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This paper describes the design, fabrication, and record performance of a new class of ultra-wideband wavelength tuning, ultra-low noise semiconductor laser, the Integrated Coherent Tunable Laser (ICTL). The ICTL device is designed for, and fabricated in, a CMOS foundry based Silicon Photonics platform, utilizing heterogeneous integration of III-V material to create the integrated gain section of the laser - enabling high-volume mass-market manufacturing at low cost and with high reliability. The ICTL incorporates three or more ultra-low loss micro-ring resonators, with large ring size, in a Sagnac loop reflector geometry, creating exceptional laser reflector performance, plus an extended laser cavity length that enables highly-coherent output; ultra-low linewidth and phase noise. This paper describes record integrated laser performance; 118 nm wavelength tuning, covering S-, C- and L-bands, with Lorentzian linewidth

Hypothesis Mixtures of colloids and supramolecular polymers may exhibit stimuli-responsive phase behaviour. However, in theoretical descriptions of such systems, the polymers are commonly described either as flexible chains or as rigid rods, while in experimental systems supramolecular polymers usually fall in between these two limits. We expect the flexibility of the polymers to have a profound effect on the stimuli-responsive phase behaviour. Theory We propose a general approach to predict the phase behaviour of colloidal hard spheres mixed with covalent or supramolecular polymers of arbitrary persistence length using free volume theory and an interpolation between flexible and rigid chains. Findings The binodals are predicted to shift to lower monomer concentrations as the persistence length is increased, making the polymers more efficient depletants. The persistence length is therefore an additional degree of freedom for manipulating the phase behaviour of colloid–polymer mixtures. We show that by manipulating the persistence length of temperature responsive supramolecular polymers, a wide range of phase diagrams with various topologies can be obtained. For example, we find phase diagrams with a critical point but no triple point or displaying two triple points for temperature-sensitive supramolecular polymers mixed with hard spheres.

Silicon nitride (SiN) waveguides with ultra-low optical loss enable integrated photonic applications including low noise, narrow linewidth lasers, chip-scale nonlinear photonics, and microwave photonics. Lasers are key components to SiN photonic integrated circuits (PICs), but are difficult to fully integrate with low-index SiN waveguides due to their large mismatch with the high-index III-V gain materials. The recent demonstration of multilayer heterogeneous integration provides a practical solution and enabled the first-generation of lasers fully integrated with SiN waveguides. However, a laser with high device yield and high output power at telecommunication wavelengths, where photonics applications are clustered, is still missing, hindered by large mode transition loss, non-optimized cavity design, and a complicated fabrication process. Here, we report high-performance lasers on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues. We also show Hertz-level fundamental linewidth lasers are achievable with the developed integration techniques. These lasers, together with high-Q SiN resonators, mark a milestone towards a fully integrated low-noise silicon nitride photonics platform. This laser should find potential applications in LIDAR, microwave photonics and coherent optical communications., Achieving high output power and low noise integrated lasers is a major challenge. Here the authors experimentally demonstrate integrated lasers from a Si/SiN heterogeneous platform that shows Hertz-level linewidth, paving the way toward fully integrating low-noise silicon nitride photonics in volume using real devices for lasing.

Silicon photonics enables wafer-scale integration of optical functionalities on chip. Silicon-based laser frequency combs can provide integrated sources of mutually coherent laser lines for terabit-per-second transceivers, parallel coherent light detection and ranging, or photonics-assisted signal processing. We report heterogeneously integrated laser soliton microcombs combining both indium phospide/silicon (InP/Si) semiconductor lasers and ultralow-loss silicon nitride (Si3N4) microresonators on a monolithic silicon substrate. Thousands of devices can be produced from a single wafer by using complementary metal-oxide-semiconductor-compatible techniques. With on-chip electrical control of the laser-microresonator relative optical phase, these devices can output single-soliton microcombs with a 100-gigahertz repetition rate. Furthermore, we observe laser frequency noise reduction due to self-injection locking of the InP/Si laser to the Si3N4 microresonator. Our approach provides a route for large-volume, low-cost manufacturing of narrow-linewidth, chip-based frequency combs for next-generation high-capacity transceivers, data centers, space and mobile platforms.

Atomic force microscopy is used to study the ordering dynamics of symmetric diblock copolymer films. The films order to form a lamellar structure which results in a frustration when the film thickness is incommensurate with the lamellae. By probing the morphology of incommensurate films in the early ordering stages, we discover an intermediate phase of lamellae arranged perpendicular to the film surface. This morphology is accompanied by a continuous growth in amplitude of the film surface topography with a characteristic wavelength, indicative of a spinodal process. Using self-consistent field theory, we show that the observation of perpendicular lamellae suggests an intermediate state with parallel lamellae at the substrate and perpendicular lamellae at the free surface. The calculations confirm that the intermediate state is unstable to thickness fluctuations, thereby driving the spinodal growth of surface structures.

Using recently derived analytical equations of state for hard rod dispersions, we predict the phase behavior of athermal rod-polymer mixtures with free volume theory. The rods are modeled as hard spherocylinders, while the nonadsorbing polymer chains are described as penetrable hard spheres. It is demonstrated that all of the different types of phase states that are stable for pure colloidal rod dispersions can coexist with any combination of these phases if polymers are added, depending on the concentrations, rod aspect ratio, and polymer-rod size ratio. This includes novel two-, three-, and four-phase coexistences and isostructural coexistences between dilute and concentrated phases of the same kind, even for the more ordered (liquid) crystal phases. This work provides insight into the conditions at which particular multiphase coexistences are expected for well-defined model colloidal rod-polymer mixtures. We provide a quantitative map detailing the various types of isostructural coexistences, which confirms an early qualitative hypothesis by Bolhuis et al. (J. Chem. Phys. 107, 1997 1551).

Mid-infrared light sources are attracting attention for use in spectroscopic sensing, thermal imaging, and infrared countermeasures. Integration of these sources on Si-based waveguides allows for more functional and complex photonic circuits to be integrated on a single chip. This paper focuses on the key aspects of this integrated platform. The operation of silicon-on-insulator waveguides beyond 4.0 μm wavelength with increasing waveguide core thickness is discussed, and the effects of various cladding materials on waveguide propagation loss is demonstrated. Low loss waveguides and Mach-Zehnder interferometers in Ge-on-Si waveguide platform are discussed and beam combiners in the form of arrayed waveguide gratings are demonstrated in both the platforms. Interband cascade lasers are integrated on silicon-on-insulator waveguides with direct bonding to realize Fabry-Perot lasers. Power scaling of integrated lasers is validated by integrating quantum cascade lasers with silicon-on-insulator beam combiners. Results for the first integrated Fabry-Perot quantum cascade lasers on Ge-on-Si waveguides are discussed, together with the potential use of these waveguides to provide a better heat sink for integrated mid-infrared light sources.

Mixtures of colloids and supramolecular polymers exhibit stimuli-responsive phase behavior. In previous work (Peters and Tuinier, Physica A510, 233 [2018]) the polymers were treated as fully flexible chains, while in experimental systems supramolecular polymers may have a certain degree of stiffness. Here we predict that for stiff rod-like supramolecular polymers phase separation can occur at much lower polymer concentrations than for flexible supramolecular polymers. Additionally, it is demonstrated that colloid–polymer interactions can significantly influence the equilibrium polymer size distribution, however this does not strongly affect the phase behavior of the mixture. At the low polymer concentrations at which the system already gets unstable, the effect of excluded volume interactions between polymers chains themselves is small. Finally, for an experimental system it is predicted that a variety of re-entrant phase transitions may be observed within a realistic temperature range as illustrated by a specific example.

A Correction to this paper has been published: https://doi.org/10.1038/s41467-021-22031-4

Silicon Photonics foundry based Integrated Coherent Tunable Laser (ICTL) devices display record performance; 118 nm wavelength tuning covering S-, C- and L-bands, Lorentzian linewidths below 100 Hz, and –155 dBc/Hz relative intensity noise.

Silicon Photonics foundry based Extended-Distributed Bragg Reflector (E-DBR) lasers for automotive FMCW LiDAR systems are described, demonstrating record Lorentzian linewidths

Visible-near infrared (VIS-NIR) spectral data are widely used for remotely estimating a number of crop health metrics. In general, these indices and models do not explicitly account for leaf surface characteristics, which themselves can be indicators of plant status or environmental responses. To explicitly include leaf surface characteristics, data are required linking optical properties to surface characteristics. We present the design and experimental validation of a goniospectropolarimeter (GoSPo) that combines the capabilities of a spectrometer, goniometer, and polarimeter. GoSPo was designed with the objective of studying the relationships between leaf surface characteristics and the resulting light reflectance, transmission, and polarization as functions of both direction and VIS-NIR spectra. Using six motors, a pneumatic system, two spectrometers, and a combination of lenses, polarizers, and mirrors, GoSPo can examine a leaf from a particular angle, approximate hemispherical transmittance and reflectance (with root-mean-square error values of 0.0189 and 0.0216 for reflectance and transmittance, respectively, compared to a spectrophotometer and integrating sphere), and obtain spectral polarization measurements without disrupting the sample between measurements. The data collected with GoSPo will aid in model development for remote sensing applications.

Aluminum gallium arsenide (AlGaAs) and related III-V semiconductors have excellent optoelectronic properties. They also possess strong material nonlinearity as well as high refractive indices. In view of these properties, AlGaAs is a promising candidate for integrated photonics, including both linear and nonlinear devices, passive and active devices, and associated applications. For integrated photonics low propagation loss is essential, particularly in nonlinear applications. However, achieving low-loss and high-confinement AlGaAs photonic integrated circuits poses a challenge. Here we show an effective reduction of surface-roughness-induced scattering loss in fully etched high-confinement AlGaAs-on-insulator nanowaveguides, by using a heterogeneous wafer-bonding approach and optimizing fabrication techniques. We demonstrate ultrahigh-quality AlGaAs microring resonators and realize quality factors up to 3.52E6 and finesses as high as 1.4E4. We also show ultra-efficient frequency comb generations in those resonators and achieve record-low threshold powers on the order of ~20 uW and ~120 uW for the resonators with 1 THz and 90 GHz free-spectral ranges, respectively. Our result paves the way for the implementation of AlGaAs as a novel integrated material platform specifically for nonlinear photonics, and opens a new window for chip-based efficiency-demanding practical applications., 19 pages

The Plateau–Rayleigh instability of a liquid column underlies a variety of fascinating phenomena that can be observed in everyday life. In contrast to the case of a free liquid cylinder, describing the evolution of a liquid layer on a solid fibre requires consideration of the solid–liquid interface. Here we revisit the Plateau–Rayleigh instability of a liquid coating a fibre by varying the hydrodynamic boundary condition at the fibre–liquid interface, from no slip to slip. Although the wavelength is not sensitive to the solid–liquid interface, we find that the growth rate of the undulations strongly depends on the hydrodynamic boundary condition. The experiments are in excellent agreement with a new thin-film theory incorporating slip, thus providing an original, quantitative and robust tool to measure slip lengths., A thin liquid coating on a fibre can break up into droplets due to the Plateau–Rayleigh instability, as for instance on a spider web. Here, Haefner et al. show that the growth rate of the droplet undulations strongly depends on the fibre–liquid boundary condition and slip accelerates the instability.

Spectral differences between aqueous solutions of NaCl and KCl have received minimal attention in previous research due to strong similarities between the two salts and the lack of motivation to differentiate between them. Correlations between salinity and absorbance have been developed previously with varying degrees of linearity but have not been tested to saturation. This work will demonstrate that correlating spectral measurements and the concentration of NaCl and KCl in water can be extended up to the saturation point of both salts and that solutions of these salts with unknown concentrations can be distinguished. Spectral data for samples of NaCl and KCl in single-salt solutions were collected up to saturation and correlations were developed for differentiating between solutions of the two species. These correlations were able to correctly identify the solution type for all solutions in the test set and estimate their concentrations with an average error of 0.9%.

We present a theory that predicts the phase behavior of hard spheres (HS) mixed with non-adsorbing supramolecular polymers in a common solvent. It combines Generalized Free Volume Theory with a mean-field model for equilibrium polymers in solution extended with scaling theory to incorporate excluded volume effects in a good solvent. The system displays similar phase stability as conventional HS-polymer mixtures, although there is a small preference for gas–liquid coexistence with respect to fluid–crystal equilibrium in the case of a HS-supramolecular polymer mixture. Phase transitions can be induced by external stimuli such as temperature or light due to the stimuli-responsive nature of the supramolecular polymer size.

In this study, a combined experimental and numerical approach is taken to further investigate the thermomechanics of shock wave formation in combustible mixtures. This study focuses on several gas mixtures including air, methane/ $$\hbox {N}_2$$ , methane/air, and biogas/air. The lean and stoichiometric combustible mixtures are studied at three different laser energy levels. The Jones blast wave theory is used to calculate the energy involved in development of the resulting shock waves and used to specify the initial conditions for the plasma in simulations. In addition, interferometry is used to gain insights into the thermodynamic conditions within the plasma kernel, for validation of the numerical model results. The energies calculated for the different mixtures studied show that shock waves generated in the combustible mixture likely gain energy early in the breakdown process from exothermic chemical reactions. Shock wave results from experiment are shown to be replicated by the model, and the variations of the density inside of the hot core region are in agreement between the simulation and experimental results.

Membrane deformation is a common phenomenon in pressurized membrane processes. It alters the transport and structural characteristics of membranes and hence can lead to a lower than estimated process performance. Therefore, it is essential to accurately characterize the membrane under representative operating conditions. This will allow for both an understanding of the underlying mechanisms for the change of membrane performance, and an optimization of the design and operation of pressure- and osmotically driven membrane processes. A novel membrane characterization method is proposed, validated and tested in this study. Using the osmotic-resistance filtration model, the membrane's water and solute permeability (A and B), as well as its structural parameter S, can be accurately determined using the method. The method is named the integrated two-stage (ITS) ABS method, as the membrane can be fully characterized at any given pressure using a single continuous test that is divided into two stages; each stage uses a different feed or draw concentration. A, B and S are calculated from the experimentally determined water and solute fluxes by performing a least-squares non-linear regression. The proposed method is robust, simple and offers more accurate predictions of the membrane's transport and structural properties than the currently most widely used reverse osmosis–forward osmosis (RO–FO) characterization method. Nanyang Technological University This research was supported by the Start-up Grant (SUG #002195- 00001) for Q.She from Nanyang Technological University.

Heterogeneous integration enables the construction of silicon (Si) photonic systems, which are fully integrated with a range of passive and active elements including lasers and detectors. Numerous advancements in recent years have shown that heterogeneous Si platforms can be extended beyond near-infrared telecommunication wavelengths to the mid-infrared (MIR) (2–20 μm) regime. These wavelengths hold potential for an extensive range of sensing applications and the necessary components for fully integrated heterogeneous MIR Si photonic technologies have now been demonstrated. However, due to the broad wavelength range and the diverse assortment of MIR technologies, the optimal platform for each specific application is unclear. Here, we overview Si photonic waveguide platforms and lasers at the MIR, including quantum cascade lasers on Si. We also discuss progress toward building an integrated multispectral source, which can be constructed by wavelength beam combining the outputs from multiple lasers with arrayed waveguide gratings and duplexing adiabatic couplers.

The demand for low-noise, continuous-wave, frequency-tunable lasers based on semiconductor integrated photonics has advanced in support of numerous applications. In particular, an important goal is to achieve a narrow spectral linewidth, commensurate with bulk-optic or fiber-optic laser platforms. Here we report on laser-frequency-stabilization experiments with a heterogeneously integrated III/V-Si widely tunable laser and a high-finesse, thermal-noise-limited photonic resonator. This hybrid architecture offers a chip-scale optical-frequency reference with an integrated linewidth of 60 Hz and a fractional frequency stability of 2.5 × 10 − 13 at 1 s integration time. We explore the potential for stabilization with respect to a resonator with lower thermal noise by characterizing laser-noise contributions such as residual amplitude modulation and photodetection noise. Widely tunable, compact and integrated, cost-effective, stable, and narrow-linewidth lasers are envisioned for use in various fields, including communication, spectroscopy, and metrology.

We demonstrate the first heterogeneously integrated laser with a Si3N4 external cavity. Through a multilayer heterogeneous integration with InP and Si, the laser shows narrow linewidth and high temperature stability expected from a Si3N4 cavity.

We observe stimulated Brillouin scattering (SBS) in AlGaAs-on-insulator integrated waveguides. A guided transverse acoustic mode has a 12.3 GHz Brillouin shift, and a full-width half-maximum of 25 MHz.

Silicon nitride (Si3N4), as a complementary metal-oxide-semiconductor (CMOS) material, finds wide use in modern integrated circuit (IC) technology. The past decade has witnessed tremendous development of Si3N4 in photonic areas, with innovations in nonlinear photonics, optical sensing, etc. However, the lack of an integrated laser with high performance prohibits the large-scale integration of Si3N4 waveguides into complex photonic integrated circuits (PICs). Here, we demonstrate a novel III-V/Si/Si3N4 structure to enable efficient electrically pumped lasing in a Si3N4 based laser external cavity. The laser shows superior temperature stability and low phase noise compared with lasers purely dependent on semiconductors. Beyond this, the demonstrated multilayer heterogeneous integration provides a practical path to incorporate efficient optical gain with various low-refractive-index materials. Multilayer heterogeneous integration could extend the capabilities of semiconductor lasers to improve performance and enable a new class of devices such as integrated optical clocks and optical gyroscopes., 14 pages, 3 figures

Recent advances in nonlinear optics have revolutionized integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as Si3N4 and SiO2. While semiconductor materials feature much higher nonlinear coefficients and convenience in active integration, they have suffered from high waveguide losses that prevent the realization of efficient nonlinear processes on-chip. Here, we challenge this status quo and demonstrate a low loss AlGaAs-on-insulator platform with anomalous dispersion and quality (Q) factors beyond 1.5 × 106. Such a high quality factor, combined with high nonlinear coefficient and small mode volume, enabled us to demonstrate a Kerr frequency comb threshold of only ∼36 µW in a resonator with a 1 THz free spectral range, ∼100 times lower compared to that in previous semiconductor platforms. Moreover, combs with broad spans (>250 nm) have been generated with a pump power of ∼300 µW, which is lower than the threshold power of state-of the-art dielectric micro combs. A soliton-step transition has also been observed for the first time in an AlGaAs resonator., Despite larger nonlinear coefficients, waveguide losses have prevented using semiconductors instead of dielectric materials for on-chip frequency-comb sources. By significantly reducing waveguide loss, ultra-low-threshold Kerr comb generation is demonstrated in a high-Q AlGaAs-on-insulator microresonator system.

In this contribution, we investigate the impact of lateral leakage for linear and nonlinear optical waveguides in lithium niobate on an insulator (LNOI). Silicon nitride (SiN) loaded and direct patterned lithium niobate cross-sections are investigated. We show that lateral leakage can take place for the TE mode in LNOI ridge waveguides (X-cut lithium niobate), due to the birefringence of the material. This work gives guidelines for designing waveguides in LNOI that do not suffer from the lateral leakage effect. By applying these design considerations, we avoided the lateral leakage effect at the second harmonic wavelength of a nonlinear optical waveguide in LNOI and demonstrate a peak second harmonic generation conversion efficiency of ~1160% W−1cm−2.

In this Letter, we demonstrate a low loss gallium arsenide and aluminum gallium arsenide on an insulator platform by heterogenous integration. The resonators on this platform exhibit record high quality factors up to 1.5×106, corresponding to a propagation loss ∼0.4 dB/cm. For the first time, to the best of our knowledge, the loss of integrated III–V semiconductor on insulator waveguides becomes comparable with that of the silicon-on-insulator waveguides. This Letter should have a significant impact on photonic integrated circuits (PICs) and become an essential building block for the evolving nonlinear PICs and integrated quantum photonic systems in the future.

Using ultralow loss waveguides and a novel cavity design, we demonstrate fully integrated lasers on silicon with a fundamental linewidth lower than 200 Hz. The lasers also possess an ultrawide wavelength tuning range of 110 nm across three optical communication bands (S+C+L). These are record results for all fully integrated semiconductor lasers that have ever been reported in literature.

The shapes of bacteria can vary widely; they may, for instance, be spherical, rod-like, string-like, or curved. In general, bacilli are highly anisotropic. For research and (bio)technological purposes, it can be useful to concentrate bacteria, which is possible by adding nonadsorbing polymers. The induced phase separation originates from a polymer-mediated depletion interaction, first understood by Asakura and Oosawa. Here, it is shown that free volume theory (FVT) can semi-quantitatively describe the phase transitions observed when adding sodium polystyrene sulfonate polymers to E. coli bacteria [Schwarz-Linek et al., Soft Matter 6, 4540 (2010)] at high ionic strength. The E. coli bacteria are described as short, hard spherocylinders. FVT predicts that the phase transitions of the mixtures result from a fluid-ABC crystal solid phase coexistence of a hard spherocylinder-polymer mixture.

Arrayed waveguide gratings (AWGs) working in the 4.7 µm wavelength range are reported on silicon-on-insulator waveguides with 1500 nm thick silicon and 2 µm thick buried oxide layers. For eight channel devices, three different channel spacings (200 GHz, 100 GHz, and 50 GHz) with cross talk levels of − 32.31 d B , − 31.87 d B , and − 27.28 d B and insertion loss levels of − 1.43 d B , − 4.2 d B , and − 2.3 d B , respectively, are demonstrated. Fourteen channel AWGs with 170 GHz channel spacing and 16 channel AWGs with 87 GHz channel spacing are shown to have a cross talk value of − 21.67 d B and − 24.30 d B and insertion loss value of − 4.2 d B and − 3.8 d B , respectively. Two AWGs with 10 nm difference in channel peak are designed, and the measurements show a 9.3 nm difference. The transmission spectrum shift as a function of temperature is found to be 0.22 nm/°C.

Compatibility to the semiconductor industry makes silicon thin-film devices attractive for thermoelectric applications. Silicon has a competitive thermoelectric power factor but a large thermal conductivity, which results in an overall small thermoelectric figure of merit, ZT. By patterning arrays of nano-sized holes with spacing less than the average phonon mean free path into the Si thin films, their thermal conductivity can be greatly suppressed, whereas their electronic properties are less affected. We fabricated and measured the electronic and thermal transport properties of such holey Si devices from 300 K to 650 K. Heat diffusion imaging, a hybrid approach that combines thermoreflectance imaging and the heat spreader method was used for the in-plane thermal conductivity measurement and gives a value of 6.00 ± 1.83 W/mK at room temperature. The power factor times temperature is about 0.52 ± 0.04 W/mK at 300 K and 1.10 ± 0.09 W/mK at 650 K. Therefore, ZT of the holey Si device is approximately 0.09 at room temperature and is at least 0.29 at 650 K. Further improvement is possible by optimizing the feature sizes and using surface doping.

Multi-spectral midwave-infrared (mid-IR) lasers are demonstrated by directly bonding quantum cascade epitaxial gain layers to silicon-on-insulator (SOI) waveguides with arrayed waveguide grating (AWG) multiplexers. Arrays of distributed feedback (DFB) and distributed Bragg-reflection (DBR) quantum cascade lasers (QCLs) emitting at ∼4.7 µm wavelength are coupled to AWGs on the same chip. Low-loss spectral beam combining allows for brightness scaling by coupling the light generated by multiple input QCLs into the fundamental mode of a single output waveguide. Promising results are demonstrated and further improvements are in progress. This device can lead to compact and sensitive chemical detection systems using absorption spectroscopy across a broad spectral range in the mid-IR as well as a high-brightness multi-spectral source for power scaling.

We demonstrate a polarization rotator integrated at the output of a GaAs waveguide producing type I second harmonic generation (SHG). Form-birefringent phase matching between the pump fundamental transverse electric (TE) mode near 2.0 $\mu$m wavelength and the signal fundamental transverse magnetic (TM) mode efficiently generates light at 1.0 $\mu$m wavelength. A SiN waveguide layer is integrated with the SHG device to form a multi-functional photonic integrated circuit. The polarization rotator couples light between the two layers and rotates the polarization from TM to TE or from TE to TM. With a TE-polarized 2.0 $\mu$m pump, type I SHG is demonstrated with the signal rotated to TE polarization. Passive transmission near 1.0 $\mu$m wavelength shows ~80 % polarization rotation across a broad bandwidth of ~100 nm. By rotating the signal polarization to match that of the pump, this SHG device demonstrates a critical component of an integrated self-referenced octave-spanning frequency comb. This device is expected to provide crucial functionality as part of a fully integrated optical frequency synthesizer with resolution of less than one part in 10$^{14}$., Comment: 7 pages, 7 figures

We demonstrate single-mode E-DBR lasers with 1kHz linewidth and >37mW output power, and ring-assisted E-DBR lasers with 500Hz linewidth, by heterogeneously integrating III-V gain material with a 15mm long ultra-low loss silicon waveguide-based Bragg reflector.

This review focuses on current research attempts to develop nano-enhanced polymeric desalination membranes. The novel contribution made by this work as compared to many recent reviews on membrane enhancement is that a critical review is made of the effect that the morphological, optical and magnetic properties of the applied nanomaterials have on the efficiency of desalination membranes. The focus on nanomaterials in this review is on both applying new chemical compositions at various concentrations, and also on altering the nanomaterials' morphology and other properties to reach the optimal membrane efficiency for desalination applications. The synthesis route has a major role of tuning the physical and chemical properties of the nanomaterials, and hence, the membrane morphological parameters can be altered, all of which are summarised in this review. The review surveys different types of nanomaterials used for membrane fabrication, such as single elements, metal oxides and nanotubes. Furthermore, mixed oxide composites and polymer/nanomaterial combinations are also considered for membrane enhancement. A wide application range is investigated for modified membranes in pressure and osmotically driven membrane processes for desalination, including reverse osmosis, forward osmosis, osmotically assisted reverse osmosis and pressure assisted forward osmosis.

We present a semiconductor laser on the heterogeneous silicon integrated platform with 40 nm tuning range across the C+L band and a record-low 2.5 kHz Lorentzian linewidth. An SOA integrated on the same chip boosts the output power from the laser by ∼10 dB.

We demonstrate fully integrated optical isolators using bonded Ce:YIG on silicon microrings with an integrated electromagnet. The isolator operates for TE mode input light and can be tuned between 1540 to 1580nm with >20dB isolation.

Heterogeneously integrated III-V/Si MZI modulators measured at high optical power levels demonstrate applicability for high SFDR analog fiber-optic links without an optical amplifier. Optical power up to 100 mW injected into the modulator shows no degradation in linearity, demonstrating 110 dB.Hz2/3 typical SFDR.

Integrated ultra-low-loss waveguides are highly desired for integrated photonics to enable applications that require long delay lines, high-Q resonators, narrow filters, etc. Here, we present an ultra-low-loss silicon waveguide on 500 nm thick Silicon-On-Insulator (SOI) platform. Meter-scale delay lines, million-Q resonators and tens of picometer bandwidth grating filters are experimentally demonstrated. We design a low-loss low-reflection taper to seamlessly integrate the ultra-low-loss waveguide with standard heterogeneous Si/III-V integrated photonics platform to allow realization of high-performance photonic devices such as ultra-low-noise lasers and optical gyroscopes.

Forced ignition, the initiation of combustion processes by rapid and localized introduction of energy, is central to the successful operation of many combustion systems. It is therefore of interest to investigate this process, starting from the introduction of energy to the emergence of self-sustained flame or the quenching of an otherwise initialized flame kernel. Since the process is highly non-equilibrium and involves various complex kinetic phenomena, it is important to understand the key aspects that control failed or successful ignition. Detailed studies of the early phases of the ignition process can lead to knowledge of more general characteristics of the problem so that reduced models of the ignition process can be developed. These reduced versions can be used in less costly computational studies to assess various ignition events. This paper reports an experimental and numerical investigations of the early phase of laser ignition. The gas mixtures, air, methane/N2 and methane/air are considered to bring out the effect of heat release on the early flow field. The mixtures are studied at three different energy levels and the Jones blast wave theory is used to deduce the energy responsible for the development of the attendant shock waves. This energy is also used to specify initial conditions for the simulations of air and methane/air processes. Additionally, interferometry is used to resolve the density field within the plasma kernel. For the methane/air simulation two chemical models are used, a global reaction model supplemented by an ignition model and a two-step mechanism. The sensitivity of the simulations to the initial geometry of the laser spark is also investigated. The blast wave and interferometry results show that in the reacting methane/air mixture the resulting shock wave is strengthened by early heat release. It is also shown that the shock wave trajectory is not strongly affected by the initial spark geometry, but it has an impact on the velocity field and on the distribution of thermodynamic properties.

We are developing midwave infrared (mid-IR) quantum cascade lasers (QCLs) and interband cascade lasers (ICLs) bonded to silicon. The heterogeneous integration of mid-IR photonic devices with silicon promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and electronic technologies. The first Fabry-Perot QCLs on silicon were bonded to pre-patterned silicon-on-nitride-on-insulator (SONOI) substrates. Lateral tapers in the III-V mesas transferred the optical mode from the hybrid III-V/Si active region into the passive silicon waveguides, with feedback provided by reflections from both the III-V tapers and the polished passive silicon facets. Lasing was observed at   4.8 m with threshold current densities as low as 1.6 kA/cm2 when operated in pulsed mode at T = 20 oC. The first mid-IR DFB lasers integrated on silicon employed gratings patterned into the silicon waveguides before bonding. Over 200 mW of pulsed power was generated at room temperature, and operated to 100 °C with T0 = 199 K. Threshold current densities were measured below 1 kA/cm2.The grating imposed considerable wavelength selectivity and 22 nm of thermal tuning, even though the emission was not spectrally pure. Ongoing research focuses on flip-chip bonding to improve heat sinking for continuous-wave operation, and arrayed waveguide gratings for beam combining. ICLs have also been bonded to silicon and the GaSb substrate has been chemically removed with an InAsSb etch-stop layer. Tapered ICL ridges designed for lasing in a hybrid III-V/Si mode have been processed above passive silicon waveguides patterned on SOI. A goal is to combine the power generated by arrays of QCLs and ICLs residing on the same chip into a single, high-quality output beam.

Quasi-phase-matched (QPM) wavelength converters are highly desirable for emerging nonlinear optics applications in photonic integrated circuits, but available waveguide and quasi-phase-matching technologies have so far constrained their realization. In this work, we present a periodically poled lithium niobate (LN) waveguide on a silicon nitride–thin film LN platform. It contains a submicrometer waveguide core for enhancing nonlinear interactions that is more than one order of magnitude smaller than those of previous QPM waveguides. Periodic poling was applied directly to the thin film LN for quasi-phase-matching by a new surface poling technology. We demonstrated 160% W−1·cm−2 normalized efficiency for second harmonic generation at 1530 nm with ultralow propagation loss (0.3 dB/cm) in the telecom band. This highly efficient and compact wavelength converter has the potential for straightforward integration with various photonic platforms, e.g., on-chip microsystems such as optical communication networks, quantum storage, and optical frequency referencing.

A multi-spectral quantum cascade laser is demonstrated on SOI, emitting at 4.6-4.7 μm with an integrated multiplexer. Low-loss spectral beam combining to a single-mode waveguide efficiently scales the output power.

An on-wafer and self-calibrated scheme is proposed and demonstrated for self-referenced microwave characterization of a silicon integrated optical transceiver. The proposed self-calibration method enables on-wafer selective extraction of microwave characteristic parameters of high-speed modulators and photodiodes in the integrated optical transceiver, without the need for extra electrical-to-optical or optical-to-electrical calibration.

This paper presents a comparative investigation of the early phase of combustion initiated by a focused pulsed laser beam and a conventional spark-discharge. The comparative approach is applied to the characterization of combustible mixtures of natural gas and biogas with varying CO2 content. Interferometry and Schlieren imaging are used to probe flame kernel formation and its subsequent transition to a self-sustained flame. The pressure rise in the chamber is also recorded by means of a fast-response piezo-electric pressure transducer. From these diagnostics, differences between the early phases of laser-induced and spark-ignition are revealed. Unlike in laser-induced ignition, spark-ignition features a delay in the transition from the early flame kernel to a self-sustained flame (attributed to heat loss), which leads to failed ignition for mixtures with high CO2 content. The role of CO2 as an ignition retardant is observed by comparing fuel/air mixtures with and without CO2.

Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Perot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for MIR silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon had previously been reported. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-oninsulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning.

An ideal photonic integrated circuit for nonlinear photonic applications requires high optical nonlinearities and low loss. This work demonstrates a heterogeneous platform by bonding lithium niobate (LN) thin films onto a silicon nitride (Sisub3/subNsub4/sub) waveguide layer on silicon. It not only provides large second- and third-order nonlinear coefficients, but also shows low propagation loss in both the Sisub3/subNsub4/suband the LN-Sisub3/subNsub4/subwaveguides. The tapers enable low-loss-mode transitions between these two waveguides. This platform is essential for various on-chip applications, e.g., modulators, frequency conversions, and quantum communications.

In December 2009, following an upgrade of the Harvard University Herbaria's heating and cooling system, a pipe burst in one room, resulting in the soaking of specimens in the adjacent cases. The soaked specimens were removed, and the degree of water damage was assessed. The saturated specimens were placed in plastic bags and immediately transferred to a walk-in freezer set at −20°C. Slightly wet specimens were spread out to air dry. Restoration of the frozen specimens involved tests to determine the most effective method for restoring them to usable condition. Test specimens of no scientific value were intentionally soaked, then dried using two procedures: (1) silica gel desiccation and (2) vacuum freeze drying. Freeze-dried specimens did not adhere to each other as much as did those that were dried with silica gel and was the method chosen. Upon their return, the dried specimens were sorted into groups: (1) those that were immediately ready to be returned to the collection, (2) those requiring m...

We demonstrate a fully integrated extended distributed Bragg reflector (DBR) laser with ∼1 kHz linewidth and over 37 mW output power, as well as a ring-assisted DBR laser with less than 500 Hz linewidth. The extended DBR lasers are fabricated by heterogeneously integrating III-V material on Si as a gain section plus a 15 mm long, low-kappa Bragg grating reflector in an ultralow-loss silicon waveguide. The low waveguide loss (0.16 dB/cm) and long Bragg grating with narrow bandwidth (2.9 GHz) are essential to reducing the laser linewidth while maintaining high output power and single-mode operation. The combination of narrow linewidth and high power enable its use in coherent communications, RF photonics, and optical sensing.