3D Diode-Cross-Coupled Tapered Lasers for Kilowatt-Class, Chip-Scale, Laser Diode Phased Arrays

In this proposal, nLight and their collaborator, Eric Johnson, of CREOL, seek to address the main limitations in generating phased arrays by using very high power single mode tapered devices that are phase locked via long “coupling” lasers. The individual diodes would be phase aligned by careful control of their drive current – this would fine-tune the phase to bring it into alignment. The coupling laser makes use of a approach pioneered by Eric Johnson’s group – using second order gratings buried inside a diode laser to vertically cross-couple through free space to a second diode laser placed above. The extension here is to use high power tapered single mode devices as the “slave lasers” in amplifier configuration, with a low power, very long cavity laser above them as a master oscillator in a 3-D configuration. Using high power single mode devices (here we target 15-W per emitter) means relatively few emitters are needed to deliver a 10-kW module – just 700 of them, corresponding to two 25 bar stacks of 200-W bars. Using a laser as the master oscillator means the locking signal is automatically phase coherent over long distances. Finally, the small number of devices required means that phasing the individual tapers together by controlling the current is a practical reality.