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In this paper we present the "3Node", which is a versatile wireless node that exploits radio frequency (RF) transmission for three tasks: communication, localization, and remote powering. To the best of our knowledge, this is the first avionics wireless node, which incorporates these three RF functions. The 3Node is tailored to operate onboard aerospace platforms, meeting RF radiation requirements, form factors, etc., and extended by the purpose at hand, e.g., sensing. In this paper, we present a prototypic proof of concept (POC) node, entirely based on commercial off-the-shelf (COTS) components, essentially just an ultra-wideband (UWB) transceiver and an industrial, scientific and medical (ISM) band remote powering receiver. The POC is designed to fulfill aerospace spectrum regulations by band-limiting the UWB signal to the wireless avionics intra-communications (WAIC) band and adjusting the output power. Our measurements show a localization accuracy of ±10cm inside an aircraft cabin mockup and a maximum data rate of 3Mbit/s. Additionally, the impact of an onboard radio altimeter (RA) on the communication performance is analyzed. Finally, we describe the wireless remote powering feature, detailing the resulting operational modes for the 3Node.

Radio-frequency (RF) wireless power transfer (WPT) is an emerging technology to replace conventional wired or battery-powered systems. In this paper, we investigate the feasibility of the RF wireless powering of sensors in wireless avionics intra-communications (WAIC) applications. The main focus is on remote powering WAIC low date rate sensors located Inside the aircraft (LI sensors). One important question is how to deploy WPT transmitters inside aircraft given the fact that the WPT transmitters can only be placed in certain positions. Our objective is to find the least number of WPT transmitters and corresponding positions for them to provide the required energy for each sensor and to satisfy certain levels of duty cycles. We convert the problem into an integer linear programming (ILP) and solve it with known ILP tools. Our simulations illustrate the feasibility of powering LI sensors with 22 transmitters for duty cycles less than 1% while keeping the human radiation exposure below the recommended reference value of 4.57 W/m2.

Low-power sensors can be integrated into an aircraft for numerous use cases. Conventionally, these sensors are powered via cables, which introduces various disadvantages to the overall efficiency of the aircraft. Alternatively, batteries may be used. However, this implies the necessity of additional maintenance for battery replacement. Another option to remove power cables is to use Radio Frequency (RF) Wireless Power Transfer (WPT) systems. Although general RF WPT technology has been studied in the literature, its feasibility for aviation use cases is not fully investigated. In this paper, we study the feasibility of RF WPT to wirelessly power low-power in-cabin sensors. In a cabin mock-up we show that RF WPT techonology is capable of almost fully covering an area of 20 seats and quantitatively assess this using Received Signal Strength Indicators (up to $28$ mW) and packet interval rate (up to $5.5$ Hz). Furthermore, we perform multi-tone sinusoidal wave experiments for power transmission scheme in a lab environment and thereby present potential ways to improve receiver sensitivity and consequently increase the WPT coverage in the cabin without changing the average transmission power. The overall results show that certain low-power cabin use cases can be supported by already existing commercial RF WPT systems., Comment: 6 pages, 10 figures, AIAA/IEEE 39th DASC 2020

In this contribution, we review the results of the ALSI project (Advanced Laser-writing for Stellar Interferometry), aimed at assessing the potential of ultrafast laser writing to fabricate mid-infared integrated optics (IO) devices with performance compatible with an implementation in real interferometric instruments like Hi5 or PFI. Waveguides for the L, L' and M bands with moderate propagation losses were manufactured in Gallium Lanthanum Sulfide and ZBLAN glasses and used to develop photonic building blocks as well as a full mid-IR 4-telescope beam combiner. We discuss the advantages and disadvantages of the tested combiners and discuss a possible roadmap for the continuation of this work., Comment: 16 pages, 9 figures, 1 table

Understanding how solar systems form and determining how unique Earth is within the Universe are some of modern astronomy's biggest quests. To date, the majority of exoplanets have been discovered using indirect techniques. Unlike indirect techniques, direct imaging separates the light from the host star and orbiting planet, enabling measurement of an exoplanet's composition for instance. Yet, direct imaging is challenging due to the small angular separation between the objects and the overwhelming glare of the host star compared to the dim planet. A powerful technique that can provide high angular resolution and contrast is nulling interferometry [1]. Astronomical interferometry has tremendously benefited from using photonic technologies developed for telecommunication, such as optical fibres and integrated photonics to provide spatial filtering of the stellar light for improved interferometric contrast as well as robustness to environmental influences [2]. However, telecommunication technology is not compatible with the mid-infrared, a spectral region of particular interest for detecting young exoplanets.

We will review the development in the last decade of discrete beam combiners (DBC), phase sensors based on the propagation of light in photonic lattices. The latest results on the development of DBC for astronomical applications will be presented, along with a new application for the complete tomography of modes at the tip of a multi-mode fiber. The possible use of the DBC in monitoring and controlling modal instabilities in high power lasers will be discussed.

The project "Novel Astronomical Instrumentation through photonic Reformatting" is a DFG-funded collaboration to exploit the recognized potential of photonics solutions for a radically new approach to astronomical instrumentation for optical/infrared high precision spectroscopy and high angular resolution imaging. We present a project overview and initial development results from our Adaptive Optics-photonic test bed, Ultrafast Laser Inscribed waveguides for interferometric beam combination and 3D printing structures for astronomical instrumentation. The project is expected to lead to important technological breakthroughs facilitating uniquely functionality and technical solutions for the next generation of instrumentation., 15 pages, 11 figures, SPIE Astronomical Telescopes + Instrumentation

This paper is one of a three-part series of papers on photonics-based mid-IR interferometry. Here, we put the emphasis on the challenges of operating integrated optics over a broad wavelength range, a natural condition in the field of Astrophysics. We report on the recent advancements made in obtaining high interferometric contrast (> 90%) through 2-telescope combiners in the mid-IR and give an outlook on more advanced functions and 4-telescope combiners.

In the era of large telescopes and RV/Transit planetary missions, nulling interferometry remains a competitive technique for the characterization of Earths and Super-earths around Sun analogs in the mid-IR (Leger 2015, ApJ 808, 194). This is a spectral range where a number of bio-signatures can be accessed from space. One challenge of nulling is to benefit from well-established and qualified infrared fibers and integrated optics capable of mitigating the instrumental constraints on the beam combination and wavefront filtering to reach high extinction ratios. Such photonics devices have reached high maturity in the near-IR range as in the case of the integrated optics (IO) beam combiner of GRAVITY at the VLTI, leading to unprecedented interferometric accuracy. Driven by the need of next-generation interferometers, we expand the photonic approach towards longer wavelengths and develop IO combiners based on the ultrafast laser writing technique. We developed single-mode, low-loss evanescent couplers in gallium lanthanum sulfide with a 50/50 splitting behavior around 3.4 µm and characterized the intrinsic chromaticity by FTS. High monochromatic and broadband contrasts are measured with unpolarized light at 3.39µm (>98%), over the L band (>95%), and over the M Band (4.5-4.8µm) (>95%). Our analysis of the interferometric visibilities and phase shows a small differential birefringence in the component and negligible differential dispersion. This results points out the promising properties of mid-infrared laser writing integrated optics devices to serve as high quality beam combiners. The extension to a four-aperture architecture appears plausible, with care to be taken about the impact of the design on the total throughput.

Photonic technology has pushed the limits of astronomy ever more in recent years. Especially, integrated optics (IO) has led to new standards in accuracy and stability in the field of astronomical interferometry where several beams need to be coherently and simultaneously combined. We follow and extend the IO concept by writing mid-IR waveguides in gallium lanthanum sulfide (GLS) using Ultrafast Laser Writing (ULI). Here, we report on the monochromatic and broadband interferometric capabilities in the mid-IR of such combiners. Finally, we outline the way to a fiber-fed IO 4-telescope instrument for next-generation astronomical interferometers.

We present the laboratory characterisation of the first working, mid-infrared, integrated optics, 4-channel interferometric beam combiner based on the properties of two-dimensional arrays of evanescently coupled waveguides. Potential applications of the component to astronomy, biology and quantum optics are proposed and discussed.

In the past two decades high precision optical astronomical interferometry has benefited from the use of photonic technologies. Today, near-infrared interferometric instruments deliver high-resolution, hyperspectral images of astronomical objects and combine up to 4 independent telescopes at a time thanks to integrated optics (IO). Following the success of IO interferometry, several initiatives aim at developing components which could combine simultaneously more telescopes and extend their operation beyond the near-infrared bands. Here we report on the development of multi-telescope IO beam combiners for mid-infrared interferometry exploiting the three-dimensional (3D) structuring capabilities of ultrafast laser inscription. We characterise the capability of a 2-telescope and a 4-telescope beam combiner to retrieve the visibility amplitude and phase of monochromatic light fields at a wavelength of 3.39 µm. The combiner prototypes exploit different 3D architectures and are written with a femtosecond laser on substrates of Gallium Lanthanum Sulfide. Supporting numerical simulations of the performance of the beam combiners show that there is still room for improvement and indicate a roadmap for the development of future prototypes.

Fringe tracking at longer wavelengths is advantageous for its larger Fried parameter (R 0 ) and longer coherence time (τ 0 ). The fringe trackers which are currently available at the VLTi (Finito, FSU, Gravity, etc.) tracks fringes at the near infrared wavelengths (H and K bands). In our work we try to explore the possibilities to track near and mid- infrared fringes using GLS based laser written integrated optics beam combiners. We simulate the atmospheric optical path difference (OPD) using Kolmogorov/Von-Karman atmospheric turbulence statistics. We also include the measured the piston noise generated due to the instrumental vibrations. Using the resulting OPD time series we can estimate the sensitivity of the fringe tracker at the L band.

Integrated optics (IO) has proven to be a competitive solution for beam combination in the context of astronomical interferometry (e.g. GRAVITY at the VLTI). However, conventional silica-based lithographic IO is limited to wavelengths shorter than 2.2μm. We report in this paper the progress on our attempt to extend the operation of IO to longer wavelengths. Previous work has demonstrated the suitability of chalcogenide devices in the MID-IR in the N band and monochromatically at 3.39 μm. Here, we continue this effort with the manufacturing of new laser written GLS IO as beam combiners designed for the astronomical L band and characterized interferometrically at 3.39 μm. In the era of multi-telescope interferometers, we present a promising solution to strengthen the potential of IO for new wavelength ranges.

In this work we propose a new geometry of discrete beam combiners (DBC) for spectrally-resolved stellar interferometry which overcomes limitations of previous designs. The new beam combiner is based on an array of coupled waveguides arranged in zig-zag pattern. It has been numerically optimized for the combination of 4 telescopes and engineered to operate in the L-band. We manufactured a first sample by direct laser writing in Gallium Lanthanum Sulfide glass, a highly transmissive material in the mid-infrared (550 nm to 10 μm). Initial near-field characterization of the fabricated sample at a wavelength of 3.4 μm are encouraging, but highlighted the necessity of a better control of the polarization dispersion of individual waveguides, as well as induced stresses from manufacturing process.

Astronomical interferometry is a unique technique that allows observation with angular resolutions on the milliarcsec scale by combining the light of several apertures hundreds of meters apart. The PIONIER and GRAVITY instruments at the Very Large Telescope Interferometer have demonstrated that silica-based integrated optics (IO) provide a small-scale and highly stable solution for the interferometric beam combination process. Yet, important science cases such as exoplanet hunting or the spectroscopic characterization of exoplanetary atmospheres are favorable for observation in the mid-IR, namely the atmospheric windows L and L' band (3-4 µm), a wavelength range that is not covered by conventional silica-based IO. Here, we propose laser-inscribed IO 2×2 couplers in ZBLAN and experimentally assess the critical properties of the component for broadband mid-IR interferometry. We measure the splitting ratio over the 2.5 to 5.0 µm range and find excellent broadband contrast over the L (3.1-3.6 µm) and L' (3.6 - 4.0 µm) bands. Furthermore, we quantify the dispersion properties of the coupler and find a phase variation as low as 0.02 rad across the L and L' band, respectively. By optimizing the NA of our injection beam, we measured a very high total throughput of 58% over the L band including Fresnel reflection and coupling losses. We also compare our findings to recent advances in mid-IR IO in GLS and discuss its advantages and disadvantages for the implementation in future mid-IR interferometers.

Context: Optical long baseline interferometry is a unique way to study astronomical objects at milli-arcsecond resolutions not attainable with current single-dish telescopes. Yet, the significance of its scientfic return strongly depends on a dense coverage of the uv-plane and a highly stable transfer function of the interferometric instrument. In the last few years, integrated optics (IO) beam combiners have facilitated the emergence of 4-telescope interferometers such as PIONIER or GRAVITY, boosting the imaging capabilities of the VLTI. However, the spectral range beyond 2.2 mm is not ideally covered by the conventional silica based IO. Here, we consider new laser-written IO prototypes made of gallium lanthanum sulfide (GLS) glass, a material that permits access to the mid-infrared spectral regime. Aims: Our goal is to conduct a full characterization of our mid-IR IO two-telescope coupler in order to measure the performance levels directly relevant for long-baseline interferometry. We focus in particular on the exploitation of the L and M astronomical bands. Methods: We use a dedicated Michelson-interferometer setup to perform Fourier transform spectroscopy on the coupler and measure its broadband interferometric performance. We also analyze the polarization properties of the coupler, the differential dispersion and phase degradation, as well as the modal behavior and the total throughput. Results: We measure broadband interferometric contrasts of 94.9% and 92.1% for unpolarized light in the L and M bands. Spectrally integrated splitting ratios are close to 50%, but show chromatic dependence over the considered bandwidths. Additionally, the phase variation due to the combiner is measured and does not exceed 0.04 rad and 0.07 rad across the L and M band, respectively. The total throughput of the coupler including Fresnel and injection losses from free-space is 25.4%. Furthermore, differential birefringence is low (

Planar microcavities with distributed Bragg reflectors (DBRs) host, besides confined optical modes, also mechanical resonances due to stop bands in the phonon dispersion relation of the DBRs. These resonances have frequencies in the sub-terahertz (10E10-10E11 Hz) range with quality factors exceeding 1000. The interaction of photons and phonons in such optomechanical systems can be drastically enhanced, opening a new route toward manipulation of light. Here we implemented active semiconducting layers into the microcavity to obtain a vertical-cavity surface-emitting laser (VCSEL). Thereby three resonant excitations -photons, phonons, and electrons- can interact strongly with each other providing control of the VCSEL laser emission: a picosecond strain pulse injected into the VCSEL excites long-living mechanical resonances therein. As a result, modulation of the lasing intensity at frequencies up to 40 GHz is observed. From these findings prospective applications such as THz laser control and stimulated phonon emission may emerge.