Single crystalline BiOCl nanosheets with oxygen vacancies for ultrafast mode-locking operation.

• The BiOCl nanosheets can be synthesized very easily with the two-step solvothermal-calcination method. • The finite element analysis on the BiOCl membrane on the tapered fiber was demonstrated initially. • The BiOCl saturable absorber mode-locked Er-doped fiber laser at 1560 nm was demonstrated for the first time, producing ∼ 990 fs pulses. In this work, we synthesized the single-crystalline square BiOCl nanosheets with oxygen vacancies via the facile solvothermal route. The prepared BiOCl nanosheets were deposited on a tapered microfiber as a saturable absorber. Via the evanescent filed interaction with the BiOCl saturable absorber, a soliton mode-locked Er-doped fiber laser was demonstrated for the first time, producing a pulse duration of 990 fs at a central wavelength of 1563 nm with a FWHM bandwidth of 3.2 nm. The signal-to-noise ratio was 36 dB at the fundamental repetition rate of 7.9 MHz. Our results confirmed that the BiOCl nanosheets with abundant oxygen vacancies could be applied for the ultrafast photonics. [ABSTRACT FROM AUTHOR]