Abstract
A novel kind of superimposed fiber Bragg gratings (SI-FBGs) named SI-sampled FBGs (SI-SFBGs) is proposed to control the phase relationship among SI sub-gratings by modulating the sampling periods. The realization of such phase-controlled SI-SFBGs just needs a single uniform phase mask and sub-micrometer precision moving stage. The success of phase-controll is expected to encourage SI-SFBGs' applications in more sophisticated fields. As a demonstration, their applications in spectral-phase en/decoding are testified by both simulation and experiment. The spectral-phase encoded (SPE) encoders with the longest code-length that FBG-based SPE encoders can achieve, i.e., 64-frequency bins, are experimentally fabricated for the first time. The results show the advantages accompanying the SI-SFBGs-based SPE encoders compared with the traditional methods.
Highlights
Among a number of kind of fiber Bragg gratings (FBGs), the superimposed (SI) FBGs are especially appealing since multiple FBGs are inscribed at the same location in the fiber, which will bring two main unique features
These features lend themselves to wide applications, such as optical filters [1,2], multiwavelength fiber lasers [3,4], multiplying the repetition rates of periodic pulse trains [5,6], frequency-amplitude en/decoding in optical code-division multiple-access (OCDMA) systems [7,8] and so on
In the former section, the principle of phase-controlling in SI-Sampled FBG (SFBG) has been introduced, and theoretically, such phase-controlled SI-SFBGs would be an ideal choice for spectral-phase encoded (SPE) encoders
Summary
Among a number of kind of fiber Bragg gratings (FBGs), the superimposed (SI) FBGs are especially appealing since multiple FBGs are inscribed at the same location in the fiber, which will bring two main unique features. The second is that these FBGs are more compact since short-length structure can accommodate more FBGs containing different wavelengths These features lend themselves to wide applications, such as optical filters [1,2], multiwavelength fiber lasers [3,4], multiplying the repetition rates of periodic pulse trains [5,6], frequency-amplitude en/decoding in optical code-division multiple-access (OCDMA) systems [7,8] and so on. For spectral-amplitude OCDMA en/decoders based on SI-FBGs [7,8], the relative phases of different wavelengths are not essential for such an incoherent OCDMA scheme Such device cannot be applied to coherent frequency domain OCDMA scheme, i.e., the spectral-phase encoded (SPE) scheme. The application in SPE OCDMA is demonstrated and experimentally validated
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