## Facts

- Corning owned patents directed to optical waveguide fibers used for long-distance telecommunications, including U.S. Patent Nos. 3,659,915 (’915), 3,884,550 (’550), and a method patent, 3,933,454 (’454).
- Optical fibers guide light by using a higher refractive-index core surrounded by lower refractive-index cladding, enabling low-loss transmission over distance.
- The ’915 patent claimed a composite fiber with a doped silica core and fused silica cladding (with optional cladding doping) configured to achieve low-loss waveguiding.
- Sumitomo developed and sold “S-3” optical fibers that served the same telecommunications function but used a different dopant arrangement, including fluorine doping in the cladding.
- Corning alleged infringement of claims 1 and 2 of the ’915 patent and claim 1 of the ’550 patent; Sumitomo contested infringement and asserted invalidity based on prior art.
- The district court held the asserted claims of the ’915 and ’550 patents valid and found infringement of the ’915 patent (and liability as to the ’550 claim), but found no infringement of the ’454 method patent.
- Sumitomo appealed the validity rulings and the ’915 infringement finding; Corning cross-appealed the noninfringement ruling on the ’454 method patent.

## Issues

1. Whether Sumitomo’s S-3 fiber infringed the ’915 patent under the doctrine of equivalents where literal infringement was conceded.
2. Whether the “all-elements” requirement demands element-by-element correspondence to specific physical components, or whether an equivalent limitation may be satisfied elsewhere in the accused device.
3. Whether the ’915 and ’550 patents were invalid in view of the prior art and related validity challenges.
4. Whether Sumitomo’s manufacturing process infringed Corning’s ’454 method patent.

## Decision

- Affirmed the judgment in all respects.
- Held that Sumitomo’s S-3 fiber infringed the asserted ’915 claims under the doctrine of equivalents.
- Rejected Sumitomo’s argument that equivalence requires one-to-one matching of each claim limitation to the same physical location or component in the accused fiber.
- Affirmed that the ’915 and ’550 patents were not shown invalid on the asserted grounds.
- Affirmed the finding that Sumitomo did not infringe the ’454 method patent.

## Legal Principles

- Doctrine of equivalents may establish infringement where the accused product performs substantially the same function, in substantially the same way, to achieve substantially the same result.
- The “all-elements” requirement is satisfied when each claim limitation is met literally or by an equivalent; equivalence is assessed with respect to the limitation, not rigidly tied to a particular physical subpart of the accused device.
- An accused device may infringe if it contains an equivalent to a claim limitation somewhere in the device, even if the equivalent is implemented in a different structural location than the claim’s illustrative arrangement.
- Appellate review gives substantial deference to district-court fact findings on technical questions, including equivalence and underlying factual predicates for validity, absent reversible error.

## Conclusion

The Federal Circuit upheld the validity of Corning’s optical-fiber structure patents and affirmed infringement of the ’915 patent under the doctrine of equivalents, holding that each claim limitation may be satisfied by an equivalent appearing elsewhere in the accused device; it also affirmed noninfringement of Corning’s separate method patent.


Corning Glass Works v. Sumitomo Elec. U.S.A., Inc., 868 F.2d 1251 (Fed. Cir. 1989)