high-Q Optical Microresonators Research Articles

Effect of Heating on the Generation and Properties of Platicons in High-Q Optical Microresonators

Effect of Heating on the Generation and Properties of Platicons in High-Q Optical Microresonators

Microresonator Effective Thermal Parameters Definition via Thermal Modes Decomposition

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.

Analysis of parameter combinations for optimal soliton microcomb generation efficiency in a simple single-cavity scheme

Dissipative Kerr solitons generated in high-Q optical microresonators provide unique opportunities for different up-to-date applications. Increasing the generation efficiency of of such signals is a problem of paramount importance. We provided comprehensive analysis and found optimal conditions providing maximal pump-to-comb conversion efficiency (up to 100\%) for the cases of a free-running and self-injection-locked pump lasers. The dependence of the optimal coupling rate on the pump power was revealed, in addition to the trade-off relations balancing the efficiency and the comb line number. The methods to increase the total comb power were also discussed.

Self-Starting Soliton–Comb Regimes in χ(2) Microresonators

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.

Optomechanical Magnetometry on a Bubble Resonator With YIG Microsphere

Magnetometry sensors have wide applications across science and technology. A magnetometer at room temperature can be made by coupling a magnetostrictive material to a high-Q optical cavity, which is crucial for achieving the high sensitivity in detecting the magnetic field. In this work, we have designed a hybrid structure based on the high-Q optical capillary microresonator filled with a yttrium iron garnet (YIG) microsphere to realize highly sensitive magnetic field sensing in the range of kHz. The device shows a peak magnetic field sensitivity of 146 pT Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–1/2</sup> at frequency of 16.85 kHz. This sensor structure provides high sensitivity in the range of 9 kHz to 100 kHz, thus allowing applications in magnetic anomaly detection and other fields.

Mode crossing induced soliton frequency comb generation in high-Q yttria-stabilized zirconia crystalline optical microresonators

We demonstrate for the first time, to the best of our knowledge, the fabrication of high- Q crystalline optical microresonators from cubic yttria-stabilized zirconia (YSZ). Intrinsic Q factors up to 80 million are obtained, indicating an upper bound absorption coefficient of 0.001 cm − 1 for YSZ crystals at the telecom wavelength. Through laser-scanned spectroscopy on a few-mode YSZ microresonator with a radius of 300 μm, we find that the mode crossing effect in the case of weak coupling can induce a repelling disruption of free spectral range values between transverse mode families. Generation of soliton and soliton crystals in such a YSZ microcomb platform operated in the normal dispersion regime is observed. A breathing comb behavior is also reported. Our finding has enriched comb generation platforms with potential multidisciplinary capabilities linked to properties of YSZ crystals in superconducting films and sensors.

Soliton based χ(2) combs in high-Q optical microresonators.

Investigations of the frequency combs in χ(3) microresonators have passed a critical point when the soliton based regimes are well established and realized on different platforms. For χ(2) microresonators, where the first harmonic (FH) and second harmonic (SH) envelopes are coupled via the SH generation and optical parametric oscillation, the comb-soliton studies are just starting. Here we report on a vast accessible dual χ(2) soliton-comb family in high-Q microresonators with the SH and FH combs centered at the pump frequency ωp and its half ωp/2. Vicinity of the point of equal FH and SH group velocities λc, available via proper radial poling, is found to be the most advantageous for the generation of spectrally broad dual FH-SH combs. Our predictions as applied to lithium niobate resonators include the dependence of comb and dissipative soliton parameters on the pump power, the deviation λp - λc, the modal quality factors and frequency detunings, and the necessary parameters of radial poling of the resonator. These predictions form a solid basis for the realization of χ(2) frequency combs.

Self-Injection Locking of a Gain-Switched Laser Diode

We experimentally observed self-injection locking regime of the gain-switched laser to high-Q optical microresonator. We revealed that comb generated by the gain-switched laser experiences a dramatic reduce of comb teeth linewidths in this regime. We demonstrated the Lorentzian linewidth of the comb teeth of sub-kHz scale as narrow as for non-switched self-injection locked laser. Such setup allows generation of high-contrast electrically-tunable optical frequency combs with tunable comb line spacing in a wide range from 10 kHz up to 10 GHz. The characteristics of the generated combs were studied for various modulation parameters - modulation frequency and amplitude, and for parameters, defining the efficiency of the self-injection locking - locking phase, coupling efficiency, pump frequency detuning.

Fundamentals of the theory of self-injection locking of multi-frequency laser diode to high-Q optical microresonator

In this work we present a theoretical model describing a phenomenon of self-injection locking of multi-frequency laser to high-Q optical microresonator. Such process allows high-power single-frequency emission with sub-kHz linewidth from the compact multi-frequency diode laser. Elaborated theory takes into account fast optical feedback due to the Rayleigh scattering, mode competition effect and Bogatov asymmetric mode interaction.

Spectrum collapse, narrow linewidth, and Bogatov effect in diode lasers locked to high-Q optical microresonators.

We present a novel method allowing high-power single-frequency emission with sub-kHz linewidth from a compact multi-frequency diode laser locked to high-Q optical microresonator. Using high-Q MgF2microresonator and multi-frequency diode laser operating at 1535 nm with the output power of 100 mW and an emission spectrum consisting of approximately 50 lines with MHz linewidth, we observed a spectrum collapse to a single line or several lines with a sub-kHz linewidth and output power power of 50 mW. The Bogatov effect predicted more than 30 years ago was observed and studied in the spectrum of the locked laser. For analysis of the considered effect, original theoretical model taking into account self-injection locking effect, mode competition and Bogatov asymmetric mode interaction was developed and numerical modeling was performed. All numerical results are in a good agreement with our experimental data. Accurate analytical estimations for the parameters critical for the considered effect were obtained. The proposed method may be applied for different types of diode lasers operating in different spectral ranges.

A resonance system of an optoelectronic oscillator based on a transmission-type planar optical disk microcavity

It is noted that the best technical characteristics of optoelectronic microwave self-oscillators (OESO) are reached in schemes employing high-Q optical microresonators (OMR) working in the traveling wave modes (TWM). A possibility of using disk OMRs excited by fundamental whispering gallery modes (WGM) has been considered. Multielement coupling devices (CD) for such resonators have been investigated. They are constructed on the basis of planar optical waveguides (POWG) located over the disk resonator surface in a region bounded by the outer and inner caustics of the WGM. Models of this device have been proposed. The corresponding calculations have been provided.

Analysis of nonreciprocal noise based on mode splitting in a high-Q optical microresonator

The whispering gallery mode optical microresonator offers a high quality factor, which enables it to act as the core component of a high sensitivity resonator optic gyro; however, nonreciprocal noise limits its precision. Considering the Sagnac effect, i.e. mode splitting in high-quality optical micro-resonators, we derive the explicit expression for the angular velocity versus the splitting amount, and verify the sensing mechanism by simulation using finite element method. Remarkably, the accuracy of the angular velocity measurement in the whispering gallery mode optical microresonator with a quality factor of 108 is 106 °/s. We obtain the optimal coupling position of the novel angular velocity sensing system by detecting the output transmittance spectra of different vertical coupling distances and axial coupling positions. In addition, the reason for the nonreciprocal phenomenon is determined by theoretical analysis of the evanescent distribution of a tapered fiber. These results will provide an effective method and a theoretical basis for suppression of the nonreciprocal noise.

Nonlinear properties of high-Q optical microresonators in normal dispersion range

We demonstrate the generation of Kerr frequency combs and platicons in whispering gallery mode crystalline microresonators in normal group velocity regime at 780 nm and 1064 nm wavelengths.

Temporal solitons in optical microresonators

Dissipative solitons can emerge in a wide variety of dissipative nonlinear systems throughout the fields of optics, medicine or biology. Dissipative solitons can also exist in Kerr-nonlinear optical resonators and rely on the double balance between parametric gain and resonator loss on the one hand and nonlinearity and diffraction or dispersion on the other hand. Mathematically these solitons are solution to the Lugiato-Lefever equation and exist on top of a continuous wave (cw) background. Here we report the observation of temporal dissipative solitons in a high-Q optical microresonator. The solitons are spontaneously generated when the pump laser is tuned through the effective zero detuning point of a high-Q resonance, leading to an effective red-detuned pumping. Red-detuned pumping marks a fundamentally new operating regime in nonlinear microresonators. While usually unstablethis regime acquires unique stability in the presence of solitons without any active feedback on the system. The number of solitons in the resonator can be controlled via the pump laser detuning and transitions to and between soliton states are associated with discontinuous steps in the resonator transmission. Beyond enabling to study soliton physics such as soliton crystals our observations open the route towards compact, high repetition-rate femto-second sources, where the operating wavelength is not bound to the availability of broadband laser gain media. The single soliton states correspond in the frequency domain to low-noise optical frequency combs with smooth spectral envelopes, critical to applications in broadband spectroscopy, telecommunications, astronomy and low phase-noise microwave generation.

On the performance of label-free resonant photonic biosensors

R photonic biosensing is a powerful technique for label-free detection of biomolecules and viruses. Specifically during the past 5 years photonic biosensning using high quality factor (high-Q) optical microresonators has been the subject of intensive research and development. High-Q optical resonance in micron and sub-micron scale provides a sensitive transduction mechanism for generating a detectable signal proportional to the molecular binding events in label-free affinity based assays. A plethora of microresonator based photonic biosensors have been demonstrated that translate the surface density of bound molecules to measurable changes in optical transmission spectrum using resonant frequency shift. Although a large volume of research has been dedicated to different designs, sensitivity improvement in specific configurations and in few cases simple analysis of the performance, less effort has been spent on developing a comprehensive framework for comparing the practical performance of resonant photonic biosensors as an important class of biosensors. Here after a brief review of the fundamental principles of photonic biosensing using microresonators and related devices, we present a framework for a fair comparison of different devices and sensor configurations. Specifically we explore the detection limit, dynamic range and noise in resonant photonic biosensors. This analysis covers Whispering-Gallery microresonators, monolithic microring cavities, gratings, photonic crystals and microcapillaries. The proposed approach also lays the ground for the development of a universal framework that also includes microelectronic and micromechanical biosensors.

Actuation of micro-optomechanical systems via cavity-enhanced optical dipole forces

We demonstrate a new type of optomechanical system employing a movable, micron-scale waveguide evanescently-coupled to a high-Q optical microresonator. Micron-scale displacements of the waveguide are observed for milliwatt(mW)-level optical input powers. Measurement of the spatial variation of the force on the waveguide indicates that it arises from a cavity-enhanced optical dipole force due to the stored optical field of the resonator. This force is used to realize an all-optical tunable filter operating with sub-mW control power. A theoretical model of the system shows the maximum achievable force to be independent of the intrinsic Q of the optical resonator and to scale inversely with the cavity mode volume, suggesting that such forces may become even more effective as devices approach the nanoscale.

High-Q optical whispering-gallery microresonators: precession approach for spherical mode analysis and emission patterns with prism couplers

High- Q optical whispering-gallery modes TE(TM) lmq in spheroidal dielectric microresonators are shown to be equivalent to precessing circular modes TE(TM) llq' with the rate of precession depending on the value of the residual resonator nonsphericity. This approach gives a natural interpretation to the characteristic two-lobe emission patterns of these modes with prism couplers. Spatial recognition of different modes on the basis of their emission patterns facilitates optimal coupling to selected modes, which is of interest for applications. Experimental results on the observation of two-lobe emission patterns and imaging of internal mode field distribution are presented. The feasibility of a single-prism transient filter and an optical delay line based on precessing modes is discussed.