DETECTOR, DETECTION SYSTEM, AND WAVELENGTH SELECTION ELEMENT

To provide a detector and a detection system which reduce erroneous detection due to light quantity saturation when a light receiving element receives unnecessary light with hight light intensity, and a wavelength selection element used for the detector and the detection system.SOLUTION: A detector 20 includes: a wavelength selection filter 211 which reflects light in a wavelength region A, and which transmits light of a wavelength not in the wavelength region A; and a light receiving element 216 for receiving the light in the wavelength region A, which has been reflected by the wavelength selection filter 211. The wavelength selection filter 211 includes a wavelength selection reflection layer 212 formed of a cholesteric liquid crystal layer.SELECTED DRAWING: Figure 2 【課題】光量の大きい不要な光を受光素子が受光した際の光量飽和に起因する誤検知が低減された検知器、検知システム、これらに用いられる波長選択素子を提供することができる。【解決手段】検知器２０は、波長域Ａの光を反射し、波長域Ａ以外の波長の光を透過する波長選択フィルタ２１１と、波長選択フィルタ２１１で反射された波長域Ａの光を受光する受光素子２１６とを備える。この波長選択フィルタ２１１は、コレステリック液晶層により形成された波長選択反射層２１２を備えている。【選択図】図２