The authors report their latest results on II-VI intersubband all-optical switches in which the 10 dB absorption saturation energy is lowered to ~2.0-2.2 pJ for 1.55-1.58 mum by decreasing the thickness of the active layer and increasing the refractive index difference between the core layer and the cladding layers in waveguides. Such low saturation energies greatly improve the switching performance. <7 pJ pump energy at 1520 nm is sufficient for realizing 10 dB switching operation at 1566 nm (switching energy: ~0.7 pJ/dB). To the best of our knowledge, these switching energy and saturation energy values are the lowest reported ones for such ultrafast intersubband all-optical switches at telecommunication wavelengths.