Micromagnetic analysis of transition noise for high-density perpendicular recording

In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated.     

Engineering issue study of triple harmonic method for in situ flying height analysis

In situ flying height testing technology is becoming more and more important in slider–disk interaction analysis and manufacturing quality control of disk drives and head-related components. Triple harmonic method is a quite promising choice for in situ flying height analysis, compared with other in situ methods reported up to now. This paper reports results of investigations on engineering issues of applying triple harmonic method for in situ flying height analysis. The paper reports results of analysis on the effects of various testing conditions on flying height testing repeatability and accuracy. Results suggest that working at reasonable high channel density and working on the ratio between third and first harmonics will be an advantage in terms of both flying height testing sensitivity and testing repeatability. Comparing with media thickness effect, the gap-length variation among different heads will be important if it is to study flying height difference among different heads and the testing is at high channel density. Also, it is suggested to work at AC erased track, in order to reduce the non-linearity caused by hard transition.     

Magneto resistance due to domain wall scattering and magneto size effect of thin Ni and Co films at low temperatures

Nickel and cobalt films illustrate alternative Bloch lines with cap switches. The strip magnetic domains become zigzag and bubbling cells for Ni and Co films, respectively, under an external field of 1.5 T. The magnetoresistances (MR) for currents parallel (CIW) to the domain walls is 15% less than those of the perpendicular (CPW) case. We also studied the magneto size effect by applying the magnetic field normal to the surface, from which the Sondheimer oscillation appears attributing to periodic striking of the surface for electrons traveling in circular motion on a plane canting to the surface. The experiments can be expressed by the magneto size effect inherited with very small specularity parameters.     

Theoretical investigation of magnetic property in paramagnetic neodymium gallium garnet under high magnetic field

The magnetic property in neodymium gallium garnet (NdGaG) is studied by the quantum theory. The ground configuration split states are calculated taking into account the spin–orbit interaction and crystal field effect. Taking account of the Nd–Nd exchange interaction, a good agreement between experimental and theoretical values can be obtained for the variation of the magnetic moment with the external magnetic field under “extreme” conditions (low temperature and high magnetic field). Moreover, the temperature dependence of magnetic moment and the magnetic susceptibility χ is also discussed. Above 30 K, the magnetization (M) shows a linear field (H_e) dependence.     

Sensing and fluorescence behaviors of complex formation between new lariat crown ethers bearing fluorescence sidearm and metal ions in methanol solution

Fluorescence spectroscopic properties of the complex formation between six new C-pivot16-crown-5 ethers bearing fluorescence side arms and metal ions are studied. Six new C-pivot 16-crown-5 ethers that carry fluorescence side arms were synthesized. The research also included the examination of different fluorescent behavior of the new lariat ethers in the presence of silver and sodium ions (Ag⁺ and Na⁺) in methanol. Because of the good fit of the cavity size of these 16-crown-5 ethers with the Ag⁺ and Na⁺ ions, remarkable change in fluorescent spectra were observed. The results showed that the new lariat crown ethers exhibited enhanced selectivity towards sodium ion, but silver ion show quenching abilities towards the ligands. Cooperative participations of the C-pivot side arm oxygen with the ring oxygen molecules in complexation was also confirmed by the single crystal X-ray crystallography of the complex, (C₂₇H₃₀O₇)·NaClO₄. The freezing of crown ring conformation and the diminishment of the chance of sidearm oscillation that occurred upon complexation with sodium ion are the main causes of fluorescent enhancement. The quenching caused by the addition of silver ion was found to explainable by the photo-induced electron transfer that results in the reduction of silver ions.     

Preparation, characterization and photocatalytic activity of polycrystalline Bi2O3/SrTiO3 composite powders

Bi₂O₃/SrTiO₃ composite powders have been prepared and their photocatalytic activities were investigated by photooxidation of methanol. These powders were characterized by UV-Visible diffuse reflectance spectra, SEM and X-ray diffraction (XRD). The results revealed that all the Bi₂O₃/SrTiO₃ composite powders exhibited higher photocatalytic activity than pure SrTiO₃, Bi₂O₃ and TiO₂ (P25) under visible light irradiation (λ>440 nm). The effects of the Bi₂O₃ contents on the photocatalytic activities of the composite powders were examined, the photocatalytic activities increased with the content of Bi₂O₃ increasing to a maximum of 83% and then decreased under visible light irradiation. The effects of the calcination temperatures on the photocatalytic activities of the composite powders were also investigated.     

Rotation-invariant pattern recognition using morphological phase-only correlation

We present a rotation-invariant nonlinear correlator based on the circular harmonic filter (CHF) and the previously proposed morphological phase-only correlator (MPC) [Q. Wang, S. Liu, Opt. Commun. 244 (2005) 93]. We refer to this correlator as a rotation-invariant MPC (RIMPC). Through computer simulation, we compare the output results of RIMPC with those of rotation-invariant MC (RIMC) and CHF when input scene is corrupted by salt-and-pepper noise, white additive Gaussian noise and cluttered background. Our results show that RIMPC yields higher discriminability, sharper and higher correlation peaks and displays better stability against the above three kinds of noise than do the RIMC and common CHF.     

Ultrafast non-linear optical properties of Ge20As25Se55 chalcogenide films

The non-resonant third-order non-linear optical properties of amorphous Ge₂₀As₂₅Se₅₅ films were studied experimentally by the method of the femtosecond optical heterodyne detection of optical Kerr effect. The real and imaginary parts of complex third-order optical non-linearity could be effectively separated and their values and signs could be also determined, which were 6.6 × 10⁻¹² and −2.4 × 10⁻¹² esu, respectively. Amorphous Ge₂₀As₂₅Se₅₅ films showed a very fast response in the range of 200 fs under ultrafast excitation. The ultrafast response and large third-order non-linearity are attributed to the ultrafast distortion of the electron orbitals surrounding the average positions of the nucleus of Ge, As and Se atoms. The high third-order susceptibility and a fast response time of amorphous Ge₂₀As₂₅Se₅₅ films makes it a promising material for application in advanced techniques especially in optical switching.     

Comparison of polarization-mode dispersion tolerances in polarization-multiplexing systems with different modulation formats

The polarization-mode dispersion (PMD) tolerance of 10 Gb/s polarization-multiplexing (PM) system is investigated. Using the importance sampling (IS) method, the outage probabilities of the PM systems with three modulation formats, including on-off keying (OOK), differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK), are quantified. When the amplified spontaneous emission (ASE) noise is assumed to be dominant, we evaluate the optical power penalties caused by the PMD effect at bit error rate (BER) of 10⁻¹². The performance of compensated PM systems with variable optical delay line is also described. The simulation results indicate that the OOK signal with higher duty cycle (DC) performs better in the PM systems with PMD compensation. It is found that the higher-order PMD impairs seriously the performance of the PM system, and phase-keying formats are more sensitive to the PMD than the OOK.     

Tunable microwave photonic notch filter using a dual-wavelength fiber laser with phase modulation

A novel tunable microwave photonic notch filter using a phase-modulated dual-wavelength fiber laser is presented. A stable dual-wavelength erbium-doped fiber laser with a linear cavity is formed by a polarization-maintaining uniform fiber Bragg grating (PM-FBG) and a polarization maintaining linearly chirped fiber Bragg grating (PM-LCFBG), both of which were fabricated on a high-birefringence (Hi-Bi) fiber. It is found that a stable room-temperature dual-wavelength operation can be achieved due to the presence of two reflection peaks arising from the orthogonal states of polarization (SOP) of the PM-FBG. Experimental results show stable dual-wavelength lasing operation with a wavelength separation of ∼0.36 nm and a large optical signal-to-noise ratio (OSNR) of over 40 dB under room temperature. The dual-wavelength fiber laser is combined with a phase modulator and a segment of single-mode fiber (SMF) as a dispersive device to form a tunable microwave photonic notch filter. By stretching the PM-FBG to tune the wavelength separation of the dual-wavelength fiber laser, a tunable microwave photonic notch filter with various free spectral ranges (FSRs) and a rejection ratio greater than 35 dB was developed.