Distributed-feedback grating used as an array-mode selector in resonant antiguided diode laser arrays: effects of the mirror facet position with respect to the grating

In resonant and nearly resonant antiguided arrays (ROW arrays), if the grating is located below the active region, a distributed-feedback (DFB) grating can function as a selector for the in-phase array mode in addition to its role as a frequency discriminator. Threshold current densities are calculated for competing (lateral) spatial modes in AR/HR coated 10- and 20-element arrays incorporating lower gratings (ROW-LDFB arrays). Calculations include the effects of random facet locations relative to the grating phase. The threshold current density, J/sub th/, of the in-phase mode and its discrimination, /spl Delta/J/sub th/, against other (array) spatial modes vary with facet location. For 20 (10) elements, J/sub th//spl ap/350-525 (400-550) A/cm² and /spl Delta/J/sub th/ reaches a maximum of 55 (58) A/cm² for 0.01/0.95 AR/HR-coated 350 μm-long devices. For 10-element arrays, the probability of in-phase operation is approximately 50%; for 20-element arrays, the probability is 100%. Preliminary experimental results from 20-element nonresonant devices with uncoated facets are near diffraction-limited beams and nearly single-frequency operation to 250 mW.