Development of an LED with a Fresnel lens

This paper presents the development of an LED with an Fresnel lens to be used in an optical sensor. In a conventional LED a lens and an element are separated, and so must be aligned. Using an LED with a Fresnel lens, both parts are combined so alignment is not necessary. The Fresnel lens was developed because of its thin structure and good optical characteristics. Conventionally, the Fresnel lens has been fabricated by means of electron beam lithography, but it was very time consuming. To solve this problem and fabricate an LED with a Fresnel lens, a diamond turning machine was developed. This machine is used to fabricate molds for Fresnel lenses. By using these molds and inserting LED chips during the injection molding process, an LED with a Fresnel lens can be fabricated. Compared to a conventional LED with a spherical lens, the thickness of the LED is reduced by 70%, and its volume by 50%. Also the LED with a Fresnel lens emits three times as much light as a conventional LED. It is expected that when this LED is used in an optical sensor, its reduced thickness and good optical characteristics will result in a thinner sensor with improved sensitivity.