Low-temperature wet chemical precipitation of YVO4:Bi,Eu nanophosphors via citrate precursors

YVO₄:Bi³⁺,Eu³⁺ nanophosphors are prepared by low-temperature wet chemical precipitations in the presence of citrate ions. Transparently dispersed YVO₄:Bi³⁺,Eu³⁺ nanophosphors crystallize from amorphous gel precursors through a gel-sol process. The homogeneity of Bi³⁺ doping process as well as the photoluminescence property are improved by using the homogeneous Bi³⁺ solution as a Bi³⁺ source instead of Bi³⁺ powder. YVO₄:Bi³⁺,Eu³⁺ nanophosphor under the irradiation of near-UV light shows peculiar photobleaching behavior through the reduction from V⁵⁺ to V⁴⁺, but this photobleach is suppressed by subsequent hydrothermal treatment. The authors also discuss the advantage of transparency of YVO₄:Bi³⁺,Eu³⁺ nanophosphor in terms of wavelength conversion as compared to micron-sized phosphor.     

Q‐switched and modelocked all‐fiber lasers based on advanced acousto‐optic devices

The interest in all‐fiber lasers is stimulated by the inherent advantages they have over bulk lasers in aspects such as heat dissipation and robustness. The performance of Q‐switched and modelocked fiber lasers can benefit enormously from the development of all‐fiber configurations. A fiber laser with strictly all‐fiber components can fulfil the requirements of mechanical stability, low maintenance, enhanced power efficiency, simplified assembly process, and low cost. In this framework, recent developments infiber acousto‐optic devices are reviewed that have demonstrated new possibilities for actively Q‐switched distributed feedback fiber lasers, modelocking lasers and doubly active Q‐switched modelocked lasers. The aim is to demonstrate the great potential of infiber devices for the active control of different types of fiber lasers.     

Diode laser wavelength modulated spectroscopy of I(2) at 675 nm

A free-running diode laser has been used to examine the spectrum of 127I(2) near 675 nm using wavelength modulation spectroscopy. Twelve transitions have been observed in the region between 14818.0 and 14819.3 cm(-1), all of which are accounted for by previously published constants. Changes in quadrupole coupling constants, DeltaeQq, have been determined for all lines. Pressure broadening and shift coefficients have been determined for two unblended lines for broadening by air, argon, and water vapor.     

Simulation Results for DWDM Systems with Ultra-High Capacity

We present stimulation results for DWDM systems with an ultra-high capacity up to 1.28 Tbit/s and spectral efficiency approaching 0.4 bit/s/Hz. The impact of signal-to-noise ratio (SNR) on parameters such as channel spacing, length of fiber, dispersion, and number of channels has been investigated and the results obtained have been explained on the basis of fiber nonlinear effects. It has been shown that with an increase in channel spacing, the SNR increases to the maximum optimum value and then decreases to a steady value. With an increase in number of channels, the SNR decreases for small wavelength spacing. For large wavelength spacing, it becomes independent of the number of channels. Keeping channel spacing constant, the SNR decreases with an increase in the length of the fiber. The SNR also improves with a small increase in dispersion of the fiber. Further, it is observed that, with increase in length over dispersion-shifted fiber, the received power decreases and the bit error rate increases.     

Analysis of circular bends in planar optical waveguides

Waveguides with circular bends are analyzed by means of a conformal transformation in conjunction with the WKB method of dealing with the nonuniform refractive index that results from the transformation. The result is a prediction of the operational parameters of the bent guide, including the loss. The transformation makes possible an intuitive understanding of the cause of the loss.     

Eye Opening Degradation due to Sideband Suppression in Direct Detection Systems for Different Signaling Formats

Abstract

The intensity distortion resulting from sideband suppression in direct detection systems is investigated analytically and through numerical simulation for unipolar binary and alternate mark inversion formats. A method to calculate the sequence leading to the highest eye opening penalty is proposed, based on the characterization of the distortion originated by the Hilbert transform of an isolated pulse and constructive/destructive addition of the distortions of pulses in different time slots. The application of the proposed method to a practical transmitter is assessed, and accurate results are shown for signals without complete sideband suppression.     

High Flattened Comb Filter with Precise Channel Spacing Based on Linearly Chirped Fiber Bragg Grating and Phase Compensation

Abstract

A novel approach to implement high flattened comb filters with precise channel spacing based on DC phase compensation is proposed. Channel wavelength error and peak reflectivity variation are discussed and calculated. A phase compensation method by simply changing the DC refractive index is proposed. Fiber Bragg gratings with different DC phase shifts are fabricated, which indicates that an arbitrary DC phase shift can be introduced precisely. A high flattened comb filter with precise 50-GHz channel spacing is realized with the help of a micrometer-precision translation stage. Then the peak reflectivity variation with and without phase compensation for different chirp coefficients is researched.     

Suppression of Output Power and NF Excursions in Cascades of Highly Inverted EDFAs with Packet-Switched Traffic

Significant output power excursions in cascades of erbium-doped fiber amplifiers (EDFAs) can cause serious problems in wavelength division multilexing (WDM) packet-switched burst-mode networks. Signal power excursions more serious than those induced by channel addition/removal in circuit switched networks can arise when data on the WDM channels is highly variable in nature. Self-similar traffic can be subject to large variation in EDFA gain. In order to prevent unacceptable error bursts, due, for example, to channel power becoming too low to preserve adequate eye opening or exceeding thresholds for optical nonlinearities, the channel power should be maintained constant. In this letter, it is shown that the sizable power and noise figure swings arising in a cascade of EDFAs with WDM burst-mode packet-switched networks with self-similar traffic can be effectively suppressed when highly inverted amplifiers are employed. The analysis is based on the application of a numerical model, which solves the transcendental equation for length averaged metastable level population of an EDFA.     

Fiber-Grating-Based Optical Limiting Amplifier Module for Dual-Wavelength,Hybrid Data Rate Transmission

A multichannel fiber-grating-based optical limiting amplifier module is proposed. Dual-wavelength, hybrid data rate transmission is demonstrated with 30 dB input dynamic range. For 5.0 and 2.5 Gbit s dual-channel transmission in a 200 km single-mode fiber, power penalty due to gain competition between channels and backreflection noise is less than 0.6 dB compared to the receiver sensitivity of 0 km, 5.0 Gbit per second single-channel operation.     

Allocation Algorithm for Optical OFDM Multimode Fiber Communication System

Abstract

A fast bits allocation algorithm is proposed for adaptively modulated optical orthogonal frequency division multiplexing multimode fiber communication system to decrease the system bit error rate caused by some orthogonal frequency division multiplexing subcarriers being located at the deep nulls in the high-frequency region of multimode fiber. Based on a lookup table scheme, the new algorithm dramatically decreases the computational complexity of the Greedy algorithm. The simulation results show that the new algorithm has the same allocation result as the Greedy algorithm, but the computational complexity is considerably lower. In addition, adaptive bits allocation can effectively reduce the system bit error rate.