Athikom Roeksabutr

Adaptive IIR notch filters based on new error criteria

Modified indirect and direct plain gradient (MIPG and MDPG) algorithms using new error criteria for second-order adaptive IIR (infinite-impulse response) notch filters (ANFs) with constrained poles and zeros are proposed in this paper. The proposed techniques are based on modifying error functions of the standard indirect and direct ANFs. In this work, the proposed error criteria are modified as the mean value of the product of the two signals which are, respectively, produced by the FIR (finite-impulse response) and IIR sections of the ANFs. Due to a non-zero slope straight line-like characteristic of the new cost functions, the gradient based adaptive algorithm rapidly converges to an optimum solution resulting in faster convergence speed than that of the conventional method. The closed form expressions for steady-state estimation bias and mean square error (MSE) of the proposed algorithms are also carried out. In addition, extensive simulations of the proposed algorithms compared to other methods are provided to support the theoretical analyses. Although, there are some limitations in the proposed algorithms, however, the demonstrated results obtained from tested algorithms at the same condition confirm that the proposed MIPG and MDPG algorithms are superior to others in convergent speed.

Direct frequency estimation based adaptive algorithm for a second-order adaptive FIR notch filter

This work deals with the problem of the frequency estimation of a sinusoidal signal corrupted by broad-band noise. The direct frequency estimation based adaptive algorithm for a second-order adaptive finite impulse response (FIR) notch filter (AFNF) is thus proposed. The proposed algorithm employs the bias removal technique to remove the bias existing in the estimated parameter. The performances including the rate of convergence and the mean square error (MSE) can be easily controlled by using only one parameter, i.e., step size parameter. Moreover, the proposed filter is simple to implement and suitable for real-time applications. In addition, the difference equations for the convergence in the mean and mean square, and the closed form expressions for the steady-state estimation bias and MSE are also carried out. Finally, the simulation results are provided to confirm the theoretical analysis.

Electrode effect of an optical fiber acousto-optic resonator for microwave optoelectronics frequency decoder

We report a further theoretical study on the effect of electrode thickness of an acousto-optic resonator using ZnO-coated on a fiber surface inserted in a fiber ring resonator to decode the microwave frequency. For the results, changing the electrode thickness can shift the frequency and the top electrode has more effect than the bottom one.

Solitons and vortices in nonlinear two-dimensional photonic crystals of the Kronig-Penney type

Solitons in the model of nonlinear photonic crystals with the transverse structure based on two-dimensional (2D) quadratic- or rhombic-shaped Kronig-Penney (KP) lattices are studied by means of numerical methods. The model can also applies to a Bose-Einstein condensate (BEC) trapped in a superposition of linear and nonlinear 2D periodic potentials. The analysis is chiefly presented for the self-repulsive nonlinearity, which gives rise to several species of stable fundamental gap solitons, dipoles, four-peak complexes, and vortices in two finite bandgaps of the underlying spectrum. Stable solitons with complex shapes are found, in particular, in the second bandgap of the KP lattice with the rhombic structure. The stability of the localized modes is analyzed in terms of eigenvalues of small perturbations, and tested in direct simulations. Depending on the value of the KPs duty cycle (DC, i.e., the ratio of the voids width to the lattice period), an internal stability boundary for the solitons and vortices may exist inside of the first bandgap. Otherwise, the families of the localized modes are entirely stable or unstable in the bandgaps. With the self-attractive nonlinearity, only unstable solitons and vortices are found in the semi-infinite gap.

DWDM Demultiplexer Using Compound Optical Ring Resonator with Fiber Bragg Grating

The paper reports a theoretical study on the effect of grating period and loop length of optical DWDM demultiplexer using compound ordinary optical ring resonator with fiber Bragg grating. For the results, changing the grating period and optical paths can adjust the center wavelength of pass-band and narrow spacing bandpass peaks (channels)

Unbiased equation error adaptive IIR notch filter

This paper presents the unbiased gradient algorithm for the equation error adaptive IIR notch filter (UEANF). The proposed algorithm employs the bias removal technique to remove the bias existing in the estimated parameter, resulting in obtaining good estimate of the parameter. Moreover, the convergence property is improved as compared with the conventional adaptive IIR notch filter (ANF). The computer simulations are provided to confirm the performances of the proposed technique.

Unbiased constrained adaptive IIR notch filter using direct frequency estimation algorithm

An unbiased constrained direct adaptive IIR notch filter is presented in this paper. The proposed algorithm employs the bias removal technique to remove the bias existing in the estimate of the filter parameter, resulting in good estimate of filter parameter. The theoretical analysis for the difference equation for the convergence in the mean is derived in closed form and confirmed by the computer simulations.

Unbiased plain gradient algorithm for adaptive 11R notch filter with constrained poles and zeros

An unbiased plain gradient (UPG) algorithm for a constrained adaptive IIR notch filter (ANF) is presented in this paper. The proposed algorithm employs the bias removal technique to remove the bias existing in the estimate of the filter parameter, resulting in good estimation. The computer simulation results have shown that the proposed technique is unbiased.

Optimum length and piezoelectric thickness of a ZnO-coated optical fiber acousto-optic microwave modulator

Optical fiber acousto-optic resonators using piezoelectric ZnO coated fiber surfaces useful for all-fiber optical phase modulator system particularly at microwave frequency region. Its theory of operation has recently been presented. In this paper, we report a study on the design of a transducer with optimum transducer length and ZnO film thickness for maximum power transfer.

Two-Component Gap Solitons in Self-Defocusing Photonic Crystals

Studies of solitons in spatially periodic (lattice) potentials have grown into a vast area of research, with profoundly important applications to nonlinear optics, plasmonics, and matter waves in quantum gases, as outlined in recent reviews [1]-[4]. In ultracold bosonic and fermionic gases, periodic potentials can be created, in the form of optical lattices (OLs), by coherent laser beams illuminating the gas in opposite directions [5]-[7]. Effective lattice potentials for optical waves are induced by photonic crystals (PhCs), which are built as permanent structures by means of various techniques [2, 8, 9], or as laser-induced virtual structures in photorefractive crystals [10]. Reconfigurable PhCs can be also based on liquid crystals [11]. Parallel to the progress in the experiments, the study of the interplay between the nonlinearity and periodic potentials has been an incentive for the rapid developments of theoretical methods [12, 13]. Both the experimental and theoretical results reveal that solitons can be created in lattice potentials, if they do not exist in the uniform space [this is the case of gap solitons (GSs) supported by the self-defocusing nonlinearity, see original works [14]-[17] and reviews [7, 18]], and solitons may be stabilized, if they are unstable without the lattice (multidimensional solitons in the case of self-focusing, as shown in Refs. [17], [19]-[25], see also reviews [1, 3, 4]). The stability of GSs has been studied in detail too—chiefly, close to edges of the corresponding bandgaps—in one [27]-[29] and two [30] dimensions alike.