The exchanged area is analogous to the core of an optical fiber and the glass substrate to the fiber cladding. Our component is schematically depicted in the right part of Fig. 1 . We use it as a two-way beam combiner with two photometric calibration signals. From an optical point of view, the reverse Y -junction acts as one of the two outputs of a classical beam splitter. The second part of the interferometric signal with a phase shift is radiated at large scale in the substrate.
Light is carried to the component thanks to standard non-birefringent silica fibers.
The latter is used with an astronomical H filter. The OPD scan and the data acquisition are not synchronized, but for each image the translating stage provides a position with an accuracy of 0.3 . To correct the raw interferogram from the photometric fluctuations, we substract a linear combination of P 1 and P 2 from I 0 . The resulting corrected interferogram is displayed in Fig.