摘要： Cylindrical vector beam (CVB) fiber lasers have attracted great attentions due to their promising applications in optical communications, super-resolution imaging and optical trapping. Recently, it has been proved that mode-selective coupler (MSC) is an efficient method for generating CVBs in all-fiber lasers [1-3]. However, to date, the reported MSC-assisted CVB lasers have a common feature that the fundamental transverse mode (LP01) oscillates in the laser cavity whereas the high-order modes are outside the laser cavity. To some extent, such cylindrical vector lasers belong to the external mode conversion, rather than the direct generation of high-order modes inside the laser cavity. In this contribution, we present an intra-cavity MSC assisted CVB fiber laser in a compact linear-cavity mode-locked by using a semiconductor saturable absorber mirror (SESAM). The laser architecture is shown in Fig. 1(a), which consists of a 5 m Er-doped fiber, a 980/1550 wavelength-division multiplexer (WDM) pumped by a 980 nm laser, a polarization controller (PC), a 90% high coupling ratio MSC with an insertion loss of 0.3 dB. A fiber end-facet mirror is sandwiched between the two fiber ferrules and a SESAM mode locker has a modulation depth of 18%. The rest of cavity consists of ~14.3 m standard single-mode fiber (SMF) and ~0.6 m few mode fiber (FMF). Self-started mode-locking occurs when the pump power reaches ~35 mW. Thanks to the high coupling efficiency of intra-cavity mode converter, LP01 mode in the SMF is sufficiently coupled to LP11 mode in the FMF when it passes through the MSC. The reflected LP11 mode from the mirror can be partially coupled back to the SMF with a low loss, resulting in the laser oscillation. In this case, the laser operates between MSC and the mirror in the LP11 mode, which outputs from the FMF, meanwhile the LP01 mode oscillates in the remaining section of the linear-cavity. Eventually, the laser can allow the direct generation of LP11 mode from the laser cavity. Typical laser output characteristics such as broadband spectra, pulse train and output power are shown in Fig. 1(b)-(e). The laser operates at the wavelength of 1562 nm with a 3-dB bandwidth of ~4.4 nm and a repetition rate of 5.2 MHz. Radially polarized and azimuthally polarized ultrafast CVBs are obtained by adjusting the PC, and corresponding donut beam profiles are demonstrated by checking the rotating intensity distribution through the linear polarizer, as presented in Fig. 1(f).