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Optical isolators, reliably integrated on-chip, are crucial components for a wide range of optical systems and applications. We introduce a new class of wideband nonmagnetic and linear optical isolators based on nonlinear frequency conversion and spectral filtering among the pump, signal, and idler wavelengths. The scheme is experimentally demonstrated using difference-frequency generation in periodically poled thin-film lithium niobate integrated devices and short- and long-pass optical filters. We demonstrate a wide bandwidth of more than 150 nm, limited only by the measurement setup, and an optical isolation ratio of up to 18 dB for the involved idler and signal waves. The difference of transmittance at the signal wavelength between forward and backward propagation is 40 dB. We also discuss pathways for substantial isolation improvement using appropriate anti-reflection coatings. The integrable isolator, operating in the telecommunication band, is characterized by a perfectly linear output versus input power dependence and can be incorporated into high-speed telecom and datacom systems as well as a variety of other applications. 

We compared an indacenodithiophene(IDT)-based fused-ring electron acceptor IDIC1 with its counterpart IHIC1 in which the central benzene unit is replaced by a naphthalene unit, and investigated the effects of the benzene/naphthalene core on the optical and electronic properties as well as on the performance of organic solar cells (OSCs). Compared with benzene-cored IDIC1, naphthalene-cored IHIC1 shows a larger π-conjugation with stronger intermolecular π–π stacking. Relative to benzene-cored IDIC1, naphthalene-cored IHIC1 shows a higher lowest unoccupied molecular orbital energy level (IHIC1: −3.75 eV, IDIC1: −3.81 eV) and a higher electron mobility (IHIC1: 3.0 × 10 −4 cm 2 V −1 s −1 , IDIC1: 1.5 × 10 −4 cm 2 V −1 s −1 ). When paired with the polymer donor FTAZ that has matched energy levels and a complementary absorption spectrum, IHIC1-based OSCs show higher values of open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency relative to those of the IDIC1-based control devices. These results demonstrate that extending benzene in IDT to naphthalene is a promising approach to upshift energy levels, enhance electron mobility, and finally achieve higher efficiency in nonfullerene acceptor-based OSCs. 

We choose the high-performance nonfullerene acceptor ITIC-Th as an example, and incorporate electron-donating methoxy and electron-withdrawing F groups onto the terminal group 1,1-dicyanomethylene-3-indanone (IC) to construct a small library of four fused-ring electron acceptors. With this series, we systematically investigate the effects of the substituents on the end-groups on the electronic properties, charge transport, film morphology, and photovoltaic properties of the ITIC-Th series. The electron-withdrawing ability increases from methoxylated to unsubstituted, fluorinated, and difluorinated IC, leading to a downshift of energy levels and a redshift of absorption spectra. Optimized organic solar cells based on the ITIC-Th series show power conversion efficiencies ranging from 8.88% to 12.1%.