Beam Propagation Method Devang Parekh 3/2/04 EE290F
Outline What is it? FFT FDM Conclusion
Beam Propagation Method Used to investigate linear and nonlinear phenomena in lightwave propagation Helmholtz’s Equation
BPM (cont.) Separating variables Substituting back in
BPM (cont.) Nonlinear Schrödinger Equation Optical pulse envelope Switch to moving reference frame
BPM (cont.) Substituting again First two-linear; last-nonlinear
Fast Fourier Transform (FFTBPM) Use operators to simplify Solution
Fast Fourier Transform (FFTBPM) A represents linear propagation Switch to frequency domain
Fast Fourier Transform (FFTBPM) Solving back for the time domain Plug in at h/2
Fast Fourier Transform (FFTBPM) Similarly for B(nonlinear) Using this we can find the envelope at z+h
Fast Fourier Transform (FFTBPM) Three step process 1. Linear propagation through h/2 2. Nonlinear over h 3. Linear propagation through h/2
Fast Fourier Transform (FFTBPM) Numerically solving Discrete Fourier Transform Fast Fourier Transform Divide and conquer method
Fast Fourier Transform (FFTBPM) Cool Pictures
Fast Fourier Transform (FFTBPM)
Finite Difference Method (FDMBPM) Represent as differential equation Apply Finite Difference Method
Finite Difference Method (FDMBPM)
Cool Pictures
Finite Difference Method (FDMBPM)
Conclusion Can be used for linear and nonlinear propagation Either method depending on computational complexity can be used Generates nice graphs of light propagation
Reference Okamoto K Fundamentals of Optical Waveguides (San Diego, CA: Academic)