Title: Micro-actuator utilizing electrostatic and Lorentz forces, and micro-actuator device, optical switch and optical switch array using the same
Abstract: The movable part 21 is fastened to the substrate 11 via flexure parts 27a and 27b, and can move upward and downward with respect to the substrate 11. The substrate 11 also serves as a fixed electrode. The movable part 21 has second electrode parts 23a and 23b which can generate an electrostatic force between these electrode parts and the substrate 11 by means of a voltage that is applied across these electrode parts and the substrate 11, and a current path 25 which is disposed in a magnetic field, and which generates a Lorentz force when a current is passed through this current path. A mirror 12 which advances into and withdraws from the light path is disposed on the movable part 21. As a result, the mobility range of the movable part can be broadened, and the power consumption can be reduced, without applying a high voltage or sacrificing small size.
Patent Number: 6,936,950 Issued on 08/30/2005 to Akagawa, et al.
| Inventors:
|
Akagawa; Keiichi (Kamakura, JP);
Suzuki; Junji (Hachioji, JP);
Ishizuya; Tohru (Tokyo, JP);
Suzuki; Yoshihiko (Funabashi, JP)
|
| Assignee:
|
Nikon Corporation (Tokyo, JP)
|
| Appl. No.:
|
792427 |
| Filed:
|
March 2, 2004 |
Foreign Application Priority Data
| Sep 17, 2001[JP] | 2001-282421 |
| Dec 03, 2001[JP] | 2001-368060 |
| Current U.S. Class: |
310/309; 385/18; 359/223 |
| Intern'l Class: |
H02N 001/00; G02B 026/08; G02B 026/10 |
| Field of Search: |
310/309
385/16-18
359/222-224
251/65,129.05,129.01
|
References Cited [Referenced By]
U.S. Patent Documents
| 5322258 | Jun., 1994 | Bosch et al.
| |
| 6198565 | Mar., 2001 | Iseki et al.
| |
| 6381381 | Apr., 2002 | Takeda et al.
| |
| 6658177 | Dec., 2003 | Chertkow.
| |
| Foreign Patent Documents |
| 05-253870 | Oct., 1993 | JP.
| |
| 08-088984 | Apr., 1996 | JP.
| |
| 2001/-042233 | Feb., 2001 | JP.
| |
| 2001/-076605 | Mar., 2001 | JP.
| |
| 03/024864 | Mar., 2003 | WO.
| |
Primary Examiner: Tamai; Karl
Attorney, Agent or Firm: Frishauf, Holtz, Goodman & Chick, P.C.
Parent Case Text
The present application is a continuation of PCT International Application No.
PCT/JP02/09023 filed Sep. 5, 2002, which is hereby incorporated by reference.
Claims
1. A microactuator comprising:
a fixed part including a first electrode part;
a movable part which is movably disposed with respect to the fixed part, and
which includes a second electrode part such that an electrostatic force is generated
between the second electrode part and the first electrode part when a voltage is
applied across the first electrode part and the second electrode part; and
a current path which is disposed in a magnetic field, and which is separated
and electrically insulated from the second electrode part;
wherein a Lorentz force is generated when current is passed through the current
path.
2. The microactuator according to claim 1, wherein the movable part comprises
a thin film.
3. The microactuator according to claim 1, wherein the current path is positioned
such that the Lorentz force is generated in a direction that causes the movable
part to move into a first position where the electrostatic force is increased.
4. The microactuator according to claim 3, wherein the movable part is movable
between the first position and a second position in which the electrostatic force
decreases or disappears; and
wherein a returning force which urges the movable part to the second position
is generated when the movable part is displaced from the second position.
5. The microactuator according to claim 4, wherein the first electrode part and
the second electrode part face each other;
wherein the movable part is mechanically connected to the fixed part via a spring
part, and a gap between the first electrode part and the second electrode part
is narrower in the first position than in the second position; and
wherein the returning force is generated by the spring part.
6. A microactuator device comprising:
the microactuator according to claim 1;
a magnetic field generating part that generates the magnetic field; and
a control part that controls the voltage that is applied across the first electrode
part and the second electrode part and the current that flows through the current
path.
7. The microactuator device according to claim 6, wherein the control part controls
the voltage and the current such that:
the movable part is caused to move into the first position by at least one of
the Lorentz force and the electrostatic force;
the movable part is held in the first position by the electrostatic force; and
current does not flow during at least a steady holding state in which the movable
part is held in the first position.
8. An optical switch comprising:
the microactuator according to claim 1; and
a mirror which is disposed on the movable part.
9. An optical switch array comprising a plurality of the optical switches according
to claim 8;
wherein the plurality of optical switches are disposed in a two-dimensional configuration.
10. The optical switch array according to claim 9, further comprising a circuit
which includes a plurality of switching elements, and wherein said circuit controls
the currant and the voltage for respective rows and columns of the optical switches
in response to row selection signals and column selection signals for each row
and column of the plurality of optical switches.
11. A microactuator comprising:
a fixed part including a first electrode part;
a movable part which is movably disposed with respect to the fixed part, and
which includes a second electrode part such that a first electrostatic force is
generated between the second electrode part and the first electrode part when a
first voltage is applied across the first electrode part and the second electrode
part; and
a current path which is disposed in a magnetic field, and which is separated
and electrically insulated from the second electrode part;
wherein a Lorentz force is generated when current is passed through the current
path; and
wherein the fixed part includes a third electrode part, and the movable part
includes a fourth electrode part, and wherein a second electrostatic force is generated
between the fourth electrode part and the third electrode part when a second voltage
is applied across the fourth electrode part and the third electrode part.
12. The microactuator according to claim 11, wherein the second electrode part
comprises the fourth electrode part.
13. The microactuator according to claim 11, wherein the current path is positioned
such that the Lorentz force is adapted to be generated in respective directions
to move the movable part into: (i) a first position where the first electrostatic
is increased, and the second electrostatic force decreases or disappears, and (ii)
a second position where the first electrostatic force decreases or disappears,
end the second electrostatic force is increased.
14. The microactuator according to claim 13, wherein a returning force is generated
which urges the movable part toward a neutral position between the first position
and the second position, when the movable part is displaced from the neutral position.
15. The microactuator according to claim 14, wherein:
the first electrode part is provided on a first side of the movable part to face
the second electrode part;
the third electrode part is provided on a second side of the movable part to
face the fourth electrode part;
the movable part is mechanically connected to the fixed part via a spring part,
a first gap between the first electrode part and the second electrode part narrows
and a second gap between the third electrode part and the fourth electrode part
widens when the movable part is moved to the first position, and the first gap
widens and the second gap narrows when the movable part is moved to the second
position, and
the returning force is generated by the spring part.
16. A microactuator device comprising:
the microactuator according to claim 11;
a magnetic field generating part that generates the magnetic field; and
a control part that controls the first voltage, the second voltage, and the current
that flows through the current path.
17. The microactuator device according to claim 16, wherein the control part
controls the first voltage, the second voltage, and the current such that:
the movable part is caused to move into the first position by at least one of
the Lorentz force and the first electrostatic force, and the movable part is caused
to move into the second position by at least one of the Lorentz force and the second
electrostatic force;
the movable part is held in the first position by the first electrostatic force,
and the movable part in the second position by the second electrostatic force;
and
the current does not flow during at least a first steady holding state in which
the movable part is held in the first position, and a second steady holding state
in which the movable part is held in the second position.
Description
TECHNICAL FIELD
The present invention relates to a microactuator, a microactuator device, an
optical switch and an optical switch array.
BACKGROUND ART
As advances have been made in micro-machining techniques, the need for microactuators
has increased in various fields. Optical switches which switch light paths utilized
in optical communications, etc., may be cited as one example of a field in which
microactuators are used. For instance, the optical switch disclosed in Japanese
Patent Application Kokai No. 2001-42233 may be cited as one example of such an
optical switch.
Microactuators generally have a fixed part, and a movable part that
can be moved by a specified force, and are held in a specified position by the
above-mentioned specified force. In conventional microactuators, an electrostatic
force is often used as the above-mentioned specified force. For example, in the
case of the microactuator that moves a micro-mirror used in the optical switch
disclosed in Japanese Patent Application Kokai No. 2001-42233, the movable part
can be moved to an upper position (position in which the micro-mirror reflects
the incident light) or a lower position (position in which the micro-mirror allows
the incident light to pass through "as is"), and can be held in these positions,
by an electrostatic force.
In such microactuators that utilize an electrostatic force, a first electrode
part is disposed on the fixed part, a second electrode part is disposed on the
movable part, and an electrostatic force is generated between the first and second
electrode parts by applying a voltage across these electrode parts.
However, in the case of conventional microactuators using an electrostatic
force as described above, the movable part is moved by an electrostatic force and
held in a specified position by an electrostatic force; accordingly, it is difficult
to broaden the range of mobility of the movable part.
The electrostatic force F1 that acts between parallel flat-plate electrodes
is as shown in the following Equation (1), where ε is the dielectric constant,
V is the potential difference, d is the inter-electrode distance, and S is the
electrode surface area.
As is seen from Equation (1), the electrostatic force F1 decreases abruptly
in inverse proportion to the square of the inter-electrode distance d as the inter-electrode
distance d increases. Accordingly, in the case of the above-mentioned conventional
microactuators, it becomes difficult to move the movable part when the inter-electrode
distance d exceeds a certain distance, so that it is difficult to broaden the mobility
range of the movable part. Furthermore, if the potential difference (voltage across
the electrodes) V is increased in an attempt to obtain a sufficient electrostatic
force F1 in the case of a large inter-electrode distance d, problems occur
in terms of the dielectric strength, and a high-voltage generating part is required.
Furthermore, if the electrode surface area S is increased in an attempt to obtain
a sufficient electrostatic force F1 in the case of a large inter-electrode
distance d, the dimensions of the device are increased, so that miniaturization,
which is the whole idea of a microactuator, is lost.
According, as a result of research, the present inventor conceived of
the use of Lorentz force instead of electrostatic force in a microactuator.
It is known that the Lorentz force F2 (N) is as shown in the following
Equation (2), where B is the magnetic flux density (T), L is the length of the
electric wire (m), and I is the current (A).
Since there is no term that stipulates the position of the electric wire in
Equation (2), the Lorentz force F2 that is generated at a constant magnetic
flux density does not vary even if the position of the electric wire changes.
The Lorentz force can be caused to act on the movable part in a microactuator
by installed a current path corresponding to the above-mentioned electric wire
in the movable part, applying a magnetic field to this current path, and causing
a current to flow through this current path. Even if the mobility range of the
movable part is broadened compared to that of a conventional device, the application
of a substantially uniform magnetic field in this range can easily be accomplished,
for example, by using a magnet or the like. Accordingly, even if the mobility range
of the movable part is broadened, a constant force can be caused to act on the
movable part regardless of the position of the movable part. Specifically, if such
a Lorentz force is used instead of an electrostatic force in a microactuator, a
constant driving force can be obtained (in principle) regardless of the position
of the movable part (unlike a case in which an electrostatic force which shows
a variation in the driving force according to the position of the movable part
is used).
For example, in the case of an inter-electrode distance of 50 μm, an electrode
shape of 50 μm square, a voltage of 5 V and a dielectric constant of 1, the
electrostatic force F1 according to the above-mentioned Equation (1) is
0.1 nN. On the other hand, if a current path with a length of 50 μm is created
in a 50 μm square electrode, and a magnetic field with a magnetic flux density
of 0.1 T is applied, a Lorentz force of 5 nN is generated when a current of 1 mA
is caused to flow. In order to obtain a force of 5 nN or greater using an electrostatic
force, the inter-electrode distance must be set at 7 μm or less, or else
the electrode shape must be set at 350 μm or greater. Accordingly, it is
seen that the Lorentz force is more advantageous for obtaining the same driving force.
Furthermore, for example, if a 20 mm square neodymium-iron-boron-type
magnet is disposed in a position that is separated from the microactuator by a
distance of 2 mm, a magnetic flux density of 0.1 T can easily be obtained.
Thus, the use of a Lorentz force instead of an electrostatic force in a microactuator
makes it possible to broaden the mobility range of the movable part without applying
a high voltage or sacrificing small size.
However, it has been demonstrated that a new problem arises in cases where
a Lorentz force is used instead of an electrostatic force in a microactuator. Specifically,
in cases where a Lorentz force is used instead of an electrostatic force, the movable
part is moved to a specified position by means of this Lorentz force, and the movable
part continues to be held in this position by the Lorentz force. Accordingly, since
the current used to generate the Lorentz force must be constantly caused to flow
in a continuous manner, the power consumption is conspicuously increased.
For instance, in the case of an application involving a large-scale optical switch,
several tens of thousands of actuators are installed in a single optical switch
device. Accordingly, there is a strong demand for a reduction in the power consumption
of the respective actuators. For example, in the case of an optical switch with
100×100 channels, it is essential that (for example) MOS switches for selecting
the channels be manufactured on a semiconductor substrate. Assuming that the resistance
of one MOS switch is 10 kΩ, then in a case where a current of 1 mA is caused
to flow continuously through this switch, the power consumption of one MOS switch
is 10 mW. In a case where the total number of MOS switches is 10,000, the power
consumption is as high as 100 W. As a result, the amount of heat generated is excessively
large, so that there are problems in terms of practical use.
DISCLOSURE OF THE INVENTION
The present invention was devised in order to solve such problems. The object
of the present invention is to provide a microactuator, microactuator device, optical
switch and optical switch array which can broaden the mobility range of the movable
part and reduce the power consumption without applying a high voltage or sacrificing
small size.
As a result of further research, the present inventor discovered that the above-mentioned
object can be achieved by constructing a microactuator so that the utilization
of an electrostatic force and the utilization of a Lorentz force can be coupled.
Specifically, the present inventor discovered that the above-mentioned object can
be achieved in a microactuator which comprises a fixed part and a movable part
that is disposed so that this movable part can move with respect to the above-mentioned
fixed part, by respectively disposing on the fixed part and movable part electrode
parts which are used in order to make it possible to cause an electrostatic force
to act on the movable part, and disposing in the movable part a current path which
is used to cause a Lorentz force to act on the movable part.
By using such means, for example, it is possible to move the movable part by
means
of a Lorentz force alone in cases where the distance between the electrode part
of the movable part and the electrode part of the fixed part is large, and to hold
the movable part by means of an electrostatic force alone in cases where the distance
between the electrode part of the movable part and the electrode part of the fixed
part is decreased. As a result, the mobility range of the movable part can be broadened,
and the power consumption can be reduced, without applying a high voltage or sacrificing
small size.
In the case of driving by an electrostatic force, since the charging-discharging
of a capacitor is performed electrically, power consumption occurs only during
charging and discharging, i.e., at points in time at which there is a change in
the voltage. Accordingly, in cases where the movable part does not move frequently,
so that the period for which the movable part is held in a specified position (a
position which is such that the distance between the electrode part of the fixed
part and the electrode part of the movable part is small) is relatively long, as
in a microactuator used in an optical switch, etc., the power consumption can be
greatly reduced if the force that is used to hold the movable part in the specified
position is generated only by an electrostatic force. For example, in a case where
the inter-electrode capacitance is 10 pF, the voltage is 5 V and the movement of
the movable part occurs once per minute, the power consumption of electrostatic
driving is 4.2 pW. In a case where the number of such microactuators used is 10,000,
the total power consumption of electrostatic driving is 42 nW. Furthermore, in
the case of a position where the distance between the electrode part of the fixed
part and the electrode part of the movable part is small, an electrostatic force
of a sufficient magnitude can be obtained even if the voltage across the two electrode
parts is relatively low and the electrode surface area is relatively small.
In the case of driving by a Lorentz force, a constant driving force can be obtained
regardless of the position of the movable part; accordingly, if the movable part
is moved by means of such a Lorentz force, the mobility range can be broadened.
The power consumption of such a Lorentz force is as follows: for example, assuming
that the resistance of the on-chip MOS switches for selecting the channels is 10
kΩ as in the example described above, then, in a case where a current of
1 mA is caused to flow through this MOS switch for 10 msec each minute (corresponding
to the movement period of the movable part), the power consumption of Lorentz force
driving is 1.7 μW. In a case where the number of microactuators is 10,000,
the total power consumption of Lorentz force driving is 17 mW, so that the power
consumption is greatly reduced compared to the power consumption of 100 W that
occurs in the case of the above-mentioned constant Lorentz force driving. Almost
all of the total power consumption is accounted for by the Lorentz force; however,
this is not a major problem in practical terms.
Thus, by mounting both a device that generates an electrostatic force and a
device that generates a Lorentz force in a microactuator, it is possible (for example)
to reduce the power consumption by generating the force that is used to hold the
movable part in a specified position by means of an electrostatic force, and to
drive the microactuator by means of a Lorentz force in cases where the gap between
the movable electrode and the fixed electrode is large, so that the mobility range
can be broadened while preventing the application of a high voltage and an increase
in the electrode surface area.
The present invention was devised on the basis of the novel findings obtained
as a result of the above-mentioned research conducted by the present inventor.
Specifically, the first invention that is used in order to achieve
the object is a microactuator (a) which comprises a fixed part and a movable part
that is disposed so that this movable part can move with respect to the fixed part,
(b) in which the fixed part has a first electrode part, and (c) in which the movable
part has a second electrode part that can generate an electrostatic force between
this second electrode part and the first electrode part by means of a voltage applied
across the first electrode part and this second electrode part, and a current path
that is disposed in a magnetic field and that generates a Lorentz force when current
is passed through this current path.
The second invention that is used in order to achieve the object is the first
invention, which is further characterized by the fact that the movable part is
constructed from a thin film.
In this invention, since the movable part is formed by a thin film, the size
and
weight of the movable part can be reduced, and the power consumption can be reduced.
Furthermore, since the movable part can be manufactured by a semiconductor process,
the manufacturing cost can be reduced, and the formation of an array is easy.
The third invention that is used in order to achieve the object is the first
invention or second invention, which is further characterized by the fact that
the current path is disposed so that a Lorentz force can be generated in a direction
that causes the movable part to move into a first position where the electrostatic
force is increased.
In this invention, since the Lorentz force that is required in order to move
the
movable part into a position where the movable part is held can be efficiently
applied, the power consumption for generating this Lorentz force can be reduced.
The fourth invention that is used in order to achieve the object is the third
invention, which is further characterized by the fact that the movable part is
disposed so that this movable part can move between the first position and a second
position in which the electrostatic force drops or disappears, and so that a returning
force which tends to return the movable part to the second position is generated.
In this invention, the movable part can move to a position that is not reached
by the electrostatic force; accordingly, the mobility range of the movable part
can be broadened. Furthermore, since the movable part is moved by the returning
force when the movable part moves into the second position, no electric power is
required for this movement.
The fifth invention that is used in order to achieve the object is the fourth
invention, which is further characterized by the fact that (a) the first electrode
part and the second electrode part are disposed facing each other, (b) the movable
part is mechanically connected to the fixed part via a spring part that possesses
spring properties so that the gap between the first and second electrode parts
narrows when the movable part is positioned in the first position, and so that
the gap widens when the movable part is positioned in the second position, and
(c) the returning force is generated by the spring part.
In this invention as well, the movable part can move to a position that is not
reached by the electrostatic force; accordingly, the mobility range of the movable
part can be broadened. Furthermore, since the movable part is moved by the returning
force when the movable part moves into the second position, no electric power is
required for this movement.
The sixth invention that is used in order to achieve the object is the first
invention or second invention, wherein the fixed part has a third electrode part,
and the movable part has a fourth electrode part that can generate an electrostatic
force between this fourth electrode part and the third electrode part by means
of a voltage applied across this fourth electrode part and the third electrode part.
In this invention, the mobility range of the movable part can be further broadened.
The seventh invention that is used to achieve the object is the sixth invention,
which is further characterized by the fact that the second electrode part is also
used as the fourth electrode part.
In this invention, since the construction is simple, the weight of the movable
part can be reduced; furthermore, since the number of manufacturing processes required
is also reduced, the manufacturing cost can be reduced.
The eighth invention that is used to achieve the object is the sixth invention
or seventh invention, which is further characterized by the fact that the current
path is disposed so that a Lorentz force can be generated in respective directions
which are such that the movable part is respectively moved into a first position
where the electrostatic force that is generated between the first and second electrode
parts is increased, and the electrostatic force that is generated between the third
and fourth electrode parts drops or disappears, and a second position where the
electrostatic force that is generated between the first and second electrode parts
drops or disappears, and the electrostatic force that is generated between the
third and fourth electrode parts increases.
In this invention, since the Lorentz force that is required in order to move
the
movable part into a position where the movable part is held can be efficiently
applied, the power consumption that is required in order to generate this Lorentz
force can be reduced.
The ninth invention that is used in order to achieve the object is the eighth
invention, which is further characterized by the fact that the movable part is
disposed so that a returning force that tends to return the movable part to a specified
position between the first and second positions is generated.
In this invention, since the movable part is moved by the returning force when
the movable part moves into the specified position, no electric power is required
for this movement.
The tenth invention that is used in order to achieve the object is the ninth
invention, which is further characterized by the fact that (a) the first electrode
part is disposed facing the second electrode part on one side with respect to the
movable part, (b) the third electrode part is disposed facing the fourth electrode
part on the other side with respect to the movable part, (c) the movable part is
mechanically connected to the fixed part via a spring part that possesses spring
properties so that a first gap between the first and second electrode parts narrows
and a second gap between the third and fourth electrode parts widens when the movable
part is positioned in the first position, and so that the first gap widens and
the second gap narrows when the movable part is positioned in the second position,
and (d) the returning force is generated by the spring part.
In this invention as well, since the movable part is moved by the returning force
when the movable part moves into the specified position, no electric power is required
for this movement.
The eleventh invention that is used in order to achieve the object is a microactuator
device which is characterized by the fact that this device comprises the microactuator
of any of the first through fifth inventions, a magnetic field generating part
that generates the magnetic field, and a control part that controls the voltage
that is applied across the first and second electrode parts and the current that
flows through the current path.
In this invention, the magnitude of the Lorentz force and the timing of the generation
of this Lorentz force can be controlled; accordingly, the microactuator can be
driven under appropriate conditions.
The twelfth invention that is used in order to achieve the object is the eleventh
invention, which is further characterized by the fact that (a) the control part
controls the voltage and the current so that the movable part is caused to move
into the first position by the Lorentz force or by the Lorentz force and the electrostatic
force when the movable part is moved into the first position, and (b) the control
part controls the voltage so that the movable part is held in the first position
by the electrostatic force, and controls the current so that this current does
not flow, at least in a steady holding state in which the movable part is held
in the first position.
In this invention, electric power that is used to generate the Lorentz force
is
required only when the movable part is moved into the first position; since only
an electrostatic force is utilized in order to hold the movable part in the first
position, the power consumption required for holding can be reduced.
The thirteenth invention that is used in order to achieve the object is a microactuator
device which is characterized by the fact that this device comprises the microactuator
of any of the sixth through tenth inventions, a magnetic field generating part
that generates the magnetic field, and a control part that controls the voltage
that is applied across the first and second electrode parts, the voltage that is
applied across the third and fourth electrode parts, and the current that flows
through the current path.
In this invention, the magnitude of the Lorentz force and the timing of the generation
of this Lorentz force can be controlled; accordingly, the microactuator can be
driven under appropriate conditions.
The fourteenth invention that is used in order to achieve the object is the thirteenth
invention, which is further characterized by the fact that (a) the control part
controls the voltage that is applied across the first and second electrode parts,
the voltage that is applied across the third and fourth electrode parts and the
current that flows through the current path so that the movable part is caused
to move into the first position by the Lorentz force or by the Lorentz force and
the electrostatic force between the first and second electrode parts when the movable
part is moved into the first position, (b) the control part controls the voltage
that is applied across the first and second electrode parts, the voltage that is
applied across the third and fourth electrode parts and the current that flows
through the current path so that the movable part is caused to move into the second
position by the Lorentz force or by the Lorentz force and the electrostatic force
between the third and fourth electrode parts when the movable part is moved into
the second position, (c) the control part controls the voltage that is applied
across the first and second electrode parts and the voltage that is applied across
the third and fourth electrode parts so that the movable part is held in the first
position by the electrostatic force between the first and second electrode parts,
and controls the current so that this current does not flow, at least in a steady
holding state in which the movable part is held in the first position, and (d)
the control part controls the voltage that is applied across the first and second
electrode parts and the voltage that is applied across the third and fourth electrode
parts so that the movable part is held in the second position by the electrostatic
force between the third and fourth electrode parts, and controls the current so
that this current does not flow, at least in a steady holding state in which the
movable part is held in the second position.
In this invention, electric power that is used to generate the Lorentz force
is
required only when the movable part is moved into the first position; since only
an electrostatic force is utilized in order to hold the movable part in the first
position, the power consumption required for holding can be reduced.
The fifteenth invention that is used in order to achieve the object is an optical
switch which is characterized by the fact that this optical switch comprises the
microactuator of any of the first through tenth inventions, and a mirror which
is disposed on the movable part.
The sixteenth invention that is used in order to achieve the object is an optical
switch array which is characterized by the fact that this optical switch array
comprises a plurality of the optical switches that constitute the fifteenth invention,
and said plurality of optical switches are disposed in a two-dimensional configuration.
The seventeenth invention that is used in order to achieve the object is the
sixteenth invention, which is further characterized by the fact that this optical
switch array comprises a circuit which contains a plurality of switching elements,
and which controls the current and the voltage for optical switches in selected
rows and columns in response to row selection signals for each row of the plurality
of optical switches and column selection signals for each column of the plurality
of optical switches.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic structural diagram which shows one example of an optical
switch system comprising an optical switch array that constitutes a first working
configuration of the present invention.
FIG. 2 is a schematic plan view which shows one of the optical switches constituting
the optical switch array shown in FIG. 1.
FIG. 3 is a schematic sectional view along line X1-X2 in FIG. 2.
FIG. 4 is a schematic sectional view along line Y1-Y2 in FIG. 2.
FIG. 5 is a schematic sectional view corresponding to FIG. 3.
FIG. 6 is a timing chart which shows the relationship (varying over time) of
the current used for the Lorentz force, the voltage used for the electrostatic
force and the position of the mirror in one of the optical switches constituting
the optical switch array shown in FIG. 1.
FIG. 7 is an electrical circuit diagram which shows the optical switch array
shown in FIG. 1.
FIG. 8 is a timing chart which shows the signals that are supplied to the respective
terminals in FIG. 7.
FIG. 9 is a schematic sectional view which shows in model form the respective
processes of the optical switch array shown in FIG. 1.
FIG. 10 is a schematic sectional view which shows in model form other respective
processes of the optical switch array shown in FIG. 1.
FIG. 11 is a schematic plan view which shows one of the optical switches constituting
an optical switch array that constitutes a second working configuration of the
present invention.
FIG. 12 is a schematic sectional view along line X3-X4 in FIG. 11.
FIG. 13 is a schematic sectional view along line Y3-Y4 in FIG. 11.
FIG. 14 is a schematic sectional view corresponding to FIG. 12.
FIG. 15 is another schematic sectional view corresponding to FIG. 12.
FIG. 16 is a timing chart which shows the relationship (varying over time) of
the current used for the Lorentz force, the voltage used for the electrostatic
force and the position of the mirror in one of the optical switches shown in FIG. 11.
FIG. 17 is an electrical circuit diagram which shows the optical switch array
constituting a second working configuration of the present invention.
FIG. 18 is a timing chart which shows the signals that are supplied to the respective
terminals in FIG. 17.
BEST MODE FOR CARRYING OUT THE INVENTION
Microactuators constituting working configurations of the present
invention, as well as microactuator devices, optical switches and optical switch
arrays using these microactuators, will be described below with reference to the figures.
First Working Configuration
FIG. 1 is a schematic structural diagram which shows one example of an optical
switch system comprising an optical switch array
1 that constitutes a first
working configuration of the present invention. For convenience of description,
X, Y and Z axes that are mutually perpendicular are defined as shown in FIG. 1
(the same is true of figures described later). The surface of the substrate
11
of the optical switch array
1 is parallel to the XY plane. Furthermore,
for convenience of description, the + side in the direction of the Z axis is referred
to as the upper side, and the - side in the direction of the Z axis is referred
to as the lower side.
As is shown in FIG. 1, this optical switch system comprises an optical switch
array
1, M optical fibers
2 used for light input, M optical fibers
3 used for light output, N optical fibers
4 used for light output,
a magnet
5 used as a magnetic field generating part that generates a magnetic
field (as will be described later) for the optical switch array
1, and an
external control circuit
6 which sends control signals used to realize light
path switching states indicated by light path switching state command signals to
the optical switch array
1 in response to these light path switching state
command signals. In the example shown in FIG. 1, M=3 and N=3; however, M and N
may respectively be arbitrary numbers.
In the present working configuration, as is shown in FIG. 1, the magnet
5
is a plate-form permanent magnet which is magnetized so that the + side in the
direction of the Y axis is the N pole, and the - side in the direction of the Y
axis is the S pole. This magnet
5 is disposed on the underside of the optical
switch array
1, and generates a magnetic field indicated by the lines of
magnetic force
5a for the optical switch array
1. Specifically,
the magnet
5 generates a substantially uniform magnetic field which is oriented
toward the - side along the direction of the Y axis with respect to the optical
switch array
1. Of course, it would also be possible to use (for example)
a permanent magnet of some other shape or an electromagnet, etc., as the magnetic
field generating part instead of the magnet
5.
As is shown in FIG. 1, the optical switch array
1 comprises a substrate
11 and M×N mirrors
12 which are disposed on the substrate
11.
The M optical fibers
2 used for light input are disposed in a plane parallel
to the XY plane so that these optical fibers guide incident light in the direction
of the X axis from one side of the substrate
11 in the direction of the
X axis. The M optical fibers
3 used for light output are disposed on the
other side of the substrate
11 so that these optical fibers respectively
face the M optical fibers
2 used for light input, and are disposed in a
plane parallel to the XY plane so that light that advances in the direction of
the X axis without being reflected by any of the mirrors
12 of the optical
switch array
1 is incident on these optical fibers. The N optical fibers
4 used for light output are disposed in a plane parallel to the XY plane
so that light that is reflected by any of the mirrors
12 of the optical
switch array
1 and that therefore advances in the direction of the Y axis
is incident on these optical fibers. The M×N mirrors
12 are disposed
on the substrate
11 in the form of a two-dimensional matrix so that these
mirrors can be moved rectilinearly in the direction of the Z axis by microactuators
(described later) in a manner that allows the mirrors to advance into and withdraw
from the respective intersection points between the exit light paths of the M optical
fibers
2 used for light input and the entry light paths of the optical fibers
4 used for light output. In the present example, furthermore, the orientation
of the mirrors
12 is set so that the normal of these mirrors forms a 45°
angle with the X axis in the plane parallel to the XY plane. Of course, this angle
may be appropriately altered, and in cases where the angle of the mirrors
12
is altered, the orientation of the optical fibers
4 used for light output
may be set in accordance with this angle. Furthermore, in this example, the mechanism
that drives the mirrors
12 is a microactuator.
In this optical switch system, the light path switching principle itself is the
same as the light path switching principle of a conventional two-dimensional optical switch.
Next, the structure of one of the optical switches used as a unit element in
the optical switch array
1 shown in FIG. 1 will be described with reference
to FIGS. 2 through 5. FIG. 2 is a schematic plan view which shows one optical switch.
FIG. 3 is a schematic sectional view along line X
1-X
2 in FIG.
2.
FIG. 4 is a schematic sectional view along line Y
1-Y
2 in FIG.
2.
FIG. 5 is a schematic sectional view corresponding to FIG. 3, and shows a state
in which the mirror
12 is held on the lower side. Furthermore, FIG. 3 shows
a state in which the mirror
12 is held on the upper side.
Besides the above-mentioned mirror
12 and the above-mentioned substrate
11 used as a fixed part, this optical switch comprises a movable plate
21
used as a movable part which is disposed so that this part can move with respect
to the substrate
11. A recessed part
13 constituting a region into
which the movable plate
21 advances is formed on the substrate
11.
In the present working configuration, a semiconductor substrate such as a silicon
substrate is used as the substrate
11, and the portion of the substrate
11 that faces the movable plate
21 constitutes a first electrode
part. Of course, it would also be possible to form a first electrode part separately
from the substrate
11 by means of a metal film, etc., on the substrate
11.
The movable plate
21 is formed by a thin film, and comprises a lower-side
insulating film
22, two second electrode parts
23a and
23b
which are formed on the lower-side insulating film
22, portions of wiring
patterns
24a and
24b which are formed on the lower-side
insulating film
22 and which are respectively used for the electrical connection
of the electrode parts
23a and
23b to specified locations
on the substrate
11, a coil layer
25 which is formed on the lower-side
insulating film
22 and which is used as a current path that is disposed
in the magnetic field generated by the magnet
5 shown in FIG.
1 and
that generates a Lorentz force when a current is passed through this coil layer,
and an upper-side insulating film
26 which covers the upper sides of the
above-mentioned elements. The second electrode parts
23a and
23b
can generate an electrostatic force between these electrode parts
23a
and
23b and the substrate
11 (which constitutes the above-mentioned
first electrode part) by means of a voltage that is applied across these electrode
parts and the substrate
11.
For example, SiN films or SiO
2 films, etc., can be used as the insulating
films
22 and
26. Furthermore, for example, metal films, etc., such
as Al films can be used as the electrode parts
23a and
23b,
wiring patterns
24a and
24b and coil layer
25.
Furthermore, since the electrode parts
23a and
23b, portions
of the wiring patterns
24a and
24b and coil layer
25
are covered by the upper-side insulating film
26, these parts should actually
be shown by hidden lines in FIG. 2; however, for convenience of graphic illustration,
the parts hidden by the upper-side insulating film
26 are also indicated
by solid lines. However, the portion of the coil layer
25 that is hidden
by the mirror
12 is indicated by hidden lines.
In the present working configuration, both end portions of the movable plate
21
in the direction of the X axis are mechanically connected to the peripheral parts
of the recessed part
13 in the substrate
11 via flexure parts
27a
and
27b used as spring parts that have spring properties, and
anchoring parts
28a and
28b, in that order. The flexure
parts
27a and
27b and anchoring parts
28a
and
28b are constructed by the lower-side insulating film
22,
the remaining portions of the above-described wiring patterns
24a and
24b, wiring patterns
29a and
29b that
are respectively used for the electrical connection of the coil layer
25
to specified locations on the substrate
11, and the upper-side insulating
film
26, all of which extend "as is" as continuations of the movable plate
21. Furthermore, the wiring patterns
29a and
29b
extend "as is" as continuations of the metal film, etc., constituting the coil
layer
25. In the anchoring parts
28a and
28b, the
wiring patterns
24a, 24b, 29a and
29b
are respectively electrically connected to specified locations on the substrate
11 via holes (not shown in the figures) formed in the lower-side insulating
film
22. The wiring patterns
24a and
24b are
electrically connected in common by wiring (not shown in the figures) formed on
the substrate
11.
As is shown in FIG. 2, the flexure parts
27a and
27b
have
a meandering shape as seen in a plan view. As a result, the movable plate
21
can move upward and downward (in the direction of the Z axis). Specifically, in
the present working configuration, the movable plate
21 can move between
an upper position (second position) (see FIGS. 3 and 4) to which the movable plate
21 is returned by spring force (returning force) of the flexure parts
27a
and
27b when no electrostatic force or Lorentz force is acting
on the movable plate
21, and a lower position (first position) (see FIG.
5) in which the movable plate
21 advances into the recessed part
13
of the substrate
11 and contacts the bottom part of this recessed part
13.
In the upper position shown in FIGS. 3 and 4, the gap between the second electrode
parts
23a and
23b of the movable plate
21 and
the substrate
11 used as the first electrode part is widened, so that the
electrostatic force that can be generated between these parts drops or disappears.
In the lower position shown in FIG. 5, the gap between the second electrode parts
23a and
23b of the movable plate
21 and the
substrate
11 used as the first electrode part is narrowed, so that the electrostatic
force that can be generated between these parts is increased.
The coil layer
25 is disposed so that a Lorentz force can be generated
in a direction (downward direction) that causes the movable plate
21 to
move into the lower position shown in FIG. 5, where the above-mentioned electrostatic
force is increased. In concrete terms, in the present working configuration, since
a magnetic field which is oriented toward the - side is generated along the direction
of the Y axis by the magnet
5 shown in FIG. 1 as described above, the coil
layer
25 is disposed so that this layer extends along the direction of the
X axis as shown in FIG.
1.
The mirror
12 is fastened to the upper surface of the movable plate
21
in an upright attitude. As was described above, the orientation of the reflective
surface of the mirror
12 is set so that the normal of this reflective surface
forms an angle of 45° with the X axis in the plane parallel to the XY plane.
A microactuator which drives the mirror
12 is formed by the constituent
elements other than the mirror
12 in the structure of the above-mentioned
optical switch.
Next, one example of the control method used, and the operation of the optical
switch accomplished by this control method, will be described with reference to
FIG. 6, with a focus on a single optical switch. FIG. 6 is a timing chart which
shows the relationship (varying over time) of the current that flows through the
coil layer
25 of one optical switch and gives rise to a Lorentz force (hereafter
referred to as the "current used for the Lorentz force"), the voltage that is applied
across the first electrode part (substrate
11) of this optical switch and
the second electrode parts
23a and
23b of the movable
plate
21, and that gives rise to an electrostatic force between these parts
(hereafter referred to as the "voltage used for the electrostatic force"), and
the position of the mirror
12 of this optical switch (and accordingly, the
position of the movable plate
21).
Initially, it is assumed that the current used for the Lorentz force is
zero and that the voltage used for the electrostatic force is zero, so that the
mirror
12 is held in the upper position as shown in FIGS. 3 and 4 by the
spring force of the flexure parts
27a and
27b. In this
state, as is shown in FIG. 3, the incident light is reflected by the mirror
12
and advances toward the front with respect to the plane of the page.
Afterward, at time T
1, control is initiated in order to switch
the position of the mirror
12 to the lower position shown in FIG.
5.
Specifically, at time T
1, the current used for the Lorentz force is set
at +I. Here, +I is a current that generates a downward-oriented Lorentz force in
the coil layer
25 that is stronger than the spring force of the flexure
parts
27a and
27b.
The mirror
12 is gradually lowered by this Lorentz force, and stops at
time T
2 at which the movable plate
21 contacts the substrate
11,
so that the mirror
12 is held in the lower position shown in FIG.
5.
The mirror
12 does not continue to be held in the lower position by the
Lorentz force "as is"; at time T
3, the voltage used for the electrostatic
force is set at V, and at time T
4, the current used for the Lorentz force
is reduced to zero. Here, V is a voltage that generates an electrostatic force
that is stronger than the spring force of the flexure parts
27a and
27b, at least when the mirror
12 is positioned in the lower
position. In the period T
2-T
3, the mirror
12 is held in the
lower position by the Lorentz force alone; in the period T
3-T
4, the
mirror
12 is held in the lower position by the Lorentz force and the electrostatic
force, and from time T
4 on, the mirror
12 is held in the lower position
by the electrostatic force alone. The period T
2-T
4 is a so-called
lower-side holding transition period in which the holding of the mirror
12
in the lower position is switched from the Lorentz force to the electrostatic force,
while the period from time T
4 on is a so-called steady period of lower-side holding.
During the period in which the mirror
12 is held in the lower position,
as is shown in FIG. 5, the incident light passes through "as is" without being
reflected by the mirror
12, and constitutes the emitted light.
Subsequently, at time T
5, control is initiated in order to switch
the position of the mirror
12 to the upper position shown in FIGS. 3 and
4. Specifically, at time T
5, the voltage used for the electrostatic force
is reduced to zero. As a result, the mirror
12 is returned to the upper
position shown in FIGS. 3 and 4 relatively quickly by the spring force of the flexure
parts
27a and
27b, and continues to be held in the
upper position by this spring force.
Thus, when the gap between the second electrode parts
23a and
23b of the movable plate
21 and the substrate
11 (first
electrode part) is large, the mirror
12 is moved into the lower position
against the spring force of the flexure parts
27a and
27b
by a Lorentz force whose magnitude does not depend on the position of the mirror
12 (i.e., the position of the movable plate
21). Accordingly, the
mobility range of the movable plate
21 can be broadened without applying
a high voltage or sacrificing small size in order to increase the electrostatic
force. Furthermore, in the steady state of holding in the lower position, where
the gap between the second electrode parts
23a and
23b
of the movable plate
21 and the substrate
11 (first electrode
part) narrows, the mirror
12 is held in the lower position by the electrostatic
force alone; accordingly, the power consumption can be reduced.
Furthermore, in the example described above, the voltage used for the
electrostatic force is set at V at time T
3 between time T
2 and time
T
4; however, the voltage used for the electrostatic force may be set at
V at any point in time during the period T
1-T
4, or the voltage used
for the electrostatic force may be set at V prior to time T
1. Moreover,
if the electrostatic force that is generated when the voltage used for the electrostatic
force is set at V is smaller than the spring force of the flexure parts
27a
and
27b when the movable plate
21 is positioned in the
upper position, then the voltage used for the electrostatic force may also be set
at V during the upper-side holding period after the movable plate
21 has
moved into the upper position following time T
5. The voltage refresh period
on the right side in the example shown in FIG. 8 (described later) corresponds
to such a case.
The optical switch array
1 shown in FIG. 1 has a plurality of optical
switches of the type shown in FIGS. 2 through 5 as the above-mentioned unit elements;
these optical switches are disposed in a two-dimensional matrix. Furthermore, the
circuit shown in FIG. 7, which contains a plurality of switching elements, is mounted
on the optical switch array
1 shown in FIG. 1 in order to realize the above-mentioned
control for each of these optical switches using a small number of control lines.
FIG. 7 is an electrical circuit diagram which shows the optical switch array
1.
In FIG. 7, nine optical switches are disposed in three rows and three columns
in order to simplify the description. Of course, there are no restrictions on these
numbers; for example, the principle is the same in a case where there are optical
switches disposed in 100 rows and 100 columns.
In terms of the electrical circuit involved, the single optical switch shown
in
FIGS. 2 through 5 may be viewed as a single capacitor (corresponding to a composite
capacitor in which a capacitor formed by the second electrode
23a and
first electrode (substrate
11) and a capacitor formed by the second electrode
23b and first electrode (substrate
11) are connected in parallel),
and a single coil (corresponding to the coil layer
25). In FIG. 7, the capacitors
and coils of the optical switches in m rows and n columns are respectively designated
as Cmn and Lmn. For example, the capacitor and coil of the optical switch at the
upper left (first row, first column) in FIG. 7 are respectively designated as C
11
and L
11.
In the circuit shown in FIG. 7, in order to reduce the number of control lines,
column selection switches Mmnb and Mmnd and row selection switches Mmna and Mmnc
are respectively provided for the capacitors Cmn and coils Lmn. One end of each
capacitor Cmn is connected to one end of the corresponding row selection switch
Mmna, the other end of this row selection switch Mmna is connected to one end of
the corresponding column selection switch Mmnb, and the other end of this column
selection switch Mmnb is connected to one end of a voltage control switch MC
1
and one end of a voltage control switch MC
2. The other end of each capacitor
Cmn is connected to ground. The other end of the voltage control switch MC
1
is connected to a clamping voltage VC, and the other end of the voltage control
switch MC
2 is connec
