Probing biexciton in monolayer WS2 through controlled many-body interaction

The monolayers of semiconducting transition metal dichalcogenides host strongly bound excitonic complexes and are an excellent platform for exploring many-body physics. Here we demonstrate a controlled kinetic manipulation of the five-particle excitonic complex, the charged biexciton, through a systematic dependence of the biexciton peak on excitation power, gate voltage, and temperature using steady-state and time-resolved photoluminescence (PL). With the help of a combination of the experimental data and a rate equation model, we argue that the binding energy of the charged biexciton is less than the spectral separation of its peak from the neutral exciton. We also note that while the momentum-direct radiative recombination of the neutral exciton is restricted within the light cone, such restriction is relaxed for a charged biexciton recombination due to the presence of near-parallel excited and final states in the momentum space.

Analysis of linear and non-linear effects in the frequency domain for a three-channel optical transmission system

This paper presents the analysis of a wavelength division multiplexer communication system in the frequency domain, with the objective of visualizing the incidence of the linear phenomena of attenuation and chromatic dispersion, together with the phenomenon of phase self-modulation, the Kerr electro-optical effect and fourth wave mixing. The analyzed system consists of a laser transmitter with a Mach-Zender modulator and a standard G.625b single-mode fiber link transmitting three optical signals of 10 mW, 25 mW and 50 mW at a fundamental wavelength of 1550 nm at a rate of 10 Gbps. This system is analyzed through a graphical user interface programmed by the authors in the Python environment, which calculates the parameters corresponding to each phenomenon and graphically represents the transmission results at distances of 50 km and 100 km. The analysis methodology consists of varying the spectral separation of the transmitted channels, initially considering a spectral separation of 2 nm and subsequently a spectral separation of 0.2 nm, observing as a result that the harmonics generated by the fourth wave mixing phenomenon considerably alter the spectral density of the transmitted signals, since the energy of the harmonics is equal to the power of the transmitted signals. On the other hand, with the spectral spacing of 0.2 nm, it is obtained that, although the harmonics alter the spectral density waveform, the bandwidth is not compromised by these additional signals.

Seasonal Spectral Separation of Western Snowberry and Wolfwillow in Grasslands with Field Spectroradiometer and Simulated Multispectral Bands

Woody plant encroachment (WPE), the expansion of native and non-native trees and shrubs into grasslands, has led to degradation worldwide. In the Canadian prairies, western snowberry and wolfwillow shrubs are common encroachers, whose cover is currently unknown. As the use of remote sensing in grassland monitoring increases, opportunities to detect and map these woody species are enhanced. Therefore, the purpose of this study is to identify the optimal season for detection of the two shrubs, to determine the sensitive wavelengths and bands that allow for their separation, and to investigate differences in separability potential between a hyperspectral and broadband multispectral approach. We do this by using spring, summer, and fall field-based spectra of both shrubs for the calculation of spectral separability metrics and for the simulation of broadband spectra. Our results show that the summer offers higher discrimination between the two species, especially when using the red and blue spectral regions and to a lesser extent the green region. The fall season fails to provide significant spectral separation along the wavelength spectrum. Moreover, there is no significant difference in the results from the hyperspectral or broadband approach. Nevertheless, cross-validation with satellite imagery is needed to confirm the current results.

Integration of radio over fiber (RoF) with fiber to the home (FTTH) schemes

Two integrating techniques and topologies for fiber optic network systems such as RoF and FTTH have been studied and presented in this project. Two digital signals with data rate 622Mb/s and 1.25Gb/s are considered as the two service signals to be hybrid. Both signals are first modulated in electrical domain by 25GHz and 5GHz sinusoidal sub carriers respectively, in order to give them enough spectral separation. Two architectures have been studied to modulate the optical carrier with these two service signals. The first model is to sum the two service signals in the electric domain and use a single leg Mach Zender Modulator (JlvlZM) to modulate the optical carrier with the electrical message signal. In the second case, the two service signals are first sent to a two leg MZM and separately modulate the light wave carrier, then the two emerging light wave signals mix at the other end of the Y branch of the MZM. The mathematical equations that represent the function of the two kinds of MZM have been formulated. Simulations of the integration of the two hybrid services have been made in MATLAB-Simulink environment and the results are shown. The developed mathematical models are used to represent the MZMs in the MATLAB program. Detector models for each architecture have been developed in order to evaluated the SNR and compare performance using Bit Error Rate (BER). The BER plots for different input setup have been plotted and presented in this project.

Integration of radio over fiber (RoF) with fiber to the home (FTTH) schemes

Two integrating techniques and topologies for fiber optic network systems such as RoF and FTTH have been studied and presented in this project. Two digital signals with data rate 622Mb/s and 1.25Gb/s are considered as the two service signals to be hybrid. Both signals are first modulated in electrical domain by 25GHz and 5GHz sinusoidal sub carriers respectively, in order to give them enough spectral separation. Two architectures have been studied to modulate the optical carrier with these two service signals. The first model is to sum the two service signals in the electric domain and use a single leg Mach Zender Modulator (JlvlZM) to modulate the optical carrier with the electrical message signal. In the second case, the two service signals are first sent to a two leg MZM and separately modulate the light wave carrier, then the two emerging light wave signals mix at the other end of the Y branch of the MZM. The mathematical equations that represent the function of the two kinds of MZM have been formulated. Simulations of the integration of the two hybrid services have been made in MATLAB-Simulink environment and the results are shown. The developed mathematical models are used to represent the MZMs in the MATLAB program. Detector models for each architecture have been developed in order to evaluated the SNR and compare performance using Bit Error Rate (BER). The BER plots for different input setup have been plotted and presented in this project.