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In this study, we propose a polarization-separated external cavity feedback structure based on a volume Bragg grating (VBG) that folds the optical path of a free-running diode laser into a non-straight direction for linewidth narrowing and central wavelength locking. By employing diode laser polarization splitting technology and external cavity feedback technology, a similar output power and narrow linewidth but a smaller current drift coefficient of central wavelength are demonstrated by comparing with the standard straight external cavity feedback structure. Experimental results show that the current drift coefficient of central wavelength reduce to 1/5 that of the traditional method. According to our research, this is the first report on folding the extended external cavity feedback optical path in a non-straight direction basing on polarization splitting technology, providing a new method for external cavity feedback based on the VBG. • A polarization-separated external cavity feedback structure based on a VBG for linewidth narrowing and central wavelength locking is proposed. • A similar output power and narrow linewidth but a smaller current drift coefficient of central wavelength are demonstrated. • The locked central wavelength as a function of operating current shifts at a rate of approximately 2.625 pm/A. [ABSTRACT FROM AUTHOR]

[Display omitted] • A super-sensitive carbon nanofiber aggregate (SSCNFA) sensor with 0.05% CNFs content has been developed. • The sensor's sensitivity is enhanced due to a well-defined conductive path between CNFs and steel mesh. • SSCNFA can detect forces as low as 0.28 N, making it suitable for stress/strain sensing and damage detection. • The sensor has a wide dynamic range, with any frequency from 1 Hz to 500 kHz available for various applications. A carbon nanofiber aggregate of exceptional sensitivity is developed. Our approach involves the development and utilization of a novel nanobrush structure of carbon nanofiber within the mortar matrix. The high number of nanostructures in the nanobrush, particularly near the electrodes, results in a greater number of nanogaps, leading to a substantial improvement in sensitivity. We are able to detect forces as small as 1 N using this sensor. The carbon nanofiber brush (CNFB) provides a well-defined conductive path for the piezoresistive functioning of the super-sensitive carbon nanofiber aggregate (SSCNFA) with significantly reduced cost. The influence of scanning frequency in impedance is rigorously investigated with alternating current (AC) based on two methods. SSCNFAs are tested in uniaxial compression to determine the highly sensitive face of cube sensor. An SSCNFA (0.05 % CNFs, dense electrodes) and a CNFA (0.5 % CNFs, wide-spaced electrodes) were tested in a sweep-frequency test under parallel compression to compare the super-sensitive performance of the new sensor. The gauge factors at various frequencies were determined. The electrical impedance measured at various frequencies provides versatility to the SSCNFA for stress monitoring. Four fixed-frequency tests were conducted to determine the resolution under uniaxial compression and examine repeatability. [ABSTRACT FROM AUTHOR]