1987-06-12
1989-10-03
Arnold, Bruce Y.
G02B 208
Patent
active
048712442
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the mounting of a movable member, for example the mounting of an optical mirror.
In the field of optical signal transmission, it is important to be able to deflect an optical beam through a controlled angle. Previous proposals have involved the location of a torsion plate using a substrate, the torsion plate defining an optical mirror and being deflectable under the control of electrostatic fields. These arrangements are complex in construction and it is difficult to obtain accurate control of the deflection angle. In addition the torsion plate has very few degrees of freedom.
In accordance with the present invention, we provide an assembly of at least two supports and a movable member mounted by respective connecting members between the supports, the electrical conductivity of the assembly being such that at least one electrically conductive path extends from a support to the movable member and thereafter to the or another support, the resistivity of the path being such that the passage of a working current along the path causes thermal expansion of one or more of the connecting members and the movable member thereby causing movement of the movable member relatively to the supports.
With this invention, control of the position of the movable member is achieved by relying on the thermal expansion properties of one or more of the connecting members and the movable member itself. This reduces the complexity of the construction and also leads to accurate control of the deflection angle. Furthermore, the invention enables constructions to be developed in which the movable member may be moved in any direction.
The invention is particularly useful when the movable member comprises an optical mirror but in other applications, the movable member may be used as a support for other optical components such as diffraction gratings, laser diodes and the like whose angular position must be accurately controlled.
Preferably, the supports, connecting members, and the movable member are all integrally formed and this may typically be achieved by using a micromachining technique to etch a substrate. For example, the assembly may be made from silicon and have relatively small dimensions. These features all lead to a relatively low manufacturing cost.
In a very simple arrangement, the movable member may be mounted between the supports by two connecting members. Preferably, however, the movable member is mounted to each support by a pair of connecting members. Conveniently, each pair of connecting members is substantially colinear, the pairs being substantially parallel.
Preferably, all the connecting members are electrically conductive since this leads to a larger number of deflection angle directions being obtainable.
In some examples, part of at least one of the electrical paths is defined by an electrically conductive portion of the movable member. Preferably, the or each electrically conductive part of the movable member has a higher resistivity than the remainder of the electrically conductive path.
In this case, thermal expansion of the movable member will cause the connecting members to deflect and thus the movable member will be moved to a position substantially parallel with its rest position thus resulting in a piston like movement. This is particularly useful where the movable member defines one end of a laser cavity.
The resistivity of the or each connecting member forming part of an electrically conductive path may be higher than the remainder of the electrically conductive path. This provides flexibility, particularly where two or more electrical paths are defined between the supports across the movable member since a larger number of deflection directions can be obtained.
Coveniently, a single current source is provided which is connected by a control means to a selected electrical path or paths. Alternatively, a number of current sources may be provided, for example one corresponding to each electrical path, control means controlling whether the current source is connected to the respe
REFERENCES:
patent: 1438974 (1922-12-01), Wente
patent: 2920529 (1960-01-01), Blythe
Patents Abstracts of Japan, vol. 6, No. 2, (P-96), (880), Jan. 8, 1982, & JP, A, 56126818, (Nippon Denshin Denwa Kosha K.K.), Oct. 5, 1981.
Arnold Bruce Y.
British Telecommunications public limited company
Gass Rebecca D.
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