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An all polarization-maintaining figure-nine cavity fiber laser, which could be self-starting in low threshold state was reported. A phase shifter was used in the resonator structure to reduce the mode-locking threshold. When the pump power reached 120 mW, a self-starting conventional soliton mode-locking could be realized, with the central wavelength of 1530 nm and the pulse width of 614.6 fs. Then the pump power gradually increased to 470 mW, which realized the conversion from soliton pulse to noise-like pulse. In this mode-locking state, the laser output power is 63.2 mW, and the corresponding noise-like pulse energy is 5.69 nJ. The constructed laser has the advantages of low mode-locking threshold, self-starting, and can realize the conversion between ultrafast pulses and high-energy pulses only by adjusting the pump power, which has extensive application values.

A flat super-continuum spectrum light source of all-fiber structure based on noise-like pulse pumping was designed. In the dispersion-managed erbium-doped fiber laser, by adjusting the polarization state in the cavity, when the pump power was 450 mW, the stable noise-like pulse mode locking was achieved, the center wavelength was 1600 nm, and the pulse width was 303 fs. When the maximum pump power was 1 W, the direct output power of the resonator was 8.6 mW, and the lower power could not effectively expand the width of the super-continuum spectrum. Therefore, an erbium-doped fiber amplifier was designed for power amplification, and the maximum output power was 338 mW. The power-amplified noise-like pulse was coupled into the highly nonlinear fiber to obtain a super-continuum spectrum. The 20 dB spectral range of super-continuum spectrum is 1 530 nm ~ 2 300 nm, and in the range of 1 736 nm ~ 2 134 nm, the flatness of the spectrum is less than 0.5 dB.

A study on a combined sensor was made for partial discharge (PD) location in oil. The sensor includes a cross-shaped ultrasonic phased array of 13 elements and four ultra-high frequency (UHF) electromagnetic sensor. The ultrasonic array can achieve the performance of 61 elements with high-order cumulant processing technology. It can improve the array aperture and direction sharpness and greatly simplify the complexity of the following circuit and reduce the manufacturing cost. The method of PD location which use expanded ultrasonic array accompanied with UHF electromagnetic array has better performance. The spatial spectrum comparing with MUSIC (multiple signal classification) method shows that virtual expanding array of the fewer number array elements with high-order cumulant processing technology has strong ability to suppress colored Gaussian noise interference. This provides the possibility for the practical application of array technology in power equipment.