Design of a compact polarizing beam splitter based on a photonic crystal ring resonator with a triangular lattice

We propose and simulate a new kind of compact polarizing beam splitter (PBS) based on a photonic crystal ring resonator (PCRR) with complete photonic bandgaps. The two polarized states are separated far enough by resonant and nonresonant coupling between the waveguide modes and the microring modes. Some defect holes are utilized to control the beam propagation. The simulated results obtained by the finite-difference time-domain method show that high transmission (over 95%) is obtained and the polarization separation is realized with a length as short as 3.1 mu m. The design of the proposed PBS can be flexible, thanks to the advantages of PCRRs.

Ultracompact triplexer by coupling and decoupling of multiple photonic crystal waveguides

We investigate numerically the self-imaging effect in a system of multiple coupled photonic crystal waveguides (M-CPCWs) with asymmetric coupling. Then two couplers of 2-CPCWs and 3-CPCWs are cascaded to form an ultracompact triplexer by employing coupling and decoupling of M-CPCWs. The wavelength of 1310 nm propagates along the input direction because the M-CPCWs are decoupled at the same decoupling frequency. The other two wavelengths (1490 and 1550 nm) are separated by combining multimode interference and the dual mode coupling effect. Only by introducing a single defect near the crossing point between two output photonic crystal waveguides (PCWs) are the high extinction ratios for the three wavelengths achieved simultaneously.

Proposal of an Ultracompact Triplexer Using Photonic Crystal Waveguide with an Air Holes Array

We propose an ultracompact triplexer based on a shift of the cutoff frequency of the fundamental mode in a planar photonic crystal waveguide (PCW) with a triangular lattice of air holes. The shift is realized by modifying the radii of the border holes adjacent to the PCW core. Some defect holes are introduced to control the beam propagation. The numerical results obtained by the finite-difference time-domain method show that the presented triplexer can separate three specific wavelengths, i.e. 1310, 1490 and 1550 nm with the extinction ratios higher than - 18 dB. The designed device with a size as compact as 12 mu m x 6.5 mu m is feasible for the practical application, and can be utilized in the system of fiber to the home.

Design of novel polarization beam splitter in two-dimensional photonic crystal

We present the design and the simulation of an ultracompact high efficiency polarization beam splitter (PBS) based on the properties of the light waves propagating in straight waveguide and composite structure photonic crystal. The splitting properties of the PBS are numerically simulated and analyzed by using the plane wave expansion (PWE) method and finite difference time domain (FDTD) method. The PBS consists of three parts, namely, input waveguide, beam structure and output waveguide. It is shown that a high efficiency and a large separating angle for TE mode and TM mode can be achieved. Owing to these excellent features, including small size and high rate, the PBS makes a promising candidate in the future photonic integrated circuits.

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.

Quantum efficiency of GaAs/AlGaAs thin films with two-dimensional photonic crystals

The optical properties of GaAs/AlGaAs thin films with photonic crystals were investigated by measuring their photoluminescence spectra. The spectral intensities, lifetimes, and quantum efficiencies decreased greatly compared with those in blank material without photonic crystals. The quantum efficiencies in the material were also calculated from spectral intensities and lifetimes and the quantum efficiencies calculated from those two methods agreed with each other to some extent.

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.

Dynamics of spontaneous emission from SiN with two-dimensional photonic crystals

We investigated the dynamics of spontaneous emission from a photonic crystal etched into a SiN slab. After fitting the decay curves of the emission to double exponential functions, we divided the dynamic process of the spontaneous emission into a fast process and a slow process. It was observed that the presence of the photonic crystal increased the proportion of the fast decay component, and consequently, the emission rate and time-integrated emission intensity were also enhanced. These enhancements were a result of the coupling of the guide modes to the leaky modes of the photonic crystal slab waveguide. (C) 2008 Optical Society of America.

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.

A photonic wire-based directional coupler based on SOI

A photonic wire-based directional coupler based on SOI was fabricated by e-beam lithography (EBL) and the inductively coupled plasma (ICP) etching method. The size of the sub-micron waveguide is 0.34 mu m x 0.34 mu m, and the length in the coupling region and the separation between the two parallel waveguides are 410 and 0.8 mu m, respectively. The measurement results are in good agreement with the results simulated by 3D finite-difference time-domain method. The transmission power from two output ports changed reciprocally with about 23 nm wavelength spacing between the coupled and direct ports. The extinction ratio of the device was between 5 and 10 dB, and the insertion loss of the device in the wavelength range 1520-1610 nm was between 22 and 24 dB, which included an about 18.4 +/- 0.4 dB coupling loss between the taper fibers and the polished sides of the device. (c) 2008 Elsevier B.V. All rights reserved.

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.