Evanescent wave modulator for medium infrared wavelengths (8-12 μm)

We present a new modulation concept for medium infrared (8 - 12 μm) wavelengths. The operation principle of the presented modulator is based on evanescent wave absorption by means of a bulk, single or multiple quantum well structure. A sub-wavelength grating ensures efficient coupling of the optical field to the absorption medium. Modulation is then achieved by depletion of this absorption medium. We present an analysis of concept parameters and point out their respective advantages and disadvantages with respect to the modulation performance. In this context, we investigated the impact of different absorption media as bulk, single and multiple quantum well structures and found that single quantum well structures are best suited for modulation purposes. Simulations pointed out that an absolute modulation depth of the order of 60% can be achieved. We also investigated the impact of the diffraction order on the modulation performance. Furthermore, some preliminary experimental results on this modulation concept are presented and compared with simulations.