Fiber optic component assembly module

An assembly module provides well-organized optical fiber component attachment features and convenient fiber routing areas for assembling and containing a fiber optic device such a telemetry module. The module comprises a first substrate having a first side and a second side. The first side includes a plurality of sidewalls and a recessed floor surface bounded by the sidewalls. Some of the sidewalls have a cavities formed therein. A plurality of channels extend from the ends of the cavities. A plurality of projections extend from the sidewalls over selected portions of the floor surface such that a lower edge of each projection is spaced apart from the floor surface. Optical fiber components (couplers, splices, etc.) may be mounted in the cavities, and optical fibers are routed to and from the optical fiber components on regions between the sidewalls and through the channels. The optical fibers are placed in the spaces between the projections and the floor surface to retain the optical fibers in selected positions. The assembly module provides for preasembled, pretested, mass produced, fiber optic coupler and excess fiber subassemblies and reduces the potential for component and fiber damage during manufacturing and allows for, but reduces the need for, the potential rework and repair associated with errors and failures during array assembly, thereby reducing manufacturing cost.

BACKGROUND OF THE INVENTION 
This invention relates generally to assembling fiber optic systems. This 
invention relates particularly to a module for holding fiber optic 
components in sensor systems such as hydrophone arrays. 
Current state of the art in either towed or fixed hydrophone array assembly 
employs tedious and precision manual labor to integrate fiber optic 
couplers and/or excess fiber lengths and/or optical fiber splices during 
the assembly of optical fiber sensor arrays. These elements are usually 
assembled, packaged and inspected with commensurate hand operations 
required. The primary disadvantages of this approach are the potential 
damage and/or loss of components and fiber due to physical breakage during 
handling, and the high labor costs associated with installing the couplers 
and/or excess fiber lengths. 
Handling and arranging optical fiber is often very tedious because of the 
tendency of optical fiber to assume a straight line configuration due to 
its stiffness. This causes loops of fiber to tend to expand outward. The 
outer edges of planar loops also tend to twist and rise up away from a 
substrate to which it is to be mounted, thereby requiring multiple bonding 
operations, which may inhibit or preclude rework or repair. 
SUMMARY OF THE INVENTION 
The present invention overcomes these and other problems by providing 
well-organized optical fiber component attachment features and convenient 
fiber routing areas. 
This invention extends the present manufacturing state of the art by 
allowing for the use of preasembled, pretested, mass produced, fiber optic 
coupler(s) and excess fiber(s) subassemblies. The compact fiber optic 
assembly module also allows integration of higher level assemblies, hence 
providing for a more modular assembly with improved testability. This 
device reduces the potential for component and fiber damage during 
manufacturing and allows for, but reduces the need for, the potential 
rework and repair associated with failures during array assembly or 
testing, thereby reducing manufacturing cost. 
A module according to the present invention for assembling and containing a 
fiber optic device comprises a first substrate having a first side and a 
second side. The first side includes a plurality of sidewalls and a 
recessed floor surface bounded by the sidewalls. Some of the sidewalls 
have cavities formed therein. A plurality of channels extend from the ends 
of the cavities; and a plurality of projections extends from the sidewalls 
over selected portions of the floor surface such that a lower edge of each 
projection is spaced apart from the floor surface. Optical fiber 
components (couplers, splices, etc.) may be mounted in the cavities, and 
optical fibers are routed to and from the optical fiber components through 
the channels. The optical fibers are placed in the spaces between the 
projections and the floor surface to retain the optical fibers in selected 
positions. 
The invention also includes an arrangement where a pair of the substrates 
are mounted to opposite ends of a plurality of spools that are suitable 
for having optical fiber coils formed thereon. The optical fiber 
components and coils may be used to form interferometric sensors, delay 
lines and other components used in forming a fiber optic hydrophone array. 
An appreciation of the objectives of the present invention and a more 
complete understanding of its structure and method of operation may be had 
by studying the following description of the preferred embodiment and by 
referring to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in FIGS. 1 and 2, a fiber optic assembly module 10 according to 
the present invention includes an upper retainer 12A and a lower retainer 
12B. The retainers 12A and 12B are mounted to opposite ends of a plurality 
of spools 16-18. The retainers 12A and 12B preferably are identical. 
Therefore, only the retainer 12 is described in detail. Components of the 
retainers 12A and 12B are designated with a number followed by the letter 
"A" and "B," respectively. It is to be understood that for each component 
described in the retainer 12A, there is a corresponding component in the 
retainer 12B. 
The fiber optic assembly module 10 may be formed from a number of materials 
(e.g., metals, plastics, elastomers, foam rubbers, etc.) using one of a 
number of different manufacturing methods (e.g., machining, injection 
molding, casting). Each of the retainers 12A and 12B as illustrated in 
FIGS. 1-4 is suitable for holding up to two fiber optic couplers that may 
be included in fiber optic devices such as fiber optic interferometric 
sensors or as part of fiber optic telemetry networks. Couplers suitable 
for use with the present invention include 2.times.2 fused biconical 
tapered couplers that are commercially available from manufacturers such 
as Gould Electronics, Inc. 
The retainer 12A may be formed from an elongated, thin, generally 
rectangular substrate 20A. A central planar floor surface 22A has an 
elongated passage 24A extending therethrough. A first cavity 26A is formed 
adjacent to edge 28A, and a second cavity 30A is formed adjacent to the 
opposite edge 32A. The cavities 26A and 30A may be of any convenient 
shape, such as generally semicylindrical or rectangular. The cavities may 
be the same shape as and provide a housing location for the couplers, 
which typically have circular cross-section cylindrical housings. 
Fiber routing channels 34A and 36A extend from the ends of the cavity 26A. 
Fiber routing channels 40A-43A also extend from the ends of the 
semicylindrical cavity 30A. A plurality of projections 50A-58A extend from 
the sides of the substrate over portions of the floor surface 22A. These 
projections 50A-58A are spaced apart from the floor surface 22A so that 
optical fibers may be retained between the projections and the floor 
surface as shown in FIGS. 1, 2 and 4. 
As shown in FIGS. 3 and 4, a fiber optic coupler that is pre-fabricated and 
contained in a cylindrical coupler package 72A may be mounted in the 
cavity 30A. A fusion splice may be installed in a container 70A, which is 
mounted in the cavity 26A. Potting of couplers and splices may be 
accomplished prior to or after installation within the module 10 (for 
pressure isolation, for example). As shown in the exemplary embodiment, 
optical fibers 74A-77A extend from the ends of the coupler package 72A and 
pass through the fiber routing channels 40A-43A, respectively. Optical 
fibers 78A-79A extend from the container 70A and pass through the fiber 
routing channels 34A and 36A. The fibers 75A, 77A, 79A are retained near 
the floor surface 22A by the projections 50A-58A. 
The retainer 12B may be used to mount a coupler container 72B in the cavity 
30B and a splice container 70B in the cavity 26B. Some of the fiber leads 
extending from the couplers may extend through the central passage 24A or 
24B for connection to the optical fiber coils 90-92 wound onto the spools 
16-17, respectively. The fiber coils 90-92 are used for applications 
requiring time division multiplexing in which optical delay lines are used 
for signal timing. The fiber leads may also be connected together and with 
fiber optic leads from an optical fiber-wound hydrophone mandrel to form 
either a Mach-Zehnder or Michelson interferometer in a manner well-known 
in the art to form an interferometric sensor as disclosed in U.S. Pat. 
Nos. 5,668,779 and 5,155,548, the disclosures of which are incorporated by 
reference into the present disclosure. Some of the leads may also extend 
through the fiber routing channels for connection to an optical telemetry 
fiber so that an array of interferometric sensors may be formed that may 
be interrogated over large distances such as 1 to 100 km. 
The recessed central cavity 23A and the projections 50A-58A allow for 
rapid, continuous and removable routing of individual fibers and efficient 
storage of fiber and fusion splices necessary to connect hydrophones, 
couplers and fibers. Excess lengths of optical fiber must also be 
accommodated. This can be achieved by winding the required length(s) of 
fiber on one or more of the spools 16-18. Spools 16-18 may be made of a 
variety of plastics and metals, and they may be fabricated by a number of 
methods. In the preferred embodiment, injection molded polycarbonate 
spools are used. Machining and stamping techniques may also be used to 
form the spools 16-18 of other materials, such as aluminum. Optical fiber 
may be wound on the spools 16-18 off-line using automated machinery. The 
spools are subsequently sandwiched between the substrates 20A and 20B and 
maybe attached to the substrate by bonding or other suitable means. 
Some applications may require installation of the fiber optic assembly 
module 12 within a housing that may be either rigid or flexible. The 
housing may be made in a variety of configurations from various materials 
using one of a number of fabrication methods. For example, square or 
cylindrical housing shapes may be used. Snap-together or hinged clam-shell 
closure mechanisms may be used to enclose the module 12. The housing may 
be made from plastic, metal or other suitable material and may be formed, 
machined or injection molded. Some applications may require intermediate 
attachment of the module assembly housing to one or more metal or 
synthetic strength members within an array of fiber optic hydrophones. 
Such applications may include, but are not limited to, fixed cable arrays, 
such as ocean bottom cables. 
FIG. 5 illustrates a plurality of assembly modules 102-107 according to 
FIGS. 1-4 arranged inside a protective shell 110 that preferably is formed 
as a flexible tube or hose. The assembly modules 102-107 may be arranged 
with optical hydrophones 140-164 to form a hydrophone array as disclosed 
in U.S. Pat. Nos. 5,515,548 and 5,345,522, the disclosures of which are 
incorporated by reference into the present disclosure. The hydrophone 
array may include one or more telemetry modules for combining and/or 
directing signals output from the hydrophones to signal processing 
electronics (not shown). These telemetry modules may be packaged within 
the assembly module 10. 
As shown in FIGS. 6 and 7, the hose has a wall 112 of thickness suitable 
for protecting the hydrophones and the assembly modules 102-107 and fiber 
optic components mounted thereon from environmental hazards that could 
cause damage to the components or that could render the components 
inoperable. 
FIG. 8 is a perspective view of an assembly module according to the present 
invention inside a clam shell type protective housing 120. The protective 
housing 120 includes an upper half 122 and a lower half 124 that 
preferably are formed as thin-walled semicylinders. The upper half 122 and 
lower half 124 preferably are hinged together along two adjacent sides. 
The inner diameter of the protective housing 120 is configured to hold the 
assembly module 10 securely. The protective housing 120 has a side wall 
126 of thickness adequate to protect the assembly module 10 and fiber 
optic components (not shown in FIG. 8 ) mounted thereon from being damaged 
during assembly or in normal usage. At each end of the protective housing 
120 there is an opening 130 to allow connecting cables (not shown) to 
extend from the housing 120 to other apparatus such as hydrophones (not 
shown). 
This invention is a novel component for the rapid and economical 
manufacturing of both towed and ocean bottom mounted linear fiber optic 
hydrophone arrays. The advantage over prior art include its 
compactness/reduced size, its ability to protect optical couplers and 
associated fiber assemblies during assembly and when deployed; the ability 
to store and protect additional/excess fiber lengths required for certain 
optic telemetry applications; and its ability to serve as an integrated 
subassembly which can be premanufactured and economically mass produced 
and tested before final array assembly. 
The present invention can be economically manufactured from a variety of 
methods, using metals, thermoplastics, composites (e.g. epoxy/glass), 
elastomers, or foam rubber materials. Subsequent installation of optical 
fibers and couplers is facilitated by the molded or machined cavities and 
channels which mechanically locate and protect the optic components. Long 
fiber lengths (used for timing delay lines, etc.) can be "prewound" onto 
each spool as required prior to final assembly of the module. The 
resulting device is a simple, economical, light weight package which can 
be utilized for a wide range of optical fiber hydrophone applications. 
The structures and methods disclosed herein illustrate the principles of 
the present invention. The invention may be embodied in other specific 
forms without departing from its spirit or essential characteristics. The 
described embodiments are to be considered in all respects as exemplary 
and illustrative rather than restrictive. Therefore, the appended claims 
rather than the foregoing descriptions define the scope of the invention. 
All modifications to the embodiments described herein that come within the 
meaning and range of equivalence of the claims are embraced within the 
scope of the invention.