Optical Fiber Light Rays (2D, Snell's Law & Bend Loss)

This 2D side-view companion traces individual light rays through an optical fiber using real geometric optics — no shortcuts, no precomputed guided/leaky lookup. Each ray is followed bounce by bounce against the actual core-cladding wall (including through a bent section), with the angle of incidence measured fresh at every hit from the wall's true local normal. Reflect if the incidence angle clears the critical angle θ_c = asin(n₂/n₁); refract and escape if it doesn't. Because the wall's normal rotates as the fiber bends while a ray's own direction between bounces does not, tightening the bend radius genuinely knocks previously-guided rays below the critical angle — real bend loss, derived, not looked up. A dispersion readout turns each guided ray's own traced path length into a real arrival-time spread at v = c/n_core, the same mechanism that limits multimode fiber bandwidth in the real world.