Micro-optics and Diffractive optics are both subfields of optics that deal with the manipulation of light at a small scale. These optical elements are usually macroscopic planar structures, built by sophisticated numerical methods based on diffraction theory, with sizes ranging from a few wavelengths to a few tens of microns.

Micro-optics

Micro-optics are often used to create optical systems that are smaller than a millimeter in size than those created with traditional optics. It relies on micro-sized optical components to manipulate the wavefront of light that is typically produced using microfabrication techniques such as photolithography and micromachining. These include lenses, mirrors, filters, and prisms. 

Many micro-optical devices rely on the same physical optics principles that are applied in big optical components, such as light refraction or reflection. The small dimensions often introduce serious performance limitations via diffraction. However, diffraction is utilized as the basic principle of operation in most micro-optical systems.

Figure 1: Micro-optics

Micro-optics has applications in a wide range of fields, including telecommunications, biotechnology, sensing, imaging, and computing. For example, it is used in fiber optic communication systems to improve the performance of optical amplifiers, in biomedical imaging systems to enable high-resolution imaging of tissues and cells, and in microelectromechanical systems (MEMS) to create microscale sensors and actuators. Microlenses have applications in beam collimation and focusing, while digital micromirror devices can be employed in compact displays. 

Diffractive optics

In contrast to traditional refractive optics which use lenses and mirrors to bend, focus, and direct light, diffractive optics use microscopic structures to bend and shape light waves. These microscopic structures are called diffractive optical elements (DOE). Diffractive optical elements are included in micro-optical systems. It consists of a series of tiny, parallel grooves that are etched onto a surface or embedded in a material. They cause the incident light to diffract, leading to constructive or destructive interference that shapes the light wavefronts. By varying the groove spacing, depth, and shape, DOEs can create a wide range of optical functions, such as focusing, beam splitting, and beam shaping. Diffractive optic devices include diffractive gratings, diffractive lenses, diffractive beam splitters, etc.

Figure 2: Diffractive lens

Diffractive optics are often used in applications such as microscopy, fiber optic telecommunications systems, medical imaging such as endoscopy & microscopy, and optical data storage. In optical data storage, it can be used to create micro-scale patterns on the surface of an optical disk that can store digital data. DOEs can also be used in the creation of holograms.