Praseodymium doped waveguide lasers

Details Praseodymium doped waveguide lasers Praseodymium doped waveguide lasers

1994-05-09

1998-03-10

Scott, Jr., Leon

Coherent light generators

Optical fiber laser

372 40, H01S 330

Patent

active

057270074

DESCRIPTION:

BRIEF SUMMARY
This invention relates to lasers and particularly to lasers for producing visible radiation.
There is currently a great deal of interest in the development of simple and compact sources of coherent visible radiation. Two promising techniques for the development of such sources are second harmonic the energy from two or more photons from a pump source are absorbed by a single ion which subsequently emits a single higher energy photon. advantage of simplicity, in that no stabilised resonant cavity is needed, but also the disadvantage that in most cases the efficiency of upconversion is found to be strongly temperature dependent so that cooling to liquid nitrogen (or lower) temperatures is required. However, Allain et fluorozirconate fibre laser operating in the green at room temperature with red krypton laser pumping.
Efforts are being made to develop a blue laser for which a variety of uses are envisaged, including use in a compact disc player where the correspondingly small spot size could provide an increase in storage capacity. demonstrated the great benefit of using the fibre geometry where the small core diameter allowed the high intensities required for efficient upconversion to be maintained over a long interaction length. Allain et al fibre lasers operating in the orange and red when pumped with an argon laser operating at 476.5 nm.
The present invention is based on our discovery that under certain conditions we have achieved lasing at room temperature in a Pr.sup.3+ -doped fluorozirconate fibre pumped in the infrared at 1.01 .mu.m and 835 nm, the lasing taking place in the blue (491 nm), green (520 nm), orange (605 nm) and red (635 nm and 715 nm).
One great attraction of pumping at infrared wavelengths is that high power laser diodes are available and so it may be possible to construct efficient, high power, all-solid-state blue green and red sources based on upconversion in Pr.sup.3+ -doped fibres. Such sources may be expected to find applications in areas such as optical data storage, undersea communications and projection televisions.
According to one aspect of the invention a laser comprises a length of Pr.sup.3+ -doped optical waveguide, and means for exciting the Pr.sup.3+ ions to an energy level in the band (.sup.3 P.sub.2, .sup.1 I.sub.6, .sup.3 P.sub.1, .sup.3 P.sub.0), in which the Pr.sup.3+ concentration is in the range substantially 50 ppm to substantially 10,000 ppm (by weight).
The waveguide is preferably in the form of a fibre.
The Pr.sup.3+ concentration is preferably in the range substantially 200 ppm to substantially 2,000 ppm (by weight).
The optical fibre is preferably a fluorozirconate fibre doped at the foregoing concentrations with Pr.sup.3+ ions.
The fibre preferably comprises a doped core clad with a further glass.
The numerical aperture of the clad fibre is preferably in the range substantially 0.1 to substantially 0.5, and is typically 0.15.
The core diameter of the fibre is preferably in the range substantially 1 .mu.m to 5 .mu.m.
The excitation means is preferably arranged to excite the Pr.sup.3+ ions from the .sup.3 H.sub.4 level, and this is preferably achieved by upconversion by way of the .sup.1 G.sub.4 level, but excitation may be achieved by transfer of energy from a co-dopant, preferably another rare earth ion.
Excitation by way of the .sup.1 G.sub.4 level is preferred because the energy gap from .sup.3 H.sub.4 to .sup.1 G.sub.4 corresponds to 1.01 .mu.m and that from the .sup.1 G.sub.4 to the .sup.1 I.sub.6, .sup.3 P.sub.1 common level in said band is 835 nm, both in the infrared range for which powerful infrared sources are available. The excitation means preferably comprises first excitation means for exciting the Pr.sup.3+ ions from .sup.3 H.sub.4 to .sup.1 G.sub.4, and second excitation means for exciting the ions from .sup.1 G.sub.4 to the .sup.1 I.sub.6, .sup.3 P.sub.1, .sup.3 P.sub.0, .sup.3 P.sub.2 levels.
It may, however, at relatively high concentrations of Pr.sup.3+ ions be possible to populate the .sup.1 G.sub.4 level by an avalanche process (photon

REFERENCES:
patent: 5185847 (1993-02-01), Ferrier
patent: 5309452 (1994-05-01), Ohishi

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