U.S. patent application number 11/137297 was filed with the patent office on 2006-11-23 for optical waveguide disk.
This patent application is currently assigned to Imation Corp.. Invention is credited to Jathan D. Edwards.
Application Number | 20060263026 11/137297 |
Document ID | / |
Family ID | 37397743 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060263026 |
Kind Code |
A1 |
Edwards; Jathan D. |
November 23, 2006 |
OPTICAL WAVEGUIDE DISK
Abstract
The invention is directed to an optical element and techniques
for creating the optical element. The optical element may comprise
an optical delay line or a similar optical part. The optical
element may have a wide variety of applications in optical data
transmission, optical computing, short term transient storing,
applications for optical timing, or a number of other applications.
Rather than drawing a long length of optical fiber, the invention
can make use of mastering and replication techniques to define a
long continuous groove in a substrate. Alternatively, an etching
process may be used. In either case, the groove is filled with an
optical material of higher index of refraction than the substrate
to define a light guide that can transmit light via total internal
reflection (TIR).
Inventors: |
Edwards; Jathan D.; (Afton,
MN) |
Correspondence
Address: |
Attention: Eric D. Levinson;Imation Corp.
Legal Affairs
P.O. Box 64898
St. Paul
MN
55164-0898
US
|
Assignee: |
Imation Corp.
|
Family ID: |
37397743 |
Appl. No.: |
11/137297 |
Filed: |
May 23, 2005 |
Current U.S.
Class: |
385/132 |
Current CPC
Class: |
B29D 11/00663 20130101;
G02B 6/138 20130101; G02B 6/122 20130101; B29C 45/0053 20130101;
G02B 6/2861 20130101; B29L 2011/0075 20130101; G02B 6/1221
20130101; G02B 6/02033 20130101; B29C 45/263 20130101 |
Class at
Publication: |
385/132 |
International
Class: |
G02B 6/10 20060101
G02B006/10 |
Claims
1-10. (canceled)
11. A method of creating an optical element comprising: forming a
continuous groove in a disk-shaped thermoplastic substrate, the
substrate defining a first index of refraction, wherein for the
continuous groove comprises injection molding the substrate to
define the continuous groove and wherein the continuous groove
defines a spiral pattern through the substrate; forming input and
output elements in the disk-shaped thermoplastic substrate via the
injection molding; and filling the groove with a material to define
an optical waveguide through the substrate, the material defining a
second index of refraction, the second index of refraction being
higher than the first index of refraction such that light can
traverse the material in the groove via total internal reflection
(TIR).
12. (canceled)
13. The method of claim 11, further comprising: creating a master
disk to define a feature that corresponds to the continuous groove;
creating one or more stampers from, the master disk; and injection
molding the substrate using one of the stampers.
14. The method of claim 11, further comprising: creating the input
element to allow light introduction into the material in the
groove, wherein the input element is formed in the substrate at one
of an inner diameter and an outer diameter of the substrate; and
creating the output element to allow light extraction from the
material in the groove, wherein the output element is formed in the
substrate at one of an inner diameter and an outer diameter of the
substrate.
15. (canceled)
16. The method of claim 11, wherein a width of the groove is
between approximately 2 and 150 microns.
17. The method of claim 11, wherein a depth of the groove is
between approximately 2 and 150 microns.
18. The method of claim 17, wherein a width of the groove and the
depth of the groove are between approximately 2 and 10 microns and
the material in the groove defines a single mode optical
waveguide.
19. The method of claim 17, wherein a width of the groove and the
depth of the groove are between approximately 30 and 100 microns
and the material in the groove defies a multi-mode optical
waveguide.
20. The method of claim 11, further comprising forming a second
material over the substrate such that the material in the groove is
substantially encased by the substrate and the second material,
wherein the second material defines an index of refraction less
than the index of refraction of the material in the groove.
21. (canceled)
Description
TECHNICAL FIELD
[0001] The invention relates to fiber optics and, more
particularly, to optical light guides that may be used as optical
delay lines or other optical computing elements.
BACKGROUND
[0002] Fiber optics are commonly used for many applications,
including data transfer applications and a number of optical
computing applications. For data transfer, light is typically
transferred down a length of optical fiber from a source to a
destination. The optical fiber comprises a light guide that
operates according to principles of total internal reflection
(TIR). The light may be modulated as it is introduced into the
optical fiber in order to encode information in the transmitted
light. For example, information may be encoded in the light by
switching the light on and off, modulating the light intensity,
modulating the frequency and wavelength of the light, or various
combinations. In some cases, a plurality of different frequencies
of light can be multiplexed on a given light guide for simultaneous
transmission.
[0003] Optical computing is viewed as a potentially high-speed
alternative to conventional computing techniques. The goal of an
entirely optical computing machine is to replace the electrical
currents and voltages common in conventional computing techniques
with manipulations of light. Current implementations typically
rely, at least in part, on opto-electronic elements wherein
electrical signals may be converted to optical signals, transferred
or manipulated, and then converted back to electrical signals.
However, purely optical computing aims to virtually eliminate the
opto-electronic components altogether, and therefore, eliminate the
need for conversions from optical to electrical signals. Light
controlled gates, light to light transistors, light amplification
devices, and a number of other optical computing components are
currently being developed to realize practical optical computing
applications.
[0004] One type of optical component that may be very useful for
optical computing, data transfer applications, or other optics
applications is an optical delay line. An optical delay line is
generally a relatively long length of optical fiber that introduces
a time delay to an optical signal. The amount of time required for
light to traverse the optical fiber (at the speed of light through
the medium) is referred to as the optical delay. Delay lines have
many applications, including applications as short-term transient
memory elements, timing elements, or phase delayed comparator
devices. In some cases, micron adjustments to the length of an
optical delay line may equate to changes in the optical delay on
the order of pico-seconds, which make optical delay lines
attractive as accurate timing elements.
[0005] Optical fiber, such as that used for optical delay lines, is
typically drawn or extruded and then wrapped around a large spool.
In some cases, the optical fiber may be drawn and then embedded in
a resin to form a more rigid and robust optical part. Features may
also be added to optical fibers, such as diffraction gratings, to
facilitate manipulation of the light that traverses the fiber.
SUMMARY
[0006] In general, the invention is directed to an optical element.
The optical element may be an injection-molded part created in a
manner similar to the creation of conventional optical data storage
devices, such as compact disks (CDs) or digital video disks (DVDs).
Unlike conventional CDs or DVDs, however, the optical element
defines an optical light guide that traverses through the element.
The optical light guide may comprise a spiral groove formed in an
injection molded substrate, and the groove may be filled with an
optical material having a higher index of refraction than the
molded substrate. An additional material having an index of
refraction that substantially matches that of the molded substrate
may be formed over the substrate to encase the optical material in
the optical part. Etched glass substrates or other substrate
materials may also be used to realize the invention, but injection
molded substrates yield cost and fabrication advantages.
[0007] Input and output elements may be formed on the optical
element such that light can be introduced at the input element,
traverse the optical material, and emerge from the output element.
The input and output elements may be accessible at the inner
diameter (ID) and outer diameter (OD) of a disk-shaped optical part
that includes a center hole.
[0008] The grooves that define the spiraling optical element may
define widths and depths of approximately 2-100 microns. While
smaller grooves can define a longer light guide through a given
substrate, larger grooves can reduce attenuation of light through
the light guide. The widths and depths of the grooves may also be
affected by the wavelength of light to be transmitted through the
optical material in the grooves. Grooves having widths and depths
of approximately 2-10 microns may be useful for single mode
applications in which a single wavelength of light is transmitted
through the light guide. Larger grooves, e.g., having widths and
depths between approximately 30-150 microns, may be needed for
multi-mode applications in which multiple wavelengths of light are
transmitted through the light guide simultaneously.
[0009] In one embodiment, the invention provides an optical element
comprising a substrate formed with a continuous groove, the
substrate defining a first index of refraction; and a material in
the groove to define an optical waveguide through the substrate,
the material defining a second index of refraction, the second
index of refraction being higher than the first index of refraction
such that light can traverse the material in the groove via total
internal reflection (TIR).
[0010] In another embodiment, the invention provides a method of
creating an optical element comprising forming a continuous groove
in a substrate, the substrate defining a first index of refraction;
and filling the groove with a material to define an optical
waveguide through the substrate, the material defining a second
index of refraction, the second index of refraction being higher
than the first index of refraction such that light can traverse the
material in the groove via total internal reflection (TIR). The
process of forming the continuous groove in the substrate may
comprise injection molding the substrate to define the continuous
groove, or possibly an etching process on glass or another
material. For injection molding of the substrate, a master disk can
be created to define a feature that corresponds to the continuous
groove, and one or more stampers may be created from the master
disk for use in an injection molding apparatus.
[0011] The invention may be capable of providing one or more
advantages. For example, the invention may substantially reduce the
cost of creating an optical element, which can be used for a wide
variety of applications. In particular, the techniques described
herein may allow the creation of optical delay lines without the
need to draw long lengths of optical fiber. Instead, mastering
techniques and high volume replication techniques may be used to
define a substrate having a continuous groove. Optical material may
then be deposited in the groove to define an optical light guide
through the substrate. The described optical elements may also have
improved quality relative to conventional optical delay lines. In
addition, the described optical elements may have improved input
and output ports formed by the mastering, replication and
deposition techniques.
[0012] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a simplified schematic plan view of an optical
element according to an embodiment of the invention.
[0014] FIGS. 2 and 3 are partial cross-sectional side views of
optical elements according to embodiments of the invention.
[0015] FIGS. 4 and 5 are flow diagrams illustrating different
techniques for creating the optical elements described herein.
[0016] FIG. 6 is a block diagram of a mastering system that may be
used in creating the optical elements described herein.
[0017] FIGS. 7-15 are a collection of partial side views
illustrating the creation of an optical element according to an
embodiment of the invention.
DETAILED DESCRIPTION
[0018] In general, the invention is directed to an optical element
and techniques for creating the optical element. The optical
element may comprise an optical delay line or a similar optical
part. The optical element may have a wide variety of applications
in optical data transmission, optical computing, short term
transient storing, applications for optical timing, or a number of
other applications. Rather than drawing a long length of optical
fiber, the invention can make use of mastering and replication
techniques to define a long continuous groove in a substrate.
Alternatively, an etching process may be used.
[0019] In general, the substrate may comprise glass, injection
molded thermoplastic, polycarbonate, polymethyl Methacrylate
(PMMA), a transmissive plastic or possibly another material. An
optical material is deposited in the groove to define an optical
light guide through the substrate. Importantly, the optical
material defines a higher index of refraction than the substrate,
which allows light to be transmitted down the optical light guide
via total internal reflection (TIR).
[0020] TIR generally refers to the phenomenon wherein light
introduced into a light guide traverses the light guide by
reflecting within the guide. TIR generally requires the light guide
to exhibit a higher index of refraction than the surrounding
environment. According to the principles of TIR, any light incident
on the edge of the light guide at an angle less than the so-called
"critical angle" cannot escape the light guide. In this manner,
light properly introduced into one end of the light guide traverses
through the light guide to the other end.
[0021] In accordance with some embodiments of the invention,
mastering techniques may be used to define a master of the
substrate used for the optical part (or an inverse of the
substrate). The master can then be electroplated to define a
stamper (or a family of stampers), which can be used in a
mass-replication process. Examples of mass-replication processes
that use metal stampers created from a master include injection
molding processes, rolling bead processes, or other
photoreplication commonly referred to as "2P" replication. In
alternative embodiments, however, the substrate may be etched or
machined to define the groove without the use of mastering and mass
replication techniques.
[0022] Once an acceptable groove is formed in the substrate, an
optical material can be deposited in the groove to define the
optical light guide through the substrate. For example, the optical
material may comprise a planarization coating that fills groove
features of the substrate. Importantly, the optical material
defines an index of refraction higher than that of the substrate,
which allows TIR principles to apply to light transmission through
the light guide. Input and output elements may be formed on the
optical element such that light can be introduced at the input
element, traverse the optical material, and emerge from the output
element. The input and output elements may be accessible at the
inner diameters (ID) and outer diameter (OD) of a disk-shaped
optical part that includes a center hole.
[0023] In one example, the optical element may be an
injection-molded part created in a manner similar to the creation
of conventional optical data storage devices, such as compact disks
(CDs) or digital video disks (DVDs). Unlike conventional CDs or
DVDs, however, the optical element defines an optical light guide
that traverses through the element. The optical light guide may
comprise a spiral groove formed in an injection molded substrate,
and the groove may be filled with an optical material having a
higher index of refraction than the molded substrate. An additional
material having an index of refraction higher than the optical
material may be formed over the substrate to encase the optical
material in the optical part. For example, the additional material
formed over the substrate to encase the optical material may define
an index of refraction that substantially matches that of the
molded substrate. Alternatively, the optical material may remain
exposed to ambient air, in which case the index of refraction of
the optical material must also be less than that of the ambient
air.
[0024] The grooves that define the spiraling optical element may
define widths and depths of approximately 2-100 microns. While
smaller grooves may define a longer light guide through the
element, larger grooves can reduce attenuation. The widths and
depths of the grooves may also be affected by the wavelength of
light to be transferred through the optical material in the
grooves. Grooves having widths and depths of approximately 2-10
microns may be useful for single mode applications in which a
single wavelength of light is transferred. Larger grooves, e.g.,
having widths and depths between approximately 30-150 microns, may
be needed for multi-mode applications in which multiple wavelengths
of light are transferred simultaneously.
[0025] The optical element may comprise an optical waveguide formed
in surface structure of disk shaped article, i.e., an optical
waveguide disk. Uses or applications of the optical element may
include uses as a data buffering delay-line, an optical MUX/DEMUX,
and a sensing element. In general, the optical waveguide disk
provides advantages in fabrication complexity and cost and size, as
compared to conventional fiber delay-line technology. Again, the
optical waveguide disk may be fabricated using either a glass
substrate with an etching process or, at lower cost, an injection
molding process similar to that used in the creation of optical
recording media such as CDs and DVDs. Other substrate materials may
also be used, particularly if etching or machining is used to
define the grooves.
[0026] FIG. 1 is a simplified schematic plan view of an optical
element 10 according to an embodiment of the invention. Optical
element 10 comprises a substrate 12 formed with a continuous groove
14. The substrate defines a first index of refraction. An optical
material is formed in groove 14 to define an optical waveguide
through substrate 12. The material in groove 14 defines a second
index of refraction, the second index of refraction being higher
than the first index of refraction such that light can traverse the
material in groove 14 via total internal reflection (TIR)
[0027] Optical element 10 may also comprise an input element 16 to
allow light introduction into the material in groove 14 and an
output element 18 to allow light extraction from the material in
groove 14. In the illustrated example, optical element 10 defines a
disk-shape, although other shapes could also be used. The
disk-shape is useful because it facilitates mastering and
mass-replication similar to the creation of conventional optical
storage disks. Groove 14 may define a spiral pattern through
substrate 12, although the invention is not necessarily limited in
that respect. In another example, the groove might alternatively
traverse back and forth in alternatively prescribed patterns
through a substrate of any desired shape. In the illustrated
example, input element 16 and output element 18 are defined at the
inner and outer diameters of substrate 12 respectively, although
these positions of the input and output elements 16 and 18 could be
reversed. A center hole can be punched in substrate 12 to define
the inner diameter and allow for access to input element 16 at the
edge of the center hole. Output element 18 may be accessed via the
outer edge of the outer diameter of optical element 10.
[0028] In some cases, a second material (not shown in FIG. 1) may
be formed over substrate 12 such that the material in groove 14 is
substantially encased by substrate 12 and the second material. In
order to ensure that the material in groove 14 still transmits
light via TIR, the second material should define an index of
refraction less than the index of refraction of the material in
groove 14. Preferably, the index of refraction of the second
material and the index of refraction of substrate 14 substantially
match. Alternatively, if the material formed in groove 14 is
exposed to ambient air, the material in groove 14 should have an
index of refraction less than that of the surrounding air.
[0029] FIG. 2 is a cross-sectional side view of optical element 20,
which may correspond to optical element 10 of FIG. 1. Optical
element 20 comprises a substrate 22 formed with a continuous groove
24 that spirals from an outer diameter to an inner diameter of
optical element. Substrate 22 defines a first index of refraction.
An optical material 25 is formed in groove 24 to define an optical
waveguide through substrate 22. Optical material 25 in groove 24
defines a second index of refraction, the second index of
refraction being higher than the first index of refraction such
that light can traverse material 25 in groove 24 via total internal
reflection (TIR). The index of refraction of optical material 25 is
also higher than the index of refraction of ambient air. As one
example, optical material 25 may comprise a liquid phase spin
coated titanium oxide film, which can be applied over substrate 22
to fill groove 24. This is one example of a class of materials
known as a spin-on glass which have been demonstrated with modest
annealing temperatures to provide a suitably high index of
refraction for a waveguide core material. For example,
approximately 60 degree Celsius annealing of a titanium oxide film
can yield an index of refraction of approximately 1.72. A glass
substrate, in contrast, may have an index of refraction of
approximately 1.50, and an injection molded polycarbonate substrate
may have an index of refraction of approximately 1.56.
[0030] The depth (D) and width (W) of groove 24 generally defines
the dimensions of the light guide through substrate 22. By way of
example, the width of groove 24 may be between approximately 2 and
150 microns. At dimensions smaller than 2 microns, light
transmission through material 25 may be difficult at wavelengths
commonly used for optical data transmission and optical computing.
In general, the dimensions of groove 24 should be approximately
five times the wavelength of light to be transmitted through
material 25. In other words, the dimensions of groove 24 should be
approximately one-half of an order of magnitude larger than the
wavelength of light to be transmitted through material 25. At
practical wavelengths less than a micron, the dimensions of groove
24 should typically be larger than 2 microns. Notably, as
wavelengths of light become smaller than 400 nanometers, the
available materials that may transmit such light via TIR become
very limited.
[0031] The depth (D) of groove 24 may also be between approximately
2 and 150 microns. The depth (D) may be approximately equal to the
width (W). In other words, the aspect ratio of grooves 24 may be
approximately one-to-one. It is generally desirable to limit the
width of grooves 24 to allow for a longer length light guide
through substrate 24, but also desirable to enlarge the width of
grooves 24 to improve light transmission. Widths and depths in the
range of 2 and 150 microns may work well for most wavelengths
(i.e., 1-2 microns) currently used in optical data transmission and
optical computing.
[0032] A single mode optical waveguide generally refers to an
optical fiber that is used to transmit a single frequency of light.
For such applications, the width (W) and the depth (D) may be
between approximately 2 and 10 microns. In contrast, a multi-mode
optical waveguide refers to an optical fiber that is used to
transmit two or more frequencies of light simultaneously. For such
multi-mode applications, the width (W) and the depth (D) may be
between approximately 30 and 150 microns.
[0033] FIG. 3 is a cross-sectional side view of another optical
element 30, which may correspond to optical element 10 of FIG. 1.
In general, optical element 30 is very similar to optical element
20 of FIG. 2. Optical element 30 comprises a substrate 32 formed
with a continuous groove 34 that spirals from an outer diameter to
an inner diameter of optical element. Substrate 32 defines a first
index of refraction. An optical material 35 is formed in groove 34
to define an optical light guide through substrate 32. Optical
material 35 in groove 34 defines a second index of refraction, the
second index of refraction being higher than the first index of
refraction such that light can traverse material 35 in groove 34
via total internal reflection (TIR). The dimensions of groove 34
may be similar to those of groove 24 (FIG. 2). The differences in
the first and second indexes of refraction may be defined such that
the so called "critical angle" ensures that light traversing
optical material via TIR will not escape.
[0034] Unlike optical element 20 of FIG. 2, optical element 30
includes an additional material 39, which forms a cover layer over
substrate 32. This additional material 39 may be formed over
substrate 32 such that material 35 in groove 34 is substantially
encased by substrate 32 and additional material 39. In order to
ensure that material 35 in groove 34 still transmits light via TIR,
the additional material 39 should define an index of refraction
less than the index of refraction of material 35 in groove 34.
Preferably, the index of refraction of the additional material 39
and the index of refraction of substrate 32 substantially match.
The additional material 39 may form a cover layer, and may comprise
glass, polycarbonate, polymethyl methacrylate (PMMA), plastic or
another suitable material having an index of refraction less than
the index of refraction of material 35 in groove 34. Additional
material 39 may be applied as a prefabricated cover layer and may
be bonded to substrate 32. Alternatively, material 39 may be
spin-coated or created in another manner.
[0035] An optical light guide (also referred to herein as an
optical waveguide) is generally an optical conduit transmitting
light of a range of wavelengths from one position to another, as
guided by the physical boundaries of the optical light guide. An
optical fiber is one form of a conventional optical waveguide
wherein the light input into one end of the fiber is conveyed with
very low losses down the fiber by total internal reflection (TIR).
An optical fiber may include a core and, optionally, an outer
cladding. Conventional optical fibers typically define a
cylindrical shape. Such conventional optical fibers are created by
drawing the material of the guide from molten glass furnaces.
Plastic materials have also been used for lower cost optical
fibers, usually with lower performance.
[0036] Optical fibers classified as multi-mode step-index fibers
typically include a 30-100 micron core. In contrast, single mode
fibers may define a core of 2-10 microns. Optical fibers may also
be characterized as graded index fibers, which include a
diffraction grading to separate or filter light through the guide.
Guides may also be elliptical core fibers that are polarization
preserving. Optical waveguide devices can also be fabricated in a
planar or rectangular geometry for use as switching elements,
modulators, beamsplitters, spectral filters, polarization
components, etc. The techniques and optical delay-line elements
described herein may be used in conjunction with devices of this
type which may be incorporated in the same optical article (i.e.,
disk). Furthermore, the elements described may include any features
that are typical to conventional fibers that are drawn and
spooled.
[0037] Moreover, the physical dimensions of the grooves (e.g.,
grooves 14, 24 and 34 in FIGS. 1, 2 and 3) may be changed or
modulated to affect light transmission through the respective
optical elements (10, 20 and 30). By modulation of the physical
dimensions, the optical properties and spectral properties of the
optical transmission can be affected in a controlled and desired
manner. In optical telecommunication, wavelength division
multiplexing and demultiplexing (WDM) is commonly used to increased
bandwidth over the light guide. In this case, each of the
wavelengths in the transmission range is encoded individually to
provide massively parallel data transmission. The multiplexing
(adding in a particular wavelength channel) and demultiplexing
(extracting a particular wavelength channel) are commonly
accomplished by Bragg gratings, Mach Zender interferometers, and
ring resonators. For example, Bragg gratings may be made with
periodic modulations in the optical properties of the
fiber/waveguide by patterned UV exposure, ion implantation, or
photolithography with a period of one-half of the design wavelength
to be reflected. Similarly, optical properties of the waveguide may
be affected by application of electrical or magnetic fields to the
waveguide material or by surface modifications via surface plasmon
effects. The optical elements described herein may be fabricated to
include any of these features common to conventional waveguides.
The addition of such features may provide a number of opportunities
for sensing applications.
[0038] In telecommunication, a delay line is a transmission line or
equivalent device used to delay a signal. A delay line can be used
to ensure that a signal input is later output after a precise
(possibly programmable) delay of time. Historically,
magnetostrictive delay lines have been used as memory elements.
Fiber optic delay lines have been proposed for the advantages of
low insertion loss (i.e., attenuation on the order of 0.5
decibels/kilometer at 1.3 micrometer wavelength independent of
modulation frequency). Fiber optic delay lines also have relatively
short delay times. For example, 1 kilometer of optical fiber
generally equates to approximately 5 .mu.s time delay. Moreover,
fiber optic delay lines may also exhibit a relatively large
time-bandwidth product (exceeding 10.sup.5 at 1.3 micrometer
wavelength). Re-circulating delay lines, tapped delay lines, and
lattice optical signal processing have been proposed for the
optical signal processing applications of frequency filtering,
bit-rate converters, convolution and correlation and matrix
operations. Because of the lack of optical random access memory in
optical computing, an optical delay line may be the only means of
optical buffering in optical signal processing architectures and
optical computing. The optical elements described herein may be
used to produce high volume low cost delay lines, which may find
application in a wide variety of fields and devices.
[0039] Commercially available fiber optic delay lines are
conventionally composed of a spool of optical fiber with length on
the order of up to 1-5 kilometers, depending on the capacity or
delay required. Such conventional delay lines may include a
transponder capable of processing signals transmitted through the
fiber. Current pricing for conventional delay lines typically range
from $200 (100 meter) to $950 (5000 meter), with package size of
approximately five square inches (32.26 square centimeters) by one
inch (2.54 centimeters), two inches (5.08 centimeters) or three
inches (7.62 centimeters) thick, depending on fiber length. Again,
the techniques described herein may be used to create optical
elements that can operate similar to conventional delay lines, but
may be fabricated at a fraction of the cost of such conventional
delay lines.
[0040] In this invention, an optical element (10, 20 or 30) may
comprise an optical waveguide disk. The disk can be fabricated
beginning with a patterning step similar to conventional optical
disk mastering, but with reduced resolution since waveguide
dimensions should be on the order of microns rather than sub-micron
feature dimensions for optical disks. By mastering a spiral groove
of desired cross-sectional width and depth suitable for either
single mode operation or multi-mode operation, conventional
processes may be used to form an optical delay-line of length equal
to the mastered spiral length.
[0041] Furthermore, analogous to convention optical mastering
functions of wobble and power modulation, master recording
waveguides with modulations in groove width or with wobbled groove
with particular characteristic lengths may be used for optical
spectral manipulation in like manner to the Bragg grating.
Depending on the spiral pitch and the disk size, the optical
waveguide disk may have varying spiral length and, thus, varying
delay times. As an example, the new and emerging "Blu-Ray" optical
media product has the shortest track-pitch of conventional optical
products at 0.32 microns. In this case, if an optical waveguide
were formed in the groove of a Blu-Ray disk having a 120 millimeter
OD, the spiral length would be almost 25 miles (40.23 kilometers),
yielding an optical transit time of 132 microseconds (assuming the
speed of light in a vacuum). In this case, however, the waveguide
dimensions would be too small for conventional telecommunication
wavelengths.
[0042] Of course, the disk size may be made non-standard in
relation to typical optical disks in diameter and thickness,
particularly if such non-standard sizes are needed to increase the
length of the delay line or otherwise advantageous for delay line
or other optical computing applications. By way of example, a disk
sized similar to conventional CDs or DVDs and having a spiral track
pitch of 3 microns can allow a 2 micron waveguide width dimension
that equates to approximately 2.63 miles (4.23 kilometers) of
waveguide length and an optical transit time (assuming the speed of
light in a vacuum) of about 14 microseconds. For a 50 micron spiral
pitch suitable for a multi-mode waveguide, the spiral length would
be 0.16 miles (0.26 kilometers), resulting in a free-air transit
time of 0.85 microsecond. The data capacity for the optical delay
line, of course, would also depend on the frequency limit of the
optical modulators used. Multiplexing (i.e., using WDM techniques)
can multiply the data capacity by N separable optical channels.
[0043] Referring again to FIG. 1, input element 16 and output
element 18 may comprise tapered coupling regions, and may be formed
by etching or mastering to enable coupling to the optical light
guide formed by the material in groove 14. If desired, input
element 16 and output element 18 may additionally include fiber
mating or registration features. Optical element 10 may be coupled
to a transponder (not shown) capable of processing signals
transmitted through the material in groove 14.
[0044] FIG. 4 is a flow diagram illustrating one technique that may
be used to create an optical element as described herein. As shown,
a master disk is created (42). The mastering process may comprise a
photolithographic process commonly used for optical disk
fabrication, or possibly another type of mastering process such as
masked etching process. The master is used to create one or more
stampers (44). For example, the master may be electroplated to
define a stamper that exhibits an inverse of the pattern on the
master. Different generations of stampers may also be created
depending on whether the desired pattern to be formed in the
replica substrate is that of the master, or an inverse of the
pattern on the master. The creation of multiple generations of
stampers can also improve productivity and output with respect to a
single master disk.
[0045] Once the desired stamper is created, the stamper may be used
to create a grooved substrate (46), e.g., using an injection
molding process, a "2P" replication process, a rolling bead
process, or the like. The groove in the substrate is then filled
with optical material to create a light guide through the substrate
(48). Optionally, a cover layer may be formed over the substrate to
encase the light guide within the substrate and the cover layer
(49).
[0046] FIG. 5 is another flow diagram illustrating an alternative
technique that may be used to create an optical element, as
described herein. While the technique of FIG. 4 may be better
suited for mass production of the optical elements, the process of
FIG. 5 may allow for the creation of higher quality optical
elements, e.g., using etched glass substrates. As shown in FIG. 5,
the substrate is etched to create a groove through the substrate
(52). The groove in the substrate is then filled with optical
material to create a light guide through the substrate (58).
Optionally, a cover layer may be formed or applied over the
substrate to encase the light guide within the substrate and the
cover layer (59). For example, the cover layer may be applied as a
prefabricated sheet bonded to the substrate or may be spin-coated
or formed or deposited in another manner.
[0047] FIG. 6 is a block diagram illustrating a mastering system 60
that may be used to create a master in the process described in
FIG. 4. In general, mastering system 60 includes a system control
62, such as a personal computer, workstation, or other computer
system. System control 62, for example, may comprise one or more
processors that execute software to provide user control over
system 60. System control 62 provides commands to spindle
controller 64 and optics controller 65 in response to user input.
The commands sent from system control 62 to spindle controller 64
and optics controller 65 define the operation of system 60 during
the mastering process.
[0048] Master 78 may comprise a disk-shaped glass substrate 76
coated with a photoresist layer 77. Other substrate materials of
suitable optical surface quality may also be used. In any case,
master 78 is carefully placed in system 60 on spindle 67. Mastering
optics 68 include a laser source and various optical conditioners
and generally provides light that exposes photoresist layer 77
according to commands by system control 62.
[0049] Spindle controller 64 causes spindle 67 to spin master disk
78, while optics controller 65 controls the positioning of
mastering optics 68 relative to master 78. Optics controller 65
also controls any on-off switching of light that is emitted from
mastering optics 68 in order to vary the characteristic of the
mastered groove. As master 78 spins on spindle 67, optics
controller 65 translates mastering optics 68 to desired positions
and causes mastering optics 68 to emit light that exposes
photoresist layer 77. The exposed photoresist layer 77 can then be
developed with a developer solution to remove exposed or unexposed
photoresist material (depending on whether a positive or negative
resist is used) to define the groove in master 78.
[0050] FIG. 7 is a partial side view of master 78 prior to
development. The dotted lines in photoresist layer 77 correspond to
the area of exposure, which follows a spiral pattern over the
surface of master 78. FIG. 8 is a partial side view of master 78
following the development step. As shown, grooves 82 appear after
the exposed area is developed.
[0051] FIG. 9 is an exemplary partial side view of master 78
further including a thin layer of nickel 92 deposited over the
grooved photoresist layer 77. FIG. 10 is a partial side view
illustrating how the thin layer of nickel 92 can be electroplated
with nickel to define a thick nickel stamper 102. FIG. 11 is a
partial side view illustrating nickel stamper 102 removed from
master 78. Upon removal of nickel stamper 102 from master 78,
master 78 may be destroyed. Stripper solution may be used to remove
excess photoresist from stamper 102.
[0052] Stamper 102 of FIG. 11 may be used in an injection molding
machine, a rolling bead machine, or another machine that replicates
using the "2P" photoreplication process. In injection molding,
stamper 102 is placed into an injection molding cavity and molten
thermoplastic is introduced to create a substrate having an inverse
of the features of stamper. In a 2P rolling bead process, stamper
102 is placed into contact with a photosensitive layer to form
features in the layer. A roller is passed over the stamper to stamp
into the photosensitive layer. The photosensitive layer is exposed
to one or more wavelengths of electromagnetic radiation to harden
the photosensitive layer, and stamper 102 is peeled away.
[0053] FIG. 12 is a partial side view illustrating the creation of
substrate 122 using stamper 102. Again, either injection molding, a
rolling bead process or another "2P" process may be used for this
substrate creation step. FIG. 13 is a partial side view
illustrating substrate 122 with stamper removed.
[0054] FIG. 14 is a partial side view illustrating the deposition
of optical material 142 in the groove of substrate 122. As
described herein, optical material 142 has a higher index of
refraction than substrate 122 and functions as a light guide.
Optical material 142 may comprise a planarization coating that
fills groove features of substrate 122. By way of example, a liquid
phase spin coated titanium oxide film may be applied over substrate
122 at a thickness such that the resulting coating fills in the
groove formed in substrate 122. This is one example of a class of
materials known as spin-on glass that has been demonstrated with
modest annealing temperature to provide suitably high index of
refraction for a waveguide core material. For example, 60 degree
Celsius annealing of liquid-phase spin-coated titanium oxide film
may yield a refractive index of 1.72.
[0055] FIG. 15 is a partial side view illustrating the addition of
an optional cover layer 152 over substrate 122. The ultimate result
is an optical waveguide disk as shown in FIG. 14 or 15. The optical
waveguide disk may have a smaller form factor than conventional
delay lines and may be considerably cheaper to fabricate than
conventional fiber delay-line technology. The surface access to the
optical waveguide disk provides additional opportunities for
sensing or modulation. Furthermore, the access to the optical
waveguide disk surface allows the possibility for the optical input
to be adjustable across the disk radius in order to vary the delay
line length.
[0056] A number of embodiments of the invention have been
described. In particular, an optical element has been described
that has potential applications in a wide variety of fiber optic
transmission and optical computing environments. Different
techniques for creating the optical element have also been
described. The described optical element may be coupled to a
transponder capable of processing signals transmitted through the
light guide formed in the element. Nevertheless, various
modifications may be made without departing from the spirit and
scope of the invention. For example, the invention may be expanded
to comprise a dual sided optical waveguide disk including
waveguides formed on both sides of a substrate. In addition,
multi-layer waveguides are contemplated by this disclosure, i.e.,
disks that include multiple layers of waveguides formed on one or
both sides of the optical waveguide disk light guide. In yet
further embodiments, multiple optical waveguide disks with optical
coupling connectivity are also contemplated by this disclosure.
[0057] As yet another added embodiment, the described optical
element may be used in a data storage cartridge that includes a
transmitter and a receiver each coupled to the light guide disk
within the cartridge. In that case, the transmitter may send data
over the light guide and then resend the same data slightly before
or upon receipt by the receiver. In this way, data may be
continuously stored in a transient manner in an optical wave guide
storage device. These and other embodiments are within the scope of
the following claims.
* * * * *