Coherent light generators – Optical fiber laser
Patent
1996-02-20
1998-05-19
Healy, Brian
Coherent light generators
Optical fiber laser
372 39, 372 40, 372 68, 359341, 359343, 385123, 385141, H01S 330, H01S 300, G02B 600
Patent
active
057545707
DESCRIPTION:
BRIEF SUMMARY
The invention relates to optical materials and methods and apparatus involving them. More specifically, the invention is concerned with optical materials capable of emitting visible and/or infrared light.
The process of resonant energy transfer between two atoms or ions which may be of a different species is known. A prerequisite for this process to occur is the existence of closely matched energy levels within the interacting atoms or ions.
The process of upconversion involves the absorption of two or more low energy infrared photons by an optically active atom or ion with the subsequent emission of a single high energy visible photon The upconversion process is particularly prevalent in rare-earth metal ions such as Er.sup.3+, Ho.sup.3+, Nd.sup.3+, Pr.sup.3+, Sm.sup.3+ and Tm.sup.3+, whose energy levels exhibit equally spaced step-like structures.
The upconversion process has been employed as an excitation method in rare-earth doped glass in the form of fibre or crystal lasers. In contrast, the resonant energy transfer process has been used in a completely different situation, such as the gaseous HeNe laser. In the HeNe laser, the He atoms are first electronically excited in a glow discharge. Subsequently, a resonant energy transfer occurs between the exited He atoms and the Ne atoms in dose proximity. As a result, the Ne atoms end up in an excited state suitable for the ensuing lasing.
Continuous-wave room temperature upconversion lasing has been demonstrated in a Pr.sup.3+ -doped fluoride fibre at blue, green and red wavelengths using infrared excitation sources. Visible lasing has also been achieved with several other rare-earth dopants such as Er.sup.3+, Ho.sup.3+, Nd.sup.3+ and Tm.sup.3+, embedded mainly in fluoride glass fibres and fluoride crystals.
However, the excitation methods employed in such lasers are very awkward, for example, two different excitation wavelengths, 835 and 1010 nm are required in the Pr.sup.3+ -doped fluoride fibre laser, and in the case of the Tm.sup.3+ -doped fluoride fibre blue laser, a very uncommon 1120 nm excitation source is required. On the other hand, crystalline upconversion lasers are typically operated at cryogenic temperatures.
The ion pair Nd.sup.3+ --Pr.sup.3+ has been used previously in a phosphate glass host for the enhancement of 1.3 .mu.m optical fibre amplifier performance. However, in that particular case, upconversion will be detrimental to the operation of 1.3 .mu.m amplification or lasing.
A requirement accordingly exists to at least minimise the awkward excitation requirements in existing upconversion lasers by using only a see wavelength excitation. This will then lead to a compact and low cost design for a visible light source, especially in the blue wavelength region, and operating at room temperature.
We have now found that this requirement can be achieved by combining the two processes of resonant energy transfer and upconversion.
According to one aspect of the present invention there is provided an optical material capable of emitting visible and/or infrared light which comprises a host matrix doped with an optical atom pair or ion pair, each pair comprising a sensitiser and an activator, said sensitiser being capable of absorbing optical excitation energy of a single wavelength and transferring this optical excitation energy to said activator so as to cause the emission of visible and/or infrared light when the activator relaxes back into any of its lower energy states.
The host matrix may be selected from any matrix capable of being doped with the optically active atom or ion pair, provided that the upconversion and resonant energy transfer process between the sensitiser and activator can occur. Preferably, the host matrix is a glass. The glass may be a fluoride-based glass such as heavy-metal fluoride or fluorozirconate glass; an oxide-based glass such as phosphate or silica glass; or a chalcogenide glass. Preferably, the host matrix is a fluorozirconate glass. A particularly preferred fluorozirconate glass is ZBLANP due to its high stabili
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Healy Brian
Telstra Corporation Limited
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