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We demonstrate a complementary metal–oxide–semiconductor (CMOS)-compatible optical parametric Bragg amplifier on an ultra-silicon-rich nitride chip. The amplifier design incorporates advantageous group index properties in a nonlinear Bragg grating to circumvent phase matching limitations arising from the bulk material and waveguide dispersion. The grating structure further augments the effective nonlinear parameter of 800 W−1/m, considerably lowering the power required for the observation of strong parametric gain. On/off optical parametric gain of 20 dB is achieved using a low peak power of 1.6 W, in good agreement with numerical calculations. This represents a 7 dB improvement in the parametric gain compared to the absence of grating enhancement which is attributed to the Bragg grating induced superior phase matching.

CMOS compatibility and 8-inch manufacturability have been highly desired in MEMS technology. In this article, we demonstrate a MEMS pyroelectric IR detector using CMOS compatible AlN and 8-inch semiconductor wafer technology. This AlN pyroelectric detector detects IR over wavelength ranging from 5 $\mu \text{m}$ to 14 $\mu \text{m}$ . In addition, this detector is designed to have added mechanical stiffness for improved device integrity. The detectors are fabricated with different sensing area dimensions to compare their performance. The best performing detector has an NEP $\sim \,\,8.87\times 10^{\text {-9}}\,\,\text {W/}\sqrt {\text {Hz}} $ and ${D} ^\ast \,\,\sim \,\,6.04\times 10^{{6}}\,\,{\text {cm}\sqrt {\text {Hz}}}/ \text {W}$ . These pyroelectric detectors are designed and built with the consideration to enable ease of monolithic integration with other components to form an integrated gas sensor system. This includes enabling detection of illumination from the front side and using an absorber stack that consists of CMOS dielectric layers. Subsequently, they will form a crucial part of the architectures for miniature photonics-based gas sensors. Their performance is a first step towards 8-inch wafer level CMOS-compatible manufacturable photonics gas sensors. [2020-0157]

We demonstrate slot waveguides on ultra-silicon-rich nitride designed for optimal high group index birefringence $( > 1)$ . High speed characterization using 30Gb/s non-return-to-zero and 56Gb/s pulsed amplitude modulation 4 data are performed on fabricated waveguides showing error-free performance.

The dispersive nonlinear refractive index of ultra-silicon-rich nitride, and its two-photon and three-photon absorption coefficients are measured in the wavelength range between 0.8 µm–1.6 µm, covering the O- to L – telecommunications bands. In the two-photon absorption range, the measured nonlinear coefficients are compared to theoretically calculated values with a simple parabolic band structure. Two-photon absorption is observed to exist only at wavelengths lower than 1.2 μm. The criterion for all-optical switching through the material is investigated and it is shown that ultra-silicon-rich nitride is a good material in the three-photon absorption region, which spans the entire O- to L- telecommunications bands.

CO 2 gas sensing responses are measured using our in-house fabricated CMOS-MEMS ScAlN-based pyroelectric detector with 12% Sc doped concentration. Leveraging on mid-IR absorption behavior of CO 2 gas caused by interaction of CO 2 with light at 4.26 µm wavelength, our ScAlN-based pyroelectric detector successfully detect CO 2 gas response ranging from CO 2 concentrations of 5000 ppm down to 200 ppm. Gas channel lengths are varied from 6 cm to 10 cm and their respective CO 2 responses are measured. Finally, with N2 as the reference gas, we calculate the gas response percentage change of CO 2 gas at different gas channel lengths and concentration.

Main complementary metal-oxide-semiconductor (CMOS)-compatible photonics platforms, i.e., silicon and silicon nitride, rely on Kerr nonlinearities for near-instantaneous modulation of optical signals. Kerr nonlinearities emerge due to the third-order susceptibility (χ(3)) and lead to several nonlinear optical processes, including the four-wave mixing (FWM). FWM is the underlying process of many applications, such as parametric amplification, optical sampling, all-optical wavelength conversion, and demultiplexing and therefore has an indispensable role in optical signal processing. The full potential of on-chip nonlinear processes can be efficiently unlocked by tuning the light-matter interactions at a greater extent via manipulating both material and structural properties of integrated photonic devices. We employ photonic crystal waveguides (PhCWgs) to engineer the structural properties of a waveguide by introducing two-dimensional periodicity in the plane of light propagation. In addition to structural engineering, the chosen material platform aims to bypass the limitations of existing CMOS-compatible platforms: the compositionally engineered ultra-silicon-rich nitride (USRN : Si7N3), eliminates two-photon absorption at 1.55 μm and possesses an order of magnitude higher Kerr nonlinearity compared to stoichiometric silicon nitride at telecommunication wavelengths. Here, we present four-wave mixing in a USRN-based, CMOS-compatible, PhCWg leading to on/off optical parametric signal gain reaching 3 dB, and a large instantaneous idler conversion efficiency of −1 dB experimentally. Enhancement of the Kerr nonlinearity in the presence of a sizable and near-constant group index allows us to demonstrate a large on/off gain per unit length of 333 dB/cm on an ultra-compact, 97 μm-long PhCWg.

We present the optical and electrical properties of AlN-based and 12% doped ScAlN-based pyroelectric detectors fabricated on 8-inch wafers respectively. Both AlN and ScAlN materials are deposited at a temperature of ~200oC, making them potential candidates for CMOS compatible MEMS pyroelectric detectors. FTIR spectroscopy is used to measure the absorption of these pyroelectric detectors over the wavelength range of ~2–14 μm and the results show absorption improvement up to ~75% for ScAlN-based pyroelectric detectors compared to that of AlN-based pyroelectric detectors at the wavelength of 4.26 μm where CO2 gas absorption of IR radiation is anticipated. Higher output current (~3-fold increase) is also observed from ScAlN-based pyroelectric detectors. Other than pyroelectric coefficient that contributes to improved performance for ScAlN-based pyroelectric detectors, we believe that absorptivity of the device also plays a major role in the performance of pyroelectric IR detectors. The results obtained from the study of the electrical and optical properties of AlN-based and ScAlN-based CMOS compatible MEMS pyroelectric detectors will bring forth potential applications of these detectors onto multi-functional integrable and monolithic platforms.

Optical pulses are fundamentally defined by their temporal and spectral properties. The ability to control pulse properties allows practitioners to efficiently leverage them for advanced metrology, high speed optical communications and attosecond science. Here, we report 11× temporal compression of 5.8 ps pulses to 0.55 ps using a low power of 13.3 W. The result is accompanied by a significant increase in the pulse peak power by 9.4×. These results represent the strongest temporal compression demonstrated to date on a complementary metal–oxide–semiconductor (CMOS) chip. In addition, we report the first demonstration of on-chip spectral compression, 3.0× spectral compression of 480 fs pulses, importantly while preserving the pulse energy. The strong compression achieved at low powers harnesses advanced on-chip device design, and the strong nonlinear properties of backend-CMOS compatible ultra-silicon-rich nitride, which possesses absence of two-photon absorption and 500× larger nonlinear parameter than in stoichiometric silicon nitride waveguides. The demonstrated work introduces an important new paradigm for spectro-temporal compression of optical pulses toward turn-key, on-chip integrated systems for all-optical pulse control.

Pyroelectric IR detector is fabricated using ScAlN with 12% doped Sc as the pyroelectric sensing material. Dielectric layers that act as absorber are added on top of the ScAlN to help in IR absorption. This ScAlN-based pyroelectric detector is characterized by illumination from a MEMS thermal emitter with a sinusoidal input waveform. D* is measured to be as high as 1.87 x 107 (cm√Hz)/W at a frequency of 13 Hz. The optical absorptance of this device at 4.26 μm CO 2 gas absorption wavelength is around 0.75, measured using FTIR. CO 2 gas sensing measurement detects electrical signal changes of ~50-100 μV.

CMOS-MEMS pyroelectric detectors based on 12%-doped ScAlN are fabricated using 8-inch MEMS wafer technology and characterized. The ScAlN pyroelectric material is deposited at a low temperature of ~200oC. The results show D* as high as 4.3 x 107 (cm√Hz)/W and NEP as low as 1.26 x 10-9 W/√Hz. This is the first demonstration of a functional CMOS-MEMS pyroelectric detector using ScAlN as the pyroelectric sensing material. Compared to AlN that usually presents D* in the range of 105-106, Sc-doped AlN brings on the promise of better performing CMOS-MEMS pyroelectric detectors that could be miniaturized, integrated with CMOS circuits and provide wider applications.

Bragg solitons are solitary waves which form as a result of the nonlinearity in the medium and the dispersion induced by a Bragg grating. We present recent results covering the dynamics of Bragg solitons. Temporal compression, fission and enhanced, coherent supercontinuum generation and tunable spectral broadening are experimentally demonstrated.

Nonlinear integrated optics leveraging platforms with high nonlinear figure of merit offer energy efficient optical signal processing capabilities. Over the last five years, CMOS-compatible ultra-silico-rich nitride (USRN) has emerged as a promising platform on which to implement various nonlinear optics functions. Bandgap engineered to maximize the Kerr nonlinearity while maintaining two-photon absorption free behavior at telecommunications wavelengths, USRN possesses a nonlinear refractive index that is 100× larger than that in stoichiometric silicon nitride. In this article, we review the recent progress made in USRN-based nonlinear integrated optics devices. The impacts it has made spanning from high gain optical parametric amplification and observations of soliton effects in photonic waveguides and photonic crystal waveguide structures will be discussed. Finally, we assess the future outlook of CMOS-compatible USRN-based nonlinear optics.

Strong temporal compression in an integrated ultra-silicon-rich nitride temporal compressor consisting of separate nonlinear and anomalously dispersive stages is demonstrated. 11× compression of 5.8ps pulses at a low input peak power of 13.3W and 9.4× increase in the pulse peak power is achieved.

With the emerging trend in miniaturization of complete optical sensor on a silicon platform for gas sensing applications, this paper presents a promising candidate towards monolithic gas sensor with features of 1) a CMOS compatible Aluminum Nitride (AlN)-based pyroelectric infrared detector (PID); 2) customized micropower high-precision CMOS integrated readout circuits. In the PID design, the sensitivity and device integrity are improved with optimized sensing area and modified layer structure. In the readout circuits, to amplify the pico-amperes current from detector, a tunable resistive transimpedance amplifier (TIA) with robust pseudo-resistor in series is proposed to achieve reduced variations against process-voltage-temperature (PVT). A micropower incremental analog-to-digital converter (ADC) is designed to digitize the voltage output from TIA. In addition, to compensate the drifts induced by local temperature change around the detector, an accurate BJT-based temperature sensor is integrated in the circuits as well. Fabricated in an 8-inch wafer, the AlN-based PID with sensing area of 0.29 mm2 achieves the detectivity of 6.04× 106 cm√ Hz/W. The readout circuits are implemented in a 40nm-CMOS process, consuming total power of 24.5 μW under 1.2-V supply. Simulation results show that the TIA gain variation is 11-bit resolution over 1 kHz bandwidth, and the temperature error over -20 °C − 80 °C is ±0.65 °C (3σ) without any calibration.

Integrated photonic nanostructures provide powerful degrees of design freedom for the engineering of light confinement and advanced lightwave manipulation functions. The ability to tailor field profiles in these on-chip devices allows enhanced light-matter interaction, strong modal confinement and the ability to engineer dispersion. Here, we present recent developments in photonic integrated circuits towards the generation of solitons, amplification, and optical waveform manipulation. By harnessing CMOS platforms with a high nonlinear figure of merit, the existence of on-chip Bragg solitons, Bragg soliton fission and solitons in photonic waveguides are experimentally observed. These demonstrations are made possible by 1,000X larger dispersion close to the band edge in on-chip Bragg gratings, an effect that arises from the interaction of forward and backward propagating fields. In addition, efficient parametric processes facilitate wavelength conversion of light and high gain amplification of signals. These efficient nonlinear mechanisms provide a possible pathway in which to realize new approaches to efficiently manipulate optical waveforms.

We demonstrate NDIR CO2 gas sensing using CMOS compatible MEMS ScAlN-based pyroelectric detectors. The ScAlN-based pyroelectric detectors are fabricated using 8-inch wafer level technology with 12 % Sc-doped AlN deposited at a temperature of ∼200 °C. Together with a blackbody thermal emitter, a 10 cm long enclosed gas channel with only inlet and outlet holes connected to tubings, and testing using 2 different reference gases (N2 and synthetic air), measurements show voltage signal drop due to CO2 gas absorption at the 4.26 μm wavelength at CO2 gas concentrations ranging from 5000 ppm down to 25 ppm. The signal change due to the CO2 gas response ranges from ∼2% at 100 ppm CO2 concentration to ∼40 % at 5000 ppm CO2 gas concentration for both CO2 gas measured in N2 and in synthetic air. CO2 gas response times are also measured for CO2 gas in N2 and in synthetic air at concentrations of 5000 ppm, 1000 ppm and 400 ppm. The gas response times measured around 2 s and lower. Introduction of humidity show some minor effect (

Parametric wavelength conversion of 30Gbps Non-Return-Zero data using degenerate four wave mixing was performed in ultra-silicon-rich nitride waveguides. A power penalty of 1.2dB was achieved at a bit error rate of 10-4.

Nonlinear CMOS Photonics allows for seamless integration with CMOS electronics and ease of manufacturability. We discus developments in USRN-based nonlinear optics. We demonstrate 8.7 soliton-effect compression in USRN waveguides, on-chip Bragg-soliton compression and fission.

Temperature tuning of spectral broadening induced by a nonlinear grating is experimentally demonstrated. The bandwidth is observed to decrease as temperature increases, corresponding to a red-shift in the high dispersion region of the Bragg grating.

Infrared gas sensors have been proven promising for broad applications in Internet of Things and Industrial Internet of Things. However, the lack of miniaturized light sources with good compatibility and tunable spectral features hinders their widespread utilization. Herein, a strategy is proposed to increase the radiated power from microelectromechanical-based thermal emitters by coating with graphene oxide (GO). The radiation can be substantially enhanced, which partially stems from the high emissivity of GO coating demonstrated by spectroscopic methods. Moreover, the sp2 structure within GO may induce plasmons and thus couple with photons to produce blackbody radiation and/or new thermal emission sources. As a proof-of-concept demonstration, the GO-coated emitter is integrated into a multifunctional monitoring platform and evaluated for gas detection. The platform exhibits sensitive and highly selective detection toward CO2 at room temperature with a detection limit of 50 ppm and short response/recovery time, outperforming the state-of-the-art gas sensors. This study demonstrates the emission tailorability of thermal emitters and the feasibility of improving the associated gas sensing property, offering perspectives for designing and fabricating high-end optical sensors with cost-effectiveness and superior performance. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

An on-chip Coarse wavelength Division Multiplexing (CWDM) has been designed, fabricated and experimentally measured, yielding 9 multiplexed wavelength channels spanning S+C+L band. The average channel crosstalk is −25 dB. All channels cover the CWDM central wavelengths stipulated by ITU standard.

The appeal of on-chip broadband supercontinuum generation (SCG) comes from its potential to pave the way to full integration of various ultrafast optics applications in frequency metrology, wavelength division multiplexing, and sensing. However, the generation of octave-spanning supercontinuum requires either the use of exceedingly short femtosecond pulses or large footprints. One promising method to achieve broadband supercontinuum is to exploit the high-order soliton fission. Bragg solitons leverage the large anomalous dispersion at the photonic band edge of nonlinear Bragg gratings, therefore they can facilitate high-order soliton fission in much shorter waveguide lengths and significantly lower powers. Soliton dynamics, especially fission, on CMOS-compatible platforms have been limited due to the nonlinear losses such as two-photon absorption and free carrier effects in silicon or low optical nonlinearities in traditional silicon nitride. We use compositionally engineered ultra-silicon-rich nitride (USRN) that possesses a large Kerr nonlinearity in the absence of two-photon absorption. Utilizing ideal nonlinear properties of USRN platform in conjunction with our monolithically integrated cascaded grating-waveguide design, we experimentally demonstrate × 4 spectral broadening enhancement, from 79 nm in the 7 mm long reference waveguide to 311 nm at the cascaded Bragg grating and waveguide device of the same footprint, using input pulses of 1.68 ps FWHM. This result is promising for generating wide supercontinuum, without the need to use sub-picosecond pulses or increasing the device footprint, by exploiting the high-order soliton dynamics availed through the simple photonic chip design consisting of a nonlinear Bragg grating and nonlinear waveguide.

Supercontinuum generation (SCG) through soliton fission provides high‐brightness, spectrally‐rich light needed for hyperspectral imaging, broadband spectroscopy, and fluorescence microscopy. The prospect of miniaturization has led to many demonstrations of this phenomenon in integrated platforms. However, due to the moderate dispersion and nonlinearity generally available in channel waveguides, femtosecond pulses have typically been required to date, as the use of picosecond pulses would require unpractically long devices to achieve soliton fission. Here, spectral bandwidth enhancement of the supercontinuum process through Bragg grating induced soliton‐effect compression and soliton fission is demonstrated. This approach uses picosecond pulses on a complementary metal oxide semiconductor (CMOS)‐compatible, millimeter‐scale platform, consisting of a monolithically integrated cladding‐modulated Bragg grating with a channel waveguide. The strong dispersion near the stopband of the grating enables compression and fission of picosecond higher‐order solitons, which enhances the spectral broadening in the channel waveguide. A 4.3 spectral bandwidth enhancement is reported, with respect to a reference waveguide of the same length. The output spectra are further studied both through simulations and experiments and determined to possess high spectral coherence. These results highlight a simple route to significantly augment the bandwidth of nonlinear processes such as SCG while maintaining low power and compact footprint.

Heterogeneously integrated heterocore microcavity III–V semiconductor lasers on silicon-on-insulator (SOI) are fabricated and demonstrated in this paper. The heterocore microcavity is realized via ultrathin silicon dioxide interlayer bonding of III–V on SOI and dual hard mask technique. The dual hard mask technique utilizes flowable oxide and silicon nitride as etch masks for III–V and SOI etchings, respectively, and hence, a single lithography is required in the fabrication. Compact optical-pumped heterocore microdisk lasers are demonstrated and their lasing performances are characterized.

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%.

In this paper, we fabricate and demonstrate a functional complementary metal-oxide-semiconductor (CMOS) compatible pyroelectric uncooled thermal detector using 12% doped Scandium Aluminum Nitride (ScAlN) as the sensing layer. The ScAlN pyroelectric material is deposited at a temperature of ∼200 °C over an 8-in. wafer area. This detector has shown, in general, improved performance compared to AlN, with specific detectivity as high as ∼ 6.08 × 10 7 cm Hz / W and noise equivalent power as low as ∼ 8.85 × 10 − 10 W / Hz. The results show the specific detectivity of ScAlN-based pyroelectric detectors in the range of 107 cm Hz / W, which is an improvement compared to AlN-based pyroelectric detectors which report specific detectivity typically in the range of 105–106 cm Hz / W. This promising result opens up the opportunities for a CMOS compatible, 8-in. wafer-level manufacturable lead-free pyroelectric detector toward low cost and high throughput, allowing microelectromechanical systems (MEMS) and CMOS integration for increased applications in CMOS–MEMS integrated devices utilizing pyroelectric detectors.

Emerging compositionally engineered complementary metal-oxide-semiconductor (CMOS)-compatible platforms have been employed for high efficiencies in various on-chip applications, including optical parametric amplification and wavelength conversion. Combining the novel nonlinear optics platforms such as ultra-silicon-rich nitride (USRN: Si7N3) with periodic waveguide structures can lead to further enhancement of material nonlinearities via the slow light effect and enable ultra-compact devices. Four-wave mixing in a USRN-based, CMOS-compatible, photonic crystal waveguide (PhCWg) leading to on/off optical parametric signal gain reaching 3 dB, and a large instantaneous idler conversion efficiency of −1 dB is explored experimentally. Enhancement of Kerr nonlinearity in the presence of a sizable and near-constant group index allows the findings on an ultra-compact, 97 μm-long PhCWg, equivalent to a large on/off gain per unit length of 333 dB/cm.

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.

Plasmonic near-field transducer (NFT) facilitates optical power transfer into a nano-spot in the recording media for heat-assisted magnetic recording. Typically, impedance matching is a condition for maximum power transfer between a given source and load. Even for waveguide-NFT-media stack system, we verify that matching the impedances of waveguide and media-stack at NFT resonance maximizes power transfer. However, it is not a sufficient condition. Since, NFT guides the light into the media-stack as symmetric and asymmetric optical modes, higher conversion of dielectric mode into a mode that exhibits maximum coupling into the media is the second condition for maximizing the power transfer into the media. In this study, operating wavelength range, material refractive indices, and NFT geometrical parameters are considered in the design space for maximizing the efficiency of an exemplary taper-based NFT structure. We first estimate the maximum efficiency and compare with the benchmark efficiency of “ideal” version of the considered NFT to confirm that the obtained efficiency is maximum. At maximum efficiency point, we show that the impedance matching between waveguide and high-index media stack is enhanced and mode-conversion efficiency into asymmetric plasmon mode is also enhanced because of high-index contrast feeding waveguide and suitable operating wavelength range.

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 $\sim 11.5$ % 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 $\sim 90$ % in our numerical example. Therefore, the overall optimization shows that the efficiency of light-delivery system can reach $\sim 9$ %–10%.

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.

The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation to be attributed to the USRN waveguide’s large nonlinearity and negligible two-photon absorption at 1550 nm.The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation...

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.