A motorcycle is easily recognized by other vehicles or pedestrians and is hardly damaged during a maximum bank, by devising the disposition of lighting fixtures. The semiconductor structure includes a substrate, a stacked structure, a dielectric layer, a conductive structure, a dielectric structure and a conductive plug. The cavity ring down system is programmed to integrate a plurality of sample portions during a rise time and a plurality of sample portions during a fall time to obtain a time constant with no sample present and a time constant with sample present. A light-shielding film is laminated on a surface of the second substrate on which the protection films are formed. The semiconductor substrate includes at least a laser source and several photodetectors.