Nai-Hsiang Sun

NUMERICAL ANALYSIS OF APODIZED FIBER BRAGG GRATINGS USING COUPLED MODE THEORY

In this paper, the coupled mode theory is used to analyze apodized fiber Bragg gratings (FBGs). Since the profile of gratings varies with the propagation distance, the coupled mode equations (CMEs) of apodized FBGs are solved by the fourth-order Runge-Kutta method (RKM) and piecewise-uniform approach (PUA). We present two discretization techniques of PUA to analyze the apodization profile of gratings. A uniform profile FBG can be expressed as a system Corresponding author: H.-W. Chang (hchang@faculty.nsysu.edu.tw).

A New Look at Numerical Analysis of Uniform Fiber Bragg Gratings Using Coupled Mode Theory

The coupled mode theory (CMT) is used to analyze uniform Fiber Bragg gratings. The multi-mode CMT is expressed as the flrst-order vector ordinary difierential equations (ODEs) with coe-cients depending on the propagation distance. We show in this paper that by changing variables, the original couple mode equations (CMEs) can be re-casted as constant coe-cient ODEs. The eigenvalue and eigenvector technique (EVVT), the analytic method for solving constant coe-cient ODEs, is then applied to solve the coupled mode equations. Furthermore, we also investigate the application of Runge- Kutta method (RKM) to the calculation of the global transfer-function matrix for CMEs. We compare the transmission and the re∞ection

Analysis of phase-matching conditions in flexural-wave modulated fiber Bragg grating

Effective refractive indexes of the core mode and various cladding modes of a tapered single-mode step-index fiber were calculated for identifying the cladding modes of phase matching for coupling with the core mode, caused by a prewritten Bragg grating together with an applied flexural wave (microbending) in the tapered region. With these coupling mechanisms, the previously reported reflection wavelength switching could be well interpreted. Between the core mode and a cladding mode, the Bragg grating caused contradirectional coupling and the flexural wave resulted in codirectional coupling of either first- or second-order diffraction. Meanwhile, the period of the acoustic-induced flexural wave was calibrated to be a few hundreds of micrometers. Based on the phase-matching calculations, the relationship between cladding radius and flexural wave period with a chosen wavelength for reflection switching was provided. Such design considerations should be helpful in implementing wavelength switches, based on flexural wave modulation of fiber Bragg grating (FBG), for the applications of wavelength division multiplexing (WDM) fiber communications.

Analysis of an Ultrashort PCF-Based Polarization Splitter

We propose a new structure of polarization splitter based on a dual-elliptical-core photonic crystal fiber. The polarization splitter has a simple and symmetric directional coupler configuration. The vector boundary element method is used to investigate the propagation characteristics of the device under various conditions. Results of the numerical calculation relevant to the design conditions are presented. A 0.3-mm-long splitter with an extinction ratio of 23 dB is obtained.

Gain flattening filter of an erbium-doped fiber amplifier based on etching long-period gratings technology

The gain-flattening filter of an erbium-doped fiber amplifier is experimentally demonstrated by using the technology of etching long-period gratings (LPGs). An error of gain flatness less than 1 dB is obtained by using three cascaded LPGs with different cladding diameters in the range from 1536 to 1565 nm.

Second-order fiber Bragg gratings

In this paper second-order fiber Bragg gratings are firstly experimentally demonstrated to have the characteristic of surface-normal radiation confirmed by measuring the radiation power of 0.012mW from the 2D far-field pattern.

Grating-assisted coupling of light between semiconductor and glass waveguides

Grating-assisted directional couplers (GADC) are designed to couple the power between two waveguides with highly dissimilar effective indices. The GADC structure is used for wavelength division multiplexed (WDM) systems to simplify coupling to optical fibers. In this paper, we use the Floquet Bloch theory to analyze this GADC structure because it provides rigorous solutions without introducing ad hoc assumptions.

Enhanced cascade ξ (2) SHG+DFG interactions based on chirp period quasi-phase-matched waveguide

A theoretic study about a 170% conversion efficiency enhancement of cascade chi(2) SHG+DFG interactions by using a chirp period quasi-phase-matched waveguide.

Enhanced Cascaded SHG+DFG Process of Femtosecond Pulses Using Chirp Quasi-Phase Matching Waveguide

This study presents a chirp quasi-phase matching (QPM) waveguide to increase the conversion efficiency of the cascaded SHG+DFG effect for femtosecond pulses. The coupled mode theory is used to analyze the cascaded SHG+DFG process. In this paper, a constructive interference zone (or cascaded SHG+DFG region) is defined as when the conversion wave and its coupling component constructively interfere with each other and have a phase difference ranging from 0 to 0.5pi or from 1.5 to 2pi. On the other hand, the region is called a destructive interference zone (or back conversion region) when the phase difference ranges from 0.5 to 1.5pi . The proposed chirp QPM waveguide is designed to extend constructive interference length and shorten destructive interference length over the waveguide. The simulation results demonstrate that for a pulsewidth of 0.6 ps, the maximum conversion efficiency of a 50-mm chirp QPM waveguide can be increased to 25 times that of a uniform QPM waveguide.

Analysis of transmission and reflection characteristics of contra-directional coupling in corrugated waveguides

Floquet-Bloch theory and Mahmoud-Beals method are used to calculate the spectrum and the power distribution of contra-directional coupling in dielectric waveguides. Results from the Floquet-Bloch theory and the Mahmoud-Beal method are in close agreement with that of the coupled mode theory.