Xiaowei Dong

Low Loss Splicing Method to Join Silica and Fluoride Fibers

By decreasing the arc power and choosing the optimal arc time, we use the FSM-20PM ARC Fusion Splicer for joining fluoride(ZBLAN) and silica fibers. The best results of the splice loss is 1.58dB, and the results can be improved if the Fusion Splicer with more stable arc power. Then glue connection is used to fix the splicing point, and the minimal loss we measured is 0.14dB. The above results show that it is possible to connect the fluoride and silica fibers by using Fusion Splicer with appropriate arc power and arc time, which will make the fabrication of these splices simpler and easier to be handled.

Theoretical analysis of transmission characteristics for all fiber, multi-cavity Fabry-Perot filters based on fiber Bragg gratings

The characteristics of transmission spectra for the all fiber, multi-cavity Fabry-Perot (FP) configuration based on fiber Bragg gratings (FBG) are theoretically analyzed and modeled. The general transmission matrix function for the structure with any number of cavities is derived, and explicit expression of the power transmission coefficient for symmetrical two-cavity FP is presented. The general conditions for flat-top single resonant peak at the central wavelength in FBG stop band are derived and verified in the numerical simulation section. The transmission peaks of single-cavity and two-cavity FP structures are compared and discussed, and results show that compared to the single-cavity FP, flatness of the top and steepness at the edge of transmission peak can be improved by introducing one more cavity. The resonant transmission peak properties of two-cavity structure are investigated in detail for various values of cavity length and FBGs with different reflection characteristics, and the design guidelines for transmission-type filters are presented. The results show that the steepness of peak slope can be improved by increase of FBG reflectivities, and these kinds of filters can be used as narrow-band single-channel selectors and multi-channel wavelength de-multiplexing by properly choosing the length of cavities and reflectivities of FBGs.

Analysis of coupling from core mode to counter-propagating radiation modes in tilted fiber Bragg gratings

Radiation-mode coupling is stronger and more efficient in tilted fiber Bragg gratings than in other fiber gratings; it has good advantage in such fields as optical communication and optical sensors. A simplified coupled-mode theory (CMT) approach is proposed for what we believe to be the first time, whose validity is demonstrated by comparing its simulation results with that of the complete CMT equations. With the simplified CMT approach, a theoretical spectral analysis of coupling from core mode to counter-propagating radiation modes in reflective tilted fiber Bragg gratings is presented. The influence of grating length, refractive index modulation amplitude and tilt angle is exhaustively investigated on the transmission spectrum characteristics. The different dependences between s-polarized and p-polarized radiation-mode coupling on grating tilt angle are discussed, and the coupling strength of 45°-tilted gratings shows the greatest polarization dependence with the limitation of backward-propagating radiation-mode coupling.

Precise method for modifying birefringence of stress-induced high-birefringence fiber

A precise method for modifying the birefringence of stress-induced high-birefringence (Hi-Bi) fiber is demonstrated by side polishing a Panda-type fiber with a maximum polished length of at least 14 cm. The polishing depth is controlled with an accuracy of 0.1 microm by piezoelectric ceramic microdisplacement. The accuracy of the birefringence is of the order of 10(-6). This method allows high-quality Hi-Bi fiber segments to be conveniently implemented with low loss at any desired birefringence between 3.17 x 10(-4) and 7.5 x 10(-5) in our experiment from one stress-induced Hi-Bi fiber and without changing the directions of the stress axes. The finite-element method is used to simulate the procedure, and the numerical results agree with the experiment.

A novel complex long-period-grating-assisted coupler

The coupled-mode equations corresponding to a novel complex long-period-grating-assisted coupler (LPGAC), which consists of both the periodic refractive index modulation and gain/loss perturbation, is introduced and the close-form analytical solution is obtained, for the first time to our knowledge. And a unique unidirectional and nonreversible filtering characteristic is achieved by adjusting the gain/loss to match with the refractive index modulation. In addition, the impact of deviations in the grating profile is also evaluated, and the results show that the required device performance can be realized by controlling the amplitude and phase deviation <5%.

Analysis for transmission characteristics of multi-cavity fiber Fabry-Perot filters based on fiber Bragg gratings

The all-fiber, multi-cavity, Fabry-Perot passband filters based on fiber Bragg gratings, up to seven, are presented and modeled. The general formulas of the transfer function for the multiple-cavity Fabry-Perot filters are derived with the transfer matrix method. Transmission spectrum characteristics of the filters with different number of cavities are simulated, analyzed and compared. Numerical results show that near-rectangular bandpass shape can be realized by choosing the proper index modulation depths for every forming FBGs. And the simulations clearly demonstrate that the more we increase the number of cavities the more the shape of the central transmission peak is getting rectangular.

Improvement on delay characteristics of cascaded chirped FBGs

Chirped fiber Bragg gratings are supposed to be cascaded for multi-channel dispersion compensation in DWDM systems. The interaction between them restricts their employment. Gaussian and Super Gaussian apodization are used to reduce the out-of-band reflection so as to suppress the interaction of the cascaded gratings. The increase of the channel spacing can also diminish the interaction.

Properties analysis for reflection-type filter composed of microring resonator array and MZI

A novel reflection-type filter composed of microring resonator array and MZI is presented and analyzed. Simulation results show that the devices can be used as reflection-type filters for DWDM system or wavelength-selective reflectors for fixed or tunable lasers by properly choosing the values of coupling ratios.

Characteristics analyses of vertically coupled microring resonators

The transfer functions of the vertically coupled microring resonator are derived. The effects of parameters such as: the coupling coefficients, the internal propagation loss and the microring’s radius on the characteristics of the resonator are analyzed theoretically. And the optimum parameters are chosen. The higher order microring resonator is compared with the single ring resonator. At last, a wide wavelength range tunable filter based on microring resonator is proposed and its structure is shown in details.

Effective methods for the fabrication of multi-wavelength FBG by using a single phase mask

The successful fabrication of multi-wavelength FBG by using the high precision exposure clamp of scanning stage that made by ourselves are introduced. Only a single phase mask is used, and the wavelengths of FBGs fit the wavelength standard of the ITU-T. FBGs with four different wavelengths are fabricated by using one phase mask, and they have been used in a 4×10Gb/s, 1000 km conventional single mode optical fiber(G.652) transmission system. In each channel, 6 FBGs are used for the dispersion compensation and the power penalty in each channel is less than 1.8dB.