Low-loss and low-polarization-dependent fiber variable optical attenuators

We present the optical performance of a compact variable optical attenuator (VOA) developed at Photintech. The presented VOA’s operation principle is based on the guided wave evanescent field manipulation. Access to the evanescent portion of the guided radiation is achieved by replacing the original waveguide’s cladding with a thermo-optic composite polymer (TOP) material. By changing the temperature of the thermo-optic (TO) material we create guided radiation partial leakage attenuating thus the light. Nevertheless, using polymer materials usually creates significant birefringence due to shrinkage during polymerization or thermal stresses during operation and the polarization dependence of such devices is relatively high. We apply a specific cladding geometry and heating electrode (pending patent of Photintech Inc.), which ensures axial compensation of the birefringence, providing thus very small polarization dependence. In-fiber design provides also low insertion loss (IL) and high dynamic range operation. Control electronics allow the VOA to operate with a precision better than 0.1dB. The developed VOA can be used in agile optical networks, for applications such as dynamic gain equalisation, dynamic channel equalisation, optical transmitter power control and receivers protection in telecommunication systems.