Jianwei Mu

Simulation of three-dimensional waveguide discontinuities by a full-vector mode-matching method based on finite-difference schemes

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.

Generation of two-cycle pulses and octave-spanning frequency combs in a dispersion-flattened micro-resonator.

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.

Hybrid nano ridge plasmonic polaritons waveguides

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.

Compact Bragg grating with embedded metallic nano-structures

A compact Bragg grating with embedded gapped metallic nano-structures is proposed and investigated theoretically. The Bragg grating consists of periodic planar metallic strips embedded in a dielectric waveguide. The grating exhibits distinct polarization characteristics due to its underlying working mechanisms of the metallic nano-strips. The grating can be considered as insulator-metal-insulator surface plasmonic polariton waveguide grating with improved light confinement for TM polarized waves. For the TE waves, significant field mismatch between metal and non-metal sections of the grating results in strong reflection. Comparison with the conventional deeply-etched grating on the same waveguide structures reveals interesting characteristics. It is concluded that the two types of grating structures share similar guidance, reflection and loss mechanisms for the TE modes. The spectral characteristics and their dependences on grating duty cycle are drastically different for the TM modes, mainly due to the SPP effect for the metal. Although the proposed grating performs slightly worse comparing to the deeply-etched grating for TE waves, its fabrication process should be easier since there will be no narrow trench (in sub-microns) deep-etching process (up to a few microns in depth) involved.

Design and fabrication of a high transmissivity metal-dielectric ultraviolet band-pass filter

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.

Silicon-on-nitride structures for mid-infrared gap-plasmon waveguiding

Silicon-on-nitride (SON) is a convenient, low-loss platform for mid-infrared group IV plasmonics and photonics. We have designed 5-layer SON channel-waveguides and slab-waveguides for the 2.0 to 5.4 μm wavelength range and have simulated the resulting three-dimensional (3D) and two-dimensional (2D) SON gap-plasmon modes. Our simulations show propagation lengths of ∼60 μm for 3D gap-strip modes having a 0.003 λ2 cross-section. Because the ∼50-nm SON (Si3N4) mode region is also a gate insulator between silver (Ag) and n-doped Silicon (Si), metal-oxide-semiconductor accumulation gating is available for electro-optical loss modulation of the gap-confined mode.

Simulation of Waveguide Crossings and Corners With Complex Mode-Matching Method

The complex mode-matching method is applied to simulation of optical waveguide structures with intersecting structures such as crossings and corners. It is demonstrated that field propagating along the direction perpendicular to the incident waveguide can be represented adequately by the complex modes defined in the incident waveguide and, therefore, can be simulated accurately by the complex mode-matching method. Power conservation is illustrated by way of examples to prove the self-consistency of the complex mode-matching method. Radiation field perpendicular to the incident waveguide axis in waveguide crossings and corners is simulated by this method and validated by the finite-difference time-domain method.

Intra-Cavity Dispersion of Microresonators and its Engineering for Octave-Spanning Kerr Frequency Comb Generation

We present an analysis on intra-cavity dispersion of a micro-resonator. As an example, different dispersion sources of a silicon nitride microring resonator are identified and evaluated over a wide wavelength range. We also show the dispersion flattening technique based on a strip/slot hybrid waveguide structure can be used to tailor the intra-cavity dispersions. Octave-spanning Kerr frequency combs are numerically simulated using 2-D-FDTD. It is shown that 7.5-fs two-cycle cavity solitons can be generated, enabling ultrawide mode-locked Kerr combs, with improved comb spectral flatness.

Towards ultra-subwavelength optical latches

We propose an electrically driven nanometer scale plasmonic optical latch integrated with Ge2Sb2Te5 chalcogenide glasses. For an effective switching length of 167 nm, the extinction ratio between the ON and OFF states of the proposed switch is as large as 10 dB, with net operation energy as low as 30.4 pJ per cycle.

A Rigorous Circuit Model for Simulation of Large-Scale Photonic Integrated Circuits

A rigorous circuit model for the simulation of large-scale photonic integrated circuit (PIC) is proposed and validated. Different from the conventional circuit theory, both guided and radiation fields are taken into consideration in the circuit model. A PIC of arbitrary size and complexity is partitioned into a collection of basic circuit elements interconnected via physical and virtual ports. The model parameters describing the terminal properties of the circuit elements are extracted by numerical techniques for photonic device simulation such as FDTD method. The performance of the entire PIC can be simulated by conventional circuit simulation algorithms based on the complex scattering matrix formalism. In contrast with the existing numerical simulation techniques, the circuit model and the simulation methodology are more flexible, efficient, and scalable for the analysis of large-scale PICs.