Mode Analysis and Design of a Low-Loss Photonic Crystal 60 degrees Waveguide Bend

The guided modes of a two-dimensional photonic crystal straight waveguide and a waveguide bend are studied in order to find the high transmission mechanism for the waveguide bend. We find that high transmission occurs when the mode patterns and wave numbers match, while the single-mode condition in the waveguide bend is not necessarily required. According to the mechanism, a simply modified bend structure with broad high transmission band is proposed. The bandwidth is significantly increased from 19 to 116 nm with transmission above 90%, and covers the entire C band of optical communication.

High transmission of slow light in the photonic crystal waveguide bends

We present the research on the transmission characteristic of slow-light-mode in the photonic crystal line-defect waveguide bends on SOL After optimizing the structure parameters in the vicinity of the bends, the normalized transmission efficiency of slow-light-mode through the photonic crystal 60 degree and 120 degree waveguide bends are as high as 80% and 60% respectively, which are 10 times higher than that in the undeformed case. To slow down light further, we design novel coupled cavity waveguide bend structures with high quality-factor. High normalized transmission efficiency of 75% and low group velocity of c/170 ( c is the light velocity in vacuum) are realized. These results are beneficial to enhance the slow light effect of photonic crystal structures and improve the miniaturization and integration of photonic crystal slow light devices.

Flexible Control of Light Propagation Using a Novel Photonic Crystal Hetero-Waveguide Based on Silicon-on-Insulator Slab

We demonstrate a photonic crystal hetero-waveguide based on silicon-on-insulator (SOI) slab, consisting of two serially connected width-reduced photonic crystal waveguides with different radii of the air holes adjacent to the waveguide. We show theoretically that the transmission window of the structure corresponds to the transmission range common to both waveguides and it is in inverse proportion to the discrepancy between the two waveguides. Also the group velocity of guided mode can be changed from low to high or high to low, depending on which port of the structure the signal is input from just in the same device, and the variation is proportional to the discrepancy between the two waveguides. Using this novel structure, we realize flexible control of transmission window and group velocity of guided mode simultaneously.

Degenerate four-wave mixing based all-optical wavelength conversion in a semiconductor optical amplifier and highly-nonlinear photonic crystal fiber parametric loop mirror

The idler is separated from the co-propagating pump in a degenerate four-wave mixing (DFWM) with a symmetrical parametric loop mirror (PALM), which is composed of two identical SOAs and a 70 m highly-nonlinear photonic crystal fiber (HN-PCF). The signal and pump are coupled into the symmetrical PALM from different ports, respectively. After the DFWM based wavelength conversion (WC) in the clockwise and anticlockwise, the idler exits from the signal port, while the pump outputs from its input port. Therefore, the pump is effectively suppressed in the idler channel without a high-speed tunable filter. Contrast to a traditional PALM, the DFWM based conversion efficiency is increased greatly, and the functions of the amplification and the WC are integrated in the smart SOA and HN-PCF PALM. (C) 2008 Elsevier B.V. All rights reserved.

The impact of imperfect symmetry on band edge modes of a two-dimensional photonic crystal with square lattice

A theoretical analysis has been performed by means of the plane-wave expansion method to examine the dispersion properties of photons at high symmetry points of an InP based two-dimensional photonic crystal with square lattice. The Q factors are compared qualitatively. The mechanism of surface-emitting is due to the photon manipulation by periodic dielectric materials in terms of Bragg diffraction. A surface-emitting photonic crystal resonator is designed based on the phenomenon of slow light. Photonic crystal slabs with different unit cells are utilized in the simulation. The results indicate that the change of the air holes can affect the polarization property of the modes. So we can find a way to improve the polarization by reducing the symmetry of the structure.

High efficiency operation of butt joint line-defect-waveguide microlaser in two-dimensional photonic crystal slab

Butt joint line-defect-waveguide microlasers are demonstrated on photonic crystal slabs with airholes in a triangular lattice. Such microlaser is designed to increase the output power from the waveguide edge directly. The output power is remarkably enhanced to 214 times higher by introducing chirped structure in the output waveguide. The lasing mode operates in the linear dispersion region of the output waveguide so that the absorption loss due to the band-edge effect is reduced. The laser resonance is illustrated theoretically using the finite difference time domain method. A practical high power efficiency of 20% is obtained in this microlaser. (C) 2008 American Institute of Physics.

Design of a compact polarization beam splitter based on a deformed photonic crystal directional coupler

In this paper a compact polarization beam splitter based on a deformed photonic crystal directional coupler is designed and simulated. The transverse-electric (TE) guided mode and transverse-magnetic (TM) guided mode are split due to different guiding mechanisms. The effect of the shape deformation of the air holes on the coupler is studied. It discovered that the coupling strength of the coupled waveguides is strongly enhanced by introducing elliptical airholes, which reduce the device length to less than 18.5 mu m. A finite-difference time-domain simulation is performed to evaluate the performance of the device, and the extinction ratios for both TE and TM polarized light are higher than 20 dB.

Passively mode-locked YVO4/Nd : YVO4 composite crystal laser with a semiconductor saturable absorber as a high reflector

A passively mode-locked diode end-pumped YVO4/Nd:YVO4 composite crystal laser with a five-mirror folded cavity was first demonstrated in this paper by using a low temperature semiconductor saturable absorber mirror grown by metal organic chemical vapor deposition. Both the Q-switching and continuous-wave mode locking operation were realized experimentally. A stable averaged output power of 10.15 W with pulse width of about 11.2-ps at a repetition rate of 113 MHz was obtained, and the optical-to-optical efficiency of 43% was achieved.

Diode-pumped passively mode-locked YVO4/Nd : YVO4 composite crystal laser with LT-In0.25Ga0.75As saturable absorber

A passively mode-locked all-solid-state YVO4/Nd:YVO4 composite crystal laser was realized with a low temperature (LT) In0.25Ga0.75As semiconductor saturable absorber mirror. The saturable absorber was used as nonlinear absorber and output coupler simultaneously. Both the Q-switch and continous-wave mode locking operation were experimentally realized. At a pump power of 4 W, the Q-switched mode locking changed to continuous wave mode locking. An average output power of 4.1 W with 5 ps pulse width was achieved at the pump power of 12 W, corresponding to an optical-optical conversion efficiency of 34.2%.

Application of fast Pade approximation in simulating photonic crystal nanocavities by FDTD technology

The exact calculation of mode quality factor Q is a key problem in the design of high-Q photonic crystal nanocavity. On the basis of further investigation on conventional Pade approximation, FDM and DFT, Pade approximation with Baker's algorithm is enhanced through introducing multiple frequency search and parabola interpolation. Though Pade approximation is a nonlinear signal processing method and only short time sequence is needed, we find the different length of sequence requirements for 2D and 3D FDTD, which is very important to obtain convergent and accurate results. By using the modified Pade approximation method and 3D FDTD, the 2D slab photonic crystal nanocavity is analyzed and high-Q multimode can be solved quickly instead of large range high-resolution scanning. Monitor position has also been investigated. These results are very helpful to the design of photonic crystal nanocavity devices. (C) 2008 Elsevier B.V. All rights reserved.