19-μm operation of a Tm:lead germanate glass waveguide laser

Abstract

We report what we believe to be the first planar-technology waveguide laser in the 2-,um region. Laser operation of the 'H4 to 3 H 6 transition of Tm 3 + ions in a lead germanate glass host has been observed in an ion-implanted planar waveguide.The development of coherent light sources in the wavelength region around 2 ,um is of interest because of the presence of absorption bands of several important molecules. Lead germanate was shown to be a particularly suitable glass host for operation of the 2-Am Tm 3 , 3 H 4 to 3 H 6 transition in fiber samples" 2 (see Fig. 1). The maximum phonon energy is greater than in fluoride glasses, leading to efficient population of the upper laser level through nonradiative decay out of the 3 F 4 pump level. The maximum phonon energy is, however, less than in silicate glasses, leading to an increase in the lifetime of the upper laser level 3 H 4 . This favorable combination of decay rates has permitted us to demonstrate, using a fiber made of modified lead germanate (55GeO 2 -2OPbO-lOBaO-lOZnO-5K 2 0), thresholds for 790-nm pumping that are easily within reach of single-stripe diode lasers. ' Waveguides based on planar technology offer a number of potential advantages over fibers. For example, there is the possibility of diode-bar side pumping for high-power operation. 3 In addition, the active region is readily accessible for fabrication of feedback gratings, possibly through the photorefractive effect. Because high doping levels are possible with this glass, compact single-longitudinal-mode devices may be possible.Recently it was shown that waveguides could be fabricated in this modified lead germanate glass by use of He' ion implantation 4 and that, in addition, the losses of these guides were significantly lower than the -1-dB cm-' value that has been typical for ion implantation. 5 In fact, losses of 0.15 dB cm-' were obtained 4 (compared with 0.02 dB cm'I for the fiber), with index profiles suitable for guiding 2-/ttm radiation. The effect of the propagation loss can be reduced further by the use of shorter cavity lengths and correspondingly higher doping levels. The use of Tm 3 + is also attractive because there exists a cross-relaxation process that offers the possibility of 200% pumping quantum efficiency for highly doped samples. To assess the prospects for active waveguide devices in lead germanate glass, we have made an initial investigation of the 2-Am Tm 3 + laser in a planar waveguide.The waveguide used in these experiments was a planar guide (i.e., with guiding in one transverse dimension) created by implantation of the polished surface of the Tm-doped glass with 2.9-MeV 3 He' ions at liquid-nitrogen temperature at a dose of 4 X 1016 ions/cm 2 . This was followed by annealing at 200'C, which was found to be the annealing temperature at which propagation losses were minimized while the index increase in the guide region remained relatively large. 4 The dark mode pattern of the resultant waveguide was investigated, and from this the refractive-index profile shown ...

Optical properties of Tm3+ ions in alkali germanate glass

“…The peak emission cross section measured in this study was in fair agreement with previous studies [9,11,13]. In general, cross section measurements are only accurate to approximately 20%.…”

“…The peak cross section occurs around 1.865 μm with a value of 5.65x10 -21 cm 2 . Measurements in lead germanate glass have reported this peak emission cross section as 4.2 x10 -21 cm 2 by Sheperd [9] and as 7.7 x10 -21 cm 2 by Balda [13]. A study by Zou [11] reports it as 6.8 x10 -21 cm 2 in alkali germanate glass.…”

“…To combat the deleterious effects of nonradiative decay, Tm:germanate glass is investigated. There are very few studies of the optical properties of Tm in germanate glass [3][4][5][6][7][8][9][10][11][12][13], and those in recent years concentrate on lead germanates [8-10, 12,13]. This study concentrates on alkali germinates.…”

Infrared-to-visible upconversion of Er^3+ ions in GeO_2–PbO–Nb_2O_5 glasses

“…5,6 Among oxide glasses, lead-germanate-based glasses combine high mechanical strength, high chemical durability, and temperature stability with good transmission in the IR region 7 up to 5.5 m, which make them promising materials for technological applications such as new lasing materials, upconverting phosphors, and optical waveguides. [8][9][10][11][12] These glasses have smaller maximum vibrational frequencies than those shown by silicate, phosphate, and borate glasses. 7,8 The reduced phonon energy increases the quantum efficiency of luminescence from excited states of rare-earth ions and the upconversion efficiency.…”

A diode-pumped channel waveguide laser fabricated in Nd:phosphate glass

“…The laser spectrum, centered about the emission peak of 1053 nm, was multimode and randomly polarized. Solid-state waveguide lasers [1][2][3][4][5] offer several attractive features that may make high efficiency and effective thermal management possible. The waveguide region is typically several microns thick, leading to high intensities of the pump light over distances much longer than the Rayleigh range.…”