Abstract: The present disclosure provides an optical assembly and a method of using an optical assembly. The optical assembly includes a carrier, a filter module on a primary surface of the carrier and disposed on a predetermined optical path, wherein the filter module includes a plurality of filter elements corresponding to a plurality of beams of different channels, a focal length adjuster disposed on the predetermined optical path, wherein at least a focal length of one of the plurality of beams is altered by the focal length adjuster, and a receiver extension configured to receive the plurality of beams via a plurality of sensing areas respectively at a receiving surface, wherein a beam size of each beams at the receiving surface is less than an area of each of the corresponding sensing areas.