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

Xunqi Wu; Joël Jacquet; Guanghua Duan

doi:10.1117/12.842689

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25 February 2010 Steep and flat bandpass filter using linearly chirped and apodized fiber Bragg grating

Xunqi Wu, Joël Jacquet, Guanghua Duan

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Proceedings Volume 7598, Optical Components and Materials VII; 75981Y (2010) https://doi.org/10.1117/12.842689
Event: SPIE OPTO, 2010, San Francisco, California, United States

Abstract

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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Xunqi Wu, Joël Jacquet, and Guanghua Duan "Steep and flat bandpass filter using linearly chirped and apodized fiber Bragg grating", Proc. SPIE 7598, Optical Components and Materials VII, 75981Y (25 February 2010); https://doi.org/10.1117/12.842689

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