Tunable and switchable all-fiber comb filter using a PBS-based two-stage cascaded Mach-Zehnder interferometer

We propose and demonstrate a novel tunable and switchable all-fiber comb filter by employing a polarization beam splitter (PBS)-based two-stage cascaded Mach-Zehnder (M-Z) interferometer. The proposed comb filter consists of a rotatable polarizer, a fiber PBS, a non-3-dB coupler and a 3-dB coupler. By simply adjusting the polarization state of the input light, the dual-function of channel spacing tunable and wavelength switchable (interleaving) operations can be efficiently obtained. The theoretical analysis is verified by the experimental results. A comb filter with both the channel spacing tunable from 0.18 nm to 0.36 nm and the wavelength switchable functions is experimentally demonstrated.     

The formation model of Ni-Cr oxides on NiCoCrAlY-sprayed coating

The atomic arrangement and distribution of oxides (Cr₂O₃, NiCr₂O₄ and NiO) on the sprayed-NiCoCrAlY coating after oxidation are analyzed. The formation and the growth model of Ni-Cr oxide phases are discussed according to the matching relationship between atoms. The outline character and a scale of spinel NiCr₂O₄ are discussed. The results show that Cr atoms can form two close-packed arrangements in the crystal plane of Cr₂O₃ perpendicular to 〈0 0 1〉 orientation. The atomic spacing in the first arrangement corresponds to double that of Ni/Ni₃Al in {1 1 1} crystal face. This suggests that Ni/Ni₃Al is the substrate for Cr₂O₃ to grow along 〈0 0 1〉 direction. The lattice mismatch between Cr₂O₃ and Ni/Ni₃Al is less than that of Al₂O₃, which indicates that Cr₂O₃ is easier to form than Al₂O₃ during the oxidation process. The atomic spacing in another close-packed arrangement of Cr₂O₃ perpendicular to 〈0 0 1〉 orientation is approximately equal to that of Ni or Cr in the plane of NiCr₂O₄ and NiO perpendicular to 〈1 1 1〉 orientation. So Cr₂O₃ can be the substrate for NiCr₂O₄ and NiO to grow in the 〈0 0 1〉 direction. NiCr₂O₄ and NiO can grow directly along the 〈1 1 1〉 orientation on each other. NiCr₂O₄ can grow outward in the planes of Cr₂O₃ perpendicular to 〈0 0 1〉 and grow inward along 〈1 1 1〉 orientation of NiO.     

Entanglement spectrum and block eigenvalue spacing distribution of correlated electron states

Entanglement spectrum of finite-size correlated electron systems are investigated using the Gutzwiller projection technique. The product of largest eigenvalue and rank of the block reduced density matrix, which is a measure of distance of the state from the maximally entangled state of the corresponding rank, is seen to characterise the insulator to metal crossover in the state. The fraction of distinct eigenvalues exhibits a ‘chaotic’ behaviour in the crossover region, and it shows a ‘integrable’ behaviour at both insulating and metallic ends. The integrated entanglement spectrum obeys conformal field theory (CFT) prediction at the metal and insulator ends, but shows a noticeable deviation from CFT prediction in the crossover regime, thus it can also track a metal–insulator crossover. A modification of the CFT result for the entanglement spectrum for finite size is proposed which holds in the crossover regime also. The adjacent level spacing distribution of unfolded non-zero eigenvalues for intermediate values of Gutzwiller projection parameter g$g$ is the same as that of an ensemble of random matrices obtained by replacing each block of reduced density matrix by a random real symmetric Toeplitz matrix. It is strongly peaked at zero, with an exponential tail proportional to e^−(n/R)s$e^{-(n/R)s}$, where s$s$ is the adjacent level spacing, n$n$ is number of distinct eigenvalues and R$R$ is the rank of the reduced density matrix.     

激光陀螺谐振腔横模特征的测量与分析

为了判定被测激光的模式特征,基于激光的频率特性,提出了一种测量激光陀螺谐振腔横模特征的方法.利用F-P扫描干涉仪,可以实时在线测量激光模式分布特性,该方法以已知F-P扫描干涉仪的频率间隔和扫频速度为比例尺,将难以测量的横模频率间隔转化为易于测量的时间间隔,通过测量从扫描干涉仪给出的谱图,计算出不同横模的频率间隔与纵模间隔的比例系数,并与该陀螺的理论比例系数进行比较,从而实现对激光陀螺谐振腔横模特征的精确判定.通过对某型环形激光谐振腔的测量实验,得到了该陀螺模式特征随着工作电流大小变化的规律:随着放电电流的增加,激光陀螺腔内所振荡的横模由单一的基模逐渐转变为基模和高阶模的混合模,并准确地判定出该谐振腔横模特征,其测量结果与理论结果误差小于2%.利用该方法横模频率间隔测量准确度可达1 MHz,重复性可达0.4 MHz.     

Atomistic simulation study on twin orientation and spacing distribution effects on nanotwinned Cu films

Affected by twin orientation and spacing distribution, different deformation and failure mechanisms of nanotwinned (NT) Cu films are discovered. For films with the same twin spacing, transition from brittle to ductile and ductile to localized necking with the increase of the slanted angle of twin boundary (TB) from 0° to 90° is examined. Two dominant slip mechanisms: (1) slip intersecting with the TBs; (2) slip parallel to the TBs can uncover the transition mechanisms with consideration of twin orientation. To maintain both relatively high strength and good ductility, the slanted angle can be set close to the ductile to localized necking transition border. Besides, the stress–strain curves obtained in this article show that the mechanical responses on both sides of the turning point 45° are asymmetric. On the other hand, the twin spacing distributions affect the ductility of NT Cu films and have almost no contribution to strengthening. The strength of the NT Cu films mainly depends on the twin density. NT Cu films with different twin spacing have worse ductility than equal twin spacing films due to the local twin spacing asymmetry. The failures can be predicted appearing at TBs adjacent to large twin spacing regions, and the failure propagation direction can also be predicted by knowing the obtuse angle decided by stacking faults and TBs.     

The dimensionality of chromatographic separations

The box-counting or capacity dimension algorithm, known from the fractal mathematics literature, is used to measure the dimensionality D of chromatographic separation techniques for any number of dimensions. It is shown that D has limit properties that match Giddings' sample dimensionality s. D values are shown to be sensitive to the uniformity of peak spacing. A number of examples are given where D is calculated for various limits in one- and two-dimensional separations and for heart-cutting separations. The use of D as a quantitative measure of multidimensional orthogonality is suggested as D, due to the scale-free nature, is not dependent on the effective separation area. The connection to statistical peak overlap theory is discussed.     

Carbon (70 MeV) and copper (120 MeV) ions irradiation effects in Makrofol-N

Makrofol-N polycarbonate was irradiated with carbon (70 MeV) and copper (120 MeV) ions to analyze the induced effects with respect to optical and structural properties. In the present investigation, the fluence for carbon and copper beams was kept in the range of 1×10¹¹– 1×10¹³ ions/cm² to study the swift heavy ion induced modifications. UV–VIS, FTIR and XRD techniques were utilized to study the induced changes. The analysis of UV–VIS absorption studies revealed that the optical energy gap was reduced by 17% on carbon irradiation, whereas the copper beam leads to a decrease of 52% at the highest fluence of 1×10¹³ ions/cm². The band gap can be correlated to the number of carbon atoms, N, in a cluster with a modified Robertson's equation. In copper (120 MeV) ions irradiated polycarbonate, the number of carbon atoms in a cluster was increased from 63 to 269 with the increase of ion fluence from 0 to 1×10¹³ ions/cm², whereas N is raised only up to 91 when the same polymer films were irradiated with carbon (70 MeV) ions under similar conditions. FTIR analysis showed a decrease in almost all characteristic absorption bands under irradiation. The formation of hydroxyl (? OH) and alkene (C?C) groups were observed in Makrofol-N at higher fluence on irradiation with both types of ions, while the formation alkyne end (R? C≡ CH) group was observed only after copper ions irradiation. The radii of the alkyne production of about 3.3 nm were deduced for copper (120 MeV) ions. XRD measurements show a decrease in intensity of the main peak and an increase of the average intermolecular spacing with the increase of ion fluence, which may be attributed to the structural degradation of Makrofol-N on swift ion irradiation.     

Grating spacing dependence of nonvolatile holographic recording with arbitrary charge transport lengths

Grating spacing dependence of nonvolatile holographic recording in doubly doped lithium niobate crystals is theoretically investigated allowing arbitrary charge transport lengths. It is shown that the nonvolatile refractive index modulation initially increases with increasing grating spacing, then a saturation behavior arises because of the dominant bulk photovoltaic effect. Although different charge transport length results in different nonvolatile refractive index modulation, the grating spacing dependence of nonvolatile holographic recording obeys almost the same rules for arbitrary charge transport lengths. The experimental results obtained by recording nonvolatile holograms in LiNbO₃:Cu:Ce crystals with different grating spacing are consistent with the theoretical analyses.     

Surface and Bulk Structure Characterization of Proton (3 MeV) Irradiated Polycarbonate

Polycarbonate (Makrofol‐N) thin films were irradiated with protons (3 MeV) under vacuum at room temperature with the fluence ranging from 1×10¹⁴ to 1×10¹⁵ protons cm^?2. The change in surface morphology, optical properties, degradation of the functional groups, and crystallinity of the proton‐irradiated polymers were investigated with atomic force microscopy (AFM), UV‐VIS, and Fourier‐transform infrared (FTIR) spectroscopy, and X‐ray diffraction (XRD) techniques, respectively. AFM shows that the root mean square (RMS) roughness of the irradiated polycarbonate surface increases with the increment of ion fluence. The UV‐VIS analysis revealed that in Makrofol‐N the optical band gap decreased by 30% at highest fluence of 1×10¹⁵ protons cm^?2. The band gap can be correlated to the number of carbon atoms, M, in a cluster with a modified Robertson's equation. The cluster size in the proton‐irradiated Makrofol‐N increased from 112 to 129 atoms with the increase of fluence from 1×10¹⁴ to 1×10¹⁵ protons cm^?2. FTIR spectra of proton (3 MeV) irradiated Makrofol‐N showed a strong decrease of almost all absorption bands at about 1× 10¹⁴ protons cm^?2. However, beyond a higher critical dose an increase in intensity of almost all characteristic bands was noticed. The appearance of a new peak at 3,500 cm^?1 (‐OH groups) was observed at the higher fluences in the FTIR spectra of proton‐irradiated polycarbonate. XRD measurements showed an increase of full width at half maximum (FWHM) and the average intermolecular spacing of the main peak, which may be due to the increase of chain scission and the introduction of ‐OH groups in the proton irradiated polycarbonate.