arXiv subjects

Johann Riemensberger

Publications and source records attributed to Johann Riemensberger.

At least 19 recordsLinked to original sources

arXiv2025

Narrow-linewidth, piezoelectrically tunable photonic integrated blue laser

Frequency-agile lasers operating in the ultraviolet-to-blue spectral range (360-480 nm) are critical enablers for a wide range of technologies, including free-space and underwater optical communications, optical atomic clocks, and Rydberg-atom-based quantum computing platforms. Integrated photonic lasers offer a compelling platform for these applications by combining low-noise performance with fast frequency tuning in a compact, robust form factor through monolithic integration. However, realizing such lasers in the blue spectral range remains challenging due to limitations in current semiconductor materials and photonic integration techniques. Here, we report the first demonstration of a photonic integrated blue laser at around 461 nm, which simultaneously achieves frequency agility and low phase noise. This implementation is based on the hybrid integration of a gallium nitride-based laser diode, which is self-injection locked to a high-Q microresonator fabricated on a low-loss silicon nitride photonic platform with 0.4 dB/cm propagation loss. The laser exhibits a sub-30 kHz linewidth and delivers over 1 mW of optical output power. In addition, aluminum nitride piezoelectric actuators are monolithically integrated onto the photonic circuitry to enable high-speed modulation of the refractive index, and thus tuning the laser frequency. This enables mode-hop-free laser linear frequency chirps with excursions up to 900 MHz at repetition rates up to 1 MHz, with tuning nonlinearity below 2%. We showcase the potential applications of this integrated laser in underwater communication and coherent aerosol sensing experiments.

physics.optics↗

arXiv2025

Copper Damascene Process-Based High-Performance Thin Film Lithium Tantalate Modulators

Interfacing electrical and optical systems is a ubiquitous requirement for modern networks. Competitive footprint, efficiency, and bandwidth figures have propelled interest in deploying integrated electro-optic modulators based on Pockels materials for such tasks. Due to its wide usage in legacy bulk electro-optic modulators, and triggered by the availability of 'on insulator' wafers, lithium niobate based devices have seen major advances. Recently, even more favorable properties have been demonstrated in lithium tantalate based devices, featuring similar Pockels effect, but exhibiting lower bias drift and lower birefringence, while equally benefiting from existing volume usage in wireless RF filters. Despite major progress in integrated modulators, these newly emerged ferro-electrical modulators cannot be integrated tightly with electronics yet using standardized processes, such as flip-chip bonding. Here, we overcome this bottleneck by incorporating the copper Damascene process in the fabrication of integrated lithium tantalate modulators. We demonstrate modulators featuring microwave losses that are ~10% lower than in designs relying on conventional gold electrodes. Our results allow us to reach data transmission figures on par with those of electro-optic modulators fabricated with other low-resistivity, yet less common, metals. Specifically, our fabricated modulators are able to achieve data transmission rates of 416 and 540 Gbit/s while preserving bit error ratios below the 25% SD-FEC threshold in a PAM4 and PAM8 transmission schemes, respectively. Together with the commercial availability of lithium tantalate as a Pockels material, our results open a path towards scalable and direct chip-on-wafer embedding of EO modulators with micro-electronic integrated circuits.

physics.optics↗

arXiv2024

Monolithic piezoelectrically tunable hybrid integrated laser with sub-fiber laser coherence

Ultra-low noise lasers are essential tools in a wide variety of applications, including data communication, light detection and ranging (LiDAR), quantum computing and sensing, and optical metrology. Recent advances in integrated photonics, specifically the development of ultra-low loss silicon nitride (Si$_3$N$_4$) platform, have allowed attaining performance that exceeds conventional legacy laser systems, including the phase noise of fiber lasers. This platform can moreover be combined with monolithic integration of piezoelectrical materials, enabling frequency agile low noise lasers. However, this approach has to date not surpassed the trade-off between ultra-low frequency noise and frequency agility. Here we overcome this challenge and demonstrate a fully integrated laser based on the Si$_3$N$_4$ platform with frequency noise lower than that of a fiber laser, while maintaining the capability for high-speed modulation of the laser frequency. The laser achieves an output power of 30 mW with an integrated linewidth of 4.3 kHz and an intrinsic linewidth of 3 Hz, demonstrating phase noise performance that is on par with or lower than commercial fiber lasers. Frequency agility is accomplished via a monolithically integrated piezoelectric aluminum nitride (AlN) micro-electro-mechanical system (MEMS) actuator, which enables a flat frequency actuation bandwidth extending up to 400 kHz. This combination of ultra-low noise and frequency agility is a useful feature enabling tight laser locking for frequency metrology, fiber sensing, and coherent sensing applications. Our results demonstrate the ability of 'next generation' integrated photonic circuits (beyond silicon) to exceed the performance of legacy laser systems in terms of coherence and frequency actuation.

physics.optics↗

arXiv2024

An ultra-broadband photonic-chip-based traveling-wave parametric amplifier

Optical amplification, crucial for modern communication and data center interconnects, primarily relies on erbium-doped fiber amplifiers (EDFAs) to enhance signals without distortion. While EDFAs were historically decisive for the introduction of dense wavelength-division multiplexing, they only cover a portion of the low-loss spectrum of optical fibers. Pioneering work on optical traveling-wave parametric amplifiers (TWPAs) utilizing intrinsic third-order optical nonlinearity has led to demonstrations of increased channel capacity and performance. TWPAs are unidirectional, offer high gain, and can reach the 3-dB quantum limit for phase-preserving amplifiers. Despite the use of highly nonlinear fibers or bulk waveguides, their power requirements and technical complexity have impeded adoption. In contrast, TWPAs based on photonic integrated circuits (PICs) offer the advantages of substantially increased mode confinement and optical nonlinearity but have been limited in bandwidth because of the trade-off with maintaining low propagation loss. We overcome this challenge by using low-loss gallium phosphide-on-silicon dioxide PICs and attain up to 35~dB of parametric gain with waveguides only a few centimeters long in a compact footprint of 0.25 square millimeters. Fiber-to-fiber net gain exceeding 10 dB across a bandwidth of approximately 140 nm is achieved, surpassing the gain window of a standard C-band EDFA. We furthermore demonstrate the capability to handle weak signals; input powers can range over six orders of magnitude while maintaining a low noise figure. We exploit these performance characteristics to amplify both optical frequency combs and coherent communication signals. This marks the first ultra-broadband, high-gain, continuous-wave amplification in a PIC, opening up new capabilities for next-generation optical communication, metrology, and sensing.

physics.optics↗

arXiv2024

Integrated Triply Resonant Electro-Optic Frequency Comb in Lithium Tantalate

Integrated frequency comb generators based on Kerr parametric oscillation have led to chip-scale, gigahertz-spaced combs with new applications spanning hyperscale telecommunications, low-noise microwave synthesis, LiDAR, and astrophysical spectrometer calibration. Recent progress in lithium niobate (LN) photonic integrated circuits (PICs) has resulted in chip-scale electro-optic (EO) frequency combs, offering precise comb-line positioning and simple operation without relying on the formation of dissipative Kerr solitons. However, current integrated EO combs face limited spectral coverage due to the large microwave power required to drive the non-resonant capacitive electrodes and the strong intrinsic birefringence of Lithium Niobate. Here, we overcome both challenges with an integrated triply resonant architecture, combining monolithic microwave integrated circuits (MMICs) with PICs based on the recently emerged thin-film lithium tantalate. With resonantly enhanced EO interaction and reduced birefringence in Lithium Tantalate, we achieve a four-fold comb span extension and a 16-fold power reduction compared to the conventional non-resonant microwave design. Driven by a hybrid-integrated laser diode, the comb spans over 450nm (60THz) with >2000 lines, and the generator fits within a compact 1cm^2 footprint. We additionally observe that the strong EO coupling leads to an increased comb existence range approaching the full free spectral range of the optical microresonator. The ultra-broadband comb generator, combined with detuning-agnostic operation, could advance chip-scale spectrometry and ultra-low-noise millimeter wave synthesis and unlock octave-spanning EO combs. The methodology of co-designing microwave and optical resonators can be extended to a wide range of integrated electro-optics applications.

physics.optics↗

arXiv2024

Fundamental charge noise in electro-optic photonic integrated circuits

Understanding thermodynamical measurement noise is of central importance for electrical and optical precision measurements from mass-fabricated semiconductor sensors, where the Brownian motion of charge carriers poses limits, to optical reference cavities for atomic clocks or gravitational wave detection, which are limited by thermorefractive and thermoelastic noise due to the transduction of temperature fluctuations to the refractive index and length fluctuations. Here, we discover that unexpectedly charge carrier density fluctuations give rise to a novel noise process in recently emerged electro-optic photonic integrated circuits. We show that Lithium Niobate and Lithium Tantalate photonic integrated microresonators exhibit an unexpected Flicker type (i.e. $1/f^{1.2}$) scaling in their noise properties, significantly deviating from the well-established thermorefractive noise theory. We show that this noise is consistent with thermodynamical charge noise, which leads to electrical field fluctuations that are transduced via the strong Pockels effects of electro-optic materials. Our results establish electrical Johnson-Nyquist noise as the fundamental limitation for Pockels integrated photonics, crucial for determining performance limits for both classical and quantum devices, ranging from ultra-fast tunable and low-noise lasers, Pockels soliton microcombs, to quantum transduction, squeezed light or entangled photon-pair generation. Equally, this observation offers optical methods to probe mesoscopic charge fluctuations with exceptional precision.

physics.optics↗

arXiv2024

Piezoelectric actuation for integrated photonics

Recent decades have seen significant advancements in integrated photonics, driven by improvements in nanofabrication technology. This field has developed from integrated semiconductor lasers and low-loss waveguides to optical modulators, enabling the creation of sophisticated optical systems on a chip scale capable of performing complex functions like optical sensing, signal processing, and metrology. The tight confinement of optical modes in photonic waveguides further enhances the optical nonlinearity, leading to a variety of nonlinear optical phenomena such as optical frequency combs, second-harmonic generation, and supercontinuum generation. Active tuning of photonic circuits is crucial not only for offsetting variations caused by fabrication in large-scale integration, but also serves as a fundamental component in programmable photonic circuits. Piezoelectric actuation in photonic devices offers a low-power, high-speed solution and is essential in the design of future photonic circuits due to its compatibility with materials like Si and Si3N4, which do not exhibit electro-optic effects. Here, we provide a detailed review of the latest developments in piezoelectric tuning and modulation, by examining various piezoelectric materials, actuator designs tailored to specific applications, and the capabilities and limitations of current technologies. Additionally, we explore the extensive applications enabled by piezoelectric actuators, including tunable lasers, frequency combs, quantum transducers, and optical isolators. These innovative ways of managing photon propagation and frequency on-chip are expected to be highly sought after in the future advancements of advanced photonic chips for both classical and quantum optical information processing and computing.

physics.optics↗

arXiv2024

Ultrafast tunable photonic integrated Pockels extended-DBR laser

Frequency-agile lasers that can simultaneously feature low noise characteristics as well as fast mode hop-free frequency tuning are keystone components for applications ranging from frequency modulated continuous wave (FMCW) LiDAR, to coherent optical communication and gas sensing. The hybrid integration of III-V gain media with low-loss photonic integrated circuits (PICs) has recently enabled integrated lasers with faster tuning and lower phase noise than the best legacy systems, including fiber lasers. In addition, lithium niobate on insulator (LNOI) PICs have enabled to exploit the Pockels effect to demonstrate self-injection locked hybrid lasers with tuning rates reaching peta-hertz per second. However, Pockels-tunable laser archetypes relying on high-Q optical microresonators have thus far only achieved limited output powers, are difficult to operate and stabilize due to the dynamics of self-injection locking, and require many analog control parameters. Here, we overcome this challenge by leveraging an extended distributed Bragg reflector (E-DBR) architecture to demonstrate a simple and turn-key operable frequency-agile Pockels laser that can be controlled with single analog operation and modulation inputs. Our laser supports a continuous mode hop-free tuning range of over 10 GHz with good linearity and flat actuation bandwidth up to 10 MHz, while achieving over 15 mW in-fiber output power at 1545 nm and kHz-level intrinsic linewidth, a combination unmet by legacy bulk lasers. This hybrid laser design combines an inexpensive reflective semiconductor optical amplifier (RSOA) with an electro-optic DBR PIC manufactured at wafer-scale on a LNOI platform. We showcase the performance and flexibility of this laser in proof-of-concept coherent optical ranging (FMCW LiDAR) demonstration, achieving a 4 cm distance resolution and in a hydrogen cyanide spectroscopy experiment.

physics.optics↗

arXiv2024

Foundry compatible, efficient wafer-scale manufacturing of ultra-low loss, high-density Si$_3$N$_4$ photonic integrated circuits

Silicon nitride (Si$_3$N$_4$) photonic integrated circuits (PICs) have shown low linear loss, negligible nonlinear loss, and high power handling over traditional silicon photonics. To achieve high-density photonic integration and high effective nonlinearity through tight optical confinement, thick stoichiometric Si$_3$N$_4$ films are indispensable. However, when using low-pressure chemical vapor deposition (LPCVD) to achieve high optical material transparency, Si$_3$N$_4$ films exhibit large tensile stress on the order of GPa. Methods for crack prevention are therefore essential. The photonic Damascene process has addressed this issue, attaining record low loss Si$_3$N$_4$ PICs, but it lacks control of the waveguide height. Conversely, precise waveguide dimension and ultra-low loss have been achieved with subtractive processing, but this method is not compatible with mass production due to the use of electron beam lithography. To date, an outstanding challenge is to attain both lithographic precision and ultra-low loss in high confinement Si$_3$N$_4$ PICs that are compatible with large-scale foundry manufacturing. Here, we present a single-step deposited, DUV-based subtractive method for producing wafer-scale ultra-low loss Si$_3$N$_4$ PICs that harmonize these necessities. By employing deep etching of densely distributed, interconnected trenches into the substrate, we effectively mitigate the tensile stress in the Si$_3$N$_4$ layer, enabling direct deposition of thick films without cracking and substantially prolonged storage duration. Lastly, we identify ultraviolet (UV) radiation-induced damage that can be remedied through rapid thermal annealing. Collectively, we develop ultra-low loss Si$_3$N$_4$ microresonators and 0.5 m-long spiral waveguides with losses down to 1.4 dB/m at 1550 nm with high production yield.

physics.optics↗

arXiv2023

Voltage-tunable OPO with an alternating dispersion dimer integrated on chip

Optical parametric oscillators enable the conversion of pump light to new frequency bands using nonlinear optical processes. Recent advances in integrated nonlinear photonics have led to create compact, chip-scale sources via Kerr nonlinearity-induced parametric oscillations. While these sources have provided broadband wavelength tuning, the ability to tune the emission wavelength via dynamically altering the dispersion, has not been attained so far. Here we present a voltage-tunable, on-chip integrated optical parametric oscillator based on alternating dispersiondimer, allowing to tune the emission over nearly 20 THz near 1550 nm. Unlike previous approaches, our device eliminates the need for a widely tunable pump laser source and provides efficient pump filtering at the drop port of the auxiliary ring. Integration of this scheme on a chip opens up the possibility of compact and low-cost voltage-tunable parametric oscillators with diverse application possibilities.

physics.optics↗

arXiv2023

Lithium tantalate electro-optical photonic integrated circuits for high volume manufacturing

Photonic integrated circuits based on Lithium Niobate have demonstrated the vast capabilities afforded by material with a high Pockels coefficient, allowing linear and high-speed modulators operating at CMOS voltage levels for applications ranging from data-center communications and photonic accelerators for AI. However despite major progress, the industrial adoption of this technology is compounded by the high cost per wafer. Here we overcome this challenge and demonstrate a photonic platform that satisfies the dichotomy of allowing scalable manufacturing at low cost, while at the same time exhibiting equal, and superior properties to those of Lithium Niobate. We demonstrate that it is possible to manufacture low loss photonic integrated circuits using Lithium Tantalate, a material that is already commercially adopted for acoustic filters in 5G and 6G. We show that LiTaO3 posses equally attractive optical properties and can be etched with high precision and negligible residues using DUV lithography, diamond like carbon (DLC) as a hard mask and alkaline wet etching. Using this approach we demonstrate microresonators with an intrinsic cavity linewidth of 26.8 MHz, corresponding to a linear loss of 5.6 dB/m and demonstrate a Mach Zehnder modulator with Vpi L = 4.2 V cm half-wave voltage length product. In comparison to Lithium Niobate, the photonic integrated circuits based on LiTaO3 exhibit a much lower birefringence, allowing high-density circuits and broadband operation over all telecommunication bands (O to L band), exhibit higher photorefractive damage threshold, and lower microwave loss tangent. Moreover, we show that the platform supports generation of soliton microcombs in X-Cut LiTaO3 racetrack microresonator with electronically detectable repetition rate, i.e. 30.1 GHz.

physics.optics↗

arXiv2023

Hertz-linewidth and frequency-agile photonic integrated extended-DBR lasers

Recent advances in the development of ultra-low loss silicon nitride (Si3N4)-based photonic integrated circuits have allowed integrated lasers to achieve a coherence exceeding those of fiber lasers and enabled unprecedentedly fast (Megahertz bandwidth) tuning using monolithically integrated piezoelectrical actuators. While this marks the first time that fiber laser coherence is achieved using photonic integrated circuits, in conjunction with frequency agility that exceeds those of legacy bulk lasers, the approach is presently compounded by the high cost of manufacturing DFB, as required for self-injection locking, as well as the precise control over the laser current and temperature to sustain a low noise locked operation. Reflective semiconductor optical amplifiers (RSOA) provide a cost-effective alternative solution but have not yet achieved similar performance in coherence or frequency agility, as required for frequency modulated continuous wave (FMCW) LiDAR, laser locking in frequency metrology or wavelength modulation spectroscopy for gas sensing. Here, we overcome this challenge and demonstrate an RSOA-based and frequency agile integrated laser tuned with high speed, good linearity, high optical output power, and turn-key operability while maintaining a small footprint. This is achieved using a tunable extended distributed Bragg reflector (E-DBR) in an ultra-low loss 200 nm thin Si3N4 platform with monolithically integrated piezoelectric actuators. We co-integrate the DBR with a compact ultra-low loss spiral resonator to further reduce the intrinsic optical linewidth of the laser to the Hertz level -- on par with the noise of a fiber laser -- via self-injection locking.

physics.optics↗

arXiv2023

A fully hybrid integrated Erbium-based laser

Erbium-doped fiber lasers exhibit high coherence and low noise as required for applications in fiber optic sensing, gyroscopes, LiDAR, and optical frequency metrology. Endowing Erbium-based gain in photonic integrated circuits can provide a basis for miniaturizing low-noise fiber lasers to chip-scale form factor, and enable large-volume applications. Yet, while major progress has been made in the last decade on integrated lasers based on silicon photonics with III-V gain media, the integration of Erbium lasers on chip has been compounded by large laser linewidth. Recent advances in photonic integrated circuit-based high-power Erbium-doped amplifiers, make a new class of rare-earth-ion-based lasers possible. Here, we demonstrate a fully integrated chip-scale Erbium laser that achieves high power, narrow linewidth, frequency agility, and the integration of a III-V pump laser. The laser circuit is based on an Erbium-implanted ultralow-loss silicon nitride Si$_3$N$4$ photonic integrated circuit. This device achieves single-mode lasing with a free-running intrinsic linewidth of 50 Hz, a relative intensity noise of $<$-150 dBc/Hz at $>$10 MHz offset, and output power up to 17 mW, approaching the performance of fiber lasers and state-of-the-art semiconductor extended cavity lasers. An intra-cavity microring-based Vernier filter enables wavelength tunability of $>$ 40 nm within the C- and L-bands while attaining side mode suppression ratio (SMSR) of $>$ 70 dB, surpassing legacy fiber lasers in tuning and SMRS performance. This new class of low-noise, tuneable Erbium waveguide laser could find applications in LiDAR, microwave photonics, optical frequency synthesis, and free-space communications. Our approach is extendable to other wavelengths, and more broadly, constitutes a novel way to photonic integrated circuit-based rare-earth-ion-doped lasers.

physics.optics↗

arXiv2023

Soliton Microcomb Generation in a III-V Photonic Crystal Cavity

Photonic crystals, material structures in which the dielectric function varies periodically in one, two, or three dimensions, can provide exquisite control over the propagation and confinement of light. By tailoring their band structure, exceptional optical effects can be achieved, such as slow light propagation or, through the creation of photonic bandgaps, optical cavities with both a high quality factor and a small mode volume. Photonic crystal cavities have been used to realize compact nano-lasers and achieve strong coupling to quantum emitters, such as semiconductor quantum dots, color centers, or cold atoms. A useful attribute of photonic crystals is the ability to create chirped mirrors. Chirping has underpinned advances in ultra-fast lasers based on bulk mirrors, but has yet to be fully exploited in integrated photonics, where it could provide a means to engineer otherwise unattainable dispersion profiles for a range of nonlinear optical applications, including soliton frequency comb generation. The vast majority of integrated resonators for frequency combs make use of microring geometries, where only waveguide width and height are varied to engineer dispersion. Generation of frequency combs has been demonstrated with one-dimensional photonic crystal cavities made of silicon nitride, but the low index contrast prevents formation of broad soliton combs. We overcome these challenges by using a photonic-crystal Fabry-Pérot resonator made of gallium phosphide, a material with a high refractive index and a Kerr nonlinearity 200 times larger than that of silicon nitride. We employ chirped photonic crystal mirrors to provide anomalous dispersion. With subharmonic pulsed pumping at an average power of 23.6 mW, we are able to access stable dissipative Kerr frequency combs. We demonstrate soliton formation with a 3-dB bandwidth of 3.0 THz, corresponding to a pulse duration of 60 fs.

physics.optics↗

arXiv2023

Frequency agile photonic integrated external cavity laser

Recent advances in the development of ultra-low loss silicon nitride integrated photonic circuits have heralded a new generation of integrated lasers capable of reaching fiber laser coherence. However, these devices presently are based on self-injection locking of distributed feedback (DFB) laser diodes, increasing both the cost and requiring tuning of laser setpoints for their operation. In contrast, turn-key legacy laser systems use reflective semiconductor optical amplifiers (RSOA). While this scheme has been utilized for integrated photonics-based lasers, so far, no cost-effective RSOA-based integrated lasers exist that are low noise and simultaneously feature fast, mode-hop-free and linear frequency tuning as required for frequency modulated continuous wave (FMCW) LiDAR or for laser locking in frequency metrology. Here we overcome this challenge and demonstrate a RSOA-based, frequency agile integrated laser, that can be tuned with high speed, with high linearity at low power. This is achieved using monolithic integration of piezoelectrical actuators on ultra-low loss silicon nitride photonic integrated circuits in a Vernier filter-based laser scheme. The laser operates at 1550 nm, features 6 mW output power, 400 Hz intrinsic laser linewidth, and allows ultrafast wavelength switching within 7 ns rise time and 75 nW power consumption. In addition, we demonstrate the suitability for FMCW LiDAR by showing laser frequency tuning over 1.5 GHz at 100 kHz triangular chirp rate with nonlinearity of 0.25% after linearization, and use the source for measuring a target scene 10 m away with a 8.5 cm distance resolution.

physics.optics↗

arXiv2022

Chaotic microcomb inertia-free parallel ranging

Ever growing pixel acquisition rates in the fields of augmented reality, autonomous driving and robotics have increased interest in solid state beam scanning without moving parts. Modern photonic integrated laser ranging advances towards passive beam steering solutions. Recently demonstrated imagers based on focal plane arrays, nanophotonic metasurfaces, and optical phased arrays enable unprecedented pixel resolution and measurement speed. However, parallelization of >100 lasers and detectors - successfully implemented in commercial time-of-flight sensors - has not been widely adopted for passive scanning approaches. Here, we show both inertia-free and parallel light detection and ranging (LiDAR) with microresonator frequency combs. We used 40 independent channels of a continuously scanned microresonator frequency comb operated in the chaotic regime in combination with optical dispersive elements to perform random modulation LiDAR with 2D passive beam steering.

physics.optics↗

arXiv2022

A heterogeneously integrated lithium niobate-on-silicon nitride photonic platform

The availability of thin-film lithium niobate on insulator (LNOI) and advances in processing have led to the emergence of fully integrated LiNbO3 electro-optic devices, including low-voltage, high-speed modulators, electro-optic frequency combs, and microwave-optical transducers. Yet to date, LiNbO3 photonic integrated circuits (PICs) have mostly been fabricated using non-standard etching techniques that lack the reproducibility routinely achieved in silicon photonics. Widespread future application of thin-film LiNbO3 requires a reliable and scalable solution using standard processing and precise lithographic control. Here we demonstrate a heterogeneously integrated LiNbO3 photonic platform that overcomes the abovementioned challenges by employing wafer-scale bonding of thin-film LiNbO3 to planarized low-loss silicon nitride (Si3N4) photonic integrated circuits, a mature foundry-grade integrated photonic platform. The resulting devices combine the substantial Pockels effect of LiNbO3 with the scalability, high-yield, and complexity of the underlying Si3N4 PICs. Importantly, the platform maintains the low propagation loss (<0.1 dB/cm) and efficient fiber-to-chip coupling (<2.5 dB per facet) of the Si3N4 waveguides. We find that ten transitions between a mode confined in the Si3N4 PIC and the hybrid LiNbO$_3$ mode produce less than 0.8 dB additional loss, corresponding to a loss per transition not exceeding 0.1 dB. These nearly lossless adiabatic transitions thus link the low-loss passive Si3N4 photonic structures with electro-optic components. We demonstrate high-Q microresonators, optical splitters, electrically tunable photonic dimers, electro-optic frequency combs, and carrier-envelope phase detection of a femtosecond laser on the same platform, thus providing a reliable and foundry-ready solution to low-loss and complex LiNbO3 integrated photonic circuits.

physics.optics↗

arXiv2022

Protected generation of dissipative Kerr solitons in supermodes of coupled optical microresonators

The driven-dissipative photonic dimer comprised of two evanescently coupled high-Q microresonators is a fundamental element of multimode soliton lattices. It has demonstrated a variety of emergent nonlinear phenomena including supermode soliton generation, symmetry breaking, and soliton hopping. In this article, we present another aspect of dissipative soliton generation in coupled resonators, revealing the advantages of this system over conventional single resonator platforms. Namely, we show that the accessibility of solitons drastically varies for symmetric and antisymmetric supermode families of the dimer. Linear measurements reveal that the coupling between transverse modes, which gives rise to avoided mode crossings, can be almost completely suppressed. We explain the origin of this phenomenon and show its crucial influence on the dissipative Kerr soliton formation process in lattices of coupled high-Q resonators of any type. Choosing a particular example of the topological Su-Schrieffer-Heeger model, we demonstrate how the edge state can be protected from the interaction with higher-order modes, allowing for the formation of topological Kerr solitons.

physics.optics↗