Measurement of a compact colorless 3 dB hybrid plasmonic directional coupler

Rational design of an integrated directional coupler for wideband operation

We consider a design procedure for directional couplers for which the coupling length is approximately wavelength-independent over a wide bandwidth. We show analytically that two coupled planar waveguides exhibit a maximum in the coupling strength, which ensures both wideband transmission and minimal device footprint. This acts as a starting point for mapping out the relevant part of phase space. This analysis is then generalized to the fully three-dimensional geometry of rib waveguides using an effective medium approximation. This forms an excellent starting point for fully numerical calculations and leads to designs with unprecedented bandwidths and compactness.

Stable hybrid plasmonic directional coupler based on an embedded silver nanostructure waveguide

In this paper, a stable hybrid plasmonic optical directional coupler based on an embedded silver nanostructure that can offer a power transfer up to 95% is presented. This optimum power transfer is obtained at an outer edge-to-edge separation of 0.58 µm between the two waveguides. The obtained propagation loss is as low as 0.0863 dB/µm. The electric field distributions of the symmetric and antisymmetric modes of the coupler are compared, and the transmission characteristics are studied in detail using the finite element method. The performances of the directional coupler have been further characterized in terms of excess loss, coupling degree, and directionality. The shortest coupling length at which the maximum power coupling occurs is obtained as 2.488 µm. The proposed compact directional coupler features good field confinement and low propagation loss, which opens the door for many device applications in photonic-integrated circuits and optoelectronic industries.

Compact and broadband data exchange for mode-division-multiplexed networks

Recently, mode-division multiplexing (MDM) technology has been used to enable high-bandwidth data transmission. Information swapping or data exchange is an essential function in such high-capacity networks. This paper presents a small, broadband on-chip optical data exchange between two multiplexed modes on the silicon-on-insulator platform. The device consists of a three-waveguide coupler in which the middle waveguide has a hybrid plasmonic structure and the two other ones are silicon waveguides. The total length and the width of the proposed structure are 15.25 μm and 1.0885 μm, respectively. The 3D finite-difference-time-domain simulation results show that the insertion loss is less than 2 dB for a broad bandwidth of 100 nm, over which the crosstalk is lower than -14.7  dB and -21.9  dB for TM0 to TM1 and TM1 to TM0 conversion, respectively.

Ultracompact and broadband silicon-based TE-pass 1 × 2 power splitter using subwavelength grating couplers and hybrid plasmonic gratings

An ultracompact TE-pass 1 × 2 power splitter, using subwavelength grating (SWG) couplers and hybrid plasmonic gratings (HPGs), is proposed and analyzed in detail. As the input strip waveguide is tapered to a narrow wire, where TE mode is cutoff, the launched TE-mode can be evenly divided with high efficiency with the help of the SWG couplers, which are placed between the central silicon wire and two nearby output branches. The injected TM-mode will be perfectly reflected by the carefully designed HPG, whose periodically varied metal layer is located above the bottom strip and SWG waveguides. Consequently, a single device combining both the functions of polarization selection and power division can be realized. This is valuable for highly dense integrated circuits. Results show that, with a period number of 4 in HPG, the present device is only ~6.2-μm-long with an extinction ratio (ER) and an insertion loss (IL) of 25.4 and 0.53 dB at 1.55 μm, respectively, and its bandwidth of ER > 20 dB is ~180 nm with the IL < 0.8 dB, showing a broadband property. Besides, fabrication tolerances to the key dimensions are analyzed and modal field evolution through the device is also presented.

Polarization-insensitive broadband 2 × 2 3 dB power splitter based on silicon-bent directional couplers

We present and demonstrate a broadband and polarization-insensitive 2×2 3 dB power splitters based on silicon-bent directional couplers (DCs). The working bandwidth can be from 1520 to 1630 nm for both TE and TM polarizations, with an excess loss less than 1 dB. The total size for the fabricated device can be as small as 50 μm, and the measurement results show good agreement with the simulations.

Integrated dual-mode 3 dB power coupler based on tapered directional coupler

A dual-mode 3 dB power coupler based on silicon-on-insulator platform for mode division multiplexing system is proposed and demonstrated. The device, which consists of a tapered directional coupler and two output bend waveguides, has a 50:50 coupling ratio around the wavelength of 1550 nm for both fundamental and first order transverse magnetic (TM₀ and TM₁) modes. Based on asymmetrical tapered structure, a short common coupling length of ~15.2 μm for both modes is realized by optimizing the width of the tapered waveguide. The measured insertion loss for both modes is less than 0.7 dB. The crosstalks are about −14.3 dB for TM₀ mode and −18.1 dB for TM₁ mode.

Recent advances in silicon-based passive and active optical interconnects

Silicon photonics has experienced phenomenal transformations over the last decade. In this paper, we present some of the notable advances in silicon-based passive and active optical interconnect components, and highlight some of our key contributions. Light is also cast on few other parallel technologies that are working in tandem with silicon-based structures, and providing unique functions not achievable with any single system acting alone. With an increasing utilization of CMOS foundries for silicon photonics fabrication, a viable path for realizing extremely low-cost integrated optoelectronics has been paved. These advances are expected to benefit several application domains in the years to come, including communication networks, sensing, and nonlinear systems.

Broadband silicon photonic directional coupler using asymmetric-waveguide based phase control

We design and demonstrate broadband directional couplers that use asymmetric-waveguide based phase control sections, on the silicon-on-insulator platform. Broadband directional couplers with various power splitting ratios, including 10%/90%, 20%/80%, 30%/70%, 40%/60% and 50%/50%, were realized for both transverse electric (TE) and transverse magnetic (TM) modes. Some of the devices exhitbit bandwidths in excess of 100 nm, and all in excess of 75 nm. The footprints of the TE mode couplers are 32 μm ×1.3 μm, or less, and those of the TM mode couplers are 13 μm ×1.3 μm, or less.

Compact and broadband mode multiplexer and demultiplexer based on asymmetric plasmonic-dielectric coupling

A compact and broadband mode (de)multiplexer utilizing the asymmetrical directional coupling between a hybrid plasmonic waveguide and a silicon nanowire waveguide is proposed. The coupling length is 13.6 μm, which is the shortest in TE0 and TE1 mode multiplexers reported, to the best of our knowledge. It shows a high mode conversion efficiency of 99.2% with excess loss of only 0.35 dB at 1550 nm. The mode multiplexing circuit exhibits a low crosstalk of less than -17  dB over a large bandwidth of 100 nm.