Nonlinear optics is a branch of optics that studies how light interacts with materials in ways that are not directly proportional to the light's intensity. In linear optics, the response of a material to light is predictable and straightforward, but in nonlinear optics, changes in light can lead to unexpected effects, such as frequency mixing or the generation of new wavelengths. This field has important applications in technologies like lasers, fiber optics, and telecommunications. Nonlinear optical effects enable advancements in signal processing and imaging, allowing for more efficient transmission of information and the development of new devices that utilize light in innovative ways.