January 2019
Spotlight Summary by Francesco Morichetti
On-chip rotated polarization directional coupler fabricated by femtosecond laser direct writing
Another story written with a femtosecond laser pen
Femtosecond laser writing is a versatile and cost effective tool to build arbitrary optical structures in a glass substrate. The beauty of this technique is that it is inherently 3D, thus removing some constraints of conventional planar processes used in integrated optics and allowing the realization of never-before-conceptualized photonic devices.
In this work by Ci-Yu Wang and coworkers, femtosecond laser writing is effectively exploited to create a novel waveguide structure that enables advanced on-chip manipulation and processing of the polarization state of the light. Conceptually, it is an optical waveguide with the unique feature that its optical axis can be arbitrarily tailored in the transverse plane, from 0° to 180°, while keeping very high transmittance. Actually, this waveguide is a rail made of two strongly coupled parallel tracks, whose relative radial and azimuthal position can be accurately (yet easily) shaped by femtosecond laser writing in order to intentionally introduce an anisotropic and inhomogeneous distribution of the refractive index, thus resulting in the desired rotation of the optical axis. By exploiting a pair of such axis-rotated waveguides, the concept of a rotated polarization direction coupler is also demonstrated, which enables performance of on-chip measurements on any pair of orthogonal bases, rather than simply on horizontal or vertical ones.
These achievements confirm once more that femtosecond laser writing can offer a lot of degrees of freedom for the realization of new device concepts, opening new avenues for the on-chip processing of optical signals. Apparently, the only limit to its powerfulness is our design creativity.
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Femtosecond laser writing is a versatile and cost effective tool to build arbitrary optical structures in a glass substrate. The beauty of this technique is that it is inherently 3D, thus removing some constraints of conventional planar processes used in integrated optics and allowing the realization of never-before-conceptualized photonic devices.
In this work by Ci-Yu Wang and coworkers, femtosecond laser writing is effectively exploited to create a novel waveguide structure that enables advanced on-chip manipulation and processing of the polarization state of the light. Conceptually, it is an optical waveguide with the unique feature that its optical axis can be arbitrarily tailored in the transverse plane, from 0° to 180°, while keeping very high transmittance. Actually, this waveguide is a rail made of two strongly coupled parallel tracks, whose relative radial and azimuthal position can be accurately (yet easily) shaped by femtosecond laser writing in order to intentionally introduce an anisotropic and inhomogeneous distribution of the refractive index, thus resulting in the desired rotation of the optical axis. By exploiting a pair of such axis-rotated waveguides, the concept of a rotated polarization direction coupler is also demonstrated, which enables performance of on-chip measurements on any pair of orthogonal bases, rather than simply on horizontal or vertical ones.
These achievements confirm once more that femtosecond laser writing can offer a lot of degrees of freedom for the realization of new device concepts, opening new avenues for the on-chip processing of optical signals. Apparently, the only limit to its powerfulness is our design creativity.
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Article Information
On-chip rotated polarization directional coupler fabricated by femtosecond laser direct writing
Ci-Yu Wang, Jun Gao, and Xian-Min Jin
Opt. Lett. 44(1) 102-105 (2019) View: Abstract | HTML | PDF