Mr. Xunqi Wu Profile

Xunqi Wu

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Proceedings Article | 2 March 2012 Paper

Broad-band laser emission and optical mode-locking of a Fabry-Perot laser formed between two Linearly Chirped Fiber Bragg Gratings

G. A. Iordachescu, X. Q. Wu, J. Jacquet

Proc. SPIE. 8257, Optical Components and Materials IX

KEYWORDS: Mirrors, Fabry–Perot interferometers, Tunable lasers, Spectrum analysis, Fiber Bragg gratings, Mode locking, Video, Fiber lasers, Oscilloscopes, Laser optics

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Experimental measurements of light emitted by a novel type of broad-band laser are presented. The laser cavity is realized by placing a Semiconductor Optical Amplifier (SOA) between two Linearly Chirped Fiber Bragg Gratings (LCFBGs). The P-I (power-current) curve of this structure and its spectral distribution of optical power at high currents show similarities with those of continuum lasers. Finally, a simple all-optical mode-locking is realized by injecting a master laser inside the cavity. The efficiency of the mode-locking is shown to be much higher in the bandwidth corresponding to the initial lasing emission.

Proceedings Article | 15 May 2010 Paper

Simulation analysis of a novel bandpass fiber filter

Xunqi Wu, Joël Jacquet, Guanghua Duan

Proc. SPIE. 7717, Optical Modelling and Design

KEYWORDS: Reflectors, Apodization, Optical filters, Mirrors, Fiber Bragg gratings, Reflectivity, Wavelength division multiplexing, Electronic filtering, Neodymium, Bandpass filters

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A theoretical analysis of a new type of bandpass fiber filter is presented in this paper, which has the favorable transmission characteristics such as low loss, high optical rejection, flat top and steep edge etc.. These parameters are very important for the Wavelength Division Multiplexing (WDM) telecommunication systems. In our structure, a continuum spectrum is achieved thanks to a resonator cavity, formed by one mirror and a Linearly Chirped Fiber Bragg Grating (LCFBG). This grating is apodized along the fiber by a Super-Gaussian window function in order to make the output curves much smoother. Furthermore, the cavity length is calculated precisely by the continuum oscillation condition and this fiber filter is mathematically modeled and resolved by Transfer Matrix Method (TMM). The more efficient transmission of filter in our structure is observed when the reflector reflectivity at the both sides of the resonant cavity is symmetrical, in that case, the maximum output is 1. So, we could vary the coupling coefficient κ to control the maximum grating reflectivity for the purpose of making it be same as that of mirror's. Rather, there are other input parameters, for instance, the chirped value C, the length of grating L_B, and the mirror reflectivity R_M, which could influence the output results such as the grating reflectivity R_B, the transmission of filter T_F, the optical rejection of filter τop, and the bandwidth of filter Δλ_F. We have firstly plotted some schematics to find out the relations between the input and output parameters, and then with the restricted conditions about the input parameters, we have found finally the preferable input and output values for our structure. Besides, we observed that the bandwidth of filter could be also changed by apodization, in other words, the Super-Gaussian apodization plays an important role not only to smoothen the curves but to vary the width of bandpass as well.

Proceedings Article | 26 February 2010 Paper

Steep and flat bandpass filter using linearly chirped and apodized fiber Bragg grating

Xunqi Wu, Joël Jacquet, Guanghua Duan

Proc. SPIE. 7598, Optical Components and Materials VII

KEYWORDS: Reflectors, Apodization, Optical filters, Mirrors, Fiber Bragg gratings, Reflectivity, Wavelength division multiplexing, Linear filtering, Electronic filtering, Bandpass filters

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The development of new optical systems requires the design of novel components that fulfill the market constraints. In particular, low loss, high optical rejection and low cost narrowband filters can play an important role for the introduction of the Wavelength Division Multiplexing (WDM) technology in the local network. So, a novel fiber filter is proposed in this article, with a special combined apodized Linearly Chirped Fiber Bragg Grating (LCFBG) which presents the preferable flat-top and steep-edge characteristics. In the design, we use a continuum cavity condition which is obtained when the effective round-trip phase of oscillated wavelength band is kept identical over the whole Bragg wavelength range. And the transmission spectra are calculated by the reconstruction of the matrixes with the continuum oscillation condition. Therefore, our works show that the ideal square shaped filter is obtained with a lower chirp value relatively together with symmetric reflectivity on both mirrors. The coupling coefficient of the FBG is adjusted to get the same reflectivity values and then to get a transmission filter close to unity. We have then introduced an apodization function of the filter to get a flatter transfer function. Various apodizations schemes have been tested. In this paper, we design and analyze a type of continuum fiber filter with the cavity formed between mirror and apodized LCFBG as reflectors. We calculate firstly the reflectivity, the transmissivity and the group time delay of LCFBG modeled by a simple and practical Transfer Matrix Method (TMM), and then the cavity is reconstructed by TMM, the length of the oscillated cavity is calculated by the continuum oscillation condition, so the output of transmission from the side of LCFBG is continuous in the corresponded reflected bandwidth of LCFBG. We obtain the results and discuss some characteristics of this type of continuum fiber filter.

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