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Dipartimento di Fisica - Politecnico di Milano

Composite inegrAted Photonic plAtform By ultrafast LasEr micromachining (CAPABLE)


The CAPABLE laboratory, financed by an ERC – Adv. Grant project (PI: Roberto Osellame), is devoted to the fabrication of integrated photonic devices through femtosecond laser micromachining. This laboratory has been developed for extending the range of processable transparent materials and for improving the accuracy and reproducibility of the fabrications. This allows to develop integrated photonic circuits in different glasses and crystals, as well to realize composite devices made of different multimaterial substrates. In this way it would be possible to choose every material for a particular task, improving the overall performances of the device.

The laboratory is equipped with state-of-the-art instrumentation for femtosecond laser micromachining of transparent substrates.

The laser source is a Pharos (Light Conversion) with a crystal of Yb:KGW as active medium, capable of emitting a laser beam with a wavelength of 1030 nm (with a maximum average power of 10 W) and its second harmonic at 515 nm (with a maximum power of 3 W). The pulse duration can be controlled via an internal compression stage, ranging from a minimum of 170 fs to some ps. Moreover, the repetition rate can be changed from a single pulse to 1 MHz. The versatility of this laser system allows to tune its parameters for achieving an optimal micromachining process for every transparent material.
The laser power can be controlled by means of a motorized attenuator; in this way it is possible to change the irradiation conditions during the writing process. The laser beam can be spatially manipulated by a liquid crystal Spatial Light Modulator (LCOS-SLM, Hamamatsu) that can impose an arbitrary phase front to the laser beam.

A three-axis air-bearing system (ABL1500 from Aerotech) is used to move the transparent sample along arbitrary trajectories in 3D with speed of several tens of cm/s and accuracy of better than 100 nm thanks to a built-in linear encoder. The sample holder is equipped with home-made setup that allows water-immersion laser micromachining, reducing the effect of spherical aberrations for waveguide writing and increasing the yield of laser ablation for material removal.

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