In the latest round of a four-year-plus patent fight between fiber laser makers IMRA America and IPG Photonics, a judge has issued a ruling that favors IMRA. Senior US District Judge Arthur J. Tarnow ruled in favor of plaintiff IMRA regarding the definition of the term "mode converter," which is at the heart of the dispute. The ruling means IMRA's definition will be the one explained to a jury deciding the case. The case concerns IMRA's US Patent No. 5,818,630, "Single-Mode Amplifiers and Compressors Built on Multi-Mode Fibers." The '630 patent employs the use of an optical amplifier to provide a more precise and higher quality light beam from a fiber laser at high power. IMRA first filed the patent infringement suit against IPG in 2006 (See IMRA Files Patent Suit Against IPG). In 2008, IPG filed a patent examination request, putting the suit on hold. In mid-2099, the patent office confirmed the validity of the patent, and IPG's subsequent request for second examination was denied. IPG's request to reconsider that denial is now pending before the director of patents. The late December ruling by Tarnow adopts IMRA's definition for the term mode converter, which is "an element capable of matching the mode of a multimode amplifier fiber." IPG had sought to limit the scope of the term "an element" to "an optical imaging system, such as a lens system, a section of tapered fiber, or a combination thereof" which is capable of matching the mode of a multimode fiber amplifier. IMRA successfully argued that the patent makes it clear that a mode converter can be an optical imaging system, but it doesn't have to be. "Specifically, in the context of this litigation and for purposes of jury instruction, a 'mode converter' shall be defined as 'an element capable of matching the mode of a multimode amplifier fiber," Tarnow ordered. The trial was scheduled to begin in August 2010; a new date has not yet been set.