Browse Prior Art Database

Collimator Alignment

IP.com Disclosure Number: IPCOM000036529D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Bassetti, LW: AUTHOR [+2]

Abstract

Astigmatism is adjusted out of the optical head of an optical disk drive data storage device by slightly defocusing the head's collimator lens. This correction is possible due to the fact that when a non- collimated light beam is passed through an anamorphic beam expander, a change in astigmatism is introduced into the beam. Therefore, a single correct position can be found for the collimator lens which is down stream of the beam expander. The collimator is moved axially to correct for the beam's astigmatism. This adjustment can be automated and controlled by a computer.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Collimator Alignment

Astigmatism is adjusted out of the optical head of an optical disk drive data storage device by slightly defocusing the head's collimator lens. This correction is possible due to the fact that when a non- collimated light beam is passed through an anamorphic beam expander, a change in astigmatism is introduced into the beam. Therefore, a single correct position can be found for the collimator lens which is down stream of the beam expander. The collimator is moved axially to correct for the beam's astigmatism. This adjustment can be automated and controlled by a computer.

The first task is to establish (1) beam squareness to the datum plane 10 of optical head 11, and (2) rough or initial collimation of beam 12 down stream of the beam expander.

Datum 10 is a plane which is parallel to the plane of the optical disk which will be transduced by the optical head. Beam 12 must be perpendicular or square to this plane. Squareness of the beam to this datum plane is adjusted by moving the laser in the orthogonal directions X and Y.

Rough astigmatism adjustment is achieved by moving collimator lens 13 in direction Z, i.e., in a direction perpendicular to the X-Y plane.

Task (1) is accomplished by centering the beam on quadrant detector #1. The beam is centered on the common junction of this photocell assembly by moving the laser in directions X and Y. In this way, orthogonality of laser beam 12 is established.

Task (2) is accomplished by moving collimator lens 13 in the Z direction in order to peak the total illumination on the four photocells of this detector. This process is repeated on quadrant detector #2, and then on quadrant detector #3. Astigmatic adjustment becomes finer on each quadrant detector. After the last adjustment at detector #3, some astigmatism may still remain in beam 12. However, in this way, rough collimation is established.

The next task is to perform final collimator lens adjustment to within 0.1 micron of its best position, resulting in less than 0.08 wave of astigmatism in light beam 12.

Two beam width measurement units 20 and 30 are mounted afocal with respect to focusing lens 40. Unit 20 measures the beam width parallel to the laser's junction. Unit 30 is rotated by 90o, and thus measures the beam width in a d...