This paper reports theoretical designs and simulations of electrooptical 2 × 2 switches and 1 × 1 loss modulators based upon GST-embedded SOI channel waveguides. It is assumed that the amorphous and crystalline phases of GST can be triggered electrically by Joule heating current applied to a 10-nm GST film sandwiched between doped-Si waveguide strips. TE o and TM o mode effective indices are calculated over 1.3 to 2.1-μm wavelength range. For 2 × 2 Mach-Zehnder and directional coupler switches, low insertion loss, low crosstalk, and short device lengths are predicted for 2.1 μm, although a decreased performance is projected for 1.55 μm. For 1.3-2.1 μm, the 1 × 1 EO waveguide has application as a variable optical attenuator and as a digital modulator, albeit with ࣚ100-ns state-transition time. Because the active material has two "stable" phases, the device holds itself in either state, and voltage needs to be applied only during transition.

We show that octave-spanning Kerr frequency combs with improved spectral flatness of comb lines can be generated in dispersion-flattened microring resonators. The resonator is formed by a strip/slot hybrid waveguide, exhibiting a flat and low anomalous dispersion between two zero-dispersion wavelengths that are separated by one octave from near-infrared to mid-infrared. Such flattened dispersion profiles allow for the generation of mode-locked frequency combs, using relatively low pump power to obtain two-cycle cavity solitons on a chip, associated with the octave-spanning comb bandwidth. The wavelength dependence of the optical loss and of the coupling coefficient and thus wavelength dependent Q-factor are also considered.

A coupled-mode formulation is described in which the radiation fields are represented in terms of discrete complex modes. The complex modes are obtained from a waveguide model facilitated by the combination of perfectly matched boundary (PML) and perfectly reflecting boundary (PRB) condition. By proper choice of the PML parameters, the guided modes of the structure remain unchanged, whereas the continuous radiation modes are discretized into orthogonal and normalizable complex quasi-leaky and PML modes. The complex coupled-mode formulation is identical to that for waveguides with loss and/or gain and can be solved by similar analytical and numerical techniques. By identifying the phase-matching conditions between the complex modes, the coupled mode formulation may be further simplified to yield analytical solutions. The complex coupled-mode theory is applied to Bragg grating in slab waveguides and validated by rigorous mode-matching method. It is for the first time that we can treat guided and radiation field in a unified and straightforward fashion without having to resort to cumbersome radiation modes. Highly accurate and insightful results are obtained with consideration of only the nearly phase-matched modes.

We demonstrate an ultra-subwavelength surface plasmonic polaritons waveguide, which can confine light in the nano-scale region with comparable low propagation loss. The mode can be squeezed to one thousandth of the diffraction spot size with micro-meter scale propagation distance and is highly sensitive to the buffer layer materials and geometric parameters. This design improves the performance of previous surface plasmonic polaritons waveguides and lends itself to complementary metal–oxide–semiconductor compatible fabrication. These waveguides can be used as a platform for active devices as well as for nano-sensing applications.

A rigorous full-vector analysis based on the finite-difference mode-matching method is presented for three-dimensional optical wave propagation problems. The computation model is facilitated by a perfectly matched layer (PML) terminated with a perfectly reflecting boundary condition (PRB). The complex modes including both the guided and the radiation fields of the three-dimensional waveguide with arbitrary index profiles are computed by a finite-difference scheme. The method is applied to and validated by the analysis of the facet reflectivity of a buried waveguide and the power exchange of a periodically loaded dielectric waveguide polarization rotator.

We introduce an efficient design approach for Ultraviolet (UV) band-pass filter based on metal-dielectric stacks. We present a general design method and then apply this design to two special cases: a UV band pass filter based on (i) Al/Al2O3 stacks as well as (ii) Ag/SiO2 stacks. As an experimental confirmation, we fabricate a UV filter with three Ag/SiO2 layer pairs on a fused silica substrate (Corning 7980), targeting a central wavelength of 320 nm. A measurement at the peak wavelength shows transmission efficiency as high as 67% in our filter.

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Theoretical modeling and numerical simulation have been performed at λ=2100  nm on silicon-on-insulator channel-waveguide directional couplers in which the outer two Si waveguides are passive and the central waveguide(s) are electro-optical (EO) "islands." The EO channel(s) utilize a 10 nm layer of Ge2Sb2Te5 phase-change-material sited at midlevel of a doped Si channel. A voltage-driven phase change produces a large change in the effective index of the TE(o) and TM(o) modes, thereby inducing crossbar 2×2 switching. A mode-matching method is employed to estimate EO switching performance in the limit of strong interguide coupling. Low-loss switching is predicted for cross-to-bar and bar-to-cross coupling lengths. These "self-holding" switches had active lengths of 500-1000 μm, which are shorter than those in couplers relying upon free-carrier injection. The four-waveguide devices had lower cross talk but higher loss than the three-waveguide devices. For the crystalline phase we sometimes used an active length that was smaller than that for the amorphous phase.