Li Jun-Qing

Self-Induced Optical Rotation of Solitons in a Chiral Fibre

From Maxwells equations and macroscopic polarization, we obtain the wave equations describing the propagation of strong light in an isotopic chiral fibre with weak spatial dispersion. By considering the possible nonlinear and dispersive effects, the nonlinear Schrodinger equations for the left- and right-circularly polarized components are derived. The mechanism to form the chiral optical solitons is discussed. The self-induced optical rotation of solitons in the chiral fibre is emphasized. An all-optical switch is proposed.

A Hybrid Optical Bistable Device Based on a Fibre Bragg Grating

We propose a hybrid optical bistable device based on a fibre Bragg grating. The experimental set-up is designed by using real communication components. The optical bistable characteristics are simulated. The feedback nonlinearity and the delay time of the device are emphasized. We discuss the potential of such a device in sensor applications.

A Novel All-Optical Switch in a Double-Loop Sagnac Ring Coupled with a Nonlinear Ring Resonator

We propose a novel configuration of all-optical switch based on a double-loop Sagnac ring coupled with a nonlinear ring resonator. In the case of self-phase modulation, the reducing switching threshold power down to mW is predicted, which is the improvement of earlier works on all-optical switches. The switch optimization is analysed. A way to increase the response speed of all-optical switches is suggested.

Hyperpolarizabilities of Chiral Molecules Based on Three-Coupled-Oscillator Model

A chiral molecular model of three coupled oscillators is established. A set of coupling equations and hyperpolarizabilities for the chiral molecules with the tripod structure are presented. The expression of second-order nonlinear susceptibility is derived for an isotropic molecular system. The calculated hyperpolarizabilities of NPAN and NPP chiral molecules are consistent with the experimental results and the applicability of this model is validated.

An all-optical switch of Mach－Zehnder interferometer type using an active fibre ring resonator

We propose an all-optical switch of the Mach–Zehnder interferometer type using an active nonlinear ring resonator and analyse the significance of the parameter A, a product of gain and total loss, for performing an ideal 1 by 2 switch. We found that in the range of 1−κ≤A≤(1−κ)1/2, the increment of A can compensate the losses inside the ring, therefore increase the finesse of the ring and enhance the nonlinearity contribution to reduce the switching power threshold effectively. We also emphasize the importance of the initial switching point and discuss the feasibility of utilizing a high-nonlinear fibre in the ring.

Optical Bistability by Using a Tunable Fibre Laser with Fibre Fabry–Perot

We observe a novel hybrid optical bistability by using an electro-optically tuned cw fibre laser with a fibre Fabry–Perot filter. The principles of the optical bistable device in two operation manners are analysed. The applications in monitoring the wavelength shift of a tunable fibre laser and fibre sensor of digital type are also discussed.

Influence of Light Polarization States on Sum-Frequency Generation in a Chiral Medium with a Two-Coupled-Oscillator Model

Sum-frequency generation (SFG) is investigated using the two-coupled-oscillator molecular model. The influence of the polarization states and angles of two incident beams on reflected and transmitted sum-frequency lights is discussed by considering the circular birefringence in a chiral medium. The different response of media with two kinds of enantiomers to polarization states of incident beams is also discussed. Furthermore, the relations between the SFG spectrum and the polarization states are studied. The theoretical result is consistent with a known experimental fact.

Surface second harmonic generation of chiral molecules using three-coupled-oscillator model

Based on the three-coupled-oscillator molecular model we proposed, the relation between the second-order susceptibilities of a chiral film and the molecular hyperpolarizabilities is given. The effect of microscopic parameters on the second-order susceptibilities is simulated numerically and the difference between the efficiencies of s-polarized second-harmonic fields induced by the left- and the right-handed circularly-polarized fundamental beams is discussed. The theoretical basis for studying second-order nonlinear optical properties of the chiral molecular media with a tripod-like structure is provided in this paper.

Surface Second-Harmonic Generation Circular Dichroism in Helix Molecular Films

The formula for the intensity of surface second-harmonic generation circular dichroism (SHG-CD) in helical molecular films is presented. The influence of the pitch and radius of helical molecules on the surface SHG-CD intensity is numerically analysed. The existence of a peak in the curves of the surface SHG-CD intensity versus the pitch and radius is predicted. The relation between the pitch and radius for different azimuthal angles is also discussed.

RELATIONSHIP BETWEEN INTENSITY OF SURFACE SECOND HARMONIC GENERATION AND MOLECULAR STRUCTURE IN HELIX MOLECULAR FILMS

The relationship between intensity of surface Second Harmonic Generation (SHG) and the pitch, radius and azimuthal angle of molecules on the surface of helix molecular films is analyzed. The values of pitch and radius corresponding to the maximal intensity of SHG have been shown to exist. The theoretical results are compared with the experimental ones reported by Mohlman et al., and the limitation of their conclusion is also pointed out.