New Focus has filed counterclaims against Photonetics in the tunable laser patent litigation that began this summer.Photonetics sued New Focus in July, alleging that its tunable lasers infringe US Patent No. 5,594,744. In September, New Focus filed counterclaims, denying the accusation and accusing Photonetics of infringing its US Patent Nos. 5,319,668 and 5,995,521.New Focus says the Photonetics patent is invalid and unenforceable. Tunable lasers are a core technology in instrumentation for spectroscopy and for testing wavelength-division-multiplexed fiber optic communications systems.