In its recent decision, Fiber, LLC. v. Ciena Corp., No. 2019-1005 (Fed. Cir. Nov. 21, 2019), the Court of Appeals for the Federal Circuit (Federal Circuit) issued a reminder that the structure necessary to satisfy the definiteness requirement for a means-plus-function in a claim cannot normally be found in material incorporated by reference. Because identifying the structure corresponding to a means-plus-function claim is necessary for understanding the claim, this is an important reminder of where to look -–and where not to look – for that corresponding structure.

Means-plus-function claiming allows a patentee to claim functionality without reciting a specific structure within the claim itself. Instead, a means-plus-function claim relies on a corresponding structure found in the corresponding patent specification. And if means-plus-function claiming is relied upon to claim functionality without an adequate disclosure of the required corresponding structure, the claim is indefinite. Means-plus-function claiming is codified in 35 U.S.C. § 112(f) (formerly 35 U.S.C. §112, ¶ 6), which states:

An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.

Generally, “essential material” may be incorporated by reference where it “is necessary to … [d]escribe the structure, material, or acts that correspond to a claimed means or step for performing a specified function as required by 35 U.S.C. 112(f).” See 37 CFR 1.57(d). However, courts have been hesitant to find structure in materials incorporated by reference unless such incorporation is expressly for the purpose of importing that structure.

In Fiber LLC v. Ciena Corp., the plaintiff Fiber had asserted claims directed to an optical beam switching system that recited a “control so that a first beam directing device will be positioned to direct the optical beam[.]” The district court held that “control” was a nonce word that was directly tied to the function of positioning the beam. After determining that “control” invoked § 112, ¶ 6, the district court looked to the specification for the corresponding structure but did not find it, and held the claims invalid for indefiniteness. Fiber argued that another patent, incorporated by reference in the specification, disclosed the necessary structure, and appealed this issue to the Federal Circuit.

The Federal Circuit panel agreed that “control” invoked § 112, ¶ 6, and that the disclosure of a generic “control” box with no indication of structure was inadequate under that statute. The panel further agreed that Fiber’s proposed incorporation by reference could not provide the corresponding structure, and affirmed the district court’s holding of indefiniteness.

The Federal Circuit’s decision in Fiber is consistent with prior opinions holding that merely “mentioning prior art references in a patent does not suffice as a specification description to give the patentee outright claim to all of the structures disclosed in those references.” Pressure Prods. Med. Supplies, Inc. v. Greatbatch Ltd., 599 F.3d 1308, 1317 (Fed. Cir. 2010). Rather, to rely on a structure in material incorporated by reference, the specification must expressly state in which specific reference the structure corresponding to the claimed functionality is found. See, e.g., Otto Bock Healthcare LP v. Össur HF & Össur Ams., Inc., 557 F. App’x 950, 955 (Fed. Cir. 2014).

The test for whether a structure is sufficiently disclosed is “whether structure is described in [the] specification, and, if so, whether one skilled in the art would identify the structure from that description.” Default Proof Credit Card Sys. v. Home Depot U.S.A., Inc., 412 F.3d 1291, 1301 (Fed. Cir. 2005). Fiber provides a reminder that when assessing means-plus-function claims, one should remember that absent a specific indication to the contrary, “material incorporated by reference cannot provide the corresponding structure necessary to satisfy the definiteness requirement for a means-plus-function clause.”