Browse Prior Art Database

Collimated Light Source With Laser Diode and Microcylindrical Lens

IP.com Disclosure Number: IPCOM000086114D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR

Abstract

Semiconductor laser diodes emit a widely divergent beam of light, because their junction widths are comparable to the wavelength of the emitted light. Applications such as optical scanners and display units, however, require a small collimated beam.

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Collimated Light Source With Laser Diode and Microcylindrical Lens

Semiconductor laser diodes emit a widely divergent beam of light, because their junction widths are comparable to the wavelength of the emitted light. Applications such as optical scanners and display units, however, require a small collimated beam.

Laser diode 10 has a thin junction 11, so that light rays 12 diverge widely in the vertical direction of the figure. (The length of junction 11 out of the plane of the figure is sufficiently great that beam 12 does not diverge as much in that direction.) Cylindrical lens 13 focuses beam 12 in the vertical direction to produce substantially collimated rays 14, so that far-field pattern 15 is small.

Lens 13 may be an optical fiber, extending out of the plane of the figure, whose axis is coplanar with junction 11. Lens 13 is spaced from junction 11 at a distance which produces the smallest far-field pattern 15. This distance is near, but not equal to, the paraxial focal length of the cylindrical lens, or is usually less than about one half the radius of lens 13. Although classical optics would predict large aberrations for such a system, lens 13 is nearly diffraction-limited if its diameter is less than about 100 times the wavelength emitted at junction 11, for common indices of refraction. This reduces the phase errors of the optical front to less than one radian which gives a pattern essentially the same as that calculated with zero phase errors.

The op...