Compact and Polarization-Independent Variable Optical Attenuator Based on a Silicon Wire Waveguide with a Carrier Injection Structure

We developed a Si variable optical attenuator (VOA) with low-polarization-dependent loss (PDL). We designed the core dimensions to reduce PDL originating from free-carrier absorption. In the core dimensions, there is a big margin for which the PDL is less than 1 dB when attenuation is -20 dB. On the basis of calculations, we fabricated the Si VOAs and evaluated them. A fabricated Si VOA exhibited PDL of 0.2 dB due to free-carrier absorption when the attenuation was -20 dB. Moreover, we verified that the PDL is less than 1 dB in a wide range of core widths, it is tolerant to fabrication error. (C) 2010 The Japan Society of Applied Physics