A non-drip, preferably self-adhesive, silicone elastomer composition crosslinkable by polyaddition, such as those polyorganosilanes bearing C2\u2550C6\u2261Si-alkenyl units and \u2261Si\u2014H units but excluding fluorinated POS. Based on the frequencies of usage of the terms, the frequencies of usage of each term are compared between a specific user and other users to find a difference therebetween, and terms for which the difference is equal to or larger than a predetermined value are presented. Also, a rear mirror is provided on the optical axis behind the receiver lens, where the rear mirror reflects towards the receiver lens the reception light beam which is refracted by the receiver lens.