arXiv subjects

M. Sumetsky

Publications and source records attributed to M. Sumetsky.

At least 19 recordsLinked to original sources

arXiv2026

Microresonators induced at the optical fiber intersections

A widely tunable free spectral range (FSR) is essential for many optical microresonator applications, but achieving it remains a significant challenge. Recently, it has been experimentally demonstrated that side-coupling between two optical fibers can induce a high-Q whispering-gallery-mode (WGM) microresonator. In contrast to broadly explored monolithic optical microresonators, this configuration enables extensive tuning of the microresonator FSR through fiber bending, tilting, and twisting. Beyond fundamental interest, this class of microresonators is particularly important for a range of critical applications, including tunable delay lines, frequency comb generators, and reconfigurable optical sensors. Here, we develop the theory of such microresonators, which has remained largely unexplored. We consider weakly twisted fibers, whose geometry can be decomposed into tilting and bending. We show that an extremely small curvature of fibers critically affects the shape and spectrum of the induced microresonators. We discuss the physical origin of this curvature and show that taking it into account leads to excellent agreement between the developed theory and the experimental results.

physics.optics↗

arXiv2026

Amplification and attenuation of light in a waveguide modulated by a travelling wave

Light propagating in an optical waveguide can gain or lose power through interaction with a travelling acoustic wave or radio-frequency modulation of permittivity. Here, we model this propagation by considering an optical wave interacting with a weak travelling-wave permittivity perturbation whose frequency is much smaller than the optical frequency and whose amplitude decays exponentially along the propagation direction. Four modulation cases are analyzed: instantaneous modulation, synchronous modulation, and the Stokes and anti-Stokes resonances. For these cases, simple expressions are obtained for the carrier and sideband transmission and reflection powers as well as for the total gain and loss powers. Although the achievable total gain remains small for realistic modulation and waveguide parameters, the anti-Stokes resonance is identified as the most promising condition for observing modulation-induced light amplification.

physics.optics↗

arXiv2025

Complete inelastic transparency of time-modulated resonant photonic circuits

Photonic circuits modulated in time can convert the input light frequency $\omega_0$ shifting it by multiples of the modulation frequency $\omega_p$ and, in certain cases, amplify the total input light power. Of special interest are photonic circuits employing microwave capacitors, which instantaneously modulate photonic waveguides with frequency $\omega_p \ll \omega_0$. While the amplification of light is negligible in such circuits, ideally, frequency conversion can be completed with the conservation of the light amplitude. Therefore, similar to the elastically transparent photonic structures (i.e., structures conserving both the light amplitude and frequency), we can say that a photonic circuit parametrically modulated in time exhibits complete inelastic transparency if a wave enters the structure with frequency $\omega_0$ and exits it with a different frequency and the same amplitude. Here, we develop an approach that allows us to introduce and investigate a broad class of time-modulated photonic circuits exhibiting complete inelastic transparency. Light enters these circuits with a resonant frequency $\omega_0$, cascades between their $N$ eigenstates separated by the modulation frequency $\omega_p$, and exits with frequency $\omega_0 + (N-1)\omega_p$ and the output amplitude close to the input amplitude. As examples, we consider circuits of ring microresonators and SNAP microresonators.

physics.optics↗

arXiv2025

Potentials with partly constant FSR: semiclassical theory and applications to SNAP microresonators

Propagation of whispering gallery modes in Surface Nanoscale Axial Photonics (SNAP) microresonators, fabricated at the optical fiber surface, is commonly described by a one-dimensional wave equation, resembling the Schr\"odinger equation, where the fiber cutoff frequency (CF) varying along the fiber length plays the role of potential and the light frequency plays the role of energy. Of particular importance for applications including frequency comb generation, frequency conversion, and signal processing are SNAP microresonators with constant free spectrum range (FSR). Here we note that, in addition to CF potentials with a globally constant FSR, the potentials having constant FSR confined within a specific spectral region may be sufficient or, in certain cases, preferable for a range of applications. We describe such potentials in semiclassical approximation and analyze their properties considering representative examples.

physics.optics↗

arXiv2024

Transformation and amplification of light modulated by a traveling wave with a relatively low frequency

The behavior of electromagnetic waves in media modulated in both time and space, extensively studied decades ago, has recently attracted renewed attention. In this work, we address a central question of this research: can light at an initial frequency $\omega_{0}$ be amplified solely by pumping with a traveling wave of much lower frequency $\omega_{p} \ll \omega_{0}$? In general, the bandwidth of the modulation-induced optical frequency-comb spectrum increases substantially when the phase velocity of the traveling wave, $v_{p}$, approaches the phase velocity of light, $v_{0}$. However, in realistic photonic waveguides, the resulting amplification remains negligible due to the unfeasible modulation strengths and waveguide parameters required. In contrast, we demonstrate that modulating an optical resonator with a traveling wave of frequency $\omega_{p}$ and phase velocity $v_{p}$ much smaller than the frequency $\omega_{0}$ and phase velocity $v_{0}$ of light can produce strong amplification. This effect is accompanied by conversion into multiple comb lines within a relatively narrow frequency band.

physics.optics↗

arXiv2024

Transformation and amplification of light modulated by a traveling wave with a relatively low frequency

The behavior of electromagnetic waves in a medium modulated in time and space, largely investigated decades ago, has recently attracted renewed interest. Here, we solve an intriguing problem of this research: can light with an initial frequency $\omega_0$ be amplified in a realistic photonic circuit solely pumped by a traveling wave with a much lower frequency $\omega_p \ll \omega_0$? Generally, the bandwidth of the modulation-induced optical frequency comb spectrum can be substantially broadened when the phase velocity of the traveling wave, $v_p$, approaches the phase velocity of light, $v_0$. However, in realistic photonic waveguides, the amplification effect remains small due to the unfeasible modulation and waveguide parameters required. In contrast, we demonstrate that modulating an optical resonator with a traveling wave that has a small phase velocity $v_p \ll v_0$ (rather than a synchronous $v_p \approx v_0$) can result in narrow-band light amplification, which is dramatically enhanced near the Brillouin phase-matching condition $\omega_p/v_p \approx 2\omega_0/v_0$. Our calculations show that the proposed amplifier of light can be realized in a lithium niobate racetrack resonator with millimeter-scale perimeter modulated by a surface acoustic wave with surprisingly small and practically achievable amplitude.

physics.optics↗

arXiv2023

Semiclassical theory of frequency combs generated by parametric modulation of optical microresonators

An optical microresonator, which parameters are periodically modulated in time, can generate optical frequency comb (OFC) spectral resonances equally spaced by the modulation frequency. Significant recent progress in realization of OFC generators based on the modulation of microresonator parameters boosted interest to their further experimental development and theoretical understanding of underlying phenomena. However, most of theoretical approaches developed to date were based on the lumped parameter models which unable to evaluate, analyse, and optimize the effect of spatial distribution of modulation inside microresonators. Here we develop the multi-quantum semiclassical theory of parametrically excited OFCs which solves these problems. As an application, we compare OFCs which are resonantly or adiabatically excited in a racetrack microresonator (RTM) and a SNAP (Surface Nanoscale Axial Photonics) bottle microresonator (SBM). The principal difference between these two types of microresonators consists in much slower propagation speed of whispering gallery modes along the SBM axis compared to the speed of modes propagating along the RTM waveguide axis. We show that, due to this difference, similar OFCs can be generated by an SBM with a much smaller size compared to that of the RTM. Based on the developed theory, we analytically express the OFC spectrum of microresonators through the spatial distribution of modulated parameters and optimize this distribution to arrive at the strongest OFCs generated with minimum power consumption.

physics.optics↗

arXiv2023

Reconfigurable microresonators induced in side-coupled optical fibers

We experimentally demonstrate that side-coupling of coplanar bent optical fibers can induce a high Q-factor whispering gallery mode (WGM) optical microresonator. To explain the effect, we consider WGMs with wavelengths close to the cutoff wavelengths (CWs) of these fibers which slowly propagate along the fiber axes. In the vicinity of the touching region, WGMs of adjacent fibers are coupled to each other, and CWs experience sub-nanoscale axial variation proportional to the coupling strength. We show that in certain cases the CW variation leads to full localization of the WGMs and the creation of an optical microresonator. By varying the characteristic curvature fiber radius from the centimeter order to millimeter order, we demonstrate fully mechanically reconfigurable high Q-factor optical microresonators with dimensions varying from the millimeter order to 100-micron order and free spectral range varying from a picometer to hundreds of picometers. The new microresonators may find applications in cavity QED, microresonator optomechanics, frequency comb generation with tunable repetition rate, tunable lasing, and tunable processing and delay of optical pulses.

physics.optics↗

arXiv2022

Optimized frequency comb spectrum of parametrically modulated bottle microresonators

The formation of optical frequency combs (OFCs) by the parametric modulation of optical microresonators is commonly described by lumped-parameter models. However, these models do not consider the actual spatial distribution of the parametric modulation (SDPM). Here, we show that the effect of the SDPM becomes of special importance for an elongated SNAP bottle microresonator (SBM) having shallow nanometre-scale effective radius variation along its axial length. The advantage of SBMs compared to microresonators with different shapes (e.g., spherical and toroidal) is that SBMs, remaining miniature, can have resonant spectrum with much smaller free spectral range and no dispersion. Therefore, SBMs can be used to generate OFCs with much lower repetition rates. We consider the resonant and adiabatic modulation of parabolic SBMs and show that it is possible to improve the flatness and increase the bandwidth of the generated OFC spectra by optimising the SDPM. We suggest that the determined optimal SDPM can be experimentally realized using piezoelectric, radiation pressure, and electro-optical excitation of an SBM.

physics.optics↗

arXiv2021

SNAP microwave optical filters

If the originally flat bottom of a wide quantum well with multiple eigenstates is periodically modulated, its eigenvalues rearrange into denser groups separated by wider gaps. We show that this effect, if implemented in an elongated bottle microresonator (also called a SNAP microresonator) allows to design microwave photonic tunable filters with an outstanding performance.

physics.app-ph↗

arXiv2021

Enhancing the impedance matched bandwidth of bottle microresonator signal processing devices

Light pulses entering an elongated bottle microresonator (BMR) from a transversely oriented input-output waveguide (microfiber) slowly propagate along the BMR length and bounce between turning points at its constricting edges. To avoid insertion losses and processing errors, a pulse should completely transfer from the waveguide into the BMR and, after being processed, completely return back into the waveguide. For this purpose, the waveguide and BMR should be impedance matched along the pulse bandwidth. Here we show how to enhance the impedance matched bandwidth by optimization of the BMR effective radius variation in a small vicinity of the input-output waveguide.

physics.optics↗

arXiv2021

Fundamental limit of the microresonator field uniformity and slow light enabled angstrom-precise straight-line translation

We determine the fundamental limit of the microresonator field uniformity. It can be achieved in a specially designed microresonator, called a bat microresonator, fabricated at the optical fiber surface. We show that the relative nonuniformity of an eigenmode amplitude along the axial length $L$ of an ideal bat microresonator cannot be smaller than ${{\frac{1}{3}}}{\pi }^2n^4_r{\lambda }^{-4}Q^{-2}L^4$, where $n_r,\ \lambda $ and $Q$ are its refractive index, the eigenmode wavelength and Q-factor. In the absence of losses ($Q=\infty $), this eigenmode has the amplitude independent of axial coordinate and zero axial speed (i.e., is stopped) within the length $L$. For a silica microresonator with $Q={10}^8$ this eigenmode has the axial speed $\mathrm{\sim}$ 10${}^{-4}$c, where c is the speed of light in vacuum, and its nonuniformity along the length 100 micron at wavelength $\lambda =1.5$ micron is $\mathrm{\sim}$ 10${}^{-7}$. For a realistic fiber with diameter 100 micron and surface roughness 0.2 nm, the smallest eigenmode nonuniformity is $\mathrm{\sim}$ 0.0003. As an application, we consider a bat microresonator evanescently coupled to high Q-factor silica microspheres which serves as a reference supporting the angstrom-precise straight-line translation over the distance $L$ exceeding a hundred microns.

physics.optics↗

arXiv2021

Microresonator devices lithographically introduced at the optical fiber surface

We present a simple lithographic method for fabrication of microresonator devices at the optical fiber surface. First, we undress the predetermined surface areas of a fiber segment from the polymer coating with a focused CO2 laser beam. Next, using the remaining coating as a mask, we etch the fiber in a hydrofluoric acid solution. Finally, we completely undress the fiber segment from coating to create a chain of silica bottle microresonators with nanoscale radius variation (SNAP microresonators). We demonstrate the developed method by fabrication of a chain of five 1 mm long and 30 nm high microresonators at the surface of a 125 micron diameter optical fiber and a single 0.5 mm long and 291 nm high microresonator at the surface of a 38 micron diameter fiber. As another application, we fabricate a rectangular 5 mm long SNAP microresonator at the surface of a 38 micron diameter fiber and investigate its performance as a miniature delay line. The propagation of a 100 ps pulse with 1 ns delay, 0.035c velocity, and negligible dispersion is demonstrated. In contrast to the previously developed approaches in SNAP technology, the developed method allows the introduction of much larger fiber radius variation ranging from nanoscale to microscale.

physics.optics↗

arXiv2020

Coupling between waveguides and microresonators: the local approach

Coupling between optical microresonators and waveguides is a critical characteristic of resonant photonic devices with complex behavior that is not well understood. When the characteristic variation length of the microresonator modes is much larger than the waveguide width, local coupling parameters emerge that are independent of the resonator mode distributions and offer a simplified description of coupling behavior. We develop a robust numerical-fitting-based methodology for experimental determination of the local coupling parameters in all coupling regimes and demonstrate their characterization along a microfiber waveguide coupled to an elongated bottle microresonator.

physics.optics↗

arXiv2020

Optical bottle microresonators with axially-uniform eigenmode field distribution

We show that the fundamental eigenmode of a shallow optical bottle microresonator (also called a SNAP microresonator) can be made exceptionally uniform along its axial length. The introduced microresonator has the effective radius variation resembling the profile of a bat with ears and wings. Remarkably, reduction of the axial size of this microresonator by cutting the wings does not alter the uniformity of its fundamental eigenmode. Being of general interest, our findings pave a way for improving the perceptibility of micro/nanoparticle sensing. These results also suggest a bottle microresonator suitable for accurate assembling of quantum emitters near the maximum of its eigenmode important in cavity quantum electrodynamics.

physics.optics↗

arXiv2019

In situ observation of slow and tunnelling light at the cutoff wavelength of an optical fiber

Slow waves and tunneling waves can meet at the cutoff wavelengths and/or transmission band edges of optical and quantum mechanical waveguides. The experimental investigation of this phenomenon, previously performed using various optical microstructures, is challenged by fabrication imperfections and material losses. Here, we demonstrate this phenomenon in situ for whispering gallery modes slowly propagating along a standard optical fiber, which possesses the record uniformity and exceptionally small transmission losses. Slow axial propagation dramatically increases the longitudinal wavelength of light and allows us to measure nanosecond-long tunneling times along tunable potential barriers having the width of hundreds of microns. This demonstration paves a simple and versatile way to investigate and employ the interplaying slow and tunneling light.

physics.optics↗

arXiv2019

Optical bottle microresonators

The optical microresonators reviewed in this paper are called bottle microresonators because their profile often resembles an elongated spheroid or a microscopic bottle. These resonators are commonly fabricated from an optical fiber by variation of its radius. Generally, variation of the bottle microresonator (BMR) radius along the fiber axis can be quite complex presenting, e.g., a series of coupled BMRs positioned along the fiber. Similar to optical spherical and toroidal microresonators, BMRs support whispering gallery modes (WGMs) which are localized inside the resonator due to the effect of total internal reflection. The elongation of BMRs along the fiber axis enables their several important properties and applications not possible to realize with other optical microresonators. The paper starts with the review of the BMR theory, which includes their spectral properties, slow WGM propagation along BMRs, theory of Surface Nanoscale Axial Photonics (SNAP) BMRs, theory of resonant transmission of light through BMR microresonators coupled to transverse waveguides (microfibers), theory of nonstationary WGMs in BMRs, and theory of nonlinear BMRs. Next, the fabrication methods of BMRs including melting of optical fibers, fiber annealing in SNAP technology, rolling of semiconductor bilayers, solidifying of a UV-curable adhesive, and others are reviewed. Finally, the applications of BMRs which either have been demonstrated or feasible in the nearest future are considered. These applications include miniature BMR delay lines, BMR lasers, nonlinear BMRs, optomechanical BMRs, BMR for quantum processing, and BMR sensors.

physics.optics↗

arXiv2018

Mahaux-Weidenm\"uller approach to cavity quantum electrodynamics and complete resonant down-conversion of the single photon frequency

It is shown that a broad class of cavity quantum electrodynamics (QED) problems - which consider the resonant propagation of a single photon interacting with quantum emitters (QEs), such as atoms, quantum dots, or vacancy centers - can be solved directly without application of the second quantization formalism. In the developed approach, the Hamiltonian is expressed through the ket-bra products of collective (photon + cavities + QEs) states. Consequently, the S-matrix of input-output problems is determined exactly by the Mahaux-Weidenm\"uller formula, which dramatically simplifies the analysis of complex cavity QED systems. First, this approach is illustrated for the problem of propagation of a photon resonantly interacting with N two-level QEs arbitrary distributed inside the optical cavity. Solution of this problem manifests the effect of cumulative action of QEs previously known for special cases. Can a similar cumulative action of QEs enhance the inelastic resonant transmission of a single photon? We solve this problem for the case of an optical cavity having two modes resonantly coupled to electronic transitions of N three-level QEs. It is shown that the described structure is the simplest realistic structure which enables the down-conversion of the single photon frequency with the amplitude approaching unity in the absence of the external driving field and for sufficiently small cavity losses and QE dissipation. Overall, the simplicity and generality of the developed approach suggest a practical way to identify and describe new phenomena in cavity QED.

physics.optics↗