A Fresnel lens receiver
The ability of a receiver to receive weak signals is primarily dependant on the sensitivity of the detector and the area of the optics used for 'gathering the light'. For laser communication Fresnel lenses offer a very large area at a minimal cost. Fresnel lenes are manufactured by etching or cutting 'prisms' into the surface of the material which in most cases is plastic. Each prism refracts the light by a slightly different angle, the ones near the center by a small angle, the prisms at the outer edge will refract light by a much larger angle. All will be designed to focus the light to a common point.
I managed to order a Fresnel lens from Comar Optics in Cambridge England. It is 284 x 284mm square and has a focal length of 212mm.
The photo's below show the frame I've built in various stages of construction and the mounting arrangement for my OPT301 detector module. This sits on a small piece of wood between two brackets rescued from a self assembly kitchen cupboard.
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