Integrated modulators of optical phase or intensity are essential elements to reconfigure dynamically the operationof a complex waveguide circuit, or to achieve convenient optical switching within a fiber network. Thermo-opticeffects are commonly exploited to achieve dynamic phase modulation in glass-based devices, since nonlinearoptical effects are weak in such substrates. Thermo-optic modulators rely on electric resistive heaters patternedon top of the waveguides: they are reliable and easy to fabricate, but they suffer from slow response, dictatedby the thermal diffusion dynamics. On the other hand, optically-coupled microstructures in glass, driven attheir mechanical resonances, may provide interesting possibilities to achieve modulation of the optical signals inthe kilohertz range and higher. In this work, we demonstrate integrated-optics intensity modulators based onmicro-cantilevers with resonant oscillation frequencies in the tens-of-kilohertz range. The mechanical structuresare realized in alumino-borosilicate glass substrate by water-assisted femtosecond-laser ablation. With the samefemtosecond laser an optical waveguide is inscribed within the oscillating beam; a waveguide also continues in thesubstrate beyond the cantilever's tip. Since the entire device, with all its optical and mechanical parts, is realizedin a single fabrication process, relative alignment is guaranteed. If the cantilever is at rest, light propagating inthe internal waveguide yields maximum coupling to the remaining part of the waveguide. When the device isexcited at resonance by means of a piezo-electric actuator, the cantilever oscillation produces periodical variationsof the coupling efficiency, with an observed contrast higher than 10 dB.
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