光栅参数对线性啁啾光纤光栅偏振特性的影响

研究了单模线性啁啾光纤光栅的偏振相关损耗特性。运用耦合模理论和传输矩阵分析法推出了反射光的偏振相关损耗,并模拟了光栅的反射谱和偏振相关损耗随光栅参数和双折射量的变化曲线。模拟显示双折射值的变化对啁啾光栅偏振相关损耗的影响非常显著, 尤其是在带边比较陡峭时。啁啾光栅的偏振相关损耗也受光栅的啁啾系数和调制深度的影响。这表明线性啁啾光栅的偏振相关损耗不光依赖光栅双折射量,还依赖其啁啾系数等其他参数。实验结果与理论模拟基本吻合。     

光栅致双折射引起偏振相关损耗的理论分析

应用耦合模理论,给出均匀布拉格光纤光栅在考虑光栅致双折射时的透射与反射系数的解析式,按照测量偏振相关损耗(PDL)的确定性与非确定性两种方法,推导出了均匀布拉格光纤光栅中偏振相关损耗的解析公式。理论分析表明,该公式能够准确分析弱双折射光纤或者各向同性光纤上写入的均匀布拉格光纤光栅的偏振相关损耗特性,同时数值模拟高双折射光纤上写入的均匀布拉格光纤光栅偏振相关损耗特性,得到的结果也与已有实验曲线相近。     

Relationship Between Chromatic Dispersion and Differential Group Delay in Weakly Birefringent Fiber Gratings

The presence of weak birefringence in fiber gratings slightly affects their amplitude response. In this case, we report that the wavelength dependencies of chromatic dispersion and differential group delay (DGD) are linked by the birefringence value. This relationship is used to analyze the grating DGD and exploited to get the grating birefringence. Experimental results are finally reported in good agreement with the theory.     

Sensing circular birefringence by polarization-dependent parameters in fiber Bragg gratings and the influence of linear birefringence

In this paper, we focus on the transmission and polarization properties of fiber Bragg grating (FBG) with magnetically induced circular birefringence. The evolutions with wavelength of transmission spectrum and the third Stokes parameter for different circular birefringence values are analyzed by implementing the Jones formalism. We demonstrate that the evolutions of polarization dependent parameters contain the information about the amount of circular birefringence. The influences of linear birefringence on these evolutions are analyzed for further practical research. The results show that for typical intrinsic linear birefringence values in FBG the influences are tolerable, while for lager linear birefringence values it maybe overwhelm the circular birefringence effect.     

Tunable PDL of twisted-tilted fiber gratings

We fabricated highly tilted fiber gratings and demonstrated that the broad-band polarization-dependent loss (PDL) of the gratings may be tuned by twisting the fiber along the length of the grating. We show that the PDL for a given twist angle can be determined from a simple Jones matrix calculation which can also take into account birefringence on the PDL axis. We combine the twisted-tilted grating with a polarization controller to form a PDL compensator and use it to minimize the polarization-dependent responsivity of a nonlinear silicon avalanche photodiode.     

光纤光栅偏振模色散的研究

分析了光纤光栅 (FBG)偏振模色散 (PMD)产生的原因 :写入光栅用的光敏光纤对紫外光吸收是不均匀的 ,呈指数型吸收。建立了光栅偏振模色散的模型 ,利用建立的模型计算了不同折射率调制的偏振模色散 ,计算的结果与用偏振模色散分析仪测得的结果符合得很好。理论和实验说明了光栅色散对偏振模色散的影响 :光纤光栅的色散增大 ,光栅的偏振模色散也增大。     

Transverse Strain Measurements Using the Birefringence Effect in Fiber Bragg Gratings

Birefringence in fiber Bragg gratings (FBGs) leads to polarization-dependent properties such as polarization-dependent loss (PDL). Although this property is not desired for telecommunications applications, we demonstrate that the PDL generated by uniform FBGs written into standard single-mode fiber can be advantageously used for transverse strain measurements, which is not directly possible through amplitude spectral measurements.     

High total dose radiation effects on temperature sensing fiberBragg gratings

Fiber Bragg gratings (FBGs) written in a 10 mol.% Ge-doped core silica fiber using a phase mask were exposed to γ-radiation. The transmission and reflection spectra were recorded during irradiation up to doses in excess of 1 MGy. There was no detectable change of the Bragg peak amplitude and the grating temperature sensitivity. The radiation-induced shift of the Bragg wavelength saturated at a dose of 0.1 MGy at a level less than 25 pm, which could still be decreased by optimization of the grating parameters. Our results confirm that FBGs are good candidates for sensing applications in radiation environments     

光栅参数对折射率剖面非均匀取样光纤光栅的影响

利用传输矩阵法,数值分析了光栅参数对折射率剖面非均匀的均匀光纤光栅及取样光纤光栅的透射谱、偏振关系损耗和偏振模色散的影响。计算结果表明,均匀光纤光栅的光栅条纹可见度及光栅周期对其偏振关系损耗和偏振模色散影响很大;改变取样光纤光栅的取样周期及光栅段长度,透射谐振峰的幅度、偏振关系损耗和偏振模色散的最大值均随取样光纤光栅长度的增加而递增。与靠近中心波长的谐振峰相比,折射率剖面非均匀导致的双折射对取样光纤光栅远离中心波长的谐振峰的影响较小。     

对40 Gb/s OTDM系统中光纤光栅色散补偿器进行偏振模色散补偿的研究

改变光纤光栅紫外曝光系统 ,在相位掩模板后插入一个旋转装置 ,使得光纤在制作过程中可以进行某种旋转。通过这种方法制作的光纤光栅偏振模色散减小到平均差分群时延 (DGD)约为 0 2ps,而没加旋转制作的光纤光栅平均DGD约为 18 2 ps。采用两个这种低偏振模色散 (PMD)的光纤布拉格光栅 (FBG) ,成功地在 4 0Gb/s光时分复用 (OTDM)系统中补偿了约 2 0 4 0 ps的色散 ,该系统在经过 12 2km普通单模光纤传输后 ,未发现PMD的影响 ,传输功率代价小于 1 4dB。     

UV-Inscribed Optical Fiber Gratings in Mid-IR Range and Their Laser Applications

We have UV-inscribed fiber Bragg gratings (FBGs), long-period gratings (LPGs), and tilted fiber gratings (TFGs) into mid-IR 2m range using three common optical fiber grating fabrication techniques (two-beam holographic, phase mask, and point-by-point). The fabricated FBGs have been evaluated for thermal and strain response. It has been revealed that the FBG devices with responses in mid-IR range are much more sensitive to temperature than that in near-IR range. To explore the unique cladding mode coupling function, we have investigated the thermal and refractive index sensitivities of LPGs and identified that the coupled cladding modes in mid-IR range are also much more sensitive to temperature and surrounding medium refractive index change. The 45 tilted fiber gratings (45-TFGs) as polarizing devices in mid-IR have been investigated for their polarization extinction characteristics. As efficient reflection filters and in-cavity polarizers, the mid-IR FBGs and 45-TFGs have been employed in fiber laser cavity to realize multi-wavelength 2 m Tm-doped CW and mode locked fiber lasers, respectively.     

Effect of the Fiber Coating on the Radiation Sensitivity of Type I FBGs

We have studied the influence of the fiber coating on the radiation sensitivity of fiber Bragg gratings (FBGs). These FBGs are draw tower gratings written before applying the coating in a fiber with a photosensitive 18-mol.% GeO$_{2}$-doped core. Using a Co$^{60}$ source we irradiated polyimide, acrylate, and ormocer coated gratings as well as mechanically stripped ormocer coated FBGs up to a 40-kGy dose. This total dose level corresponds to a near-earth space radiation environment mission. We show that the coating type must be taken into account for correctly interpreting ionizing radiation effects on FBGs.      

Narrow-depressed cladding fiber design for minimization of claddingmode losses in azimuthally asymmetric fiber Bragg gratings

The cladding and radiation mode loss characteristics of photo-induced gratings written in fibers with a narrow-depressed inner cladding are compared to the properties of gratings written in matched clad, photosensitive clad, and wide-depressed cladding fibers under varying grating azimuthal asymmetry conditions. Fibers with narrow-depressed claddings are found to have lower cladding mode losses for small degrees of asymmetry than previously proposed fiber designs for cladding-mode reduction     

Polarization mode dispersion in spun fibers with different linearbirefringence and spinning parameters

This paper shows how the initial linear birefringence determines the necessary spinning parameters to produce spun fiber with optimum differential group delay (DGD) and polarization mode dispersion (PMD) properties. DGD measurements are reported on two pairs of fibers, each pair having been fabricated from a particular fiber preform. The fiber pairs each consist of a sample of spun and unspun fiber. These measurements are then compared with theoretical simulations for each fiber to determine the required range of spinning parameters for a given initial linear birefringence. These results should help in optimizing the spinning parameters for producing high-performance spun fibers     

Effect of PDL on the DOP feedback signal in PMD compensation

The impact of polarization dependence loss (PDL) on the degree of polarization (DOP) feedback signal in polarization mode dispersion (PMD) compensation is analyzed. PDL affects DOP only in the presence of PMD, and in the presence of PMD and PDL, DOP relates not only to both PMD and PDL vectors but also to the principal states of polarization (SOPs) components of the output signal; on the other hand, it adds new frequency dependence and is no longer independent of system bit rate. The PDL minimum endangering PMD compensation is determined by the step size of the PMD compensating algorithm and the differential group delay (DGD) value in optical fiber systems. DOP could no longer act as the feedback signal in PMD compensation unless the PDL in the fiber system has been effectively eliminated before PMD compensation.