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Correlated photon pair generation is demonstrated using ultra-silicon-rich nitride waveguides. Waveguides with a length of 10 mm, nonlinear parameter of 530 W−1/m and anomalous dispersion are used to achieve spontaneous four-wave mixing. A generated coincidence rate of 2.40 × 105 counts per second is achieved, and derived from a measured coincidence rate of ∼ 1 counts per second at the maximum coupled power of 5 mW, in line with the expected quadratic dependence of spontaneous four-wave mixing efficiency on power. Utilizing picosecond pulses as the pump, we achieve a measured coincidence rate of up to 1.8 counts per second, resulting in a generated coincidence rate of 2.20 × 10−2 counts per pulse at the maximum peak power of 8.33 W. 2.3 times larger coincidence-to-accidental ratio is also obtained using a pulsed pump compared to that achieved with a continuous-wave pump. Further enhancements via the use of ring resonators may be adopted.

Nonlinear optical properties of ultra-silicon-rich nitride are investigated. The nonlinear refractive index and two-photo and three-photon absorption coefficients are measured in the range of 0.8pm-1.6pm covering the C- and L-bands.

We demonstrate pulse compression using ultra-silicon-rich nitride grating devices. Frequency chirp from a waveguide is temporally synchronized by a dispersive grating to achieve temporal compression by a factor of 4.3. When reversed, spectral compression of 2.3× is achieved.

We demonstrate the optical pulse compression of 2ps laser down to 230fs pulse resulting in 8.7 times compressed using a USRN waveguide. The process is facilitated by high-order soliton formation arising from a large nonlinear parameter and anomalous group velocity dispersion.

Correlated single photons provide a means to drive applications such as quantum computing and quantum communications. Correlated single photons can be generated via parametric down conversion in second–order nonlinear media or spontaneous four–wave mixing in third–order nonlinear media. In particular, complementary metal–oxide–semiconductor (CMOS) technology allows for seamless integration with electronics, providing the potential for a completely on-chip solution for quantum information processing. Ultra–silicon–rich nitride platform is a backend CMOS compatible platform, that has already been used to obtain high gain optical parametric amplification, wideband supercontinuum and enhanced nonlinearity in photonic crystal waveguides due to its large nonlinearity. In this work, we demonstrate correlated photon pair generation based on spontaneous four–wave mixing using ultra-silicon-rich nitride waveguides for the application in CMOS–based optical quantum technologies. A CW pump at a wavelength of 1555.747nm amplified using an EDFA is filtered through five wavelength division multiplexers (WDM) with a bandwidth of 1.2nm, providing 175dB suppression of EDFA induced pump sideband noise. The filtered quasi–TE pump, adjusted using a fiber polarization controller, is coupled into an ultra–silicon–rich nitride waveguide using a lensed fiber. A SiO2 cladded waveguide with a width of 550nm and height of 300nm possesses a high nonlinear parameter of 530W^-1/m with anomalous dispersion necessary for spontaneous four-wave mixing. The waveguide output is coupled into a lensed fiber and 7 cascaded WDMs are used to provide 245dB of residual pump filtration. The pump–suppressed output is spectrally separated into signal/idler part using WDMs. We refer to lower (higher) frequency photon as the signal (idler). The spontaneously generated signal and idler photons are filtered using cascaded tunable band pass filters (OTF) centered at 1571.24nm and cascaded WDMs centered at 1540.56nm, respectively. The bandwidth of the tunable OTF and WDM is 0.5nm and 1.2nm, therefore the correlated signal/idler photons are observed within the bandwidth window of 0.5nm induced by the OTF. The signal and idler photons are measured using InGaAs/InP avalanche photodetectors. The time correlation between signal and idler photons is obtained using a time interval analyzer with a detection efficiency of 20% and dead time of 15μs.The time bin is set to 81ps and the photon collection time is 240s. The coincidence peak is located ~11ns in the time–bin histogram due to the optical-path difference between the tunable OTF and WDM at respective signal and idler sides. The experimental raw coincidence counts (Hz), calculated by subtracting the accidental rate from the coincidence peak, show a quadratic increase with respect to coupled pump power. At the maximum coupled power of 5mW, the raw coincidence count is ~1Hz. We achieve a raw coincidence–to–accidental ratio (CAR) of up to 3. Therefore, we succeeded to observe correlated photon pair generation based on spontaneous four–wave mixing using the ultra–silicon–rich-nitride waveguide as a CMOS compatible platform, for future applications in quantum technologies.

Four–wave mixing (FWM) serves as the physical basis for various nonlinear phenomena including wavelength conversion, parametric amplification, and frequency combs. FWM on a chip has been implemented using CMOS platforms, chalcogenide glasses and III–V materials. On-chip, waveguide based stimulated FWM techniques have been mostly demonstrated using a coherent pump and coherent signal to focus on broadband spectral tuning for operation in high–speed and multi–channel wavelength division multiplexing network. Though FWM using incoherent light has the potential to provide large optical conversion efficiency, such demonstrations remain largely confined to fiber–experiments and involved narrow–band signals/idlers. Furthermore, the FWM based on a pulsed laser and a broadband incoherent source has yet to be implemented. In this work, we demonstrate integrated ultra–silicon–rich nitride parametric converters that perform wavelength conversion of a broadband incoherent source with a bandwidth of ~100nm at the -20dB level. A 500fs pulsed pump is combined with an incoherent superluminescent diode (SLD) as the signal and parametric gains between 12dB – 27dB is demonstrated as well as cascaded FWM. A 500fs pulsed laser centered at 1.555μm and an incoherent SLD with a 20dB bandwidth spanning from 1.6 – 1.7μm are used as the pump and signal respectively. The pump and signal are combined with a wavelength division multiplexer and coupled into an ultra–silicon–rich nitride waveguide with 10mm length, 700nm width and 400nm height. The waveguide is designed to have a larger nonlinear parameter of 330W^-1/m while possessing anomalous dispersion of -0.92ps^2/m, necessary for phase matched parametric conversion. At a coupled peak power of 4.6W, an idler spanning from 1.43 – 1.52μm at the -20dB level is generated. At a maximum input signal power of 0.71mW, a second idler appears at the blue side of the first generated idler because of cascaded FWM induced between pump of 1.555μm and the first idler peak of 1.48μm. At a coupled peak power of 2.8W, an idler spanning from 1.46 to 1.52μm is generated. The experimental idler bandwidth agrees well with the calculation based on degenerate FWM phase–matching condition. The broadened idler powers are calculated by integrating the energy of each signal and idler with respect to wavelength to obtain optical conversion efficiencies. The integrated idler power is 3.4dBm and 13.4dBm, corresponding to idler parametric gain of 12dB and 18dB respectively at a coupled peak power of 2.8 and 4.6W, respectively. The application of the SLD signal to a supercontinuum that is generated at a coupled peak power of 26W spectrally spanning 1.1 – 1.7μm is observed to generate an idler power of 14dBm within the wavelength range of 1.18 – 1.42μm as well as an idler conversion efficiency/gain of 27dB. Therefore, we achieved broadband wavelength conversion based on stimulated FWM using a pulsed pump and broadband incoherent signal that facilitate the spectrum spanning from 100nm, sufficient to cover parts of the E– and S–bands an representing large conversion efficiency and parametric gains of 12dB – 27dB.

Optical parametric amplifiers rely on the high Kerr nonlinearities and low two-photon absorption (TPA) to achieve large optical amplification. The high Kerr nonlinearity enables efficient energy transfer from the optical pump to the signal. On the other hand, the TPA process competes with the amplification process, and thus should be eliminated. Through Miller’s rule and Kramers-Kronig relations, it is known that the material’s Kerr nonlinearity scales inversely proportional to the band-gap, while the TPA process occurs when the photon energy is larger than the band-gap energy and Urbach tails, thus presenting a trade-off scenario. Based on these requirements, we have designed a CMOScompatible, band-gap engineered nitride platform with ultra-rich silicon content. The silicon nitride material is compositionally engineered to have a band-gap energy of 2.1 eV, which is low enough to confer a high Kerr nonlinearity, but still well above the energy required for the TPA process to occur. The new material, which we called ultra-silicon-rich nitride (USRN), has a material composition of Si7N3, a high Kerr nonlinearity of 2.8x10-13 cm2/W, and a negligible TPA coefficient. In optical amplification experiments, 500 fs pulses at 14 W peak power and centered around 1560 nm are combined with continuous wave signals. The maximum parametric gain of the signal could reach 42.5 dB, which is one of the largest gains demonstrated on CMOS platforms to date. Moreover, cascaded four-wave mixing down to the third idler, which was usually observed for mid-infrared silicon waveguides, is unprecedentedly observed at this spectrum.

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–Perot (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.

CMOS-compatible nonlinear optics platforms with negligible nonlinear losses and high nonlinearity are of great merit. Silicon, silicon nitride and Hydex glass have made significant headway in nonlinear optical signal processing, though none of these platforms possesses the highly sought after combination of high nonlinearity and negligible nonlinear losses. In this manuscript, we present a nonlinear optics platform based on silicon-rich nitride, deposited at a low temperature of 250°C compatible with back-end CMOS processing. The silicon-rich nitride is designed and engineered in composition to have a bandgap of 2.05 eV, such that the two-photon absorption edge is well below 1.55 μm. The designed and developed waveguides have a nonlinear parameter of 550 W−1/m, 500 times larger than that in silicon nitride waveguides, while at the same time not possessing two-photon and free-carrier losses. Using 500-fs pulses, we generate supercontinuum exceeding 0.6 of an octave.

Continuous wave four-wave mixing (FWM) in ultra-silicon-rich nitride photonic crystal waveguides (PhCWs) is demonstrated using low coupled pump powers. A conversion efficiency of −37 dB was observed using a 776 um long PhCW.

We demonstrate Bragg soliton dynamics on CMOS-compatible platform for the first time. We provide complete time-resolved measurements of record high-order soliton compression and show third-order dispersion induced fission in an ultra-silicon-rich nitride cladding-modulted Bragg grating.

Nonlinear optics leveraging CMOS-compatible, ultra-silicon-rich nitride devices is presented. Films are engineered to possess high Kerr nonlinearity and negligible two-photon absorption at telecommunications wavelengths. We demonstrate high-gain optical parametric amplifiers, wavelength conversion, supercontinuum sources and slow light enhanced devices.

Electrically pumped heterogeneously integrated III-V/SiO2 semiconductor on-chip lasers with different types of etched facet reflectors are designed and fabricated and their lasing performances are characterized and compared. The III-V quantum-well-based epitaxial layers are bonded on silica-on-silicon substrates and fabricated to form Fabry-Perot lasers with dry-etched rear facets. Three types of reflectors are demonstrated, which are etched facets terminated by air, benzocyclobutene, and metal with a thin layer of SiO2 insulator in-between. The laser devices are characterized and compared, including lasing threshold, external quantum efficiency, and output power, and show the impact of different types of etched facet reflectors on lasing performance.

Ring resonators on silicon rich nitride for potential use as rare-earth doped amplifiers pumped at 1310 nm with amplification at telecommunications-band are designed and characterized. The ring resonators are fabricated on 300 nm and 400 nm silicon rich nitride films and characterized at both 1310 nm and 1550 nm. We demonstrate ring resonators exhibiting similar quality factors exceeding 10,000 simultaneously at 1310 nm and 1550 nm. A Dysprosium-Erbium material system exhibiting photoluminescence at 1510 nm when pumped at 1310 nm is experimentally demonstrated. When used together with Dy-Er co-doped particles, these resonators with similar quality factors at 1310 nm and 1550 nm may be used for O-band pumped amplifiers for the telecommunications-band.

We experimentally demonstrate a CMOS compatible optical parametric amplifier based on Si 7 N 3 waveguides which are compositionally tailored that the 1550nm wavelength resides within the multi-photon regime, while possessing large nonlinear parameter of 550 W−1/m, 500 times larger than that in Si 3 N 4 .

We study ultrafast spectral characteristics of our ultra-short ultra-slicon rich nitride (USRN) waveguide with large Kerr nonlinearity (γ∼550W−1/m) and negligible nonlinear loss. The output spectra of USRN ring resonator and short-length waveguide broaden around 2 times and 4 times wider than that in 500 fs input pulses, respectively. Negligible nonlinear loss including two-photon absorption at near-infrared wavelength rages is proven by the linear increase in both the output bandwidth and power versus input peak power up to 100 W. The bandwidth broadens by 200 nm per millimeter of USRN waveguide implying that our ultra-short USRN waveguide acquires higher spectra-broaden efficiency compared other CMOS-platforms operating at telecommunication bands.

An 8-channel coarse wavelength division multiplexer (CWDM) based on coupled vertical gratings has been designed, fabricated and characterized. The devices are implemented on the ultra-silicon-rich nitride (USRN) platform. The demonstrated device possesses 8 CWDM channels. The absence of free spectral range (FSR) enabled the overall multiplexed bandwidth to span across the S + C + L bands. The CWDM channels meet the specifications stipulated by the International Telecommunications Union G.694.2 standard. The average channel crosstalk is -25dB. Pseudo-Random Bit Sequence 231-1 Non-Return-Zero data at 30Gb/s was launched into the device and a clear eye diagram was obtained. The device was further used with a USRN waveguide generating supercontinuum to create a multi-wavelength source emitting light at 8 CWDM wavelengths.

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.

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 Si[subscript 7]N[subscript 3], that possesses a high Kerr nonlinearity (2.8 × 10[superscript −13] cm[superscript 2] W[superscript −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., Singapore Ministry of Education. Academic Research Fund (AcRF) Tier 2 grant, Singapore. Agency for Science, Technology and Research (PSF grant), SUTD-MIT International Design Centre (IDC), Temasek Laboratories, National Research Foundation of Singapore (Medium Sized Centre Program)

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 SiN x /SiO 2 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 SiH 4 /N 2 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.

CMOS-compatible nonlinear optics platforms with high Kerr nonlinearity facilitate the generation of broadband spectra based on self-phase modulation. Our ultra – silicon rich nitride (USRN) platform is designed to have a large nonlinear refractive index and low nonlinear losses at 1.55 μm for the facilitation of wideband spectral broadening. We investigate the ultrafast spectral characteristics of USRN waveguides with 1-mm-length, which have high nonlinear parameters (γ ∼ 550 W−1/m) and anomalous dispersion at 1.55 μm wavelength of input light. USRN add-drop ring resonators broaden output spectra by a factor of 2 compared with the bandwidth of input fs laser with the highest quality factors of 11000 and 15000. Two – fold self phase modulation induced spectral broadening is observed using waveguides only 430 μm in length, whereas a quadrupling of the output bandwidth is observed with USRN waveguides with a 1-mm-length. A broadening factor of around 3 per 1 mm length is achieved in the USRN waveguides, a value which is comparatively larger than many other CMOS-compatible platforms.

Low temperature (200◦C) direct bonding of InP and Si3N4 coated silicon wafers using oxygen plasma surface treatment has been demonstrated, which transfers InP-based thin films onto Si substrates for heterogeneous photonic integration. Pulling test shows a high bonding energy comparable to the InP fracture energy. The high crystalline quality of the bonded thin film is preserved, as evident from photoluminescence and high resolution X-ray diffraction measurements. Cross-sectional transmission electron microscopy shows an intimately bonded interface with no observable defects generated near the bonded interface. A thin layer of amorphous oxide about 6 nm thick has been detected at the bonded interface. The hydrophilic interface obtained by oxygen plasma activation helps to achieve high quality bonding. Due to the high thermal conductivity of Si3N4, these high quality bonded structures of InP/Si with Si3N4 sandwiched in-between have potential applications in enhancing performance of high power Si photonic integrated devices. © 2012 The Electrochemical Society. [DOI: 10.1149/2.051205jes] All rights reserved.

A simple, one step technique for depositing ultrasmooth gold films using pulsed laser deposition is demonstrated by optimizing process para­meters. The smoothest film having a root-mean-square roughness of 0.17 nm (including the substrate roughness of 0.11 nm) for a 35 nm thick film on a silicon substrate are obtained by introducing a nitrogen flow in the chamber during deposition. We postulate that the reduction in surface roughness caused by nitrogen gas pressure in the chamber is due to the force of the gas flow acting against the flow of the plasma plume containing Au atoms. The gas acts as a filter that reduces the kinetic energy of the gold adatoms. This is the best result reported so far for a single step deposition of gold. It is a step towards low-loss planar gold films for surface plasmon applications.

The generation of broadband light within the telecommunication band has been instrumental to the design and characterization of advanced optical devices and systems. In this paper, stimulated degenerate four-wave mixing of an ultra-silicon rich nitride waveguide is investigated using a pulsed pump at 1.555 μm and incoherent broadband sources emitting in the 1.65 μm wavelength region as a signal. The waveguide possesses a large nonlinear parameter of 330 W−1/m as well as anomalous dispersion, required for phase matched parametric processes. The broadband idler ranging from 1.43 μm to 1.52 μm is generated using a coupled peak power of 4.6 W, spanning ∼100 nm at the −20 dB level, which is sufficient to cover parts of the E- and S-bands. The spectral span of the generated idler also agrees well with the calculation based on the phase-matching condition governing degenerate four-wave mixing. Cascaded incoherent four-wave mixing is also observed. Using a supercontinuum pump spanning from 1.1 to 1.7 μm with a co...

CMOS platforms with a high nonlinear figure of merit are highly sought after for high photonic quantum efficiencies, enabling functionalities not possible from purely linear effects and ease of integration with CMOS electronics. Silicon-based platforms have been prolific amongst the suite of advanced nonlinear optical signal processes demonstrated to date. These include crystalline silicon, amorphous silicon, Hydex glass, and stoichiometric silicon nitride. Residing between stoichiometric silicon nitride and amorphous silicon in composition, silicon-rich nitride films of various formulations have emerged recently as promising nonlinear platforms for high nonlinear figure of merit nonlinear optics. Silicon-rich nitride films are compositionally engineered to create bandgaps that are sufficiently large to eliminate two-photon absorption at telecommunications wavelengths while enabling much larger nonlinear waveguide parameters (5x–500x) than those in stoichiometric silicon nitride. This paper reviews recent developments in the field of nonlinear optics using silicon-rich nitride platforms, as well as the outlook and future opportunities in this burgeoning field.

Patterned gallium nitride nanowires and nanodots have been grown on n-Si (100) substrates by pulsed laser deposition. The nanostructures are patterned using a physical mask, resulting in regions of nanowire growth of different densities. The field emission (FE) characteristics of the patterned gallium nitride nanowires show a turn-on field of 9.06 V/μm to achieve a current density of 0.01 mA/cm2 and an enhanced field emission current density as high as 0.156 mA/cm2 at an applied field of 11 V/μm. Comparing the peak FE current densities of both the nanowires and nanodots, the peak FE current density of nanowires is around 700 times higher than that of the peak FE current density of nanodots since nanodots have a lower aspect ratio compared to nanowires. The field emission results indicate that, besides density difference, crystalline quality as well as the low electron affinity of gallium nitride, high aspect ratio of gallium nitride nanostructures will greatly enhance their field emission properties.

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.

This paper presents the overview of heterogeneous III-V/Si photonic integration configuration as a platform technology. The efficient adiabatic optical coupling between the active III-V/Si ridge waveguide and thin silicon-on-insulator (SOI) passive nanophotonic waveguide section is addressed.

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.

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–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.

Optically-pumped microsquare cavity laser on InP-based multiple-quantum-wells (MQW) material platform is demonstrated. Continuous wave operation is achieved for microsquare cavity with footprint as small as 4×4μm 2 . Numerical mode analysis and experimental characterization of the microsquare laser are conducted, and the results are compared with the commonly used microdisk cavity laser fabricated on the same platform. The microsquare laser shows a lower lasing threshold and infers a higher differential efficiency than the microdisk counterpart. The microsquare cavity laser has sufficiently high quality factor, and higher pumping injection efficiency due to the more evenly distributed field profile as compared to that of the microdisk. Experimental result also shows that the microsquare laser has better temperature stability than the microdisk. These results promise a potential alternative laser structure for onchip light source applications.

GaN nanowires were grown on gold-coated sapphire substrates by pulsed laser ablation of a target of GaN powder in low-pressure nitrogen gas. The laser ablation induced Ga and N plasma directly towards the substrate to initialize the vapor–liquid–solid (VLS) growth mechanism. The morphological and structural properties of the GaN nanowires were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nanowires formed crystalline and have lengths from 300 to 500 nm with diameters of around 50 nm. The tips of the nanowires were observed to be more conducting which further confirmed the VLS growth mechanism. In addition, the electrical properties of these nanowires were also examined.

Supercontinuum generation over 0.6 of an octave is demonstrated at 1.55µm on silicon-rich nitride waveguides. The SRN films are engineered to have a band gap of 1.85eV, and do not suffer from two-photon absorption at 1.55µm. The SRN waveguides have a large nonlinear parameter of 550W-1/m, 500 times larger than that in silicon nitride waveguides.

We demonstrate low power four wave mixing using silicon rich nitride waveguides, engineered in bandgap to eliminate two photon absorption at 1.55µm, while preserving a high nonlinear parameter of 550 W−1/m. Broadband conversion over 170nm is demonstrated using a low pump power of 4.7 dBm.

Two InP-based III–V semiconductor etching recipes are presented for fabrication of on-chip laser photonic devices. Using inductively coupled plasma system with a methane free gas chemistry of chlorine and nitrogen at a high substrate temperature of 250 °C, high aspect ratio, anisotropic InP-based nano-structures are etched. Scanning electron microscopy images show vertical sidewall profile of 90° ± 3°, with aspect ratio as high as 10. Atomic Force microscopy measures a smooth sidewall roughness root-mean-square of 2.60 nm over a 3 × 3 μm scan area. The smallest feature size etched in this work is a nano-ring with inner diameter of 240 nm. The etching recipe and critical factors such as chamber pressure and the carrier plate effect are discussed. The second recipe is of low temperature (−10 °C) using Cl2 and BCl3 chemistry. This recipe is useful for etching large areas of III–V to reveal the underlying substrate. The availability of these two recipes has created a flexible III–V etching platform for fabrication of on-chip laser photonic devices. As an application example, anisotropic InP-based waveguides of 3 μm width are fabricated using the Cl2 and N2 etch recipe and waveguide loss of 4.5 dB mm−1 is obtained.

We present the design, fabrication, and characterization of photonic crystal waveguides (PhCWs) on an ultra-silicon-rich nitride (USRN) platform, with the goal of augmenting the optical nonlinearities. The design goals are to achieve an optimized group index curve on the PhCW band edge with a non-membrane PhCW with symmetric SiO2 undercladding and overcladding, so as to maintain back-end CMOS compatibility and better structural robustness. Linear optical characterization, as well as nonlinear optical characterization of PhCWs on ultra-silicon-rich nitride is performed at the telecommunication wavelengths. USRN's negligible two-photon absorption and free carrier losses at the telecommunication wavelengths ensure that there is no scaling of two-photon related losses with the group index, thus maintaining a high nonlinear efficiency. Self-phase modulation experiments are performed using a 96.6 μm PhCW. A 1.5π phase shift is achieved with an input peak power of 2.5 W implying an effective nonlinear parameter ...

We report on gallium nitride (GaN) nanowires grown using pulsed laser ablation, adopting the vapor–liquid–solid (VLS) growth mechanism. The GaN nanowires are obtained based on the principle that a catalyst is required to initiate the nanowires growth. Locations of the GaN nanowires are patterned using femtosecond laser and focused ion beam. Scanning electron microscopy (SEM) is used to characterize the nanowires. This patterning of GaN nanowires will enable selective growth of nanowires and bottom-up assembly of integrated electronic and photonic devices.

Silicon nanophotonic platform based on a silicon-on-insulator substrate enables dense photonic integration due to transparency for light propagation and ultra-high refractive index contrast for light confinement. Here, we integrate silicon together with III-V for high-efficiency heterogeneous Silicon/III-V and short vertical optical interconnect access. The fabrication involves 3 critical processes: 1) obtaining more than 80% maximum bonded areas of Si with III-V, 2) precise alignment of III-V nano-devices on top of the passive devices and 3) vertical sidewall etch profile of Si and III-V devices. The measurement results show around 90% coupling efficiency. The realization of this heterogeneous Si/III-V integration platform will open up enormous opportunities for photonic system on silicon through integrating various devices.

This paper will review the top down technique of ICP etching for the formation of nanometer scale structures. The increased difficulties of nanoscale etching will be described. However it will be shown and discussed that inductively coupled plasma (ICP) technology is well able to cope with the higher end of the nanoscale: features from 100nm down to about 40nm are relatively easy with current ICP technology. It is the ability of ICP to operate at low pressure yet with high plasma density and low (controllable) DC bias that helps greatly compared to simple reactive ion etching (RIE) and, though continual feature size reduction is increasingly challenging, improvements to ICP technology as well as improvements in masking are enabling sub-10nm features to be reached. Nanoscale ICP etching results will be illustrated in a range of materials and technologies. Techniques to facilitate etching (such as the use of cryogenic temperatures) and techniques to improve the mask performance will be described and illustrated.

We design and demonstrate optically pumped microlasers with a hetero-core cavity formed by III-V and silicon-on-insulator (SOI) materials. Hetero-core cavities with identical lateral dimension are fabricated. The cavity is formed by III-V layer with thickness of 210 nm on top of SOI layer with thickness of 300 nm via SiOsub2/subinterlayer wafer bonding. Continuous wave laser operation is achieved for a diameter down to 2 μm with a corresponding mode volume of 0.07λsup3/supand quality factor of 1.3×10sup4/sup. The architecture renders an alternative laser structure for heterogeneous laser-on-chip, with no dedicated vertical coupling mechanism needed between the two materials' layers.

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.

Nanophotonic chip coupling using an optical thin-film stack forming a micro graded-refractive-index (GRIN) lens with a super-high numerical aperture (NA) that is highly compact (tens of micron long) and can be directly integrated is presented. We explore the lens' integration on the surface of Silicon-On-Insulator (SOI) platform with an asymmetric GRIN profile. We show that to achieve high efficiency for optical coupling between an optical fiber and a nanophotonic waveguide with a sub-wavelength (lambda/n) beam size, conventional asymmetric parabolic GRIN profile is no longer adequate due to the super-high NA needed (3.1), which results in severe spatial beam aberration at the focal plane. We present an efficient algorithm to computationally generate the ideal GRIN profile that is completely aberration free even at super-high NA, which improves the coupling efficiency from ~66% (parabolic case) to ~95%. A design example involving an optical thin-film stack using an improved dual-material approach is given. The performance of the thin-film stack is analyzed. This thin-film stack based GRIN lens is shown to be high in coupling efficiency, wavelength insensitive and compatible with standard thin-film process.

Mode simulations for surface plasmonic nano-waveguides are presented for applications in developing nanometer sized laser cavities. The structure considered is a semiconductor quantum well sandwiched between metal layers. The simulations show that the plasmonic waveguide follow the dispersion relations of a conventional dielectric waveguide. An estimate for the gain requirement on the quantum well structure is also provided.

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.