Chongcheng Fan

Dual-core photonic Crystal fiber for dispersion compensation

A novel design of dual-core photonic crystal fiber (DCPCF) consisting of pure silica and air is proposed in this letter. In addition to potential low loss, simulation shows that dispersion of this DCPCF can reach -18 000 ps/(nm/spl middot/km).

High channel-count comb filter based on chirped sampled fiber Bragg grating and phase shift

Based on strongly chirped sampled fiber Bragg grating and phase shifts, a novel approach to obtain high channel-count comb filters is proposed in this letter. Various channel spacing can be achieved by a single strongly chirped phase mask where the required phase shifts can be gained by a precise translation stage. Comb filters with channel spacing of 50, 100, and 200 GHz are then designed with the same phase mask. Experimentally, a 35-channel 100-GHz channel-spacing comb filter is fabricated, from which one can expect that high-performance comb filter with various channel spacing can be fabricated by conventional technology.

Equivalent phase shift in a fiber Bragg grating achieved by changing the sampling period

It is proposed and demonstrated experimentally for the first time to achieve the desired phase shifts within one channel of a sampled Bragg grating by changing the sampling period. Only ordinary phase masks and submicrometer precision are needed, leading to improved flexibility, repeatability, and cost-effectiveness in fiber Bragg grating design and fabrication especially when multiple and mutable phase shifts are required. Based on this method, a /spl pi/-shift and two bipolar encoders for direct-sequence optical code-division multiple-access systems are obtained experimentally, which are in good agreement with simulation.

Novel flat multichannel filter based on strongly chirped sampled fiber Bragg grating

A novel optical fiber filter based on a strongly chirped sampled Bragg grating is proposed for wavelength-division-multiplexing (WDM) system applications. It features in multiple equalized passbands with flat-top steep-edge nearly linear phase response and high transmittance. Refractive index modulation amplitude with Gaussian spatial profile is used within the samples, which contributes to the marked improvement of the filter performance. Furthermore, there are also multiple flat and equalized stopbands to be used as multichannel optical add/drop filters in a WDM system.

Transient analysis in discrete fiber Raman amplifiers

Analytical expressions, basic rules and physical interpretation of transient phenomena in discrete fiber Raman amplifiers (FRAs) are presented in this paper, and agree well with simulation results. Characteristics of transience in gain-clamped FRAs are also discussed based on these analytical expressions.

A novel method to achieve various equivalent chirp profiles in sampled Bragg gratings using uniform-period phase masks

Properly designed sampling function of a sampled Bragg grating can produce an equivalent chirp profile within reflection bands with non-zero Fourier orders. This method has the advantage that various equivalent chirp profiles can be achieved while the phase mask used in the fabrication process needs not to have any chirp. The principle of this method is demonstrated by the fabrication of a sampled fiber Bragg grating with a linear equivalent chirp profile using a uniform-period phase mask.

Noise performance analysis of bi-directionally pumped distributed fiber Raman amplifiers with consideration of fiber nonlinearity and its impact on EDFA output OSNR

Abstract Under small-signal assumption, equivalent noise figure normalized by fiber nonlinearities (NENF) of bi-directionally pumped distributed fiber Raman amplifiers (BiDFRA) is derived. Amplified spontaneous Raman scattering noise and double Rayleigh scattering noise are both included. The relation between NENF and Raman gain, forward Raman gain percentage is investigated under different polarization factor and Rayleigh scattering coefficient. It agrees well with numerical simulation results. Based on the analytical expression, the optical signal-to-nose ratio (OSNR) improvement of hybrid pre-BiDFRA/erbium-doped fiber amplifier (EDFA) compared with sole EDFA is studied. It is shown that there is an optimum Raman gain and forward Raman gain percentage to maximize the OSNR improvement. Finally, some guidelines on BiDFRA design are proposed.

Abrupt and asymptotic transience in DWDM systems using backward-pumped fiber Raman amplifier

Abrupt power transience in wide (C+L)-band dense wavelength division multiplexing systems caused by stimulated Raman scattering during channel add/drop is investigated both theoretically and experimentally. It is found that adding L- or C-band channels leads to abrupt decrease or increase in surviving C- or L-band channels and is constructively or destructively added to the asymptotic transience in a system using backward-pumped fiber Raman amplifiers. Dropping of L- or C-band channels also leads to reversed consequences. The impact of channel add/drop on the steady-state Raman gain in such systems is also investigated.

Design of long-period fiber gratings with fast-varying parameters

A transfer matrix of an arbitrary period in a long-period fiber grating (LPFG) is derived. Cascade of such matrixes can easily be used to calculate the overall performance of LPFG, with fast variation in parameters (which is common practice in LPFGs) such as period length, strength, etc. Results show that the difference in transmittivity between our work and traditional coupled-mode theory becomes obvious, when abrupt change such as /spl pi/ phase-shift occurs. This method can be used in the mask design aiming at overall performance optimization through period-by-period pattern adjustment.

A novel simple measurement technique of equivalent chirp in the grating period of sampled Bragg grating

In this letter, based on the proposed concept of Moire sampled Bragg grating (SBG), the equivalent chirp rates of various Fourier orders in a sampled Bragg grating with chirp in the sampling period (CSP) is demonstrated for the first time via a simple novel experimental method using phase mask rotation and dual exposure technique. Difference between experimental data and calculated results is less than 9%.