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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 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.

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.

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.

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 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.

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.

Hydrogen-doped indium oxide (In2O3:H) has emerged as a highly transparent and conductive oxide, finding its application in a multitude of optoelectronic devices. Recently, we have reported on an atomic layer deposition (ALD) process to prepare high quality In2O3:H. This process consists of ALD of In2O3:H films at 100 °C, followed by a solid phase crystallization step at 150–200 °C. In this work, we report on a detailed electron microscopy study of this crystallization process which reveals new insights into the crucial aspects for achieving the large grain size and associated excellent properties of the material. The key finding is that the best optoelectronic properties are obtained by preparing the films at the lowest possible temperature prior to post-deposition annealing. Electron microscopy imaging shows that such films are mostly amorphous, but feature a very low density of embedded crystallites. Upon post-deposition annealing, crystallization proceeds merely from isotropic crystal grain growth of these embedded crystallites rather than by the formation of additional crystallites. The relatively high hydrogen content of 4.2 at. % in these films is thought to cause the absence of additional nucleation, thereby rendering the final grain size and optoelectronic properties solely dependent on the density of embedded crystallites. The temperature-dependent grain growth rate has been determined, from which an activation energy of (1.39 ± 0.04) eV has been extracted. Finally, on the basis of the observed crystallization mechanism, a simple model to fully describe the crystallization process has been developed. This model has been validated with a numerical implementation thereof, which accurately predicts the observed temperature-dependent crystallization behaviour.

We introduce an alternative type of probe for scanning tunneling microscopy (STM). Instead of using a needle-like tip made from a piece of metallic wire, a sharp-edged cleaved insulating substrate, which is initially covered by a thin conductive film, is used. The sharp tip is formed at the intersection of the two cleaved sides. Using this approach a variety of materials for STM probes can be used, and functionalization of STM probes is possible. The working principle of different probes made of metallic (Pt, Co, and CoB), indium-tin oxide, as well as Cu/Pt and Co/Pt multilayer films are demonstrated by STM imaging of clean Cu(001) and Cu(111) surfaces as well as the epitaxial Co clusters on Cu(111).

Recent advances in MEMS technology have brought forward a new class of high-density stretchable/flexible electronics as well as large displacement MEMS devices. The in-situ electro-mechanical characterization of such devices is challenging since it requires: (i) highly delicate sample handling, (ii) controlled application of large (hundreds of µm) multi-axial displacements to mimic service conditions, (iii) integrated electrical testing and (iv) fast actuation for cyclic testing. Techniques already developed for small-scale testing in literature fall short to meet the combined set of requirements. To this end, a characterization methodology that fulfills all these requirements is developed and presented here. The technique is based on a piezo-driven micro-tensile stage, which provides large multi-axial displacements with high resolution and fast actuation (4000 µm/s). This is combined with a method for sample microfabrication on a test-chip to warrant delicate sample handling. Proof-of-principle experiments are shown for multi-axial mechanical characterization, electrical characterization and high cycle fatigue testing of micron-sized highly stretchable interconnects. Experiments are conducted under in-situ microscopic observation using optical microscopy, scanning electron microscopy, and high-resolution profilometry. The generic platform proposed here can be used for other problems where similar requirements are faced, e.g. other miniaturized, large displacement electro-mechanical applications that are currently being developed.

Miniaturization of displacement sensors for nanoscale metrology is a key requirement in many applications such as accelerometry, mass sensing, and atomic force microscopy. While optics provides high resolution and bandwidth, integration of sensor readout is required to achieve low-cost, compact, and parallelizable devices. Here, we present a novel integrated opto-electro-mechanical device for displacement sensing that has sub-nanometer resolution. The proposed sensor is a micron-sized double-membrane photonic crystal cavity with integrated electro-optical readout, directly addressed via an on-chip waveguide. This sensor displays a noise floor down to 7 fm/Hz and is suitable for the realization of integrated arrays.

An array of monolithic wide-tunable lasers is integrated using selective area growth to shift the bandgap of their gain section. A gap-free tuning is demonstrated from the combination of the tuning ranges of the lasers, and single-mode operation is verified.

Selective area growth is used for the first time in the TU/e generic integration platform to modify independently the bandgap of active sections. A chip combining 4 tunable lasers with shifted wavelength ranges has been fabricated. A 96 nm wide tuning range is demonstrated.

A negatively-chirped InP-MZM modulated by a 1-Vpp PAM4 signal enables 112Gbit/s/λ data transmission with reduced digital processing complexity. SSMF-links longer than 3-km (KP4-preFEC) or 4-km (HD-preFEC) without digital dispersion pre/post compensation are successfully demonstrated.

ArF deep UV (193 nm) lithography was successfully applied to fabricate Arrayed Waveguide Gratings in generic Indium Phosphide technology. The sub-dB transmission losses demonstrate the advantages of scaling down the minimum feature size to 100 nm.

The influence of the use of on-wafer probes for mm-wave antenna-on-chip (AoC) measurements is investigated. On-wafer probes are widely used for analyzing integrated circuits. Although not specifically designed for this, on-wafer probes are also commonly used to characterize AoCs. The probe design provided a transition from coaxial cable to co-planar waveguide. As a test case, a monopole AoC is used to demonstrate several effects that influence an accurate calibration of the test set-up. It is shown that on-chip calibration is preferred and provides more accurate de-embedding of parasitic effects. In addition, it is shown that the polarization purity is seriously affected by the coupling between AoC and probe tip.

Ultracompact optical submodules for parallel optical interconnects are demonstrated based on a three-level silicon interposer, which is fabricated through a low-cost wet etching process. Using three steps of wet etching of silicon, a multilevel cavity is formed for embedding and flip-chipping optical and electrical dies, and opening optical through-silicon vias. In order to reduce thermal coupling between CMOS and GaAs dies, a 50- $\mu \text{m}$ thermal isolation air gap is formed between dies as a part of the assembly concept, and thermal simulations and experiments are carried to validate its effectiveness. Based on this 3-D packaging concept, compact 4 mm $\times6$ mm, 10-Gb/s 12-channel transmitter and receiver submodules are fully assembled and tested. Clear and uniform eye patterns for both modules are captured at 10 and 15 Gb/s for every channel. Bit error rate (BER) testing is also performed. Both transmitter and receiver submodules show uniform BER curves, with receiver sensitivity spreading less than 1 dB at a BER lower than 10−12. Also, crosstalk for both modules is tested, yielding only a 0.1- and 0.8-dB additional penalty for transmitter and receiver, respectively.

We present finite difference thermal modeling to predict temperature distribution, heat flux, and thermal resistance inside lasers with different waveguide geometries. We provide a quantitative experimental and theoretical comparison of the thermal behavior of shallow-ridge (SR) and buried-heterostructure (BH) lasers. We investigate the influence of a split heat source to describe p-layer Joule heating and nonradiative energy loss in the active layer and the heat-sinking from top as well as bottom when quantifying thermal impedance. From both measured values and numerical modeling we can quantify the thermal resistance for BH lasers and SR lasers, showing an improved thermal performance from 50K/W to 30K/W for otherwise equivalent BH laser designs.

We report a novel type of monolithically integrated tunable semiconductor laser. The tuning is achieved by three intracavity Mach–Zehnder interferometers, realized in passive waveguides and using voltage-controlled electro-optic phase modulators requiring only four control voltages. The potential of the design is demonstrated by a realized laser system that shows an optical linewidth of 363 kHz, output power of 3 mW, and a record tuning range of 74.3 nm. Such a continuous wavelength span is in excess of any monolithic semiconductor laser reported up to date. Precision of the tuning mechanism is demonstrated by a scan over a 0.89-GHz-wide absorption line of acetylene. The laser design is suitable for a number of applications, including gas spectroscopy, telecommunication, and optical coherence tomography. The laser has been fabricated in a multi-project wafer run on an indium phosphide-based generic photonic foundry platform and demonstrates the potential of these technology platforms.

InP PIC technologies offer unsurpassed optoelectronic performance and are a key enabler for high-performance optical transceivers. InP lasers are the default solution for the communications lasers operating in the 1300–1600 nm wavelength window. As integration technologies continue to mature and information rates scale up, increasingly sophisticated monolithic techniques are deployed for both discrete devices and integrated circuits for longer-reach networking and higher data rates. The possibility to engineer the band gap across the wafer delivers a rich range of functions in an ever-decreasing footprint. Lasers are combined with additional devices such as modulators, multiplexers, detectors and hybrids within the same chip. Wafer scale production offers a proven route to cost-effective, high-volume production. Monolithic integration reduces cost through reduced test time and simplified assembly and packaging. This chapter reviews the techniques, capabilities and future potential for InP-integrated photonics with a particular reference to requirements in the rapidly evolving data interconnect market, driven in particular by data centres, where energy efficiency, bandwidth and volume production are crucial.

The potential of structuring thermoplastic polymers by convection only, using a combination of static mixer elements, which easily produce stratified structures with thousands of layers, and the black box concept that serves to elegantly combine materials in standard co-extrusion technology is investigated. The aim is to obtain an alternative for routes that try to structure organic matter such as polymers down to submicrometer levels, usually via self-organization based on phase separation. Structure is characterized by its complexity, here defined by the level of hierarchy. Horizontal stratification, parallel to the surface, is level 0. Vertical stratification connected to horizontal surface layers, is level 1. A series of horizontal stratifications in distinct places vertically connected to the surface layers is level 2. Higher levels of hierarchy finally result in dendritic structures that are fractal. Applications of complex structures with a huge interface and guaranteed cocontinuity throughout the whole cross section of the products are found in, for example, membranes for fuel cells and gas separators, and in miniaturizing electronic and optical devices such as photovoltaic cells. (Figure presented.).

In this paper, we propose a novel way for 3D packaging of optical and electrical dies for parallel optical interconnections based on wet etched silicon interposer. The process flow of silicon interposer fabrication is demonstrated. Through three steps of deeply wet etching of silicon, a multi-level cavity is formed for embedding and flip-chipping of optical die and electrical die, and the optical through silicon vias for optical I/Os are opened. After flip chip bonding, a designed 50 µm air gap is formed between electronics and optics for thermal isolation. The heat transfer is also simulated to validate the thermal isolation air gap between dies. After fabricating, a 10 Gbps 12-channel receiver is assembled on the silicon interposer, and the sub-module is scaled down to 4 mm by 6 mm. The performance of the fully assembled sub-module is tested on a probe station. Clear eye patterns are captured for each channel. Bit error rate (BER) testing is also performed showing uniform BER with performance matching that of commercial MM receiver.

We report charge transport measurements in nanoscale vertical pillar structures incorporating ultrathin layers of the organic semiconductor poly(3-hexylthiophene)(P3HT). P3HT layers with thickness down to 5 nm are gently top-contacted using wedging transfer, yielding highly reproducible, robust nanoscale junctions carrying high current densities (up to $10^6$ A/m$^2$). Current-voltage data modeling demonstrates excellent hole injection. This work opens up the pathway towards nanoscale, ultrashort-channel organic transistors for high-frequency and high-current-density operation., Comment: 30 pages, 8 figures, 1 table

In this paper a generic monolithic photonic integration technology platform and tunable laser devices for gas sensing applications at 2 μm will be presented. The basic set of long wavelength optical functions which is fundamental for a generic photonic integration approach is realized using planar, but-joint, active-passive integration on indium phosphide substrate with active components based on strained InGaAs quantum wells. Using this limited set of basic building blocks a novel geometry, widely tunable laser source was designed and fabricated within the first long wavelength multiproject wafer run. The fabricated laser operates around 2027 nm, covers a record tuning range of 31 nm and is successfully employed in absorption measurements of carbon dioxide. These results demonstrate a fully functional long wavelength photonic integrated circuit that operates at these wavelengths. Moreover, the process steps and material system used for the long wavelength technology are almost identical to the ones which are used in the technology process at 1.5μm which makes it straightforward and hassle-free to transfer to the photonic foundries with existing fabrication lines. The changes from the 1550 nm technology and the trade-offs made in the building block design and layer stack will be discussed.

In this paper, we present the detailed characterization of a semiconductor ring passively mode-locked laser with a 20 GHz repetition rate that was realized as an indium phosphide based photonic integrated circuit (PIC). Various dynamical regimes as a function of operating conditions were explored in the spectral and time domain. A record bandwidth of the optical coherent comb from a quantum well based device of 11.5 nm at 3 dB and sub-picosecond pulse generation is demonstrated.

In this Letter, we present a method to prepare a mixed electron-beam resist composed of a positive resist (ZEP520A) and C 60 fullerene. The addition of C 60 to the ZEP resist changes the material properties under electron beam exposure significantly. An improvement in the thermal resistance of the mixed material has been demonstrated by fabricating multimode interference couplers and coupling regions of microring resonators. The fabrication of distributed Bragg reflector structures has shown improvement in terms of pattern definition accuracy with respect to the same structures fabricated with normal ZEP resist. Straight InP membrane waveguides with different lengths have been fabricated using this mixed resist. A decrease of the propagation loss from 6.6 to 3.3¿¿dB/cm has been demonstrated.

Grating couplers are widely used to couple light between photonic integrated circuits and optical fibers. Here, we fabricate and characterize a device based on a buried metal grating. In contrast to dielectric gratings, simulations predict strongly reduced parasitic leakage of light to the substrate and are performance independent of the optical buffer thickness, while using standard fabrication processes with high yield. The gratings show a 3 dB bandwidth of 61 nm and chip-to-fiber coupling efficiency of 54%, which makes them attractive building blocks for on-wafer testing and dense optical interconnects.

We demonstrate an efficiency enhancement of an InP nanowire (NW) axial p-n junction solar cell by cleaning the NW surface. NW arrays were grown with in situ HCl etching on an InP substrate patterned by nanoimprint lithography, and the NWs surfaces were cleaned after growth by piranha etching. We find that the postgrowth piranha etching is critical for obtaining a good solar cell performance. With this procedure, a high diode rectification factor of 10(7) is obtained at ±1 V. The resulting NW solar cell exhibits an open-circuit voltage (Voc) of 0.73 V, a short-circuit current density (Jsc) of 21 mA/cm(2), and a fill factor (FF) of 0.73 at 1 sun. This yields a power conversion efficiency of up to 11.1% at 1 sun and 10.3% at 12 suns.

We demonstrated for the first time an azimuthally polarized laser source from an electrically driven metallic cavity nanolaser with a physical cavity volume of 0.146 ¿3 (¿¿=¿1416¿nm). Single TE01 mode lasing at 78¿K was achieved by taking the advantages of the large free spectral range in such nanoscale lasers and the azimuthal polarization of lasing emission was verified experimentally. Mode shift controlled by device cavity radius was observed over a large wavelength range from 1.37¿µm to 1.53¿µm. Such metallic cavity nanolaser provides a compact electrically driven laser source for azimuthally polarized beam.

Metallic-Cavity lasers or plasmonic nanolasers of sub-wavelength sizes have attracted great attentions in recent years, with the ultimate goal of achieving continuous wave (CW), room temperature (RT) operation under electrical injection. Despite great efforts, a conclusive and convincing demonstration of this goal has proven challenging. By overcoming several fabrication challenges imposed by the stringent requirement of such small scale devices, we were finally able to achieve this ultimate goal. Our metallic nanolaser with a cavity volume of 0.67{\lambda}3 ({\lambda}=1591 nm) shows a linewidth of 0.5 nm at RT, which corresponds to a Q-value of 3182 compared to 235 of the cavity Q, the highest Q under lasing condition for RT CW operation of any sub-wavelength laser. Such record performance provides convincing evidences of the feasibility of RT CW metallic nanolasers, thus opening a wide range of practical possibilities of novel nanophotonic devices based on metal-semiconductor structures., Comment: This paper has been withdrawn by the author after the final publication in Optics Express, 21, 4728(2013)

Photovoltaic cells based on arrays of semiconductor nanowires promise efficiencies comparable or even better than their planar counterparts with much less material. One reason for the high efficiencies is their large absorption cross section, but until recently the photocurrent has been limited to less than 70% of the theoretical maximum. Here we enhance the absorption in indium phosphide (InP) nanowire solar cells by employing broadband forward scattering of self-aligned nanoparticles on top of the transparent top contact layer. This results in a nanowire solar cell with a photovoltaic conversion efficiency of 17.8% and a short-circuit current of 29.3 mA/cm2 under 1 sun illumination, which is the highest reported so far for nanowire solar cells and among the highest reported for III–V solar cells. We also measure the angle-dependent photocurrent, using time-reversed Fourier microscopy, and demonstrate a broadband and omnidirectional absorption enhancement for unpolarized light up to 60° with a wavelength average of 12% due to Mie scattering. These results unambiguously demonstrate the potential of semiconductor nanowires as nanostructures for the next generation of photovoltaic devices.

Approaching the theoretically limiting open circuit voltage (V-oc) of solar cells is crucial to optimize their photovoltaic performance. Here, we demonstrate experimentally that nanostructured layers can achieve a fundamentally larger Fermi level splitting, and thus a larger V-oc, than planar layers. By etching tapered nanowires from planar indium phosphide (InP), we directly compare planar and nanophotonic geometries with the exact same material quality. We show that the external radiative efficiency of the nanostructured layer at 1 sun is increased by a factor 14 compared to the planar layer, leading to a 70 mV enhancement in V-oc. The higher voltage arises from both the enhanced outcoupling of photons, which promotes radiative recombination, and the lower active material volume, which reduces bulk recombination. These effects are generic and promise to enhance the efficiency of current record planar solar cells made from other materials as well.

Adding photonic functions to silicon electronics has become an important research theme in the last decade. Here we present an approach based on heterogeneously integrating an indium phosphide based membrane on silicon. Within this membrane we realized a range of photonic functions with competitive performances: lasers, fast detectors, waveguides, filters, couplers, modulators etc. This contribution describes the technologies and the results.

Progress on the development of a long wavelength (∼2 µm) generic monolithic photonic integration technology on indium phosphide substrate and a novel concept of a tunable laser realized as a photonic integrated circuit using such technology are presented. Insights into the development of active and passive waveguide structures which are used to define a limited set of on-chip functionalities in the form of building blocks will be given. A novel tunable laser was proposed and designed using such predefined set of basic building blocks. The laser geometry features an intra-cavity wavelength tuning mechanism based on asymmetric Mach-Zehnder interferometers in a nested configuration. The photonic integrated circuit chip was fabricated within the first long wavelength multi-project wafer run. The experimental evaluations of the fabricated device show a record tuning range of 31 nm around 2027 nm and successful measurements of a 0.86 GHz wide absorption line of carbon dioxide. These results provide a demonstration of a fully functional photonic integrated circuit operating at wavelengths that are much longer than those in the typical telecommunication windows as well as the use of indium phosphide based generic photonic integration technologies for gas sensing applications.

Monolithic integration of four widely tunable extended cavity lasers suitable for gas detection is presented. Each laser features a precise, grid-less tuning mechanism with a low-linewidth, single-mode output over a wide wavelength range of 74nm.

We investigated the passivation of III-V semiconductor nanostructures using wet-chemical ammonium sulfide treatment and SiOx encapsulation. We achieved an ultra-low surface recombination velocity value of ~530 cm/s enabling the future development of high-performance room-temperature nanolasers.

We present a 26 nm tunable Coupled Cavity Laser based on a novel interferometer and fabricated in a low-cost generic foundry process, with SMSR above 40 dB and fibre coupled power > 5mW.

We report the experimental demonstration of two coupled laser cavities via self-imaging interference in a multimode waveguide. The coupling is optimized by considering images formed by two coherent phase-delayed signals at the input of a 3×3 splitter. As a result, the complex transfer coefficients of the coupling element can be chosen to increase the mode selectivity of the coupled system. A demonstration is given by the successful fabrication of a tunable laser with a side-mode suppression ratio (SMSR) up to 40 dB and a 6.5 nm tuning range. The laser delivers milliwatts of output power to a lensed fiber and is fully compatible with processes supporting vertically-etched sidewalls.

Generic InP foundry processes allow monolithic integration of active and passive elements into a common p-n doped layerstack. The passive loss can be greatly reduced by restricting the p-dopant to active regions. We report on a localized Zn-diffusion process based on MOVPE, which allows to reduce waveguide loss from 2 dB/cm to below 0.4 dB/cm. We confirm this value by fabrication of a 73 mm long spiral ring resonator, with a record quality factor of 1.2 million and an extinction ratio of 9.7 dB.

A tunable laser for single line gas spectroscopy is realized as a monolithic photonic integrated circuit in an InP based generic foundry platform. The laser operates at wavelengths around 2.0 μm and has a tuning range of 22 nm.

We experimentally demonstrate a laser with weak optical feedback, which shows broad regions of operation without relaxation-oscillation induced instabilities. Here, the side mode suppression is above 40 dB, independent of the feedback phase.

We report on an integrated approach to obtain multiwavelength emission from semiconductor ring lasers with filtered optical feedback. The filtered feedback is realized on-chip employing two arrayed-waveguide gratings to split/recombine light into different wavelength channels. Through experimental observations and numerical simulations, we find that the effective gain of the different modes is the key parameter which has to be balanced in order to achieve multiwavelength emission. This can be achieved by tuning the injection current in each amplifier.

Wavelength tunable and switchable lasers are widely used in telecommunication networks as they allow flexible wavelength division multiplexing, fast optical signal routing, and all-optical signal processing. In this work, we characterize the wavelength switching speed of a tunable semiconductor ring lasers using filtered optical feedback. Semiconductor ring lasers nowadays are promising sources in photonic integrated circuits because they do not require cleaved facets or mirrors to form a laser cavity. They are interesting from a nonlinear dynamics point of view due to the existence of two counter propagating modes that interact with each other which allows semiconductor ring lasers to be used as all-optical switches and as all-optical memories. The wavelength of the semiconductor ring laser is controlled by a feedback section which consists of two arrayed waveguide gratings, four semiconductor optical amplifiers and waveguides to connect the different components. The filtered optical feedback is realized by employing the two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback strength of each wavelength channel independently. The switching is achieved by changing the currents injected in the semiconductor optical amplifier gates. Experimentally, we observe a wavelength transition time of 5 ns. However, we also noticed a non-negligible delay in the switching process. We discuss this delay time and the different parameters which have an effect on it. We can numerically reproduce the experimental results using rate equations taking into account the effect of spontaneous emission. The simulations also demonstrate that the wavelength transition time and the delay can be further decreased by controlling the phase in the feedback section and by increasing the strength of the feedback.

Coupling of two Fabry-Perot cavities via a 3x3 Multimode Interference Reflector is presented. We measure SMSR close to 40 dB and a tuning range of 7 nm for 1.2 mm cavities with 5% length difference.

Using monolithic integration technology we have designed and fabricated tunable lasers in the 1.5 µm region with a demonstrated tuning range of 60 nm and single mode operation. This performance is achieved using intracavity tunable Mach-Zehnder interferometers that use voltage controlled phase modulators. In this paper we will discuss design considerations and advantages of such tunable lasers.