C-and L-bands Research Articles

The effect of fiber length and signal power on the flattened gain Raman amplifier

Raman Fiber Amplifiers offer an adjustable gain spectrum in terms of band width ,gain window and gain spectrum shape ,thus the composite Raman gain can be very flat over a wide band In this work an investigation on Raman gain with backward pumping is introduced using twelve pump lasers with optimum pump power to produce gain flattened for 94 nm band width from 1520 to 1614 nm that contains 100 equal spaced channels, with again ripple of 1.28dB which contain the C-and L-band. Over 25 Km span. Then the effect of fiber length on the gain flatting were introduced and the gain saturation have been analyzed.

All-fiber integrated saturable absorber-tunable wavelength filter for Q-switching laser in both C- and L-bands.

We proposed and experimentally demonstrated combining a nonlinear optic saturable absorber and a wideband-tunable spectral filter in a single graphene oxide (GO) film deposited fiber optic device. The GO film was prepared on the cleaved facet of an optical fiber applying two sequential processes: the electrical deposition to make a thick GO film using an arc fusion splicer, followed by the laser pulse drilling to form a multi-layered GO film. The GO deposited fiber facet and a pristine fiber facet formed an asymmetric Fabry-Perot interferometer (FPI), whose spectral response was flexibly controlled by adjusting the air gap between them. An all-fiber ring laser cavity was built using the proposed device as a tunable saturable absorber along with erbium-doped fiber as a gain medium in the L-band. Stable Q-switching laser pulse trains were successfully generated, whose pulse duration was in the order of a few microseconds and its peak wavelength was tunable over 40nm from 1564 to 1604nm covering both C-and L-bands. At a certain condition, we also obtained Q-switching pulses simultaneously lasing at the double wavelengths, 1573.3 and 1586.7nm. Detailed device fabrication processes and laser characteristics are described to elucidate the high potential of 2-dimensional material films in nonlinear optics.

Forest and Forest Change Mapping with C- and L-band SAR in Liwale, Tanzania

Abstract. As part of a Tanzanian-Norwegian cooperation project on Monitoring Reporting and Verification (MRV) for REDD+, 2007-2011 Cand L-band synthetic aperture radar (SAR) backscatter data from Envisat ASAR and ALOS Palsar, respectively, have been processed, analysed and used for forest and forest change mapping over a study side in Liwale District in Lindi Region, Tanzania. Land cover observations from forest inventory plots of the National Forestry Resources Monitoring and Assessment (NAFORMA) project have been used for training Gaussian Mixture Models and k-means classifier that have been combined in order to map the study region into forest, woodland and non-forest areas. Maximum forest and woodland extension masks have been extracted by classifying maximum backscatter mosaics in HH and HV polarizations from the 2007-2011 ALOS Palsar coverage and could be used to map efficiently inter-annual forest change by filtering out changes in non-forest areas. Envisat ASAR APS (alternate polarization mode) have also been analysed with the aim to improve the forest/woodland/non-forest classification based on ALOS Palsar. Clearly, the combination of C-band SAR and L-band SAR provides useful information in order to smooth the classification and especially increase the woodland class, but an overall improvement for the wall-to-wall land type classification has yet to be confirmed. The quality assessment and validation of the results is done with very high resolution optical data from WorldView, Ikonos and RapidEye, and NAFORMA field observations.

Contributions of Franz–Keldysh and Avalanche Effects to Responsivity of a Germanium Waveguide Photodiode in the $\hbox{L}$-Band

When driven with a high-voltage reverse bias of 15 V, a germanium photodiode with a silicon waveguide exhibits responsivity of over 1.14 A/W in the entire C-and L-bands. The high responsivity in the L-band is due to Franz-Keldysh (F-K) and avalanche effects. We prove by numerical calculation that the high responsivity under high bias driving is due to both effects. For accuracy in the calculation, we consider a change in the thickness of depletion layer in the germanium mesa with bias voltage. Calculation results, considering the contributions of both effects, show good agreement with measurement results. Considering the contributions of both effects to minimum detection limit, we discuss optimization for dark current and the electric field applied to Ge.

Monitoring Wheat and Rapeseed by Using Synchronous Optical and Radar Satellite Data—From Temporal Signatures to Crop Parameters Estimation

This paper investigates the sensitivity of multi-temporal SAR data acquired at different frequencies (X-, C-and L-bands), polarizations (HH, VV, VH and HV) and incidence angles (from 24° to 53°) during the growing season of two winter crops (rapeseed and wheat). This study was part of a multi-sensor crop-monitoring experiment that was performed from February to November 2010 (MCM’10). During the experiment, dense series of satellite data were acquired in microwave, optical and thermal domains (more than 150 images were provided by TerraSAR-X, Radarsat-2 Alos, Formosat-2, Spot-4/5 and Landsat-5/7) were synchronous with ground measurements over an agricultural area located in southwestern France, near Toulouse. An angular normalization of radar signals is first performed for each crop type at X-and C-bands by using a dense temporal satellite series and the complementarity provided by microwave and optical data. The results show that the angular sensitivity of radar backscatter decreases with the increase of the vegetation index (from 0.4 dB.°ˉ1 over bare soils to 0.05 dB.°ˉ1 for fully vegetated fields). Lower angular sensitivity is observed at X-band (compared to C-band), and for the cross-polarized signal. Analyses of the temporal signatures of the radar backscatter show a well-marked signal dynamic at X-, C-and L-bands, depending on the crops and theirs associated phenological stages. During the stems elongation of wheat while the NDVI increases of 0.2, a dynamic of 10 dB is observed at X-band and at C-band with VV polarization. Interesting behaviors are also observed during the crop senescence with an increase of several dB (depending on the sensor configuration), while the NDVI decreases of 0.5. Over rapeseed, cross-polarized backscatters offer promising dynamic of 6 dB during the seed development, while the NDVI saturates at maximum values. The use of radar signals, in complement of optical, for crop parameters monitoring is achieved in terms of leaf area index and crop height estimations. Over rapeseed, best correlations between crop parameters and radar signals are obtained at C-band, by combining co-and cross-polarized backscatters (R2 > 0.61). Over wheat, best results are achieved by using X-band data (R2 > 0.64).

Classification Accuracy of Multi-Frequency and Multi-Polarization SAR Images for Various Land Covers

This paper presents the land cover classification capabilities of fully versus partially polarimetric SAR data for C- and L-band frequencies. Maximum Likelihood classifier with complex Wishart distribution and artificial neural network classifier (ANN) have been used for classification. The change in accuracy due to the phase information of SAR data is also assessed by comparing the classified results of intensity and complex images for all the possible polarization combinations at L- and C-band. In all the combinations, fully polarimetric data provides highest accuracy and it is not much different from that of complex partial polarimetric (HH, VV) combination. The accuracies obtained with various partial polarimetric combinations are dependent on the land cover types. Among L-, C- and X-bands, L-band offers better accuracy. By combining all bands data, accuracy improved by 7%.The accuracy has been improved slightly by combining the three components of van Zyl decomposition with the combination of X-, C-and L-band. IRS-P6 optical data over the same area has been used to compare the classification accuracy between optical and SAR data.

Effects of Gamma Irradiation on Erbium Indiffused Lithium Niobate Substrate

The effects of γ-radiation on Erbium (Er) doped LiNbO3, subsrate are investigated by measuring the photoluminescence (PL) spectra at different radiation doses and by performing the x-ray diffraction (XRD) analysis before and after γ-irradiation. The PL spectra are found to change significantly with γ-irradiation of dose 11.46 rad or above, γ-irradiation effects both the C-and L-bands of the erbium spectra. XRD study reveals that γ-ray exposure of dose 15.62 rad leads to morphological modification of the surface, with the appearance of a strong (101) Er2O3 peak and a (104) LiNbO3, peak along with the (006) and other peaks.

Deriving forest canopy parameters for backscatter models using the AMAP architectural plant model

A new approach using an architectural plant model to feed various theoretical scattering models is presented as a better interpretation of future remote sensing data acquired over natural media. The method is based on the architectural plant model (AMAP), which integrates knowledge of botanical growth processes and real plant measurements. AMAP is encapsulated in a flexible interface software called AMAP2SAR that allows one to (1) simulate a three-dimensional (3-D) plant such as a tree, (2) transform the tree into a collection of cylinders, and (3) feed theoretical models such as radiative transfer (RT) models. The method is illustrated by an example of Austrian black pine plantations in southern France. Simulated characteristics of black pines are validated for stands up to 50 years old and for a given environment. The results show the ability to derive classical forest parameters as well as those needed for electromagnetic models (such as geometry) as a function of age. Vertical profiles of canopy elements are derived and point out the vertical heterogeneity of the stands after they are 20 years old for parameters having an impact on the backscatter such as diameter and number of branches. Consequently, the crown layer variability with age and canopy depth should be considered in RT models. An RT model is modified in order to take account of accurate canopy descriptions and deal with encouraging modeling results at Cand L-band over the same test site.

400-channel arrayed-waveguide grating with 25 GHz spacing using 1.5%- waveguides on 6-inch Si wafer

A large-scale arrayed-waveguide grating with a 400-channel and 25 GHz spacing using 1.5%-/spl Delta/ silica-based waveguides on a 6-inch Si wafer has been realised. Good demultiplexing properties have been obtained over the full Cand L-band range with an on-chip loss of 3.8 to 6.4 dB and a far-end crosstalk of -30 dB.

Microwave remote sensing of hydrological parameters on the NOPEX area

A research project aimed at evaluating the microwave remote sensing methods for producing some basic parameters of land surfaces which influence the hydrological cycle, on a regular basis, has been conducted within the framework of the European Northern Hemisphere Climate Processes Land-surface Experiment (NOPEX) and Forest-Dynamic and Monitoring (Forest-Dynamo) experiments. In this paper, the sensitivity of the backscattering coefficient at C-and L-bands to soil moisture, surface roughness and herbaceous and arboreous biomass has been investigated by analysing experimental data collected with Synthetic Aperture Radar in Northern Europe by the airborne EMISAR during the European Multisensor Airborne Campaign (EMAC), organised by the European Space Agency and in Italy during the Multisensor Airborne Campaign (MAC-91) and the Shuttle Imaging Radar (SIR-C) experiment, both organised by NASA with the cooperation of the Italian Space Agency. An analysis of SSM/I (Special Sensor Microwave Imager) radiometric satellite images, carried out over several Scandinavian regions, which has shown sensitivity to seasonal changes of vegetation and snow cover of microwave emission, is also reported.

Rotation measures of extragalactic radio sources viewed through the molecular clouds Cepheus A and L1551

VLA data on polarized sources in 11 high-velocity molecular flow regions at C-and L-band frequencies with 50 MHz resolution are analyzed to derive the Faraday rotation measures (RM) of the magnetic fields associated with the flows. The survey revealed the L1551 field, which has a strong source behind the molecular flow, and Cep A, where numerous polarized sources are located near the flow. The calculations of the RM were based on least squares analyses of the polarized intensity, position angle and total intensity maps. Differences were calculated in the RMs for different lines of sight in order to determine the causes of variations in the electron densities and magnetic fields within the clouds. The magnetic field within the L1551 flow was estimated to be 0.1 mG, indicating the presence of significant shock ionization at relative velocities exceeding 50 km/sec. Further observational techniques that may be employed to increase the understanding of the physical characteristics of bipolar flows are discussed. 31 references