[Paper Review] Enhanced nonlinear optical figure-of-merit at 1550nm for silicon nanowires integrated with graphene oxide layered films

Yuning Zhang, Jiayang Wu+6 more|arXiv (Cornell University)|Apr 17, 2020

Advanced Fiber Laser Technologies60 references32 citations

TL;DR

The paper demonstrates that coating SOI silicon nanowires with layered graphene oxide films markedly enhances Kerr nonlinearity, boosting the nonlinear parameter by 16x and the nonlinear figure of merit by ~20x to above 5.

ABSTRACT

Layered 2D GO films are integrated with silicon on insulator (SOI) nanowire waveguides to experimentally demonstrate an enhanced Kerr nonlinearity, observed through selfphase modulation (SPM). The GO films are integrated with SOI nanowires using a large area, transfer free, layer by layer coating method that yields precise control of the film thickness. The film placement and coating length are controlled by opening windows in the silica cladding of the SOI nanowires. Owing to the strong mode overlap between the SOI nanowires and the highly nonlinear GO films, the Kerr nonlinearity of the hybrid waveguides is significantly enhanced. Detailed SPM measurements using picosecond optical pulses show significant spectral broadening enhancement for SOI nanowires coated with 2.2 mm long films of 1 to 3 layers of GO, and 0.4 mm long films with 5 to 20 layers of GO. By fitting the experimental results with theory, the dependence of the n2 for GO on layer number and pulse energy is obtained, showing interesting physical insights and trends of the layered GO films from 2D monolayers to quasi bulk like behavior. Finally, we show that by coating SOI nanowires with GO films the effective nonlinear parameter of SOI nanowires is increased 16 times, with the effective nonlinear figure of merit (FOM) increasing by about 20 times to greater than 5. These results reveal the strong potential of using layered GO films to improve the Kerr nonlinear optical performance of silicon photonic devices.

Motivation & Objective

• Demonstrate enhanced Kerr nonlinearity in SOI nanowire waveguides via graphene oxide (GO) layered films.
• Develop a large-area, transfer-free layer-by-layer coating method to control GO film thickness and placement.
• Quantify the Kerr nonlinearity enhancement through self-phase modulation measurements with ps pulses.
• Extract n2 dependence on GO layer number and pulse energy to understand GO behavior from monolayers to quasi-bulk.
• Evaluate the impact on the nonlinear figure of merit for practical silicon photonic devices.

Proposed method

• Integrate GO layered films with SOI nanowires using a large-area, transfer-free layer-by-layer coating process.
• Control GO film thickness and placement by creating windows in the silica cladding of the SOI nanowires.
• Perform self-phase modulation (SPM) measurements using picosecond optical pulses to assess spectral broadening.
• Fit experimental SPM data to theoretical models to extract the effective n2 as a function of GO layer number and pulse energy.
• Compare Kerr nonlinearity improvements with different GO layer counts (2.2 mm films with 1–3 layers; 0.4 mm films with 5–20 layers) to reveal trends from monolayer to quasi-bulk behavior.

Experimental results

Research questions

• RQ1 How does integrating graphene oxide layered films with silicon nanowires affect Kerr nonlinearity at 1550 nm?
• RQ2 What is the dependence of the nonlinear refractive index n2 on GO layer number and pulse energy?
• RQ3 Can GO films significantly enhance the nonlinear figure of merit of silicon nanowire devices for practical photonics?
• RQ4 What is the relationship between GO layer thickness and observed SPM-induced spectral broadening in SOI nanowires?

Key findings

• GO-coated SOI nanowires exhibit significantly enhanced Kerr nonlinearity due to strong mode overlap with GO films.
• Experimentally observed spectral broadening from SPM increases with GO film length (2.2 mm) and layer count (1–3 layers; 0.4 mm with 5–20 layers).
• Fitting results show n2 for GO depends on layer number and pulse energy, revealing a transition from 2D monolayers to quasi-bulk behavior.
• The effective nonlinear parameter of SOI nanowires increases by 16× when coated with GO films.
• The effective nonlinear figure of merit (FOM) increases by about 20×, attaining values greater than 5.