Semiconductor lasers under external perturbations can manifest a broad variety of complex dynamics in their output power, from periodicity to high dimensional chaos. One of their characteristic behaviors, when submitted to optical feedback, is their excitability. These optical excitable devices, that mimic neuronal behavior, can serve as building-blocks for novel, brain-inspired information processing systems. Neuronal systems represent and process the information of a weak external input through correlated electrical spikes. Semiconductor lasers with low to moderate optical feedback, i.e. in the low frequency ﬂuctuations (LFF) regime, display optical spikes with intrinsic temporal correlations, similar to those of biological neurons. Here we study the laser optical spiking dynamics under the inﬂuence of direct pump current modulation, focusing on the inﬂuence of the modulation frequency and amplitude. We characterize time correlations in the sequence of optical spikes by using symbolic ordinal analysis. This powerful tool allows detecting symbolic patterns in the laser output, and to quantify the eﬀect of the frequency and amplitude of the modulation on the patterns probabilities. The experimental results are in good qualitative agreement with simulations of the Lang and Kobayashi model.