Milan M. Milosevic

Low loss silicon waveguides for the mid-infrared

Silicon-on-insulator (SOI) has been used as a platform for near-infrared photonic devices for more than twenty years. Longer wavelengths, however, may be problematic for SOI due to higher absorption loss in silicon dioxide. In this paper we report propagation loss measurements for the longest wavelength used so far on SOI platform. We show that propagation losses of 0.6-0.7 dB/cm can be achieved at a wavelength of 3.39 µm. We also report propagation loss measurements for silicon on porous silicon (SiPSi) waveguides at the same wavelength.

Silicon waveguides and devices for the mid-infrared

We report on the design, fabrication, and characterization of silicon-on-insulator rib and strip waveguides at wavelengths longer than 3.7µm. Propagation losses of 1.5±0.2 dB/cm at 3.73µm and 1.8±0.2 dB/cm at 3.8µm have been measured for rib waveguides, whilst submicron strip waveguides exhibited propagation losses of 4.6±1.1 dB/cm at the wavelength of 3.74µm. A 1×2 multimode interference (MMI) splitter and racetrack resonators based on submicron strip waveguides are also examined. Optical losses of 3.6±0.2 dB/MMI and a racetrack resonator Q-value of 8.2k are obtained at 3.74µm.

Silicon photonic waveguides for different wavelength regions

In this paper, we present our work on three silicon waveguide structures that are suitable for three different wavelength regions: near-, mid- and far-infrared. Design rules for standard rib SOI waveguides are given. Both single mode and polarization independence in these waveguides are discussed. A hollow-core waveguide suitable for gas-sensing applications in the mid-infrared wavelength region is also analysed. Finally, fabrication and experimental results for free standing waveguides, which may find application in the mid- and perhaps far-infrared wavelength regions, are presented.

Design Rules for Single-Mode and Polarization-Independent Silicon-on-Insulator Rib Waveguides Using Stress Engineering

There is a trend towards miniaturization of silicon photonic circuits due to superior performance and small cost. Design rules that must be imposed on the geometry of optical waveguides to make them behave as polarization-independent and single-mode devices are well known for waveguides with relatively large cross sections and for some small cross-sectional rib waveguides with vertical sidewalls and an air top cladding. The influence of the top oxide cover on waveguide birefringence was analyzed recently, but only for relatively large cross-sectional waveguides. This paper reports simulations for both single-mode and polarization-independent behavior for small cross-sectional waveguides with variable rib width, etch depth, top oxide cover thickness, and side-wall angle. The results show that the stress-induced effects must be taken into account to satisfy both requirements. Design rules to maintain birefringence-free operation and to satisfy single-mode behavior for small rib silicon-on-insulator (SOI) waveguides are presented.

Scattering Loss Estimation Using 2-D Fourier Analysis and Modeling of Sidewall Roughness on Optical Waveguides

We report an accurate scattering loss 3-D modeling technique of sidewall roughness of optical SOI waveguides based on Fourier and finite-difference time domain (FDTD) analysis methods. The Fourier analysis method is based on the image recovery technique used in magnetic resonant imaging. Losses for waveguides with isotropic and anisotropic roughness are calculated for wavelengths ranging from 1550 to 3800 nm and compared with reported results in literature. Our simulations show excellent agreement with published experimental results and provide an accurate prediction of roughness-induced loss of 3-D arbitrary shaped optical waveguides.

Athermal waveguides for optical communication wavelengths

We report on the design, fabrication, and characterization of temperature insensitive strip silicon-on-insulator racetrack resonators. The influence of various parameters, such as waveguide width, waveguide height, ring radius, coupling length, ring gap, and operating wavelength, on temperature-dependent wavelength shift is examined. A resonant wavelength shift of 0.2 pm/K at a 1550 nm wavelength is measured for 335 nm × 220 nm waveguides. A significant reduction of waveguide propagation losses, improved ring Q value, and higher extinction ratio are obtained after overlaying the silicon waveguides with a polymer cladding.

Silicon waveguides for the 3–4 µm wavelength range

In this paper we report propagation and bend loss measurements for silicon-on-insulator (SOI) and silicon-on-sapphire (SOS) waveguides at 3.39 µm wavelength. Preliminary experimental results for SOI rib waveguides at around 3.8 µm are also given.

Waveguides for mid-infrared group IV photonics

In this paper we present preliminary work on group IV photonic waveguides that may be suitable for mid-infrared wavelengths. Fabrication and experimental results for two waveguide structures are given.

Athermal and low loss ridge silicon waveguides

In this paper, we investigate athermal and low propagation loss silicon-on-insulator (SOI) rib waveguides. Propagation losses have been modeled for different dimensions of ridge waveguides achieving good agreement with experimental measurements. At certain waveguide widths, it is possible to obtain low propagation losses for both TE (transverse electric) and TM (transverse magnetic) modes. Racetrack ring resonator structures based on ridge waveguides covered by a polymer have been fabricated, aiming for an athermal design and therefore, a very small temperature dependent wavelength shift. Design guidelines for temperature insensitive and small propagation loss ridge waveguides are presented in this paper together with experimental data.

Determination of the quasi-TE mode (in-plane) graphene linear absorption coefficient via integration with silicon-on-insulator racetrack cavity resonators

We examine the near-IR light-matter interaction for graphene integrated cavity ring resonators based on silicon-on-insulator (SOI) race-track waveguides. Fitting of the cavity resonances from quasi-TE mode transmission spectra reveal the real part of the effective refractive index for graphene, n(eff) = 2.23 ± 0.02 and linear absorption coefficient, α(gTE) = 0.11 ± 0.01dBμm(-1). The evanescent nature of the guided mode coupling to graphene at resonance depends strongly on the height of the graphene above the cavity, which places limits on the cavity length for optical sensing applications.