We propose and simulate numerically a permittivity-tunable metamaterial channel, which is composed of alternating layers of graphene and silica. The real part of the permittivity of the proposed metamaterial can be tuned from a positive value to a negative one for a broadband width. Furthermore, optical waves can pass through the metamaterial channel only when its permittivity is tuned to zero. Inspired by this intriguing property of the graphene–silica metamaterial, three basic electro-optical logic gates, including NOT, NOR, and NAND gates, were proposed and numerically investigated by using the finite element method. Taking advantage of the permittivity-tunable property of graphene, the working wavelength of the proposed electro-optical logic gates can be actively controlled by tuning the external voltage applied on the graphene–silica metamaterial. These tunable and ultracompact electro-optical logic gates could benefit the development of nanoscale optical devices for highly integrated photonic circuits.
An elliptical multilayer-core fiber (EMCF) with low nonlinearity for wide-band dual-mode operation was proposed. The EMCF, in which only the HE11 and HE21 modes could be propagated, supported a distinct dual-mode operation. The characteristics of the EMCF, including modal properties, the operating wavelength, the transmission loss, the effective area, and the bending loss, were systematically investigated. For EMCFs, a large modal diameter (33.48 μm) was achieved to reduce the fiber nonlinear penalty; meanwhile, the bending loss could be kept in a lower level. In addition, the single-polarization property in EMCFs could be realized by combining stress applying elements.
In this presentation, the universal structure of one-dimensional photonic crystal (1-D PC) is constructed, and its optical transmission properties are analyzed by transfer matrix method (TMM). A case that there are two kinds of medium as a period is studied in detail. It is concluded that the reflectivity in photonic band-gap (PBG) increases with the increasing of periodical number, and the bandwidth of PBG has direct relation with the difference between two kinds of dielectric constant, three methods for extending PBG are discussed. When defect layer is inserted, a defect mode appears in the PBG. The concept of optimal periodical number is presented, and it is found that this optimal periodical number is only relative to the ratio of dielectric constant (K). Using multi-objective optimization method, we educe the curve and equation relation between optimal periodical number and K for the first time. In addition, the change in the number of defect mode with the variation of the defect layer's thickness is analyzed, and it is explained by the theory of F-P cavity.
The splice losses between PCF and SMF and between two PCFs with different structure are analyzed based on mode field radius of the fibres, respectively. And the effect of each structure parameter on the splice loss was discussed.
The optical properties of near elliptical core polarization maintaining photonic crystal fiber are analyzed by using a full vector model. We classify guided modes in the near elliptical core photonic crystal fibers (PCFs) according to the minimum waveguide sectors and its appropriate boundary conditions. Because the field patterns of the near elliptical core PCF is similar to that of rectangular waveguide, the guided modes are labeled in this PCF in the same way as in rectangular waveguide. The numerical results exhibit that the modal birefringence of elliptical core PCF is at least one order of magnitude higher than the conventional elliptical polarization-maintaining fibers (PMF). Zero walkoff point occur at the longer wavelength than that of convention elliptical PMF. This can restrain the first order polarization mode dispersion. This fiber has a number of potential applications in polarization control and management.
In this paper, we proposed a novel SPSM PCF and analyzed its optical properties with a full vector model. Considering the opposite parity of each guided mode in the fiber with symmetric structure, we improved the full vector model we developed previously. The numerical result demonstrated that the algorithm proposed is very efficient for analyzing the PCFs with symmetric structure. It only needs relatively few terms to obtain good results that the computation time can be reduced greatly. It is also confirmed that the fiber structure proposed is very efficient and can operate at SPSM region from the wavelength 1.37mm to 1.70mm.
The modal characteristics of dual-core photonic crystal fibers are analyzed by a full vector supercell method. The fundamental and second order modes of dual-core PCF consist of a pair of even and odd modes with different polarization, the parity properties of the modal electric field are illuminated. Based on the analysis of parity of modal electric fields, we investigated the vector modal interference in dual-core PCF. The power transfer induced by interference of different mode pair is investigated. It is the interference between two same polarized modes that contribute to the inter-core coupling of power. It is shown that the optical power will oscillate from one core to the other. The dependence of the coupling coefficients on wavelength and structural parameter for different polarization is discussed.
Long period fiber gratings couple the fundamental guided mode to forward propagating cladding modes. A Characteristic of LPGs in SMF is that their spectral properties (resonant wavelength and coupling strength) are sensitive to the refractive index of the surface surrounding the cladding region. Because of this, LPGs are typically packaged unrecoated to obtain insensitive spectral properties. In this paper the effective index model combined with the coupling-mode theory are used to study the characteristics of LPGs based on photonic crystal fiber (PCF). After plenty of numerical simulation, the results demonstrate that PCF-based LPGs will be more insensitive to the surrounding medium than those written in SMF.
A novel supercell overlapping method is developed to analyze the PCFs. The dielectric constant of the PCF is considered as the sum of two different periodic dielectric structures which can be expanded in cosine functions.
Combining perfectly matched layer (PML) for the boundary treatment, we present an efficient compact 2-dimensional finite-difference time-domain (2D FDTD) method for modeling photonic crystal fibers. For photonic crystal fibers, if we assume that the propagation constant along the propagation direction is fixed, three-dimensional hybrid guided modes can be calculated by using only a two-dimension mesh. Because of using the real variable method, the computation time, i.e., it is of order N. Comparing with the plane wave expansion method, FDTD make the computation time and computer memory are significantly reduced. The numerical results for a triangular lattice
photonic crystal fiber are in very good agreement with the results from the local basis function method. This method can easily be used for any complicated inclusions.
Twin core erbium-doped fiber is fabricated using a combination of MCVD, solution doping and post processing technique. This paper mainly study the birefringence of twin-core Erbium doped fiber including geometrical and stress birefringence. First we analysis the mode distribution of twin core fiber and geometrical birefringence by supercell lattice orthogonal function method using the structure parameters measured. Then the geometrical birefringence also calculated from the couple theory. The calculated result showed that two elliptical cores would have higher geometrical birefringence than two circular cores. Generally the Er-doped fiber is high Germanium doped to keep high Numerical Aperture (NA), which cause high thermal expansion coefficient difference between the core and the cladding, and the stress birefringence is anisotropic. According the distribution of stress field, we calculated the stress birefringence in the area of assembling of light power, which approximate to 10<sup>-4</sup>. The investigation proved that twin core Erbium doped
fiber has high birefringence and good polarization maintaining characteristics.
A full vector method based on supercell lattice method is applied for modeling the microstructured optical fibers (MOF). With this new method, the class and degeneracy of modes in MOF are discussed based on symmetry analysis. We classify the modes of MOF into nondegenerate or degenerate pairs according to the minimum waveguide sectors
and its appropriate boundary conditions. It is shown that the modes of MOF can be labeled by its step index fiber analogs, except the modes with the same symmetry as MOF. The doublet of the degenerate pairs in which both have the same symmetry as MOF will be split into two nondegenerate modes by the reduced symmetry of the fiber.