An ultra-compact broadband 2 × 2 3 dB power splitter is proposed and demonstrated by utilizing a subwavelength- grating (SWG)-assisted asymmetric directional coupler. In the present design, a subwavelength grating is inserted into the straight coupling region of an asymmetric directional coupler, so that the refractive index and the dispersion properties of this structure are engineered for achieving an ultra-broad bandwidth and an ultra-compact footprint. For the present power splitter with a straight coupling region as short as 5.25 μm, the bandwidth is as large as 300 nm (1400∼1700 nm) for achieving an imbalance of <0.4 dB and an excess loss of <0.33 dB for the fundamental transverse electrical (TE) mode. The fabricated splitter works well with an imbalance less than 0.5 dB and with an excess loss less than 1 dB in a broad wavelength-band from 1450 to 1650 nm.

Ultra-Compact Broadband 2 × 2 3 dB Power Splitter Using a Subwavelength-Grating-Assisted Asymmetric Directional Coupler

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A review of silicon subwavelength gratings: building break-through devices with anisotropic metamaterials

On-chip mode-manipulation is one of the most important physical fundamentals for many photonic integrated devices and circuits. In the past years, great progresses have been achieved on subwavelength silicon photonics for on-chip mode-manipulation by introducing special subwavelength photonic waveguides. Among them, there are two popular waveguide structures available. One is silicon hybrid plasmonic waveguides (HPWGs) and the other one is silicon subwavelength-structured waveguides (SSWGs). In this paper, we focus on subwavelength silicon photonic devices and the applications with the manipulation of the effective indices, the modal field profiles, the mode dispersion, as well as the birefringence. First, a review is given about subwavelength silicon photonics for the fundamental-mode manipulation, including high-performance polarization-handling devices, efficient mode converters for chip-fiber edge-coupling, and ultra-broadband power splitters. Second, a review is given about subwavelength silicon photonics for the higher-order-mode manipulation, including multimode converters, multimode waveguide bends, and multimode waveguide crossing. Finally, some emerging applications of subwavelength silicon photonics for on-chip mode-manipulation are discussed.

/pdf/subwavelength-silicon-photonics-for-on-chip-mode-6u1e9gvhzt.pdf

Subwavelength silicon photonics for on-chip mode-manipulation

Abstract Subwavelength structures such as subwavelength gratings (SWGs) and subwavelength metamaterials are capable of tailoring the optical properties of materials and controlling the flow of light at the nanoscale. The effective indices of the subwavelength structured strip and slab waveguides can be changed in a wide range by choosing an appropriate duty cycle or a filling factor of silicon, which provides an effective method to manipulate the optical field and achieve effective index matching for functional devices. Recent advances in nanofabrication techniques have made it possible to implement subwavelength structures in silicon strip and slab waveguides. Here we review various approaches used to design subwavelength structures and achieve exotic optical responses and discuss how these structures can be used to realize high-performance silicon photonic devices. Both one-dimensional SWG devices and two-dimensional subwavelength metamaterial devices are covered in this review, including subwavelength structure–based polarization handling devices, mode manipulation devices, and building blocks for integrated optical interconnects. Perspectives on subwavelength structured silicon photonic devices are also discussed.

/pdf/subwavelength-structured-silicon-waveguides-and-photonic-3zml374num.pdf

Subwavelength structured silicon waveguides and photonic devices

We demonstrate adiabatic couplers (ADCs) with design-intended splitting ratios (SRs) for the silicon-on-insulator (SOI) platform. The operational principle, numerical simulations, and experimental results on the designed ADC are presented. In the operational principle, we derive the analytical relationship between the SR and the effective index-difference, based on which we calculate the corresponding SRs under various output waveguide width-differences at a central wavelength of 1310 nm. For the simulation process, a segmented optimization method is employed to analyze the adiabatic transition process through the ADC. From the experiment results, broadband ADCs with design-intended power SRs, from 7%/93% to 50%/50%, are fabricated and then tested over a bandwidth of 100 nm, i.e., from 1260 to 1360 nm for the fundamental transverse electric (TE) mode. Furthermore, the thermal stability of the ADC is investigated. When increasing the stage temperature from 20  $^\circ$ C to 50  $^\circ$ C, the variances of the SRs for different wavelengths across O band are within 1.3%, which makes the design a potential candidate for performance robustness against temperature variations.

Adiabatic Coupler With Design-Intended Splitting Ratio

We demonstrate a compact high-performance adiabatic 3-dB coupler for the silicon-on-insulator platform. The refractive index of the gap region between two coupling waveguides is effectively increased using subwavelength grating, which leads to high-performance operation and a compact design footprint, with a mode-evolution length of only 25 µm and an entire device length of 65 µm. The designed adiabatic 3-dB coupler has been fabricated using electron beam lithography and the feature size used in our design is CMOS compatible. The fabricated device is characterized in the wavelength range from 1500 nm to 1600 nm, with a measured power splitting ratio better than 3 ± 0.27 dB and an average insertion loss of 0.20 dB.

Compact high-performance adiabatic 3-dB coupler enabled by subwavelength grating slot in the silicon-on-insulator platform

An ultra-broadband, compact adiabatic coupler in silicon-on-insulator platform is presented. It has 70 μm coupling length and a splitting ratio of 3±0.8 dB over bandwidth > 160 nm measured jointly in the C- and O-bands.

Heba Tamazin

Papers

Compact high-performance adiabatic 3-dB coupler enabled by subwavelength grating slot in the silicon-on-insulator platform

Ultra-broadband Compact Adiabatic Coupler in Silicon-on-Insulator for Joint Operation in the C- and O-Bands