Sheared polymer network liquid crystal for fast-response variable optical attenuators

A variable optical attenuator (VOA) at λ=1.55 μm using a sheared polymer network liquid crystal (SPNLC) is demonstrated. SPNLC is fabricated by mixing ∼15 wt % photo-polymerizable monomer in a LC host. To polymerize the SPNLC cell, a two-step UV curing process was adopted. Before shearing, the cell scatters light strongly, but after shearing the cell becomes highly transparent in the near IR region. Using an E7-based SPNLC, the attenuation of our VOA is rather insensitive to wavelength over the ITU C-band. The rise time and decay time were measured to be 35 μs and 205 μs, respectively, at room temperature. Such a response time is at least one order magnitude faster than the state-of-the-art nematic competitors. Comparing with other polymer-stabilized liquid crystals, the SPNLC exhibits a lower driving voltage and negligible light scattering loss in the IR spectral region. A reflection type, polarization-independent VOA with ∼240 μs response time and -32 dB dynamic range was demonstrated at room temperature and 35 V _rms voltage.