Maitreyee Saha

High power laser fiber fabricated through vapor phase doping of Ytterbium

We present the characteristics of an ytterbium-doped alumino-silicate fiber, fabricated through vapor phase doping of aluminum and ytterbium in the core, along with silica and in conjunction with the modified chemical vapor deposition process. The vapor phase doping of rare-earths provides the opportunity to fabricate large core active fibers with a uniform distribution of dopants. The fibers fabricated exhibited low OH− content, negligible center dip and good optical properties. Lasing performance was tested up to output power of 105 W, with a slope efficiency of 77% with respect to launched pump power. The linear variation of the laser power with a pump shows its potentiality for further power scaling.

Vapor Phase Doping of Rare-Earth in Optical Fibers for High Power Laser

This letter describes an optimized vapor phase doping technique using modified chemical vapor deposition system to fabricate rare-earth doped optical fibers for a high power laser. The process comprises deposition of aluminium oxide and ytterbium oxide in vapor phase simultaneously in combination with silica during formation of the core layer. The process parameters have been judiciously controlled to deliver aluminium chloride and rare-earth-chelate compounds to the reaction zone without decomposition and/or condensation of the precursor materials prior to the reaction zone. The standardization of the process parameters resulted in a good repeatability with a very low variation of dopant concentrations throughout the length of the preform. The fabricated fibers exhibit good optical properties with lasing efficiency of 76% at 1.06 μm.

An Optimized Vapor Phase Doping Process to Fabricate Large Core Yb-Doped Fibers

The paper demonstrates a standardized process of vapor phase doping to fabricate large core Yb-doped preforms with longer useful length in reproducible manner. The optimization of the process led to successful achievement of Yb-doped core thickness of 4.5 mm (in 14.8 mm of preform diameter) by depositing up to 30 number of core layers with controlled amount of generated precursor vapors. The influence of the process parameters was studied rigorously to enhance the useful preform length up to 380 mm. A combination of Yb and Al in different proportions was doped into the core with uniform dopant concentration along the length by adjusting few process parameters efficiently. The Al2O3 concentration up to the level of 17.8 mol% has been achieved successfully which resulted in NA of 0.31. This is the highest ever doping of Al in passive fibers by any modified chemical vapor deposition process. The Yb2O3 content in the active fibers is as high as 0.47 mol%.

Large core Yb-doped optical fiber through vapor phase doping technique

Rare earth (RE) doped optical fibers have shown tremendous progress for producing high power fiber lasers for industrial, medical and strategic applications. However, fabrication of large core, high Yb-doped fiber is still a challenge through conventional process due to poor repeatability and limitation regarding core size. This paper presents successful fabrication of Yb-doped fibers through vapor phase doping technique. Preform fabrication was carried out using a specially constructed MCVD system containing High Temperature Vapor Delivery Unit with sublimators for Al and Yb precursors. The novelty of the present work lies in deposition of Al2O3 and Yb2O3 in vapor phase simultaneously with silica during formation of sintered core layer which result in uniform dopants distribution in the preform. The fibers exhibited lasing efficiency of 76% with low ‘photodarkening effect’.

Yb-Doped Pedestal Silica Fiber Through Vapor Phase Doping for Pulsed Laser Applications

This letter describes successful fabrication and detail characterization of ytterbium (Yb)-doped pedestal aluminosilicate fibers through vapor phase doping technique using modified chemical vapor deposition system (MCVD). Fabricated preforms have uniform step-index profiles devoid of any profile ripples, central dip, and/or core-clad interface defects, which are very common to the preforms made by a solution doping method. Fibers with a pedestal design exhibit good optical properties, low photodarkening-induced losses, high SNR values, and higher efficiencies making them suitable for high-power pulsed laser applications as compared with normal Yb-doped fibers. One of the pedestal fibers has demonstrated the output energy of 186 μJ with the 1.86-W average power. The pulse has a width of 100 ns at a 10-kHz repetition rate, which provides a peak power of 1.86 kW.

Broadband generation by multiple four-wave mixing process due to ASE Q-switching in high-power double-clad ytterbium-doped fiber amplifier

Broadband output from 1060nm to 1700nm and cascaded four-wave mixing generated red light pulsing is observed in a fiber amplifier set up consisting of a 5.5m double clad, double D shaped Ytterbium doped fiber, a single clad passive fiber for excess pump absorption and a splitter, both with and without a CW seed. Self-pulsing occurs from ASE due to passive Q-switching by saturable absorption effect of the active fiber and also depends on splice loss. The pulses generate broadband output by multiple four-wave mixing process with maximum broadening efficiency near 1300nm which is the zero dispersion wavelength for silica fiber. Pulses traveling both in forward and backward direction have enough peak power and energy to damage splice points and fiber components. When seeded the self-pulsing and broadband generation is often suppressed but again generate at increased pump powers.

Yb-doped Pedestal Aluminosilicate Fiber through Vapor Phase Doping for High Power Laser Applications

Presenting fabrication process and characteristics of large core Yb-doped optical fibers with pedestal design using vapor phase doping technique. Preforms have uniform step-index profiles. Fibers exhibit good optical properties, suitable for high power laser applications.

Spatial, Spectral and Temporal Study of Self-pulsing in CW Yb-Fiber Laser due to Saturable Absorption Effect

Self-pulsing in a CW Yb-fiber laser due to saturable absorption (SA) is explored in spatial, spectral and temporal domain. Shorter active fiber length removed this effect at the cost of increased unabsorbed excess pump power.

H 2 -blocking in Yb-doped fiber through pump excitation to enhance photodarkening resistivity

The enhancement of photodarkening resistivity as high as 95% is achieved through H₂-treatment of Yb-doped fiber, irrespective of Yb-concentration. H₂-blocking employing the pump excitation in the fiber indicates negligible photodarkening even after post-diffusion of interstitial-H₂.