Advances in Optical Microresonators

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (15 January 2024) | Viewed by 6132

Special Issue Editors


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Guest Editor
Faculty of Physics, Lomonosov Moscow State University, 119991 Moscow, Russia
Interests: optical microresonator; high-quality factor; whispering gallery modes; narrow-linewidth laser; frequency stabilization; self-injection locking; optical frequency combs; microcombs

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Guest Editor
Institute of Applied Physics of the Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia
Interests: optical microresonators; whispering gallery modes; fiber-based microspheres; microsphere lasers; Raman microlasers; optical frequency combs
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Special Issue Information

Dear Colleagues,

Optical microresonators are unique tools for photonic engineering and fundamental research. Their main advantage is an achievable ultrahigh-quality factor at small sizes that makes it possible to utilize nonlinear effects even at milliwatt-scale pump power. Initially, a quality factor exceeding 108 was demonstrated for whispering gallery modes in fused silica spheres. Subsequently, in disks made of high-purity CaF2, a Q~ 1011 was achieved, a record for microresonators.

Currently, microresonators made of a wide variety of transparent dielectrics are used to create filters, modulators, and various sensors in the range from mid-IR to ultraviolet. The frequency self-injection locking effect makes it possible to create ultra-compact lasers with a sub-Hz linewidth.

The development of photonic chip manufacturing technology brought in new insights, allowing a flexible mass production of microresonator-based structures. The most mature one at present is the CMOS-compatible Si3N4 platform on which the Q-factor of ring resonators exceeding 109 was reached, and numerous devices have been demonstrated, including generators of soliton frequency combs for applied and fundamental metrology and even quantum-squeezed light sources. The rich nonlinear dynamics combined with the multimode nature and the possibility of using various materials and topologies provides unlimited opportunities for further research and development in this area.

Prof. Dr. Igor A. Bilenko
Dr. Elena Anashkina
Guest Editors

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Keywords

  • optical microresonator
  • optical microcavity
  • microring resonator
  • whispering gallery mode
  • self-injection locking
  • optical frequency comb
  • microcomb
  • soliton microcomb
  • dissipative soliton
  • platicon
  • dual microcomb

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Published Papers (4 papers)

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Research

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17 pages, 4567 KiB  
Article
Asymmetrical Cross-Polarization Coupling in a Whispering-Gallery Microresonator
by Karleyda Sandoval and A. T. Rosenberger
Photonics 2024, 11(2), 170; https://doi.org/10.3390/photonics11020170 - 11 Feb 2024
Viewed by 1181
Abstract
Cross-polarization coupling between transverse electric (TE) and transverse magnetic (TM) whispering-gallery modes in an optical microresonator produces effects such as coupled-mode induced transparency (CMIT). The detailed analytical theory of this coupling indicates that the TE-to-TM and TM-to-TE couplings may have different strengths. Using [...] Read more.
Cross-polarization coupling between transverse electric (TE) and transverse magnetic (TM) whispering-gallery modes in an optical microresonator produces effects such as coupled-mode induced transparency (CMIT). The detailed analytical theory of this coupling indicates that the TE-to-TM and TM-to-TE couplings may have different strengths. Using an experimental setup centered around a hollow bottle resonator and polarization-sensitive throughput detection, that had been used in previous CMIT experiments, this asymmetry was confirmed and studied. By fitting the throughput spectra of both polarizations to the numerical output of a basic model, the asymmetry parameter defined as the ratio of the coupling amplitudes was determined from the output power in the polarization orthogonal to that of the input. The results of many experiments give a range for this ratio, roughly from 0.2 to 4, that agrees with the range predicted by the detailed theory. An analytical approximation of this ratio shows that the main reason for the asymmetry is a difference in the axial orders of the coupled modes. In some experimental cases, the orthogonal output is not well fitted by the model that assumes a single mode of each polarization, and we demonstrate that this fitting discrepancy can be the result of additional mode interactions. Full article
(This article belongs to the Special Issue Advances in Optical Microresonators)
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10 pages, 1947 KiB  
Article
Active Optical Tuning of Azopolymeric Whispering Gallery Mode Microresonators for Filter Applications
by Gabriel H. A. Jorge, Filipe A. Couto, Juliana M. P. Almeida, Victor A. S. Marques, Marcelo B. Andrade and Cleber R. Mendonça
Photonics 2024, 11(2), 167; https://doi.org/10.3390/photonics11020167 - 9 Feb 2024
Viewed by 1466
Abstract
Light confinement provided by whispering gallery mode (WGM) microresonators is especially useful for integrated photonic circuits. In particular, the tunability of such devices has gained increased attention for active filtering and lasering applications. Traditional lithographic approaches for fabricating such devices, especially Si-based ones, [...] Read more.
Light confinement provided by whispering gallery mode (WGM) microresonators is especially useful for integrated photonic circuits. In particular, the tunability of such devices has gained increased attention for active filtering and lasering applications. Traditional lithographic approaches for fabricating such devices, especially Si-based ones, often restrict the device’s tuning due to the material’s inherent properties. Two-photon polymerization (2PP) has emerged as an alternative fabrication technique of sub-diffraction resolution 3D structures, in which compounds can be incorporated to further expand their applications, such as enabling active devices. Here, we exploited the advantageous characteristics of polymer-based devices and produced, via 2PP, acrylic-based WGM hollow microcylinders incorporated with the azoaromatic chromophore Disperse Red 13 (DR13). Within telecommunication range, we demonstrated the tuning of the microresonator’s modes by external irradiation within the dye’s absorption peak (at 514 nm), actively inducing a blueshift at a rate of 1.2 nm/(Wcm−2). Its thermo-optical properties were also investigated through direct heating, and the compatibility of both natural phenomena was also confirmed by finite element simulations. Such results further expand the applicability of polymeric microresonators in optical and photonic devices since optically active filtering was exhibited. Full article
(This article belongs to the Special Issue Advances in Optical Microresonators)
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21 pages, 4155 KiB  
Article
Microresonator Effective Thermal Parameters Definition via Thermal Modes Decomposition
by Vladislav I. Pavlov, Nikita M. Kondratiev, Artem E. Shitikov and Valery E. Lobanov
Photonics 2023, 10(10), 1131; https://doi.org/10.3390/photonics10101131 - 9 Oct 2023
Cited by 1 | Viewed by 1372
Abstract
High-Q optical microresonators are particularly efficient practical tools of modern applied optics and photonics. Using them, one inevitably faces the problem of thermal effects. Accurate determination of effective thermal parameters of high-Q microresonators (effective thermal relaxation rate and optical absorption rate) is of [...] Read more.
High-Q optical microresonators are particularly efficient practical tools of modern applied optics and photonics. Using them, one inevitably faces the problem of thermal effects. Accurate determination of effective thermal parameters of high-Q microresonators (effective thermal relaxation rate and optical absorption rate) is of particular importance for developing microresonator-based devices. Our investigation looks into diverse methodologies to estimate these effective parameters for such systems, ultimately revealing a divergence between the commonly employed simplified model, the direct numerical approach, and classical analytical formulas. We introduce a novel approach to calculate effective parameters based on the decomposition of the thermal field into microresonator thermal modes, which inherently considers the intricate geometry and material anisotropy inherent in microresonators, as well as the influence of external conditions. The method for the accurate determination of the effective thermal parameters of the microresonator for corresponding thermal modes is developed. As a result of applying this method, we modified the classical approach for the simulation of thermal effects in optical microresonators for better agreement with the numerical simulations. By accounting for the complexities of microresonator shapes, material properties, and external factors, our proposed method contributes to a more accurate understanding of thermal dynamics and enhances the predictive capabilities of simulations for these systems. We demonstrated the application of this method on the example of integrated microring resonators, but it can be used to analyze thermal effects in other microresonator platforms. Full article
(This article belongs to the Special Issue Advances in Optical Microresonators)
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Review

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25 pages, 2497 KiB  
Review
Self-Starting Soliton–Comb Regimes in χ(2) Microresonators
by Sergey Smirnov, Evgeni Podivilov and Boris Sturman
Photonics 2023, 10(6), 640; https://doi.org/10.3390/photonics10060640 - 1 Jun 2023
Viewed by 1265
Abstract
The discovery of stable and broad frequency combs in monochromatically pumped high-Q optical Kerr microresonators caused by the generation of temporal solitons can be regarded as one of the major breakthroughs in nonlinear optics during the last two decades. The transfer of the [...] Read more.
The discovery of stable and broad frequency combs in monochromatically pumped high-Q optical Kerr microresonators caused by the generation of temporal solitons can be regarded as one of the major breakthroughs in nonlinear optics during the last two decades. The transfer of the soliton–comb concept to χ(2) microresonators promises lowering of the pump power, new operation regimes, and entering of new spectral ranges; scientifically, it is a big challenge. Here we represent an overview of stable and accessible soliton–comb regimes in monochromatically pumped χ(2) microresonators discovered during the last several years. The main stress is made on lithium niobate-based resonators. This overview pretends to be rather simple, complete, and comprehensive: it incorporates the main factors affecting the soliton–comb generation, such as the choice of the pumping scheme (pumping to the first or second harmonic), the choice of the phase matching scheme (natural or artificial), the effects of the temporal walk off and dispersion coefficients, and also the influence of frequency detunings and Q-factors. Most of the discovered nonlinear regimes are self-starting—they can be accessed from noise upon a not very abrupt increase in the pump power. The soliton–comb generation scenarios are not universal—they can be realized only under proper combinations of the above-mentioned factors. We indicate what kind of restrictions on the experimental conditions have to be imposed to obtain the soliton–comb generation. Full article
(This article belongs to the Special Issue Advances in Optical Microresonators)
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