Investigation of Millimetre Wave Generation by Stimulated Brillouin Scattering for Radio Over Fibre Applications

Table of Contents

1 Introduction

1.1 The Merging of Optical and Wireless Telecommunications

1.2 Motivation and Scope

1.3 Outline

2 Millimetre Wave Applications

2.1 Closed Requests

2.2 Public Request

2.2.1 Current Commercial Applications of mm-Waves

2.2.2 Future Mobile Communication Systems – Radio Over Fibre

2.2.2.1 Properties of Radio Over Fibre

2.2.2.2 Radio Over Fibre Applications

3 Millimetre Wave Generation Systems

3.1 Electrical Millimetre Wave Generation

3.1.1 Yttrium-Iron-Garnet Oscillators

3.1.2 Gunn Oscillators

3.1.3 Electron Tubes

3.1.4 Frequency Multiplier

3.2 Optical Millimetre Wave Generation

3.2.1 Direct Detection

3.2.2 Heterodyne Detection

3.2.2.1 Mode Locking

3.2.2.2 Injection Locking

3.2.2.3 Optical Phase Locking

3.2.2.4 Optical Frequency Multiplying by Modulation

3.2.2.5 Unconventional Millimetre Wave Generation Techniques

4 Stimulated Brillouin Scattering

4.1 Basics

4.2 Intensity Equations

4.3 Gain Characteristics

4.4 Threshold

4.5 Gain Bandwidth Broadening

4.6 Amplification Processes

5 Backround Theory on Stimulated Brillouin Scattering

5.1 Basics

5.2 Derivation of the Differential Equation System

5.2.1 The Nonlinear Wave Equation

5.2.2 Investigation of the Wave Equation for the Density Modulation

5.2.3 The Complete Differential Equation System

5.3 Analysis

6 Simulations

6.1 Shooting Method

6.2 Results

6.2.1 Simulation of Basic Brillouin Interactions

6.2.2 Diverse Amplification Scenarios

6.2.2.1 Different Pump Powers and Constant Signal Power

6.2.2.2 Different Signal Powers and Constant Pump Power

6.2.3 Optimum Fibre Length

6.2.4 Simulation of Pump Power Drifts

6.2.5 Simulation of Frequency Detuning

6.2.6 Conclusion

7 Experimental Verifications

7.1 Frequency Comb Generation

7.2 Brillouin Amplification Properties

7.2.1 Different Pump Powers at Constant Signal Power

7.2.2 Different Signal Powers at Constant Pump Power

7.3 Heterodyne Detection of Optical Frequency Components

7.3.1 Chromatic Dispersion Effects

7.3.2 Optic-Electric Conversion

7.3.3 Spectral Properties

7.3.4 Noise Measurements

7.3.4.1 Phase Noise

7.3.4.2 Amplitude Noise

7.3.5 Stability

7.3.5.1 Short Term Power Fluctuations

7.3.5.2 Long Term Power Fluctuations

7.4 Conclusion

8 Carrier Modulation

8.1 Set-up

8.2 Modulation Format

8.2.1 Time Domain

8.2.2 Frequency Domain

8.3 Modulation Results Back to Back

8.4 Modulation Results after Radio Propagation

8.5 Conclusion

9 Limitations

9.1 Bias Drift

9.2 Polarisation Penalties

9.3 Stabilisation

9.4 Modulation Bandwidth

9.5 Brillouin Amplifier Noise

9.6 Location of Pump Sources

10 Conclusion

11 Future Work

12 References

13 Authors Publications

14 Appendix

Research Objectives and Topics

The primary objective of this dissertation is to investigate a new, simple, and flexible method for generating millimetre waves for use in Radio Over Fibre (ROF) systems. The research aims to develop a system that achieves high performance through a heterodyne detection principle, specifically leveraging the non-linear effect of stimulated Brillouin scattering for signal amplification, while addressing challenges like signal bandwidth and system stability.

• Investigation of millimetre wave generation using stimulated Brillouin scattering in optical fibres.
• Development of a theoretical framework and differential equation system to model the Brillouin-based amplification process.
• Simulation and experimental verification of frequency comb generation and heterodyne detection techniques.
• Evaluation of system performance, including modulation, noise properties, and stability in ROF applications.

Excerpt from the Book

Summary of Chapters

1 Introduction: Provides an overview of the merging of optical and wireless telecommunications and outlines the thesis structure.

2 Millimetre Wave Applications: Discusses current commercial and non-public applications of Extremely High Frequencies (EHF) and the concept of Radio Over Fibre.

3 Millimetre Wave Generation Systems: Reviews state-of-the-art electrical and optical generation techniques, focusing on heterodyne detection.

4 Stimulated Brillouin Scattering: Explains the fundamental properties of Stimulated Brillouin Scattering (SBS) as a non-linear effect useful for optical amplification.

5 Backround Theory on Stimulated Brillouin Scattering: Derives a complex differential equation system to mathematically describe the SBS-based amplification of multiple frequency components.

6 Simulations: Presents numerical simulations based on the derived equations to optimize the experimental set-up and analyze system performance under various scenarios.

7 Experimental Verifications: Validates the theoretical and simulated models through practical experimental results, detailing the frequency comb generation and amplification performance.

8 Carrier Modulation: Describes the implementation of a modulation scheme to facilitate data transmission using the generated millimetre wave carrier.

9 Limitations: Analyzes the practical constraints of the proposed system, such as bias drift and polarization-related power penalties.

10 Conclusion: Summarizes the thesis findings and confirms the effectiveness of the proposed Brillouin-based millimetre wave generation method.

11 Future Work: Suggests improvements and further research directions, including fully automatic system control and the exploration of different fibre types.

Keywords

Millimetre Waves, Radio Over Fibre, Stimulated Brillouin Scattering, Optical Generation, Heterodyne Detection, Brillouin Gain, Frequency Comb, Phase Noise, Optical Amplification, Nonlinear Wave Equation, Millimetre Wave Photonics, System Stability, Data Modulation, Fibre Optics, Differential Equation System

Frequently Asked Questions

What is the primary focus of this research?

The research focuses on investigating a new and simple method for generating millimetre waves for use in Radio Over Fibre systems, utilizing stimulated Brillouin scattering for signal amplification.

What are the core technical themes covered in this dissertation?

The work explores millimetre wave generation techniques, the non-linear properties of optical fibres, differential equation modeling of signal amplification, and experimental verification of modulation and transmission.

What is the ultimate goal of the proposed system?

The goal is to provide a flexible and high-performance carrier generation method that simplifies the architecture of remote antenna units in modern broadband radio communication networks.

Which scientific methods are employed?

The research uses both analytical modeling—deriving differential equation systems for non-linear optical wave interactions—and extensive numerical simulations, validated by experimental laboratory setups.

What is addressed in the main part of the thesis?

The main body covers the theoretical background of stimulated Brillouin scattering, the derivation of the governing equations for wave interaction, detailed numerical simulations for system optimization, and a multi-part experimental verification including frequency comb generation and data transmission.

Which keywords best characterize this work?

Key terms include Millimetre Waves, Radio Over Fibre, Stimulated Brillouin Scattering, Heterodyne Detection, and System Stability.

How does stimulated Brillouin scattering (SBS) contribute to the system?

SBS acts as a high-gain, narrow-band optical amplifier, which is critical for selectively amplifying specific sidebands in the generated frequency comb to create the desired millimetre wave signal.

What role does the Mach-Zehnder Modulator (MZM) play?

The MZM is used to generate the optical frequency comb through non-linear amplitude modulation, which serves as the basis for the subsequent heterodyne detection and millimetre wave generation.