Optical nonlinearity enhancement with graphene-decorated silicon waveguides

Abstract

Broadband on-chip optical frequency combs (OFCs) are important for expanding the functionality of photonic integrated circuits. Here, we demonstrate a huge local optical nonlinearity enhancement using graphene. A waveguide is decorated with graphene by precisely manipulating graphene’s area and position. Our approach simultaneously achieves both an extremely efficient supercontinuum and ultra-short pulse generation. With our graphene-decorated silicon waveguide (G-SWG), we have achieved enhanced spectral broadening of femtosecond pump pulses, along with an eightfold increase in the output optical intensity at a wavelength approximately 200 nm shorter than that of the pump pulses. We also found that this huge nonlinearity works as a compressor that effectively compresses pulse width from 80 to 15.7 fs. Our results clearly show the potential for our G-SWG to greatly boost the speed and capacity of future communications with lower power consumption, and our method will further decrease the required pump laser power because it can be applied to decorate various kinds of waveguides with various two-dimensional materials.

Evaluation of graphene optical nonlinearity with photon-pair generation in graphene-on-silicon waveguides

“…Thus, our results clearly reflect the graphene-induced optical NLE. The NLE obtained here agrees well with our previously reported value [16]. In that work, the nonlinear coefficients γ sw and γ gsw for the waveguide width W of 600 nm were numerically calculated to be 117 and 1150 /W/m, respectively, with the overlap between the mode field distribution and graphene, under the assumption that the effective nonlinear refractive index n 2,eff of graphene is 1 × 10 −13 m 2 /W (the nonlinear refractive index n 2 of bulk silicon was assumed to be 4.2 × 10 −18 m 2 /W [45]).…”

“…According to a simple theoretical analysis using coupled-wave equations [38][39][40][41], up to a ten-fold graphene-induced optical nonlinearity enhancement (NLE) was estimated from the observed photon-pair generation rates. The NLE agrees well with our previously reported value [16] estimated via supercontinuum generation in GSWs, which were fabricated with the same process as the samples in this work. Figure 1 shows a schematic of our GSW [16].…”

“…The NLE agrees well with our previously reported value [16] estimated via supercontinuum generation in GSWs, which were fabricated with the same process as the samples in this work. Figure 1 shows a schematic of our GSW [16]. The silicon waveguides, with the fixed total length L of 0.5 mm and the widths W of 500, 600, and 700 nm, were fabricated on a silicon-on-insulator (SOI) substrate with a 250-nm-thick silicon layer using electron-beam (EB) lithography and electron cyclotron resonance-reactive ion etching (ECR-RIE).…”

“…Of these, graphene's third-order optical nonlinearity, which is responsible for its saturable absorption and nonlinear refractive index change, has been shown to be extremely large due to the linear band structure of π-electrons [6]. This remarkable property along with the ultrafast carrier dynamics [7] is highly beneficial for the application of graphene to nonlinear-optical processes such as mode-locking of ultrafast pulsed lasers [8][9][10], wavelength conversion [5,[11][12][13], nonlinear harmonic generation [7,14,15], and supercontinuum generation [16].…”

Transforming silicon into a high performing in tegrated nonlinear photonics platform by integrati on with 2D graphene oxide films

“…The giant Kerr nonlinearity of 2D layered materials such as graphene, graphene oxide (GO), black phosphorus, and transition metal dichalcogenides (TMDCs) has been widely recognized and has enabled diverse nonlinear photonic devices with high performance and new functionalities [28][29][30][31][32]. In particular, enhanced spectral broadening of optical pulses has been reported for SOI nanowires with transferred MoS2 and graphene [33][34][35].…”