Ultrafast carrier dynamics in InN epitaxial films was investigated by using femtosecond time-resolved pump-probe reflectivity measurements with a photon energy of 1.58eV. The hot electron relaxation time decreased with increasing electron density (n), measuring at n−0.5. The result was contradictory to what was expected from the hot phonon effect and the screening effect. The authors attributed this result to the important role played by electron-electron scattering in hot electron relaxation.

The indices of refraction, extinction constants and complex conductivities of the GaN film for frequencies ranging from 0.2 to 2.5 THz are obtained using THz time-domain spectroscopy. The results correspond well with the Kohlrausch stretched exponential model. Using the Kohlrausch model fit not only provides the mobility of the free carriers in the GaN film, but also estimates the relaxation time distribution function and average relaxation time.

This work demonstrated a new approach of planar multi-channel wavelength division multiplexing (WDM) system using photonic crystal structures. The system consists of a waveguide that is realized by a defect row of photonic crystal and high Q-value micro-cavities with asymmetric super-cell design. Two-Dimension (2-D) Finite-Difference-Time-Domain (FDTD) method is performed for simulation in this paper. The results showed good ability to filter an incident pulse into six spectral channels with a FHWM improved from 3.6 nm to 1.4 nm and the coherence length improved from 0.667 cm to 1.716 cm at the center wavelength 1550 nm channel and no transmission degradation. Six-channel coarse wavelength division multiplexing (CWDM) from 1490~1590 nm with channel spacing of 20 nm which defined by ITU-T Recommendation G.694.2 are presented. And the inter-channel cross-talk is smaller than -17 dB. The device design is leading the way to achieve CWDM specification and has good capability to extend the application of communication filed and fiber optical sensor field.

We propose a general method for analyzing a multilayer optical waveguide with all nonlinear layers. This general method can be degenerated into some special cases, such as symmetric or asymmetric nonlinear optical waveguide structures, the intensity-dependent refractive index with self-focusing nonlinear medium, hollow waveguides, and multilayer systems. Based on this general method, the analysis and calculation of complicated multilayer optical planar waveguides can be achieved easily. The analytical and numerical results show excellent agreement.

Terahertz time-domain spectroscopy has been employed to measure the optical constants of ytterbium-doped yttrium aluminum garnet ͑Yb x Y 1−x ͒ 3 Al 5 O 12 ͑Yb:YAG͒ crystals for nominal x values of 0.0, 0.1, 0.2, 0.5, 0.8, and 1.0 in the frequency range from 0.2 to 1.8 THz. The real refractive indices for Yb:YAG crystals increase linearly with the concentration of Yb 3+ . The experimental results can be fitted by the Sellmeier equation. The results imply that the phonon modes of the Yb:YAG crystals shift to lower frequencies with substitution of Yb for Y. The extinction coefficients of the Yb:YAG crystals are smaller than 0.05.