Guofang Fan

Towards a Realistic Modelling of Ultra-Compact Racetrack Resonators

We discuss all the necessary parameters to describe optical racetrack micro resonators fabricated with silicon on insulator (SOI) technology. We focus on some fundamental aspects crucial for a comprehensive and realistic modelling of racetrack resonators as building blocks of complex add-drop filters, like SCISSOR (Side-Coupled Integrated Spaced-Sequences of Resonators) or CROW (Coupled Resonator Optical Waveguides). When the radius of curvature is lower than 5 μm, and/or the separation gaps between waveguide and resonator is small, dispersion law, effective index mismatch, and mode mismatch between bend and straight waveguides are relevant for modelling. A new mode solver, specifically suited for high index contrast small mode area waveguides, is used whose results are compared with the measurement of the optical response of some resonant devices.

Optical Waveguides on Three Material Platforms of Silicon-on-Insulator, Amorphous Silicon and Silicon Nitride

Optical waveguides on three material platforms of silicon-on-insulator (SOI), amorphous silicon (a-Si:H) and silicon nitride are analyzed for realization of an optical compact link compatible with CMOS technology. The three material properties are presented. The optical components on the three potential material platforms are put together for a comparison, in which, straight, bent waveguides, and multimode-interference beam splitters for an optical link are designed, fabricated, and measured. The comparison results of simulation and measurement show that a-Si:H has a similar performances with SOI material but lower cost and good feasibility of photonic integration on silicon.

Highly integrated optical 8x8 lambda-router in silicon-on-insulator technology: comparison between the ring and racetrack configuration

In this paper, we demonstrate a compact 8x8 λ-router using multimode-interference (MMI) crossing based on the microring resonator. The 8x8 λ-router was designed and fabricated with a CMOS compatible silicon on insulator technology. MMI is used to reduce the cross talk and the crossing losses of the device. Microrings with a nominal radius of 2.5 μm and small variations of 10 nm of the nominal value allow respectively a free spectral range of 32 nm and spacing between channels of 4 nm. The experimental results are in good agreement with the modeling. The basic add drop filters of the devices exhibit losses of -2 dB and on/off contrast of the resonance of 20 dB. The total losses for one channel are about -4 dB and the imbalance between the 8 channels is lower than 2 dB.

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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A powerful shooting algorithm, which is the combination of the simple shooting method and the modified Newton method, dedicated to fibre Raman amplifier (FRA) design is proposed and numerically demonstrated for the first time, to the best of our knowledge. An effective initial-guess-providing scheme for the shooting method has also been proposed. The interactions among the pumps, signals, forward and backward amplified spontaneous emission, and co- and counter-propagating Rayleigh scattering components have all been taken into account in the theoretical model used by the proposed method. Studies in comparison with previously proposed methods show that the proposed new method is faster and more robust than the previously proposed ones. This new method can be used in the gain and noise performance design of FRAs with various kinds of geometries including forward pumping, backward pumping, or bi-directional pumping.

-Router With Multimode-Interference Waveguide Crossings on Silicon-on-Insulator Technology

The overlap integral of guided acousto-optic interaction is investigated theoretically. The overlap integral of YZ-LiNbO3 (Y-cut crystal, Z-propagating surface acoustic wave) is discussed with different penetration depths for TE- and TM-polarized light. Some valuable results are obtained for the design of acousto-optic devices.

An efficient shooting method for fibre Raman amplifier design

A numerical analysis is presented about the performance of non-collinear acousto-optic interaction in LiNbO3 guiding structures. To get the optimal design for a higher diffraction, the SAW power required for 100% diffraction (P 100) dependences on the length of acousto-optic (AO) interactions, guided optical mode, waveguide depth and driving frequency are investigated. Some valuable results are obtained for design of guided-wave acousto-optic devices.

Overlap integral in integrated acousto-optic devices

In this paper, we develop an analytical model of an integrated acousto-optical (AO) device with arms modulated by a single surface acoustic wave beam. A comparison between one-arm and two-arm modulation is presented, which shows that two-arm modulation can significantly enhance modulation efficiency by an optimized design. A detailed analysis of the influence of static phase difference on the behavior of the AO devices has been provided, and some interesting results have been obtained. These will be helpful for an optimized design of AO devices for different functionalities.

Theoretical analysis and design of non-collinear guided-wave acousto-optic devices

We present one theoretical analysis about the two resonators system. The model shows good agreement with other theoretical approaches. The properties of the system have been studied using the model. We also provide the analysis about the electromagnetically induced transparency (EIT) in the two resonators system,which shows, properly designed, the system exhibits a narrow high-quality-factor(Q) EIT-like resonant mode.