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Abstract
A new method is proposed and demonstrated for fabricating phase-shifted fiber Bragg gratings (FBGs) using a variable-velocity scanning UV laser beam in combination with a shielded phase mask. The transmission properties of phase-shifted FBGs were analyzed based on coupled-mode theory and a transfer matrix method. The grating is divided into three parts to allow for easier analysis of FBG properties. These segments included a uniform FBG1 and FBG2 which were separated by a shielded section. A novel phase-shifted FBG was fabricated using this method, in which the refractive indices of FBG1 and FBG2 were different. Transmission properties of these phase-shifted FBGs were simulated numerically using MATLAB, and the experimental results and simulated results are in good agreement. In addition to the length and effective refractive index of the shielded section, the phase shift value of a phase-shifted FBG was also found to be dependent on the lengths and effective refractive indices of FBG1 and FBG2. Moreover, we predicted that changing the scanning velocity for fabricating FBG2 would adjust phase shift value, which exhibits a positive linear relationship with the scanning velocity. These results can provide guidelines for fabricating any phase shift value FBGs. This technique is simple, convenient, and may be developed further for use in fabricating novel tunable fiber filters or DFB fiber lasers.
Highlights
The phase-shifted fiber Bragg gratings (FBGs) are currently of significant interest to researchers due to their inherent advantages, such as flexibility, immunity to electromagnetic interference, and small size [1]
We proposed a new method for fabricating unique phase-shifted FBGs using a scanning UV laser beam together with a shielded phase mask
The transmission spectra of the uniform FBG1 were simulated in MATLAB using coupled-mode theory and a transfer matrix method
Summary
The phase-shifted fiber Bragg gratings (FBGs) are currently of significant interest to researchers due to their inherent advantages, such as flexibility, immunity to electromagnetic interference, and small size [1]. Phase-shifted FBGs exhibit a characteristic of narrow transmission window as a type of band-pass filter [2] They are widely used in many applications such as dense wavelength-division-multiplexing (DWDM) [3,4], high-fineness tunable optical filters [5,6,7], and distributed feedback (DFB) fiber lasers [8,9]. An extensive variety of methods have been reported for phase-shifted FBG fabrication, such as Moire method [14], moving fiber-scanning beam method [8,15], and shielded phase mask method [16], Other techniques have included the creation of internal micro-structures [13], overexposure to a near-infrared femtosecond laser with a uniform phase mask [17] These methods have specific disadvantages as detailed in the comparison of phase-shifted FBG fabrication methods presented by Chehura et al [18]. These methods feature fabrication limitations, such as complex systems, poor tolerance, insufficient repeatability, and high processing time
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