We present the results of a scaling study of monolithic differential p
airs of optical thyristors, The devices are depleted thyristors, inten
ded for high-frequency and high-sensitivity operation, According to th
e measurements, the optical switching energy scales with area and equa
ls to 15 aJ/mu m(2). The smallest pair with mesas of 10 x 15 mu m(2) o
perates with 2.6 fJ of light input. Sub-femtojoule optical switching e
nergy is expected in the near future.