Coherent light generators – Particular beam control device – Producing plural wavelength output
Patent
1995-10-10
1998-11-03
Bovernick, Rodney B.
Coherent light generators
Particular beam control device
Producing plural wavelength output
372 6, 385 37, H01S 310
Patent
active
058320113
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser, and in particular to a laser whose operating wavelength may be easily altered.
2. Related Art
The development of compact, relatively inexpensive lasers, in particular semi-conductor lasers, but more recently also fibre lasers, has led to an enormous growth in optical communication systems. Initially lasers in optical communications systems were used simply as a source of optical frequency noise, the wavelength and bandwidth of these lasers being relatively unimportant. The parallel development of optical fibres, used as the transmission medium in these telecommunications systems, rapidly led to a requirement for lasers to operate within specific wavelength ranges. Thus it was discovered that optical fibres made from the preferred material of silica, exhibited three low loss "windows" in the optical spectrum, centred at approximately 850 nm, 1300 nm and 1550 nm. Single wavelength point to point optical communications systems thus required laser sources whose operating wavelength lay within one of the low loss windows of the optical fibre used. These simple types of optical communications systems are the ones which are predominately in use at present in telecommunications networks, however there is a requirement for future optical communications networks to utilise the huge spectral bandwidth available from optical fibres more efficiently.
In addition to simply utilising several wavelengths on the same point to point optical communications link, there are many proposals to use hundreds, or even thousands, of different wavelengths across multipoint optical networks. Such proposals may be based on a broadband optical path approach or a wavelength selective optical path approach, or on some combination of the two approaches. A feature of the broadband approach is that any signal injected into the network is broadcast to all receivers whether it is needed or not. This may be considered inefficient but it can lead to a good degree of flexibility, and this is exploited for example by means of Passive Optical Network configurations see for example J R Stern et Al "Passive Optical Local Networks for telephony applications and beyond", Electronics Letters Volume 23, number 24, 1255-1257, November 1987. A feature of wavelength selective optical networks is that optical power at a given wavelength is directed only to where it is required and a given wavelength can be reused in different parts of the network. This leads to a reduction in the total number of different wavelengths needed for a given network throughout, but requires that wavelength multiplexing and demultiplexing components are provided in the network, see for example G R Hill "A wavelength routing approach to optical communications networks" IEEE INFOCOM '88.
The aim for both of these approaches, is to extend the optical network as far as possible to the customer, preferably supplying an optical communications link to the customer's premises.
The demands made of laser sources for such future optical communications networks are thus quite different from those placed on laser sources presently used.
SUMMARY OF THE INVENTION
According to the present invention there is provided a laser comprising first and second feedback elements defining a laser cavity, a gain medium within the laser cavity, a demountable optical connector and an optical waveguide, wherein the second feedback element is wavelength selective, the demountable optical connector is located between the gain medium and the second feedback element and the optical waveguide is located to direct optical radiation between the demountable optical connector and the second feedback element.
Thus the present applicant has realised that if a demountable optical connector is provided within the cavity of a laser, between the gain medium and a wavelength selective feedback element, the wavelength selective feedback element alone may be easily exchanged for another such element so as to alter simply and cheapl
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Bovernick Rodney B.
British Telecommunications public limited company
Wise Robert E.
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