Note: Descriptions are shown in the official language in which they were submitted.
wo 9l/0~022 PC~/GB90/()lS83
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" MOUNTING OPlICAL COMPONENTS
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This invention relates to optical components and optical component
mounts. The invention finds an important application in mounting
miniature lenses in optical devices of the kind used for optical
`. communications technology.
:
Taking as an example an optical fibre comrnunications system, many
of the devices used in such a system transmit light between their
; ~ 10 components in the form of a light beam travelling through free space. The
distance over which the light travels as a beam is typically a few
: rnicrometres, but may be up to several millimetres and more.
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. Whatever the distance, accurate and stable alignment between the
l 5 starting and finishing points of the bearn is an obvious necessity if coupling
losses are to be kept low. Often, the beam will pass through a lens which is
provided to relax particular alignment constraints. In a transmitter, the
- lens will typically focus the light output of a light source such as a laser,
.i.;l for example, onto the end of an optical fibre; in a receiver, the light
" ` 2 0 emerging from a fibre end may be collimated by a lens to be incident on a
` . photodetector such as a PIN photodiode, for exarnple.
. ~
An optical transmitter in which light emerging from a laser is
focused by a spherical lens onto the end of an optical fibre is described in
2 5 published international patent application WO88/10018 ("Optical Devices",
BT&D Technologies Ltd.).
;~:
The pre~iously mentioned need for good optical alignment
constitutes one of the recurrent problems in the manufacture of optical
-" 3 0 devices for use in optical cornrnunications systems and the like. Adequate
alignment present difficult problems owing to the smallness of the
components themselves; the high accuracy required of the alignment,
typically just a few micrometres or less; and to the need to ensure that
- ~ alignment will remain stable for the device lifetime of 25 years or more.
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WO 91/06022 PCI/GB90/01583
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The present invention is concerned with providing a mounting
arrangement for optical devices that provides good long term alignment at
- a relatively low manufacturing cost.
.
According to a first aspect of the present invention, a mounting
arrangement for optical components comprises a support member capable
- of plastic deformation in and parallel to its major plane, the support
member being provided with means to mount one or more optical
. components thereon. ! ',,.. ' 10
According to a second aspect of the present invention, a mounting
arrangement for miniature optical lenses comprises a support member
capable of plastic deformation in and parallel to its major plane, the
support member being provided with means to mount one or more optical
1 5 components thereon.
' ~ Preferably the support member is plastically deformable also in a
direction normal to said major plane.
:,',
According to a third aspect of the present invention, a lens mount
~; for a miniature optical lens comprises a support member capable of plastic
deformation in and parallel to its major plane. Movement out of the plane `may also be provided for.
2 S The support member according to the present invention preferably
, comprises a frame structure.
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- The frame structure defines an essentially enclosed space with
- mounting locations for optical components being conveniently located
3 0 within this space. For example, the frame structure may be provided with
: an optical component mount projecting into the interior of the space
defined by the frame structure. If desired, mounting locations for optical
~ components may instead, or additionally, be provided on the exterior of
; the frarne struceure.
;; 3 5
The frame structure may be open towards its associated base; that is
to say, an essentially enclosed space is defined only once the frame
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WO 91/06022 PCrtC B90/0 1583
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structure has been mounted on its base. $uch an open frame structure
often enables the mounted optical components to be closer to the base than
would be the case for a corresponding closed frame structure.
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5 The support member may comprise two or more relatively rigid
portions which are linked by relatively deformable portions. Instead,
however, the support member may be of similar deformability
substantially throughout.
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Where the support member is of a frarne structure having corners,
`. the corners may provide defoImable zones.
The material which forrns the deforrnable portions of the support
member needs to have low resilience so that the shape imposed by an
adjustment is retained.
The afore-described arrangements according to the present invention allow
- ~ adjus~nents, such as re-alignrnent of optical lenses, for example, to be
performed after assembly.
- The present invention will now be described further by way of
example only with reference to the accompanying drawings, of which:-
. Figure 1 is a perspective schematic view of a lens mount in accordance
2 5 with the present invention, wi~ Figure la illustrating the adjustability of
the lens mount of Figure 1;
:
Figure 2 shows a schematic view of an optical device assembly comprising
a plurality of optical components;
. 3 0
Figures 3j~ to 3c and Figure 4 are schematic front views of embodiments
. . illustrating various modifications over Figure 1;
Figures 5 is a sectional view taken along line V-V of Figure 3a:
Figure 6 illustrates a practical arrangement for supplying lens mounts
attached to a feeder strip; and
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WO 91/06022 PCr/GE390/01583
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Figure 7 illustrates further modifications of the present invention.
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Referring now also to the figures, Figure 1 shows a lens mount 1
- - 5 comprising an approximately diamond shaped frame portion 2 and integral
therewith a straight foot section 3. Projecting into the interior of the
frame from its corner opposite the foot section 3 is a lug 4. The lug 4 has
an aperture 5 which makes a press fit with a lens 6.
,. .
As illustrated in Figures 3a to 3c, for example, the aperture 5 may
` be of any suitable shape which makes a push fit with the lens 6. The lens 6
~- is a spherical lens, although other forms of lens may be used such as, for
example, a graded index rod lens (not sho vn).
':
Figure la is a schematic presentation of the manner in which the
frame 1 of Figure 1 can be adjusted to position the lens 6 of Figure 1 in the
, appropriate position. As illustrated by the arrows, the lens can be moved
up or down (U<-->D), left and right (L<-->R) and forwards and
backwards (F<-->B). In general, most practically performed adjustments
2 0 will be made up of a combination of movements in two or, possibly, all
` three directions described here. It should be noted that the up-down
movement and left-right movement lie generally within the plane defined
by the frame, while the front-back movement is arc-like in a direction
- approximately normal to that plane.
2s
` ` To adjust the position of the lens 6, the frarne 1 is deformed by
applying an external force by means of a suitable tool (not shown). The
. deformation of the frame 1 may occur, essentially, in one of two ways:
either the frame as a whole distorts, or distortion is restricted to dedicated
` 3 0 portions of the frarne, such as the hinge points indicated by empty circles
. in Figure 13. Such hinge points may be points of lower material strength,
for example, or be regions of high stress concentration under an applied
; load. Since self-deforrnation under operating conditions is clearly
undesirable, the material strength of ~he frame needs accordingly to be
; 3 5 chosen such that deformation requires the application of a tool.
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WO 91/06022 PCI`/C~ B90/0 1583
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Figure 2 shows the lens mount 1 mounted on a block 12 together
with a light source 13 and an optical fibre 11. The frarne 1 and the block
12 are mounted on an intermediate base 10. The frame 1 is affixed to the
block 12 by means of two spaced spot welds 7. In order to enable spot
. 5 welds to be made, the foot section 3 of the frame 1 extends beyond the
corners of the frame 1 itself. Brazing, soldering or organic adhesives may
- replace the spot welds in appropriate circumstances.
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- The procedure to align the light source 13, the optical fibre 11 and
the lens 6 in the lens mount 1 is, essentially, a ~ial and error method.
Thus, affixing a lens mount 1 proceeds as follows:- The light source 13 is
switched on and the lens mount 1 is positioned to achieve the desired
alignment between it, the source 13, and the fibre 11. In this position, tne
lens mount 1 is attached to the block 12, in the manner described above.
The procedure of affixing the lens mount 1 on the block 12 will tend to
disturb the previously achieved alignment, especially so in the case of spot
welding. Any such misalignment occurring during that procedure is then
corrected, with the light source 13 still under power, by deforming the
lens mount 1 witn a suitable tool (not shown) until the desired optical
alignment is obtained. The necessary degree of accuracy in obtaining
alignment and hence the exact procedure for obtaining it will largely
depend on the particular application. A greater degree of alignment
; ~ accuracy will normally be required for a single mode fibre than for a
i multimode fibre, for example.
; 2 5
- ~ ~ Figures 3a to 3c show three different embodiments of the
; approximately diamond shaped frame of Figure 1. The frame of Figure 3a
`- is substantially identical with that of Figure 1, save that its lens is push-fit
; ~ mounted in a hexagonal aperture 35.
3 0
The frame of Figure 3b differs from that of Figure 3a primarily in
that t'ne centre section of the foot section 3 has been removed, leaving two
~; side portions 33 of the foot sec~ion 3. This enables the lug 4 depending
from the top of the frame to be longer than in Figure 1 which, in turn,
3 5 einables the lens to be mounted in a lower position relative to the foot
section 3 than would be possible with the frame of Figure 3a.
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WO 91/(K022 PCI/GB90/01583
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The frame of Figure 3c has a short foot section 38 which would be
"~ used in situations where the frarne is to be affixed to the front rather than
- the top of the base 10 of Figure 2. In addition Figure 3c illustrates an
` approximately s~uare aperture, with rounded corners, where the lens is
S held in place by the four straight sides of the aperture.
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The individual characteristics of the three examples 3a to 3c can
obviously be combined in various ways to form frames of the kind shown
in Figure 1.
Another embodiment of the invention is shown in Figure 4. The
frame shown in Figure 4 is, essentially, an inverted T shape in which the
aperture 5 for mounting the lens is located at the far end of the stem 42 of
the T, and in which the foot section 43 is formed by the crossbar of the T.
15 Nearest the crossbar, the stem 42 is weakened by two offset slots 47 and
. 4B, to form the bridge 44 which is a zone of mechanical weakness. As will
be readily appreciated, slot 47 and 48 permit left to right movement by
bending deformation of the bridge 44. Up and down movement of the
. portion 42 causes shear deformation of dle bridge 44, while movement to
2 0 the back and the front causes a torsional deforrnatic)n of the bridge 44.
. Additional zones of weakness may be provided, e.g. with the aid of
additional slots (not shown), to obta~n a greater range of adjustability.
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Figure S is a section along the line V-V of Figure 3a and illustrates
- 2 5 in greater detail the position of the lens 6 within the frame 1. As shown,
the lens 6 m~kes a push fit with the sides of the aperture 35 in the lug 4.
,:
In order to reduce unwanted reflections, the lens 6 is provided with
. an anti-reflection coating 67. The anti-reflection coating 67 is preferably
i` 3 0 applied to the lens only after the lens has been inserted into the frame 1.
Indeed, it is one of the advantages of using a frarne such as that provided
. by the present invention, tha~ the frame 1 can be used as a convenient
. clamp for holding the lens 6 duling anti-reflection coating and, of course,
-~ thereafter.
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i ` WO 91/06022 PCr~GB90/01583
~ 2066~40`
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;~ Referring now specifically to Fi~ure 6, the frames, shown here with
lenses 66 inserted, are conveniently forrned along a strip 67 and attached to
the strip along a break line 68.
S In use, lenses are inserted into the apertures of frames 61 and are
then anti-reflection cozted. Subsequently each frame 61 is snapped off the
strip 67 along the break line 68, and attached to a base such as base block
10 in Figure 2.
A further modified forrn of the present invention is shown in Figure
7. The frame shown there is modified to permit mounting thereon an
assembly of a photodiode and a lens, such as is described, for example, m
~` published international patent application W089/05467 ("Light Sources",
BT&D Technologies Ltd).
1 5
The frame 71 Figure 7 is an open frame having a central section 76
depending on each end via a strip 74 from a support arm 72, 73, whereby
` the outer ends of the support arm provide the foot section 73 for securing
the frame 71 to a base (not shown) such as base 10 of Figure 2.
~` The material of the frame is preferably chosen to closely match the
expansion coefficient of the base to which the frarne is to be secured.
-` ~ Often the base will form the heat sink for an active device such as a laser
or light ernitting diode. If the base is a diamond heat sink the frame is
2 5 preferably made of Invar~. If the base is copper, the material for the
frame may be nickel; and in the case of a silicon base, KovarTM is a
material with a suitably matched expansiQn coefficient.
~.,,
Depending on the required size and the material of the frarne, the
3 0 frame can be formed by methods such as mechanical stamping, photo
etching, machining, spark erosion, or laser cutting. The aperture for
accornrnodating the lens can be sirnilarly formed.
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In all the afore-described cases the material thickness, stiffness,
3 5 deformability and other material parameters are chosen, for a given design
- of frarne, such that in use the frame resists deformation even when subject
to moderate shocks, while being suf~Iciently pliable to be deformed with
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the aid of an adjustment tool. Where the frame is designed to have clearly
defined deforrnation zones, the dimensions etc. of its deformable zones will
be chosen accordingly.
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