椭圆孔六角点阵聚合物光子晶体光纤的偏振特性研究

基于全矢量平面波方法,以聚甲基丙烯酸甲酯为基材,设计了一种高双折射光子晶体光纤,并对其传输性质和偏振特性进行了数值模拟。结果表明,椭圆孔六角点阵聚合物光子晶体光纤的双折射是由于包层的不对称性引起的全局双折射,通过调节椭圆率,发现该光纤可以以单模方式在一合适波段运行,该波段与聚合物光纤的低损耗通信窗口一致。并且在 时,其双折射最高可达 。该研究结果为高双折射聚合物光子晶体保偏光纤的制备提供了理论依据。     

Measurement of intermodal coupling in weakly multimode fibre optics

Using selective mode excitation via the cladding of an etched step-index weakly multimode fibre, and spatial mode separation at the output using a similarly etched section, intermodal coupling has been measured, mode-by-mode in the first seven guided modes of the fibre. Experimentally the observation has been made that most coupling terms remain less than -20 dB after 500 m of fibre.<>     

Leaky optical fibre for large mode area singlemode operation

A novel optical fibre structure is introduced for large mode area singlemode operation. The fibre consists of a cladding index profile that increases monotonically in the radial direction. It is shown that the fibre can introduce exceedingly high leakage losses to the high-order modes, while maintaining a low loss to the fundamental mode. Numerical results are presented for power-law index profiles.     

Investigation of Acoustooptic Mode Coupling on a Long-Period Fiber Grating

It is indicated theoretically that the cladding mode generated by a long-period fiber grating (LPFG) can be coupled further to another unsymmetrical cladding mode via acoustooptic effect. A novel technique to tune the transmission spectrum of an LPFG is proposed and demonstrated experimentally by applying an acoustic wave with proper frequency and intensity.     

High-sensitivity pressure sensor based on tilt fibre Bragg grating radial load effect

In this paper, a simple and novel optical fibre pressure sensor with tilt fibre Bragg grating is put forward. The radial compression and rebound on tilt fibre Bragg grating (TFBG) cause grating angle and length change, meanwhile, its cladding mode spectra decrease sharply. Some transmission spectrum characteristics, such as amplitude, extinction ratio value, wavelengths of cladding and Bragg modes, are extracted and analyzed. It shows that they are nearly linear with the radial pressure on surface of bare TFBG. Among them, the extinction ratio value with high sensitivity of 0.7 dB/N can keep consistent with pressure. The max amplitudes of some cladding mode resonance are good linear with radial press with sensitivity of 0.18 dB/N. The relation between each mode resonance wavelength shift and radial press on TFBG keeps good linearity with 0.8-pm/N sensitivity. By means of choosing tygon elastic pad material imposed on bare TFBG, the pressure sensitivity with amplitude of 0.21 dB/N and extinction ratio of 0.25 dB/N is obtained in order to use in practical engineering.     

Metal-assisted coupling to hollow-core photonic crystal fibres

Selective coupling to the fundamental mode of short hollow-core photonic bandgap fibres without exciting cladding modes is improved by gold-coated fibre end facets. Cladding modes are suppressed by 20-30 dB for single-and multimode fibre launch, respectively, while in-band power loss is 3-8 dB.     

Simultaneous measurement of strain and temperature using single tilted fibre Bragg grating

Tilted fibre Bragg grating (TFBG) with grating planes tilted at an angle of 3deg corresponding to the fibre axis shows core mode and a large number of cladding-mode resonances in its transmission. Discriminating temperature and strain simultaneously using a single tilted fibre Bragg grating is proposed and demonstrated experimentally. The wavelength shifts of the TFBG in response to temperature and strain are investigated. The results show that the cladding modes and core mode have different strain sensitivities while the temperature sensitivities are equal. So, it is possible to monitor the core-mode resonance and the cladding-mode resonances of the TFBG spectrum, allowing the separation of the temperature and strain induced wavelength shifts.     

积分法求解长周期光纤光栅透射谱研究

基于光纤光栅的模式耦合理论,用德拜势能法对纤芯、包层内的电磁场进行矢量分析,得到纤芯及各包层中的各矢量场分量的表达式,求解出纤芯和包层模的耦合常数和有效折射率后,利用数值积分的方法通过求解耦合模方程得到光纤光栅的透射率。积分法是一种较为精确的求解透射谱方法,为长周期光纤光栅的优化设计和其在光纤通信、光纤传感领域的高精度测量提供理论依据。     

Fused single mode fibre access couplers

Single mode fibre access couplers have been fabricated by chemically etching most of the glass cladding material surrounding the fibre core, and thermally fusing the fibres together in the etched region. The resulting couplers have low loss and are both durable and insensitive to ambient temperature variations.     

Generation of high-repetition-rate optical pulse using cascaded long-period fibre gratings

The generation of high-repetition-rate optical pulses using cascaded long-period fibre gratings is proposed. The pulse multiplication is realised by exploiting the difference in the propagation constant of the core and a cladding mode in a standard singlemode fibre. Two, four and eight times pulse multiplication have been successfully implemented with a minimum repetition period of 2.4 ps.     

Towards high-index glass based monomode holey fibre with large mode area

A high-index (n=1.80) glass based holey fibre was fabricated. The conventional capillary-stacking technique was used to make this fibre characterised by a complicated microstructured cladding. Monomode guidance was observed at 800 nm in this fibre and the effective mode area A/sub eff/ was measured as /spl sim/40 /spl mu/m/sup 2/.     

积分法求解长周期光纤光栅透射谱研究

基于光纤光栅的模式耦合理论,用德拜势能法对纤芯、包层内的电磁场进行矢量分析,得到纤芯及各包层中的各矢量场分量的表达式,求解出纤芯和包层模的耦合常数和有效折射率后,利用数值积分的方法通过求解耦合模方程得到光纤光栅的透射率。积分法是一种较为精确的求解透射谱方法,为长周期光纤光栅的优化设计和其在光纤通信、光纤传感领域的高精度测量提供理论依据。     

Stress birefringence in single-mode fibres

The core and cladding of a glass fibre exposed to axial tension become optically uniaxial. The modified characteristic equation is presented and, for the fundamental mode, the changes in the most important propagation parameters have been calculated.     

中短波HgCdTe金属接触的退火研究

为制备良好的碲镉汞金属接触,研究了热退火处理对中短波Hg空位掺杂碲镉汞金属接触的影响。对中短波HgCdTe-Sn/Au接触及中波HgCdTe-Cr/Au接触经不同条件退火后的接触进行了测量。对于短波碲镉汞,p型HgCdTe-Sn/Au接触经95 ℃,30 min退火可降低比接触电阻2个量级,而经125 ℃,30 min退火可降低3个量级;离子注入的n型HgCdTe-Sn/Au接触则容易形成欧姆接触。对于中波碲镉汞,退火前p型HgCdTe-Sn/Au接触平均比接触电阻为10-1 Ωcm2量级,经适当条件退火可以降低3个量级;此外,Sn/Au比Cr/Au更适合作为中波HgCdTe的接触金属。因而HgCdTe金属接触可通过一定退火处理得到改善。     

Design criterion for low-loss optical coupler tapers

A criterion for the local taper angle of a low-loss single-mode fibre coupler is established by considering the dominant mode coupling in the coupler taper. Effects due to structure parameters, such as cladding/core thickness ratio, corecladding index difference and core separation, are investigated. It is found that the criterion for the coupler taper can be well approximated by that for the single-mode fibre taper with the same structure parameters.     

Two kinds of tension in fiber Bragg gratings with cladding etched as the sinusoidal function

A new grating structure with cladding etched as the sinusoidal function along the length direction is introduced. The cladding area of the grating varies as the sinusoidal function along fiber axes. The coupled mode theory is used to analyze its performance. Compared with the linearly chirped grating, the new structure exhibits an ideal box spectrum with steep edges when the tension is applied on the gratings in two different ways. For the type B grating, without tension after writing, it has a ...     

The influence of a fibre structure on optical loss in a graded-index fibre

For designing a fibre structure, the influence of structural parameters on optical loss is investigated experimentally for a graded-index fibre. The fibre with large cladding/outer-layer index difference and small cladding thickness is found to have large excess loss near excitation points, such as a launching point and a splicing point.     

大空气孔微结构光纤光栅反射谱分析

采用有限元方法和耦合模理论,分析了圆型大空气孔微结构光纤Bragg光栅的光谱特性,并进行了数值计算.结果表明,随纤芯半径的增大,此类光纤光栅纤芯模式和包层模式的谐振蜂向长波长方向漂移.随包层空气孔半径的增大,包层谐振峰向长波方向漂移,并逐渐趋于稳定值.随包层空气孔中填充材料折射率的增大,纤芯模式谐振峰中心波长不变,而第...     

基于倾斜光纤光栅的温度不敏感振动传感器

提出了一种基于倾斜光纤光栅与多模光纤相结合的温度不敏感振动传感器,其振动传感头是在倾斜光纤光栅与单模光纤之间加入一小段多模光纤所组成。倾斜光纤光栅的反射光谱有布拉格模和包层模两部分组成,其中多模光纤的作用是将倾斜光纤光栅反射包层模耦合到单模光纤的基模。倾斜光纤光栅包层模对外界振动很敏感,通过传感器的包层模平均输出功率完成对外界振动物理量测量。由于采用强度解调的方式,可以大大降低传感器装置的复杂性。实验表明：当传感器温度从20 ℃上升到70 ℃时,传感器的输出平均光功率均方根误差为0.01 μW,其反射光谱平均输出功率影响很小,故可以避免外界温度对测量结果的影响。     

Cladding-surrounding interface insensitive long-period grating

A long period grating is presented, the resonant peak of which is not sensitive to the interface between the cladding and the surrounding media of a fibre. The spectral behaviour of the resonant peak is investigated using index matching oils and mechanical scratching on the cladding surface of the fibre.