Energy and Power Requirements for Alteration of the Refractive Index

The ability to manipulate the refractive index is a fundamental principle underlying numerous photonic devices. Various techniques exist to modify the refractive index across diverse materials, making performance comparison far from straightforward. In evaluating these methods, power consumption emerges as a key performance characteristic, alongside bandwidth and footprint. Here a comprehensive comparison of the energy and power requirements for the most well‐known index change schemes is undertaken. The findings reveal that while the energy per volume for index change remains within one or two orders of magnitude across different techniques and materials, the power consumption required to achieve switching, 100% modulation, or 100% frequency conversion can differ significantly, spanning many orders of magnitude. As it turns out, the material used has less influence on power reduction than the specific resonant or traveling wave scheme employed to enhance the interaction time between light and matter. Though this work is not intended to serve as a design guide, it does establish the limitations and trade‐offs involved in index modulation, thus providing valuable insights for photonics practitioners. Modifyinga material's refractive index by the amount comparable to its initial value requiresenergy per unit volume ΔUst within 1‐100 kJ/cm−3 range, irrespective of the method.Achieving optical switching by changing phase by 180 degrees depends more on the effective interaction time τ between photons and matter than ΔUst .Tailoring τ enables the minimization of power requirements.