Light intensity attenuation device and method

The invention provides an automatic light intensity attenuation device of an alignment system used in a photoetching machine, which comprises a controller, an optical filter, a motor and a photoelectric sensor. The automatic light intensity attenuation device is characterized in that the motor drives the optical filter to rotate and is used for regulating an attenuation value of incident light, and the photoelectric sensor is used for feeding back a rotating angle of the optical fiber to the controller. A round variable neutral density optical fiber is adopted in the invention, and transmitted light density is linearly attenuated through absorption and reflection in a range from a visible light area to a near infrared area. The motor is controlled by the controller so as to control the rotation of the optical filter, therefore, the automatic stepless attenuation of light intensity is conveniently realized.