U.S. patent application number 12/642498 was filed with the patent office on 2010-06-24 for fiber optic diffraction grating.
This patent application is currently assigned to CHIRAL PHOTONICS, INC.. Invention is credited to Victor Churikov, Victor Il'ich Kopp.
Application Number | 20100158438 12/642498 |
Document ID | / |
Family ID | 42266243 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100158438 |
Kind Code |
A1 |
Churikov; Victor ; et
al. |
June 24, 2010 |
Fiber Optic Diffraction Grating
Abstract
The present invention is directed to an optical fiber grating
having a core, that is capable of controlling the light signal
transmission therethrough by causing at least one of: at least one
spectral peak, and/or at least one spectral dip in its core light
transmission spectrum, corresponding to at least one predetermined
wavelength. The inventive optical fiber diffraction grating
comprises at least one longitudinally positioned structural element
of a predetermined geometric profile and that is configured for
diffracting a portion of the transmitted light signal at at least
one predefined wavelength thereof, from at least one core mode into
at least one of: at least one cladding mode and/or at least one
radiating mode. Various embodiments of a number of novel techniques
for fabrication of the inventive optical fiber diffraction grating
are provided, inclusive of a novel technique for fabricating the
inventive grating from a single material. Advantageously, such
novel fabrication techniques rely on configuration of a desired
geometric profile for the at least one structural element portion
of the novel grating, each profile comprising a number of readily
configurable parameters that can be selected and/or adjusted during
fabrication, to produce a variety of novel fiber diffraction
gratings, each having a corresponding specific desirable core
transmission spectrum having at least one of: least one spectral
peak, and/or at least one spectral dip therein, corresponding to at
least one specific desired wavelength, dependent on the
configuration of the applicable geometric profile.
Inventors: |
Churikov; Victor; (West
Patterson, NJ) ; Kopp; Victor Il'ich; (Fair Lawn,
NJ) |
Correspondence
Address: |
EDWARD ETKIN, ESQ.
Law Office of Edward Etkin, PC, 228 West End Avenue, Suite A
Brooklyn
NY
11235
US
|
Assignee: |
CHIRAL PHOTONICS, INC.
Pine Brook
NJ
|
Family ID: |
42266243 |
Appl. No.: |
12/642498 |
Filed: |
December 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61138907 |
Dec 18, 2008 |
|
|
|
Current U.S.
Class: |
385/28 ;
385/37 |
Current CPC
Class: |
G02B 6/02376 20130101;
G02B 6/02361 20130101; G02B 2006/0209 20130101; G02B 6/021
20130101; G02B 6/02357 20130101 |
Class at
Publication: |
385/28 ;
385/37 |
International
Class: |
G02B 6/34 20060101
G02B006/34 |
Claims
1. A fiber diffraction grating for controlling a light signal
transmission of a predetermined at least one wavelength
therethrough, comprising: a modified optical fiber having at least
one core mode, and at least one of: at least one cladding mode and
at least one radiating mode, said modified optical fiber further
comprising: at least one structural element having a predetermined
geometrical profile, wherein said predetermined geometrical profile
is configured to diffract a light signal of said at least one core
mode at at least one diffracted wavelength, selected from the at
least one predetermined wavelength.
2. The fiber diffraction grating of claim 1, wherein said
predetermined geometrical profile comprises a predetermined helical
pitch, a predetermined helical diameter, and a single predetermined
handedness.
3. The fiber diffraction grating of claim 2, wherein said
predetermined pitch and said predetermined diameter are further
configured to couple light into at least one of said at least one
radiating mode.
4. The fiber diffraction grating of claim 2, wherein said
predetermined pitch and said predetermined diameter are further
configured to couple into at least one of said at least one
cladding mode.
5. The fiber diffraction grating of claim 2, wherein the light
signal transmission comprises a core transmission spectrum,
representative of the light signal transmitted in said at least one
core mode, and wherein said predetermined pitch and said
predetermined diameter are further configured to produce at least
one of: a spectral dip or a spectral peak in said core transmission
spectrum.
6. The fiber diffraction grating of claim 2, wherein said modified
optical fiber comprises a microstructured optical fiber that has
been twisted, in accordance with a predefined twist profile, to
produce therein said at least one structural element of said
predetermined helical pitch and said predetermined helical
diameter.
7. The fiber diffraction grating of claim 1, wherein the light
signal transmission comprises a core transmission spectrum,
representative of the light signal transmitted in said at least one
core mode, and wherein said modified optical fiber comprises a
microstructured optical fiber having at least one predefined
distortion in lateral periodicity therein that is configured to
produce at least one predefined defect state, each causing a
corresponding at least one spectral dip in said core transmission
spectrum.
8. The fiber diffraction grating of claim 1, wherein said at least
one structural element comprises a plurality of longitudinal
channels defined within said modified optical fiber, and sized and
positioned in accordance with a first predetermined pattern.
9. The fiber diffraction grating of claim 8, wherein at least a
portion of said plural longitudinal channels are filled with one
of: vacuum, air, a predetermined gaseous substance, or a
predetermined dielectric material.
10. The fiber diffraction grating of claim 1, wherein said at least
one structural element comprises a plurality of longitudinal
grooves defined in said modified optical fiber, and sized and
positioned in accordance with a first predetermined pattern.
11. The fiber diffraction grating of claim 10, wherein at least a
portion of said plural longitudinal grooves are filled with one of:
air, or a predetermined dielectric material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present patent application claims priority from the
commonly assigned co-pending U.S. provisional patent application
61/138,907 entitled "Fiber Optic Diffraction Grating", filed Dec.
18, 2008.
FIELD OF THE INVENTION
[0002] The present invention relates generally to fiber grating
type structures, and more particularly to an optical fiber grating
capable of diffracting a portion of a light signal transmission
therethrough at at least one predefined wavelength thereof.
BACKGROUND OF THE INVENTION
[0003] Fiber gratings are incorporated into components that form
the backbone of modern information and communications technologies,
and are suitable for a wide range of applications, such as
information processing and optical fiber communication systems
utilizing wavelength division multiplexing (WDM). There are many
different fiber grating types and configurations, with a wide
variety of capabilities. For example, fiber Bragg gratings are
useful in lasing, filtering and sensing applications. Various Bragg
grating configurations also include chirped fiber gratings useful
in chromatic dispersion compensators and apodized fiber gratings
that are used to eliminate sidelobes in signal transmission
spectra. Another type of fiber grating--a long period grating--is
of particular interest in sensing and filtering applications. Light
passing through a long period grating is modified rather than
reflected, as occurs in fiber Bragg gratings. Also, unlike a fiber
Bragg grating, a long period grating is typically used for coupling
the mode of the fiber core into the fiber cladding. A long period
grating has a spectral characteristic with multiple transmission
gaps. The positions of these gaps along the spectral range depend
on the refractive index of a medium outside the cladding of the
fiber. Thus, changing the outside refractive index produces a shift
in the transmission gaps. Typically, the period of a long period
grating is significantly longer than the wavelength of light
passing through the grating.
[0004] However, there are also a number of important applications
for which an optical fiber grating constructed and configured to
produce at least one spectral dip (corresponding to at least one
predefined wavelength) in the transmission spectrum of a light
signal being transmitted therethrough, for which such a grating
would be the only practical solution, or for which it would be the
best solution (or at least a more optimal solution than a long
period grating). This is especially the case in applications where
fiber gratings of very small lengths are desirable or
necessary.
[0005] There are also useful applications for which it would be
advantageous to provide the above-described diffraction grating
that is substantially produced from a single material (as opposed
to conventional gratings which typically have cores and claddings
of different materials (or which may use the same material for the
core and cladding with one of the materials being doped by another
material), to ensure a predetermined minimum index contrast value
therebetween. Additionally, there are applications for which it
would be useful to have a grating capable of producing at least one
spectral peak in its core light transmission spectrum,
corresponding to at least one predetermined wavelength.
[0006] It would thus be desirable to provide an optical fiber
grating for controlling the light signal transmission therethrough
by diffracting a portion of the transmitted light signal at at
least one predefined wavelength thereof, causing at least one of:
at least one predetermined spectral dip, and/or at least one
predetermined peak, in the resulting light transmission spectrum,
each corresponding to the at least one wavelength of the diffracted
portions(s) of the transmitted light signal. It would also be
desirable to provide the above-described fiber optic diffraction
grating that may be readily fabricated in its entirety from a
single material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] In the drawings, wherein like reference characters denote
corresponding or similar elements throughout the various
figures:
[0008] FIG. 1A shows a schematic diagram of a cross-sectional view
of a first exemplary embodiment of the fiber optic diffraction
grating of the present invention;
[0009] FIG. 1B shows a schematic diagram of a side view of the
first exemplary embodiment of the fiber optic diffraction grating
of FIG. 1A;
[0010] FIG. 2A shows a schematic diagram of a cross-sectional view
of a second exemplary embodiment of the fiber optic diffraction
grating of the present invention; and
[0011] FIG. 2B shows a schematic diagram of a side view of the
second exemplary embodiment of the fiber optic diffraction grating
of FIG. 2A.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to an optical fiber
grating having a core, that is capable of controlling the light
signal transmission therethrough by causing at least one of: at
least one spectral peak, and/or at least one spectral dip in its
core light transmission spectrum, corresponding to at least one
predetermined wavelength.
[0013] The inventive optical fiber diffraction grating comprises at
least one longitudinally positioned structural element of a
predetermined geometric profile and that is configured for
diffracting a portion of the transmitted light signal at at least
one predefined wavelength thereof, from at least one core mode into
at least one of: at least one cladding mode and/or at least one
radiating mode. Various embodiments of a number of novel techniques
for fabrication of the inventive optical fiber diffraction grating
are provided, inclusive of a novel technique for fabricating the
inventive grating from a single material.
[0014] Advantageously, such novel fabrication techniques rely on
configuration of a desired geometric profile for the at least one
structural element portion of the novel grating, each profile
comprising a number of readily configurable parameters that can be
selected and/or adjusted during fabrication, to produce a variety
of novel fiber diffraction gratings, each having a corresponding
specific desirable core transmission spectrum having at least one
of: least one spectral peak, and/or at least one spectral dip
therein, corresponding to at least one specific desired wavelength,
dependent on the configuration of the applicable geometric
profile.
[0015] Other objects and features of the present invention will
become apparent from the following detailed description considered
in conjunction with the accompanying drawings. It is to be
understood, however, that the drawings are designed solely for
purposes of illustration and not as a definition of the limits of
the invention, for which reference should be made to the appended
claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The present invention is directed to an optical fiber
grating having a core, that is capable of controlling the light
signal transmission therethrough by causing at least one of: at
least one spectral peak, and/or at least one spectral dip in its
core light transmission spectrum, corresponding to at least one
predetermined wavelength. The inventive optical fiber diffraction
grating accomplishes the above, by providing at least one
longitudinal structural element therein of a predetermined
geometric profile and that is configured for diffracting a portion
of the transmitted light signal at at least one predefined
wavelength thereof, from at least one core mode into at least one
of: at least one cladding mode and/or at least one radiating
mode.
[0017] In various embodiments of the inventive optical fiber
diffraction grating, an number of novel techniques for fabrication
thereof are provided, inclusive of a novel technique for
fabricating the inventive grating from a single material.
Advantageously, the various novel fabrication techniques provided
for the novel fiber diffraction grating in accordance with the
present invention rely on configuration of a desired geometric
profile for the at least one structural element portion of the
novel grating, each profile comprising a number of readily
configurable parameters that can be selected and/or adjusted during
fabrication, to produce a variety of novel fiber diffraction
gratings, each having a corresponding specific desirable core
transmission spectrum having at least one of: least one spectral
peak, and/or at least one spectral dip therein, corresponding to at
least one specific desired wavelength, dependent on the
configuration of the applicable geometric profile.
[0018] It is well known that in conventional optical fibers the
necessary index contrast between the fiber core and cladding, to
ensure that a light signal being transmitted therethrough would
substantially travel in a core mode, can be achieved in a number of
different ways, for example by using materials with sufficiently
different refractive index for each of the core and the cladding,
through doping of the core with an appropriate material, and in
other well-known ways.
[0019] In recent years, a different solution, for producing an
optical fiber capable of guiding light through its core, has been
successfully developed--microstructured ("MS") optical fibers are
fibers that enable a different way of guiding light through their
cores, and that can be fabricated from a single material (without
necessity for doping the core). Instead of a conventional core, the
MS fibers in essence provide a "virtual" core, that is defined by a
set of specially configured and positioned predetermined
longitudinal elements disposed around the fiber's central
longitudinal axis. For example, these longitudinal elements may be
a periodic array of longitudinal channels (i.e., "holes") in the
cladding positioned around the fiber's central axis to define a
"core", with light transmitted therethrough now being guided in
such a core. This advantageous light confinement to/within the MS
fiber core takes effect, and is determined by, at least one of the
following two main reasons: [0020] (1) effective refractive index
of the cladding is lower that the region of the MS "core", and/or
[0021] (2) the structure of periodic array of channels results in
Bragg reflections in the MS fiber structure that cause the MS
"core" to guide light, for example through a centermost
channel.
[0022] In accordance with various embodiments of the present
invention, the novel optical fiber diffraction grating may be
readily produced and configured, either by processing a
conventional MS fiber structure in a novel manner (as described
below in connection with FIGS. 1A and 1B), and/or by preparing a
specially configured novel structure based on, but departing, at
least in part, from MS fiber principles.
[0023] Referring now to FIGS. 1A and 1B, a first embodiment of the
inventive optical fiber diffraction grating is shown as diffraction
grating 10, based on a MS fiber structure perform 12a having a
virtual core 14, and having at least one MS element 16a positioned
and configured to produce a sufficient degree of light confinement
to define the core 14 (for example, as shown in FIG. 1A, at least
one MS element 16a may comprise a plurality of concentrically
positioned sets of longitudinal channels in the fiber structure.
This MS fiber 12a configuration produces a core mode in the core
14, however at least some portion of the energy of a light signal
transmitted through the core 14 in fact propagates into the
cladding 18, essentially forming light transmission spectrum
"tails" (in the direction of the channels)
[0024] In accordance with the present invention, the diffraction
grating 10 is produced by twisting the MS structure preform 12a, to
produce a modified structure 12 having at least one structural
element 16b therein, of a predefined geometric profile, comprising
specifically selected values for at least a twist helical pitch HP
(e.g., at a certain pitch angle), and a twist helical diameter HD
(and in connection with this inventive embodiment also comprising a
"twist profile").
[0025] As the MS structure preform 12a is twisted, the
abovementioned "tails" begin to cross the forming at least one
structural element 16b, and with a properly selected geometric
profile (i.e., for predetermined values of HP and HD), Bragg
reflections, configured to diffract the light signal from a core
mode of at least one predetermined wavelength traveling through the
core 14, for at least one particular desired wavelength, away from
the core 14 (thus essentially extracting at least a portion of the
light signal from the core 14, and causing a corresponding dip in
the core transmission spectrum). In one embodiment of the present
invention, at certain wavelengths the resulting core transmission
may appear similar to that of a long period grating (although in
the case of the inventive grating 10, the spectral dips in the
transmission spectrum would not me sensitive to any outside
medium).
[0026] Advantageously, the various parameters (HP, HD, etc.) of the
geometric profile of the at least one structural element 16b, may
be selected and/or configured to produce at least one spectral dip,
and/or at least one spectral peak in the core transmission spectrum
for one or more predefined desired wavelengths. The geometric
profile of the at least one structural element 16b, may be also
selected and/or configured to produce at least one radiating mode
(i.e., in which Bragg reflections cause the diffracted portion of
the light signal to leave the fiber completely). Therefore,
advantageously, the novel diffraction grating 10, may achieve the
desired diffraction in at least one of: at least one cladding mode,
and/or at least one radiating mode.
[0027] While the use of a single material, with plural channels as
MS elements, for the perform 12a is advantageous for certain
applications (such as for sensor elements that may be heated in a
manner sufficient to cause the resulting grating 10 to expand and
then contract, in other embodiments of the invention, the at least
one MS element 16a (e.g., channels) can be filled with different
materials (e.g., vacuum, air, a predetermined gaseous substance, or
a predetermined dielectric material, etc.) or may otherwise
comprise regions of a different refractive index from the cladding
18. The advantage of this approach, is that it allows a greater
level of control of the index contrast between the core 14 and the
cladding 18. If this embodiment is utilized then both of the light
confinement principles (1) and (2) described above are jointly
applicable, with the impact of each principle being dependent on
the positioning of the MS elements 16a within the perform 12a. In
another embodiment of the invention, the MS elements 16a may
comprise a plurality of groves (not shown).
[0028] Referring now to FIGS. 2A and 2B, a second embodiment of the
inventive optical fiber diffraction grating is shown as diffraction
grating 40, based on a specially configured MS fiber structure 50,
having a virtual core 52, and having a plurality of structural
elements 56 positioned and configured to produce a sufficient
degree of light confinement to define the core 52, and to also
produce at least one predefined distortion in lateral periodicity
58, between the plural structural elements thereof, that
advantageously results in at least one predefined narrow defect
state in the light transmission spectrum in a transverse direction,
which causes a corresponding at least one spectral dip in the core
transmission spectrum for at least one wavelength that corresponds
to the at least one defect state.
[0029] Distortion 58 can be achieved in a number of different ways.
For example, if distances between each concentric set of different
plural structural elements 56 are substantially the same (e.g.,
D1), then the least one predefined distortion in lateral
periodicity 58 may be readily produced by configuring the distance
between two predetermined plural element 56 sets (selected based on
the needed spectral position corresponding to the desired defect
state), can be configured as D2, different from other uniform D1s.
Other inventive ways of achieving at least one distortion 58, for
example by altering the size of one or more particular concentric
sets of plural elements 56, or by using one or more particular
concentric sets of plural elements 56 composed of a different
material than core 54 (i.e., having different refractive indices
therefrom). The diffracting grating 40 is advantageous in that it
does not require the structure 50 to be twisted or to otherwise be
physically manipulated (other than the pre-configuration necessary
to produce the at least one distortion 58).
[0030] Thus, while there have been shown and described and pointed
out fundamental novel features of the invention as applied to
preferred embodiments thereof, it will be understood that various
omissions and substitutions and changes in the form and details of
the devices and methods illustrated, and in their operation, may be
made by those skilled in the art without departing from the spirit
of the invention. For example, it is expressly intended that all
combinations of those elements and/or method steps which perform
substantially the same function in substantially the same way to
achieve the same results are within the scope of the invention. It
is the intention, therefore, to be limited only as indicated by the
scope of the claims appended hereto.
* * * * *