Consider a dielectric slab waveguide that has a thin GaAs layer of thickness 0.25 μm between two AlGaAs layers. The refractive index of GaAs is 3.6 and that of the AlGaAs layers is 3.4. What is the cutoff wavelength beyond which only a single mode can propagate in the waveguide, if the refractive index does not vary greatly with the wavelength? If a radiation of wavelength 860 nm (corresponding to bandgap radiation) is propagating in the GaAs layer, what is the penetration of the evanescent wave into the AlGaAs layers? What is the mode field width (MFW) of this radiation?

Consider a dielectric slab waveguide that has a thin GaAs layer of thickness 0.25 μm between two AlGaAs layers. The refractive index of GaAs is 3.6 and that of the AlGaAs layers is 3.4. What is the cutoff wavelength beyond which only a single mode can propagate in the waveguide, if the refractive index does not vary greatly with the wavelength? If a radiation of wavelength 860 nm (corresponding to bandgap radiation) is propagating in the GaAs layer, what is the penetration of the evanescent wave into the AlGaAs layers? What is the mode field width (MFW) of this radiation?