian linewidth of some of the comb lines can, surprisingly, be narrower than that of the pump laser. This work elucidates information about the physical limits in phase coherence of soliton microcombs and illustrates a new strategy for the generation of spectrally coherent light on chip.

physics.optics↗

arXiv2021

Thermal noise reduction in soliton microcombs via laser self-cooling

Thermal noise usually dominates the low-frequency region of the optical phase noise of soliton microcombs, leading to decoherence and limiting many aspects of applications. In this work, we demonstrate a simple and reliable way to mitigate this noise by laser cooling with the pump laser. The key is rendering the pump laser to simultaneously excite two neighboring cavity modes from different families that are respectively red and blue detuned, one for soliton generation and the other one for laser cooling.

physics.optics↗

arXiv2021

Integrated, ultra-compact high-Q silicon nitride microresonators for low-repetition-rate soliton microcombs

Multiple applications of relevance in photonics, such as spectrally efficient coherent communications, microwave synthesis or the calibration of astronomical spectrographs, would benefit from soliton microcombs operating at repetition rates <50GHz. However, attaining soliton microcombs with low repetition rates using photonic integration technologies represents a formidable challenge. Expanding the cavity volume results in a drop of intracavity intensity that can only be offset by an encompassing rise in quality factor. In addition, reducing the footprint of the microresonator on a planar integrated circuit requires race-track designs that typically result into extra modal coupling losses and disruptions into the dispersion, preventing the generation of the dissipative single soliton state. Here, we report the generation of sub-50GHz soliton microcombs in dispersion-engineered silicon nitride microresonators. In contrast to other approaches, our devices feature an optimized racetrack design that minimizes the coupling to higher-order modes and reduces the footprint size by an order of magnitude to ~1mm2. The statistical intrinsic Q reaches 19 million, and soliton microcombs at 20.5GHz and 14.0GHz repetition rates are successfully generated. Importantly, the fabrication process is entirely subtractive, meaning that the devices can be directly patterned on the Si3N4 film. This standard approach facilitates integration with further components and devices.

physics.optics↗

arXiv2021

Overcoming the quantum limit of optical amplification in monolithic waveguides

Optical amplifiers are essential in numerous photonic applications. Parametric amplifiers, relying on a nonlinear material to create amplification, are uniquely promising as they can amplify without generating excess noise. Here, we demonstrate amplification based on the 3rd order nonlinearity in a single chip, while in addition reporting a noise figure significantly below the conventional quantum limit when operated in phase-sensitive mode. Our results show the potential of nanophotonics for realizing continuous-wave parametric amplification that can enable applications in optical communications, signal processing and quantum optics across a wide range of frequencies.

physics.optics↗

arXiv2020

Dissipative Kerr solitons in photonic molecules

Many physical systems display quantized energy states. In optics, interacting resonant cavities show a transmission spectrum with split eigenfrequencies, similar to the split energy levels that result from interacting states in bonded multi-atomic, i.e. molecular, systems. Here, we study the nonlinear dynamics of photonic diatomic molecules in linearly coupled microresonators and demonstrate that the system supports the formation of self-enforcing solitary waves when a laser is tuned across a split energy level. The output corresponds to a frequency comb (microcomb) whose characteristics in terms of power spectral distribution are unattainable in single-mode (atomic) systems. Photonic molecule microcombs are coherent, reproducible, and reach high conversion efficiency and spectral flatness whilst operated with a laser power of a few milliwatts. These properties can favor the heterogeneous integration of microcombs with semiconductor laser technology and facilitate applications in optical communications, spectroscopy and astronomy.

physics.optics↗

arXiv2019

Switching dynamics of dark-pulse Kerr comb states in optical microresonators

Dissipative Kerr solitons are localized structures that exist in optical microresonators. They lead to the formation of microcombs --- chip-scale frequency combs that could facilitate precision frequency synthesis and metrology by capitalizing on advances in silicon photonics. Previous demonstrations have mainly focused on anomalous dispersion microresonators. Notwithstanding, localized structures also exist in the normal dispersion regime in the form of circulating dark pulses, but their physical dynamics is far from being understood. Here, we report the discovery of reversible switching between coherent dark-pulse Kerr combs, whereby distinct states can be accessed deterministically. Furthermore, we reveal that the formation of dark-pulse Kerr combs is associated with the appearance of a new resonance, a feature that has never been observed for dark-pulses and is ascribed to soliton behavior. These results contribute to understanding the nonlinear physics in few-mode microresonators and provide insight into the generation of microcombs with high conversion efficiency.

physics.optics↗

arXiv2019

High-Q Si3N4 microresonators based on a subtractive processing for Kerr nonlinear optics

Microresonator frequency combs (microcombs) are enabling new applications in frequency synthesis and metrology from high-speed laser ranging to coherent optical communications. One critical parameter that dictates the performance of the microcomb is the optical quality factor (Q) of the microresonator. Microresonators fabricated in planar structures such as silicon nitride (Si3N4) allow for dispersion engineering and the possibility to monolithically integrate the microcomb with other photonic devices. However, the relatively large refractive index contrast and the tight optical confinement required for dispersion engineering make it challenging to attain Si3N4 microresonators with Qs > 10 000 000 using standard subtractive processing methods. In this work, we achieve ultra-smooth Si3N4 microresonators featuring mean intrinsic Qs around 11 million. The cross-section geometry can be precisely engineered in the telecommunications band to achieve either normal or anomalous dispersion, and we demonstrate the generation of mode-locked dark-pulse Kerr combs as well as soliton microcombs. Such high-Qs allow us to generate soliton microcombs with photodetectable repetition rates, demonstrated here for the first time in Si3N4 microresonators fabricated using a subtractive processing method. These results enhance the possibilities for co-integration of microcombs with high-performance photonic devices, such as narrow-linewidth external-cavity diode lasers, ultra-narrow filters and demultiplexers.

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