An all-optical bandpass microwave filter that is implemented using an optical phase modulator and equivalent-chirped superstructured fiber Bragg gratings (SFBGs) to generate negative coefficients is presented in this paper. It is well known that SFBGs, also called sampled FBGs, contain many Fourier orders in their spectrum. By appropriately chirping the period of the sampling function of the SFBG, it is possible to achieve an equivalent chirp in the +1 and the -1 orders. This method allows the fabrication of FBGs with different equivalent chirp rates by using a single uniform phase mask. While other methods to create chirped FBGs require multiple phase masks or variable tension on the optical fiber during the FBG writing process, the use of SFBGs eases the requirements for the fabrication of specific phase and amplitude responses. This is achieved by tailoring the sampling function of the SFBG instead of the Bragg period of the phase mask. In this paper, a two-tap all-optical bandpass microwave filter is demonstrated by using an equivalent-chirped SFBG. The negative coefficients of the filter are realized by exploiting the characteristics of the phase-modulation-to-intensity-modulation (PM-IM) conversion in the CFBG.
A single sideband (SSB) modulation scheme using a superstructure fiber Bragg grating (FBG) for a remotely controlled
photonic true time-delay (TTD) beamforming system is presented in this paper. Photonic true time-delay (TTD) is
considered a promising technique for wideband phased array antennas, as it allows beam steering of the antenna without
the beam squint problem. For remotely controlled phased array antennas, the dispersive properties of a single mode fiber
induce a power penalty at discrete RF frequencies when a double sideband (DSB) modulation scheme is used. The SSB
modulation scheme is an effective way to eliminate this power penalty as only one sideband is transmitted and thus no
beating is possible upon the recovery of the electrical signal by a photodetector. This paper presents for the first time a
theoretical model as well as experimental results of a SSB modulation scheme based on a superstructure grating with
two phase shifts. The true-time delay system considered utilizes a discrete uniform Bragg prism which allows discrete
beam steering capabilities for the phased array antenna.
A single sideband (SSB) modulation scheme using a fiber-based equivalent phase shifted Bragg grating for a remotely controlled photonic true time-delay (TTD) beamforming module is presented in this paper. Photonic TTD is considered a promising technique for wideband phased array antennas (PAA) as it allows beam steering of the antenna without the beam squint problem. For remotely controlled phased array antennas, the dispersive properties of a single mode fiber induce a power penalty at higher RF frequencies when a double sideband (DSB) modulation scheme is used. The SSB modulation scheme is an effective way to eliminate this power penalty as only one sideband is transmitted and thus there is no cancellation between the two signals generated by beating the upper sideband with the optical carrier and the lower sideband with the optical carrier at a photodetector. This paper presents for the first time experimental results of a SSB modulation scheme using an equivalent phase shifted fiber Bragg grating. The true-time delay system considered utilizes a discrete uniform fiber Bragg grating prism which allows discrete beam steering capabilities for the phased array antenna.
This paper presents a simulation study of a true-time-delay system for wideband phased array antenna employing a waveguide Bragg grating prism. The Bragg grating prism is constructed of chirped Bragg gratings strategically positioned in order to achieve beam steering capabilities. The effects of double- and single-sideband modulation on the performance of the system are studied. Finally, the effects of apodization of the gratings are also discussed.
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