Graphene-based BPSK and QPSK modulators working at a very high bit rate (up Tbps range)

A J Wirth-Lima,W Bezerra-Fraga

doi:10.1007/s11082-021-02928-6

Abstract

We are presenting graphene-based Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) modulators, which can operate in the range from the TeraHertz up to the infrared. It is noteworthy that these devices have huge advantages over the silicon Mach–Zehnder optical modulators (MZMs) with lateral PN-junction rib-waveguide phase shifters. Among the countless advantages, we can mention, for example, that these modulators consist of only one waveguide and have a much simpler application system of the modulator signal (gate voltage) than in silicon-based MZMs. Other huge advantages are greater efficiency, and yet, they are cheaper and have shorter lengths [and consequently, greater integration in photonic integrated circuit (PIC)]. The first step to present these modulators was to detail the graphene theory that is involved in this device. After this step, we show the project, numerical simulations, and analyses related to our graphene-based BPSK and QPSK modulators. We believe that these modulators will contribute to the generation of new devices made up of 2D materials, which should revolutionize this area of science.

Highlights

Coherent optical modulations, i.e., techniques of light modulations propagating in optical fibers using modulations of the amplitude, frequency, and phase of electromagnetic radiation, as well as signal transmission in two polarizations, were widely researched in the 1980s
We are presenting graphene-based Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK) modulators, which can operate in the range from the TeraHertz up to the infrared
We show the project, numerical simulations, and analyses related to our graphene-based BPSK and QPSK modulators

Summary

Introduction

I.e., techniques of light modulations propagating in optical fibers using modulations of the amplitude, frequency, and phase of electromagnetic radiation, as well as signal transmission in two polarizations, were widely researched in the 1980s. (Figure 1) That occurs because the effective refractive index and the absorption coefficient of the silicon waveguides can be controlled, by changing the concentration of free-carriers (holes and electrons), i.e., by plasma dispersion effect In this type of optical signal modulation, a reverse electrical voltage and a modulating signal are applied at the PN junctions. To avoid losses due to the change in conductivity caused by interband transitions (firstorder process), it is necessary to block these interactions by increasing the value related to the graphene’s chemical potential In this way, only surface plasmons polaritons in graphene (GSPPs) with a frequency above the limit, that is, ħw ⁄μ = 2 → w = 2μ ⁄ħ, suffer this type of attenuation [17]. For graphene on SiO2/Si the Dirac value was VD ≈ 25 V [39]

Graphene-based BPSK and QPSK modulators

Conclusions

22 Figure 8