All articles starting with O

Optical clock

An optical clock is an atomic clock that keeps time using an optical transition in trapped ions or atoms, outperforming caesium clocks by about a factor of 100.

Oct 22, 2026

An optical clock network links optical atomic clocks at separate laboratories by phase-stabilized fiber, comparing frequencies remotely at uncertainties approaching the clocks' own, chiefly in Europe.

Optical clock tests of general relativity

Optical clock tests of general relativity measure gravitational redshift, the prediction that clocks tick faster at higher gravitational potential, using optical atomic clocks accurate to about 10⁻¹⁸.

Oct 22, 2026

Optical clock transition qubits

An optical clock transition qubit is a quantum bit encoded in the ground and metastable clock states of atoms like strontium or ytterbium, offering very long coherence.

Optical cluster state

An optical cluster state is a highly entangled multipartite state of photons that serves as the resource for measurement-based (one-way) quantum computing, proposed by Raussendorf and Briegel in 2001.

Optical coating

An optical coating is one or more thin films deposited on an optical surface to change how it reflects or transmits light, working by interference and used in nearly every optical system.

Optical coating deposition

Optical coating deposition is the manufacture of thin-film optical coatings by evaporation, sputtering, and ion-beam sputtering, balancing film density, spectral stability, deposition rate, substrate temperature, and cost per part.

Optical coating materials

Optical coating materials are dielectric, metallic, and semiconductor substances deposited as thin films on optical surfaces to control reflection, transmission, and spectral filtering, typically in alternating quarter-wave layers.

Optical code-division multiple access

Optical code-division multiple access (OCDMA) is a multiplexing technique in which each user's data on a shared optical channel is encoded with a unique optical code, letting receivers separate users by correlation.

Optical coherence elastography

Optical coherence elastography (OCE) is a non-invasive imaging technique that measures the mechanical stiffness of tissues and cells using optical coherence tomography, first demonstrated in 1998.

Optical coherence microscopy

Optical coherence microscopy (OCM) is an optical imaging method combining low-coherence interferometry with confocal gating, producing label-free, cellular-resolution en face images of scattering tissue, proposed in 1994 as a noninvasive optical biopsy.

Optical coherence tomography

Optical coherence tomography (OCT) is a non-invasive optical imaging technique that produces cross-sectional images of biological tissue, first demonstrated at MIT in 1991 and widely used in ophthalmology.

Optical coherence tomography angiography

Optical coherence tomography angiography (OCTA) is a noninvasive imaging method that visualizes blood flow in the retinal and choroidal microvasculature without dye, commercially available since 2014.

Optical coherence-domain reflectometry

Optical coherence-domain reflectometry (OCDR), also called optical low-coherence reflectometry, is an interferometric technique using a low-coherence light source to record depth-resolved reflectivity profiles, first reported in 1987.

Oct 22, 2026

Optical conductivity

Optical conductivity is the frequency-dependent electrical conductivity of a material, its linear current response to an alternating electric field, whose static limit is the dc conductivity.

Optical correlator

An optical correlator is an optical information-processing system that compares an input scene and a reference by performing their cross-correlation with lenses, used for real-time pattern recognition in applications such as missile guidance.

Optical critical dimension

Optical critical dimension metrology, most often called scatterometry, is a model-based optical technique that measures dimensions and shapes of nanostructures on semiconductor wafers for in-line chip manufacturing process control.

Optical current transformer

An optical current transformer is a power-system device that measures current via the Faraday effect on polarized light, offering no core saturation and a wide dynamic range.

Optical delay line

An optical delay line is a device that makes a beam of light arrive later by a known, often adjustable amount, usually by lengthening its path.

Optical depth

Optical depth, also known as optical thickness, is a dimensionless measure of how strongly a medium attenuates light, with transmitted light falling exponentially as depth increases.

Oct 21, 2026

Optical Devices

Optical devices are items or components used to detect, manipulate, or analyze light, such as lenses, mirrors, prisms, and optical fibers, underpinning fields from telecommunications to medicine.

Optical diffraction tomography

Optical diffraction tomography (ODT) is a label-free imaging method that reconstructs the 3D refractive index of transparent samples from light scattered at many angles, yielding protein concentration and dry mass in live cells.

Optical disc

An optical disc is a flat, circular storage medium read and written by a focused laser, running from the CD (1982) through DVD (1995) to Blu-ray (2003).

Optical disc drive

An optical disc drive (ODD), also called an optical drive, is a device that uses laser light to read and write CDs, DVDs, and Blu-ray Discs, and has largely disappeared from new laptops.

Optical feedback

Optical feedback in lasers is the reinjection of a laser's own light reflected from an external surface, a nuisance for communications lasers and the basis of self-mixing interferometric sensors.

Optical fiber

Optical fiber, also called fiber optics, is a thin glass or plastic strand that guides light by total internal reflection and carries most of the world's internet and telephone traffic.

Optical fiber connector

An optical fiber connector, also called a fiber optic connector, is a demateable termination that aligns fiber cores with a precision ferrule; common styles include SC, LC, ST, and FC.

Optical flat

An optical flat is a piece of glass or fused silica polished to a known flatness, used to measure surface flatness by interference fringes under monochromatic light.

Optical flow

Optical flow is the pattern of apparent motion of pixels between consecutive video frames, a 2D vector field central to computer vision tasks like tracking, video compression, and autonomous driving.