A pump laser is a laser used to provide an excitation light source for a fiber laser or fiber amplifier. The emission wavelength of a 980nm pump laser is approximately 980 nanometers (nm).
ASE broadband light generated by erbium-doped fiber is amplified spontaneous emission light generated by short-wavelength laser pumping erbium-doped fiber. As shown in the following diagram, the pumped rare earth ions transition between upper and lower energy levels to generate spontaneous emission light, which is amplified in the stimulated emission process. This process is repeated continuously, and even a fairly high output power can be achieved under sufficient pumping conditions. (ASE=Amplified Spontaneous Emission, amplified spontaneous emission light)
For polarization-maintaining (PM) optical fiber, assuming that the polarization direction of the input linearly polarized light is in the middle of the fast axis and the slow axis, it can be decomposed into two orthogonal polarization components. As shown in the figure below, the two light waves initially have the same phase, but because the refractive index of the slow axis is greater than that of the fast axis, their phase difference will increase linearly with the propagation distance.
Depending on the active region material, the band gap width of the semiconductor material of the blue light semiconductor laser varies, so the semiconductor laser can emit light of different colors. The active region material of the blue light semiconductor laser is GaN or InGaN.
For panda and bowtie PM fibers, due to non-ideal coupling conditions, external stress on the fiber, and defects in the fiber, the polarization direction of part of the light will shift to the orthogonal direction, reducing the output extinction ratio.
Optical coherence tomography is a low-loss, high-resolution, non-invasive medical imaging technology developed in the early 1990s. It combines optical technology with ultrasensitive detectors. Using modern computer image processing, OCT fills the gap in resolution and imaging depth between microscopes and ultrasound imaging. The imaging resolution of OCT is about 10~15 μm, which is clearer than that of intravascular ultrasound (IVUS), but OCT cannot image through blood. Compared with IVUS, its tissue penetration ability is lower, and the imaging depth is limited to 1-2mm.
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