Much research has been performed into applications of visible vortex Laguerre-Gaussian modes, including chiral material fabrication. These will demand compact, robust sources at a range of emission wavelengths. We have developed an ultracompact vortex laser source with a blue (442nm) diode pumped Pr3+ doped water-proof fluoro-aluminate glass (Pr:WPFGF) fibre laser, emitting red (638nm) and, for the first time, orange (612nm) vortex modes, in addition to balanced dual wavelength emission. The laser uses a standard microscope slide as an interferometric output coupler to convert the internal Gaussian mode into a vortex output, yielding high quality first order vortex modes in a compact setup. We additionally demonstrate the broad (∼5 nm) emission bands in the orange (610 nm), red (637 nm) and infrared regions (698 nm), with the potential for green (530 nm) and cyan (485 nm) emission.
As announced the other day, the 2018 Nobel Prize in Physics was given for the development of optical tweezers and ultrashort pulse lasers. Optical technology is constantly advancing and penetrating into various industrial fields. Recently, the power of fiber lasers is remarkably increasing, and therefore, it becomes a promising processing tool for metalworking and its marketing value is also increasing. In addition, now we already have many processes that cannot be done without laser, and this trend will continue in the future. However, we often hear from potential users of optical technology who work at machining, "I understand the importance of optical technology, but I am hesitating to introduce because I do not know how to use". This is the same from the actual feeling as an optical researcher of me, and I feel the lack of optical engineers who realize new technological ideas. In other words, the current state of the industry is in short supply of optical engineers. As a factor of short supply of optical engineers, mostly optical education is often in charge of the Department of Electrical and Electronic Engineering, Faculty of Engineering at Japanese universities, and therefore, most of the students that have learnt optics are employed as electrical/electronic engineers after graduation. Meanwhile, it is also true that efforts to resolve at various universities have begun. While introducing our optical education (student experiment: Control of polarization state), we will examine optical education at university and its role for the optical industry.
We have demonstrated a high power red fiber laser with a Pr-doped waterproof fluoro-aluminate glass fiber
(Pr:WPFGF). When 800 mW pumping power of a blue/violet GaN laser diode (GaN-LD) was launched into the
Pr:WPFGF (core diameter 8 μm, length 40 mm) with dielectric coating on both end surfaces to construct a resonator, the
maximum output laser power at 638 nm was obtained to be 311.4 mW that is higher than previously reported Pr:ZBLAN
fibers. The threshold power was evaluated to be 52.1 mW, and the slope efficiency was calculated to be 41.6%.
Assuming the resonator to be a Fabry-Perot resonator, we can calculate the output power to be 336 mW at 800 mW
pump power and the slop efficiency to be 44.2%. These theoretical values show good agreement with experimental ones.
Transparent Ce:GdYAG ceramics were synthesized from the oxide powder produced by a co-preparation method in the
composition of (GdγY0.999-γCe0.001)3Al5O12. The sample showed transparency as high as 80 % at 800 nm. A broad
emission band of Ce3+: 5d→4f transition shifted from 530 nm to 560 nm with increasing Gd content. The color
coordinates (x, y) under blue LED excitation and quantum yield (QY) were evaluated with an integrating sphere. The
color coordinates of the sample under blue LED excitation were increased with increasing thickness. By substituting
Gd3+ for Y3+, the color coordinates also shifted to lower right and became closer to the Planckian locus in the
chromaticity diagram. The red shift was explained by the energy change of 5d level of Ce3+ by the substitution of Gd3+for Y3+. With increasing excitation wavelength, the color coordinates of the γ=0 sample shifted from blue to yellow. This
result is related to the shape of excitation band of the sample. The QY of the γ=0 sample was almost excitation
wavelength independent in the range of 400 ~470 nm.
We successfully drew a low-loss Dy-doped optical fiber (0.3dB/m at 532nm) of a waterproof fluoro-aluminate glass
system and demonstrated yellow laser oscillation in the Dy3+-doped fluoride fiber pumped by a 398.8-nm GaN laser
diode. The maximum output power was 10.3 mW and the slope efficiency was 17.1% at 575 nm. Since the fluoro-aluminate-
glass system has a remarkable water resistance advantage compared to ZBLAN glass, Dy-doped fluoro-aluminate
glass fiber is expected to contribute to making a solid-state yellow fiber laser with high chemical durability
without a frequency doubling technique.
Bi-doped silica glass is a new broadband infrared fluorescence material. We drew optical fibers with the Bi doped silica
glass for the fiber core and evaluated the fluorescence spectrum. The FWHM of fluorescence spectrum is measured to be
390 nm. When this broad band spectrum is used as an OCT light source, the expected axial resolution is calculated to be
1.9μm, This is comparable to the axial resolution (Δz~1μm) by Ti:Al2O3 system. And we also examined the local
structure of Bi ion in Bi-doped silica glass. These are analyzed by ESR, EXAFS, XPS, and 27Al-NMR. According to
these results, the structural model of Bi luminescent center is proposed that Bi5+ ion with 6-fold coordination exists close
to Al3+ ion with 6-fold coordination.
We report optical amplification in a bismuth-doped silica glass and fiber at 1300 nm region. The optical gain was obtained in a bismuth-doped silica glass at five different wavelengths between 1260 and 1360 nm and the amplification bandwidth was greater than 75 nm. This new gain medium is expected to be useful for application in ultra-wide broadband optical communication. A 5.8 dB gain was observed at 1308 nm in an 8.0 cm bismuth-doped silica fiber. A launched pump power of 152 mW was obtained using an 810-nm laser diode. Simultaneous amplification of two signals from a dual-wavelength near 1300 nm region, the closest to the important telecommunications window, was also achieved. This technique can be used for wavelength division multiplexing optical amplifiers at 1300 nm, which is the range of zero-dispersion for silica fibers.
Silica glass is one of the most attractive materials for a high-average-power laser. We have developed a new laser material base don silica glass with zeolite method which is effective for uniform dispersion of rare earth ions in silica glass. High quality medium, which is bubbleless and quite low refractive index distortion, must be required for realization of laser action. As the main reason of bubbling is due to hydroxy species remained in the gelation same, we carefully choose colloidal silica particles, pH value of hydrochloric acid for hydrolysis of tetraethylorthosilicate on sol-gel process, and temperature and atmosphere control during sintering process, and then we get a bubble less transparent rare earth doped silica glass. The refractive index distortion of the sample also discussed.
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