Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-07-16
2001-09-18
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S031000, C385S033000, C385S034000, C359S199200, C359S199200
Reexamination Certificate
active
06292604
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the coupling of light from an optical waveguide end, to one or more other optical waveguides via an at least partially reflective optical element.
BACKGROUND OF THE INVENTION
It is common practice to couple light from an optical waveguide such as an optical fibre to one or more optical fibres via an at least partially transmissive, partially reflective optical element. For example a dichroic filter is often disposed between a pair of collimating/focusing lenses such as graded index (GRIN) lenses to provide a wavelength division multiplexing (WDM) function.
FIG. 1
illustrates a prior art WDM filter, wherein wavelengths of light &lgr;
1
and &lgr;
2
are launched into a first port at an end face of a GRIN lens
12
a
and wherein light of wavelength &lgr;
1
is reflected from a filter
14
which passes light of wavelength &lgr;
2
. The lines indicating the path of the beam as it is partially reflected and partially transmitted through the filter represents a ray through the centre of the beam launched into the lens
12
a
.
FIGS. 2 and 3
illustrate the beam's shape and path for light launched into a port along the optical axis of the lens and for light launched into a port offset from the optical axis respectively.
Prior art
FIG. 4
illustrates a typical arrangement of one side of a WDM filter wherein an optical fibre tube
8
holding two optical fibres at predetermined locations is shown optically coupled with an adjacent GRIN lens
12
c
which is juxtaposed to a filter
14
. Fibre tubes or sleeves of this type provide a convenient way of holding two or more optical fibres a fixed distance apart such that the pair of fibres can then be moved without damaging them. Furthermore, the tube allows the fiber ends (and tube) to be polished such that the end face is slanted to lessen the effects of unwanted back reflections.
Heretofore, there has been no known reason to align pairs of optical fibres at the slanted, polished end face of the sleeve in any special orientation except with regard to pairs of optical fibres being offset a same distance from the optical axis. The term pair relates to two optical fibres which via some reflective element are optically coupled to one another.
Prior art
FIG. 13
illustrates pairs of optical fibres (A,B), (C,D), and (E,F) disposed at a slanted end face of a fibre tube
8
. By placing a reflective element at an appropriate location and position, and by providing an appropriate collimating/focusing lens, light from one of each of the pairs will couple into the other of the pair in an expected fashion.
What is unexpected, is that if the fibres are located at any locations other than along one particular line through the optical axis, coupling will be negatively affected. For example the positioning of the pair of optical fibres shown in
FIG. 5
is least favourable for optimum coupling in a WDM filter. This is illustrated in more detail in
FIG. 6
, where the path AC and the path CB are of different lengths illustrated by &Dgr;L due to the position of the fibres
13
a
and
13
b
on the slanted end face of the sleeve
8
.
FIG. 7
more clearly illustrates the problem with haphazardly disposing the fibre equidistant from the longitudinal axis of the sleeve or more importantly from a line extending from the optical axis of the lens
12
d
wherein a beam leaving the output fibre at point A is perfectly collimated at the reflective surface
16
through point C, and wherein the reflection from
16
is focused at point D along the dashed line
18
, instead of being focused at point B coincident with the optical fibre end.
It is an object of this invention to provide an arrangement of optical fibres within a tube or sleeve that will couple light in an optimum manner.
It is a further object of this invention to provide an optical system wherein a preferred coupling is achieved with essentially no additional components from previous similar coupling methods.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided, a WDM filter comprising:
a first optical fibre tube having two or more optical fibres contained therein;
a second optical fibre tube having at least one optical fibre contained therein, the second optical fibre tube being optically aligned with one of the two or more optical fibres contained in the first optical fibre tube; an inwardly facing end face of the first fibre tube being slanted so as to reduce the effects of back reflections, the slanted end face having a slant of less than 15 degrees and greater than 2 degrees from a line orthogonal to a longitudinal axis of the optical fibre tube;
collimating/focusing lenses disposed between the first and second optical fibre tubes, the collimating lens having an optical axis;
an at least partially reflective optical filter disposed between the collimating/focusing lenses;
end faces of the two or more optical fibres being disposed along a line at the end face of the slanted tube at locations equidistant from the longitudinal axis of the lens and at locations such that light launched from one of the at least two optical fibre end faces is collimated at a collimating location at or near the optical filter and such that collimated light at the collimating location is focused at another of the at least two optical fibre end faces.
In accordance with the invention, there is provided, an optical filter comprising:
a wavelength dependent at least partially reflective optical filter;
an optical fibre tube having two optical fibres contained therein, a cross-section of the optical fibre tube through longitudinal axis thereof delineating an end face disposed toward the at least partially reflective optical filter that is slanted with respect to a line normal to the longitudinal axis of the optical fibre tube, the slant angle being between 2 and 10 degrees, wherein end faces of the at least two optical fibres lie on a line across the end face of the tube being a shortest line across the slanted end face of the tube through the longitudinal axis.
In accordance with the invention, there is further provided, a WDM filter comprising:
first and second back-to-back collimating/focusing lenses each having an optical axis;
a filter element disposed between the back-to-back lenses,
a sleeve having a longitudinal axis that is parallel with the optical axis of the first lens, the sleeve being adjacent the first lens and having two optical fibres contained therein, end faces of the fibres and the sleeve being cut and or polished to slant to lessen the unwanted effects of back reflections;
the slanted end faces of the fibres lying on a line that is substantially perpendicular to the longitudinal axis of the sleeve.
In accordance with the invention, there is yet further provided, an optical filter comprising:
an optical fibre tube having two or more optical fibres contained therein, an inwardly facing end face of the first fibre tube being slanted so as to reduce the effects of back reflections, the slanted end face having a slant of less than 15 degrees and greater than 2 degrees from a line orthogonal to a longitudinal axis of the optical fibre tube;
a collimating/focusing lens disposed adjacent an end of the optical fibre tube, the collimating/focusing lens having an optical axis;
an at least partially reflective optical element disposed adjacent the collimating/focusing lens, end faces of the two or more optical fibres being disposed along a line at the end face of the slanted tube at locations equidistant from the longitudinal axis of the lens and at locations such that light launched from one of two or more optical fibre end faces is collimated at a collimating location at or near the optical filter and such that collimated light at the collimating location is focused at another of the at least two optical fibre end faces.
REFERENCES:
patent: 4213677 (1980-07-01), Sugimoto et al.
patent: 5642447 (1997-06-01), Pan et al.
patent: 5642448 (1997-06-01), Pan et al.
patent: 5652814 (1997-07-01), Pan et al.
patent: 5845023 (1998-12-01), Le
Bovernick Rodney
JDS Fitel Inc.
Pak Sung
Teitelbaum Neil
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