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Photo-diode Array Spectrometer

IP.com Disclosure Number: IPCOM000050341D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Basilico, AR: AUTHOR [+2]

Abstract

In an array of photo-diodes, each diode responds to a particular wavelength or to a range of wavelengths. The diodes are constructed for light to travel along the length of the depletion region in the plane of the junction instead of at right angles to the plane of the junction. The spectrometer uses the characteristic that silicon absorbs shorter wave-lengths at a greater rate than it absorbs longer wavelengths. The device has several diffusions of differing lengths so that each junction absorbs a particular portion of the incident light across a different range of wavelengths. The current signals from different diodes are processed to calculate the intensity of each wavelength.

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Photo-diode Array Spectrometer

In an array of photo-diodes, each diode responds to a particular wavelength or to a range of wavelengths. The diodes are constructed for light to travel along the length of the depletion region in the plane of the junction instead of at right angles to the plane of the junction. The spectrometer uses the characteristic that silicon absorbs shorter wave-lengths at a greater rate than it absorbs longer wavelengths. The device has several diffusions of differing lengths so that each junction absorbs a particular portion of the incident light across a different range of wavelengths. The current signals from different diodes are processed to calculate the intensity of each wavelength.

Light of a particular wavelength has an initial intensity designated I(o), and this intensity falls off exponentially according to a constant that is designated alpha (Beer's Law). Alpha is different for different wavelengths and is greater for short wavelengths and smaller for longer wavelengths. For this calculation, the distance from the light receiving surface to the junction is designated d and the length of the junction is designated d'. The light absorption is calculated by integrating the exponential junction between d and d'. Since absorption occurs as light interacts with the silicon to produce hole-electron pairs, the junction current is proportional to light absorption. The signals are processed to determine the intensity of each wavelength.

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