"Fast" pulse (8µs) low current (10µA - 100µA) amplification for optocouplers
CMOS logic gates have an extremely high input impedance, and most of them have enough drive strength to drive LEDs directly (LVC is rated for 24 mA). In this case, you can use a simple buffer:



If you need multiple buffers, you can have eight with the 74LVC244/74LVC541, or sixteen with the 74LVC16244/74LVC16541.



Alternatively, if you want to build it from discrete components, you can switch the LED with a MOSFET that switches on at a low gate voltage and has a small gate capacitance, such as the BSS138: