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This letter demonstrates the chaotic precoding approach in multiple-input multiple-output space frequency block coded orthogonal frequency division multiplexing (MIMO SFBC-OFDM) communication syste...

We report numerical investigation of mid-infrared supercontinuum (SC) generation in all-normal dispersion (ANDi) As39Se61 chalcogenide photonic crystal fiber (PCF). Numerical results, obtained by using the Finite-Difference Frequency-Domain (FDFD) method, indicate that desirable dispersion properties can be achieved by adjusting the air holes diameter and ANDi regime is obtained over the entire wavelength range with a PCF pitch and air holes diameter of 1.8 µm and 0.7 µm, respectively. Besides, the optimized design has a nearly zero dispersion wavelength of 3.45 µm and exhibits high Kerr nonlinearity of 5.89 w−1 m−1. By pumping 50 fs duration laser pulses at 3.45 µm, we demonstrate the generation of a broad, ultraflat-top and highly coherent SC spectrum extending from 2.43 µm to 4.85 µm at 4 dB spectral flatness and from 1.95 µm to 6.58 µm at 8 dB, by employing very low energy pulses of 50 pJ and 250 pJ, respectively. Owing to its remarkable optical characteristics, the proposed SC source based on As39Se61 chalcogenide glass PCF is found to be suitable for various potential mid-infrared applications such as optical coherence tomography, mid-infrared spectroscopy and metrology.

All normal dispersion (ANDi) and highly nonlinear chalcogenide glass photonic crystal fiber (PCF) is proposed and numerically investigated for a broad, coherent and ultra-flat mid-infrared supercontinuum generation. The proposed PCF consists of a solid core made of Ga8Sb32S60 glass surrounded by seven rings of air holes arranged in a triangular lattice. We show by employing the finite difference frequency domain (FDFD) method that the Ga8Sb32S60 PCF dispersion properties can be engineered by carefully adjusting the air holes diameter in the cladding region and ANDi regime is achieved over the entire range of wavelengths with a zero chromatic dispersion around 4.5 μm. Moreover, we demonstrate that injecting 50 fs width and 20 kW peak power laser pulses (corresponding to a pulse energy of 1.06 nJ) at a pump wavelength of 4.5 μm into a 1 cm long ANDi Ga8Sb32S60 PCF generates a broad, flat-top and perfectly coherent SC spectrum extending from 1.65 μm to 9.24 μm at the 20 dB spectral flatness. These results make the proposed Ga8Sb32S60 PCF an excellent candidate for various important mid-infrared region applications including mid-infrared spectroscopy, medical imaging, optical coherence tomography and materials characterization.

This paper deals with the Peak to Average Power Ratio (PAPR) drawback appeared in Filter-Bank Multi-Carriers with Offset-QAM (FBMC-OQAM) which is the candidate waveform in 5G wireless communication systems. A post-Inverse Discrete Fourier Transform (IDFT) Discrete Sliding Norm Transform (DSNT) is proposed based on L2-metric and the norm of five samples at each sliding operation. The overlapping structure of FBMC-OQAM is considered in the proposed L2-by-5 DSNT formulation. It can significantly reduce the PAPR in FBMC-OQAM systems, which ensures a linear amplification at the High Power Amplifier (HPA) and avoids signal distortion. The main advantages of this technique are its lower computational complexity compared to the known techniques, and the fact that it does not require any Side Information (SI) at the receiver. Simulation results show that the L2-by-5 DSNT technique can achieve an improvement of 40% in PAPR reduction at CCDF = 10–3 compared to the original FBMC-OQAM system.

We design an all-solid Photonic Crystal Fiber (PCF) with all-normal dispersion profile to achieve broadband, ultraflat-top and coherent supercontinuum generation in the mid-infrared spectral region, by using sub-nanojoule laser pulses. Two environment friendly and thermally compatible chalcogenide glasses, namely $${\mathrm {Ge}}_{15} {\mathrm {Sb}}_{15}{\mathrm {Se}}_{70}$$ and $${\mathrm {Ge}}_{20}{\mathrm {Se}}_{80}$$ , are used as background material and for solid rods, respectively. To the best of our knowledge, this is the first report of an all-solid PCF made of non-toxic ChG glasses for MIR SC generation. The finite difference method is employed to investigate and optimize the guiding linear and nonlinear properties. Simulations results indicate that high Kerr nonlinearity up to $$2.21 ~{\mathrm {~W}}^{-1} {\mathrm {~m}}^{-1}$$ at $$3 ~\upmu {\mathrm {m}}$$ and all-normal dispersion profile over the entire wavelength range are successfully achieved for a structure design with cladding pitch $$\Lambda =3 ~\upmu {\mathrm {m}}$$ and solid rods diameter $$d=1.4 ~\upmu {\mathrm {m}}$$ . Furthermore, by pumping at $$3 ~\upmu {\mathrm {m}}$$ a $$50 ~{\mathrm {fs}}$$ duration optical pulses with a total energy of $$900 ~{\mathrm {pJ}}$$ into $$10 {\mathrm {~mm}}$$ PCF long, a bright, broadband and perfectly coherent supercontinuum spectrum with $$-5 {\mathrm {~dB}}$$ bandwidth covering the wavelength range from $$1.6 ~\upmu {\mathrm {m}}$$ to $$7 ~\upmu {\mathrm {m}}$$ , is generated. The proposed all-solid PCF based SC laser source is found promising for various potential mid-infrared applications, covering the molecular fingerprint region, such as high resolution imaging of biological tissues, monitoring of greenhouse gases and materials characterization.

Ultra−WideBand (UWB) technology was approved by the Federal Communications Commission (FCC) in February 2002 (FCC, 2002). According to the FCC regulations, the frequency band from 3.1 to 10.6 GHz can be used for short−range and high speed wireless communications systems. This recent allocation of a very wide spectrum of frequencies for the devices uses, with effective isotropic radiated power (EIRP) less than 41dBm/MHz has presented numerous exciting opportunities and challenges for antenna designers. UWB antennas should be effective in transmitting, compact, non dispersive, and have a good wide impedance bandwidth properties, these features are desirable for both indoor and outdoor hand−held UWB applications. In practical UWB applications, microstrip antennas that can be directly printed onto printed circuit boards (PCBs) are the most promising candidates. Such a PCB antenna has a low profile, a low manufacturing cost and can easily be integrated with other parts of monolithic microwave integrate circuit (MMIC) for a transceiver or any other UWB system. To satisfy such requirements, various types of planar antennas have been developed for UWB communications over the last few years. Also, several bandwidth enhancement techniques have been reported, to improve the impedance bandwidth of these antennas. Microstrip UWB antennas are usually constructed by etching a radiator onto the dielectric substrate of a piece of the PCB and a partial ground plane onto the opposite side if the antenna is fed by microstrip transmission line or on the same side in the case of coplanar waveguide (CPW) feeding. In the literature, many different microstrip UWB antennas with circular, elliptical, triangular, rectangular, hexagonal, and so on patches are currently being considered for UWB applications. This chapter presents an overview of UWB antennas design an characterization, some novel designs were investigated and presented. The first class of studied UWB antennas is microstrip monopole antennas including the microstrip/CPW−fed modified − elliptical monopole antennas. The second class is for UWB slot antennas, where a novel stepped inverted cone slot antenna with different stub shapes is proposed for UWB applications. In the third class a notched band UWB antenna is presented; the proposed UWB have been developed to notch−band UWB antenna by inserting a U−shape slot into patch. The advantage of this approach is that the stop−band filter (slot) can directly integrated in antenna structure. The study includes detailed parametric analysis of the antennas performances with relation to the desirable properties for UWB antennas. 15

We numerically demonstrate mid-infrared supercontinuum generation in dispersion-engineered chalcogenide glass channel waveguide. The proposed ridge waveguide consists of arsenic pentasulfide (As2S5) strip deposited on magnesium fluoride (MgF2) substrate and air acting as an upper cladding. The structure parameters are calculated and optimized by using the fully vectorial finite-difference in the frequency-domain (FDFD) method Results indicates that the proposed waveguide exhibits an all normal dispersion (ANDi) profile over a wide spectral range with a zero dispersion wavelength (ZDW) around 2 μm. By solving the generalized nonlinear Schrodinger equation, we demonstrate supercontinuum generation extending from the near infrared to the mid infrared region. Indeed, a broad and perfectly coherent ultra-flat supercontinuum spectrum spanning the region from 700 to 5200 nm is successfully generated by using a 25 kW peak power 100 fs input pulse pumped at 2.5 μm, in a waveguide of 5 mm length.

Mid-infrared supercontinuum (SC) generation in normally dispersive photonic crystal fiber (PCF) made of GeS2-Ga2S3-CsI chalcohalide glass, is theoretically investigated. The finite difference method is employed to compute and optimize the different linear and nonlinear parameters of the fundamental guided mode. Simulation results indicate that the all-normal regime of dispersion over the entire wavelength range is achieved by properly reducing the diameter of the core neighboring air holes. The pulse propagation within the core of the proposed PCF and the SC generation process are accurately modelled and optimized, by numerically solving the generalized nonlinear Schrodinger equation. Both of Self Phase Modulation (SPM) and Optical Wave Breaking (OWB) effects are identified as the dominant nonlinear mechanisms involved in the pulse spectral broadening process. By launching at 3 μm, a 3 nJ energy and 50 fs duration input pulse into 15 mm long PCF, a broadband and highly coherent mid-infrared SC spectrum spanning the spectral region from 1.45 μm to 5.95 μm at 20 dB, is successfully generated.

In this paper, we numerically demonstrate broadband, ultraflat-top and highly coherent mid-infrared Supercontinuum (SC) generation in an all-normal dispersion (ANDi) Ge15Sb15Se70 chalcogenide Circular Lattice Photonic Crystal Fiber (CL-PCF). The propagation properties of the fundamental mode are computed with the Finite Difference Method (FDM). Numerical results show that ANDi regime is obtained over the entire mid-infrared wavelength range with a cladding pitch and air holes diameter of Λ = 2 μm and d = 0.8 μm, respectively. Besides, the proposed CL-PCF exhibits small effective mode area and high Kerr nonlinearity up to 1.96 W−1 m−1 at 3 μm. Ultrashort pulse propagation inside the CL-PCF core is modelled by using the Generalized Non-Linear Schrodinger Equation (GNLSE). Simulation results show that by pumping at 3 μm laser pulses with a total energy of 0.6 nJ and duration of 50 fs, into 10 mm long of the CL-PCF, generates an ultrabroadband and highly coherent SC spanning the wavelength region from 1.86 μm to 5.35 μm within less than 3 dB spectral dynamics. By increasing the initial pulse energy to attain 1 nJ, the generated SC bandwidth increases too and reaches 4.53 μm in the spectral range extending from 1.67 μm to 6.2 μm at 4 dB spectral level. Moreover, the proposed CL-PCF based SC source is found promising for application in Optical Coherence Tomography (OCT) with an axial resolution of 0.87 μm, achieved when pumping 1 nJ energy and 50 fs duration optical pulses.

Orthogonal frequency division multiplexing (OFDM) systems have inferior nonlinear performance due to their high peak to average power ratio (PAPR) characteristics, which degrades the performance in optical wireless communication systems. A modified asymmetrically clipped optical (ACO)-OFDM system with low PAPR by introducing a discrete sliding norm transform (DSNT) as low-complexity post-inverse discrete Fourier transform processing is proposed. Numerical results show that the proposed DSNT-ACO-OFDM achieves about 50% PAPR reduction, while maintaining a competitive bit error rate performance compared with the conventional schemes.

This paper is aimed at proposing a novel printed microstrip-fed slot antenna suitable for wireless ultra-wideband (UWB) communication systems. The proposed antenna has been designed for operating at GHz frequency band. The synthesis of the antenna is carried out by means of parametric study of the main parameters. The result is a printed stepped-circular-shaped slot antenna exhibiting a good impedance matching with different tuning stubs. To demonstrate the effectiveness of the proposed UWB antenna, the results from numerical validations and experimental tests are presented and discussed.

5. CONCLUSIONS The dispersion characteristics of thin layer radome of LiTi-ferrite under external DC-magnetic are presented. Resulted absorbing power coefficients graph verifies the dispersion relation graph obtained by quasi-TEM cutoff frequency range. As discussed, this is a very simple approach which ignores reflections at the ferrite-air interfaces, as well as multiple reflections between the ferrite and antenna layers, but it is found to give a reasonable justification of the attenuation through the radome layer. More sophisticated (e.g., full-wave) analysis may be necessary if the ferrite layer is in direct contact with the antenna or array. It is seen that the frequency where maximum attenuation occurs can be tuned by adjusting the bias field. Also, note that the attenuation is greater for higher frequencies, primarily because the ferrite layer looks electrically thicker.

EMW Publishing, USA.; International audience; In most existing transmitted-reference ultra-wideband (TR-UWB) communication systems, receivers use the standard Gaussian approximation (SGA) for multiuser interference (MUI). It is an assumption used in most conventional multiuser systems, where the MUI tends to a Gaussian process by the central limit theorem, and convergence is relatively fast with respect to the number of users. However, for TR-UWB systems which are developed for short-range applications, we have a small number of active users. In this case, significant performance degradation is found in TR-UWB receivers due to the impreciseness of SGA. In this paper, we show that the Middleton class-A model is a more appropriate statistical model for MUI modeling in TR-UWB systems than the often used SGA. A closed-form expression for the probability density function (PDF) of the TR-UWB system under MUI, Gaussian noise and impulsive alpha-stable interference is developed. All these analytical results are confirmed by numerical simulations. (17 References).

International audience; We experimentally demonstrate the feasibility of the bandwidth tuning of a liquid-crystal based bandpass Lyot filter. This bandwidth tuning is achieved by applying a voltage to vary the birefringence of the liquid-crystal cells whose optical path difference takes predefined discrete values. We show that for a 2-stage liquid-crystal Lyot filter and at lambda i = 1.543 um, the measured 3-dB bandwidth varies from 17 nm to 60 nm when the applied voltage increases from 0 V to 5.24 V. The shape of the transmission response remains unchanged during the bandwidth tuning process.

A novel printed monopole antenna fed by a coplanar waveguide (CPW) is proposed in view of ultra-wideband applications. Its impedance bandwidth defined by a voltage standing-wave ratio (VSWR