Chunte A. Lu

Self-Synchronous and Self-Referenced Coherent Beam Combination for Large Optical Arrays

A novel and highly accurate electronic technique for phase locking arrays of optical fiber amplifiers is demonstrated. This is the only electronic phase locking technique that does not require a reference beam. The measured phase error for this system is lambda /20. A model for calculating the signal-shot noise-limited phase errors and the phase-modulation-induced phase errors is developed. For the first time, nine fiber amplifiers are coherently combined. The total power in the phase locked array is 100 W.

Two-dimensional diffractive coherent combining of 15 fiber amplifiers into a 600 W beam

We demonstrate coherent beam combining using a two-dimensionally patterned diffractive optic combining element. Fifteen Yb-doped fiber amplifier beams arranged in a 3×5 array were combined into a single 600 W, M²=1.1 output beam with 68% combining efficiency. Combining losses under thermally stable conditions at 485 W were found to be dominated by spatial mode-mismatch between the free space input beams, in quantitative agreement with calculations using the measured amplitude and phase profiles of the input beams.

Coherent beam combining of fiber amplifiers in a kW regime

Single-frequency coherent beam combination (CBC) of 16 fiber lasers with kW class output power is presented. In addition, kW scale CBC of three Photonic Crystal Fiber (PCF) amplifiers in a filled aperture configuration is reported.

Electronic phasing of high power fiber amplifier arrays

A novel robust phase locking architecture has demonstrated coherent beam combination 725-W from five 145-W fiber amplifiers. The technique uses a single photodetector and no reference beam. The measured rms phase error was lambda/60.

Active coherent superposition of five fiber amplifiers at 670W using multiplexed volume Bragg gratings

We present an experimental study on active coherent combining of five Yb (Ytterbium)-doped fiber laser amplifiers that employs multiplexed volume Bragg gratings (MVBGs), reporting a combining efficiency of 82% and near-diffraction limited beam quality at a combined input power of 380 W, and 70% combining efficiency with equal beam quality at 670 W input power.

Narrow linewidth coherent beam combining of optical fiber amplifier arrays

The first theory for two novel coherent beam combination architectures that are the first electronic beam combination architectures that completely eliminate the need for a separate reference beam are presented. Experimental results demonstrating the coherent addition of a 3 by 3 array of fiber amplifiers with a total phase locked power of 100-W are also described.

Coherent beam combination of fiber laser arrays via multiplexed volume Bragg gratings

We report the first experimental demonstration of active coherently combining of fiber laser arrays with multiplexed volume Bragg gratings up to 70W combined output power with diffraction limited beam quality achieved at 82% combining efficiency.

Phasing of High Power Fiber Amplifier Arrays

We report locking the phase of a five element 725-W amplifier array and in addition we report phase locking off the backscatter from a remote object. The rms phase error was measured to be ?/60.

A Novel Technique for Electronic Phasing of High Power Fiber Amplifier Arrays

A novel robust phase locking architecture has demonstrated coherent beam combination 725-W from five 145-W fiber amplifiers. The technique uses a single photodetector and no reference beam. The measured rms phase error was lambda/60.

On-chip unstable resonator cavity 2-μm quantum well lasers

Focused ion beam milling was used to fabricate on-chip unstable resonator cavity quantum well laser devices. A cylindrical mirror was formed at the back facet of the broad area device emitting near 2 μm. Compared to the Fabry-Pérot cavity device, the unstable resonator cavity device exhibits a 2x diffraction limited beam. The preliminary results demonstrate that a much higher brightness can be reached in this class of broad area devices.