1989-11-13
1991-05-21
Ullah, Akm
350 9620, G02B 632
Patent
active
050169653
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to optical coupling.
In various opto-electronic and electro-optical assemblies it is necessary to align elements of the assembly so that light output from one element is input to another element. If the light emitting element emits a diverging beam then in order to couple a substantial portion into the light receiving element it is necessary to position the light receiving facet of the receiving element close to the light emitting facet of the emitting element. In some instances this close positioning cannot be achieved: for example if the light emitting element is on a support that is subject to movement such as thermal expansion or vibration and the light receiving element is such that it can not be flexibly mounted then it becomes difficult to mount the light receiving element sufficiently close to the light emitting element without impariing the performance of the light receiving element. If a common support is used a flexible connection is required between the receiver and the package wall which would restrict the bandwidth due to the effects of parastic capacitances and/or inductances inherent in a flexible connection. On the other hand mounting the receiving element off the transmitting element support increases the distance between the elements and also introduces alignment problems caused by the relative movement of the elements.
SUMMARY OF THE INVENTION
The present invention provides a device package comprising a light emitting element supported on a first mounting and a light receiving element supported on a second mounting and in which, when operating, relative movement occurs between the light emitting element and the light receiving element, and a lens assembly supported on said first mounting for directing light from the light emitting element on to the light receiving element, the lens assembly comprising a first lens located with the light emitting element at its focus and a second lens aligned with the first lens and with the light receiving element located within the focal range of the second lens.
The first element may be a light generating element or may be a light processing element. Within the context of this specification, the expression `light emitting element` means having a light output and includes elements that process a light input without generation of light. The first element may be a light source without an optical input or may have an optical input provided by a fibre or a previous optical element.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is now described by way of example with reference to the accompanying drawings in which:
FIG. 1 is a schematic illustration of light output from a light emitting element;
FIG. 2 is a schematic illustration of a lens assembly used in a preferred embodiment of the invention; and
FIG. 3 is a schematic cross section through a preferred embodiment of device package according to the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Referring now to FIG. 1, a light emitting element 1 emits a cone of light having an apex angle .alpha.. The light emitting element 1 envisaged by the present invention may be a source device such as a modulated laser transmitter or a signal processing element such as a filter or a laser amplifier that receives an optical signal as well as emitting light. (Within the context of this specification the expressions optical, light, elecro-optical and opto-electronic should be construed to relate not only to the visible spectrum but also the near and far infra red and the ultra violet regions of the electromagnatic spectrum). If the element 1 is a semiconductor laser then the angle .alpha. will typically be in the range of 20.degree. to 60.degree.. Due to the divergence of the output light any element into which it is to be directed needs to be positioned sufficiently close to collect a substantial proportion of the output light if the coupling is to be efficient.
Thus if a photodiode, for example, with a light receiving facet of 100 .mu.m is to rec
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Constantine Philip D.
Marshall Ian W.
British Telecommunications public limited company
Ullah Akm
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