Chu-En Lin

Magnetic hardening mechanism study in FePt thin films

Fe100−xPtx alloy thin films with x=25–67 at. % were prepared by dc magnetron sputtering on naturally oxidized Si substrates. Effects of film composition, annealing temperature (300–650 °C), annealing time (5–120 min), and cooling rate (furnace cooling or ice water quench cooling) on the magnetic properties were investigated. Optimum conditions for saturation magnetization and coercivity of the Fe100−xPtx alloy films were found with x=50 at.%, annealed at 600 °C for 30 min and cooled by ice water quenching. Our experimental data suggests that the magnetic hardening in Fe100−xPtx alloy thin films is mainly due to the fct γ1-FePt phase and the domain wall pinning effect. The domain nucleation mechanism is dominated in samples with furnace cooling; the domain wall pinning mechanism dominates in samples cooled with ice water quenching.

High speed interferometric ellipsometer

A novel high speed interferometric ellipsometer (HSIE) is proposed and demonstrated. It is based on a novel differential-phase decoder which is able to convert the phase modulation into amplitude modulation in a polarized heterodyne interferometer. Not only high detection sensitivity but also fast response ability on ellipsometric parameters (EP) measurements based on amplitude-sensitive method is constructed whereas different amplitudes with respect to P and S polarized heterodyne signals in this phase to amplitude modulation conversion is discussed. The ability of HSIE was verified by testing a quarter wave plate while a real time differential-phase detection of a liquid crystal device versus applied voltage by using HSIE was demonstrated too. These results confirm that HSIE is able to characterize the optical property of specimen in terms of EP at high speed and high detection sensitivity experimentally.

Electro-optic Ti:PPLN waveguide as efficient optical wavelength filter and polarization mode converter

We report the first experimental demonstration of electrically controlled Solc-type optical wavelength filters and TE-TM mode converters based on Ti-diffused periodically poled lithium niobate (Ti:PPLN) waveguides. A maximum mode conversion efficiency or a peak spectral transmittance of ~99% in the telecom C-L bands was obtained from a 9-mm long, 21.5-21.8-mum multiple-grating Ti:PPLN waveguide device with a switching voltage of as low as 22 V or 0.99 Vxd(mum)/L(cm), where d is the electrode separation and L is the electrode length. The spectral range of this device can be tuned by temperature at a rate of ~0.758 nm/ degrees C.

High Q-factor microring resonator wrapped by the curved waveguide.

In this work, we study the performances of ring resonators of different type by analyzing the bending loss and the condition of the critical coupling. We propose that the bending loss of microring can be reduced by wrapping a concentrically curved waveguide. The difference of propagation constant between two concentrically curved waveguides can be tuned by adjusting the bus waveguide width to optimize the critical coupling. Furthermore, we propose to enlarge the difference of the propagation constant between two concentrically curved waveguides to maintain the circulating light in the ring to obtain higher quality factor. In this study, the highest quality factor that we measured is 7 × 105.

Paired circularly polarized heterodyne ellipsometer

We develop a paired circularly polarized heterodyne ellipsometer (PCPHE), in which a heterodyne interferometer based on a two-frequency circularly polarized laser beam is set up. It belongs to an amplitude-sensitive ellipsometer that is able to provide not only a wider dynamic range of polarization modulation frequency but also a higher detection sensitivity than that of a conventional photometric ellipsometer. A real-time and precise measurement of ellipsometric parameters, which demonstrated an accuracy of less than 1 nm on thickness measurement of SiO(2) thin film deposited on silicon substrate, can be applied with the PCPHE.

Electro-optic narrowband multi-wavelength filter in aperiodically poled lithium niobate

We report on an iterative design scheme for and the first experimental demonstration of active narrowband multi-wavelength filters based on aperiodically poled lithium niobate crystals. A simultaneous transmission of 8 wavelengths, each with a ~0.45-nm linewidth and nearly 100% peak transmittance, was achieved in such a device. The transmission spectrum of this device can be tuned by temperature at a rate of ~0.65 nm/ degrees C.

Identification of mirror waves by the phase difference between perturbed magnetic field and plasmas

A new approach is proposed to identify mirror waves based on the 90 degrees phase difference between the magnetic field and plasma fluctuations. Magnetosheath observations, the linear MHD theory, and one-dimensional hybrid simulations support that the 90 degrees phase difference is a special character for mirror waves. This phase difference is independent of Doppler shift which means that our result remains the same in both the satellite (laboratory) and the plasma frames of reference. Therefore it is useful to distinguish mirror waves from slow waves which also have an anticorrelation (i.e., 180 degrees out of phase) relationship between magnetic field strength and plasma density fluctuations. The time evolution in the later stage shows that the dominant perturbed components are the magnetic field fluctuation along the background magnetic field B-0 and the velocity fluctuation perpendicular to B-0 and the wave vector k. A higher coherence and a stable 90 degrees phase difference between these two dominant components are found as time increases. The coherence between this velocity component and the plasma density is also high with a 90 degrees phase difference. A tendency is found that the longer wavelengths are progressively generated when mirror waves grow in simulation.

Monolithically integrated multi-wavelength filter and second harmonic generator in aperiodically poled lithium niobate

We report on the design and experimental characterization of aperiodically poled lithium niobate (APLN) crystals for use in monolithically integrated dual nonlinear-optical devices. A cascade and a single aperiodic-domain-structure designs based on simulated annealing method were constructed in LiNbO(3) to simultaneously perform as 4-channel electro-optically active (EOA) filters and 4-channel frequency doublers in the telecom band. We found that we could obtain a 2.44-fold enhancement in second-harmonic-generation conversion efficiency and a 2.4-time reduction in filter transmission bandwidth with the single APLN device over the cascade one when the same device length of 2 cm and the EOA field of 1027 V/mm were used.

Diode-pumped, actively internal-Q-switched Nd:MgO:PPLN laser.

We demonstrated a diode-pumped, electro-optically internal-Q-switched laser system fabricated using a Nd:MgO:PPLN. We obtained laser pulses of pulse energy > 2.45 muJ and pulse width ~28 ns from this internal-Q-switched laser system with 2% output coupling.

Kinetics of Glucose Mutarotation Assessed by an Equal-Amplitude Paired Polarized Heterodyne Polarimeter

A dual-frequency equal-amplitude paired polarization heterodyne polarimeter (DEPHP) was set up in order to precisely measure the mutarotation rate constants of D-glucose in tridistilled water. The DEPHP is based on a balanced detector detection scheme for measurement of the optical rotation angle of D-glucose/water solution during the conversion process between alpha-D-glucose and beta-D-glucose while in a nonequilibrium state. The DEPHP can perform shot-noise-limited detection, so that the total optical rotation angle together with the mutarotation rate constants of alpha-D-glucose and beta-D-glucose conversion can be measured with high sensitivity. In this experiment, the sensitivity of the optical rotation angle measurement was 8.3 x 10(-5) deg/cm, while the total (k), forward (k(1)) and reverse (k(2)) mutarotation rate constants of D-glucose were found to be k = 7.67 x 10(-5) s(-1), k(1) = 2.76 x 10(-5) s(-1), and k(2) = 4.91 x 10(-5) s(-1), respectively, in tridistilled water. Moreover, using the DEPHP, we can measure the specific rotation angles of alpha-D-glucose and beta-D-glucose in water at 632.8 nm. They were 105 degrees and 12 degrees, respectively. Finally, the detection sensitivity of the DEPHP system is also discussed.