Study of optical signal distribution networks for coherent semiconductor amplifier arrays

The demand for high power semiconductor laser sources has lead to active research in semiconductor laser and amplifier arrays. We have evaluated three design concepts for providing coherent optical power to a semiconductor amplifier array. The proposed amplifier array will employ amplification of a distributed single frequency master oscillator signal to achieve coherent output power over a large aperture. Conceptually, the amplification scheme is similar to that of the microwave traveling wave amplifiers. Previous experiments have shown that approximately 1 mW of coherent signal per channel is sufficient to saturate the individual amplifiers of the amplifier array. The networks provide splitting and amplification of the master oscillator signal to meet the power requirement. The authors show the layout of all three network designs on the same chip. The experiments indicate that the tree design is the most desirable approach for distributing coherent signal on 25 micron pitch. The average output power per channel is very close to the goal of 1 mW and the average fractional coherence exceeds ninety percent.