In order to realize the high efficiency and high focusing coupling and steering of optical waveguide, a variable period focused grating coupler is designed by using the Bragg condition and the Finite Difference Time Domain (FDTD) method. Firstly, the relationship between the structural factors of the grating and the diffraction angle of the coupled light is derived based on the Bragg condition and the plane waveguide eigenmode equation. The effects of etching depth, grating period, duty cycle and other structural factors on the coupled light passing through the grating are obtained. Then, FDTD is used to simulate the diffraction field of uniform grating with different structure parameters. The uniform grating with different structures is combined and the variable period grating coupler are obtained. Finally, the structure parameters of variable-period grating coupler are optimized, and the optimum coupling efficiency and focusing angle are obtained. The coupling efficiency of the optimized variable period grating coupler is 62.37%. It provides a theoretical basis for the practical application of optical interconnection.
The rudimental microparticle contaminants and airborne molecular contaminants (AMCs) will obviously reduce the lifetime of the lens widely used in the high peak power laser system. An inline contaminants sensor based on the optical microfiber (OM) is here proposed. Due to Van Der Waals force and electrostatic attraction, contaminants are easily adhered to the surface of OM, which will cause an obvious perturbation to the evanescent field transmitted in the OM. The additional loss, caused by the adhered contaminants, has been theoretically analyzed and simulated. The corresponding experiments have also been carried out, and the experimental results agree well with the simulation. The inline containments sensor based on OM has potentially wide sensing range for many kinds of determinate absorptive materials.
Fiber Bragg grating sensors have been attracted more attention due to its excellent advantages, such as small size, light
weight, low cost, immunity to electromagnetic interference, multiplexing and so on, which offer a widely application in
optical sensing and communication field. Following the appearance of micro/nano-fiber (MNF), it is imperative to
develop the manufactured technology of MNF devices, MNF Bragg gratings are the important passive device among
these. In this paper, we simulate the effective refractive index in fiber core using two-layer model. Meanwhile, we
present a new method to fabricate a 6μm diameter fiber Bragg grating through successive improvement of
manufactured technology. The small cladding diameter fiber was obtained by immersing an optical photosensitive fiber
in different concentrations of hydrofluoric acid solutions. Then a MNF is fabricated from the small cladding diameter
fiber by drawing. Finally a 6μm-diameter fiber Bragg grating was written using phase mask technology with a higher
reflection. The testing results of this grating showed a good agreement with the simulation.
An in-line fluidic absorption coefficient sensor based on the optical microfiber (OM) is proposed. We calculate the
insertion loss of the OM per millimeter after immerged into liquid with various absorption coefficients. Then a 1.8μm
diameter OM with 10 millimeters uniform waist region is used to analyze the absorption of pure water, and the
absorption spectrum from 1525nm-1565nm is achieved from the experiment, agreeing well with the reported absorption
coefficient. The in-line fluidic absorption coefficient sensor has potentially wide sensing range by controlling the
construction of OM for many kinds of absorptive liquids with lower refractive index than silica.