The invention relates to a resonant cavity enhanced photodetector comprising a first and a second reflection means forming the said cavity and means of absorption of photons of an incident light beam, characterised in that it also comprises at least one electro-optical element inside the said cavity, intended for tuning the wavelength of the said photodetector. The engine transmits control information indicating a method of controlling displaying a related-advertisement to a sub-device that receives the related-advertisement related to the main advertisement from a server and displays the received related-advertisement. A canoe accessory has a thickened attachment portion for engagement in the slot to attach the accessory to the canoe. The hook member has a closure portion fixed for pivotal movement with the hook portion, and blocking the opening when the hook member is in the stored position. Controlling the positions of the movable pieces according to the pattern encodes paper size.