Hongliang Ren

Photonic crystal channel drop filter with a wavelength-selective reflection micro-cavity

In the paper, a novel three-port channel drop filter in two dimensional photonic crystals (2D PCs) with a wavelength-selective reflection micro-cavity is proposed. In the structure, two micro-cavities are used. One is used for a resonant tunneling-based channel drop filter. The other is used to realize wavelength-selective reflection feedback in the bus wave-guide, which consists of a point defect micro-cavity side-coupled to a line defect waveguide based on photonic crystals. Using coupled mode theory in time, the conditions to achieve 100% drop efficiency are derived thoroughly. The simulation results by using the finite-difference time-domain (FDTD) method imply that the design is feasible.

Channel drop filter in two-dimensional triangular lattice photonic crystals

Based on two-dimensional photonic crystals with a triangular lattice, a channel drop filter with a wavelength-selective reflection microcavity is designed. In the structure, two microcavities are used. One is used for a resonant tunneling-based channel drop operation. The other is used to realize wavelength-selective reflection feedback in the bus waveguide. The phase term, which is derived by means of coupled-mode theory to achieve close to 100% drop efficiency, is satisfied by modifying the sizes of the border air holes next to the bus waveguide section between the two cavities. Using the finite-difference time-domain method, the simulation results show complete power transfer between the bus and drop waveguides via the system.

A Novel Design of 2-D Photonic Crystal Directional Coupler With High Extinction Ratio and Short Coupling Length

In this paper, a novel structure of a 2 times 2 directional coupler with high extinction ratio, small coupling length, and decoupling input/output channels is proposed, based on a 2-D photonic crystal with a hexagonal lattice of air holes. A total length of the coupling component of 24a and an extinction ratio of -35.07 dB are achieved in simulation using the finite difference time-domain method. Potential applications of this novel structure in wavelength demultiplexing and 4 times 4 directional coupling switches are addressed.

Photonic Crystal Three-Port Channel Drop Filter Based on One-Way Waveguide

We design a highly efficient three-port channel drop filter (CDF) with only one channel drop micro-cavity based on photonic crystal (PC) one-way waveguide. According to the coupled mode theory in time, the conditions to achieve 100% drop efficiency are derived thoroughly. The numerical results are all calculated by using the finite element method, and accord well with the theoretical analysis. Compared with previous three-port CDF based on general dielectric PC, the CDF based on PC one-way waveguide first shows almost complete channel drop tunneling at resonance via only one channel drop micro-cavity without the need for any reflection feedback.

Polarization modulation of electromagnetic waves scattered from a quasi-homogeneous anisotropic medium

We show that, within the accuracy of the first-order Born approximation, the spatially uniform spectral degree of polarization (sDOP) of electromagnetic waves (EW) generally converts into a spatially depolarized distribution once the EW scatters from a quasi-homogeneous (QH) anisotropic medium. The influence of the anisotropic correlation lengths of the QH medium and that of the initial polarization of the EW incident on the sDOP of the scattered field are analyzed, separately. The results obtained may be of essential significance to the polarization imaging of anisotropic media, e.g.?for obtaining knowledge of biological tissues or the determination of spatially anisotropic particles.

Highly Sensitive Intensity Detection by a Self-Interference Micro-Ring Resonator

A novel highly sensitive intensity detection method has been proposed based on a self-interference ring resonator, where it is obtained by introducing an additional interference sensing arm between two coupling regions in the conventional planar add-drop micro-ring resonator. By means of dissipative and dispersive coupling mechanisms, optical path length changes of sensing arm not only bring the shift in a resonant wavelength, but also result in the variation of the linewidth and extinction of the spectrum. Using the analytical expression of the transmittance, it is proved that this sensor can monitor optical path length changes of sensing arm with a theoretical detection limit (5.6 × 10-3 nm) by measuring intensity variations at a certain transmission valley.

Ultra-wideband optical diode based on photonic crystal 90° bend and directional coupler

We propose an ultra-wideband optical diode device based on two-dimensional square-lattice photonic crystals. For the device, the odd mode is completely transmitted in one direction and converted to the fundamental even mode, but completely reflected in the other direction. The operation bandwidth of the device is preserved within a rather wide range of frequencies, which is over 6.5% of the central frequency. A directional coupler and 90° bend are utilized as the composite function device with mode filter and mode converter. It is possible that the photonic crystal device can help to construct on-chip optical logical devices and benefit greatly to the optical systems with multiple spatial modes.

Design of reconfigurable optical add/drop multiplexer based on two-dimensional photonic crystals

A reconfigurable optical add/drop multiplexer (R-OADM) device is proposed based on 2-D photonic crystals (2-D PCs) with a triangular lattice of air holes. It consists of channel add/drop filters, two bends with 120-deg bending angles, and a 2×2 directional coupler switch. Chirp structures are introduced in the directional coupler switch to improve its extinction ratio. At λ=1550 nm, the device is ultracompact with a net footprint 30×22 µm, excluding its external device. It is far smaller in size than other corresponding devices implemented through ring resonators. The device is numerically calculated by the finite-difference time-domain (FDTD) method, and simulation results confirm that the R-OADM device can be used for dynamically wavelength routing.

Change detection of multi-temporal remote sensing data based on image fusion and fuzzy clustering

We present a novel method based on image fusion and fuzzy clustering for change detection in remote sensing images. Firstly, the difference images by differencing operator and log-ratio operator are decomposed using Undecimated Discrete Wavelet transform (UDWT). Then, wavelet coefficients are fused to obtain multiscale feature vectors. By taking into account the spatial-neighborhood information, a change detection algorithm based fuzzy local-information C-means (FLICM) clustering is developed to obtain final detection results. Experiment confirms that the proposed approach does better than the differencing and log-ratio operators.

Photonic crystal one-way delay waveguide

In the paper, we have proposed a structure with only one photonic crystal (PC) micro-cavity side-coupled to a PC one-way waveguide to generate strong on-resonance optical delay. According to the coupled mode theory (CMT), the resonator system can maintain a 100% transmission spectrum throughout the complete resonant bandwidth, which is also demonstrated by the numerical results calculated by the finite element method (FEM). As a temporal Gaussian pulse is launched, the simulation results show that the device introduces a strong pulse delay while maintaining total transmission efficiency within the resonant bandwidth, and the resonator structure may be of great significance for making delay lines in optical buffer applications.