Electrically switchable structural patterns and diffractions in a dual frequency nematic liquid crystal

Electrically driven structural patterns in liquid crystals(LCs)have attracted considerable attention due to their electrooptical applications.Here,we disclose various appealing reconfigurable LC microstructures in a dual frequency nematic LC(DFNLC)owing to the electroconvection-induced distortion of the LC director,including one-dimensional rolls,chevron pattern,two-dimensional grids,and unstable chaos.These patterns can be switched among each other,and the lattice constants are modulated by tuning the amplitude and frequency of the applied electric field.The electrically switchable self-assembled microstructures and their beam steering capabilities thus provide a feasible way to tune the functions of DFNLC-based optical devices.

4 × 20 GHz silica-based AWG hybrid integrated receiver optical sub-assemblies

Both the 4 × 20 GHz coarse wavelength division multiplexing and LAN-WDM receiver optical sub-assemblies（ROSAs） were developed. The ROSA package was hybrid integrated with a planar lightwave circuit arrayed waveguide grating（AWG） with 2% refractive index difference and a four-channel top-illuminated positive-intrinsicnegative photodetector（PD） array. The output waveguides of the AWG were designed in a multimode structure to provide flat-top optical spectra, and their end facet was angle-polished to form a total internal reflection interface to realize vertical coupling with a PD array. The maximum responsivity of ROSA was about 0.4 A/W, and its 3 dB bandwidth of frequency response was up to 20 GHz for each transmission lane. The hybrid integrated ROSA would be a cost-effective and easy-assembling solution for 100 Gb E data center interconnections.

Polymerization enabled reduction of the electrically induced birefringence change in nematic liquid crystals

Electric fields modify the optical properties of nematic liquid crystals(NLCs) by changing the nematic molecular orientation or order parameters, which enables electro-optic applications of NLCs. However, the field-induced optic change is undesirable in some cases. Here, we experimentally demonstrate that polymer stabilization weakens the birefringence change of NLCs caused by the nanosecond electrically modified order parameter effect. The birefringence change is reduced by 65% in the NLC doped with 25% reactive monomer, which is polymerized close to the nematic-to-isotropic phase transition. This technique could be used in liquid crystal devices where the birefringence change is unfavored.

A data-driven health indicator extraction method for aircraft air conditioning system health monitoring

Prognostics and Health Management(PHM) has become a very important tool in modern commercial aircraft. Considering limited built-in sensing devices on the legacy aircraft model,one of the challenges for airborne system health monitoring is to find an appropriate health indicator that is highly related to the actual degradation state of the system. This paper proposed a novel health indicator extraction method based on the available sensor parameters for the health monitoring of Air Conditioning System(ACS) of a legacy commercial aircraft model. Firstly, a specific Airplane Condition Monitoring System(ACMS) report for ACS health monitoring is defined. Then a non-parametric modeling technique is adopted to calculate the health indicator based on the raw ACMS report data. The proposed method is validated on a single-aisle commercial aircraft widely used for short and medium-haul routes, using more than 6000 ACMS reports collected from a fleet of aircraft during one year. The case study result shows that the proposed health indicator can effectively characterize the degradation state of the ACS, which can provide valuable information for proactive maintenance plan in advance.

Submicrosecond electro-optical switching of one-dimensional soft photonic crystals

Soft photonic crystals are appealing due to their self-assembly ability,wide tunability,and multistimuli-responsiveness.However,their response time is relatively slow,ranging from milliseconds to minutes.Here,we report submicrosecond switching of chiral liquid crystals(LCs)with 1D photonic microstructures,where electric fields modify the orientational order of molecules and quench their fluctuations,rather than altering the orientation.Thus,the adjusted refractive indices result in a fast shift of the photonic bandgap,on the order of 100 ns,which is four orders of magnitude faster than conventional electro-optic switching in cholesterics.This work offers tremendous opportunities for soft photonic applications.