Low-loss and compact photonic lantern based on a step-index double cladding fiber.

The fulfilment of the adiabatic criterion is indispensable for the realization of a low-loss photonic lantern (PL), concurrently imposing a stringent restriction on the taper transition length of the PL. Here, by relaxing the adiabatic criterion, a low-loss and compact PL based on a step-index double cladding fiber (SI-DCF) is theoretically proposed and experimentally demonstrated. The use of SI-DCF can reduce the mode field diameter (MFD) expansion ratio during the tapering processing and greatly decrease the taper transition length required for adiabatic tapering. We initially evaluate the variation of both MFD and effective refractive index (RI) along the fiber tapering based on three types of fiber structures, including the modified standard single-mode fiber (SSMF), the graded-index fiber (GIF), and the proposed SI-DCF. In comparison with the commonly used fiber geometry, the SI-DCF can reduce the MFD expansion ratio from 77.73% to 38.81%, leading to more than half reduction of the tapering length for both 3-mode and 6-mode PLs. Then, two kinds of SI-DCF with different core diameters are fabricated to realize a 3-mode PL. The fabricated PL possesses a 1.5 cm tapering length and less than 0.2 dB insertion loss (IL). After splicing with the commercial few-mode fiber, the PL has an average IL of 0.6 dB and more than 13 dB LP11 mode purity over the C-band. Finally, a transfer matrix measurement indicates that the fabricated PLs have a mode coupling of less than -10 dB at 1550 nm.

Seven lower toxicity celastrol derivatives by biotransformation of Pestalotiopsis sp. LGT-1.

Biotransformation of toxic components by plant endophytes has become an effective method to reduce the toxicity of target compounds and discover lead compounds. In this context, an endophytic fungus, Pestalotiopsis sp. LGT-1, from Tripterygium wilfordii Hook F. (TwHF), was used to reduce the toxicity of celastrol which is also produced by TwHF and is considered an attractive molecule with a variety of biological activities. Seven celastrol derivatives (1-7) were isolated from the coculture fermentation broth of LGT-1 and celastrol. Their structures were elucidated by spectroscopic data analysis including 1D and 2D NMR, as well as HRESIMS. Their absolute configurations were determined by analysis of NOESY, ECD data and NMR calculations. In cell proliferation experiments, the toxicity of seven compounds was 10.11- to 1.24-fold lower in normal cells than the prototype compound celastrol. These derivatives serve as potential candidates for future pharmaceutical applications.

High-precision angular rate detection based on an optomechanical micro hemispherical shell resonator gyroscope.

Cavity optomechanics with picometer displacement measurement resolution has shown vital applications in high-precision sensing areas. In this paper, an optomechanical micro hemispherical shell resonator gyroscope (MHSRG) is proposed, for the first time. The MHSRG is driven by the strong opto-mechanical coupling effect based on the established whispering gallery mode (WGM). And the angular rate is characterized by measuring the transmission amplitude changing of laser coupled in and out from the optomechanical MHSRG based on the dispersive resonance wavelength shift and/or dissipative losses varying. The detailed operating principle of high-precision angular rate detection is theoretically explored and the fully characteristic parameters are numerically investigated. Simulation results show that the optomechanical MHSRG can achieve scale factor of 414.8 mV/ (°/ s) and angular random walk of 0.0555 °/ h1/2 when the input laser power is 3 mW and resonator mass is just 98 ng. Such proposed optomechanical MHSRG can be widely used for chip-scale inertial navigation, attitude measurement, and stabilization.

In-line mode-dependent loss equalizer with femtosecond laser induced refractive index modification.

We demonstrate an in-line all-fiber mode-dependent loss (MDL) equalizer with femtosecond laser induced refractive index (RI) modification. By inscribing an RI-modified structure into the core of a few-mode fiber (FMF), a differential mode attenuation (DMA) can be achieved for LP01 and LP11 modes. The DMA can serve as an in-line MDL equalizer for the long-haul mode-division multiplexing transmission system. Through numerical simulations, we identify that the LP01 mode has a larger attenuation than that of higher-order modes, where the sign of DMA is contrary to that of the conventional FMF links and devices. Finally, a proof-of-concept experiment is implemented by inscribing an RI modified region with a width of 4 µm, a height of 13 µm, and a length of 200 µm into the FMF core. An average additional attenuation of 8.4 dB and 3 dB can be applied to the LP01 and LP11 modes over the C-band, respectively, leading to an MDL equalization range of 5.4 dB. Meanwhile, the average polarization dependent loss (PDL) of the LP01 and LP11 modes induced by the in-line MDL equalizer is approximately 0.3 dB over the C-band. Power matrix measurement indicates that the in-line MDL equalizer has a negligible mode coupling. The proposed in-line MDL equalizer with a wider range and low insertion loss is feasible by precise manipulation of femtosecond laser inscription.

Isolation of two bis(silyl)nickel complexes with Si-Si bond formation in a single-crystal-to-single-crystal fashion.

A unique penta-coordinate nickel complex [{1,2-C6H4(SiMe2)(SiH)}2Ni(PEt3)(depe)] (6) that generates two new Si-Si single bonds has been prepared exclusively by the reaction of a chelating silyl hydride 1-(dimethylsilyl)-2-silylbenzene (4) and Ni(depe)(PEt3)2 (depe = Et2PCH2CH2PEt2) in a 2 : 1 ratio. Complex 6 is the first example of mononuclear silyl nickel complexes containing a Si-Si single bond formed in situ. Interestingly, framework 6 exhibits reversible single-crystal-to-single-crystal transformations upon the removal and rebinding of the coordinating PEt3 molecule, which give rise to a PEt3-free complex [{1,2-C6H4(SiMe2)(SiH)}2Ni(depe)] (6'), concomitant with the alteration of the coordination geometry of central metal atoms.