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Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging the gap between volatile information in the photonic domain and non-volatile information in the magnetic domain, without the need for any intermediary electronic conversion. Specifically, these systems exhibit strong spin-orbit torque effects, fast domain wall motion and single-pulse all-optical switching of the magnetization. An important open challenge to bring these materials to the brink of applications is to achieve long-term stability of their magnetic properties. In this work, we address the time-evolution of the magnetic moment and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayers with various capping layers. Over the course of three months, the net magnetic moment and compensation temperature change significantly, which we attribute to quenching of the Gd magnetization. We identify that intermixing of the capping layer and Gd is primarily responsible for this effect, which can be alleviated by choosing nitrides for capping as long as reduction of nitride to oxide is properly addressed. In short, this work provides an overview of the relevant aging effects that should be taken into account when designing synthetic ferrimagnets based on Co and Gd for spintronic applications., Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging the gap between volatile information in the photonic domain and non-volatile information in the magnetic domain, without the need for any intermediary electronic conversion. Specifically, these systems exhibit strong spin-orbit torque effects, fast domain wall motionand single-pulse all-optical switching of the magnetization. An important open challenge to bring these materials to the brink of applications is to achieve long-term stability of their magnetic properties. In this work, we address the time-evolution of the magnetic moment and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayerswith various capping layers. Over the course of three months, the net magnetic moment and compensation temperature change significantly, which we attribute to quenching of the Gd magnetization. We identify that intermixing of the capping layer and Gd is primarily responsible for this effect, which can be alleviated by choosing nitrides for cappingas long as reduction of nitride to oxide is properly addressed. In short, this work provides an overview of the relevant aging effects that should be taken into account when designing synthetic ferrimagnets based on Co and Gd for spintronic applications.

In monolithic photonic integrated circuits (PICs), an optimized active/passive integration is needed to provide efficient coupling and low amount of interface reflections between amplifiers and passive components. A 1300 nm semiconductor optical amplifier (SOA) on InP substrate and optimized for butt-joint reflections is investigated. Material performance were assessed from measurements of broad area lasers. Room temperature operation reveals 1.2 W single facet output power with threshold current around 100 A/cm2 per well. Characteristic temperatures of T0 = 75 K and T1 = 294 K were obtained. A compact model description of the SOA, suitable for the design of PICs and rate equation analysis, was applied to parametrize the unsaturated gain measurements. Current injection efficiency of 0.65, transparency carrier density of 0.57 1018 cm−3, and free carrier absorption losses up to 15 cm−1 were extracted from fitting the data. The model is verified with measurements of optical gain saturation. A modal gain of 15 dB for a 600 μm long narrow ridge SOA leads to output saturation power higher than 30 mW at 7 kA/cm2. This building block contributes to the development of an InP monolithic integration technology in the 1300 nm range, which can enable the use of photonic integrated circuits in many kind of applications.

Spectral sensing is an emerging field driven by the need for fast and non-invasive methods for the chemical analysis of materials in agri-food, healthcare, and industrial applications. We demonstrate a near-infrared spectral sensor, based on a scalable fabrication process and combining high responsivity, narrow linewidth, and low noise. The sensor consists of 16 resonant-cavity-enhanced photodetectors, each showing a unique spectral response consisting of narrow peaks. The spectral sensor thereby covers the wavelength range between 890 and 1650 nm, where organic materials show relevant spectral features from first and second overtones. For the fabrication of the detector arrays, we propose a simple and scalable fabrication approach that yields largely improved device characteristics with respect to the grey-scale electron-beam lithography process reported earlier. Through a series of five optical lithography steps, tuning layers of silicon nitride are deposited stepwise to obtain 16 different thicknesses and reduced surface roughness. With this novel fabrication approach, the obtained photodetectors achieve an average peak linewidth of 55 nm, a maximum peak responsivity of 0.3 A/W, and high suppression of the non-resonant background. We also demonstrate the impact of these improvements on the sensing performance for two relevant problems through an experiment and a set of simulations. With lateral dimensions of ∼1.4 × 1.4 mm2, the proposed photodetector array can be the key to robust, portable, and low-cost sensing instrumentation for on-site material analysis in various application fields.

We report a versatile method for improving post-bonding wafer alignment accuracy and BCB thickness uniformity in stacks bonded with soft-baked BCB. It is based on novel BCB-based micro-pillars that act as anchors during bonding. The anchor structures become a natural part of the bonding interface therefore causing minimal interference to the optical, electrical and mechanical properties of the bonded stack. We studied these properties for fixed anchor density and various anchor heights with respect to the adhesive BCB thickness. We demonstrated that the alignment accuracy can be improved by approximately an order of magnitude and approach the fundamental pre-bond alignment accuracy by the tool. We also demonstrated that this technique is effective for a large range of BCB thicknesses of 2–16 μm. Furthermore we observed that the thickness non-uniformities were reduced by a factor of 2–3 × for BCB thicknesses in the 8–16 μm range.

Femtosecond laser-pulse excitation provides an energy efficient and fast way to control magnetization at the nanoscale, providing great potential for ultrafast next-generation data manipulation and nonvolatile storage devices. Ferromagnetic van der Waals materials have garnered much attention over the past few years due to their low dimensionality, excellent magnetic properties, and large response to external stimuli. Nonetheless, their behaviour upon fs laser-pulse excitation remains largely unexplored. Here, we investigate the ultrafast magnetization dynamics of a thin flake of Fe$_3$GeTe$_2$ (FGT) and extract its intrinsic magnetic properties using a microscopic framework. We find that our data is well described by our modelling, with FGT undergoing a slow two-step demagnetization, and we experimentally extract the spin-relaxation timescale as a function of temperature, magnetic field and excitation fluence. Our observations indicate a large spin-flip probability in agreement with a theoretically expected large spin-orbit coupling, as well as a weak interlayer exchange coupling. The spin-flip probability is found to increase when the magnetization is pulled away from its quantization axis, opening doors to an external control over the spins in this material. Our results provide a deeper understanding of the dynamics van der Waals materials upon fs laser-pulse excitation, paving the way towards two-dimensional materials-based ultrafast spintronics., Supplementary information included

All-optical switching (AOS) of magnetization by a single femtosecond laser pulse in Co/Gd based synthetic ferrimagnets is the fastest magnetization switching process. On the other hand, He ion irradiation has become a promising tool for interface engineering of spintronic material platforms, giving rise to significant modification of magnetic properties. In this paper, we explore the use of He ion irradiation to enhance single pulse AOS of Co/Gd bilayer-based synthetic ferrimagnets. The intermixing of the constituent magnetic layers by He ion irradiation was both numerically simulated and experimentally verified. We theoretically modeled the effects of intermixing on AOS using the layered microscopic 3-temperature model and found that AOS is enhanced significantly by breaking the pristine Co/Gd interface through intermixing. Following this notion, we studied the threshold fluence of AOS as a function of He ion irradiation fluence. We found that the AOS threshold fluence can be reduced by almost 30%. Our study reveals the control of AOS by He ion irradiation, which opens up an industrially compatible approach for local AOS engineering. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement Nos. 860060 and 861300. This project is also part of the research programme financed by the Netherlands Organisation for Scientific Research (NWO). Solliance and the Dutch province of Noord-Brabant are acknowledged for funding the TEM facility.

Illicit-drug production, trafficking and seizures are on an all-time high. This consequently raises pressure on investigative authorities to provide rapid forensic results to assist law enforcement and legal processes in drug-related cases. Ideally, every police officer is equipped with a detector to reliably perform drug testing directly at the incident scene. Such a detector should preferably be small, portable, inexpensive and shock-resistant but should also provide sufficient selectivity to prevent erroneous identifications. This study explores the concept of on-site drugs-of-abuse detection using a 1.8 × 2.2 mm2 multipixel near-infrared (NIR) spectral sensor that potentially can be integrated into a smartphone. This integrated sensor, based on an InGaAs-on-silicon technology, exploits an array of resonant-cavity enhanced photodetectors without any moving parts. A 100% correct classification of 11 common illicit drugs, pharmaceuticals and adulterants was achieved by chemometric modelling of the response of 15 wavelength-specific pixels. The performance on actual forensic casework was investigated on 246 cocaine-suspected powders and 39 MDMA-suspected ecstasy tablets yielding an over 90% correct classification in both cases. These findings show that presumptive drug testing by miniaturized spectral sensors is a promising development ultimately paving the way for a fully integrated drug-sensor in mobile communication devices used by law enforcement.

Butt-joint regrowth is widely used in photonic integration, but it has been challenging to break the density-quality tradeoff due to the edge growth rate enhancement (GRE) effect. In this work, we propose a scheme to circumvent this tradeoff by using large regrowth masks whose centers are exposed to epi-growth for neutralization of the excessive species. With the GRE under control, epi-stacks with arbitrarily large sizes supporting dense arrays can be butt-joint integrated with minimal compromise to their epitaxy quality. In our experiment, multi-quantum-well-based material of an exceptionally large area of 0.5 × 1.7 mm2 was epitaxially integrated with passive InP material on the same wafer. A more than 20 × reduction in edge topology compared to conventional methods was achieved.

Formation of Ge-rich prismatic inclusions in the hexagonal SiGe shell of GaP-Si-SiGe nanowires is reported and discussed in relation to a growth model that explains their origin. An accurate TEM/EDX analysis shows that such prisms develop right on top of any {112[combining macron]0} facet present on the inner GaP-Si surface, with the base matching the whole facet extension, as large as tens of nanometers, and extending within the SiGe shell up to a thickness of comparable size. An enrichment in Ge by around 5% is recognized within such regions. A phase-field growth model, tackling both the morphological and compositional evolution of the SiGe shell during growth, is exploited to assess the mechanism behind the prism formation. A kinetic segregation process, stemming from the difference in surface mobility between Ge (faster) and Si (slower), is shown to take place, in combination with the evolution of the SiGe shell morphology. Actually, the latter moves from the one templated by the underlying GaP-Si core, including both {101[combining macron]0} and {112[combining macron]0} facets, to the more energetically convenient hexagon, bounded by {101[combining macron]0} facets only. Simulations are shown to accurately reproduce the experimental observations for both regular and asymmetric nanowires. It is then discussed how a careful control of the GaP core faceting, as well as a proper modulation of the shell growth rate, allows for direct control of the appearance and size of the Ge-rich prisms. This tunability paves the way for a possible exploitation of these lower-gap regions for advanced designs of band-gap-engineering.

We demonstrate a near-infrared (900-1650nm) spectral sensor based on an array of 16 pixels for classifying and quantifying materials and their composition. These pixels consist of resonant-cavity enhanced photodetectors containing a thin absorbing layer, tuning element and cavity. Using a wafer-scale optical lithography process, we achieve a tunable, wavelength-specific response with narrow linewidths of 50nm and high responsivity (R>0.1A/W). The customizability of the response, small-size and robustness make it suitable for portable spectroscopic solutions in a wide variety of applications. The sensing performance is demonstrated on the prediction of moisture in rice with a coefficient of determination of R^2=0.95.

A butt-joint SOA design for InP on Si membrane (IMOS) platform is proposed. The new design features the butt-joint interface between the SOA and passive nanophotonic waveguide, which makes the interface a factor of 2 to 6 shorter than in the current twin-guide SOAs, with possibility to reduce it further to factor of 5-10. This makes the new SOA a promising candidate for high-speed directly modulated lasers (DML) applications, where extremely short SOAs (40-100 μm long) and short distances between reflectors are usually required.

Our previously reported 17.8 % efficiency InP nanowire solar cell1 showed a short-circuit current Isc of 29.3 mA/cm2, which is not far from the theoretical maximum Isc = 34.6 mA/cm2, but the loss in the open circuit voltage with respect to the radiative limit still amounted to 272 mV. To avoid this loss and reach the radiative limit we have to increase both the internal radiative efficiency ηPlint and the photon escape probability Pesc towards unity, as shown by the last term in Eq. 1. 'Equation Presented' We report top-down etched InP nanowires intended to both optimize the amount of light outcoupling as well as the directionality of the emitted light. The photon entropy loss is governed by the ln ϵin/ϵout term, which is responsible for a 300 mV loss in the open circuit voltage. To circumvent this loss, we need to redirect all the emitted photoluminescence from the cell back to the sun (ϵin = ϵout), For this purpose, we have fabricated PMMA microlenses by using a reflow process, which can be precisely positioned with respect to the InP nanowires.

III/V semiconductor solar cells feature the highest photon conversion efficiencies (PCE), but they are still too expensive for terrestrial application. Conventional nanowire (NW) solar cells already partially resolve this issue since they can be grown on a silicon substrate and feature a low filling factor (the ratio of the 180 nm NW diameter to 500 nm NW pitch, squared). We take the next step by depositing PMMA micro-lenses with a diameter of 6 μm on top of a NW-array with the same 6 μm pitch, allowing to reduce the material consumption by more than 3 orders of magnitude. According to our FDTD simulations, the material consumption can even be further decreased by reducing the NW length with a factor of 2 down to 1 μm, since the lens is focusing the solar radiation near the top of the nanowires. We also expect a significantly increased Voc due to an increased internal radiative efficiency (IRE) at a higher excitation power. Preliminary measurement show an increase in Voc of at least 50 mV for randomly positioned microlenses on top of a dense NW array with 0.5 μm pitch.

We present a novel approach to NIR spectral sensing using a handheld module based on a miniaturized integrated detector array. Applicability of the sensor is demonstrated in monitoring moisture in grains and classification of plastics.

We present our latest results on 1300 nm band optical amplifiers and Fabry-Perot lasers in the development of a 1300nm active\passive photonic integration platform on InP. Modal gain, material transparency, temperature dependence are reported and analyzed for amplifiers that are optimized for low butt-joint reflections.

We present broadband MMI couplers, developed for a novel integration platform on InP with active/passive integration capabilities for the 1300nm wavelength range. Low loss (

The low throughput of atomic force microscopy (AFM) is the main drawback in its large-scale deployment in industrial metrology. A promising solution would be based on the parallelization of the scanning probe system, allowing acquisition of the image by an array of probes operating simultaneously. A key step for reaching this goal relies on the miniaturization and integration of the sensing mechanism. Here, we demonstrate AFM imaging employing an on-chip displacement sensor, based on a photonic crystal cavity, combined with an integrated photodetector and coupled to an on-chip waveguide. This fully-integrated sensor allows high-sensitivity and high-resolution in a very small footprint and its readout is compatible with current commercial AFM systems.

Conversion between signals in the microwave and optical domains is of great interest both for classical telecommunication and for connecting future superconducting quantum computers into a global quantum network. For quantum applications, the conversion has to be efficient, as well as operate in a regime of minimal added classical noise. While efficient conversion has been demonstrated using mechanical transducers, they have so far all operated with a substantial thermal noise background. Here, we overcome this limitation and demonstrate coherent conversion between gigahertz microwave signals and the optical telecom band with a thermal background of less than one phonon. We use an integrated, on-chip electro-optomechanical device that couples surface acoustic waves driven by a resonant microwave signal to an optomechanical crystal featuring a 2.7 GHz mechanical mode. We initialize the mechanical mode in its quantum ground state, which allows us to perform the transduction process with minimal added thermal noise, while maintaining an optomechanical cooperativity >1, so that microwave photons mapped into the mechanical resonator are effectively upconverted to the optical domain. We further verify the preservation of the coherence of the microwave signal throughout the transduction process. Electro-optomechanical conversion between optical and microwave photons is achieved with minimal added noise by cooling the mechanical oscillator to its quantum ground state. This has potential for future coherence-preserving transduction.

For decades, near-infrared (NIR) spectroscopy has been a valuable tool for material analysis in a variety of applications, ranging from industrial process monitoring to quality assessment. Traditional spectrometers are typically bulky, fragile and expensive, which makes them unsuitable for portable and in-field use. Thus, there is a growing interest for miniaturized, robust and low-cost NIR sensors. In this study, we demonstrate a handheld NIR spectral sensor module, based on a fully-integrated multipixel detector array, sensitive in the 850–1700 nm wavelength range. Differently from a spectrometer, the spectral sensor measures a limited number of NIR spectral bands. The capabilities of the spectral sensor module were evaluated alongside a commercially available portable spectrometer for two application cases: to quantify the moisture content in rice grains and to classify plastic types. Both devices achieved the two sensing tasks with comparable performance. Moisture quantification was achieved with a root mean square error (RMSE) prediction of 1.4% and 1.1% by the spectral sensor and spectrometer, respectively. Classification of the plastic type was achieved with a prediction accuracy on unknown samples of 100% and 96.4% by the spectral sensor and spectrometer, respectively. The results from this study are promising and demonstrate the potential for the compact NIR modules to be used in a variety of NIR sensing applications.

Hydrogen-bonded cyclohexanoic derivatives are applied in a structural colored cholesteric liquid crystal (CLC) helical polymer that demonstrates an extraordinary dual thermal response. Integration of the dynamic hydrogen-bonded cyclohexanoic acid derivatives in the CLC polymer as supramolecular crosslinks yields an immediate and irreversible loss of the green structural color upon exposure to temperatures above the cholesteric-to-isotropic transition temperature (TNI) caused by the helical order loss. Exposure to temperatures below the TNI yields a gradual irreversible red color shift of the reflected wavelength over broad temperature and time ranges. Most likely due to polymerization confinement in combination with the dynamics of the carboxylic acid hydrogen bonds, helical unwinding takes place over time causing the red shift of the reflected wavelength. The temperature response can be programmed by altering the chemical composition of the liquid crystal mixture. Furthermore, the green, structural color of the polymer can also be easily changed making it possible to print different colored indicators combined with different respective temperature responses on a single substrate. The printed optical sensors can be easily delaminated by dissolving the non-covalent crosslinked polymer. Such optical polymer materials are attractive for easy processable time–temperature integrators and thermal paper.

Near-infrared spectroscopy (NIR) is widely used today in applications ranging from monitoring industrial manufacturing processes to assessing the chemical composition and quality of products and materials. However, the challenge remains in reducing size and cost of these spectroscopic devices, while maintaining their sensitivity and robustness. The miniaturisation of spectral sensors is essential to expanding their application beyond dedicated stations in industrial settings and analytical labs, into the hands of non-specialists working on-site and eventually to consumers. The design of current portable NIR sensor systems is mostly inspired by conventional instruments that use gratings or interferometers. The drawback of these approaches is that they are complex to assemble and contain movable parts that are susceptible to shocks and mechanical vibrations.

Silicon (Si) donors in GaAs have been the topic of extensive studies since Si is the most common and well understood n-type dopant in III-V semiconductor devices and substrates. The indirect bandgap of AlAs compared to the direct one of GaAs leads to interesting effects when introducing Si dopants. Here we present a study of cross-sectional scanning tunneling microscopy (X-STM) and density functional theory (DFT) calculations to study Si donors in AlAs at the atomic scale. Based on their crystal symmetry and contrast strengths, we identify Si donors up to four layers below the (110) surface of AlAs. Interestingly, their short-range local density of states (LDOS) is very similar to Si atoms in the (110) surface of GaAs. Additionally we show high-resolution images of Si donors in all these layers. For empty state imaging, the experimental and simulated STM images based on DFT show excellent agreement for Si donor up to two layers below the surface.

Spectral sensing in the near-infrared range is of increasing interest for application areas ranging from industrial processes to the agri-food sector, as it allows measuring the chemical composition of organic materials in a fast and non-destructive manner. On-field applications demand spectral sensors with a large spectral range, low angular dependence, robust geometry and small footprint, while being manufacturable on large scale at low cost. To meet these requirements, we developed a multi-pixel array of resonant-cavity enhanced detectors using an InP-membrane-on-silicon platform, where each of the 16 pixels provides an individual photoresponse with a number of resonances, which together cover the wavelength range of 800-1700 nm. The pixels consist of two metal mirrors, which enclose an InP p-i-n photodiode with an InGaAs absorber layer and a tuning layer, which varies in thickness to create the individual photoresponses of different pixels. The multi-pixel arrays are fabricated by adhesive wafer bonding followed by a series of lithography steps to define the tuned pixels and metal contacts for the photocurrent read-out. Despite the limited number of measurement channels with broad spectral response, information on the chemical composition of the sample can be directly retrieved using chemometrics. The sensing capabilities for our spectral sensors are demonstrated with two practical application cases: determination of the nutritional information in raw milk and the classification of different plastic types. For both experiments, the photocurrent measurements from the sensor were used directly in regression or classification algorithms based on partial least squares analysis, leading to convincing prediction performance. This shows that the fabricated spectral sensor can retrieve chemical information for a broad set of sensing problems. Simulations have shown that for a specific sensing problem the prediction performance of the spectral sensor can be further improved by an optimized selection of the available spectral responses.

We developed a method to easily transfer optical structures from a semiconductor substrate to a fiber-tip facet without the need for glues and preserving the pristine or functionalized condition of the structure surface. An opening is etched on the back of the fabrication wafer and the structure is suspended via breakable support. The transfer is achieved by mechanical contact with the fiber facet. Using a photonic crystal structure designed for high vertical coupling at the Gamma point a reflectance fiber-tip sensor with refractive index sensitivity of 120 nm/RIU has been assembled and could be further functionalized for application in biosensing.

We have experimentally demonstrated a 1x8 WDM polarization-insensitive multicast switch based on bulk SOAs. Results show net gain of 11dB, broadband and error-free operation with 0.55dB power penalty at 10GBps NRZ-OOK, and crosstalk

Silicon and Germanium have an indirect band gap, which limits their use in optoelectronic devices. Here, we show that we can create a direct band gap in Si 1-x Ge x alloys by changing the crystal structure from cubic to hexagonal. DFT calculations predict a strong optical transition for 0.651-x Ge x alloys have been fabricated and efficient light emission has been observed.

We present an efficient and flexible method to realize micro- and nano-optical structures on the tip of optical fibers. We demonstrate this approach for a fiber-tip sensor consisting of a photonic crystal (PhC) structure in a semiconductor membrane on the cleaved facet of a telecom fiber. The PhC structure is fabricated on a wafer by lithography and etching and then transferred to the fiber facet by a simple mechanical pickup process through an opening in the substrate, without the need for adhesives or a micromanipulator. Due to its reliability, scalability, and the use of wafer-scale fabrication methods, this process increases the possibilities for fiber-tip applications at the industrial level. With the fabricated fiber tip sensors, we demonstrate sensing of the refractive index and temperature, with resonance wavelength shifts of 120 nm/RIU and 95 pm/K, respectively.

The original version of this Article contained an error in the Discussion, which incorrectly read ‘In summary, we have demonstrated an integrated optomechanical displacement sensor featuring 30 fm·Hz−1/2 imprecision’. The correct version states ‘45’ in place of ‘30’. This has been corrected in both the PDF and HTML versions of the Article.

We present a novel method to fabricate fiber-tip sensors. Using high-throughput semiconductor fabrication methods combined with a simple fiber-attachment scheme, we can mass-produce the sensors, preserving their surface unaltered. We experimentally demonstrate the sensor performance.

Optical read-out of motion is widely used in sensing applications. Recent developments in micro- and nano-optomechanical systems have given rise to on-chip mechanical sensing platforms, potentially leading to compact and integrated optical motion sensors. However, these systems typically exploit narrow spectral resonances and therefore require tuneable lasers with narrow linewidth and low spectral noise, which makes the integration of the read-out extremely challenging. Here, we report a step towards the practical application of nanomechanical sensors, by presenting a sensor with ultrawide (∼80 nm) optical bandwidth. It is based on a nanomechanical, three-dimensional directional coupler with integrated dual-channel waveguide photodiodes, and displays small displacement imprecision of only 45 fm/Hz1/2 as well as large dynamic range (>30 nm). The broad optical bandwidth releases the need for a tuneable laser and the on-chip photocurrent read-out replaces the external detector, opening the way to fully-integrated nanomechanical sensors., On-chip mechanical sensing platforms require tuneable lasers with narrow linewidth and low spectral noise, making read-out challenging. Here, the authors report a nanomechanical sensor with 80nm bandwidth, displacement imprecision of 45 fm/Hz1/2 as well as a dynamic range greater than 30 nm with integrated photodetectors.

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) is of great interest in thin-film magnetism because of its ability to stabilize chiral spin textures. It can be quantified by investigating the frequency nonreciprocity of oppositely propagating spin waves. However, as the iDMI is an interface interaction, the relative effect reduces when the films become thicker, making quantification more difficult. Here, we utilize all-electrical propagating spin-wave spectroscopy to disentangle multiple contributions to spin wave frequency nonreciprocity to determine the iDMI. This is done by investigating nonreciprocities across a wide range of magnetic layer thicknesses (from 4 to 26 nm) in Pt/Co/Ir, Pt/Co/Pt, and Ir/Co/Pt stacks. We find the expected sign change in the iDMI when inverting the stack order and a negligible iDMI for the symmetric Pt/Co/Pt. We additionally extract a difference in surface anisotropies and find a large contribution due to the formation of different crystalline phases of the Co, which is corroborated using nuclear magnetic resonance and high-resolution transmission-electron-microscopy measurements. These insights will open up avenues to investigate, quantify, and disentangle the fundamental mechanisms governing the iDMI, and pave a way toward engineered large spin-wave nonreciprocities for magnonic applications.

Photonic integration in a micrometer-thick indium phosphide (InP) membrane on silicon (IMOS) offers intrinsic and high-performance optoelectronic functions together with high-index-contrast nanophotonic circuitries. Recently demonstrated devices have shown competitive performances, including high side-mode-suppression ratio (SMSR) lasers, ultrafast photodiodes, and significant improvement in critical dimensions. Applications of the IMOS devices and circuits in optical wireless, quantum photonics, and optical cross-connects have proven their performances and high potential.

Low-excess-loss arrayed waveguide gratings are enabled by unique application of deep UV lithography in InP integrated photonics through reduced feature sizes and, more specifically, well-resolved inter-waveguide gap dimensions. Submicrometer wafer-flatness is shown to be required to achieve the critical dimension uniformity better than 10 nm on 3-in substrates. Arrayed waveguide grating devices were fabricated and the effect of inter-waveguide gap scaling on the excess losses was measured and compared to simulations. Excess losses down to 0.15 dB were demonstrated to be lower than predicted with the 2-D simulations. The tapering of the etch depth inside the gaps due to the lag effect of the etch process may explain the improvements.

We present a simple to process tunable laser, fabricated in a low-cost generic fabrication process and based on two coupled Fabry-Perot cavities. The complex coupling coe cients of the coupling element are analytically derived from a 3x3 MMI using coupled mode theory and chosen to maximize the SMSR during lasing operation. Additionally, one of the cavities contains a reflective interferometer, which acts as coarse wavelength selector. This interferometer is derived from a Michelson Interferometer, by replacing the two independent mirrors with our optimized coupling element, leading to a doubled Free Spectral Range. As a result, we obtained a tuning range of 26 nm with potential for beyond 40 nm, a SMSR larger than 40 dB and fiber coupled power up to 9 dBm.

We determine the chemical changes associated with viscosity reduction when heavy oil is cracked in subcritical water. The viscosity reduction has a temperature threshold for onset of 290 °C—this suggests an enhanced acid cracking regime associated with the maximisation of water dissociation at these conditions aided by the already increased solubility. The mean molecular weight is reduced by nearly 50%. Oxygen and sulphur are reduced by about half of this—either by expelled gas effluent ( $${\text{H}}_{2} {\text{S}}$$ ) or by conversion into mono-aromatic base sulphur-containing structures. The amount of lower branched paraffins is increased.

III-V semiconductors such as InP are highly efficient light absorbers for photoelectrochemical (PEC) water splitting devices. Yet, their cathodic stability is limited due to photocorrosion and the measured photocurrents do not necessarily originate from H2 evolution only. We evaluated the PEC stability and activation of model p-InP(100) photocathodes upon photoelectrochemical passivation (i.e. repeated surface oxidation/reduction). The electrode was subjected to a sequence of linear potential scans with or without intermittent passivation steps (repeated passivation and continuous reduction, respectively). The evolution of H2 and PH3 gases was monitored by online electrochemical mass spectrometry (OLEMS) and the Faradaic efficiencies of these processes were determined. Repeated passivation led to an increase of the photocurrent in 0.5 M H2SO4, while continuous reduction did not affect the photocurrent of p-InP(100). Neither H2 nor PH3 formation increased to the same extent as the photocurrent during the repeated passivation treatment. Surface analysis of the spent electrodes revealed substantial roughening of the electrode surface by repeated passivation, while continuous reduction left the surface unaltered. On the other hand, photocathodic conditioning performed in 0.5 M HCl led to the expected correlation between photocurrent increase and H2 formation. Ultimately, the H2 evolution rates of the photoelectrodes in H2SO4 and HCl are comparable. The much higher photocurrent in H2SO4 is due to competing side-reactions. The results emphasize the need for a detailed evaluation of the Faradaic efficiencies of all the involved processes using a chemical-specific technique like OLEMS. Photo-OLEMS can be beneficial in the study of photoelectrochemical reactions enabling the instantaneous detection of small amounts of reaction by-products.

The standardization of photonic integration processes for InP has led to versatile and easily accessible generic integration platforms. The generic integration platforms enable the realization of a broad range of applications and lead to a dramatic cost reduction in the development costs of photonic integrated circuits (PICs). This paper addresses the SMART Photonics generic integration platform developments. The integration technology based on butt joint active-passive epitaxy is shown to achieve a platform without compromising the performance of the different components. The individual components or building blocks are described. A process design kit is established with a comprehensive dataset of simulation and layout information for the building blocks. Latest results on process development and optimization are demonstrated. A big step forward is achieved by applying high-resolution ArF lithography, which leads to increased performance for AWGs and a large increase in reproducibility and yield. The generic nature of the platform is demonstrated by analyzing a number of commercial multiproject wafer runs. It is clear that a large variety of applications is addressed with more than 200 designs from industry as well as academia. A number of examples of PICs are displayed to support this. Finally, the design flow is explained, with focus on layout-aware schematic-driven design flow that is required for complex circuits. It can be concluded that generic integration on InP is maturing fast and with the current developments and infrastructure it is the technology of choice for low cost, densely integrated PICs, ready for high-volume manufacturing.

Vertical organic field-effect transistors (VOFETs) provide an advantage over lateral ones with respect to the possibility to conveniently reduce the channel length. This is beneficial for increasing both the cut-off frequency and current density in organic field-effect transistor devices. We prepared P3HT (poly[3-hexylthiophene-2,5-diyl]) VOFETs with a surrounding gate electrode and gate dielectric around the vertical P3HT pillar junction. Measured output and transfer characteristics do not show a distinct gate effect, in contrast to device simulations. By introducing in the simulations an edge layer with a strongly reduced charge mobility, the gate effect is significantly reduced. We therefore propose that a damaged layer at the P3HT/dielectric interface could be the reason for the strong suppression of the gate effect. We also simulated how the gate effect depends on the device parameters. A smaller pillar diameter and a larger gate electrode-dielectric overlap both lead to better gate control. Our findings thus provide important design parameters for future VOFETs.

Spectrometry is widely used for the characterization of materials, tissues, and gases, and the need for size and cost scaling is driving the development of mini and microspectrometers. While nanophotonic devices provide narrowband filtering that can be used for spectrometry, their practical application has been hampered by the difficulty of integrating tuning and read-out structures. Here, a nano-opto-electro-mechanical system is presented where the three functionalities of transduction, actuation, and detection are integrated, resulting in a high-resolution spectrometer with a micrometer-scale footprint. The system consists of an electromechanically tunable double-membrane photonic crystal cavity with an integrated quantum dot photodiode. Using this structure, we demonstrate a resonance modulation spectroscopy technique that provides subpicometer wavelength resolution. We show its application in the measurement of narrow gas absorption lines and in the interrogation of fiber Bragg gratings. We also explore its operation as displacement-to-photocurrent transducer, demonstrating optomechanical displacement sensing with integrated photocurrent read-out., Fully integratable spectrometers have trade-offs between size and resolution. Here, the authors present a nano-opto-electro-mechanical system where the functionalities of transduction, actuation and detection are fully integrated, resulting in an ultra-compact high-resolution spectrometer with a micrometer-scale footprint.

In this work, the decisive role of rigidity, orientation, and order in the smectic liquid crystalline network on the anisotropic proton and adsorbent properties is reported. The rigidity in the hydrogen-bonded polymer network has been altered by changing the cross-link density, the order by using different mesophases (smectic, nematic, and isotropic phases), whereas the orientation of the mesogens was controlled by alignment layers. Adding more cross-linkers improved the integrity of the polymer films. For the proton conduction, an optimum was found in the amount of cross-linker and the smectic organization results in the highest anhydrous proton conduction. The polymer films show anisotropic proton conductivity with a 54 times higher conductivity in the direction perpendicular to the molecular director. After a base treatment of the smectic liquid crystalline network, a nanoporous polymer film is obtained that also shows anisotropic adsorption of dye molecules and again straight smectic pores are favored over disordered pores in nematic and isotropic networks. The highly cross-linked films show size-selective adsorption of dyes. Low cross-linked materials do not show this difference due to swelling, which decreases the order and creates openings in the two-dimensional polymer layers. The latter is, however, beneficial for fast adsorption kinetics.

In this paper, compact optical subassemblies are demonstrated based on a novel silicon interposer, which is designed and fabricated in a wafer scale process. The interposer includes the design of optical and electrical connections. A low-cost fabrication method, wet etching, is used to define light inputs and outputs as well as create the required recesses in the interposer to embed the chips into the silicon wafer at the same time. Impedance matched traces, for the high speed signals of the CMOS and opto-electronic ICs, are designed using advanced design system software and transferred onto the interposer by photolithography and electro-plating, which are accomplished on the deeply etched topology. The whole process flow of the silicon interposer patterning is designed and demonstrated, and the challenges are discussed. After the process, the optoelectronic dies and their complimentary CMOS parts are flipped and bonded on the interposer in close proximity, and a mechanical optical interface (MOI) is mounted for light coupling. Both transmitter and receiver subassemblies provide 12 parallel optical interconnections, and are scaled down to an area measuring 6 by 8 mm. Signal integrity testing is performed on a probe station for 10 Gb/s data signal delivering clear eye patterns for all channels (in both Rx and Tx subassemblies). The performance is further characterized using bit error rate (BER) testing. Both transmitter and receiver assemblies outperform a reference SFP+, with receiver sensitivity of-10 dBm at a BER lower than 10-12 after compensating for the MOI insertion loss. Finally, we also test the assemblies for crosstalk and demonstrate that the current design has a maximal additional penalty lower than 0.2 and 0.8 dB for transmitter and receiver, respectively.

Nanoscale light sources using metal cavities have been proposed to enable high integration density, efficient operation at low energy per bit and ultra-fast modulation, which would make them attractive for future low-power optical interconnects. For this application, such devices are required to be efficient, waveguide-coupled and integrated on a silicon substrate. We demonstrate a metal-cavity light-emitting diode coupled to a waveguide on silicon. The cavity consists of a metal-coated III–V semiconductor nanopillar which funnels a large fraction of spontaneous emission into the fundamental mode of an InP waveguide bonded to a silicon wafer showing full compatibility with membrane-on-Si photonic integration platforms. The device was characterized through a grating coupler and shows on-chip external quantum efficiency in the 10−4–10−2 range at tens of microamp current injection levels, which greatly exceeds the performance of any waveguide-coupled nanoscale light source integrated on silicon in this current range. Furthermore, direct modulation experiments reveal sub-nanosecond electro-optical response with the potential for multi gigabit per second modulation speeds., Despite much progress, nanoscale light sources suitable for photonic integration are lacking. Here, the authors present a metal-cavity nanopillar LED on a silicon substrate working at telecommunications wavelengths, which demonstrates compatibility with membrane-on-Si photonic integration platforms.

An integrated semiconductor spectral sensor is demonstrated. It is based on an array of resonant- cavity-enhanced photodetectors covering the short-wavelength infrared region. Its robustness and small footprint make this device suitable for on-site spectral sensing applications.

We developed a high-throughput fabrication method of releasable photonic structures for lab-on-fiber technology. Fiber mounting is achieved without additional ma- chining and preserving the device surface. Our concept is demonstrated with sensing ex- periments.

In this paper, an optical switch based on a microelectromechanical phase modulator is presented. Phase tuning is achieved by tuning the vertical gap between two vertically coupled waveguides through the application of a reverse bias on a p-i-n junction. An effective refractive index tuning Δneff of 0.03 and a phase shift of more than 3π rad at telecom wavelengths are measured with an on-chip Mach–Zehnder interferometer (MZI), with a phase-tuning length of only 140 μm. With a bias voltage of 5.1 V, a half-wave-voltage-length product (Vπ L) of 5.6 × 10−3 V·cm is achieved. Furthermore, optical crossbar switching in a MZI is demonstrated with a 15 dB extinction ratio using an actuation voltage of only 4.2 V. Our work provides a solution to on-chip, low-voltage phase modulation and optical switching. The switch is fabricated on an indium-phosphide membrane on a silicon substrate, which enables the integration with active components (e.g., amplifiers, lasers, and detectors) on a single chip.In this paper, an optical switch based on a microelectromechanical phase modulator is presented. Phase tuning is achieved by tuning the vertical gap between two vertically coupled waveguides through the application of a reverse bias on a p-i-n junction. An effective refractive index tuning Δneff of 0.03 and a phase shift of more than 3π rad at telecom wavelengths are measured with an on-chip Mach–Zehnder interferometer (MZI), with a phase-tuning length of only 140 μm. With a bias voltage of 5.1 V, a half-wave-voltage-length product (Vπ L) of 5.6 × 10−3 V·cm is achieved. Furthermore, optical crossbar switching in a MZI is demonstrated with a 15 dB extinction ratio using an actuation voltage of only 4.2 V. Our work provides a solution to on-chip, low-voltage phase modulation and optical switching. The switch is fabricated on an indium-phosphide membrane on a silicon substrate, which enables the integration with active components (e.g., amplifiers, lasers, and detectors) on a single chip.

A nano-opto-electro-mechanical transducer for displacement sensing is presented. It consists of a double-membrane photonic crystal cavity integrated with electro-optical read-out and on-chip light-delivery. The operation is demonstrated by atomic force microscope actuation and photocurrent sensing.

The interfacial Dzyaloshinksii-Moriya interaction (iDMI) is of great interest in thin-film magnetism because of its ability to stabilize chiral spin textures. It can be quantified by investigating the frequency non-reciprocity of oppositely propagating spin waves. However, as the iDMI is an interface interaction the relative effect reduces when the films become thicker making quantification more difficult. Here, we utilize all-electrical Propagating Spin Wave Spectroscopy (PSWS) to disentangle multiple contributions to spin wave frequency non-reciprocity to determine the iDMI. This is done by investigating non-reciprocities across a wide range of magnetic layer thicknesses (from 4 to 26 nm) in Pt/Co/Ir, Pt/Co/Pt, and Ir/Co/Pt stacks. We find the expected sign change in the iDMI when inverting the stack order, and a negligible iDMI for the symmetric Pt/Co/Pt. We additionally extract a difference in surface anisotropies and find a large contribution due to the formation of different crystalline phases of the Co, which is corroborated using nuclear magnetic resonance and high-resolution transmission-electron-microscopy measurements. These insights will open up new avenues to investigate, quantify and disentangle the fundamental mechanisms governing the iDMI, and pave a way towards engineered large spin-wave non-reciprocities for magnonic applications., 12 pages, 2 figures

In this paper we review the recent developments in the nanophotonic platform IMOS. High-performance optical amplifier based on twin-guide active-passive integration scheme has been demonstrated, enabling continuous wave operated lasers on IMOS. Future work will seek to integrate more advanced components, such as $> \mathrm{67GHz}$ detectors, polarization controllers and optical modulators in the same membrane.