Kim Peng Lim

Demonstration of heterogeneous III–V/Si integration with a compact optical vertical interconnect access

Heterogeneous III-V/Si integration with a compact optical vertical interconnect access is fabricated and the light coupling efficiency between the III-V/Si waveguide and the silicon nanophotonic waveguide is characterized. The III-V semiconductor material is directly bonded to the silicon-on-insulator (SOI) substrate and etched to form the III-V/Si waveguide for a higher light confinement in the active region. The compact optical vertical interconnect access is formed through tapering a III-V and an SOI layer in the same direction. The measured III-V/Si waveguide has a light coupling efficiency above ~90% to the silicon photonic layer with the tapering structure. This heterogeneous and light coupling structure can provide an efficient platform for photonic systems on chip, including passive and active devices.

Heterogeneously integrated III-V laser on thin SOI with compact optical vertical interconnect access.

A new heterogeneously integrated III-V/Si laser structure is reported in this report that consists of a III-V ridge waveguide gain section on silicon, III-V/Si optical vertical interconnect accesses (VIAs), and silicon-on-insulator (SOI) nanophotonic waveguide sections. The III-V semiconductor layers are introduced on top of the 300-nm-thick SOI layer through low temperature, plasma-assisted direct wafer-bonding and etched to form a III-V ridge waveguide on silicon as the gain section. The optical VIA is formed by tapering the III-V and the beneath SOI in the same direction with a length of 50 μm for efficient coupling of light down to the 600 nm wide silicon nanophotonic waveguide or vice versa. Fabrication details and specification characterizations of this heterogeneous III-V/Si Fabry-Perot (FP) laser are given. The fabricated FP laser shows a continuous-wave lasing with a threshold current of 65 mA at room temperature, and the slope efficiency from single facet is 144  mW/A. The maximal single facet emitting power is about 4.5 mW at a current of 100 mA, and the side-mode suppression ratio is ∼30  dB. This new heterogeneously integrated III-V/Si laser structure demonstrated enables more complex laser configuration with a sub-system on-chip for various applications.

Heterogeneous Integrated III–V Laser on Thin SOI With Single-Stage Adiabatic Coupler: Device Realization and Performance Analysis

A III-V on silicon heterogeneous integrated laser with highly efficient single-stage adiabatic coupler is presented in this paper. The structure consists of an electrically pumped III-V ridge waveguide gain section on silicon, III-V/Si optical adiabatic coupler, and silicon-on-insulator (SOI) nanophotonic waveguide. The adiabatic coupler is 50-μm long and is formed by tapering the III-V ridge and the underneath thin SOI waveguide along the same direction for efficient coupling of light between III-V ridge and silicon waveguide. Fabrication details and characterizations of this heterogeneous III-V/Si Fabry-Pérot (FP) laser are presented. Experimental data show that such structure has a low taper end reflection of ~-37 dB, and a high optical coupling efficiency of ~85%. The fabricated FP laser shows a high differential quantum efficiency of 23.78% under pulse operation at room temperature. The maximal single facet emitting power is about 7.5 mW, and the side-mode suppression ratio is ~30 dB. Thermal characterization shows a length normalized thermal independence of 20.02 °C·mm/W. Since this new heterogeneously integrated III-V/Si laser structure is realized directly on thin SOI, it offers a potential solution for developing more complex, efficient, and scalable integrated on-chip subsystems for various applications.

Efficient Integrated Light-Delivery System Design for HAMR: Maximal Optical Coupling for Transducer and Nanowaveguide

Light-delivery system for heat-assisted magnetic recording consists of laser, waveguide, and plasmonic near-field transducer (NFT). The overall efficiency of light-delivery system is determined by the efficiency of optical power transfer from waveguide to media via the plasmonic NFT and coupling of light from laser to waveguide. In this paper, we present an overall efficiency optimization of the light-delivery system, including the waveguide-NFT-media coupling efficiency by improving the waveguide mode-plasmon mode conversion and waveguide-media-stack impedance matching and laser-to-waveguide coupling efficiency using multi-layer graded refractive-index (GRIN) cladding layer. We show that a high refractive-index waveguide improves waveguide mode-to-asymmetric plasmon mode conversion and also improves characteristic impedance matching with the media stack resulting in a maximal optical power transfer efficiency of 11.5% between the waveguide and the media via a taper-based NFT. The multi-layer GRIN cladding structure acts as a collimating lens with a high numerical aperture, which can achieve laser-to-waveguide coupling efficiency of 90% in our numerical example. Therefore, the overall optimization shows that the efficiency of light-delivery system can reach 9%-10%.

Broadband antireflection for a high-index substrate using SiN x /SiO2 by inductively coupled plasma chemical vapour deposition

This paper presents the development of broadband antireflection coating for a high-index substrate such as Si using SiN x /SiO2 by inductively coupled plasma chemical vapour deposition (ICP-CVD). The thin-film design employs a simulated annealing method for a minimal average reflectance over the wavelength range and incidence angles involved, which gives the optimized refractive index and thickness of each layer of the thin-film stack under different layer numbers. Using ICP-CVD, the SiN x material system is optimized by tuning the SiH4/N2 gas ratio. The corresponding thin-film characterization shows the precise refractive index/film thickness control in deposition, and the deposited film also has a low absorption coefficient and smooth surface. The double-layer SiN x /SiO2 coating with the optimized refractive index and thickness for broadband antireflection is demonstrated experimentally. The average reflectance of the Si surface is reduced from ~32% to ~3.17% at normal incidence for a wavelength range from 400 to 1100 nm.

Effects of SiO 2 hard masks on si nanophotonic waveguide loss for photonic device integration

As the basic building block for photonic device integration, silicon nanophotonic waveguide requires low-loss propagation for high-performance ultra-compact photonic device. We experimentally study silicon dioxide hard masks grown by two different methods, i.e., thermal oxidation and plasma-enhanced chemical vapor deposition (PECVD) for silicon nano-waveguides fabrication and their effects on the propagation loss. It is found that the denser and smoother quality of thermally grown silicon dioxide increases the etch selectivity against silicon and reduces the line edge roughness transferred to the silicon nano-waveguide sidewalls, hence resulting in a lower loss as compared with the PECVD silicon dioxide hard mask. With thermally grown silicon dioxide as a hard mask, the silicon nano-waveguides loss can be halved for a 650-nm-wide nano-waveguide, and the loss is comparable with a waveguide fabricated with a resist etch mask.

Design of ultrasmall plasmonic coaxial lasers on Si

Abstract. An ultrasmall plasmonic coaxial laser made of metal–semiconductor–metal on a silicon substrate through an interlayer bonding was designed. From the effective refractive indices and the transparent material gain, the nanoscale structural dimensions with both the radius and the width at 80 nm for the coaxial plasmonic waveguide were decided. The influence of the interlayer bonding material on the optimization of resonant wavelength and Q-factor was evaluated. A three-dimensional body-of-revolution finite-difference time-domain method was used to show that a coaxial cavity with a SiO2 interlayer can laze at around 1480-nm wavelength with a net optical threshold power density of about 800  W/cm2 and a subwavelength mode volume of 0.014(λ/2n)3. This nanolaser on silicon platform will benefit those working on nanophotonic integrated circuits.

Design, fabrication and demonstration of heterogeneously III-V/Si laser with a compact optical vertical interconnect access

A new heterogeneously integrated III-V/Si laser structure is reported in this letter, which consists of a III-V ridge waveguide gain section on silicon, III-V/Si optical vertical interconnect accesses (VIAs) and silicon-oninsulator (SOI) nanophotonic waveguide sections. The III-V semiconductor layers are introduced on top of the 300 nm thick SOI layer through low temperature, plasma assisted direct wafer-bonding and etched to form III-V ridge waveguide on silicon as the gain section. The optical VIA is formed by tapering the III-V and the beneath SOI in the same direction with a length of 50 μm for efficient coupling of light down to the 600 nm wide silicon nanophotonic waveguide or vice versa. Fabrication details and specification characterizations of this heterogeneous III-V/Si Fabry–Pérot (FP) laser are given. The fabricated FP laser shows a continuous-wave lasing with a threshold current of 65 mA at room temperature and the slope efficiency from single facet is 144 mW/A. The maximal single facet emitting power is about 4.5 mW at a current of 100 mA and the side-mode suppression ratio is ~30 dB. This new heterogeneously integrated III-V/Si laser structure demonstrated enables more complex laser configuration with a sub-system on-chip for various applications.

Development of broadband antireflection of high-index substrate using SiNx/SiO2

Broadband antireflection coatings are commonly required in many silicon or III-V compound semiconductor based optoelectronic devices such as solar cells, photodetectors, and image sensors so as to enhance light conversion efficiency. Conventional approach using a single-layer antireflection coating is simple and commonly used in industry but it has a limited working bandwidth. To achieve broadband or even omni-directional characteristics, structures using thick graded refractive index (GRIN) multilayers or nanostructured surfaces which have equivalent graded refractive index profile have been proposed and demonstrated. In this paper, we will show our development of broadband antireflection for high index substrate using SiNx/SiO2 via inductively coupled plasma chemical vapour deposition (ICPCVD). Global optimization of thin-film broadband antireflection coating using adaptive simulated annealing is presented. Unlike the conventional optical coating design which uses the refractive index of available materials, the optimization approach used here decides the optimal values of the refractive index as well as the thickness of each layer. The first thin-film material optimization is carried out on the ICP-CVD machine operating at low temperature of 250°C by tuning the SiH4/N2 gas ratio. The demonstrated double layer antireflection thin film reduces the average reflectance of Si surface from ~32% to ~3.17% at normal incidence for wavelength range from 400 to 1100 nm. This optical thin-film design and material development can be extended to optical wavelength filters and integrated micro-GRIN devices.

Graded-index thin-film stack for cladding and coupling.

A graded-index multilayer thin-film stack is optimized to act as a cladding layer on top of a silicon (Si) nanowaveguide and also a collimator for chip coupling where the waveguide ends. The numerical example shows an optimized graded-index profile from 2.35 to 1.45 provides an optical coupling to the standard single-mode fiber with efficiency close to 90% while retaining tight light confinement for the Si nanowaveguide. The corresponding material realization of a graded-index profile with a Si-rich nitride SiNx/SiON/SiO2 system is explored using inductively coupled plasma chemical vapor deposition, and a SiNx cladded Si waveguide is demonstrated.