Fast Modulation of Terahertz Quantum Cascade Lasers Using Graphene Loaded Plasmonic Antennas

Abstract

We report the fast amplitude modulation of a quantum cascade laser emitting in single-mode operation in the terahertz frequency range by employing compact, integrated devices based on the interplay between plasmonic antenna arrays and monolayer graphene. By acting on the carrier concentration of graphene, the optical response of these plasmonic resonances was modified. The modulator’s characteristics have been studied by using both time domain spectroscopic laser systems, yielding the broad frequency response of these resonant arrays, and quantum cascade lasers, providing us with a narrow and stable laser source, a mandatory prerequisite for the determination of the modulation speed of these devices. The measured modulation speed exhibits a cutoff frequency of 5.5 MHz ± 1.1 MHz. These results represent the first step toward the realization of fast integrated circuitry for communications in the terahertz frequency range.

Bolometric detection of terahertz quantum cascade laser radiation with graphene-plasmonic antenna arrays

“…The results of the electrical characterization on this sample are reported in figure 2 together with the characterization of a similar device which has exposed graphene in the whole array area of 1 × 1.2 mm 2 . This non-encapsulated sample, as shown in figure 2(a), exhibited a Dirac point above 120 V, consistent with exposed strongly p-doped CVD grown graphene and in agreement with what has been already reported in [15,16]. The array with L = 23.5 µm was shorted towards the gate.…”

“…The main detection mechanism was attributed to the photovoltaic effect. Here we exploit arrays of planar antennas fabricated in series, following an approach already exploited in the midinfrared range [14] and a fabrication design which is reminiscent of what has been already reported for THz amplitude modulators [15,16]. However, since the antennas are finally connected to the source and drain pads, they not only provide the plasmonic resonance capable of concentrating the light in the gap region, but they also act as electrodes, thus efficiently collecting all the photocurrent contributions arising from the illuminated graphene areas.…”

2D Materials for Optical Modulation: Challenges and Opportunities

“…In the free space modulation scheme where the incident light penetrates and interacts with the material only once, the light–matter interaction is usually not strong enough for applications that require a relatively large modulation depth. To enhance the light–material interaction, the 2D material can be integrated with various resonant structures, such as metal plasmonic antenna arrays, Fano resonant structures ( Figure a,c), photonic crystal cavities, (Figure d) and metasurfaces (Figure f) . In these cases, the metal structures were designed to have a plasmonic or Fano resonance at mid‐infrared or THz wavelength.…”

All-integrated terahertz modulators

“…The miniaturization of the device was key in order to reduce all the capacitances and impedances in the circuit, which otherwise would limit the modulation speed. Interestingly, in this work, an indirect measurement of the frequency roll-off was proposed, which was developed in parallel by the group in Cambridge [67,68], working on the realization of graphene/plasmonic amplitude modulators operating external to the cryostat based on antenna and interdigitated bow-tie arrays. The advantages of an external modulation scheme lie in the possibility of modulating different frequencies separately, paving the way for independent frequency and phase modulation in quadrature with a single source.…”

“…In Ref. [67], the large capacitance of the graphene areas limited the modulation speed to ~5.5 MHz. In the architecture reported in Ref.…”