Radiation implosion was first developed by Klaus Fuchs and John von Neumann in the United States, as part of their work on the original "Classical Super" hydrogen-bomb design.
Their work resulted in a secret patent filed in 1946, and later given to the USSR by Fuchs as part of his nuclear espionage.
However, their scheme was not the same as used in the final hydrogen-bomb design, and neither the American nor the Soviet programs were able to make use of it directly in developing the hydrogen bomb (its value would become apparent only after the fact).
He presented the idea to Edward Teller, who realized that radiation compression would be both faster and more efficient than mechanical shock.
This combination of ideas, along with a fission "spark plug" embedded inside the fusion fuel, became what is known as the Teller–Ulam design for the hydrogen bomb.
According to these documents, an X-ray lens, not a reflector, was used to transfer the energy from primary to secondary during the making of the first Chinese H-bomb.
In an indirect drive system, the target is surrounded by a shell (called a Hohlraum) of some intermediate-Z material, such as selenium.