Experimental demonstration of single-mode fiber coupling using adaptive fiber coupler

Coupling plane wave into a single-mode fiber （SMF） with high and steady coupling efficiency is crucial for fiber- based free-space laser systems, where random angular jitters are the main influencing factors of fiber coupling. In this paper, we verified a new adaptive-optic device named adaptive fiber coupler （AFC） which could compensate angular jitters and improve the SMF coupling efficiency in some degree. Experiments of SMF coupling under the angular jitter situation using AFC have been achieved. Stochastic parallel gradient descent （SPGD） algorithm is employed as the control strategy, of which the iteration rate is 625 Hz. In closed loop, the coupling efficiency keeps above 65% when angular errors are below 80/3tad. The compensation bandwidth is 35 Hz at sine-jitter of 15 ~rad amplitude with average coupling efficiency of above 60%. Also, experiments with simulated turbulence have been studied. The average coupling efficiency increases from 31.97% in open loop to 61.33% in closed loop, and mean square error （MSE） of coupling efficiency drops from 7.43% to 1.75%.

Wavelength dependent loss of splice of single-mode fibers

After reviewing three different definitions of mode field diameter of single-mode fibers, coupled efficiency calculation methods associated with lateral offset, longitude separation and wavelength, the effects produced by them, and the influences of splicing defects were discussed in detail. The regularities of the effects were studied according to the first order derivation of couple efficiency formula, and a simplified formula for couple efficiency calculation was presented under the circumstance of slight misalignment, with respect to wavelength, 2, and in a good agreement with the theoretical model. The simplified formula provides a new but simple approach to evaluate wavelength dependent couple efficiency of single-mode fibers. Theoretical analyses and numerical calculations show that, when those defects exist, the wavelength produces additional effects on the couple loss that growth of wavelength causes an increase on the couple efficiency for the lateral offset or longitude separation whereas lessens the couple efficiency due to angular misalignment or mode fields mismatching, and that the wavelength degrades the couple efficiency distinctly when λ≥2.5 μm whereas it distorts the couple slightly in range of λ≤2λ≤2 μm.

Optical Pulse Compression Based on High-doped Erbium Fiber Amplifier and Standard Single-mode Fiber

Proposed is a novel optical pulse compression technique based on high-doped erbium fiber amplifier and standard single-mode fiber(SMF). We used the amplifier with the erbium ion concentration of 6.3×10-3 to amplify a hyperbolic secant pulse from a regeneratively mode-locked fiber laser. The central wavelength, pulsewidth and peak power of the pulse are 1 550 nm, 12.5 ps and 3 mW, respectively. Then the amplified pulse with peak power level corresponding to a higher-order soliton is compressed when it propagates through a 3-km-long single-mode fiber. Studied are the compressed pulses under different pump powers and fiber lengths. The results show that it can get a narrower pulse, and solve the difficulty that pulses at low power can not be compressed directly in the fiber. And the construct is compact.

Single-mode antiresonant terahertz fiber based on mode coupling between core and cladding

Based on the index-induced mode coupling between the higher-order mode in core and the fundamental mode in cladding tubes,the single-mode operation can be realized in any antiresonant fibers(ARFs)when satisfying that the area ratio of cladding tube and core is about 0.46:1,and this area ratio also should be modified according to the shape and the number of cladding tubes.In the ARF with nodal core boundary,the mode in core also can couple with the mode in the wall of core boundary,which can further enhance the suppression of high-order mode.Accordingly,an ARF with conjoint semi-elliptical cladding tubes realizes a loss of higher-order mode larger than 30 dB/m;simultaneously,a loss of fundamental mode loss less than 0.4 dB/m.

FAST EVALUATION OF THE CHARACTERISTICS OF SINGLE-MODE OPTICAL FIBERS

This paper describes a method for fast engineering evaluation of the transmission characteristicsof single-mode optical fibers.A versatile microcomputer program is presented which can be utilized to ana-lyze mode field characteristics of single-mode fibers with arbitrary refractive index profiles.Our computationshows that the mathematical algorithm and the corresponding programs developeod in this paper are rela-tively simple and accurate enough for the engineenring design of single-mode fibers for optical communica-tion systems.

Single-polarization single-mode hollow-core negative curvature fiber with nested U-type cladding elements

Hollow-core negative curvature fibers(HC-NCFs)have become one of the research hotspots in the field of optical fiber because of their potential applications in the data and energy transmissions.In this work,a new kind of single-polarization single-mode HC-NCF with nested U-type cladding elements is proposed.To achieve the single-polarization single-mode transmission,we use two different silica tubes in thickness,which satisfy the resonance and anti-resonance conditions on the U-type cladding elements and the cladding tubes,respectively.Besides,the elliptical elements are introduced to achieve good single-mode performance.By studying the influences of the structure parameters on the propagation characteristics,the optimized structure parameters are obtained.The simulation results show that when the wavelength is fixed at 1550 nm,the single-polarization single-mode transmission is achieved,with the polarization extinction ratio of 25749 and minimum high-order mode extinction ratio of 174.Furthermore,the confinement loss is only 0.0015 dB/m.

Frequency-stabilized Yb：fiber comb with a tapered single-mode fiber

We demonstrate a stable Yb：fiber frequency comb with supercontinuum generation by using a specially designed tapered single-mode fiber, in which a spectrum spanning from 500 nm to 1500 nm is produced. The carrier-envelope offset signal of the Yb：fiber comb is measured with a signal-to-noise ratio of more than 40 dB and a linewidth narrower than 120 kHz. The repetition rate and carrier-envelope offset signals are simultaneously phase locked to a microwave reference frequency.

A tunable comb filter using single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop

A novel tunable comb filter composed of a single-mode/multimode/polarization-maintaining-fiber-based Sagnac fiber loop is proposed and experimentally demonstrated. The filter tunability is achieved by rotating the polarization controller. The spectral shift is dependent on rotation direction and the position of the polarization controller. In addition, the adjustable range achieved by rotating the half-wave-plate polarization controller is twice higher than that of the quarter-wave-plate one.

E-SMF和NZ-DSF在城域网中的应用

透明的光网络将使光波长不经过中继在整个环内传送,更远的传送距离和更高的传送比特将给城域网设备带来新的挑战。正确选择光纤对于确保系统性能和经济性则显得至关重要。分析表明,低于70km,采用E—SMF是最经济的;超过200km,则正色散系数NZ-DSF是最恰当的选择。

Self-starting all-fiber PM Er:laser mode locked by a biased nonlinear amplifying loop mirror

A compact all-fiber polarization-maintaining Er:laser using a nonlinear amplifying loop mirror is reported. Fundamental single-pulse mode-locking operation can always self start, with a cavity round-trip decreased from ~ 4.7 m to~ 1.7 m. When the pulse repetition rate is 121.0328 MHz, output pulse is measured to have a center wavelength/3-d B spectral bandwidth/radio frequency signal to noise ratio(SNR)/pulse width of 1571.65 nm/18.70 nm/80 d B/477 fs, respectively. Besides, three states including the exponential growth, damping state, and steady state are investigated through the build-up process both experimentally and numerically. Excellent stability of this compact Er:laser is further evaluated,demonstrating that it can be an easy-fabrication maintenance-free ultrafast candidate for the scientific area of this kind.

Polarization Characteristics of the Deformed Low-Mode Fiber Waveguides with Polarization Conservation

In this work the results of polarization researches of low-optical fiber waveguides with conservation of polarization are presented. Obtained results quite convincingly testify regarding a high sensitivity low-mode regime of work of an optical fiber to anisotropic external influences, in comparison with one-mode regime of work of the same fibre. This result, can represent a big practical value at the realization of high-sensitivity fiber-optical devices of different physical values.

A high-efficiency grating coupler between single-mode fiber and silicon-on-insulator waveguide

We present the design of a diffractive grating structure and get the optimal parameters which can achieve more than 75%coupling efficiency（CE） between single-mode fiber and silicon-on-insulator（SOI） waveguide through 2D finite-different time-domain（FDTD） simulation.The proposed architecture has a uniform structure with no bottom reflection element or silicon overlay.The structure,including grating couplers,adiabatic tapers and interconnection waveguides can be fabricated on the SOI waveguide with only a single electron-beam lithography（ICP） step,which is CMOS-compatible.A relatively high coupling efficiency of 47.2%was obtained at a wavelength of 1562 nm.

Matched-Cladding Single-Mode Optical Fiber Optimized at 850 nm Wavelength

A single-mode optical fiber with quadratic curve index profile in core layer is introduced. The profile is optimized at 850 ran wavelength. The 850 nm bandwidth of this fiber can reach up to 2056.35 MHz.km. This fiber can be used at 850 nm, 1310 nm, and 1550 nm wavelength.

A fiber micro-vibration sensor based on single-mode fiber ring laser

A new micro-vibration sensor based on single-mode fiber ring laser is put forward. The Mach-Zehnder interferometric （MZI） detection technique is presented for interrogating laser frequency shift due to the measurand （piezoelectric transducer （PZT） is used to simulate the micro-vibration） induced laser cavity strain from both single- and multi-mode lasers. In the experiment, compared with multi-mode laser sensors, the single-mode laser sensor is proved to be a sensor with high resolution. When the PZT is driven by the analog signal （0.03 rad near 2 kHz）, the signal-to-noise ratio （SNR） of output signal from the single-mode laser sensor is close to 55 dB and the sensitivity of the sensor is about 5 ×10^-5 rad/Hz1/2.

Transmission of 2.5 Gb/s WDM Channels Spaced at 5 GHz over 480 km of Single-Mode Fiber

We demonstrate the transmission of 2.5-Gb/s WDM signals spaced at 5 GHz over 480 km of single-mode fiber. The results indicate that it should be possible to transmit more than one thousand 2.5-Gb/s channels spaced at 5 GHz over long distance.

LP_(01) to LP_(11) mode convertor based on side-polished small-core single-mode fiber

An all-fiber LP_(01)-LP_(11) mode convertor based on side-polished small-core single-mode fibers(SMFs) is numerically demonstrated. The linearly polarized incident beam in one arm experiences π shift through a fiber half waveplate, and the side-polished parts merge into an equivalent twin-core fiber(TCF) which spatially shapes the incident LP_(01) modes to the LP_(11) mode supported by the step-index few-mode fiber(FMF). Optimum conditions for the highest conversion efficiency are investigated using the beam propagation method(BPM) with an approximate efficiency as high as 96.7%. The proposed scheme can operate within a wide wavelength range from 1.3 μm to1.7 μm with overall conversion efficiency greater than 95%. The effective mode area and coupling loss are also characterized in detail by finite element method(FEM).

单模光纤弯曲半径对光纤陀螺标度因数稳定性的影响（英文）

在采用低偏和保偏混合光路的混偏光纤陀螺的光学架构中,包含了一些单模光纤元件和单模光纤。当单模光纤发生弯曲时,光纤中传输的纤芯导波模式和单模光纤中的界面反射波模式之间将会发生相互干涉,导致光的传输特性受到影响。提出了单模光纤弯曲对光纤陀螺标度因数稳定性影响的数学模型。仿真和实验结果表明:当温度发生变化时,单模光纤弯曲会导致传输光的中心波长发生漂移和振荡,从而影响光纤陀螺标度因数稳定性。中心波长振荡的振幅与弯曲半径直接相关。

长周期光纤光栅横向压力传感特性的研究

介绍了在普通单模光纤中利用振幅掩模板法制作长周期光纤光栅 ,并对这种长周期光纤光栅的双折射效应进行了研究 ,对利用这种长周期光纤光栅的双折射效应制作传感器的可能性进行了探讨。结果表明 :普通单模光纤中长周期光纤光栅的双折射效应对光纤横向压力具有很高的灵敏度和良好的线性响应 ,其灵敏度比以前报道的光纤布喇格光栅高出 2个数量级 ,因此可利用这种光纤光栅制作低成本、高效率的光纤光栅压力传感器。

基于多模-单模-多模结构和光纤布拉格光栅同时测量温度和折射率

利用单模光纤(SMF)中的包层模与纤芯导模之间的干涉,提出了一种基于多模-单模-多模(MSM)结构与布拉格光栅(FBG)级联可同时测量温度和折射率的传感器。基于MSM结构的干涉谱和FBG的透射峰对温度和折射率具有不同响应灵敏度的特点,利用敏感矩阵实现了对温度和折射率的同时测量。实验测得MSM结构和FBG的温度灵敏度分别为0.055 2nm/℃和0.015 8nm/℃,MSM结构的折射率灵敏度为109.702nm/RIU,而FBG对折射率变化不敏感。温度和折射率的测量精度分别为±0.32℃和±0.002 3。实验显示提出的MSM结构的温度灵敏度比单模-多模-单模(SMS)结构传感器提高了5倍,同时由于SMF中的包层模对外界环境的变化较敏感,该MSM结构也可应用于其他传感领域。

半导体激光器到单模光纤的高效耦合技术

本文在阐述了半导体激光器到单模光纤的耦合损耗来源之后，对几种典型的耦合技术作了较为详细的分析和比较，明确了增大数值孔径、减小系统球差和椭圆度校正三个主要因素对进一步提高耦合效率的意义。最后，探讨了耦合技术的发展前景。