Integrated Terahertz Graphene Modulator with 100% Modulation Depth

Abstract

Terahertz (THz) frequency technology has many potential applications in nondestructive imaging, spectroscopic sensing, and high-bit-rate free-space communications, with an optical modulator being a key component. However, it has proved challenging to achieve high-speed modulation with a high modulation depth across a broad bandwidth of THz frequencies. Here, we demonstrate that a monolithically integrated graphene modulator can efficiently modulate the light intensity of the THz radiation from a THz quantum cascade laser with a 100% modulation depth for certain region of the pumping current, as a result of the strongly enhanced interaction between the laser field and the graphene enabled by this integration scheme. Moreover, the small area of the resulting device in comparison to existing THz modulators enables a faster modulation speed, greater than 100 MHz, which can be further improved through optimized designs of the laser cavity and modulator architectures. Furthermore, as the graphene absorption spectrum is broadband in nature, our integration scheme can be readily scaled to other wavelength regions, such as the mid-infrared, and applied to a broad range of other optoelectronic devices.

Graphene-plasmon polaritons: From fundamental properties to potential applications

“…In the infrared and THz ranges, intraband transitions dominate, resulting in an optical conductivity well described by the Drude model [39]. Liang et al demonstrated that a monolithically integrated graphene modulator can efficiently modulate the light intensity with a 100% modulation depth for a certain region of the pumping current at the THz range [40]. At infrared frequencies, electrical control of a plasmonic resonance using large-area graphene was demonstrated based on graphene-covered plasmonic nanowire [111] and metasurface systems [112], respectively.…”

“…Compared to plasmon polaritons in noble metals [31], graphene-plasmon polaritons (GPPs) exhibit even stronger mode confinement and relatively longer propagation distance, with an additional unique ability of being electrically or chemi- [24,[32][33][34]. These extraordinary features of graphene plasmons have stimulated intense lines of investigation into both the fundamental properties of graphene plasmons [35][36][37] and potential applications in metamaterials [30,38], modulators [39,40], photodetectors [41], and sensors [42,43]. Naturally, plasmon properties depend on the charge-carrier density, and high doping levels of graphene can be achieved either by electrostatic top-gating [44] or by chemical doping with surface treatment [45].…”

Optical modulators with 2D layered materials

“…Graphene modulators working at the THz region (Fig. 4a,b) 21,85-90 have been demonstrated through modulation of the intra-band absorption, giving good modulation performance, such as >93% modulation depth 89,90 . Ref.…”

“…4c,d). In this THz spectral range, the demonstrated modulation speed is on the order of KHz or MHz range [85][86][87][88][89][90] , which is limited by the large size (~mm, comparable to the THz beam waist) of the device.…”

Characteristics of terahertz wave modulation using wavelength-selective photoexcitation in pentacene/Si and TIPS pentacene/Si bilayers

“…Several methods for achieving near-perfect modulation efficiency of THz transmission using VO 2 -based plasmonic nanoslots, integrated graphene layers, conjugated polymers, and organicbased hybrid structures were reported. 9,[16][17][18][19][20][21] In particular, the technologies based on organic/inorganic hybrid structures enable highly efficient photo-induced modulation of THz wave transmission that is caused by the metallization of an organic layer because of a charge transfer from the silicon (Si) substrate to the organics. 19 This method has advantages such as high modulation efficiency, broadband modulation, and structural simplicity for easy fabrication.…”