Saturable Absorption in 2D Nanomaterials and Related Photonic Devices

Wide‐spectral saturable absorption (SA) has been experimentally demonstrated in two‐dimensional (2D) nanomaterials with outstanding performance, such as low saturation intensity, deep modulation depth, and fast recovery time of excited carriers. Hence, 2D nanomaterials can be utilized as saturable absorbers for mode‐locking or Q‐switching to generate laser pulses with short duration and high repetition rate. Here, the SA properties of graphene, layered transition metal dichalcogenides, Group‐V elements, and other 2D nanomaterials are reviewed by summarizing their slow‐ or fast‐ saturable absorption behavior using the modified Frantz–Nodvik model or the steady‐state solution of Hercher's rate equations. The dependence of SA in 2D nanomaterials on excitation wavelength, linear absorption coefficient, and pulse duration is also explained. Finally, the applications of these 2D nanomaterials in a range of pulsed lasers are summarized. Saturable absorption induced by Pauli‐blocking allows intense light to pass while low‐intensity light is absorbed. This can be utilized for mode‐locking to generate ultrashort laser pulses. Saturable absorption in a wide range of 2D nanomaterials and related photonic devices is reviewed, together with its applications in mode‐locked lasers, using slow‐ and fast‐saturable absorption models.