Optical Feedback - in Science

In Science

The optical feedback discussed so far—video feedback, created by a camera pointing at its own monitor—is actually just one particular example of optical feedback. Perhaps the most obvious example of optical feedback in science is the optical cavity found in almost every laser, which typically consists of two mirrors between which light is amplified. In the late 1990s it was found that so-called unstable-cavity lasers produce light beams whose cross-section present a fractal pattern.

Optical feedback in science is often closely related to video feedback, so an understanding of video feedback can be useful for other applications of optical feedback. Video feedback has been used to explain the essence of fractal structure of unstable-cavity laser beams. The page discovery of fractal lasers gives an account of laser fractals, the developments of this work, links to further reading, and relates the laser context with video feedback systems.

Video feedback is also useful as an experimental-mathematics tool. Examples of its use include the creation of Fractal patterns using multiple monitors or multiple images created using mirrors.

The page video feedback in science provides an overview.

Softology's Video Feedback page provides links and information about real and simulated video feedback.

Optical feedback is also found in the image intensifier tube and its variants. Here the feedback is usually an undesirable phenomenon, where the light generated by the phosphor screen "feeds back" to the photocathode, causing the tube to oscillate, and ruining the image. This is typically suppressed by an aluminum reflective screen deposited on the back of the phosphor screen, or by incorporating a microchannel plate detector.

Optical feedback has been used experimentally in these tubes to amplify an image, in the manner of the cavity laser, but this technique has had limited use.

Optical feedback has also been experimented with as an electron source, since a photocathode-phosphor cell will 'latch' when triggered, providing a steady stream of electrons. See US Patent 4,531,122 for a typical application.