Fiber quarter-wave plates and magneto-optical fibers are important components that greatly affect the sensitivity of fiber-optic current sensors. A Tb:YAG crystal-derived silica fiber (TYDSF) was fabricated using a CO2 laser-heating drawing technique. The linear birefringence of TYDSF was measured as 6.661×10-6 by a microscope birefringence measurement instrument. A fiber quarter-wave plate was fabricated by TYDSF at 1310 nm, which produced circularly polarized light with a polarization extinction ratio of 0.34 dB. Additionally, the linear birefringence of TYDSF was decreased by 22% by annealing at 750°C for 7 h, and the Verdet constants of annealed TYDSF were measured to be 9.83, 6.67, and 3.48rad/(T·m) at 808, 980, and 1310 nm, respectively.

提出了一种基于环形芯结构的掺铒涡旋光纤。针对该涡旋光纤的放大性能，分析了其高折射率环和掺杂区域宽度对增益性能的影响。仿真结果表明，该光纤可支持1~2阶涡旋光模式，且C波段内的模式增益均高于35.4 dB。通过搭建实验装置对环形芯掺铒涡旋光纤的放大性能进行了测试。实验结果表明，在1530 nm波长处涡旋光的模式增益最大值高达32.6 dB。此环形芯掺铒涡旋光纤可广泛应用在长距离、大容量的空分复用光纤通信等领域中。

为了解决随机线性双折射对光纤磁光特性测量的影响，采用旋转光纤（SF）结合法拉第旋转镜（FRM）的测量方法，研究了FRM对旋转光纤磁光特性测量的影响。首先，从理论方面研究旋转光纤与FRM的引入如何减小光纤中的随机线性双折射对磁光特性测量的影响，并搭建基于FRM的旋转光纤磁光特性测试系统。当光源波长为1310 nm时，FRM作用前的旋转光纤费尔德常数都比未旋转光纤的大，且旋转光纤的节距越短，费尔德常数越大。特别是旋转光纤的节距为1.0 mm时，其费尔德常数为0.8304 rad/（T·m），比未旋转光纤的费尔德常数［0.8029 rad/（T·m）］增大了约3.43%。当测试系统加入FRM后，不同光纤的费尔德常数测量值相较于未使用FRM的光纤费尔德常数测量值都有一定幅度的增大，尤其相比于节距为1.0 mm时的旋转光纤更进一步提高了7.50%，并且在FRM作用前后不同光纤费尔德常数测量值的均方差分别为0.99%和0.61%，说明FRM的引入提高了掺杂光纤费尔德常数的测量精度与稳定性。

采用一种具有中心凹陷的三角芯＋环型的折射率剖面设计，利用外部气相沉积(OVD)工艺制备了新型非零色散位移G.655.D光纤。实验结果表明：在1550 nm和1625 nm波长处，光纤的衰减值分别为0.195 dB/km和0.203 dB/km，截止波长为1200 nm；将光纤绕在半径为25 mm的圆柱体上100圈，此时其在1550 nm和1625 nm波长处的宏弯损耗值分别低于0.027 dB和0.045 dB；该光纤在1530～1625 nm波段的色散为1.6～9.5 ps/(nm·km)，尤其是在1550 nm波长处，其有效面积达到72 μm²，比常规G.653光纤大1.4倍。通过这种设计和方法制备的光纤可以实现零色散波长的平移，获得良好的纵向色散均匀性、较低的弯曲损耗以及较大的有效面积，适用于1530～1625 nm波段的密集波分复用应用，在长距离光纤通信中对四波混频(FWM)、交叉相位调制(XPM)等非线性效应具有较好的抑制作用，可以减少色散管理成本，具有非常重要的应用价值。

We fabricate a high-performance Bi/Er/La co-doped silica fiber with a fluorescence intensity of -33.8dBm and a gain coefficient of 1.9 dB/m. With the utilization of the fiber as a gain medium, a linear-cavity fiber laser has been constructed, which exhibits a signal-to-noise ratio of 74.9 dB at 1596 nm. It has been demonstrated that the fiber laser has a maximum output power of 107.4 mW, a slope efficiency of up to 17.0%, and a linewidth of less than 0.02 nm. Moreover, an all-fiber single-stage optical amplifier is built up for laser amplification, by which the amplified laser power is up to 410.0 mW with pump efficiency of 33.8%. The results indicate that the laser is capable of high signal-to-noise ratio and narrow linewidth, with potential applications for optical fiber sensing, biomedicine, precision measurement, and the pump source of the mid-infrared fiber lasers.

A single-frequency distributed Bragg reflector (DBR) fiber laser at 1030 nm has been demonstrated using a 0.7 cm long homemade Yb:YAG crystal-derived silica fiber (YCDSF). The absorption and emission cross sections of the YCDSF are 4.93×10-20cm2 at 980 nm and 1.1×10-20cm2 at 1030 nm. Using this gain fiber, an over 255 mW continuous-wave lasing in the constructed laser has been obtained at single transverse and longitudinal mode operation. The slope efficiency and the pump threshold of the fiber laser were up to ～35% and as low as 25 mW, respectively. The fiber laser also demonstrated an optical signal-to-noise ratio of 79 dB and a beam quality factor of 1.016 in two orthogonal directions. Its power fluctuation at 210.5 mW was less than 0.85% of the average power within 13 h. Moreover, the relative intensity noise and linewidth of the laser are also investigated at the different pump powers. The results indicate that the single-frequency DBR fiber laser has potential applications in high-quality seed sources and high-precision optical sensing.

We have demonstrated the highly efficient excitation of the linearly polarized mode (LP₀₁) in ring-core fibers (RCFs) by tapering the spliced point between the RCF and the standard single-mode fiber (SMF) to optimize all-fiber orbital angular momentum (OAM) generation. The tapering technique has been investigated theoretically and experimentally. Before tapering, only 50% of light can be coupled from SMFs to RCFs. The modal interference spectrum with an extinction ratio (ER) of ～9 dB is observed, showing that higher-order modes are excited in RCF. By tapering the spliced point, 90% of light is coupled, and the ER is minimized to be ～2 dB, indicating that the higher-order modes are effectively suppressed by tapering. Such tapered spliced points of RCF–SMF are further applied for all-fiber OAM generation. The efficiencies of OAM₊₁ and OAM_?1 generation are found to be enhanced by approximately 11.66% and 12.41%, respectively, showing that the tapered spliced point of the RCF–SMF is a feasible way to optimize OAM generation.

提出了一种在环形芯光纤中激发高阶涡旋光模式的方法,通过控制锥形微透镜单模光纤与环形芯光纤之间的倾斜角度和错位距离,实现了高阶涡旋光模式的激发。由数值模拟与实验测试结果可知,倾斜角度和错位距离分别约为8°和2 μm时,高质量的二阶涡旋光模式被激发。此外,由于锥形微透镜光纤具有聚焦光束的特性,其倾斜错位激发可以提高光的耦合效率,该方法与使用普通单模光纤的错位激发法相比,光的耦合效率提高13%左右。激发出的高阶涡旋光模式在高分辨率显微镜、光学微观操纵和光学传感等应用领域中具有巨大的应用潜力。

We experimentally demonstrate two kinds of all few-mode fiber (FMF) ring lasers with high-order mode (HOM) oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams (OVBs); the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams (CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and Q-switched HOM beams in all-FMF laser cavities.

A few-mode erbium-doped fiber (FM-EDF) is fabricated using modified chemical vapor deposition in combination with liquid solution. The core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm, respectively. The refractive index difference is 0.98%, numerical aperture (NA) is 0.17, and normalized cut-off frequency at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as a higher-order mode gain medium. Furthermore, a long period fiber grating (LPFG) is fabricated, which can convert LP₀₁ mode to LP₁₁ mode, and its conversion efficiency is up to 99%. The first-order orbital angular momentum (OAM) is also generated by combining the LPFG and polarization controller (PC). Then, an all-fiber amplification system based on the FM-EDF and LPFG, for LP₁₁ mode and first-order OAM beams, is built up. Its on-off gain of the LP₁₁ mode beam is 37.2 dB at 1521.2 nm. The variation, whose transverse mode field intensity of first-order OAM is increased with the increase of pumping power, is obvious. These show that both the LP₁₁ mode and first-order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification scheme, which can be used in the optical communication fields.