Dispersion characteristics of SOI-based slot optical waveguides

The invention of the slot waveguide had enabled a number of interesting novel linear or nonlinear optical applications by guiding light in nanometers-wide low index slots guarded by high-index slabs. As one of its key characteristics, the low modal index for this kind of waveguides has been demonstrated by many studies. However, their higher order dispersion properties have not been thoroughly investigated yet, while the growing size and complexity of these devices and their potential nonlinear optical applications involving short optical pulses demand further understanding in their dispersion behavior. We here carry out a numerical study on the higher order dispersion characteristics of the SOI-based slot structures around the 1550 nm wavelength. Our results show that they could have significantly different second order dispersion properties in contrast to the traditional channel SOI waveguides. Their potentially large normal dispersion could have an impact on various nonlinear or linear applications. The relationship between the dispersion performance and the waveguide design is also investigated, and the results could show further venues to optimize or control the dispersion properties of such waveguides.     

Propagation of ultrafast pulses in the anomalous-dispersion regime of silicon-on-insulator strip nanowaveguides

The dynamic evolution of ultrafast high-intensity pulses with a 100 fs half-width at 1/e intensity point based on the silicon-on-insulator (SOI) strip nanowaveguides is considered and investigated numerically under the condition of anomalous group-velocity dispersion (GVD) regime. For ultrafast high-intensity pulses propagating in millimeter-long SOI nanowaveguides, the interplay between the dispersion and nonlinear effects such as the two-photon absorption, free-carrier absorption, free-carrier dispersion, and self-phase modulation has to be taken into account, which results in the significant optical wave breaking phenomenon that occurs near the pulse leading edge for an unchirped Gaussian pulse in the anomalous GVD regime. However, when the input Gaussian pulse with linear up-chirp is introduced, the position of the optical wave breaking shifts from the leading pulse edge to its trailing edge along the several millimeters-long SOI nanowaveguides.     

Simplified design of low-loss and flat dispersion photonic crystal waveguide on SOI

A low-loss and flat dispersion line-defect photonic crystal waveguide is proposed with a simplified waveguide-design on silicon-on-insulator (SOI) based on hexagonal lattice of 2D photonic crystals. A propagation loss of 3.6 dB/mm and flat dispersion over a large wavelength band is reported with an easy-to-implement design without disturbing the periodicity (keeping lattice constant and hole diameter fixed) in the line-defect photonic crystals. The combined effect of photonic crystals (in-plane periodicity) and the vertical layers on SOI results in efficient waveguiding and dispersion characteristics.     

Modulational instability in a silicon-on-insulator directional coupler: role of the coupling-induced group velocity dispersion

We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced group velocity dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations.     

High quality factor in a two-dimensional photonic crystal cavity on silicon-on-insulator

We propose a design for high quality factor two-dimensional (2D) photonic crystal cavities on silicon-on-insulator (SOI). A quality factor of up to 1.2×10(7) with a modal volume of 2.35(λ/n)(3) is simulated. A very high quality factor of 200,000 is experimentally demonstrated for a 2D cavity fabricated on SOI.     

Enhanced stimulated Raman scattering in slow-light photonic crystal waveguides

We investigate for the first time, to our knowledge, the enhancement of the stimulated Raman scattering in slow-light silicon-on-insulator (SOI) photonic crystal line defect waveguides. By applying the Bloch-Floquet formalism to the guided modes in a planar photonic crystal, we develop a formalism that relates the intensity of the downshifted Stokes signal to the pump intensity and the modal group velocities. The formalism is then applied to two prospective schemes for enhanced stimulated Raman generation in slow-light photonic crystal waveguides. The results demonstrate a maximum factor of 104(66,000) enhancement with respect to SOI channel waveguides.     

Effects of multi-band mixing on the spin-polarized transport in quasi-one-dimensional electron waveguides

We present numerical calculations of the energy dispersion of spin-polarized electrons in quasi-one-dimensional electronic waveguides in the presence of Rashba spin–orbit interaction (SOI), by using an efficient expanded basis method. Within this model, the general mixing between any two subbands is taken into account. We investigate the properties of spin-polarized transport in the nonuniform SOI system. It is found that the multi-band mixing brings significant effects on the properties of multiple subbands transport in the regime of high energy, especially for the cases of the wide waveguide, the strong SOI and the long extension of the SOI region.     

Ultrafast femtosecond all-optical modulation through nondegenerate two-photon absorption in silicon-on-insulator waveguides

We present numerical investigations of ultrafast femtosecond (with time duration of 100 fs at 1/e intensity point) all-optical modulation of a pump-probe wave arrangement by using nondegenerate two-photon absorption (TPA), namely cross absorption, inside silicon-on-insulator (SOI) optical waveguides. Our results show that when a pump pulse with femtosecond duration and a continuous probe wave are co-propagating along the SOI, the probe wave can be modulated inversely by the ultrafast pump pulse, whose modulation depth depends strongly on the system parameters such as the waveguide length, the peak power and initial chirp of the pump wave, the group velocity dispersion (GVD), etc.; this means that the modulation depth can be improved by an appropriate increase of the waveguide length, the pump peak, and the initial chirp, in addition, which has a larger value for the probe wavelength in the normal dispersion regime compared with the case of abnormal dispersion when the center wavelength of the pump wave is located at the zero-dispersion wavelength.     

Eliminating the birefringence in silicon-on-insulator ridge waveguides by use of cladding stress

We propose and demonstrate the use of the cladding stress-induced photoelastic effect to eliminate modal birefringence in silicon-on-insulator (SOI) ridge waveguides. Birefringence-free operation was achieved for waveguides with otherwise large birefringence by use of properly chosen thickness and stress of the upper cladding layer. With the stress levels typically found in cladding materials such as SiO2, the birefringence modification range can be as large as 10(-3). In arrayed waveguide grating demultiplexers that were fabricated in a SOI platform, we demonstrated the reduction of the birefringence from 1.2 x 10(-3) (without the upper cladding) to 4.5 x 10(-5) when a 0.8-microm oxide upper cladding with a stress of -320 MPa (compressive) was used. Because the index changes induced by the stress are orders of magnitude smaller than the waveguide core-cladding index contrast, the associated mode mismatch loss is negligible.     

Influence of the structure parameters on the gain and noise figure in silicon parametric amplifiers based on SOI Rib waveguides

Gain and Noise figure (NF) characteristics in dual-pump parametric amplifier based on silicon on insulator (SOI) Rib waveguides are numerically investigated in the presence of nonlinear losses. The impact of structure parameters of the silicon optical parametric amplifiers (SOPAs) on the gain and the NF are also analyzed. The results show that both the height and the width of the silicon on insulator (SOI) can affect the gain and the NF of SOPAs. 354 nm bandwidth (3 dB) and 8.135 maximum gain can be achieved by tailoring the structure parameters of the SOI rib waveguides. Moreover, the dispersion and the effective mode area of SOI are also analyzed.     

Strategies to increase the modal gain in heterogeneously integrated III–V amplifiers on silicon-on-insulator

A novel waveguide shape is proposed to take advantage of the high index contrast in adhesively bonded III–V on silicon-on-insulator (SOI) waveguides for application in on-chip semiconductor optical amplifiers. By decreasing the effective index of the top contact layer, the confinement in the active region can be increased by 70%, boosting the achievable modal gain and reducing the required device length to achieve a certain gain. This technique could reduce the footprint of amplifiers, lasers and other active devices integrated on the SOI platform.     

Oxidation process of SiGe on SOI substrates

The oxidation of SiGe film epitaxial grown on top of SOI wafers has been studied. These SiGe/SOI samples were oxidized at 700, 900, 1100 °C. Germanium atoms were rejected from SiGe film to SOI layer. A new Si_1−xGe_x (x is minimal) layer formed at SiGe/Si interface. As the germanium atoms diffused, the new Si_1−xGe_x (x is minimal) layer moved to Si/SiO₂ interface. Propagation of threading dislocation in SiGe film to SOI substrate was hindered by the new SiGe/Si interface. Strain in SOI substrate transferred from SiGe film was released through dislocation nucleation and propagation inner. The relaxation of SiGe film could be described as: strain relaxed through strain equalization and transfer process between SiGe film and SOI substrates. Raman spectroscopy was used to characterize the strain of SiGe film. Microstructure of SiGe/SOI was observed by transmission electron microscope (TEM).     

Polarization beam splitter based on a photonic crystal heterostructure

The design and characterization of a photonic crystal (PC) polarization beam splitter (PBS) that operates with an extinction ratio of greater than 15 dB for both polarizations are presented. The PBS is fabricated on a silicon-on-insulator (SOI) wafer where the input and output ports consist of 5 mum wide ridge waveguides. A large spectral shift is observed in the dispersion plots of the lowest-order even (TE-like) and odd (TM-like) modes due to the SOI confinement. Because of this shift, the TE-like mode is close to a directional gap at the top of the band, and the TM-like mode is in a low-frequency regime where the dispersion surface is almost isotropic. We show that the TE-like mode has very high reflection at the interface between the two PCs, whereas the TM-like mode exhibits a very high transmission.     

Compensation for multimode fiber dispersion by adaptive optics

Adaptive optics is used to compensate for modal dispersion in digital transmission through multimode fiber (MMF). At the transmitter, a spatial light modulator (SLM) controls the launched field pattern. An estimate of intersymbol interference (ISI) caused by modal dispersion is formed at the receiver and fed back to the transmitter, where the SLM is adjusted to minimize ISI. Error-free transmission of 10 Gbit/s non-return-to-zero signals through standard 50 microm graded-index MMFs up to 11.1 km long is demonstrated. It is shown that a single SLM can compensate for modal dispersion across a 600 GHz bandwidth.     

Strain analysis of free-standing strained silicon-on-insulator nanomembrane

Based on the ultra-thin strained silicon-on-insulator(s SOI) technology, by creatively using a hydrofluoric acid(HF)vapor corrosion system to dry etch the Si O2 layer, a large area of suspended strained silicon(s Si) nanomembrane with uniform strain distribution is fabricated. The strain state in the implemented nanomembrane is comprehensively analyzed by using an UV-Raman spectrometer with different laser powers. The results show that the inherent strain is preserved while there are artificial Raman shifts induced by the heat effect, which is proportional to the laser power. The suspended s SOI nanomembrane will be an important material for future novel high-performance devices.     

Optical wave breaking of high-intensity femtosecond pulses in silicon optical waveguides

We have investigated numerically the propagation of high-intensity femtosecond optical pulses with pulsewidth of 100 fs (half width at 1/e maximum) on the silicon-on-insulator (SOI) optical waveguide when the central wavelength of the pulse locates in the normal dispersion region. Results show that the combined effects of group-velocity dispersion (GVD), third-order dispersion (TOD), self-phase modulation (SPM), and free-carrier dispersion (FCD) can lead to the phenomenon of optical wave breaking that manifests as an asymmetric profile and oscillation near the trailing edge of the pulse. Moreover, the optical wave breaking will be experienced from generation to disappearance during propagation.     

Sequential Parameter Estimation Using Modal Dispersion Curves in Shallow Water

Existing sequential parameter estimation methods use the acoustic pressure of a line array as observations. The modal dispersion curves are employed to estimate the sound speed profile(SSP) and geoacoustic parameters based on the ensemble Kalman filter. The warping transform is implemented to the signals received by a single hydrophone to obtain the dispersion curves. The experimental data are collected at a range-independent shallow water site in the South China Sea. The results indicate that the SSPs are well estimated and the geoacoustic parameters are also well determined. Comparisons of the observed and estimated modal dispersion curves show good agreement.     

SOI全内反射型光波导电光开关模型研究

根据受抑全反射的光学隧道效应和Ｇｏｏｓ－Ｈａｎｃｈｅｎ位移分析ＳＯＩ全内反射型光波导开关中导模的传输和反射特性。在讨论等离子体色散效应，ｐ－ｎ结大注入效应的基础上，分析了全内反射光波导开关的电学性质。设计了该器件的结构以数和电学参数。     

椭圆芯手征光纤的基模特性研究

对椭圆芯手征光纤进行了严格的求解，得到了模式场的解析解；推了了模式特征方程；并对基模的偶模和奇模特征方程进行数值求解，研究了手征参数对不同椭圆比下基模的色散曲线，双折射，模间色散等特性的影响。     

The mass normalization of the displacement and strain mode shapes in a strain experimental modal analysis using the mass-change strategy

The classic experimental modal analysis (EMA) is a well-known procedure for determining the modal parameters. The less frequently used strain EMA is based on a response measurement using strain sensors. The results of a strain EMA are the modal parameters, where in addition to the displacement mode shapes the strain mode shapes are also identified. The strain EMA can be used for an experimental investigation of a stress–strain distribution without the need to build a dynamical model. It can also be used to determine the modal parameters when, during modal testing, a motion sensor cannot be used and so a strain sensor is used instead. The displacement and strain mode shapes that are determined with the strain EMA are not mass normalized (scaled with respect to the orthogonality properties of the mass-normalized modal matrix), and therefore some dynamical properties of the system cannot be obtained. The mass normalization can be made with the classic EMA, which requires the use of a motion sensor. In this research a new approach to the mass normalization in the strain EMA, without using a motion sensor, is presented. It is based on the recently introduced mass-change structural modification method, which is used for the mass normalization in an operational modal analysis. This method was modified in such a way that it can be used for the mass normalization in the strain EMA. The mass-normalized displacement and strain mode shapes were obtained using a combination of the proposed approach and the strain EMA. The proposed approach was validated on real structures (beam and plate).