Static and dynamic hysteresis loops of TbFeCo amorphous films are measured by vibrating sample magnetometry (VSM) and magneto-optical Kerr rotation. The static VSM loop shows a faster magnetization reversal than the static Kerr loop does. The dynamic Kerr hysteresis loop in a sinusoidal alternating magnetic field at 1.14kHz shows a large increase in coercivity with respect to the static coercivity. The ultrafast dynamics of laser-induced demagnetization and magnetization recovery is studied by femtosecond time-resolved polar Kerr rotation spectroscopy, and shows a subpicosecond demagnetization and several hundreds of picosecond magnetization recovery process, which suggests gigahertz writing rate possible.

In order to measure photoinduced dynamic magnetization reversal by single laser pulse, alternating magnetic field is synchronized with the femtosecond laser pulse such that the magnetization state is reset before each single laser pulse. For perpendicularly magnetized L10 FePt films, the dynamic magnetization reversal process is accompanied by the nucleation of reversed domains and the barrierless transient domain wall motion at low magnetic fields and subsequent pinned domain wall motion at the switching field. The switching field does not change with the pump-probe delay time.

Ultrafast dynamics of genuine magneto-optical recording across ferrimagnetic compensation points is demonstrated in GdFeCo films using time-resolved polar Kerr spectroscopy combined with a laser-synchronized sinusoidal alternating magnetic field which can reinitialize irreversible initial magnetization state to laser radiating. The external field dependence of magnetization reversal dynamics is measured and shows that reversal rate accelerates with increasing external fields. Analysis of the magnetization reversal dynamics with Bloch equation shows the magnetization reversal rate is linearly dependent on the external fields within experimental errors, which supports quantitatively that the mechanism of magneto-optical recording in rare earth-transition metal ferromagnetic films is related to the formation and growth of the reversed domains. It is also shown that nucleation field is obviously larger than hot coercivity shown in the anomalous hysteresis loop.

To date most research on optical networking has concentrated on wavelength-division multiplexing (WDM), which routes different packets according to the wavelength of the optical carrier. Optical time-division multiplexing (OTDM) is considered as an alternative to WDM for future networks and with single stream data rates of 100 Gb/s using a single wavelength at high (up to 100 Gbit/s) data rates [1][2][3] .In this paper we have developed a model of an all optical router based on the terahertz optical asymmetric demultiplexer (TOAD). The model architecture is based on a system which has as its input an OTDM packet containing header and payload information. The model simulates extraction of header information from the data stream using one TOAD, which is subsequently used to make a routing decision. The payload information is routed through a second TOAD according to the information contained in the header.Simulations require the use of the TOAD in two distinct modes 1). A bit level demultiplexer for the header 2). A frame level demultiplexer for the payload. Consequently less stringent requirements are required with regard to the TOAD switch resolution for payload demultiplexing compared to header demultiplexing. However, as our simulations show the wider window allowed in case 1 introduces a higher level of residual crosstalk. In case 2 the higher resolution imposes a greater restriction on the jitter present.At this stage a simple 1 by 2 router is presented, however further work will enhance the model to a network with multiple inputs and outputs.

Ultrafast spin dynamics has for the first time been studied in perpendicular magnetized granular films. For FePt continuous films and FePt–MgO and FePt–Ag granular films with femtosecond laser excitations, the coercivity HC and the saturation Kerr rotation θKS are dramatically reduced, accompanied by a sharp increase in the reflectivity R. Afterward, these physical quantities are slowly recovered. The changes in HC, θKS, and R are all different among FePt, FePt–MgO, and FePt–Ag films. The difference is caused by different film thicknesses and in particular by the surface plasmon resonance of metallic nanoparticles.