Novel thermo-optic variable optical attenuators and digital optical switches based on polymer waveguide

Abstract

Novel polymer-based variable optical attenuators (VOA) and digital optical switches (DOS) are proposed for the highly integrated circuit including add-drop multiplexer (ADM) and optical crossconnects (OXC). Two types of VOAs are Introduced based on mode filtering and radiation, respectively, and two basic ideas are presented for the performance enhancement of the conventional DOS: one is the crosstalk improvement of conventional 1 $\times$ 2 DOS by VOA attachment, which attenuates residual optical powers in the off-state arm of the DOS; and the other Is the definition of a zero voltage state in 2 $\times$ 2 DOS using asymmetric Y-branches. The optimizations of the proposed VOA``s and DOS``s are carried out using the finite element method (FEM) and beam propagation method (BPM); the optimized devices are then fabricated using fluorinated UV-curable polymers through the conventional 4-inch silicon wafer process. The VOA based on mode filtering shows a low operating power of less than 30mW due to the superior thermo-optic effect of polymer material. Less than 1.0 dB of the device insertion loss is achieved at 1550 nm. Device characteristics with a closed-loop feedback control circuit are investigated in order to minimize wavelength dependent loss and the temperature dependence of attenuation level. The fabricated 1 $\times$ 2 DOS with VOA based on mode filtering (Type 1) shows an enhanced crosstalk of < -40 dB and a loss of 1.5 dB at 1550 nm when the applied power consumption is 80 mW. The 1 $\times$ 2 DOS with VOA based on radiation (Type 2) is proposed for lower loss. Since the VOA based on radiation uses two waveguide arms of the Y-branch in the DOS, Type 2 has the same waveguide structure as the conventional 1 $\times$ 2 DOS. The fabricated device shows a very low crosstalk of < -70 dB, and a low insertion loss of < 1.1 dB at 1550 nm when the power consumption is 200 mW. Type 2 shows lower loss and lower crosstalk than Type 1. However, Type 1 shows lower power...