Fundamental limit of single-mode integral-field spectroscopy

The special optical fibers, with large mode field, are developed for fabricating high power optical fibers passive components. If a conventional fiber optical laser is used as optical source, the coupling efficiency between special optical fibers and conventional single mode fibers (SMFs) need to be improved. We investigate the specialty optical fibers property and its effect on the coupling efficiency using an electric arc fusion splicer. Improper splicing parameters can lead to coupling efficiency sharply decreased. Several splicing methods are utilized, and all the results are proposed. Comparing these results, we find a set of splicing parameters for reducing the scattering loss at the splice point. It was demonstrated that properly splicing parameters can make coupling efficiency greatly increased; furthermore, a balance between splicing strength and coupling loss was achieved.

Negative curvature hollow-core fibers (NC-HCFs) can boost the excellent performance of HCFs in terms of propagation loss, nonlinearity, and latency, while retaining large core and delicate cladding structures, which makes them distinctly different from conventional fibers. Construction of low-loss all-fiber NC-HCF architecture with conventional single-mode fibers (SMFs) is important for various applications. Here we demonstrate an efficient and reliable fusion splicing method to achieve low-loss connection between a NC-HCF and a conventional SMF. By controlling the mode-field profile of the SMF with a two-step reverse-tapering method, we realize a record-low insertion loss of 0.88 dB for a SMF/NC-HCF/SMF chain at 1310 nm. Our method is simple, effective, and reliable, compared with those methods that rely on intermediate bridging elements, such as graded-index fibers, and can greatly facilitate the integration of NC-HCFs and promote more advanced applications with such fibers.

The paper presents the method and instrumental system for modeling and optimizing technological modes of direct metal reduction processes in a jet-emulsion aggregate (JER). Stages of the method are considered. The first one is the problem statement: formation of target conditions, choice of the process type, the task and system of optimization criteria. The second stage includes selection of the object of study: setting parameters of input and output flows, process parameters, stages and subprocesses. The third one includes thermodynamic modeling to assess the final equilibrium state in which optimization problem is solved to determine the best conditions for implementation of the processes of metal reduction from oxides in model systems. The fourth stage is development of metallurgical technology (finding the optimum modes and ways for achieving these modes by specified output stream parameters). And the final one is process optimization in technical and economic indicators. As part of the fourth stage, the complex of mathematical models has been developed that reflects relationship of flows and processes in a metallurgical unit. The structure of instrumental system is presented, in which mathematical models and an algorithm for determining optimal technological modes are implemented. A set of optimization criteria has been developed and a scheme for solving two types of optimization problems are presented: finding optimal conditions for reduction processes in thermodynamic systems and determining optimal modes of direct metal reduction. Application of the method to develop optimal technological modes of direct metal production in a JER-type aggregate is shown: metal production from cast iron and mill scale; direct reduction of metal from dusty ores and iron-containing man-made materials; obtaining manganese alloys from carbonate and oxide ores; processing titanium-magnetite concentrates with an almost complete separation of iron-containing and titaniumcontaining component; and direct reduction of iron with associated production of high-calorie synthesis gas.

A bidirectional lightwave 100 km transmission system capable of delivering 80 cable television (CATV) analogue video signals using conventional singlemode fibre (SMF) or large effective area fibre (LEAF) has been demonstrated experimentally for the first time. Elimination of both Rayleigh backscattered crosstalk from the opposite-direction signal and amplified spontaneous emission noise is required to improve the system carrier-to-noise ratio. Satisfactory system performance can be achieved regardless of whether an SMF or LEAF 100 km link is used. However, the composite second-order quality of the LEAF link is superior to that of the SMF link. This technology should play an important role in leased fibre links for trunk delivery between any two multiple system operators across another CATV-operator system.

The evolution of cosine-super Gaussian (CSG) pulses propagating in a conventional single mode fiber (SMF) has been proposed. The propagation properties of CSG pulses are numerically studied by using split-step Fourier method, and the effects of initial phase φ0 and order of the pulse m are analyzed. Results show that when φ0 is increased to 80 rad, the first order CSG pulse will be compressed in a relatively long fiber, and then broaden monotonically; the higher order CSG pulses will experience a short compression first, and then broaden monotonically. In addition, the CSG pulses are compared with simple Gaussian pulses and Hyperbolic secant pulses. The results indicate that the Hyperbolic secant pulse broaden fastest; the simple Gaussian pulse broaden secondly; CSG pulses broaden slowest, which is most insensitive to the dispersion of fiber. The research work will pave a way to realize a special pulse in large-capacity, and long-range communications.

Optimization of vibration frequencies of an elastic plate in an ideal fluid: PMM vol. 39, n≗5, 1975, pp. 889–899

Discussion on the monotonicity principle of the two-stage problem in joint optimal operation of cascade hydropower stations

Spliced-fiber mode filter for 1060-nm single-mode transmission

In astronomy and related fields there is a pressing need to efficiently inject light, transmitted through the atmosphere, into a single-mode fibre. However this is extremely difficult due to the large, rapidly changing aberrations imprinted on the light by the turbulent atmosphere. An adaptive optics system must be used, but its effectiveness is limited by non-common-path aberrations and insensitivity to certain crucial modes. Here we introduce a new concept device - the hybrid mode-selective photonic lantern - which incorporates both focal plane wavefront sensing and broadband single-mode fibre injection into a single photonic package. The fundamental mode of an input multimode fibre is directly mapped over a broad (1.5 to 1.8μm) bandwidth to a single-mode output fibre with minimal (<0.1%) crosstalk, while all higher order modes are sent to a fast detector or spectrograph for wavefront sensing. This will enable an AO system optimised for maximum single-mode injection, sensitive to otherwise 'blind' modes and avoiding non-common-path wavefront-sensor aberrations.

Device-to-device (D2D) communications and full-duplex (FD) communications, which can improve the spectrum efficiency (SE) of mobile communications, have received much attention. To further improve the SE, some researchers have begun to integrate FD into D2D communications, which will generate more transmission modes. Since different modes have different advantages and disadvantages, the mode selection problem needs further study. In this paper, we investigate the mode selection problem for FD-enabled two-way D2D communications to improve the SE. Four transmission modes, i.e., FD underlay mode, half-duplex (HD) underlay mode, FD overlay mode and HD overlay mode, are considered. For each mode, we maximize the system SE while fulfilling the minimum rate requirements and maximum transmit power constraints for both cellular and D2D users. For FD underlay mode, the optimization problem can be transformed into a difference of convex functions (D.C.) programming and the concave-convex procedure (CCCP) algorithm can solve the problem efficiently. For HD underlay mode and FD overlay mode, we can use search plus CCCP algorithm to solve the optimization problem. For HD overlay mode, we only need to search for the optimal solution. After obtaining the maximum SE of four modes, we can select the maximum one as the optimal mode. Numerical results are presented to illustrate the effects of the channel gains and self-interference cancellation ability on the maximum SE of four modes and the transmission mode selection.

Ultra-weak fiber Bragg grating (UWFBG) arrays are key elements for constructing large-scale quasi-distributed sensing networks for structural health monitoring. Conventional methods for creating UWFBG arrays are based on in-line UV exposure during fiber drawing. However, the UV-induced UWFBG arrays cannot withstand a high temperature above 450 °C. Here, we report for the first time, to the best of our knowledge, a new method for fabricating high-temperature-resistant UWFBG arrays by using a femtosecond laser point-by-point (PbP) technology. UWFBGs with a low peak reflectivity of ∼ - 45 dB (corresponding to ∼ 0.0032%) were successfully fabricated in a conventional single-mode fiber (SMF) by femtosecond laser PbP inscription through fiber coating. Moreover, the influences of grating length, laser pulse energy, and grating order on the UWFBGs were studied, and a grating length of 1 mm, a pulse energy of 29.2 nJ, and a grating order of 120 were used for fabricating the UWFBGs. And then, a long-term high-temperature annealing was carried out, and the results show that the UWFBGs can withstand a high temperature of 1000 °C and have an excellent thermal repeatability with a sensitivity of 18.2 pm/°C at 1000 °C. A UWFBG array consisting of 200 identical UWFBGs was successfully fabricated along a 2 m-long conventional SMF with an interval of 10 mm, and interrogated with an optical frequency domain reflectometer (OFDR). Distributed high-temperature sensing up to 1000 °C was demonstrated by using the fabricated UWFBG array and OFDR demodulation. As such, the proposed femtosecond laser-inscribed UWFBG array is promising for distributed high-temperature sensing in hash environments, such as aerospace vehicles, nuclear plants, and smelting furnaces.

A dynamically selective multiwavelength cross-connect for wavelength division multiplexed (WDM) networks based on fibre Bragg gratings (FBGs) and optical switches is reported. Dynamically single- or multi-channel cross-connect functionality can be realized according to control of the optical switches and the FBGs' arrangement. Bit-error-rate performance with negligible power penalty is achieved in a 2.5Gbs-1x3 WDM channels over 100km conventional single-mode fibre (SMF) network demonstration. The characteristics of low channel crosstalk, uniform channel loss, high scalability and cascadability, and low cost of this device could provide more reconfiguration flexibility and network survivability for WDM networks.

We present the novel design of a spot-size converter (SSC) for high efficiency coupling between a conventional single-mode fiber (SMF) and a standard silicon nanowire. Our design involves evanescent coupling between a stack of Si3N4/SiO2 alternating layers and a standard silicon nanowire. The proposed SSC coupler demonstrates highly broadband performance with a polarization dependence of less than 0.62 dB and an expected taper loss of less than 1.0 dB, over 100 nm bandwidth ranging from 1.5 to 1.6 µm. To the best of our knowledge, the proposed SSC achieves the highest broadband coupling for both polarizations between a fiber with a large mode-field diameter (i.e., SMF-28) and a standard silicon nanowire.

A Rayleigh backscattering (RBS) assisted Brillouin erbium fiber laser scheme with multiwavelength narrow linewidth output is proposed and investigated experimentally. The stimulated Brillouin scattering and RBS take place at two conventional single-mode fibers (SMFs), respectively. RBS is used as a mechanism to compress the linewidth of each Stokes component, and it has been realized and maximized in conventional SMF by optimizing injection power of Stokes light through adjusting variable optical attenuator (VOA). By adjusting VOA attenuation, the laser can obtain three wavelengths output with 3 dB linewidth less than 2 KHz for each wavelength, or six wavelengths output with 3 dB linewidth less than 5 KHz.

In this Letter, a long-range optical fiber displacement sensor based on an extrinsic Fabry-Perot interferometer (EFPI) built with a strongly coupled multicore fiber (SCMCF) is proposed and demonstrated. To fabricate the device, 9.2 mm of SCMCF was spliced to a conventional single-mode fiber (SMF). The sensor reflection spectrum is affected by super-mode interference in the SCMCF and the interference produced by the EFPI. Displacement of the SMF-SCMCF tip with respect to a reflecting surface produces quantifiable changes in the amplitude and period of the interference pattern in the reflection spectrum. Since the multicore fiber is an efficient light collecting area, sufficient signal intensity can be obtained for displacements of several centimeters. By analyzing the interference pattern in the Fourier domain, it was possible to measure displacements up to 50 mm with a resolution of approximately 500 nm. To our knowledge, this is the first time that a multicore fiber has been used to build a displacement sensor. The dynamic measurement range is at least seven times larger than that achieved with an EFPI built with a conventional SMF. Moreover, the SMF-SCMCF tip is robust and easy to fabricate and replicate.