Tunable Er3+-doped fiber amplifiers covering S and C+L bands over 1490-1610 nm based on discrete fundamental-mode cutoff filters

We demonstrate thermo-optically tunable Er3+-doped fiber amplifiers covering S and C+L bands (1490-1610 nm) using fundamental-mode cutoff filters discretely located in a 17.5 m long standard Er3+-doped fiber. The material dispersion and waveguide structure of the tapered fibers are locally modified to produce high-cutoff-efficiency filters that make the unwanted amplified spontaneous emission highly attenuated at the longer wavelengths, and the optical gain is thus moved toward the shorter wavelengths. The maximal signal gains are measured to be 18.92, 37.18, and 15.19 dB with 980 nm pump power of 135 mW in the S, C, and L bands, respectively.     

中心下陷的负色散光纤

利用非等温等离子体化学气相沉积成功制得了具有折射率中心下陷的负色散光纤 (RDF)。该光纤在保持较好的抗弯曲性能与偏振模色散的同时 ,有效面积达到 4 5 μm2 ,且在 15 5 0nm处的色散为 - 19.6 5ps/(nm·km) ,色散斜率为 - 0 .132ps/(nm2 ·km)。此外 ,通过优化光纤纤芯各层的掺杂原子浓度 ,在 15 30nm处光纤的氢损降到了0 .0 1dB/km。由负色散光纤与具有超大有效面积的非零色散位移光纤 (ULAF)组成的色散管理光纤对在 15 30nm到16 2 5nm波长范围内的色散斜率小于 0 .0 0 6ps/(nm2 ·km) ,且最大色散值小于 0 .2ps/(nm·km)。同时 ,15 5 0nm波长处的衰耗为 0 .2 2 4dB/km ,且在 15 30nm到 16 2 5nm波段范围内衰耗较为平坦。该色散管理光纤对可以在无需色散补偿模块的前提下应用于大容量高速率的长距离波分复用 (WDM)系统。     

Large negative dispersion in dual-concentric-core photonic crystal fiber with hybrid cladding structure based on complete leaky mode coupling

Considering the optical stability of solution, the sugar-solution is infused into the outer core ring of dual-concentric-core photonic crystal fiber (DCCPCF). The influences of structure parameters and solution concentration on the phase and loss matching are comprehensively analyzed. By choosing the appropriate outer core mode to completely couple with the inner core fundamental mode, the large negative dispersion PCF around 1.55 μm is designed, which has the dispersion value of − 39,500 ps/km/nm as well as bandwidth of 7.4 nm and effective mode area of 28.3 μm². The designed PCF with hybrid cladding structure can effectively compensate the positive dispersion of conventional single mode fiber, and suppress the system perturbation caused by a series of nonlinear effects. Considering the mode field mismatching between the DCCPCF and the tapered fiber, the calculated connection loss around 1.55 μm is below 3 dB. In addition, the equivalent propagation constants of two leaky modes are deduced from the coupled-mode theory, and the complete mode coupling case can be well predicted by comparing the real and imaginary parts of propagation constants.     

双波长抽运拉锥光子晶体光纤产生超连续谱研究

利用1064 nm抽运光在总长度为1 m的光子晶体光纤(PCF)的前半段(77 cm)通过四波混频产生747 nm短波信号光,并对光纤的后半段进行拉锥处理,拉锥光纤具有707 nm和1177 nm两个零色散点(ZDW).利用1064 nm抽运光和产生的747 nm信号光共同在两个零色散点之间的反常色散区抽运拉锥光子晶体...     

Fabrication of tapered fiber based ring resonator

Tapered fiber based ring resonators are fabricated and its optical characteristic is investigated in detail. The ring resonator is fabricated by coiling the tapered fiber, which is firstly made by heating and stretching a piece of optical fiber, after the polymer protective cladding has been removed The comb filter with a constant free spectral range (FSR) and the maximum extinction ratio of 4.2 dB is achieved by a single-mode fiber based ring resonator. The FSR of ring resonator can be adjusted by controlling the diameter of the ring. The extinction ratio is improved in the polarization maintaining fiber based ring resonator where the maximum extinction ratio of 14 dB is achieved at 1531 nm region.     

大容量长距离传输用低非线性效应非零色散位移光纤

利用非等温等离子体化学气相沉积 (PCVD)工艺制备了一种适合于大容量高速率长途干线网与城域网的中芯下陷型纤芯结构非零色散位移光纤。该光纤的有效面积大于 95 μm2 ,在 15 5 0nm波段的色散值约为9ps/(nm·km) ,有效的抑制了传输过程中光非线性效应的产生。通过对光纤剖面结构的优化设计 ,光纤的 15 5 0nm处的传输损耗降到约 0 .2 1dB/km ,与传统单模光纤的熔接损耗低于 0 .11dB ,且在直径为 6 0mm圆筒上绕 10 0圈后在 14 6 0nm到 16 2 5nm波长范围所引起的附加弯曲损耗均低于 0 .0 2dB/km。同时 ,该光纤色散斜率低于0 .0 6 5 ps/(nm2 ·km) ,偏振模色散 (PMD)小于 0 .0 5 ps·km-1/2 。此外 ,由于光纤的零色散点移到了 14 30nm以下 ,使波分复用 (WDM)传输在S波段 (14 6 0～ 15 30nm)、C波段 (15 30～ 15 6 5nm)、L(15 6 5～ 16 2 5nm)波段上都兼容。     

A High Efficiency Yb3+-doped Fiber Ring Cavity Laser with Narrow Line-widthRound-trip Dispersion Calculation for Martinez Pulse Stretcher

A novel Yb3+-doped fiber ring cavity laser pumped by a 977 nm laser diode is presented with its output laser wavelength of 1060 nm. Based on a fiber Bragg grating (FBG), the laser exhibits 0.20 nm line-width, 7.5 mW laser output power, 40 dB signal-to-noise ratio (SNR) and 66% slope efficiency.This paper proposed a ray-tracing model for the Martinez stretcher, derived the calculation formulae for the stretcher of a grating-spherical mirror system and discussed the error for the total dispersion resulted from the spatial dispersion. The calculated results show that the error could be ignored for the beam returned to the stretcher for the second pass in the wavelength range of 750 nm and 850 nm.     

Study of mode propagation with 632.8-nm laser in tapered fiber

The material dispersion of a tapered fiber is described by Sellmeier＇s equation. The dependence of refractive index on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of 632.8 nm is used in the experiment. When the cutoff frequency of the fiber is less than the laser frequency, the guiding modes of a singl~-mode fiber （at 1550 am） are investigated. The results show that the original single-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light in the taper region are analyzed. By controlling the taper end size of the fiber, the unique tapered fiber can convert a multi-mode beam into a single-mode one.     

高斜率效率L波段宽带可调谐光纤环形腔激光器

利用环形腔结构在L波段获得了43nm(1567.1nm-1610.1nm）范围的宽带连续可调谐激光输出。由于同时采用了高浓度掺铒光纤和1480nm激光二极管（LD）抽运源，极大地降低了激光器的抽运阈值，提高了斜率效率和输出功率。在整个可调范围内，激光器的输出功率达10．9dBm-12.1dBm(95mW抽运），信噪比高于60dB，在1585nm的斜率效率为0．201。     

All-fiber Yb:fiber frequency comb

We demonstrate an all-fiber Yb:fiber frequency comb with a nonlinear-amplifying-loop-mirror-based Yb:fiber laser oscillator. The fiber-spliced hollow-core photonic bandgap fiber was used as dispersion compensator, which was also directly spliced to a piece of tapered photonic crystal fiber for an octave-spanning spectrum. The spectrum of the compressed 107 fs laser pulses was broadened, covering 600 nm to 1300 nm in a high-nonlinearity tapered fiber for f to 2 f beating. The signal-to-noise ratio of offset frequency was measured to be 22 dB.     

飞秒泵浦不同锥长微结构光纤超连续谱的产生

对飞秒脉冲泵浦下,不同锥长及锥腰直径的微结构光纤的超连续谱产生进行了实验研究。采用“快速低温拉锥方法”,在保持d/Λ不变的情况下,对实验室自制的空气孔间距Λ=6.53 μm,归一化孔径d/Λ=0.79的微结构光纤进行了拉锥,分别得到6,8,10 mm等不同锥长微结构光纤。理论计算表明,随着锥长变长,锥腰直径变小,锥腰处零色散波长向短波移动：未拉锥及6,8和10 mm锥微结构光纤锥腰处零色散波长分别为1 129,885,806和637 nm。利用中心波长为810 nm,重复频率76 MHz,脉宽120 fs的钛蓝宝石飞秒激光器对拉锥后微结构光纤进行了实验研究：锥长为6 mm时,泵浦光中心波长位于整根光纤的正常色散区,锥腰的零色散点附近,内脉冲拉曼散射和级联四波混频是光谱初始展宽的主要因素。泵浦功率达到450 mW时,在可见波段390～461 nm及红外波段1 134～1 512 nm形成-5 dB的平坦宽带连续光谱。泵浦功率达到500 mW时,出现366～2 450 nm覆盖紫外、可见、近红外、中红外的超连续谱,其光谱红蓝移边缘已经接近实验用微结构光纤的传输带宽。锥长为8 mm、泵浦功率为450 mW时,在群速度匹配和群加速度失配的共同影响下,连续谱蓝移边缘达到366 nm,比6 mm锥时蓝移9 nm;锥长为10 mm时,由于锥腰处零色散点移动到可见光区域,可见区光谱仍能满足相位匹配条件。通过级联四波混频效应,在可见区域实现了频率上转换及光谱蓝移。泵浦光功率达到500 mW时,在382～412 nm得到谱宽仅为30 nm,转换效率达到27.7%的频率上转换。     

Anomalous dispersion in a solid, silica-based fiber

We demonstrate an all-solid (nonholey), silica-based fiber with anomalous dispersion at wavelengths where silica material dispersion is negative. This is achieved by exploiting the enhanced dispersion engineering capabilities of higher-order modes in a fiber, yielding + 60 ps/nm km dispersion at 1080 nm. By coupling to the desired higher-order mode with low-loss in-fiber gratings, we realize a 5 m long fiber module with a 300 fs/nm dispersion that yields a 1 dB bandwidth of 51 nm with an insertion loss of approximately 0.1 dB at the center wavelength of 1080 nm. We demonstrate its functionality as a critical enabler for an all-fiber, Yb-based, mode-locked femtosecond ring laser.     

Octave-spanning supercontinuum generation of vortices in an As2S3 ring photonic crystal fiber

We propose As(2)S(3) ring photonic crystal fiber (PCF) for supercontinuum generation of optical vortex modes. Due to the large material index contrast between As(2)S(3) and air holes in the designed ring PCF, there is a two-orders-of-magnitude improvement of the difference between the effective refractive indices of different vortex modes compared with regular ring fiber. The design freedom of PCFs enables a low dispersion (<60 ps/nm/km variation in total) over a 522 nm optical bandwidth. Moreover, the vortex mode has a large nonlinear coefficient of 11.7/W/m at 1550 nm with a small confinement loss of <0.03 dB/m up to 2000 nm. An octave-spanning supercontinuum spectrum of the vortex mode is generated from 1196 to 2418 nm at -20 dB by launching a 120 fs pulse with a 60 W peak power at 1710 nm into a 1 cm long As(2)S(3) ring PCF.     

Defect and lattice structure for air-silica index-guiding holey fibers

We propose new design parameters for index-guiding holey fiber that can provide flexibility in defect and lattice design and adiabatic mode transformation capability. The new defect consists of a central air hole and a germanosilicate ring surrounding it, which results in a large-area annulus mode profile, low splice losses to standard fiber, 0.7 dB at 1.55 microm, and chromatic dispersion with a low slope, 0.002 ps/km nm2.     

High-order mode based dispersion compensating modules using spatial mode conversion

High-Order Mode Dispersion Compensating Modules (HOM-DCM) using spatial optical transformations for mode conversion are reviewed. It is shown that mode transformers using this technology can be designed to transform the LP₀₁ mode of SMF fibers to the LP₀₂ mode of specially designed dispersion compensating High-Order Mode Fiber (HOMF), with typical insertion loss of ∼1 dB, and typical extinction ratio to other modes less than -20 dB. The HOMF itself can provide high negative dispersion [typically in the range of 400-600 ps/(nm km)], and high negative dispersion slope, allowing efficient compensation of all types of transmission fiber. Combining two mode transformers with HOMF and possibly trim fiber for fine-tuning, results, for example, in a HOM-DCM that compensates 100 km LEAF? fiber, with Insertion loss < 3.5 dB, and Multi-Path Interference (MPI) < -36 dB. MPI phenomena in HOM-DCMs is characterized, and shown to comprise both coherent and incoherent parts, and to result from both the mode transformers and fiber coupling within the HOMF. MPI values of < -36 dB have been shown to allow error free transmission of 10 Gb/s signals over up to 6000 km. Finally, a number of applications well suited to the properties of HOM-DCMs are reviewed.     

A High Efficiency Yb3+-doped Fiber Ring Cavity Laser with Narrow Line-width

A novel Yb3+-doped fiber ring cavity laser pumped by a 977 nm laser diode is presented with its output laser wavelength of 1060 nm. Based on a fiber Bragg grating (FBG), the laser exhibits 0.20 nm line-width, 7.5 mW laser output power, 40 dB signal-to-noise ratio (SNR) and 66% slope efficiency.     

矩形晶格高偏振、低损耗铋锗镓光子晶体光纤的结构设计及性能分析

非对称结构光子晶体光纤应用广泛。其良好的偏振特性、灵活的色散调控能力以及低限制损耗品质,对于优化与改善偏振光纤器件、非线性光学光纤、光通信光纤、光纤传感器等性能发挥着关键的作用。选用高折射率铋锗镓激光玻璃为材料,设计了八边形阵列、矩形晶格排列的光子晶体光纤,纤芯缺陷区包层及外包层均为圆形空气孔。模拟实验数据显示,结构参数为M=0.5,0.6时,在波长为1.55 μm处的双折射系数分别为1.16×10⁻²和1.33×10⁻²;在近红外波段短波区,矩形晶格结构光子晶体光纤的色散范围分别在±30 ps·nm⁻¹·km⁻¹之间及−18～32 ps·nm⁻¹·km⁻¹之间。色散斜率较低,曲线具有零色散点,展现了良好的连续谱调控能力;在1.00～1.90 μm波段内,当M=0.5,0.6时,光纤限制损耗稳定在10⁻⁷～10⁻⁹ dB·km⁻¹之间;在1.55 μm处,限制损耗测量值分别为2.32×10⁻⁷和1.62×10⁻⁸ dB·km⁻¹。     

A High Efficiency Yb~(3 )-doped Fiber Ring Cavity Laser with Narrow Line-width

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Mode-locked all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator

Active mode-locking of long-cavity all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator (AOM) is reported. The proposed AOM combines the advantages of intermodal coupling induced by standing flexural acoustic waves in a double-ended tapered fiber. We focus our attention on the effects of large tapered transitions to improve the bandwidth modulation. Our approach permits the implementation of broad modulation bandwidth (13 nm), high modulation depth (50 %), and low optical loss (1.1 dB) in an 80-μm configuration. The effects of the AOM in the laser performance are also investigated. Transform-limit optical pulses of 25 ps temporal width and 2.7 W peak power were obtained at 2.46 MHz repetition rate.     

一种新型混合双包层光子晶体光纤的色散特性研究

以多极法理论为基础,设计了一种混合双包层结构的光子晶体光纤.通过改变其五层空气孔的四个结构参数（内层空气孔直径、外层空气孔直径、六边形孔间距和八边形孔间距）,理论上实现了色散绝对值在144—20 μm的波段内变化仅为125 ps·km^-1·nm^-1的平坦色散特性.在此情况下对其损耗进行了数值模拟,使所设计的光纤在144—20 μm的宽波段范围内具有小于0005 dB/km的低限制损耗特性. 关键词： 光子晶体光纤 多极法 平坦色散 限制损耗