N x M optical switch

Details N x M optical switch N x M optical switch

2000-06-16

2002-07-02

Ullah, Akm E. (Department: 2874)

Optical waveguides

With optical coupler

Switch

C359S199200, C359S627000, C385S140000, C385S124000

Reexamination Certificate

active

06415067

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to optical switches and more particularly, to an optical switch having a movable wedge or a plurality of movable wedges, which serve to steer a beam of light.
BACKGROUND OF THE INVENTION
Optical switches of various kinds are well known for selectively switching light from a waveguide, such as optical fibre or light-conducting path, to another.
To fulfill this requirement, it has been well known to provide 2×2 optical switches having two ports on each side, wherein the switch is configurable to make a connection between ports
1
and
2
and simultaneously to provide a connection between ports
3
and
4
. Alternatively, such switches are configurable to provide simultaneous connections between ports
1
and
4
, and ports
3
and
2
. Hence these prior art switches have two states; a first state wherein two bar connections are formed and a second state wherein 2 cross connections are formed. Providing suitable coupling in both switching states, and providing a switch that is fast enough, and tolerant of physical disturbances is a daunting task most switch manufacturers face.
A well known optical switch made by JDS Fitel Inc. has been sold in the United States since Feb. 11, 1992 under the product number SR22xx-ONC. This optical switch includes a pair of GRaded INdex (GRIN) lenses having a reflector or mirror that can be selectively disposed therebetween. Each GRIN lens has two ports offset from the optical axis (OA) of the lens.
In a graded index medium that has a refractive index that varies with position, optical rays follow curved trajectories, instead of straight lines. By judicious selection of the refractive index, a GRIN rod can behave like a conventional optical element such as a prism or a lens. Lenses of this type are produced under the trade name “SELFOC”; the mark is registered in Japan and owned by the Nippon Sheet and Glass Co. Ltd. GRIN lenses are used extensively as a means of coupling optical signals from one waveguide such as an optical fiber, to another, for example, in optical switches. The use of GRIN lens provides a number of advantages over other conventional lenses. For example, GRIN lenses are relatively inexpensive, compact, and furthermore have parallel flat end faces. In particular, the flat end face of the GRIN lens allows a single lens to be used as a means of collimating or focusing light.
An optical arrangement is shown in
FIG. 1
, wherein two quarter pitch GRIN lenses
10
a
and
10
b
are disposed so that their collimating ends are adjacent one another in a back-to-back relationship. A very thin optical element in the form of a filter
12
is sandwiched therebetween. The filter
12
can be coated directly on one of the inwardly facing end faces of the lenses, or alternatively may be coated on a substrate that is anti-reflection coated and sandwiched between the two GRIN lenses
10
a
and
10
b
. It should be noted, that the optical axes of the input/output fibres
11
a
and
11
b
are parallel with the optical axes of the two GRIN lenses. Since the beam traversing the lenses
10
a
and
10
b
about the filter element
12
is at a location substantially coincident with the optical axes of the GRIN lenses, the light input orthogonal to the end face of the lens
10
a
at port P
1
, propagates through the filter
12
and through the second lens
10
b
and exits at port P
2
as a focused beam that is parallel to the input beam and the optical axes of the lenses
10
a
and
10
b.
FIG. 2
illustrates an offset that occurs when a gap is present between a pair of coaxial GRIN lenses
12
a
and
12
b.
The beam exiting the lens
12
a
intersects the end face equidistant from the optical axis indicated by lines
20
a
and
20
b
, which define the outer most limits of the beam as it traverses the lens
12
a
end face. However, due to the gap between the lenses
12
a
and
12
b
, the beam traverses the inwardly facing end face of the lens
12
b
having its outermost limits defined by the locations
22
a
and
22
b
which are not equidistant from the optical axis OA of the second lens
12
b
. This beam shift downward results in the output beam being directed upward along the optical axis of the optical fibre
14
b
. Accordingly, substantial coupling losses may occur between an input port on a first GRIN lens and an output port on a second GRIN lens, when the input and output ports are disposed adjacent the optical axes of the two GRIN lenses, and wherein a gap separating the GRIN lenses causes a beam propagating from the input port through the first GRIN lens to be shifted as it traverses the element towards the output port and enters the second lens at an offset to the optical axis of the lens. To overcome this disadvantage and to provide a more efficient optical coupling, the fibre
14
b
is provided at an angle &thgr;>0 degrees with respect to the optical axis of the lens.
It is also possible, as shown in
FIG. 3
, to launch the beam
30
at a judiciously selected angle &thgr;
S
at the left input end face of the GRIN lens
16
b
in such a way that the beam is selectively directed towards a desired output port location at the right output end face of the GRIN lens
16
b
. Moreover, by ensuring that the beam has its centre substantially coincident with the optical axis OA of the lens, the beam thus propagates through the lens
16
b
and exits the output end of the lens parallel to the OA of the lens. From a manufacturing standpoint, when using GRIN lenses in switches or routers, it is preferable to use a transmissive switching optical element, in which zero or a number of internal reflections in each plane, and/or any number of refractions, are imposed on the incident light between the lenses rather than a reflective element imposing one reflection, to route, shift, or direct a beam from one port to an alternate port when the element is disposed between lenses. Thus, by providing a transmissive element such as a prism, the switch is much less sensitive to angular deviation and misalignment of the element than a switch using a reflective element such as a mirror. For example, in comparing angular sensitivity based on a 0.05 dB excess insertion loss criterion, an existing single mirrorbased switch has a typical angular tolerance of 0.007 degrees. An existing prism-based switch has an angular tolerance of 0.03 degrees, whereas the transmissive optical wedge-based switch described in accordance with this invention has an angular tolerance of 1.4 degrees.
It is an object of the instant invention to provide an improved optical switch having a transmissive wedge movable between two GRIN lenses for changing the angle of the collimated beam by a selected amount so that the output beam exits the output end face substantially parallel to the optical axis of the GRIN lenses, regardless of the connect state.
It is an object of this invention to provide a relatively inexpensive and easy to manufacture switch that will serve as an N×M optical switch.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided an optical switch comprising:
at least one input port on one side for launching an optical signal along an input optical path;
at least two output ports on an opposite side for receiving the optical signal, a first of the at least two output ports optically coupled to the at least one input port; and
a light transmissive wedge having at least two non-parallel surfaces, the wedge movable into and out of the input optical path, the wedge movable at least between first, second, and third positions corresponding to first, second, and third connect states, respectively.
In accordance with this invention, there is provided a method for switching a beam of light from one of a plurality of output ports to another, comprising the step of:
receiving at an input port a beam of light parallel to the optical axis of a first GRIN lens, the first GRIN lens for collimating the beam of light;
transmitting the optical signal along an optical path to a second GRIN lens optically coupled to the

Affiliated with

Also associated with

Rating

N x M optical switch does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with N x M optical switch, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and N x M optical switch will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2838330