Determination of optical Kerr nonlinearity of a photonic bandgap structure by Z-scan measurement

Through analysis of the dispersion relation in a photonic bandgap structure, the effective optical Kerr non-linearity that determines a Z-scan profile particularly near the stop-band edges, is derived. Near and inside the stop band, the nonlinear optical phase change that originates from an off-resonant response is converted into a change in nonlinear optical intensity through Bragg reflection. The Z-scan measurement of a cholesteric liquid-crystal photonic bandgap structure confirmed that off-resonant Kerr nonlinearity is responsible for the characteristic open-aperture Z-scan profiles near the stop-band edges.