U.S. patent application number 11/547610 was filed with the patent office on 2007-08-09 for optical waveguide, optical waveguide module and method for forming optical waveguide.
This patent application is currently assigned to THE FURUKAWA ELECTRIC CO., LTD.. Invention is credited to Masahito Morimoto, Masao Shinoda.
Application Number | 20070183730 11/547610 |
Document ID | / |
Family ID | 35125215 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070183730 |
Kind Code |
A1 |
Morimoto; Masahito ; et
al. |
August 9, 2007 |
Optical waveguide, optical waveguide module and method for forming
optical waveguide
Abstract
An optical waveguide comprising a core and a clad characterized
in that a desired part is heated and transited to machining strain
release state, the part transited to the machining strain release
state is curved with a specified bending radius and transited to
machining strain state. That part of the optical waveguide is
heated to a temperature within a range between the bending point
and softening point and transited to machining strain state. The
optical waveguide is an optical fiber having the outer diameter not
shorter than 50 .mu.m. The optical waveguide has the outer diameter
not shorter than ten times of the mode field diameter of the
optical waveguide. The optical waveguide has a bending radius of
5.0 mm or less and difference equivalent of refractive index
&Dgr;.sub.1 between the core and clad falls within a range of
0.8-3.5%.
Inventors: |
Morimoto; Masahito; (Tokyo,
JP) ; Shinoda; Masao; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
THE FURUKAWA ELECTRIC CO.,
LTD.
TOKYO
JP
|
Family ID: |
35125215 |
Appl. No.: |
11/547610 |
Filed: |
March 30, 2005 |
PCT Filed: |
March 30, 2005 |
PCT NO: |
PCT/JP05/06169 |
371 Date: |
April 17, 2007 |
Current U.S.
Class: |
385/129 |
Current CPC
Class: |
G02B 6/2552
20130101 |
Class at
Publication: |
385/129 |
International
Class: |
G02B 6/10 20060101
G02B006/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2004 |
JP |
2004-111211 |
Claims
1. An optical waveguide having a core and a clad, wherein a
specified portion is heated to move into a process distortion free
state, said portion moved into the process distortion free state is
bent in a curved line at a specified bend, radius under the process
distortion state.
2. An optical waveguide according to claim 1, wherein said portion
of said optical waveguide is heated to a temperature within a range
of not less than a folding point to not more than softening point
to move the process distortion state.
3. An optical waveguide according to claim 1 or 2, wherein said
optical waveguide is an optical fiber having an outer diameter of
50 .mu.m.
4. An optical waveguide according to claim 1 or 2, wherein an outer
diameter of said optical waveguide is not less than 10 times of
mode field diameter of said optical waveguide.
5. An optical waveguide according to any one of claims 1 to 4, said
bend radius is not more than 5.0 mm.
6. An optical waveguide according to any one of claims 1 to 5, a
core/clad equivalent refractive index difference .DELTA..sub.1 of
said optical waveguide is within a range from not less than 0.8% to
not more than 3.5%.
7. An optical waveguide module comprising multiple optical
waveguides described in any one of claims 1 to 6, wherein said
multiple optical waveguides are arrayed and at least some part of
said optical waveguides is fixed to a member comprising a
positioning mechanism.
8. An optical waveguide module comprising a optical waveguide
described in any one of claims 1 to 6, wherein to at least one end
of said optical waveguide, an optical waveguide having an core/clad
equivalent refractive index difference .DELTA..sub.2 of not less
than 0.2% is fusion bonded, the fusion bonded portion is heated to
reduce mismatch of said core/clad equivalent refractive index
differences .DELTA. and mismatch of mode field diameters.
9. An optical waveguide module comprising an optical wave guides
described in any one of claims 1 to 6, wherein said optical
waveguide is fixed on a sheet while being wired on the sheet.
10. An optical waveguide module comprising an optical wave guides
described in any one of claims 1 to 6, wherein said optical
waveguide is fixed between at least two sheets while being wired
therebetween.
11. An optical waveguide module according to claim 9 or 10, wherein
multiple optical waveguides are provided and fixed while being
wired.
12. An optical waveguide module according to any one of claims 9 to
11, wherein a material of said sheet has flexibility.
13. A method of forming an optical waveguide comprising the steps
of: heating a specified portion of an optical waveguide; moving
said portion of said optical waveguide into a process distortion
free state; bending said portion moved into the process distortion
free state at a specified bend radius; and moving said portion of
said optical waveguide into a process distortion state while being
bent at the specified bend radius.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to miniaturization of optical
components, particularly an optical waveguide, an optical waveguide
module which can convert the optical waveguide direction at a
minute size and a method for converting an optical waveguide
direction.
BACKGROUND OF THE INVENTION
[0002] Now action speed of electric circuits is approaching that of
optical transmission circuits. However a principle barrier to
increase action speed of the electric circuits is higher than that
to increase action speed of optical transmission circuits
operational speed. This is because time constant due to static
electric capacity associated with electric circuits increases by
the high speed action. Therefore, research and development is
actively conducted on fusion of electric circuit and optical
circuit to partly compensate a high speed action of electric
circuit with an optical transmission path.
[0003] Specifically, VCSEL (Vertical Cavity Surface Emitting Laser)
is installed in an electric circuit substrate and light signal
emitted there is injected into an optical fiber and optical
waveguide to propagate, and the light signal is received with
installed PD (Photodiode) to transmit. Studied is a method for
embedding an optical fiber and an optical waveguide into an
electric circuit substrate itself, and a method employing an
optical fiber and an optical waveguide as substitute for an
existing electric cord between plurality of electric circuit
substrates. And, for example, an organic waveguide sheet (a
polyamide waveguide sheet is a typical waveguide sheet) and an
optical fiber sheet are proposed.
[0004] VCSEL is a surface emitting laser and the laser emits in a
vertical direction with respect to the installed electric circuit
substrate. When the electric circuit substrate is installed in a
vertical direction, the laser emits in a parallel direction with
respect to the electric circuit substrate. Such laser installation
killing advantages of high-density multiple installation of VCSEL
is not generally utilized.
[0005] Further, since the optical waveguide and the optical fiber
which are embedded in the electric circuit substrate waveguide in
parallel with the electric circuit substrate, 90 degree change of
an optical waveguide direction is required to combine the laser
emit from VCSEL with these optical waveguide and optical fiber.
[0006] With regard to such a method for changing 90 degree
direction of optical waveguide, studied are a method comprising
steps of grinding end surfaces of optical fiber and waveguide at 45
degree and forming mirror by subjecting metal vapor deposition to
change 90 degree, and a method of changing with a mirror having 45
degree angle.
[0007] Further, it is different from necessity of 90 degree
direction change of optical waveguide in application region, but
for example with FTTH in which optical fibers are wired in users'
houses, it is necessary to secure a space for gently bending
optical fibers in room corners and hole portions through which the
optical fibers pass from outside to inside the house general fibers
can not be bent in less than several cms due to problems of
mechanical characteristic and optical characteristic, thereby ended
up spoiling interior arrangement and landscape. Correspondingly,
optical fibers capable of being bent mechanically and optically
even at the minimum bend radius of 15 mm have been developed
recently.
[0008] Further, as an application of converting optical waveguide
direction with ultraminiatur, a method of reducing the specified
portion of the optical fiber into extremely minute diameter and
bending it is proposed and commercialized. In this method in which
the reduced portion of the optical fiber diameter is about several
.mu.m to 10 .mu.m, even if this fine optical fiber is bent at a
radius of 1 mm, a bend distortion due to the bend becomes not more
than 1%, thereby the optical fiber can be sufficiently mechanically
bent. Further although it is not a configuration where light is
confined with fiber of this fine portion alone, a relation between
light and environment (air) is referred to a relation between core
and clad in combination of this fine optical fiber and its exterior
environment, i.e. air. And it functions as a waveguide equivalently
having ultra high equivalent refractive index difference of several
tens % and even with a minute bend radius it can be bent without
light loss.
Patent Reference 1: U.S. Patent publication No. 2203/0165291A1
Patent Reference 2: U.S. Pat. No. 5,138,676
Patent Reference 3: Japan Laid-open Unexamined Patent Publication
2000-329950
Non Patent Reference 1: Ohki et al. "Development of 60 bps Parallel
Optical Interconnect Module (ParaBIT-IF)" IEICE 2000 Technical
Report EMD2000-7)
Non Patent Reference 2: Shimizu et al. "Optical I/O Built-in System
LSI module (3) Design of Optical Coupling System" IEICE 2003
Electronics Society Convention C-3-125
Non Patent Reference 3: Sasaki et al. "Optical I/O Built-in System
LSI module (5) Development of Substrate implementation Connector
Optical coupling System Design" IEICE 2003 Electronics Society
Convention C-3-127
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0009] First, in the above mentioned method where end surfaces of
the optical fiber and the waveguide are ground at 45 degree and a
mirror is formed by subjecting the ground surface to metal vapor
deposition to perform 90 degree conversion, it is not easy to
highly accurately grind the optical fiber and the waveguide at 45
degree. And further step such as metal vapor deposition requires
large-scale manufacturing facility. At implementation time, it also
requires to install the 45-degree surface straight above or
straight below with respect to the circuit substrate without fail.
This implementation is not easy. Further in this method, after 90
degree conversion from the core of the optical fiber and the core
of the waveguide, a beam diameter is increased because light
waveguides in the medium having no waveguide structure, thereby
good coupling is difficult to obtain.
[0010] Further in the method of converting with a mirror having 45
degree which requires a minute mirror for miniaturization,
components including lens parts are added for positioning with this
minute mirror and for controlling beam expansion caused by beam
propagation in the air before the mirror portion. Therefore the
number of components is increased and positioning them is not
easy.
[0011] Furthermore, in the system associated with interspaces
propagation in which end surfaces of light emission to the space
from the waveguide and the optical fiber take big return loss, no
reflection coating and angle grinding are required. No reflection
coating requires large scale equipment, and as for angle grinding,
positioning with 45 degree mirror is further difficult in some
cases because optical beam radiation direction deviates from the
optical axis in the waveguide and optical fiber.
[0012] Next, an optical fiber capable of bending mechanically and
optically even with the minimum bend radius of 15 mm is effective
outdoor while in the narrow indoor space, allowable smaller bending
radius is much better. In the case the radius smaller than the
bending radius of 15 mm is desired, it is impossible to use.
[0013] In the method of bending where the specified portion of the
optical fiber having minute radius, because the outer diameter is
extremely thin, about several .mu.m, there is a problem of breakage
during handling. Further in this method, a return loss of the bend
portion is sensitive to the external environment change because
basically the external environment functions as a clad. That means,
when water dew condensation occurs in this minute diameter portion
because of an environmental temperature and a temperature change,
optical confinement in the minimum bending portion due to pseudo
ultra high .DELTA. does not work.
[0014] In order to maintain optical confinement in the minimum
bending portion, this minute diameter portion requires air sealing
while being exposed to gas including air. That means, the minute
diameter portion requires air sealing by disposing in the cavity,
but this is not easy. Further, even if the minute diameter portion
is small, the structure portion air sealing and protecting it has
to be larger than the minute diameter portion.
[0015] In addition, organic waveguide sheets and optical fiber
sheets are proposed as the above mentioned optical fibers and
optical waveguides. First, an optical loss of state of art organic
waveguide sheets is about 0.2 dB/cm which is very large, and
optical power loss is 3 dB with only 15 cm transmission, i.e. less
than half. When optical signals transmit from an optical electric
fusion bonded substrate to a back plane, further to another optical
electric fusion bonded substrate, the optical signals transmit for
a distance ranging from several tens cms to 1 m. In this case, even
with transmission loss alone of the waveguide regardless of a
connection loss and the like of a coupler, an optical loss of
maximum about 20 dB occurs. Therefore, when optical transmission is
conducted using a state or art organic waveguide, the transmission
is ended up limited to a short distance transmission. Further,
characteristics of the organic waveguides are changeable to
temperature. And long term reliability in the condition of high
temperature and high humidity as in the electric circuit is lower
than that of the optical fiber.
[0016] On the contrary, an optical fiber sheet is wired with
multiple optical fibers sandwiched with flexible plastic films and
characteristics are determined by the optical fiber. With regard to
a transmission loss of the optical fiber, a silica glass optical
fiber is about 0.2 dB/km while the organic waveguide is 0.2 dB/cm.
Transmission loss of the silica glass optical fiber is remarkably
small in terms of cm and km. And the transmission distance within
the optical electric circuit fusion bonded substrate is several ms
at maximum, therefore the transmission loss is negligible small. In
the case of plastic optical fiber, the transmission loss is
increased several dB to several tens dB/km. For example even with
500 dB/Km loss, the loss is also low about 1/40 compared with the
organic waveguide of about 0.5 dB/m. Therefore there are no
substantial problems.
[0017] However, in this optical fiber sheet where multiple optical
fibers are wired with lights in the specified place, wired lights
are crossed and optical loss occurs depending on the crossing. The
wiring configuration prevents the light losses due to this
crossing. A buffer material is considered to use in the crossing
portion, but this measure affects yield rate and leads to cost up.
And there is a problem with the wiring on the sheet that the
bending radius can not be reduced because the optical fiber is
optically and mechanically strong.
[0018] Generally since optical loss increase and mechanical
breakage are concerned in the silica glass optical fiber at bending
radius of not more than 15 mm, wiring at the radius more than that
is required. Therefore optical fiber is difficult to make small and
wiring configuration is also limited. With regard to mechanical
strength of the optical fiber sheet using the silica glass optical
fiber, e.g. Japan Patent Unexamined Publication 2000-329950
proposes using a carbon coat fiber in which the optical fiber
surface is coated with carbon. However it has had a problem that
surface of the carbon coated optical fiber is dark and the color
can not be discriminated even if this fiber is covered and
colored.
[0019] In the case of preparing optical electric fusion bonded
substrate which is embedded with an optical fiber sheet in an
electric circuit substrate, the optical fiber generates
microbendloss caused by unevenness of the electric circuit
substrate surface. It is easy to understand if we consider that
small unevenness hits the surface of the optical fiber to produce
lateral pressure so that minute bends continuously generate in a
longitudinal direction of the optical fiber. Such microbendloss
occurs in some cases when temperature of a single unit of optical
fiber sheet is lowered. A flexible plastic film forming the sheet
contracts at low temperature, the optical fiber contracts a little
because it is a glass, and the optical fiber surges finely due to
difference between contract lengths.
[0020] The present invention is made to solve the above mentioned
objects. The object is to provide an optical waveguide, optical
waveguide module and a method of converting optical waveguide
direction, wherein the number of components is small, positioning
is not required, the optical waveguide direction is converted with
extremely small portion, special protection mechanism such as air
sealing is not required because it is not sensitive to external
environment change.
MEANS FOR SOLVING PROBLEMS
[0021] The inventor has been dedicated to studying to solve the
conventional object. As a result, it is found that a specified
portion of an optical waveguide is heated to the specified
temperature so that the portion of the optical waveguide becomes in
a process distortion free state and bending process is preformed at
a specified bending radius while keeping the state, thereby capable
of bending in a distortion free state.
[0022] The present invention is made based on the above-mentioned
research accomplishment and a first embodiment of an optical
waveguide related to the present invention is the optical waveguide
wherein an optical waveguide having a core and a clad, and a
specified portion is heated to move into a process distortion free
state, said portion moved into the process distortion free state is
bent in a curved line at a specified bend radius to move into a
process distortion state.
[0023] In a second embodiment of an optical waveguide related to
the present invention, said portion of said optical waveguide is
heated to a temperature within a range of not less than a folding
point to not more than softening point to move the process
distortion state.
[0024] In a third embodiment of an optical waveguide related to the
present invention, said optical waveguide is an optical fiber
having an outer diameter of 50 .mu.m. Material of the optical fiber
includes silica glass, all plastic, and plastic clad.
[0025] In a fourth embodiment of an optical waveguide related to
the present invention, an outer diameter of said optical waveguide
is not less than 10 times of mode field diameter of said optical
waveguide.
[0026] In a fifth embodiment of an optical waveguide related to the
present invention, said bend radius is not more than 5.0 mm.
[0027] In a sixth embodiment of an optical waveguide related to the
present invention, a core/clad equivalent refractive index
difference .DELTA..sub.1 of the optical waveguide is within a range
from not less than 0.8% to not more than 3.5%, preferably within a
range from not less than 1.0% to not more than 3.0%. The equivalent
refractive index difference is a difference between the maximum
refractive index of the core portion and the minimum refractive
index of the effective clad portion. And a profile of optical fiber
refractive index includes a single-peaked type profile and a W-type
profile, etc. and the profile is not especially limited.
[0028] A first embodiment of an optical waveguide module related to
the present invention comprises multiple optical waveguides
mentioned above and said multiple optical waveguides are arrayed
and at least some part of said optical waveguides is fixed to a
member comprising a positioning mechanism.
[0029] A second embodiment of an optical waveguide module related
to the present invention comprises multiple optical waveguides
mentioned above and to at least one end of said optical waveguide,
an optical waveguide having an core/clad equivalent refractive
index difference .DELTA..sub.2 of not less than 0.2% is fusion
bonded, the fusion bonded portion is heated to reduce mismatch of
said core/clad equivalent refractive index differences .DELTA. and
mismatch of mode field diameters.
[0030] A third embodiment of an optical waveguide module related to
the present invention comprises any one of optical wave guides
mentioned above, wherein said optical waveguide is fixed on a sheet
while being wired on the sheet.
[0031] A fourth embodiment of an optical waveguide module related
to the present invention comprises any one of optical wave guides
mentioned above, wherein said optical waveguide is fixed between at
least two sheets while being wired therebetween.
[0032] A fifth embodiment of an optical waveguide module related to
the present invention comprises multiple optical waveguides for use
and they are fixed while being wired.
[0033] In a sixth embodiment of an optical waveguide module related
to the present invention, a material of said sheet for use has
flexibility. As this material, used films are polyamide,
polyethylene terephthalate, low-density or high-density
polyethylene, polypropylene, polyester, nylon 6, nylon 66,
ethylene-tetrafluoroethylene copolymer, poly 4-methyl venten,
polyvinylidene chloride, plastic polyvinyl chloride, polyetherester
copolymer, ethylene-vinyl acetate copolymer, soft polyurethane,
etc.
[0034] In a first embodiment of a method of forming optical
waveguide related to the present invention, a method of forming an
optical waveguide comprising steps of:
[0035] heating a specified portion of an optical waveguide;
[0036] moving said portion of said optical waveguide into a process
distortion free state;
[0037] bending said portion moved into the process distortion free
state at a specified bend radius; and
[0038] moving said portion of said optical waveguide into a process
distortion state while being bent at the specified bend radius.
Here an optical fiber is used as the optical waveguide, and all
plastic or plastic clad used as material enables small bending
without bend loss. Besides, an operation at high temperature is not
required not as in the silica glass optical fiber.
EFFECT OF THE INVENTION
[0039] With the optical waveguide of the present invention, the
specified portion is bent at the specified radius while reducing
connection loss caused by fusion bonding to convert the optical
waveguide direction to the specified angle. Further miniaturization
of the optical waveguide module is realized using these.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a schematic diagram showing an optical waveguide
bent by using arc discharge.
[0041] FIG. 2 is a schematic diagram showing a third and a fifth
modes of an optical waveguide related to the present invention FIG.
3 is a schematic diagram showing a sixth mode of optical waveguide
related to the present invention.
[0042] FIG. 4 is a schematic diagram showing an optical waveguide
module in which arrayed optical waveguides are fixed to a
member.
[0043] FIG. 5 is a schematic diagram showing a second mode of the
optical waveguide module related to the present invention.
[0044] FIG. 6 is also a schematic diagram showing the second mode
the optical waveguide module related to the present invention.
[0045] FIG. 7 is a schematic diagram showing an optical fiber
sheet.
[0046] FIG. 8 is a schematic diagram showing application of the
optical waveguide module to a corner wiring in the house.
[0047] FIG. 9 is a schematic diagram showing application of the
optical waveguide module to an electric optical circuit fusion
substrate.
EXPLANATION OF REFERENCE NUMERALS
[0048] 1 Optical Fiber [0049] 2 Arc Discharge [0050] 3 Electrode
[0051] 4 Specified Portion [0052] 5 Positioning Mechanism [0053] 6
Member [0054] 7 Fusion Bonding Portion [0055] 8 Sheet [0056] 9
Window [0057] 10 Optical Waveguide Module [0058] 11 Electric
Optical Circuit Fusion Substrate
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0059] Embodiments of the present invention will be described in
detail with reference to drawings hereinafter.
First Embodiment
[0060] FIG. 1 is a schematic diagram showing a first mode of an
optical waveguide related to the present invention. The specified
portion of the optical waveguide is heated by arc discharge to high
temperature (more than holding point, less than softening point)
and the optical waveguide is bent at a prescribed radius). Since
this optical waveguide becomes in a thermoneutral environment after
the bent portion of the optical waveguide is bent at high
temperature, there is no distortion due to bent. That means it is
processed in such that an initial state is a bend state. When the
optical waveguide is deformed after processed state, distortion
occurs to cause breakage. When the optical waveguide is bent before
the process, distortion does not occur to prevent breakage.
[0061] However, when this bent portion is restored to linear state,
distortion occurs to cause breakage. Selection whether an initial
distortion free state is a linear state or a bent state ends up
preventing breakage when required forms are made. Since the present
invention is purposed to convert the optical waveguide direction in
the minute space, breakage is prevented by the process in such that
a conversion state is the initial distortion free state.
[0062] When this process is performed, the required portion of the
optical waveguide may be heated by any means including arc
discharge, burner, furnace, etc., but the purpose is bending at the
same time of heating while freeing process distortion.
Second Embodiment
[0063] FIG. 2 is a schematic diagram showing third and fifth modes
of an optical waveguide related to the present invention. In these
modes where an optical waveguide direction is converted at a minute
space, actually usable size is specified based on physical size of
the used optical waveguide. In these modes, an external diameter a
of the optical waveguide is not less than 50 .mu.m, and a bend
radius R is not more than 5.0 mm. That means, it is not physically
possible that an optical waveguide with an external diameter a of
50 .mu.m is bent at a bend radius R of 50 .mu.m. It is neither easy
to handle an optical waveguide with an external diameter a of less
than 50 .mu.m. Therefore, the minimum external diameter a of an
optical waveguide is specified 50 .mu.m to secure easy handling and
the bend radius of used optical waveguide is specified 10 times of
the minimum external diameter to physically realize the bend.
[0064] Further, since 125 .mu.m of external diameter is convertible
diameter with the typical optical waveguide generally used, applied
scope of the present invention is remarkably broaden by employing
this external diameter. Furthermore, a method of the present
invention is advantageous to employ with not more than 5.0 mm of
the bend radius R. That means, when using an optical fiber having
the minimum diameter at a bend radius R exceeding 5.0 mm, breakage
distortion is not reached depending on the bend radius and
distortion free process of the present invention is not required in
some cases. While, in the case of not more than 5.00 mmm of bend
radius R, distortion free process of the present invention is
required even with an optical waveguide having 50 .mu.m of the
minimum external diameter R which is not difficult to handle.
[0065] In this embodiment, an optical fiber having an external
diameter a of 80 .mu.m is bent at 90 degree with a bend radius R of
1 mm.
Third Embodiment
[0066] FIG. 3 is a schematic diagram showing sixth mode of optical
waveguide related to the present invention. A method for preventing
mechanical breakage is focused in the optical waveguide direction
in the minute space according to the second embodiment. However in
this embodiment the optical waveguide direction can be converted in
the minute space while maintaining optical characteristics in good
condition. An equivalent refractive index difference .DELTA..sub.1
between core and clad of the optical waveguide is within a range
from not less than 0.8% to not more than 3.5%, preferably within a
range from not less than 1.0% to not more than 3.0%. In the
generally used optical waveguide, an general difference
.DELTA..sub.1 between the core and the clad is around 0.3%.
However, when the optical waveguide having an equivalent refractive
index difference .DELTA..sub.1 of about 0.3% is bent at bend radius
R of not more than 5.0 mm, light confined in the core is not
confined any more and is radiated to the clad, thereby drastically
increasing light loss at the bending portion.
[0067] However, even though an equivalent refractive index
difference .DELTA..sub.1 is within a range from not less than 0.8%
to not more than 3.5%, preferably within a range from not less than
1.0% to not more than 3.0%, and a bend radius R is 0.5 mm, it is
possible to hold the light loss at the bending portion under 0.5
dB. With high equivalent refractive index difference .DELTA..sub.1
exceeding 3.5%, it is possible to make bend loss lower even with
bend radius of not more than 0.5 mm. In this case, since a mode
field diameter is required to minimize in order to maintain a
single mode operation, external connection is difficult. Therefore,
preferable is an equivalent refractive index difference
.DELTA..sub.1 within a range from not less than 1.5% to not more
than 3.5%.
[0068] In this embodiment, an optical fiber with an equivalent
refractive index difference .sub.1 of 2.5% is used to bend at 90
degree an optical waveguide assumed to have an external diameter a
of 80 .mu.m and a bend radius R of 1 mm. A used wavelength is 1.3
.mu.m.
Embodiment 4
[0069] FIG. 4 is a schematic diagram showing a first mode of the
optical waveguide module related to the present invention. In this
mode optical waveguide module, the optical waveguides of the
present invention are arrayed and multiple channels can be
collectively converted in. The module of the present invention has
an entrance portion where characteristics of an optical waveguide
are compatible with those of the general optical waveguide enables
good characteristic connection with external equipment.
[0070] In this embodiment, the optical fiber having an external
diameter a of 80 .mu.m, and equivalent refractive index difference
.DELTA..sub.1 of 2.5% is fixed to the member comprising a
positioning mechanism. The optical waveguide direction is converted
from input to output at 90 degree and grind end faces of both input
and output are inclined and ground at every 4 degree against 90
degree faces. Twelve horizontal linear lines are spaced at 125
.mu.m intervals.
Fifth Embodiment
[0071] FIG. 5 is a schematic diagram showing second mode of the
optical waveguide module related to the present invention. In this
mode optical waveguide module, fusion bonded are the first optical
waveguide having a core/clad equivalent refractive index difference
.DELTA..sub.1 within a range from not less than 0.8% to not more
than 3.5%, preferably within a range from not less than 1.0% to not
more than 3.0%, and the second optical waveguide having an
core/clad equivalent refractive index difference .DELTA..sub.2 of
not less than 0.2%. The fusion bonded portion is heated to reduce
mismatch of said core/clad equivalent refractive index differences
.DELTA. and mismatch of mode field diameters and the required
portion of the optical waveguide is heated to bend.
[0072] That means, in the second mode optical waveguide module, the
optical waveguide and general optical waveguide are different in
core/clad equivalent refractive index in order to use the optical
waveguide having a high equivalent refractive index difference.
Further, since they are also different in equivalent refractive
index difference, a mode field diameter of the general optical
waveguide is different from that of the optical waveguide of the
present invention used in an optical waveguide direction converting
member. Those having different refractive indexes are contacted
with each other and a light signal is transmitted through the
contact portion to reflect light in a portion of refractive index
boundary. This phenomenon should be avoided in the optical
communication. Generally, not less than 50 dB is required as a
reflection attenuation amount.
[0073] When those having different mode field diameters are
connected with each other, connection loss due to diameter
difference occurs in the connected portion. The mode field diameter
of the optical waveguide used in the optical waveguide direction
converting member of the present invention is about 3 .mu.m, while
the mode field diameter of the general optical waveguide depending
on used wavelength is about 10 .mu.m. If those having different
diameters are connected with each other leaving as they are, the
connection loss is not less than 5 dB. It is effective to
facilitate connection of external equipment and laser that the
general optical fiber and external equipment are connected and then
they are connected to the optical waveguide converting member of
the present invention.
[0074] In the second mode, in order to reduce loss of connection
and reflection, fusion bonded are the first optical waveguide
having a core/clad equivalent refractive index difference
.DELTA..sub.1 within a range from not less than 0.8% to not more
than 3.5%, preferably within a range from not less than 1.0% to not
more than 3.0% and the second optical waveguide having an core/clad
equivalent refractive index difference .DELTA..sub.2 of not less
than 0.2%. The fusion bonded portion is heated to reduce mismatch
of said core/clad equivalent refractive index differences .DELTA.
and mismatch of mode field diameters, thereby increasing reflection
attenuation and restricting connection loss. In this method, a
reflection attenuation is not less than 50 dB and a connection loss
is about 0.2 dB.
[0075] In this embodiment, used is an optical fiber with an outer
diameter a of 80 .mu.m, a bend radius R of 1 mm, and an equivalent
refractive index difference .DELTA..sub.1 of 2.5% for bending 90
degree and in a single optical waveguide mode by using wavelength.
And, at one side of this optical fiber, an optical fiber with outer
diameter a of 80 .mu.m and an equivalent refractive index
difference .DELTA..sub.2 of 0.35% and in a single optical waveguide
mode by using wavelength is fusion bonded, the fusion bonded
portion is heated with gas burner to reduce mismatch of the
equivalent refractive index differences .DELTA. and mismatch of
mode field diameters. Using wavelength is 1.3. Measurement result
is a reflection attenuation amount is 50 dB and connection loss is
0.2 dB.
Sixth Embodiment
[0076] FIG. 6 is also a schematic diagram showing the second mode
of the optical waveguide module related to the present
invention.
[0077] In this mode of the optical waveguide module, at both ends
of the first optical waveguide having an core/clad equivalent
refractive index difference .DELTA..sub.1 within a range from not
less than 0.8% to not more than 3.5%, preferably within a range
from not less than 1.0% to not more than 3.0%, the second optical
waveguide having a core/clad equivalent refractive index difference
.DELTA..sub.2 of not less than 0.2% is fusion bonded. And the
fusion bonded portion is heated to reduce mismatch of said
core/clad equivalent refractive index differences .DELTA. and
mismatch of mode field diameters, and the required portion of the
optical waveguide is heated to bend.
[0078] In the fifth embodiment, the optical waveguide
characteristically compatible with general optical waveguides is
fusion bonded at only one side of the optical waveguide direction
converting member, and the bonded portion is heated to r mismatch
of said core/clad equivalent refractive index differences .DELTA.
and mismatch of mode field diameters. While, in the sixth
embodiment, the optical waveguide characteristically compatible
with general optical waveguides is fusion bonded at both ends of
the optical waveguide direction converting member and the fusion
bonded portion is heated to mismatch of said equivalent refractive
index differences .DELTA. and mismatch of mode field diameters.
Thereby both sides of the optical waveguide direction converting
member are easy to connect with the external equipment.
[0079] In this embodiment, used is an optical fiber with an outer
diameter a of 80 .mu.m, a bend radius R of 1 mm, and an equivalent
refractive index difference .DELTA..sub.1 of 2.5% for bending 90
degree and in a single optical waveguide mode by using wavelength.
And, at both sides of this optical fiber, an optical fiber with
outer diameter a of 80 cm and an equivalent refractive index
difference .DELTA..sub.2 of 0.35% and in a single optical waveguide
mode by using wavelength is fusion bonded, the fusion bonded
portion is heated with gas burner to reduce mismatch of the
equivalent refractive index differences .DELTA. and mismatch of
mode field diameters. Using wavelength is 1.3.mu.. Measurement
result is a reflection attenuation amount is more than 50 dB and
connection loss is about 0.4 dB.
Seventh Embodiment
[0080] FIG. 7 is a schematic diagram showing an optical waveguide
module of fourth to sixth mode. In the present invention, an
optical waveguide module is prepared to have an optical waveguide
installed in the sheet having an core/clad equivalent refractive
index difference .DELTA..sub.1 within a range from not less than
0.8% to not more than 3.5%.
[0081] This embodiment uses an optical fiber having general
diameters, a glass portion outer diameter of 125 .mu.m, and a
coating outer diameter of 250 .mu.m, while it uses an optical
waveguide having a remarkably big core/clad equivalent refractive
index difference .DELTA..sub.1 of 2.5% compared to the general
equivalent refractive index difference .DELTA..sub.1 of about 0.3%
in the single mode optical fiber.
[0082] With the optical waveguide module prepared using this
optical fiber which has relatively big equivalent refractive index
difference .DELTA..sub.1 compared to the general equivalent
refractive index difference .DELTA..sub.1 of the single mode
optical fiber, losses are reduced even if the optical waveguide
module is applied with surge and bend. Specifically, a loss
fluctuation test is conducted at a temperature cycle from
-40.degree. C. to +80.degree. C. while the optical waveguide module
having general optical fiber is being sandwiched and pressed by two
sheets of sandpaper. The test result that the loss is maximum of 20
dB at -40.degree. C. is extremely bad. According to the result of
the test which is conducted with the optical waveguide module in
the same conditions but an equivalent refractive index difference
.DELTA..sub.1 of 2.5%, the maximum loss fluctuation value is about
0.1 dB at the temperature cycle from -40.degree. C. to +80.degree.
C. and loss fluctuation is hardly found.
[0083] Even in the case that the equivalent refractive index
difference .DELTA..sub.1 is decreased to 1.5%, the loss fluctuation
in the above mentioned test is also about 0.1 dB. However, with the
lower equivalent refractive index difference .DELTA..sub.1, the
loss fluctuation gradually increased, and with the equivalent
refractive index difference .DELTA..sub.1 of 1%, the loss
fluctuation of the above mentioned test becomes maximum about 0.5
dB. There are no practical problems even with 0.5 dB. The optical
waveguide module of the present invention uses an optical waveguide
direction converting element of the prior art connected thereto to
realize an electric optical fusion circuit substrate having
excellent optical transmission characteristic and connection
characteristic. Therefore, in view of connectivity with the optical
waveguide direction converting element of the prior art, the
equivalent refractive index difference .DELTA..sub.1 is specified
to be the minimum value of not less than 1.5% which is used in the
optical waveguide direction converting element of the prior
art.
[0084] Further, with bigger equivalent refractive index difference
.DELTA..sub.1, the loss fluctuation decreases. With excessively big
equivalent refractive index difference .DELTA..sub.1, a mode field
diameter in the optical fiber decreases. In view of a high position
accuracy at the connection time and connectivity with the optical
waveguide direction converting element of the prior art,
.DELTA..sub.1 is set not more than 3.5%.
[0085] A small outer diameter a of the glass portion enables
mechanically small bend. However, with excessively small diameter,
light confined in the core emits due to thin clad to generate
transmission loss. Therefore, the clad outer diameter is set to be
at least 10 times of the mode field diameter to control this
transmission loss.
[0086] Further, being thin makes weak for the loss fluctuation test
at the temperature cycle form -40.degree. C. to +80.degree. C.
which is conducted in this embodiment. However in the fiber with
mode field diameter of 5 .mu.m having an optical fiber diameter a
of 50 .mu.m with an equivalent refractive index difference
.DELTA..sub.1 of not less than 1.5%, the maximum loss fluctuation
is about 0.1 dB and it is confirmed that excellent characteristic
is maintained.
Eighth Embodiment
[0087] FIG. 8 is a schematic diagram showing application of the
optical waveguide module of the present invention to a corner
wiring in the house. Wiring of the optical waveguide in a room
corner in the house used to need to secure several cms for the
minimum bend radius of the conventional optical waveguide. However,
the optical waveguide module of the preset invention came to enable
the corner wiring in a size of not more than 1 cm as a module size.
FIG. 8 shows it is possible to bend at 90 degree.
[0088] FIG. 9 is a schematic diagram showing application of the
optical waveguide module of the present invention to an electric
optical fusion circuit substrate. The electric optical fusion
circuit substrate has a configuration in which an optical waveguide
module is sandwiched with two sheets of electric circuit
substrates, and the optical waveguide module of the present
invention is installed at the ends of optical waveguide direction
converting member at 90 degree to the electric circuit
substrates.
[0089] With optical waveguide related to the present invention, the
specified portion is bent at the specified radius while reducing
connection losses due to the fusion bonding, thereby the optical
waveguide can be converted at the specified angle. Further, with
those, a size of the optical waveguide can be reduced and utility
value in industry is increased.
* * * * *