Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-05-06
2002-02-12
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S016000, C385S074000
Reexamination Certificate
active
06347170
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and system for use in optical fiber technology. More particularly, this invention relates to a method and system for manufacturing an improved wavelength division multiplexed coupler.
BACKGROUND OF THE INVENTION
In optical fiber technology, wavelength division multiplexed (WDM) couplers are used to combine or separate optical signals having different wavelengths. As the WDM couples are being more broadly applied in the telecommunications, data communications and CATV industries, the fiber optic component industry is now confronted with increasing requirements for WDM couplers with higher level of performance and reliability as well as lower cost.
The performance and reliability of the WDM couplers depend heavily on their design and packaging technologies. Currently, two major kinds of design and packaging technologies are being widely employed in manufacturing the WDM couplers and each kind has its own advantages and disadvantages. In applying a first kind of technology for designing and packaging the WDM couplers, all optical parts are bonded together by applying epoxy bonding. The applications of this first type of WDM couplers show potential reliability risk of epoxy bonding in long-term operation.
FIG. 1A
shows the structure of a typical WDM coupler manufactured according to the first kind of design and packaging technology based on epoxy bonding. The WDM coupler includes a dual fiber pigtail
25
, a GRIN lens
35
, a WDM filter
40
, a GRIN lens
50
, and a single fiber pigtail
60
. In a typical manufacturing process, the GRIN lens
35
, the WDM filter
40
and the GRIN lens
50
are first fixed together by applying a heat-curing epoxy
45
. The relative position of the GRIN lens
35
to the fiber pigtail
25
is adjusted to achieve a lowest transmission loss from the input fiber
15
to the output fiber
20
for optical signals having reflection wavelengths. Then the dual fiber pigtail
25
is fixed to the GRIN lens
35
by applying a heat-curing epoxy
30
. Then the relative position of the GRIN lens
50
to the fiber pigtail
60
is adjusted to achieve a lowest transmission loss from the input fiber
15
to the output fiber
65
for optical signals having transmission wavelengths. And then, the single fiber pigtail
60
is fixed to the GRIN lens
50
by applying a heat-curing epoxy
55
. The conventional method and system provides the WDM couplers with good performance and reliability suitable for many types of applications. However, the WDM couplers manufactured according to the conventional method and system have a risk of failure when they are applied in high power optical transmission systems. In general, the heat-curing epoxies inevitably spread over all the optical paths in the WDM couplers. More specifically, the heat-curing epoxies
30
,
45
and
55
spread over the optical paths between the dual fiber pigtail
25
and the GRIN lens
35
, between the GRIN lenses
35
,
50
and the WDM filter
40
and between the GRIN lens
50
and the single fiber pigtail
60
, respectively. Under long-term operation, the epoxies
30
,
45
and
55
when exposed to the transmitted optical signals may gradually become degraded and susceptible to damages and thus lead to unreliable performance after continuously absorbing the optical signal energy. In the typical WDM coupler, the diameter of the optical signal beam is changing from about 10 m at the epoxy
30
to about 450 m at the epoxy
45
to about 10 m at the epoxy
55
. Thus, the optical signal power densities at the epoxies
30
and
55
are about 2500 times higher than that at the epoxy
45
. Therefore, the risk for high optical power damage is significantly higher at the epoxies
30
and
55
than at the epoxy
45
. The difficulties are specially pronounced for transmission of optical signals of high power. Because of the heat absorption problem, many optical system designers and operators now prefer or even demand to have all optical paths of the WDM couplers epoxy-free. Due to the significantly high power density and thus reliability risk, as the first step toward all epoxy-free optical paths, the optical system designers and operators now require not to use any epoxy on the optical paths between the GRIN lenses and the fiber pigtails. However, by applying the conventional WDM method and system, this epoxy-free optical path requirement can not be easily achieved. Thus, further development of reliable fiber optic components with high level of performance and reliability is limited by these difficulties.
In a pending patent application as shown by
FIG. 1B
, entitled “Improved Wavelength Division Multiplexed Coupler ”, filed recently by the present inventor, improvements are achieved for the reliability of the WDM couplers in long-term high-power operation. In the pending application, epoxies are prevented to spread over or diffused into the optical paths between the GRIN lenses
110
′
160
′ and the fiber pigtails
135
′
175
′ by employing several holding tubes
120
′
130
′ and
165
′. As a result, the optical paths between the GRIN lenses and the fiber pigtails are epoxy-free. The improved WDM couplers have significantly reduced risk of high optical power damage. Therefore, the improved WDM couplers can be employed in fiber optic components for broadened applications with being much less limited by the reliability problems of the WDM couplers as that encountered in the prior art. Since production costs have been being an important factor in practical implementation of fiber optic technologies, it is highly desirable that production costs would be as low as possible. However, in the pending application, a special single fiber pigtail
175
′ formed by cutting off one of two fibers of a high-concentricity dual fiber pigtail as that shown by
FIG. 1B
, is employed. The purpose of the use of the special single fiber pigtail is to obtain the same optical signal outgoing orientation of the single fiber collimator as that of the dual fiber collimator. A difficult arises when the optical signal outgoing orientation of the single fiber collimator is different from that of the dual fiber collimator. Specifically, when aligning the outgoing orientation to achieve a lowest transmission loss, a poor contact between the end surfaces of the holding tubes
120
′ and
165
′ will be configured because the holding tubes
120
′ and
165
′ must be slightly slanted to adjust for the difference of outgoing orientation angles. Thus the reliability of epoxy bonding between the single and dual collimators is degraded. A specially configured single fiber pigtail is used to resolve this difficulty by cutting off one of the two fibers to form a single fiber pigtail to achieve the same outgoing orientation as a dual fiber pigtail. However, as the high-concentricity dual fiber pigtails are much more expensive compared to standard single fiber pigtails, a high cost is paid for providing this improvement for the WDM couplers. Thus, further development of the WDM couplers must be engaged to lower the improvement cost when it is still limited by these difficulties.
Therefore, a need still exists in the art of design and manufacturing of the WDM couplers to provide improved material compositions, device structure, and manufacturing processes to overcome the difficulties discussed above. Specifically, a technique to provide the WDM couplers with epoxy-free optical paths between the GRIN lenses and the fiber pigtails at lower cost is required.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide an improved design and process for fabricating a WDM coupler with improved reliability at lower cost. While the epoxies are prevented to spread over or diffused into the optical paths between the GRIN lenses and the fiber pigtails, the low-cost standard single fiber pigtails are used to replace the expensive special single fiber pigtails. Therefore, the aforementioned difficulties and
JDS Uniphase Inc.
Lin Bo-In
Ullah Akm E.
LandOfFree
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