Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-04-20
2001-02-06
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S033000, C385S016000, C385S074000
Reexamination Certificate
active
06185347
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.
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. In the present invention, improvements over this type of WDM couplers are disclosed.
FIG. 1
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.
Therefore, a need still exists in the art of design and manufacturing of the WDM couplers to provide new 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 epoxy-free is required. As the first step to fully overcome the above-discussed difficulties, a technique to provide the WDM couplers with epoxy-free optical paths between the GRIN lenses and the fiber pigtails is required.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a new design and process for fabricating a WDM coupler with improved reliability by preventing the epoxies to spread over or diffused into the optical paths between the GRIN lenses and the fiber pigtails. By eliminating the epoxies from the optical paths between the GRIN lenses and the fiber pigtails, the aforementioned difficulties and limitations in the prior art can be significantly improved.
Specifically, it is an object of the present invention to provide a design and process to fix all optical parts 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 of the WDM couplers. As a result, the optical paths between the GRIN lenses and the fiber pigtails are epoxy-free according to the new method and system of the WDM couplers of this invention. The WDM couplers produced according to the presently improved design and process have significantly reduced risk of high optical power damage. Therefore, the WDM couplers of this invention 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.
Briefly, in a preferred embodiment, the present invention discloses a WDM coupler comprising a dual fiber collimator and a single fiber collimator. First, the dual fiber collimator includes a WDM filter attached to a first GRIN lens by applying a first heat-curing epoxy. The dual fiber collimator further includes the first GRIN lens inserted an fixed into a first holding tube by applying a second heat-curing epoxy. The dual fiber collimator further includes a second holding tube holding a dual fiber pigtail. The dual fiber pigtail is disposed at a first optimal position from the first GRIN lens to achieve a lowest reflection loss. The first and second holding tubes are in contact with each other. The dual fiber pigtail held by the second holding tube and the first holding tube are fixed together by applying a third heat-curing epoxy. The WDM coupler further includes a single fiber collimator that includes a third holding tube holding and fixing a second GRIN lens and a single fiber pigtail therein by applying a fourth and a fifth heat-curing epoxies. The single fiber pigtail is disposed at a second optimal position from the second GRIN lens to achieve a lowest transmission loss. The dual and single fiber collimators are bonded together by applying a sixth heat-curing epoxy to fix the first and third holding tubes together. The dual fiber collimator is aligned with the single fiber collimator with the first and the third holding tubes securely bonded together by the sixth heat-curi
Lin Bo-In
Palmer Phan T. H.
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