Method for optical modulation at periodic optical structure band edges

摘要

In the band edge region, transmission and reflection of an optical wave can be made very sensitive to the change in radiation wavelength, a change in the modulator material refractive index, and/or a change in the material absorption. Controlling these parameters with the increased level of sensitivity is provided by modulation using the band edge region. A preferred embodiment method of the invention uses a periodic optical structure (i.e., a grating) on top of an optical waveguide structure. The combination of the periodic structure and the optical waveguide is designed so that the reflection and/or transmission of the guided wave have broad pass bands with narrow transition bands. The optical structure is exposed to an incident laser radiation with wavelength in one of the transition bands. Modulation of the incident laser radiation is controlled by the change in refractive index or absorption in the optical guided wave structure produced by the modulation voltage. The incident radiation is in transition band, instead of the center portion of the pass band. A preferred method for designing a suitable periodic optical structure having broad pass bands with narrow transition bands uses a high coupling coefficient between the periodic structure and the optical waveguide mode. Increasing the product of the coupling coefficient and the length of the grating narrows the transition region band and increases sensitivity of the modulation.