Input key assembly and input device

An input device comprising:

• a plurality of input keys,
• wherein at least one of the input keys comprises:
• an input key assembly comprising
• a keycap,
• a substrate,
• an elastic deformable shell-like structure disposed between the substrate and the keycap, wherein the elastic deformable shell-like structure comprises
• a peripheral base portion in abutment with the substrate,
• an apex portion in abutment with the keycap, wherein the peripheral base portion tapers towards the apex portion, and
• a plunger-like element extending from underneath the apex portion and away from the apex portion, wherein a free-end of the plunger-like element is opaque, and
• an optical sensing arrangement disposed on the substrate to transmit a light beam and sense an interruption to the light beam,
• wherein the elastic deformable shell-like structure and the optical sensing arrangement are arranged in a manner so as to interrupt the light beam with the free-end of the plunger-like element when the keycap is depressed to deform the elastic deformable shell-like structure for collapsing the apex portion relative to the peripheral base portion to move the plunger-like element along a longitudinal axis of the plunger-like element.