Browse Prior Art Database

MODULATOR ALIGNMENT DEVICE

IP.com Disclosure Number: IPCOM000024880D
Original Publication Date: 1982-Aug-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 128K

Publishing Venue

Xerox Disclosure Journal

Abstract

This apparatus is described to assist in the alignment of an optical beam to a light modulator. All adjustments are relative and do not require precision or absolute measurements. The apparatus is particularly useful when aligning optical systems in which a modulator is a component. With the aid of this apparatus, interchange-ability of the modulator, the laser and other components can be made without extensive realignment and without the use of highly trained personnel.

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Page 1 of 4

(EROX DECLOSURE JOURNAL

MODULATOR ALIGNMENT DEVICE Proposed Donald H. Wolpert Classification

U.S. C1. 350/96

Int. C1. G02b 5/14

OPTICAL BEAM

FIG* /a

-

WSPLACEMENT

FIG. lb

Volume 7 Number 4 July/August 1982

4 OPT I= BEAM

245

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MODULATOR ALIGNMENT DEVICE (Cont'd)

This apparatus is described to assist in the alignment of an optical beam to a light modulator. All adjustments are relative and do not require precision or absolute measurements. The apparatus is particularly useful when aligning optical systems in which a modulator is a component. With the aid of this apparatus, interchange- ability of the modulator, the laser and other components can be made without extensive realignment and without the use of highly trained personnel.

In an laser scanning system ke., Raster Output Scanner) employing a modulator to turn the beam "on and off" at high video rates, alignment to the modulator is always a difficult task. The most critical tolerances and angles are alignment to the Bragg angle and alignment to the center line of the acoustic wave emanating from the modulator transducer, see Figure la. It should be noted that alignment to the acoustic beam is not necessarily to the physical centerline of the transducer. The optical beam is usually positioned close to the transducer to obtain a strong interaction and maximum throughput or diffraction efficiency. Although the beam is close, it is usually in a transition region between the transducer's acoustic near field and far fields. Depending on the optical beam position relative to the acoustic field pattern, strong constructive or destructive fields can be en- countered. For this reason small deviations of the optical beam or physical movement of the modulator crystal are required to obtain maximum interaction. The physical height of the modulator transducer may be on the order of 0.01 inches with an acoustic window on the order of 0.0002 inches. To obtain maximum acoustic/optical interaction alignment is required, sometimes within 0.0002 inches. This kind of aperture makes alignment and interchangeability virtually impossible.

To overcome these limitations, it is suggested that a plane parallel plate be mounted with the modulator as an assembly. An optical beam traversing a plane parallel plate undergoes a displacement that i...