Ultrasensitive polarized-light photodetectors based on 2D hybrid perovskite ferroelectric crystals with a low detection limit

Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications.Two-dimensional(2D)hybrid perovskite ferroelectrics,in which the coupling of spontaneous polarization(P_(s))and light favors the dissociation of photo-induced carriers,have taken a booming position within this portfolio.However,polarized-light photodetectors with a low detectionlimit remain unexplored in this 2D ferroelectric family.In this work,the high-quality individual crystals of a 2D perovskite ferroelectric,BA_(2)CsPb_(2)Br_(7)(1,where BA^(+)is n-butylammonium),were used to fabricate ultrasensitive polarized-light detectors.Its unique bilayered structural motif results in quite strong electric and optical anisotropy with a large absorption ratio of a_(c)/α_(a)≈3.2(λ=405 nm).Besides,the presence of ferroelectric Psalso endows high built-in electric field along the polar c-axis that favors photoelectric activities.Under an extremely low detectable limit of 40 n W/cm^(2),the detector of 1 exhibits a notable dichroism ratio(I_(ph)^(c)/I_(ph)^(a)≈1.5),a large responsivity of~39.5 m A/W and a specific detectivity of~1.2×10^(12)Jones.Moreover,crystal-based devices of 1 also exhibit a fast response speed(~300μs)and excellent anti-fatigue merits.This work highlights great potentials of hybrid perovskite ferroelectrics toward polarized-light photodetection.

Resolving the problem of cross sensitivity in fiber Bragg grating sensor based on the principle of polarized-light interference

The article introduces an advanced approach of fiber grating strain demodulation based on the principle of polarized-light interference.This method can solve the problem of cross sensitivity in fiber Bragg grating sensor.As for the yttrium vanadate(YVO4)crystal polarized-light interferometer,if there are two different fiber Bragg gratings that have a p rad phase difference,one is used for strain sensor and the other is used for temperature compensating.Then the problem of cross sensitivity can be overcome.The analyses of the strain demodulation resolution show that with a decrease in crystal thickness the resolution increases.The experiment shows that when the thickness of YVO_(4) crystal is 0.5 mm,the effect of cross-sensitivity will be reduced to 0.13μe/°C,which is 1.6%of the effect used by only one fiber Bragg grating for strain measure.And when the thickness is 0.1 mm the cross-sensitivity will be reduced to 0.0067μe/°C,which is less than 0.08%.Less thickness of crystal is beneficial for the resolution of strain measure,but the machining of small thickness crystal is difficult.To solve this problem,a new scheme of polarized-light interferometer with the structure of double layer crystal was analyzed.