We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thuliumbismuth co-doped fiber (TBF) as a gain medium in conjunction with a carbon nanotube (CNT)-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 mW. OCIS codes: 320.0320, 140.0140.
The effects of the length t of elements 1 and 5 are also analyzed, and the results are shown in Figure 7. It is observed that when the length t decreases, the resonant frequency of the antenna is shifted to high frequencies and the impedance matching is also degraded. On the other hand, when the length t increases, the resonant frequency of the antenna decreases and the impedance matching is also degraded. The antenna directivity and gain are also computed and listed in Table 1 for comparison. The results indicate that there exists an optimal length t for achieving a maximum antenna gain. This is largely because, with an optimal length t chosen, the null excited currents will occur near points C, D, E, and F (see Fig. 4), as desired. In this case all portions in elements 1, 3, and 5 are of the same phase, thus optimal constructive radiation for the proposed antenna can be expected. Also note that the optimal length t (56 mm) for achieving a maximum antenna gain (see Table 1) is the same as that for achieving a maximum impedance bandwidth (see Fig. 7). Figure 8 plots the measured radiation patterns at 2442 MHz for the constructed prototype. Good omnidirectional radiation pattern in the azimuthal plane ( x-y plane) is seen. In the elevation plane ( x-z and y-z planes), small or negligible side lobes are also seen. The measured results in general also agree with the simulated radiation patterns shown in Figure 9. Figure 10 presents the measured and simulated antenna gain against frequency for the constructed prototype. Good agreement between the measured and simulated results is observed. A high antenna gain of about 6.6 -6.8 dBi for frequencies across the 2.4-GHz band is obtained, which is much higher than that of a conventional half-wavelength dipole antenna.
CONCLUSIONA high-gain printed dipole antenna has been proposed, constructed, and tested. The proposed antenna has a simple configuration and is easy to implement with a low cost. A constructed prototype suitable for application in the 2.4-GHz band for WLAN operation has been studied. The prototype has a narrow width of 10 mm and a total length of 202 mm only (1.64 wavelengths at 2442 MHz) and performs as a good collinear array antenna with three in-phase half-wavelength resonant elements. A high antenna gain level of about 6.6 -6.8 dBi for frequencies across the 2.4-GHz band has been obtained. This antenna gain level is much larger than that of a conventional half-wavelength dipole antenna. 1559.4 and 1563.4 nm, respectively. A bandwidth of 85.6 nm (1515.4 -1601.0 nm) and 67.3 nm (1545.2-1612.5 nm) was obtained for the feedback and nonfeedback systems, respectively, at a power density of Ϫ30 dBm/nm.1. B. Drozd and W.T. Joines, Comparison of coaxial dipole antennas for applications in the near-field and far-field regions, Microwave J 47 (2004), 160
We demonstrated and compared picoseconds pulsed fiber lasers based on Titanium dioxide based saturable absorbers (SAs); 20 cm long Titanium dioxide-doped fiber (TiO2DF) and Titanium dioxide PVA film (TiO2PF) in the 1.5-micron region. The laser cavity utilized 2.4 m long Erbium-doped fiber (EDF) as the gain medium. A self-starting pulsed laser with a consistent repetition rate of ∼1 MHz emerged stably with the incorporation of TiO2 based SAs. The TiO2DF SA produced 9.74 ps pulsed laser at a central wavelength of 1553 nm within a pump power range of 106-142 mW. The fiber SA promoted slightly higher slope efficiency and maximum pulse energy of 13.17% and 8.56 nJ, respectively in comparison with the film SA. On the other hand, the TiO2PF SA generated stable 3.89 ps pulsed laser at an operating wavelength of 1560 nm within 86-142 mW pump power range. The film SA also produced slightly greater maximum output power of 12.17 mW and maximum peak power of 3.43 kW, respectively at the maximum pump power. The results confirmed that both TiO2 SAs can be good alternative pulse modulator in the 1.5-micron region.
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