We present a simulation study on the chirping characteristics of a directly modulated 40 Gbps laser diode and evaluate its performance for use in high-speed optical fiber links. The effects of the linewidth enhancement factor (α) and gain suppression on the laser chirp and the maximum fiber transmission length are investigated. The chirp characteristics include the frequency peak-to-peak chirp of the time-varying frequency and shift of the emission wavelength. The performance of 40 Gbps optical fiber link is evaluated in terms of the eye diagram and quality factor of the received signal, which helps in predicting the maximum fiber length that achieves error-free transmission. The results show that when α increases from 1 to 10, the overshoots of the relaxation oscillations become strong, resulting in a sharp increase in laser peak-to-peak chirp from 21.8 to 205 GHz. The increase of gain suppression factor form ε = 0.5 × 10–17 cm3 to ε = 5 × 10–17 cm3 dampens out the overshoots and slightly reduces the peak-to-peak chirp from 19.5 to 193.3 GHz. Although the gain suppression works to reduce the laser chirp, it causes a significant wavelength shift relative to the emission wavelength of the non-modulated laser, which degrades the efficiency of the laser diode. On the other hand, the gain suppression is shown to increase the degree of eye-opening and the corresponding Q-factor of the fiber link on a reverse action of the linewidth enhancement factor. As fiber length increases, the influences of α and ε on chirp characteristics become more significant. The maximum fiber length (Lmax) is shown to decrease with the increase in α and/or ε; when α increases from 1 to 10, Lmax decreases from 5.89 to 0.78 km at ε = 5 × 10–17 cm3, and decreases from 2.52 to 0.3 km at ε = 0.5 × 10–17 cm3.

Introduction: The purpose of this study is to investigate and compare the effects of the antimicrobial agents Moringa oleifera and bioactive glass nanoparticles activated by femtosecond laser light on the biomimetic dentin remineralization using teeth having carious dentin ICDAS code 3. Methods and Materials: A total of 27 dentin surface samples were divided into three groups: the first group was treated with a Moringa oleifera extract, while the second group was treated with bioactive glass nanoparticles, and as for the control group, the third group received no additional agent. All groups were subjected to femtosecond laser light at three different wavelengths: 390 nm, 445 nm, and 780 nm. The photoactivation of each sample was achieved using the femtosecond laser light for 5 min with an average power rating of 300 mW, a pulse duration of 100 fs, and a pulse repetition rate of 80 Hz. The mineral content of the samples was obtained and analyzed using the laser-induced breakdown spectroscopy (LIBS). The LIBS analysis was conducted with the following laser light parameters: average power of ~215 mW, wavelength of 532 nm, pulse duration of 10 ns, and a pulse repetition rate of 10 Hz. Results: Most studied samples exhibited a relative increase in the mineral content that may enhance biomimetic remineralization. Moringa oleifera photoactivated by femtosecond laser light at 445 nm achieved a significant increase in mineral content. Conclusion: Using the femtosecond laser light to activate the relatively cheap and commercially available antimicrobial agent Moringa oleifera supports the strategy of minimal invasive approaches for the treatment and biomimetic remineralization of carious dentin ICDAS code 3.

We present a numerical simulation study on the effect of the linewidth enhancement factor (α) of semiconductor laser and dispersion management methods of optical fibers on the performance of 40-Gb/s directly-modulated fiber links and their application in WDM systems. The dispersion management methods include the use of non-zero dispersion-shifted fiber (NZ-DSF), dispersion-compensating fiber (DCF), and fiber Bragg grating (FBG). The optimal values of the α-parameter and the best dispersion management method are applied to design and simulate a four-channel × 40-Gb/s WDM fiber system. The obtained results show that the increase in the α-parameter and/or fiber length reduces the performance of both the 40-Gb/s optical link and the WDM system. Regarding the 40-Gb/s optical link, when α = 1, using –NZ-DSF or + NZ-DSF, DCF with SSMF, and FBG with SSMF work to increase the transmission length from 1.6 km of a standard single-mode fiber (SSMF) to 7.2, 26.5, and 40 km, respectively. Whereas at α = 3.5, the maximum transmission length reaches 1.2 km when using SSMF, –NZ-DSF, or + NZ-DSF, while it increases to 13 and 35 km when using DCF with SSMF, and FBG with SSMF, respectively. In the designed WDM system, the use of FBG with SSMF is predicted as the most effective method for dispersion management. The maximum transmission length reaches 25 km when α = 1, but reduces to 12 km when α = 3.5.