Humidity Resistant Carbon Nanotubes‐Styrene Methyl‐Methacrylate Polymer Composite for Ultrafast Laser

Abstract Carbon nanotube (CNT)–polymer composite films are key elements in widespread photonic and optoelectronic applications. One particular successful application is to produce ultrashort optical pulses in the laser cavity. Nevertheless, such composite film may suffer from severe humidity/water degradation, from which the laser may even stop generating regular pulses. Here, surfactant‐free CNT–styrene methyl‐methacrylate polymer composite film is fabricated. Based on such film‐type saturable absorber, a self‐starting passively mode‐locked erbium‐doped fiber laser with the capability of generating ≈1 ps pulses is demonstrated. From the perspective of experimental measurements and numerical simulations, the effectiveness of a saturable absorber in generating ultrashort pulses is confirmed. The operating composite film can survive under fully immersed water condition for 30 days. More importantly, after the non‐operating composite film has been fully soaked in the water tank for 2 days, it can still mode‐lock the laser as it is in dry air condition, confirming the humidity resistance capability. In addition, it is experimentally found that the mechanical packaging of the composite film has an impact on the survival time of composite film under water immersion.