The LBTEK Slit-Adjustable Fiber Optic Attenuator can be used for controlling the luminous flux between fiber-coupled output beams. The slit-adjustable fiber optic attenuator is equipped with an LB74UV fiber collimating lens at each end, with an adjustable slit in the middle to regulate the luminous flux. Its operating principle involves the incident light being collimated after passing through the first lens, then adjusted in luminous flux via the adjustable slit, and finally coupled into the output fiber through the second collimating lens. The fiber optic attenuator connects to the fiber via an SMA905 connector, ensuring consistent attenuation for light within the operating wavelength range of 185–2500 nm. After connecting the fiber, the distance between the fiber end face and the lens can be adjusted using the set screw, with a maximum adjustable travel of 5 mm. The attenuation level is controlled via a mechanical adjustment wheel, allowing for adjustable light attenuation from 0% to 100%. Once the target luminous flux is achieved, it can be locked in place using the side M3 plastic thumb screw.