Space-saving integrated 3-way branching unit switch module

Abstract

Aspects of the present disclosure describe systems, methods, and structures directed to an integrated three-way branching unit switch module suitable for subsea applications.

Description

[Technical field]

[0001] The present disclosure relates generally to optical communication systems, methods and structures, and more particularly to a space-saving integrated three-way branching unit switch module that is particularly applicable to undersea applications. [Background technology]

[0002] As is known in the optical communications art, undersea optical communication facilities and cables have become an increasingly important component of worldwide communications, including the Internet. Branching units are particularly important components of such undersea facilities. Given this importance, improvements in branching units would be a welcome addition to the art. Summary of the Invention

[0003] An advancement in the art is provided by aspects of the present disclosure directed to a space-saving integrated three-way branching unit switch module that is particularly well suited for subsea applications.

[0004] In sharp contrast to the prior art, systems, methods and structures according to the present disclosure are directed to a three-way branching unit switch module for undersea optical communications configured to be connected to first, second and third optical cables, each of which is in optical communication with a ground station A, B or C, respectively, the module having a first pair of switches in optical communication with the first optical cable, a second pair of switches in optical communication with the second optical cable and a third pair of switches in optical communication with the third optical cable, wherein one switch of the first, second and third pairs of switches is in optical communication with one of the other two pairs of switches, respectively, and the other switch of the first, second and third pairs of switches is in optical communication with the other of the other two pairs of switches, respectively.

[0005] A more complete understanding of the present disclosure may be realized by reference to the accompanying drawings. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram of a submarine fiber optic cable system known in the art.

[0007] [Diagram 2] FIG. 2 is a plot of a GAWBS spectrum according to an embodiment of the present disclosure.

[0008] [Diagram 3] FIG. 3 is a schematic diagram of a BU connection showing fiber pairs and possible connection paths in dashed lines according to an embodiment of the present disclosure.

[0009] [Figure 4(A)] Figure 4(A) is a schematic diagram showing BU connections for a BU that does not have a switch and has a 1x2 switch connected to its connection side with earth station A. The 1x2 switch is shown, solid lines indicate occupied paths within the BU, dotted lines indicate unoccupied paths within the BU, and greyed out fibers indicate fibers that are not carrying traffic. [Figure 4(B)] Figure 4(B) is a schematic diagram showing BU connections for a BU that does not have a switch and has a 1x2 switch connected to its connection side with earth station A. The 1x2 switch is shown, solid lines indicate occupied paths within the BU, dotted lines indicate unoccupied paths within the BU, and greyed out fibers indicate fibers that are not carrying traffic.

[0010] [Figure 5(A)] FIG. 5(A) is a schematic diagram illustrating BU connections for a BU with a three-way switch in different states of the switch according to an embodiment of the present disclosure. [Figure 5(B)] FIG. 5(B) is a schematic diagram illustrating BU connections for a BU with a three-way switch in different states of the switch according to an embodiment of the present disclosure. [Figure 5(C)]FIG. 5(C) is a schematic diagram illustrating BU connections for a BU with a three-way switch in different states of the switch according to an embodiment of the present disclosure.

[0011] [Figure 6] FIG. 6 is a schematic diagram illustrating a topology of the inventive 1×2 architecture according to an embodiment of the present disclosure.

[0012] [Figure 7] FIG. 7 is a schematic diagram illustrating four possible module states for an architecture using twelve 1×2 switches, according to an embodiment of the disclosure.

[0013] [Figure 8] FIG. 8 is a schematic diagram illustrating an example alternative configuration for achieving State 1, according to an embodiment of the present disclosure.

[0014] [Figure 9] FIG. 9 is a schematic diagram of an exemplary switch and circulator design including six 1×2 switches and six circulators in accordance with an embodiment of the disclosure, where the circulators are shown as circles and arrows indicate the direction of traffic for each connection.

[0015] [Figure 10] FIG. 10 is a schematic diagram illustrating four possible module states of an architecture using six 1×2 switches and six circulators, according to an embodiment of the present disclosure.

[0016] [Figure 11] FIG. 11 is a schematic diagram illustrating an example alternative configuration for achieving State 1 using SwC, according to an embodiment of the present disclosure.

[0017] [Figure 12] FIG. 12 is a schematic diagram illustrating an example topology of a 2×2 switch configuration according to an aspect of the disclosure.

[0018] [Figure 13] FIG. 13 is a schematic diagram illustrating four possible module states for an architecture using only six 2×2 switches, according to an embodiment of the disclosure.

[0019] [Figure 14] FIG. 14 is a schematic diagram illustrating four possible module states for a configuration including only six 2×2 switches, according to an embodiment of the disclosure.

[0020] [Figure 15(A)] FIG. 15(A) is a schematic diagram illustrating two states of the 2×2 switch configuration used in FIG. 13 according to an embodiment of the disclosure. [Figure 15(B)] FIG. 15(B) is a schematic diagram illustrating two states of the 2×2 switch configuration used in FIG. 14 according to an embodiment of the present disclosure.

[0021] [Figure 16] FIG. 16 is a schematic diagram illustrating an example of a 2×2 switch in which the top two inputs and the bottom two outputs are fiber-coupled and include a switchable gate that switches traffic between two states, in accordance with an embodiment of the disclosure.

[0022] [Figure 17] FIG. 17 is a schematic diagram illustrating an example of a switchable gate having double-sided reflective surfaces adjacent to a transmissive region, where the dotted lines correspond to the transmissive section and the solid lines correspond to the reflective section, according to an embodiment of the present disclosure.

[0023] [Figure 18] FIG. 18 is a schematic diagram illustrating the three switches sw1, sw2, and sw3 shown in FIG. 14 configured in a simple manner for easy integration at the first level, according to an embodiment of the disclosure.

[0024] [Figure 19]FIG. 19 is a schematic diagram illustrating the three switches sw1, sw2, sw3 shown in FIG. 18 configured in a simple manner for easy integration at the second level, according to an embodiment of the disclosure.

[0025] [Figure 20] FIG. 20 is a schematic diagram illustrating a similar version of the configuration shown in FIG. 19, according to an embodiment of the present disclosure.

[0026] [Figure 21] FIG. 21 is a schematic diagram illustrating an integrated switch configuration with a 45° angle of incidence and a fixed mirror on top, according to an embodiment of the disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Exemplary embodiments are more fully described in the drawings and detailed description, however, embodiments in accordance with the present disclosure may be embodied in many different forms and are not limited to the specific or exemplary embodiments set forth in the drawings and detailed description.

[0028] The following merely illustrates the principles of the present disclosure, and it should thus be understood that those skilled in the art will be able to devise various configurations which embody the principles of the present disclosure, even if not explicitly described or shown herein, and which are within the spirit and scope of the present disclosure.

[0029] Furthermore, all examples and conditional terms given herein are meant for educational purposes only to aid in the understanding of the principles of the present disclosure and the concepts presented by the inventors to further the present technology, and should not be construed as being limited to the specifically given examples and conditions.

[0030] Moreover, all statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Moreover, such equivalents are intended to include both currently known equivalents as well as equivalents developed in the future, i.e., elements developed that perform the same function, regardless of structure.

[0031] Thus, for example, it will be appreciated by those skilled in the art that any block diagrams herein are conceptual views illustrating illustrative circuitry embodying the principles of the disclosure.

[0032] Unless otherwise specified, the drawings herein, including the figures, are not drawn to scale.

[0033] As illustrated, aspects of the present disclosure include an underwater communications cable (i.e., subsea) branching unit (BU) that advantageously provides path diversity with improved connectivity while exhibiting a space-saving design, including a housing unit that is much smaller than those offered in the art.

[0034] By way of additional background, reference is made to Figure 1, which is a schematic diagram of an exemplary undersea optical fiber communication cable system as is commonly known in the art. As shown in Figure 1, data to be transmitted originates at any one cable station. It is sent via an undersea cable to another cable station across the ocean.

[0035] As one skilled in the art can readily understand and observe from viewing this diagram, a submarine cable has two main components: (1) cable spans and (2) repeaters. Cable spans can range from 40 km to 150 km or even longer, but are typically in the 50-80 km range. Such cable spans are often simply referred to in the art as spans.

[0036] A cable span may include several elements as shown, but for the purposes of this specification, our primary focus is on fiber optic cables. As known in the art, optical fibers are very thin strands of glass capable of guiding light with low loss. Optical fibers are very thin, typically only about 250 microns in diameter.

[0037] Typically, optical fibers consist of a roughly cylindrical piece of pure silica glass. Light is guided through a doped central core surrounded by a cladding. The core usually has a diameter of around 5-12 micrometers, and the cladding has a diameter of around 125 micrometers. The glass is then further coated with a polymer for protection, typically resulting in an overall diameter of 250 micrometers.

[0038] Generally, a fiber optic cable contains many individual fibers, each capable of carrying additional data, so data capacity is roughly proportional to the number of fibers in the cable.

[0039] Because optical fibers are very thin, in principle it is possible to greatly increase the cable capacity by adding more fibers. However, this is not the case due to the power limitations of fiber optic transmission systems that use fiber optic cables. Fiber has low loss, and as a result of such low loss, the optical power can drop to 1% after just one span. Therefore, after one span, the light passing through the fiber needs to be amplified.

[0040] Amplification is provided by active amplifier components housed in another major component of the undersea cable system, commonly called a repeater. Within the repeater there is usually one amplifier dedicated to each fiber. One of the limitations on the number of fibers that can be supported in a cable system is the number of amplifiers that can be housed in the repeater. Another limitation is the limited power present in undersea systems.

[0041] As is known, each amplifier uses electrical power to increase the optical power, and such power must necessarily be supplied from both ends of a submarine cable system that can span thousands of kilometers.

[0042] In FIG. 1, note further elements known in the art as Branching Units (BUs). These Branching Units are typically installed under the sea. They contain components that allow traffic to be sent in multiple directions. Such steering / redirection is typically achieved by switches, with or without wavelength selectivity. As will be readily understood and appreciated by those skilled in the art, components such as buses are placed within enclosures that protect them from the undersea environment.

[0043] It should be noted that there is generally a limit to the maximum size of the enclosure that can be installed underwater, which also has cost implications. Generally, larger enclosures mean higher costs, so a smaller size switching design is advantageous. Another factor that influences the enclosure size is the number of fiber pairs in the cable. The more fiber pairs that need to be switched, the more switching components need to be placed in the enclosure, which requires the enclosure size to be larger.

[0044] As will now be shown and explained, the inventive concepts disclosed herein provide an optical fiber cable transmission system with improved path diversity in the event of partial link failure or damage, and the present approach accomplishes this while maintaining the highest achievable capacity while minimizing overall system cost.

[0045] Of relevance to this disclosure are branching units (BUs), which are typically located underwater. A branching unit usually contains several "arms" and components that allow optical traffic to be directed to either arm. Such functionality is typically provided by components including switches in the BU, with or without wavelength selectivity. These components are located in a waterproof / rugged BU enclosure that is protected from the environment. An illustrative example of such a BU enclosure is shown in FIG. 1.

[0046] Those skilled in the art will readily understand and appreciate that there are practical limitations on the maximum size of a BU enclosure that can be installed underwater, which also has cost implications. Generally, larger enclosures are more costly. Therefore, it is desirable to have a small size of the switching unit. Yet another factor that contributes to the size of the enclosure is the number of fiber pairs in the undersea cable. The more fiber pairs that need to have switching functionality, the more switching components need to be placed in the enclosure, which requires a larger size of the enclosure.

[0047] Additionally, as will be appreciated by those skilled in the art, subsea / undersea optical cable transmission systems must exhibit sufficient / improved path diversity for unpredictable cases of failure, and such diversity must be provided while maintaining maximum achievable capacity (connectivity) at a relatively low cost.

[0048] 2 is a schematic diagram of an exemplary undersea optical fiber communication cable system in which path diversity is achieved by a branching unit according to an embodiment of the present disclosure. As shown in the figure and as would be readily understood by one skilled in the art, the figure illustrates an example in which path diversity helps improve connectivity. Specifically, instead of connecting ground station A only to ground station B, as is required for most traffic, a BU is used to split into two paths, connecting A to both B and C, and connecting B to C.

[0049] Of course, in some cases, a connection between B and C may already exist via an undersea cable or terrestrial network. If damage occurs in a high-risk area, such as between BU and B, BU and C, or B and C, alternate routes can be utilized to maintain connectivity during repairs. To achieve this functionality, the BU must be able to forward traffic from A to B, or A to C, or B to C. Such functionality is called Three-Way Switching (3WS).

[0050] As mentioned above, undersea cables in a submarine system typically have multiple fiber pairs. Each fiber in a pair transports traffic in opposite directions between the same two endpoints. In some configurations, the same number of fiber pairs are connected to all three cables connecting to a BU. This is due to cost considerations and limitations on the maximum number of fiber pairs that can be accommodated in a cable.

[0051] In a situation where there is damage between BU and B, all traffic may be connected between A and C. However, if there is no damage, the cable operator may reallocate traffic depending on the traffic load between AB, AC and BC accordingly. Those skilled in the art will readily appreciate that it is preferable to control how much capacity is allocated between the connections, but the total capacity achievable may depend on the configuration.

[0052] FIG. 3 is a schematic diagram illustrating a BU connection, where each solid line corresponds to a fiber pair and dashed lines indicate possible connection paths, according to an embodiment of the present disclosure.

[0053] Figure 3 shows a connection diagram that can achieve this function in a four fiber pair system. Referring to this diagram, as an example, traffic on fiber pair 1 from A can be connected to either fiber pair 1 in B or fiber pair 2 in C. Traffic on fiber pair 1 from B can be connected to either fiber pair 1 in A or fiber pair 1 in C. Traffic on fiber pair 1 from C can be connected to either fiber pair 1 in B or fiber pair 2 in A. Traffic on fiber pair 2 from A can be connected to either fiber pair 2 in B or fiber pair 1 in C. Traffic on fiber pair 2 from C can be connected to either fiber pair 1 in A or fiber pair 2 in B. To find the connections for fiber pairs 3 and 4, simply replace 1 with 3 and 2 with 4.

[0054] The connection diagram in Figure 3 shows that this design can be further simplified if we keep in mind that switching is limited to two fiber pairs. For example, in the example in Figure 3, switching might be limited to between fiber pairs 1 and 2, another switching might be limited to between fiber pairs 3 and 4, and so on. Even if the cable has a large number of fiber pairs (e.g. 24 or 36), switching only occurs between groups of two fiber pairs. From now on, we will refer to these as switching groups.

[0055] 4(A) and 4(B) are schematic diagrams showing BU connections for a BU that does not have a switch and has a 1×2 switch connected to the connection side with earth station A. The 1×2 switch is shown, solid lines indicate occupied paths within the BU, dotted lines indicate unoccupied paths within the BU, and greyed out fibers indicate fibers that are not carrying traffic.

[0056] From this diagram, the advantage of using a switch within the BU can be inferred. As shown in Figure 4(A), there is no switch. The connections can be set up in various ways, but in this case, maximum connectivity can be achieved if desired. Maximum connectivity means that all fiber pairs are connected and can carry traffic. In this example of a four fiber pair system, there are a total of six connections carrying traffic. Unfortunately, this configuration has a major drawback. If any connection fails, four of the six connections are lost. There is no way to protect the system from such a scenario. For example, if a failure occurs between the BU and ground station C, ideally we would like to redirect all traffic to link AC, but this is not possible. In many cases, one of the paths is preferred over the other. For example, there are cases where the ground station is much farther away than the BU compared to B or C. In such cases, it is important to make sure that the traffic is connected to either B or C. This can be achieved by adding a switch as shown in Figure 4(B). Here, the switch is a 1x2 switch, which tends to be the most reliable and saves cost and space. With such a switch installed, if there is damage either between BU and B or between BU and C, all traffic can be switched to the healthy side until repair is completed. However, the drawback is that in the absence of damage, the maximum number of connections is limited to only four connections. As can be seen from Figure 4(B), four fiber pairs must wait without connections in case a failure occurs in another branch.

[0057] 5(A), 5(B) and 5(C) are schematic diagrams showing BU connections for a BU with a three-way switch in different switch states according to an embodiment of the present disclosure. With reference to these figures, it can be seen that a three-way switching function for all fiber pairs can be achieved by adding a switch to every fiber pair from every ground station. In this case, the connections can be configured to provide both advantages shown in FIG. 4(A) and FIG. 4(B).

[0058] In fact, Figure 5(A) shows the same connection as Figure 4(A), and Figure 5(B) shows the same connection as Figure 4(B). Moreover, as shown in Figure 5(C), full protection of traffic at any ground station can be achieved, not just traffic from ground station A. However, a major challenge and drawback of this method of achieving three-way connectivity is that it requires three times the number of switches.

[0059] Our disclosure describes how to achieve 3WS functionality using low-cost, highly reliable switches. We present two designs with different advantages, as we will explain. The first design uses 1x2 switches, which have the lowest overall insertion loss. The second design is based on 2x2 switches, which has slightly higher insertion loss but uses half the number of switches, making it more cost-effective and occupying less space.

[0060] FIG. 6 is a schematic diagram showing the topology of the inventive 1×2 architecture according to an embodiment of the present disclosure. Note that unlike previous figures where each fiber pair is represented by a single line, FIG. 6 explicitly shows each fiber in the fiber pair. Here, we are interested in a switching group consisting of two fiber pairs from three stations, so there are a total of 12 fibers. Connecting a 1×2 switch to each fiber means 12 1×2 switches. These switches can be identical and bidirectional, or they can be unidirectional. In that case, the switch connected to the transmitter side receives the signal on a single circle port, and the switch connected to the receiver side receives the signal from one of the two circle ports. Each switch has two states independent of the other switches. Thus, the module has a total of

number

[0061] Further referring to Figure 6, Figure 6 shows the fiber pairs connected to the switch with hexagons in the diagram labeled as XnY, where X is A, B or C corresponding to the connected ground station, n is the number of the fiber pair 1 or 2, and Y is T representing the transmitter or R representing the receiver. For example, A1R corresponds to the fiber of fiber pair 1 that connects the switch to the receiver of ground station A. C2T is the fiber of fiber pair 2 that carries the signal from the transmitter of ground station C to the switch. Each rectangle in the diagram corresponds to one 1x2 switch. The three filled circles in each switch represent switching nodes. One circle on the back side establishes a connection to any circle on the front side at a time.

[0062] Figure 7 is a schematic diagram showing the four possible module states for a 12x1x2 switch architecture. Connections carrying traffic are shown with thick colored arrows, while connections carrying no traffic are shown with thin lines / arrows. As shown in this diagram, it can be seen how a 12x1x2 switch architecture can achieve all four states outlined in Table 1. The arrows indicate the direction of the connections carrying traffic and no traffic in the configuration, while the thick arrows indicate the connections carrying traffic and their direction. There are two ways to achieve state 1 in this architecture. Alternative configurations are shown in Figure 4. Note that in this architecture, traffic on all connections is unidirectional.

[0063] FIG. 8 is a schematic diagram illustrating an example alternative configuration for achieving State 1, according to an embodiment of the present disclosure.

[0064] FIG. 9 is a schematic diagram of an exemplary switch and circulator design including six 1×2 switches and six circulators, with the circulators shown as circles and arrows indicating the direction of traffic for each connection, according to an embodiment of the disclosure. This design reduces the number of active components by half, improving the overall reliability of the module. It also takes up less space. FIG. 9 shows the architecture of this design.

[0065] As can be observed in Fig. 10, which is a schematic diagram illustrating four possible module states of an architecture using six 1x2 switches and six circulators according to an embodiment of the present disclosure, it should be noted that the SwC can achieve all four states shown in Table 1. Traffic carried on connections is indicated by thick arrows, while connections that do not carry traffic are indicated by lines / arrows.

[0066] Those skilled in the art will understand that a circulator is a passive component that receives light at which port and directs it in which direction. As an example, looking at circulator 3 marked as CR3 in the configuration of state=1 in FIG. 10, the light coming from B1T is directed to the port connected to the switch. The light coming from the switch to the circulator is directed to the port connected to the fiber marked as B1R. Comparing the 12-switch design with the SwC, it can be seen that the number of active components (the switch is an active component) is reduced by half. Since passive components are less prone to failure, the reliability of the SwC design is expected to be higher. Moreover, since the circulator is expected to be small compared to the switch, it is also possible to integrate the switch and the circulator in the same package. As a result, this design has the advantage of saving space compared to the prior art.

[0067] However, this design has two drawbacks. First, in a SwC, the circulator and the switch are placed in series. Thus, the traffic experiences insertion loss in both components (twice, for a total of four components). In contrast, in a 12-switch configuration, the traffic experiences insertion loss in only two switches. Second, as indicated by the black arrows, some connections carry traffic in both directions simultaneously. This is generally an undesirable feature in some systems, as it can cause coherent interference.

[0068] As with the 12-switch configuration, in the SwC case, there are two possible ways to achieve the configuration in state 1. Alternative configurations are shown in Figure 11.

[0069] Here we describe a third design, which we refer to as the 6-switch design (6S), that requires only six 2x2 switches to achieve the four states in Table 1. This design reduces the number of active components to just six and does not require an additional circulator, thus avoiding the extra losses caused by the circulator while still achieving fully unidirectional traffic.

[0070] FIG. 12 is a schematic diagram illustrating an example topology of a 2×2 switching architecture according to an embodiment of the disclosure. The hexagons in the diagram indicate fiber pairs connected to the switches labeled XnY. X is A, B, or C corresponding to the connected ground station. n is the number of the fiber pair, which is 1 or 2, and Y is T representing a transmitter or R representing a receiver. For example, A1R corresponds to the fiber of fiber pair 1 that connects the switch to the receiver of ground station A. C2T is the fiber of fiber pair 2 that delivers the signal from the transmitter of ground station C to the switch. Each brown rectangle in the diagram corresponds to one 2×2 switch. The four black circles in each switch represent switching nodes. The four switching nodes are connected to either.

[0071] The connections to achieve the four states in Table 1 are shown diagrammatically in FIG. 13, which is a schematic diagram showing the four possible module states illustrated for an architecture using only six 2×2 switches.

[0072] Table 1 explains in more detail how to achieve all four states. To achieve state 1, i.e. one connection each between A and B, A and C, and B and C, the red line shows the traffic flow from A1T to B2R (A1T has its transmitter connected to fiber pair 1 at ground station A, and B2R has its receiver connected to fiber pair 2 at ground station B), while the light red arrow shows the return traffic from B2T to A1R. The green arrow shows the traffic flow from A2T to C2R, and the light green arrow shows the return traffic from C2T to A2R. The blue arrow shows the traffic flow from C1T to B1R, and the light blue arrow shows the return traffic from B1T to C1R.

[0073] Similarly, to achieve state 2, i.e. two connections between A and B without a connection to ground station C, in this case we do not have a connection to the ground station C, but we still utilize the switch connected to the fiber pair connected to ground station C. We have labeled the switch to illustrate state 2. As in state 1, traffic is sent from A1T to B2R via sw1 and sw6, as shown by the blue arrows. The return path, shown by the light blue arrows, connects B2T to A1R via sw6 and sw1. Since two connections must be established between ground stations A and B, a second connection is needed. This connection must connect A2T to B1R and B2T to A1R. However, there is no direct connection between sw2, which is connected to A2T, and sw5, which is connected to B1R. Therefore, sw2 and sw5 can be connected via sw3, since there is no ground station connected. Similarly, we patch the connection between sw1 and sw6 via sw4 to allow B1T to connect to A2R.

[0074] Note that for states 2, 3, and 4, some connections must pass through a total of three switches, instead of just two switches as in the first design with 12 1x2 switches.

[0075] Another advantage of using this last design configuration with six 2x2 switches is that if a ground station is not connected to another ground station, traffic is automatically returned. For example, in state 2, when ground station C is disconnected, traffic from C1T is returned to C1R and traffic from C2T is returned to C2R. Compare this to the first design with twelve 1x2 switches. In state 2, traffic from C1T and C2T is blocked at the switches and there is no traffic returning to C1R and C2R. In subsea systems, typically all amplifiers in the link are kept on at all times and are configured to have a specific input power for designed operation, especially to properly monitor the amplifiers and the link. As a result, for design 6S, there is always traffic passing through the link connected to the receiver at or near the design power level.

[0076] We now show and explain how Design 3 can be further integrated, except that Design 3 is cast in a similar but slightly different way to illustrate the most effective way to achieve this integration.

[0077] 14 is a schematic diagram illustrating four possible module states illustrated for an architecture using only six 2×2 switches, according to an embodiment of the disclosure. Connections within the switches and connections between the switches are shown.

[0078] Although it may not be obvious at first glance that the configurations in Figures 14 and 13 are similar, it is easy to see that they both provide the same functionality as the four states in Table 1. [Table 1]

[0079] FIG. 15(A) is a schematic diagram showing two states of the configuration of the 2×2 switch used in FIG. 13 according to an embodiment of the present disclosure, and FIG. 15(B) is a schematic diagram showing two states of the configuration of the 2×2 switch used in FIG. 14 according to an embodiment of the present disclosure.

[0080] To further understand why the architectures in Figures 13 and 14 are similar, Figures 15(A) and 15(B) show functional diagrams of the 2x2 switches used in these two cases. In both cases, the 2x2 switch has two possible states: pass or reflect. In this diagram, we can clearly see that these two switches perform the same function, since although there is a crossover in the pass state, which can occur depending on the design choices of the switch, one can be converted to the other by flipping which fiber is connected to which end on the left.

[0081] Figure 14 clearly shows that the connections of the switching groups can be split into two disjoint groups. The top group includes A1T, A2R, B2T, B1R, C2T and C1R connected to each other through three switches sw1, sw2 and sw3, while the bottom group consists of A1R, A2T, B2R, B1T, C1R and C1T connected to the remaining three switches sw4, sw5 and sw5. The connections between these three groups are essentially the same, so we will first focus on merging these two groups of three switches. Essentially, we will focus on merging three 2x2 switches.

[0082] As highlighted earlier, for the design configuration with 2x2 switches, all connections between the switches shown in Figure 14 carry traffic in all four states. Furthermore, a key driver for the integrated design is that the connections between the switches are fixed. This provides the first level of integration, allowing the fiber pigtail lengths between the three switches to be as short as possible. In fact, one of the largest wastes of space is simply providing sufficient protection for the fiber pigtails at the input or output of the switches. From here on, we will refer to this as the first level of integration. The main feature of this integration is that the fiber pigtails are kept short enough between the switches that protective sleeves are unnecessary and eliminated.

[0083] We now describe how we can move to a second, deeper level of integration. Essentially, what we do is recognize that because the connections between sw1, sw2, and sw3 are fixed, we can eliminate the unnecessary repeated fiber coupling stage. To further illustrate this, in FIG. 16, we show an exemplary diagram of a 2×2 switch capable of the functionality shown in FIG. 15.

[0084]

[0013] Referring to Figure 16, Figure 16 is a schematic diagram illustrating an example of a 2x2 switch according to an embodiment of the disclosure, where the top two inputs and bottom two outputs are fiber coupled and include a switchable gate that switches traffic between two states. Light from the two input fibers passes through the switchable gate before being coupled to the bottom two output fibers. Gates can be created by a variety of mechanisms, but the simplest example is both a transmissive surface adjacent to a reflective surface that can insert light into or remove light from the path. An example of such a gate is shown diagrammatically in Figure 17.

[0085] FIG. 17 is a schematic diagram illustrating an example of a switchable gate having both reflective surfaces adjacent to a transmissive region, where the dotted lines correspond to the transmissive section and the solid lines correspond to the reflective section, according to an embodiment of the present disclosure.

[0086] Figures 16 and 17 show that by moving the mirror out of the light path, the switch can be switched between the transmissive and reflective states shown in Figure 15. Note that in this example, the angle of the light incident on the mirror is 30° with respect to the normal to the surface, but the angle can be chosen almost arbitrarily as long as all the fibers are properly aligned.

[0087] FIG. 18 is a schematic diagram showing the three switches sw1, sw2, and sw3 shown in FIG. 14 configured in a simple manner for easy integration at the first level, according to an embodiment of the present disclosure. As can be seen, FIG. 18 shows how the exemplary switch configurations of FIG. 16 can be combined to obtain the functionality of the three switches sw1, sw2, and sw3 of FIG. 14. It is clear that this same configuration can be used to achieve the functionality of switches sw4, sw5, and sw6. It can be seen how the configuration of FIG. 18 can be used for first level integration. In the exemplary configuration shown in FIG. 18, the input and output fibers connecting the switches to each other are retained. The length of these fibers is not specified. However, they can be made short enough and protected within the integrated switch housing so that fiber protection sleeves are not required, thus achieving significant space savings. Furthermore, these fibers are well protected and short, which makes them more reliable.

[0088] In looking at the configuration shown in FIG. 18, it should become apparent that there is no need to couple light out of the fiber between the switches, and the switches can be eliminated to achieve a second level of integration as shown in FIG.

[0089] It can be seen that the functionality required for a three-way switch can be achieved by combining the three switches sw1, sw2 and sw3 of Figure 14 in the format shown in Figure 19. As mentioned above, the six switches required are reduced to two groups of three switches of the same configuration.

[0090] According to an embodiment of the present disclosure, the three switches can be replaced with the configuration shown in FIG. 19. It can be seen that the functionality of a three-way switch can be achieved by simply moving three mirrors in and out of the optical path. It can be seen that by moving from the first level of integration to the second level, i.e., from the configuration shown in FIG. 18 to the configuration shown in FIG. 19, the switch can be made more compact since all the fibers and fiber-coupled components can be removed. This results in fewer components, a smaller size, lower insertion loss, and improved reliability.

[0091] Note that the design shown in Figure 19 can be constructed in a similar manner to that shown in Figure 20. The only difference is which connections have multiple reflections from the mirror and which have no reflections or only one reflection, which can prove advantageous for various applications.

[0092] In describing the configuration shown in Figure 16, it was noted that the switch can be configured in a variety of ways, particularly the angle of incidence with respect to the normal to the mirror surface can be varied. One angle of incidence that is particularly important is 45°, as this has been found to be easier for alignment and other purposes. While this configuration can be extended to many different angles, Figure 21 shows a specific example having a 45° angle of incidence.

[0093] Figure 21 is a schematic diagram showing the configuration of an integrated switch with a 45° incidence angle and a fixed mirror on top according to an embodiment of the present disclosure. Note that similar to the relationship between Figures 19 and 20, Figure 21 can be designed in the same way.

[0094] In general, it is possible to design 1x3 switches to realize a three-way switch, but it should be noted that such switches are more complex compared to 2x2 switches. They require more gates (mirrors, etc.) to be adjusted or gates to be adjusted at multiple angles. This choice reduces the reliability of the component for the application in the example above. This is especially true if a latching function is required, which is also the case for the application in the example above. A latching function means that the switch will retain its last setting or return to a pre-determined setting in case of power loss. We have chosen an example whose main focus is simplicity, where the gates need to be adjusted to the on (mirror in in this example) or off position (mirror out of the light path in this example). Such simplicity provides the required level of reliability.

[0095] Furthermore, note that while we have shown the gate function as an example using mirrors, it could be of other forms and the principle of the invention would still remain the same since our design relies on combining three switches and removing the fiber coupling components. Let us repeat the last point in a different way: the simplest and most reliable version of the switch is 1×2. However, recently, 2×2 switches with latching functions have also become increasingly available, mostly based on the fact that this function can be achieved with a very simple setup. By taking advantage of the simple geometry and the fact that the connections between the switches are fixed, whatever the underlying simple mechanism may be, it can be further integrated by removing the fiber coupling components. Since the switching mechanism is already simple and reliable enough, the integrated version will be just as reliable and will be even more reliable since it uses fewer components.

[0096] Although the present disclosure has been illustrated herein using certain specific examples, those skilled in the art will recognize that the present teachings are not so limited. Accordingly, the present disclosure should be limited only by the scope of the claims appended hereto.

Claims

1. A three-way branching unit switch module for undersea optical communications, the branching unit switch module being configured to be connected to first, second and third optical cables, each of the optical cables being in optical communication with a ground station A, B or C, respectively, the branching unit switch module comprising: The module comprises: a first pair of switches in optical communication with the first optical cable; a second pair of switches in optical communication with the second optical cable; a third pair of switches in optical communication with the third optical cable; having the first, second and third pairs of switches each being in optical communication with one of the other two pairs of switches; the first, second and third pairs of switches each having a respective other switch in optical communication with a respective other switch of the other two pairs of switches; each of said switches being a 2×2 switch; The 2×2 switch is a switch housing to which two inputs and two outputs are respectively connected to individual optical fibers of an optical cable; a switchable gate having a transmissive surface and reflective surfaces adjacent to said transmissive surface, said switchable gate transmitting light from one input to one output or reflecting light from said one input to the other output.

2. [Table 1] 2. The branching unit switch module of claim 1, configured to provide connections to said ground stations A, B, C according to a table of:

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