1,720,982 research outputs found
Four-port SNAP microresonator device
Full text linkIt is well known from quantum mechanics that the transmission amplitude of a symmetric double-barrier structure can approach unity at the resonance condition. A similar phenomenon is observed in optics for light which propagates between two waveguides weakly coupled through a microresonator. Examples of microresonators used for this purpose include ring, photonic crystal, toroidal, and bottle microresonators. However, ring and photonic crystal photonic circuits, once fabricated, cannot be finely tuned to arrive at the mentioned resonant condition. In turn, it is challenging to predictably adjust coupling to toroidal and bottle microresonators by translating the input–output microfibers, since the modes of these resonators are difficult to separate spatially. Here we experimentally demonstrate a four-port micro-device based on a SNAP microresonator introduced at the surface of an optical fiber. The eigenmodes and corresponding eigenwavelengths of this resonator are clearly identified for both polarization states by the spectrograms measured along the length of the fiber. This allows us to choose the resonant wavelength and simultaneously determine the positions of the input–output microfiber tapers to arrive at the required resonance condition
SNAP microresonators introduced by strong bending of optical fibers
Full text linkWe introduce a new method of the fabrication of surface nanoscale axial photonic (SNAP) microresonators through strong bending of an optical fiber. We experimentally demonstrate that geometric deformation and refractive index variation induced by bending is sufficient for the formation of a SNAP bottle resonator with nanoscale effective radius variation (ERV) along the fiber axis. In our experiment, we bend the optical fiber into a loop and investigate the properties of the fabricated tunable bottle resonator as a function of the loop dimensions. We find that the introduced ERV is approximately proportional to the local curvature of the loop, while the ERV maximum is proportional to the maximum of the loop curvature squared. The advantages of the demonstrated method are its simplicity, robustness, and ability to mechanically tune introduced resonant structures. This is of crucial importance for the creation of robust and tunable SNAP devices for applications in optical classical and quantum signal processing and ultraprecise sensing
Rectangular SNAP microresonator fabricated with a femtosecond laser
Full text linkSurface nanoscale axial photonics (SNAP) microresonators, which are fabricated by nanoscale effective radius variation (ERV) of the optical fiber with subangstrom precision, can be potentially used as miniature classical and quantum signal processors, frequency comb generators, and ultraprecise microfluidic and environmental optical sensors. Many of these applications require the introduction of nanoscale ERV with a large contrast α, which is defined as the maximum shift of the fiber cutoff wavelength introduced per unit length of the fiber axis. The previously developed fabrication methods of SNAP structures, which used focused CO2 and femtosecond laser beams, achieved α∼0.02 nm∕μm. Here we develop a new, to the best of our knowledge, fabrication method of SNAP microresonators with a femtosecond laser, which allows us to demonstrate a 50-fold improvement of previous results and achieve α∼1 nm∕μm. Furthermore, our fabrication method enables the introduction of ERV that is several times larger than the maximum ERV demonstrated previously. As an example, we fabricate a rectangular SNAP resonator and investigate its group delay characteristics. Our experimental results are in good agreement with theoretical simulations. Overall, the developed approach allows us to reduce the axial scale of SNAP structures by an order of magnitude
Slow Cooking of Photonic Microresonators
Full text linkNew techniques to improve the fabrication precision of microphotonic devices is required to develop their applications in optical signal processing, telecommunication and quantum computing. In addition, advances in microfluidic sensing using WGM (whispering gallery mode) spectroscopy, has shown to be a worthwhile endeavour to achieve ultrahigh sensing of biological, chemical and mechanical processes, reaching single molecule detection. This thesis simultaneously advances these fields via the incorporation of microfluidics on the SNAP (surface nanoscale axial photonics) platform. This work has culminated in the discovery of the slow cooking phenomenon which originates from the silica-water interaction at a water-filled microcapillary fibre. Chapter 1 presents a background to WGM microfluidic sensing and a review of the known silica-water interaction processes. In Chapter 2, we offer the theoretical background to SNAP technology [1,2], which uses nanoscale modifications of the effective radius variation (ERV) of optical fibres to develop photonic microresonator devices such as frequency comb generators [3,4], delay lines [5], optical buffers [6], and, tunable [7] and transient [8] microresonators. We characterize the discovered slow-cooking phenomenon in Chapter 3, measuring the temporal and spatial variations of the cut-off resonant wavelength (CWV). Our experimentally simple setup uses two microfibres (MF) to couple into a water-filled capillary fibre. The first MF excites WGMs in the fibre to detect the CWV of the resonant wavelength. The second MF is used for optical heating by broadband light of optical power 56-100 mW, which evanescently penetrates into and becomes absorbed by water to induce heating [9] and water motion [10]. We demonstrate the fabrication of SNAP microresonators over hour-long optical heating durations, which displays linear growth for sufficient heating power and time. However, for higher slow-cooking powers and durations, the growth becomes nonlinear and nonmonotonic. We advance our fabrication precision by reducing the slow-cooking duration in Chapter 4, to achieve precision in CWV of 1.3 pm/10mins limited by the OSA resolution. We propose that further reduction of the slow-cooking duration can achieve 0.02 pm/10secs in CWV corresponding to precision of just 0.6 pm in ERV. This estimated fabrication precision improves the developed laser post-processing techniques [11,12] on the SNAP platform by two orders of magnitude. Throughout the thesis we attempt to relate the observed CWVs to known silica-water interaction processes. Most prominently, we suggest the observations of the de- and re-hydroxylation at ambient temperatures [13] in Chapter 3 and the structural relaxation of silica after heating ceases in Chapter 4. To our knowledge, these are the first experimental demonstration of these processes using WGM spectroscopy. Overall, the demonstrated integration of microfluidics with SNAP technology produces a multitude of avenues worthy of pursuit, summarized in Chapter 5. These include advances in the fabrication of the aforementioned photonic devices and enhancement of microfluidic sensing capabilities which can be applied to a variety of fields of interest
2 input/output microfibres SNAP experiment:fabrication and characterization
Full text linkThis work described the application of two microfibers for the first time to experimentally investigate tunneling phenomena in SNAP. The axial WGM distribution along a SNAP fiber is governed by 1D time-independent Schrödinger equation. The transmission spectrum of microfiber orthogonally coupled with SNAP fiber were measured with 1μm incremental step microfiber scanning along SNAP fiber. The microfibers were fabricated with sapphire tube and CO2 laser heat-and-pull setup. Uniform SNAP fibers prepared with hot sulphuric/nitric acid stripping shows the general trend of exponential decay.However, the problem of deep cracks prevented the accurate determination of tunneling time. Symmetric SNAP double resonators with nano-engineered radius variations along uniform SNAP fibers were fabricated using CO2 laser annealing technique. The observed energy level splitting due to the effect of resonant tunnelling between equal energy levels demonstrates the ultra-precise-tuning of height, shape and separation of the double resonators. The transmission surface plots for both S11 and S12 closely matches the theoretical SNAP model based on Levenberg-Marquardt least squares fitting algorithm and bare Green’s function construction method. The reviewed tunneling time literature is intended as a self-contained framework for further SNAP tunneling time research
Bottle Micro-Resonator Engineering with Surface Nanoscale Axial Photonics
Full text linkWhispering gallery mode (WGM) micro-resonators have attracted significant attention in recent years due to their diverse applications in sensing, optical communications, and frequency comb generation. The Surface Nanoscale Axial Photonics (SNAP) platform has risen as a notable technique for creating photonic structures with ultra-low loss, characterized by extraordinary precision to the tune of 0.1 angstroms. This thesis presents two novel and complementary approaches for fabricating WGM-based bottle micro-resonators. The first approach involves a permanent deformation method, wherein SNAP microresonators are fabricated using a heat treatment process with a butane flame. The second approach introduces a reversible deformation technique based on elastic bending, offering tunability and adaptability for various applications. The non-disruptive nature of this second method allows for its integration with other fabrication techniques. Both methods provide angstrom-precise control over fabrication, resulting in stable and high quality bottle resonators. We thoroughly investigate and experimentally validate these fabrication approaches, demonstrating high fabrication precision and quality factors. A comparison of the advantages and limitations of each method contributes to a deeper understanding of SNAP-based micro-resonator fabrication and paves the way for future advancements in the rapidly evolving field of photonics
Nonlinear Optical Effects and Their Applications: From Parametric Amplification in Coupled Waveguides to Modulation Instabilities in Fibre Ring Resonators
Full text linkThis thesis investigates nonlinear optical phenomena in two coupled waveguides and fibre ring resonators, with a particular emphasis on optical parametric amplification (OPA), modulation instability (MI), and optical frequency comb (OFC) generation. The work is divided into two parts. The first part investigates OPA in dual-core waveguide systems. By exploiting coupling-induced dispersion, we demonstrate flexible dispersion engineering that enables broadband gain, even in normally dispersive waveguides. Analytical and numerical models are developed to assess the impact of pump power and phase fluctuations on system stability. Additionally, we explore intermodal four-wave mixing in dual-core fibres, revealing how frequency-dependent coupling and power imbalance between the waveguides lead to asymmetric gain and signal–idler separation into distinct supermodes. These findings offer design strategies for efficient, robust, and tunable amplifiers in both fibre and integrated photonic platforms. The second part focuses on MI in nonlinear optical resonators. We study filter-induced MI in a fibre ring cavity with an intracavity amplifier, demonstrating enhanced MI and efficient energy transfer to spectral sidebands. In parametrically driven resonators with quadratic nonlinearity, we analyse filter-induced MI and show its role in enabling tunable OFC generation. Furthermore, we uncover a new dynamical regime in Kerr resonators: period-4 MI, characterised by temporal patterns repeating every four cavity round trips. Analytical gain expressions are derived and validated through numerical simulations. Together, these results advance the understanding and control of nonlinear wave dynamics in optical systems, providing novel mechanisms for amplification, frequency conversion, and complex temporal pattern formation, with implications for both fundamental science and practical photonic technologies
Delay of light in an optical bottle resonator with nanoscale radius variation : dispersionless, broadband, and low-loss
Full text linkIt is shown theoretically that an optical bottle resonator with a nanoscale radius variation can perform a multinanosecond long dispersionless delay of light in a nanometer-order bandwidth with minimal losses. Experimentally, a 3 mm long resonator with a 2.8 nm deep semiparabolic radius variation is fabricated from a 19??µm radius silica fiber with a subangstrom precision. In excellent agreement with theory, the resonator exhibits the impedance-matched 2.58 ns (3 bytes) delay of 100 ps pulses with 0.44??dB/ns intrinsic loss. This is a miniature slow light delay line with the record large delay time, record small transmission loss, dispersion, and effective speed of light
Potentials with partly constant free spectral range and their application to SNAP microresonators
No full textPropagation 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 Schrödinger 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
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