Fiber Ring Resonator Research Articles

Q‐switched thulium‐doped fibre ring lasers operating at 1.9 μm using multi‐walled carbon nanotubes in UV‐curing resin

The passively Q-switched operation of all-fibre thulium fibre lasers using UV-curing resin doped with multi-walled carbon nanotubes as a saturable absorber is demonstrated. A single-mode thulium-doped silica fibre is pumped by a laser diode emitting at 1.63 µm through a wavelength-division multiplexing coupler. Unidirectional laser output from the fibre ring resonator is attained by using the retroreflector at the counter-directional output port. The fibre laser exhibits 1.9 µm wavelength pulsed oscillation at a repetition rate of 7.2 kHz. When the pump power is increased to 161 mW, the output pulse power is measured by 150 mW with a pulse width of 3.2 µs.

光纤环形谐振腔输入功率波动对谐振式光纤陀螺的影响

光纤环形谐振腔输入功率波动对谐振式光纤陀螺的影响

光纤环形谐振腔输入功率波动对谐振式光纤陀螺的影响

光纤环形谐振腔输入功率波动对谐振式光纤陀螺的影响

Fiber ring resonator using a cavity ring‐down interrogation technique for curvature sensing

ABSTRACTIn this work, it is demonstrated a fiber ring resonator connected to an interrogation system usually implemented on a cavity ring‐down technique. A long‐period grating (LPG) was inserted in the resonant cavity, being operated as a curvature sensor. The experimental results demonstrate that using this setup, different sensitivities can be achieved in terms of analyzing decay time over the radius of the curvature and over curvature. The LPG sensor presented higher sensitivity with larger radius of curvature, namely 6.91 μs/m. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:267–270, 2016

Comparative analysis of fiber ring resonator based on different fibers

Abstract A fiber ring resonator (FRR) is the core element in a resonant fiber optic gyro (RFOG) and its resonant depth, finesse and sensitivity determine the performance of RFOG. A configuration of FRR based on air-core photonic bandgap fiber (PBF), photonic crystal fiber (PCF) and panda polarization-maintaining fiber (PMF) is proposed, and the resonant depth, finesse and sensitivity of the FRR are comparative analyzed fully and in depth. It's found that: the FRR using PCF and PBF have better resonant depth than that of using PMF; the FRR using PCF has nearly the same performance as that using PMF, and may be a trade-off used in FRR before the existence of better PBF; the key factor that whether the FRR resonates in optimal resonant state is whether αc and kc of directional coupler satisfy the optimal resonant condition. These theoretical results are helpful to further study and optimize the RFOG based on different fibers.

Resonant micro-optic gyro using a short and high-finesse fiber ring resonator.

A novel hybrid integrated scheme is proposed for a high-performance resonant micro-optic gyro (RMOG), which requires a low-loss micro-ring resonator for mass production. A new record for the RMOG is established experimentally with a short fiber ring resonator and an integrated signal detecting and processing circuit. The finesse of the short fiber ring resonator with a length of 60 cm and a diameter of 4.77 cm is as high as 202, and the theoretical sensitivity of the RMOG is better than 0.3°/h assuming the average optical intensity at the photodetector is 1 mW. The 60 cm long spliceless micro-ring resonator is experimentally proved to be sufficient for a tactical-grade RMOG. An angle random walk coefficient of 0.64°/√h and a typical bias stability below 9.6°/h for the integration time of 50 s are successfully demonstrated using an innovative open-loop approach for an operation time of 1600 s.

Effect of Fresnel reflections in a hybrid air-core photonic-bandgap fiber ring-resonator gyro.

A novel hybrid polarization-maintaining (PM) air-core photonic bandgap fiber (PBF) ring resonator is firstly demonstrated by using a conventional solid-core PM fiber optical coupler formed by splicing a section of PM air-core PBF into the resonator. Due to Fresnel reflections exist at the two junctions between the air-core PBF and the solid-core fiber, the forward output signal of this hybrid ring resonator is the normal resonant curve with the superposition of the lightwaves that experienced even numbers of Fresnel reflections and the backward output signal is composed of lightwaves that experienced odd numbers of Fresnel reflections. Rigorous derivations of the forward and backward output signals are given out. The biggest resonant depth and finesse of the hybrid air-core PBF ring resonator predicted are 0.352 and 6.3 respectively by assuming a splice loss of 1.8 dB per junction. These predictions are finally confirmed by testing both the forward and backward output signals of the hybrid ring resonator. With the countermeasures against the influences of the odd numbers of Fresnel reflections, a bias stability of 0.007°/s is successfully demonstrated in a hybrid PM air-core PBF ring-resonator gyro.

Investigations on an all-tunable fiber ring resonator

The architecture of an all-tunable optical fiber ring resonator is described in detail in this paper. This architecture has been firstly modeled using an original CAD approach. The simulation results demonstrate a total control of both the absolute frequency and the free spectral range of the final optical resonance comb generated by the optical resonator. The different experimental setups used to characterize the tunable resonator are described and the obtained results proving the concept are also provided.

Wigner Representation for Investigation of Entangled Photon Evolution in Four-Wave Mixing Process within a Fiber Ring Resonator

The aim of this study is to analyze the quantum correlation of entangled photons for four-wavemixing process within Kerr nonlinear susceptibility χ(3) of an optical fiber ring resonator. The main system Hamiltonian composes of two types of coupling photon modes, including pumping and parametric-down conversion. Wigner representation is applied to the Heisenberg equation of motion derived from the system Hamiltonian in order to obtain the corresponding stochastic equations of motion in a c-number. Quantum trajectories obtained from the stochastic equation of motion of photon states are then derived. Finally, the entanglement inseparability criteria for a pair of entangled photonfrom a numerical approach is also satisfied.

Characteristics of slow light from coupled fiber ring resonators

ABSTRACTThis article optimizes the conditions for the formation of slow light produced by coupled fiber ring resonators. Investigated parameters include the number of rings, ring length, splitting ratio of couplers, and ring losses. The optimized parameters included two rings in the resonator, equal length of the rings, and splitting ratios of 90:10 and 50:50 for the couplers. Under these conditions, a slow light delay time of 32.0668 ns was achieved, which corresponds to a group velocity of 3.43 × 107 m/s.

Investigation of refractive index sensing based on Fano resonance in fiber Bragg grating ring resonators.

In this paper we theoretically investigate a ring resonant cavity obtained by closing on itself a π-shifted fiber Bragg grating, to be used for refractive index sensing applications. Differently from a conventional π-shifted fiber Bragg grating, the spectral structure of this cavity is characterized by an asymmetric splitting doublet composed by a right side resonance having an asymmetric Fano profile and a left side resonance having a symmetric Lorentzian profile. The right side resonance shows a narrower and sharper peak than all the other kinds of resonance achievable with both conventional ring resonators and π-shifted fiber Bragg gratings. A reduction of the resonant linewidth with respect to a conventional π-shifted Fiber Bragg grating and a fiber ring resonator, having the same physical parameters, is theoretically proved, achieving up to five orders of magnitude improvement with respect to the usual ring resonator. Due to these resonance features, the π-shifted Bragg grating ring resonator results suitable for RI sensing applications requiring extremely narrow resonances for high resolution measurements. In particular, by assuming a refractive index sensing to detect the presence of sugar in water, the sensor can show a theoretical resolution better than 10-9 RIU.

Stable single-longitudinal-mode erbium-doped fiber laser with narrow linewidth utilizing parallel fiber ring resonator incorporating saturable absorber and fiber Bragg grating

A stable, single-frequency, narrow linewidth ring erbium-doped fiber laser (EDFL) is proposed and demonstrated experimentally. The main ultranarrow filter of the ring cavity EDFL is realized by an improved Mach–Zehnder interferometer, which consists of two parallel optical fiber ring resonators (FRRs). The FRRs share a saturable absorber and a fiber Bragg grating. Attributed to the Vernier effect, the single longitudinal mode operation is successfully obtained. The output of the EDFL can present good performance with a narrow linewidth of 1.09 kHz at 1549.57 nm and a high optical signal-to-noise ratio of 68 dB. Meanwhile, the laser has a relatively low threshold of 10.7 mW. In addition, the central wavelength variation and power fluctuation of the laser are less than 0.002 nm and 0.2 dB, respectively, showing favorable stability.

Fiber ring resonator based slow-light and high sensitivity gas sensing technology

A high sensitivity gas sensing technology based on fiber ring resonator slow-light is proposed and demonstrated in this paper. Slow-light produced by coupled resonator induced transparency in a fiber ring resonator has been studied theoretically and experimentally. Influences of parameters, such as cycle numbers, coupling ratio of couplers, ring loss and coupler additional loss, on slow-light characteristics of the fiber ring resonator were analyzed theoretically and numerically in detail. The delay time of slow-light in the fiber ring resonators has been measured using time domain measuring method, and the maximum delay time of 34.18ns at wavelength of 1531.63nm has been obtained, which is in accord with theoretical analysis. The gas absorption coefficient at the wavelength of 1531.63nm where slow-light generated reached 2.41, which increased by 6.73 times the figure for the traditional method. It is the first time to measure gas concentration by using slow-light in fiber ring resonators, and the method is simple in structure and easy to implement.

Enhanced Flat Broadband Optical Chaos Using Low-Cost VCSEL and Fiber Ring Resonator

Low-cost vertical-cavity surface-emitting laser (VCSEL) and semiconductor optical amplifier (SOA) have been explored experimentally in a setup with a fiber ring resonator to generate flat broadband chaos. The effect of the frequency detuning between the fiber grating frequency and the free-running VCSEL's frequency, and the bias current of the SOA on the bandwidth of chaos has been studied. The results show that the bandwidth of the chaos is strongly dependent on the frequency detuning and the bias current of the SOA. Using the conventional definition of chaos bandwidth, the bandwidth of chaos with the fiber ring resonator can be about three times greater than that with a conventional mirror. In order to consider the flatness of the chaos spectra, the flat bandwidth of chaos is redefined as the frequency range between dc and the frequency where the power fluctuation is within ±3 dB. With this definition, the flat bandwidth of chaos with the fiber ring resonator is >10 times higher than that with conventional mirror feedback.

Carbon-nanotube-based passively mode-locked fiber lasers modulated with sub-loop

We have proposed a carbon-nanotube-based passively mode-locked fiber laser, which consists of two fiber ring resonators, for the first time to author's best knowledge. The proposed laser in the main cavity is coupled with a fiber sub-loop, which is connected with a 2×2 optical coupler. Without the sub-loop, uniform-spaced conventional solitons are achieved in the fiber ring laser. With the sub-loop, the fiber laser generates a train of pulses modulated with a periodic envelop. The modulation period and pulse-pulse separation are ∼160 and ∼4.3ns, which are determined by the lengths of the main cavity and the sub-loop, respectively.

Analytical Treatment of the Ring Resonator Passive Systems and Bandwidth Characterization Using Directional Coupling Coefficients

We have shown that an add/drop system connected to a single microring resonator could be constructed using the fiber optics, where it can be used to generate a single soliton carrier, in which the tuning and manipulation of the bandwidth is performed to control the output signals. The chaos filtering via the add/drop device is implemented by using suitable parameters of the system. The coupling coefficient of the system is considered to be an effective parameter to determine the output intensity power of the system. In order to optimize the system, the smaller coupling coefficient is required. The bandwidth of the generated pulse changes respects to variation of the coupling coefficient. Here the chaotic signals which are used widely in communication, for variation of coupling coefficients is analyzed. To recover the pulses from the chaotic noises in the fiber ring resonator, we use the add/drop filter system with the appropriate parameters, where the insertion loss and gain of the system is measured. As a result, the increase of the coupling coefficients leads to increase of the bandwidth of the soliton pulse. In order to use ultra-short soliton pulses applied in optical communication, lower coupling coefficient is admired where, the power control can be performed within the system.

Simple method for locking birefringent resonators.

We report on a simple method of locking a laser to a birefringent cavity using polarization spectroscopy. The birefringence of the resonator permits the simple extraction of an error signal by using one polarization state as a phase reference for another state. No modulation of the light or the resonator is required, reducing the complexity of the laser locking setup. This method of producing an error signal can be used on most birefringent optical resonators, even if the details of birefringence and eigenpolarizations are not known. This technique is particularly well suited for fiber ring resonators due to the inherent birefringence of the fiber and the unknown nature of that birefringence. We present an experimental demonstration of this technique using a fiber ring.

Reducing polarization-fluctuation induced drift in resonant fiber optic gyro by using single-polarization fiber

A novel hybrid single-polarization (SP) fiber ring resonator is demonstrated by using a polarization-maintaining coupler formed by splicing a section of SP fiber into the resonator. The SP fiber selectively eliminates the unwanted resonance by introducing high loss for the unwanted eigenstates of polarization in the resonator. The calculated result shows that this hybrid SP resonator is a good candidate for a tactical-grade performance gyro with a high environmental temperature stability. The experiment shows that the desired resonance in the resonator can keep an excellent stability in a wide temperature range, thus the temperature-dependent polarization-fluctuation drift in the resonant fiber optic gyro is sufficiently suppressed. As a result, a random walk coefficient of 0.08°/√h and a typical bias stability below 0.3°/h for an integration time of 300 s have been carried out.

Nonlinear refractive index measurement utilizing bistable behavior of double coupling optical fiber ring resonator

A novel approach for measuring the nonlinear refractive index of an optical fiber utlizing the bistable behavior of the double coupling optical fiber ring resonator was proposed and investigated. The switch-off or switch-on power decreases with an increase in the nonlinear refractive index n2 (m2/W), and the dependence of swith-off or switch-on power on the nonlinear refractive index was analyzed numerically. Simulation results showed that the switch-off power and switch-on power (in dBW) decreased linearly with log10(n2) in a 100-m-length fiber ring resonator, when n2 changed from 3.2 × 10−20 m2/W to 2.5 × 10−17 m2/W or nearly n2 = 3.2 × 10−20 m2/W. These mean that high accuracy as well as large-scale nonlinear refractive index measurement can be achieved by the proposed approach.

Design and Analysis of an all-fiber MZI Interleaver Based on Fiber Ring Resonator

An all-fiber Mach-Zehnder interferometer (MZI) interleaver using one planar 3×3 fiber coupler, one 2×2 fiber coupler and one 8-shaped fiber ring resonator is developed by the new configuration. Based on its structure, the output spectrum expression is established and described by using the principle of fiber transmission and the matrix transfer function. The results of numerical simulation indicate that when the length difference of interference arms and the coupling coefficients of the couplers are some certain values, it obtains a uniform flat-top passband and similar to rectangular output spectrum. Compared with the traditional MZI interleaver, the isolation in stopband and the rolloff in transition band are strengthen, the 25dB stopband bandwidth and 0.5dB passband bandwidth are simultaneously remarkably improved. Compared with the asymmetrical ring resonator MZI interleaver, the influence of transmission loss on extinction ratio can be effectively reduced. The device has a certain ability to resist the deviation, which reduces the difficulties in fabricating it. The experiment results agree with the theoretical analysis well. The interleaver designed by the proposed approach has favorable performance, which has the potential application value in optical fiber communication system.