U.S. patent application number 15/091107 was filed with the patent office on 2016-10-27 for optical fiber for silicon photonics.
The applicant listed for this patent is Corning Incorporated. Invention is credited to Scott Robertson Bickham, Dana Craig Bookbinder, Ming-Jun Li, Pushkar Tandon.
Application Number | 20160313502 15/091107 |
Document ID | / |
Family ID | 57136492 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160313502 |
Kind Code |
A1 |
Bickham; Scott Robertson ;
et al. |
October 27, 2016 |
OPTICAL FIBER FOR SILICON PHOTONICS
Abstract
An optical fiber for efficient coupling of optical signals to
photonic devices. The glass optical fiber includes a core region,
an optional inner cladding region, a depressed index region, and an
outer cladding region. The relative refractive index profile of the
fiber is designed to provide large effective area and low bending
losses at wavelengths of interest for photonic devices. The
photonic devices may be silicon photonic devices with an operating
wavelength at or near 1310 nm.
Inventors: |
Bickham; Scott Robertson;
(Corning, NY) ; Bookbinder; Dana Craig; (Corning,
NY) ; Li; Ming-Jun; (Horseheads, NY) ; Tandon;
Pushkar; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
57136492 |
Appl. No.: |
15/091107 |
Filed: |
April 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62151031 |
Apr 22, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 6/03666 20130101;
G02B 6/0365 20130101; G02B 6/03627 20130101; G02B 6/30
20130101 |
International
Class: |
G02B 6/036 20060101
G02B006/036; G02B 6/30 20060101 G02B006/30 |
Claims
1. An optical fiber comprising: a core region, said core region
having an outer radius r.sub.1 in the range from 4 to 8 microns and
a relative refractive index .DELTA..sub.1max in the range from
0.12% to 0.33%; a depressed index cladding region surrounding said
core region, said depressed index cladding region having a relative
refractive index .DELTA..sub.3 less than -0.25%, and a trench
volume of at least 25% .DELTA.-micron.sup.2; and an outer cladding
region surrounding said depressed index cladding region, said outer
cladding region having an outer radius r.sub.4; wherein said
optical fiber has a mode field diameter (MFD) at 1310
nm.gtoreq.10.0 microns, a cable cutoff wavelength 1260 nm, and a
bending loss at 1310 nm, as determined by the mandrel wrap test
using a mandrel having a diameter of 15 mm, of .ltoreq.0.45
dB/turn.
2. The optical fiber of claim 1, wherein said outer radius r.sub.1
is in the range from 4 to 7 microns and said relative refractive
index .DELTA..sub.1 is in the range from 0.15% to 0.40%.
3. The optical fiber of claim 2, wherein said outer radius r.sub.3
is in the range from 15 to 25 microns, said relative refractive
index .DELTA..sub.3 is less than -0.35%, and said trench volume is
at least 80% .DELTA..mu.m.sup.2.
4. The optical fiber of claim 3, wherein said outer radius r.sub.4
is at least 60 microns and said relative refractive index
.DELTA..sub.4 is in the range from -0.05% to 0.10%.
5. The optical fiber of claim 4, wherein said optical fiber has an
effective area at 1310 nm of at least 75 micron.sup.2 and said
bending losses are less than 0.1 dB/turn.
6. The optical fiber of claim 5, wherein said outer radius r.sub.1
is in the range from 4 to 6 microns and said relative refractive
index .DELTA..sub.1 is in the range from 0.15% to 0.25%.
7. The optical fiber of claim 1, wherein said optical fiber has an
effective area at 1310 nm of at least 90 micron.sup.2 and said
bending losses are less than 0.1 dB/turn.
8. The optical fiber of claim 1, further comprising: an inner
cladding region surrounding said core region, said inner cladding
region having an outer radius r.sub.2 in the range from 5 to 20
microns and a relative refractive index .DELTA..sub.2 in the range
from -0.10% to 0.20%, said depressed cladding index region
surrounding said inner cladding region.
9. The optical fiber of claim 8, wherein said inner cladding region
has an outer radius r.sub.2 in the range from 7 to 15 microns and a
relative refractive index .DELTA..sub.2 in the range from -0.05% to
0.10%.
10. The optical fiber of claim 9, wherein said outer radius r.sub.1
is in the range from 4 to 7 microns and said relative refractive
index .DELTA..sub.1 is in the range from 0.15% to 0.40%.
11. The optical fiber of claim 10, wherein said outer radius
r.sub.3 is in the range from 15 to 25 microns, said relative
refractive index .DELTA..sub.3 is less than -0.35%, and said trench
volume is at least 80% .DELTA.-micron.sup.2.
12. The optical fiber of claim 11, wherein said outer radius
r.sub.4 is at least 60 microns and said relative refractive index
.DELTA..sub.4 is in the range from -0.05% to 0.10%.
13. The optical fiber of claim 12, wherein said optical fiber has
an effective area at 1310 nm of at least 75 micron.sup.2 and
bending losses at 1310 nm of less than 0.1 dB/turn on a 15 mm
diameter mandrel.
14. The optical fiber of claim 13, wherein said outer radius
r.sub.1 is in the range from 4 to 6 microns and said relative
refractive index .DELTA..sub.1 is in the range from 0.15% to
0.25%.
15. An integrated system comprising a silicon photonic device
optically coupled to an optical fiber, said optical fiber having: a
core region, said core region having an outer radius r.sub.1 in the
range from 2 to 8 microns and a relative refractive index
.DELTA..sub.1 in the range from 0.10% to 0.50%; a depressed index
cladding region surrounding said core region, said depressed index
cladding region having an outer radius r.sub.3 in the range from 10
to 25 microns, a relative refractive index .DELTA..sub.3 less than
-0.25%, and a trench volume of at least 40% .DELTA.-micron.sup.2;
and an outer cladding region surrounding said depressed index
cladding region, said outer cladding region having an outer radius
r.sub.4 of at least 55 microns and a relative refractive index
.DELTA..sub.4 in the range from -0.10% to 0.20%; wherein said
optical fiber has an effective area at 1310 nm of at least 75
micron and bending losses at 1310 nm, as determined by the mandrel
wrap test using a mandrel having a diameter of 15 mm, of less than
0.45 dB/turn.
16. The integrated system of claim 15, wherein said silicon
photonic device includes a silicon-on-insulator waveguide, said
optical fiber optically coupling to said silicon-on-insulator
waveguide.
17. The integrated system of claim 15, further comprising an
interface between said silicon photonic device and said optical
fiber, said optical fiber optically coupling to said interface,
said interface optically coupling to said silicon photonic
device.
18. The integrated system of claim 17, wherein said silicon
photonic device includes a silicon-on-insulator waveguide, said
interface optically coupling to said silicon photonic device
through said silicon-on-insulator waveguide.
19. The integrated system of claim 17, wherein said interface
comprise an interfacing waveguide, said optical fiber coupling to
said interface through said interfacing waveguide.
20. The integrated system of claim 19, wherein said interfacing
waveguide is a planar waveguide.
21. The integrated system of claim 19, wherein said interfacing
waveguide is a polymer waveguide.
22. The integrated system of claim 15, further comprising a light
source, said light source producing an optical signal having a
wavelength in the range from 1200 nm to 1400 nm, said optical
signal propagating from said silicon photonic device to said
optical fiber.
Description
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119 of U.S. Provisional Application Ser. No.
62/151,031 filed on Apr. 22, 2015 the content of which is relied
upon and incorporated herein by reference in its entirety.
FIELD
[0002] This description pertains to optical fibers for applications
in silicon photonics and integrated optical systems. More
particularly, this description pertains to optical fibers designed
for efficient coupling to waveguides used in silicon photonics
packages. Most specifically, this description pertains to single
mode optical fibers having large effective area and low bending
losses.
BACKGROUND
[0003] The need for greater bandwidth and higher data transmission
rates has motivated efforts to develop next-generation platforms
for information storage and delivery. It is widely believed that
optical information systems will provide superior performance to
today's microelectronics-based systems. Integrated optical systems
based on silicon photonics are a leading replacement technology for
microelectronic systems. Silicon photonics interfaces with standard
CMOS technologies and WDM (wavelength division multiplexing) to
convert electrical signals to optical signals, to transmit optical
signals, and to reconvert optical signals to electrical signals. In
disaggregated systems, transfer of signals between units occurs
through optical links that provide high bandwidth and high data
transfer rates.
[0004] Deployment of silicon photonics has been limited by
packaging. In order to operate efficiently, losses in the transfer
of optical signals to and from silicon photonic devices need to be
minimized. A proposed silicon photonics device includes a silicon
chip (substrate) for receiving electrical signals and producing
optical signals and an SOI (silicon-on-insulator) waveguide for
coupling light from the chip to a polymer waveguide. The polymer
waveguide includes a core and a cladding and transfers the optical
signal to an optical link for delivery to other devices. Polymer
waveguides are one preferred practical conduit for transferring
light from the chip to an optical link because they offer ease of
manufacturing and flexibility in design.
[0005] Efficient operation of silicon photonic devices requires low
loss coupling of the optical signal from the silicon chip to the to
the optical link. Success in minimizing coupling losses between the
chip and polymer waveguide has been achieved through adiabatic
coupling techniques. See, for example, I. M. Soganci et al., Opt.
Express 21(13), 16075-16085 (2013). Although optical fibers have
been used in conjunction with silicon photonic devices,
insufficient progress has been made in tailoring the
characteristics of optical fibers to minimize coupling losses.
There is a need for new optical fibers with performance
characteristics suitable for use in silicon photonics
assemblies.
SUMMARY
[0006] The present description provides an optical fiber designed
for integration with silicon photonic devices. The fiber features
high coupling efficiency with silicon photonic devices . The
refractive index profile of the fiber is designed to maximize the
efficiency of signal transfer between the fiber and silicon
photonic device. The refractive index profile of the fiber is
further designed to minimize bending losses in the fiber to provide
greater flexibility in deployment without compromising
performance.
[0007] The optical fiber includes a core region, an optional inner
cladding region, a depressed index cladding region, and an outer
cladding region.
[0008] The present disclosure extends to:
An optical fiber comprising:
[0009] a core region, said core region having an outer radius
r.sub.1 in the range from 4 to 8 microns and a relative refractive
index .DELTA..sub.1max in the range from 0.12% to 0.33%;
[0010] a depressed index cladding region surrounding said core
region, said depressed index cladding region having a relative
refractive index .DELTA..sub.3 less than -0.25%, and a trench
volume of at least 25% .DELTA.-micron.sup.2; and
[0011] an outer cladding region surrounding said depressed index
cladding region, said outer cladding region having an outer radius
r.sub.4;
[0012] wherein said optical fiber has a mode field diameter (MFD)
at 1310 nm.gtoreq.10.0 microns, a cable cutoff wavelength 1260 nm,
and a bending loss at 1310 nm, as determined by the mandrel wrap
test using a mandrel having a diameter of 15 mm, of .ltoreq.0.45
dB/turn.
[0013] The present disclosure extends to:
An optical fiber comprising:
[0014] a core region, said core region having an outer radius
r.sub.1 in the range from 4 to 8 microns and a relative refractive
index .DELTA..sub.1max in the range from 0.12% to 0.33%;
[0015] a depressed index cladding region surrounding said core
region, said depressed index cladding region having a relative
refractive index .DELTA..sub.3 less than -0.25%, and a trench
volume of at least 25% .DELTA.-micron.sup.2; and
[0016] an outer cladding region surrounding said depressed index
cladding region, said outer cladding region having an outer radius
r.sub.4;
[0017] wherein said optical fiber has a mode field diameter (MFD)
at 1310 nm.gtoreq.10.0 microns, a cable cutoff wavelength 1260 nm,
and a bending loss at 1310 nm, as determined by the mandrel wrap
test using a mandrel having a diameter of 15 mm, of .ltoreq.0.1
dB/turn.
[0018] The present disclosure extends to:
An integrated system comprising a photonic device optically coupled
to an optical fiber, said optical fiber having:
[0019] a core region, said core region having an outer radius
r.sub.1 in the range from 2 microns to 8 microns and a relative
refractive index .DELTA..sub.1 in the range from 0.10% to
0.50%;
[0020] a depressed index cladding region surrounding said core
region, said depressed index cladding region having an outer radius
r.sub.3 in the range from 10 to 25 microns, a relative refractive
index .DELTA..sub.3 less than -0.25%, and a trench volume of at
least 40% .DELTA.-microns.sup.2; and
[0021] an outer cladding region surrounding said depressed index
cladding region, said outer cladding region having an outer radius
r.sub.4 of at least 55 microns and a relative refractive index
.DELTA..sub.4 in the range from -0.10% to 0.20%;
[0022] wherein said optical fiber has an effective area at 1310 nm
of at least 75 micron and bending losses at 1310 nm, as determined
by the mandrel wrap test using a mandrel having a diameter of 15
mm, of less than 0.45 dB/turn.
[0023] The present disclosure extends to:
An integrated system comprising a photonic device optically coupled
to an optical fiber, said optical fiber having:
[0024] a core region, said core region having an outer radius
r.sub.1 in the range from 2 microns to 8 microns and a relative
refractive index .DELTA..sub.1 in the range from 0.10% to
0.50%;
[0025] a depressed index cladding region surrounding said core
region, said depressed index cladding region having an outer radius
r.sub.3 in the range from 10 to 25 microns, a relative refractive
index .DELTA..sub.3 less than -0.25%, and a trench volume of at
least 40% .DELTA.-microns.sup.2; and
[0026] an outer cladding region surrounding said depressed index
cladding region, said outer cladding region having an outer radius
r.sub.4 of at least 55 microns and a relative refractive index
.DELTA..sub.4 in the range from -0.10% to 0.20%;
[0027] wherein said optical fiber has an effective area at 1310 nm
of at least 75 micron and bending losses at 1310 nm, as determined
by the mandrel wrap test using a mandrel having a diameter of 15
mm, of less than 0.10 dB/turn.
[0028] Additional features and advantages will be set forth in the
detailed description which follows, and in part will be readily
apparent to those skilled in the art from the description or
recognized by practicing the embodiments as described in the
written description and claims hereof, as well as the appended
drawings.
[0029] It is to be understood that both the foregoing general
description and the following detailed description are merely
exemplary, and are intended to provide an overview or framework to
understand the nature and character of the claims.
[0030] The accompanying drawings are included to provide a further
understanding, and are incorporated in and constitute a part of
this specification. The drawings are illustrative of selected
aspects of the present description, and together with the
specification serve to explain principles and operation of methods,
products, and compositions embraced by the present description.
Features shown in the drawing are illustrative of selected
embodiments of the present description and are not necessarily
depicted in proper scale.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter of the
written description, it is believed that the specification will be
better understood from the following written description when taken
in conjunction with the accompanying drawings, wherein:
[0032] FIG. 1 is a schematic depiction in cross-section of a fiber
having a core, an inner cladding region, a depressed index cladding
region, an outer cladding region, a primary coating and a secondary
coating.
[0033] FIG. 2 is a schematic depiction in cross-section of a fiber
having a core, a depressed index cladding region, an outer cladding
region, a primary coating and a secondary coating.
[0034] FIG. 3 depicts an illustrative refractive index profile of
the glass portion of an optical fiber.
[0035] The embodiments set forth in the drawings are illustrative
in nature and not intended to be limiting of the scope of the
detailed description or claims. Whenever possible, the same
reference numeral will be used throughout the drawings to refer to
the same or like feature.
DETAILED DESCRIPTION
[0036] Reference will now be made in detail to illustrative
embodiments of the present description.
[0037] The present description provides optical fibers for
applications in silicon photonics and other integrated optical
systems. The fibers are suitable for coupling optical signals to
silicon photonic devices, including devices coupled to the fiber
via polymer waveguides. The refractive index profile of the fiber
is designed to improve coupling efficiency to insure minimal losses
in the transfer of optical signals between the fiber and a polymer
waveguide. Of particular interest is coupling efficiency for
optical signals having a wavelength at or near 1310 nm. Most effort
in silicon photonics has emphasized optical signals with
wavelengths in the 1.5 .mu.m spectral region because of the wide
availability of lasers and LEDs that operate in this spectral
region. Dispersion losses in optical fibers, however, are less in
the 1.3 .mu.m spectral region than in the 1.5 .mu.m spectral region
and increasing attention is being directed at silicon photonic
devices and systems that operate in the 1.3 .mu.m spectral region.
There is accordingly a need to design fibers customized for
integration with silicon photonic systems that operate in the 1.3
.mu.m spectral region.
[0038] The fibers disclosed herein are well suited for efficient
coupling to silicon photonic devices that generate or transfer
optical signals at or near 1310 nm. The fibers feature large
effective area and low bending losses and provide high coupling
efficiency to silicon photonic devices. The characteristics of the
fiber, in particular, permit efficient transfer of optical signals
to or from polymer waveguides.
[0039] An explanation of selected terms as used herein is now
provided:
[0040] Selected measurements reported herein may be expressed in
units of microns or square microns. The unit "microns" may also be
expressed as ".mu.m" or "micron". Similarly, the unit "micron
squared" may also be expressed as ".mu.m.sup.2", "micron" or
"microns".
[0041] "Radial position" or the radial coordinate "r" refers to
radial position relative to the centerline (r=0) of the fiber.
[0042] The "refractive index profile" is the relationship between
refractive index or relative refractive index and fiber radius. For
relative refractive index profiles depicted herein as having step
boundaries between adjacent core and/or cladding regions, normal
variations in processing conditions may preclude obtaining sharp
step boundaries at the interface of adjacent regions. It is to be
understood that although boundaries of refractive index profiles
may be depicted herein as step changes in refractive index, the
boundaries in practice may be rounded or otherwise deviate from
perfect step function characteristics. It is further understood
that the value of the relative refractive index may vary with
radial position within the core region and/or any of the cladding
regions. When relative refractive index varies with radial position
in a particular region of the fiber (core region and/or any of the
cladding regions), it may be expressed in terms of its actual or
approximate functional dependence or in terms of an average value
applicable to the region. Unless otherwise specified, if the
relative refractive index of a region (core region and/or any of
the cladding regions) is expressed as a single value, it is
understood that the relative refractive index in the region is
constant, or approximately constant, and corresponds to the single
value or that the single value represents an average value of a
non-constant relative refractive index dependence with radial
position in the region. Whether by design or a consequence of
normal manufacturing variability, the dependence of relative
refractive index on radial position may be sloped, curved, or
otherwise non-constant.
[0043] "Relative refractive index," as used herein, is defined in
Eq. 1 as:
.DELTA. i % = 100 ( n i 2 - n ref 2 ) 2 n i 2 Eq . 1
##EQU00001##
where n.sub.i is the maximum refractive index in region i, unless
otherwise specified, and n.sub.ref is the refractive index of pure
silica glass, unless otherwise specified. Accordingly, as used
herein, the relative refractive index percent is relative to pure
silica glass. As used herein, the relative refractive index is
represented by .DELTA. (or "delta") or .DELTA.% (or "delta %) and
its values are given in units of "%", unless otherwise specified.
Relative refractive index may also be expressed as .DELTA.(r) or
.DELTA.(r)%.
[0044] The average relative refractive index (.DELTA..sub.ave) of a
region of the fiber is determined from Eq. 2:
.DELTA. ave = .intg. r inner r outer .DELTA. ( r ) r ( r outer - r
inner ) Eq . 2 ##EQU00002##
where r.sub.inner is the inner radius of the region, r.sub.outer is
the outer radius of the region, and .DELTA.(r) is the relative
refractive index of the region.
[0045] The term ".alpha.-profile" refers to a relative refractive
index profile .DELTA.(r) that has the following functional form Eq.
3:
.DELTA. ( r ) = .DELTA. ( r 0 ) [ 1 - [ r - r 0 ( r 1 - r 0 ) ]
.alpha. ] Eq . 3 ##EQU00003##
where r.sub.o is the point at which .DELTA.(r) is maximum, r.sub.1
is the point at which .DELTA.(r) is zero, and r is in the range
r.sub.i.ltoreq.r.ltoreq.r.sub.f, where r.sub.i is the initial point
of the .alpha.-profile, r.sub.f is the final point of the
.alpha.-profile, and .alpha. is a real number. .DELTA.(r.sub.0) for
an .alpha.-profile may be referred to herein as .DELTA..sub.max or,
when referring to a specific region i of the fiber, as
.DELTA..sub.i,max.
[0046] "Effective area" of an optical fiber is defined in Eq. 4
as:
A eff = 2 .pi. [ .intg. 0 .infin. ( f ( r ) ) 2 r r ] 2 .intg. 0
.infin. ( f ( r ) ) 4 r r Eq . 4 ##EQU00004##
where f(r) is the transverse component of the electric field of the
guided optical signal and r is radial position in the fiber.
"Effective area" or "A.sub.eff" depends on the wavelength of the
optical signal and is reported herein for wavelengths of 1310 nm
and 1550 nm. Specific indication of the wavelength will be made
when referring to "Effective area" or "A.sub.eff" herein.
[0047] The "mode field diameter" or "MFD" of an optical fiber is
defined in Eq. 5 as:
MFD = 2 w w 2 = 2 .intg. 0 .infin. ( f ( r ) ) 2 r r .intg. 0
.infin. ( f ( r ) r ) 2 r r Eq . 5 ##EQU00005##
where f(r) is the transverse component of the electric field
distribution of the guided optical signal and r is radial position
in the fiber. "Mode field diameter" or "MFD" depends on the
wavelength of the optical signal and is reported herein for
wavelengths of 1310 nm and 1550 nm. Specific indication of the
wavelength will be made when referring to "Effective area" or
"A.sub.eff" herein.
[0048] "Trench volume" is defined in Eq. 6 as:
V Trench = 2 .intg. r Trench , inner r Trench , outer .DELTA.
Trench ( r ) r r Eq . 6 ##EQU00006##
[0049] where r.sub.Trench,inner is the inner radius of the trench
region of the refractive index profile, r.sub.Trench,outer is the
outer radius of the trench region of the refractive index profile,
.DELTA..sub.Trench(r) is the relative refractive index of the
trench region of the refractive index profile, and r is radial
position in the fiber. Trench volume is a positive quantity and
will be expressed herein in units of % .DELTA..mu.m.sup.2, which
may also be expressed as % .DELTA.-.mu.m.sup.2, or %
.DELTA.micron.sup.2, or % .DELTA.-micron.sup.2.
[0050] "Chromatic dispersion", herein referred to as "dispersion"
unless otherwise noted, of an optical fiber is the sum of the
material dispersion, the waveguide dispersion, and the intermodal
dispersion. In the case of single mode waveguide fibers, the
inter-modal dispersion is zero. Dispersion values in a two-mode
regime assume intermodal dispersion is zero. The zero dispersion
wavelength (.lamda..sub.0) is the wavelength at which the
dispersion has a value of zero. Dispersion slope is the rate of
change of dispersion with respect to wavelength.
[0051] The cutoff wavelength of an optical fiber is the minimum
wavelength at which the optical fiber will support only one
propagating mode. For wavelengths below the cutoff wavelength,
multimode transmission may occur and an additional source of
dispersion may arise to limit the fiber's information carrying
capacity. Cutoff wavelength will be reported herein as a fiber
cutoff wavelength or a cable cutoff wavelength. The fiber cutoff
wavelength is based on a 2-meter fiber length and the cable cutoff
wavelength is based on a 22-meter cabled fiber length. The 22-meter
cable cutoff wavelength is typically less than the 2-meter cutoff
wavelength due to higher levels of bending and mechanical pressure
in the cable environment.
[0052] The bend resistance of an optical fiber may be gauged by
bend-induced attenuation under prescribed test conditions. Various
tests are used in the art to assess bending losses in fibers. For
purposes of the present disclosure, bending losses are determined
by a mandrel wrap test. In the mandrel wrap test, the fiber is
wrapped around a mandrel having a specified diameter and the
increase in attenuation due to the bending (relative to a straight
fiber) at a particular wavelength is determined. Attenuation in the
mandrel wrap test is expressed in units of dB/turn, where one turn
refers to one revolution of the fiber about the mandrel.
[0053] The present fibers include a core region and a cladding
region surrounding the core region. The fibers may also include a
primary coating surrounding the cladding region, and a secondary
coating surrounding the primary coating. The cladding region may
include an inner cladding region and an outer cladding region. The
cladding may further include a depressed index cladding region. The
depressed index cladding region is a cladding region having a lower
relative refractive index than adjacent inner and/or outer cladding
regions. The depressed index cladding region may also be referred
to herein as a trench or trench region. The depressed index
cladding region may surround the inner cladding region and/or may
be surrounded by the outer cladding region. The refractive index
profile of the core region may be designed to minimize attenuation
losses while maintaining a large mode field diameter for the fiber.
The primary and secondary coatings may be selected to protect the
mechanical integrity of the core and cladding and to minimize the
effects of external mechanical disturbances on the characteristics
of the optical signal guided in the fiber. The primary and
secondary coatings may insure that losses due to bending and other
perturbing forces are minimized. The depressed index cladding
region may also contribute to a reduction in bending losses.
[0054] Whenever used herein, radius r.sub.1 and relative refractive
index .DELTA..sub.1(r) refer to the core region, radius r.sub.2 and
relative refractive index .DELTA..sub.2(r) refer to the inner
cladding region, radius r.sub.3 and relative refractive index
.DELTA..sub.3(r) refer to the depressed index cladding region, and
radius r.sub.4 and relative refractive index .DELTA..sub.4(r) refer
to the outer cladding region, It is understood that the central
core region is substantially cylindrical in shape and that the
surrounding inner cladding, depressed index cladding, and outer
cladding regions are substantially annular in shape. Annular
regions may be characterized in terms of an inner radius and an
outer radius. Radial positions r.sub.1, r.sub.2, r.sub.3 and
r.sub.4 refer herein to the outermost radii of the central core
region, inner cladding region, depressed index cladding region,
outer cladding region, respectively. When two regions are directly
adjacent to each other, the outer radius of the inner of the two
regions coincides with the inner radius of the outer of the two
regions. In one embodiment, for example, the fiber includes a
depressed index cladding region surrounded by and directly adjacent
to an outer cladding region. In such an embodiment, the radius
r.sub.3 corresponds to the outer radius of the depressed index
cladding region and the inner radius of the outer cladding
region.
[0055] As will be described further hereinbelow, the relative
refractive indices of the central core region, inner cladding
region, depressed index cladding region, and outer cladding region
may differ. Each of the regions may be formed from silica glass or
a silica-based glass. Variations in refractive index may be
accomplished by incorporating updopants or downdopants at levels
known to provide a targeted refractive index or refractive index
profile using techniques known to those of skill in the art.
Updopants are dopants that increase the refractive index of the
glass relative to the undoped glass composition. Downdopants are
dopants that decrease the refractive index of the glass relative to
the undoped glass composition. In one embodiment, the undoped glass
is pure silica glass. When the undoped glass is pure silica glass,
updopants include Cl, Br, Ge, Al, P, Ti, Zr, Nb, and Ta, and
downdopants include F and B. Regions of constant refractive index
may be formed by not doping or by doping at a uniform
concentration. Regions of variable refractive index may be formed
through non-uniform spatial distributions of dopants.
[0056] A schematic cross-sectional depiction of a first of many
coated fibers in accordance with the present disclosure is shown in
FIG. 1. Fiber 10 includes core region 20, cladding region 30,
primary coating 40, and secondary coating 50. Cladding region 30
includes inner cladding region 31, depressed index cladding region
33, and outer cladding region 35. Inner cladding region 31 is
optional and may be omitted as shown for fiber 15 in FIG. 2.
[0057] A representative refractive index profile for the glass
portion (core and cladding regions) of an optical fiber is
presented in FIG. 3. FIG. 3 shows a rectangular trench profile for
a fiber (101) having a core region (1) with outer radius r.sub.1
and relative refractive index .DELTA..sub.1, an inner cladding
region (2) extending from radial position r.sub.1 to radial
position r.sub.2 and having relative refractive index
.DELTA..sub.2, a depressed index cladding region (3) extending from
radial position r.sub.2 to radial position r.sub.3 and having
relative refractive index .DELTA..sub.3, and an outer cladding
region (4) extending from radial position r.sub.3 to radial
position r.sub.4 and having relative refractive index
.DELTA..sub.4. In the profile of FIG. 3, the depressed index
cladding region (3) may be referred to herein as a trench and may
have a constant refractive index that is less than the refractive
indices of the inner cladding region (2) and the outer cladding
region (4). Core region (1) has the highest relative refractive
index in the profile. Core region (1) may include a lower index
region at or near the centerline (known in the art as a "centerline
dip") (not shown). It should be noted that the inner cladding
region (2) is optional and may be eliminated as noted hereinabove.
When inner cladding region (2) is missing, depressed index region
(3) is directly adjacent core region (1).
[0058] The relative ordering of relative refractive indices
.DELTA..sub.1, .DELTA..sub.2, .DELTA..sub.3, and .DELTA..sub.4
satisfy the conditions
.DELTA..sub.1>.DELTA..sub.4>.DELTA..sub.3 and
.DELTA..sub.1>.DELTA..sub.2>.DELTA..sub.3. The values of
.DELTA..sub.2 and .DELTA..sub.4 may be equal or either may be
greater than the other, but both .DELTA..sub.2 and .DELTA..sub.4
are between .DELTA..sub.1 and .DELTA..sub.3.
[0059] The relative refractive index .DELTA..sub.1 of core region
(1) may be in the range from 0.10% to 0.50%, or in the range from
0.12% to 0.33%, or in the range from 0.15% to 0.40%, or in the
range from 0.20% to 0.35%, or in the range from 0.15% to 0.25%. The
radius r.sub.1 of central core region (1) may be in the range from
2 .mu.m to 8 .mu.m, or in the range from 4 .mu.m to 8 .mu.m, or in
the range from 3 .mu.m to 7 .mu.m, or in the range from 4 .mu.m to
6 .mu.m.
[0060] The relative refractive index .DELTA..sub.1 of core region
(1) may be described by an .alpha.-profile having an a value in the
range from 2 to 100, or in the range from 3 to 75, or in the range
from 4 to 50, or in the range from 5 to 35, or in the range from 6
to 25, or in the range from 2 to 4, or in the range from 8 to 15,
or in the range from 10 to 14, or in the range from 11 to 13, or of
about 10, or of about 12, or of about 14. In embodiments in which
the relative refractive index .DELTA..sub.1 corresponds to an
.alpha.-profile, the maximum value .DELTA..sub.tmax of
.DELTA..sub.1 may be in the range from 0.10% to 0.50%, or in the
range from 0.12% to 0.33%, or in the range from 0.15% to 0.40%, or
in the range from 0.20% to 0.35%, or in the range from 0.15% to
0.25%.
[0061] The relative refractive index .DELTA..sub.2 of inner
cladding region (2) may be in the range from -0.10% to 0.20%, or in
the range from -0.05% to 0.10%, or in the range from -0.05% to
0.05%. The radius r.sub.2 of inner cladding region (2) may be in
the range from 5 .mu.m to 20 .mu.m, or in the range from 7 .mu.m to
15 .mu.m, or in the range from 8 .mu.m to 12 .mu.m.
[0062] The relative refractive index .DELTA..sub.3 of depressed
index cladding region (3) may be less than -0.25% or less than
-0.30%, or less than -0.35%, or less than -0.40%, or less than
-0.45%, or less than -0.50%, or in the range from -0.50% to -0.20%,
or in the range from -0.50% to -0.30%, or in the range from -0.45%
to -0.30%. The radius r.sub.3 of depressed index cladding region
(3) may be in the range from 10 .mu.m to 25 .mu.m, or in the range
from 15 .mu.m to 25 .mu.m, or in the range from 15 .mu.m to 20
.mu.m. The trench volume of depressed index cladding region (3) may
be at least 25% .DELTA..mu.m.sup.2, or at least 40%
.DELTA..mu.m.sup.2, or at least 60% .DELTA..mu.m.sup.2, or at least
80% .DELTA..mu.m.sup.2, or at least 100% .DELTA..mu.m.sup.2, or at
least 120% .DELTA..mu.m.sup.2, or in the range from 40%
.DELTA..mu.m.sup.2 to 150% .DELTA..mu.m.sup.2, or in the range from
60% .DELTA..mu.m.sup.2 to 140% .DELTA..mu.m.sup.2, in the range
from 80% .DELTA..mu.m.sup.2 to 140% .DELTA..mu.m.sup.2.
[0063] The relative refractive index .DELTA..sub.4 of outer
cladding region (4) may be in the range from -0.10% to 0.20%, or in
the range from -0.05% to 0.10%, or in the range from -0.05% to
0.05%. The radius r.sub.4 of outer cladding region (4) may be at
least 50 .mu.m, or at least 55 .mu.m, or at least 60 .mu.m, or in
the range from 55 .mu.m to 70 .mu.m, or in the range from 60 .mu.m
to 65 .mu.m, or about 62.5 .mu.m.
[0064] Optical fibers with relative refractive index profiles as
described herein feature high mode field diameters, large effective
areas, short cutoff wavelengths, and low bending losses.
[0065] The mode field diameter of the fiber at a wavelength of 1310
nm may be at least 10.0 .mu.m, or at least 10.5 .mu.m, or at least
11.0 .mu.m, or at least 11.4 .mu.m, or in the range from 9.0 .mu.m
to 12.0 .mu.m, or in the range from 10.0 .mu.m to 12.0 The mode
field diameter of the fiber at a wavelength of 1550 nm may be 10.5
.mu.m, or at least 11.0 .mu.m, or at least 11.5 .mu.m, or at least
12.0 .mu.m or in the range from 9.5 .mu.m to 12.5 .mu.m, or in the
range from 10.5 .mu.m to 12.5
[0066] The effective area of the present fibers at a wavelength of
1310 nm may be at least 75 .mu.m.sup.2, or at least 80 .mu.m.sup.2,
or at least 90 .mu.m.sup.2, or at least 100 .mu.m.sup.2, or at
least 105 .mu.m.sup.2, or in the range from 60 .mu.m.sup.2 to 120
.mu.m.sup.2, or in the range from 70 .mu.m.sup.2 to 120
.mu.m.sup.2, or in the range from 80 .mu.m.sup.2 to 120
.mu.m.sup.2. The effective area of the present fibers at a
wavelength of 1550 nm may be at least 75 .mu.m.sup.2, or at least
85 .mu.m.sup.2, or at least 95 .mu.m.sup.2, or at least 105
.mu.m.sup.2, or at least 115 .mu.m.sup.2, or in the range from 75
.mu.m.sup.2 to 130 .mu.m.sup.2, or in the range from 85 .mu.m.sup.2
to 130 .mu.m.sup.2, or in the range from 95 .mu.m.sup.2 to 130
.mu.m.sup.2.
[0067] The present fibers may have a cutoff wavelength (LP11 mode)
of less than1250 nm, or less than 1200 nm, or less than 1150 nm, or
less than 1100 nm, or less than 1050 nm, or less than 1000 nm. The
present fibers may have a cable cutoff wavelength (LP11 mode) of
less than or equal to 1300 nm, or less than or equal to 1280 nm, or
less than or equal to 1260 nm, or less than or equal to 1250
nm.
[0068] The bending loss of the present fibers at 1310 nm as
determined by the mandrel wrap test using a mandrel having a
diameter of 10 mm may be less than 1.5 dB/turn, or less than 1.0
dB/turn, or less than 0.50 dB/turn, or less than 0.30 dB/turn, or
less than 0.20 dB/turn, or less than 0.10 dB/turn, or less than
0.05 dB/turn, or less than 0.02 dB/turn, or less than 0.01 dB/turn.
The bending loss of the present fibers at 1310 nm as determined by
the mandrel wrap test using a mandrel having a diameter of 15 mm
may be less than 1.0 dB/turn, or less than 0.50 dB/turn, or less
than 0.45 dB/turn, or less than 0.20 dB/turn, or less than 0.10
dB/turn, or less than 0.05 dB/turn, or less than 0.02 dB/turn, or
less than 0.01 dB/turn, or less than 0.005 dB/turn. In some
preferred embodiments, the bending loss at 1310 nm as determined by
the mandrel wrap test using a mandrel having a diameter of 15 mm is
less than 0.45 dB/turn. In some other preferred embodiments, the
bending loss at 1310 nm as determined by the mandrel wrap test
using a mandrel having a diameter of 15 mm is less than 0.1
dB/turn. The bending loss of the present fibers at 1310 nm as
determined by the mandrel wrap test using a mandrel having a
diameter of 20 mm may be less than 0.15 dB/turn, or less than 0.10
dB/turn, or less than 0.07 dB/turn, or less than 0.05 dB/turn, or
less than 0.03 dB/turn, or less than 0.02 dB/turn, or less than
0.01 dB/turn, or less than 0.005 dB/turn. The bending loss of the
present fibers at 1310 nm as determined by the mandrel wrap test
using a mandrel having a diameter of 30 mm may be less than 0.10
dB/turn, or less than 0.05 dB/turn, or less than 0.03 dB/turn, or
less than 0.02 dB/turn, or less than 0.01 dB/turn, or less than
0.007 dB/turn, or less than 0.005 dB/turn.
[0069] The core and cladding of the present coated fibers may be
produced in a single-step operation or multi-step operation by
methods which are well known in the art. Suitable methods include:
the double crucible method, rod-in-tube procedures, and doped
deposited silica processes, also commonly referred to as chemical
vapor deposition ("CVD") or vapor phase oxidation. A variety of CVD
processes are known and are suitable for producing the core and
cladding layer used in the coated optical fibers of the present
invention. They include external CVD processes, axial vapor
deposition processes, modified CVD (MCVD), inside vapor deposition,
and plasma-enhanced CVD (PECVD).
[0070] The glass portion of the coated fibers may be drawn from a
specially prepared, cylindrical preform which has been locally and
symmetrically heated to a temperature sufficient to soften the
glass, e.g., a temperature of about 2000.degree. C. for a silica
glass. As the preform is heated, such as by feeding the preform
into and through a furnace, a glass fiber is drawn from the molten
material. See, for example, U.S. Pat. Nos. 7,565,820; 5,410,567;
7,832,675; and 6,027,062; the disclosures of which are hereby
incorporated by reference herein, for further details about fiber
making processes.
EXAMPLES
[0071] Exemplary fibers in accordance with the present description
are now described and modeled to illustration one or more
advantageous features disclosed herein.
[0072] The exemplary fibers have relative refractive index profiles
of the type shown in FIG. 4 with modification of the relative
refractive index of the core region to an .alpha.-profile. The
fibers included a core region (1), an inner cladding region (2), a
depressed index cladding region (3) and an outer cladding region
(4). The relative refractive index .DELTA..sub.1 of core region (1)
was an .alpha.-profile with .alpha..sub.1=12 and maximum relative
refractive index .DELTA..sub.1max. The base composition of the
exemplary fibers was undoped silica glass (.DELTA.=0). Regions with
.DELTA.>0 and .DELTA.<0 were obtained by inclusion of
updopants and downdopants, respectively. The radii and relative
refractive indices of the different regions of the exemplary fibers
are shown in Table 1 and Table 2. Table 1 and Table 2 also include
the trench volume of the depressed index cladding region of each
exemplary fiber. Units of each parameter are listed in Table 1. The
notation "EX" signifies "Example" and provides a distinguishing
reference to each exemplary fiber. Comp. EX 1 and Comp. EX 2 are
comparative examples. The notation "na" refers to "not applicable"
and signifies that each of Comparative Example 1 and Comparative
Example 2 lacks a trench in the index profile.
TABLE-US-00001 TABLE 1 Comp. Comp. Parameter EX 1 EX 2 EX 1 EX 2 EX
3 .DELTA..sub.1, max (%) 0.295 0.192 0.24 0.21 0.18 R.sub.1 (.mu.m)
5.3 6.55 4.7 4.9 5.05 .alpha..sub.1 12 12 12 12 12 .DELTA..sub.2
(%) na na 0.00 0.00 0.00 R.sub.2 (.mu.m) na na 9 9 9 .DELTA..sub.3
(%) na na -0.4 -0.45 -0.45 R.sub.3 (.mu.m) na na 18 18 19
.DELTA..sub.4 (%) 0 0 0.00 0.00 0.00 R.sub.4 (.mu.m) 62.5 62.5 62.5
62.5 62.5
TABLE-US-00002 TABLE 2 Parameter EX 4 EX 5 EX 6 EX 7 EX 8 EX 9
.DELTA..sub.1, max (%) 0.15 0.125 0.235 0.175 0.30 0.22 R.sub.1
(.mu.m) 5.5 6.85 5.8 6 5.15 6 .alpha..sub.1 12 12 12 12 2 2
.DELTA..sub.2 (%) 0.00 0 0 0 0 0 R.sub.2 (.mu.m) 9 9 12 6 12 12
.DELTA..sub.3 (%) -0.45 -0.35 -0.45 -0.2 -0.45 -0.45 R.sub.3
(.mu.m) 19 17.6 21 18.3 21 21 .DELTA..sub.4 (%) 0.00 0 0 0 0 0
R.sub.4 (.mu.m) 62.5 62.5 62.5 62.5 62.5 62.5
[0073] Selected optical properties of the two comparative examples
and each exemplary fiber were modeled and are listed in Table 3 and
Table 4. The bend losses were modeled based on the mandrel wrap
test and are reported in units of dB/turn, where the diameter of
the mandrel used for the test is listed in Table 3 and Table 4. The
examples outlined in Tables 1 and 2 show optical fibers having MFD
at 1310 nm of larger than 10 microns, cable cutoff of less than
1260 nm and bend loss at 1310 nm for a mandrel diameter of 15 mm of
less than 0.45 dB/turn.
TABLE-US-00003 TABLE 3 Comp. Comp. Parameter EX 1 EX 2 EX 1 EX 2 EX
3 MFD at 1310 nm (.mu.m) 10.12 12.54 10.03 10.45 10.88 MFD at 1550
nm (.mu.m) 11.38 14.09 11.09 11.43 11.84 A.sub.Eff at 1310 nm
(.mu.m.sup.2) 81.6 125.2 79.0 86.3 94.2 A.sub.Eff at 1550 nm
(.mu.m.sup.2) 99.9 153.3 95.5 102.8 111.0 Dispersion at 1310 nm
1.39 2.13 1.979 2.68 3.17 (ps/nm/km) Dispersion at 1550 nm 18.51
19.67 20.54 21.33 21.82 (ps/nm/km) Dispersion Slope at 1310 nm
0.0881 0.0896 0.0934 0.094 0.0942 (ps/nm.sup.2/km) Dispersion Slope
at 1550 nm 0.0594 0.0612 0.0657 0.0658 0.0657 (ps/nm.sup.2/km) Zero
dispersion wavelength 1294 1286 1289 1281 1276 (nm) Bend loss at
1310 nm 11.55 102.2 0.010 0.007 0.004 (dB/turn (10 mm diameter))
Bend loss at 1310 nm 1.22 48.4 0.002 0.002 0.002 (dB/turn (15 mm
diameter)) Bend loss at 1310 nm 0.197 24.5 0.001 0.001 0.001
(dB/turn (20 mm diameter)) Bend loss at 1310 nm 0.00035 2.93 0.0002
0.0003 0.0005 (dB/turn (30 mm diameter)) 22 m Cable Cutoff (nm)
1258 1253 1251 1257 1255 Trench Volume (% .DELTA.-.mu.m.sup.2) na
na -97 -109 -126
TABLE-US-00004 TABLE 4 Parameter EX 4 EX 5 EX 6 EX 7 EX 8 EX 9 MFD
at 1310 nm (.mu.m) 11.44 12.41 11.23 10.09 10.08 11.54 MFD at 1550
nm (.mu.m) 12.3 13.16 12.81 11.0 11.71 13.1 A.sub.Eff at 1310 nm
(.mu.m.sup.2) 106 131.3 94.5 84.6 75.7 100 A.sub.Eff at 1550 nm
(.mu.m.sup.2) 122 146.0 123.7 97.6 101.8 129.3 Dispersion at 1310
nm 3.93 4.6 0.3 3.55 -1.49 0.738 (ps/nm/km) Dispersion at 1550 nm
22.47 22.9 19.37 20.97 17.47 19.8 (ps/nm/km) Dispersion Slope at
1310 nm 0.0939 0.0929 0.0949 0.0893 0.0935 0.0952 (ps/nm.sup.2/km)
Dispersion Slope at 1550 nm 0.0652 0.0641 0.0682 0.0601 0.0687
0.068 (ps/nm.sup.2/km) Zero dispersion wavelength 1268 1260 1307
1270 1326 1302 (nm) Bend loss at 1310 nm (dB/turn 0.005 0.120 1.36
0.296 1.155 0.507 (10 mm diameter)) Bend loss at 1310 nm (dB/turn
0.002 0.051 0.02 0.10 0.409 0.113 (15 mm diameter)) Bend loss at
1310 nm (dB/turn 0.001 0.057 0.044 0.049 0.139 0.025 (20 mm
diameter)) Bend loss at 1310 nm (dB/turn 0.0004 0.011 0.022 0.028
0.017 0.0012 (30 mm diameter)) 22 m Cable Cutoff (nm) 1249 1260
1249 1246 1252 1249 Trench Volume (% .DELTA.-.mu.m.sup.2) -126 -80
-134 -60 -134 -134
[0074] In addition to optical fibers, the present disclosure
extends to integrated systems that incorporate the fibers. In one
embodiment, the integrated system includes a photonic device and
the present fiber. The photonic device includes a microelectronic
chip, a light source (e.g. semiconductor laser or LED), and a
waveguide. In one embodiment, the light source operates at a
wavelength at or near 1310 nm (e.g. in the range from 1250 nm to
1350 nm, or in the range from 1275 nm to 1325 nm, or in the range
from 1290 nm to 1320 nm, or in the range from 1200 nm to 1400 nm).
The photonic device may be coupled to an interface that includes a
waveguide for exchanging optical signals between the photonic
device and external elements of the integrated system. The photonic
device may be an active device that receives an electrical signal,
converts the electrical signal to an optical signal, directs the
optical signal to the waveguide and delivers the optical signal
through the waveguide to the interface or interfacing waveguide for
delivery to external devices. Alternatively, the photonic device
may be a passive device that receives and transfers an optical
signal to an interface for delivery to external devices. The
integrated system includes a fiber of the type disclosed herein.
The fiber may be coupled directly to the photonic device or coupled
to the photonic device through an interface or interfacing
waveguide. The integrated system may also include peripheral
devices such as modulators, detectors, multiplexers,
demultiplexers, etc.
[0075] In one embodiment, the photonic device is a silicon photonic
device. The silicon photonic device may include a silicon chip and
a silicon-on-insulator waveguide optically coupled to the silicon
chip. The silicon photonic device may also include a light source.
The light source may be a silicon-based light source. The
silicon-on-insulator waveguide may be optically coupled to an
interface. The interface may include an interfacing waveguide and
may permit transfer of optical signals to or from external devices
and the silicon chip or a silicon-on-insulator waveguide. The
interfacing waveguide may be a thin film waveguide or a planar
waveguide. The interfacing waveguide may be a polymer waveguide.
The optical fiber may be coupled to the interfacing waveguide and
preferably has an effective area and mode field diameter that
permits exchange of optical signals with the interfacing waveguide
with minimal losses. The relative refractive index characteristics
of the present fibers are designed to enable efficient exchange of
optical signals with interfacing waveguides, including planar
waveguides and polymer waveguides. The large mode field diameters
provided by the present optical fibers reduce coupling losses
between the optical fibers and integrated optical systems or
silicon photonics chip assemblies. For example, coupling losses of
standard G.652 single mode optical fibers with silicon photonics
chip assemblies can be greater than 2 dB. Coupling losses between
the present optical fibers and silicon photonics chip assemblies,
in contrast, can be less than 1.5 dB, or less than 1.0 dB, or less
than 0.5 dB.
[0076] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order. Accordingly, where a method
claim does not actually recite an order to be followed by its steps
or it is not otherwise specifically stated in the claims or
descriptions that the steps are to be limited to a specific order,
it is no way intended that any particular order be inferred.
[0077] It will be apparent to those skilled in the art that various
modifications and variations can be made without departing from the
spirit or scope of the illustrated embodiments. Since
modifications, combinations, sub-combinations and variations of the
disclosed embodiments that incorporate the spirit and substance of
the illustrated embodiments may occur to persons skilled in the
art, the description should be construed to include everything
within the scope of the appended claims and their equivalents.
* * * * *