The Silicon Nitride Waveguide (Si3N4) typically does not have a cladding, especially in the context of on-chip optical waveguides. While some processes may involve a polyimide coating, this is uncommon. The evanescent field exists above the waveguide surface, particularly when the beam's angular diameter is significantly smaller than the full reflection angle. Narrow beams generate only an evanescent field, while unfocused light sources, such as on-chip LEDs, produce propagation modes above the waveguide.
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If the question is in context of on-chip optical waveguide, answer is "likely no cladding". Some processes have polyimide coating over top silicon nitride, but polyimide option is uncommon.Sciencestd said:
Evanescent as long as beam angular diameter is much smaller than full reflection angle.Sciencestd said:
Narrow beams will produce only evanescent field above waveguide; unfocused (i.e. on-chip LED) will produce propagation modes above waveguide.Sciencestd said: