# Design, Fabrication, and Characterization of Graphene-Silicon Nitride Integrated Mode Filters

## TL;DR

This paper presents a new type of optical filter using graphene and silicon nitride to reduce signal interference in high-speed communication systems.

## Contribution

The paper introduces a novel fabrication method for graphene-silicon nitride mode filters with optimized design and performance.

## Key findings

- The filter achieves a maximum contrast of 123 dB/cm between TE0 and TE1 modes at 1569 nm.
- Minimum loss of −38 dB/cm is achieved for the TE1 mode.
- The fabrication process includes a new etching approach to protect graphene nanoribbons.

## Abstract

We present the design, fabrication, and characterization
of broadband
graphene-silicon nitride integrated mode filters working in the optical
C-band, centered at a wavelength of 1.55 μm. The devices presented
here prevent modal crosstalk, thus avoiding signal degradation in
multimode communication systems. In particular, the fabricated filters
are based on a dual-mode silicon nitride waveguide, partially covered
by a centered graphene nanoribbon that induces a stronger absorption
for the TE0 mode than for the TE1 mode. The
geometry of the design has been optimized to minimize the length and
insertion losses of the device. A complete fabrication process, including
the transfer and lithography of commercial graphene, has been developed.
A novel approach was introduced during the etching step, which entailed
the simultaneous curing of the resist to encapsulate the graphene
nanoribbons prior to the deposition of the upper cladding. Finally,
transmission through an array of fully fabricated filters of varying
lengths was characterized with a measurement setup employing optical
fiber coupling. The maximum experimentally measured contrast between
the TE0 and TE1 modes is 123 dB/cm, achieved
at a wavelength of 1569 nm, simultaneously with a minimum loss of
−38 dB/cm for the TE1 mode. Overall, we fully demonstrate
an integrated mode filter based on commercial graphene that paves
the way for the implementation of integrated multimode optical communication
systems.