Abstract
How to enhance the optical nonlinearity of saturable absorption materials is an important question to improve the functionality of various applications ranging from the high power laser to photonic computational devices. We demonstrate the saturable absorption (SA) of VO2 film attributed to the large difference of optical nonlinearities between the two states of the phase-transition materials (VO2). Such VO2 film demonstrated significantly improved performance with saturation intensity higher than other existing ultrathin saturable absorbers by 3 orders due to its unique nonlinear optical mechanisms in the ultrafast phase change process. Owing to this feature, a Q-switched pulsed laser was fabricated in a waveguide platform, which is the first time to achieve picosecond pulse duration and maintain high peak power. Furthermore, the emission of this VO2 waveguide laser can be flexibly switched between the continuous-wave (CW) and pulsed operation regimes by tuning the temperature of the VO2 film, which enables VO2-based miniature laser devices with unique and versatile functions.
Highlights
The progress in the nonlinear optical material research has paved the way for many revolutionary inventions, such as the photonic computational devices, high power lasers, and super-resolution optical imaging techniques[1,2,3,4,5]
The ultrathin VO2 film was fabricated by the Pulsed Laser Deposition (PLD)
The morphology of the VO2 film was characterized by an Atomic Force Microscope (Fig. 1b, scratches are made to measure the thickness of the film)
Summary
The progress in the nonlinear optical material research has paved the way for many revolutionary inventions, such as the photonic computational devices, high power lasers, and super-resolution optical imaging techniques[1,2,3,4,5]. The conventional saturable absorption mechanisms are based on the photon-induced electron excitation In this nonlinear process, the electrons are further excited from the first excited state to higher energy states. The saturable absorption relied on a different mechanism, i.e., Contrast Nonlinear Transmission, has been proved to have more optimal nonlinear behaviors. It is based on the ultrafast phase transition of the VO2 to manipulate the transmittance of the light. In this work, based on the Contrast Nonlinear Transmission, a significantly improved design, i.e., a tunable pulsed waveguide laser with picosecond duration, was proposed and implemented based on passive Q-switching. The temperature tuning of the VO2 film has been applied to develop unique CW-pulsed switching laser system
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