Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-07-17
2002-01-08
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000, C359S298000, C359S223100, C385S014000
Reexamination Certificate
active
06337760
ABSTRACT:
BACKGROUND
1. Field of Invention
The present invention relates to micromechanical machines, and in particular to micromechanical mirrors used to direct light beams. This application is related to the subject matter disclosed in U.S. Pat. No. 5,835,256 to Huibers, and U.S. Pat. No. 6,046,840 to Huibers, the subject matter of each being incorporated herein by reference.
2. Related Art
FIG. 1
illustrates one architecture of an optical switch
2
(e.g. an optical cross-connect) using opposing micromechanical mirrors formed, for example, over a silicon substrate. Information carrying (modulated) light signals arrive through input optical fibers
100
that are each coupled to conventional input terminals
101
. Each light signal is collimated into a light beam that is directed to one of several output optical fibers
102
. Light beam directional steering is accomplished using the micromechanical mirrors in mirror arrays
104
and
106
. Fine mirror tilt angle control is desirable to properly direct each light beam to one of several conventional output terminals
103
, each coupled to one of the output fibers
102
.
For example, a conventional information carrying light signal (e.g., modulated laser light) arrives though input fiber
100
b.
The signal exits the end of fiber
100
b
and is collimated by conventional optics (lens) to form light beam
110
that is incident on mirror
104
b.
Electrodes (not shown) deflect mirror
104
b
so as to direct beam
110
towards mirror array
106
. The angle of deflection for mirror
104
b
is controlled by a switching algorithm that activates the electrodes such that light beam
110
is directed to the correct mirror in array
106
. As depicted, mirror
104
b
directs beam
110
to mirror
106
b,
but alternatively may direct the beam to mirror
106
a
or
106
c.
The switching algorithm also actuates electrodes (not shown) that control the deflection angles of the mirrors in array
106
, thereby directing light beams reflected from array
104
into the output fibers. As shown in
FIG. 1
, mirror
106
a
directs light into fiber
102
a,
mirror
106
b
directs light into fiber
102
b,
and mirror
106
c
directs light into fiber
102
c.
FIG. 2
illustrates a second architecture for another micromechanical optical switch
4
. This second architecture uses a single micromirror array
120
and a fixed mirror
122
to produce a folded optical path. Input and output optical fibers are mixed in fiber array
124
, and each fiber is coupled to conventional input or output terminals
125
as appropriate. Input light signals are collimated into a light beam and directed at a first mirror in array
120
. The light beam is reflected from the first mirror in array
120
so as to reflect from fixed mirror
122
onto a second mirror in array
120
. The second mirror is then angled to direct the light beam to the appropriate output fiber. For instance,
FIG. 2
shows light beam
126
reflecting from mirrors
121
a,
122
, and
120
b
to reach output fiber
124
b.
FIG. 2
also shows mirror
120
alternatively tilted to a second angle so as to reflect beam
126
from mirrors
122
and
120
c
towards output fiber
124
c.
Architectures such as those illustrated in
FIGS. 1 and 2
are preferable to cascaded binary cross-over switches for cross-connecting large numbers of optical fibers. A switch using one or two two-dimensional micromechanical mirror arrays can cross-connect, for example, 30×30 optical fiber arrays. In contrast, hundreds of cascaded binary cross-over switches would be required for such a cross-connect.
Micromechanical mirror configurations are known.
FIG. 3
shows, for example, “reflective surface”
140
(shown in cutaway by dashed lines) that is “suspended by four flexure hinges”
142
and “posts”
144
as disclosed in U.S. Pat. No. 5,808,780 ['780 patent]. Four “electrodes”
146
a-d
underlie reflective surface
140
.
The '780 patent states that the electrodes are “activated with a known analog voltage. The different levels of voltage available in the analog domain determine which of several deflected states the member assumes. Once a known analog voltage is applied, the segmented electrodes allow fine-tuning of the member's position” in order to maintain the member parallel to it's original position.
As the '780 patent discloses, the embodiment illustrated therein has a mirror with only two stable positions, though the electrodes could allow a third stable position. The '780 patent further states that the illustrated embodiment has only one input light path, though it could have two light paths passing light onto the reflective surface
32
. The light could then be switched for one path or the other or both into one of four output paths for the two illustrated positions, or one of six output paths if there were a third position.
It is desirable to have an optical switch with at least one micromechanical mirror array, in which the mirror elements are capable of being deflected to a relatively large number of positions and angles, thereby permitting light beams from a large number of input fibers to be simultaneously directed to a large number of output fibers. Fine mirror tilt angle control is desirable, however, because the beam directed towards an optical fiber typically should be within a few tens of micrometers (&mgr;m) of the output fiber's end for sufficient light to enter the fiber. The control system that provides such fine control should be dynamic in order to compensate for mirror angle variations caused by temperature changes, for example. It is also desirable in some instances to use a digital control system to produce the electrostatic fields used to tilt the mirrors.
SUMMARY
A light beam steering device includes a mirror plate that is mechanically coupled to an optically transmissive substrate by flexures that permit the mirror plate to tilt around a plurality of axes. The plate can be tilted in any direction (up to a tilt angle limit dictated by, e.g. the flexures and the tilt space). Therefore, an input light signal from an N×N array can be directed to any output member on the same array or on a separate NxN output array. The optically transmissive substrate is spaced apart from a device substrate so that the mirror plate is between the optically transmissive and device substrates. Electrically conductive electrodes are formed on the device substrate opposite the mirror plate. The optically transmissive substrate can be fully or substantially transparent.
The mirror plate can be tilted in any direction, up to the tilt angle limit. The mirror is tilted to various angles by creating an electrostatic attractive force between the mirror plate and one or more selected electrodes. In addition, the mirror plate can be pulled away from the optically transmissive substrate by creating an electrostatic attractive force between the mirror plate and all electrodes. The electrodes can be formed in an array having various configurations. The electrodes in some electrode array embodiments receive analog (continuously variable) electric signals. The electrodes in other electrode array embodiments receive electric signals that are associated with one of two binary logic states.
The direction towards a target of the reflected portion of a light beam that is incident on the mirror plate is monitored and adjusted in various ways. In one embodiment the reflected portion of the beam is passed through a beam splitter. One split beam portion continues towards the target (e.g., output fiber) while another split beam portion is incident on a photodetector array. The position of the beam portion that is incident on the photodetector array correlates to the direction of the beam portion directed towards the target. An adjustment circuit uses information from the photodetector array to correct the direction of the beam portion that is traveling towards the target by adjusting the amount of charge on the electrodes under the mirror plate. In another embodiment, a second light source shines light
Heureux Peter J.
Huibers Andrew G.
Stockton John K.
Epps Georgia
Lucas Michael A.
Muir Gregory R.
Reflectivity, Inc.
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