Shuqin Guo

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.

Spectrum Changes Produced by Scattering of Light With Tunable Spectral Degree of Coherence from a Spatially Deterministic Medium

Within the validity of the first-order Born approximation, we study the spectrum changes generated by the scattering of light with a tunable spectral degree of coherence (SDOC) from a spatially deterministic medium. Before interacting with the medium, a scalar plane wave is incident upon Youngs pinholes, which are employed to produce the incident wave with a tunable SDOC. By assuming that both the scattering potential of the medium and the spectrum of incident plane waves obey Gaussian profiles, the spectrum of the scattered field is derived as a linear combination of Fourier transforms of the scattering potentials. Changes in the spectrum of the scattered field are strongly dependent on the scattering angle, the effective radius of the medium, and Youngs pinhole parameter. Moreover, red shifts occurring in the scattered field can be enhanced by either reducing the scattering angle or increasing the effective radius. The results presented here generalize the previous reports, where the light with prescribed functions of the SDOC scattered from a deterministic medium was considered.

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.

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.

Realization of ultra-broadband dispersion-flattened in dual-cladding photonic crystal fiber

We design a kind of dual-cladding photonic crystal fiber (DC-PCF), in which air holes arranged in the vicinity of the core (inner-cladding) is smaller than the other air holes (outer-cladding). By numerical simulation, the dispersion characteristic of this novel PCF is investigated. Dispersion curves will become comparatively flat while gradually reducing the air holes arranged in inner cladding under fixing the air holes of outer cladding. An ultra-flattened dispersion can be realized when the air holes size of inner-cladding dwindling down to an optimum size. As an example, the DC-PCF demonstrates an extraordinary flattened dispersion around 9.8ps/nm.km within ±0.4ps/nm/km fluctuation range in an ultra-broad wavelength range from 1.0μm to 2.0μm . Furthermore, when the air holes arranged in the second layer nearing the core is reduced slightly, the flattened dispersion curve even can parallel shift from 11.8ps/nm/km to 7.8ps/nm/km, 6.2ps/nm/km, 4.0ps/nm/km at the wavelength around 1.55μm.

Highly efficient channel drop filter based on photonic crystal oneway waveguide

We design a highly efficient channel drop filter (CDF) with only one channel drop micro-cavity based on photonic crystal (PC) one-way waveguide. By means of the new nature of waveguide-cavity interaction, over 95% channel drop efficiency can be realized in the structure. Some multichannel drop filters with high drop efficiencies are also engineered based on such the structure. These numerical results are all calculated by using the finite element method (FEM), which agrees well with the theoretical analysis result.

Sub-picosecond chirped return-to-zero nonlinear optical pulse propagating in dense dispersion-managed fibre

By numerical simulation, we show that the fourth-order dispersion (FOD) makes sub-picosecond optical pulse broaden as second-order dispersion (SOD), makes optical pulse oscillate simultaneously as third-order dispersion (TOD). Based on above two reasons, sub-picosecond optical pulse will be widely broaden and lead to emission of continuum radiation during propagation. Here, resemble to two- and third-order dispersion compensation, fourth-order dispersion compensation is also suggested in a dispersion-managed optical fiber link, which is realized by arranging two kinds of fiber with opposite dispersion sign in each compensation cell. For sake of avoiding excessively broadening, ultra short scale dispersion compensation cell is required in ultra high speed optical communication system. In a full dispersion compensation optical fiber system which path average dispersion is zero about SOD, TOD, and FOD, even suffering from affection of high order nonlinear like self-steep effect and self-frequency shift, 200 fs gauss optical pulse can stable propagate over 1000 km with an optimal initial chirp. When space between neighboring optical pulse is only 2 picoseconds corresponding to 500 Gbit/s transmitting capacity, eye diagram is very clarity after 1000 km. The results demonstrate that ultra short scale dispersion compensation including FOD is need and effective in ultra-high speed optical communication.