Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-05-10
2001-08-28
Spyrou, Cassandra (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S024000, C385S031000, C385S033000, C385S059000, C385S060000, C385S080000, C385S084000
Reexamination Certificate
active
06282339
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 couplers 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, reliability and cost 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 &mgr;m at the epoxy
30
to about 450 &mgr;m at the epoxy
45
to about 10 &mgr;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 “Low-Cost Wavelength Division Multiplexed Coupler With Flexible and Precise Optical Path Adjustment”, filed recently by the present inventor, improvements are achieved for both the long-term high-power operation reliability and cost of the WDM couplers. In the pending application, while 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
′,
165
′ and
180
′. Also, low-cost standard single fiber pigtails are used to replace expensive special single fiber pigtails. As a result, while the optical paths between the GRIN lenses and the fiber pigtails are epoxy-free, the costs of the WDM couplers are also reduced. The improved WDM couplers have significantly reduced risk of high optical power damage and lower cost Therefore, the improved WDM couplers can be employed in fiber optic components for broader scope of applications that is much less limited by the reliability and cost problems of the WDM couplers as that encountered in the prior art However, in the pending application, there is still epoxy diffused onto the optical path between the WDM filter
105
′ and the GRIN lens
110
′. Therefore, there is still risk that in the long-term high-power operation, the epoxy
115
′ may gradually become degraded and susceptible to damages and thus leads to unreliable performance after continuously absorbing the optical signal energy. Thus, further development of the WDM couplers with high level of reliability is 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 all optical paths being epoxy free is required. Since production costs have been being an important factor prohibiting practical implementation of fiber optic technology, it is also highly desirable that the cost of such a technology would be as low as possible.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide an improved design and process for fabricating a low-cost WDM coupler with improved reliability by preventing the epoxies to spread over or diffused into all the optical paths. By eliminating the epoxies from all the optical paths, the aforementioned difficulties and limitations in the prior art and the pending application can be fully overcome.
Specifically, it is an object of the present invention to provide a design and process to fix all optical parts of the WDM couplers together by applying heat-curing epoxies. Several holding tubes are used between the GRIN lenses and the fiber pigtails to prevent the heat-curing epoxies from spreading over or diffused to the optical paths between the GRIN lenses and the fiber pigtails. Also, a special heat-curing epoxy and a special curing process are used to fix the WDM filter to the GRIN lens to prevent the heat-curing epoxy to enter the optical path between the WDM filter and the GRIN lens. As a result, all the optical paths are epoxy-free according to the new method and system of the WDM couplers of this invention. The WDM couplers produced according to the prese
Boutsikaris Leo
JDS Uniphase Inc.
Lin Bo-In
Spyrou Cassandra
LandOfFree
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