Fiber Ring Resonator Research Articles

Optical tactile sensor based on a flexible optical fiber ring resonator for intelligent braille recognition.

Inspired by human skin, bionic tactile sensing is effectively promoting development and innovation in many fields with its flexible and efficient perception capabilities. Optical fiber, with its ability to perceive and transmit information and its flexible characteristics, is considered a promising solution in the field of tactile bionics. In this work, one optical fiber tactile sensing system based on a flexible PDMS-embedded optical fiber ring resonator (FRR) is designed for braille recognition, and the Pound-Drever-Hall (PDH) demodulation scheme is adopted to improve the detection sensitivity. Theoretical simulations and experimental verifications show that by adopting a bionic sliding approach and a Multilayer Perceptron Neural Network, a single FRR with a hardness gradient design can detect eight different tactile pressures in braille characters with an accuracy of 98.57%. Furthermore, after training and testing, the MLP-LSTM model classifies time series signals, thereby achieving completely accurate encoding of braille keywords and braille poems. The advantages of the optical fiber tactile sensing system in this study are that the high-quality factor FRR can detect subtle differences in braille dots, it is not affected by changes in optical power due to its relies on PDH frequency demodulation, and the application of machine learning algorithms can enhance the robustness to slight pressure errors and simplify the recognition process. This solution opens up what we believe is a new optical approach for bionic tactile perception and has important potential value in promoting human-computer interaction, smart medical care, and other fields.

White-Light-Driven Ultrahigh-Resolution Fiber Ring Resonator Array Based on Frequency Division Multiplexing Technology

White-Light-Driven Ultrahigh-Resolution Fiber Ring Resonator Array Based on Frequency Division Multiplexing Technology

Time-delay signature elimination of chaotic laser via a self-feedback antisymmetric resonator.

A scheme for generating a chaotic output from a semiconductor laser while eliminating the time-delay signature (TDS) is proposed, leveraging the multi-path feedback provided by a self-feedback antisymmetric coupling fiber ring resonator (SACFRR). A theoretical model is developed to elucidate the feedback perturbation process in the proposed structure. The multi-path feedback can be modeled by incorporating the unit impulse response of the SACFRR into the modified Lang-Kobayashi-based model. We successfully eliminated the TDS using the SACFRR structure in our experimental demonstration. Further investigation into the impact of the coupling coefficient on the TDS revealed that the optimal value is 0.3, which results in the largest mapping area with the TDS below 0.03. The proposed structure is highly effective and simple to implement and integrate. As a result, the chaotic laser generated by this structure can serve as an efficient optical source for encrypted communications, chaotic Lidar, and random bit generation.

Observation of modulation instability in a coherently driven active fiber ring resonator at 2 μm wavelength.

We report the first, to our knowledge, observation of the nonlinear phenomenon known as modulation instability (MI) in a coherently driven fiber resonator pumped at 1972 nm. To compensate for the very high losses in this spectral region, we have integrated a thulium-doped fiber amplifier inside the cavity. Lower losses allow a lower MI threshold, leading to the observation of this phenomenon at a moderate input power. The results align closely with the numerical simulations of the system. Our study shows that active compensation of loss can be implemented in the 2 µm wavelength range to construct fiber ring cavities with high finesse. It paves the way to the observation of more complex nonlinear effects optical frequency comb through cavity soliton generation.

Resonant fiber optic gyroscope driven by a broadband light source based on an over-coupled state fiber ring resonator

The resonant fiber optic gyroscope (RFOG) driven by a broadband light source has advantages over conventional RFOGs in terms of structure, solution, etc., and provides new ideas for the commercialization of RFOGs. In this paper, the basic working principle of RFOG driven by a broadband light source is introduced. The optimal modulation coefficients are provided for sinusoidal wave modulation. The influence of the length of the fiber-optic ring resonator (FRR) and the coupling coefficient of the fiber coupler on the sensitivity is analyzed. The FRR is constructed in the over-coupled state to improve the utilization of optical power, and thus significantly increase the system sensitivity. In experiments, an RFOG prototype with a diameter of 13 cm, a height of 7 cm, and a fiber ring length of 210 m is produced. A bias instability (BI) of 0.06°/h and an angular random walk (ARW) of 0.01∘/h are obtained.

Highly stable Brillouin laser with controllable tuning based on fiber ring resonator

The design and fabrication processes of the stimulated Brillouin laser (SBL) are complex, and it is affected by many factors such as temperature and resonance shift. In this study, we have fabricated a Brillouin laser using a fiber ring resonator with Q factor = 7.1 × 108 and resonance depth (h) = 96%. The free spectral range automatic feedback control technology is proposed to realize the accurate matching of the resonant mode and the Stokes mode. The influence of temperature on the SBL frequency shift is suppressed. The fluctuation range of SBL’s frequency decreases by 5 times. The maximum steady state output of the SBL at the best matching position is realized, and the output power fluctuation range decreases by 15 times. The power stability of the SBL reaches 4.85 × 10−6, which is improved by two orders of magnitude. This simple scheme provides convenience for the application of the SBL, such as sensing and other applications.

High resolution and large measurement range voltage sensing based on an optoelectronic oscillator utilizing an unbalanced Mach-Zehnder interferometer.

A voltage sensor with high resolution and large measurement range based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The key component in the cavity to select the oscillating signal is a finite impulse response (FIR)-microwave photonic filter (MPF) which consists of a sinusoidal broadband optical signal, an unbalanced Mach-Zehnder interferometer (MZI), a section of dispersion compensating fiber, and a photodetector. The center frequency of the FIR-MPF is mainly determined by the free spectral range (FSR) of the FIR-MPF. In the lower arm of the MZI, a cylindrical piezoelectric ceramic (PZT) wrapped with a section of optical fiber acts as voltage sensing head. Due to the inverse piezoelectric effect of PZT, the variation of the voltage will cause radial deformation of the cylindrical PZT and then lead to the change of the FSR of the MZI, determining the shift of center frequency of FIR-MPF as well as the frequency of the oscillating signal of the OEO. Thus, by monitoring the shift of the oscillation frequency of the OEO using an electric spectrum analyzer or a digital signal processor, a high-speed interrogation and high-resolution voltage measurement can be realized. Additionally, in the proposed scheme, an infinite impulse response (IIR)-MPF consisting of a fiber ring resonator is cascaded with the FIR-MPF to ensure the single-mode oscillation of the OEO. The experimental results show that a total range of 1700 V voltage sensing from - 200 V to 1500 V is accomplished with the voltage sensitivity of 0.25 GHz/100 V and the resolution of 0.3 V. By adjusting the proportion of the length of single mode fiber between two branches of MZI, the impact of temperature can be greatly reduced. The proposed sensor offers advantages such as a large measurement range, high resolution, high-speed interrogation, and stability to temperature disturbances, making it highly suitable for sensing applications in smart grids.

Novel Forward Brillouin Scattering measurement technique based on high-Q fiber ring resonator

The conventional detection of Forward Brillouin Scattering (FBS) in optical fibers requires of interferometric techniques using lengths of tens of meters. In this paper, we demonstrate an alternative approach that provides efficient and high-resolution detection of FBS signals, while using just a 20 cm length section of bare fiber. It consists of a pump and probe scheme using a fiber ring resonator as the interrogation system of the mechanical vibration, which modulates the resonances. The result is an amplitude modulated optical trace which allows the detection of resonances R0,m and TR2,m.

Optimization of Fiber Ring Resonator transmission spectrum based on multi-beam interference theory and transfer matrix theory

Optimization of Fiber Ring Resonator transmission spectrum based on multi-beam interference theory and transfer matrix theory

High-resolution photonic-assisted microwave frequency identification based on an ultrahigh-Q hybrid optical filter

Photonic-assisted microwave frequency identification has been extensively studied in civil and defense applications due to its distinct features including wide frequency coverage, large instantaneous bandwidth, high frequency resolution, and immunity to electromagnetic interference. In this paper, we propose and experimentally demonstrate an approach for high-resolution frequency identification of wideband microwave signals by linearly mapping the microwave frequencies to the time delays of the optical pulses. In the proposed system, an ultrahigh-Q hybrid optical filter is a key component, which consists of a fiber ring resonator (FRR) and a silicon photonic racetrack micro-ring resonator (MRR). The FRR has an ultra-narrow bandwidth of 7.6 MHz and a small free spectral range (FSR) of 292.5 MHz, while the MRR has a bandwidth of 167.5 MHz and a large FSR of 73.8 GHz. By precisely matching the resonance wavelengths of the FRR and the MRR, a hybrid optical filter with an ultrahigh Q-factor and a large FSR is realized, which is much preferred to realizing a high resolution and a wide measurement range for microwave frequency identification. An experiment is performed and different types of microwave signals are identified. A frequency measurement range as broad as 33 GHz from 2 to 35 GHz, a frequency resolution as high as 15 MHz and a measurement accuracy as high as 5.6 MHz are experimentally demonstrated. The proposed frequency identification system holds great advantages including high frequency resolution, high measurement accuracy, and wide frequency coverage, which can find extensive applications in next-generation electronic warfare and cognitive radio systems.

Palm-sized, vibration-insensitive, and vacuum-free all-fiber-photonic module for 10−14-level stabilization of CW lasers and frequency combs

Compact and robust frequency-stabilized laser sources are critical for a variety of fields that require stable frequency standards, including field spectroscopy, radio astronomy, microwave generation, and geophysical monitoring. In this work, we applied a simple and compact fiber ring-resonator configuration that can stabilize both a continuous-wave laser and a self-referenced optical frequency comb to a vibration-insensitive optical fiber delay-line. We could achieve a thermal-noise-limited frequency noise level in the 10 Hz–1 kHz offset frequency range for both the continuous-wave laser and the optical frequency comb with the minimal frequency instability of 2.7 × 10−14 at 0.03-s and 2.6 × 10−14 at 0.01-s averaging time, respectively, under non-vacuum conditions. The optical fiber spool, working as a delay reference, is designed to be insensitive to external vibrations, with a vibration sensitivity of sub-10−10 (1/g) and a volume of 32 ml. Finally, the ring-resonator setup is packaged in a palm-sized aluminum case with 171-ml volume with a vibration-insensitive spool, as well as an even smaller 97-ml-volume case with an ultracompact 9-ml miniaturized fiber spool.

GHz Figure‐9 Er‐Doped Optical Frequency Comb Based on Nested Fiber Ring Resonators (Laser Photonics Rev. 17(11)/2023)

GHz Figure‐9 Er‐Doped Optical Frequency Comb Based on Nested Fiber Ring Resonators (Laser Photonics Rev. 17(11)/2023)

Asymmetric Mach-Zehnder prism interferometer coupler-based combined fiber ring resonator system for a Brillouin gyroscope.

Brillouin fiber-optic gyroscope (BFOG) is a fiber ring resonator (FRR)-based ring laser gyroscope with a large dynamic range and high sensitivity. Previous BFOGs operated under simultaneous resonance of the pump and Brillouin laser light in the FRR, resulting in complex control systems. This article introduces an asymmetric prism Mach-Zehnder interferometer coupler (APMZIC)-based FRR system, in which the coupling ratio of pump light is large, while the Brillouin laser resonates in the cavity with a negligible coupling loss, resulting in a simple control system. We analyzed the characteristics of the APMZIC and its combined resonator system both theoretically and experimentally and verified the feasibility of connecting the APMZIC with the resonant cavity of a Brillouin laser. This coupler system is compact, easy to fabricate, highly stable, and exhibits good repeatability, which are necessary for miniaturizing lasers and gyroscopes.

GHz Figure‐9 Er‐Doped Optical Frequency Comb Based on Nested Fiber Ring Resonators

AbstractThe field of optical‐frequency‐combs (OFCs) has seen significant progress in recent years due to the advance of mode‐locked fiber lasers with low‐noise performance and long‐term reliability. With the emergence of applications, OFCs with repetition rates close to GHz have become highly sought after. However, generating GHz fiber‐based combs with low noise remains a significant challenge. In this study, a GHz figure‐9 Er‐doped OFC based on a nested fiber ring resonator is presented. By matching the free‐spectral range (FSR) of external and internal optical resonators, an 11‐fold increase in repetition rate from 82 MHz to 907 MHz is achieved. Notably, it is demonstrated that a single pulse operation with long‐term FSR matching can be achieved without any active feedback control. The comb offset frequency is detected using f‐to‐2f technique to ensure high coherence between pulses, which is distinguished from harmonic mode‐locking. The results show that the nested resonators are capable of generating GHz ultrafast OFC pulses with low phase noise via a more flexible cavity design than conventional short‐cavity solutions. This work provides a valuable contribution to the field of ultrafast laser and optical metrology, which demonstrates the potential of nested‐resonators for generating low noise OFCs with boosted repetition rate.

Light-Matter Interaction at the Transition between Cavity and Waveguide QED.

Experiments based on cavity quantum electrodynamics (QED) are widely used to study the interaction of a light field with a discrete frequency spectrum and emitters. More recently, the field of waveguide QED has attracted interest due to the strong interaction between propagating photons and emitters that can be obtained in nanophotonic waveguides, where a continuum of frequency modes is allowed. Both cavity and waveguide QED share the common goal of harnessing and deepening the understanding of light-matter coupling. However, they often rely on very different experimental setups and theoretical descriptions. Here, we experimentally investigate the transition from cavity to waveguide QED with an ensemble of cold atoms that is coupled to a fiber-ring resonator, which contains a nanofiber section. By varying the length of the resonator from a few meters to several tens of meters, we tailor the spectral density of modes of the resonator while remaining in the strong coupling regime. When increasing the resonator length, we observe a continuous transition from the paradigmatic Rabi oscillations of cavity QED to non-Markovian dynamics reminiscent of waveguide QED.

Research on Optical Fiber Ring Resonator Q Value and Coupling Efficiency Optimization.

The coupling efficiency of the fiber ring resonator has an important influence on the scale factor of the resonant fiber gyroscope. In order to improve the scale factor of the gyroscope, the coupling efficiency of the fiber ring resonator and its influential factors on the scale factor of the gyroscope are analyzed and tested. The results show that the coupling efficiency is affected by both the splitting ratio of the coupler and the loss in the cavity. When the coupling efficiency approaches 0.75 at the under-coupling state, the scaling factor of the gyroscope is the highest. This provides a theoretical reference and an experimental basis for the enhancement of the scaling factor of the resonant fiber gyroscope with the fiber ring resonator as the sensitive unit, providing options for multiple applications such as sea, land, sky and space.

Optical fiber temperature sensor based on beat frequency and Vernier effect of fiber ring resonator composite cavity

A fiber temperature sensing scheme based on beat frequency and Vernier effect of fiber ring resonator (FRR) with composite cavity is proposed and experimentally demonstrated. The optical FRR as a sensor is put into the linear cavity fiber laser, and Vernier effect is generated when the resonance spectrum of the optical FRR and the longitudinal mode of the laser are superimposed. The beat frequency envelope spectrum corresponding to the longitudinal mode Vernier spectrum is used to realize fiber ring sensing in electrical domain, and the sensing information is obtained by tracing the envelope of beat frequency signal, which has the advantages of stable system, simple structure, low cost and high sensitivity.

Ring Resonator of Hollow-Core Photonic Crystal Fiber Based on Spatial Coupling Scheme

In this paper, we proposed a hollow-core photonic crystal fiber (HCPCF) ring resonator based on a spatial coupling method, and the component is only 22×30×6mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . When using a 7-core photonic crystal fiber with a mode field diameter of 10um, a ring resonator with the measured finesse of 18 can be built, indicating that the coupling loss is as low as 0.41dB. Compact and low-loss closed resonator is accomplished using a highly integrated free space silicon optical bench manufactured by deep silicon etching and tiny optical lens package technology, which promotes the practicality of the HCPCF gyro. In addition, two important factors affecting the spatial optical coupling efficiency, the lens type and the fiber mode field size, are investigated in this paper. The obtained results are instructive for all spatial optical coupling systems.

Temperature-Insensitive and Sensitivity-Enhanced FBG Strain Sensor by Using Parallel MPF

A temperature-insensitive and sensitivity-enhanced FBG strain sensor with the Vernier effect is proposed and demonstrated. The FBG sensor consists of two FBGs with different Bragg wavelengths as the sensing heads and two parallel-installed fiber ring resonator (FRR)-based microwave photonic filters (MPF) as the interrogation devices. The measurements can be read from the frequency shift in the notch of the envelope signal. Thanks to the Vernier effect produced by the parallel-FRR-based MPF, the sensitivity of the proposed sensor to strain is improved about 23 times compared with the single FRR-based strain sensor, which is experimentally demonstrated to be −33.862 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> . And the sensitivity of the sensor to temperature was drastically decreased from 325.583 kHz/°C to 1.031 kHz/°C. The unique merits of the proposed sensor, such as high sensitivity, high resolution, and stability against random disturbances, give the sensor great potential for sensing applications in complex environments.

Quasi-distributed demodulation of fiber ring resonators based on microwave photonic time division multiplexing

Quasi-distributed demodulation of fiber ring resonators based on microwave photonic time division multiplexing