Optical cavity. An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers. Light confined in the cavity reflect multiple times producing standing waves for certain resonance frequencies. The standing wave patterns produced are called modes; longitudinal modes differ only in frequency while transverse modes differ for different frequencies and have different intensity patterns across the cross section of the beam. Different resonator types are distinguished by the focal lengths of the two mirrors and the distance between them. Optical cavities are designed to have a large Q factor;[1] a beam will reflect a very large number of times with little attenuation.
Resonator modes[edit] Resonator types[edit] Spherical cavity[edit] Stability[edit] Stamp. Numerical aperture. The numerical aperture with respect to a point P depends on the half-angle θ of the maximum cone of light that can enter or exit the lens. General optics[edit] In most areas of optics, and especially in microscopy, the numerical aperture of an optical system such as an objective lens is defined by is constant across an interface. In air, the angular aperture of the lens is approximately twice this value (within the paraxial approximation).
The NA is generally measured with respect to a particular object or image point and will vary as that point is moved. In microscopy, NA generally refers to object-space NA unless otherwise noted. In microscopy, NA is important because it indicates the resolving power of a lens. Numerical aperture is used to define the "pit size" in optical disc formats.[2] Numerical aperture versus f-number[edit] Numerical aperture is not typically used in photography. . , which is defined as the ratio of the focal length to the diameter of the entrance pupil: thus , and not. s06p257.pdf (application/pdf Object) Model of an axially strained weakly guiding optical fiber modal pattern | Publications. Speckle pattern. Laser speckle on a digital camera image from a green laser pointer. This is a subjective speckle pattern. (Note that the color differences in the image are introduced by limitations of the camera system.) Explanation[edit] The speckle effect is a result of the interference of many waves of the same frequency, having different phases and amplitudes, which add together to give a resultant wave whose amplitude, and therefore intensity, varies randomly.
If each wave is modelled by a vector, then it can be seen that if a number of vectors with random angles are added together, the length of the resulting vector can be anything from zero to the sum of the individual vector lengths—a 2-dimensional random walk, sometimes known as a drunkard's walk. In the limit of many interfering waves the distribution of intensities becomes exponential , where is the mean intensity.[2] Subjective speckles[edit] This can be explained as follows. Objective speckles[edit] A photograph of an objective speckle pattern. Diffraction. Diffraction pattern of red laser beam made on a plate after passing a small circular hole in another plate Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.
These characteristic behaviors are exhibited when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. Similar effects occur when a light wave travels through a medium with a varying refractive index, or when a sound wave travels through a medium with varying acoustic impedance. Since physical objects have wave-like properties (at the atomic level), diffraction also occurs with matter and can be studied according to the principles of quantum mechanics.
Richard Feynman[3] wrote: Examples[edit] The effects of diffraction are often seen in everyday life. History[edit] Mechanism[edit] where and. Optical fiber cable. A TOSLINK optical fiber cable with a clear jacket. These cables are used mainly for digital audio connections between devices. An optical fiber cable is a cable containing one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
Design[edit] A multi-fiber cable Left: LC/PC connectors Right: SC/PC connectors All four connectors have white caps covering the ferrules. For indoor applications, the jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid (e.g. Fibre-optic cable in a Telstra pit An optical fiber breakout cable For use in more strenuous environments, a much more robust cable construction is required. A critical concern in outdoor cabling is to protect the fiber from contamination by water. Capacity and market[edit] Reliability and quality[edit] Cable types[edit] Jacket material[edit] Interference (wave propagation) Swimming Pool Interference[1] Interference of waves from two point sources. Magnified-image of coloured interference-pattern in soap-film. The black "holes" are areas where the film is very thin and there is a nearly total destructive interference.
Consider, for example, what happens when two identical stones are dropped into a still pool of water at different locations. Each stone generates a circular wave propagating outwards from the point where the stone was dropped. When the two waves overlap, the net displacement at a particular point is the sum of the displacements of the individual waves. At some points, these will be in phase, and will produce a maximum displacement.
Geometrical arrangement for two plane wave interference Interference fringes in overlapping plane waves A simple form of interference pattern is obtained if two plane waves of the same frequency intersect at an angle. It can be seen that the two waves are in phase when and are half a cycle out of phase when for waves from. Standing wave. Two opposing waves combine to form a standing wave. For waves of equal amplitude traveling in opposing directions, there is on average no net propagation of energy. Moving medium[edit] As an example of the first type, under certain meteorological conditions standing waves form in the atmosphere in the lee of mountain ranges. Such waves are often exploited by glider pilots.
Standing waves and hydraulic jumps also form on fast flowing river rapids and tidal currents such as the Saltstraumen maelstrom. Opposing waves[edit] In practice, losses in the transmission line and other components mean that a perfect reflection and a pure standing wave are never achieved. Another example is standing waves in the open ocean formed by waves with the same wave period moving in opposite directions. Mathematical description[edit] In one dimension, two waves with the same frequency, wavelength and amplitude traveling in opposite directions will interfere and produce a standing wave or stationary wave. And. Optics on the Web. Links to optics-related applets, tutorials and web sites of interest. NOTE: Some applets no longer work with the most recent Java. If possible, try running on an earlier version. In some cases, I've found alternate applets that are similar and that will run on most browsers (I use Chrome, Safari and Firefox).
If you find a link that doesn't work, please email me. If you find a link that should be here, let me know that as well. This list was last updated 1/09. Applications of Optics in Communications (Fiber Optics), Manufacturing, Medicine (including the eye) and More Societies, Organizations and Online Magazines This site contains a huge collection of tutorials and applets covering most of an introductory optics course. This is an optics tutorial for chemistry students. INTRODUCTION TO WAVES and WAVE BEHAVIOR.