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SINGLE GRADED INDEX (GRIN) LENS FOR ACTIVE-OPTICAL TARGET DETECTION

IP.com Disclosure Number: IPCOM000006495D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-09
Document File: 4 page(s) / 155K

Publishing Venue

Motorola

Related People

James C. Peterson: AUTHOR

Abstract

A compact, active optical system, utilizing graded index (GRIN) rod lenses, was previously proposed for target detection applications. Referring to Figure la, that system concept comprised transmit fibers 1 separate from receive fibers 2, GRIN-rod lenses 3 and 4, a spherical collector/reflector 5, and a common window 6. Both fibers 1 and 2 would be cemented with index matching epoxy 7 to GRIN-rod lenses 3 and 4. Transmitter 8 employs a % pitch GRIN-rod lens 3 which colIiiates the light 9 emitting from fiber 1 and is aimed out the com- mon window 6 (common since both transmitted and received light energy passes through the same window). This transmitted light wave 30 becomes a reflected light wave 31 off target 10 and is collected by spherical reflec- tor 5 through common window 6. The light energy is focussed onto one side of a % pitch GRIN-rod lens 4, which translates the image to receive fiber 2 cemented to the lens's other side. The receiver GRIN-rod lens 4 is used to eliminate the need for fiber-end polishing, which is a high cost manufacturing procedure. Transmit signal 32 is sourced from a pulsed laser diode (not shown in the figure), coupled into transmit fiber 1. Receive fiber 2 guides the collected light energy 33 to an optical photodetector (also not shown).

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MOTOROLA INC. Technical Developments Volume 16 August 1992

SINGLE GRADED INDEX (GRIN) LENS FOR ACTIVE-OPTICAL TARGET DETECTION

by James C. Peterson

  A compact, active optical system, utilizing graded index (GRIN) rod lenses, was previously proposed for target detection applications. Referring to Figure la, that system concept comprised transmit fibers 1 separate from receive fibers 2, GRIN-rod lenses 3 and 4, a spherical collector/reflector 5, and a common window 6. Both fibers 1 and 2 would be cemented with index matching epoxy 7 to GRIN-rod lenses 3 and 4. Transmitter 8 employs a % pitch GRIN-rod lens 3 which colIiiates the light 9 emitting from fiber 1 and is aimed out the com- mon window 6 (common since both transmitted and received light energy passes through the same window). This transmitted light wave 30 becomes a reflected light wave 31 off target 10 and is collected by spherical reflec- tor 5 through common window 6. The light energy is focussed onto one side of a % pitch GRIN-rod lens 4, which translates the image to receive fiber 2 cemented to the lens's other side. The receiver GRIN-rod lens 4 is used to eliminate the need for fiber-end polishing, which is a high cost manufacturing procedure. Transmit signal 32 is sourced from a pulsed laser diode (not shown in the figure), coupled into transmit fiber 1. Receive fiber 2 guides the collected light energy 33 to an optical photodetector (also not shown).

  This target detecting concept is rejected due to the high angular sensitivity of the transverse location of fibers 1 & 2 relative to the end of GRIN-rod lenses 3 and 4 because of the small focal length of these lenses. Labo- ratory tests showed a sensitivity of approximately 0.5 degree per mil (thousandth of an inch) transverse motion of either fiber 1 or 2. The preferred embodiment sche- matically illustrated in Figure lb eliminates the problem of high angular alignment sensitivity discussed above.

Referring now to figure lb, the concept is to use a

Single' GRIN-rod lens 12 for both the transmit and receive

fibers I3 and 14. Automatic angular alignment between the transmit and receive fibers 13 and 14 is achieved by use of a channel 15 through the center of GRIN-rod lens 12 and inserting receive fiber 14 part-way into chan- nel 15, and afixing transmit fiber 13 over channel 15 on

28

the other side. Transmit fiber 13 may be inserted slightly into channel 15 to assure proper alignment between fibers 13 and 14. The channel is filled with an index matching, ultra-violet (uv) curing epoxy before inserting receive fiber 14. After receive fiber 14 has been slid the proper distance into channel 15 to obtain the focal position, the epoxy is cured by shining uv light onto the lens.

  Two variations of this concept is shown in Figure 2. Figure 2a illustrates how a standard '/4 pitch lens 16 is used to accomplish the task. It shows an optical ray-trace of a standard NSG GRIN-rod lens catalog part. The optical transmission waveleng...