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High density multi-fiber connector for optical interconnection

Authors:
  • Independent Researcher

Abstract and Figures

As the performance limits of electrical transmission become apparent In such equipment as servers and routers, optical interconnection technology is drawing attention. Furukawa Electric has been developing, In anticipation of application to optical interconnection, optical high-density multi-fiber connectors. In this paper, compact multifiber ferrule μ-Joint is presented, along with MU-type plug and backplane connector, both based on μ-Jolnt. The μ-Joint has a cross section about one quarter that of conventional MT ferrule, so that it allows for high-density mounting with a low insertion loss of 0.5 dB or lower. Tests In conformity to Telcordia GR-1435-CORE have been carried out to confirm that the ferrule has high long-term reliability.
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1. INTRODUCTION
Data traffic on the Internet continues to increase due to the
growth of moving picture delivery and the like, resulting in a
requirement for high-speed, large-capacity signal transmis-
sion functionality for servers and routers. Thus, the issue of
inadequate transmission performance of electrical wiring is
gradually emerging due to the increased number in signal
transmission lines. Accordingly, optical interconnection
technology is recently drawing attention as a promising
means to solve this problem. Moreover, in terms of space
reduction, optical interconnection is expected to enhance
heat dissipation efficiency in high-end systems such as
servers and super computers, so that application of optical
interconnection technology to signal transmission between
boards and racks is becoming a real possibility.
We have been developing the optical interconnection
technology assumed to be applied to equipment wiring,
in which optical fibers, optical connectors, and high-
speed optical modules are downsized than conventional
counterparts to constitute the product family of
OptoUnity 1).
In this paper, small-sized multi-fiber optical connectors
capable of high-density mounting will be reported for their
structures and evaluation results, including μ-Joint con-
nector plug and adapter, which have, using ultra-compact
multi-fiber ferrule μ-Joint, the same outer dimensions as
for the MU connector 2).
2. DEVELOPMENT CONCEPT
Figure 1 shows a schematic illustration of application of
the connectors developed here. Development was
advanced based on the concept mentioned below,
assuming that the connectors are mainly used on board
ends for signal transmission between boards and racks.
1) Should be smaller than the conventional MT ferrule and
MPO connector, enabling high-density mounting.
2) Should be compatible with ThreadWave 1), the bend-
insensitive fiber for optical interconnection of Furukawa
Electric.
3) Should allow for low insertion-loss connection.
4) Should be provided with high long-term reliability.
With respect to insertion loss, the target was set at 0.5 dB
or lower even in case single-mode (SM) fiber is used, in
consideration of total loss budget for ultra-fast transmission
in the future. In terms of long-term reliability, the develop-
ment target for loss variation after the tests in conformity to
Telcordia GR-1435-CORE was set at 0.3 dB or lower.
3. ULTRA-COMPACT MULTI-FIBER
FERRULE μ-JOINT
An ultra-compact multi-fiber ferrule μ-Joint capable of
high-density mounting has been developed. Figure 2
compares μ-Joint with MT ferrule conventionally used.
High-Density Multi-Fiber Connectors for Optical Interconnection
by Naoya Nishimura *, Katsuki Suematsu *, Masao Shinoda * and Masato Shiino *
As the performance limits of electrical transmission become apparent in such
equipment as servers and routers, optical interconnection technology is
drawing attention. Furukawa Electric has been developing, in anticipation of application to
optical interconnection, optical high-density multi-fiber connectors. In this paper, compact multi-
fiber ferrule μ-Joint is presented, along with MU-type plug and backplane connector, both based
on μ-Joint. The μ-Joint has a cross section about one quarter that of conventional MT ferrule, so
that it allows for high-density mounting with a low insertion loss of 0.5 dB or lower. Tests in
conformity to Telcordia GR-1435-CORE have been carried out to confirm that the ferrule has high
long-term reliability.
ABSTRACT
* FITEL-Photonics Lab., R&D Div.
ThreadWave ribbon
(co ntaining 80-µm diameter fiber)
Applied
place
Optical module
Rack Backplane
Figure 1 Schematic illustration of application of the developed
connectors.
Furukawa Review, No. 34 2008 13
The dimensions of μ-Joint is about half that of MT ferrule,
and about 25% in cross section. It uses 0.4-mm diameter
stainless steel guide pins, and is adapted to ThreadWave
optical fiber having a cladding diameter of 80 μm, and
core diameters of about 50 μm and about 5 μm for multi-
mode (MM) fiber and SM fiber, respectively. ThreadWave
MM fiber has a relative reflective index difference
Δn
of
about 2%, so that it is less susceptible to bending loss
increase, permitting an allowable bending radius
R
of
5 mm. Moreover, whereas a fiber ribbon generally has a
fiber pitch of 250 μm, that of ThreadWave fiber ribbon is
125 μm, making it suitable for compact optical wiring on
printed circuit boards, etc.
Improving the accuracy of ferrule is essential to realize
low insertion loss. In order to achieve the target insertion
loss of 0.5 dB, the target fiber-hole position error was
designed to be not more than 0.5 μm. Figure 3 shows the
measurement results of the misalignment of fabricated
μ-Joint ferrules, in which the fiber-hole position error of
0.5 μm or lower is achieved by improving the dimensional
accuracy of the mold.
4. MU-TYPE HOUSING
Whereas MPO connector is commonly used for multi-fiber
optical connection, MU connector housing is adopted
here aimed at higher mounting density. The MU connec-
tor is standardized, and is practically used in transmission
equipment installed in telephone stations.
Figure 4 shows μ-Joint-MU connector plugs and a duplex
adapter, where the μ-Joint ferrule is applied to the MU
housing. The plugs come in two types --male with guide
pins, and female without guide pins-- and they are used in
opposition to each other. A push-pull coupling mechanism
is provided for ease of connection and disconnection. The
adapter has a pitch of 4.5 mm between connectors, mak-
ing possible higher mounting density than the MPO con-
nector. In order to reduce costs, we have adopted the
design such that the plug shares several off-the-shelf parts
with the MU connector that is commercially available, and
that two identically shaped parts are assembled back-to-
back to constitute the adapter.
The ferrule compression force at the time of connector
engagement is an important parameter to achieve physical
contact (PC). In consideration of its application to back-
plane, the μ-Joint-MU connector plug was designed to pro-
vide a compression force equivalent to that of MU connec-
tors. But, since this raised some fears of insufficient com-
pression force when the ferrule was applied to a multi-fiber
connector, the method of polishing the ferrule endface was
optimized to ensure PC connection. Figure 5 shows the
results of PC connection verification tests on fabricated
connectors, in which the insertion loss was measured
before using an index matching material on the mating
portion and after applying the matching material in drops.
It can be seen that the difference between the two mea-
surements are extremely small, and hence PC connection
has been achieved with respect to all the fibers studied.
5. BACKPLANE HOUSING
In anticipation of application to optical backplanes,
μ-Joint-BP connector has been developed, in which the
µ-Joint ferrule
MT ferrule
Figure 2 Comparison of MT ferrule and μ-Joint ferrule.
Frequency
0
20
40
60
80
100
120
140
0.80.70.60.50.40.30.20.1
Av g. 0 .19
Ma x. 0. 49
Min. 0.01
S t d. 0 . 11
n = 360
Fiber-hole position error R(µm)
X-axis
Y-axis R(R2=X2+Y2
Figure 3 Fiber-hole position error of μ-Joint ferrules.
µ-Joint-MU
connector plugfemale
µ-Joint-MU
connector plugmale
Duplex
adapter
Figure 4 μ-Joint-MU connector plug and duplex adapter.
Furukawa Review, No. 34 2008 14
High-Density Multi-Fiber Connectors for Optical Interconnection
μ-Joint-MU connector plug is adapted to a backplane
connector. Figure 6 shows the connector developed here.
The μ-Joint-BP connector has a structure such that the
printed circuit board housing engages with the backplane
housing, allowing for connection and disconnection en
bloc of multiple connectors together with the board.
Moreover, simultaneous use of electrical connectors on
the board is possible. Since the μ-Joint-BP connector is
designed to have a compression force equivalent to that
of the MU connector --a single-fiber connector, excessive
loads on the latch portion made of plastics can be avoid-
ed while the mounting density is significantly improved.
Inheriting the mating mechanism of the single-fiber MU
connector, the accuracy in the positioning mechanism of
the μ-Joint-BP connector has been improved along with
the mounting density enhancement.
6. EVALUATION RESULTS
Figures 7 and 8 show the insertion loss of μ-Joint connec-
tor plugs developed here engaged with an adapter. The
insertion loss for MM fiber is 0.14 dB maximum at the
measurement wavelength of 850 nm, and is 0.41 dB maxi-
mum for SM fiber at 1310 nm --satisfactory insertion loss
characteristics in each case.
Figure 9 shows the insertion loss of μ-Joint-BP connec-
tor. The loss is 0.30 dB maximum at the measurement
wavelength of 1310 nm.
Reliability evaluation tests in conformity to Telcordia
GR-1435-CORE were carried out to confirm that the con-
nectors have good environmental and mechanical char-
acteristics. The results are shown in Table 1. Specifically,
Figures 10 and 11 show the results of thermal cycling
tests and durability tests, respectively, of μ-Joint-MU plug
connected with an adapter. Test conditions for thermal
cycling tests are:
-
40~75, 8 hours/cycle, 336 hours;
and those for durability tests are: 200 times in total, either
endface of connector is cleaned every 25 times, both
endfaces of connector are cleaned every 50 times. The
insertion loss variations for thermal cycling tests and
durability tests are 0.1 dB or lower and less than 0.2 dB,
respectively --satisfactory results.
0
0.1
0.2
0.3
0.4
0.5
0.50.40.30.20.10
Av g. 0.16
Max. 0.41
Min. 0.05
St d. 0 .10
n = 96
Insertion loss without index matching materialdB
Insertion loss with index matching material(dB)
Figure 5 Results of physical contact verification tests of
μ-Joint-MU.
Printed circuit
board housing
Backplane
housing
Figure 6 μ-Joint-BP connector.
0
20
40
60
80
100
120
140
160
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Insertion lossdB
Frequency
Ma x. 0.14
Min. 0.01
Ave. 0.03
Std. 0.03
n = 96
Measurement wavelength: 850 nm
Figure 7 Insertion loss of μ-Joint-MU connector for multi-mode
fiber.
Figure 8 Insertion loss of μ-Joint-MU connector for single-
mode fiber.
Furukawa Review, No. 34 2008 15
High-Density Multi-Fiber Connectors for Optical Interconnection
REFERENCES
1) M. Iwase et al.: Furukawa Review, No. 32, pp. 26 (2007)
2) R. Nagase et al.: NTT Gijutsu Journal, Vol. 15, No. 10, pp. 8 (2003)
(in Japanese)
7. CONCLUSION
Ultra-compact multi-fiber optical connectors comprising
μ-Joint-MU connector plug, adapter, and backplane con-
nector have been developed, in anticipation of application
to optical interconnection. The evaluation results have
shown that the connectors have good initial performance
as well as long-term reliability.
0
20
40
60
80
100
120
140
160
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Insertion lossdB
Frequency
Max. 0.30
Min. 0 .01
Ave. 0.09
Std. 0.06
n= 48
Measurement wavelength: 1310 nm
Figure 9 Insertion loss of μ-Joint-BP connector for single-
mode fiber.
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
Timehour
Insertion loss v ariation
-60
-10
40
90
140
190
240
290
Temp.(℃)
ch1
ch2
ch3
ch4
ch5
ch6
ch7
ch8
ch9
ch10
ch11
ch12
Temp.(℃)
30020010 0
Measurement wavelength: 1310 nm
Figure 10 Thermal cycling test results of μ-Joint-MU connector
for single-mode fiber.
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
200150100500
Repetition times
Insertion loss v ariation(dB)
ch1
ch2
ch3
ch4
ch5
ch6
ch7
ch8
ch9
ch 10
c h11
ch 12
Measurement wavelength: 1310 nm
Figure 11 Durability test results of μ-Joint-MU connector for
single-mode fiber.
Table 1 Results of reliability test.
Test item Test conditions (GR-1435-CORE)
Test results
μ
-
Joint
-
MU
(SM)
μ
-
Joint
-
BP
(SM)
Thermal
aging test 85, 336 hr 0.1 dB or
lower
0.1 dB or
lower
Humidity
test 65, RH 95%, 336 hr 0.15 dB or
lower
0.1 dB or
lower
Thermal
cycling test
-
40~75, 8 hr/cycle, 42 cycle 0.1 dB or
lower
0.1 dB or
lower
Vibration
test
1.5 mm in amplitude,
3 directions, each 2 hrs
0.1 dB or
lower
0.1 dB or
lower
Tension
test
Media 1 (fiber ribbon), Level 1,
Load: 2.2 N
0.15 dB or
lower
0.1 dB or
lower
Impact test Impacting on concrete block
9 times from 1.5-m height
0.1 dB or
lower
0.1 dB or
lower
Durability
test
Repeated connection and
disconnection, 200 times in total
0.2 dB or
lower
0.2 dB or
lower
Furukawa Review, No. 34 2008 16
High-Density Multi-Fiber Connectors for Optical Interconnection
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Electric transmission in a system and in such equipment as a high-speed server, a router, and an LSI, tester is reaching its limit, and introduction of optical transmission is considered. We are developing the OptoUnity products as an effort in providing the optical inter-connectlon technology that realizes high-speed transmission and a high density package with a concept of miniaturization. This paper introduces the development of small clad diameter optical fiber ThreadWave, micro multi-core ferrule μ-Joint, MU type plug, back plane connector, and right-angled connector μ-Curve, and passive alignment assembly plastic package parallel optical module μ-POEM.
  • M Iwase
M. Iwase et al.: Furukawa Review, No. 32, pp. 26 (2007)
  • R Nagase
R. Nagase et al.: NTT Gijutsu Journal, Vol. 15, No. 10, pp. 8 (2003) (in Japanese)