Haoshuo Chen

The influence of structural relaxation on the density and Young’s modulus of metallic glasses

The Young’s modulus E of metallic glasses increases by ∼7% while the density ρ increases by only ∼0.5% upon annealing near the glass transition temperature. ρ and E of an ’’ideal’’ glass are calculated to approach the crystalline values within 0.5 and 10%, respectively. The large decrease in E of ∼30% observed upon vitrification of many glass‐forming alloys may be attributed mainly to the frozen‐in excess volume. The rates of increase in E associated with decrease in volume V, −d lnE/d lnV, during structural relaxation, crystallization, and thermal expansion are large and ∼15, 17, and 10, respectively. Structural reconstruction and consequent electron redistribution near the Fermi surface are suggested to be responsible for the large −d lnE/d lnV observed.

73.7 Tb/s (96 x 3 x 256-Gb/s) mode-division-multiplexed DP-16QAM transmission with inline MM-EDFA

Transmission of a 73.7 Tb/s (96 x 3 x 256-Gb/s) DP-16QAM mode-division-multiplexed signal over 119 km of few-mode fiber transmission line incorporating an inline multi mode EDFA and a phase plate based mode (de-)multiplexer is demonstrated. Data-aided 6 x 6 MIMO digital signal processing was used to demodulate the signal. The total demonstrated net capacity, taking into account 20% of FEC-overhead and 7.5% additional overhead (Ethernet and training sequences), is 57.6 Tb/s, corresponding to a spectral efficiency of 12 bits/s/Hz.

Silicon Photonic Integrated Mode Multiplexer and Demultiplexer

A novel passive integrated optical circuit for mode-multiplexing and demultiplexing six channels, LP01 and LP11 modes in a few-moded fiber, is designed and tested. A push-pull solution is proposed and demonstrated to excite the LP11 modes with a high extinction ratio. The circuit can outperform present bulk-optics solutions through its compactness and stability, and it has the potential advantages of high coupling efficiency and excellent mode crosstalk suppression.

The influence of quenching procedures on the kinetics of embrittlement in a Fe40Ni40B20 metallic glass

The kinetics of mechanical stability (embrittlement), stress relief, and crystallization of Fe40Ni40B20 metallic glassy ribbons obtained by different melt spin quenching processes were investigated. Ribbons made with higher rate of quenching exhibit better mechanical stability over those made with lower quenching rate. The thermal stability, temperatures, and activation energies for crystallization of all ribbons, however, are identical. The rates of stress relief are higher for ribbons made with higher quenching rate. Values of activation energy for stress relief are about the same for all ribbons. These activation energies for stress relief are also close to those values reported for structural relaxation.The kinetics of mechanical stability (embrittlement), stress relief, and crystallization of Fe40Ni40B20 metallic glassy ribbons obtained by different melt spin quenching processes were investigated. Ribbons made with higher rate of quenching exhibit better mechanical stability over those made with lower quenching rate. The thermal stability, temperatures, and activation energies for crystallization of all ribbons, however, are identical. The rates of stress relief are higher for ribbons made with higher quenching rate. Values of activation energy for stress relief are about the same for all ribbons. These activation energies for stress relief are also close to those values reported for structural relaxation.

Kinetics of low temperature structural relaxation in two (Fe‐Ni)‐based metallic glasses

Structural relaxation processes below the glass transition temperature have been investigated calorimetrically via isothermal annealing and the time shift method for (Fe.5Ni.5)75P16B6Al3 and Fe40Ni40P14B6 glasses. The relaxation spectra are described by broad distributions in both activation energies and frequency factors. The low temperature anneals stabilize a portion of the relaxation spectrum and the annealed sample upon heating shows an endothermic reaction above the annealing temperature. The effects of successive annealing are additive provided that the anneals are followed by a lower temperature one. The results may account for many aging behaviors, such as the wide variation in activation energies, ’’reversibility’’ in Curie temperature and the cross‐over phenomenon.

Correlation between elastic constants and flow behavior in metallic glasses

The addition of glass formers, B and P, raises not only the shear stiffness but also the tensile yield strain (ey) of Fe‐ and Co‐based glasses. ey increases by a factor of 2 from 1.23×10−2 for Pt–Ni–P glasses to 2.45×10−2 for Fe–B glasses as the Poisson’s ratio decreases from 0.42 to 0.32. The Vickers hardness of a Fe75B25 glass attains 1300 kg/mm2 which is the highest value reported for metallic glasses. The directionality of interatomic forces either due to atomic ordering or s‐d hybrid bonding in transition metals is proposed to be responsible for this behavior.

Sub‐sub Tg structural relaxation in glassy polymers

Structural relaxation in a temperature range from 32 to 62° K glass transition has been investigated, for the first time, for a nearly monodisperse polystyrene using a differential scanning calorimeter and a thermal mechanical analyzer. Low temperature anneals in the vicinity of 320 K stabilize the glassy structure and lead to volume contraction. Upon heating, the annealed samples show an excess endothermic peak and exhibit a gradual expansion associated with structural recovery above the annealing temperature. Significantly, the samples recover the initial heat content and volume without reheating through the glass transition temperature. This sub‐Tg structural relaxation behavior is in many respects distinct from that commonly observed near the glass transition. Kinetics of relaxation processes are also discussed.

Optically Tunable Frequency-Doubling Brillouin Optoelectronic Oscillator With Carrier Phase-Shifted Double Sideband Modulation

An optically tunable frequency-doubling optoelectronic oscillator (FD-OEO) based on stimulated Brillouin scattering (SBS) and carrier phase-shifted double sideband (CPS-DSB) modulation is proposed and demonstrated. SBS effect provides narrowband filtering for the OEO to generate an oscillation signal with frequency equal to the Brillouin frequency shift, while a CPS-DSB modulation by using a dual-parallel Mach-Zehnder modulator is implemented to double the oscillation frequency. Owing to the wavelength-dependent Brillouin frequency shift, frequency tunability is realized by tuning the wavelength of the laser source. In the experiments, frequency-doubling microwave signals from 18.38 to 18.74 GHz are generated when the wavelength of the laser source is tuned from 1565 to 1535 nm.

The evidence of structural relaxation as the origin of Curie temperature aging in metallic glass

Kinetics of both isothermal Curie temperature aging and enthalpy recovery of a metallic glass (Fe0.5Ni0.5)75P16B6Al3 near the glass temperature obey approximately a logt law, where t is the annealing time. The frequency factors ke of the first‐order rate reaction were obtained by assuming the configurational entropy as the rate determining factor. ke’s obtained agree reasonably with the temperature dependence of viscous flow. This is evidence that Curie temperature aging and thermal heat recovery of metallic glasses have the same origin, associated with structural relaxation, and can be described by the entropy model of viscous flow.

Compact spatial multiplexers for mode division multiplexing

Spatial multiplexer (SMUX) for mode division multiplexing (MDM) has evolved from mode-selective excitation, multiple-spot and photonic-lantern based solutions in order to minimize both mode-dependent loss (MDL) and coupler insertion loss (CIL). This paper discusses the implementation of all the three solutions by compact components in a small footprint. Moreover, the compact SMUX can be manufactured in mass production and packaged to assure high reliability. First, push-pull scheme and center launch based SMUXes are demonstrated on two mostly-popular photonic integration platforms: Silicon-on-insulator (SOI) and Indium Phosphide (InP) for selectively exciting LP01 and LP11 modes. 2-dimensional (2D) top-coupling by using vertical emitters is explored to provide a coupling interface between a few-mode fiber (FMF) and the photonic integrated SMUX. SOI-based grating couplers and InP-based 45° vertical mirrors are proposed and researched as vertical emitters in each platform. Second, a 3-spot SMUX is realized on an InP-based circuit through employing 45° vertical mirrors. Third, as a newly-emerging photonic integration platform, laser-inscribed 3D waveguide (3DW) technology is applied for a fully-packaged dual-channel 6-mode SMUX including two 6-core photonic lantern structures as mode multiplexer and demultiplexer, respectively.