Refractive variable optical attenuator fabricated by silicon deep reactive ion etching

We report on a novel refractive variable optical attenuator with a wedge-shaped silicon optical leaker, in which a part of the light signal is successively transmitted and refracted outside the acceptance angle of the output fiber. This device can be simply fabricated using a deep reactive ion etching and does not require sidewall metallization. We have theoretically estimated its optical characteristics and experimentally showed its high performances, such as low insertion loss of 0.6 dB and wide attenuation range of 43 dB. The fabricated device also showed a high return loss of over 39 dB even in an air-ambient condition and its polarization-dependent loss was smaller than 10% of the attenuation level.