Optimized Fiber Design Research Articles

Inverse Design of Equivalent-Graded-Index Photonic-Crystal Fiber Based on Empirical Dispersion Formula

Equivalent-graded-index photonic-crystal fiber (EGI-PCF) is a modified photonic-crystal fiber (PCF) where the cladding is not required to be periodic. A radial gradient of the equivalent refractive index distribution provides extra freedom to efficiently tailor the dispersion of EGI-PCF. However, such additional complexity makes the manual fiber design much more challenging where the time consumption becomes too much to be afforded eventually. In this paper, we for the first time propose the method of computer-aided inverse fiber design (CAFD) based on empirical dispersion formula to circumvent this hurdle. We apply the differential evolution (DE) genetic algorithm to seek for the optimized EGI-PCF design with a target of specific dispersion profile. In the dispersion oriented EGI-PCF design, the use of empirical formula instead of numerical simulation (e.g., finite-element method) is proved to greatly reduce the run-time of CAFD and simplifies the fitness function evaluation as much as possible. We adopt our method and demonstrate a design of EGI-PCF with a near-zero ultra-flattened dispersion in the whole S+C+L band, which merely costs a few seconds of a laptop to return an optimized fiber design. Thus improvement of efficiency is about three orders of magnitude faster than any previous CAFD attempts as far as we learn. In the end, we use our method to explore an EGI-PCF design with a unique dispersion profile of all-normal dispersion-decreasing along the fiber length centered around 1 μm that plays a key role for the self-similar pulse evolution in a fiber laser/amplifier.

Liquid-Filled Highly Asymmetric Photonic Crystal Fiber Sagnac Interferometer Temperature Sensor

In this paper, we theoretically designed and numerically studied a high-resolution and ultrasensitive photonic crystal fiber temperature sensor by selective filling of a liquid with high thermo-optic coefficient in one of the airholes of the fiber. The finite element method was utilized to study the propagation characteristics and the modal birefringence of the fiber under different ambient temperatures. A large base birefringence value of 7.7 × 10−4 as well as a large birefringence sensitivity of almost 29% to a 10 °C temperature variation was achieved for the optimized fiber design with liquid chloroform between 15 °C and 35 °C. We also studied the performance of the proposed optical fiber in a temperature sensing Sagnac interferometer. An average linear temperature sensitivity of 17.53 nm/°C with an average resolution of 5.7 × 10−4 °C was achieved over a temperature range of 20 °C (15 °C to 35 °C).

Simultaneous Measurement of Salinity and Temperature in Gold-Coated D-Shaped Photonic Crystal Fiber Using Four-Wave Mixing Technique

We propose a novel nonlinear technique for simultaneous measurement of salinity and temperature of water in a gold coated D-shaped photonic crystal fiber (DPCF). In this novel nonlinear technique, the sensitivity is calculated numerically through a degenerate four-wave mixing scheme by tracking the wavelength shift of the Stokes and anti-Stokes lines for various concentrations of NaCl and temperatures. The optimized fiber design with lattice pitch of 4.49 $\mu$ m, airhole diameter of 2.892 $\mu$ m, and with a gold layer of 39.5nm enables effective sensitivities of 1.6nm/(kg/kg) for salinity and of 12.31nm/ $^{\circ }$ C for temperature when light is launched at the pumping wavelength of 1070.4nm in 2cm of length of a DPCF. To our knowledge, the obtained sensitivity is much higher than that of other simultaneous measurement techniques. This novel nonlinear sensor has been demonstrated with high resolution of about 8.625 $\times$ $10^{-4}$ (kg/kg) and 9.74817 $\times$ $10^{-7}$ $^{\circ }$ C for salinity and temperature measurements, respectively.

Characterization and modelling of inter-core coupling in coherent fiber bundles.

Recent developments in optical endomicroscopy (OEM) and associated fluorescent SmartProbes present a need for sensitive imaging with high detection performance. Inter-core coupling within coherent fiber bundles is a well recognized limitation, affecting the technology's imaging capabilities. Fiber cross coupling has been studied both experimentally and within a theoretical framework (coupled mode theory), providing (i) insights on the factors affecting cross talk, and (ii) recommendations for optimal fiber bundle design. However, due to physical limitations, such as the tradeoff between cross coupling and core density, cross coupling can be suppressed yet not eliminated through optimal fiber design. This study introduces a novel approach for measuring, analyzing and quantifying cross coupling within coherent fiber bundles, in a format that can be integrated into a linear model, which in turn can enable computational compensation of the associated blurring introduced to OEM images.

Optimal fiber design for large capacity long haul coherent transmission [Invited

Fiber figure of merit (FOM), derived from the GN-model theory and validated by several experiments, can predict improvement in OSNR or transmission distance using advanced fibers. We review the FOM theory and present design results of optimal fiber for large capacity long haul transmission, showing variation in design results according to system configuration.

Group Delay Management and Multiinput Multioutput Signal Processing in Mode-Division Multiplexing Systems

Multi-input multi-output (MIMO) digital signal processing (DSP) for mode-division multiplexing (MDM) may have high complexity, owing to a plurality of modes and a potentially long group delay (GD) spread in multimode fiber (MMF). This paper addresses the management of GD in MMF and its implications for the complexity and performance of MIMO DSP. First, we review the generalized Jones and Stokes representations for modeling propagation in MMF, and describe key GD properties derived using the two representations. Then, we describe three approaches for GD management: 1) optimized fiber design, 2) mode coupling, and 3) GD compensation. For approach 1), we explain design principles for minimizing the GD spread. We review experimental results to date, showing that fabrication nonidealities significantly increase the GD spread, and this approach alone may not achieve sufficiently low GD spread. For approach 2), we describe mechanisms for inducing intragroup and intergroup coupling. We describe mode scrambler designs based on photonic lanterns or long-period fiber gratings, both of which can ensure strong intergroup coupling. For approach 3), we review GD-compensated system design principles and show that GD compensation is only partially effective in the presence of random intragroup or intergroup coupling. Finally, we provide an overview of adaptive MIMO frequency-domain equalization algorithms. Considering tradeoffs between complexity, performance, and adaptation time, we show that the GD spread is a key factor determining the feasibility of MIMO DSP, and its feasibility requires judicious GD management.

The effects of non-uniform temperature distribution and locally distributed anisotropic properties on thermal buckling of laminated panels

The present paper is concerned with the optimal design problem of thermal buckling for fiber reinforced laminated panels. The effects of non-uniform temperature fields and locally distributed anisotropic properties on the thermal buckling behavior are studied. In this analysis, based on the classical lamination theory in conjunction with the Hamilton’s principle, the critical thermal buckling temperature difference is deduced. The numerical results show that under the non-uniform thermal loads the isotropic panel performs as anisotropic structure and it also show that the center of panel is more sensitive to the thermal effects than the edges. The effects of thermal load on panels with different boundary conditions are also investigated and it is found that the panel edges with loose constraint are more sensitive to temperature effect than with strict constraint. In the optimal fiber design problem for thermal buckling, by comparing the critical thermal buckling temperature difference of nine types of panels with different fiber distribution, it is found that the short fiber distribution can largely improve the critical thermal buckling temperature difference of fiber reinforced laminated panels. Finally, using the genetic algorithm the optimal fiber distribution is obtained for an eight-layer symmetrical panel.

Er-doped high-aspect-ratio core rectangular fiber producing 5 mJ, 13 ns pulses at 1572 nm

We have produced 5 mJ, 13 ns pulses using a very large-mode-area rectangular fiber containing a high-aspect-ratio core with dimensions of ~30 μm×580 μm. The rectangular fiber design retains a thin cladding dimension ~0.5 mm, which is compatible with a compact coiled package. We have developed a theoretical model that achieves good agreement with the experimental data. This model indicates that an optimized fiber design can be scaled to pulse energies of several tens of millijoules. We also discuss a strategy for maintaining good beam quality in both transverse dimensions of this fiber.

Optimization of Hollow-Fiber Design and Low-Pressure Membrane System Operation

An approach is presented for the numerical optimization of low-pressure membrane filtration processes. A multidimensional optimization of an ultrafiltration system is formulated for cost minimization and numerically solved for key optimal design and operating variables. Hollow-fiber ultrafiltration operation under steady-state conditions is assumed and optimized with respect to fiber radius, fiber length, crossflow velocity, transmembrane pressure, and system recovery. Optimizations are performed over variable raw water conditions using a sequential quadratic programming (SQP) algorithm. For typical small to moderately sized low-pressure membrane facilities (≈1 mgd), optimal fiber design and membrane system operation is predicted to be largely influenced by the characteristic dominance of capital costs over operating costs. Thus, total treatment costs tend to be optimal at values of decision variables where permeate fluxes are maximized, within the constraints prescribed by the system, and assuming a fixed membrane cost per unit area. For raw waters demonstrating apparent to significant membrane fouling, optimal membrane treatment is predicted to be achieved by using relatively narrow hollow fibers and relatively high crossflow velocities. For relatively clean raw waters demonstrating very high sustainable permeate fluxes, operating at low crossflow velocities—or perhaps even under the dead-end mode of operation—appears to provide the most cost-effective operation.

Guiding and concentrating hard x-rays by using a flexible hollow-core tapered glass fiber

A 1.6-m-long, flexible, hollow glass fiber with a gradually diminishing bore diameter has been used efficiently to compress the size of an x-ray beam as it reflects from the inside walls of the fiber by total external reflection. The transmission characteristics of the fiber are reported for monochromatic synchrotron radiation of 8.04, 13, and 20 keV, as well as for CuKalpha radiation from a conventional x-ray tube. Intensity enhancements as large as 10 that correspond to a transmission efficiency of 54% were observed. The high efficiency of this prototype fiber supports the idea that this confinement technique should yield intensity gains of many orders of magnitude as the optimal fiber design is achieved.

Theoretical and experimental investigation of a resonantly pumped thulium doped fluorozirconate fiber amplifier at around 810 nm

The potential of thulium-doped fluorozirconate fibers to provide an efficient AlGaAs diode pumped traveling wave amplifier at wavelengths around 810 nm is investigated. The authors present calculations and experimental measurements of the small signal gain when excitation is resonant with the upper laser level, with a view to predicting the upper limits of performance for optimized fiber design. The theoretical treatment involves numerical determination of the evolution of pump and signal power (and hence gain) along the length of the fiber as a function of wavelength, spectral lineshapes and lifetimes, and geometrical factors. Amplification over the range 800-830 nm has been achieved in multimoded fiber with a best observed gain of 22 dB at 806 nm. >

Noise characteristics of erbium-doped fiber amplifier pumped at 980 nm

A noise figure of 2.9+or-0.4 dB, measured in a high-gain erbium-doped fiber amplifier for input signals in the range -35 to -15 dBm and for pump powers of >5.8 mW, is discussed. The spontaneous emission factor n/sub sp/ was 0.99+or-0.09 for input signals less than -15 dBm. These low figures are attributable to the optimized fiber design and the use of a pump wavelength of 980 nm, at which erbium operates as a true three-level system. These two factors contribute to the very low ( approximately 500 mu W) pump threshold seen in fiber, which permits nearly complete inversion to be achieved for the low pump powers employed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>