The future space-based gravitational wave detector Laser Interferometer Space Antenna (LISA) requires bidirectional exchange of light between its two optical benches on board of each of its three satellites. The current baseline foresees a polarization-maintaining single-mode fiber for this backlink connection.Phase changes which are common in both directions do not enter the science measurement, but differential ("non-reciprocal") phase fluctuations directly do and must thus be guaranteed to be small enough.We have built a setup consisting of a Zerodur™ baseplate with fused silica components attached to it using hydroxide-catalysis bonding and demonstrated the reciprocity of a polarization-maintaining single-mode fiber at the 1 pm/ √ Hz level as is required for LISA. We used balanced detection to reduce the influence of parasitic optical beams on the reciprocity measurement and a fiber length stabilization to avoid nonlinear effects in our phase measurement system (phase meter). For LISA, a different phase meter is planned to be used that does not show this nonlinearity. We corrected the influence of beam angle changes and temperature changes on the reciprocity measurement in post-processing.
The Laser Interferometer Space Antenna (LISA) is a joint ESA NASA mission to be launched in 2018. It is an interferometric gravitational wave detector with a measurement band going from 0.1 mHz to 1 Hz. The conceptual interferometer design is unique and includes many challenging aspects that must be analysed in terms of their stability in advance to the mission. One of these new features is the so-called backside fibre link, which connects the two optical benches on-board each spacecraft. In its optical fibre, two frequency shifted laser beams are counter-propagating. LISA will only reach its design sensitivity, if these two beams inside this fibre experience the same pathlength changes down to a level of approximately 1 pm/ √ Hz in the mHz range. In this paper, we present the construction of a quasi-monolithic interferometer that represents a cutout of the LISA interferometry concerning the backside fibre link. In order to ensure a high thermal and mechanical stability of the interferometer, the hydroxide-catalysis bonding technique was applied. For the construction of the interferometer, a number of new alignment techniques and solutions were developed that are suitable for LISA prototype experiments.
The technical embodiment of the Huygens-Fresnel principle, an optical phased array (OPA) is an arrangement of optical emitters with relative phases controlled to create a desired beam profile after propagation. One important application of an OPA is coherent beam combining (CBC), which can be used to create beams of higher power than is possible with a single laser source, especially for narrow linewidth sources. Here we present an all-fiber architecture that stabilizes the relative output phase by inferring the relative path length differences between lasers using the small fraction of light that is back-reflected into the fiber at the OPA's glass-air interface, without the need for any external sampling optics. This architecture is compatible with high power continuous wave laser sources (e.g., fiber amplifiers) up to 100 W per channel. The high-power compatible internally sensed OPA was implemented experimentally using commercial 15 W fiber amplifiers, demonstrating an output RMS phase stability of λ/194, and the ability to steer the beam at up to 10 kHz.
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