CA2361509A1 - High-performance nxn optical matrix switch using double-size butterfly network of 2x2 switching units - Google Patents
High-performance nxn optical matrix switch using double-size butterfly network of 2x2 switching units Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0005—Switch and router aspects
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
- H04Q11/0005—Switch and router aspects
- H04Q2011/0037—Operation
- H04Q2011/0049—Crosstalk reduction; Noise; Power budget
Abstract
An NxN optical waveguide matrix switch using double-size butterfly network of 2x2 switching units is proposed in this invention. In the NxN matrix switches, the complexity, the power consumption, the wavelength sensitivity, the insertion loss, and the blocking are main problems. In this invention, the NxN optical waveguide matrix switch uses a double size butterfly.network where one size of the butterfly network is specially used for switching operations and the other one for balancing and testing the optical outputs at the OFF-state. So, not only can nonblocking degree be met, but also both the numbers of switching units and switching stages can be decreased. Especially in the large-scale NxN
matrix switches, this advantage becomes more apparent. As a result, the complexity, the insertion loss and the power consumption can be significantly reduced. If the wavelength sensitive switching units are used in this type of devices, at the different operation levels, the switching units are designed at different central wavelengths to uniformly cover the whole wavelength range. So, the wavelength sensitivity of the whole device can be depressed. Therefore, the final performance of NxN optical matrix switch becomes low insertion loss, wavelength insensitive and nonblocking.
matrix switches, this advantage becomes more apparent. As a result, the complexity, the insertion loss and the power consumption can be significantly reduced. If the wavelength sensitive switching units are used in this type of devices, at the different operation levels, the switching units are designed at different central wavelengths to uniformly cover the whole wavelength range. So, the wavelength sensitivity of the whole device can be depressed. Therefore, the final performance of NxN optical matrix switch becomes low insertion loss, wavelength insensitive and nonblocking.
Description
High-Performance NxN Optical Matrix Switch Using Double-Size Butterfly Network of 2x2 Switching Units Technical Field The present invention is an NxN optical waveguide matrix switch symmetrically using double-size butterfly network of 2x2 switch units. The 2x2 switch units are preferred to be Mach-Zehnder interferometer type because it has two advantages of low power consumption and low access loss. It relates to a high-isolation, low propagation loss, and low-power-consumption optical switch for an optical communication system, optical interconnects, optical cross-connect, and a large-scale fiber-optic network system.
Backsround of the Invention Today, the rapid development and applications of fiber-optic telecommunication systems are stimulating various photonics networks based on some new microstructure optoelectronic technologies instead of mechanical individual devices. Among various microstructure optoelectronic technologies, integrated optics represents a promising strategy in this field. One implementation of this strategy relies on the integration of optoelectronic interconnects on a host Si substrate, and thus requires feasible optoelectronic technologies in order to produce Si-based photonic devices. As progress is made on a variety of photonic networks, such as the optical cross-connects (OXCs), the dense wavelength division multiplexing (DWDM) and other kinds of optical networks, large-scale optical matrix switches are indispensable. These networks can provide flexible operations such as routing, restoration, and reconfiguration in the DWDM
systems.
In long-haul transport networks, a hybrid technology is employed and traffic is transported optically, but most of operations are implemented as electronic systems. The switching and communication need to convert optical streams to electronic signals and then convert these signals to optical streams. The optical-electrical-optical (0E0) conversion based networks suffer from several inherent deficiencies such as high cost, lack of scalability and performance limitation. In local area networks, optical switching is an attractive candidate switching and communication. The optical matrix switch is one of most important components in constructing the photonic switching systems including the optical DWDM networks, the OXCs and multi-channel testing systems. The maximum number of subscribers will strongly depend on the properties of the individual matrix switches. The requirements for the implementation of such matrix switches in a system are low loss and low crosstalk. Furthermore, the switch points of the devices should have uniform switch characteristics and stable operating characteristics. Today, research and development of optical matrix switches have had significant progress with planar optical waveguides and had some applications in fiber-optic communication systems.
They are based on both the thermo-optic (TO) waveguides and the electro-optic (E0) waveguides.
Typical contributions are made by the US Lynx Photonic Networks and the Japan's NTT.
The TO matrix switch and the EO matrix switch are two promising candidates for the future photonic switching systems and the reconfigurable optical interconnects of switching systems. The former is generally based on silica-on-silicon waveguides or polymeric waveguides, while the latter is generally based on LiNb03 diffused waveguides. For the large scale optical matrix switches, the silica-based planar lightwave circuits (PLC's) is the most promising technical approach because it has lowest propagation loss, reliable fabrication technique, easy mass-production, polarization insensitivity, and easy interfacing with fibers. The nodes of the optical matrix switches are the 2x2 switch units that can be either Mach-Zehnder interferometer-type or digital-optical switch. The TO waveguide devices using silica-on-silicon waveguides have shown an exciting advantage over the currently used mechanical and bulk optic devices in fiber-optic communications because of their great flexibility in fabrication and processing as well as speedy operations than the mechanical ones. The EO
waveguide devices using diffused LiNb03-based waveguides have also presented a promising application in the future with its high-speed operation, low loss and mature manufacturing technology.
Most of optical switching devices in production today use an opto-mechanical means to implement optical steering. This is accomplished through the separation, or the alignment, or the reflection of the light beam by an opto-mechanical driven mirror. These designs offer good optical performance, but have some drawbacks. One is slow speed.
The typical settling times for switching are from lOms to 100ms. Even for some large-scale optical matrix switches, the setting times for switching are from 100's of milliseconds to 1 second. The other disadvantage of the opto-mechanical switches includes the noise and size. These disadvantages could be acceptable in the conventional small-scale photonics networks, but today's high capacity communications really could not continue to suffer from these out-of age properties. To overcome some of these limitations, non-mechanical and no-moving-part optical matrix switch now reaching the market can use a variety of design concepts.
Totally there are two kinds of no-moving-part 2x2 optical waveguide switches:
one uses the Mach-Zehnder interferometer (MZI) configuration and the other one is digital optical switch. 1 x2 and 2x2 switches are basic units for building the large-scale matrix switches and optical crossconnect (OXC) systems. The former has two advantages: low power consumption and low access loss, and a disadvantage: wavelength sensitive. The latter has two disadvantages: high power consumption and high access loss, and an advantage: wavelength insensitive. Thereby, the TOS using the MZI
configuration is suitable for low thermal coefficient (dn/dT) and high reliability material such as PECVD-based silica-on-silicon and EOS using the MZI configuration currently uses the LiNb03 diffused waveguides and will probably employ the reliable EO polymers in the future.
Summary of the Invention An NxN optical waveguide matrix switch using double-size butterfly network of 2x2 switching units is proposed in this invention. In the conventional NxN matrix switches, generally N to 2N switching stages and an NxN to 2NxN matrix of switching units are required to meet the optical signal communication between the input ports and the output ports. As a result, the device size, the complexity and the propagation loss are headache problems in the large-scale matrix switches. In this invention, the NxN
optical waveguide matrix switch uses a double size butterfly network where the number of switching stages is logz + 2 , so not only can nonblocking degree and measurability be increased, but also both the number of 2x2 switching units and the number of switching operation stages can be decreased. More important is the number of switching operation stages is significantly reduced compared with what is used in the conventional optical matrix switches.
Especially in the large-scale NxN matrix switches, this advantage becomes more apparent. Thus, the propagation loss can be reduced to a much lower value than the conventional devices and the large-scale optical matrix switches can be built in the same size of wafers. Generally there are two kinds of 2x2 waveguide optical switches: Mach-Zehnder interferometer (MZI) switch and digital optical switch (DOS). The former has two main advantages: lower power consumption and lower access loss, and a main disadvantage: wavelength sensitive. The latter has a main advantage:
wavelength insensitive and two critic disadvantages: higher power consumption and higher access loss. The power consumption, the propagation loss and the wavelength sensitivity are three most important issues of a large-scale optical matrix switch based on an accumulation of all the switching units and optical path that optical signals pass through.
Therefore, the MZI type optical switch is preferred to use as a switching unit because it can directly meet two issues of the large-scale optical matrix switches with its two main advantages. Whereas, its disadvantage: wavelength sensitive can be solved by another way in this invention. If the wavelength sensitive 2x2 switching units such as MZI type optical switches are used as the switching units of the NxN optical waveguide matrix switch, at the different switching stages, the 2x2 switching units are designed of different central wavelengths to uniformly cover the whole wavelength range in this invention. So, the wavelength sensitivities among all the switching stages can be compensated for one another. Finally the performance of NxN optical matrix switch based on this invention becomes wavelength insensitive.
In a desirable embodiment according to the present invention, a 2N size full butterfly network is divided into two parts: one is used to perform an NxN switching operation and the other is used to have a high isolation outputs between any two adjacent ports and test output performance at off state. In addition, the two separate parts of butterfly network for switching operations and testing performance at the OFF-state can balance the optical paths and switching stages during it is performing the operations. In every switching unit, the MZI type switch is preferred and designed to work at different wavelengths to decrease the wavelength sensitivity of the whole NxN optical matrix switch based on this invention.
Brief Descriution of the Drawing FIG. 1 is the configuration of an NxN optical matrix switch using the double-size mufti-stage butterfly network of 2x2 switch units: (a) the top view and the construction of the NxN optical matrix switch and (b) the cross-section view. This structure comprises two parts: the testing area of NxN and the switching area of NxN.
FIG. 2 is the configuration and operation principle of a 4x4 optical matrix switch using 8x8 butterfly networks: (a) the complete construction, (b) the basic linking principle, and (c) an operation example.
FIG. 3 is the topology of 8-size butterfly network configuration: (a) the one-stage construction and (b) the three-stage construction.
FIG. 4 is the detailed structures of two kinds of Mach-Zehnder interferometer type 2x2 switch as a switch unit or node of the butterfly network configuration: (a) the normal Mach-Zehnder interferometer and (b) the inverse Mach-Zehnder interferometer.
Detailed Description of the Invention The matrix switches must be nonblocking, that means every input must have the possibility to be interconnected to every output. In order to achieve this point, a design of matrix switch must meet a rearrangeable nonblocking network of permutation nodes involving the smallest possible number of switching units. Thus, a nonblocking optical matrix switch is a communication network between N input ports and N output ports. In fact, various communication networks have been studied and used for a long time in the conventional electrical communication systems. There are several popular networks for nonblocking communications of both electrical and optical networks such as crossbar, perfect shuffle, crossover, and butterfly. The crossbar network needs N
switching stages for the nonblocking communication between N input ports and N output ports, which generally causes a higher propagation loss for the large-scale matrix switches. The links among the switching points, however, are simple and easy to be built with optical technique, so it is widely used in today's optical matrix switches. The latter three kinds of networks have a common advantage that they all only need logz + 1 switching stages for the nonblocking communications between N input ports and N output ports, but they have different structures of links among all the switching points, and these three structures of links have different complexities and difficulties in design and fabrication in optical devices. Among these three networks, the butterfly has been demonstrated to have the most regular links and is the easiest to be designed and fabricated in both free-space optical approaches and the PLCs. Especially, as described above, the PLCs technique is most promising in the fiber-optic communication systems.
Figure 1 is the NxN optical waveguide matrix switch built with a double-size butterfly network where Fig. 1 (a) is the top view and Fig. 1 (b) the cross-section view. This NxN
optical matrix switch comprises a substrate 20, cladding 22, active switching units 24a, 24b, 24c and 24d, passive switching units 26a, 26b, 26c and 26d, waveguide links 28a, 28b and 28c for the active switching units, waveguide links 30a, 30b and 30c for the passive switching units, electrodes 32a, 32b, 32c and 32d deposited on the active switching units and electrodes 34a, 34b, 34c and 34d for the passive switching units. As shown in Fig. 1 (a), the butterfly structure of the NxN optical matrix switch based on this invention is divided into two areas: one is used to implement the switching operations with external controls and called switching operation area and the other one is used to test optical performance at the OFF-state and balance the optical paths for the optical signals.
The active switching units 24a through 24d are used for the switching operations area, so the electrodes 32a through 32d are required. The passive switching units 26a through 26d are used to pass through optical signals at the OFF-state, so the electrodes 34a through 34d are not required or optional. In the switching operations area, the input ports at the input end are labeled as So , S, , through SN_, , and the output ports at the output end are labeled as So , S; , through SN_, . In the testing area, the input ports at the input end are labeled as To , T, , through TN_, , and the output ports at the output end are labeled as To , T,' , through TN_, . In fact, the switching operations area and the testing area are symmetric with each other if the electrodes are deposited for both the switching operations area and the testing area. So, these two areas are equivalent to each other. In other words, the switching operations area can be used as the testing area and the testing area used as the switching operations area. From the viewpoint of functions, the switching operations area is core part of the optical matrix switch based on this invention.
Namely, in the switching operations area, each switching unit has to have two switching options for any input optical signal, so the modulating electrodes 32a through 32d are necessary for each unit to implement the switching operations. Whereas, the testing area is used for testing the isolation and uniformity among all the output ports at the OFF-state of the whole system and balancing the optical paths among all the optical links during the optical switching units are operating. Namely, in the testing area, each switching unit does not have to have two switching options, but one operation state at the OFF-state. So, once the testing area is specialized, all the electrodes 34a through 34d for the passive switching units can be ignored, but the optical structure used in each switching unit should be the same as the counterpart of the switching operations area. Figure illustrates an NxN optical matrix switch using a double-size butterfly network as depicted in this invention when N=4. In other words, a 4x4 optical matrix switch using an 8x8 butterfly network. Figure 2(a) shows the complete link construction of the 4x4 optical matrix using 8x8 butterfly network based on this invention. The input ports of the switching operations area are So , S, , SZ and S3 , and the output ports of the switching operations area are So , S; , Sz and S3 . In the same manner, the input ports of the testing area are To , T, , TZ and T3 , and the output ports of the testing area are To , T' , Tz and T3 .
The four columns of switching units 24a, 24b, 24c and 24d in the switching operations area and the four columns of switching units 26a, 26b, 26c and 26d in the testing area are connected into a 8x8 butterfly network by the three-stages of links 28a, 28b and 28c in the switching operations area and the three stages of links 30a, 30b and 30c in the testing area. Figure 2(b) illustrates the operating principle of the 4x4 optical matrix switch using 8x8 butterfly network based on this invention. In the practical operations for all the optical signals: 36a, 36b, 36c and 36d, not can all the links be used. Only some of them can be used like the solid lines of Fig. 2(b) and some of them can never be used and are always at the idle state like the dashed lines of Fig. 2(b). If the four optical signals 36a, 36b, 36c and 36d are launched into four input ports: So , Sl , SZ and S3 , respectively, they have to pass through the first column 24a of switching units of the switching area first at the OFF-state of the switching units 24a, i.e., no modulating effects are applied onto these switching units. Then, these four optical signals: 36a, 36b, 36c and 36d will be butterfly connected to the second column 26b of the switching units of the testing area by the linking stage 28a. Forward butterfly connections to the successive stages 30b and 30c of links are performed only in the testing area and the OFF-state switching operations in the testing area are performed by the second column 26b, the third column 26c and the fourth column 26d of the switching units, respectively. Finally, as shown in Fig. 2(b), these four optical signals are output in the inverse order of the input. Thus, all the straight links (the dashed lines) of the testing area cannot be used and only the butterfly links (the solid lines) are used. Even the first column 26a of the switching units of the testing area and the first stage 30a of all the links from these switching units are always in the idle state. Note that all the optical signals must be coming out from the output ports of the testing area if no modulating effect applied onto the switching units of the switching area, so any linking path of an optical signal from one input port to one output port of the switching operations area must be based on the modulating effect applied onto the switching units for switching operations. For example, as shown in Fig. 2(c), if the switching units having hatched lines indicate the modulated state, i.e., the first switching unit from top of units 24a, the first switching unit from top of units 24b, the third switching unit from top of units 24c and the third switching unit from top of units 24d, the optical signal 36a launched into the input port So of this 4x4 optical matrix switch will be coming out at the output port Sz . As depicted in Fig. 2(c), the operating process has been marked with the bigger lines. The same optical signal 36a can also have other output choices by modulating different group of switching units, so one optical signal can choose any one among the four output ports. In the same manner, all other optical signals: 366, 36c and 36d have the same four output choices as the optical signal 36a.
Even an NxN optical matrix switch can be constructed in this style. Therefore, an NxN
optical matrix switch can be implemented based on the operation principle defined by this invention.
The waveguide switch based on the Mach-Zehnder interferometer (MZI) configuration contains two 3d8 directional couplers connected by two waveguide arms. This kind of switches basically exploits the phase property of the light. The input light is split and sent to two separate waveguide arms by the first 3dB directional coupler, then combined and split one last time by the second 3dB directional coupler. One or two of the waveguide arms are modulated to produce a difference of optical path length between these two waveguide arms. The modulating means can be either thermo-optic (TO) or electro-optic (E0). If these two optical paths are the same length, light chooses one exit, if they are different it chooses the other. As a 2x2 switch, for one input optical signal, the isolation between two output ports is important because it directly determines the isolation between two output ports for the same input optical signal. The isolation is strongly dependent of the coupling ratio of the two 3dB directional couplers. Namely, the closer to 50% the coupling ratio of the 3dB directional coupler is, the higher the isolation of the 2x2 switch is, and further more the higher the ON/OFF extinction ratio of each output port is. In theory, if the coupling ratio of the 3dB coupler is exactly 50%
(i.e., -3dB), the isolation between two output ports should be infinity. In fact, no perfect 3dB
directional coupler exists because the errors in both design and fabrication, especially in fabrication, are not avoidable. So, a real isolation of around 20 dB is not easy for any 2x2 waveguide switch having an MZI configuration to be achieved. In the real fiber-optic communications, not only isolation of more than 20 dB is popularly required for the protection switching systems, but also is the isolation of more than 30 dB, even more than 40 dB is always and strictly required for some more important DWDM
networks such as typical optical add/drop multiplexing systems. Fortunately, the NxN
matrix switches generally have several stages of MZI operations, so the isolation is easy to meet.
The butterfly network has a size of N = 2" where N indicates the network size (the port number) and n the number of linking stages. The butterfly network is suitable for various multistage networks (MN) in which the link interconnection patterns often include sizes N , N l 2 , N l 4 , etc. The perfect shuffle, the crossover, and the butterfly networks are topologically equivalent because each node has two fan-in and two fan-out lines. For a one-stage butterfly network, as shown in Fig. 3(a), with two fan-in lines or two fan-out lines at each node, one is a straight interconnect line and the other is a butterfly interconnect line. We define the address numbers of the nodes with straight lines and butterfly interconnect lines as KS , and Kb ( Ks, Kb = 0,1,..., N -1) , respectively, on the output end and as k on the input end. For the butterfly network, we have the following relations:
Ks = k (k = 0,1,..., N -1) ( 1 ) _ k+Nl2 (k < Nl2) Kb k-Nl2 (N/2 <_ k < N) (2) To analyze and compare the construction features of the butterfly network, let us define 8 = K~ - k , which represents the interconnect angles of link lines from the input end to the output end. Then, we have, from Eqs. (1) and (2), 85 = Ks - k = 0 (k = 0,1,..., N -1) (3) N l 2 (k < N l 2) (4) Sb =Kn-k=
-Nl2 (N/2 <- k < N) Note from Eqs. (3) and (4) that not only the interconnect angles of the straight interconnect lines ( 8S ) but also those of the butterfly interconnect lines ( 8b ) are independent of the number of address nodes k ; that is, not only all the straight interconnect lines but also the butterfly interconnect lines are parallel, which is also easy to see in Fig. 3(a). In other words, the butterfly networks have more architectural advantages, which is important for the implementation of the PLCs.
As mentioned above, the normal butterfly network has the same advantages as other two networks: perfect shuffle and crossover. The first is that loge + 1 operation stages are needed for an N port network. The second is that there is a connection line between any port at input end and any port at output end. A normal butterfly network with N=8 is shown in Fig. 3(b). Then we have the following mathematical relation to describe the topology of this network. The topology of a multistage network is defined by three physical parameters: (1) the type of switching element comprising a node, (2) the number of node stages, and (3) the link interconnections provided between adjacent node stages.
Both fully connected data butterfly networks with N nodes require loge + 1 node stages, in which each node stage is labeled in sequence from 0 to loge . The input (leftmost) node stage is assigned label 0 , and the output (rightmost) node stage is assigned label logz . Each switching unit (node) in a particular node stage is assigned a unique physical address with an address bit (K;_" K;_Z,..., Ko) , where i = loge . The physical address identifies the unit's relative location within the node stage, with the top node labeled as 0 and the bottom node labeled as N -1.
In the butterfly networks a pair of interconnections provided by the links within link stage i can be mapped as B° and B;' . These points represent the straightforward connection and the butterfly connection, respectively, and they map a node (K;_,,...,K;,...,Ko); in node stage i two nodes in node stage i+1. The relationships between the node in node stage i and the two nodes in node stage i + 1 are described by B,,°(K;_,K;_Z,...,K,_;+,,...,Ko) _ (K;K;_,,...,K,_;+I,...,...,0,...,K,_;_,,...,K,);+, for link (K;_,,K;_Z,...,K,);+, , 0 5 i < 1, (5) B; (K;_,K;_z,...,K,_;+,,...,Ko) _ (K;K;_,,...,K,_;+,,...,...,1,...,K,_;_,,...,K,);+, for link (K;_,, K;_z,..., K, ).+, , 0 <_ i < 1, (6) Then for the (i + 1)th stage the link relationship of K;+, is shown by K° , = K; , K; = 0,1,..., N -1, 0 <_ i < 1, (7) K; +Nl2',[(j-1)Nl2' < K;+, <_ jNl2']
K'+' = K~ _ ~r/2'~~jNl2' <_ K,+, < jNl2'~
j =1,2,...,2') . (8) As mentioned above, every node of the butterfly network has two fan-in lines and two fan-out lines at all the operating stages, and every node of input end has one fan-in line and two fan-out lines, and every node of output end has two fan-in lines and one fan-out line. Each node indicates a switching unit and needs a 2x2 or 1 x2 switch to perform its options of links. As well known, totally there are two kinds of 2x2 optical waveguide switches: the MZI type and the DOS. The former has two main advantages: lower power consumption and lower access loss, and a main disadvantage: wavelength sensitive. The latter has a main advantage: wavelength insensitive and two main disadvantages: higher power consumption and higher access loss. The power consumption, the propagation loss and the wavelength sensitivity are three most important issues of a large-scale optical matrix switch based on an accumulation of all the switching units and the optical paths that optical signals pass through. Thus, the MZI type optical switch is preferred to use as a switching unit because it can directly meet two issues of the large scale optical matrix switches with its two main advantages and its disadvantage: wavelength sensitive can be solved by another way in this invention. If the wavelength sensitive 2x2 switching units such as MZI type optical switches are used as the switching units of the NxN
optical waveguide matrix switch, at the different switching stages, the 2x2 switching units are designed for different central wavelengths to uniformly cover the whole wavelength g range. So, the wavelength sensitivities among all the switching stages can be compensated for one another. Finally the performance of NxN optical matrix switch based on this invention becomes wavelength insensitive. In addition, in order to balance the switching operations at different switching stages, two kinds of MZI
switches: the normal type and the inverse type are suggested to alternatively use.
Figure 4(a) and Figure 4(b) show two types of MZI type switches: the normal type and the inverse type. As shown in Fig. 4(a), the normal MZI unit is composed of two 3dB
directional couplers 38a and 38b connected by two waveguide arms. One heater deposited on one of two arms, which is used to modulate the optical path of MZI unit. In this MZI unit, two waveguide arms have the equal length, so it is called normal MZI
configuration. Two input ports are labeled as 42a and 42b, and two output ports as 44a and 44b. If an optical signal 46a is launched into the input port 42a, it is split into two parts at 50% coupling ratio by the first 3d8 directional coupler 38a, then these two parts are combined into one optical signal again by the second 3dB directional coupler 38b. If the heater (or electrode) 40 is not activated (at the OFF-state), this combined optical signal is sent to the output port 44b by the second 3d8 directional coupler.
This coupling process at the OFF-state is the same as one 100% directional coupler because these two waveguide arms have an equal optical length and no extra optical phase change is induced. So, this type of MZI is called normal configuration. If the heater (or electrode) 40 is activated by electrical power (or electric field) to produce an optical phase change of ~c (at the ON-state), this optical signal 46a is sent to the output port 44a. In the same manner, if an optical signal 46b is launched into input port 42b, it will come out at the output port 44a at the OFF-state and will come out at the output port 44b at the ON-state.
In an inverse MZI configuration, as shown in Fig. 4(b), between two 3dB
directional couplers 48a and 48b, two waveguide arms have phase difference of ~. So, this type of MZI is called as inverse MZI configuration. A heater (or electrode) 50 is deposited on one of two waveguide arms. Two input ports are labeled as 52a and 52b, and two output ports as 54a and 54b. If an optical signal 56a is launched into the input port 52a, it is split into two parts at 50% coupling ratio by the first 3dB directional coupler 48a and then these two parts are combined into one optical signal again by the second 3d8 directional coupler 48b. If the heater (or electrode) 50 is not activated (at the OFF-state), there has been an optical phase difference of ~ between two waveguide arms, so the combined optical signal is sent to output port 54a. This coupling process is exactly the inverse to one 100% directional coupler, so it is called inverse MZI configuration. If the heater (or electrode) 50 is activated by electrical power (or electric field) to produce an extra optical phase change of ~ (at the ON-state), this combined optical signal 56a is sent the output port 54b by the second 3dB directional coupler 486. In the same manner, if an optical signal 56b is launched into input port 52b, it will come out at the output port 54b at the OFF-state and will come out at the output port 54a at the ON-state.
Finally two useful papers for understanding the topology of "butterfly network" are the following:
~ Butterfly interconnection implementation for n-bit parallel full-adder and subtracter by Sun, et al., Optical Engineering, Vol. 31, No. 7, July 1992, pp.
1575;
~ Butterfly interconnection networks and their applications in information processing and optical computing: application in fast Fourier transform-based optical information processing by Sun, et al., Applied Optics, Vol. 32, No.
35, December 1993, pp. 7184-7193.
Backsround of the Invention Today, the rapid development and applications of fiber-optic telecommunication systems are stimulating various photonics networks based on some new microstructure optoelectronic technologies instead of mechanical individual devices. Among various microstructure optoelectronic technologies, integrated optics represents a promising strategy in this field. One implementation of this strategy relies on the integration of optoelectronic interconnects on a host Si substrate, and thus requires feasible optoelectronic technologies in order to produce Si-based photonic devices. As progress is made on a variety of photonic networks, such as the optical cross-connects (OXCs), the dense wavelength division multiplexing (DWDM) and other kinds of optical networks, large-scale optical matrix switches are indispensable. These networks can provide flexible operations such as routing, restoration, and reconfiguration in the DWDM
systems.
In long-haul transport networks, a hybrid technology is employed and traffic is transported optically, but most of operations are implemented as electronic systems. The switching and communication need to convert optical streams to electronic signals and then convert these signals to optical streams. The optical-electrical-optical (0E0) conversion based networks suffer from several inherent deficiencies such as high cost, lack of scalability and performance limitation. In local area networks, optical switching is an attractive candidate switching and communication. The optical matrix switch is one of most important components in constructing the photonic switching systems including the optical DWDM networks, the OXCs and multi-channel testing systems. The maximum number of subscribers will strongly depend on the properties of the individual matrix switches. The requirements for the implementation of such matrix switches in a system are low loss and low crosstalk. Furthermore, the switch points of the devices should have uniform switch characteristics and stable operating characteristics. Today, research and development of optical matrix switches have had significant progress with planar optical waveguides and had some applications in fiber-optic communication systems.
They are based on both the thermo-optic (TO) waveguides and the electro-optic (E0) waveguides.
Typical contributions are made by the US Lynx Photonic Networks and the Japan's NTT.
The TO matrix switch and the EO matrix switch are two promising candidates for the future photonic switching systems and the reconfigurable optical interconnects of switching systems. The former is generally based on silica-on-silicon waveguides or polymeric waveguides, while the latter is generally based on LiNb03 diffused waveguides. For the large scale optical matrix switches, the silica-based planar lightwave circuits (PLC's) is the most promising technical approach because it has lowest propagation loss, reliable fabrication technique, easy mass-production, polarization insensitivity, and easy interfacing with fibers. The nodes of the optical matrix switches are the 2x2 switch units that can be either Mach-Zehnder interferometer-type or digital-optical switch. The TO waveguide devices using silica-on-silicon waveguides have shown an exciting advantage over the currently used mechanical and bulk optic devices in fiber-optic communications because of their great flexibility in fabrication and processing as well as speedy operations than the mechanical ones. The EO
waveguide devices using diffused LiNb03-based waveguides have also presented a promising application in the future with its high-speed operation, low loss and mature manufacturing technology.
Most of optical switching devices in production today use an opto-mechanical means to implement optical steering. This is accomplished through the separation, or the alignment, or the reflection of the light beam by an opto-mechanical driven mirror. These designs offer good optical performance, but have some drawbacks. One is slow speed.
The typical settling times for switching are from lOms to 100ms. Even for some large-scale optical matrix switches, the setting times for switching are from 100's of milliseconds to 1 second. The other disadvantage of the opto-mechanical switches includes the noise and size. These disadvantages could be acceptable in the conventional small-scale photonics networks, but today's high capacity communications really could not continue to suffer from these out-of age properties. To overcome some of these limitations, non-mechanical and no-moving-part optical matrix switch now reaching the market can use a variety of design concepts.
Totally there are two kinds of no-moving-part 2x2 optical waveguide switches:
one uses the Mach-Zehnder interferometer (MZI) configuration and the other one is digital optical switch. 1 x2 and 2x2 switches are basic units for building the large-scale matrix switches and optical crossconnect (OXC) systems. The former has two advantages: low power consumption and low access loss, and a disadvantage: wavelength sensitive. The latter has two disadvantages: high power consumption and high access loss, and an advantage: wavelength insensitive. Thereby, the TOS using the MZI
configuration is suitable for low thermal coefficient (dn/dT) and high reliability material such as PECVD-based silica-on-silicon and EOS using the MZI configuration currently uses the LiNb03 diffused waveguides and will probably employ the reliable EO polymers in the future.
Summary of the Invention An NxN optical waveguide matrix switch using double-size butterfly network of 2x2 switching units is proposed in this invention. In the conventional NxN matrix switches, generally N to 2N switching stages and an NxN to 2NxN matrix of switching units are required to meet the optical signal communication between the input ports and the output ports. As a result, the device size, the complexity and the propagation loss are headache problems in the large-scale matrix switches. In this invention, the NxN
optical waveguide matrix switch uses a double size butterfly network where the number of switching stages is logz + 2 , so not only can nonblocking degree and measurability be increased, but also both the number of 2x2 switching units and the number of switching operation stages can be decreased. More important is the number of switching operation stages is significantly reduced compared with what is used in the conventional optical matrix switches.
Especially in the large-scale NxN matrix switches, this advantage becomes more apparent. Thus, the propagation loss can be reduced to a much lower value than the conventional devices and the large-scale optical matrix switches can be built in the same size of wafers. Generally there are two kinds of 2x2 waveguide optical switches: Mach-Zehnder interferometer (MZI) switch and digital optical switch (DOS). The former has two main advantages: lower power consumption and lower access loss, and a main disadvantage: wavelength sensitive. The latter has a main advantage:
wavelength insensitive and two critic disadvantages: higher power consumption and higher access loss. The power consumption, the propagation loss and the wavelength sensitivity are three most important issues of a large-scale optical matrix switch based on an accumulation of all the switching units and optical path that optical signals pass through.
Therefore, the MZI type optical switch is preferred to use as a switching unit because it can directly meet two issues of the large-scale optical matrix switches with its two main advantages. Whereas, its disadvantage: wavelength sensitive can be solved by another way in this invention. If the wavelength sensitive 2x2 switching units such as MZI type optical switches are used as the switching units of the NxN optical waveguide matrix switch, at the different switching stages, the 2x2 switching units are designed of different central wavelengths to uniformly cover the whole wavelength range in this invention. So, the wavelength sensitivities among all the switching stages can be compensated for one another. Finally the performance of NxN optical matrix switch based on this invention becomes wavelength insensitive.
In a desirable embodiment according to the present invention, a 2N size full butterfly network is divided into two parts: one is used to perform an NxN switching operation and the other is used to have a high isolation outputs between any two adjacent ports and test output performance at off state. In addition, the two separate parts of butterfly network for switching operations and testing performance at the OFF-state can balance the optical paths and switching stages during it is performing the operations. In every switching unit, the MZI type switch is preferred and designed to work at different wavelengths to decrease the wavelength sensitivity of the whole NxN optical matrix switch based on this invention.
Brief Descriution of the Drawing FIG. 1 is the configuration of an NxN optical matrix switch using the double-size mufti-stage butterfly network of 2x2 switch units: (a) the top view and the construction of the NxN optical matrix switch and (b) the cross-section view. This structure comprises two parts: the testing area of NxN and the switching area of NxN.
FIG. 2 is the configuration and operation principle of a 4x4 optical matrix switch using 8x8 butterfly networks: (a) the complete construction, (b) the basic linking principle, and (c) an operation example.
FIG. 3 is the topology of 8-size butterfly network configuration: (a) the one-stage construction and (b) the three-stage construction.
FIG. 4 is the detailed structures of two kinds of Mach-Zehnder interferometer type 2x2 switch as a switch unit or node of the butterfly network configuration: (a) the normal Mach-Zehnder interferometer and (b) the inverse Mach-Zehnder interferometer.
Detailed Description of the Invention The matrix switches must be nonblocking, that means every input must have the possibility to be interconnected to every output. In order to achieve this point, a design of matrix switch must meet a rearrangeable nonblocking network of permutation nodes involving the smallest possible number of switching units. Thus, a nonblocking optical matrix switch is a communication network between N input ports and N output ports. In fact, various communication networks have been studied and used for a long time in the conventional electrical communication systems. There are several popular networks for nonblocking communications of both electrical and optical networks such as crossbar, perfect shuffle, crossover, and butterfly. The crossbar network needs N
switching stages for the nonblocking communication between N input ports and N output ports, which generally causes a higher propagation loss for the large-scale matrix switches. The links among the switching points, however, are simple and easy to be built with optical technique, so it is widely used in today's optical matrix switches. The latter three kinds of networks have a common advantage that they all only need logz + 1 switching stages for the nonblocking communications between N input ports and N output ports, but they have different structures of links among all the switching points, and these three structures of links have different complexities and difficulties in design and fabrication in optical devices. Among these three networks, the butterfly has been demonstrated to have the most regular links and is the easiest to be designed and fabricated in both free-space optical approaches and the PLCs. Especially, as described above, the PLCs technique is most promising in the fiber-optic communication systems.
Figure 1 is the NxN optical waveguide matrix switch built with a double-size butterfly network where Fig. 1 (a) is the top view and Fig. 1 (b) the cross-section view. This NxN
optical matrix switch comprises a substrate 20, cladding 22, active switching units 24a, 24b, 24c and 24d, passive switching units 26a, 26b, 26c and 26d, waveguide links 28a, 28b and 28c for the active switching units, waveguide links 30a, 30b and 30c for the passive switching units, electrodes 32a, 32b, 32c and 32d deposited on the active switching units and electrodes 34a, 34b, 34c and 34d for the passive switching units. As shown in Fig. 1 (a), the butterfly structure of the NxN optical matrix switch based on this invention is divided into two areas: one is used to implement the switching operations with external controls and called switching operation area and the other one is used to test optical performance at the OFF-state and balance the optical paths for the optical signals.
The active switching units 24a through 24d are used for the switching operations area, so the electrodes 32a through 32d are required. The passive switching units 26a through 26d are used to pass through optical signals at the OFF-state, so the electrodes 34a through 34d are not required or optional. In the switching operations area, the input ports at the input end are labeled as So , S, , through SN_, , and the output ports at the output end are labeled as So , S; , through SN_, . In the testing area, the input ports at the input end are labeled as To , T, , through TN_, , and the output ports at the output end are labeled as To , T,' , through TN_, . In fact, the switching operations area and the testing area are symmetric with each other if the electrodes are deposited for both the switching operations area and the testing area. So, these two areas are equivalent to each other. In other words, the switching operations area can be used as the testing area and the testing area used as the switching operations area. From the viewpoint of functions, the switching operations area is core part of the optical matrix switch based on this invention.
Namely, in the switching operations area, each switching unit has to have two switching options for any input optical signal, so the modulating electrodes 32a through 32d are necessary for each unit to implement the switching operations. Whereas, the testing area is used for testing the isolation and uniformity among all the output ports at the OFF-state of the whole system and balancing the optical paths among all the optical links during the optical switching units are operating. Namely, in the testing area, each switching unit does not have to have two switching options, but one operation state at the OFF-state. So, once the testing area is specialized, all the electrodes 34a through 34d for the passive switching units can be ignored, but the optical structure used in each switching unit should be the same as the counterpart of the switching operations area. Figure illustrates an NxN optical matrix switch using a double-size butterfly network as depicted in this invention when N=4. In other words, a 4x4 optical matrix switch using an 8x8 butterfly network. Figure 2(a) shows the complete link construction of the 4x4 optical matrix using 8x8 butterfly network based on this invention. The input ports of the switching operations area are So , S, , SZ and S3 , and the output ports of the switching operations area are So , S; , Sz and S3 . In the same manner, the input ports of the testing area are To , T, , TZ and T3 , and the output ports of the testing area are To , T' , Tz and T3 .
The four columns of switching units 24a, 24b, 24c and 24d in the switching operations area and the four columns of switching units 26a, 26b, 26c and 26d in the testing area are connected into a 8x8 butterfly network by the three-stages of links 28a, 28b and 28c in the switching operations area and the three stages of links 30a, 30b and 30c in the testing area. Figure 2(b) illustrates the operating principle of the 4x4 optical matrix switch using 8x8 butterfly network based on this invention. In the practical operations for all the optical signals: 36a, 36b, 36c and 36d, not can all the links be used. Only some of them can be used like the solid lines of Fig. 2(b) and some of them can never be used and are always at the idle state like the dashed lines of Fig. 2(b). If the four optical signals 36a, 36b, 36c and 36d are launched into four input ports: So , Sl , SZ and S3 , respectively, they have to pass through the first column 24a of switching units of the switching area first at the OFF-state of the switching units 24a, i.e., no modulating effects are applied onto these switching units. Then, these four optical signals: 36a, 36b, 36c and 36d will be butterfly connected to the second column 26b of the switching units of the testing area by the linking stage 28a. Forward butterfly connections to the successive stages 30b and 30c of links are performed only in the testing area and the OFF-state switching operations in the testing area are performed by the second column 26b, the third column 26c and the fourth column 26d of the switching units, respectively. Finally, as shown in Fig. 2(b), these four optical signals are output in the inverse order of the input. Thus, all the straight links (the dashed lines) of the testing area cannot be used and only the butterfly links (the solid lines) are used. Even the first column 26a of the switching units of the testing area and the first stage 30a of all the links from these switching units are always in the idle state. Note that all the optical signals must be coming out from the output ports of the testing area if no modulating effect applied onto the switching units of the switching area, so any linking path of an optical signal from one input port to one output port of the switching operations area must be based on the modulating effect applied onto the switching units for switching operations. For example, as shown in Fig. 2(c), if the switching units having hatched lines indicate the modulated state, i.e., the first switching unit from top of units 24a, the first switching unit from top of units 24b, the third switching unit from top of units 24c and the third switching unit from top of units 24d, the optical signal 36a launched into the input port So of this 4x4 optical matrix switch will be coming out at the output port Sz . As depicted in Fig. 2(c), the operating process has been marked with the bigger lines. The same optical signal 36a can also have other output choices by modulating different group of switching units, so one optical signal can choose any one among the four output ports. In the same manner, all other optical signals: 366, 36c and 36d have the same four output choices as the optical signal 36a.
Even an NxN optical matrix switch can be constructed in this style. Therefore, an NxN
optical matrix switch can be implemented based on the operation principle defined by this invention.
The waveguide switch based on the Mach-Zehnder interferometer (MZI) configuration contains two 3d8 directional couplers connected by two waveguide arms. This kind of switches basically exploits the phase property of the light. The input light is split and sent to two separate waveguide arms by the first 3dB directional coupler, then combined and split one last time by the second 3dB directional coupler. One or two of the waveguide arms are modulated to produce a difference of optical path length between these two waveguide arms. The modulating means can be either thermo-optic (TO) or electro-optic (E0). If these two optical paths are the same length, light chooses one exit, if they are different it chooses the other. As a 2x2 switch, for one input optical signal, the isolation between two output ports is important because it directly determines the isolation between two output ports for the same input optical signal. The isolation is strongly dependent of the coupling ratio of the two 3dB directional couplers. Namely, the closer to 50% the coupling ratio of the 3dB directional coupler is, the higher the isolation of the 2x2 switch is, and further more the higher the ON/OFF extinction ratio of each output port is. In theory, if the coupling ratio of the 3dB coupler is exactly 50%
(i.e., -3dB), the isolation between two output ports should be infinity. In fact, no perfect 3dB
directional coupler exists because the errors in both design and fabrication, especially in fabrication, are not avoidable. So, a real isolation of around 20 dB is not easy for any 2x2 waveguide switch having an MZI configuration to be achieved. In the real fiber-optic communications, not only isolation of more than 20 dB is popularly required for the protection switching systems, but also is the isolation of more than 30 dB, even more than 40 dB is always and strictly required for some more important DWDM
networks such as typical optical add/drop multiplexing systems. Fortunately, the NxN
matrix switches generally have several stages of MZI operations, so the isolation is easy to meet.
The butterfly network has a size of N = 2" where N indicates the network size (the port number) and n the number of linking stages. The butterfly network is suitable for various multistage networks (MN) in which the link interconnection patterns often include sizes N , N l 2 , N l 4 , etc. The perfect shuffle, the crossover, and the butterfly networks are topologically equivalent because each node has two fan-in and two fan-out lines. For a one-stage butterfly network, as shown in Fig. 3(a), with two fan-in lines or two fan-out lines at each node, one is a straight interconnect line and the other is a butterfly interconnect line. We define the address numbers of the nodes with straight lines and butterfly interconnect lines as KS , and Kb ( Ks, Kb = 0,1,..., N -1) , respectively, on the output end and as k on the input end. For the butterfly network, we have the following relations:
Ks = k (k = 0,1,..., N -1) ( 1 ) _ k+Nl2 (k < Nl2) Kb k-Nl2 (N/2 <_ k < N) (2) To analyze and compare the construction features of the butterfly network, let us define 8 = K~ - k , which represents the interconnect angles of link lines from the input end to the output end. Then, we have, from Eqs. (1) and (2), 85 = Ks - k = 0 (k = 0,1,..., N -1) (3) N l 2 (k < N l 2) (4) Sb =Kn-k=
-Nl2 (N/2 <- k < N) Note from Eqs. (3) and (4) that not only the interconnect angles of the straight interconnect lines ( 8S ) but also those of the butterfly interconnect lines ( 8b ) are independent of the number of address nodes k ; that is, not only all the straight interconnect lines but also the butterfly interconnect lines are parallel, which is also easy to see in Fig. 3(a). In other words, the butterfly networks have more architectural advantages, which is important for the implementation of the PLCs.
As mentioned above, the normal butterfly network has the same advantages as other two networks: perfect shuffle and crossover. The first is that loge + 1 operation stages are needed for an N port network. The second is that there is a connection line between any port at input end and any port at output end. A normal butterfly network with N=8 is shown in Fig. 3(b). Then we have the following mathematical relation to describe the topology of this network. The topology of a multistage network is defined by three physical parameters: (1) the type of switching element comprising a node, (2) the number of node stages, and (3) the link interconnections provided between adjacent node stages.
Both fully connected data butterfly networks with N nodes require loge + 1 node stages, in which each node stage is labeled in sequence from 0 to loge . The input (leftmost) node stage is assigned label 0 , and the output (rightmost) node stage is assigned label logz . Each switching unit (node) in a particular node stage is assigned a unique physical address with an address bit (K;_" K;_Z,..., Ko) , where i = loge . The physical address identifies the unit's relative location within the node stage, with the top node labeled as 0 and the bottom node labeled as N -1.
In the butterfly networks a pair of interconnections provided by the links within link stage i can be mapped as B° and B;' . These points represent the straightforward connection and the butterfly connection, respectively, and they map a node (K;_,,...,K;,...,Ko); in node stage i two nodes in node stage i+1. The relationships between the node in node stage i and the two nodes in node stage i + 1 are described by B,,°(K;_,K;_Z,...,K,_;+,,...,Ko) _ (K;K;_,,...,K,_;+I,...,...,0,...,K,_;_,,...,K,);+, for link (K;_,,K;_Z,...,K,);+, , 0 5 i < 1, (5) B; (K;_,K;_z,...,K,_;+,,...,Ko) _ (K;K;_,,...,K,_;+,,...,...,1,...,K,_;_,,...,K,);+, for link (K;_,, K;_z,..., K, ).+, , 0 <_ i < 1, (6) Then for the (i + 1)th stage the link relationship of K;+, is shown by K° , = K; , K; = 0,1,..., N -1, 0 <_ i < 1, (7) K; +Nl2',[(j-1)Nl2' < K;+, <_ jNl2']
K'+' = K~ _ ~r/2'~~jNl2' <_ K,+, < jNl2'~
j =1,2,...,2') . (8) As mentioned above, every node of the butterfly network has two fan-in lines and two fan-out lines at all the operating stages, and every node of input end has one fan-in line and two fan-out lines, and every node of output end has two fan-in lines and one fan-out line. Each node indicates a switching unit and needs a 2x2 or 1 x2 switch to perform its options of links. As well known, totally there are two kinds of 2x2 optical waveguide switches: the MZI type and the DOS. The former has two main advantages: lower power consumption and lower access loss, and a main disadvantage: wavelength sensitive. The latter has a main advantage: wavelength insensitive and two main disadvantages: higher power consumption and higher access loss. The power consumption, the propagation loss and the wavelength sensitivity are three most important issues of a large-scale optical matrix switch based on an accumulation of all the switching units and the optical paths that optical signals pass through. Thus, the MZI type optical switch is preferred to use as a switching unit because it can directly meet two issues of the large scale optical matrix switches with its two main advantages and its disadvantage: wavelength sensitive can be solved by another way in this invention. If the wavelength sensitive 2x2 switching units such as MZI type optical switches are used as the switching units of the NxN
optical waveguide matrix switch, at the different switching stages, the 2x2 switching units are designed for different central wavelengths to uniformly cover the whole wavelength g range. So, the wavelength sensitivities among all the switching stages can be compensated for one another. Finally the performance of NxN optical matrix switch based on this invention becomes wavelength insensitive. In addition, in order to balance the switching operations at different switching stages, two kinds of MZI
switches: the normal type and the inverse type are suggested to alternatively use.
Figure 4(a) and Figure 4(b) show two types of MZI type switches: the normal type and the inverse type. As shown in Fig. 4(a), the normal MZI unit is composed of two 3dB
directional couplers 38a and 38b connected by two waveguide arms. One heater deposited on one of two arms, which is used to modulate the optical path of MZI unit. In this MZI unit, two waveguide arms have the equal length, so it is called normal MZI
configuration. Two input ports are labeled as 42a and 42b, and two output ports as 44a and 44b. If an optical signal 46a is launched into the input port 42a, it is split into two parts at 50% coupling ratio by the first 3d8 directional coupler 38a, then these two parts are combined into one optical signal again by the second 3dB directional coupler 38b. If the heater (or electrode) 40 is not activated (at the OFF-state), this combined optical signal is sent to the output port 44b by the second 3d8 directional coupler.
This coupling process at the OFF-state is the same as one 100% directional coupler because these two waveguide arms have an equal optical length and no extra optical phase change is induced. So, this type of MZI is called normal configuration. If the heater (or electrode) 40 is activated by electrical power (or electric field) to produce an optical phase change of ~c (at the ON-state), this optical signal 46a is sent to the output port 44a. In the same manner, if an optical signal 46b is launched into input port 42b, it will come out at the output port 44a at the OFF-state and will come out at the output port 44b at the ON-state.
In an inverse MZI configuration, as shown in Fig. 4(b), between two 3dB
directional couplers 48a and 48b, two waveguide arms have phase difference of ~. So, this type of MZI is called as inverse MZI configuration. A heater (or electrode) 50 is deposited on one of two waveguide arms. Two input ports are labeled as 52a and 52b, and two output ports as 54a and 54b. If an optical signal 56a is launched into the input port 52a, it is split into two parts at 50% coupling ratio by the first 3dB directional coupler 48a and then these two parts are combined into one optical signal again by the second 3d8 directional coupler 48b. If the heater (or electrode) 50 is not activated (at the OFF-state), there has been an optical phase difference of ~ between two waveguide arms, so the combined optical signal is sent to output port 54a. This coupling process is exactly the inverse to one 100% directional coupler, so it is called inverse MZI configuration. If the heater (or electrode) 50 is activated by electrical power (or electric field) to produce an extra optical phase change of ~ (at the ON-state), this combined optical signal 56a is sent the output port 54b by the second 3dB directional coupler 486. In the same manner, if an optical signal 56b is launched into input port 52b, it will come out at the output port 54b at the OFF-state and will come out at the output port 54a at the ON-state.
Finally two useful papers for understanding the topology of "butterfly network" are the following:
~ Butterfly interconnection implementation for n-bit parallel full-adder and subtracter by Sun, et al., Optical Engineering, Vol. 31, No. 7, July 1992, pp.
1575;
~ Butterfly interconnection networks and their applications in information processing and optical computing: application in fast Fourier transform-based optical information processing by Sun, et al., Applied Optics, Vol. 32, No.
35, December 1993, pp. 7184-7193.
Claims (6)
1. An optical waveguide device comprising:
a substrate;
2N x (log~ + 2) switch units are arranged on said substrate as a 2N x (log~ +
a substrate;
2N x (log~ + 2) switch units are arranged on said substrate as a 2N x (log~ +
2) matrix to form double-size butterfly network (with 2N width);
a lower cladding layer and an upper cladding layer surrounding all the waveguides;
a heater (or modulating electrode) for every switch unit.
2. Based on claim 1, the waveguide switches with MZI configuration based on the present invention are intendly thermo-optically modulated by applying an electric power from the modulating electrode.
a lower cladding layer and an upper cladding layer surrounding all the waveguides;
a heater (or modulating electrode) for every switch unit.
2. Based on claim 1, the waveguide switches with MZI configuration based on the present invention are intendly thermo-optically modulated by applying an electric power from the modulating electrode.
3. Based on claim 1, the waveguide switches with MZI configuration based on the present invention can also be electro-optically modulated by applying an electric field from the modulating electrode.
4. The optical matrix switch with double-size butterfly network configuration based on this invention is nonblocking. One size: N x (log~ + 2) is used for switching operations and the other size: N x (log~ + 2) is used for testing at the OFF-state.
5. Both the normal MZI configuration and the inverse MZI configuration are used to balance the optical paths in the optical matrix switch based on this invention.
6. For a given wavelength range, the switch units at different switching operation stages are designed at different central wavelengths to uniform the wavelength dependence of optical performance of the optical matrix switch based on this invention.
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| CA 2361509 CA2361509A1 (en) | 2001-10-22 | 2001-10-22 | High-performance nxn optical matrix switch using double-size butterfly network of 2x2 switching units |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018013987A1 (en) * | 2016-07-14 | 2018-01-18 | Ayar Labs, Inc. | Laser module for optical data communication system |
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2001
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2018013987A1 (en) * | 2016-07-14 | 2018-01-18 | Ayar Labs, Inc. | Laser module for optical data communication system |
| US10771160B2 (en) | 2016-07-14 | 2020-09-08 | Ayar Labs, Inc. | Laser module for optical data communication system |
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