Doris Keh Ting Ng

Silicon/III-V laser with super-compact diffraction grating for WDM applications in electronic-photonic integrated circuits.

We have demonstrated a heterogeneously integrated III-V-on-Silicon laser based on an ultra-large-angle super-compact grating (SCG). The SCG enables single-wavelength operation due to its high-spectral-resolution aberration-free design, enabling wavelength division multiplexing (WDM) applications in Electronic-Photonic Integrated Circuits (EPICs). The SCG based Si/III-V laser is realized by fabricating the SCG on silicon-on-insulator (SOI) substrate. Optical gain is provided by electrically pumped heterogeneous integrated III-V material on silicon. Single-wavelength lasing at 1550 nm with an output power of over 2 mW and a lasing threshold of around 150 mA were achieved.

Heterogeneous Si/III-V integration and the optical vertical interconnect access

A new heterogeneous Si/III-V integration and the optical vertical interconnect access to the silicon-on-insulator (SOI) nanophotonic layer is proposed and designed. The III-V semiconductor layers are directly bonded to the SOI layer and etched to form the Si/III-V waveguide (after removal of the substrate), which has no air-trench or SOI channel waveguide underneath as the prior art. The design example shows a 1.5 μm wide Si/III-V waveguide has a confinement factor of ~24% in a 100 nm-thick active region for effective light amplification/absorption. The optical vertical interconnect access is realized through tapering both the III-V semiconductor waveguide and SOI layer in the same direction. Optimization using a simple approximated two-dimensional modal presented gives ~100% coupling efficiency with a 25 μm long optical vertical interconnect access. A three-dimensional finite-difference-time-domain electromagnetic simulation verifies the design numerically and also shows the proposed structure has a good alignment tolerance for fabrication.

Exploring High Refractive Index Silicon-Rich Nitride Films by Low-Temperature Inductively Coupled Plasma Chemical Vapor Deposition and Applications for Integrated Waveguides

Silicon-rich nitride films are developed and explored using an inductively coupled plasma chemical vapor deposition system at low temperature of 250 °C with an ammonia-free gas chemistry. The refractive index of the developed silicon-rich nitride films can increase from 2.2 to 3.08 at 1550 nm wavelength while retaining a near-zero extinction coefficient when the amount of silane increases. Energy dispersive spectrum analysis gives the silicon to nitrogen ratio in the films. Atomic force microscopy shows a very smooth surface, with a surface roughness root-mean-square of 0.27 nm over a 3 μm × 3 μm area of the 300 nm thick film with a refractive index of 3.08. As an application example, the 300 nm thick silicon-rich nitride film is then patterned by electron beam lithography and etched using inductively coupled plasma system to form thin-film micro/nano waveguides, and the waveguide loss is characterized.

Design and Analysis of Optical Coupling Between Silicon Nanophotonic Waveguide and Standard Single-Mode Fiber Using an Integrated Asymmetric Super-GRIN Lens

Comprehensive design and analysis of optical coupling between silicon nanophotonic waveguide and standard single-mode fiber is presented. The coupling structure employs an integrated asymmetric graded refractive index (GRIN) lens deposited at the end of the tapered waveguide, and the GRIN lens has an optimized refractive index profile with a super high numerical aperture for aberration-free subwavelength focusing/collimating. The influence of end-facet reflection of the GRIN lens on the coupling efficiency is investigated. The optimized GRIN lens with a proper antireflection coating shows a coupling efficiency of ~90% between a 300-nm-thick silicon nanophotonic waveguide and a standard single-mode fiber. A 3-D modeling and simulation of the GRIN lens is carried out. The influences of fiber displacement and angular misalignment on the coupling efficiency are analyzed. The overall systematic design and analysis indicate that this integrated GRIN-lens-based optical coupler offers a compact and efficient solution for nanophotonic waveguide coupling with a good alignment tolerance.

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.

Electrically pumped heterogeneously integrated Si/III-V evanescent lasers with micro-loop mirror reflector

An electrically pumped heterogeneously integrated Si/AlGaInAs evanescent laser with micro-loop mirror (MLM) as high reflectors at both ends is experimentally demonstrated. Finite-difference time-domain simulation shows that 98% reflectivity can be achieved with micro-loop mirror formed by single-mode silicon-on-insulator (SOI) waveguides. The laser based on a Si/III-V hybrid gain waveguide and passive SOI MLM reflectors is fabricated and single-mode continuous-wave (CW) lasing is achieved at room temperature with a lasing threshold current density of 2.5 kA/cm2.

Pushing the limits of CMOS optical parametric amplifiers with USRN:Si7N3 above the two-photon absorption edge.

CMOS platforms operating at the telecommunications wavelength either reside within the highly dissipative two-photon regime in silicon-based optical devices, or possess small nonlinearities. Bandgap engineering of non-stoichiometric silicon nitride using state-of-the-art fabrication techniques has led to our development of USRN (ultra-silicon-rich nitride) in the form of Si7N3, that possesses a high Kerr nonlinearity (2.8 × 10−13 cm2 W−1), an order of magnitude larger than that in stoichiometric silicon nitride. Here we experimentally demonstrate high-gain optical parametric amplification using USRN, which is compositionally tailored such that the 1,550 nm wavelength resides above the two-photon absorption edge, while still possessing large nonlinearities. Optical parametric gain of 42.5 dB, as well as cascaded four-wave mixing with gain down to the third idler is observed and attributed to the high photon efficiency achieved through operating above the two-photon absorption edge, representing one of the largest optical parametric gains to date on a CMOS platform.

Generic Heterogeneously Integrated III–V Lasers-on-Chip With Metal-Coated Etched-Mirror

In this paper, electrically pumped III-V quantum-well lasers bonded on SiO2 with a metal-coated etched-mirror are reported. There are three key features for the device demonstrated: (i) The metal-coated etched-mirror ensures that the lasers can be used as on-chip light source and provides high reflectance, but requires no additional fabrication steps due to our process design, (ii) the bonded III-V on SiO2 enables high-light confinement in the active region due to high index contrast between III-V and SiO2. Moreover, it promises a flexible choice of host substrate, in which the silicon substrate could also be replaced with other materials, and (iii) the active III-V region is sufficiently close to the SiO2 interlayer, allowing the laser mode to overlap with SiO2. This facilitates effective optical coupling with in-plane passive waveguides, which can be fabricated from thin film of amorphous silicon, silicon nitride or other waveguide materials, to form a subsystem on chip through in-plane integration. The laser devices demonstrated have the lowest threshold of 50 mA, a maximum output power of 9 mW, and a differential quantum efficiency of 27.6%.

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.