Individual spatial modes of a phase-locked injection laser array

Abstract

The oscillating spatial modes of an eleven-stripe gain-guided phase-locked AIGaAs injection laser array with a multiple quantum well active layer are observed by spectrally resolving its far-field radiation pattern. Nine distinct patterns are identified. The widening of the most intense outer lobes correlates with the shift of the wavelength of the mode to shorter wavelengths. The origin of the observed far fields is not consistent with a uniform array of emitters with equal coupling between the elements. When the array is placed in an external cavity containing a mirror, it is possible to select individual spatial modes of the compound resonator as observed in the spectrally integrated far-field patterns. A large number of patterns are observed, including the fundamental mode. Many of the far-field patterns selected with the external resonator follow the same correlation in angular separation of the outer lobes and the wavelength shift of the longitudinal modes as the native array. The external reflector induces asymmetry in the intensity distribution for many of the patterns. Operation of a phase-locked laser array in conjunction with an external resonator is shown to be a useful technique for spatial mode selection.