Читать книгу 2D Monoelements - Группа авторов - Страница 50

As an excellent nonlinear absorption material, antimonene has broadband nonlinear optical response, high photothermal efficiency, strong Kerr nonlinearity, low saturable intensity, high two-photon absorption coefficient, and large cross-section, offering the potential nonlinear optical applications in all-solid-state lasers, fiber lasers, optical switchers, optical modulators, and optical thresholders [42–47].

Wang et al. first reported the passively Q-switched Nd³⁺ solid-state lasers using few-layer antimonene peeled off by the LPE as the saturable absorber (SA) [42]. With antimonene/quartz as the passively Q-switcher, the laser operations were realized at 946, 1,064 nm in Nd:YAG crystal with pulse widths of 209, 129 ns and peak powers of 1.48, 1.77 W, while the laser emission of Nd:YVO₄ crystal generated at 1,342 nm with pulse width and peak power of 48 ns and 28.17 W, respectively. By fitting the saturable absorption results of nanosecond laser pulses, the saturable intensities of antimonene were obtained to be 0.43 MW/cm² at 532 nm and 0.53 MW/cm² at 1064 nm. In this work, the 1,342 nm Nd:YVO₄ laser achieved the best results, including the shortest pulse width (48 ns), the highest peak power (28.17 W), and the largest single pulse energy (1.36 μJ). The following drawbacks often occurred in passive Q-switching, including the degradation, failed saturable absorber, and inaccurate modification of repetition rate. To overcome the drawbacks in passive Q-switching, Wang et al. devised an actively Q-switched fiber laser with an antimonene-based all-optical modulator (AOM) as a Q-switcher [43]. The antimonene nanosheets fabricated by the LPE were deposited onto a 10 μm microfiber, which was then employed to devise an AOM with a fiber-type Michelsom interferometer (MI) due to the obvious photothermal effect of antimonene. The antimonene-based AOM exhibited a large phase modulation capacity with a conversion efficiency of 0.049 π mW⁻¹, and at the same time, it achieved the intensity modulation with large modulation depth of 25 dB. Also, this AOM showed a long-term stability with only 8.2% decline of phase conversion efficiency after 1 month (Figure 2.7a). The obtained active Q-switching pulses possessed a microsecond duration (the rise time constant of 3.2 ms) and tunable repetition rate ranging from 0.96 to 6.64 kHz (Figure 2.7b).

Using the strong Kerr nonlinearity of antimonene, Song et al. devised a new type of optical device based on few-layer antimonene (FLA)-decorated microfiber, which was operated both as an all-optical Kerr switcher and an all-optical wavelength converter [46]. The FLA-based Kerr switcher featured a high extinction ratio of 12 dB with a long-time stability, which could be used to realize the process of controlling light by light in optical communication systems (Figure 2.7c). In addition, by taking advantage of the four-wave mixing (FWM) effect, the designed FWM-based wavelength converter achieved a high conversion efficiency of 63 dB and converted efficiently the modulated radio frequency (RF) signals to the sidebands with a maximum frequency of ~18 GHz, which was a vital part in the optical signal processing (Figure 2.7d). In another work, Song et al. also employed FLA-decorated microfiber as an all-optical pulse thresholder to effectively suppress the noise in the transmission system, by which the signal to noise ratio (SNR) was largely improved (~10 dB) [47].

Figure 2.7 (a) Phase shift of the antimonene-based AOM as a function of pump power before and after 1 month. (b) Calculated active Q-switching pulse trains at different repetition rates (0.96, 2.02, 6.64 kHz). (c) The calculated extinction ratio of the FLA-based Kerr switcher. (d) FWM output spectra of the FLA-decorated microfiber with RF modulation (10 GHz). (a, b) Reproduced with permission [43]. Copyright 2019, Wiley-VCH. (c, d) Reproduced with permission [46]. Copyright 2018, Wiley-VCH.