Data pattern dependence of VCSEL far-field distributions

The far field divergence angle distribution of vertical-cavity surface-emitting lasers is found to exhibit dependence on the data pattern driving the lasers. Two 50% duty cycle 1.25-Gb/s data patterns chosen to cause the same thermal conditions but with frequency content differing by a factor of 16 resulted in changes in the beam profile distributions with up to a 30% power variation in the central on-axis portion of the beam. Examination of the temporal waveforms as a function of far field angle revealed overshoot in the on-axis power and undershoot in the off-axis portion of the beam.