1,721,130 research outputs found
Novel optical fibers for high power lasers
No full textHigh power fiber lasers have several applications thanks to their outstanding features such as good beam quality, all fiberized compact device size, robustness, wavelength tuning, high wall-plug efficiency, and low cost. Due to these features high power fiber lasers are replacing other solid-state lasers for several applications. Fiber lasers are being used commercially for several applications such as surgery, material processing (cutting, drilling, polishing etc.), oil and gas sensing, pumping several other lasers, and space communication etc. However, nonlinear effects restrict the output power level of fiber lasers. Although reducing power density by using large core diameter fibers can increase the threshold of non-linear effects, however large core diameter leads to multimode behavior and is prone to bend-induced effective area reduction. Several novel large mode area fibers have been proposed to scale the output power level. However, the advantages of all-fiberized device and low cost disappear as most of these fibers involve complex fabrication and cannot be spliced to optical components such as conventional pump fibers. This thesis deals with novel large mode area fibers which are suitable for mass scale production and can offer low cost production compared to other competitive fiber designs thanks to their simple design. These novel fibers are all-solid and can be easily spliced to other fibers, thus can lead to an all-fiberized device. Moreover, some of the novel fibers proposed in this thesis offer the delocalization of powers of the higher order modes outside the core. This delocalization of the higher order modes can be useful to ensure an effective single mode operation in a double clad configuration. The proposed novel fibers offer better or competitive mode area scaling performance compared to other competitive fibers.In this thesis, firstly conventional step-index fibers have been exploited for mode area scaling by reducing the refractive index of the actively doped core with respect to the cladding. Prior to this thesis, the lowest reported NA of a Yb-Al doped fiber was 0.048 corresponding to 0.0008 refractive index of core with respect to cladding. In this thesis, optimized solution doping process leads to a NA of 0.038 for a Yb and Al doped core corresponding to 0.0005 refractive index of core with respect to cladding. This reduction in NA of core leads to an effective area increase from ~450µm2 to ~700µm2 at 32cm bend diameter ensuring effective single mode operation. This is the lowest NA ever reported using cost-effective solution doping process to the best of author’s knowledge, which is widely used in manufacturing of rare-earth doped fiber. Further, in a 4%-4% laser configuration, a 35µm core diameter 0.038 NA fiber shows high laser efficiency (~81%) with good M2 (~1.1) value of output beam at 1040nm. Thesis also reports a novel fiber design known as single trench fiber, where a passive Ge-doped ring has been added around the core. This ring known as resonant ring facilitates the suppression of the higher order modes thanks to resonant coupling between modes of core and ring. The combination of ultra-low NA (~0.038) and a surrounding ring can lead to an effective single mode operation of fiber having a core diameter as large as of 50µm offering an effective area of ~1,500µm2 at ~40cm bend diameter. A 40µm core diameter single trench fiber has been successfully fabricated in house and shows robust effective single mode behavior. Further, a 30µm single trench fiber has been tested in a master oscillator power amplifier configuration delivering ~23.5ps pulses at 13.5MHz repetition rate carrying up to ~3.8µJ pulse energy corresponding to >160kW peak power and ~52.3W of average power, while maintaining ~76% slope efficiency. Numerical Performance of STF has also been reported at other wavelengths such as 1550nm and 2000nm. A detailed comparative analysis has been performed with other competitive fiber designs showing the advantages of single trench fiber over other fiber designs. Further, another fiber design known as multi trench fiber has also been proposed. Multi trench fiber can scale effective area as large as of 12,000µm2 in a rod-type configuration. Multi-trench fibers offer several advantages such as easy cleaving and splicing thanks to the all solid structure; however refractive index of active core has to be same as of passive cladding. Nevertheless, this fiber has shown a strong potential for applications in ultrafast rod-type fiber lasers. A 90µm core diameter passive fiber has been fabricated in house using rod-in-tube technique in conjunction with modified chemical vapour process.Experiments ensure an effective single mode operation. Furthermore, this fiber also shows the potential to be used for beam delivery applications with a small core diameter thanks to effective single mode operation over a wide range of bend radii. MTFs of 30µm and 20µm core diameter have been successfully fabricated and both ensure robust single mode operation over a wide range of bend radii at 1060nm and 632nm respectively. Numerical simulations show the possibility of a 10µm fiber to be effectively single moded at a wavelength of 300nm.<br/
Dataset for Large Mode Area Single Trench Fiber for 2µm Operation
No full textPerformance of single trench fibers has been investigated using Finite Element Method at 2µm wavelength. Numerical investigations show that an effective single mode operation for large effective area between 3,000-4,000µm2 and 2,000-3,000µm2 can be achieved at ~40cm and ~25cm bend radius respectively by exploiting high delocalization of the higher order modes. Achievement of a large effective-area can be very useful to address non-linear effects. Moreover, single trench fiber offers certain advantages such as low-cost fabrication and easy post-processing (such as cleaving and splicing) thanks to the all-solid fiber design.</span
Large mode area single trench fiber for 2 µm operation
No full textPerformance of single trench fibers has been investigated using finite-element method at 2 µm wavelength. Numerical investigations show that an effective singlemode operation for large effective area between 3000-4000 µm2 and 2000-3000 µm2 can be achieved at ~40 and ~25 cm bend radius, respectively, by exploiting high delocalization of the higher order modes. Achievement of a large effective-area can be very useful to address nonlinear effects. Moreover, single trench fiber offers certain advantages such as low-cost fabrication and easy post-processing (such as cleaving and splicing) thanks to the all-solid fiber design
Mode area scaling with multi-trench rod-type fibers
No full textWe propose a novel all-solid rod-type fiber structure that presents a cylindrical symmetry and low refractive-index contrasts. Effectively single-mode propagation for the fundamental mode is ensured thanks to resonant couplings between Higher Order Modes (HOMs) and cladding modes. Numerical simulations demonstrate the possibility of achieving a fundamental mode effective area as large as 5000µm2 at a wavelength of 1.06µm in fibers ensuring a high leakage loss ratio (>100) between the HOMs and the fundamental mode while keeping the fundamental mode leakage losses at a level lower than 0.2dB/m. Further scaling to an effective area of 12,200µm2 at 1.06µm in an effectively singlemode fiber is also presented by exploiting the power delocalization of several HOMs on top of the high-leakage loss filtering
Bending performance of large mode area multi-trench fibers
No full textBending performance of the Multi-trench Fibers (MTFs) has been investigated using the Finite Element Method. Numerical investigations show that MTFs can provide low-loss effective single mode operation under bent configuration, thanks to the resonant coupling of the Higher order Modes (HOMs). Large ratio between the HOMs and the Fundamental Mode (FM) losses can be ensured, although the ratio drops with increasing Effective Area (Aeff) of the FM. MTFs provide better losses ratio between the HOMs and the FM in comparison with other fibers like step-index, W-type, and parabolic fibers.<br/
Large mode area multi trench fiber for UV and visible transmission
No full textPlots of the figures in paper</span
Robust single-mode all-solid multi-trench fiber with large effective mode area
No full textWe experimentally demonstrate all-solid 30 and 90 µm core diameter multi-trench fibers. Measurements ensure an effective single-mode operation over a wide range of bend radius in the case of 30 µm core fiber, making it suitable for applications like beam delivery and compact fiber lasers. On the other hand, a 90 µm core fiber ensures an effective single-mode operation and shows good potential for rod-type fiber laser applications. Both fibers were fabricated by the conventional modified chemical vapor deposition process in conjunction with the rod-in-tube technique, hence making them suitable for mass production
Breaking the stringent trade-off between mode area and NA for efficient high-power fiber lasers around 2 μm
No full textWe propose a novel approach of exploiting the LP02 mode in ultra-high NA confined-doped M-type fibers to ensure effective single-mode operation, thereby breaking the trade-off between mode-area scaling and ultra-high NA.This novel approach opens the door to highly rare-earth doped fibers suitable for power scaling applications. Therefore enabling, simultaneously scaling of power and slope efficiency of fiber lasers
Large mode area multi-trench fiber for UV and visible transmission
No full textWe experimentally demonstrate all-solid 10 and 20 µm core diameter multi-trench fibers for UV and visible wavelengths. Measurements ensure an effective single-mode operation over a wide range of bend radii, which is suitable for applications such as beam delivery. Both fibers were fabricated by the conventional modified chemical vapor deposition process, which is suitable for mass production. Moreover, all-solid fiber design ensures easy cleaving and splicing
Specialty fibers for high power fiber lasers
No full textThis paper reviews our recent work on novel large-mode area fibers for high power lasers and amplifiers. An ultra-low-NA fiber and single-trench fiber have been proposed for mode area scaling of the fundamental mode. In case of single trench fiber design, resonant coupling of the higher order modes has been exploited to achieve effective single mode operation in fiber with large effective mode area. Our proposed fiber designs are easy to fabricate using conventional low-loss fiber fabrication techniques, and moreover, being all solid structure, they ensure easy cleaving and splicing. A monolithic and compact high power fiber laser/amplifier device with a good output beam quality can be achieved using Single-trench fiber design
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