Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-07-16
2004-09-21
Lee, John R. (Department: 2881)
Optical waveguides
With optical coupler
Switch
C385S008000
Reexamination Certificate
active
06795603
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical cross-connect for connecting and switching optical paths of a plurality of optical signals in an optical communication system, and more particularly to an analog beam-steering free-space optical switch that is constructed using micro-machining technology.
The development of the “Information Society” is advancing the development and deployment of optical communication systems that enable high-capacity information transfer. To meet the increasing demands of communication, this type of optical communication system employs Wavelength Division Multiplexing (WDM) transmission technology in which signals of different wavelengths are superposed on a single optical fiber for transmission and reception. In addition to a Point-to-Point mode in which communication between two points is joined using optical multiplexer/demultiplexers, this transmission technology introduces an Add-Drop mode for adding and dropping specific wavelengths at relay stations.
In order to implement this type of communication system, a light source adapted for high-speed modulation, optical fiber for high-capacity transmission, broadband fiber amplifiers, and multi-channel wavelength filters are indispensable. Of these components, optical switches that can selectively switch optical signals of any wavelength from a plurality of input ports and connect the optical signals to prescribed output ports is an important key technology for flexibly handling constantly changing communication demands as well as for coping with failures in communication lines.
On the other hand, the conversion to all-optical communication in which optical signals are transmitted without conversion to electrical signals is being advanced as one way for the development of optical communication systems in order to realize lower optical communication costs, system simplification, and faster transmission rate. This communication method is directed to using, in a large-scale switch for setting optical paths, an all-optical OXC (Optical Cross-Connect) as an optical switch. The “all-optical connection” refers to the way of connecting optical paths without first converting light to electricity and then connecting the electrical transmission lines.
An all-optical optical switch requires from small-scale switches having one-input and two-output (1×2) to large-scale switches having 1000×1000 or more input and output ports.
FIG.
1
(
a
) shows a small-scale optical switch (1×2) of the prior art, and FIG.
1
(
b
) shows an example of hierarchically assembled small-scale optical switches. The small-scale optical switch is constructed using a driving circuit for mechanical connection
14
, made up by a solenoid coil
11
and a permanent magnet
15
, to selectively connect one input-side optical fiber
12
to either one of two output-side optical fibers
13
(NTT, R&D, Vol. 48, No. 9: 1999, pp. 665-673).
In the figure, reference numerals
16
and
17
stand for a movable fiber on the input side and static fibers on the output side, respectively. All these fibers are contained in a ferrule
18
. The input and output optical fibers are externally connected through optical connectors
20
.
As shown in FIG.
1
(
b
), when using this type of small-scale optical switch, an N×M multi-input-multi-output optical switch can be constituted by hierarchically assembling a plurality of small-scale optical switches
104
. Nevertheless, the hierarchically assembled switch is not suitable for a large-scale switch because optical loss increases as the number of levels in the hierarchical structure increases.
FIG. 2
shows an example of a large-scale all-optical optical switch of the prior art, FIG.
2
(
a
) showing a schematic view of the optical switch, FIG.
2
(
b
) showing an entire optical switch array, FIG.
2
(
c
) showing the arrangement of optical devices that constitute a portion of the optical switch array, and FIG.
2
(
d
) showing the constitution of each individual optical device.
The optical device shown in
FIG. 2
is an example of a free-space optical cross-connect for realizing inter-fiber optical connections in which micro-actuators individually drive micromirror elements arrayed by means of MEMS technology.
The example of the prior-art optical switch shown in FIG.
2
(
a
) is made up by input ports
19
, output ports
20
, and two optical switch arrays
2101
and
2102
. Input ports
19
are constituted by input-side fiber array
15
that is made up by N optical fibers secured to a through-hole array (not shown in the figure) of capillary array
1701
, and collimation lens array
1801
. Output ports
20
are similarly constituted by: output-side fiber array
16
that is made up by M optical fibers secured to capillary array
1702
, and lens array
1802
.
In this device, two optical switch arrays
2101
and
2102
are constituted by two-dimensionally arranging optical switch elements (hereinbelow referred to as optical switches)
105
in matrix form, wherein the number of the optical switches corresponds to the number of input/output ports, as shown in FIGS.
2
(
b
) and (
c
). Each optical switch
105
is composed of an optical device section and a micro-actuator. In FIGS.
2
(
c
) and (
d
), only the optical device is shown, and the micro-actuator is not shown in the figure.
The optical device is made up by: micromirror
203
; mirror frame
303
that surrounds and pivotally bears micromirror
203
to rotate (tilt) micromirror
203
around the Ry axis; and frame
703
that surrounds and pivotally bears mirror frame
303
to rotate mirror frame
303
around the Rx axis.
Under electrostatic driving torque generated by a micro-actuator (not shown in the figure), micromirror
203
is capable of both tilting around the Ry axis and tilting around the Rx axis by means of mirror frame
303
that is rotatable around the Rx axis. The optical device is thus driven by the biaxial electrostatic driving torque generated by a micro-actuator to enable steering with respect to two degrees of freedom (around the axes in the Rx and Ry directions in FIG.
2
(
d
)). This mode of drive is hereinafter referred to as biaxial drive.
Micromirror
203
and mirror frame
303
are pivotally borne by hinge springs
503
and
603
, respectively, and are thus pulled back by an elastic restoring force proportional to the angle of rotation (tilt angle). Micromirror
203
and mirror frame
303
are at rest at the angle of tilt at which the electrostatic driving torque and elastic restoring force are in equilibrium.
A laser beam incident on micromirror
203
can thus be reflected in any direction.
This switch array allows changing the optical paths of beams as described hereinbelow (analog beam steering).
As shown in FIG.
2
(
a
), optical signals exit from input port
19
and are collimated by passage through lens array
1801
. An optical signal that has been collimated is then incident on micromirror
203
of optical switch array
2101
that corresponds to the micro-lens in lens array
1801
through which the optical signal of interest has passed. The reflected beam is steered by the biaxial drive of micromirror
203
such that the reflected beam of the optical signal is directed in a prescribed direction. The optical signal, emerging from optical switch array
2101
, is next incident on a prescribed micromirror of second optical switch array
2102
. Biaxial drive of the micromirror of second optical switch array
2102
directs the reflected beam of the optical signal to an optical fiber of output port
20
to take out the optical signal.
FIG. 3
shows the details of the optical device of the optical switch, FIG.
3
(
a
) being a plan view of an example of a biaxial-driven free-space optical switch of the optical device, and FIG.
3
(
b
) being a plan view of the hinge springs.
Micromirror
203
is pivotally borne by mirror frame
303
by means of a pair of hinge springs
503
, and this mirror frame
303
is similarly pivotally borne by outer frame
703
by means of a pair of hinge springs
603
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