Optical nonlinearity: Kerr switching and XGM

Two all-optical mechanisms where one beam controls another. These illustrate the mechanisms, not a full device simulation.

Part 1 - Kerr switching of a Mach-Zehnder

Control intensity Ic 0.000

Δφ = 0.000 rad T = 1.000

A control beam writes a phase via n = n0 + n2·I on one MZI arm: Δφ = π(Ic / Iπ), Iπ = 1. Output transmission T = cos²(Δφ/2) goes from 1 at Ic = 0 to 0 at Ic = 1, switching the gate.

Part 2 - Cross-gain modulation (XGM) in an SOA

Pump intensity Ipump 0.000

probe_out = 1.000 suppression = 0.0 dB

A strong pump saturates the gain seen by a weak probe: probe_out = 1 / (1 + Ipump / Isat), Isat = 1. The pump depletes carriers, lowering the gain for the probe (inverting logic).