Patent Application
20120321241
The present invention relates generally to telecommunications systems and in particular to optical switches and associated methods.
Communications technologies and uses have greatly changed over the last few decades. In the fairly recent past, copper wire technologies were the primary mechanism used for transmitting voice communications over long distances. As computers were introduced the desire to exchange data between remote sites became desirable for many purposes. The introduction of cable television provided additional options for increasing communications and data delivery from businesses to the public. As technology continued to move forward, digital subscriber line (DSL) transmission equipment was introduced which allowed for faster data transmissions over the existing copper phone wire infrastructure. Additionally, two way exchanges of information over the cable infrastructure became available to businesses and the public. These advances have promoted growth in service options available for use, which in turn increases the need to continue to improve the available bandwidth for delivering these services, particularly as the quality of video and overall amount of content available for delivery increases.
One promising technology that has been introduced is the use of optical fibers for telecommunication purposes. Optical fiber network standards, such as synchronous optical networks (SONET) and the synchronous digital hierarchy (SDH) over optical transport (OTN), have been in existence since the 1980s and allow for the possibility to use the high capacity and low attenuation of optical fibers for long haul transport of aggregated network traffic. These standards have been improved upon and today, using OC-768/STM-256 (versions of the SONET and SDH standards respectively), a line rate of 40 gigabits/second is achievable using dense wave division multiplexing (DWDM) on standard optical fibers.
As these (and other) optical networks are being deployed, there is an increasing need to provide efficient solutions for switching and routing information within and between such networks. Currently, specialized optical switches are available for large optical networks, which specialized switches are typically extremely expensive since they are developed for specific types of core networks. In addition to providing basic switching functionality, these types of specialized optical switches also typically provide value-added features such as accounting, rate-limiting, etc.
As optical technology is maturing, the cost related to its use is decreasing. Also, as networking and communication systems are imposing greater requirements associated with capacity and sustainability, optical-based solutions are becoming more attractive for system architecture designs. However, smaller networking systems typically have different requirements than those of large optical networks. In other words, specific solutions might have to be developed on a system basis, rather than on a more generic network basis. While expensive solutions might be affordable for some networks, they might not be acceptable at a node level.
In order to build networking systems based on optical technologies, there is a need to provide simple, scalable, reliable and affordable solutions for optical switches and crossbars. The current available technologies for providing optical crossbars and switches typically require the use of mirrors and MEMS technology. Depending on the implementation, such optical switching solutions can be extremely complicated and expensive, especially when they are built for controlling traffic on networks, not for smaller-scale systems.
Moreover, the usage of mirrors and MEMS technology in optical switches brings with it certain potential drawbacks. For example, in such optical switches, mirrors are provided on printed circuit boards (PCBs) or other electronic devices. While mirrors can be used to redirect optical signals, they lack the capability of selectively reflecting only a specific optical wavelength without the help of a specific optical filter. Additionally, the use of mirrors requires more space on a PCB or an electronic device, apart from the fact that mirrors might be required to move in order to allow the optical signals to be reflected in the required direction. For the mirrors in an optical switch to move, MEMS technology can be used, which can lead to simple or complex solutions, depending on the flexibility with which the mirrors have to move. Typically, since MEMS technology is basically a means to move extremely small components or devices mechanically, there exists an inherent operation/repair risk related to limitations and problems that can arise because of such mechanical movements.
Other alternatives for building optical switches can be based on a mix of technology choices. For example, optical switches can be designed which include conversions between the optical and the electrical domains, which could allow the use of traditional layer 2 switches, such as Ethernet switches. While systems could be built relatively easily using those technologies, such solutions are expensive in terms of energy consumption, space and components. Ideally, efficient solutions should avoid any transitions from the optical domain.
Accordingly, it would be desirable to provide optical switches or crossbars which overcome the aforedescribed drawbacks.
Systems and methods according to these exemplary embodiments provide for optical interconnection using optical splitters and interferometer-based optical switching. Optical signals can be routed from an input port to one or more output ports via at least one splitter and at least one interferometer, e.g., a Mach Zehnder interferometer. According to one exemplary embodiment, signal degradation associated with signal splitting is mitigated by using a binary tree of splitters and interferometers between input ports and output ports.
According to an exemplary embodiment, an optical interconnect system includes a plurality of input ports for receiving optical signals, a plurality of input waveguides, each connected to one of the plurality of input ports, for guiding the optical signals, a plurality of output ports, a plurality of output waveguides, each connected to one of the plurality of output ports, wherein the plurality of input waveguides and the plurality of output waveguides are disposed in an orthogonal relationship, at least one connecting optical waveguide portion disposed between each input waveguide and each output waveguide to convey an optical signal from a respective input port toward a respective output port, and wherein the at least one connecting optical waveguide portion includes at least one optical splitter and at least one interferometer disposed downstream of each optical splitter to selectively block, or let pass, the optical signal toward the respective output port.
According to another exemplary embodiment, a method for conveying optical wavelengths in an optical interconnect includes the steps of receiving optical signals at a plurality of input ports, conveying the optical signals via a plurality of input waveguides, each connected to one of the plurality of input ports, splitting, at each interconnecting point between one of the plurality of input waveguides and one of a plurality of output waveguides, an optical signal from the one of the plurality of input waveguides toward the one of the output waveguides, and selectively blocking or passing the optical signal downstream of the interconnecting point using an interferometer, wherein the plurality of input waveguides and the plurality of output waveguides are disposed in an orthogonal relationship.
According to another exemplary embodiment, a method for manufacturing an optical interconnect system includes manufacturing an optical interconnect device by providing a plurality of input ports on a substrate, forming a plurality of input waveguides, each connected to one of said plurality of input ports, on the substrate, providing a plurality of output ports on the substrate, forming a plurality of output waveguides, each connected to one of the plurality of output ports, on the substrate in an orthogonal relationship relative to the plurality of input waveguides, and providing at least one optical splitter and at least one interferometer at each interconnecting point between one of the plurality of input waveguides and one of the plurality of output waveguides, each interferometer being configured to selectively block, or pass, an optical signal received from a corresponding optical splitter.
The accompanying drawings illustrate exemplary embodiments, wherein:
MEMS Micro-Electro-Mechanical System
MZI Mach-Zehnder Interferometer
MZM Mach-Zehnder Modulator
PCB Printed Circuit Board
PLC Planar Light wave Circuit
WDM Wavelength-Division Multiplexing
The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.
According to exemplary embodiments an optical crossbar or switch can be built using interferometer technology, such as Mach-Zehnder Interferometer (MZI) technology. Because the MZI technology is well-known per se and has been proven to be stable and reliable in production, it would be advantageous to develop an optical crossbar or switch based on that technology. The MZI technology is thus used in exemplary embodiments, for example, for its effect of dynamically blocking (or not) an optical signal by virtue of MZI's phase shifting capabilities.
By using a controller, the MZIs can be used to block or allow the optical signals through junctions in a switching interconnect based on an applied electric field on a splitted span of the MZIs. Since optical signals are either blocked or not at each MZI, it becomes possible to chain them together using the controller to configure the MZIs to route an optical signal and to provide a 1-to-1 or a 1-to-N relationship between an incoming port and one or several outgoing ports. In other words, it is possible to create a unicast or a multicast forwarding capability.
To allow a large number of input and output ports on the same device, an orthogonal layout (waveguides crossing at 90 degree) can be used to minimize undesired interference between any input and output waveguides. According to one exemplary embodiment, an N-level binary-tree like structure is used at each input port in order to minimize the number of optical signal degradations.
An optical switch or crossbar can be seen as a component with several optical ports connected thereto. Each port can either be a port used to only receive, to only send, or to both receive and send, optical channels. For example, in
An interferometer is a device used to interfere two or several waves together, generating a pattern of interference created by their superposition. When two waves with the same frequency combine, the resulting pattern is determined by the phase difference between the two waves-waves that are in phase will undergo constructive interference while waves that are out of phase will undergo destructive interference. Most interferometers use light or some other form of electromagnetic wave.
Typically, a single incoming beam of coherent light will be split into two identical beams by a grating or a partial mirror. Each of these beams will travel a different route, called a path, until they are recombined. By traveling a different path before arriving at the recombination point, a phase difference is created between the two identical beams. It is this introduced phase difference that creates the interference pattern between the initially identical waves. If a single beam has been split along two paths, then the phase difference is diagnostic of anything that changes the phase along the paths. This could be a physical change in the path length itself or a change in the refractive index along the path.
There exist several different types of interferometers, such as the Mach-Zehnder, the Mickelson and the Sagnac interferometer. The choice of the right interferometer for a particular need mainly depends on each interferometer's strengths and weaknesses. In the context of these exemplary embodiments where a large number of interferometers are envisioned to be required in order to provide optical switching capabilities, it seems that the Mach-Zehnder interferometer technology would provide the best solution, however the present invention is not limited to that particular technology. For example, the Mach-Zehnder interferometer seems to offer the best tolerance to misalignment, the best stability, as well as being a commercially proven technology, although other interferometer technologies could be used instead.
While a Mach-Zehnder interferometer can be used as a phase modulator, exemplary embodiments instead use MZIs as filters, i.e. for their capability to block or not block an optical wavelength. As shown in
However, when an electric field is applied to plates 214, 216, then a 180 degree induced phase shift is applied on the optical signal carried by the bottom waveguide, which causes the two optical signals being recombined on the outgoing optical waveguide 212 with a 180 degree phase shift. Such a phase shift is considered to be a destructive interference that blocks completely the incoming optical signal 202 from being output on the outgoing optical waveguide 212. In other words, applying or not an electric field on the bottom waveguide via plates 214, 216 can be used to block, or not block, the incoming optical signal 202. As mentioned earlier, the phase shift can be created by controlling the length of the path, or the refractive index of the waveguide.
Thus, to summarize the MZI 200 of
Using, for example, the above-described MZI technology, one way to create an optical crossbar, or switch, according to exemplary embodiments is to combine an orthogonal design of the input and the output optical waveguides with splitters and MZI filters. An example is shown in
The input and output waveguides, e.g., 305 and 307 illustrated in
One limitation of this approach is that, at each intersection with an outgoing channel, the optical signal is split in two, which means a loss of approximately 3 dB of the signal strength at each intersection. The more branches (ports), the more signal degradation towards the edge of the switching matrix. For the example of
According to another exemplary embodiment, in order to minimize the limitation of the 3 dB loss at each splitting intersection according to the exemplary embodiment of
For example, as shown in the exemplary embodiment of
Another advantage of the exemplary embodiment of
As mentioned above, in order to coordinate the operation of optical crossconnects according to these exemplary embodiments, a controller 420 can be provided for efficiently managing all of the MZIs (only the subset 402-412 shown in
In the context where optical signals from several incoming ports are to be switched to one or more outgoing ports, one N-level binary tree-like design can be provided per incoming port as shown in
The foregoing exemplary embodiments present various advantages and benefits in optical switching and crossconnect design. For example, compared with technologies such as MEMS and micro-ring resonators for developing an optical crossbar or switch, another advantage for using MZIs could be that the design can provide a solution for unicast and for multicast traffic. In other words, it is possible to control several MZIs in order to let the optical signal reach only one output port, or several ones. Obviously, the signal strength at the output port will be attenuated depending on the number of stages in the N-level binary tree-like structure, but the signal strength can, however, be the same at every output port when using the exemplary embodiment of
Utilizing the above-described exemplary systems according to exemplary embodiments, a method for conveying optical signals in an optical interconnect is shown in the flowchart of
As mentioned above, exemplary embodiments also provide potential advantages in terms of manufacturing. An exemplary method for manufacturing an optical interconnect device is illustrated in the flowchart of
According to another exemplary embodiment, chaining several of the MZI filters described above in a back to back configuration could also be implemented. Assuming, for such an embodiment, that there would be provided as many chained MZIs as there would be wavelengths on an input port, chaining the MZIs in a back to back configuration wherein each MZI can be tuned to selectively block or pass a particular wavelength would provide support for multiple wavelengths per input port. This exemplary embodiment would thus increase the number of MZIs, but allow support for WDM. In the context of the binary-tree like design described above, each MZI would be replaced by a chain of MZIs.
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.
