Wide-Band High-Performance Optical Modulator Based on a Stack of Graphene and h-BN Layers

Engineering Optics Nanoscience Electrical Engineering Chemistry Physics Condensed Matter Physics
optical modulator plasmonics graphene h-BN modulation depth loss electro-optical modulation

Research on High-Performance Wideband Optical Modulators: Innovative Design Based on Stacked Graphene and Hexagonal Boron Nitride Structures

Research Background and Problem Statement

With the rapid development of optical communication technology, electro-optic modulators play a crucial role in modern telecommunication systems. However, achieving high modulation depth while reducing insertion loss has been a significant challenge in this field. In recent years, two-dimensional materials such as graphene, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS₂) have garnered widespread attention due to their unique optoelectronic properties. Particularly, graphene is considered an ideal material for developing high-performance optical modulators because of its high carrier mobility, tunable optical properties, and strong interaction with surface plasmon polaritons (SPPs).

Although some progress has been made in optical modulators based on graphene, these devices often suffer from insufficient modulation depth or excessive insertion loss. Additionally, traditional modulator designs typically rely on thick dielectric layers, which limit their integration density and bandwidth. Therefore, how to achieve wideband optical modulators with both high modulation depth and low loss through optimized material combinations and structural design has become a key scientific issue that needs to be addressed.

Paper Source and Author Information

This paper, titled “Wide-Band High Performance Optical Modulator Based on a Stack of Graphene and h-BN Layers with Plasmonic Edge Mode”, was co-authored by Hossein Karimkhani and Mohammad Ataul Karim. Hossein Karimkhani is from the Faculty of Electrical and Computer Engineering at the University of Tabriz, Iran, while Mohammad Ataul Karim is from the Department of Electrical and Computer Engineering at the University of Massachusetts Dartmouth, USA. The paper was published in the journal Optical and Quantum Electronics in 2025, with the DOI 10.1007/s11082-025-08057-8.

Research Content and Methods

a) Research Process and Experimental Design

The core objective of this study is to design and validate a high-performance wideband optical modulator based on graphene, h-BN, and MoS₂. The research is divided into several main steps:

1. Modulator Structure Design

The research team proposed a non-centrosymmetric multilayer structure consisting of two layers of graphene, two layers of h-BN, and one layer of MoS₂. The substrate is SiO₂/Si, with silver (Ag) layers embedded in the SiO₂ and positioned between the upper and lower graphene layers. This design leverages the strong light absorption capability of graphene and the high dielectric strength of h-BN, while enhancing the localization of the optical field through the edge mode of the Ag layers.

2. Numerical Simulation and Modeling

To evaluate the performance of the modulator, the researchers employed three-dimensional finite-difference time-domain (3D FDTD) numerical simulations. The simulation utilized perfectly matched layer (PML) boundary conditions with 64 PML layers set to minimize reflection effects. The researchers calculated the modulator’s performance metrics, including modulation depth (MD), figure of merit (FOM), and extinction ratio (ER), across different wavelengths (1.3–1.8 μm), temperatures (300 K to 600 K), and chemical potentials (0 eV and 0.65 eV).

3. Electrical and Optical Property Analysis

The research team further analyzed the effect of the chemical potential of graphene layers on the modulator’s performance. By varying the external voltage, the carrier concentration of graphene can be adjusted, thereby altering its optical properties. The researchers also used the Kubo equation and Drude model to calculate the conductivity and dielectric constant of graphene, exploring changes in its real and imaginary parts under different chemical potentials.

4. Feasibility Assessment of Fabrication Processes

To verify the feasibility of the proposed modulator design, the research team provided a detailed description of the fabrication process, including: - Using UV lithography to create patterns on the SiO₂ substrate; - Depositing Ag layers via electron-beam evaporation and lift-off processes; - Growing graphene and h-BN layers using chemical vapor deposition (CVD); - Completing the assembly of the entire device through multiple rounds of electron-beam evaporation and lift-off processes.

b) Key Results and Data Analysis

1. Modulation Depth and Insertion Loss

The study found that at a wavelength of 1.3 μm, the maximum modulation depth of the modulator reached 42.05 dB/μm, with an insertion loss of only 5.723 dB/μm. This performance significantly outperforms similar devices reported in existing literature. Additionally, as the wavelength increased from 1.3 μm to 1.8 μm, the modulation depth gradually decreased but remained at a relatively high level (e.g., 23.43 dB/μm at 1.55 μm). Notably, when the chemical potential increased from 0 eV to 0.65 eV, the insertion loss significantly decreased, indicating the modulator’s excellent low-loss performance.

2. Figure of Merit and Extinction Ratio

The modulator achieved a maximum figure of merit (FOM) of 12.45 at a wavelength of 1.8 μm and a highest extinction ratio (ER) of 99.51 dB at 1.3 μm. These results demonstrate that the modulator not only exhibits excellent modulation capabilities but also effectively suppresses noise signals, enabling high signal-to-noise ratio operation.

3. Temperature Stability

The researchers also tested the modulator’s performance under different temperature conditions. The results showed that even at high temperatures up to 600 K, the modulator’s performance remained relatively stable, with minimal variation in insertion loss. This indicates that the modulator has strong resistance to temperature fluctuations, making it suitable for practical applications.

4. Energy Efficiency and Bandwidth

The modulator consumes only 58.34 fJ/bit of energy, far less than many existing single-layer graphene modulators (typically over 1 pJ/bit). Additionally, it supports a modulation bandwidth of up to 657 GHz, meeting the demands of future high-speed optical communication systems.

c) Conclusions and Significance

In summary, this study successfully designed and validated a high-performance wideband optical modulator based on graphene, h-BN, and MoS₂. The modulator exhibits outstanding performance in terms of modulation depth, insertion loss, energy efficiency, and bandwidth, particularly showing great potential for applications in the O-band (1.3 μm). Its compact architecture and low power consumption make it highly suitable for next-generation integrated photonic circuits and chip-scale platforms.

d) Research Highlights

  1. Innovative Structural Design: By introducing thin h-BN layers to replace traditional thick dielectric layers, the performance of the modulator was significantly improved.
  2. High Modulation Depth and Low Insertion Loss: Achieved a modulation depth of 42.05 dB/μm at 1.3 μm wavelength while maintaining low insertion loss.
  3. Excellent Energy Efficiency: Consumes only 58.34 fJ/bit of energy, far below existing technologies.
  4. Wide Bandwidth and Temperature Stability: Supports a modulation bandwidth of up to 657 GHz and demonstrates good stability under high-temperature conditions.

e) Other Valuable Information

The research team also provided a detailed equivalent circuit model to analyze the modulator’s energy consumption and bandwidth characteristics. Additionally, they noted that further optimization of waveguide design and material selection could reduce insertion loss and enhance the modulator’s competitiveness.

Significance and Value of the Research

This study not only provides new insights into the design of high-performance optical modulators but also advances the application of two-dimensional materials in photonics. Its findings are of great significance for the development of high-speed, low-power optical communication systems and future photonic integrated circuits. Moreover, the design concept of this modulator can be extended to other emerging fields, such as optical computing, 5G/6G fronthaul systems, and quantum information technology, showcasing broad application prospects.