Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-08-31
2002-06-11
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S033000, C385S052000, C385S078000, C385S080000
Reexamination Certificate
active
06404954
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical couplers for fiber-optic systems. More particularly, it provides a novel type of coupling devices that permit fiber-optic components to be aligned in various ways, including an angled-axis alignment.
BACKGROUND ART
Fiber-optic networks are emerging as the transmission media of choice of telecommunications. Crucial to the performance of a fiber-optic network is the precise alignment and reliable coupling of various fiber-optic components, such as optical fiber carriers, GRIN lenses, and optical filters.
FIG. 1A
depicts a method prevalent in the art for coupling optical fibers to a GRIN lens. By way of example, an optical fiber carrier in the form of a fiber holder
100
, carrying two optical fibers
101
,
102
, and a GRIN lens
103
are brought together in close proximity and held in place by an epoxy joint
104
. Both UV epoxy and high temperature epoxy are generally employed as the adhesive agent. In some applications, the assembly may involve a two-step process: a UV epoxy is applied first as a fixing to secure the alignment of two adjacent optical elements, such as fiber holder
100
and GRIN lens
103
; and a high temperature epoxy is then added to further strengthen the coupling. Since the UV epoxy is considerably viscous, its application also serves to prevent the high temperature epoxy from spreading over to the sensitive optical surfaces.
The above prior art method of coupling fiber-optic elements renders several shortcomings, notably: 1) a bulky epoxy joint often cracks as ambient temperature fluctuates, due to different thermal expansion properties optical elements and epoxy may possess; and 2) moisture tends to degrade the performance of epoxy. Consequently, the alignment and the coupling between fiber-optic elements deteriorate over time, affecting the overall stability of the optical network. Moreover, because of the aforementioned problems inherent to epoxy, any gap between two fiber-optic elements bridged by epoxy, such as gap
105
between fiber holder
100
and GRIN lens
103
in
FIG. 1A
, must be small, which dictates that GRIN lens
103
in this case have a precise pitch, typically a quarter-pitch (0.25). This is an expensive, and at times impractical, proposition.
FIG. 1B
provides an exaggerated depiction of the spatial arrangement between fiber holder
100
and GRIN lens
103
shown FIG.
1
A. GRIN lens
103
is used to collimate and focus light beams
115
,
116
emerging from fibers
101
,
102
respectively to point
107
on its back-end face
108
, so that light can be passed onto succeeding fiber-optic elements in the network. Because light refracts at a front-end face
109
of fiber holder
100
and subsequently at a front-end face
110
of GRIN lens
103
, an axis
111
of GRIN lens
103
must be oriented at an angle &thgr;, albeit small (typically about a few degrees), relative to an axis
112
of fiber holder
100
, to ensure that light beams
115
,
116
eventually converge to the designated location, point
107
.
FIGS. 2A-2B
show two other prior art fiber-optic couplers, disclosed in U.S. Pat. No. 6,023,542. In
FIG. 2A
, a fiber holder
33
, carrying two optical fibers
30
,
31
, is enclosed in a quartz cylinder
46
on one end and coupled to a GRIN lens
34
by way of an epoxy
48
on the other. Cylinder
46
and GRIN lens
34
are further arranged to center in a cylindrical housing
47
. Despite the presence of two cylindrical housings
46
,
47
in this case, the coupling between fiber holder
33
and GRIN lens
34
relies nonetheless on epoxy
48
, rendering it susceptible to the same shortcomings as described above. In the optical coupler shown in
FIG. 2B
, a GRIN lens
35
and a fiber holder
36
are bridged and held in place by a quartz cylinder
44
, which is further telescoped within a second cylindrical housing
45
. The physical arrangement in this system, however, does not permit fiber holder
36
and GRIN lens
35
to be aligned in such a way that their respective axes are oriented at an angle, such as the angled-axis alignment illustrated in FIG.
1
B.
Hence, there is a need in the art for more effective, reliable, and versatile fiber-optic couplers that overcome the shortcomings of the prior art coupling devices.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of this invention to present a novel class of fiber-optic couplers that enable fiber-optic elements in an angled-axis alignment to be coupled in a secure and reliable manner. It is another object of the present invention to permit a variable gap between two successive optical elements. It is a further object of the present invention to provide methods for coupling fiber-optic elements.
An important advantage of the fiber-optic couplers of the present invention is that they allow fiber-optic elements to be spatially arranged in various ways, yet still attaining secure and reliable coupling. Another advantage of the fiber-optic couplers of the present invention is that the coupling is less susceptible to extraneous effects such as temperature variations and moisture erosion. Moreover, by allowing a variable gap between two optical elements in a fiber-optic coupler of the present invention, a variety of GRIN lenses with less than a quarter-pitch can be employed, which is highly desirable in practice. Further advantages of the fiber-optic couplers of the present invention include their simple assembly, versatility, and adaptability for a variety of applications.
These and other objects and advantages of the present invention will become apparent from the following description and accompanying drawings.
SUMMARY OF THE INVENTION
The present invention provides a fiber-optical coupler in which two or more optical elements are bridged and held in place by a sleeve. A first side of the sleeve partially encompasses and is in contact with a first optical element, and a second side of the sleeve partially encompasses and is in contact with a second optical element via an adhesive agent. The length and the inner diameter of the bridging sleeve can be so chosen to allow the axes of the first and second fiber-optic elements to be oriented at an angle. Such an alignment is termed an angled-axis alignment, hereinafter.
The fiber-optic coupler of the present invention further permits a variable gap of empty space between the first and second optical elements. In an application where the first optical element is a fiber holder and the second optical element is a GRIN lens, for instance, the allowance of a gap permits a GRIN lens with less than a quarter-pitch to be used. In addition, there can be one or more optical elements sandwiched between the first and second optical elements.
By choosing a sleeve having thermal expansion properties and geometrical attributes that closely match those of the optical elements it embraces, the coupling between the optical elements in the fiber-optic coupler of the present invention is much less susceptible to ambient temperature variations and moisture erosion, hence more reliable and enduring.
The bridging sleeve is typically made of glass, or metal (e.g., stainless steel). The inner cross-section (i.e., the cross-section of the hollow interior) of the sleeve may have varying shape and size along a length of the sleeve, so as to correspond to the geometric attributes of the optical elements it contains. The adhesive agent can be an epoxy, or a solder. Both UV and high temperature epoxies are typically employed. The optical elements that are to be coupled can be optical fiber holders (or connectors), GRIN lenses, optical isolators, and optical filters, etc.
A plurality of the fiber-optic couplers described above can be further cascaded, providing a secure and reliable way of interconnecting a variety of optical elements which may require different alignments. Moreover, two or more fiber-optic couplers, in simple or cascaded form, can be telescoped within and bridged by one or more additional sleeves, to further facilitate the interconnections in a fiber-optical network.
The
Xu Jingyu
Zhu Steven Guoxin
Lumen Intellectual Property Services
Oplink Communications Inc.
Sanghavi Hemang
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