On account of the unique features including long distance, high spatial resolution, high precision, and anti-electromagnetic interference, optical frequency domain reflectometry (OFDR), having been regarded as one of the major technique in distributed fiber-optic sensing (DFOS), has been widely applied in fields such as optical fiber network, aerospace, traffic facilities, and structural health monitoring. The essence of OFDR lies in the generation of the linearly frequency swept optical frequency-modulated continuous-wave (OFMCW) probe with high coherence, low phase noise, high linearity, and wide sweep range. High performance measurement has demanded the improvement in the performance of OFMCW probe, including the high dynamic coherence, highly linearized frequency sweep, and a broad sweep range. To date, either direct modulation or external modulation based generation techniques suffer from the trade-off between large sweep range and low phase noise, namely, high coherence. Therefore, in order to improve the performance, there is an urgent need to achieve simultaneously the extension of sweep range and enhancement of coherence. This paper aims at the introduction of the current progress in the technologies for the generation of linearly frequency swept OFMCW probe.First, the operational principle for the DFOS based on linearly frequency swept OFMCW has been introduced. Based on the principle, theoretical analysis have been conducted on the factors affecting measurement performance, including the sweep range, phase noise, and sweep nonlinearity. In general, the sweep range directly determines the Fourier transform-limited spatial resolution (Eq.7). Thus, improving spatial resolution hinges on expanding the sweep range. In addition, the measurement distance is largely dictated by the laser phase noise (Fig.3), making it essential to suppress the phase noise and thus to achieve the enhancement of the laser coherence. This is especially critical for long-distance measurement and sensing. Besides, sweep nonlinearity usually leads to the dispersion for the power of the central peak of the beat signal (Fig.4), which affects both the spatial resolution and the sensing accuracy. Hence, in order to realize a high precision, long distance measurements and sensing, it is urgently required for the suppression and compensation of the sweep nonlinearity.Second, this paper systematically reviews the methods for improving the sensing performance, mainly including two aspects: sweep range expansion and phase noise suppression. High-order sidebands sweeping is a common approach to expand the sweep range. Nevertheless, the spectrum aliasing issue of the adjacent sidebands limits further range expansion. To address this limitation, optical injection locking and optical phase-locked techniques have been proposed. Stitching multiple sections of sweeps is a promising strategy, including multi-laser stitching, recirculating frequency-shifting stitching, and multi-comb modes stitching. However, the effective stitching of multi-segment sweeps and the errors introduced by sweeps gaps remain challenging and this requires further investigation. Finally, Fourier-domain mode-locking (FDML) is an emerging technique that has been adopted to implement fast and wide frequency sweeping, but it suffers from poor coherence.Phase and frequency noise suppression is a crucial technique for enhancing coherence and improving the performance of self-coherent detection, including methods such as pre-distortion and optical phase-locked loop (OPLL). Predistortion is typically implemented via different algorithms, which are usually considered compact, straightforward and effective. However, it is limited to correcting fixed nonlinearities. In contrast, OPLL is a dynamic feedback correction technique that facilitates highly coherent and linear frequency sweeps by locking to a stable reference, such as a laser with a narrower linewidth or a stable interferometer based on optical cavity or fiber reference. In this context, the laser phase error extraction based on the unbalanced Mach-Zehnder interferometer (UMZI) has shown prominent advantages in the generation of OFMCW waveforms. Regarding on this technique, several OFMCW generation methods based on delayed self-interferometry OPLL structures have been proposed and employed in OFDR measurements. In conclusion, this paper summarized the current progress in the generation of OFMCW probe. For future prospect, OFMCW based technique increasingly demonstrates its advantages in the measurement and sensing and it is poised to make a significant contribution in geophysics, scientific research, and other emerging fields.