Coherent light generators – Optical fiber laser
Patent
1988-07-21
1990-03-20
Gonzalez, Frank
Coherent light generators
Optical fiber laser
372 71, 372 93, 372108, 350 9615, H01S 330
Patent
active
049107372
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concernes bistable optical devices, more particularly those useful for optical communications systems and the like.
Devices are sought which can be interfaced with and incorporated in optical fibre systems. These then would have potential applications to switching, memory and regenerative amplifier components and systems.
BACKGROUND ART
Optical bistability (the existence of two distinct, stable output states corresponding to a single input state) has been demonstrated using several techniques e.g. nonlinear dispersion, self-focussing and saturable absorption ("Optical Bistability", C. M. Bowden, M. Ciftan and H. R. Robl, Plenum 1981). To obtain optical bistability, the output of the optical device must be a nonlinear function of some input parameter and sufficient degree of feedback should be incorporated. High light intensities are required in order to achieve the necessary nonlinear behaviour.
Nonlinear absorption in a saturable absorber has been demonstrated as a technique for achieving bistable behaviour in e.g. semiconductor-type lasers--see for example "Bistablility and pulsations in semiconductor lasers with inhomogeneous current injection", C. Harder et al, IEEE J. Quantum Electron, 1982, QE-18 pp
DISCLOSURE OF THE INVENTION
The present invention is intended to provide a bistable optical device that is fully compatible with conventional optical fibres and integrated optics devices, and which can be readily jointed to these components.
In accordance with the invention thus there is provided a bistable optical device comprising:
an optical cavity laser having input and output reflecting means, one at each end thereof; and,
a pumping source, optically coupled to the input end of the cavity laser, to inject pumping radiation therein; wherein,
the cavity includes a length of doped single-mode optical fibre, the dopant thus being of rare-earth or transition metal ions which ions exhibit a three-level lasing transition; and,
the output coupling provided by the output reflecting means and the length of this fibre, both being provided such that there is a region of saturable absorption at the output end of the fibre.
A technique has now been developed for incorporating significant quanties of rare-earth and other dopants into the core or cladding of an optical fibre (S. B. Poole, D. N. Payne and M. E. Fermann, Electronics Letters, 21, pp. 737-738, 1985). Using this fibre, it has been possible to fabricate a new type of laser, the single-mode fibre laser (R. J. Mears, L. Reekie, S. B. Poole and D. N. Payne, Electronics Letters, 21, pp. 738-740, 1985). These lasers have a number of advantages over their bulk glass counterparts, namely no auxiliary cooling requirement, ultra-low lasing threshold and the ability to operate in a CW mode. Notably, it is possible to achieve CW operation with 3-level lasers, which have traditionally been operated only in a pulsed mode due to the required cooling and threshold requirements.
In order to obtain lasing in a 3-level laser, it is necessary to bleach (i.e. saturate) the absorption of the doped glass at the lasing wavelength. By virtue of the small core radius of single-mode optical fibre (.perspectiveto.5 .mu.m), saturation is easily achieved for pump powers of only a few mW at any point in the fibre. By appropriate choice of fibre length and output coupling, it is possible to obtain a region of saturable absorption in a 3-level single-mode fibre laser.
The device aforesaid is advantageous in that it is fully compatible with conventional optical fibres and integrated optics devices and can be readily jointed to these components. Such a device can also be used in conjunction with other fibre optic and integrated optic devices such as, for example, directional coupler, polarisers, exposed field devices and modulators.
Whilst it is convenient to employ optical mirrors as the reflecting means, end face polishing or distributed feedback reflection grating implimentation are not precluded from the general scope of this invention. Cou
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Daino et al; "New All-Optical . . . Birefringent Fibers"; Optics Letters, vol. 11, No. 1; 01/1986; pp. 42-44.
Jauncey et al; "Efficient Diode-Pumped . . . Fibre Laser"; Electronics Letters, vol. 22, No. 4; 01/13/1986; pp. 198-199.
Mears et al; "Rare-Earth-Doped Fiber Lasers"; Technical Digest of the Optical Fiber Communication Conference, 24-26; 02/1986; Atlanta, U.S.A., IEEE; pp. 62-64; Tul 15.
IEEE J. Quantum Electron, 1982, QE-18 pp. 1351-1361, C. Harder et al., "Bistability and Pulsations in Semiconductor Lasers with Inhomogenous Current Injection".
Electronics Letters, vol. 21, No. 17, pp. 737-738, 1985, Poole, S. B. et al., "Fabrication of Low Loss Optical-Fibres Containing Rare Earth Ions".
Electronics Letters, vol. 21, No. 17, pp. 738-740, 1985, Mears, R. J. et al., "Neodymium-Doped Silica Single-Mode Fibre Lasers".
Mears Robert J.
Payne David N.
Poole Simon B.
Reekie Laurence
Gonzalez Frank
Plessey Overseas Limited
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