U.S. patent application number 09/764600 was filed with the patent office on 2002-08-08 for fiber modulator and associated method.
This patent application is currently assigned to The Boeing Company. Invention is credited to Rice, Robert Rex.
Application Number | 20020105713 09/764600 |
Document ID | / |
Family ID | 25071194 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020105713 |
Kind Code |
A1 |
Rice, Robert Rex |
August 8, 2002 |
FIBER MODULATOR AND ASSOCIATED METHOD
Abstract
An optical modulator and an associated modulation method are
provided that utilize an optical fiber as the active medium such
that the resulting fiber modulator is relatively inexpensive, but
maintains high performance standards. The fiber modulator includes
a core and a cladding surrounding the core which collectively form
a longitudinally extending optical fiber capable of supporting the
propagation of optical signals. The fiber modulator also includes
first and second regions within the cladding and extending
longitudinally therealong for establishing an internal bias
electrical field across the core. The first and second regions are
disposed on opposite sides of the core and have positive and
negative electrical charges, respectively. The fiber modulator
further includes first and second electrodes disposed on the
cladding proximate the first and second regions, respectively, and
extending longitudinally therealong. By applying electrical
signals, such as radio frequency (RF) signals, to the first and
second electrodes, the optical signals propagating through the core
of the optical fiber can be linearly phase modulated. The optical
fiber may have a rectangular shape in lateral cross section with a
pair of opposed major surfaces and a pair of opposed minor
surfaces. In this instance, the first and second regions and the
first and second electrodes are all generally disposed proximate a
respective major surface of the optical fiber.
Inventors: |
Rice, Robert Rex; (Simi
Valley, CA) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
The Boeing Company
|
Family ID: |
25071194 |
Appl. No.: |
09/764600 |
Filed: |
January 18, 2001 |
Current U.S.
Class: |
359/254 ; 385/1;
385/2; 385/4 |
Current CPC
Class: |
G02F 2201/12 20130101;
G02F 1/0115 20130101 |
Class at
Publication: |
359/254 ; 385/1;
385/2; 385/4 |
International
Class: |
G02F 001/03; G02F
001/07; G02F 001/01; G02F 001/035; G02F 001/295 |
Claims
That which is claimed:
1. A fiber modulator comprising: a core having a first index of
refraction; a cladding surrounding said core and having a second
index of refraction that is less than the first index of
refraction; first and second regions within said cladding on
opposite sides of said core, said first and second regions having
positive and negative electrical charges, respectively, for
establishing an internal bias electrical field across said core;
and first and second electrodes disposed on said cladding proximate
said first and second regions, respectively, whereby electrical
signals applied to said first and second electrodes serve to
modulate optical signals propagating through said core.
2. A fiber modulator according to claim 1 wherein said core and
cladding extend in a longitudinal direction, and wherein said
cladding has rectangular shape in lateral cross section.
3. A fiber modulator according to claim 2 wherein said cladding has
a pair of opposed major surfaces and a pair of opposed minor
surfaces, and wherein said first and second regions and said first
and second electrodes are all disposed proximate respective major
surfaces of said cladding.
4. A fiber modulator according to claim 1 wherein said core and
cladding extend in a longitudinal direction, and wherein said first
and second regions and said first and second electrodes all also
extend in the longitudinal direction.
5. A fiber modulator according to claim 1 wherein said core is
adapted to support optical signal propagation in a single mode.
6. A fiber modulator according to claim 1 wherein said core is
doped with a rare earth dopant such that said core is capable of
amplifying the optical signals propagating therethrough in response
to optical pumping.
7. A fiber modulator comprising: a longitudinally extending optical
fiber comprising a core and a cladding surrounding said core, said
optical fiber having a rectangular shape in lateral cross section;
first and second regions within said cladding and extending
longitudinally therealong, said first and second regions disposed
on opposite sides of said core and having positive and negative
electrical charges, respectively; and first and second electrodes
disposed on said optical fiber and extending longitudinally
therealong, said first and second electrodes disposed proximate
said first and second regions, respectively.
8. A fiber modulator according to claim 7 wherein said optical
fiber has a pair of opposed major surfaces and a pair of opposed
minor surfaces, and wherein said first and second regions and said
first and second electrodes are all disposed respective major
surfaces of said optical fiber.
9. A fiber modulator according to claim 7 wherein said optical
fiber is adapted to support optical signal propagation in a single
mode.
10. A fiber modulator according to claim 7 wherein said core is
doped with a rare earth dopant such that said core is capable of
amplifying the optical signals propagating therethrough in response
to optical pumping.
11. A method of modulating optical signals propagating along an
optical fiber having a core and a cladding surrounding the core,
the method comprising: establishing an internal DC bias electrical
field across the core, establishing the internal DC bias electrical
field comprising providing first and second regions within the
cladding on opposite sides of the core that have positive and
negative electrical charges, respectively; and applying electrical
signals to electrodes extending lengthwise along the cladding while
the internal DC bias electrical field is established across the
core, thereby modulating the optical signals propagating through
the core.
12. A method according to claim 11 wherein applying electrical
signals comprises applying RF signals to the electrodes.
13. A method according to claim 12 wherein applying RF signals
comprises applying RF signals to one end of the electrodes such
that the RF signals propagate lengthwise along the electrodes
concurrent with the propagation of optical signals through the
core.
14. A method according to claim 11 wherein applying electrical
signals comprises selecting the electrical signals to be applied to
the electrodes such that an electrical field established by the
electrical signals applied to the electrodes is smaller than the
internal DC bias electrical field.
15. A method according to claim 11 further comprising optically
pumping the core in order to amplify the optical signals
propagating through the core concurrent with the modulation of the
optical signals.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to optical
modulators and associated modulation methods and, more
particularly, to an optical modulator utilizing an optical fiber as
the active medium and an associated modulation method.
BACKGROUND OF THE INVENTION
[0002] An increasing number of telecommunications, computer and
other networks rely upon optical fibers, as opposed to electrical
wiring, for signal transmission. Each of these optical networks
typically includes a number of optical modulators for encoding the
data to be transmitted via the optical fibers so that the encoded
data can ride upon an optical carrier signal. As such, optical
modulators are in great demand with increasing emphasis being
placed upon the speed at which the optical modulator operates and
the cost of the optical modulator.
[0003] While optical modulators are widely utilized in conventional
optical networks, the demand for optical modulators will likely
grow as internet service providers offer an increasing number of
wideband services to both businesses and residential customers.
Unfortunately, the conventional optical modulators that are capable
of modulating signals over a wide frequency band are
disadvantageously expensive, as described in more detail below. In
fact, optical modulators may be the most costly components of some
fiber optic communication systems.
[0004] A conventional optical modulator includes a single crystal
substrate formed of a ferroelectric material that lacks internal
symmetry, such as single crystal lithium niobate (LiNbO.sub.3). A
ferroelectric material possesses a spontaneous dielectric
polarization and, consequently, also exhibits a linear electrooptic
effect, i.e., a Pockels effect. As a result, the refractive index
of a single crystal substrate exhibiting a linear electrooptic
effect changes linearly with an applied electric field.
Accordingly, optical signals propagating through an in-diffused
single mode waveguide fabricated on a single crystal substrate
exhibiting a linear electrooptic effect can be phase modulated by
applying an appropriate electric field. Typically, the electric
field is created by applying an electrical signal to electrodes on
opposite sides of the single crystal substrate.
[0005] An optical modulator, such as an optical modulator
fabricated from single crystal lithium niobate, can be
characterized by its half-wave switching voltage V.sub.s and its
electrical bandwidth .DELTA.f. The half-wave switching voltage is
the voltage that must be applied across the single crystal
substrate in order to induce a phase shift of .pi.. It is generally
desirable for the half-wave switching voltage to be less than about
10 volts such that solid state driver amplifiers can be utilized to
create the electric field across the single crystal substrate. In
addition, the electrical bandwidth of an optical modulator is the
frequency band over which the modulation response remains within 3
dB of the peak value. For example, the electrical bandwidth of a
conventional optical modulator is in the tens of gigahertz.
[0006] In order to fabricate an optical modulator, the single
crystal material is drawn from a high temperature melt according to
a Czochralski process. The crystal is then poled by annealing the
crystal at elevated temperatures in the presence of an applied
electrical field that aligns the ferroelectric domains in the same
direction. The crystal is next cut into thin wafers and the major
surfaces of each wafer are polished to an optical grade finish.
Utilizing photolithography, a mask that defines the desired
waveguide pattern is then formed upon a polished surface of the
substrate. After processing the photoresist, titanium metal is
typically deposited on the surface and is then in-diffused at high
temperatures to form the single mode waveguides. Metal electrodes
are then deposited on the polished surface of the substrate in the
same pattern of the waveguides. Since a plurality of modulators can
be formed upon a single substrate, the individual optical
modulators are then cut or otherwise separated from the remainder
of the wafer. The optical modulator is then packaged with fiber
optic pigtails and radio frequency (RF) connections in a hermetic
package with corresponding single mode optical fiber
connectors.
[0007] Although the resulting optical modulator can reliably phase
modulate the optical signals transmitted via the single mode
waveguides within an optical network, the process for fabricating a
conventional optical modulator requires precise dimensional control
and is relatively expensive. As such, the resulting optical
modulators also are disadvantageously expensive, especially
relative to other components within an optical network. As such, it
would be desirable to provide reliable optical modulators that can
be fabricated in a less expensive manner.
SUMMARY OF THE INVENTION
[0008] An optical modulator and an associated modulation method are
therefore provided that utilize an optical fiber as the active
medium such that the resulting fiber modulator is less expensive,
but maintains high performance standards. In this regard, the fiber
modulator of the present invention includes a core having a first
index of refraction and a cladding surrounding the core and having
a second index of refraction that is less than the first index of
refraction. As such, the core and the surrounding cladding
generally form a longitudinally extending optical fiber capable of
supporting the propagation of optical signals through the core
thereof. The fiber modulator also includes first and second regions
within the cladding and extending longitudinally therealong for
establishing an internal bias electrical field across the core. The
first and second regions are therefore disposed on opposite sides
of the core and have positive and negative electrical charges,
respectively. The fiber modulator further includes first and second
electrodes disposed on the cladding proximate the first and second
regions, respectively, and extending longitudinally therealong. By
applying electrical signals, such as radio frequency (RF) signals,
to the first and second electrodes, the optical signals propagating
through the core of the optical fiber can be linearly phase
modulated.
[0009] In one advantageous embodiment, the optical fiber and, more
particularly, the cladding has a rectangular shape in lateral cross
section. As such, the optical fiber has a pair of opposed major
surfaces and a pair of opposed minor surfaces. In this embodiment,
the first and second regions and the first and second electrodes
are all preferably disposed proximate a respective major surface of
the optical fiber. For example, the first region and the first
electrode can be disposed proximate a first major surface and the
second region and the second electrode can be disposed proximate an
opposed second major surface.
[0010] Preferably, the optical fiber is a single mode fiber such
that the core is adapted to support optical signal propagation in a
single mode. In addition, the optical fiber may serve not only as
the active medium of a fiber modulator, but also as an amplifier,
i.e., a fiber amplifier. In this instance, the core may be doped
with a rare earth dopant to thereby amplify the optical signals
propagating therethrough if the optical fiber is also appropriately
pumped.
[0011] In operation, an internal DC bias electrical field is
established across the core. According to the present invention,
the internal DC bias electrical field is established by the first
and second regions that have positive and negative electrical
charges, respectively, and that are positioned on opposite sides of
the core. While the internal DC bias electrical field is applied
across the core, electrical signals are also applied to the
electrodes that extend lengthwise along opposite sides of the
optical fiber to thereby linearly phase modulate the optical
signals propagating through the core of the optical fiber.
Typically, the electrical signals applied to the electrodes are RF
signals. In one embodiment, for example, the RF signals can be
applied to one end of the electrodes such that the RF signals
propagate lengthwise along the electrodes concurrent with the
propagation of the optical signals through the core of the optical
fiber. Preferably, the electrical signals that are applied to the
electrodes are selected such that the resulting electrical field
established by the electrical signals is smaller than the internal
DC bias electrical field. As such, the internal DC bias electrical
field can induce a linear electrooptic effect within an optical
fiber that would otherwise exhibit a quadratic electrooptic effect,
i.e., a Kerr effect. As a result of the linear electrooptic effect,
the smaller electrical field created by the electrical signals
applied to the electrodes serves to linearly modulate the optical
signals propagating through the optical fiber. Concurrent with the
modulation of the optical signals, the optical signals can be
amplified if the core of the optical fiber has been appropriately
doped with a rare earth dopant and is optically pumped.
[0012] Since it is premised upon optical fiber technology, the
fiber modulator of the present invention can therefore be
fabricated at much lower cost than conventional optical modulators.
As such, the resulting fiber modulator generally is less expensive.
However, a fiber modulator of the present invention that includes
an optical fiber as the active medium still maintains high
performance levels with respect to the linear phase modulation of
the optical signals propagating therealong.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0014] FIG. 1 is a perspective view of a fiber modulator according
to one embodiment of the present invention; and
[0015] FIG. 2 is a cross-sectional view of the fiber modulator of
FIG. 1 taken along line 2-2.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0017] Only single crystal structures that lack internal symmetry,
such as single crystal lithium niobate as described above, exhibit
a linear electrooptic effect, i.e., a Pockels effect. However, all
transparent dielectric materials exhibit a quadratic electrooptic
effect, i.e., a Kerr effect. For purposes of explanation, the
linear electrooptic effect can be considered to be the quadratic
electrooptic effect biased by the spontaneous polarization in a
ferroelectric single crystal material. Although not wishing to be
bound by theory, it is therefore suggested that a permanent
electric field applied to a transparent dielectric material that
otherwise exhibits a quadratic electrooptic effect can induce a
linear electrooptic effect.
[0018] By way of example, a transparent dielectric material, such
as a glass or liquid, generally has a non-linear refractive index n
that is defined as follows:
n=n.sub.1+n.sub.2E.sup.2 (1)
[0019] wherein n.sub.1 is the linear refractive, E is the applied
electric field and n.sub.2 is the Kerr constant. As such, the term
n.sub.2E.sup.2 is the nonlinear portion of the refractive index.
According to the present invention, a relatively large internal DC
bias electrical field E can be applied across a transparent
material that otherwise exhibits a quadratic electrooptic effect
such that the application of a relatively small application
.delta.B thereafter produces a linear modulation of the refractive
index .delta.n. In this instance, the cumulative refractive index
is n+.delta.n in instances in which the total applied electrical
field is E+.delta.E. As such, equation 1 can be rewritten as
follows:
n+.delta.n=n.sub.1+n.sub.2(E+.delta.E).sup.2=n.sub.1+n.sub.2(E.sup.2+2E.de-
lta.E+.delta.E.sup.2) (2)
[0020] Since the term .delta.E.sup.2 is small, this term can be
eliminated and the equation can then be solved for .delta.n as
follows:
.delta.n=2n.sub.2E.delta.E (3)
[0021] As illustrated by equation 3, the refractive index of a
transparent material, such as an optical fiber, varies linearly in
response to the electrical field created by relatively small
electrical signals once the transparent material has already been
strongly biased by a relatively large internal DC bias electrical
field E.
[0022] According to the present invention, a fiber modulator 10 is
provided that includes an active medium comprised of a transparent
material in the form of an optical fiber and, more preferably, a
single mode optical fiber. As shown in FIGS. 1 and 2, the optical
fiber includes a single mode core 12 and a cladding 14 that
surrounds the core. In order to appropriately guide the optical
signals through the core, the core has a first index of refraction
that is greater than the second index of refraction of the
cladding.
[0023] As depicted in FIG. 1, the optical fiber and, as a result,
both the core 12 and the cladding 14 extend in a longitudinal
direction. According to one advantageous embodiment of the present
invention, the optical fiber and, more particularly, the cladding
has a rectangular shape in lateral cross-section. Although the
optical fiber could be square in lateral cross-section, the
rectangularly shaped optical fiber generally includes a pair of
opposed major surfaces 16 and a pair of opposed minor surfaces 18.
In this regard, it is noted that while the embodiment of the fiber
modulator 10 depicted in FIGS. 1 and 2 includes major and minor
surfaces that intersect at a right angle, the corners of the
optical fiber and, more particularly, the comers of the cladding
can be rounded while still being considered to have a rectangular
shape in lateral cross-section for purposes of the present
invention. Even though the cladding has a rectangular shape in
lateral cross-section, the core is typically circular in lateral
cross section.
[0024] The core 12 and the cladding 14 of the optical fiber can be
formed from various materials as known to those skilled in the art.
However, in one advantageous embodiment, the core can be formed of
silica doped with germanium and the cladding can be formed of
undoped silica.
[0025] The fiber modulator 10 of the present invention also
includes first and second regions 20, 22 having positive and
negative electrical charges, respectively. As shown, the first and
second regions are disposed within the cladding 14 on opposite
sides of the core 12. More particularly, the first and second
regions are preferably disposed proximate a respective major
surface 16 of the optical fiber. In the embodiment depicted in
FIGS. 1 and 2, for example, the first and second regions are
preferably disposed within medial portions of respective major
surfaces of the optical fiber and are generally in alignment with
one another. As shown, the first and second regions are preferably
centered relative to the respective major surfaces of the optical
fiber so as to be disposed on opposite sides of the core.
[0026] As described below, the first and second regions 20, 22 are
generally implanted into opposite sides of the cladding 14 and, as
such, generally have a U-shape with substantially linear sides and
arcuate bottom that bows inwardly toward the core 12. In this
regard, each of the first and second regions is preferably sized
the same and has a width in the direction of the respective major
surface that is much broader than the diameter of the core.
[0027] The first and second regions 20, 22 include an electrical
charge of the appropriate polarity such that the first region has a
positive electrical charge and the second region has a negative
electrical charge. Typically, the first and second regions are
formed such that the positive and negative electrical charges,
respectively, are substantially equal. As a result of the positive
and negative electrical charges, the first and second regions
establish an internal DC bias electrical field across the core 12.
Generally, the internal DC bias electrical field has a relatively
large magnitude, such as 10,000, 20,000 or more volts per
centimeter. Although not wishing to be bound by theory, it is
believed that the relatively large internal DC bias electrical
field created by the first and second regions induces a linear
electrooptic effect within the transparent material, i.e., within
the optical fiber, that would otherwise exhibit a quadratic
electrooptic effect.
[0028] The fiber modulator 10 of the present invention also
includes first and second electrodes 24, 26 disposed on the optical
fiber and, more particularly, on the cladding 14 proximate the
first and second regions 20, 22, respectively. As shown in FIGS. 1
and 2, the first and second electrodes preferably overlie the first
and second regions, respectively. In addition, the first and second
electrodes are preferably somewhat wider than the first and second
regions, respectively, such that each electrode spans a greater
percentage of the major surface 16 than the respective region.
While the electrodes can be formed of various conductive materials,
the electrodes are typically formed of a metal, such as gold with
an adhesion layer formed of titanium and platinum.
[0029] In order to modulate the optical signals propagating through
the core 12 of the optical fiber by altering the phase of the
optical signals, electrical signals and, more typically, RF signals
are applied to the first and second electrodes 24, 26. The
electrical signals applied to the electrodes create an additional
electrical field .delta.E. This additional electrical field
.delta.E is substantially smaller than the internal DC bias
electrical field established by the first and second regions 20,
22. For example, the electrical field established by the electrical
signals applied to the electrodes is typically no more than about
10% of the internal DC bias electrical field.
[0030] By applying a voltage .delta.V to the electrodes 24, 26 that
extend along an optical fiber of length L and thickness d, a phase
shift .delta..phi. is introduced that is defined as:
.delta..phi.=(4.pi.n.sub.2LE/.lambda.d).delta.V (4)
[0031] In addition to the internal DC bias electrical field, the
phase shift is also partially based upon the aspect ratio of the
optical fiber which is defined as the ratio of the length L of the
optical fiber to the thickness d of the optical fiber, i.e., the
distance between the opposed major surfaces 16 of the optical
fiber. Advantageously, the aspect ratio and, in turn, the phase
shift can be quite large. For example, the length of the optical
fiber can easily be 30 centimeters and the thickness of the optical
fiber can be 30 micrometers such that the aspect ratio is
approximately 10.sup.4. Additionally, the internal DC bias
electrical field is also generally sizable. As such, substantial
phase shifts can be generated with the application of only a
relatively small voltage .delta.V to the opposed electrodes.
[0032] Based upon equation (4) set forth above, the half-wave
voltage V.sub.s for the fiber modulator 10 of the present invention
that is necessary in order to induce a phase shift of .pi. can be
defined as:
V.sub.s=.lambda.d/4n.sub.2LE (5)
[0033] In instances in which the half-wave voltage V.sub.s is
applied across a section of the electrodes 24, 26 that extends
along a length of the optical fiber that is equal to the thickness
of the optical fiber, the half-wave voltage V.sub.s set forth in
equation (5) can be rewritten as:
V.sub.s=.lambda./4n.sub.2E (6)
[0034] The fiber modulator 10 of the present invention can
therefore advantageously linearly modulate the optical signals
propagating therealong due to the linear relationship between the
voltage applied to the opposed electrodes 24, 26 and the resulting
phase shift. In order to provide this linear modulation, an
internal DC bias electrical field must first be established across
the core in order to induce the linear electrooptic effect within
the optical fiber that otherwise would exhibit a quadratic
electrooptic effect.
[0035] In operation, an internal DC bias electrical field is
therefore established across the core 12. As described above, the
internal DC bias electric field is established by the first and
second regions 20, 22 within the cladding 14 on opposite sides of
the core that have positive and negative electrical charges,
respectively. While the internal DC bias electric field is
established across the core, electrical signals, such as RF
signals, are applied to the electrodes 24, 26 in order to phase
modulate the optical signals propagating through the core. In one
advantageous embodiment, the RF signals are applied to one end of
the electrodes. The RF signals then propagate along the length of
the optical fiber at a velocity of C/{square root}K wherein c is
the speed of light and K is the relative dielectric constant. Since
the dielectric constant of a common optical fiber formed of
germanonsilicate glass is about 2.5, the propagation of the RF
signal lengthwise along the electrodes and the propagation of
optical signals through the core of the optical fiber are nearly
synchronized.
[0036] In addition to serving as the active medium of the fiber
modulator 10 of the present invention, the optical fiber can also
serve as a fiber amplifier for amplifying the optical signals. In
this regard, the core 12 would preferably be doped with rare earth
ions and optically pumped as known to those skilled in the art so
as to amplify the optical signals propagating therealong. Thus, the
optical fiber can serve as a dual-function component in order to
simultaneously amplify and modulate optical signals propagating
therealong.
[0037] Generally, the optical refractive index is different for
light polarized parallel and perpendicular to the internal DC bias
electric field. As such, the fiber modulator 10 can preserve the
polarization of the optical signals being input into the optical
fiber in either of these two principle directions.
[0038] In order to fabricate the fiber modulator 10, an optical
fiber preform having a circular core 12 and a cladding 14
surrounding the core that has a rectangular shape is provided. As
known to those skilled in the art, an optical fiber preform is
provided that includes a core with a greater index of refraction
than that of the surrounding cladding. An optical fiber could then
be drawn from the preform that preserves the rectangular shape. By
appropriate selection of the cross-sectional dimensions of the
optical fiber and the respective indices of refraction of the core
and cladding, the optical fiber can be designed to be a single mode
fiber that supports the propagation of optical signals in only a
single mode at the design wavelength .lambda.. For example, the
core may have a diameter of 10 micrometers or less, while the
cladding has a diameter of several tens of micrometers. Either
during or following the drawing process, the first and second
regions 20, 22 having positive and negative electrical charges,
respectively, are formed. Typically, ions having a positive charge
are injected on one side of the optical fiber and ions having a
negative charge are injected on the opposed side of the optical
fiber. For example, the ions can be injected by means of an ion
implantation or electron injection process. Metal can then be
deposited on the opposed sides of the optical fiber proximate one
of the first and second regions in order to form the electrodes 24,
26 that serve as RF waveguides in one embodiment.
[0039] As will be apparent from the foregoing description, the
fiber modulator 10 of the present invention is premised upon fiber
optic technology and can therefore be formed in a relatively
efficient and inexpensive manner such that the cost of the
resulting fiber modulator is reduced relative to conventional
optical modulators. However, the fiber modulator of the present
invention maintains high performance standards and can reliably
phase modulate the optical signals propagating along the optical
fiber by applying appropriate electrical signals to the opposed
electrodes 24, 26.
[0040] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *