periodic refractive index · reflection spectrum · sensing
530 nm
10
10 mm
Physics: Fiber Bragg Grating: periodic variation of refractive index along fiber core with period Λ ≈ 0.5 μm. Bragg condition: λ_B = 2n_eff·Λ. Reflectivity R = tanh²(κL) where coupling coefficient κ = πΔn/λ_B. Bandwidth Δλ ≈ λ_B·Δn/n_eff (weak grating) or λ_B·Λ/L (strong). Temperature sensitivity ~10 pm/°C; strain sensitivity ~1.2 pm/με. Chirped FBGs (varying Λ) act as broadband reflectors or dispersion compensators. Used as wavelength-selective filters in DWDM optical networks and as strain gauges in civil/aerospace structures.