U.S. patent application number 11/194071 was filed with the patent office on 2006-02-02 for optical fiber connected body with mutually coaxial and inclined cores, optical connector for forming the same, and mode conditioner and optical transmitter using the same.
This patent application is currently assigned to KYOCERA CORPORATION. Invention is credited to Yoshihiro Kobayashi.
Application Number | 20060024001 11/194071 |
Document ID | / |
Family ID | 35732299 |
Filed Date | 2006-02-02 |
United States Patent
Application |
20060024001 |
Kind Code |
A1 |
Kobayashi; Yoshihiro |
February 2, 2006 |
Optical fiber connected body with mutually coaxial and inclined
cores, optical connector for forming the same, and mode conditioner
and optical transmitter using the same
Abstract
An optical fiber connected body including a first optical fiber
having a core and a clad, and a second optical fiber having a core
and a clad, with its end connected optically to an end of the first
optical fiber, in which the core center of the first optical fiber
and the core center of the second optical fiber are mutually
deviated at the interface of the first optical fiber and the second
optical fiber, a light beam entering the second optical fiber from
the first optical fiber is inclined to the central axis of the
second optical fiber.
Inventors: |
Kobayashi; Yoshihiro;
(Kitami-shi, JP) |
Correspondence
Address: |
HOGAN & HARTSON L.L.P.
500 S. GRAND AVENUE
SUITE 1900
LOS ANGELES
CA
90071-2611
US
|
Assignee: |
KYOCERA CORPORATION
|
Family ID: |
35732299 |
Appl. No.: |
11/194071 |
Filed: |
July 28, 2005 |
Current U.S.
Class: |
385/50 ;
385/88 |
Current CPC
Class: |
G02B 6/381 20130101;
G02B 6/3829 20130101 |
Class at
Publication: |
385/050 ;
385/088 |
International
Class: |
G02B 6/36 20060101
G02B006/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 28, 2004 |
JP |
P 2004-220065 |
Nov 25, 2004 |
JP |
P 2004-340344 |
Dec 27, 2004 |
JP |
P 2004-375130 |
Jan 28, 2005 |
JP |
P 2005-020888 |
Claims
1. A optical fiber connected body comprising: a first optical fiber
having a core and a clad, and a second optical fiber having a core
and a clad, with its end connected optically to an end of said
first optical fiber, wherein the core center of said first optical
fiber and the core center of said second optical fiber are mutually
deviated at the interface of said first optical fiber and said
second optical fiber, and a light beam entering said second optical
fiber from said first optical fiber is inclined to the central axis
of said second optical fiber.
2. An optical connector for forming said optical fiber connector
according to claim 1, comprising: a first fixing member for fixing
said first optical fiber, and a second fixing member for fixing
said second optical fiber, wherein the core center of said first
optical fiber and the core center of said second optical fiber are
mutually deviated at the interface of said first optical fiber and
said second optical fiber, and said first fixing member and said
second fixing member are connected so that light beam entering said
second optical fiber from said first optical fiber is inclined to
the central axis of said second optical fiber.
3. The optical connector according to claim 2, wherein said first
optical fiber is a single mode optical fiber and said second
optical fiber is a multimode optical fiber, and said first fixing
member and said second fixing member are connected so that the
distance between the core center of said first optical fiber and
the core center of said second optical fiber is 10 to 25 .mu.m, and
that the light beam entering said second optical fiber from said
first optical fiber is inclined by 3 to 25 degrees to the central
axis of said second optical fiber.
4. The optical connector according to claim 2, wherein, supposing
the direction linking the core center of said first optical fiber
and the core center of said second optical fiber to be X-axis, the
central axis direction of said second optical fiber to be Z-axis,
and the direction at right angle to the X-axis and Z-axis to be
Y-axis, and further supposing the axis by deviating the Y-axis by
the distance .delta. between the core center of said first optical
fiber and the core center of said second optical fiber in the
X-direction to be Y'-axis, and the axis by deviating the Z-axis by
the distance .delta. in the X-direction to be Z'-axis, said light
beam exists inside of a plane formed by the Y'-axis and
Z'-axis.
5. The optical connector according to claim 2, wherein said first
fixing member has a first ferrule for holding said first optical
fiber, and said second fixing member has a second ferrule for
holding said second optical fiber, at least one of said first
ferrule or second ferrule holds optical fiber at a position
deviated from its central axis, and said first ferrule and the
second ferrule are inserted into a bent cylindrical sleeve.
6. A mode conditioner comprising said optical fiber connected body
according to claim 1, wherein said first optical fiber is a single
mode optical fiber, and said second optical fiber is a multimode
optical fiber.
7. The mode conditioner according to claim 6, wherein said
multimode optical fiber is provided parallel to said optical fiber
connector.
8. The mode conditioner according to claim 6, wherein said first
optical fiber and said second optical fiber are connected so that
the distance between the core center of said first optical fiber
and the core center of said second optical fiber is 10 to 25 .mu.m,
and that light beam entering said second optical fiber from said
first optical fiber is inclined by 3 to 25 degrees to the central
axis of said second optical fiber.
9. The mode conditioner according to claim 6, wherein supposing the
direction linking the core center of said first optical fiber and
the core center of said second optical fiber to be X-axis, the
central axis direction of said second optical fiber to be Z-axis,
and the direction at right angle to the X-axis and Z-axis to be
Y-axis, and further supposing the axis by deviating the Y-axis by a
distance .delta. between the core center of said first optical
fiber and the core center of said second optical fiber in the
X-direction to be Y'-axis, and the axis by deviating the Z-axis by
the distance .delta. in the X-direction to be Z'-axis, said light
beam exists inside of a plane formed by the Y'-axis and
Z'-axis.
10. The mode conditioner according to claim 6 further comprising: a
reinforcing member disposed around the outer circumference of
connecting portion of said first optical fiber and said second
optical fiber, a connection sleeve for covering said reinforcing
member, and an adhesive applied to fill in the gap between said
connection sleeve and said reinforcing member.
11. An optical transmitter comprising: a laser diode, a fiber stab
for holding a first optical fiber in a through-hole, and a sleeve
for inserting a plug ferrule, which holds a second optical fiber in
a through-hole, from outside, said sleeve being fitted on said
fiber stab, wherein, when said plug ferrule is inserted, said first
optical fiber in said fiber stab and said second optical fiber in
said plug ferrule are optically connected so as to compose said
optical fiber connected body according to claim 1.
12. The optical transmitter of claim 11, wherein the core portion
of said first optical fiber is inclined to the clad, at least near
the end of the plug ferrule side of said fiber stab.
13. The optical transmitter according to claim 11, wherein the
through-hole of said fiber stab is inclined to the central axis of
said fiber stab, at least near the end of the plug ferrule side of
said fiber stab.
14. The optical transmitter according to claim 11, wherein the
diameter of through-hole of said fiber stab at the plug ferrule
side is greater than that at the laser diode side, and said first
optical fiber is curved within the through-hole at the plug ferrule
side of said fiber stab.
15. The optical transmitter according to claim 11, wherein the
distance between the core center of said first optical fiber and
the core center of said second optical fiber is 5 to 30 .mu.m, and
light beam entering said second optical fiber from said first
optical fiber is inclined by 3 to 25 degrees to the central axis of
said second optical fiber.
16. The optical transmitter according claim 11, wherein supposing
the direction linking the core center of said first optical fiber
and the core center of said second optical fiber to be X-axis, the
central axis direction of said second optical fiber to be Z-axis,
and the direction at right angle to the X-axis and Z-axis to be
Y-axis, and further supposing the axis by deviating the Y-axis by a
distance .delta. between the core center of said first optical
fiber and the core center of said second optical fiber in the
X-direction to be Y'-axis, and the axis by deviating the Z-axis by
the distance .delta. in the X-direction to be Z'-axis, said light
beam exists inside of a plane formed by the Y'-axis and
Z'-axis.
17. The optical transmitter according to claim 11, wherein the clad
of said first optical fiber has a eliminating means for eliminating
clad mode light.
18. The optical transmitter according to claim 17, wherein the clad
of said first optical fiber has an inside clad of smaller
refractive index than in the core, and an outside clad disposed at
the outside side of the inside clad and having a greater refractive
index than the inside clad.
19. The optical transmitter according to claim 18, wherein a dopant
for attenuating an optical signal is contained at least in part of
the outside clad.
20. The optical transmitter of claim 18, wherein the clad of said
first optical fiber has an intermediate clad having the same
refractive index as the core of said first optical fiber, disposed
between an outside clad and an inside clad.
21. The optical transmitter according claim 18, wherein the clad of
said first optical fiber has an intermediate clad disposed between
an outside clad and an inside clad, said intermediate clad having a
smaller refractive index than said inside clad.
22. The optical transmitter according to claim 18, wherein a light
attenuating dopant is contained at least in part of the side closer
to the core of said inside clad.
23. The optical transmitter according to claim 11, wherein said
first optical fiber is a single mode optical fiber, and said second
optical fiber is a multimode optical fiber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical fiber connected
body in which optical fibers are connected with each other, which
is used in optical communications, an optical connector for forming
the same, and a mode conditioner and an optical transmitter optical
connector using the same.
[0003] 2. Description of the Related Art
[0004] Systems used for connecting computers include 10-megabit
Ethernet (registered trademark) and 100-megabit Fast Ethernet
(registered trademark), and they are further to be replaced by
gigabit Ethernet (registered trademark) of larger transmission
capacity. For superfast large capacity transmission, development
has been started for 10-gigabit Ethernet (registered
trademark).
[0005] For high speed and large capacity of data transmission,
transmission system must be changed from electrical signal to
optical signal. Optical signal is further demanded to be changed
from optical signal emitted by light emitting diode (LED) to
optical signal emitted by laser diode (LD). Communication cables
are also changed from copper wires to multimode optical fiber and
further to single mode optical fiber for the benefits of high speed
and large capacity of transmission.
[0006] On the other hand, cable networks of the multimode optical
fibers are already established, and it is attempted to realize high
speed and large capacity transmission by using them. When LD light
is put in the multimode optical fiber, since the spot size of LD
light is smaller than the core diameter of the multimode optical
fiber, the core is not sufficiently filled with light, and
excitation is not successful. It is hence devised to put the LD
light directly into the single mode optical fiber, and bond it to
an existing multimode optical fiber.
[0007] In an existing multimode optical fiber, however, a
dimple-like portion that is low in refractive index may be formed
in the central area as shown in FIG. 19B in its manufacturing
process. Accordingly, when the single mode optical fiber receiving
the LD light is connected to the multimode optical fiber, some of
the modes may be dispersed, and various signals may interfere with
each other. As a result, an accurate signal cannot be received in
the receiver, and the transmission distance is extremely
shortened.
[0008] It is hence proposed to connect the single mode optical
fiber and the multimode optical fiber by deviating the central
axis. For example, Japanese Laid-open Patent Application No.
2001-13375 discloses an optical connector for connecting the single
mode optical fiber and the multimode optical fiber by deviating the
central axis of cores.
[0009] Japanese Laid-open Patent Application No. 2000-231027
discloses a mode conditioner using a patching cord connecting the
single mode optical fiber and the multimode optical fiber by
deviating the central axis of cores, at the transmission side.
[0010] Japanese Laid-open Patent Application No. 2000-147334
discloses an optical transmitter with mode conditioner having a
single mode optical fiber eccentric in the central axis of core
provided in a fiber stab. To this optical transmitter, a plug
ferrule having the multimode optical fiber is connected for making
optical transmission.
[0011] By using these optical fibers, mode conditioner, and optical
transmitter with mode conditioner, the light passing through the
single mode optical fiber enters the multimode optical fiber by
evading a dimple-like portion low in refractive index formed in the
central area as shown in FIG. 19B. Hence, suppressing abnormal
dispersion of modes, data can be transmitted efficiently.
SUMMARY OF THE INVENTION
[0012] In the conventional configuration, however, when the
transmission speed becomes faster and the transmission distance
becomes longer, abnormal dispersion of modes cannot be suppressed
sufficiently. For example, in the case of Ethernet having
transmission speed of up to 1 gigabit, abnormal dispersion of modes
hardly occurs in the conventional configuration. But in the
10-megabit Ethernet, at transmission distance of 550 m, some of the
modes of incident light are dispersed. As a result, various signals
interfere with each other, and accurate signal cannot be received
in the receiver.
[0013] It is hence an object of the present invention to provide an
optical fiber connected body capable of suppressing abnormal
dispersion of modes and transferring signals efficiently, event at
faster transmission speed and longer transmission distance.
[0014] According to the present invention, an optical fiber
connected body comprises:
[0015] a first optical fiber having a core and a clad, and
[0016] a second optical fiber having a core and a clad, with its
end connected optically to an end of the first optical fiber,
[0017] wherein the core center of the first optical fiber and the
core center of the second optical fiber are mutually deviated at
the interface of the first optical fiber and the second optical
fiber, and
[0018] a light beam entering the second optical fiber from the
first optical fiber is inclined to the central axis of the second
optical fiber.
[0019] Preferably, the first optical fiber is a single mode optical
fiber and the second optical fiber is a multimode optical fiber.
Since the core center of the first optical fiber and the core
center of the second optical fiber are eccentric, and the light
enters obliquely in the axial direction of the second optical
fiber, abnormal dispersion of modes is less likely to occur than in
the prior art, and signals do not interfere with each other, and
signals can be transmitted efficiently.
[0020] The distance between the core center of the first optical
fiber and the core center of the second optical fiber is preferred
to be 5 to 30 .mu.m, or more preferably 5 to 25 .mu.m. The light
beam entering the second optical fiber from the first optical fiber
is preferred to be inclined by 3 to 25 degrees to the central axis
of the second optical fiber.
[0021] Supposing the direction linking the core center of the first
optical fiber and the core center of the second optical fiber to be
X-axis, the central axis direction of the second optical fiber to
be Z-axis, and the direction at right angle to X-axis and Z-axis to
be Y-axis, and further
[0022] supposing the axis by deviating the Y-axis by the portion of
the distance between the core center of the first optical fiber and
the core center of the second optical fiber in the X-direction to
be Y'-axis, and the axis by deviating the Z-axis by the portion of
the distance between the core center of the first optical fiber and
the core center of the second optical fiber in the X-direction to
be Z'-axis,
[0023] the light beam entering the second optical fiber from the
first optical fiber is preferred to be present inside of a plane
formed by the Y'-axis and Z'-axis.
[0024] The optical fiber connected body of the invention can be
applied in optical connector, mode conditioner, optical
transmitter, etc.
[0025] An optical fiber connector of the present invention
comprises:
[0026] a first fixing member for fixing a first optical fiber,
and
[0027] a second fixing member for fixing a second optical
fiber,
[0028] wherein the core center of the first optical fiber and the
core center of the second optical fiber are mutually deviated at
the interface of the first optical fiber and the second optical
fiber, and the first fixing member and the second fixing member are
connected so that the light beam entering the second optical fiber
from the first optical fiber is inclined to the central axis of the
second optical fiber.
[0029] A mode conditioner of the present invention comprises a
connector between a single mode optical fiber and a multimode
optical fiber,
[0030] wherein the core center of the single mode optical fiber and
the core center of the multimode optical fiber are mutually
deviated at the interface of the single mode optical fiber and the
multimode optical fiber, and
[0031] the light beam entering the multimode optical fiber from the
single mode optical fiber is inclined to the central axis of the
multimode optical fiber.
[0032] An optical transmitter of the present invention
comprises:
[0033] a laser diode,
[0034] a fiber stab for holding a first optical fiber in a
through-hole, and
[0035] a sleeve for inserting a plug ferrule, which holds a second
optical fiber in a through-hole, from outside, the sleeve being
fitted into the fiber stab,
[0036] wherein, when the plug ferrule is inserted, the first
optical fiber in the fiber stab and the second optical fiber in the
plug ferrule are optically connected,
[0037] the core center of the first optical fiber and the core
center of the second optical fiber are mutually deviated at the
interface of the first optical fiber and the second optical fiber,
and
[0038] the light beam entering the second optical fiber from the
first optical fiber is inclined to the central axis of the optical
fiber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1A is a sectional view of an optical connector in
embodiment 1.
[0040] FIG. 1B is a partially magnified sectional view of
connecting portion of optical fibers of the optical connector in
FIG. 1A.
[0041] FIG. 2 is a schematic diagram showing an incident direction
of a light beam into the second optical fiber.
[0042] FIG. 3 is a schematic diagram showing an incident direction
of a light beam into the second optical fiber.
[0043] FIG. 4A is a schematic diagram of a mode conditioner in
embodiment 2.
[0044] FIG. 4B is a partially magnified sectional view of
connecting portion of optical fibers of the mode conditioner in
FIG. 4A.
[0045] FIG. 5A is a sectional view of an optical transmitter in
embodiment 3.
[0046] FIG. 5B is a partially magnified sectional view of
connecting portion of optical fibers of the optical transmitter in
FIG. 5A.
[0047] FIG. 6 is a partially magnified sectional view showing other
example of connecting portion of optical fibers.
[0048] FIG. 7 is a partially magnified sectional view showing other
example of connecting portion of optical fibers.
[0049] FIG. 8 is a partially magnified sectional view showing other
example of connecting portion of optical fibers.
[0050] FIG. 9 is a partially magnified sectional view showing other
example of connecting portion of optical fibers.
[0051] FIG. 10 is a partially magnified sectional view showing
other example of connecting portion of optical fibers.
[0052] FIG. 11 is a sectional view of a single mode optical fiber
having eliminating means of a clad mode light, and a schematic
diagram showing refractive index distribution corresponding to this
section.
[0053] FIG. 12 is a sectional view of a single mode optical fiber
having eliminating means of a clad mode light in other example, and
a schematic diagram showing refractive index distribution
corresponding to this section.
[0054] FIG. 13 is a sectional view of a single mode optical fiber
having eliminating means of a clad mode light in other example, and
a schematic diagram showing refractive index distribution
corresponding to this section.
[0055] FIG. 14 is a sectional view of a single mode optical fiber
having eliminating means of a clad mode light in other example, and
a schematic diagram showing refractive index distribution
corresponding to this section.
[0056] FIG. 15 is a partially magnified sectional view showing an
example of connecting portion of optical fibers.
[0057] FIG. 16 is a partially magnified sectional view showing
other example of connecting portion of optical fibers.
[0058] FIG. 17 is a schematic diagram of a measuring system of
transmission distance in example 1.
[0059] FIG. 18 is a schematic diagram of a measuring system of
transmission distance in example 2.
[0060] FIG. 19A is a schematic diagram of refractive index
distribution in an ideal multimode fiber.
[0061] FIG. 19B is a schematic diagram of refractive index
distribution in an actual multimode fiber.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0062] In this embodiment, the invention is applied in an optical
connector. The optical connector of the embodiment is an optical
connector for connecting both ends of a pair of optical fibers, in
which the optical fibers are connected so that the core centers of
the optical fibers are mutually deviated, and that an incident beam
from one optical fiber enters at an inclination to the axial center
of other optical fiber.
[0063] According to the optical connector of the embodiment, when a
single mode optical fiber is connected to a multimode optical
fiber, abnormal dispersion occurring in the multimode optical fiber
can be suppressed. Therefore, even at fast transmission speed and
long transmission distance, abnormal dispersion of modes is
suppressed, and signals can be transferred at high efficiency.
Dispersion occurring in the multimode optical fiber is specifically
described below.
[0064] The multimode optical fiber of graded index type (called
multimode optical fiber hereinafter) is designed and manufactured
so that refractive index distribution of core may decline from the
center to outside in an accurate quadratic curve as shown in FIG.
19A in order to suppress band deterioration (mode dispersion) due
to delay difference between modes. In the multimode optical fiber,
however, a dimple-like portion low in refractive index may be
formed in the central area as shown in FIG. 19B. Accordingly, some
of the modes of the incident light may be dispersed, and various
signals may interfere with each other. FIGS. 19A and 19B are
refractive index distribution diagrams of the multimode optical
fiber having abnormal low refractive index in the core center, in
which the axis of abscissas represents the distance from the core
central axis, and the axis of ordinates represents the refractive
index.
[0065] Such refractive index distribution may lead to deterioration
of transmission performance. Generally, the multimode optical fiber
is used in optical transmission at hundreds of Mb/s or less, and
the LED is mainly used in the light source for optical
transmission, and the problem has not been serious so far.
Recently, however, the existing multimode optical fiber is demanded
to be used in very fast optical transmission of Gb/s class. It is
hence an urgent problem how to suppress transmission deterioration
while using the optical fiber having refractive index distribution
as shown in FIG. 19B.
[0066] In the multtimode optical fiber having refractive index
distribution as shown in FIG. 19B, since the refractive index is
small in the core center, and the light propagating through the
core center is faster than the light propagating through the core
peripheral part. Therefore, light pulses are transmitted, the
pulses are dispersed due to delay difference between the light
passing through the core center and the light passing through the
core peripheral part. Such delay causing dispersion is called
differential mode delay (DMD). Such phenomenon is likely to occur
when light of high degree of parallelism is concentrated in the
central area of optical fiber core.
[0067] In the optical transmitter, if the transmission speed is the
same, the specification may be different depending on the type of
conforming optical fiber or wavelength of light source. In the case
of optical transmission of Gb/s class by the multimode optical
fiber, LD is more beneficial than LED from the viewpoint of
response speed of element. Also from the viewpoint of dispersion,
the LD of longer wavelength (1300 nm band) is superior to the LD of
shorter wavelength (for example, about 850 nm band), and the
transmission distance can be extended further.
[0068] In particular, when long wavelength LD is used, output light
easily enters the core center of the multimode optical fiber in a
state of high degree of parallelism, and hence it is important to
suppress the DMD of the multimode optical fiber.
[0069] FIG. 1A is a sectional view of optical connector 10 of the
embodiment.
[0070] An example of FC type optical connector is explained. A pair
of optical fiber fixing tools 3, 3' are fitted against each other.
The optical fiber fixing tools 3, 3' comprise (a) ferrules 1, 1'
having axial holes 1a, 1a' for inserting and fixing optical fibers
11, 11', and (b) ferrule supports 2, 2' having recesses 2a, 2a' to
be engaged with ferrules 1, 1', and through-holes 2b, 2b'
communicating with the recesses 2a, 2a' and coaxial with the axial
holes 1a, 1a' of the ferrules 1, 1'. Optical fibers 11, 11' are
inserted into axial holes 1a, 1a' of the ferrules 1, 1', and
through-holes 2b, 2b' of the ferrule supports 2, 2' are filled with
an adhesive 3, so that the optical fibers 11, 11' are fixed.
[0071] The pair of ferrules 1, 1' are held by a bent sleeve 14. An
adapter coupling 15 having threads at both ends is disposed on the
outer circumference of the sleeve 14. Coupling nuts 16 are fitted
to the threads at both ends of the adapter coupling 15. The ferrule
support 2 is disposed in each coupling nut 16, and a spring 17 is
disposed between the inner wall of the coupling nut 16 and the
flange-like protrusion of the ferrule support 2. By the pressing
force of the spring 17 disposed between the coupling nut 16 and
ferrule support 2, the leading ends of the ferrules 1, 1' of the
optical fiber fixing tools 3, 3' are fitted to each other. As a
result, the optical fibers 11, 11' are optically connected to each
other.
[0072] FIG. 1B is a magnified view of abutting portion of optical
fiber 11 and optical fiber 11'. Herein, the optical fiber 11 is
supposed to be a single mode optical fiber, and the optical fiber
11' is a multimode optical fiber. The incident side ferrule 1 has
its axial hole 1a nearly in the center of the outer circumference,
and the single mode optical fiber 11 is adhered and fixed to the
axial hole 1a. The exit side ferrule 1' has its axial hole 1a' at a
position eccentric from the center of the outer circumference, and
the multimode optical fiber 11' is adhered and fixed to the axial
hole 1a'. The core center 11b of the single mode optical fiber 11
and the core center 11b' of the multimode optical fiber 11' are
deviated from each other by .delta.. Instead of the axial hole 1a'
of the ferrule 1', the axial hole 1a of the ferrule 1 may be set
eccentric. Further, both the axial hole 1a of the ferrule 1 and
axial hole 1a' of the ferrule 1' may be set eccentric by different
extents.
[0073] As shown in FIG. 1A, the sleeve 14 is cylindrical, and an
inner hole 14a of the sleeve 14 is bent at the center 14b.
Accordingly, as shown in FIG. 1B, the ferrule 1 and ferrule 1' abut
against each other obliquely by way of the sleeve (not shown).
Therefore, the core central axis of optical fiber 11 is inclined to
the core central axis of optical fiber 11'. That is, the light beam
entering the optical fiber 11' from the optical fiber 11 advances
at an inclination to the optical axis of the optical fiber 11'.
[0074] Thus, in the embodiment, the core center of the single mode
optical fiber 11 and the core center of the multimode optical fiber
11' are mutually deviated, and the light beam emitted from the
single mode optical fiber 11 enters the multimode optical fiber
obliquely to its optical axis. Therefore, the light beam emitted
from the single mode optical fiber 11 enters the multimode optical
fiber 11' obliquely by evading the dimple-like portion low in
refractive index in the central area. As a result, occurrence of
DMD in the multimode optical fiber 11' can be suppressed
effectively. That is, abnormal dispersion of modes hardly occurs,
and the signals can be transmitted efficiently without mutual
interference.
[0075] FIG. 2 is a conceptual diagram of incident direction when
the light enters the multimode optical fiber 11'. Suppose the
direction linking the incident position 18a of light beam and the
core central position 11b' to be X-axis; the axial direction of
optical fiber 11' to be Z-axis, and the direction at right angle to
X-axis and Z-axis to be Y-axis. Suppose the distance between the
incident position 18a of the light beam and the core central
position 11b' to be .delta., the axis of Y-axis deviated by .delta.
in X-axis direction to be Y'-axis, and the axis of Z-axis deviated
by .delta. in X-axis direction to be Z'-axis.
[0076] In the optical connector 10 of the embodiment, the
eccentricity .delta. of the core central position 11b of optical
fiber core 11 to the core center 11b' of optical fiber 11' is
preferred to be defined in a range of 10 to 25 .mu.m. If the
eccentricity amount .delta. is less than 10 .mu.m, the eccentric
effect is not obtained, and the light may get into the dimple-like
portion low in refractive index in the central area of the
multimode optical fiber 11', and abnormal dispersion of modes
occurs. If the eccentricity amount .delta. is more than 25 .mu.m,
since the core diameter of the multimode optical fiber 11' is 50
.mu.m or 62.5 .mu.m, the incident light may run out of the core
portion, and the light may not be propagated correctly. A more
desired effect is obtained by adjusting the eccentricity amount in
a range of 15 to 20 .mu.m.
[0077] Preferably, the incident beam 18 from the optical fiber 11
enters the optical fiber 11' at an angle .psi. of 3 to 25 degrees
to its axial center. If the angle .psi. is less than 3 degrees,
angle shifting effect is not obtained, and the light may get into
the dimple-like portion low in refractive index in the central area
of the multimode optical fiber 11', and abnormal dispersion of
modes occurs. If the angle .psi. is more than 25 degrees, the
incident angle is too large, and the light once correctly entering
the core portion may escape to the clad portion, and the light may
not be propagated correctly. A more desired effect is obtained by
adjusting the angle .psi. in a range of 5 to 15 degrees.
[0078] More preferably, as shown in FIG. 2, the incident beam 18
from the optical fiber 11 should advance in a plane formed between
Y'-axis and Z'-axis.
[0079] Thus, together with by setting the core central position 11b
of the single mode optical fiber 11 eccentric relatively by
.delta., and inclining the incident beam 18 from the single mode
optical fiber 11 by angle .psi., as shown in FIG. 3, the light
entering the core 11a' of the multimode optical fiber of graded
index type propagates spirally. As a result, the optical signal is
transmitted while evading the dimple-like portion low in refractive
index in the central area of the multimode optical fiber 11'.
Therefore, occurrence of abnormal dispersion of modes is suppressed
more effectively, and a high speed signal can be transmitted in a
longer distance (for example, longer than 550 m).
[0080] In the optical connector of the embodiment, a pair of
ferrules are bonded by a bent sleeve, and the axial hole of at
least one ferrule is set eccentric, and the optical fibers are
connected to each other. In this manner, the optical fibers can be
easily connected without requiring any particular processing. In
the explanation made so far, the single mode optical fiber 11 is
fixed in the center of the ferrule 1, and the multimode optical
fiber 11' is fixed away from the center of the ferrule 1'. However,
the configuration is not specified as far as the core central
positions 11b, 11b' of the single mode optical fiber 11 and the
multimode optical fiber 11' are deviated from each other.
[0081] The material of ferrules 1, 1' includes zirconia, alumina,
other ceramics, glass, stainless steel, other metals, LCP, PPS,
PES, PEI, other plastics, or mixed materials of them.
[0082] The structure of sleeve 14 may be split sleeve having a slit
in the longitudinal direction, or precision sleeve without slit,
etc. The material of sleeve 14 may be zirconia, phosphor bronze,
plastics, etc. Processing method of sleeve 14 is material cutting
or injection molding. In particular, injection molding of plastics
is preferred because any complicated shape can be manufactured at a
relatively low cost.
Embodiment 2
[0083] In this embodiment, the invention is applied in a mode
conditioner. The mode conditioner of the embodiment has a junction
of fusing and bonding one end of the single mode optical fiber and
one end of the multimode optical fiber, and a patching cord having
an optical connector is provided at other end of the both. The
central positions of cores at the junction are set eccentric
mutually, and the central axes of the cores are inclined, and fused
and adhered.
[0084] FIG. 4A is a block diagram of mode conditioner 40 of the
embodiment. The mode conditioner 40 of the embodiment is a mode
conditioner 40 of patching cord type for bonding to an integral
type optical transceiver 32. The patching cord is a fiber code that
has optical connecters on both ends. In the embodiment shown in
FIG. 4A, a short distance from a transmitting device 31 such as LAN
device to an optical fiber end panel (patch panel) 34 is connected
by a patching code. A dual mode conditioner 40 shown in FIG. 4A has
a structure of bonding twin optical connectors 44 and 45 by means
of two patching cords. In the midst of patching cords, a junction
46 for optical cords is provided. The optical connector 44 is
detachably connected to the optical transceiver 32 having laser
light source. The optical connector 45 is detachably connected to
the patch panel 34. Optical fiber cord for transmission 35 is
detachably connected to the patch panel 34.
[0085] The patching cord connected to the optical receiver side of
the optical transceiver 32 is composed of the multimode optical
fiber 43. On the other hand, the patching cord connected to the
optical transmitter side of the optical transceiver 32 is composed
by connecting the single mode optical fiber 41 and the multimode
optical fiber 42. The single mode optical fiber 41 is disposed at
the optical transceiver 32 side. The mode conditioner of the
present invention may be equipped only with an optical
transmitter.
[0086] The single mode optical fiber 41 and the multimode optical
fiber 42 are connected same as in embodiment 1. That is, at the
junction 46, the centers of cores are mutually eccentric, and
central axes of cores are mutually inclined, and fused and adhered.
Therefore, the light entering the single mode optical fiber 41 from
the optical transceiver 32 is deviated from the core center of the
multimode optical fiber 42 when the multimode optical fiber 42, and
enters obliquely to the optical axis of the multimode optical
fiber. That is, the light enters in the higher mode alone. Hence
the light rarely enters the dimple-like portion low in refractive
index in the core center, and abnormal dispersion of modes is
suppressed. Therefore signals can be transmitted efficiently by
preventing mutual signal interference.
[0087] In this embodiment, too, the eccentricity .delta. of the
core central position of the single mode optical fiber 41 to the
core center of the multimode optical fiber 42 is preferred to be 10
to 25 .mu.m, or more preferably 15 to 20 .mu.m. The angle .psi. of
incident beam from the single mode optical fiber 41 to the axial
center of the multimode optical fiber 42 is preferred to be 3 to 25
degrees, or more preferably 5 to 15 degrees. Further, as shown in
FIG. 2, the incident beam from the single mode optical fiber 41
preferably advances in a plane formed between Y'-axis and
Z'-axis.
[0088] FIG. 4B is a partially magnified sectional view of
connecting portion 46 provided in the midst of patching cord. The
multimode optical fiber 43 is patching cord at the light reception
side directly penetrates through the connecting portion 46. On the
other hand, the single mode optical fiber 41 and the multimode
optical fiber 42 for composing the patching code at the light
transmission side are mutually fused and bonded in the junction 46.
The surrounding of fusing and bonded area of the single mode
optical fiber 41 and the multimode optical fiber 42 is fixed by a
reinforcing member 45b. The entire connecting portion is covered
with connection sleeve 46a, and the inside of the connection sleeve
46a is filled with filler 46c.
[0089] The connection sleeve 46a is composed of, for example,
alumina, zirconia, other ceramics, stainless steel, other metals,
crystallized glass or other glass materials. Any material may be
used as far as rigidity is high. The shape of connection sleeve 46a
is not particularly specified. For example, the connection sleeve
46a may be processed in a cylindrical pipe easily, and the cost may
be reduced.
[0090] The reinforcing member 46b protects the fusing and bonding
portion of optical fibers, and is preferred to be somewhat high in
rigidity. However, the junction may be broken if attempted to fix
the fusing and bonding portion mechanically by the reinforcing
member 46b of high rigidity. It is hence preferred to form the
reinforcing member 46b by coating with covering material of optical
fiber, such as nylon 66, polyester elastomer or other resin. In
this forming method of reinforcing member 46b, a commercial
recoater for fused ceramics may be used. Hence, the reinforcing
member 46b of high reliability can be formed easily and at low
cost.
[0091] The filler 46c is used for fixing the inner circumference of
connection sleeve 46a and outer circumference of reinforcing member
46b. The material of filler 46c includes epoxy adhesive,
ultraviolet curing adhesive, photo effect adhesive, and other
adhesives. It is particularly preferred to use silicon adhesive for
the filler 46c.
[0092] The mode conditioner 40 may be used together with any
transmission fiber, such as the multimode optical fiber without
abnormal refractive index distribution shown in FIG. 19B. Mode
conditioner is not required at the reception side. Therefore, the
reception side patching cord may be composed of one multimode
optical fiber 43 such as ordinary optical jumper, and optical
connectors 44, 45 can be connected at both ends. As reception side
patching cord, for example, the multimode optical fiber 43 may be
fused without deviating the cores at the junction 46.
Embodiment 3
[0093] In this embodiment, the invention is applied in an optical
transmitter with a mode conditioner. The optical transmitter of the
embodiment has a split sleeve disposed on the optical axis of laser
diode, and a fiber stab having a single mode optical fiber is
inserted at the light incident side of the split sleeve, while a
plug ferrule having an optical fiber is inserted at the light exit
side. The fiber stab and plug ferrule can abut against each other
at opposite ends. The single mode optical fiber in the fiber stab
and arbitrary optical fiber in the plug ferrule are connected to
each other, with the central positions of the cores being deviated
relatively, and the mutual optical axes being inclined.
[0094] FIG. 5A is a sectional view of the optical transmitter of
the invention. The optical transmitter in FIG. 5A has a laser diode
51, and it is designed to realize optical transmission by
connecting to a plug ferrule 55 having a multimode optical fiber
56. The optical transmitter 50 comprises a semiconductor laser unit
62 accommodating a semiconductor laser 51, and an optical
receptacle 64 for inserting a plug ferrule 55. The optical
receptacle 64 includes a metal holder 63, a fiber stab 52 having a
single mode optical fiber 53 in a through-hole, and a split sleeve
54. The fiber stab 52 has its rear end fitting into the
through-hole of the metal holder 63, and the light emitted from the
semiconductor laser 51 enters here. The split sleeve 54 for
inserting the plug ferrule 55 is fitted to the leading end of the
fiber stab 52. The both ends of the fiber stab 52 is polished. The
fiber stab 52 is preferably composed of zirconia ceramics. The
split sleeve 54 is also made of zirconia ceramics, preferably.
[0095] The split sleeve 54 is disposed on the optical axis 61 of a
laser diode 1. The fiber stab 52 inserted at the incident side of
the split sleeve 54 abuts against the plug ferrule 55 inserted from
the exit side of the split sleeve 54. The single mode optical fiber
53 in the fiber stab 52 and the multimode optical fiber 56 in the
plug ferrule 55 are optically connected, and the light emitted from
the laser diode 51 enters the multimode optical fiber 56. That is,
the light from the laser diode 51 passes through the fiber stab 52
made of zirconia ceramics before entering the multimode optical
fiber 56. At this time, the core center of the single mode optical
fiber 53 and the core center of the multimode optical fiber 56 are
mutually deviated. The optical fibers are connected so that the
optical axis of the single mode optical fiber 53 may be inclined to
the optical axis of the multimode optical fiber 56.
[0096] FIG. 5B is a partially magnified view showing the junction
of optical fibers in the optical transmitter shown in FIG. 5A. As
shown in FIG. 5B, the through-hole 52a of fiber stab 52 spreads
near the interface with the plug ferrule 55. In the expanded
portion 52a of through-hole, the single mode optical fiber 53 is
bent and the adhesive 59 is cured. When the plug ferrule 55 abuts
against such fiber stab 52, the center of core 53a of the single
mode optical fiber and the center of core 56a of the multimode
optical fiber are mutually deviated. At the same time, the optical
axis of the single mode optical fiber 53 is inclined to the optical
axis of the multimode optical fiber 56. For example, the leading
end of the single mode optical fiber 53 is bent so that the core
center of the single mode optical fiber 53 may be deviated by about
20 .mu.m from the core center of the multimode optical fiber 56,
and that the light emitted from the single mode optical fiber 53
may enter the multimode optical fiber 56 by inclining about 10
degrees to its optical axis. As a result, the transmission light
passing through the core of the single mode optical fiber 53 enters
the multimode optical fiber 56 by deviating about 20 .mu.m from its
optical axis and inclining by about 10 degrees. Therefore, the
light does not get into the portion of low refractive index in the
central area of the multimode optical fiber 56, or if entering, it
is a very small amount, and deterioration of transmission
characteristic by band deterioration due to DMD can be avoided.
That is, as shown in FIG. 3, optical signal propagates spirally in
the core of the multimode optical fiber of graded index type, and
light is transmitted by avoiding the dimple-like portion low in
refractive index in the central area of the multimode optical
fiber. Therefore, abnormal dispersion of mode is suppressed, and
signal interference is prevented. Hence, optical transmission at
high speed and in long distance (for example, 550 m or more) is
realized.
[0097] A high speed optical data transmission system using the
multimode optical fiber 56 can be realized at low cost. This mode
conditioner may be also used in the transmission fiber using the
multimode optical fiber not having abnormal refraction index
distribution as shown in FIG. 19B. In the case of optical
transmitter with the mode conditioner as in this embodiment, as
compared with the mode conditioner of patching cord type in
embodiment 2, the following advantages are obtained. That is, in
the optical transmitter with the mode conditioner of this
embodiment, it does not require difficult operation of fusing and
connecting by deviating the core centers of the single mode optical
fiber and the multimode optical fiber. After fusing the strands of
optical fiber, it does not require the operation of connecting
cabler or reinforcing member or covering the connection parts.
Further, it is not required to manage the special patching cords by
distinguishing from ordinary patching cords, and the system
construction is much easier.
[0098] In this embodiment, too, the eccentricity .delta. of the
core central position of the single mode optical fiber 53 to the
core center of the multimode optical fiber 56 is 5 to 30 .mu.m,
more preferably 10 to 25 .mu.m, and most preferably 15 to 20 .mu.m.
The angle .psi. of incident beam from the single mode optical fiber
53 to the axial center of the multimode optical fiber 56 is 3 to 25
degrees, or preferably 5 to 15 degrees. Further, as shown in FIG.
2, the incident beam from the single mode optical fiber preferably
advances in a plane formed between Y'-axis and Z'-axis.
[0099] The material of fiber stab 52 and plug ferrule 55 includes
zirconia, alumina, other ceramics, glass, stainless steel, other
metals, LCP, PPS, PES, PEI, other plastics, or mixed materials of
them. The structure of the, split sleeve 54 may be a sleeve having
a slit in the longitudinal direction, or a precision sleeve without
a slit. The material of the split sleeve 54 may be zirconia,
phosphor bronze, plastics, etc. Processing method of the split
sleeve 54 is material cutting or injection molding used in
plastics. In particular, injection molding is preferred because any
complicated shape can be manufactured at a relatively low cost.
[0100] Variations of connection method of the single mode optical
fiber 53 and the multimode optical fiber 56 are explained.
[0101] FIG. 6 shows an example of bending of only core 53a of the
single mode optical fiber 53 near the end 57. Such single mode
optical fiber 53 can be manufactured, for example, by manufacturing
an optical fiber preliminarily in a state of large outer
circumference of clad 53b, and polishing or etching the outer
circumference of the clad 53b while bending the leading end of the
optical fiber. FIG. 7 shows an example of the single mode optical
fiber 53, of which core 53a is entirely formed obliquely to the
outer circumference of the clad 53b. Such single mode optical fiber
53 can be manufactured by polishing or etching after manufacturing
an optical fiber of large outer circumference of the clad 53b.
[0102] FIG. 8 shows bending of the inner hole 52a near end 57 of
the fiber stab 52. Such bent inner hole 52a is formed as follows.
First, using YAG laser processing machine, an inner hole is
engraved along the axial center from the end of incident side of
the fiber stab 52, and stopped before penetrating to other end.
Starting from a position deviated from the axial center, from the
exit side end of the fiber stab 52, a hole is opened obliquely
toward the axial center, until communicating with the formed inner
hole.
[0103] FIG. 9 shows the core center of the single mode optical
fiber 53 and the core center of the multimode optical fiber 56 are
deviated by inclining the fiber stab 52 itself to the plug ferrule
55. Alternatively, the plug ferrule may be inclined to the fiber
stab 52.
[0104] FIG. 10 shows the fiber stab 52 is cut in two sections. In
the incident side fiber stab 52', an inner hole is formed along the
axial center, and in the exit side fiber stab 52'', an inner hole
is formed obliquely to the axial center. In the space between the
incident side fiber stab 52' and the exit side fiber stab 52'', the
single mode optical fiber 53 is straightened. If, however, the
optical fiber 53 may be broken due to thermal expansion of members,
the optical fiber may be deflected in this portion.
Embodiment 4
[0105] In this embodiment, in the optical transmitter with the mode
conditioner explained in embodiment 3, an example of providing the
single mode optical fiber with means for suppressing a clad mode
light is explained.
[0106] By using eliminating means of the clad mode light, the
coupled power ratio (CPR) can be enhanced. The CPR is a difference
in optical output between when the plug ferrule 55 having the
multimode optical fiber is inserted in the optical transmitter
shown in FIG. 5A, and when the plug ferrule 55 having the single
mode optical fiber is inserted in the same optical transmitter. The
CPR is a reference value showing whether the light is entering by
evading sufficiently the center of the multimode optical fiber 56
or not.
[0107] By using the optical transmitter disclosed in Japanese
Patent Application Laid-Open No. 2000-147334, in order to satisfy
the CPR standard of gigabit Ethernet (registered trademark) of
IEEE, the length of eccentric single mode optical fiber (=length of
fiber stab) must be sufficiently long (for example, 2 cm or more),
as known from measurements. If the length of fiber stab is short,
the light entering the clad of the eccentric single mode optical
fiber is not attenuated sufficiently, but is coupled to the
multimode optical fiber, and is coupled near the center of the
multimode optical fiber. However, the substrate length of optical
transceiver for gigabit Ethernet (registered trademark) is only
about 2 to 3 cm, and it is difficult to mount an optical
transmitter of long fiber stab on this substrate.
[0108] In the optical transmitter of embodiment 3, by providing the
clad 53b of the single mode optical fiber 53 with eliminating means
of the clad mode light, the optical signal entering the clad 53b
can be attenuated, and entry into the multimode optical fiber 56
can be prevented. Therefore, the CPR can be improved without
extending the length of the fiber stab.
[0109] The clad mode light eliminating means may be realized by
various structures as explained below.
[0110] In the single mode optical fiber 53 shown in FIG. 11, the
outside clad 53d is larger in refractive index than the inside clad
53c. At least in part of high refractive index clad portion 53d, a
light attenuating dopant region containing dopant for attenuating
optical signal is formed.
[0111] As shown in FIG. 11, the single mode optical fiber 53 is
composed of a core 53a for propagating light, an inside clad 53c,
and an outside clad 53d as absorbing portion of clad mode.
Specifically, for example, it may be formed as follows. In the core
53a, for example, GeO2 is doped in quartz glass in order to add a
refractive index difference from the clad 53b. The core diameter of
the single mode optical fiber 53 is 8 .mu.m, and the relative
refractive index difference between the core 53a and the inside
clad 53c is, for example, 0.3%. At this time, the breakage
wavelength is about 1.1 .mu.m. Further, in order to attenuate the
intensity of optical signal, Co (cobalt) is doped in the core 53a.
The content of Co is adjusted so as to obtain light attenuation
amount of 30 dB at optical fiber length of 22.4 mm and wavelength
of 1.31 .mu.m. The inside clad 53c is made of pure quartz glass,
and its outside diameter is, for example, about 40 .mu.m. In the
outside clad 53d, same as in the core 53a, GeO2 is doped, and the
GeO2 concentration is gradually increased in radial direction from
inside, and the concentration near the outer circumference is
adjusted to be nearly constant at the relative refractive index
difference of 0.15%. The outside diameter is 125 .mu.m, same as in
standard optical fiber. The relative refractive index difference
from the core of outside clad 53d is about half of the relative
refractive index difference from the core of the inside clad 53c,
but since it is sufficiently remote from the core 53a, there is no
effect on the optical signal propagating through the core 53a.
[0112] The single mode optical fiber 53 in FIG. 12 has an
intermediate clad 53e having same refractive index as the core 53a
as eliminating means of the clad mode light, between the outside
clad 53d and the inside clad 53c of the single mode optical fiber
53. The outside clad 53d and the inside clad 53c may have a
refractive index of general clad.
[0113] Specifically, the structure may be composed as follows. In
the core 53a, GeO2 is doped in quartz glass in order to add
refractive index difference from the clad 53b. The relative
refractive index difference of the core 53a and the inside clad 53c
is 0.3%, and the diameter of the core 53a is 8 .mu.m. The breakage
wavelength is about 1.1 .mu.m. The inside clad 53c contains V
(vanadium) in order to attenuate the intensity of optical signal.
The content of V is adjusted so as to obtain light attenuation
amount of 20 dB at optical fiber length of 22.4 mm and wavelength
of 1.31 .mu.m. The inside clad 53c and the outside clad 53d are
made of pure quartz glass, the outside diameter of the inside clad
53c is about 75 .mu.m, and the outside diameter of the outside clad
53d is 125 .mu.m, same as in standard optical fiber. In the
intermediate clad 53e acting as means for the eliminating clad mode
light, GeO2 is doped same as in the core 53a, and the relative
refractive index difference from the inside clad layer 53c or the
outside clad layer 53d is set almost constant at 0.3%. The outside
diameter of the intermediate clad 3e is 100 .mu.m. As a result, the
clad mode light goes out of the intermediate clad 53e.
[0114] The single mode optical fiber 53 in FIG. 13 has an
intermediate clad 53f having smaller refractive index than in the
outside clad 53d or the inside clad 53c, provided between the
outside clad 53d or the inside clad 53c. This intermediate clad
layer 53f is eliminating means of the clad mode light.
[0115] Specifically, for example, the structure is as follows. In
the core 53a, GeO2 is doped as dopant in quartz glass in order to
add refractive index difference from the inside clad 53c. The core
diameter is 8 .mu.m, and the relative refractive index difference
of the core 53a and the inside clad 53c is 0.3%. At this time, the
breakage wavelength is about 1.1 .mu.m. The inside clad 53c is a
clad mode capturing part, and is doped almost uniformly with Co as
dopant, and its outside diameter is about 40 .mu.m. The outside
clad 53d is made of pure quartz glass, and its outside diameter is
125 .mu.m, same as in standard optical fiber. The low refractive
index portion 53f is a layer uniformly doped with F (fluorine) in a
width of 15 .mu.m, in the outside of the inside clad 53c, and
inside of the outside clad 53d. The concentration of F is adjusted
so that the relative refractive index may be almost constant at
-0.15%. Since the low refractive index portion 53f is away from the
core 53a, there is almost no effect on the optical signal
propagating in the core 53a. The optical signal advancing in the
inside clad 53c is entrapped in the inside clad 53c.
[0116] The single mode optical fiber 53 in FIG. 14 has a light
attenuation dopant region 53g in the single mode optical fiber in
FIG. 13. The light attenuation dopant region 53g is, for example, a
region doped with Co (cobalt), and it is a region contacting with
the core 53a of the inside clad 53c. Of the region of the inside
clad 53c, between the region doping Co and the region not doping
Co, there is almost no difference in refractive index distribution.
As shown in FIG. 14, in the refractive index distribution, the
portion of the core 53a has the largest refractive index. The
refractive index of the intermediate clad layer 53f (low refractive
index region) is smaller than that of the inside clad 53c.
Therefore, the light signal advancing in the inside clad 53c is
entrapped in the inside clad 53c including the light attenuation
dopant region 53g, and is also attenuated in the light attenuation
dopant region 53g. The doping region of dopant is smaller, and the
manufacturing cost is lowered.
[0117] When the single mode optical fiber having such clad mode
light eliminating means is used as the fiber stab, the single mode
optical fiber 53 in the fiber stab 52 and the multimode optical
fiber 56 in the plug ferrule 55 can be connected so that the mutual
axes may be parallel to each other. For example, as shown in FIG.
15 or FIG. 16, the center of core 53a of the single mode optical
fiber in the fiber stab 52 is set at a position deviated from the
center of core 56a of the multimode optical fiber 56 by 5 to 30
.mu.m. However, the single mode optical fiber 53 in the fiber stab
52 and the multimode optical fiber 56 in the plug ferrule 55 are
mutually parallel in the optical axes. As shown in FIG. 15, the
through-hole of the fiber stab 52 may be set eccentric, or as shown
in FIG. 16, the single mode optical fiber 53 with an eccentric core
may be used. Since the core center of the single mode optical fiber
53 in the fiber stab 52 is deviated from the core center of the
multimode optical fiber 56 in the plug ferrule 55, the transmission
light passing through the core of the single mode optical fiber 53
in the fiber stab 52 enters the multimode optical fiber 56 at a
position off its center. Accordingly, the light does not enter the
portion of low refractive index in the central area of the
multimode optical fiber 56, and if entering, the amount is very
small, and hence transmission characteristic deterioration due to
DMD can be suppressed to a certain extent. Moreover, since the clad
53b of the single mode optical fiber 53 has eliminating means of
the clad mode light, the optical signal entering the clad 53b is
attenuated, hardly entering the multimode optical fiber 56, so that
the CPR may be improved.
EXAMPLES
Example 1
[0118] The following experiment was conducted by using the optical
connector shown in FIG. 1.
[0119] A ferrule of zirconia ceramics was manufactured in outside
diameter D of 2.5 mm, length L of 10.5 mm, and through-hole
diameter d of 0.126 mm. In an incident side ferrule 1, a single
mode optical fiber 11 was adhered and fixed, and in an exit side
ferrule 1', a multimode optical fiber 11' was adhered and fixed. By
deviating the central positions 11b, 11b' of optical fibers
mutually by .delta., and optical fibers were connected end to end,
in a state of optical axes of optical fibers being inclined by
angle .psi.. Herein, the eccentric amount .delta. was 5, 9, 10, 15,
20, 25, and 30 .mu.m in examples, and 0 .mu.m in comparative
example. The inclination angle .psi. was 2, 3, 10, 20, 25, 26
degrees in examples, and 0 degree in comparative example. In
various combinations, the transmission distance was measured while
extending the optical fiber length at 50 m increments. The
multimode optical fiber was 1960A (Lucent Technology), which has
the core diameter was 62.5 .mu.m, and the clad diameter was 125
.mu.m.
[0120] As shown in FIG. 17, from an E/O converter 72 of a
transceiver 71, an optical signal was emitted at wavelength of 1310
nm and transmission speed of 10 Gbit/sec, and was connected to the
single mode optical fiber 11, and was further connected to the
multimode optical fiber 11' to be measured, by way of the optical
connector 10 of the invention. The light transmitted through the
multimode optical fiber 11' was received in an O/E converter 75 of
a receiver 74 by way of a general optical connector 73, and was
converted into an electrical signal, and it was checked whether the
signal was transmitted correctly or not. Maximum length of the
correct signal transmission is shown in Table 1. TABLE-US-00001
TABLE 1 ##STR1## Note *Comparative example Dotted line frame shows
examples in preferred range of the invention. Double lie frame
shows examples in particularly preferred range of the
invention.
[0121] At eccentricity amount .delta. of 0 .mu.m (comparative
example), transmission distance was 0 m regardless of angle .psi..
At angle .psi. of 0 degree (comparative example), transmission
distance did not reach up to 100 m. In the examples of the
invention, by contrast, transmission distance of over 100 m was
recorded. In particular, when the eccentricity amount .delta. was
in a range of 10 to 25 .mu.m, and the angle .psi. was in a range of
3 to 25 degrees, transmission distance was longer than 550 m, and
favorable values were obtained. In particular, the eccentricity
amount .delta. was in a range of 15 to 20 .mu.m, and the angle
.psi. was in a range of 5 to 15 degrees, transmission distance was
750 m, and long transmission distance was obtained.
[0122] It is hence known that the signals are transmitted
efficiently by deviating the core centers of optical fibers
relatively, and inclining the light beam entering one optical fiber
from other optical fiber.
Example 2
[0123] The mode conditioner 40 shown in FIGS. 4A and 4B was
manufactured as follows. Optical connectors 41, 45 were SC type
connectors. Connection sleeve 46a at junction 46 was a stainless
steel cylindrical piece. Reinforcing member 46b was made of a
coated polyester elastomer. Filler 46c was a silicon resin.
[0124] The single mode optical fiber 41 and the multimode optical
fiber 42 were adhered and fixed. At this time, the core
eccentricity amount .delta. and inclination angle .psi. of the
single mode optical fiber 41 and the multimode optical fiber were
same as in example 1. The single mode optical fiber 41 and the
multimode optical fiber 42 were same as in example 1.
[0125] A shown in FIG. 18, an optical signal was emitted from an
optical transceiver 82 of LAN device 81 at wavelength of 1310 nm
and transmission speed of 10 Gbit/sec, and was connected to the
single mode optical fiber 41, and was further connected to the
multimode optical fiber 42 to be measured, by way of the mode
conditioner 40 of the invention. The light transmitted through the
multimode optical fiber 42 was received in an O/E converter 85 of a
receiver 84 by way of the optical connectors 45, 83, and was
converted into an electrical signal, and it was checked if a
correct signal was transmitted or not.
[0126] The maximum length of the transmission of correct signal was
same as in example 1.
Example 3
[0127] The optical transmitter as shown in FIG. 5A was manufactured
as follows.
[0128] The core center of the single mode optical fiber 53 of the
fiber stab 52 was deviated from the core center of the multimode
optical fiber 56 in the plug ferrule 55 in a direction of 20 .mu.m.
The direction of the light beam entering from the single mode
optical fiber 53 was inclined by 10 degrees from the optical axis
of the multimode optical fiber 55. Both ends of the fiber stab 52
made of zirconia ceramics were polished, and abutted against the
plug ferrule 55 by means of split sleeve 4 similarly made of
zirconia ceramics.
[0129] As other example, an optical transmitter was manufactured by
forming clad mode light eliminating means as shown in FIG. 11 in
the single mode optical fiber 53. That is, the outside clad 53d of
the single mode optical fiber 53 had a larger refractive index than
the inside clad 53c, and a dopant for attenuating the optical
signal was contained at least in part of the outside clad 53d of
high refractive index. In the core 53a, GeO2 was doped in quartz
glass for adding refractive index difference from the clad 53b. The
diameter of core 53a was 8 .mu.m, and the relative refractive index
difference of the core 53a and the clad 53b was 0.3%. The breakage
wavelength was about 1.1 .mu.m. Co (cobalt) was doped in the clad
53d for further attenuating the intensity of the optical
signal.
[0130] As comparative example, as shown in FIG. 15, an optical
transmitter was manufactured by connecting the single mode optical
fiber 53 and the multimode optical fiber 56 by deviating the core
centers mutually by 20 .mu.m and setting the optical axes parallel
to each other.
[0131] Anyway, the single mode optical fiber 53 was made of
commercial material of SMF-20T of Corning, and the multimode
optical fiber 56 was 1960A (Lucent Technology) that has the core
diameter of 62.5 .mu.m and the clad diameter of 125 .mu.m.
[0132] An optical signal was emitted from a laser diode 51 at
wavelength of 1310 nm and transmission speed of 10 Gbit/sec, and
the light transmitted through the multimode optical fiber 56 was
received, and was converted into an electrical signal, and
transmission distance of correct signal was measured. Results are
shown in Table 2. TABLE-US-00002 TABLE 2 Inclination of optical
Eliminating Transmission Eccentricity axis means distance .mu.m)
Example 3(1) 20 .mu.m 10 degrees No 305 Example 3(2) 20 .mu.m 10
degrees Yes 510 Comparative 20 .mu.m No No 25 example
[0133] In comparative example, transmission distance was only 25 m,
and in the example inclining the optical axis, the transmission
distance was extended to 305 m. In the example using the clad mode
light eliminating means, the transmission distance was 510 m, and
the transmission distance had been improved substantially. Thus,
the invention presents the optical transmitter curtailed in the DMD
and improved in the CPR.
Comparative Example
[0134] As reference example, a single mode optical fiber having the
clad mode light eliminating means shown in FIGS. 11 and 13 was
prepared, and a transmitter with the mode conditioner was
fabricated by using a conventional single mode optical fiber of
comparative example.
[0135] The single mode optical fiber having the clad mode light
eliminating means shown in FIG. 11 was manufactured as follows. The
optical fiber consisted of the core 53a, the inside clad 53c, and
the outside clad 53d of a clad mode absorbing portion, and in the
core 53a, GeO2 was doped in quartz glass for adding refractive
index difference from the 53b. The core diameter was 8 .mu.m, and
the relative refractive index difference of the core 53a and the
clad 53b was 0.3%. The breakage wavelength was about 1.1 .mu.m. Co
(cobalt) was doped in the core 53a for attenuating the intensity of
the optical signal.
[0136] The single mode optical fiber having the clad mode light
eliminating means shown in FIG. 13 was manufactured as follows.
Between the outside clad 53d and the inside clad 53c of the single
mode optical fiber 3, an intermediate clad 53f having smaller
refractive index than in the outside clad 53d and the inside clad
53c was formed. In the core 53a, for adding the refractive index
difference from the inside clad 53c, GeO2 was doped as dopant in
quartz glass. The core diameter was 8 .mu.m, and the relative
refractive index difference of the core 53a and the inside clad 53c
was 0.3%. The breakage wavelength was about 1.1 .mu.m. The inside
clad 53c was the clad mode capturing portion, and Co was doped
uniformly as dopant, and the outside diameter is set at 40 .mu.m.
The outside clad 53d was made of pure quartz glass, and its outside
diameter was 125 .mu.m, same as in standard optical fiber. The
intermediate clad (low refractive index portion) 53f was formed, at
the outer side of the inside clad 53c and the inner side of the
outside clad 53d, in a width of 15 .mu.m. The intermediate clad 53f
was a layer in which F (fluorine) was doped uniformly, and its
concentration was adjusted so that the relative refractive index
might be almost constant at -0.15%.
[0137] The single mode optical fiber in comparative example was
made of a commercial material SMF-20T of Corning.
[0138] The optical transmitter was composed as shown in FIG. 5A.
The core centers of the single mode optical fiber 53 and the
multimode optical fiber 56 were mutually deviated by 20 .mu.m.
Their optical axes were parallel to each other. In the multimode
optical fiber 56, the core diameter was 62.5 .mu.m, and the clad
diameter was 125 .mu.m.
[0139] In the measuring method, an optical signal was emitted from
a laser diode 1 at wavelength of 1310 nm and transmission speed of
1 Gbit/sec, and the light transmitted through the multimode optical
fiber 56 by way of the single mode optical fiber 53 was received,
and was converted into an electrical signal, and transmission
distance of correct signal was measured. Results are shown in Table
3. TABLE-US-00003 TABLE 3 Inside Intermediate Transmission clad
clad Outside clad distance .mu.m) Example of Yes No High 310
refractive index clad portion + light attenuating dopant Example of
Yes Low Yes 330 refractive index portion Comparative Common 25
example
[0140] In comparative example, transmission distance was only 25 m,
and in the example forming the clad mode light eliminating means
shown in FIG. 11, the transmission distance was 310 m. In the
example forming the clad mode light eliminating means shown in FIG.
13, the transmission distance was 330 m, and the transmission
distance had been improved substantially.
* * * * *