Spin-entangled orbital angular momentum filter of photons based on a chiral long-period fiber grating.

The orbital angular momentum (OAM) of light is particularly promising for multi-channel data transmission in optical fiber communications. In the implementation, one of the impediments is the lack of an effective all-fiber method to demultiplex and filter OAM modes. To solve the problem, by utilizing the inherent spiral characteristics of a chiral long-period fiber grating (CLPG), we propose and demonstrate experimentally a CLPG-based scheme for filtering spin-entangled OAM of photons. We unveil theoretically and verify experimentally that the co-handed OAM with the same chirality of helical phase wavefront as CLPG couples to higher-order cladding modes and suffers loss, while the cross-handed OAM with the opposite chirality freely passes in CLPG. Meanwhile, by combining its grating characteristics, CLPG can realize the filtering and detection of a spin-entangled OAM with arbitrary order and chirality without exerting extra loss for other OAM. Our work has great potential in analyzing and manipulating spin-entangled OAM, paving the way for the development of all-fiber OAM applications.

Synthesis of digermylene-stabilized linear tetraboronate and boroxine.

Two newly discovered linear compounds tetraboronate and boroxine stabilized by digermylene are reported, which feature a B4O5 chain and a B3O3 ring, respectively. DFT calculations reveal that not only can digermylene stabilize the electron-deficient boron centers, but also increase the energies of the LUMOs of the boron moiety. Our results provide a hint for the development of boronate covalent organic frameworks.

Ag-mediated cascade decarboxylative coupling and annulation: a convenient route to 2-phosphinobenzo[b]phosphole oxides.

The first facile and practical silver-mediated cascade reaction of arylpropiolic acids with diarylphosphine oxides has been developed, providing a general, one step approach to structurally sophisticated 2-phosphinobenzo[b]phosphole oxide frameworks of importance in materials science via sequential decarboxylative C-P cross-coupling and C-H/P-H functionalization with operational simplicity and excellent functional group compatibility.

Reactivity of Germylene toward Phosphorus-Containing Compounds: Nucleophilic Addition and Tautomerism.

A series of phosphorus-substituted germanium(II) complexes, L(1)GeR [L(1) = CH{(CMe)(2,6-(i)Pr2C6H3N)}2; 2, R = PPh2; 4, R = OPPh2; 5a, R = OP(O)Ph2; 5b, R = OP(O) (O(n)Bu)2; 6a, R = OP(S)Ph2; 6b, R = OP(S)(OEt)2], were synthesized through the direct activation of various organic phosphorus compounds by N-heterocyclic ylide-like germylene 1. These compounds were characterized by IR and NMR spectroscopy, and 4, 5a, 6a, and 6b were further investigated by X-ray crystallography. Interestingly, the reaction of 1 with Ph2P(O)H produced the tricoordinated phosphorus(III) species L(1)GeOPPh2 (4) rather than the expected isomeric product L(1)GeP(O)Ph2. The reaction of 1 with dialkylthiophosphoric acid and diphenylthiophosphinic acid resulted in the products 6a and 6b containing the P═S double bond rather than the P═O double bond.

Multi-modal label-free imaging based on a femtosecond fiber laser.

We demonstrate multi-mode microscopy based on a single femtosecond fiber laser. Coherent anti-Stokes Raman scattering (CARS), stimulated Raman scattering (SRS) and photothermal images can be obtained simultaneously with this simplified setup. Distributions of lipid and hemoglobin in sliced mouse brain samples and blood cells are imaged. The dependency of signal amplitude on the pump power and pump modulation frequency is characterized, which allows to isolate the impact from different contributions.

Single fiber laser based wavelength tunable excitation for CRS spectroscopy.

We demonstrate coherent Raman spectroscopy (CRS) using a tunable excitation source based on a single femtosecond fiber laser. The frequency difference between the pump and the Stokes pulses was generated by soliton self-frequency shifting (SSFS) in a nonlinear optical fiber. Spectra of C-H stretches of cyclohexane were measured simultaneously by stimulated Raman gain (SRG) and coherent anti-Stokes Raman scattering (CARS) and compared. We demonstrate the use of spectral focusing through pulse chirping to improve CRS spectral resolution. We analyze the impact of pulse stretching on the reduction of power efficiency for CARS and SRG. Due to chromatic dispersion in the fiber-optic system, the differential pulse delay is a function of Stokes wavelength. This differential delay has to be accounted for when performing spectroscopy in which the Stokes wavelength needs to be scanned. CARS and SRG signals were collected and displayed in two dimensions as a function of both the time delay between chirped pulses and the Stokes wavelength, and we demonstrate how to find the stimulated Raman spectrum from the two-dimensional plots. Strategies of system optimization consideration are discussed in terms of practical applications.

Adiabatic circular polarizer based on chiral fiber grating.

Based on the adiabatic coupling principle, a new scheme of a broadband circular polarizer formed by twisting a high-birefringence (Hi-Bi) fiber with a slowly varying twist rate is proposed. The conditions of adiabatic coupling for the adiabatic polarizer are first identified through analytical derivations. These conditions are easily realized by choosing a reasonable variation of the twist rate. Moreover, the bandwidth of the polarizer is able to be directly determined by the twist rates at the two ends. Finally, the broadband characteristics of the polarizer are demonstrated by simulations. It is also shown that the performance of the polarizer can be remarkably improved by accomplishing a multi-mode phase-matching along the grating or by using of the couplings of the core mode to lossy modes.