GNLSELab

Optical Fiber Simulation

A single-page web application for numerical simulation of ultrashort pulse propagation in optical fiber, built on the Generalized Nonlinear Schrödinger Equation (GNLSE). Covers dispersion, nonlinear effects (SPM, SRS, self-steepening), soliton dynamics, and link power budget analysis.

Features

Simulation Engine

• IP-RK45 solver - Interaction Picture method with RK45 adaptive step control; absorbs the linear dispersion operator analytically and applies the nonlinear operator in the interaction picture frame
• Solver stability guard - automatically detects divergence (ΔE > 200 % or ΔE > 50 % with peak amplitude × 5) and returns an error before producing corrupted plots
• Physics toggles - Raman scattering (SRS) and self-steepening can be switched on/off independently via checkboxes
• Full dispersion Taylor series - β₂ slider (−50 to +50 ps²/km) with higher-order terms fixed to PCF values

Diagnostics - 13 Simultaneous Plots

Section	Plots
Communication Analysis	Eye Diagram (full-width) - overlaid 10 Gbps NRZ traces showing signal quality
Evolution Maps	Spectral evolution λ vs Z (linear & log dB), Temporal evolution τ vs Z (linear & log dB)
Output Slices	Output spectrum PSD [dB], Spectral slices (input · mid · output), Output pulse power, Temporal slices
Pulse Dynamics	Instantaneous frequency / chirp δν(τ), Spectral phase φ(λ), Peak power P/P₀ vs Z, Spectral bandwidth σ_ν vs Z

Live Terminal (SSE)

• Streams simulation log in real time via Server-Sent Events
• Logs dispersion length L_D, nonlinear length L_NL, soliton order N, regime classification, and energy conservation check
• [PARAM] change tracking - every slider/input/select change is logged as [PARAM] Label: old → new in orange
• [PRESET] logging - preset selection and parameter reset are logged
• ↓ Download Log - exports the full terminal session as a .txt file with a timestamped entry

Stats Bar (6 metrics)

Soliton Order (N) · Peak Intensity · BER · Total Loss · Link Margin · Link Status (PASS / FAIL) - all computed live on every parameter change.

Presets

Key	Description	λ₀	P_peak	L_fiber	β₂	Pulse
Dudley SC	Supercontinuum (default)	835 nm	10 kW	15 cm	−11.8 ps²/km	Sech
Soliton Fission	Soliton propagation	835 nm	8 kW	50 cm	−11.8 ps²/km	Sech
Soliton Fission	Higher-order fission	1064 nm	20 kW	10 cm	−11.8 ps²/km	Sech
Dispersive Wave	DW generation	835 nm	5 kW	15 cm	−11.8 ps²/km	Sech
Telecom SMF	Standard SMF-28 regime	1550 nm	3 kW	30 cm	−20.0 ps²/km	Gaussian
Low Power	Normal dispersion, weak NL	1064 nm	1 kW	20 cm	+20.0 ps²/km	Gaussian

Save & Import

• ↓ Save Results - saves all 12 plots as PNG + params.txt + terminal_log.txt in a timestamped folder under results/YYYY-MM-DD_HH-MM-SS/
• ↑ Import params.txt - loads a previously saved params.txt back into all controls, logging each restored value in the terminal

How to Run

Please check code/setup.md.

API Endpoints

Method	Route	Description
GET	/	Serves the UI
GET	/api/log/stream	SSE stream of simulation log lines
POST	/api/simulate/physics	Runs IP-RK45 solver; returns 12 base64 PNG plots + stat values
POST	/api/simulate/link	Computes link power budget; returns loss, margin, PASS/FAIL
POST	/api/save/plots	Saves plots, params, and logs into a timestamped results/ folder
POST	/api/ai/chat	Returns AI-based parameter recommendations (ChatGPT / Gemini / Ollama)