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What is an optical sensor?
What is an optical sensor?
An optical sensor is a sensor that can measure the intensity of electromagnetic waves in a wavelength range between UV light and near infra red. The basic measurement device is the photodiode. Combining a photodiode with some electronics makes a pixel (PIcture ELement).
Photodiodes are used by Melexis in linear optical arrays, CMOS cameras, DVD chips...
How does it work?
Light, from the sensing point of view, is made of discrete energy packets, called photons. Each photon carries a quantum of energy, depending on the light source. This quantity of energy defines the wavelength of the photon.
When falling on Silicon, photons will interact or collide with atoms with a probability related to their wavelength. Outside the UV-Visible-NIR wavelength range, the probability is null. When colliding with an atom, each electron releases its energy to generate heat and ejects an electron from the atom, thus creating an electron/hole pair that will contribute to the conduction process.
Under biasing, the charge carriers (electrons and holes) will flow in an electrical circuit. This electrical signal can then be used (like in a solar cell) or measured (like in a pixel). The easiest way to measure this tiny current is to measure the charge of a capacitor.
location: Concord, NH
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