(Reuters) - Optical fiber firm Lumentum Holdings Inc said on Tuesday it has raised its buyout offer for Coherent Inc to about $7 billion, the latest in a three-way battle for the laser maker. Lumentum had previously raised the offer to $6.9 billion on March 17, following which optical components maker II-VI Inc said it would pay $7 billion to acquire Coherent. Under the revised offer, Coherent shareholders would receive $230 in cash and 0.6724 of a Lumentum share for each share they own. Coherent was put into play after Lumentum, a supplier of 3D sensors used in Apple iPhone’s Face ID, offered $5.7 billion for the company in January, triggering rival bids from MKS Instruments Inc and II-VI last month.