Bismuth telluride topological insulator nanosheet saturable absorbers for q-switched mode-locked Tm:ZBLAN waveguide lasers

Nanosheets of bismuth telluride (Bi2Te3), a topological insulator material that exhibits broadband saturable absorption due to its non‐trivial Dirac‐cone like energy structure, are utilized to generate short pulses from Tm:ZBLAN waveguide lasers. By depositing multiple layers of a carefully prepared Bi2Te3 solution onto a glass substrate, the modulation depth and the saturation intensity of the fabricated devices can be controlled and optimized. This approach enables the realization of saturable absorbers that feature a modulation depth of 13% and a saturation intensity of 997 kW/cm2. For the first time to our knowledge, Q‐switched mode‐locked operation of a linearly polarized mid‐IR ZBLAN waveguide chip laser was realized in an extended cavity configuration using the topological insulator Bi2Te3. The maximum average output power of the laser is 16.3 mW and the Q‐switched and mode‐locked repetition rates are 44 kHz and 436 MHz, respectively. Novel saturable absobers for ultrashort‐pulsed operation of mid‐infrared waveguide chip lasers have been fabricated by depositing multiple layers of nanosheets of topological insulator material onto a glass substrate. By optimizing the number of spin coating layers, highly stable Q‐switched mode‐locked pulse trains have been generated in an external‐cavity Thulium‐ZBLAN depressed‐cladding waveguide laser. These results pave the way for the realization of fully integrated ultrashort‐pulsed chip lasers in the mid‐infrared.