Anisotropic transport in quantum waveguides due to the spin-orbit interactions

We theoretically investigate the charge transport in the quantum waveguides in the presence of the Rashba spin-orbit interaction and the Dresselhaus spin-orbit interaction. We find that the interplay between the Rashba spin-orbit interaction and Dresselhaus spin-orbit interaction can induce a symmetry breaking and consequently leads to the anisotropic charge transport in the quantum waveguides, the conductance through the quantum waveguides depends sensitively on the crystallographic orientations of the quantum waveguides. The anisotropy of the charge transport can even survive in the presence of disorder effect in realistic systems.

An investigation of the mode characteristics of SOI submicron rib waveguides using the film mode matching method

The mode characteristics of SOI (silicon-on-insulator) submicron rib waveguides are very different from those of micrometer-sized ones. Using the full-vector film mode matching method, we propose a simple criterion to determine whether a waveguide mode is guided or not. The single-mode condition for deep-etched waveguides is obtained using this criterion. We also obtain the inherent TM mode leakage and sharp cancelation effects due to TE-TM mode coupling in shallow-etched rib waveguides from numerical simulations, which agree well with the analytical results based on total internal reflection and interference theories.

Effects of waveguide length and pump power on the efficiency of wavelength conversion in silicon nanowire waveguides

We point out the use of a wrong definition for conversion efficiency in the literature and analyze the effects of the waveguide length and pump power on conversion efficiency according to the correct definition. The existence of the locally optimal waveguide length and pump power is demonstrated theoretically and experimentally. Further analysis shows that the extremum of conversion efficiency can be achieved by global optimization of the waveguide length and pump power simultaneously, which is limited by just the linear propagation loss and the effective carrier lifetime. (C) 2009 Optical Society of America

Four-channel reconfigurable optical add-drop multiplexer based on photonic wire waveguide: erratum

An erratum is presented to correct the calculation of the filtering bandwidth of the micro-ring resonator. (C) 2009 Optical Society of America

Single-mode condition for silicon rib waveguides with large cross sections

The single-mode condition for silicon rib waveguides with large cross sections is obtained using a numerical method based on the finite-difference beam propagation method (FD-BPM). An ultrawide computation window is used to contain the wide mode profile near cutoff. Comparison with previous results shows that the formula predicted by the mode-matching technique is in a better agreement with our results. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

Single-mode behaviour judgment of optical waveguides by imaginary-distance beam propagation method under perfectly matched layer boundary condition

Imaginary-distance beam propagation method under the perfectly matched layer boundary condition is applied to judge single-mode behaviour of optical waveguides, for the first time to our knowledge. A new kind of silicon-on-insulator-based rib structures with half-circle cross-section is presented. The single-mode behaviour of this kind of waveguide with radius 2mum is investigated by this method. It is single-mode when the slab height is not smaller than the radius.

Single-mode condition for silicon rib waveguides with trapezoidal cross-section

Single-mode condition for silicon rib waveguides with trapezoidal cross-section was obtained using a numerical method based on imaginary-distance beam propagation method with non-uniform discretization. Both quasi-transverse-electric and quasi-transverse-magnetic modes were investigated. Simulated single-mode condition is given by a modified equation. Comparison with reported results shows that the Marcatili's method is in a better agreement with our results. (C) 2003 Elsevier B.V. All rights reserved.

Multimode interference 3-dB coupler in silicon-on-insulator based on silicon rib waveguides with trapezoidal cross section

A 3-dB multimode interference optical coupler based on rib waveguides with trapezoidal cross section was designed and fabricated on silicon-on-insulator wafer. Potassium hydroxide (KOH) anisotropic chemical etching of silicon was used to fabricate the waveguides to obtain smooth interface. A modified finite-difference beam propagation method was used to simulate the multimode rib waveguide with slope interfaces. The rms roughness of etching interface is as small as 1.49 nm. The propagation loss of the waveguide is 1.3 dB/cm at wavelength of 1.55 mum. The fabricated 3-dB coupler has a good uniformity of 0.2 dB.

Silica-based 64-channel arrayed waveguide gratings with double functions

Silica-based 64-channel arrayed waveguide gratings (AWGs) with double functions and 0.4 nm (50 GHz) channel spacing have been designed and fabricated. On the same component, Gauss and flat-top output response spectra are obtained simultaneously. The test results show that when the insertion loss ranges from 3.5 dB to 6 dB,the crosstalk is better than -34 dB, the 1 dB bandwidth is 0.12 nm, the 3 dB bandwidth is 0,218 nm, and the polarization-dependent loss (PDL) is less than 0.5 dB for Gauss response. When the insertion loss ranges,from 5.8 dB to 7.8 dB, the crosstalk is better than -30 dB, the 1 dB bandwidth is 0.24 nm, the 3 dB bandwidth is 0.33 nm, and the PDL is less than 0.2 dB for flat-top response.

A novel design of grating couplers for efficient broadband coupling between silicon-on-insulator nanophotonic waveguides and fibres

A novel design of out-of-plane grating couplers is proposed for coupling between silicon-on-insulator nanophotonic waveguides and single-mode fibres. The coupler with the first-order diffraction coupling to the optical fibre is actually a second-order reflected grating with two times of period of the first-order grating. To enhance outcoupled power, a back hole is designed to form in the silicon substrate and a kind of metals is placed on the top acting as a reflection layer. The coupler is optimized using coupled-mode- based simulations, showing that, the coupling efficiency to and from tapered optical fibre can be as high as 85% with 1 dB bandwidth about 23nm.

Thermo-optical switch matrix based on silicon-on-insulator waveguides

A thermo-optical waveguide switch matrix is designed and fabricated on silicon-on-insulator wafer. Multi-mode interferometers are used as power splitters and combiners in a Mach-Zehnder structure. Inductively coupled plasma reactive ion etching is used to fabricate the waveguides. The rise and fall times of the switch matrix are 13 mu s and 7 mu s, respectively. Switch cells have an average switching power consumption of 340 mW.

Calculation of propagation loss in photonic crystal waveguides by FDTD technique and Pade approximation

The propagation losses in single-line defect waveguides in a two-dimensional (2D) square-lattice photonic crystal (PC) consisted of infinite dielectric rods and a triangular-lattice photonic crystal slab with air holes are studied by finite-difference time-domain (FDTD) technique and a Pade approximation. The decaying constant beta of the fundamental guided mode is calculated from the mode frequency, the quality factor (Q-factor) and the group velocity v(g) as beta = omega/(2Qv(g)). In the 2D square-lattice photonic crystal waveguide (PCW), the decaying rate ranged from 10(3) to 10(-4) cm(-1) can be reliably obtained from 8 x 10(3)-item FDTD output with the FDTD computing time of 0.386 ps. And at most 1 ps is required for the mode with the Q-factor of 4 x 10(11) and the decaying rate of 10(-7) cm(-1). In the triangular-lattice photonic crystal slab, a 10(4)-item FDTD output is required to obtain a reliable spectrum with the Q-factor of 2.5 x 10(8) and the decaying rate of 0.05 cm(-1). (c) 2004 Elsevier B.V. All rights reserved.

Research on improved methods of reduction of bend loss of silicon-on-insulator waveguides

Improved methods of reduction of bend loss of silicon-on-insulator waveguides were simulated and analyzed by means of effective index method (EIM) and two dimensional beam propagation method (2D-BPM). The simulation results indicate that two different methods, one of which are introducing an offset at the junction of two waveguides and the other is etching groove at the outside of bend waveguide, can decrease bend loss. And the later one is more effective. Meanwhile, experiments validate them. By etching groove, the insertion loss of bend waveguide of R = 16mm, transverse displacement 70mum was decreased 5dB. And its bend loss was almost eliminated.

A method for analyzing the coupling of 3-D tapered rib waveguides with fibers

The fields in 3-dimensional tapered waveguides are unstable compared with the fields in the straight waveguides. In the case of waveguide-to-fiber coupling and fiber-to-waveguide coupling, a sequence of short straight waveguides has been modeled to approximate the 3-dimensional tapered waveguide; and the unstable incident and reflected fields, as well as their derivatives, were determined by the beam propagation method(BPM). Then free space radiation mode(FSRM) was employed to calculate the reflected and transmitted powers. Analysis results of the coupling of fiber with silicon-on-insulator(SOI) tapered rib waveguides showed the feasibility of the method.

Full counting statistics of transport through two-channel Coulomb blockade systems

A mesoscopic Coulomb blockade system with two transport channels is studied in terms of full counting statistics. It is found that the shot noise and skewness are crucially affected by the quantum mechanical interference. In particular, the super-Poisson behavior can be induced as a consequence of constructive interference, and can be understood by the formation of effective fast-and-slow transport channels. Dephasing and finite temperature effects are carried out together with physical interpretations.