Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-03-22
2002-04-23
Schuberg, Darren (Department: 2872)
Optical waveguides
With optical coupler
Switch
C385S019000, C385S128000, C385S140000, C359S199200, C359S199200
Reexamination Certificate
active
06377724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related to optical component manufacturing and more particularly to protective coatings used in manufacturing optical components.
2. Technical Background
Variable optical attenuators (VOAs), 1×2 switches, and 2×2 switches are non-limiting examples of photonic devices which use a multiclad coupler. In these applications, the coupler requires a protective coating at the taper region to protect the coupler from breakage during the normal handling associated with assembly of the devices as well as during the functioning of the device. In the devices listed above, the coupler is flexed to attenuate the light signal propagating in the device. Any properties of the coating that degrade the optical signal are undesirable. Thus, the application of the coating must not negatively impact the attenuation response of the coupler after it is incorporated into the device.
FIG. 1
depicts an exemplary variable optical attenuator (VOA)
20
which uses a multiclad coupler
22
and a servomotor
26
. Coupler
22
includes an input fiber
28
and two output fibers
30
and
32
. First output fiber
30
is the output of VOA
20
and second output fiber
32
acts as a “dead-end” lead. An optical signal passes from input fiber
28
to either first output
30
or second output
32
through taper region
24
which couples the light signal from fiber
30
to fiber
32
. Flexing coupler
22
at taper region
24
by different amounts via servomotor
26
causes more or less of the light signal to be transmitted to the dead-end fiber
32
. The amount of flexing controls the attenuation of the signal. Thus, tapered region
24
functions as a commutator.
FIG. 2
depicts an optical step response
10
that was generated by an optical switch having a coupler without a coating in the tapered region. As depicted in
FIG. 1
, the tapered region is moved between a first unflexed position to a second flexed position, at the time of switching, T
sw
. The first position corresponds to a signal transmission state
12
wherein the insertion loss is approximately zero. The second state corresponds to a signal attenuation state
14
wherein the insertion loss is approximately 19.3 dB. Note that the plot of the insertion loss as depicted in
FIG. 1
a
is a square-wave. The insertion loss in both the first state and the second state is substantially constant. This is a desired response. Unfortunately, the coupler represented by
FIG. 2
does not have a coating. It is unprotected and susceptible to breakage.
In one approach that has been taken, couplers have been coated with a cationic ultraviolet (UV) curable epoxy system.
FIG. 3
depicts the insertion loss response
10
of the switch of
FIG. 2
having a coupler that is coated with the cationic UV epoxy. Again, the tapered region is moved between a first unflexed position to a second flexed position, at the time of switching, T
sw
. IL
swc
is the peak insertion loss of the coated coupler at the time of switching (T
sw
). IL
swc
overshoots the insertion loss IL
swu
of the uncoated coupler in the attenuation state. IL
swu
is used a reference insertion loss value. Peak insertion loss IL
swc
is followed by hysteresis
12
, which is the decay of the peak insertion loss IL
swc
to IL
swu
. IL
&Dgr;sw
=¦IL
swc
−IL
swu
¦ and represents the absolute value of the difference between the peak insertion loss of the coated coupler at the time of switching and the insertion loss of the uncoated coupler in the second state. As shown in
FIG. 3
, IL
&Dgr;sw
=23 dB−19.3 dB=3.7 dB. This formula is used to accommodate a coating material that generates a peak insertion loss IL
swc
that undershoots IL
swu
.
It is useful to measure hysteresis
12
in terms of its decay time T
D
. The decay time T
D
is a measure of the time it takes for peak insertion loss IL
swc
to decay to IL
swu
. As depicted in
FIG. 3
, the cationic ultraviolet (UV) curable epoxy system produces transients that have a decay time T
D
lasting approximately 14 seconds. As depicted, the decay of the transient hysteresis continues for several minutes. In more rigorous terms, T
D
is defined as T
D
=T
1
−T
sw
, wherein T
sw
is the time at which the coupler is switched from the first state to the second state, and T
1
is the time at which peak insertion loss IL
swc
decays to IL
D
. IL
D
=(0.27)IL
&Dgr;sw
=(0.27)¦IL
swc
−IL
swu
¦, which represents an exponential decay over time.
When the device is commutated from the second position to an unflexed first position at time T
usw
, a second hysteresis
16
is generated. The analysis discussed above with respect to hysteresis
12
can be used to analyze hysteresis
16
. As depicted, its decay time will also last several minutes. Both hysteresis
12
and hysteresis
16
are undesirable and illustrate the unwanted transients produced by the coating immediately after switch commutation. Another drawback to the cationic ultraviolet (UV) curable coating is that it is colorless. It is difficult to determine that the coating has been applied.
What is needed is a protective coating that does not generate the unwanted optical transients and hysteresis produced by earlier approaches. An optical device is needed that settles into a quiescent state immediately after commutation. Furthermore, the protective coating should include a tinted material. Since clarity is important, the tinted material should allow internal areas in the coupler to be viewed through the coating.
SUMMARY OF THE INVENTION
The present invention overcomes the aforementioned disadvantages as well as others. In accordance with the teachings of the present invention, the coating protects optical devices without generating unwanted optical side effects during flexing. The coating adheres readily to the glass of the waveguide component. The coating has a tint so that it can be readily ascertained that the coating has been applied, but also has sufficient clarity so that the internal areas in the component may be viewed. In one embodiment a UV coating cures to a tack free state in air so that a nitrogen blanket is not required during the cure. A solvent based coating such as a lacquer can also be used. The coating also does not degrade when exposed to relatively severe environmental conditions.
One aspect of the present invention is an optical device for directing a light signal. The optical device includes a commutation region movable between a first position corresponding to a signal transmission state, and a second position corresponding to a signal attenuation state. A protective coating is disposed on the commutation region that does not substantially introduce insertion loss transients when the commutation region is moved between the first position and the second position.
In another aspect, the present invention includes a method of directing a light signal in an optical device having a first output, and a commutation region movable between a first position corresponding to a signal transmission state, and a second position corresponding to a signal attenuation state. The method includes the steps of applying a protective coating onto the commutation region. Directing a light signal into the optical device. Moving the commutation region from the first position to the second position to thereby attenuate the light signal in the first output, whereby the protective coating does not substantially produce insertion loss transients in the optical device.
In yet another aspect, the present invention includes a method of fabricating an optical device, the optical device having a commutation region movable between a first position corresponding to a signal transmission state, and a second position corresponding to a signal attenuation state. The method including the steps of providing a coating material. Applying the coating material to the commutation region, wherein the coating material does not substantially produce insertion loss transients when the comm
Bookbinder Dana C.
Fabian Michelle D.
Agon Juliana
Boutsikaris Leo
Corning Incorporated
Schuberg Darren
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