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According to the datasheet, the maximum continuous forward current is 50mA. One can exceed this if you reduce the duty cycle at reasonably high frequencies (for example, they specify the output rise and fall times using a 100mA 10% duty cycle at 10kHz).
The forward voltage, Vf, is dependent on the current and temperature. The highest possible Vf is 1.8V, when driven at 100mA (at low duty cycle, as described above) at -60°C. The lowest Vf occurs at low drive current and high temperatures. At 100°C and 5mA, Vf would be about 1.1V.
Here is the graph from the datasheet showing Vf with respect to forward current:
Here is the link to the datasheet where I obtained this information.