Reduced manufacturing complexity optical channel...

Details Reduced manufacturing complexity optical channel... Reduced manufacturing complexity optical channel...

2001-02-16

2002-06-18

Hellner, Mark (Department: 3662)

Optical: systems and elements

Optical amplifier

C359S341100, C359S341300

Reexamination Certificate

active

06407852

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in general to fiber optic communication systems and components therefor, and is particularly directed to an augmentation of the V-groove-installed, optically pumped waveguide amplifier channels employed in the integrated optical amplifier architecture described in the above-referenced '823 application. Rather than configure a respective waveguide amplifier channel pulled from a compound glass structure, containing both a core and a substantial volume of cladding material, comprised of an inner cladding layer surrounded by an outer cladding layer, surrounding the core, the present invention places a single inner clad core directly into a respective V-groove. The inner clad core is inserted into the V-groove so as to allow fiber optic adhesive, such as low refractive index epoxy, to be supplied to and/or allowed to form around the inner clad, and thereby physically secure the fiber in the groove and also provide an optical pump beam-confining, outer pseudo-cladding around the inner clad. The resulting structure may then be lapped to a planar surface through which optical pumping energy is introduced.
BACKGROUND OF THE INVENTION
Because of bundle density limitations associated with the individual buffered fibers and connector interface configurations of legacy, single mode optical fiber cables (a reduced complexity cross-section of one of which is shown at
10
in FIG.
1
), especially those containing a relatively large number of ‘fiber’ strands, optical communication equipment and component suppliers have begun offering relatively thin, or flat multiple optical fiber-containing ribbons and small form factor multi-channel connector interfaces. As further shown in
FIG. 2
the flat, rectangular cross-section of such a multi-fiber ribbon
20
facilitates densely packing a relatively large number of such fibers
21
within a physical volume that is both compact and readily conformal with a variety of housing and equipment surfaces.
Unfortunately, when employed in applications requiring amplification of optical signals transported by the various fibers of the ribbon cable, such as in long haul repeaters, it is necessary to break out each individual fiber
21
from the ribbon, as illustrated in
FIG. 3
, and then connect each fiber to its own dedicated optical amplifier unit. Such an optical amplifier unit, a block diagram of which is shown in FIG.
4
and an optical fiber signal transport view of which is shown in
FIG. 5
, is typically a relatively large sized and costly piece of equipment.
These size and cost drawbacks are due to the number of individual fiber-interfaced components employed, long loops
31
of optical pumping energy absorbing and amplifying material (such as erbium-doped fiber) required for gain, the need for relatively narrow spectrum, distributed feedback laser diode pumps
32
(which require thermoelectric coolers and associated control circuits therefor), as well as the substantial hand labor necessary to physically interface individual components and the input and output ports
33
,
34
of each amplifier unit with a respective fiber of the ribbon fiber bundle.
Advantageously, these and other shortcomings of conventionally having to use individual fiber-dedicated light amplifiers are effectively obviated by the multi-fiber ribbon-interfaced optical amplifier architecture described and shown in the '823 application, respective diagrammatic side and tops views of a prism-coupled embodiment of which are shown in
FIGS. 6 and 7
. As shown therein, the main body of this improved multi-fiber ribbon-interfaced amplifier comprises a support substrate
40
made of a bulk material such as a glass, and having a generally planar surface
41
, in which a plurality of spatially adjacent (e.g., parallel) optical waveguide channels
43
are formed.
The waveguide channels
43
are optically coupled with an array of pumping energy sources
74
, whose optical pumping energy outputs are introduced into the optical waveguide channels by means of a multi-channel optical interface
70
arranged adjacent to the substrate surface
41
. As a non-limiting example, the substrate
40
may contain twelve optical waveguide channels
43
, corresponding to the number of (single mode, nominal 1550 nm wavelength) fibers within currently commercially available, reduced form factor multi-optical fiber ribbons. For purposes of reducing the complexity of the drawings, the partial diagrammatic plan view of
FIG. 7
shows six of the twelve waveguide channels
43
in the support substrate
40
.
The optical waveguide channels
43
have mutually adjacent center-to-center spacings that conform with mutually adjacent, center-to-center (nominally 250 microns) spacings
54
of the optical fibers
53
of an ‘upstream’ (multiple input signal-conveying) section of industry standard, multi-optical fiber ribbon
50
-
1
, and a ‘downstream’ (multiple amplified signal-conveying) section of multi-fiber ribbon
50
-
2
. In order to effect mechanical and optical end coupling between respective sections
50
-
1
and
50
-
2
of multi-fiber ribbon and optical waveguide channels
43
of the substrate
40
, multi-fiber ribbon interface connectors
55
and
56
may be employed.
The relatively narrow (widthwise) dimensions of the components of this multi-channel fiber optic amplifier allow the amplifier to be configured such that its width-wise dimension essentially conforms with that of a section of reduced form factor multi-fiber ribbon. The resulting form factor of this highly integrated optical amplifier architecture is considerably reduced compared to conventional cable-installed structures, which require a separate break-out to a dedicated amplifier device for each fiber strand, as described above. For a twelve channel application, the overall width of the multi-channel optical amplifier may be slightly larger than three millimeters.
FIG. 8
is a partial perspective view of an optical waveguide channel and an associated pumping energy source, such as that contained in an M×N spatial array of pumping energy sources, as well as a portion of the optical interface used to image the output of the pumping source into the channel. As shown therein, a respective optical waveguide channel
43
comprises a central (signal transport) core
62
, through which a signal light beam from an upstream ribbon fiber propagates, and an adjacent inner cladding layer
61
, with an outer cladding layer
63
, that partially surrounds the core
62
. The signal transport core
62
is dimensioned to have a cross section that may nominally conform with that of an associated ribbon fiber, so that the core
62
serves as the principal signal transport medium and amplifying medium through the amplifier for a signal light beam coupled thereto from a respective ribbon fiber of the input multi-fiber ribbon section
50
-
1
.
For this purpose, the core
62
may comprise an optically transmissive material whose photonically stimulated, energy state transfer properties readily absorb optical energy supplied by a one or more light amplification pumping sources (such as pumping sources that emit a nominal 980 nm optical beam) and provides emitted radiation-stimulated amplification of the (nominal 1550 nm) signal beam. As a non-limiting example of a suitable material, the core
62
may comprise erbium ytterbium-doped phosphate glass (e.g., phosphate glass containing 22% Yb
3+
and 2.2% Er
3+
).
The inner cladding
61
surrounding the core
62
may comprise a glass material, that is like or similar to that of the core, but is undoped, and having a slightly lower index of refraction. The cladding layer
61
serves to both improve the focusing tolerance window upon which one or more pumping optical energy beams are imaged for amplifying the signal beam propagating in the core
62
, and allows an increase in power density (watts/cm
2
) of the incident pumping source beam along the gain interaction length of the core. This clad core waveguide structure may be formed by a controlled i

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