Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-09-07
2004-03-23
Nasri, Javaid H. (Department: 2839)
Optical waveguides
With optical coupler
Switch
Reexamination Certificate
active
06711319
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to an optical switch and more particularly to an optical switch having a converging optical element.
BACKGROUND OF THE INVENTION
Optical switches for switching light signals between different optical fibers are known. A known optical switch
100
is shown in
FIGS. 1A
,
1
B,
1
C and
1
D. The optical switch
100
is composed of input collimator array
110
for receiving multiple light beams, each representing an optical signal, via associated optical fibers
50
. For clarity, only one optical fiber is shown in
FIGS. 1A
,
1
B and
1
D. A light beam is output from input collimator array
110
and directed onto a first micromirror that forms part of input micromirror array
120
. The first micromirror can be rotated about at least one axis to direct the light to a second micromirror the forms part of output micromirror array
121
. The second micromirror can be rotated about at least one axis to direct the light beam received from the first micromirror into the collimator corresponding to the second micromirror. The collimator is part of the output collimator array
111
. Micromirror arrays
120
and
121
each incorporate micromirrors
25
(FIG.
1
C).
In the optical switch
100
, the input collimator array
110
must be very accurately aligned with respect to the input micromirror array
120
to make the light beam output by each collimator impinge on the center of the micromirror associated with that collimator. To achieve this alignment throughout the input collimator array, the collimators must be aligned so that they output light beams that are accurately parallel to one another. Such accuracy is difficult and expensive to achieve in production. Additionally, the input collimator array must incorporate custom collimators that each generate an output light beam that converges at the input micromirror array. This is less convenient and more expensive than using a standard collimator that generates parallel output light beam.
Similar considerations apply to the output collimator array
111
, which must be accurately aligned with the output micromirror array
121
to ensure that the optical signal reflected by a particular output micromirror is properly coupled into its associated collimator of the output collimator array. Moreover, the optical beam propagates directly from the input micromirror array to the output micromirror array. As noted above, the collimators of the input collimator array should be configured to ensure that the light beam has the correct waist and curvature at the input micromirror array. Otherwise, the free space propagation of the light beam from the input micromirror array to the output micromirror array results in the light beam expanding to be much larger than the micromirrors of the output micromirror array.
A second example of a known optical switch is shown in FIG.
1
D. In this, a fixed mirror
125
is interposed between an input micromirror array
120
and an output micromirror array
121
to redirect the light beam from input micromirror array
120
onto output micromirror array
121
. Folding the optical path between the input micromirror array and the output micromirror array in this manner reduces the dimensions of the optical switch. However, as the fixed mirror
125
is flat, expansion or contraction of the beam diameter between the input and output micromirror arrays
120
and
121
, respectively, occurs as if the mirror were not present. As before, the collimators of the input collimator should be custom devices configured to ensure the proper waist w
0
and curvature of the optical beam at the input micromirror array
120
.
In the optical switches just described, the beam size at the output micromirror array limits how small the micromirrors may be. Large micromirrors increase the physical size of the optical switch and require more energy to switch them quickly. Moreover, a beam size larger than the micromirrors attenuates the optical signal, and can additionally result in crosstalk between the different optical signals that pass through the optical switch. Also, as described above, the alignment between the micromirror arrays and their respective collimators is critical. Finally, in the optical switches just described, approximately half of the angular range of those of the micromirrors located at and near the edges of the array is wasted. This means that, if all the micromirrors are identical as is usually desirable, fabrication of the micromirrors is more difficult than it need be because of the need to provide them with an increased angular range.
Thus, what is needed is an optical switch in which the beam size of the light beams that pass through the optical switch is small at the micromirror arrays, in which the alignment between the micromirror arrays and their respective collimators is less critical, in which the collimators do not have to output light beams that are accurately parallel, in which standard collimators that generate parallel beams of light can be used and in which micromirrors having an angular range corresponding to that of the micromirrors near the center of the array can be used throughout.
SUMMARY OF THE INVENTION
The invention provides an optical switch that comprises an input collimator, an output collimator, an input mirror, an output mirror and a converging optical element. The input collimator receives, collimates and outputs an input light beam. The input mirror is arranged to receive the light beam from the input collimator. The output mirror is arranged to receive the light beam reflected by the input mirror and reflects the light beam into the output collimator. The converging optical element is located to receive the light beam reflected by the input mirror and reflects the light beam onto the output mirror.
The converging optical element is located relative to the input mirror and the output mirror such that the waist of the light beam at the output mirror is similar in size to that at the input mirror.
An imaging element may be located between either or both of the input collimator and the output collimator and a respective one of the input mirror and the output mirror. The imaging element makes alignment between the collimators and their respective mirrors less critical, allows collimator forming part of an array to output respective light beams at different angles and allows the full range of angular movement of the mirror to be used.
The invention also provides an optical switch that comprises an input collimator, an output collimator, an input mirror, an output mirror and an imaging element. The input collimator receives, collimates and outputs an input light beam. The input mirror is arranged to receive the light beam from the input collimator. The output mirror is arranged to receive the light beam reflected by the input mirror and reflects the light beam into the output collimator. The imaging element images at least one of the input collimator and the output collimator on a respective one of the input mirror and the output mirror. The advantages conferred by the imaging element are described above.
The invention additionally provides a first method for switching an optical signal. In this, an optical switch including an input mirror and an output mirror is provided. The light beam is received, and is directed towards the input mirror. The orientation of the input mirror is adjusted to direct the light beam onto the output mirror. The light beam is converged after reflection by the input mirror and prior to reflection by the output mirror. The orientation of the output mirror is also adjusted.
Finally, the invention provides a second method for switching an optical signal. In this, an optical switch including an input collimator, an input mirror, an output mirror and an output collimator is provided. At least one of the input collimator and the output collimator is imaged onto a respective one of the input mirror and the output mirror. The light beam is received at the input collimator. The orientation of the input mirror is adjusted to
Agilent Technologie,s Inc.
Hardcastle Ian
Nasri Javaid H.
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