Variable light attenuator of improved air-gap type with extremely low returning light

This paper presents an in-line variable light attenuator of improved air-gap type with extremely low return light loss for single-mode transmission, constructed using the modified structure of the optical connector. Optical attenuation is adjustable through changing the axial distance between the slanted end-faces of a pair of the ferrules aligned within an aligning sleeve. As the result, maximum attenuation was 30 dB at a slanted angle of 8 degrees, and 40 dB at a slanted angle of 12 degrees, at an air-gap of 1.5 mm and at a wavelength of 1.31 μm. The return light loss achieved was less than 60 dB at a slanted angle of 8 degrees or more