Yen-Chung Chiang

Improved three-point formulas considering the interface conditions in the finite-difference analysis of step-index optical devices

A general relation, considering the interface conditions, between a sampled point and its nearby points is derived. Making use of the derived relation and the generalized Douglas scheme, the three point formulas in the finite-difference modeling of step-index optical devices are extended to fourth order accuracy irrespective of the existence of the step-index interfaces. With numerical analysis and numerical assessment, several frequently used formulas are investigated.

Improved full-vectorial finite-difference mode solver for optical waveguides with step-index profiles

A general relation considering an interface condition between a sampled point and its nearby points in the finite-difference analysis of optical waveguides, is derived. Our formulation is a full-vectorial one, and the interface can be oblique to the global coordinate axes or even can have curvature. Using the derived formulation, optical waveguide structures with arbitrary step-index profiles can be dealt with. The validity of the proposed method is examined by comparing the numerical calculation with the analytical solution of a step-index optical fiber. The method is also applied to the analysis of fused fiber-optic couplers and compared with prior analysis using the surface integral equation method.

Finite-Difference Modeling of Dielectric Waveguides With Corners and Slanted Facets

With the help of an improved finite-difference (FD) formulation, we investigate the field behaviors near the corners of simple dielectric waveguides and the propagation characteristics of a slant-faceted polarization converter. The formulation is full-vectorial, and it takes into consideration discontinuities of fields and their derivatives across the abrupt interfaces. Hence, the limitations in conventional FD formulation are alleviated. In the first investigation, each corner is replaced with a tiny arc rather than a really sharp wedge, and nonuniform grids are adopted. Singularity-like behavior of the electric fields emerge as the arc becomes smaller without specific treatment such as quasi-static approximation. Convergent results are obtained in the numerical analysis as compared with results from the finite-element method. In the second investigation, field behaviors across the slanted facet are incorporated in the formulation, and hence the staircase approximation in conventional FD formulation is removed to get better modeling of the full-vectorial properties.

Finite-Difference Frequency-Domain Analysis of 2-D Photonic Crystals With Curved Dielectric Interfaces

An improved finite-difference frequency-domain method based on Taylor series expansion, local coordinate transformation, and boundary condition matching is developed for analyzing the band diagrams of 2-D photonic crystals. This newly proposed scheme can deal with piecewise homogeneous structures with curved dielectric interfaces. It also shows much better performance in modeling structures of highly index contrast ratio. We have verified this improved scheme with frequently-used plane-wave expansion method through the calculation of the band diagrams of a 2-D photonic crystal with square lattice. We also compare the scheme with the staircase approximation. We further improve the convergence behavior by adopting high-order terms. The result of this adopting is also demonstrated.

Pseudospectral Frequency-Domain Formulae Based on Modified Perfectly Matched Layers for Calculating Both Guided and Leaky Modes

We propose a new pseudospectral frequency-domain (PSFD) formulation within the modified perfectly matched layer (MPML) for absorbing both radiation losses and evanescent waves. By applying the improved PSFD method on Chebyshev-Gauss-Lobatto mesh points, both guided and leaky modes of optical waveguides can be solved from Helmholtzs equations for the transverse-magnetic components. To ensure the global accuracy of the PSFD-MPML method, new and appropriate boundary conditions are derived at each subdomain in the MPML region. By comparing the analytic solution of a step-index single-mode fiber and the results by adopting our method, the convergence behavior of the proposed method on the guided modes is examined. To demonstrate the validity and usefulness of our method on the leaky modes, the one-ring triangular holey fiber is taken as another example.

A 60 GHz CMOS VCO Using a Fourth-Order Resonator

In this letter, a 60 GHz voltage-controlled oscillator (VCO) implemented in the 90 nm CMOS process is presented. By using a fourth-order LC resonator, the proposed VCO oscillates at its second pole frequency to achieve high speed operation with fully differential output phases and a wide tuning range with a larger size of varactors. The measured oscillation frequencies of the proposed VCO are from 58.76 to 63.94 GHz corresponding to an 8.44% tuning range. The measured phase noise is -91.53 dBc/Hz at 1 MHz frequency offset for the highest output frequency. The core circuit consumes 7.2 mW power from a 1.2 V dc supply.

A V-Band Push-Push VCO With Wide Tuning Range Using

A V-band push-push voltage-controlled oscillator (VCO) with wide tuning range implemented in the 0.18 μm CMOS process technology is presented in this letter. The output signal with frequency twice that of the VCO core is extracted from the center tap of inductors rather than the one-quarter wavelength transmission line. The measured oscillating frequency of the VCO is from 67.18 to 74.84 GHz corresponding to a 10.79% tuning range. At the 74.84 GHz output frequency, the measured phase noises at 1 MHz and 10 MHz frequency offsets are -74.83 dBc/Hz and -102.53 dBc/Hz, respectively. The core circuit draws a 13.5 mA current from a 1.8 V power supply.

0.18~\mu{\rm m}

Analysis of optical waveguides with thin metal films is studied by the multidomain pseudospectral frequency-domain (PSFD) method. Calculated results for both guiding and leaky modes are precise by means of the PSFD based on Chebyshev-Lagrange interpolating polynomials with modified perfectly matched layer (MPML). By introducing a suitable boundary condition for the dielectric-metallic interface, the stability and the spectrum convergence characteristic of the PSFD-MPML method can be sustained. The comparison of exact solutions of highly sensitive surface plasmon modes in 1D dielectric-metal waveguides and those calculated by our PSFD-MPML demonstrates the validity and usefulness of the proposed method. We also apply the method to calculate the effective refractive indices of an integrated optical waveguide with deposition of the finite gold metal layer which induces the hybrid surface plasmon modes. Furthermore, the 2-D optical structures with gold films are investigated to exhibit hybrid surface plasmon modes of wide variations. We then apply hybrid surface plasmon modes to design novel optical components-mode selective devices and the polarizing beam splitter.

CMOS Process

In this paper, a two-stage low-noise amplifier (LNA) designed for V-band applications is presented. Both stages are the common source-common gate (CS-CG) cascoded topologies with inductive degeneration structure for minimizing the noise figure (NF). This proposed LNA is implemented in a GaAs 0.15μm pHEMT process technology, which achieves a peak gain of 12.1 dB, a NF of 5.456 dB, and an input P1dB of -20 dBm at the 56.8 GHz frequency. The 3dB bandwidth is from 54.9 GHz to 58 GHz. The power consumption of the proposed LNA is 26.6 mW from the 1.8V voltage supply.

Analysis of optical waveguides with ultra-thin metal film based on the multidomain pseudospectral frequency-domain method

An improved finite-difference frequency-domain method based on Taylor series expansion, local coordinate transformation, and boundary condition matching is developed for analyzing the band diagrams of 2-D photonic crystals. This newly proposed scheme can deal with piecewise homogeneous structures with curved dielectric interfaces. It also shows much better performance in modeling structures of highly index contrast ratio. We have verified this improved scheme with frequently-used plane-wave expansion method through the calculation of the band diagrams of a 2-D photonic crystal with square lattice. We also compare the scheme with the staircase approximation. We further improve the convergence behavior by adopting high-order terms. The result of this adopting is also demonstrated.