We present a characterization bench of a complete photonics correlation scheme for mid-infrared heterodyne interferometry. The bench can handle very high bandwidths RF signals generated by the heterodyne beating of celestial light with a local oscillator on future generation mid-infrared detectors. The bench is composed of a first two-beam stage allowing the mixing of the "science" source with the local oscillator and a second photonics correlation stage made with telecom components. We present the first experimental proof of concept. Two possible photonics correlation concepts including a patented double loop correlation are introduced.
KEYWORDS: Signal processing, Optical correlators, Analog electronics, Picosecond phenomena, Digital signal processing, Transmitters, Standards development, Signal detection, Signal analyzers, Physics
We demonstrate a novel architecture enabling the correlation in real-time of broadband RF signals (> GHz). Contrary to conventional digital correlators, our technique is analog: no digitization nor digital signal processing is required. The correlation is performed in the optical domain, enabling the processing of multi GHz signals. Moreover, the proposed architecture calculates in real-time the correlation function for more than 200 values of the delay simultaneously. Applications of the technique range from radio-astronomy, to transmitter localization by Time Difference of Arrival.
The extension of infrared interferometry to an array with a large number of telescopes and kilometric baselines such as the Planet Formation Imager represents an exciting but formidable challenge. Such an infrastructure will require major technological developments, with several key aspects still to be solved on a mid and long term horizon. Mid-infrared heterodyne interferometry is considered as one potential technology despite its well documented lower sensitivity but its stronger scalability and lower hard infrastructure requirements. Exploring pathfinder instruments is a way to increase the maturity of interferometric technologies. In this study we propose to use the 8 VLTI telescopes (Unit and Auxiliary) as a coherent array using infrared heterodyne interferometry by exploiting the potential of state of the art technology in the field of high bandwidth detectors, laser frequency combs, fiber links and innovative photonics correlator. We analyze the sensitivity of an eight beam combining heterodyne instrument called V8 and present a possible sub-system breakdown. By comparing its performances with the ones advertised by ESO for MATISSE we conclude that V8, despite its lower sensitivity, has an interesting science potential since it allows to trade a higher limiting magnitude with an incomparable better mapping capability. As such it should be a formidable tool to explore evolved stars complex mass-loss processes. Moreover, it should allow the interferometry community to explore pathways for future long-baseline arrays, combining or not, direct and heterodyne interferometry.
The path toward a large imaging interferometer in the infrared, as proposed within the framework of the Planet Formation Imager initiative, represents an incredibly exciting and complex challenge of future infrared interferometry. In this context, heterodyne detection has been proposed as a potential alternative in order to recombine a large number of telescopes, with kilometric baselines, in a practical infrastructure, despite a poorer sensitivity compared to classical interferometry. Among the different building blocks necessary to an infrared heterodyne interferometer, the detection and correlation of wide-bandwidth signals remains a big obstacle, in particular to gain further in sensitivity. Here, we propose to address the problem of transport and correlation of wide- bandwidth signals over kilometric distances by presenting the concept of a photonic correlation dedicated to infrared heterodyne interferometry. We present the concept, the implementation and the experimental results for the correlation of two signals with a phase modulation implementation, its possible extrapolation to a larger number of telescopes and spectral channels, and an alternative correlation scheme based on amplitude modulation.
Optical frequency combs are the enabling technology of a myriad of areas of science and engineering, where the line frequency spacing plays a fundamental role in their areas of application. Here, we review recent research work on the proposal and experimental demonstration of a set of signal processing techniques based on linear phase-only operations, inspired by the theory of the Talbot effect. These are aimed at re-distributing the energy of periodic spectral waveforms, such as frequency combs, achieving an arbitrary control of their line spacing. The energy-preserving nature of such techniques provides them with the capability of mitigating the noise of the signals of interest in a deterministic way, even allowing for the detection and measurement of signals entirely buried under the noise floor.
Contrary to the intense debate about brain oxygen dynamics and its uncoupling in mammals, very little is known in
birds. In zebra finches, picosecond optical tomography (POT) with a white laser and a streak camera can measure in vivo
oxy-hemoglobin (HbO2) and deoxy-hemoglobin (Hb) concentration changes following physiological stimulation
(familiar calls and songs). POT demonstrated sufficient sub-micromolar sensitivity to resolve the fast changes in
hippocampus and auditory forebrain areas with 250 μm resolution. The time-course is composed of (i) an early 2s-long
event with a significant decrease in Hb and HbO2, respectively -0.7 μMoles/L and -0.9 μMoles/L (ii) a subsequent
increase in blood oxygen availability with a plateau of HbO2 (+0.3μMoles/L) and (iii) pronounced vasodilatation events
immediately following the end of the stimulus. One of the findings of our work is the direct link between the blood
oxygen level-dependent (BOLD) signals previously published in birds and our results. Furthermore, the early
vasoconstriction event and post-stimulus ringing seem to be more pronounced in birds than in mammals. These results in
bird, a tachymetabolic vertebrate with a long lifespan, can potentially yield new insights for example in brain aging.
VASAO is an ambitious project that explores new conceptual direction in the field of astronomical adaptive optics. In
the era of 8 meter and larger telescopes, and their instrument costs and telescope time pressure, there is a natural niche
for such ground-breaking conceptual development in the 4 meter class telescope. The aim of VASAO is to provide
diffraction limited imaging in the visible with 100% sky coverage; the challenge (but potential rewards) arises from the
simultaneity of these requirements. To this end, CFHT is conducting a feasibility study based on the polychromatic
guide star concept (Foy et al., 1995 [4]) coupled with a high order curvature AO system, presented in this paper.
A number of experiments have been started (or carried out) to study the challenges and limits of the techniques involved
in an operational setting; these include the FlyEyes detector, and a polychromatic tip-tilt test on natural stars.
Because such a project straddles such a fine line between facility instrument and experimental facility, careful thought
has to be given to the balance between modes of operations and potential astrophysical targets.
A European Laser Guide Star (LGS) test facility is proposed for the 4.2m William Herschel Telescope (WHT) on La
Palma. It will test the next-generation Adaptive Optics (AO) LGS technologies to aid risk mitigation of Extremely Large
Telescope (ELT) LGS AO systems. In particular, critical scaling of current LGS AO technologies to ELT dimensions
will be tested. For example, experiments addressing increased spot elongation, cone effect and the order of correction
required.
A pan-European consortium proposes to construct test facility infrastructure on the WHT for a number of risk mitigating
experiments. The infrastructure includes the construction of a Nasmyth platform based controlled environment 'Ground-based
Adaptive optics Innovative Laboratory' (GRAIL), an experimental test environment 'Testbed integration facility'
(TIF) and some common-experiment equipment such as the Common Re-Imaging AO System.
Experiments that are proposed for this facility cover the areas of laser technologies, spot elongation, LGS wavefront
sensing, parallel launch concepts, Multi-Object AO, atmospheric characterisation, co-phasing and real-time control
system risk mitigation.
The differential atmospheric tip-tilt can be measured using a Polychromatic Laser Guide Star. A two photon excitation
has been proposed. It consists in exciting the 4D5/2 level of mesospheric sodium atoms with two identical lasers operating
at 589 nm and 569 nm. With two modeless lasers of 2×15W at the mesosphere level, this scheme will produce a returned
flux at 330 nm of about 4×104 photons/s/m2. Thanks to our modeless laser, we propose a new method which consists in
exciting directly the 4P3/2 sodium level with one photon excitation, using a single laser operating at 330 nm. This
solution was previously rejected probably because of strong saturation problems using single longitudinal mode lasers.
We show that 1 W modeless laser at 330 nm can produce the same returned flux at 330 nm. This solution will save at
least 400 k€ of equipment. Moreover, our new method is very promising in terms of simplicity but also in terms of flux
because the returned flux above will probably be not sufficient for getting a good Strehl ratio. We propose very efficient
solid state laser systems for the production of tens of watts at 330 nm.
A new ultrafast Diffuse Optical Tomography (DOT) has been developed for real time in vivo brain metabolism monitoring in songbird. The technique is based on space resolved time of flight measurements of the photons across the brain tissues. A three dimensional reconstruction of the brain activity is foreseeable by means of a double space and time sampling of the reflectance signal. The setup and the treatment procedure are described in depth and promising preliminary results showing the response of brain tissues to hypercapnia stimulations (increase of CO2) are presented.
We demonstrate the possibility of using periodically poled lithium
niobate crystals (PPLN) as a direct source of entangled photon
pairs. Two configurations are studied. The first enables the
generation of polarization-entangled states from a one-dimensional
PPLN structure at different frequencies; the second is dedicated
to the production of frequency-entangled states from a
bi-dimensional PPLN structure. The engineering of both of these
PPLN structures are described from a theoretical perspective.
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