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Optical amplifiers
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Johan Nilsson, Jesper Laegsgaard, Anders Bjarklev
V-groove side-pumping (VSP) is another approach to cladding-pumping, that offers many of the advantages that GTwave fibers provide, with comparable performance [47,48]. An additional advantage is that VSP amplifiers can be made with any double-clad fiber. On the other hand, while conceptually simple, the fabrication of the v-groove as well as the pump launch are relatively complex issues. A v-groove is fabricated in the side of a double-clad fiber, penetrating into the inner cladding but leaving the (erbium-doped) core intact. Then, pump light from a laser diode is launched through the opposite side of the fiber, and hits the v-groove from within the fiber. The light is then deflected off the v-groove facet by ∼90°, along the fiber axis and inside the inner cladding, via total internal reflection. Thus, the pump light is launched into the inner cladding of the double-clad fiber, while signal-carrying fibers can be spliced to its ends.
Ultrafast Fiber Lasers
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
Many high-power fiber lasers are based on double-clad fiber. The gain medium forms the core of the fiber, which is surrounded by two layers of cladding. The lasing mode propagates in the core, while a multimode pump beam propagates in the inner cladding layer. The outer cladding keeps this pump light confined. This arrangement allows the core to be pumped with a much higher power beam than could otherwise be made to propagate in it, and allows the conversion of pump light with relatively low brightness into a much higher-brightness signal. As a result, fiber lasers and amplifiers are occasionally referred to as “brightness converters.” A doped optical fiber is an essential component that is used as a gain medium to generate and amplify an optical signal for fiber lasers and amplifiers. In general, the signal to be amplified and a pump laser are multiplexed into the doped fiber, and the signal is amplified through interaction with the doping ions. The most common example is the erbium-doped fiber (EDF), where the core of a silica fiber is doped with trivalent erbium ions and can be efficiently pumped with a laser at a wavelength of 980 nm or 1480 nm, and exhibits gain in the 1,550 nm region; the ytterbium-doped fiber, where the core of a silica fiber is doped with trivalent ytterbium ions and can be efficiently pumped with a laser at a wavelength of 980 nm or 915 nm, and exhibits gain in the 1064 nm region; and the thulium-doped fiber, where the core of a silica fiber is doped with trivalent thulium ions and can be efficiently pumped with a laser at a wavelength of 790 nm or 1560 nm, and exhibits gain in the 2000 nm region. By using glasses with a composition ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers (Er doped, Ho doped, or Tm doped), the wavelengths can be extended to visible and mid-infrared (IR) regions such as 2.7 and 3 μm.
Lissajous confocal fluorescent endomicroscopy with a lever mechanism and a frequency separation by an asymmetric polymer tube
Published in International Journal of Optomechatronics, 2023
Jintaek Im, Yeonhee Chang, Myung Ho Lee, Dukho Do, Kyuhang Lee, Daegab Gweon, Cheol Song
Various methods have been developed to integrate fluorescence imaging optical components into an endomicroscopic probe. For instance, an optical fiber bundle can transmit numerous pixel intensities through tens of thousands of single-mode cores[12] with the advantage that beam scanning does not have to be embedded in the probe end. However, there is an intrinsic limit to spatial resolution due to the core-to-core spacing.[13] Even though several imaging algorithms are suggested to remove the honeycomb pattern caused by core-to-core spacing, there must be unsampled pixels causing noise and contrast reduction on the processed image.[14] On the other hand, a point-scanning method that scans a single optical fiber, such as single-mode fiber (SMF) or double-clad fiber (DCF), can enhance image quality while diminishing speckle contrast.[15]
Optimizing the pump wavelength to improve the transverse mode instability threshold of fiber laser by 3.45 times
Published in Journal of Modern Optics, 2021
Yingchao Wan, Baolai Yang, Peng Wang, Xiaoming Xi, Hanwei Zhang, Xiaolin Wang
To study the TMI threshold characteristics of different pumping wavelengths, a forward-pumped fiber laser oscillator is built, as shown in Figure 2. Three groups of 969nm and 976nm wavelength-stabilized LD were injected into the laser resonator through a (6 + 1) ×1 forward pump and signal combiner ((6 + 1) ×1 FPSC). The resonator is composed of ytterbium-doped double-clad fiber (YDF) and a pair of fiber gratings with a central wavelength of 1080nm. The reflectivity of the high reflected fiber Bragg grating (HR FBG) is 99.9%, and the 3dB reflecting bandwidth is 4nm. The output coupler fiber Bragg grating (OC FBG) is 10%, and the 3dB reflecting bandwidth is 1.7nm. The core and cladding diameters of ytterbium-doped double-cladding fibers are 30 and 400 μm, respectively. The absorption coefficient at 915 nm is 0.88 dB/m, and the length is 20 m. The power of a single group of 969 and 976 nm stable wavelength LD are above 500W. In the experiment, the minimum bending diameter of ytterbium-doped double-clad fiber was set as 85mm in order to increase the loss of HOMs. The laser generated in the resonator passes through the cladding light stripper (CLS) and is output from the quartz block head (QBH). CLS filters out unabsorbed pump light and HOMs generated in the laser. The signal arm of the (6 + 1) ×1 beam combiner is bevel cut at 8° to avoid self-excitation of the laser due to feedback light. Finally, a QBH with the same size as the passive fiber is utilized to output the signal laser and eliminate the end facet reflection. Then, the laser is injected through a beam splitting system into a power meter (PM), optical spectrum analyzer (OSA), photodetector (PD), and M2 Analyzer to measure and record the output power, spectrum, time domain, and beam quality factor M2, respectively. Components of the fiber laser system, including LDs, (6 + 1)×1 FPSC, YDF, HR FBG, OC FBG, and CLS are put on water cooled plates sink to realize efficient heat management and ensure stability in high power operation.