Multiple-slot Waveguide Research Articles

Optimization of multiple-slot waveguides for biochemical sensing.

In this work, we analyze and optimize an optical biochemical sensor using silicon multiple-slot waveguides. The rigorous optimization procedure considers parameters such as ridge width, slot width, the number of slots, and the effect of residual silicon left at the bottom of the slot region. These parameters are then optimized using a figure of merit to achieve the highest possible sensitivity to bulk and surface changes in the upper cladding of the sensor. The multiple-slot structure is then studied in a bend configuration in order to construct ring-resonator-based sensors. A bulk sensitivity of 912nm/refractive index unit is achieved for a change in bulk refractive index, which is three times better than single-slot waveguides.

Efficient perfectly vertical fiber-to-chip grating coupler for silicon horizontal multiple slot waveguides

Horizontal multiple slot waveguides of polysilicon and silicon nanocrystalline oxide were grating coupled to a surface normal fiber array. Measurements yielded a coupling efficiency of 60% per grating. The fabrication-tolerant, four-stage grating design was genetically evolved from a random seed without starting from first-principle design. Theoretical coupling efficiency was 68% and was re-designed to 63% after accommodating all sources of fabrication error. To our knowledge, this is the first implementation of a purely polysilicon and silicon nanocrystalline oxide slot waveguide platform.

Low-Loss Multiple-Slot Waveguides Fabricated by Optical Lithography and Atomic Layer Deposition

We demonstrate silicon-based multiple-slot waveguides filled with dual atomic layer deposited oxide layers. Slot modes for both polarizations, transverse electric (TE) and transverse magnetic (TM), are supported in the waveguide. Propagation loss in the order of 8 dB/cm is achieved for the TE-polarization and 4 dB/cm for the TM-polarization in the waveguides with dual (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) thin film layers. The devices are fabricated using low-temperature complementary metal-oxide-semiconductor compatible processes. To our knowledge, this is the first demonstration of dual-filled slot waveguides.

Investigation of Terahertz Wave Propagation Along Shielded Dielectric Multiple-Slot Waveguide

In this paper, a shielded dielectric multiple-slot waveguide is presented and demonstrated by theoretical calculation at terahertz frequencies. Some electromagnetic analysis of waveguide currently employed simplified intrinsic frequency dispersion models for the bulk conductivity of normal metals used in terahertz wave structures. This paper has compared various conductivity models for gold between 0.1-3 THz. The dielectric loss, conductor loss, total propagation loss with different conductivity models and E-field distribution has been obtained by numerically solving the complex eigenvalue equation for the propagation constant. The analysis results are in agreement with the assumption of R. Sun et al. and the experimental results obtained by H. Sun et al. The propagation loss deviation between various models is less than 3% at 0.2-0.5 THz. Comparisons with other slot waveguides are also given. The analysis results show that the proposed line has lower propagation attenuation than other slot waveguides.

Bending efficiency analysis of horizontal single- and multiple-slot waveguide microrings

The bending efficiencies of three-dimensional (3D) horizontal single- and multiple-slot waveguide microrings are analyzed using the effective index and modified transfer matrix methods. The effects of waveguide parameters, low-index material, high-index material, asymmetric structure, and asymmetric slots on the bending loss are studied. The results show that the bending efficiency can be enhanced by applying asymmetric structures and asymmetric slots. In addition, it is demonstrated that the bending loss increases with the increase of the number of slots. However, by using proper thicknesses for different high-index layers of the horizontal multiple-slot waveguide, it is possible that the horizontal multiple-slot waveguide can provide a lower bending loss than the single-slot one.

A design for a photonic syringe with multimode coupled slot waveguides

A design is proposed that allows non-stationary field distribution with Bragg gratings in multiple slot waveguides. Selective coupling between modes is achieved or suppressed, according to controllable selection rules, based on mode symmetry. By applying such rules, backward pulling radiation pressure - i.e. toward the light source - can be obtained inside the slots. A mode-switching filter is also proposed, which allows the switching between forward and backward direction of radiation pressure. This "light-actuated" syringe could have potential applications for bidirectional particle trapping and manipulation, optofluidics, optomechanics and biotechnology.

Bending Efficiency of Bent Multiple-Slot Waveguides

The bending efficiency of three-dimensional bent multiple-slot waveguides is studied by applying a combined method of effective-index and modified transfer-matrix methods. The effects of asymmetric structure, asymmetric slots, and asymmetric middle strips on the bending efficiency are investigated. We show that the bending efficiency can be improved by the use of asymmetric structures and asymmetric middle strips. The bending efficiency of different slot waveguides (up to quintuple-slot structure) is compared. It is revealed that although the single-slot waveguide in general provides the lowest bending loss for the same waveguide parameters, it is possible that the multiple-slot waveguide can present a lower bending loss than the single-slot one.

Enhanced Evanescent Confinement in Multiple-Slot Waveguides and Its Application in Biochemical Sensing

The interaction of light propagating in the wave-guiding structures with the surrounding media through its evanescent field has been used to detect biochemical activities without labeling the target molecules. By introducing multiple slots in a dielectric waveguide, we found that a much stronger evanescent field could be achieved in the surrounding media while still maintaining good optical confinement. The experimental demonstration of microring resonator sensors using single-mode waveguides having three slots indicates a 5-fold increase in sensitivity for homogeneous sensing and more than 3-fold increase in sensitivity for surface sensing in comparison to those of a waveguide without slots. Numerical simulations suggest an even higher sensitivity enhancement (as high as 100 times) as more slots and larger waveguide widths are used.

Vertical multiple-slot waveguide ring resonators in silicon nitride

This article describes the first demonstration of ring resonators based on vertical multiple-slot silicon nitride waveguides. The design, fabrication and measurement of multiple-slot waveguide ring resonators with several coupling distances and ring radii (70 microm, 90 microm and 110 microm) have been carried out for TE and TM polarizations at the wavelength of 1.3 microm. Quality factors of 6,100 and 16,000 have been achieved for TE and TM polarization, respectively.

Simulation Demonstration and Experimental Fabrication of a Multiple-Slot Waveguide

A multiple-slot waveguide is presented and demonstrated through theoretical simulation. Taking a double-slot waveguide as an example, the results show a nearly 30% enhancement of optical intensity compared with the traditional single-slot waveguide with the same slot gap width. Therefore, the E-field intensity of the slot can be increased by adding another smaller slot. A double-slot waveguide with oxide and air as low index slot materials is realized experimentally and the formation processes of the slots are analyzed.

Simple and effective calculation of modal properties of bent slot waveguides

Three-dimensional bent slot waveguides are analyzed using a combined effective-index method/modified transfer-matrix method. The effective refractive index and bending loss of the guided mode can be acquired. The results closely match those calculated by the full-vectorial finite-difference method. This method also enables the calculation of field distribution, useful in estimating power confined in the narrow slot, and can handle asymmetric bent slot waveguides, bent multiple-slot waveguides, and hybrid bent slot waveguides. This approach has advantages of simplicity, versatility, and time-saving calculation, which are beneficial for the quick design of devices using bent slot waveguides.

Horizontal single and multiple slot waveguides: optical transmission at λ = 1550 nm

We experimentally demonstrate the optical transmission at 1550 nm of the fundamental slot modes (quasi-TM modes) in horizontal single and multiple slot waveguides and ring resonators consisting of deposited amorphous silicon and silicon dioxide. We demonstrate that the horizontal multiple slot configuration provides enhanced optical confinement in low index slot regions compared to a horizontal single slot structure with the same total SiO2 layer thickness by comparing their thermo-optic coefficients for the horizontal slot ring resonators. We show in these early structures that horizontal slot waveguides have low propagation loss of 6 approximately 7 dB/cm. The waveguide loss is mainly due to a-Si material absorption. The addition of a-Si/SiO(2) interfaces does not introduce significant scattering loss in a horizontal multiple slot waveguide compared to a horizontal single slot waveguide.