Coherent light generators – Optical fiber laser
Patent
1992-12-16
1994-01-11
Bovernick, Rodney B.
Coherent light generators
Optical fiber laser
385142, H01S 330
Patent
active
052788504
DESCRIPTION:
BRIEF SUMMARY
This invention relates to wave-guiding structures and, more specifically, it relates to wave-guiding structures in which the lasing species is erbium, eg the ion Er.sup.3+. The lasing species is contained in a silica based glass.
During the period 1985-1990 there has been substantial interest in the use of photonic amplifiers in telecommunications optical networks. This has included both semiconductor devices in which the primary source of power is electrical as well as wholly optical devices in which a signal at one optical wavelength is amplified and the power to drive the amplification is derived from a pump optical signal at a different frequency. The wholly optical devices can be configured in the form of a fibre wave-guide which is geometrically compatible with the transmission fibre in the telecommunications network. This geometrical compatibility confers substantial operating advantages and these advantages have given substantial technical significance to research into lasing structures and especially into lasing structures which can be implemented in the form of fibre.
Wavelengths in the range 1500 nm to 1600 nm have been recognised as particularly suitable for use in optical telecommunications and, therefore, photonic amplifiers which amplify at these wavelengths are of particular interest. It has been recognised that erbium, eg the ion Er.sup.3+, will, when suitably pumped, lase at these wavelengths. Thus photonic amplifiers based on erbium as a lasing species have been extensively studied.
More recently it has been recognised that erbium contained in a host glass of silica and germania has an operational bandwidth which is undesirably narrow for some applications. For example, it may be desired to operate a frequency division multiplex which uses optical signals at both 1530 nm and 1560 nm. It has been found difficult to achieve satisfactory amplification at both of these wavelengths because of the narrow operational bandwidth of the erbium lasing species.
It has now been most surprisingly discovered that the operational bandwidth of the erbium can be increased to a satisfactory extent by the presence of only a small quantity of alumina in a host glass containing 3.degree.-30.degree./o mole of germanium in silica. The fact that the concentration of alumina is surprisingly low is of substantial operational importance because the alumina has very little effect on the other operational parameters of the wave-guide structure.
According to this invention the path region of a wave-guiding structure is wholly or partly formed of a laser composition which has 0.1 ppm molar to 5000 ppm molar of erbium contained in a host glass which consists essentially of SiO.sub.2, GeO.sub.2, Al.sub.2 O.sub.3 and additives. In this composition the amount of the additive is less than 5.degree./o by weight, preferably less tan 1.degree./o by weight. The path region contains x mole .degree./o of the GeO.sub.2 and ax mole .degree./o of the Al.sub.2 O.sub.3 wherein x=3-30 and is less than 0.35 (eg a is in the range 0.001 to 0.35), preferably a=0.01-0.25, ie the mole ration of Ge:Al is more than 2.8 and preferably Ge:Al=1:0.1-0.25.
There are two major variants of this invention. In the first variant the path region is of approximately uniform composition and it consists entirely of the lasing composition.
In the second variant of the invention the composition of the path region is designed to be non uniform. The concentration of the erbium is greater in the central path region than at the periphery thereof. Preferably the path region consists of two regions, namely an inner region and an outer region which surrounds the inner region. The inner region is preferably of approximately uniform composition and it consists entirely of the lasing composition as specified above. The outer region consists of a different glass which may have the same refractive index as the inner region. The inner region preferably constitutes not more than a quarter, eg 5.degree./o to 25.degree./o, of the cross-sectional area of the path region.
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REFERENCES:
patent: 5210631 (1993-05-01), Huber et al.
patent: 5225925 (1993-07-01), Grubb et al.
Becker et al., "Erbium-Doped Fiber Amplifier Pumped in the 950-1000 nm Region", IEEE Photonics Lett., No. 1, Jan. 1990.
Patent Abstracts of Japan, vol. 11, No. 328, Oct. 27, 1987, and JP-A-62 111208 (Nippon Telegraph & Telephone Corp.) May 22, 1987.
Optical Fiber Communication Conference, Feb. 9, 1989, Houston, Texas, Brocko: "Rare-Earth-Doped Optical Fibers by the Outside Vapor Deposition Process", p. 20.
IEEE Photonics Technology Letters, vol. 2, No. 1, Jan. 1990, New York, pp. 18-20; Chen et al: "A Widely Tunable Erbium-Doped Fiber Laser Pumped at 532 nm".
IEEE Photonics Technology Letters, vol. 2, No. 1, Jan. 1990, New York pp. 35-37; Becker et al: "Erbium-Doped Fiber Amplifier Pumped in the 950-1000 NM Region."
14th European Conference on Optical Communication, Sep. 15, 1988, Brighton, UK, pp. 433-436; Poole: "Fabrication of Al.sub.2 O.sub.3 Co-Doped Optical Fibres by a Solution-Doping Technique".
EPO Search Report.
Ainslie Benjamin J.
Craig-Ryan Susan P.
Barns Stephen W.
Bovernick Rodney B.
British Telecommunications
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