Reconfigurable and tunable microwave-photonics bandpass-slicing filter using a dynamic gain equalizer

Abstract

surface is smaller than that of the flat surface. That is because the Brewster angle between ground and snow is 50°. The 50°angle in snow corresponds to 35°in air by Snell's law. However, at the higher frequency of 36.5 GHz in Figure 4, volume scattering becomes important and obscures the Brewster-angle effect of the snow-ground interface. At 36.5 GHz, rough-surface brightness temperatures are lower than that of flat surface for both V-polarization and H-polarization.Figures 5 and 6 compare results of flat and rough surfaces as a function of observation angle for the case of larger grain size of diameter equal to 0.6 mm. Volume scattering becomes important at 18.7 GHz. The Brewster-angle effect of the snow-ground interface disappears. The roughness decreases the brightness temperatures.Figures 7 and 8 compare the results of flat and rough surfaces as a function of depth of snow; the grain size is also 0.6 mm. At 18.7 GHz, since the observation angle is 30°(which is less than the Brewster angle of 35°), the brightness temperatures of rough surface is smaller than flat surface for V-polarization.In Figure 8, we see that at 36.5 GHz, saturation occurs at large snow depth. Volume scattering becomes dominant and roughness has a negligible effect. Brightness-Temperature Variations with Grain Size and Snow DepthFigures 9 and 10 show the angular variations of brightness temperatures for several grain-size diameters. The brightness temperatures decrease with increasing grain size. Emission from the ground is scattered and cannot reach the air region, thus accounting for the decrease in brightness temperatures.Figures 11 and 12 show that, for small grain size, brightness temperatures depend weakly on the thicknesses of the snow layer. For larger grain size, brightness temperatures decrease with snow depth at 18.7 GHz. For 36.5 GHz, saturation effects occur as a function of snow depth. ACKNOWLEDGMENTSThe research presented in this paper was supported by RGC Central Allocation Grant no. 8730017 of Hong Kong and NASA of the United States. 1. C.M. Lam and A. Ishimaru, Mueller matrix calculation for a slab of random medium with

Radio-frequency low-coherence interferometry

“…However, they can be mitigated by use of standard MWP technology. For instance, compensation of third-order dispersion β 3 can be accomplished by means of dispersion compensating fiber [14], tunable dispersion-compensation modules based on linearly chirped fiber Bragg gratings [15], or programmable spectral phase filters [16]. Besides, the use of single-sideband modulation [17] is a well-established technique to avoid the CSE, and the dynamic range can be enlarged by use of specific techniques increasing the gain of the fiber-optics link [7].…”

Broadband Linearization of Dispersive Delay Line Using a Chirped Fiber Bragg Grating

“…For the opposite possibility (D G < 0 but now with a G > 1) the only fiber option is DCF, for which D F < 0. The compensations reported in [6] and [7] are also described by (9): if we consider an SMF coil as the primary dispersive line, then D G >0 and a G = −2.7, so that the only possibility is again DCF. The 387-mm long CFBG showed an average insertion loss of ∼1.85 dB in the design band and a peak-to-peak phase ripple value of 0.09 rad.…”

“…It is worth mentioning, however, that non-linear dispersive delay lines with non-zero TOD also find application for creating single-passband MWP with chirped phase response [11]. Dispersive delay-line linearization by TOD compensation in single-passband MWP has been achieved by use of dispersioncompensating fiber (DCF) [6], [7] and of programmable amplitude/phase filters [8]- [10]. Interestingly though, to our knowledge, chirped fiber Bragg gratings (CFBG), extensively used in MWP systems [12] and in particular in chirped millimeter-wave pulse generators using CFBG with tunable TOD [13], seem not have been used for this purpose.…”

Reconfiguring the frequency response of dispersive‐channel radio over fiber systems by using fiber photonic filters: Application to transmission of multiplexed microwave subcarriers

“…An important issue, related to the dispersive media‐broadband optical source schemes, is the reconfiguration and tunability of the microwave frequency response. Many papers report on the tunability of the frequency response [7–14]. Most of these works are based on a set of TLs and either standard optical fibers [8] or fiber Brag gratings [9–11], as the dispersive media.…”

“…In the work reported in Ref. 13, the reconfiguration is based on the shaping of the emission from an EDFA by a dynamic gain equalizer; this shaping is followed by an optical filtering or slicing. A simple scheme describes the reconfiguration as based on varying the injection current on a multimode Fabry‐Pérot laser [14].…”