Photonic Circuitry Research Articles

Integrated on Chip Platform with Quantum Emitters in Layered Materials

AbstractIntegrated quantum photonic circuitry is an emerging topic that requires efficient coupling of quantum light sources to waveguides and optical resonators. So far, great effort is devoted to engineering on‐chip systems from 3D crystals such as diamond or gallium arsenide. In this study, room‐temperature coupling is demonstrated of quantum emitters embedded in layered hexagonal boron nitride to an on‐chip aluminum nitride waveguide. 1.35% light coupling efficiency is achieved in the device and transmission of single photons through the waveguide is demonstrated. The results serve as foundation for integrating layered materials to on‐chip components and realizing integrated quantum photonic circuitry.

High power GaInNAs superluminescent diodes emitting over 400 mW in the 1.2 μm wavelength range

A high-power superluminescent diode emitting over 400 mW in the 1.2 μm range is reported. The active region is based on a single GaInNAs/GaAs quantum well positioned within a low-confinement vertical waveguide and a lateral ridge waveguide geometry, ensuring single transverse mode operation. The peak wall-plug efficiency and the differential efficiency in the linear region were 22.8% and 0.38 W/A, respectively. The full width at half-maximum spectral width for the maximum output power was 22 nm, corresponding to a spectral power density of 19 mW/nm, a threefold increase compared to continuous wave superluminescent diodes based on a quantum dot active region operating in the same wavelength range. Besides exhibiting excellent optical and electrical properties, the GaInNAs active region enhances operation at elevated temperatures. In this respect, an output power of about 210 mW is demonstrated at operation temperatures as high as 60 °C, while 150 mW is still emitted at 70 °C. The unique combination of parameters demonstrated makes these GaInNAs QW-based superluminescent diodes particularly attractive for hybrid integration with silicon photonic circuitry, enabling the demonstration of compact solutions for sensing, optical coherence tomography, and other emerging concepts exploiting photonic integration technology and requiring single transversal mode operation, good efficiency, broadband high spectral power density, and uncooled operation at elevated temperatures.

Scalable Quantum Integrated Circuits on Superconducting Two-Dimensional Electron Gas Platform

To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrier-free interface between two different materials is necessary. The S-Sm junction with high interface transparency will then facilitate the observation of the induced hard superconducting gap, which is the key requirement to access the topological phases (TPs) and observation of exotic quasiparticles such as Majorana zero modes (MZM) in hybrid systems. A material platform that can support observation of TPs and allows the realization of complex and branched geometries is therefore highly demanding in quantum processing and computing science and technology. Here, we introduce a two-dimensional material system and study the proximity induced superconductivity in semiconducting two-dimensional electron gas (2DEG) that is the basis of a hybrid quantum integrated circuit (QIC). The 2DEG is a 30 nm thick In0.75Ga0.25As quantum well that is buried between two In0.75Al0.25As barriers in a heterostructure. Niobium (Nb) films are used as the superconducting electrodes to form Nb- In0.75Ga0.25As -Nb Josephson junctions (JJs) that are symmetric, planar and ballistic. Two different approaches were used to form the JJs and QICs. The long junctions were fabricated photolithographically, but e-beam lithography was used for short junctions’ fabrication. The coherent quantum transport measurements as a function of temperature in the presence/absence of magnetic field B are discussed. In both device fabrication approaches, the proximity induced superconducting properties were observed in the In0.75Ga0.25As 2DEG. It was found that e-beam lithographically patterned JJs of shorter lengths result in observation of induced superconducting gap at much higher temperature ranges. The results that are reproducible and clean suggesting that the hybrid 2D JJs and QICs based on In0.75Ga0.25As quantum wells could be a promising material platform to realize the real complex and scalable electronic and photonic quantum circuitry and devices.

Scalable Quantum Integrated Circuits on Superconducting Two-Dimensional Electron Gas Platform.

To form a coherent quantum transport in hybrid superconductor-semiconductor (S-Sm) junctions, the formation of a homogeneous and barrier-free interface between two different materials is necessary. The S-Sm junction with high interface transparency will then facilitate the observation of the induced hard superconducting gap, which is the key requirement to access the topological phases (TPs) and observation of exotic quasiparticles such as Majorana zero modes (MZM) in hybrid systems. A material platform that can support observation of TPs and allows the realization of complex and branched geometries is therefore highly demanding in quantum processing and computing science and technology. Here, we introduce a two-dimensional material system and study the proximity induced superconductivity in semiconducting two-dimensional electron gas (2DEG) that is the basis of a hybrid quantum integrated circuit (QIC). The 2DEG is a 30 nm thick In0.75Ga0.25As quantum well that is buried between two In0.75Al0.25As barriers in a heterostructure. Niobium (Nb) films are used as the superconducting electrodes to form Nb- In0.75Ga0.25As -Nb Josephson junctions (JJs) that are symmetric, planar and ballistic. Two different approaches were used to form the JJs and QICs. The long junctions were fabricated photolithographically, but e-beam lithography was used for short junctions' fabrication. The coherent quantum transport measurements as a function of temperature in the presence/absence of magnetic field B are discussed. In both device fabrication approaches, the proximity induced superconducting properties were observed in the In0.75Ga0.25As 2DEG. It was found that e-beam lithographically patterned JJs of shorter lengths result in observation of induced superconducting gap at much higher temperature ranges. The results that are reproducible and clean suggesting that the hybrid 2D JJs and QICs based on In0.75Ga0.25As quantum wells could be a promising material platform to realize the real complex and scalable electronic and photonic quantum circuitry and devices.

Nanowires for Photonics.

All-photonic integrated circuits are promising platforms for future systems beyond the limitation of Moore's law. Over the last several decades, one-dimensional (1D) nanowires have demonstrated great potential in photonic circuitry because of their unique 1D structure to effectively generate and tightly confine optical signals as well as easily tunable optical properties. In this Review, we categorize nanowires based on the optical properties (i.e., semiconducting, metallic, and dielectric nanowires) for their potential photonic applications (as light emitters or plasmonic and photonic waveguides). We further discuss the recent efforts in integration of nanowire-based photonic elements toward next-generation optical information processors. However, there are still several challenges remaining before the nanowires are fully utilized as photonic building blocks. The scientific and technical challenges and outlooks are provided to indicate the future directions.

Generation and sampling of quantum states of light in a silicon chip

Implementing large instances of quantum algorithms requires the processing of many quantum information carriers in a hardware platform that supports the integration of different components. While established semiconductor fabrication processes can integrate many photonic components, the generation and algorithmic processing of many photons has been a bottleneck in integrated photonics. Here we report the on-chip generation and processing of quantum states of light with up to eight photons in quantum sampling algorithms. Switching between different optical pumping regimes, we implement the Scattershot, Gaussian and standard boson sampling protocols in the same silicon chip, which integrates linear and nonlinear photonic circuitry. We use these results to benchmark a quantum algorithm for calculating molecular vibronic spectra. Our techniques can be readily scaled for the on-chip implementation of specialised quantum algorithms with tens of photons, pointing the way to efficiency advantages over conventional computers.

Enhancing second-harmonic generation using dipolar-parity modes in non-planar plasmonic nanocavities

There is an active demand to develop efficient nanoscale nonlinear sources for applications in photonic circuitry, quantum optics, and biosensing. To this end, plasmonic systems have been utilized to boost the nonlinear signal generation; however, high efficiencies of frequency conversion for realistic applications remain a challenge. Metal-insulator-metal (MIM) nanocavities are good candidates for strongly concentrating the fields at the nanoscale to enhance the optical nonlinearities; however, they typically suffer from the requirement to have a quadrupolar resonance at the emission wavelength. Here we introduce non-planar MIM nanocavities with a nonlinear spacer that can strongly enhance the second-harmonic generation (SHG), despite having fundamental and emission modes of the same parity. Our experimental and numerical results indicate that the enhancement is due to the non-planar design of the cavities and the bulk nonlinearity of the spacer layer.

Enhancing functionalities of atomically thin semiconductors with plasmonic nanostructures

Abstract Atomically thin, two-dimensional, transition-metal dichalcogenide (TMD) monolayers have recently emerged as a versatile platform for optoelectronics. Their appeal stems from a tunable direct bandgap in the visible and near-infrared regions, the ability to enable strong coupling to light, and the unique opportunity to address the valley degree of freedom over atomically thin layers. Additionally, monolayer TMDs can host defect-bound localized excitons that behave as single-photon emitters, opening exciting avenues for highly integrated 2D quantum photonic circuitry. By introducing plasmonic nanostructures and metasurfaces, one may effectively enhance light harvesting, direct valley-polarized emission, and route valley index. This review article focuses on these critical aspects to develop integrated photonic and valleytronic applications by exploiting exciton–plasmon coupling over a new hybrid material platform.

Single-Mode Lasing from Imprinted Halide-Perovskite Microdisks.

Halide-perovskite microlasers have demonstrated fascinating performance owing to their low-threshold lasing at room temperature and low-cost fabrication. However, being synthesized chemically, controllable fabrication of such microlasers remains challenging, and it requires template-assisted growth or complicated nanolithography. Here, we suggest and implement an approach for the fabrication of microlasers by direct laser ablation of a thin film on glass with donut-shaped femtosecond laser beams. The fabricated microlasers represent MAPbBr xI y microdisks with 760 nm thickness and diameters ranging from 2 to 9 μm that are controlled by a topological charge of the vortex beam. As a result, this method allows one to fabricate single-mode perovskite microlasers operating at room temperature in a broad spectral range (550-800 nm) with Q-factors up to 5500. High-speed fabrication and reproducibility of microdisk parameters, as well as a precise control of their location on a surface, make it possible to fabricate centimeter-sized arrays of such microlasers. Our finding is important for direct writing of fully integrated coherent light sources for advanced photonic and optoelectronic circuitry.

A dependency of emission efficiency of poly-silicon light-emitting device on avalanching current

A novel polysilicon light emitting device (LED) was realized in a standard complementary metal oxide semiconductor (CMOS) process that is based on a p-n junction reverse bias configuration. This LED can emit visible light based on the reverse bias p-n junctions in the dark. The central emitting doped structure element of this LED is n+-p-n+-p-n+ stacked layout, which is similar to two reverse bias p-n junctions and two forward bias p-n junctions connected in series. The device mechanism for the visible light emitting process is defined by means of an avalanche breakdown process that occurs between the highly doped n+ region and the lightly doped p region in the reverse bias p-n junctions. By using hot carriers generated in avalanche process, the emission spectrum from the device exhibits a wide spectrum whose wavelength range is from 400 nm to 900 nm at an operating voltage of 16 V. We compare the designed light intensities at the different wavelengths in other to obtain the dependency of the light emission at various wavelengths under different currents conditions. From the experimental observations, and based on the calculation of the quantum efficiency and power conversion efficiencies as related to the light emission, we confirmed that this particular LED has a better efficiency than three-terminal gated diode. The silicon light source could find some applications in on-chip optical interconnect and in electro-optical conversions in future all-silicon integrated photonic circuitry.

Hollow Core Light Cage: Trapping Light Behind Bars

Optical waveguides represent the key element of integrated planar photonic circuitry having revolutionized many fields of photonics ranging from telecommunications, medicine, environmental science, and light generation. However, the use of solid cores imposes limitations on applications demanding strong light–matter interaction within low permittivity media such as gases or liquids, which has triggered substantial interest toward hollow core waveguides. Here, we introduce the concept of an on-chip hollow core light cage that consists of free-standing arrays of cylindrical dielectric strands around a central hollow core implemented using 3D nanoprinting. The cage operates by an antiresonant guidance mechanism and exhibits extraordinary properties such as (1) diffractionless propagation in “quasi-air” over more than a centimeter distance within the ultraviolet, visible and near-infrared spectral domains, (2) unique side-wise direct access to the hollow core via open spaces between the strands speeding up ga...

Spatially-Controllable Hot Spots for Plasmon-Enhanced Second-Harmonic Generation in AgNP-ZnO Nanocavity Arrays.

Plasmon-enhanced second-harmonic generation (PESHG) based on hybrid metal-dielectric nanostructures have extraordinary importance for developing efficient nanoscale nonlinear sources, which pave the way for new applications in photonic circuitry, quantum optics, and biosensors. However, the relatively high loss of excitation energies and the low spatial overlapping between the locally enhanced electromagnetic field and nonlinear materials still limit the promotion of nonlinear conversion performances in such hybrid systems. Here, we design and fabricate an array of silver nanoparticle-ZnO (AgNP-ZnO) nanocavities to serve as an efficient PESHG platform. The geometry of AgNP-ZnO nanocavity arrays provides a way to flexibly modulate hot spots in three-dimensional space, and to achieve a good mutual overlap of hot spots and ZnO material layers for realizing efficient SH photon generation originating from ZnO nanocavities. Compared to bare ZnO nanocavity arrays, the resulting hybrid AgNP-ZnO design of nanocavities reaches the maximum PESHG enhancement by a factor of approximately 31. Validated by simulations, we can further interpret the relative contribution of fundamental and harmonic modes to Ag-NP dependent PESHG performances, and reveal that the enhancement stems from the co-cooperation effect of plasmon-resonant enhancements both for fundamental and harmonic frequencies. Our findings offer a previously unreported method for designing efficient PESHG systems and pave a way for further understanding of a surface plasmon-coupled second-order emission mechanism for the enhancement of hybrid systems.

Thin film diamond membranes bonded on-demand with SOI ring resonators

The hybrid integration of single-crystal (SC) diamond membranes with on-chip optical devices has the potential to service many applications, spanning non-linear optics to quantum photonics with embedded diamond colour centres. Limited dimensions of high optical quality diamond however restrict the size and number of devices that can be fabricated on a single chip, which impedes the use of diamond in large photonic integrated circuitry. Here we show the fabrication and integration of a 1 μm thick SC diamond membrane with a silicon photonic device. The quality of the diamond-silicon interface is measured using SEM and optical techniques. Silicon microring resonators are measured after integration with the diamond film and show a low excess loss of 0.4 dB and a group index dispersion that is dependent on the mode confinement in the diamond layer.

Comparative Analysis of Ni- and Ni0.9Pt0.1-Ge0.9Sn0.1 Solid-State Reaction by Combined Characterizations Methods

GeSn-based alloys present a novel pathway towards the monolithic integration of light sources in mid infrared CMOS-compatible Si photonic circuitry [1]. Semiconductor optoelectronic devices need efficient metallic contacts to receive and deliver power and signal. Ni-stanogermanides (Ni-GeSn) have been proposed as a promising candidate material to reach both low specific contact (Rc) and sheet resistance (Rsh) [2,3] to contact efficiently GeSn-based photonic or electronic devices. However, a low thermal stability of these layers has been evidenced, together with compound agglomeration and segregation [4]. As a solution to these problems Wang et al. showed that the co-sputtering of Ni and Pt extended the thermal stability of the stanogermanides to higher temperatures. Thus leading to a broader window for stanogermanidation and suppressing, to some extent, agglomeration and degradation [4]. In this work, we propose a comparative and comprehensive study of the solid-state reaction of Ni and Ni0.9Pt0.1 films with compressively-strained, 60 nm-thick Ge0.9Sn0.1 layers, epitaxially grown on Ge-buffered Si (100) substrates. Prior to metallization, surface preparation was performed with a 1 min dip in 1% diluted HF sequentially rinsed in deionized water and dried with a N2 gun. Then, 10 nm of Ni or Ni0.9Pt0.1 were deposited by physical vapor deposition and capped with 7 nm of TiN. The Ni and Ni0.9Pt0.1-Ge0.9Sn0.1 phase sequence and crystalline evolution were monitored by in-situ x-ray diffraction (XRD) using an Empyrean PANalytical X-ray diffractometer equipped with a copper (Cu Kα) source, a linear detector (PIXcel1D) and a HTK 1200 Anton Paar furnace working under secondary vacuum. Profiles were acquired from 50 to 600 °C, with 5 °C steps and a scanning time of 7 min per temperature step. The phase analysis was complemented by ex-situ in-plane reciprocal space map with a Rigaku SmartLab X-ray diffractometer. Additionally, samples metallized with the same procedure were ex-situ annealed for 30 s at temperatures ranging from 150 up to 550 °C (with 50 °C steps), in a rapid thermal annealing (RTA) treatment in a N2 environment. The evolution of the surface morphology and the electrical properties were measured by atomic force microscopy (AFM) in Tapping mode with a Bruker FastScan equipment and sheet resistance (Rsh) with a four-point probe meter. AFM and Rsh evidenced that Pt addition improves both morphological and electrical properties of the layers at high temperature. The addition of Pt prevents the surface Root-mean-square (RMS) roughness from increasing with temperature (Figure 1) and postpones morphological surface degradation. Concerning the electrical properties (Figure 2), a plateau where sheet resistance remains stable and low is obtained with Pt addition between 350 and 450 °C. Meanwhile, a sudden increase of Rsh values for Ni-system is observed, this immediately after obtaining the minimum values (9.1 Ω/sq at 350 °C). XRD results for the Ni-Ge0.9Sn0.1 system (Figure 3) reveal a sequential growth in which the first phase appearing corresponds to a Ni-rich phase, i.e. Ni5(Ge0.9Sn0.1)3. Then, at 245 °C, the mono-stanogermanide phase Ni(Ge0.9Sn0.1) is observed; this latter is stable up to 600 °C. The addition of 10 at.% of Pt in Ni thin films (Figure 4) modifies the reaction kinetics, evidenced by the delay in Ni consumption together with a snowplow phenomenon. Additionally, it strongly affects the phase formation sequence promoting PtSnx compound formation and β-Sn segregation as well as a preferential out-of-plane orientation of the mono-stanogermanide phase. Further, the Ni0.9Pt0.1 mono-stanogermanide is unstable and a destabilization of the system is observed to the benefit of the Ni mono-stanogermanide phase, around the 345 – 355 °C temperature range. A summary of the phase formation sequence for both systems is given in Figure 5. The potential impact on device integration of these observations will be discussed. Even though the addition of Pt complicates the solid-state reaction, it was observed that its beneficial impact on surface morphology has an important role for maintaining the integrity of the electrical properties.

Topological light-trapping on a dislocation

Topological insulators have unconventional gapless edge states where disorder-induced back-scattering is suppressed. In photonics, such edge states lead to unidirectional waveguides which are useful for integrated photonic circuitry. Cavity modes, another type of fundamental component in photonic chips, however, are not protected by band topology because of their lower dimensions. Here we demonstrate that concurrent wavevector space and real-space topology, dubbed as dual-topology, can lead to light-trapping in lower dimensions. The resultant photonic-bound state emerges as a Jackiw–Rebbi soliton mode localized on a dislocation in a two-dimensional photonic crystal, as proposed theoretically and discovered experimentally. Such a strongly confined cavity mode is found to be robust against perturbations. Our study unveils a mechanism for topological light-trapping in lower dimensions, which is invaluable for fundamental physics and various applications in photonics.

Localized All‐Optical Control of Single Semiconductor Quantum Dots through Plasmon Polariton‐Induced Screening

AbstractDue to their ability to strongly modify the local optical field through the excitation of surface plasmon polaritons (SPPs), plasmonic nanostructures are often used to reshape the emission direction and enhance the radiative decay rate of quantum emitters, such as semiconductor quantum dots (QDs). These features are essential for quantum information processing, nanoscale photonic circuitry, and optoelectronics. However, the modification and enhancement demonstrated thus far have typically led to drastic alterations of the local energy density of the emitters, and hence their intrinsic optical properties, leaving little room for active control. Here, dynamic tuning of the energy states of a single semiconductor QD is demonstrated by optically modifying its local dielectric environment with a nearby plasmonic structure, instead of directly coupling it to the QD. This technique leaves intact the intrinsic optical properties of the QD, while enabling a reversible all‐optical control mechanism that operates below the diffraction limit at low power levels.

Determination of hot carrier energy distributions from inversion of ultrafast pump-probe reflectivity measurements

Developing a fundamental understanding of ultrafast non-thermal processes in metallic nanosystems will lead to applications in photodetection, photochemistry and photonic circuitry. Typically, non-thermal and thermal carrier populations in plasmonic systems are inferred either by making assumptions about the functional form of the initial energy distribution or using indirect sensors like localized plasmon frequency shifts. Here we directly determine non-thermal and thermal distributions and dynamics in thin films by applying a double inversion procedure to optical pump-probe data that relates the reflectivity changes around Fermi energy to the changes in the dielectric function and in the single-electron energy band occupancies. When applied to normal incidence measurements our method uncovers the ultrafast excitation of a non-Fermi-Dirac distribution and its subsequent thermalization dynamics. Furthermore, when applied to the Kretschmann configuration, we show that the excitation of propagating plasmons leads to a broader energy distribution of electrons due to the enhanced Landau damping.

One-Dimensional Plasmonic Nanoparticle Chain Lasers

Controlling and generating coherent light fields in the nanoscale is critical for reducing the size of photonic circuitry. There are several demonstrations of zero-, one-, two-, and three-dimensional nanolaser architectures. Here we experimentally demonstrate a one-dimensional plasmonic laser, which consists of a periodic chain of aluminum nanoparticles and organic gain media. Lasing is observed at visible wavelengths, with clear thresholds and line widths down to 0.11 nm. Lasing occurs in a dark mode that extends over the whole structure, even outside the pumped area. The single lithography step fabrication and one-dimensional character allow for easy integration of these laser sources with other plasmonic structures.

Non‐Volatile Silicon Photonics Using Nanoscale Flash Memory Technology

AbstractNonvolatile flash memory technology is widely used in our daily life. Following the recent progress in silicon photonics, there is now an opportunity to embed flash memories also in photonic applications. As of today, chip scale photonic devices, e.g., micro‐resonators, are becoming essential building blocks in modern silicon photonics. However, their properties, such as their resonance frequencies, fluctuate due to fabrication tolerances, significantly limiting their applicability. Here, by integrating the well‐established non‐volatile flash memory technology into silicon photonic circuitry, this major obstacle is tackled and electrical post trimming of such resonators is demonstrated. Specifically, the Metal‐Oxide‐Nitride‐Oxide‐Silicon (MONOS) structure is used to trap charges in the thin silicon nitride layer, located in close proximity to the silicon device layer. This enables accumulating charges in the silicon, modifying the effective index of the optical mode and consequently the resonance frequency. By doing so, a robust and CMOS compatible nonvolatile memory solution is provided, which not only allows for precise trimming of the resonance frequency of the photonic device, but can also be easily manufactured and commercialized. This approach paves the way for efficient utilization of photonic structures such as resonators and interferometers in chip scale silicon photonics and electro optic systems, with a wide range of applications spanning from filters, switches and modulators, to sensors, and even lasers.

Highly Efficient Nonlinear Optical Conversion in Waveguiding GaSe Nanoribbons with Pump Pulses Down to a Femto‐Joule Level

AbstractLayered GaSe flakes have revealed strongest second‐harmonic (SH) generation among all the two‐dimensional (2D) atomic crystals measured up to now. However, the unique feature of physical atomic thickness at nanometer scale prevents their practical applications in efficient nonlinear optical conversion due to limited light–matter interaction length. In this work, high quality single‐crystal GaSe nanoribbons (NRs) are fabricated and demonstrated as waveguides with good performance. By taking advantage of the strong confinement and long interaction length of the waveguiding approach, significantly enhanced nonlinear light–matter interaction is observed in GaSe NRs. Based on transverse SH generation, a single GaSe NR‐configured optical auto‐correlator is constructed for ultrashort pulse characterization. Because of the large second‐order nonlinear susceptibility, high sensitivity down to few femto‐joule (fJ) is realized. To the best of our knowledge, this is the highest energy sensitivity among the reported nanoscale auto‐correlators. Such NR waveguides and devices are highly compatible with standard optical fiber systems. The presented results may enable the construction of future energy efficient nonlinear photonic circuitry, chips, and devices.