In this article, a distributed strain sensing system based on a standard single-mode fiber is implemented using the Phase-Optical Frequency Domain Reflectometry (ϕ-OFDR). Compared to traditional amplitude cross-correlation algorithms, phase demodulation can achieve higher sensing resolution, but it is more susceptible to phase noise interference. To address this issue, an adaptive phase noise suppression algorithm based on the adjacent window boundary continuity conditions has been proposed to correct error phase jumps in the phase unwrapping process and recover the phase difference curve. Additionally, wavelet denoising is employed to eliminate Gaussian white noise in the linear phase term, which weakens the trade-off between sensing resolution and accuracy. With a spatial resolution of 15.8 μm, the system achieved a sensing resolution of 1.5 mm, and a root mean square error of 0.9343 μϵ in single mode fiber.

Wiener deconvolution offers the advantages of effectively suppressing noise, restoring image details, and enhancing signal processing accuracy. It has been successfully applied in image denoising for distributed fiber-optic sensing. However, the effective application of Wiener deconvolution in optical frequency-domain reflectometry (OFDR) systems has not yet been reported. The challenge lies in obtaining an effective point spread function (PSF) or blur function to minimize spatial resolution degradation during image processing. To the best of our knowledge, we first proposed a high spatial resolution OFDR system based on Wiener deconvolution. Crucially, we have theoretically and experimentally validated that the auto-correlation function of local Rayleigh scattering spectrum serves as the PSF for the OFDR system. We have optimized the selection range of the PSF in both spatial and frequency domains to achieve the highest spatial resolution. The effectiveness of this algorithm and its superior denoising performance were validated by comparison with Gaussian filtering. Finally, through multiple experiments, we have demonstrated that the proposed Wiener deconvolution method can restore events at a spatial resolution of 200 $\mu \text{m}$.

A novel scheme to realize distributed bending sensing along the few mode fiber based on optical frequency domain reflectometry is proposed. The feasibility of the proposed method has been demonstrated both theoretically and experimentally on a two-mode fiber. The bending information is obtained by demodulating the changes of the effective refractive index and differential mode delay between LP ₀₁ and LP ₁₁ modes. The experimental results are in good agreement with those obtained by simulation when the bending diameter changes from 4 to 8 cm. We believe that this characterization method paves the way for developing high spatial resolution distributed bending sensor and can also be generalized to more modes case.

We demonstrate a narrow linewidth 1064 nm DFB laser diode by employing a piece of Rayleigh scattering enhanced fiber to provide distributed feedback. Introducing local defects in the high numerical aperture fiber with femtosecond laser micromachining enhances Rayleigh scattering by 60.23 dB in comparison with standard single-mode fiber in common use. Based on the external distributed feedback from the Rayleigh scattering enhanced fiber with a length of 3 m, a 1064 nm laser diode with an intrinsic linewidth of 94 Hz, a frequency noise of 3.85 Hz ² /Hz@1MHz, and a side-mode suppression ratio of 83.98 dB was experimentally demonstrated. More interesting is that such a narrow linewidth laser diode can operate at any wavelength within its tuning range due to the wavelength self-adaptivity of the Rayleigh scattering based distributed feedback. The work demonstrated here provides a method for miniaturized and integrated narrow linewidth lasers with continuous wavelength tunability.

We propose and demonstrate a novel concept of Brillouin fiber swept laser with narrow linewidth based on mode following effect. Utilizing the synergy of the Brillouin gain spectrum and cavity mode, the real-time mode following effect is achieved. In the experiment, a tunable laser source was employed to realize synchronous tuning of Brillouin gain spectrum for matching the shift of cavity mode induced by an intra-cavity piezoelectric transducer wound with gain fiber. We theoretically analyzed the influence of the driving parameters and wound fiber length on the frequency sweep range. Experimental results show that the obtained maximum continuous frequency sweep range is ∼445.76 MHz while the driving frequency is 12 kHz and the wound fiber length is 12 m, which is consistent with the theoretical analysis. This new type of fiber swept laser has huge potential application value in optical sensing and communication system.

Liquid-level sensors are required in modern industrial and medical fields. Optical liquid-level sensors can solve the safety problems of traditional electrical sensors, which have attracted extensive attention in both academia and industry. We propose a distributed liquid-level sensor based on optical frequency domain reflectometry and with no-core fiber. The sensing mechanism uses optical frequency domain reflectometry to capture the strong reflection of the evanescent field of the no-core fiber at the liquid–air interface. The experimental results show that the proposed method can achieve a high resolution of 0.1 mm, stability of ±15 μm, a relatively large measurement range of 175 mm, and a high signal-to-noise ratio of 30 dB. The sensing length can be extended to 1.25 m with a weakened signal-to-noise ratio of 10 dB. The proposed method has broad development prospects in the field of intelligent industry and extreme environments.