CA2386352A1 - Nxn optical matrix switch using modified cross-connect of 1xn switches - Google Patents

Abstract

An N×N optical matrix switch using a modified cross-connection of 1×N switches is proposed in this invention where the 1×N switch unit is built with the cascaded 2×2 switching nodes. In this invention, the optical outputs at the OFF-state are separated from the output ports at the ON-state where the switching operations are required.
Meanwhile, all the switching paths have to pass the same number of switching units and the same number of the activated switching units, so the high uniformity among all the optical paths can be implemented, and not only is a low power consumption required for a switching operation, but also the same power consumption is needed for all the switching operations. Especially this advantage is very apparent with optical integrated technology such as waveguides. If the wavelength sensitive switching nodes are used in this type of devices, at different operation codes of any optical path, the switching units are designed at different central wavelengths to uniformly cover the whole wavelength range so that the wavelength sensitivity of the whole device can be depressed. Therefore, the final performance of N×N optical matrix switch based on the present invention includes low insertion loss, low power consumption, high operating speed, compact device size, wavelength insensitivity and nonblocking.

Description

NxN Optical Matrix Switch Using Modified Cross-Connect of 1xN Switches Technical Field The present invention is an NxN optical matrix switch using a modified cross-connection of 1xN switches that are built with 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 excess loss. It relates to a high-isolation, low insertion loss, and low-power-consumption optical switch for an optical communication system, optical interconnects, optical cross-connect, and a fiber-optic network system.
Background of the Invention Today, the rapid development and applications of fiber-optic communication 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, 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 mufti-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.
Most of optical switching devices in production today, typically the fiber-optic switches, 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 such as low insertion loss and reliable operation as well as mature technologies for designing and manufacturing, but have two typical 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 is big size.
The advantages of the fiber-optic switches based on the opto-mechanical technologies come from the use of direct or indirect fiber-to-fiber couplings, and the disadvantages of this type of optical switches come from the use of moving-parts. These disadvantages, however, 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, one selection is taking the advantages and overcoming the disadvantages of this type of optical switches, and the other selection is looking for other technical approaches that can support non-mechanical and no-moving-part optical matrix switches. Today, research and development of optical matrix switches have shown that the planar optical waveguides and the micro-electro-mechanical system (MEMS) are two promising technologies for developing advanced optical communication components in the near future.
The thermo-optic (TO) matrix switch and the electro-optic (E0) matrix switch are two promising planar waveguide optical switches for the future photonic switching systems and the reconfigurable optical interconnection of switching systems. For the TO 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 or 1x2 switch units. 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 are generally based on diffused LiNb03-based waveguides and have also presented a promising application in the future with its high-speed operation, low loss and mature manufacturing technology.
Basically 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 (DOS). 1x2 and 2x2 switches are basic units for building the matrix switches and the 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 TO switch using the MZI configuration is suitable for low thermal coefficient (dn/dT) and high reliability material such as PECVD-based silica-on-silicon and EO switch using the MZI configuration currently uses the LiNb03 diffused waveguides and will probably employ the reliable EO polymers in the future. In addition, the MZI configuration can also be used to build 2x2 fiber-optic switches with the fiber couplers.
Summary of the Invention An NxN optical matrix switch using a modified cross-connection of 1xN switches is proposed in this invention where the 1xN switch unit is built with the cascaded 2x2 switching nodes. In the NxN matrix switches, the operating speed, the device size, the complexity, the power consumption, the wavelength sensitivity, the insertion loss, and the blocking are main problems. In this invention, the optical outputs at the OFF-state are separated from the output ports at the ON-state where the switching operations are required, so the isolation between two adjacent channels can be greatly improved.
Meanwhile, all the switching paths have to pass the same number of switching units and the same number of the activated switching units, so the high uniformity among all the optical paths can be achieved, and not only is a low power consumption required for a switching operation, but the same power consumption is needed for all the switching operations. Especially, in both the small-scale and the large-scale NxN matrix switches, this advantage is very apparent. As a result, the complexity, the insertion loss and the power consumption can be significantly reduced. This matrix switch structure is proposed based on physical approach where no-moving parts are included. Typically, the optical integrated circuits based on planar waveguide technology and the fiber-optic networks based on fiber technologies are two effective approaches. Thus the operating speed of the optical switches based on the present invention could be significantly increased.
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 insensitivity and two critic disadvantages: higher power consumption and higher access loss. The power consumption, the insertion loss and the wavelength sensitivity are three most important issues of an optical matrix switch. Therefore, the MZI type optical switch is preferred to use as a switching unit because it can directly meet two issues of the optical matrix switches with its two main advantages. Whereas, its disadvantage: wavelength sensitivity can be solved by another way in this invention as described above. If the wavelength sensitive 2x2 switching units such as MZI type optical switches are used as the switching units of the NxN optical matrix switch, at the different switching stages, the 2x2 switching units are designed at 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 includes low insertion loss, high-speed operation, low power consumption, wavelength insensitivity, compact device size and nonblocking.
In a desirable embodiment according to the present invention, 2N 1xN switches are used to form a nonblocking NxN matrix optical switch with a modified cross-connection where the 1xN switch is built with the cascaded 2x2 switches. In addition, the two groups of 1xN optical switches are specially distributed in one wafer to reduce the device size and complexity, and 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 Drawins FIG. 1 is the configuration of an NxN optical matrix switch using the magnified cross-connect of 1xN switches where the 1xN switch is built with the cascaded 2x2 switching nodes: (a) the top view and the construction of the NxN optical matrix switch and (b) the cross-section view.

FIG. 2(a) is the configuration of 1xN optical switch built with N-cascaded 2x2 Mach-Zehnder switching nodes and FIG. 2{b) is of Nxl optical switch built with N-cascaded 2x2 Mach-Zehnder switching nodes.
FIG. 3 is the configuration and operation principle of a 4x4 matrix optical switch using 8 1x4 optical switch that is built with 4 cascaded 2x2 Mach-Zehnder switching nodes: (a) the complete construction and (b) an example of the operation principle.
FIG. 4 is the definition of the modified optical cross-connect network for the NxN
matrix optical switch using the switching units.
FIG. 5 is the detailed structures of the Mach-Zehnder interferometer type 2x2 switch as a switching unit or node having the inverse operations used in the present invention: (a) is based on the thermal-optic modulation and (b) the electro-optic modulation.
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. To build an optical nonblocking communication between N input ports and N output pons directly using 2x2 switches as units, 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 different switching stages (from 2 to 2N) for the nonblocking communication between N input ports and N output ports among N channels, so both the insertion loss of devices and the power consumption for switching operation are not uniform and sometimes very high. 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 this advantage is transparent only in large-scale matrix communication and the links among all the switching points are complex.
Another interconnection structure in the nonblocking matrix communication is cross-connection between N 1xN switches and N Nxl switches wherein the main devices are 1xN or Nxl switches. Unlike opto-mechanical technology, the physical approaches having no moving parts such as the optical waveguide and fiber technologies are not easy to directly form a 1xN or Nxl switching units, the sole approach is using the N-cascaded structure of 2x2 or 1x2 switching units. The 2x2 or 1x2 switching units could be based on either the MZI or DOC configuration. In the present invention, a kind of nonblocking NxN optical matrix switches based on a modified one-stage optical cross-connect network between N
1xN
optical switches and N Nxl optical switches. Both the 1xN and Nxl optical switches are built with the N-cascaded 2x2 or 1x2 optical switches, and the MZI switching units are preferred in the optical matrix switches based on the present invention. With this kind of optical matrix structure, all the optical paths pass through the same number of 2x2 switching units and the same number of switching units is activated for all the switching operations. So, not only is the insertion loss low and uniform, but the low power consumption is required for switching operations.
Figure 1 is the NxN optical waveguide matrix switch built with a modified one-stage optical cross-connection between N 1xN optical switches and N Nxl optical switches 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, input switching units 24a, 24b, 24c and 24d, output switching units 26a, 26b, 26c and 26d, waveguide links 28a, 28b, 28c and 28d for connecting 24a-26a, 24b-26b, 24c-26c and 24d-26d, respectively, electrodes 30a, 30b, 30c and 30d deposited on the input switching units and electrodes 32a, 32b, 32c and 32d on the output switching units. As shown in Fig. 1 (a), the structure of the NxN optical matrix switch based on this invention is divided into two areas:
one is composed of N rows of 2x2 switching units and arranged in the upper site as input area and the other one is also composed of N rows of 2x2 switching units and arranged in the lower site as the output area. The switching units can be either the MZI or the DOS 2x2 (or 1x2) optical switches, but the switching units must operate bar-state switching at the OFF-state (the unmodulated state) and the cross-state switching at the ON-state (the modulated state). In each row of switching units of the input area, N
switching units are cascaded to form a 1xN optical switch, so N rows of switching units in the input area form N 1xN optical switches. In the same manner, in each row of switching units of the output area, N switching units are cascaded to form a Nx 1 optical switch, so N rows of switching units in the output area form N Nxl optical switches. Namely, 2 NxN
matrices of switching units form the input area and the output area. As shown in Fig.
1, the input switching units 24a through 24d are used to have the 1xN switching operations, so the electrodes 30a through 30d are required to make each switching unit have two output states. The output switching units 26a through 26d are used to have the Nxl switching operations, so the electrodes 32a through 32d are required to make each switching unit have two output states. Between the columns of the input area and the corresponding columns of the output area, there is a shift of one column in permutation so that the connection between the outputs of the switching units in the input area and the inputs of the switching units in the output area at the corresponding columns can be easy with cross-connect links 28a through 2$d. All the input ports of the input area are labeled as So , S, , through SN_, , and the output ports at the output area are labeled as So , S; , through SN_, . While all the output ports of the input area are labeled as To , T, , through TN_1, and the input ports at the output area are labeled as To , T' , through TN_1. As mentioned above, each row of the input matrix is composed of N cascaded 2x2 or 1x2 switching units to form a 1xN optical switch and each row of the output matrix is composed of N cascaded 2x2 or 1x2 switching units to form an Nxl optical switch as shown in Fig. 2(a) and Fig. 2(b), respectively. For a 1xN optical switch based on the present invention, as shown in Fig. 2(a), one input port can have N+1 output ports: one output port is the other end of the cascaded switching units line and the other N output ports are formed by the N switching units 24a through 24d and labeled as 34a through 34d. When an optical signal 38 is launched into the input port S , it can pass through all N cascaded switching units 24a through 24d and exits at the other end T of the N
cascaded switching units line if no optical switching unit is activated by a modulating process. Once one of the optical switching units 24a through 24d is activated by a modulating process, this optical signal 38 can exit at the expected output port of the activated switching unit to form an optical output signal 40. Note that the output end of the N-cascaded switching units line is not used as switching operations, but it can be used to test the performance of the lx:h1 optical switch at the OFF-state. That is why it is labeled as T . For an Nxl optical switch based on the present invention, as shown in Fig.

2(b), N+1 input ports correspond one output port. One input port is the input end of the N-cascaded switching units line and it is never used for the Nxl switching operations, but it can also be used to test the optical performance of the Nx 1 optical switch at the OFF-state, so it is labeled as T~ to match the output end S~ of the N-cascaded switching units line. The other N input ports are provided by the N switching units 26a through 26d and labeled as 36a through 36d. No matter which input port is used to launch an optical signal 42, it can not enter the N-cascaded switching units line and can only go to the unused output port (or called idle part) of the 2x2 switching unit where it is launched.
But, when a 2x2 switching unit is activated by a modulating process, it is immediately switched to the output port of the 2x2 switching unit that is connected to the N-cascaded switching units line and can pass through all left switching units of the line and exits at the only output end S~ of the N-cascaded switching units line to form the output optical signal 44. As shown in Fig. 1, in the NxN optical matrix switches based on the present invention, any optical communication between one input port and one output port is the path selection of the optical signal through a 1xN operation and an Nxl operation, so all the path selections of optical signals between the N input ports and the N
output ports pass the same number of the switching units (N+1) and the same number of switching units (2) is required to be activated for a switching operation. Even all the optical paths are almost same. Consequently, this kind of NxN optical matrix switches based on the present invention at least have two extra advantages in performance as well as bi-directional and nonblocking communication: 1) the uniform optical performance and 2) the lower power consumption, both of which are important issues for a matrix optical switch. Figure 3 illustrates an NxN optical matrix switch using a modified optical cross-connection between N 1xN optical switching units and N Nxl optical switching units as depicted in this invention when N=4. In other words, a 4x4 optical matrix switch is built by using the modified optical cross-connection between 4 1x4 optical switching units and 4 4x1 optical switching units. Figure 3(a) shows the linking construction of the modified optical cross-connection between 4 1x4 optical switches and 4 4x1 optical switches for building the 4x4 optical matrix switch based on this invention when the switch is at the OFF-state and Figure 3(b) shows the operating principle of the 4x4 matrix optical switch with an operating sample. The input ports of the input area are So , S, , S2 and S3 , and the output ports of the output area are Sa , S; , SZ and S3 . In the same manner, the output ports of the input area are To , T, , T2 and T3 , and the input ports of the output area are To , T,~ , Ti and T3 . The four columns of switching units 24a, 24b, 24c and 24d in the input area and the four columns of switching units 26a, 26b, 26c and 26d in the output area are arranged as two matrices, so the input area and the output area are called input and output matrices, respectively. These two matrices are connected by the links 28a, 28b, 2$c and 28d. If the four optical signals 46a, 46b, 46c and 46d are launched into four input ports:
~"~ .....~.-.._-,.,.,-..~.....

So , S, , SZ and S3 , respectively, as shown in Fig. 3(a), every signal can pass through the 4 cascaded switching units of the row where they are launched and exit at their own output ports To , T, , T2 and T3 , respectively, at the OFF-state, i.e., no modulating effects are applied onto these switching units. Note from Fig. 3(a) that all the optical signals must be coming out from the output ports of the input area if no modulating effect applied onto the switching units. So, as shown in Fig. 3(b), for any switching operation, its linking path of an optical signal from one input port to one output port of the matrix optical switch must be built up based on the modulating effect applied onto one switching unit of the input matrix and one switching unit of the output matrix for switching operations. For example, as shown in Fig. 3(b), if the switching units having shadows indicate the modulated state, i.e., the first switching unit from top of units 24a and the first switching unit from top of units 26a, the optical signal 46a launched into the input port So of this 4x4 optical matrix switch will be coming out at the output port SN_,. As depicted in Fig. 3(b), the operating process has been marked with the bigger lines. The same optical signal 46a can also have other output choices by modulating different pair of switching units in the input and output matrices, respectively, so one optical signal can choose any one among the four output ports. In the same manner, all other optical signals: 46b, 46c and 46d have the same four output choices as the optical signal 46a.
Even all the four signals can be operated simultaneously. An NxN optical matrix switch can be constructed in this style by extending the input ports and output ports into N.
Therefore, an NxN optical matrix switch can be implemented based on the operation principle defined by this invention.
In terms of the operating principle as depicted in Fig. 1 through Fig. 3, the communication between any input and any output ports is only based on one linking line and this linking line is defined by the column location. Thus, for an NxN
matrix optical switch based on the present invention, the modified optical cross-connection must have a precision mathematic definition so that the linking rules can be followed for any N value, and this mathematic definition is also true when the matrix optical switches based on the present invention are used inversely, namely, the output ports are used as the input ports and the input ports used as output ports. This attribute is referred to as bi-directional operation. Figure 4 illustrates the mathematic definition of the modified optical cross-connection for the NxN matrix optical switch based on the present invention.
As mentioned above with Fig. 1 (a), the communication for an NxN matrix optical switch is operated between N input ports So , S, , through SN_, , and N the output ports So , S; , through SN_, . As shown in Fig. 4, the columns of the switching units are labeled Co , C, , through CN_, . For the communication between the input port k ( k = 0,1,..., N
-1 ) and the output port k' ( k' = 0,1,..., N -1 ), only the column is needed to be addressed for connecting the output end of the switching unit at this column in the input matrix and the input end of the switching unit at this column in the output matrix as defined by C=(N-1)-(k+k'), for (k+k' ~N) (1) C=(2N-1)-(k+k'), for (k+k' >-N) (2) As mentioned above, each node indicates a switching unit and needs a 2x2 or 1x2 switch to perform its options of links. As well known, in the low-index-contrast waveguides, typically 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 sensitivity. The latter has a main advantage:
wavelength insensitivity and two main disadvantages: higher power consumption and higher access loss. The power consumption, the insertion loss and the wavelength sensitivity are three most important issues of an optical matrix switch based on an feature 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 optical matrix switches with its two main advantages and its disadvantage: wavelength sensitivity can be solved by another way in this invention. If the wavelength sensitive switching units such as MZI type optical switches are used as the switching units of the NxN optical waveguide matrix switch, at the different columns, the switching units are designed for different central wavelengths to uniformly cover the whole wavelength 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 should be added the wavelength insensitivity. In addition, the matrix optical switches based on the present invention do not have to be limited in NxN type. The MxN optical matrix switches can also be built based on the present invention wherein M 1xN optical switches and the N Mxl optical switches are used.
The waveguide switch based on the MZI configuration contains two 3dB
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 dif,~erence of optical path length between these two waveguide arms.
The modulating means can be either the TO or the EO. 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 of importance. 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 3d8 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 is the isolation of more than 20 dB
popularly required for the protection switching systems, but also 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, in the NxN
optical matrix switches based on the present invention, all the optical signals pass through the same number of MZI units (N+1), so each optical signal has N+1 MZI
operations and only two of these N+1 MZI units are activated. So, not only the uniformity of optical performance among all the ports can be achieved a high level, but also the isolation is easy to meet because it is based on the accumulated effect of N+1 MZI
operations. In accordance with the operating principle of the NxN optical switches based on the present invention, the switching unit must operate the bar-state output at the OFF-state and the cross-state output at the ON-state, so only the inverse type of 2x2 MZI
optical switch is suggested to use. Of course, the normal type MZI units, which operate the cross-state output at the OFF-state and the bar-state output at the ON-state, can also be used because the design for a normal type 2x2 MZI optical waveguide switch is easier than the inverse type 2x2 MZI optical waveguide switch, but the permutation among all the switching units and distribution of waveguide paths are relatively difficult compared to the use of the inverse type of 2x2 MZI optical switches.
Figure 5 shows the inverse type of 2x2 MZI optical switch where Figure 5(a) is the schematic of the electrode (heater) for the TO modulation and Figure 5(b) is of the electrodes for the EO modulation. The inverse MZI unit is composed of two 3dB
directional couplers 48a and 486 connected by two waveguide arms. As shown in Fig. 5, between two 3dB directional couplers 48a and 48b, two waveguide arms have phase difference of ~ or an odd integer of ~t. So, this type of MZI is called as inverse MZI
configuration. For the TO modulation, as shown in Fig. 5(a), one heater 50 is deposited on one of two arms and used to modulate the optical path of MZI unit with a TO
effect.
For the EO modulation, as shown in Fig. 5(b), two electrodes 50a and 50b are deposited on the two sides of one waveguide arm and used to modulate the optical path of MZI unit with an EO effect whereof waveguides are generally formed by the diffused LiNb03 or EO polymers. Two input pons 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 3dB directional coupler 48b. For either the TO modulation as shown in Fig. 5(a), if the heater (or electrode) 50 is not activated (at the OFF-state) or the EO modulation as shown in Fig. 5(b), if the electrodes 50a and SOb are 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 that the normal MZI configuration should have, so it is called inverse MZI configuration. If the heater 50 is activated by electrical power for the TO
modulation or the electrodes 50a and 50b are activated by electric field to produce an extra optical phase change of ~t (at the ON-state) so that the optical phase difference between two waveguide arms becomes 0 or an even integer of ~t, this combined optical signal 56a is sent to the output port S4b by the second 3dB directional coupler 48b. 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 come out at the output port 54a at the ON-state.
What is described above is mainly based on the low-index-contrast waveguides (Typically D = 0.3% - 2.0% ) no matter the TO or the EO modulation is used in the waveguide switches. In fact, the other type of waveguides, high-index-contrast waveguides (Typically core: cladding index is 1.5:1 up to 3.5:1) also receives much more attention in industry because the high-index-contrast waveguides can really give some paramount advantages over the law-index-contrast waveguides. Typically, the high-index-contrast waveguides supporting tightly confined modes act as optical wires, so they can be bent, twisted, and split without any loss of light. But, the high-index-contrast waveguides really have inherent drawbacks compared to the low-index-contrast waveguides. Typically, the crossings of the high-index-contrast waveguides can result in considerable scattering and cross talk at the intersecting junctions, but the low-index-contrast waveguides can pass through one another with little interference.
More importantly the high-index-contrast waveguides can form new functional components such as microring resonators as building blocks for the very large-scale integrated (VLSI) photonics and it is possible for these new functional components to become active and non-wavelength-selective such as 2x2 or 1x2 optical switches. Once this type of optical switching units based on the high-index-contrast waveguides are available, the NxN
optical matrix switches based on the present invention can be implemented with a two-layer regime that uses the high-index-contrast waveguides to form the 2x2 or 1x2 switching units at the top layer and the low-index-contrast waveguides to carry optical signals or beams. Then the optical matrix switches based on the present invention will perform a significant potential in applications with a radically different concept because the high-index-contrast and the low-index-contrast waveguides are independent and both of them are working at their own optimized points. In addition, the NxN
optical matrix switches based on the present invention can also be implemented directly with fiber couplers where the modulation can be based on the TO effect, a magnetic-optic (MO) effect, a pressure, or others. To date, the commercially mature fiber couplers mainly include the polished fiber coupler and the fused fiber coupler. The former has the access loss of light for each coupler is about O.OOSdB, which is much lower than what is for the best cases in the waveguide couplers. The later has the access loss of light for each coupler is about O.IdB. Although the access loss is relatively high compared to the polished one, it needs a much easier fabrication technique.

Claims (9)

1. An optical waveguide device comprising:
a substrate;
2N2 optical switching units are arranged on said substrate as two N × N
matrix with a modified cross-connection between two groups of 2×2 or 1×2 optical switching units to form a N × N matrix optical switch;
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 electrodes.

4. The optical matrix switch with a modified optical cross-connecting configuration based on this invention is nonblocking. This regime comprises two N × N
matrices of 2×2 switching units: One matrix is used for the input and the test of optical signals at the OFF-state and the other matrix is used for switching operations at the ON-state.

5. Although both the normal MZI configuration and the inverse MZI
configuration can be used based on this invention because the locating of the output signal of each switching unit cannot finally impact the possibility of applications, the inverse MZI
configuration is preferred in 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.

7. The optical matrix switches based on the present invention can be implemented with a hybrid structure of the low-index-contrast and the high-index-contrast waveguides for the switching operations and optical signals (or beams) propagations, respectively, at two separate layers.

8. The optical matrix switches based on the present invention can be implemented with fiber couplers and interconnections where the modulating approach can be the TO
effect, a magnetic-optic (MO) effect, a pressure or others.

9. The M×N (M does not equal to N) optical matrix switches can also be built based on the present invention.