Periodic Reporting for period 4 - QUANtIC (Quantum Nanowire Integrated Photonic Circuits)
Periodo di rendicontazione: 2023-07-01 al 2024-12-31
Future applications in on-chip data processing, communication, storage and metrology are destined to exploit photonics as a key enabling technology due to the outstanding high-speed and low-noise properties of photons. One of the most promising visions is, thereby, the on-chip integration of light sources onto platforms of waveguide-based classical and quantum circuits and the ability to transduce and manipulate classical and non-classical (quantum) states of light. Silicon (Si) or silicon-on-insulator (SOI) based photonic circuitry is probably the best platform to realize such optical links, however, an outstanding challenge in developing such next-generation photonic and quantum technologies is to realize deterministic and high-efficiency active light sources coupled to integrated Si- or SOI-based photonic circuitry. One of the most promising candidates for implementing highly efficient emitters and quantum light sources are nanostructured III-V semiconductors. In particular, light sources incorporated in the form of III-V semiconductor nanowires (NW) are emerging as very promising platform. The objective of this action was to combine the unprecedented features of semiconductor NWs and realize first demonstrations of high-performance classical and non-classical light sources monolithically integrated onto photonic/quantum circuits for on-chip communication and metrology.
This project has succeeded in delivering many of the key objectives related to the design, materials development, integration and exploration of functional classical and non-classical on-chip light sources using quantum NW-heterostructures.
One essential objective was the investigation of ultrasmall nanowire (NW) lasers at near-infrared and mid-infrared wavelengths (including the telecom-band wavelength range) and their coupling performance to underlying photonic circuitries. To this end, suitable III-V NW materials were developed with optimized resonator structures in the single-NW limit that host natural Fabry-Perot cavities and which can be deterministically placed on technologically relevant silicon photonic platform. Primarily focusing on the GaAs NW-material platform, which is technologically highly relevant but faces substantial materials challenges, NW-lasers were successfully realized both in the intrinsic bulk form (GaAs, InAs NW-lasers) as well as by novel ternary (GaAsSb) and more complex core-multishell (NW-quantum well type) gain media. Substantial work was aimed at realizing low threshold lasing performance over wide ranges of operation temperature (including room temperature) at Si-transparent wavelengths (e.g. telecom O-band, 1.3 µm) as well as at mid-infrared wavelengths (~2.5-3 µm). Such unique vertical-cavity nanolasers were also examined with respect to their light coupling efficiency to Si photonic circuits. Under optimized geometries and proper mirror design, large coupling efficiencies of >50% were achieved and first vertically, on-chip coupled NW-lasers at telecom-bands were demonstrated.
Important achievements were also made towards the realization of electrically driven III-V NW sources, which present an outstanding technological milestone. In this regard, coaxially p-i-n doped NW laser diode structures were established, where some of the challenging doping characteristics were solved and functional heterostructures established. Importantly, optical pumping was demonstrated on fully p-i-n doped NW-laser diode structures as-grown on Si platform with lasing thresholds that are on par with those reported for undoped NW-laser structures. While no electrically injected device could be demonstrated within the duration of this project, the research performed and insights gained along this direction hold great promises for successful outcomes in the near term.
For non-classical NW-based light sources that address new types of quantum photonic integrated circuits (QPIC), a fundamentally novel architecture was realized that embeds single quantum dots (QD) as ideal sources for high-brightness single photons. Such deterministic sources are a key ingredient for quantum technological applications in secure data communication and distributed quantum computing. First, through numerical simulations a vertical-cavity architecture was designed for maximizing light coupling and propagation of single photons into a silicon-on-insulator (SOI)-based QPIC. By placing the QD emitter close to the SOI-based WG, peak power coupling efficiencies of up to > 80% were realized. With these guidelines, Si waveguides on SOI platform were demonstrated experimentally and the monolithic growth of NW cavities with embedded quantum dot (QD) emitters pursued. Best-practice NW-QD materials were developed using GaAs(Sb)-InGaAs materials, where numerous studies have shown their excellent axial growth characteristics and distinct emission characteristics of the embedded, deterministic emitter. This sources provide a straightforward route to realize a scalable platform for on-chip quantum light sources integrated on next-generation QPICs.
The results of this action have been successfully disseminated within the research community, including a large number (>20) of peer-reviewed publications and many presentations at international conferences.
One essential objective was the investigation of ultrasmall nanowire (NW) lasers at near-infrared and mid-infrared wavelengths (including the telecom-band wavelength range) and their coupling performance to underlying photonic circuitries. To this end, suitable III-V NW materials were developed with optimized resonator structures in the single-NW limit that host natural Fabry-Perot cavities and which can be deterministically placed on technologically relevant silicon photonic platform. Primarily focusing on the GaAs NW-material platform, which is technologically highly relevant but faces substantial materials challenges, NW-lasers were successfully realized both in the intrinsic bulk form (GaAs, InAs NW-lasers) as well as by novel ternary (GaAsSb) and more complex core-multishell (NW-quantum well type) gain media. Substantial work was aimed at realizing low threshold lasing performance over wide ranges of operation temperature (including room temperature) at Si-transparent wavelengths (e.g. telecom O-band, 1.3 µm) as well as at mid-infrared wavelengths (~2.5-3 µm). Such unique vertical-cavity nanolasers were also examined with respect to their light coupling efficiency to Si photonic circuits. Under optimized geometries and proper mirror design, large coupling efficiencies of >50% were achieved and first vertically, on-chip coupled NW-lasers at telecom-bands were demonstrated.
Important achievements were also made towards the realization of electrically driven III-V NW sources, which present an outstanding technological milestone. In this regard, coaxially p-i-n doped NW laser diode structures were established, where some of the challenging doping characteristics were solved and functional heterostructures established. Importantly, optical pumping was demonstrated on fully p-i-n doped NW-laser diode structures as-grown on Si platform with lasing thresholds that are on par with those reported for undoped NW-laser structures. While no electrically injected device could be demonstrated within the duration of this project, the research performed and insights gained along this direction hold great promises for successful outcomes in the near term.
For non-classical NW-based light sources that address new types of quantum photonic integrated circuits (QPIC), a fundamentally novel architecture was realized that embeds single quantum dots (QD) as ideal sources for high-brightness single photons. Such deterministic sources are a key ingredient for quantum technological applications in secure data communication and distributed quantum computing. First, through numerical simulations a vertical-cavity architecture was designed for maximizing light coupling and propagation of single photons into a silicon-on-insulator (SOI)-based QPIC. By placing the QD emitter close to the SOI-based WG, peak power coupling efficiencies of up to > 80% were realized. With these guidelines, Si waveguides on SOI platform were demonstrated experimentally and the monolithic growth of NW cavities with embedded quantum dot (QD) emitters pursued. Best-practice NW-QD materials were developed using GaAs(Sb)-InGaAs materials, where numerous studies have shown their excellent axial growth characteristics and distinct emission characteristics of the embedded, deterministic emitter. This sources provide a straightforward route to realize a scalable platform for on-chip quantum light sources integrated on next-generation QPICs.
The results of this action have been successfully disseminated within the research community, including a large number (>20) of peer-reviewed publications and many presentations at international conferences.
The photonic circuit integrated NW-lasers are new on-chip Fabry-Perot type nanolaser sources, which are unique due to their small sub-µm2 footprint, single mode character, high spontaneous emission coupling factors and site-selective integration capabilities. As such they are predestined as energy-efficient nanolaser sources with high-density integration potentials, going beyond the state-of-the-art of other types of nanolaser sources.
For example, the development of individual vertical-cavity NW-lasers showcase a profound advancement over other existing technologies, since these present some of the smallest nanolasers that can be integrated in scalable manners on-chip. Not only have these NW-lasers shown potential at telecom-band wavelengths for low-loss optical interconnects, but also as miniaturized coherent light sources at mid-infrared (MIR) wavelengths, alluring various applications in chip-based sensing and metrology.
In similar ways, for vertical-cavity NW-QD emitters coupled to QPIC, our results show the first monolithic pathway for creating deterministic quantum light sources directly on-chip through the beneficial NW-waveguide geometry. This guarantees not only broadband coupling of embedded emitters but large enhancements in the on-chip coupling characteristics due to enhanced light-matter interactions (Purcell effect). These results go well beyond other approaches, and first demonstrations of on-chip integrated NW-QDs based on GaAs(Sb)-InGaAs axial NW heterostructures could be realized. Thanks to the excellent scalability of the position-control of NW-WG cavities on QPIC this will, in the future, allow the realization of multi-photon Boson sampling experiments from on-chip QDs. Such on-chip QPIC NW-QD sources will further offer exceptional platforms for creating spin networks with charged QDs at nodes for on-chip communication via photons.
For example, the development of individual vertical-cavity NW-lasers showcase a profound advancement over other existing technologies, since these present some of the smallest nanolasers that can be integrated in scalable manners on-chip. Not only have these NW-lasers shown potential at telecom-band wavelengths for low-loss optical interconnects, but also as miniaturized coherent light sources at mid-infrared (MIR) wavelengths, alluring various applications in chip-based sensing and metrology.
In similar ways, for vertical-cavity NW-QD emitters coupled to QPIC, our results show the first monolithic pathway for creating deterministic quantum light sources directly on-chip through the beneficial NW-waveguide geometry. This guarantees not only broadband coupling of embedded emitters but large enhancements in the on-chip coupling characteristics due to enhanced light-matter interactions (Purcell effect). These results go well beyond other approaches, and first demonstrations of on-chip integrated NW-QDs based on GaAs(Sb)-InGaAs axial NW heterostructures could be realized. Thanks to the excellent scalability of the position-control of NW-WG cavities on QPIC this will, in the future, allow the realization of multi-photon Boson sampling experiments from on-chip QDs. Such on-chip QPIC NW-QD sources will further offer exceptional platforms for creating spin networks with charged QDs at nodes for on-chip communication via photons.