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Optical Engineering

Electro-optic fringe locking and photometric tuning using a two-stage Mach–Zehnder lithium niobate waveguide for high-contrast mid-infrared interferometry
Author(s): Guillermo Martin; Samuel Heidmann; Jean-Yves Rauch; Laurent Jocou; Nadège Courjal
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Paper Abstract

We present an optimization process to improve the rejection ratio in integrated beam combiners by locking the dark fringe and then monitoring its intensity. The method proposed here uses the electro-optic effect of lithium niobate in order to lock the dark fringe and to real-time balance the photometric flux by means of a two-stage Mach–Zehnder interferometer waveguide. By applying a control voltage on the output Y-junction, we are able to lock the phase and stay in the dark fringe, while an independent second voltage is applied on the first-stage intensity modulator, to finely balance the photometries. We have obtained a rejection ratio of 4600 (36.6 dB) at 3.39 μm in transverse electric polarization, corresponding to 99.98% fringe contrast, and shown that the system can compensate external phase perturbations (a piston variation of 100 nm) up to around 1 kHz. We also show the preliminary results of this process on wide-band modulation, where a contrast of 38% in 3.25- to 3.65-μm spectral range is obtained. These preliminary results on wide-band need to be optimized, in particular, for reducing scattered light of the device at the Y-junction. We expect this active method to be useful in high-contrast interferometry, in particular, for astronomical spatial projects actually under study.

Paper Details

Date Published: 14 March 2014
PDF: 8 pages
Opt. Eng. 53(3) 034101 doi: 10.1117/1.OE.53.3.034101
Published in: Optical Engineering Volume 53, Issue 3
Show Author Affiliations
Guillermo Martin, Institut de Planétologie et d’Astrophysique de Grenoble (France)
Samuel Heidmann, Institut de Planétologie et d’Astrophysique de Grenoble (France)
Jean-Yves Rauch, FEMTO-ST (France)
Laurent Jocou, Institut de Planétologie et d’Astrophysique de Grenoble (France)
Nadège Courjal, FEMTO-ST (France)

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