Study on Fabry–Perot cavity consisting of two chirped fiber Bragg gratings

Combined the effective mirror surface model with the transfer matrix method, a detailed theoretical and numerical study on Fabry–Perot cavity consisting of two chirped fiber Bragg gratings is investigated. Results demonstrate that transmission responses of the Fabry–Perot cavity can be adjusted by changing the cascading sequences of the two gratings. When the two gratings are connected in the direction of same chirping, approximately uniform resonance and group delay are exhibited. However, some distinctive non-uniformity of the neighboring resonance peaks intervals is shown if the two gratings are cascaded in the opposite chirping sequences. In addition, for the Fabry–Perot cavity constructed by chirped-fiber-Bragg-gratings with different amplitudes or bandwidths, efficient resonances are achieved only in the common reflection range.     

ESD sensitivity of AlGaAs and InGaAsP based Fabry–Perot laser diodes

The sensitivity to electrostatic discharges of Fabry–Perot laser diodes with InGaAsP as active layer material has been tested and compared to Fabry–Perot lasers based on AlGaAs as active layer material. In the case of the forward-bias ESD pulses we observed a substantially lower degradation threshold voltage for the AlGaAs type lasers as compared to the InGaAsP type lasers. A detailed analysis of the optical and electrical parameters before and after ESD test with particular emphasis on the characteristic temperature and optical emission spectra changes has been done. Effective suppression of the optical emission on a ns-time scale due to device heating during the forward-bias ESD pulses has been evidenced by monitoring the light emission during ESD pulses.     

Strain-insensitive and high temperature fiber sensor based on a Mach–Zehnder modal interferometer

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64 pm/°C from 200 °C to 1000 °C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675 °C/με. The reasons for realizing the high temperature sensitivity is also discussed.     

D–A copolymer with high ambipolar mobilities based on dithienothiophene and diketopyrrolopyrrole for polymer solar cells and organic field-effect transistors

Donor–acceptor (D–A) type conjugated polymers have been developed to absorb longer wavelength light in polymer solar cells (PSCs) and to achieve a high charge carrier mobility in organic field-effect transistors (OFETs). PDTDP, containing dithienothiophene (DTT) as the electron donor and diketopyrrolopyrrole (DPP) as the electron acceptor, was synthesized by stille polycondensation in order to achieve the advantages of D–A type conjugated polymers. The polymer showed optical band gaps of 1.44 and 1.42 eV in solution and in film, respectively, and a HOMO level of 5.09 eV. PDTDP and PC₇₁BM blends with 1,8-diiodooctane (DIO) exhibited improved performance in PSCs with a power conversion efficiency (PCE) of 4.45% under AM 1.5G irradiation. By investigating transmission electron microscopy (TEM), atomic force microscopy (AFM), and the light intensity dependence of J_SC and V_OC, we conclude that DIO acts as a processing additive that helps to form a nanoscale phase separation between donor and acceptor, resulting in an enhancement of μ_h and μ_e, which affects the J_SC, EQE, and PCE of PSCs. The charge carrier mobilities of PDTDP in OFETs were also investigated at various annealing temperatures and the polymer exhibited the highest hole and electron mobilities of 2.53 cm² V⁻¹ s⁻¹ at 250 °C and 0.36 cm² V⁻¹ s⁻¹ at 310 °C, respectively. XRD and AFM results demonstrated that the thermal annealing temperature had a critical effect on the changes in the crystallinity and morphology of the polymer. The low-voltage device was fabricated using high-k dielectric, P(VDF-TrFE) and P(VDF-TrFE-CTFE), and the carrier mobility of PDTDP was reached 0.1 cm² V⁻¹ s⁻¹ at V_d = −5 V. PDTDP complementary inverters were fabricated, and the high ambipolar characteristics of the polymer resulted in an output voltage gain of more than 25.