Multiport switch for optical performance monitor

The present invention provides a switch assembly for use with a single-port OPM to realize a multi-port OPM having improved reliability. In one embodiment, an N×1 optical switch assembly, wherein N is an integer greater than one, is provided. The optical switch assembly includes N optical input ports, N micro-electro-mechanical system (MEMS) variable optical attenuators (VOAs), where each MEMS VOA is optically coupled to a respective optical input port and is operable between an on position and an off position, and an N×1 optical combiner optically coupled to the N MEMS VOAs. Each MEMS VOA is configured to transmit an optical signal from a respective one of the optical input ports to the N×1 optical combiner in the on position and to not transmit the optical signal in the off position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fiber optic networks, and more particularly, to monitoring the performance of fiber optic networks.

2. Description of the Related Art

Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. As the traffic on fiber optic networks increases, monitoring and management of the networks become increasingly more significant issues. To monitor the network, the spectral characteristics of an optical signal at particular points in the network are determined and analyzed. This information may then be used to alter the performance of the network if the signal characteristics are less than optimal. Real time monitoring of this information is also important during setup and reconfiguration of the network.

FIG. 1Aillustrates a bi-directional, wavelength division multiplexed (WDM) optical network100which utilizes an optical performance monitor (OPM) assembly130between a first node120and a second node140. The multichannel optical network100comprises banks of light sources105a,bwhich provide the light carrier wavelengths upon which the signals are modulated. These light sources, each occupying a different channel, are combined into a single optical fiber through a fiber-optic multiplexer (not shown). The signals then travel along optical fibers110a-dbetween the two nodes120,140. Each carrier wavelength, or channel, carries one signal in the WDM system. The totality of multiplexed signals carried by the optical fibers110a-din each direction is herein referred to as a composite signal. Occasionally, the signals have to be amplified by optical amplifiers125a,b, such as Erbium Doped Fiber Amplifiers (EDFAs) or Raman amplifiers, due to attenuation of the signal strength. Typically, an optical signal is amplified after it travels approximately eighty kilometers or fifty miles.

The OPM assembly130may be located at various locations within the network100for the purpose of monitoring the characteristics of the optical signal so that the performance of the optical components of the network100may be determined. In one example, optical taps115a,care located proximate to respective upstream ports of the optical amplifiers125a,band optical taps115b,dare located proximate to respective downstream ports of the optical amplifiers125a,b. Providing upstream115a,cand downstream taps115b,dfor the OPM130proximate the optical amplifiers125a,ballows the OPM assembly130to measure the composite signal on either side of the optical amplifiers125a,band monitor the performance of the optical amplifiers125a,b. Alternatively or in addition to monitoring the optical amplifiers125a,bin the network100, the OPM120may be used to monitor add/drop stations135a,bin the network100as illustrated inFIG. 1B.

Typically, manufacturers offer only a single-port OPM130a. In order to allow the single-port OPM130ato accommodate a line from each of the taps115a-d, a 4×1 optical switch assembly130bis provided. The 4×1 switch assembly130bincludes a mechanical switch130c-ffor each of the four lines. Typically, these switches130c-fare actuated continuously cycling through all input ports on the order of once per second. In order to have an acceptable service lifetime on the order of ten to twenty years, the switches need to endure about one billion cycles. Conventional mechanical switches, however, typically fail after about a million cycles. Therefore, frequent replacement of the mechanical switches is necessary.

As the foregoing illustrates, there exists a need in the art for a more reliable switch assembly for an OPM.

SUMMARY OF THE INVENTION

The present invention provides a switch assembly for use with a single-port OPM having improved reliability. In one embodiment, an N×1 optical switch assembly, wherein N is an integer greater than one, is provided. The optical switch assembly includes N optical input ports, N micro-electro-mechanical system (MEMS) variable optical attenuators (VOAs), where each MEMS VOA is optically coupled to a respective optical input port and is operable between an on position and an off position, and an N×1 optical combiner optically coupled to the N MEMS VOAs. In an “on” position, each MEMS VOA is configured to transmit an optical signal from a particular optical input port of the optical switch assembly to the N×1 optical combiner. In an “off” position, each MEMS VOA is configured to not transmit the optical signal.

Use of the MEMS VOAs instead of conventional switches advantageously improves the service life of the switch assembly. This improvement is due to the slight amount of actuation displacement of the MEMS mirror during operation, which limits fatigue stresses sustained by the MEMS VOAs over time.

DETAILED DESCRIPTION

FIG. 2illustrates a four port optical performance monitor (OPM) assembly200having a 4×1 optical switch assembly220, according to one embodiment of the present invention. The OPM assembly200may replace the OPM assembly130in the optical networks100ofFIGS. 1A and 1B. As shown, the OPM assembly200includes a 4×1 switch assembly220, a single-port OPM205, a controller210, and a switch driver215. The switch assembly220includes four input ports230a-d, four micro-electro-mechanical system (MEMS) variable optical attenuators (VOAs)300a-d, and a 4×1 optical combiner225.

Each of the input ports230a-dmay be optically coupled to a respective one of the optical taps115a-dofFIG. 1. Each of the input ports230a-dis also optically coupled to a respective MEMS VOA300a-d. Each of the MEMS VOAs300a-dis operable between an “on” position and an “off” position by application of an electrical current from the switch driver215. Each MEMS VOA300a-dis configured to transmit an optical signal from a respective input port230a-dto the optical combiner225in the “on” position and to not transmit an optical signal from the respective input port230a-din the “off” position. As described in greater detail herein, only one of the MEMS VOAs300a-dis in the “on” position at any particular time during operation of the OPM assembly200. Importantly, any increase in insertion losses caused by using MEMS VOAs in the switch assembly220can be easily compensated for by increasing an input power range of the single-port OPM.

The optical combiner225serves as an interface between the four input ports230a-dand the single-port OPM205. The 4×1 optical combiner225may be constructed using two 2×1 combiners in series with a third 2×1 combiner or by using planar lightwave circuit (PLC) technology.

The single-port OPM205may be any one of several known in the art. One suitable single-port OPM205, illustrated inFIG. 2A, is a Fabry-Perot interferometer205. The Fabry-Perot interferometer205is an optical filter which can be tuned to scan its center resonance wavelength through a certain wavelength range. The Fabry-Perot interferometer205includes two planar partial optical reflectors205b,dwhich are parallel (preferably, exactly parallel) and placed at a distance from each other, with an optical medium205cbetween them. The two partial optical reflectors205b,dand the medium205cin between them form a cavity of certain optical length. The resonance center wavelength of the cavity equals to the optical cavity length divided by n+½, where n is an integer greater than or equal to zero. A cavity has multiple such resonance center wavelengths. There are at least three ways to realize tuning the resonance wavelength of the Fabry-Perot interferometer205: 1) by tilting the angle of the reflector relative to the incident optical beam, 2) by changing the distance between the two reflectors205b,d, and 3) by changing the refractive index of the optical medium205cbetween the reflectors205b,d.

In operation, collimated (by collimating lens205a) polychromatic light is input into the Fabry-Perot interferometer205through the outside face of the first partial optical reflector205b. Those wavelengths of the light which match the resonance wavelength of the Fabry-Perot interferometer205exit the interferometer from the side opposite an input optical fiber205fand are sampled by the photodetector205e. The photodetector205ecan then output the power of these wavelengths for analysis. All other wavelengths of the light are not transmitted through Fabry-Perot interferometer205to the photodetector205edue to destructive interference. Fabry-Perot interferometers are well known in the art and will not be further discussed here.

The controller210is electrically coupled to the single-port OPM205and the switch drivers215, each of which is electrically coupled to a respective one of the MEMS VOAs300a-d. In operation, the controller215signals one of the MEMS VOAs300a-d, for example300a, via the respective one of the switch drivers215, into the “on” position, either by providing or removing an electrical current or voltage (depending on the default setting of the MEMS VOA300a). A sample of the composite optical signal is then transmitted from the tap115a, through the port230a, the MEMS VOA300a, and the combiner225into the single-port OPM205. The single-port OPM205then measures the desired parameters, i.e. power level and noise level, of the composite optical signal. The controller210then receives the desired parameters from the single-port OPM205. Upon receiving the signal or series of signals from the single-port OPM205, the controller210shuts off the MEMS VOA300aand turns on another one of the other three MEMS VOAs, for example MEMS VOA300b. The above-process is then repeated for the signal from the tap115b.

The controller210may be responsible for analyzing the data received from the single-port OPM205to determine the performance of amplifier125a, or the controller210may transfer the data to a computer (not shown) for analysis. If the amplifier125ais not operating properly or optimally, parameters of the optical amplifier125amay be adjusted or the amplifier may even be serviced or replaced. A similar process may also be performed for MEMS VOAs300c,dto monitor the performance of the amplifier125b.

The order of the above-described steps is not important. For example, an entire cycle of switching and sampling may be performed before the data is analyzed and the order of switching may be arbitrary. Alternatively, the single-port OPM may have its own controller in which case the controller210would only handle switching control upon a signal from the OPM controller.

FIG. 3illustrates a micro-electro-mechanical system (MEMS) variable optical attenuator (VOA)300suitable for use with the 4×1 optical switch of the four port optical performance monitor ofFIG. 2. As shown, the MEMS VOA300is in the “on” position and includes an input photonic component304, a collimating lens (not shown), a movable reflecting mirror306, and an output photonic component308. A light beam310exits the input photonic component304(and travels through the collimating lens) and then reaches the reflecting focusing mirror306. The reflecting mirror306reflects the light beam310(back through the collimating lens and) into a focused light beam312. One or more mirror actuators314, preferably electrostatic actuators, actuate the reflecting mirror306between an on position and an off position. The movable focusing mirror306steers and controllably aligns (on position) or misaligns (off position) the light beam onto a receiving face316of the photonic device. The controlled misalignment of the light beam onto the receiving face enables an attenuation of the optical signal by allowing only a small portion, preferably substantially no portion, of the reflected light beam to enter the photonic component308for transmission.

The movable focusing mirror306may be or comprise a concave mirror, a diffractive mirror, a diffractive concave mirror, a Fresnel mirror, a Zone plate mirror, or another suitable movable focusing mirror known in the art.

The input photonic component304and the output photonic component308may each be a wave guide, a planar wave guide, an optical fiber, an optical lens, a spherical lens, an aspherical lens, a ball lens, a GRIN lens, a C-lens, a lens system, a prism, a mirror or a collimator, or another suitable photonic component for transmitting and/or receiving the light beam.

Alternatively, the mirror actuators314of the MEMS VOAs300may be actuators selected from the group consisting of an electro-mechanical actuator, a piezo-electric actuator, a thermo-mechanical actuator, an electromagnetic actuator, and a polymer actuator. The polymer actuator may include an electro-active polymer actuator, an optical-active polymer, a chemically active polymer actuator, a magneto-active polymer actuator, an acousto-active polymer actuator and a thermally active polymer actuator.

The focusing mirror306and the mirror actuators314are integrated onto a substrate320. The substrate320and one or more substrate elements322may each be or comprise a wafer. The substrate320and the substrate elements322may comprise suitable materials known in the art, such as a single wafer of glass or semiconductor material. The substrate320may be two or a plurality of coupled substrate elements322. The substrate elements322may be individual wafers and may be bonded, adhered, or otherwise coupled with a suitable coupling technique known in the art. The substrate320and substrate elements322may be suitable substrate materials known in the art, to include semiconductor material, glass, silica, ceramic, metal, metal alloy, and polymer. The semiconductor material may be suitable substrate materials, to include Silicon, Silicon Carbide, Gallium Arsenide, Gallium Nitride, and Indium Phosphide.

MEMS VOAs such as the one depicted inFIG. 3are known to those skilled in the art. As is also known, the MEMS VOAs300a-dmay be structurally integrated into a MEMS VOA array. In addition, the switch assembly220may be structurally integrated as one physical unit. Further, the entire OPM assembly200may be structurally integrated as one physical unit.

Use of the MEMS VOAs instead of conventional switches advantageously improves the service life of the switch assembly220. This improvement is due to the slight amount of actuation displacement of the MEMS VOAs, which limits fatigue stresses sustained by the MEMS VOAs over time.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. For example, the 4×1 switch assembly220is only a preferred embodiment of the present invention. Alternatively, the switch assembly (and thus the OPM assembly and the combiner) may have dimensions of N×1 (or 1×N), wherein N is an integer greater than one. (As persons skilled in the art recognize, OPMs usually referred to as N port instead of N×1.) In view of the foregoing, the scope of the present invention is determined by the claims that follow.