Xinhou Liu

Tunable Ultranarrow Dual-Channel Filter Based on Sampled FBGs

A new kind of ultranarrow dual-bandpass fiber Bragg grating is proposed and demonstrated, for the first time to the authors best knowledge, with a symmetrical technique in which the first and second half gratings are sampled with the period of 0-and-pi and pi-and-0, respectively. This kind of grating can achieve dual-wavelength operation with a symmetrical spectrum. The unique spectral property of the proposed gratings is analyzed by means of Fourier theory and confirmed experimentally. By integrating the proposed grating with the 0-and-pi sampling grating, an ultranarrow dual-channel filter is designed in principle and demonstrated experimentally whose 3-dB bandwidth is less than 1 pm. By stretching the gratings, the two wavelengths of the proposed filter can be tuned whereas their channel spacing remains unchanged.

Improved coupling technique of ultracompact ring resonators in silicon-on-insulator technology

In order to improve the coupling coefficient between a bus waveguide and a bent waveguide of an ultracompact microring to obtain the critical coupling, a design using a bent bus waveguide with reduced width is provided to maintain a better phase matching and increase the coupling. A full vectorial finite difference model, specifically suited for high index contrast and smaller size waveguides, for example, a waveguide in the silicon-on-insulator (SOI) technology, is developed. As a validation, the straight and bent waveguides are simulated using this model, whose results are compared with the results deduced from the measurement results of the ultracompact ring resonators in SOI technology. Also, the model solver is performed to simulate the design, and an experiment is implemented to testify the design.

The Basic Building Block of

Optical properties of the λ-router basic building block are simulated using a matrix method. Experiments are performed for the -router basic building block with multimode-interference (MMI) crossings, which shows large free spectral range (~35 nm) and more than 24 dB on/off contrast of the drop resonance. Theoretical and experimental results reveal that the λ-router basic building block with MMI crossings can suppress the crosstalk (defined as the difference between the drop efficiency and the throughput attenuation at resonance), offer relatively symmetric resonance, and increase the on/off contrast of the drop resonance, compared with a λ-router building block using conventional crossings.

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Modulation instability (MI) induced by two strong beams and a weak beam via cross phase modulation is investigated. Multiple four-wave-mixing (FWM) processes associated with the MI in low-birefringence fibers are studied both theoretically and experimentally. The coupled-mode equations describing the MI-induced FWM nonlinear interactions between pump waves and sideband waves are derived. Theoretical and experimental results show that, on the assistance of MI, new optical frequencies can be generated quite efficiently from multiple FWM processes. More than eleven sidebands are experimentally achieved by the MI-driven multiple FWM processes. The transfer of energy from pumps to sidebands can be dramatically enhanced by the MI-induced parametric process. The experimental observations by using a piece of highly nonlinear dispersion-flattened photonic-crystal fiber confirm our theoretical predictions.