Optical waveguides – With disengagable mechanical connector – Optical fiber/optical fiber cable termination structure
Reexamination Certificate
2000-06-30
2002-06-04
Healy, Brian (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber/optical fiber cable termination structure
C385S059000, C385S065000, C385S089000, C385S092000
Reexamination Certificate
active
06398424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-channel optical connector and, more particularly, to a rugged-type multi-channel optical connector for use with optical transmitter modules and optical receiver modules.
2. Description of the Related Art
Recently, communication systems designers are vigorously adapting their designs for the use of optical fiber technology in various communication fields. Optical communication systems enable use of high frequency signals and suffer less signal loss than conductor based technologies and are therefore better suited for the high bandwidth communications that are increasingly in demand. Optical communication systems are suitable to use in high speed-long distance transmission systems.
During optical transmission of data, one channel of serial data is generally utilized for transmitting parallel data on N channels. In this case, the transmission speed of the serial data should be at least N times faster than each of the parallel data channels. High speed transmission circuits require expensive equipment; therefore, multiple transmission channels are often utilized to reduce the burden of a high speed transmitting circuit. In order to use multiple optical channels, a plurality of optical transmission systems, each including a light source, an optical fiber, and light detector, are required. For multi-channel optical transmitter/receiver modules, an accurate alignment of optical fibers with sources and detector is required not only for each channel but also for adjacent channels. Therefore, multi-channel optical transmitter/receiver modules need an optical connector which is highly accurate and, consequently, is more complicated than that of a single channel optical transmitter/receiver module.
FIG. 1
is an exemplary schematic diagram illustrating an active alignment method for a multi channel optical connector
101
and laser diodes
100
. In order to arrange laser diodes
100
, for example, with respect to optical fibers
110
, laser diodes
100
are first fixed so that they are separated by regular, usually uniform, intervals. Next, optical fibers
110
are fixed on a block
120
having grooves with the same regular intervals with which the laser diodes have been fixed. Then, laser diodes
100
and optical fibers
110
are aligned by moving block
120
with respect to laser diodes
100
. Block
120
can be moveable in all three directions. An optimal alignment between optical fibers
110
and laser diodes
100
can be achieved by monitoring the optical output power from each optical fiber of optical fibers
110
while moving block
120
. When the output power from each of the optical fibers
110
is maximized, block
120
can be fixed relative to diodes
100
. This method is referred to as the active alignment method because the maximum output power is sought by monitoring the optical output power from fibers
110
. The active alignment method can approach the optimum arrangement, however it requires expensive equipment and a lot of labor hours to accomplish. Further, the active alignment method does not lend itself to systems where plugable connectors are desirable.
FIG. 2
is an exemplary schematic diagram illustrating a passive alignment method for a multi channel optical connector
201
and optical devices
200
. In contrast to the active alignment method illustrated in
FIG. 1
, the passive alignment method does not include monitoring optical output power. Multi channel optical connector
201
includes an optical device array block
210
with optical devices
200
, each electrically coupled to one of electrical conductors
211
, arranged to have regular, uniform, intervals. Multi channel optical connector
201
also includes a multi channel optical fiber block
220
having optical fibers
221
arranged with the same regular intervals as that of optical devices
200
of optical device array block
210
. Optical device array block
210
can be fixed on a substrate (not shown) by soldering. Multi channel optical fiber block
220
can be plugable. Optical fibers
221
are then aligned with optical devices
200
when multi channel optical fiber block
220
is plugged into optical device array block
210
. Optical devices
200
can be laser diodes or photodiodes. Even though the passive alignment method is not optimized as with the active alignment method, it has the advantage of being faster (requiring fewer labor hours), requires less expensive equipment, and therefore is less expensive to perform.
FIG. 3
illustrates a conventional method of assembling connector
201
of FIG.
2
. Typically, an optical transmitter/receiver module will include two connectors such as connector
201
of
FIG. 2
, arranged such that light sources in one module are coupled with light detectors in the other module via optical fibers. Optical fibers
320
are inserted in grooves
311
on a connector block
310
. Optical fibers
320
can be multi mode or single mode optical fibers. Grooves
311
guide optical fibers
320
into holes
322
, typical 250 &mgr;m diameter holes, in connector block
310
. Grooves
311
have uniform intervals between any two adjacent grooves
311
. Optical fibers
320
are fixed in place by a cover
300
, which can also be grooved with grooves
312
having the same uniform intervals as connector block
310
. Connector block
310
is usually made from a plastic material for ease of manufacturing and lowered cost. End facets
321
of optical fibers
320
are usually smoothly polished in order to facilitate the coupling of light into and out of optical fibers
320
.
TABLE 1 shows the result of a calculation for an allowable tolerance of the alignment depending on the various diameters of optical fibers and a coupling efficiency between the optical fiber and the optical devices. The calculations in TABLE 1 are based on several parameters. The allowable tolerance for alignment between a laser diode and an optical fiber is based on the requirement that more than about 90% of the maximum optical output of the laser diode be coupled into the optical fiber. The allowable tolerance of alignment between an optical fiber and a photo diode is based on the requirement that more than about 90% of the maximum light output from the optical fiber be coupled into the photo diode. The divergence angle of the laser diode beam is assumed to be about 15°. The diameter of the light receiving aperture of the photodiode is assumed to be about 200 &mgr;m. Additionally, the laser diode is separated by about 450 &mgr;m from the optical fiber.
TABLE 1
Laser diode -
Optical fiber -
Laser diode -
Optical fiber -
Optical fiber
Optical fiber Allowable
Photo diode Allowable
Optical fiber Maximum
Photo diode Maximum
Total maximum
core diameter
tolerance of alignment
tolerance of alignment
coupling efficiency
coupling efficiency
Coupling efficiency
0.5
mm
±140 &mgr;m
±90 &mgr;m
100%
21%
21%
0.25
mm
±40 &mgr;m
±45 &mgr;m
90%
67%
60%
0.0625
mm
±20 &mgr;m
±65 &mgr;m
16%
100%
16%
If a 0.5 mm core diameter plastic optical fiber is used, it would be possible to manufacture a connector having approximately 100 &mgr;m of allowable tolerance of alignment between the optical fiber and the laser diode by plastic molding. However, only 21% of the light output from the optical fiber can be coupled into the photodiode. Alternatively, if a 0.25 mm core diameter plastic optical fiber is used, 67% of the light output from the optical fiber can be coupled to the photodiode. The decreased diameter of the optical fiber can bring three times the signal to the photo diode without increasing the output of the laser diode; however, the allowable tolerance of alignment between the optical fiber and the laser diode would be reduced by an amount 0.29 that of the 0.5 mm diameter plastic optical fiber. It is very difficult to manufacture such a connector and satisfy the allowable tolerances with plastic molding. The passive alignment method is generally accomplished with plastic optical f
Jin Yong-Sung
Lee Hyung-Jae
Son Yung-Sung
Edwards Gary J.
Healy Brian
PhotonAge, Inc.
Skjerven Morrill LLP
Wood Kevin S
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