Effect of the incident light beam conditions, such as the beam profile, the beam size, and the incident angle on the beam propagation and the firing characteristics of the radial-firing optical fiber tip comprised of conically shaped air pocket was investigated by the simulation using the ray-tracing method. Regardless of the different Gaussian profiles of the incident beam, no significant difference in the maximum firing angle but a little increase in the firing power was found with the increase of the axial distance of the Gaussian profile. With the increase of the incident beam size, no significant difference in the maximum firing angle was found but the relative firing power decreased and the extent of the power decrease depended on the numerical aperture (NA) of the fiber. On the other hand, the incident beam angle (BA) dependence of the firing power was significant, decreased to 65.9% and 31.9% for the RFF tip of NA 0.12 and NA 0.22, respectively, with the increase of the incident BA from 0 deg to 12 deg but the maximum firing angles did not show much decrease, smaller than 5 deg. The present modified simulation considering the incident light beam size and angle clearly showed the very close power distribution of the firing beam with respect to the firing angle obtained by the experimental results.
In this study, highly Dy3+-doped germano-borate glasses for different dopant concentrations ranging from 20 to 30 mol% were fabricated and their physical, optical, and MO properties were investigated. The characteristic thermal parameters disclosed good thermal stability of <100 °C against crystallization in the studied glasses. In addition, the glasses showed a high optical transmission of ~ 85% in the NIR region of 1550 nm. A very large Verdet constant of approximately -5.36 rad/(T·m) at 1550 nm was obtained in the glass containing 30 mol% Dy2O3. Therefore, this glass might be a promising MO material for applications in the NIR region.
We experimentally demonstrated torsion sensing characteristics of a highly-birefringent asymmetric two-core photonic crystal fiber (HB-ATCPCF) in the Sagnac loop configuration. Two cores in the HB-ATCPCF exhibit distinct birefringence properties and light launched into them propagate with negligible coupling. The transmission interference spectrum of the device shows six frequency peaks in the spatial domain, which corresponds to the two Sagnac and four Mach-Zehnder interference spectra characterized by the four-beam interference model. Torsion response of the device was investigated by measuring the shift of the peak wavelength and the fringe visibility of the fiber interferences using fast Fourier transform-based spectrum-demodulation method.
We propose and demonstrate a highly sensitive micro-fluidic temperature sensor based on a two-core photonic crystal fiber (TCPCF). TCPCF has two cores of small asymmetry in sizes that serves as two arms in the inline Mach-Zehnder interferometer (MZI). Using manual gluing and subsequent infiltration technique, the cladding air holes near one core are selectively filled with polymer of high thermo-optic coefficient, which makes its core-mode effective index sensitive to temperature variation and induces large thermo-optic mismatch between the two cores. A high sensitivity of 1.595 nm/ oC is achieved in our experiment, which is almost 200 times improved from that of the sensor device before polymer infiltration process.
We experimentally demonstrate a novel all-fiber Sagnac loop hybrid interferometer (SLHI) based on a highlybirefringent photonic crystal fiber with two asymmetric cores. Two cores exhibit unique birefringence properties and the light launched into them propagates with negligible coupling. Fast Fourier transform analysis of the transmission spectrum shows six frequency peaks in the spatial domain due to multiple interferences comprising the intra-core and inter-core mode interferences characterized by the four-beam interference model. The device response is investigated under the application of torsion, strain and temperature by measuring the phase-shift responses of three fiber interferences in the SLHI. The device application in simultaneous multi-parameter measurement is also discussed.
Refractive index variation in rare-earth doped specialty fiber can be possible through resonantly enhanced optical nonlinearity with the assistance of an optical pumping. The quantity of the variation under low-power optical pumping is enough to induce phase shift of 2π. By using this nonlinear effect in the specialty fiber, optical imaging system can perform phase shift-based optical imaging without mechanically controlled phase stepping. The pump-induced refractive index from the specialty fiber in reference arm of interferometer can produce optical delay depending on applied optical pumping power. At low optical power under few hundred mW, optical delay corresponding to 2π can be yielded in the reference arm efficiently. Contrast to the conventional mechanical phase stepping method, optically actuated phase stepping with the specialty optical fiber can avoid drawback of mechanical hysteresis and requirement of high voltage controllable electronics. The feasibility of the proposed method on optical imaging is suggested with demonstrating full range imaging in optical coherence tomography. Extended imaging range under optical phase stepping was successfully presented. The proposed method could be applied for detailed control of phase shift-based interferometry.
We have recently reported azobenzene-coated fiber Bragg grating (FBG) for ultraviolet (UV) sensor. In this paper, we introduce an etched FBG for the strain sensitivity enhancement of the UV fiber grating sensors, which is inversely proportional to the fiber diameter. The sensitivity of the etched FBG with a diameter of ~60 μm is improved to be greater than twice of the original 125 μm fiber. In addition, the sensor system designed on the basis of the round-trip configuration can be used for many practical sensing applications in the field.
KEYWORDS: Fiber lasers, Optical pumping, High power lasers, Fusion splicing, Reliability, Laser systems engineering, Structured optical fibers, Photonics, High power fiber lasers, Laser applications
Recently, the high power fiber laser has attracted much attention and the laser power combiner is one of the key components for power scaling in the high power laser system. Up to now, several methods have been exploited to develop the combiner and among them the tapered fusion bundling method becomes one of the most popular and reliable technology. In the conventional tapered fusion bundling method, the input fibers were bundled with the honeycomb configuration then fused tapered and spliced to the output fiber. In the method, however, the fiber ports configuration was constrained to certain values such as 3×1, 7×1, 19×1, and 35×1 to satisfy the compactness and reliability in the bundling procedure. In this study, we suggest a novel double bundling method to make combiners with the large flexibility in the fiber port configuration. In making the (14-18)×1 combiners, seven input fibers in the honeycomb stacking configuration was fused bundled and a single layer of secondary 7-11 fibers were stacked outside of the bundle and subsequently tapered and spliced to a output fiber. As a result, (14-18)×1 laser power combiners were made using 105/125 μm input fibers (0.15 NA) and a 200/220 μm output fiber (0.46 NA). In the bundling procedures a LPG torch was used and process parameters such as the gas flow and the tapering length/speed/frequency were optimized. The power transmission efficiency of the combiner was larger than 93% in all ports at the handling power of 100 W.
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