A bow-tie shaped optical fiber loop and ring with double couplers

A theoretical study of a bow-tie shaped optical fiber loop and a ring with double couplers is carried out. The expressions for the circulating (resonant) intensity and the two output (reflected and transmitted) intensities are derived and the computed results are presented as graphs. The special characteristics, advantages, and possible applications of this type of fiber loop and ring, in comparison with other types, are discussed.     

Electro-optic wavelength-tunable fiber ring laser based on cascaded composite Sagnac loop filters

A continuous wavelength-swept fiber ring laser with a lithium niobate waveguide electro-optic polarization controller in an intracavity fiber Sagnac loop is experimentally demonstrated. Composite fiber Sagnac loop filters are cascaded to demonstrate discrete wavelength switching of a single-wavelength fiber ring laser. Stable single-longitudinal-mode operation is achieved by use of a Sagnac loop saturable-absorber filter.     

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XII. Dependence of the zero drift in fiber ring interferometers in orthogonal polarization modes on the range of temperature variation in an optical fiber

Temperature dependences of the zero drift in a fiber ring interferometer (FRI) without a polarizer in the presence of random inhomogeneities in a single-mode optical fiber in the FRI loop are obtained by numerical simulation. The results are compared with known experimental data. It is shown that FRIs using a superluminescent diode as a source of nonmonochromatic radiation and a loop made of a single-mode optical fiber with weak linear birefringence can find application as low-accuracy fiber-optic gyroscopes and FRIs with a loop made of a single-mode optical fiber with strong linear birefringence can be used as medium-accuracy fiber-optic gyroscopes.     

Erbium doped fiber ring laser for optical wavelength conversion

We experimentally investigate the gain saturation effect of a piece of 8 m long Erbium doped fiber (EDF), we introduce a theoretical model for the EDF ring loop, and our simulation results show very good cross-gain modulation (XGM) and wavelength conversion. We also experimentally investigate the XGM in an EDF ring loop system. Based on the study of the XGM in the EDF ring loop system, a wavelength conversion is designed with the EDF ring loop system. The EDF ring loop systems as a wavelength conversion is experimentally demonstrated by converting a sinusoidal modulated optical signal at wavelength of 1551 nm to an optical signal at wavelength of 1553.3 nm.     

Stable wavelength tunable fiber ring laser for true-time delay system

In this paper, we propose and experimentally demonstrate a novel wavelength tunable fiber ring laser source for a photonic beamforming system to control phased-array antenna. In this fabrication, a Sagnac loop composed of a polarization-maintaining (PM) coupler and a piece of high-birefringence (Hi-Bi) PM fiber is acted as a comb filter to make the frequency spacing equal. The wavelength of the output signal is controlled by the tunable filter outside the Sagnac loop. The intensities of the output signals with different wavelengths increased or decreased at the same frequency spacing are equal. A five-channel true-time delay system consisting of this tunable fiber source and five grating delay lines for discrete beamsteering has been demonstrated. In the experiment, the output signals of the tunable fiber ring with the equal frequency spacing have the same intensity of about 5.9 dBm and the same high signal to noise ratio (SNR) of 40 dB. If the tunable filter in this laser is replaced by a micro-electro-mechanical systems (MEMS) tunable filter, the speed of switching wavelength will increase rapidly.     

Room temperature multiwavelength erbium-doped fiber ring laser using a highly nonlinear photonic crystal fiber

A multiwavelength laser source is demonstrated with a high power erbium-doped fiber amplifier as the gain medium. A highly nonlinear photonic crystal fiber (PCF) is inserted in the ring cavity to provide nonlinear gain by four-wave mixing. A Sagnac loop is incorporated in the ring cavity serving as a comb-like multichannel filter. The comparison between fiber ring laser without PCF and with PCF shows that the highly nonlinear PCF can generate a larger number of excited wavelengths and help stabilize the output power.     

基于半导体光放大器的可调谐多波长光纤激光器

报道了一种新型环形腔可调谐多波长光纤激光器,腔内以半导体光放大器为增益介质,利用高双折射光纤构成的高双折射环形镜的滤波特性,在室温下,获得了基本符合ITU-T标准100GHz的17个波长以上的稳定多波长输出.各信道峰值功率差小于6 dB,线宽小于0.102 nm,信噪比大于25 dB.通过调节高双折射环形镜内的偏振控制器状态实现了这一组波长整体在50GHz范围内连续可调谐.并利用实验方法,对该光纤激光器应用于掺铒光纤放大器对多信道放大性能测试的可行性进行了初步探讨.     

Dual-wavelength switchable erbium-doped fiber ring laser based on merged sagnac and intermodal interferences in sagnac loop mirror

A simple but novel concept of switchable dual-wavelength erbium-doped fiber ring laser is proposed and experimentally demonstrated. It is based on a Sagnac loop mirror incorporating a high birefringence few-mode fiber and polarization controller (PC). Since its transmission properties depend on the PC state, the proposed fiber ring laser can operate in the random combination of two wavelengths by adjusting only the PC settings. The potential lasing lines are determined by simultaneous occurrence of the Sagnac and intermodal interferences in the Sagnac loop mirror. All lasing emissions have the optical signal to noise extinction ratio higher than 45 dB and their power fluctuations lower than 0.5 dB.     

Influence of the irregularity of twisting of the birefringence axes of single-mode optical fibers on the polarization nonreciprocity of fiber ring interferometers

A particular example of the so-called minimum-configuration fiber ring interferometer whose loop comprises two different-length segments of a single-mode optical fiber with the same linear birefringence but different twisting is used to show that even in the case where the birefringence axes at the loop input coincide with the polarizer transmission direction, the phenomenon of polarization nonreciprocity of the fiber ring interferometer can emerge. It is shown that polarization nonreciprocity can be eliminated by the proper adjustment of the axes of a single-mode optical fiber, but the above adjustment should be changed if the waveguide temperature is changed. It is also shown that polarization nonreciprocity is a function of the light wavelength and the polarization nonreciprocity value in a fiber ring interferometer varies quasiperiodically in response to the temperature change in an optical fiber with random irregularities.     

Stable multiwavelength fiber ring laser with equalized power spectrum based on a semiconductor optical amplifier

We experimentally demonstrated a new structure of a multiwavelength semiconductor optical amplifier (SOA) ring laser based on a fiber Sagnac loop filter that can generate up to 25 stable output lasing wavelengths at room temperature. By varying the length of a polarization-maintaining (PM) fiber within the Sagnac loop filter, the wavelength spacing between the output lasing wavelengths can be changed to a desired value. By tuning a polarization controller (PC) within the Sagnac loop filter, stable multiwavelength 1550-nm operation with up to 17 lasing lines within 3 dB power level variation and with a wavelength spacing of ∼0.8 nm was achieved. The optical signal-to-noise ratios (OSNRs) of all the lasing wavelengths are greater than 40 dB.     

Theoretical analysis of feedback high birefringence fiber loop mirror for application in single-frequency fiber lasers

A feedback high birefringence fiber loop mirror with a piece of erbium-doped fiber and a polarization controller is newly proposed. When the erbium-doped fiber is properly pumped to offset the loss of the feedback ring in the loop mirror, narrowband transmission peaks with large effective free spectral range can be achieved by the intrinsic vernier effect between orthogonally polarized lights respectively traveling along the two primary axes of the high birefringence fiber. In addition, the side transmission suppression ratio can reach about 6 dB. These special properties are independent of the polarization state of the input signal, which makes it feasible for the proposed feedback high birefringence fiber loop mirror to be employed as a narrowband filter in single-frequency fiber lasers.     

Figure-eight actively-passively mode-locked erbium-doped fiber laser

The advantages of using nonlinear optical loop mirror (NOLM) to compress pulse with slight amplitude fluctuation and reflected energy loss are analyzed in theory. Experimentally the NOLM is placed in an actively mode-locked erbium-doped fiber ring laser to form a figure-eight actively and passively mode-locked fiber laser. 12 ps mode-locked pulses centered at 1.543 μm were obtained with the modulation frequency of 2.498748700 GHz. 3.715 mW output power is achieved with 50 mW pump power.     

Methods for calculating the temperature zero drift initiated in fiber ring interferometers by random inhomogeneities in single-mode optical fibers

The specific features of the existing methods used for calculating the temperature zero drift initiated in fiber ring interferometers (FRIs) by linear coupling between polarization eigenmodes at random inhomogeneities in single-mode optical fibers are analyzed. The ranges of applicability of each method are determined. It is demonstrated that numerical simulation with a variation in the temperature of the single-mode optical fiber of the FRI loop is the most complex and, at the same time, the most universal method.     

Tunable multiwavelength SOA-fiber ring laser based on Sagnac loop mirror incorporating few-mode high birefringence fiber

A tunable multiwavelength fiber ring laser based on a semiconductor optical amplifier and Sagnac loop mirror incorporating a piece of few-mode high birefringence fiber (FM-HBF) is proposed and experimentally demonstrated. It is accomplished by simply adjusting a polarization controller in the Sagnac loop mirror because birefringence of the FM-HBF is polarization dependent. Tunable multiwavelength operation up to 11 oscillating lines at about 2.1 nm interval is stably achieved with an optical side-mode suppression ratio over 35 dB.     

光纤腔衰荡光谱技术及其最新进展

阐述了腔衰荡光谱技术的基本原理及应用;从结构设计的角度考虑,归纳出光纤衰荡腔的三种基本结构,并对光纤腔衰荡光谱技术及其最新进展进行了评述;报道了我们采用脉冲光纤环衰荡光谱技术进行液体检测取得的最新进展;在总结光纤腔衰荡光谱技术优点的基础上,展望了其发展前景。     

光纤腔衰荡光谱技术及其最新进展

阐述了腔衰荡光谱技术的基本原理及应用;从结构设计的角度考虑,归纳出光纤衰荡腔的三种基本结构,并对光纤腔衰荡光谱技术及其最新进展进行了评述;报道了我们采用脉冲光纤环衰荡光谱技术进行液体检测取得的最新进展;在总结光纤腔衰荡光谱技术优点的基础上,展望了其发展前景.     

Effect of polarization nonreciprocity in rotating fiber ring interferometers

The effect of polarization nonreciprocity in sensors of angular velocity of rotation—fiber ring interferometers (FRIs)—is considered for arbitrary polarization of eigenmodes of the single-mode optical fiber of an FRI loop and arbitrary polarization state of radiation at the FRI input. A new method for detecting the polarization nonreciprocity in an FRI is proposed. Numerical estimations are made.     

Tunable multi-wavelength fiber ring laser based on a Hi-Bi fiber loop mirror

A novel tunable multi-wavelength fiber ring laser based on semiconductor optical amplifier(SOA)is proposed by using a high-birefringence(Hi-Bi)fiber loop mirror(FLM)as wavelength filter.With this configuration,the wavelength spacing of this laser can be varied by using the different lengths of Hi-Bi fiber.8 wavelengths spacing on 450 GHz are experimentally obtained with more than 25-dB signal-to-noise ratio(SNR)for each channel using 1.28-m Hi-Bi fiber in Hi-Bi FLM.The output power variation between different channels is measured to be less than 5.9 dB.The linewidth of each channel is compressed from 0.347 to 0.186 nm by 1.5-m unpumped erbium-doped fiber(EDF).Meanwhile,17 wavelengths spacing on ITU-gird(100 GHz)are also obtained with 5.9-m Hi-Bi fiber in Hi-Bi FLM.All these channels can be tuned together over 0.4 nm.     

环形光纤激光器中的半导体光波导调制器

对环形光纤激光器中的半导体光波导调制器进行了理论研究，结果表明，光纤环中的偏振控制器对光的偏振态的控制以及半导体光皮导对光的偏振态的调节构成了激光器的主要调制机理，为环形光纤激光器的自调Ｑ及锁模的新机制提供了理论依据。     

Fiber-feedback continuous-wave and synchronously-pumped singly-resonant ring optical parametric oscillators using reverse-proton-exchanged periodically-poled lithium niobate waveguides

We describe guided-wave singly-resonant reverse-proton-exchanged (RPE) periodically-poled lithium niobate (PPLN) waveguide ring optical parametric oscillators (OPOs) in which the feedback was provided via a single-mode fiber pigtailed to the waveguide. Wavelength selection was achieved by means of a fiber Bragg grating inside the feedback loop. The SRO threshold for the synchronously-pumped OPO was below 1 mW of average coupled pump power.