Optical modulators, widely used in modern telecommunication systems, are key photonic components that allow altering the amplitude, phase, frequency, or polarization of a light beam. Such a demand is actually extending also to the far-IR or terahertz (THz) frequency range of the electromagnetic spectrum (0.1–10 THz, 3000 – 30 μm), an emerging frontier research field in quantum science.

Graphene, the most widely tested 2D material, display a large potential for the development of optoelectronic devices and components capable to actively manipulate IR light. By electrically shifting the Fermi energy below or above the Dirac point light absorption at energies > 2 EF can be tuned from the 2.3%, typical of intrinsic single layer graphene (SLG), to almost zero.

In the framework of the European Graphene Flagship, our group has developed efficient and compact THz modulators based on electrolyte-gated graphene structures and Salisbury-like quarter wavelength reflection cavities, working in the 2-5 THz range. By integrating the modulators with a THz quantum cascade laser frequency comb, in an external cavity configuration, fine-tuning of the intermode beatnote frequency is also demonstrated. This opens intriguing perspectives for short pulse generation, phase-locking, frequency tuning/chirping, phase modulation, and metrological referencing.


Structure of electrolyte gated graphene-based THz modulators:

  • Substrate: Rigid (silicon wafer, glass), or flexible (kapton)
  • Back reflector gold electrode: prepared by e-beam evaporation
  • Salisbury mirror cavity of thickness 10-20 μm

Membrane (Polycarbonate, polypropylene & optical tissue) soaked with ionic liquid or Ionic Gel

  • Top window: Single layer graphene on quartz


Fabrication/Characterization techniques:

  • Clean Room fully equipped for micro- and nano-fabrication of devices (e-beam evaporator, spin coater, mask aligner, surface profilometer, wet chemical stations, device manipulation, cleaving and mounting stages.
  • Micro Raman spectroscopy to exploit the Fermi level tuning of the graphene in active device also to ensure the thickness of ionic gel.
  • FTIR spectroscopy in THz range under vacuum to evaluate the percentage reflectivity and modulation depth of the devices.
  • C-V and I-V electrical characteristics


EU Graphene Core2 “Graphene Based Disruptive Technologies” – THz Photonics (cnr.it)


People involved:

Sarfraz S.M.A.

Scamarcio Gaetano

Pogna Eva


Research units: