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Timestamp: 2019-04-20 11:28:26+00:00

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Two-dimensional (2D) materials with potential applications in photonic and optoelectronic devices have attracted increasing attention due to their unique structures and captivating properties. However, generation of stable high-energy ultrashort pulses requires further boosting of these materials’ optical properties, such as higher damage threshold and larger modulation depth. Here we investigate a new type of heterostructure material with uniformity by employing the magnetron sputtering technique. Heterostructure materials are synthesized with van der Waals heterostructures consisting of MoS2 and Sb2Te3. The bandgap, carrier mobility, and carrier concentration of the MoS2-Sb2Te3-MoS2 heterostructure materials are calculated theoretically. By using these materials as saturable absorbers (SAs), applications in fiber lasers with Q-switching and mode-locking states are demonstrated experimentally. The modulation depth and damage threshold of SAs are measured to be 64.17% and 14.13 J/cm2, respectively. Both theoretical and experimental results indicate that MoS2-Sb2Te3-MoS2 heterostructure materials have large modulation depth, and can resist high power during the generation of ultrashort pulses. The MoS2-Sb2Te3-MoS2 heterostructure materials have the advantages of low cost, high reliability, and suitability for mass production, and provide a promising solution for the development of 2D-material-based devices with desirable electronic and optoelectronic properties.
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Fig. 1. State-of-the-art SA devices using the MoS2-Sb2Te3-MoS2 heterostructure. (a) Schematic of macrostructure and (b) surface structure of the fabricated MoS2-Sb2Te3-MoS2 heterostructure SA. Sb2Te3 (7 nm thickness) is in the middle of MoS2 (8 nm thickness). The gold film with 117 nm thickness is deposited on the polished fused silica substrate as a broadband reflection mirror. (c) SEM image of the surface of deposited MoS2-Sb2Te3-MoS2 heterostructure film. (d) SEM image of the film thickness.
Fig. 2. Atomic and electronic structures of the MoS2-Sb2Te3-MoS2 heterostructure. (a) Side and (b) top views of the MoS2-Sb2Te3-MoS2 heterostructure. In (b), the detailed matching pattern of the (7×7)/(2×2) MoS2-Sb2Te3-MoS2 heterostructure is shown. The (7×7) MoS2 supercell is highlighted with yellow color, and the (2×2) Sb2Te supercell is denoted by the blue area. (c) Unfolding band structure of the MoS2-Sb2Te3-MoS2 heterostructure. Here, the Fermi level is defined as zero. (d) Band alignment of the MoS2-Sb2Te3-MoS2 heterostructure. The corresponding energy levels of pure MoS2 and Sb2Te3 slabs are shown in both sides.
Fig. 3. Standard two-arm transmission setup. The SAM is the MoS2-Sb2Te3-MoS2 heterostructure SA mirror.
Fig. 4. Characterization of the MoS2-Sb2Te3-MoS2 heterostructure SA mirror. (a) The modulation depth is 64.17%. (b) Raman spectrum of the MoS2-Sb2Te3-MoS2 heterostructure. (c), (d) Threshold damage condition of the MoS2-Sb2Te3-MoS2 heterostructure film at 12 mW.
Fig. 5. Configuration of the mode-locked EDF laser. WDM, wavelength-division multiplexer; LD, laser diode; SMF, single-mode fiber; EDF, erbium-doped fiber; OC, optical coupler; PC, polarization controller; PI-ISO, polarization-independent isolator; SAM, MoS2-Sb2Te3-MoS2 heterostructure SA mirror.
Fig. 6. Typical Q-switching characteristics. (a) Q-switched pulse trains. (b) Optical spectrum. (c) Q-switched pulse duration at 600 mW pump power. (d) RF spectrum at the fundamental frequency and wideband RF spectrum (inset).
Fig. 7. (a) Pulse duration and repetition rate versus incident pump power. (b) Average output power and single pulse energy versus incident pump power.
Fig. 8. Experimental results of fiber laser with mode-locked states. (a) Optical spectrum. (b) Pulse duration. (c) RF spectrum. (d) Phase noise.

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