II-VI's latest proposal calls for it to pay $220 cash plus 0.91 share for each Coherent share.
Lumentum, the San Jose, Calif., provider of optical and photonic products, said it has until midnight Pacific Time Monday, March 22, to amend its own recently raised proposal.
On Wednesday, Lumentum raised its offer to $220 per share in cash and 0.61 shares per Coherent share. The total value of that deal was estimated to be $6.9 billion. That bid was up from its previous offer that valued the company at $6.6 billion.
Under terms of the companies' merger agreement, Coherent would be required to pay Lumentum a $217.6 million termination fee if it chooses a rival bid.
At the time, Coherent set a deadline by which Lumentum, by which it already had agreed to be acquired, had to at least match II-VI's offer.
As part of Lumentum's revised proposal, the Menlo Park, Calif., private-equity group Silver Lake said it would make a $1 billion equity investment in the combined company.
Coherent shares at last check were 2.6% higher at $263.55. Shares of Lumentum dropped 2.6% to $86.08 while II-VI fell 4.2% to $70.28.