Fault-tolerant variable fiber-optic attenuator using three-dimensional beam spoiling

A variable fiber-optic attenuator (VFOA) in a compact folded optical structure is introduced using the basic principles of optical beam misalignment via three-dimensional (3-D) beam spoiling. Key features include high resolution of control, the ability to tune the attenuation response, and the fault tolerant attenuator design. Experimental proof of concept demonstration using one dual fiber collimator and a three-axis controlled mirror as a 3-D beam spoiling element shows a high 52.4 dB dynamic range and a very low optical loss of 0.12 dB at 1550 nm wavelength. The measured polarization dependent loss is 0.02 dB. In addition, multiwavelength VFOA performance indicates an average 52.4 dB maximum optical attenuation with a ±0.04 dB fluctuation over a 70 nm bandwidth. A wavelength dependent loss of 0.10 dB is also measured with a fluctuation of ±0.04 dB.