We demonstrate a new method for simultaneously measuring the phase retardation and optic axis of a compensation film by using an axially-symmetric sheared polymer network liquid crystal (AS-SPNLC). The AS-SPNLC is a liquid crystal structure with radial director distribution and its phase retardation has a gradient change from center to edges. When overlaying a tested compensation film with a calibrated AS-SPNLC cell between crossed polarizers, the optic axis and phase retardation value of the compensation film can be determined. This method is particularly useful for those optical systems whose optic axis and phase retardation are dynamically changing.
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 Vrms voltage.
Most liquid crystal display (LCD) devices use two ITO-glass substrates in order to confine the fluidic LC. To align the LC molecules, the inner surfaces of the substrates were coated with a thin polyimide (PI) layer. These PI layers are mechanically buffed in order to produce uniform molecular alignment. To reduce weight, the single-substrate approach has been explored recently in which the LC device consists of a substrate and a thin polymer film. The major technical challenge is how to align the LC molecules on the polymer film side. In this paper, we demonstrate a new single-substrate IPS-LCD. The LC cell consists of an anisotropic LC polymer film and an interdigitated ITO-glass substrate. The anisotropic film not only behaves as a substrate but also helps align the LC molecules. Compared to the LCD using two glass substrates, the new device has almost the same bright state and the same dark state. Our new device exhibits a higher contrast ratio (~514:1) because of good LC alignment. The driving voltage is low, and the response time is reasonably fast. The measured rise time is ~8ms and decay time is ~63 ms using a 12-μm cell gap and E7 LC mixture. This technology is particularly attractive for making single-substrate displays and also has potential for a double-layered guest-host display and a flexible display using IPS LCDs.
Surface effects on the phase separation dynamics, morphologies, and electro-optic properties of thin polymer-dispersed liquid crystal (PDLC) cells are investigated. Four types of surface alignment layers were studied: ITO only, Polyimide (PI) without rubbing, homogeneous cell, and 90° twisted nematic (TN) cell. The ITO-only and non-rubbed PI cells do not provide enough anchoring force to prevent LC droplets flow and coalesce. As a result, the droplets are larger and less uniform. For the homogeneous and TN cells with sufficiently high anchoring energy, almost all the nucleated LC droplets grow at a fixed position during phase separation. The appearance of the coalescence is not obvious and the formed LC droplets are relatively uniform. For the rubbed cells with polar anchoring energy >2x 10-4 J/m2, the droplet size is smaller and more uniform than those in the conventional PDLC cell. The phase separation dynamics determine the final composite morphology which affects the electro-optic properties of a PDLC device. The morphologies in the homogeneous and TN cells are similar, but the TN cell is polarization independent while the homogeneous cell is polarization dependent. Moreover, the TN PDLC cell exhibits a higher contrast ratio. The light shutter made of TN PDLC shows no haze and 5-10 ms response time.