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Tunable injecting or extracting optical device for WDM signals as filter to add or drop optical carrier signal or channel - uses thermo-optical effect or electro-optical effect to modify refraction index of one optical path of each phase shift stage
Tunable injecting or extracting optical device for WDM signals as filter to add or drop optical carrier signal or channel - uses thermo-optical effect or electro-optical effect to modify refraction index of one optical path of each phase shift stage
The tunable optical device comprises a number of directional couplers (AD1-AD6) and a number of phase-shift stages (SF1-SF5), alternately connected in cascade. Each phase shift stage defines a certain optical path length difference (~DL1-~DL5) between two distinct optical paths of the stage, causing a periodic response characteristic with a spectral separation between two adjacent peaks of the periodic response characteristic sufficient to contain all deselected wavelengths of the multiplexed channels when a peak of the periodic response characteristic is centred on a selected wavelength. Tuning is performed by modifying the refraction index of one path of the phase stages by Joule effect heating strips (L1-L5) placed adjacent to a straight portion of one of the two optical paths that compose each phase-shift stage or by metallic field plates adapted to receive a signal suitable to modify the electric field intensity. The first two stages of the phase-shift stages have differences of length of optical paths different from each other and in a preestablished ratio while the remaining phase-shift stages have differences of length of optical paths identical.
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