Optical nonlinearity refers to the phenomenon where the response of a material to light changes depending on the intensity of that light. In linear optics, the relationship between light intensity and the material's response is straightforward, but in nonlinear optics, this relationship becomes more complex. This can lead to effects such as frequency doubling, where a material generates light at twice the frequency of the incoming light. Nonlinear optical effects are utilized in various applications, including lasers, optical switching, and telecommunications. These effects enable technologies like supercontinuum generation, where a broad spectrum of light is produced from a single wavelength, enhancing the capabilities of optical systems.