Method for improving the resolution and accuracy against birefringence dispersion in distributed polarization cross-talk measurements

We present a novel method for improving the spatial resolution and amplitude accuracy of distributed polarization cross-talk measurements in a polarization maintaining (PM) fiber against its birefringence dispersion. We show that the broadening of measured polarization cross-talk peaks caused by birefringence dispersion can be restored by simply multiplying the measurement data with a compensation function. The birefringence dispersion variable in the function can be obtained by finding the widths of measured cross-talk envelopes at known distances along the fiber. We demonstrate that this method can effectively improve spatial resolution and amplitude accuracy of the space-resolved polarization cross-talk measurements of long PM fibers.     

Method for improving the resolution and accuracy against birefringence dispersion in distributed polarization cross-talk measurements

We present a novel method for improving the spatial resolution and amplitude accuracy of distributed polarization cross-talk measurements in a polarization maintaining (PM) fiber against its birefringence dispersion. We show that the broadening of measured polarization cross-talk peaks caused by birefringence dispersion can be restored by simply multiplying the measurement data with a compensation function. The birefringence dispersion variable in the function can be obtained by finding the widths of measured cross-talk envelopes at known distances along the fiber. We demonstrate that this method can effectively improve spatial resolution and amplitude accuracy of the space-resolved polarization cross-talk measurements of long PM fibers.     

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.     

Dynamic arbitrary waveform shaping in a continuous fiber

We present a low-loss dynamic waveform shaping technique for high-repetition-rate signals by independent phase and amplitude control of spectral lines in a continuous fiber. Our system employs uniform fiber Bragg gratings to separate the spectral lines and provides independent amplitude and phase control for each line via an in-line polarization controller and an in-line fiber stretcher, respectively. Several distinct waveforms are experimentally demonstrated by manipulating five spectral lines with a spectral resolution of 0.12 nm and a temporal resolution of 17 ps. Better temporal resolution can be achieved by increasing the bandwidth through additional spectral lines.     

Generation of radially polarized light beams of high quality using a step-index optical fiber

We present an experimental setup to generate radially polarized beams without using high-cost optical elements. In the setup a four-segment polarization converter is used in front of the fiber to produce a pseudo radially polarized beam. A traditional step-index fiber which supports only LP₀₁ and LP₁₁ modes is then used as a mode-cleaning device. A commercial mechanical fiber-squeezer polarization controller is applied to produce adequate pressure and twist onto the fiber. The four-segment polarization converter and the fiber squeezer polarization controller are adjusted by turns for improving the beam quality in intensity and polarization. Additionally, several methods of characterizing the polarization properties of radially polarized beams are reviewed. One of the latest methods is applied for characterizing the polarization properties of the radially polarized beams produced by using our technique. The results show the highquality of the obtained beams.     

Experimental observation and analysis of novel pulse properties in erbium-doped fiber ring laser with normal cavity dispersion

We demonstrate the experimental observation of different operation states in erbium-doped fiber ring laser with normal cavity dispersion. The Q-switching, Q-switching mode-locking (QML), continuous wave mode-locking (CML), harmonic mode-locking (HML), double-pulse and multiple-pulse operation states can be manipulated by only adjusting the polarization controller with the same pump power. The output spectral bandwidth and pulse width of operation states are measured. The central wavelength dynamics of different operation states achieved by adjusting the polarization controller are also observed and analyzed. It is shown that pulse width, polarization, chirp and stability of different operation states are diverse by using nonlinear polarization rotation technique.     

Polarization controller for hollow-core fiber

We demonstrate a universal polarization controller for hollow-core fibers, a simple device consisting of three twisted fiber sections that makes use of the inherent birefringence of the air-core fiber. The device 5% bandwidth at 1550 nm is calculated from measured data to be approximately 13 nm.     

高重复频率全光纤被动锁模掺铒光纤激光器

报道了一种高重复频率全光纤非线性偏振旋转锁模掺铒光纤激光器, 获得了重复频率217 MHz的锁模脉冲输出. 该激光器使用一个偏振相关隔离器和一个偏振控制器即可获得稳定的锁模脉冲输出, 结构简单, 系统稳定. 激光器锁模脉冲的脉冲宽度为69 fs, 3 dB光谱宽度为56 nm, 射频频谱信噪比为76 dB.     

Highly Birefringent Photonic Crystal Fibers BUsing Asymmetric Core Design

We demonstrate a highly birefringent photonic crystal fiber by utilizing the asymmetric core design. Based on spectral measurements of the polarization mode interfering, we estimate that the fiber has a beat length of about 0.33 mm at 1545 nm.     

Switchable Multi-Wavelength Erbium-Doped Fiber Lasers based on a Mach-Zehnder Interferometer Using a Twin-Core Fiber

A switchable multi-wavelength erbium-doped fiber ring laser based on a compact in-fiber Mach-Zehnder interferometer comb filter at room temperature is presented. The comb filter is formed by splicing a section of twin-core fiber between two single mode fibers. By adjusting the states of the polarization controller appropriately, the laser can be made to operate in stable single-, dual- and three-wavelength lasing states. The operation principle is based on spectral hole burning induced by the saturated effect and polarization hole burning.     

Performance of a wavelength-tunable erbium-doped fiber laser using a Sagnac interferometer

We experimentally demonstrate a wavelength-tunable erbium-doped fiber laser that is composed of a ring cavity and a single-mode fiber Sagnac interferometer in a new and simple arrangement. We find that the fiber laser output wavelength is tunable by adjusting the filter effect of the Sagnac fiber loop through a fiber polarization controller set there. The quasi-single-wavelength continuously tunable laser outputs could be achieved within some wavelength range. The multi-wavelength laser outputs could also be observed under some appropriate settings of the polarization controller. A theoretical demonstration of the wavelength tunability about the transmission-type Sagnac loop filter has also been achieved using the Jones calculus theory.     

Comparison of pulse evolutions in low and ultra-large anomalous dispersion mode-locked fiber lasers

We have investigated and compared the pulse evolutions in low and ultra-large anomalous dispersion erbium-doped fiber lasers mode-locked by the nonlinear polarization rotation technique. Two lasers deliver the pulses that exhibit quite distinct characteristics such as pulse duration, spectral width, and spectral sidebands. Experimental observations show that the spectral width decreases from several nanometers to less than one nanometer whereas pulse duration extends about three times by changing the cavity dispersion from −0.03 to −15.50 ps². The solitons in ultra-large anomalous fiber laser show dips in the optical spectrum, which is quite distinct from that of conventional solitons observed in low anomalous regime.     

In-line polarization controller that uses a hollow optical fiber filled with a liquid crystal

We demonstrate an in-line polarization controller based on a hollow optical fiber filled with a nematic liquid crystal by fabricating thin-film electrodes on the cladding of a fiber. The polarization controller consists of three control sections with fixed optic axes, which operate as phase retarders. The phase retardation in each section is controlled by the magnitude of the applied electric field. The full wave retardation voltage of the polarization controller is approximately 85 V.     

基于野外测量研究植被冠层偏振光谱反射特性

植被冠层反射太阳光会产生部分偏振光,这为偏振遥感探测提供了信息源。利用地基平台开展野外偏振测量是非常重要的研究,它不仅能获取植被冠层本质的偏振反射特性,而且还可以与机载或者星载平台数据进行匹配;虽然研究者们已经通过机载或者星载偏振探测器获取了大量植被冠层的偏振反射信息,但是关于地面植被冠层偏振反射分布特性的研究却很少。因此,为了详细研究植被冠层的偏振反射特性,基于野外多角度高光谱偏振测量与偏振反射物理机制,分析了植被冠层偏振光谱特性及其偏振反射分布特性;随后,反演了两种偏振模型的参数,将测量值与模拟值进行对比分析。研究结果发现,植被冠层的偏振反射具有明显的各项异性特征,而且与波长之间存在微弱的关系;同时,偏振模型可以很好地模拟植被冠层的偏振反射信息,可以作为研究植被冠层的理论依据。该研究测量的偏振反射信息与模型计算值之间呈现良好的吻合性,既描述了植被冠层偏振反射分布特性,又证明模型的有效性和测量结果的准确性。对植被冠层偏振特性的详细研究,不仅有助于完整地解释植被冠层与电磁波之间的辐射响应特征,而且对于偏振遥感对地观测以及地表偏振信息对大气偏振信息的研究也具有重要科学价值。     

一种高速率、高精度的全光纤偏振控制方法

提出了一种结构简单、高速率、高精度的全光纤偏振控制方法, 并对方案进行了详细的理论分析. 理论和实验结果表明:本方案可以自动补偿光纤系统由于环境变化使光纤发生形变产生的额外双折射效应, 提高了系统的抗干扰能力. 实验获得了31 dB消光比, 此方案有望在实际中得到广泛应用. 关键词： 光纤偏振控制器 双折射效应 法拉第旋转镜     

Highly birefringent photonic crystal fibers

We report a strongly anisotropic photonic crystal fiber. Twofold rotational symmetry was introduced into a single-mode fiber structure by creation of a regular array of airholes of two sizes disposed about a pure-silica core. Based on spectral measurements of the polarization mode beating, we estimate that the fiber has a beat length of approximately 0.4 mm at a wavelength of 1540 nm, in good agreement with the results of modeling.     

宽带可调谐掺Yb3+双包层光纤激光器的研究

利用闪耀光栅构成可调谐Littrow外腔,对掺Yb³⁺双包层光纤激光器的波长调谐输出进行了实验研究.激光调谐输出波长范围70nm.针对光纤内的双折射效应对激光的输出功率的影响,实验中使用了在线光纤偏振控制器,从而有效地减小了调谐曲线的起伏及其与荧光谱的差别,并得到了窄线宽、线偏振、宽带调谐的激光输出.     

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.     

窄线宽高信噪比可调谐掺Er3+光纤激光器

基于偏振态调谐原理,利用多个偏振控制器在环形腔掺Er3+光纤激光器中实现了连续可调谐、窄线宽、高信噪比的单频激光输出.连续调谐宽度达22 nm (1538～1560 nm),3 dB谱线宽度小于0.1 nm,光信号-自发辐射噪音比大于45 dB,最大输出功率约1 mW.在10～50 mW泵浦功率范围内,输出功率波动幅度小于1 dB.在室温下,工作数十个小时,中心波长漂移小于0.05nm.     

Single-pixel polarimetric imaging spectrometer by compressive sensing

We present an optical system that performs polarimetric spectral imaging with a detector with no spatial resolution. This fact is possible by applying the theory of compressive sampling to the data acquired by a sensor composed of an analyzer followed by a commercial fiber spectrometer. The key element in the measurement process is a digital micromirror device, which sequentially generates a set of intensity light patterns to sample the object image. For different configurations of the analyzer, we obtain polarimetric images that provide information about the spatial distribution of light polarization at several spectral channels. Experimental results for colorful objects are presented in a spectral range that covers the visible spectrum and a part of the NIR range. The performance of the proposed technique is discussed in detail, and further improvements are suggested.