The Grasse Satellite Laser Ranging (SLR) station (ID7845), part of the International Laser Ranging Service (ILRS) network, participates to various laser applications including SLR, Lunar Laser Ranging (LLR), Time Transfer by Laser Link (T2L2), high-resolution imagery, and debris detection. Since 2014, in collaboration with the France Space Agency (CNES), the Grasse station has been upgrading in order to be able to take part in laser communication (lasercom) experiments. The main challenges of these experiments are the implementation of a complete laser communication chain from space to ground and the characterization of the turbulent atmosphere during the optical data transfer. Several campaigns have been successfully performed and planned since 2015 between Grasse station and lasercom terminal at low Earth orbit, SOTA onboard SOCRATES [5], OPALS integrated on ISS [6], and recently DLR's OSIRIS mission [7]. To prepare for possible higher data-rate lasercom campaigns in the near future (OSIRISv1 at 40 Mbps, OSIRISv2 and Optelµ at 1 Gbps, OSIRISv3 at 10 Gbps) Grasse SLR station is upgrading on lasercom optical bench, with a fine auto-tracking system and a high sensitivity telecom detector. In the proceeding, we will describe the architecture of our optical bench for high data-rate lasercom link and some primary results of the lasercom link between OSIRISv1 [14] (onboard FlyingLaptop satellite) and the station.
We present a high performance, low cost, simple setup for long term temperature stabilization of a 2 m optical fiber ring cavity for laser frequency stabilization applications thanks to birefringence of the fiber and its dependence on temperature. The fiber temperature is controlled, at millisecond time scale by LED (light emissive diode) illumination. This allows reaching a temperature stability of 0.1 μK at 100 seconds for the 2 m long PM ring fiber cavity. This is a reduction of the fiber temperature by a factor of 2×105 (from 20 mK to 0.1 μK) and 5×105 (from 300 mK to 0.6 μK), at 100 seconds and at 105 seconds, respectively, with respect to the ambient temperature variations.
We present two different laser ranging systems under development, both based on the use of a high frequency modulated beam. The first range meter makes no use of interferometry: only the phase of the return beam is detected, in a way that rejects cyclic errors due to optical and electronic crosstalk. An Allan deviation slightly better than 10nm has been obtained with this simple system. The other range meter should provide better resolution, at the expense of a somewhat more sophisticated procedure, as it involves both time-of-flight and interferometry measurements.
We present a laser ranging system, under development, that uses a high frequency modulated beam to achieve sub-nm resolution by the combined use of interferometric and time-of-flight measurements. We first describe how the absolute distance is extracted from a two-mode interference signal. In particular we show that the signal, which presents both optical and synthetic wavelength scales, is essential to achieve nm-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. Then we present results obtained with the telemeter implemented on an optical table, for a distance of about four meters, implemented by folding the laser beam path to the target. The challenge here is to achieve a phase and amplitude measurement of two 20 GHz signals with a resolution well below 10-4 cycle and 10-4, respectively, despite the fact that the signal undergoes very strong (×3 ) amplitude changes.
Distributed feedback (DFB) diode lasers are convenient, small footprint and robust single mode laser sources. DFB lasers have an emission linewidth in the MHz to several MHz range, which may be too large for some applications, such as cold atom physics, optical clocks, laser ranging, lidar or gas sensing... Control of the diode forward current allows for the control the frequency of the emitted laser beam.
Optical transmissions between earth and space have been identified as key technologies for future high data rate transmissions between satellites and ground. CNES is investigating the use of optics both for High data rate direct to Earth transfer from observation satellites in LEO, and for future telecommunications applications using optics for the high capacity Gateway link.
In collaboration between CNES, NICT, Geoazur, the first successful lasercom link between the micro-satellite SOCRATES and an OGS in Europe has been established. This paper presents some results of telecom and scintillation first data analysis for 4 successful links in June & July 2015 between SOTA terminal and MEO optical ground station (OGS) at Caussols France. The telecom and scintillation data have been continuously recorded during the passes by using a detector developed at the laboratory. An irradiance of 190 nW/m2 and 430 nW/m2 has been detected for 1549 nm and 976 nm downlinks at 35° elevation. Spectrums of power fluctuation measured at OGS are analyzed at different elevation angles and at different diameters of telescope aperture to determine fluctuations caused by pointing error (due to satellite & OGS telescope vibrations) and caused by atmospheric turbulence. Downlink & Uplink budgets are analyzed, the theoretical estimation matches well to measured power levels. Telecom signal forms and bit error rates (BER) of 1549 nm and 976 nm downlink are also shown at different diameters of telescope aperture. BER is 'Error Free' with full-aperture 1.5m telescope, and almost in ‘good channel’ with 0.4 m sub-aperture of telescope. We also show the comparison between the expected and measured BER distributions.
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