U.S. patent application number 11/415923 was filed with the patent office on 2007-11-01 for waveguide polarization beam splitters and method of fabricating a waveguide wire-grid polarization beam splitter.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Charles T. Black, Gian-Luca Bona, Timothy J. Dalton, Nicholas C.M. Fuller, Roland Germann, Maurice McGlashan-Powell, Chandrasekhar Narayan, Robert L. Sandstrom.
Application Number | 20070253661 11/415923 |
Document ID | / |
Family ID | 38648388 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070253661 |
Kind Code |
A1 |
Black; Charles T. ; et
al. |
November 1, 2007 |
WAVEGUIDE POLARIZATION BEAM SPLITTERS AND METHOD OF FABRICATING A
WAVEGUIDE WIRE-GRID POLARIZATION BEAM SPLITTER
Abstract
A method in effectuating the redirection of light which is
propagated within a waveguide, and which eliminates the necessity
for a bending of the waveguide, or the drawbacks encountered in
directional changes in propagated light involving the need for
sharp curves of essentially small-sized radii, which would
resultingly lead to excessive losses in light. In this connection,
the method relates to the fabricating and the provision of a
wire-grid polarization beam splitter within an optical waveguide,
which utilizes a diblock copolymer template to formulate the
wire-grid.
Inventors: |
Black; Charles T.; (New
York, NY) ; Bona; Gian-Luca; (San Jose, CA) ;
Dalton; Timothy J.; (Ridgefield, CT) ; Fuller;
Nicholas C.M.; (Ossining, NY) ; Germann; Roland;
(Wangen, CH) ; McGlashan-Powell; Maurice; (Mount
Vernon, NY) ; Narayan; Chandrasekhar; (San Jose,
CA) ; Sandstrom; Robert L.; (Chestnut Ridge,
NY) |
Correspondence
Address: |
SCULLY SCOTT MURPHY & PRESSER, PC
400 GARDEN CITY PLAZA
SUITE 300
GARDEN CITY
NY
11530
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
38648388 |
Appl. No.: |
11/415923 |
Filed: |
May 1, 2006 |
Current U.S.
Class: |
385/11 ;
216/24 |
Current CPC
Class: |
G02B 6/136 20130101;
B29D 11/00759 20130101; G02B 6/126 20130101; G02B 2006/1215
20130101 |
Class at
Publication: |
385/011 ;
216/024 |
International
Class: |
G02B 6/27 20060101
G02B006/27; B29D 11/00 20060101 B29D011/00 |
Claims
1. A method of fabricating an optical waveguide polarization beam
splitter, wherein said beam splitter incorporates a wire-grid array
in said waveguide for facilitating the transmission or reflection
of light propagated within said waveguide in dependence upon
incident polarization of the propagated light: a) depositing a
dielectric waveguide substrate layer onto a base layer; b) applying
a light guiding film of a dielectric material onto the exposed
surface of said waveguide substrate; c) providing a diblock
copolymer template having an array of pores formed therethrough; d)
masking off pores to provide a single line of said template pores;
e) etching at least one trench downwardly through said guiding film
to said waveguide substrate surface; f) depositing metal wire
material into said line of pores formed in said diblock polymer
template material; g) stripping said diblock copolymer material
while permitting metal wire to remain embedded in said waveguide
guiding film; h) etching off excess metal wire material down to the
exposed surface of said waveguide guiding film; and i) depositing a
cover layer of a dielectric material onto said waveguide guiding
film.
2. A method as claimed in claim 1, wherein said waveguide substrate
and cover layer are each constituted of SiO.sub.2 or doped
SiO.sub.2.
3. A method as claimed in claim 1, wherein said waveguide guiding
film is constituted of SiO.sub.2.
4. A method as claimed in claim 1, wherein said waveguide guiding
film possesses a higher index of refraction than the indices of
refraction of said waveguide substrate and cover layers.
5. A method as claimed in claim 1, wherein said pores each have a
diameter in the range of about 50-100 nm and are spaced from each
other in the range of about 150-200 nm.
6. A method as claimed in claim 1, wherein said pores are masked
off so as to leave a single row of diblock copolymer template pores
extending at an angle relative to the initial direction of light
propagation into said waveguide.
7. A method as claimed in claim 6, wherein said angle extends at
about 45 degrees across said waveguide.
8. A method as claimed in claim 1, wherein said diblock copolymer
is selected from the group of materials consisting of polystyrene
and polymethylmethacrylate and composites thereof.
9. A method as claimed in claim 1, wherein said diblock copolymer
comprises a spin-on copolymer template provided in said waveguide
guiding film.
10. A method as claimed in claim 1, wherein said metal wire is
sputter deposited into said line of pores formed in said diblock
polymer template material.
11. A method as claimed in claim 1, wherein said metal wire is
selected from the group of materials consisting of gold, silver
copper, anodized aluminum and alloys of said metals.
12. A method as claimed in claim 3, wherein said waveguide guiding
film has a thickness of about 2 microns.
13. A method as claimed in claim 1, wherein said array of pores are
formed using a film of porous anodized aluminum.
14. An optical waveguide polarization beam splitter, wherein said
beam splitter comprises a wire-grid array in said waveguide so as
to facilitate the transmission or reflection of light propagated
within said waveguide in dependence upon incident polarization of
the propagated light said wire-grid array comprising a metal dot
array formed within said waveguide, said waveguide further
comprising a planar, slab-shaped waveguide structure having
superimposed layers of a dielectric substrate, a SiO.sub.2 layer
and a guiding film layer, said metal dot array extending diagonally
across and downward in said guiding film layer, whereby photons of
light propagated by a photonic integrated circuit having electrical
field vectors parallel to the metal dot array are reflected at an
angle relative to the initial direction of light with the waveguide
while photons with an electrical field vector perpendicular to the
metal dot array facilitate light to continue to propagate in the
initial direction of transmission thereof.
15-16. (canceled)
17. A waveguide polarization beam splitter, as claimed in claim 14,
wherein said metal dot array has a strippable diblock copolymer
deposited thereon so as to form a pore line having pore diameters
within a range of about 50-100 nm at pore spacings within a range
of about 150-200 nm.
18. A waveguide polarization beam splitter, as claimed in claim 17,
wherein said diblock copolymer is selected from the group of
materials consisting of polystyrene, polymethylmethacrylate and
composites thereof.
19. A waveguide polarization beam splitter, as claimed in claim 14,
wherein said metal dot array forming said wire-grid is selected
from the group of materials consisting of anodized aluminum, gold,
silver and copper and alloys of said metals.
20. A waveguide polarization beam splitter, as claimed in claim 14,
wherein said beam splitter comprises a ridged waveguide structure
having intersecting waveguide sections extending at 90 degrees
relative to each other; a parallel metal wire-grid row with 50-100
nm diameter wire pores and 150-200 nm wire spacing extending
diagonal across the intersection of said waveguide sections; and a
strippable diblock polymer material covering said metal wire grid
pores.
21. A waveguide polarization beam splitter, as claimed in claim 20,
wherein said copolymer template is formed by a spun-on template
extending into the guiding film layer of said waveguide
structure.
22. A waveguide polarization beam splitter, as claimed in claims 14
or 21, wherein a cover layer of a dielectric material is deposited
on the guiding film layer of said waveguide structure.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to waveguide polarization beam
splitters, and particularly, pertains to a wire-grid polarization
beam splitter including a planar or ridged waveguide, which is
adapted to either transmit or reflect light within the waveguide in
dependence upon incident polarization.
[0003] Furthermore, the present invention also relates to a novel
method of fabricating a waveguide polarization beam splitter, and
particularly a wire-grid polarization beam splitter with a planar
or a ridge waveguide, which is adapted to be utilized in order to
either transmit or reflect light within the waveguide in dependence
upon incident polarization.
[0004] In essence, a waveguide polarization beam splitter comprises
a key element in a photonic integrated circuit, whereby beam
splitters of that type can be advantageously employed as
directional couplers, as well as being useful as directional
modulators and switches when utilized in conjunction with a
polarization rotational waveguide element.
[0005] Nevertheless, it is conceivable that problems may be
encountered in connection with the redirecting of light within a
waveguide, for instance, such as at an angle of 90 degrees relative
to the direction of initial propagation of the light upon use
thereof with a polarization-rotating element, as may be currently
known in the technology.
[0006] In view of the above-mentioned problem, which is prevalent
in the present-state of the technology, various investigations have
been conducted and attempts made in addressing the issue of
redirecting light in different directions, the latter of which are
at sharp angles relative to the original direction of propagation
of the light within a waveguide. Ordinarily, this redirecting of
the propagated light has been implemented through the utilization
of cylindrical waveguides, for example, such as in the form of
optical fibers, or through the intermediary of ridged waveguides,
which, however, are subject to being burdened with large losses of
light, thereby resulting in poor and consequently unsatisfactory
degrees of efficiencies when the radii of curvature in redirecting
the lights are reduced so as to be extremely small in size.
Consequently, these light losses are generally ascribed as being
due to so called a micro-bending phenomenon.
[0007] 2. Discussion of the Prior Art
[0008] Heretofore, this particular aspect in the problems of
encountered light losses has not been fully addressed in the
technology, and any practical attempt in solving this problem in
the redirection of the propagated light has ordinarily be in the
employment of a directional coupler. However, directional couplers
are primarily passive devices and enable only a fraction of the
incident light to be redirected, whereby the redirected light is
again bounded by relatively large radii of curvatures, which are
necessitated due to the limitations resulting from micro-bending
losses. Although attempts have been made at switching all of the
light successfully into one arm of a directional coupler, such as
by means of LiNb0.sub.3 and other kinds of electro-optical
waveguide elements, the deviation of the light from the original
direction thereof is, however, again limited in scope. Furthermore,
although various types of wire-grid polarization beam splitters
have been developed in the technology, none are designed to be
operative within a waveguide and, consequently, are of essentially
limited value within the context of the subject matter of the
present invention.
SUMMARY OF THE INVENTION
[0009] In order to obviate or ameliorate the drawbacks which are
encountered in the technology, the present invention is directed to
the provision of a novel method in effectuating the redirection of
light which is propagated within a waveguide, and which eliminates
the necessity for a bending of the waveguide, or the drawbacks
encountered in directional changes in propagated light involving
the need for sharp curves of essentially small-sized radii, which
would resultingly lead to excessive losses in light. In this
connection, the present invention is directed to a method of
fabricating and in the provision of a wire-grid polarization beam
splitter within an optical waveguide, which utilizes a diblock
copolymer template.
[0010] In essence, the use of diblock copolymers in connection with
the forming of templates are known in the technology, having
specific reference, for example, to C. T. Black and K. W. Guarini,
"Structural Evolution of Cylindrical Phase Diblock Copolymer Thin
Films", J. Poly Sci. Part A 42, 1970 (2004); C. T. Black, K. W.
Guarini, R. L. Sandstrom, S. Yeung and Y. Zhang, "Formation of
Nanometer-Scale Dot Arrays from Diblock Copolymer Templates, Mat.
Res. Soc. Symp. Proc. 728, S491 (2002); and K. W. Guarini, C. T.
Black, K. R. Milkove and R. L. Sandstrom, "Sub-Lithographic
Patterning Using Self-Assembled Polymers for Semiconductor
Applications", J. Vac. Sci. Tech. B, 19 2784 (2001).
[0011] All of these structures, as disclosed in the above-mentioned
literature, are directed to the provision of various templates
utilizing diblock copolymer template pore formations in a nanometer
scale, preferably, but not limited to such as 50 to 100 nm diameter
thin-film template pore formations, and wherein the basic concept
thereof is generally known in the technology. However, none of the
disclosures, as set forth hereinabove, or in any other prior art
publications, are directed to the utilization of such diblock
copolymer thin films in conjunction with a method of fabricating a
waveguide wire-grid polarization beam splitter.
[0012] In connection with the foregoing, diblock copolymers provide
a highly desirable variety in the formation of possible
nanostructures, such as in being able to implement their size
tunability and in their manufacturing process compatibility. In
particular, highly acceptable diblock copolymer thin-films
employable for the inventive purposes are generally constituted of
suitable materials, preferably such as polystyrene (PS) or
polymethylmethacrylate (PMMA), although numerous other copolymer
materials would also be applicable thereto. The structures and
concepts of forming such diblock copolymer thin films are readily
and clearly discussed in the above-mentioned literature, which are
publications of the International Business Machines Corporation,
the assignee of the present application, and the disclosures of
which are incorporated herein by reference in their entireties.
[0013] In particular, as set forth hereinabove, pursuant to the
invention, by means of the novel waveguide wire-grid polarization
beam splitter, light can be conducted at an angle of 90 degrees
relative to the original direction of propagation thereof to a grid
(such as in a TM mode). Thus, when an electrical field vector is
perpendicular to the grid (TE mode) the direction of propagation of
the light through the waveguide is undisturbed and light continues
traveling in its original direction. However, when utilized with a
polarization-rotating element, this device would then enable the
directional switching of the light as a function of
polarization.
[0014] Accordingly, it is an object of the invention to provide a
novel waveguide wire-grid polarization beam splitter for the
transmission or reflection of light and redirection thereof within
a waveguide.
[0015] Another object of the present invention resides in the
provision of an optical waveguide wire-grid polarization beam
splitter, wherein the optical waveguide utilizes a diblock
copolymer template for the function of the wire-grid.
[0016] A further object of the invention resides in the provision
of a method of forming a waveguide wire-grid polarization splitter
in a waveguide, which utilizes a diblock copolymer template for the
fabrication of the wire-grid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Reference may now be made to the following detailed
description of the invention, illustrative of various embodiments
and aspects in connection with the fabrication of a wire-grid
polarization beam splitter within an optical waveguide through the
use of a diblock copolymer template; and wherein:
[0018] FIG. 1 illustrates a diblock copolymer template pore
formation structure possessing 50 to 100 nm sized pores;
[0019] FIG. 2 illustrates a planar or slab type waveguide, which is
built up to a guiding film layer, such as doped SiO.sub.2;
[0020] FIG. 3 illustrates a ridged waveguide structure with a
wire-grid polarization beam splitter pursuant to the present
invention;
[0021] FIG. 4 illustrates a planar or slab waveguide with a
wire-grid polarization beam splitter;
[0022] FIG. 5 illustrates a ridged waveguide structure with a
spun-on diblock copolymer template; and
[0023] FIG. 6 illustrates a ridged waveguide structure with a
masked off diblock copolymer film arrangement.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring in specific detail to the invention, it is noted
that, in essence, the structure of the waveguide polarization beam
splitter is predicated on the concept that a grid of parallel
metallic wires reflect radiation of one polarization while
transmitting the other polarization, providing that the wavelength
of the light is approximately 10 times larger than the period of
the grid, or in the present instance, the metal dot array wire or
wires. Through an application of this principle, it is possible to
construct such a wire-grid within a waveguide structure by the
inventive techniques, as disclosed and elucidated hereinbelow.
[0025] As illustrated in FIG. 1 of the drawings, a template 10,
which is constituted of a diblock copolymer, possesses a pore
formation 12 (in the nanometer scale), which pores are in a
generally well-ordered or uniformly hexagonal template array. The
template 10 is employable in a waveguide light polarization
arrangement or structure, as described hereinbelow and incorporates
a pore diameter size range of preferably from about 50-100 nm, and
with a pore spacing of preferably from about 150-200 nm, although
other pore diameter sizes and spacings are contemplateable within
the context and scope of the invention. The diblock copolymer
materials may comprise polystyrene (PS) or polymethylmethacrylate
(PMMA), although other copolymers and composites thereof may also
be suitable in the forming of the waveguide template, as described
in the above-mentioned literature.
[0026] A waveguide structure 14 of an embodiment, which is of a
planar or slab-like shape, as shown in FIG. 2, may be fabricated by
standard or known methods of a supportive or base substrate 16,
which is constituted of a suitable dielectric material, for
example, such as Si. A dielectric waveguide layer 18 possessing an
index of refraction (ns) is superimposed on the base layer 16, and
could typically be constituted of SiO.sub.2. A light guiding film
20 possessing a higher index of refraction (nf) is then deposited
on that dielectric layer 18, and could be constituted of SiON. A
cover layer or capping layer 22 having a lower index of refraction
(nc) can then be deposited on the guiding film 20, and can be
constituted of SiO.sub.2 or doped SiO.sub.2, although other
dielectric materials can be employed with the invention.
[0027] In the case of a ridged waveguide 30, as shown in FIG. 3,
the structure comprises two intersecting sections 32, 34 of the
waveguide 30. At the location of the intersection 36 of these two
waveguide sections 32, 34, a mesh-like metal dot array wire 38,
each incorporating a pore diameter ranging from about 50 to 100 nm
and with spacings therebetween of from about 150 to 200 nm, as
shown in FIG. 1, is placed across a diagonal 40 of this
intersection 36 to a vertical depth of 1-5 microns extending into
the guiding film layer. Light propagating through the one waveguide
section 32 will either be transmitted or reflected at an angle of
90 degrees at the locale of this intersection 36, whereby the 90
degree reflection would then allow light to now propagate into the
second waveguide section 34, which is perpendicular or at a right
angle to the first waveguide section 32. Photons 44 whose
electrical field vectors are parallel to these metal dot array wire
elements would then be reflected 90 degrees, so as to then
propagate or travel at 90 degrees relative to their original
direction within the planar waveguide, i.e., the metal dot array
wire spacings would totally reflect the incoming beam of light.
Photons 46 with an electrical field vector perpendicular to these
metal dot array wire elements would continue to propagate in their
original direction, which was determined by their initial
propagating condition (unaffected by the metal dot array wire). The
advantage resides in the fact that the light is now capable of
turning sharp corners (for example, 90 degrees) and the metal dot
wire array or grid 38 can be incorporated into the monolithic
waveguide structure 30. At this time, this novel construction is
not readily possible to implement in the technology with the use of
conventional directional light couplers or other conventional light
polarization beam splitters.
[0028] In the case of the planar or slab-like waveguide 14, as
represented in FIG. 4, the metal dot array wire or grid 38 would be
placed at an angle of 45 degrees relative to the direction 44 of
the propagated light, as in FIG. 3. The number of spacing widths
between these metal dot array wires or elements is designed to be
sufficient in order to be able to intercept the entire width of the
launched or initially propagated light beam (.about.1 mm) traveling
through the waveguide.
[0029] Reverting to FIG. 5 of the drawings, there is illustrated a
ridged waveguide structure 50, comprising a first waveguide 52 and
a second waveguide 54 extending at 90 degrees relative thereto, so
as to form a configuration similar to that of FIG. 3. However, in
this instance, at the intersection 56 between the waveguides 52,
54, the latter of which include a guiding film layer 58, 60, such
as, for example, of doped SiO.sub.2, although this can also be
SiON, there is provided a spun-on diblock copolymer template 62.
The template may be of a diblock copolymer material, which
possesses a pore size and pore spacing, as described in connection
with that of FIG. 1 of the drawings, i.e., such as polystyrene or
polymethylmethacrylate, or the like.
[0030] In the embodiment of FIG. 6, the waveguide structure 70,
which has the first and second waveguide sections 72, 74 extending
at 90 degrees relative to each other, is built up to the guiding
film dielectric layer 76 with a mask 78 leaving a line of 50 to 100
nm pores from the diblock copolymer template 80. This line 80 of
template pores is directed at 45 degrees relative to incident light
across from the intersection 82 between the waveguide sections 72,
74.
[0031] In essence, a method setting forth a unique and advantageous
technique for fabricating the waveguide grid (such as a metal dot
array wire or wires) light polarization beam splitter entails the
following method steps: [0032] 1) Depositing the waveguide
substrate consisting of a dielectric material having an appropriate
thickness, for example, such as about 8 microns in the case of
SiO.sub.2 onto Si or other similar substrate; [0033] 2) Depositing
the core or guiding film of an appropriate thickness, such as 2
microns for SiON or doped SiO.sub.2; [0034] 3) Applying a spin-on
random diblock copolymer, as described hereinabove, to prepare the
surface for vertically-oriented cylindrical phase template pores,
and curing in a vacuum oven, then rinsing in toluene for a
monolayer formation of selective random copolymers; [0035] 4)
Subsequently, applying (as in step 3) a spin-on
polystyrene-polymethylmethacyrate (30% PS-70% PMMA) diblock
copolymer and curing in a vacuum oven, then optionally exposing the
substrate to ultraviolet (UV) light, then removing PMMA from the
cylindrical pores in acetic acid and a deionized water rinse to
create a porous polystyrene template; [0036] 5) Masking off all
pores with the exception of a single row of template pores at 45
degrees relative to the direction of light propagation while
permitting for a remainder of 75 to 100 nm of polymer on either
side of this line of pores; [0037] 6) Deep etching trenches (2
microns for SiON core) through the core utilizing a 50 degree line
of pores as a template down to a substrate layer, for example
SiO.sub.2, by utilizing reactive ion etching (RIE); [0038] 7)
Sputter depositing or atomic layer depositing (ALD) a metal wire,
such as Au, Ag, Cu, or the like, into 50 to 100 nm diameter lines
of holes; [0039] 8) Removing the mask from the line formed of
template pores; [0040] 9) Removing the remaining diblock copolymer
using either oxygen plasma, ozone or solvent
(e.g.--1-methyl-2-pyrrolidone (NMP)), or combinations thereof,
while permitting the metal wire to remain embedded in the core or
guiding film of the waveguide; [0041] 10) Removing excess metal
down to the surface guiding layer of the waveguide (for example,
SiON) using chemical mechanical polishing (CMP), wet etching, or
combinations thereof; and [0042] 11) Depositing a cover layer of
SiO.sub.2 or other suitable dielectric material onto the waveguide
surface.
[0043] Alternatively, subsequent to the dielectric substrate having
been deposited, a layer of diblock copolymer of a thickness
corresponding to that of the guiding film dimension, for example, 2
microns in the case of SiON, can be deposited and developed into 2
micron deep pores. This process entails use of an electric field to
vertically align the diblock copolymer cylindrical pores (see,
e.g.--T. Thurn-Albrecht, J. Schotter, G. A. Kastle, N. Emley, M. T.
Tuominen, T. P. Russell, T. Shibauchi, L. Krusin-Elbaum, K.
Guarini, and C. T. Black, "Ultrahigh Density Nanowire Arrays Grown
in Self-Assembled Diblock Copolymer Templates", Science 290, 2126
(2000)). The excess pores can be masked off, as described
hereinabove in step 5), and the pores at 50 degrees relative to the
direction of propagation can be filled with a metal, in accordance
with step 7).
[0044] The diblock copolymer is then removed in accordance with
steps 8) and 9) and a deposition of the guiding layer of the
waveguide (2 microns thickness of SiON, in this instance) is
followed by the deposition thereon of the dielectric cover
layer.
[0045] Other alternative methods in creating the wire-grid arrays
may also utilize applying porous anodic alumna to create the
template of 50-100 diameter pores. This technique may also
incorporate deep trench etching in a manner similar to that
described above used in combination with diblock copolymer
templates, wherein the anodized aluminum provides a further novel
aspect, which may be utilized in conjunction with the present
invention.
[0046] While the present invention has been particularly shown and
described with respect to preferred embodiments thereof, it will be
understood by those skilled in the art that the foregoing and other
changes in forms and details may be made without departing from the
scope and spirit of the present invention. It is therefore intended
that the present invention not be limited to the exact forms and
details described and illustrated, but fall within the scope of the
appended claims.
* * * * *