Fujikura Ltd & Anor v Sterlite Technologies Limited

A patent claim is not insufficient merely because its boundaries present practical puzzles. A purposive construction may accommodate reasonable approximations where the specification and the skilled person’s practical knowledge show that exact geometric perfection was not intended.

For sufficiency, the claimant’s technical contribution must be assessed across the claim’s breadth. Invalidity requires evidence of realistic embodiments within the claim that do not provide the promised technical benefit. An alleged collocation is unavailable where the claimed features interact in a way relevant to the invention.

Experimental imperfections do not defeat infringement unless they are shown to make a material difference to the result. A representative sample may support infringement across a product range where the pleaded case and evidence justify the necessary extrapolation.

Fujikura, the proprietor and exclusive licensee of a European patent concerning optical fibre cables, claimed that Sterlite’s Celesta range infringed the patent. Sterlite denied infringement and counterclaimed for invalidity on insufficiency, lack of inventive step, clarity and collocation grounds.

The patent concerned an intermittently-adhered optical fibre ribbon cable with alternating recesses and protrusions on its sheath. Claim 1 required the recess cross-sectional area to fall between 1.3 mm² and 4.8 mm² and required the cable to be suitable for insertion into a micro-duct by air blowing.

The central issues were the construction of micro-duct and the geometrical test required by the claim, the validity of the claim over Pedder and an AFL brochure, whether the claim was insufficient or obvious, and whether experiments on a 432F sample established infringement across the relevant Celesta range.

1. Validity. The claim was valid. The technical contribution included identifying the effect of seal tightness in the air-blowing equipment and disclosing a recess-area range intended to optimise air retention and cable blowability. The claim was not insufficient across its breadth merely because it did not require features such as rib twist, diameter limits beyond suitability for a micro-duct, or a particular protrusion design. The Defendant had not shown realistic embodiments within the claim that failed to provide the promised benefit.
2. Obviousness. Neither Pedder nor the AFL brochure supplied an adequate route to the claimed combination of an intermittently-adhered ribbon and the specified recess area. The skilled team would have faced a wide range of possible cable sizes and protrusion designs, with no reasonable expectation of success. The attacks depended on hindsight and failed. The collocation argument also failed because the internal ribbon structure and external protrusion design interacted in a way relevant to blowability. A collocation approach is available only where the features are truly independent.
3. Construction and insufficiency. Micro-duct was not limited to ducts having an internal diameter below 16 mm. The claim’s circular or elliptical closed curve was to be understood purposively and practically as an approximation to the air seal around a real-world cable. It need not be a perfect circle or ellipse, perfectly tangential, or centred identically at every point. The claim remained capable of construction and implementation.
4. Infringement. The experimental imperfections did not justify rejecting the evidence. The Defendant had not shown that alternative measurements or criticisms would materially alter the recess-area result. On the balance of probabilities, the 432F sample fell within the claimed range. The Claimants were entitled to rely on the sample as exemplary and to extrapolate using the pleaded product information and die-diameter calculations. The patent was therefore infringed by the 144F, 288F and 432F Celesta cables; the claim concerning 576F cables was abandoned.

First-instance decision. The judgment records an earlier case-management decision refusing an amendment to Sterlite’s pleadings: [2025] EWHC 2066 (Pat). No appeal was sought from that decision.