Single site for healing dual optical rings

Details Single site for healing dual optical rings Single site for healing dual optical rings

1999-03-05

2002-06-18

Chan, Jason (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200

Reexamination Certificate

active

06407835

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to fiberoptic communications networks and, more specifically, to a method and an apparatus for controlling transmissions over fiberoptic networks.
BACKGROUND ART
While signals within telecommunications and data communications networks have traditionally been exchanged by transmitting electrical signals via electrically conductive lines, an alternative medium of data exchange is the transmission of optical signals through optical fibers. Information is exchanged in the form of modulated laser-generated light. The equipment for efficiently generating and transmitting the optical signals has been designed and implemented, but the design of optical switches for use in telecommunications and data communications networks is problematic. As a result, switching requirements within a network that transmits optical signals are often satisfied by converting the optical signals to electrical signals at the inputs of a switching network, then reconverting the electrical signals to optical signals at the outputs of the switching network.
Recently, alternate optical switching systems have been developed. U.S. Pat. No. 5,699,462 to Fouquet et al., which is assigned to the assignee of the present invention, describes a switching matrix that may be used for routing optical signals from one of a number of parallel input optical fibers to any one of a number of parallel output optical fibers. An isolated first switching element
110
is shown in FIG.
1
. The optical switch of
FIG. 1
is formed on a substrate. The substrate may be silicon, but other materials may be used. The silicon substrate includes planar waveguides defined by a lower cladding layer
114
, a core
116
, and an upper cladding layer (not shown). The core material is primarily silicon dioxide, but with other materials that achieve a desired index of refraction for the core. The cladding layers should be formed of a material having a refractive index that is sub-stantially different from the refractive index of the core material, so that optical signals are guided along the waveguides.
The core
116
is patterned to form an input waveguide
120
and an output waveguide
126
of a first optical path and to define a second input waveguide
124
and a second output waveguide
122
of a second optical path. The upper cladding layer is then deposited over the patterned core material. A chamber
128
is formed by etching a trench through the core material and the two cladding layers to the substrate. The waveguides intersect the trench at an angle of incidence greater than the critical angle of total internal reflection (TIR) when the location
130
aligned with the waveguides is filled with vapor or gas. Thus, TIR diverts light (A) from the input waveguide
120
to the output waveguide
122
to exit as light (B), forming route (A→B). When an index-matching fluid resides within the location
130
between the aligned waveguides
120
and
126
, the light (A) propagates through the trench
128
to exit the switching element as light (D), forming route (A→D). The trench
128
is positioned with respect to the four waveguides such that one sidewall of the trench passes through the intersection of the axes of the waveguides.
The above-identified patent to Fouquet et al. describes a number of alternative approaches to alternating the first switching element between a transmissive state and a reflective state. One approach is illustrated in FIG.
1
. The first switching element
110
includes two microheaters
150
and
152
that control the position of a bubble within the fluid-containing chamber
128
. The fluid within the chamber has a refractive index that is close to the refractive index of the core material
116
of the four waveguides
120
-
126
. Fluid fill-holes
154
and
156
may be used to provide a steady supply of fluid, but this is not critical. In the operation of the first switching element, one of the heaters
150
and
152
is brought to a temperature sufficiently high to form a gas bubble. Once formed, the bubble can be maintained in position with a reduced current to the heater. In
FIG. 1
, the bubble is positioned at the location
130
of the intersection of the four waveguides. Consequently, an input signal along the waveguide
120
will encounter a refractive index mismatch upon reaching the chamber
128
. This places the first switching element in a reflecting state, causing the optical signal along the waveguide
120
to be redirected to the output waveguide
122
. However, even in the reflecting state, the second input waveguide
124
is not in communication with the output waveguide
126
.
If the heater
150
at location
130
is deactivated and the second heater
152
is activated, the bubble will be attracted to the off-axis heater
152
. This allows index-matching fluid to fill the location
130
at the intersection of the waveguides
120
-
126
. The first switching element
110
is then in a transmissive state, since the input waveguide
120
is optically coupled to the collinear waveguide
126
.
A concern with optical switching elements of the type shown in
FIG. 1
is that in the transmissive state, a small amount of light is reflected from the switch. Reflection during the transmissive state is a result of the less than precise match between the indices of refraction of the fluid filling the chamber
128
and the waveguide core material
116
. A precise match between the indices is difficult to accomplish because multiple considerations impact the selection of a fluid. For example, because the fluid is manipulated using thermal energy, the thermal properties of the fluid must also be considered. As the mismatch between the refractive index of the fluid and the refractive index of the core material increases, the portion of an optical signal that is reflected at the switch increases. Currently, the incidentally reflected light is not beneficially utilized in switching systems. On the contrary, if the incidentally reflected light leaks into an adjacent waveguide, the result can be undesirable crosstalk.
What is needed is an apparatus and a method for advantageously utilizing light that is incidentally reflected from a fluid-manipulable optical switch when the switch is in a transmissive state. What is further needed is such an apparatus and method that introduce little or no crosstalk.
SUMMARY OF THE INVENTION
An apparatus and a method for controlling transmissions over an optical network include at least one traffic detector connected to an optical switch to receive incidentally reflected light when the switch is in a transmissive state. By utilizing the detection of incidentally reflected light, the traffic detector non-intrusively monitors the conditions of signal transmission capabilities to the switch. Depending upon detection of a fault condition, the optical switch is set in a reflective state or a transmissive state.
The apparatus includes a fluid-manipulable chamber, two inputs and two outputs. The inputs and outputs are waveguides that channel optical signals to and from the fluid-manipulable chamber. Under fault-free conditions in which signal transmissions are detected to be normal, a first input is connected to a first output, while a second input is connected to a second output. However, when a fault condition is detected, the two inputs exchange outputs by reversing the fluid-manipulable chamber with respect to its ability to propagate optical signals through the chamber.
In a preferred embodiment, the fault-free condition is one in which the fluid-manipulable chamber is in the reflective state. In this state, there is an absence of fluid at the interfaces of the inputs with the walls of the chamber. The resulting mismatch of indices of refraction at the interfaces causes optical signals to be reflected. In this preferred embodiment, the reflected signals from the first input are channeled to the first output, and the reflected signals from the second input are channeled to the second output. At least one of the two outputs is

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