Broadband Black Phosphorus Optical Modulator in the Spectral Range from Visible to Mid‐Infrared

Abstract

Promising BP fi eld-effect transistors and absorbers for solar cells have already been demonstrated [ 17,19 ] and proposed. [ 20 ] Apart from the promising applications as transistors or absorbers, the nonlinear response of this 2D semiconductor to applied fi elds is also amazing. The possible nonlinear response properties are determined by the crystalline structure based on the Neumann principle. [ 21 ] Structurally, bulk BP crystals belong to the space group C mca, which indicates that the multilayered BP crystal has a center of inversion and has no second-order nonlinearity, including piezoelectric, ferroelectric, Pockels, second harmonic generation, etc. effects. For the third-order nonlinearity, the saturable absorption of BP has been studied recently and the results pointed out that few-layered BP has a nonlinear response in the visible to mid-infrared range with a large saturable intensity, which is defi ned as the optical intensity at the point where the optical absorption coeffi cient is reduced to half of its original value. In addition to the direct bandgap, which determines the effi cient absorption and emission properties, the optical nonlinearity theoretically indicates that BP should be a potential broadband saturable absorber that can be applied for modulating visible to mid-infrared lasers with large pulse energy. However, up to now, only few BP applications have been demonstrated in 1.5-to 1.9-µm fi ber lasers [22][23][24][25] and there are no reports on their use in bulk lasers either. Here, we report for the fi rst time the experimental realization of a BP pulse modulator and its applications in crystal lasers in the wavelength range of the visible to the mid-infrared. The results widen the spectral range of BP applications and experimentally identify that BP is a promising broadband optical modulator in optics beyond electronics. Results and Discussion Characterization of BP Broadband Modulator and Saturable Absorption MeasurementsThe mechanically exfoliated BP fl akes were investigated by Raman spectroscopy. The Raman shifts after stimulation by a laser with a wavelength of 633 nm are presented in Figure 1 a. From this fi gure, we observe that the peaks appear at 369.2 cm −1 , 439.0 cm −1 , and 467.5 cm −1 , corresponding to one out-of-plane vibration mode A 1 g and two in-plane vibration modes B 2 g and A 2 g , respectively. [ 26,27 ] It is well known that Black phosphorus (BP), a two-dimensional (2D) material, has a direct bandgap that can be tuned by changing the layers and applied strain, which fi lls the lacuna left by graphene topological insulators and transition-metal dichalcogenides. Theoretically, the direct and tunable bandgap should enable broadband applications for optoelectronics with high effi ciencies in the spectral range from the visible to the mid-infrared. Here, a BP broadband optical modulator is experimentally constructed and passively modulated lasers at 639 nm (red), 1.06 µm (near-infrared), and 2.1 µm (mid-infrared) are realized by using a BP optical modulator as the...

Dual-wavelength, passively Q-switched Tm:YAP laser with black phosphorus saturable absorber

“…9. A maximum Qswitched pulse energy was calculated as 39.5 μJ, which was higher than any other result ever achieved with BP SA [14][15][16][17][18][19][20][21][22][23][24] and a corresponding maximum pulse peak power of 218 W was obtained. Considering the laser mode radius on the BP SAM, which was estimated to be about 116 μm by using ABCD matrix theory, the intracavity fluence on the BP SAM was calculated to be about 4.38 J/cm 2 .…”

“…Moreover, the direct bandgap of BPs can be tuned from 0.35 eV for bulk to 2.0 eV for monolayer structure [13], well bridging the zero bandgap of graphene and large bandgap of TMDs. Until now, BP has been successfully employed as SAs in bulk lasers at different wavelengths of 639 nm [14], 1.0 μm [15], 2.0 μm [16], 2.72 μm [17], and in fiber lasers at various wavelengths of 1.5 μm [18][19][20],1.9 μm [21], 2.8 μm [22]. In 2015, our group successfully demonstrated the generation of 6.1 ps pulses from a BP mode-locked bulk laser at 1064 nm for the first time [23].…”

Black phosphorus as saturable absorber for the Q-switched Er:ZBLAN fiber laser at 28 μm

“…So far, the saturable absorption of BP has been demonstrated experimentally by Q-switched or mode-locked lasers from 0.6 to 2.0 μm wavelength. [27][28][29][30].…”

Recent Progress in 2D Material‐Based Saturable Absorbers for All Solid‐State Pulsed Bulk Lasers

“…Zhang et al. realized a BP passively Q‐switched bulk visible laser operating at 639 nm with a shortest pulse width of 189 ns and a pulse energy of 104 nJ . Luo et al.…”