Fiber Ring Research Articles

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.

Temporal manipulation of period-2 polarization domain wall solitons in a nonlinear fiber Kerr resonator

We report on the experimental demonstration of temporal manipulations of dissipative polarization domain wall solitons in a Kerr nonlinear resonator operated in a period-doubled configuration. Our experiments are performed in a coherently driven normally dispersive fiber ring cavity, in which polarization domains emerge in virtue of a spontaneous symmetry breaking phenomenon. The addition of a lumped birefringent defect into the cavity forces their polarization components to swap on a two-round-trip cycle, thus protecting them from the deleterious impact of the system’s asymmetries. We exploit these symbiotic dynamics in proof-of-concept buffering experiments, in which these dissipative structures are addressed individually and temporally manipulated through phase-encoded perturbations imprinted onto the driving beam. Our results provide new insights into the practical exploitation of spontaneous symmetry breaking mechanisms and the use of two-component dissipative structures for all-optical data storage applications.

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

Reduction of the Relative Intensity Noise of Broadband Sources Using Dual Fiber Ring Resonator

Reduction of the Relative Intensity Noise of Broadband Sources Using Dual Fiber Ring Resonator

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.

Design of New Photonic Crystal Fiber for Orbital Angular Momentum Modes Transmission

In order to achieve the flexibility and miniaturization of orbital angular momentum (OAM) fiber coupler, it is necessary to continuously design and optimize the base fiber to cooperate with the efficient transmission of multiplexed beam. It is more advantageous to use the photonic crystal fiber (PCF) instead of ring fiber in the coupler design. We have proposed a new fiber based on circular PCF structure to support high performance OAM modes transmission. The optimal parameters are selected to realize the stable transmission of 4 OAM mode groups with high mode quality. In the wavelength range of 1.2 μm∼2.0 μm, the confinement loss of low order mode is less than 10−8 dB/m, and the mode purity is more than 81.7%. Because of its flexible structure and low loss characteristics, the proposed OAM fiber can be widely used in the design of optical fiber devices in modular division multiplexing (MDM) communication systems.

Narrow linewidth fiber laser with multiple unpumped EDF fiber loops and self-injection feedback

In this paper, we proposed a narrow linewidth single-longitudinal-mode (SLM) fiber laser, which was realized by employing a triple-cascaded unpumped erbium doped fiber (EDF) Sagnac loops structure with Rayleigh backscattering (RBS) feedback. Narrow linewidth SLM laser output can be achieved by using the unpumped EDF loops. However, it is generally difficult to achieve laser emission with a linewidth below 1 kHz and a power of tens of milliwatts. In this paper, we propose a fiber laser with multiple unpumped Er-doped fiber loops and self-injection feedback. The cascade of multi-unpumped Er-doped fiber rings is employed to reduce the linewidth of the laser, while the self-injection feedback based on RBS is used to improve the stability of the laser and further compress the laser linewidth. By only utilizing three unpumped Er-doped fiber rings cascaded, we obtain an output beam with a linewidth of 723.05 Hz and laser power of 21.52 mW with 0.30 dB fluctuation during a period time of 30 min at the pump power of 170.6 mW. After introducing the feedback mechanism based on RBS into the fiber laser, an output laser with a linewidth of 530.11 Hz and a laser power of 8.57 mW with 0.23 dB fluctuation in 30 min can be obtained at the pump power of 268.68 mW. Compared with the fiber laser with one unpumped Er-doped fiber ring, the linewidth is reduced more than two times.

Temporal characteristics of stationary switching waves in a normal dispersion pulsed-pump fiber cavity.

Kerr cavities driven in the normal dispersion regime are known to host switching waves. These consist of a traveling wavefront that connects separate regions associated with high- and low-intensity steady states of the cavity. In this Letter, we drive a 230-m custom built fiber ring cavity with strong normal dispersion using nanosecond pulses, allowing us to directly resolve the fine structure of individual switching waves, including resonant oscillations occurring over periods of the order of ∼10 ps. We demonstrate the intimate connection between the temporal and spectral features of the dispersive waves associated with switching waves, while also investigating how these dispersive waves evolve with cavity parameters, namely the frequency detuning and pump desynchronization. Furthermore, by applying a localized and temporary perturbation to our driving field in the presence of a phase modulation trapping potential, we are able to generate a stable and persistent dark pulse, allowing us to directly observe and model the interlocking of two stationary switching waves under quasi-CW pumping conditions. These results further verify the accuracy of the dispersive wave formalism used, and show that their temporal modulation frequency and decay rate in a pulsed-pumped cavity are accurately captured from theory previously applied to CW-pumped systems.

Versatile wavelength tunable noise-like pulse generation from an erbium doped fiber laser using an intra-cavity Michelson interferometer

We report, versatile wavelength tunable mode locked noise-like pulses (NLP) from an erbium doped fiber ring laser, using a novel intra-cavity Michelson interferometer (MI) as a tunable filter. Our results demonstrate independent control of the central wavelength and the bandwidth using fine and coarse controls in one arm of the MI. The central wavelength is continuously tunable across the entire C-band (1530 nm to 1566 nm), while the bandwidth can be varied from 3 nm to 19.5 nm. The NLPs have a repetition rate of 1.307 MHz with pulse energies of ∼1 nJ. Additionally, harmonic mode-locked states and NLP pairs can also be produced using the same laser. On account of the adaptable output spectrum, we believe, such lasers will be useful for a variety of applications including sensing, spectroscopy and optical coherence tomography. The MI-based fiber laser can also serve as an ideal platform for gaining insight and exploring the rich dynamics of NLPs.

Integrated Fiber Ring Laser Temperature Sensor Based on Vernier Effect with Lyot-Sagnac Interferometer.

The Vernier effect created using an incorporated Lyot-Sagnac loop is used to create an ultra-high sensitivity temperature sensor based on a ring laser cavity. Unlike standard double Sagnac loop systems, the proposed sensor is fused into a single Sagnac loop by adjusting the welding angle between two polarization-maintaining fibers (PMFs) to achieve effective temperature sensitivity amplification. The PMFs are separated into two arms of 0.8 m and 1 m in length, with a 45° angle difference between the fast axes. The sensor's performance is examined both theoretically and experimentally. The experimental results reveal that the Vernier amplification effect can be achieved via PMF rotating shaft welding. The temperature sensitivity in the laser cavity can reach 2.391 nm/°C, which is increased by a factor of more than eight times compared with a single Sagnac loop structure (0.298 nm/°C) with a length of 0.8 m without the Vernier effect at temperatures ranging from 20 °C to 30 °C. Furthermore, unlike traditional optical fiber sensing that uses a broadband light source (BBS) for detection, which causes issues such as low signal-to-noise ratio and broad bandwidth, the Sagnac loop can be employed as a filter by inserting itself into the fiber ring laser (FRL) cavity. When the external parameters change, the laser is offset by the interference general modulation, allowing the external temperature to be monitored. The superior performance of signal-to-noise ratios of up to 50 dB and bandwidths of less than 0.2 nm is achieved. The proposed sensor has a simple structure and high sensitivity and is expected to play a role in biological cell activity monitoring.

Single-Frequency Continuous-Wave Self-Sweeping Fiber Laser Based on Separated Gain and Absorption Dynamics Gratings

A new cavity scheme for a self-sweeping fiber laser with separated gain and absorption dynamics gratings is presented. The scheme is experimentally realized in an Er-doped ring fiber laser generating in the continuous-wave (CW) regime near the wavelength of 1604 nm. Switching between single longitudinal mode stabilization and wavelength self-sweeping regimes is demonstrated by controlling the intracavity losses in the laser. The pump power and optimization of the intracavity losses made it possible to demonstrate record sweeping range of 2.6 nm in a single-frequency self-sweeping regime in the telecommunication L-band.

Hybrid Mode-Locked Fiber Ring Laser Using Graphene Saturable Absorbers to Generate 20 and 50-GHz Pulse Trains

Optical pulses at high repetition rates are generated using rational harmonic mode locking and saturable absorber made of graphene nanoparticles in a fiber laser. The pulse generation from the fiber laser is modeled by solving the Generalized Nonlinear Schrodinger Equation. The computation involved varying the various saturable absorption parameters, such as linear and nonlinear absorption coefficients. Experimentally stable pulse trains at 20 GHz and 50 GHz are generated with a pulse width of ∼ 2.7 ps. This result agrees with the simulation.

Polarization Stability of Spun Fiber Resonator for Resonant Fiber Optic Gyro

As an important inertial navigation sensor, resonant fiber optic gyro (RFOG) has become a research hotspot in recent years due to its advantages of light weight and high stability. The optical effects in the fiber ring resonator(FRR), such as scattering effects, polarization mode crosstalk, etc., are the bottleneck restricting the development of RFOG, and they are also the key problems that researchers are trying to solve. Aiming at the problem of polarization noise, this paper conducts in-depth theoretical and experimental research on polarization stability using spun fiber resonator for the first time. Compared with a common polarization-maintaining fiber (PMF) resonator of the same length, the results show that the RFOG using the spun fiber resonator has improved temperature stability compared to the conventional resonator structure. This research provides a new idea for the polarization noise suppression method of RFOG, and lays an important foundation for the practical application of spun fiber in RFOG.

Random number generation using spontaneous symmetry breaking in a Kerr resonator.

We demonstrate an all-optical random number generator based on spontaneous symmetry breaking in a coherently driven Kerr resonator. Random bit sequences are generated by repeatedly tuning a control parameter across a symmetry-breaking bifurcation that enacts random selection between two possible steady-states of the system. Experiments are performed in a fiber ring resonator, where the two symmetry-broken steady-states are associated with orthogonal polarization modes. Detrimental biases due to system asymmetries are suppressed by leveraging a recently discovered self-symmetrization phenomenon that ensures the symmetry-breaking dynamics act as an unbiased coin toss, with a genuinely random selection between the two available steady-states. We optically generate bits at a rate of 3 MHz without post-processing and verify their randomness using the National Institute of Standards and Technology and Dieharder statistical test suites.

Coherent optical gyroscope on the basis of the bidirectional ultra-short pulse Erbium ring fiber laser

A gyroscopic effect has been studied in the bidirectional ultra-short pulse erbium-doped fiber ring laser hybridly mode-locked with a co-action of a Single-Walled Carbon Nanotube-based saturable absorber (SWCNT-SA) and Nonlinear Polarization Evolution introduced by means of the short-segment polarizing fiber. Owing to the Kerr nonlinearity contribution through self-phase modulation and self-steepening effects to the carrier-to-envelope phase slip of both clockwise (CW) and counterclockwise (CCW) solitons, wideband controllable tuning of a gyroscope bias point has been demonstrated by means of an appropriate adjustment of either intracavity polarization or pump power. Angular velocity detected ranges from 0.12 deg/s to 360 deg/s while the highest rotation sensitivity reaches 7 kHz/(deg/s) for 0.79 m2 single-coil ring gyroscope being in agreement with the calculated scale factor value. The gyroscope dead band with upper limit of ≈5.15 deg/s corresponding to the beat-note frequency of ≈15 kHz has been detected during clockwise rotation of the gyroscope. The highest gyroscope resolution of ≈0.01 deg/s=38 deg/h has been estimated on the basis of the bias point drift measurement.

Brillouin laser spectrometer based on spectral compression

We introduce a spectrometer design that uses Brillouin lasing to perform broadband spectral compression. This approach enables the entire C-band (optical frequencies covering 4 THz, or 25 nm) to be compressed into a 230 MHz wide RF spectrum—allowing a 4 THz wide optical spectrum to be monitored continuously using a standard analog-to-digital converter. This technique is based on the linear dependence of the Brillouin frequency shift on optical wavelength. To use this dependence for spectral analysis, we couple the input optical spectrum into a fiber ring cavity where it acts as an optical pump, exciting a frequency-shifted Brillouin lasing spectrum. The Brillouin lasing spectrum is then referenced to a copy of the original optical spectrum using heterodyne detection, converting the Brillouin frequency shift associated with each lasing mode to the RF domain. The narrow linewidth of the lasing modes enables a precise measurement of individual lines with an uncertainty of 28 MHz (0.2 pm) across a 4 THz band at an update rate of 200 Hz. This simple approach, constructed using standard fiber-coupled telecom components, provides an efficient method for high-resolution, broadband spectral analysis.

Liquid-Core-Microtubule-Enhanced Laser Sensor for High-Resolution Temperature Measurement

We present a fiber laser temperature sensor based on temperature dependence whisper gallery mode-based microcavity. Three different thermo-optic coefficient liquids are injected into a thin wall thickness microtubule for different temperature sensitivity of whisper gallery mode shift. The sensor temperature sensitivity increases with the absolute value of the liquid core thermo-optic coefficient. The theoretical model of whisper gallery mode temperature response is analyzed. A liquid core microtubule is inserted into the erbium-doped fiber ring laser cavity as the optical filter and sensing unit simultaneously, so the lasing wavelength can be used to detect the temperature change of the medium. Due to the narrow spectral width of sensing laser, a high sensing resolution system is experimentally confirmed. With the combination of liquid core to increase the sensitivity and fiber ring laser cavity to increase sensing resolution, the high sensitivity 112.8 pm/°C of sensing system is demonstrated and the thermal resolution is 8.16 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> °C.

Laser2: A two-domain photon-phonon laser.

The laser is one of the greatest inventions in history. Because of its ubiquitous applications and profound societal impact, the concept of the laser has been extended to other physical domains including phonon lasers and atom lasers. Quite often, a laser in one physical domain is pumped by energy in another. However, all lasers demonstrated so far have only lased in one physical domain. We have experimentally demonstrated simultaneous photon and phonon lasing in a two-mode silica fiber ring cavity via forward intermodal stimulated Brillouin scattering (SBS) mediated by long-lived flexural acoustic waves. This two-domain laser may find potential applications in optical/acoustic tweezers, optomechanical sensing, microwave generation, and quantum information processing. Furthermore, we believe that this demonstration will usher in other multidomain lasers and related applications.

Relocking and Locking Range Extension of Partially Locked AMLL Cavity Modes with Two Detuned RF Sinusoids

Actively mode-locked fiber ring lasers (AMLLs) with loss modulators are used to generate approximately 100ps pulses with 100MHz repetition. RF detuning around the fundamental frequency, f0, causes a loss in phase lock (unlocking) of cavity modes and partial mode locking. Multiple RF inputs are shown, theoretically, to relock and extend the locking range of cavity modes in a detuned partially mode-locked AMLL. A custom-built Yb3+-doped AMLL with f0=26MHz, and operating wavelength of 1064nm, was used to experimentally verify the theoretical predictions. Two RF sinusoidal signals with constant phase and equal amplitude resulted in an extension of the range by Xn=6.4kHz in addition to the range Rn=14.34kHz with single input for the mode n=10. An increase in locking range was also observed for higher modes. Pulsewidth reduction to approximately 205ps from about 2ns was also observed in the AMLL.

Widely-tunable all-fiber Tm doped MOPA with > 1 kW of output power.

In this paper, we report on a high-power and widely tunable thulium-doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system. The master oscillator is a Tm fiber ring laser incorporating a tunable bandpass filter to realize narrow linewidth and wavelength tunable operation. The MOPA generated 1010 W ∼1039 W of output power over a tuning range of 107 nm from 1943 to 2050nm with slope efficiencies of more than 51% and spectra linewidth of ∼0.5 nm. Power stability (RMS) in ∼10 min scale is measured to be ∼0.52%. A diffraction-limited beam quality factor M2 of ∼1.18 is measured at 920 W of laser output. Output power is pump-limited without the onset of parasitic oscillation or amplified spontaneous emission (ASE) even at the maximum power level. This is the first demonstration, to the best of our knowledge, on an all-fiber integrated wavelength-tunable TDFL at 2 µm with output power exceeding 1 kW.