Information
-
Patent Grant
-
6463186
-
Patent Number
6,463,186
-
Date Filed
Friday, October 6, 200023 years ago
-
Date Issued
Tuesday, October 8, 200221 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 385 39
- 385 27
- 385 6
- 385 16
- 385 15
- 385 53
- 385 57
- 385 40
- 385 41
- 385 12
- 385 140
- 356 450
- 356 473
-
International Classifications
-
Abstract
System and method for attenuation of light or optical switching of light, or a portion thereof, from a first optical fiber to a second optical fiber in a relatively short time interval. Two fibers are physically coupled over a length that is equal to an initial optical coupling length, where full transfer of light energy can occur from the second fiber to the first fiber. The physical coupling region of the fibers is immersed in a magnetostrictive material upon which a magnetic induction of controllable strength is impressed. When the magnetic induction is changed from a first selected value to a second selected value, optical switching or optical attenuation occurs between the fibers or in a single fiber. The optical coupling apparatus may include a Mach-Zehnder interferometer and may include first and second magnetostrictive materials in the first and second arms, respectively, of the interferometer. The magnetostrictive material(s) and/or the interferometer may be temperature-controlled to provide improved control of these components.
Description
FIELD OF THE INVENTION
This invention relates to optical switches and optical attenuators.
BACKGROUND OF THE INVENTION
In fiber optical communication systems in use today, couplers split optical signals into multiple paths or combine signals for transmission over one path. Two fibers, each considered as an optical waveguide, are pressed closely together so that energy that leaves one fiber is, for the most part, captured and used by the other (contiguous) fiber. Assuming that no energy is lost within a fiber due to Fresnel transmission through the boundary (due to absence of total internal reflection within the fiber), a small amount of optical energy can escape form the fiber in the form of an evanescent wave, which has an amplitude that decays very rapidly with increasing distance from the fiber boundary. A fiber coupler seeks to capture this evanescent wave energy emitted by a first fiber in a contiguous second fiber. Because the evanescent energy is the same fraction of the total optical energy available at a separation gap of width D
g
between the two fibers, over a characteristic optical coupling length or distance L
c
, substantially all energy from the first fiber can be coupled into the second fiber. Over a second (consecutive) characteristic distance L
c
, the energy coupled into the second fiber will return to the first fiber by the same mechanism. The coupling length L
c
varies with wavelength and with the dimensions and refractive indices of the fiber and of the ambient medium.
FIG. 1
illustrates how optical energy, initially present in a first fiber
11
, is progressively coupled into a second contiguous fiber
12
over a first distance L
c
and is then progressively coupled back into the first fiber over a second distance L
c
. In many circumstances, it is difficult to control the relative amounts of light appearing in each of the first fiber and the second fiber beyond the coupling region shown in FIG.
1
.
A single mode thermo-optic switch, disclosed recently by Photonic Integration Research, uses a modified Mach-Zehnder interferometer with equal (rather than unequal) fiber lengths between two fiber couplers that define the interferometer and provides a thin film heater adjacent to the fiber in one arm. When the heater is activated, the change in fiber temperature causes a change in refractive index of the heated fiber, which changes the effective length of the heated fiber and causes interference between light beams propagating in the two interferometer arms. The apparatus behaves as a wavelength switch for light, but with rather slow reactions, requiring switching times that are estimated to be seconds or tens of seconds.
What is needed is an approach that allows the relative amounts of light appearing in each of the first and second fibers at a selected wavelength beyond the coupling region to be controlled so that, if desired, all light appears in a selected one of the first and second fibers. Preferably, this approach should allow the relative amounts of light appearing in each fiber to be changed slowly and continuously, if desired, or to be changed abruptly. Preferably, this approach should be applicable to any wavelength within a selected range. Preferably, this approach should not require a substantial increase in the volume occupied by the apparatus vis-a-vis the volume occupied by the fibers and light source. Preferably, a reaction time for switching or attenuating light with a selected wavelength should be a small fraction of a second.
SUMMARY OF THE INVENTION
These needs are met by the invention, which provides a first approach for magnetically controlling the optical coupling length L
c
through use of a magnetostrictive (MS) material that changes its optical coupling length L
c
, its gap width D
g
and/or the refractive indices of the two fibers within the coupling length L
c
, in response to a change in strength of a magnetic induction field impressed on the material. This approach is applied to provide an optical switch or optical attenuator in which light propagating in a first optical fiber is switched on, switched off or attenuated by application of a magnetic induction of appropriate strength and orientation to the fiber.
In a second approach, a Mach-Zehnder interferometer (MZI) is provided for a pair of fibers or channels, with a first fiber, but not a second fiber, including a magnetostrictive element and the two fibers being subsequently coupled using a standard fiber coupler. An MZI includes first and second fibers extending between a first fiber coupler and a second fiber coupler, spaced apart, with the two fiber lengths between the couplers being different by a selected length difference, with the coupling coefficients preferably being 50 percent at each coupler. Light propagating in, say, the first fiber (or second fiber) may be fully transmitted, partly transmitted or blocked, depending upon the length difference, the refractive indices of the fibers and the light wavelength. When a magnetic field impressed on the magnetostrictive element is changed, transmission or blockage of light at the second coupler is changed. A second magnetostrictive element, having the same MS material or, preferably, another MS material with different characteristics, is optionally positioned in an MZI arm including the second fiber, to provide additional control over the change in refractive index and/or physical length of the first and second MS elements.
Optionally, the system used in the first approach and/or in the second approach is positioned within a temperature control module to provide improved control over the MS characteristics of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
illustrates coupling of energy between first and second contiguous fibers over two consecutive optical coupling lengths L
c
.
FIGS. 2 and 3
illustrate two embodiments using magnetostrictive activity to control the length L
c
for coupling between first and second contiguous fibers.
FIGS. 4 and 5
illustrate two embodiments using magnetostrictive activity in a modified Mach-Zehnder interferometer device to control coupling between first and second fibers.
DESCRIPTION OF BEST MODES OF THE INVENTION
FIG. 2
illustrates a first embodiment
20
of the invention, wherein a first fiber
21
and a second fiber
22
are physically coupled together in a physical coupling region
28
. An input end
21
-
1
of the first fiber
21
receives light from a light source
23
having a selected wavelength component with a selected wavelength λ. At least one of the output ends,
21
-
2
and
22
-
2
, of the first and second fibers is connected to a light application device
24
to receive light from the light source
23
. A tube
25
, which may be cylindrical, of magnetostrictive (MS) material is positioned contiguous to and surrounding the fibers,
21
and
22
, in the physical coupling region
28
to firmly press the fibers together. A coil or sequence of current carrying lines
26
-i (i=1, 2, . . . ), fed by a controllable current source
27
, is provided adjacent to the magnetostrictive tube
25
in a circumferential or transverse direction to impress a longitudinally oriented magnetic induction B with controllable induction strength on the magnetostrictive material.
A magnetostrictive (MS) material belongs to a special class of materials that responds to change in an ambient magnetic field by a change in its optical coupling length L
c
, in its gap width D
g
and/or in the refractive indices of the material (two fibers) within the coupling length L
c
. Many MS materials manifest a fractional change in length in a selected direction of the order of 10-100×10
−6
. One of the most attractive MS materials is iron-cobalt alloy, Fe
a
Co
1−a
, with 0≦a≦1, which has a saturation magnetostriction parameter of between 10×10
−6
and 120×10
−6
. Other attractive magnetostrictive materials include Co, Ni, Fe
b
Ni
1−b
, (Tb
c
Dy
1−c
)Fe
2
, TbFe
2
, Fe
0.8
B
0.2
, Fe
0.4
Ni
0.4
B
0.2
, ceramics of Fe
3
O
4
, Fe
2
NiO
4
, and Fe
2
CoO
4
, and metallic glasses of FeSiB and (FeNi)SiB, with 0≦b,c≦1. These materials are generally magnetically soft so that a small electrical current is usually needed to drive the magnetostrictive action.
As the impressed longitudinal magnetic induction strength B
long
is changed from a first value B
long,1
(e.g., 0 Gauss) to a second value B
long,2
(e.g., 1 Gauss or 10 Gauss or 100 Gauss), the length L
c
of the optical coupling region changes from L
c
(B
long,1
) to L
c
(B
long,2
), in response to change in length of the contiguous tube
25
. The optical coupling length L
c
(λ,n
1
,n) may change by about 10-120 ppm, in response to change of the magnetic induction strength.
In a first version of this embodiment, the first fiber
21
and the second fiber
22
are physically coupled together in the region
28
over a physical coupling length L
p
that is initially substantially equal to the optical coupling length L
c
(λ,n
1
,n) of the fibers for light of wavelength λ, when the first magnetic induction strength B
long,1
satisfies
L
c
(B
long,1
)=
L
c
(λ,
n
1
,
n
)=
L
p
. (1)
Here, n
1
and n are the refractive indices of the fiber core and the ambient medium, respectively, and these indices may vary weakly with wavelength of the light. In this version, substantially all light in the first fiber
21
is coupled into the second fiber
22
over the optical coupling region
28
for the initial induction strength B
long,1
, and substantially no light appears initially in the first fiber at the light application device
24
.
As the impressed magnetic induction strength changes to B
long,2
, the optical coupling length changes from L
c
(B
long,1
) to L
c
(B
long,2
), and this latter length value is now substantially different from (substantially greater than or substantially less than) the initial optical coupling length L
c
(λ,n
1
,n). A fraction of the light that has been coupled into the second fiber
22
is recoupled into (or is not coupled from) the first fiber
21
, because
L
c
(B
long,2
)≠
L
c
(λ,
n
1
,n
). (2)
A fiber refractive index may also change, for example, through a stress associated with the a mismatch in the elastic strains induced in the magnetostrictive and fiber materials.
A fraction, depending upon the magnetostrictive material used and the induction strengths B
long,1
and B
long,2
, of the light that would have been carried by the second fiber
22
beyond the physical coupling region
28
now appears in the first fiber
21
at the light application device
24
, through partial “spoiling” of the complete transfer of light to the second fiber
22
. The system
20
shown in
FIG. 2
behaves as an optical switch.
In order to switch 100 percent of the light from a first fiber to a second fiber, the optical coupling length L
c
must be increased (or decreased) by one-half of a wavelength, which is 0.775 μm for a wavelength of λ=1.55 μm. If the magnetostrictive material Fe
2
CoO
4
, with ms=100×10
−6
, is used for a tube enclosing the first and second optical fibers, the required tube length is 7.750 mm. The current required to reach saturation magnetostriction is 10-50 milliamps with 500 turns of coil, which will produce a magnetic field strength of about 10 Oersteds.
The system illustrated in
FIG. 2
can also serve as an optical attenuator. The electrical current provided by the current source
27
, and thus the magnetic field impressed upon the magnetostrictive tube
25
, may be varied to provide a change in physical coupling length that is a controllable fraction of λ/2 so that the light intensity in one of the first and second fibers,
21
and
22
, varies continuously from zero intensity to maximum intensity. This approach permits the light intensity to be controlled through control of the current source
27
. Control of the current source may be implemented in an open loop manner (no feedback) or may be implemented by providing a control module
27
C that receives a signal representing light intensity received from the second fiber at the light application device
24
and adjusts the current source to achieve a desired light intensity, through closed loop feedback.
In a second embodiment
30
of the invention, illustrated in
FIG. 3
, first and second optical fibers,
31
and
32
, are physically coupled over a physical coupling region
38
c
in a waveguide on a substrate
38
s
that is preferably constructed from SiO
x
on Si or on other substrates. The fibers,
31
and
32
, in the physical coupling region
38
are surrounded by a contiguous region
35
of magnetostrictive material. A conductive strip, sequence of current-carrying lines or other means
36
with an associated current source
37
, to impress a magnetic induction in a selected direction across the magnetostrictive region
35
. A light application device
34
is connected to at least one of the output ends,
31
-
2
and
32
-
2
, of the fibers,
31
and
32
, to receive light delivered in one or both of these fibers.
Operation of the system
30
is similar to operation of the system
20
. With an initial magnetic induction strength B
long,1
impressed on the magnetostrictive region
35
, the physical coupling length L
p
and the optical coupling length L
c
(B
long,1
) are substantially equal and Eq. (1) applies. With a selected second magnetic induction strength B
long,2
) impressed on the magnetostrictive region
35
, the new optical coupling length L
c
(B
long,2
) is no longer equal to the physical coupling length L
p
, and Eq. (2) applies. Full coupling of the light into the second fiber
32
is now partially “spoiled”, and a portion of this light now appears in the first fiber
31
at the light application device
34
.
Some MS materials manifest substantial temperature sensitivity. The system
20
in FIG.
2
and/or
30
in
FIG. 3
optionally includes a temperature control module (shown as
39
in FIG.
3
), surrounding at least the MS material and optionally other components of the system, to control the temperature of the MS material (and related components) to within 1-3° C., and preferably to within 0.5° C.
The system
30
can also serve as an optical attenuator, through open loop or closed loop control of the current source
37
, in a manner similar to that discussed in connection with the system
20
in FIG.
2
. Where automatic control of the current source
37
is desired, a current control module
37
C is provided that receives a signal representing light intensity received at the light application device
34
and adjusts the current source to achieve a desired light intensity, through closed loop feedback.
In a third embodiment
40
of the invention, shown in
FIG. 4
, two optical fibers,
41
and
42
, are assembled as a Mach-Zehnder interferometer (“MZI”), defined by first and second fiber couplers,
43
and
44
, each of which is preferably a 3 dB coupler so that 50 percent of the incident light in the first fiber
41
is coupled into the second fiber
42
at the first fiber coupler
43
. A light application device
49
is connected to an output end of at least one of the first and second fibers,
41
and
42
.
As illustrated in
FIG. 4
, an MZI has two arms,
45
A and
45
B, of unequal lengths, L
1
and L
2
, respectively, with refractive index n. Each arm is defined by first and second 3 dB optical fiber couplers,
43
and
44
, arranged serially. The initial part of each arm,
45
A and
45
B, immediately following a first fiber coupler
43
, carries an equal energy portion of a single light beam. However, because of the length difference, or equivalent time delay
τ=
n
·(
L
2
−L
1
)/
c,
(3)
interference occurs at the second fiber coupler
44
, resulting in transmission of light in the first and second fibers beyond the second fiber coupler with transmissivity factors of
T
1
(
f
τ)={1−cos(2
πf
τ)}/2=sin
2
(π
f
τ), (4)
T
2
(
f
τ)={1−cos(2
πf
τ)}/2=cos
2
(π
f
τ), (5)
f=c/n
λ, (6)
where f is the frequency of a particular wavelength included in the incident light. For frequencies near
f=f
(pass)=
m
/τ(
m
=1, 2, 3, . . . ),
(7)
that frequency or wavelength component is passed by the second fiber coupler
44
with no loss or a small transmissivity loss and is extinguished (almost) completely by the first fiber. For frequencies near
f=f
(exiting)=(
m
+0.5)/τ(
m
=0, 1, 2, 3, . . . ),
(8)
that frequency or wavelength component is extinguished by the second fiber coupler
44
substantially completely and is passed by the first fiber coupler
44
with no loss or a small transmissivity loss. The full width at half maximum (FWHM) for this filter is
Δ
f=FWHM=
½τ. (9)
A lightwave, traveling in one or both of the fibers,
41
and
42
, should have a narrow band Δλ of wavelengths (e.g., Δλ≦n
1
·(L
2
−L
1
)/R with R=5-1000)), with each fiber passing different wavelength components.
In the embodiment
40
in
FIG. 4
, a magnetostrictive tube or element
46
A, contiguous to the first fiber
4
, a current source
47
A and current-conducting strip or coil
48
A are positioned in the first arm
45
A of the MZI, between the first and second fiber couplers,
43
and
44
. Quasi-monochromatic light having a narrow wavelength component centered at a wavelength λ
1
is introduced into the first fiber
41
and is coupled into the second fiber
42
by the first fiber coupler
43
. When a first magnetic induction B
1
(e.g., 0-1 Gauss) is applied to the magnetostrictive tube
46
A, the relative time delay τ
1
for the two arms of the MZI satisfies
τ
1
=m/f=m·n
1
·λ
1
/c
(
m
=0, 1, 2, 3, . . . ),
(10)
so that the transmissivity T
1
at the second fiber coupler
44
is substantially 100 percent. In this situation, substantially all light is received at the two fibers,
41
and
42
, beyond the second fiber coupler
44
.
When a selected second magnetic induction B
2
(e.g., 1 Gauss or 10 Gauss or 100 Gauss) is applied to the magnetostrictive tube
46
A, the first fiber
41
experiences a change in optical coupling length L
c
, and the relative time delay τ
2
for the two arms of the MZI satisfies
τ
2
=m/f
=(
m
+0.5)·
n
1
·λ
1
/c
(
m
=0, 1, 2, 3, . . . ),
(11)
and the transmissivity T
2
at the second fiber coupler drops to substantially 0. The situations can be reversed, with the transmissivities satisfying T
1
=0 and T
2
=1. In either situation, the system
40
behaves as an optical switch for narrowband light introduced into the first fiber, or into the second fiber, and received at a light application device
49
. Where the first arm
45
A includes first and second arm components with fiber lengths L
1,1
and L
1,2
, respectively, with the respective refractive indices n
1,1
, and n
1,2
, the time delay in Eq. (3) is replaced by
τ=(
n
2
·L
2
−n
1,1
·L
1,1
−n
1,2
·L
1,2
)/
c,
(12)
where n
2
is the refractive index of the fiber in the second arm
45
B
The system illustrated in
FIG. 4
can also serve as an optical attenuator. The electrical current provided by the current source
47
A, and thus the magnetic field impressed upon the magnetostrictive tube
46
A, may be varied to provide a change in the relative time delay τ that is a controllable fraction of the FWHM so that the light intensity in one of the first and second fibers,
41
and
42
, varies continuously from zero intensity to maximum intensity. This approach permits the light intensity to be controlled through control of the current source
47
A. Control of the current source may be implemented in an open loop manner (no feedback) or may be implemented by providing a control module
47
C that receives a signal representing light intensity received at the light application device
49
and adjusts the current source to achieve a desired light intensity, through closed loop feedback. If the change in optical coupling length L
c
is χ·λ/2, where χ is a selected fraction (e.g., k<χ<k+1, with k=0, ±1, ±2, ±3, etc.), the attenuation will vary controllably with the fraction χ.
Optionally, the second arm
45
B of the system
40
in
FIG. 4
includes a second magnetostrictive tube or element
46
B, a second current source
47
B (which may, but need not, coincide with the first current source
47
A) and a second current-conducting coil or strip
48
B. Each of the two arms,
45
A and
45
B, of the MZI manifests MS action when one or both of the current sources,
47
A and
47
B, is activated. Preferably, the MS materials used in the first and second magnetostrictive elements,
46
A and
46
B, have one or more different characteristics so that these two elements can be controlled individually or cooperatively to enhance the MS action. For example, the magnetostrictive materials used in the first and second elements,
46
A and
46
B, may be Fe
a
Co
1−a
(0≦a≦1) and Ni, which have positive and negative MS coefficients, respectively, so that interference of the light beams from the arms,
45
A and
45
B, combined in the second coupler
44
is enhanced or made stronger. Alternatively, the MS materials used in the first and second elements,
46
A and
46
B, may have the same characteristics, but the first and second current sources,
47
A and
47
B, may be driven independently.
In a fourth embodiment
50
of the invention, illustrated in
FIG. 5
, first and second optical fibers,
51
and
52
, are physically coupled through an MZI, defined by first and second fiber couplers,
53
and
54
, constructed as part of a waveguide
59
A on a substrate
59
B that is preferably constructed from SiO
x
on Si or on other substrates. The fibers,
51
and
52
, in the MZI are surrounded by a contiguous region
56
of magnetostrictive material. A conductive strip, sequence of current-carrying lines or other means
58
A with an associated current source
57
A, to impress a selected magnetic induction B in a selected direction across the magnetostrictive region
56
A in the first arm
55
A. A light application device
60
is connected to an output end of at least one of the first and second,
51
and
52
, to receive light delivered in one or both of these fibers. Operation of the embodiment
50
is similar to operation of the embodiment
40
.
The system
50
can also serve as an optical attenuator, through open loop or closed loop control of the current source
57
, in a manner similar to that discussed in connection with the system
40
in FIG.
4
. Where automatic control of the current source
57
is desired, a current control module
57
C is provided that receives a signal representing light intensity received at the light application device
59
and adjusts the current source to achieve a desired light intensity, through closed loop feedback.
Optionally, the second arm
55
B of the system
50
in
FIG. 5
includes a second magnetostrictive tube or element
56
B, a second current source
57
B (which may, but need not, coincide with the first current source
57
A) and a second current-conducting coil or strip
58
B. Each of the two arms,
55
A and
55
B, of the MZI manifests MS action when one or both of the current sources,
57
A and
57
B, is activated. Preferably, the MS materials used in the first and second magnetostrictive elements,
56
A and
56
B, have one or more different characteristics (e.g., positive and negative MS coefficients) so that these two elements can be controlled individually or cooperatively to enhance the MS action, analogous to the situation for the system
40
in FIG.
4
. Alternatively, the MS materials used in the first and second elements,
56
A and
56
B, may have the same characteristics, but the first and second current sources,
57
A and
57
B, may be driven independently.
The system
40
in FIG.
4
and/or
50
in
FIG. 5
optionally includes a temperature control module (shown as
61
in FIG.
5
), surrounding at least the MS element(s) and the MZI, and optionally other components of the system, to control the temperature of the MS material and of the MZI (and of related components) to within 1-3° C., and preferably to within 0.5° C.
Reaction time for optical switching or attenuation is a sum of time required to switch current and to establish a magnetic field in the ms material and is estimated to be of the order of μsecs to msecs.
Claims
- 1. An optical system for controlling light, the system comprising:first and second optical fibers that are physically coupled together as part of a Mach-Zehnder interferometer, having a selected length Lc, each fiber having a first end and a second end; a source of light including light with a selected wavelength λ, connected to the first end of the first fiber; a first control structure and a second control structure, surrounding and contiguous to the first and second fibers, respectively, in the optical coupling region, the first and second control structures including respective first and second magnetostrictive materials; and magnetic field means for impressing a first magnetic field of controllable induction strength on the first magnetostrictive material so that, when the impressed induction has a first selected value, a first selected amount of light is received at the second end of the first fiber, and when the impressed induction has a second selected value, a second selected amount of light is received at the second end of the first fiber, and for impressing a second magnetic field of a second controllable induction strength on the second magnetostrictive material so that, when the second impressed induction has a first selected value, a first selected amount of light is received at the second end of the second fiber, and when the second impressed induction has a second selected value, a second selected amount of light is received at the second end of the second fiber, wherein one of the first magnetostrictive material and the second magnetostrictive material has a positive magnetostrictive coefficient and the other of the first magnetostrictive material and the second magnetostrictive material has a negative magnetostrictive coefficient.
- 2. The system of claim 1, wherein said first selected amount of light is substantially no light.
- 3. The system of claim 1, wherein at least one of said first selected amount of light and said second selected amount of light is light is no larger than a selected threshold amount.
- 4. The system of claim 1, wherein at least one of said first selected amount of light and said second selected amount of light is no smaller than a selected threshold amount.
- 5. The system of claim 1, further comprising a receiver of said light connected to said output end of at least one of said first fiber and said second fiber.
- 6. The system of claim 1, wherein at least one of said first and second magnetostrictive materials is drawn from a group of materials consisting of FeaCo1−a, (0≦a≦1), Co, Ni, FebNi1−b, (0≦b≦1), (TbcDy1−c)Fe2 (0≦c≦1), TbFe2, Fe0.8B0.2, Fe0.4Ni0.4B0.2, ceramics of Fe3O4, Fe2NiO4, and Fe2CoO4, and metallic glasses of FeSiB and (FeNi)SiB.
- 7. The system of claim 1, wherein said magnetic field means provides said magnetic field with said induction strength that is at least sufficient to change said optical coupling length Lc by an amount that is approximately equal to λ/2.
- 8. The system of claim 1, wherein said magnetic field means provides said magnetic field with said induction strength that is at least sufficient to change said optical coupling length Lc by a selected amount that is approximately equal to χ·λ/2, where k<χ<k+1 and k is a selected integer.
- 9. The system of claim 1, wherein at least one of said first impressed magnetic induction value and said second impressed magnetic induction value is at least 1 Gauss.
- 10. The system of claim 1, further comprising a temperature control mechanism, surrounding and controlling a temperature of at least one of said first magnetostrictive material and said second magnetostrictive material.
- 11. The system of claim 1, wherein at least one of said first and second magnetostrictive materials is drawn from a group consisting of Ni and FeaCo1−a, where a is a selected value in a range 0≦a≦1.
- 12. A method for controlling light, the method comprising:physically coupling first and second optical fibers in a Mach-Zehnder interferometer having a selected length Lc, with each fiber having a first end and a second end; providing a source of light, including light with a selected wavelength λ, at the first end of the first fiber; receiving light at the second end of at least one of the first fiber and the second fiber; providing a first control structure and a second control structure, surrounding and contiguous to the first and second fibers, respectively, in the physical coupling region, the control structure including respective first and second magnetostrictive materials; and impressing a magnetic field of controllable induction strength on the first magnetostrictive material so that, when the impressed induction has a first selected value, a first selected amount of light is received at the second end of the first fiber, and when the impressed induction has a second selected value, a second selected amount of light is received at the second end of the first fiber; impressing a second magnetic field of a second controllable induction strength on the second magnetostrictive material so that, when the second impressed induction has a first selected value, a first selected amount of light is received at the second end of the second fiber, and when the second impressed induction has a second selected value, a second selected amount of light is received at the second end of the second fiber; and choosing one of the first magnetostrictive material and the second magnetostrictive material to have a positive magnetostrictive coefficient and choosing the other of the first magnetostrictive material and the second magnetostrictive material to have a negative magnetostrictive coefficient.
- 13. The method of claim 12, further comprising choosing said first selected amount of light to be substantially no light.
- 14. The method of claim 12, further comprising choosing at least one of said first selected amount of light and said second selected amount of light is light to be no larger than a selected threshold amount.
- 15. The method of claim 12, further comprising choosing at least one of said first selected amount of light and said second selected amount of light to be no small er than a selected threshold amount.
- 16. The method of claim 12, further comprising providing a receiver of said light connected to said output end of at least one of said first fiber and said second fiber.
- 17. The method of claim 12, further comprising choosing at least one of said first and second magnetostrictive materials from a group of materials consisting of FeaCo1−a, (0≦a≦1), Co, Ni, FebNi1−b, (0≦b≦1), (TbcDy1−c)Fe2 (0≦c≦1), TbFe2, Fe0.8B0.2, Fe0.4Ni0.4B0.2, ceramics of Fe3O4, Fe2NiO4, and Fe2CoO4, and metallic glasses of FeSiB and (FeNi)SiB.
- 18. The method of claim 1, further comprising providing said magnetic field with said induction strength that is at least sufficient to change said optical coupling length Lc by an amount that is approximately equal to λ/2.
- 19. The method of claim 12, further comprising providing said magnetic field with said induction strength that is at least sufficient to change said optical coupling length Lc by a selected amount that is approximately equal to χ·λ/2, where k<χ<k+1 and k is a selected integer.
- 20. The method of claim 12, further comprising choosing at least one of said first impressed magnetic induction and said second impressed magnetic induction to have an induction value of at least 1 Gauss.
- 21. The method of claim 12, further comprising providing a temperature control mechanism, surrounding and controlling a temperature of at least one of said first magnetostrictive material and said second magnetostrictive material.
- 22. The method of claim 12, further comprising choosing at least one of said first and second magnetostrictive materials from a group consisting of Ni and FeaCo1−a, where a is a selected value in a range 0≦a≦1.
- 23. A method for controlling light, the method comprising:physically coupling first and second optical fibers in an optical coupling region having a selected length Lc, with each fiber having a first end and a second end; providing a source of light, including light with a selected wavelength λ, at the first end of the first fiber; receiving light at the second end of at least one of the first fiber and the second fiber; providing a first control structure, surrounding and contiguous to the first and second fibers in the physical coupling region, the control structure including a magnetostrictive material, where the magnetostrictive material is drawn from a group of materials consisting of FeaCo1−a, (0≦a≦1), Co, Ni, FebNi1−b,(0≦b≦1), (TbcDy1−c)Fe2 (0≦c≦1), TbFe2, Fe0.8B0.2, Fe0.4Ni0.4B0.2, ceramics of Fe3O4, Fe2NiO4, and Fe2CoO4, and metallic glasses of FeSiB and (FeNi)SiB; and impressing a magnetic field of controllable induction strength on the first magnetostrictive material so that, when the impressed induction has a first selected value, a first selected amount of light is received at the second end of the first fiber, and when the impressed induction has a second selected value, a second selected amount of light is received at the second end of the first fiber.
- 24. A method for controlling light, the method comprising:physically coupling first and second optical fibers in an optical coupling region having a selected length Lc, with each fiber having a first end and a second end; providing a source of light, including light with a selected wavelength λ, at the first end of the first fiber; receiving light at the second end of at least one of the first fiber and the second fiber; providing a first control structure, surrounding and contiguous to the first and second fibers in the physical coupling region, the control structure including a first magnetostrictive material; and impressing a magnetic field of controllable induction strength on the first magnetostrictive material, where the induction strength is chosen to change the optical coupling length Lc by a selected amount that is approximately equal to χ·λ/2, where k<χ<k+1 and k is a selected integer, thereby providing an amount of light at the second end of the first fiber that is controllably attenuated relative to a maximum amount of light that can be received at the second end of the first fiber.
- 25. The method of claim 24, further comprising providing said attenuated amount of light at said second end of said first fiber that is approximately equal to I(max)·sin2(πχ/2), where I(max) is the maximum amount of light that can be received at said second end of said first fiber.
US Referenced Citations (9)