A bidirectional fiber pulsed-laser utilizing ethylene glycol as a mode-locker has been successfully proposed and demonstratedfor the first time. The glycol saturable absorber (SA) is createdby filling ethylene glycol into a cannula,which serves to connect the end facets of two optical patch cords, ultimately forming a sandwich structure. The modulation depth of the glycol-SA is 9.6%, being adequate for mode-locking operation. Based on such an SA, the laser pulses propagating in the clockwise and counterclockwise directions are both achieved by adjusting the polarization state and pump power in the cavity to balance the intra-cavity dispersion and nonlinearity. The obtained laser pulse in one direction operates at the fundamental frequency of 24.31 MHz, with a center wavelength of 1568.28 nm and a 3 dB bandwidth of 0.65 nm; the pulse in the other direction transmitting in the same frequency rate, has a center wavelength of 1568.34 nm and a 3 dB bandwidth of 0.68 nm. With the superiority of fast response time, broad working bandwidth, high damage threshold, low cost,and simplicity in fabrication,this SAs have expansive application prospects in ultrafast photonics and nonlinear optics.
This paper presents a study on continuous wave tunable CO2 lasers, which could be used in good pumping source of optically pumped gas THz laser. A series of comparative experiments to investigate the effects of cavity structure and discharge current on laser tunability and output power was conducted. The wavelength selection of CO2 lasers primarily achieved by altering the angle of incidence of the blazing grating. Two enclosed CO2 laser tubes were designed and customized, one was used for external cavity structure and the other was used for semi-external cavity structure research. Using the semi-external cavity structure, 78 lines was obtained at the range of 9-11μm, and achieved 60.7 W of laser output power at a wavelength of 10.59 μm. A beam quality factor of M2 = 1.68 was measured using the traveling 90/10 knife-edge method.
We propose an optical parametric loop mirror whose reflectivity is adjustable by setting two tunable optical attenuators in Sagnac loop. The scheme of the optical parametric loop mirror is consisted of a nonlinear four wave mixing medium, a dispersive element, two optical attenuators, and a beam splitter. The generated four wave mixing wave can be totally separated from signal and pumps no matter how the beam splitter ratio is. When the beam splitter ratio is more than 0.5, we can separate the four wave mixing wave from pumps and signal completely by adjust the efficiency of the first attenuator, and when the beam splitter ratio is less than 0.5, we can also separate the four wave mixing wave from pumps and signal completely by adjust the efficiency of the second attenuator. Our research can help to generate and separate frequency degenerate twin beams in experiment.
The train wheelset is a crucial part of railway vehicles, and its damage may lead to serious safety accidents. Therefore, it is imperative to detect tread damage timely and accurately. With the rapid development of deep learning, the image detection method based on a convolutional neural network (CNN) has played an important role. Single Shot MultiBox Detector (SSD) is one of the fastest algorithms in the target detection field. The algorithm has achieved excellent results in target detection, but there is a low recognition rate for small targets. Therefore, we propose an improved SSD target detection algorithm. The Original SSD algorithm is ineffective in detecting small targets with pits and cracks, so conv3-3 is selected to join the detection. We optimize convolution kernel parameters; the convolution layer contains more small target details. Compared with the original SSD, the Mean Average Precision (MAP) of tread defect is improved by 4.38%, and the MAP of small target detection is enhanced by 7.24%. This algorithm has a better performance in detection accuracy.
Foreign fibers in cotton have serious adverse effects on the quality of textile products, so its effective identification and elimination has important significance and social value. To solve the above problems, we propose a fusion image pretreatment method based on limited contrast adaptive histogram equalization ( CLAHE ) and wavelet analysis ( WT ), The collected cotton polarization images were processed by WT & CLAHE, which effectively improved the contrast of anisotropic fibers in cotton images, and laid the foundation for the rapid and accurate identification of various anisotropic fibers in cotton in the later stage, It laid a foundation for the rapid and accurate identification of all kinds of anisotropic fibers in cotton in the later stage. Compared with manual and systematic detection, the results showed that technical personnel and detection system could accurately detect and identify dead leaves, white paper and color paper without interference from external environment and foreign fiber size. For white wool, hair and mulch film due to similar color or shape is small, technical personnel in the detection is easy to miss, and the detection system in WT & CLAHE image pretreatment, white wool, hair and mulch film detection accuracy is obviously due to artificial detection, especially for the mulch film this is not easy to detect foreign fiber has good recognition effect.
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