In Situ and Dynamic Reconfiguration of Nonlinear Optical Absorption by Carbon Nanotube Optical Fiber

ABSTRACT Nanomaterial‐based nonlinear optical absorbers, such as saturable absorbers and optical limiters, have been widely employed for laser intensity manipulation. However, their nonlinear absorption regimes are typically constrained by static nonlinear responses within specific spectral regions. Tuning the operational regime generally necessitates material functionalization or complex post‐treatments. Consequently, reconfiguring the nonlinear absorption regime in a monolithic device remains challenging. Here, we demonstrate in situ manipulation of the nonlinear interaction strength using an optical fiber‐integrated single‐walled carbon nanotube absorber, which exhibits reconfigurable nonlinear optical absorption. Our monolithic device enables dynamic onset tuning of optical limiting within a designated spectral excitation energy range, in addition to supporting saturable absorption operation. Furthermore, leveraging the tunable nonlinear optical response of a saturable absorber, we realize a passively mode‐locked fiber laser with an unprecedented tuning range of 10 GHz and a side‐mode‐suppression ratio exceeding 30 dB, surpassing other nanomaterial saturable absorber‐based GHz light sources. Our device fabrication strategy features a simple configuration and low cost compared to static nonlinear optical absorbers, and it can be readily extended to other types of nonlinear optical nanomaterial absorbers. This approach may find immediate applications in flexible light intensity control, optical signal processing, and intelligent physical systems requiring dynamic nonlinear activation functions.