Search

Much of the progress in Astronomy has been driven by instrumental developments, from the first telescopes to fiber fed spectrographs. In this review we describe the field of astrophotonics, a combination of photonics and astronomical instrumentation that has the potential to drive the next generation of developements. We begin with the science cases that have been identified as possibly benefiting from astrophotonic devices. We then discuss devices, methods and developments in the field along with the advantages they provide. We conclude by describing possible future developments in the field and their influence on astronomy., 99 pages, 7 figures - Invited review article for The Astronomy and Astrophysics Review. Submitted on 9 Nov 2018, Resubmission 8 Nov 2020

Stellar interferometry performed in integrated photonic devices allows to increase the angular resolution of a ground-based telescope. Here we present the fabrication and characterization of a low-loss polarization insensitive photonic circuit for astrophotonics, whose geometry was engineered to combine interferometrically up to eight input beams. The employed fabrication technique consisted in the femtosecond laser micromachining followed by a thermal annealing to reduce the birefringence of the waveguides. The fabricated device was characterized to validate its functioning in terms of polarization insensitivity, good transmission and proper beam combination, thus benchmarking its suitability with real on-sky observations.

Astrophotonics is an emerging tool for increasing the angular resolution in ground-based sky observations. Due to the unpolarized nature of celestial light, it is necessary to operate with fully polarization insensitive integrated devices. In this respect, here we show that a thermal annealing after the femtosecond laser writing of waveguides reduces their birefringence of more than order of magnitude, providing integrated circuits whose behaviour is insensitive to the polarization of the input light. As a validation of this technique, we present the successful fabrication of a low-loss integrated device for performing stellar interferometry of up to 8 input beams.

We will show the first results for a pupil remapping device with an integrated optics discrete beam combiner. Our expected monochromatic visibility functions are in good agreement with simulation and experiment. The device will be used for our upcoming on-sky tests at 4-m Willian-Herschel Telescope (WHT) in canary islands.

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

We report recent results on passive mid-infrared integrated optics from the project “Advanced Laser-writing for Stellar Interferometry” and shortly describe the perspectives of their hybridisation with active components for the benefit of the spectro-interferometry technique.

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 astronomical J-band (1.25 micrometres) is a relatively untapped wave-band in long-baseline infrared interferometry. It allows access to the photosphere in giant and super-giant stars relatively free from opacities of molecular bands. The J-band can potentially be used for imaging spots in the 1350 nm ionised iron line on slowly rotating magnetically-active stars through spectro-interferometry. In addition, the access to the 1080 nanometres He I line may probe out flows and funnel-flows in T-Tauri stars and allow the study of the star-disk interaction. We present the progress in the development of a six-inputs, J-band interferometric beam combiner based on the discrete beam combiner (DBC) concept. DBCs are periodic arrays of evanescent coupled waveguides which can be used to retrieve simultaneously the complex visibility of every baseline from a multi-aperture interferometer. Existing, planned or future interferometric facilities combine or will combine six or more telescopes at the time, thus increasing the snapshot uv coverage from the interferometric measurements. A better uv coverage will consequently enhance the accuracy of the image reconstruction. DBCs are part of the wider project Integrated astrophotonics that aims to validates photonic technologies for utilisation in astronomy. Before manufacturing the component we performed extensive numerical simulations with a coupled modes model of the DBC to identify the best input configuration and array length. The 41 waveguides were arranged on a zig-zag array that allows a simple optical setup for dispersing the light at the output of the waveguides. The component we are currently developing is manufactured in borosilicate glass using the technique of multi-pass ultrafast laser inscription (ULI), using a mode-locked Yb:KYW laser at the wavelength of 1030 nm, pulse duration of 300 fs and repetition rate of 1 MHz. After annealing, the written components showed a propagation loss less than 0.3 dB/cm and a negligible birefringence at a wavelength of 1310 nm, which makes the components suitable for un-polarized light operation. A single mode fiber-to-component insertion loss of 0.9 dB was measured. Work is currently in progress to characterize the components in spectro-interferometric mode with white light covering the J-band spectrum.

Hi-5 is a high-contrast (or high dynamic range) infrared imager project for the VLTI. Its main goal is to characterize young extra-solar planetary systems and exozodiacal dust around southern main-sequence stars. In this paper, we present an update of the project and key technology pathways to improve the contrast achieved by the VLTI. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5~$\mu$m) and advanced fringe tracking strategies. We also address the strong exoplanet science case (young exoplanets, planet formation, and exozodiacal disks) offered by this wavelength regime as well as other possible science cases such as stellar physics (fundamental parameters and multiplicity) and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed., Comment: 15 pages, 3 figures, SPIE proceedings, based on arXiv:1801.04148

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

As compared to single-mode fibers (SMFs), photonic lanterns could ease the coupling of starlight to single-mode astrophotonic instruments. Here we investigate numerically the advantage of using lanterns as compared to SMFs for seeing-limited and low-order adaptive telescopes. We find the turbulence strength below which focal-ratio-matched photonic lanterns provide an average flux per output equal to that of a sole SMF. Lastly, we look into the advantage of having a low-order adaptive optics (AO) as a way of relaxing the demand on the lantern size and complexity.

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.

The Planet Formation Imager (PFI) is a near- and mid-infrared interferometer project with the driving science goal of imaging directly the key stages of planet formation, including the young proto-planets themselves. Here, we will present an update on the work of the Science Working Group (SWG), including new simulations of dust structures during the assembly phase of planet formation and quantitative detection efficiencies for accreting and non-accreting young exoplanets as a function of mass and age. We use these results to motivate two reference PFI designs consisting of a) twelve 3m telescopes with a maximum baseline of 1.2km focused on young exoplanet imaging and b) twelve 8m telescopes optimized for a wider range of young exoplanets and protoplanetary disk imaging out to the 150K H2O ice line. Armed with 4x8m telescopes, the ESO/VLTI can already detect young exoplanets in principle and projects such as MATISSE, Hi-5 and Heimdallr are important PFI pathfinders to make this possible. We also discuss the state of technology development needed to make PFI more affordable, including progress towards new designs for inexpensive, small field-of-view, large aperture telescopes and prospects for Cubesat-based space interferometry., Comment: Presented at 2018 SPIE Astronomical Telescopes + Instrumentation, Austin, Texas, USA. See www.planetformationimager.org for more information

Optical communication between optical ground stations (OGS) and geostationary (GEO) satellites is a promising technology for future high-speed data transfer between Earth and space. However, such optical communication links suffer from distortions caused by atmospheric turbulence. To explore adaptive optics mitigation of this effect both in the uplink and the downlink beam, we have developed an adaptive optics testbed. In an earlier publication [1], we reported on the results of uplink compensation. In this contribution, we wish to elaborate more on the efficiency of downlink compensation. Further, we will highlight the differences between uplink and downlink compensation.

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.

We present a preliminary experimental chemical-physical characterisation of the structural modification of Gallium Lanthanum Sulfide (GLS) glass occurring during ultrafast laser inscription of waveguides in thermal regime. Our measurements with a micro-Raman spectrograph confirmed previous reports of negligible chemical modification of the irradiated glass. Additionally, the observed onset of significant long-range stress patterns surrounding the irradiated regions indicate that GLS is subject to an irradiation-induced densification of the glass network. We discuss the consequences of these observations for the amelioration of the laser inscription techniques in chalcogenide glasses and, potentially, for the understanding of their microscopic structure.

We present a new concept of an integrated optics component capable of measuring the complex amplitudes of the modes at the tip of a multimode waveguide. The device uses a photonic lantern to split the optical power carried by an $N$-modes waveguide among a collection of single-mode waveguides that excite a periodic array of at least $N^2$ single-mode evanescently-coupled waveguides. The power detected at each output of the array is a linear combination of the products of the modal amplitudes-a relation that can, under suitable conditions, be inverted allowing the derivation of the amplitudes and relative phases of the modal mixture at the input. The expected performance of the device is discussed and its application to the real-time measurement of modal instability in high power fiber lasers is proposed., 5 pages, 4 figures, to be published in Optics Letters

Introduction Stomatitis is a common and potentially dose-limiting adverse event of the mammalian target of rapamycin (mTOR) inhibitor therapy. To minimize dose reductions or treatment delays that may affect therapeutic outcomes, management includes patient education, pain management strategies, and drug treatment. The aim of this study was to evaluate the effectiveness of a topically-applied galenical preparation to minimize the impact of everolimus-associated oral mucositis in patients with advanced cancer. Methods Patients receiving everolimus plus exemestane for advanced breast cancer or everolimus alone for advanced renal cancer were eligible for inclusion. All patients were advised on procedures to maintain good oral hygiene and directed to use a dexamethasone-containing galenical preparation at the first signs of mucositis. Questionnaires were administered at baseline, and after cycles one, two, and three to evaluate the presence, duration, and intensity of oral mucositis. Results Of the 19 patients included in the study (mean age 66 years; 16% male), mucositis developed in 10.5%, 47.4%, and 52.6% of patients after the first, second, and third cycles of everolimus, respectively. The median time to development of mucositis was 18.0 days, and the median time to mucositis resolution was 30.0 days. After the first, second, and third cycles of therapy, 5.3%, 10.5%, and 10.5% of patients required interruption of everolimus therapy; however, no dosage reductions for mucositis were necessary. Conclusions Patient education and the provision of an effective galenical preparation can minimize the effect of mTOR inhibitor-related mucositis. Electronic supplementary material The online version of this article (doi:10.1007/s40487-016-0032-0) contains supplementary material, which is available to authorized users.

We review the potential of Astrophotonics, a relatively young field at the interface between photonics and astronomical instrumentation, for spectro-interferometry. We review some fundamental aspects of photonic science that drove the emer- gence of astrophotonics, and highlight the achievements in observational astrophysics. We analyze the prospects for further technological development also considering the potential synergies with other fields of physics (e.g. non-linear optics in condensed matter physics). We also stress the central role of fiber optics in routing and transporting light, delivering complex filters, or interfacing instruments and telescopes, more specifically in the context of a growing usage of adaptive optics., SPIE Astronomical Telescopes and Instrumentation conference, June 2016, 21 pages, 10 Figures

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.

We conduct an extensive numerical study to single out the best performing rectangular array of evanescently coupled waveguides (discrete beam combiner) that can be used as an integrated optic beam combiner for 6-telescopes at once. We found that the performance of a discrete beam combiner only depends on the conditioning of the Visibility to Pixel Matrix (V2PM) describing it. However, we found that the condition number of V2PM pertaining to different beam combiner architectures cannot be compared. We further report on the possible input waveguide configuration of an 8-telescope discrete beam combiner featuring 8x8 or 9x9 waveguides.

The Planet Formation Imager (PFI) project aims to image the period of planet assembly directly, resolving structures as small as a giant planet's Hill sphere. These images will be required in order to determine the key mechanisms for planet formation at the time when processes of grain growth, protoplanet assembly, magnetic fields, disk/planet dynamical interactions and complex radiative transfer all interact - making some planetary systems habitable and others inhospitable. We will present the overall vision for the PFI concept, focusing on the key technologies and requirements that are needed to achieve the science goals. Based on these key requirements, we will define a cost envelope range for the design and highlight where the largest uncertainties lie at this conceptual stage., 14 pages, 5 figures, Proceedings of SPIE 2016

Experiments where a laser-generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 1015 Wcm(-2) and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale length and hence nonlocal transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [A. Nishiguchi et al., Phys. Rev. Lett. 53, 262 (1984)] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, v(N)/C(s) approximate to 10.

A laser generated proton beam was used to measure the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target. At intensities of 10 15 W cm -2, the significant hot electron production and strong heat fluxes result in non-local transport becoming important to describe the magnetic field dynamics. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that fast advection of the magnetic field from the focal region occurs via the Nernst effect at significantly higher velocities than the sound speed, v N/c s ≈ 10. © 2011 IOP Publishing Ltd.

Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I∼1×1015 W cm−2. Through the well known ∇ne×∇Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be ≈400±100 μm. Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique conditions and have possible implications for multiple beam applications such as inertial confinement fusion experiments.Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I∼1×1015 W cm−2. Through the well known ∇ne×∇Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be ≈400±100 μm. Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique co...

We explore adaptive optics (AO) pre-compensation for optical communication between Earth and geostationary (GEO) satellites in a laboratory experiment. Thus, we built a rapid control prototyping breadboard with an adjustable point-ahead angle where downlink and uplink can operate both at 1064 nm and 1550 nm wavelength. With our real-time system, beam wander resulting from artificial turbulence was reduced such that the beam hits the satellite at least 66% of the time as compared to merely 3% without correction. A seven-fold increase of the average Strehl ratio to (28 ± 15)% at 18 μrad point-ahead angle leads to a considerable reduction of the calculated fading probability. These results make AO pre-compensation a viable technique to enhance Earth-to-GEO optical communication.

The Planet Formation Imager (PFI) initiative aims at developing the next generation large scale facility for imaging astronomical optical interferometry operating in the mid-infrared. Here we report on the progress of the Planet Formation Imager Technical Working Group on the beam-combination instruments. We will discuss various available options for the science and fringe-tracker beam combination instruments, ranging from direct imaging, to non-redundant fiber arrays, to integrated optics solutions. Besides considering basic characteristics of the schemes, we will investigate the maturity of the available technological platforms at near- and mid-infrared wavelengths., Comment: 17 pages, 7 figures, Proceedings of SPIE 2016

Clinical decision making in oncology is based so far on the evidence of efficacy from high-quality clinical research. Data collection and analysis from experimental studies provide valuable insight into response rates and progression-free or overall survival. Data processing generates valuable information for medical professionals involved in cancer patient care, enabling them to make objective and unbiased choices. The increased attention of many scientific associations toward a more rational resource consumption in clinical decision making is mirrored in the Choosing Wisely campaign against the overuse or misuse of exams and procedures of little or no benefit for the patient. This cultural movement has been actively promoting care solutions based on the concept of "value". As a result, the value-based decision-making process for cancer care should not be dissociated from economic sustainability and from ethics of the affordability, also given the growing average cost of the most recent cancer drugs. In support of this orientation, the National Comprehensive Cancer Network (NCCN) has developed innovative and "complex" guidelines based on values, defined as "evidence blocks", with the aim of assisting the medical community in making overall sustainable choices.

The Planet Formation Imager (PFI) Project has formed a Technical Working Group (TWG) to explore possible facility architectures to meet the primary PFI science goal of imaging planet formation in situ in nearby star- forming regions. The goals of being sensitive to dust emission on solar system scales and resolving the Hill-sphere around forming giant planets can best be accomplished through sub-milliarcsecond imaging in the thermal infrared. Exploiting the 8-13 micron atmospheric window, a ground-based long-baseline interferometer with approximately 20 apertures including 10km baselines will have the necessary resolution to image structure down 0.1 milliarcseconds (0.014 AU) for T Tauri disks in Taurus. Even with large telescopes, this array will not have the sensitivity to directly track fringes in the mid-infrared for our prime targets and a fringe tracking system will be necessary in the near-infrared. While a heterodyne architecture using modern mid-IR laser comb technology remains a competitive option (especially for the intriguing 24 and 40{\mu}m atmospheric windows), the prioritization of 3-5{\mu}m observations of CO/H2O vibrotational levels by the PFI-Science Working Group (SWG) pushes the TWG to require vacuum pipe beam transport with potentially cooled optics. We present here a preliminary study of simulated L- and N-band PFI observations of a realistic 4-planet disk simulation, finding 21x2.5m PFI can easily detect the accreting protoplanets in both L and N-band but can see non-accreting planets only in L band. (abridged -- see PDF for full abstract), Comment: 12 pages, 4 Figures, Proceedings of SPIE 2016

Regular two-dimensional lattices of evanescently coupled waveguides may provide in the near future photonic components capable of combining interferometrically and simultaneously a large number of telescopes, thus easing the imaging capabilities of optical interferometers. In this paper, the theoretical modeling of the so-called Discrete Beam Combiners (DBC) is described and compared to the conventional model used for photonic beam combiners for astronomical interferometry. The performance of DBCs as compared to an ideal two quadrature beam combiner is discussed and applications to astronomical instrumentation analyzed.

We investigate an observed lack of excitation symmetry of discrete diffraction patterns in periodic arrays of waveguides written by ultrafast laser inscription (ULI) in gallium lanthanum sulfide glasses. We found experimentally that successive waveguides written with identical parameters are detuned from the previous one by Δβ ∼ 0.2–0.5 mm−1. We show that by varying the writing speed of successive waveguides, we increase the symmetry of the array and reduce the detuning by a factor of 2. After careful analysis of possible physical causes, observations suggest that the density of the laser irradiated material is affected by long range stresses induced by ULI.

Arrays of evanescently coupled waveguides can be used to retrieve simultaneously the first-order correlation functions in multiple-field interferometry. Here it is shown that this remarkable property of waveguide arrays is enabled only by the existence of nonlocal interaction, i.e., non-nearest-neighbor coupling between the waveguides.

Although advances in imaging techniques have allowed earlier diagnosis of renal cell carcinoma (RCC) in recent decades, one-third of patients who have undergone radical resection of organ-confined disease will eventually develop metastases. The treatment of metastatic RCC was revolutionized by the advent of targeted therapy with tyrosine kinase inhibitors. We have followed seven patients with metastatic RCC who were treated with first-line pazopanib at our center. The case of one of these patients is described here in detail. The patient was first diagnosed with RCC in 1999 and metastases were detected in 2006 and 2012. Treatment with pazopanib at the standard dose of 800 mg/day for 29 months led to a partial response that persisted over time. Side effects (hypertension and painful mucositis) were successfully managed with supportive care at our oral therapy clinic. Early management of adverse events using a multidisciplinary approach is paramount to the favorable outcome of treatment with pazopanib and other targeted agents.

International audience; We experimentally demonstrate controllable nonlinear modulation of optical guiding in ultrafast laser-written evan-escently coupled waveguide arrays in bulk gallium lanthanum sulfide chalcogenide glass. The intensity-dependentresponse is validated by simulating light propagation in waveguide arrays with instantaneous Kerr nonlinearityusing a discrete continuous spatiotemporal unidirectional Maxwell equation model. The intensity-drivenmodulation of transmission in multicore structures acts as a potential saturable absorber at kilowatt thresholdlevels

This work aims at highlighting the plasma generation dynamics and absorption when a Bessel beam propagates in glass. We developed a simple diagnostics allowing us to retrieve clear indications of the formation of the plasma in the material, thanks to transmission measurements in the angular and wavelength domains. This technique featured by the use of a single chirped pulse having the role of pump and probe simultaneously leads to results showing the plasma nonlinear absorption effect on the trailing part of the pulse, thanks to the spectral-temporal correspondence in the measured signal, which is also confirmed by numerical simulations. (C) 2015 AIP Publishing LLC.

Nulling interferometry has been identified as a competitive technique for the detection of extrasolar planets. In its basic form, the technique consists of combining out-of-phase a single pair of telescopes to effectively null the light of a bright star and reveal the dim glow of the companion. However, in order to mitigate the effect of the stellar leaks through the interferometer, a broad angular central null is required. The hierarchical combination of several pairs of telescopes can accomplish this task. We have manufactured and tested with monochromatic light an integrated optics component, which combines a linear array of four telescopes in the nulling mode envisaged by Angel and Woolf [Astroph. J.475, 373-379 (1997).10.1086/apj.1997.475.issue-1ASJOAB0004-637X]. By simulating in the laboratory the motion of a star in the sky, we could measure the expected angular transmission of the four-telescope nuller. Moreover, the tests have demonstrated a broad nulling scaling as the fourth power of the baseline delay.

We exploit a slightly noncollinear second-harmonic cross-correlation scheme to map the 3D space-time intensity distribution of an unknown complex-shaped ultrashort optical pulse. We show the capability of the technique to reconstruct both the amplitude and the phase of the field through the coherence of the nonlinear interaction down to a resolution of 10 $\mu$m in space and 200 fs in time. This implies that the concept of second-harmonic holography can be employed down to the sub-ps time scale, and used to discuss the features of the technique in terms of the reconstructed fields., Comment: 16 pages, 6 figures

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 (

Nulling interferometry has been identified as a competitive technique for the detection of extrasolar planets. The technique consists in combining out-of-phase pairs of telescopes to null effectively the light of a bright star an reveal the dim glow of the companion. We have manufactured and tested with monochromatic light an integrated optics component which combines a linear array of 4 telescopes in the nulling mode envisaged by Angel & Wolf (1997). Our testbench simulates the motion of a star in the sky. The tests have demonstrated a nulling scaling as the fourth power of the baseline delay., SPIE Astronomical Telescopes and Instumentation Conference 2014, Paper 9146-77, 7 pages, 5 figures