GRIN lens with integral filter simplifies couplers

Oct. 1, 2002
Rod-shaped gradient-index (GRIN) lenses are commonly used to couple light into and out of optical fibers.

Rod-shaped gradient-index (GRIN) lenses are commonly used to couple light into and out of optical fibers. Such lenses have a refractive-index profile that varies parabolically with radius and are usually fabricated with flat end faces. Thin-film optical filters—such as tap, edge, wavelength-division-multiplexing, and coarse-wavelength-division-multiplexing (CWDM) filters—are commonly used with GRIN lenses in telecommunications. Typically, thin-film filters are deposited on a separate glass substrate, then combined with GRIN lenses to construct three-port couplers and modules. These devices are often assembled manually through tedious alignment and production steps, including epoxy bonding to attach filter chips to lenses.

A three-port module contains two gradient-index (GRIN) lenses and an optical filter. Depositing the filter coating on the end of one of the GRIN lenses (inset photo), rather than fabricating a separate optical filter and bonding it to the lens, simplifies assembly and results in a rugged device.
Click here to enlarge image

null

Engineers at NSG (Tokyo, Japan) have eliminated the glass filter substrate by developing filter-on-lens technology (FOL), in which thin-film coatings are sputtered directly on the end face of the GRIN lens to produce a single integrated device (see figure). Historically, the thermal-coefficient mismatch between lens and coating materials has made this process difficult. But adjustments made to the coating process have enabled NSG engineers to create monolithic tap, edge, and CWDM couplers with their FOL process. The integrated nature of these devices means that lens and filter alignment do not change appreciably over time, temperature-dependent loss is low, and two Fresnel losses—one at the lens and another at the filter—are eliminated.

The single integrated subassembly reduces production steps by eliminating the need to align, assemble, and cure the filter subcomponent. The result is fewer inspection steps, reduced handling of the optics, and a lower risk of lens contamination. Because FOL technology eases x-y axis alignment tolerances in the production of three-port assemblies, it is well suited for automated assembly. The FOL lens/filters themselves are currently undergoing the final stages of reliability and performance testing; NSG manufacturing sites are gearing up for high-volume production.

Sponsored Recommendations

Request a free Micro 3D Printed sample part

April 11, 2024
The best way to understand the part quality we can achieve is by seeing it first-hand. Request a free 3D printed high-precision sample part.

How to Tune Servo Systems: The Basics

April 10, 2024
Learn how to tune a servo system using frequency-based tools to meet system specifications by watching our webinar!

Motion Scan and Data Collection Methods for Electro-Optic System Testing

April 10, 2024
Learn how different scanning patterns and approaches can be used in measuring an electro-optic sensor performance, by reading our whitepaper here!

How Precision Motion Systems are Shaping the Future of Semiconductor Manufacturing

March 28, 2024
This article highlights the pivotal role precision motion systems play in supporting the latest semiconductor manufacturing trends.

Voice your opinion!

To join the conversation, and become an exclusive member of Laser Focus World, create an account today!