Redundancy improvements in semiconductor-based optical communication systems

Abstract

Techniques are provided for improving redundancy in semiconductor-based optical communication systems. For example, two or more semiconductor optical amplifiers (SOAs) can be provided in an optical repeater, and each SOA can form a respective amplification path. When a failure occurs on a first SOA, a second SOA different from the first SOA can be selected. In one example, the selection can be based on wavelength division multiplexing (WDM), and in another example, the selection can be based on optical switching. The two or more SOAs (and other optical components) can be integrated in the same substrate package.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to the field of optical communication systems. More specifically, the present disclosure relates to improving redundancy in optical communication systems that include semiconductor-based components. BACKGROUND

[0002]

[0003] Long-haul optical communication systems, such as undersea optical communication systems, often suffer from signal attenuation caused by a variety of factors, including scattering, absorption, and bending. To compensate for the attenuation, these long-haul systems can include a series of optical amplifiers or “repeaters” spaced apart along a transmission path between a transmitter and a receiver. The repeaters amplify the optical signal in a manner that allows for reliable detection at the receiver. Typically, multiple repeaters are positioned along the transmission path depending on the length of the optical communication system.

[0004] Examples of optical amplifiers commonly used in long-haul optical communication systems include Raman amplifiers, which involve amplifying an optical signal based on the stimulated Raman scattering (SRS) phenomenon, and erbium-doped fiber amplifiers (EDFAs), which can include an erbium-doped core fiber that is pumped with light from a laser diode to amplify the optical signal. Other types of optical amplifiers based on differently doped active optical fibers are also possible. These include, but are not limited to, praseodymium-doped, bismuth-doped, and gallium-doped fiber amplifiers. Another type of optical amplifier is a semiconductor optical amplifier (SOA), which can be configured to amplify incident light through stimulated emission. For example, as light travels through the active region of a SOA, it can cause electrons to lose energy in the form of photons and return to the ground state. The “stimulated” photons can have the same wavelength as the optical signal, which effectively amplifies the optical signal.

[0005] While SOAs are commonly used in telecommunications systems, SOAs can be implemented in long-haul optical communication systems, which can include terrestrial and undersea applications. However, one exemplary disadvantage of SOAs is that they are a functionally “all-or-nothing” type of amplifier. For example, if a portion of a SOA fails, the entire SOA can fail. Further, if no current is applied to a SOA, the SOA can be completely ineffective. As a result, when a system implements SOAs that are ineffective or in a failure mode, they can become highly opaque within the system. Therefore, there is a need to design semiconductor-based communication systems, such as SOA- implemented systems, with sufficient redundancy mechanisms so that they can operate for their required system lifetime. SUMMARY

[0006] Embodiments of the present disclosure relate to techniques for improving redundancy in semiconductor-based optical communication systems. In one embodiment, an apparatus can include at least a wavelength division multiplexing (WDM) circuit, a first semiconductor optical amplifier (SOA), and a second SOA. The first SOA can correspond to a first operating wavelength, and the second SOA can correspond to a second operating wavelength. The WDM circuit can be configured to receive an optical signal at the first operating wavelength and provide the received optical signal to the first SOA to amplify the optical signal, or can be configured to receive an optical signal at the second operating wavelength and provide the received optical signal to the second SOA to amplify the optical signal.

[0007] In another embodiment, an apparatus includes at least an optical switching circuit, a first SOA, and a second SOA, where the first SOA and the second SOA are coupled to the optical switching circuit. The optical switching circuit can be configured to receive an optical signal and provide the received optical signal to the first SOA to amplify the optical signal, or can be configured to receive an optical signal and provide the received optical signal to the second SOA to amplify the optical signal.

[0008] In yet another embodiment, a substrate package can include at least one optical combiner, at least one optical switch, a first SOA, and a second SOA. The first SOA and the second SOA can be coupled to the at least one optical combiner and the at least one optical switch. Further, the at least one optical combiner, the at least one optical switch, the first SOA, and the second SOA can be integrated in the substrate package. The at least one optical switch can be configured to provide an optical signal to the first SOA or the second SOA to amplify the optical signal.

[0009] In another embodiment, a method can include sending a first optical signal to an optical repeater, the optical repeater including at least a first SOA and a second SOA, where the first SOA amplifies the sent first optical signal. The method can also include determining that the first SOA in the optical repeater is non-functional or in a failure mode; selecting the second SOA or switching to the second SOA; and sending a second optical signal such that the second SOA amplifies the second optical signal. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 An exemplary optical communication system is shown.

[0011] Figures 2A-2B An exemplary redundancy configuration using WDM is shown.

[0012] Figure 3 An exemplary redundancy configuration using an optical switch is shown.

[0013] Figure 4 An exemplary redundancy configuration using an optical switch with polarization multiplexing is shown.

[0014] Figure 5 An exemplary redundant configuration using SOA integration is shown.

[0015] Figure 6 An exemplary redundant configuration for multiple fiber pairs is shown. DETAILED DESCRIPTION

[0016] The present invention relates to improved redundancy in semiconductor-based communication systems. For example, improved redundancy can be achieved by implementing two or more semiconductor optical amplifiers (SOAs) that form two or more different amplification paths, respectively. The two or more SOAs can be implemented in the same optical repeater. According to one embodiment, wavelength division multiplexing (WDM) can be used to select a particular SOA amplification path by transmitting an optical signal at a predetermined operational wavelength via a transmitter. According to another embodiment, an optical switch connecting the two or more SOAs can be used to select a particular amplification path. According to another embodiment, the two or more SOAs can be integrated with other optical components (such as combiners, optical switches, etc.) in a substrate package, thereby improving overall efficiency at least at the component level within the system.

[0017] As mentioned above, SOAs can be "all or nothing" components, and when implemented in long-haul optical communication systems, their failure in the system can cause many problems. Accordingly, the examples and / or embodiments described herein overcome the aforementioned problems associated with SOA-based (or any other semiconductor-based) optical communication systems. One advantage of the present invention is that by providing two or more different amplification paths for amplifying an optical signal, signal amplification is not interrupted when a failure occurs on one of those paths. Signal amplification on the paths can be easily switched using WDM or optical switching mechanisms. Another advantage of the present invention is that two or more SOAs and other optical components are implemented in the same substrate package, which improves efficiency and redundancy at least at the component level within the optical communication system.

[0018] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the drawings.

[0019] With reference to the drawings, Figure 1An exemplary bidirectional optical communication system 101 is shown. Bidirectional optical communication system 101 can use high-bandwidth optical fiber to transmit large amounts of data over long distances. Bidirectional data transmission can be achieved by configuring pairs of fiber paths within the optical fiber and transmitting one or more channels (e.g., wavelength division multiplexed channels) over each fiber pair.

[0020] As shown, optical communication system 101 can include terminals 103 and 105 connected by two unidirectional optical paths 111, 121 that together form a bidirectional optical path pair. Optical path 111 can transmit information from a transmitter 113 at terminal 103 to a receiver 115 at terminal 105 in one direction (e.g., to the right). Optical path 121 can transmit information from a transmitter 125 at terminal 105 to a receiver 123 at terminal 103 in the other direction (e.g., to the left). With respect to terminal 103, optical path 111 is an outbound path and optical path 121 is an inbound path. Optical path 111 can include optical fibers 117-1 through 117-n and optical amplifiers 119-1 through 119-n, and optical path 121 can include optical fibers 127-1 through 127-n and optical amplifiers 129-1 through 129-n. It should be understood that in some examples, transmitter 113 and receiver 123 can be housed together as a transponder at terminal 103, and similarly, transmitter 125 and receiver 115 can also be housed together as a transponder at terminal 105.

[0021] An optical path pair (e.g., optical paths 111, 121) can be configured as a set of amplifier pairs 119-1 through 119-n and 129-1 through 129-n within repeaters 131-1 through 131-n connected by pairs of optical fibers 117-1 through 117-n and 127-1 through 127-n, which can be included in an optical fiber cable along with optical fibers supporting additional path pairs. Each repeater 131 can include a pair of amplifiers 119, 129 for each path pair, and can include additional amplifiers for additional path pairs. Optical amplifiers 119, 129 can utilize EDFA or other rare-earth-doped fiber amplifiers, Raman amplifiers, or semiconductor optical amplifiers (SOAs). Coupling paths 133-1 through 133-n can be coupled between optical paths 111, 121 in one or more of repeaters 131-1 through 131-n, for example. It should be understood that the term "coupled" or "coupling" as used herein refers to a direct or indirect connection and / or a wired or wireless connection, and is not intended to be limiting in any way.

[0022] While an exemplary embodiment of the optical communication system 101 is shown and described, variations of the optical communication system 101 are within the scope of the present disclosure. The optical communication system 101 can include, for example, more pairs of optical paths and more or fewer repeaters. Alternatively, the optical communication system 101 can not include any optical amplifiers, or can include optical pump sources adapted to achieve optical gain by performing Raman amplification within the optical fibers connecting the repeaters, instead of optical amplifiers.

[0023] Further, it should be appreciated that a transmitter, a receiver, a transponder containing a transmitter and a receiver, or any other suitable device for transmitting and receiving data can include at least one memory and one or more processors (e.g., CPUs, ASICs, FGPA, any conventional processor, etc.) to execute instructions stored in the memory, for example, to identify and locate external attacks based on a state of polarization (SOP) analysis, as will be further described below.

[0024] Figure 2A An exemplary wavelength division multiplexing (WDM) redundancy configuration 200 is shown in accordance with an embodiment. The WDM redundancy configuration 200 can be implemented in an optical repeater. As shown, the redundancy configuration 200 in a repeater can include a WDM circuit 201, two separate SOAs 202 and 206, which can form two separate amplification paths 204 and 208, respectively. Thus, when the amplification path 202 is used as a primary path, the amplification path 208 can be considered a redundant path (or vice versa).

[0025] In one example, WDM communications can be used by one or more transponders to transmit one or more optical signals. The use of WDM communications can allow a transmitter at the one or more transponders to transmit the optical signal(s) at a predetermined wavelength. The SOA 202 and the SOA 206 can each correspond to a predetermined operational wavelength. Thus, for example, when the WDM circuit 201 receives an optical signal (or a portion thereof) at a wavelength or wavelength range corresponding to the operational wavelength of the SOA 202, the SOA 202 can be used to amplify the optical signal alone. Similarly, when the WDM circuit 201 receives an optical signal at a wavelength corresponding to the operational wavelength of the SOA 206, the SOA 206 can be used to amplify the optical signal alone.

[0026] Accordingly, a particular optical amplification path (e.g., path 204 or path 208) can be selected to amplify an optical signal by transmitting the optical signal at a particular operational wavelength or wavelength range corresponding to the SOA associated with that amplification path. It should be appreciated that the operational wavelength or wavelength range corresponding to SOA 202 is different than the operational wavelength or wavelength range corresponding to SOA 206. It should also be appreciated that the corresponding operational wavelength or wavelength range can be selected from any suitable electromagnetic spectrum, such as the EU / NATO / US ECM radio frequency bands (bands A through N), ITU radio frequency bands, IEEE radio frequency bands (HF, VHF, UHF, L, S, CX, K, V, W, mm, etc.).

[0027] According to one embodiment, electrical power efficiency can be improved by turning on only one SOA in the repeater at a time while turning off the others. Accordingly, when an SOA in the repeater (e.g., SOA 202) fails or is inoperative, an “unused” or unpowered SOA (e.g., SOA 206) can be “turned on” by configuring or tuning the transmitter to transmit an optical signal at an operational wavelength or wavelength range corresponding to the unused or unpowered SOA. In some examples, the transmission band can be selected by switching the drive current on or off to the corresponding SOA.

[0028] There are many advantages to implementing a WDM-based redundant configuration in a repeater, such as minimizing insertion loss, eliminating additional active optical components, and having minimal impact on the noise figure (NF) of the amplifier. Another advantage can be that the output WDM signal can be replaced by a passive optical combiner when the power budget allows for additional loss in the system without compromising the NF.

[0029] Figure 2B Another example of a redundant configuration 240 is shown in accordance with an embodiment. As shown, configuration 240 is similar to redundant configuration 200 of Figure 2A , except that in Figure 2B more than two SOAs (e.g., SOAs 242 and 244 and up to “n” SOAs) can be arranged in the optical repeater. Each of SOAs 242, 244, and SOA n can correspond to a respective operational wavelength or wavelength range. Accordingly, when WDM circuit 241 receives an optical signal transmitted at a particular operational wavelength or wavelength range corresponding to an SOA, WDM circuit 241 can select that SOA to amplify the optical signal, as described above. Moreover, similar to redundant configuration 200 of Figure 2A , only one SOA can be turned on at a time to conserve power.

[0030] Figure 3An exemplary optical switch redundancy configuration 300 is shown in accordance with an embodiment. The optical switch redundancy configuration 300 can be implemented in an optical repeater. As shown, one or more optical switches or optical switching circuits 301 can be coupled to two or more SOAs 302, 304, up to SOA "n." While two separate optical switches are shown, it should be appreciated that one optical switch can perform the functionality of both switches, or it should also be appreciated that the two optical switches can be disposed in one optical switching circuit package. Figure 3 While two separate optical switches are shown, it should be appreciated that one optical switch can perform the functionality of both switches, or it should also be appreciated that the two optical switches can be disposed in one optical switching circuit package.

[0031] According to exemplary embodiments, the optical switching circuit 301 can be configured to select or switch to an SOA without being limited to a particular bandwidth. Further, as described above in connection with exemplary redundancy configurations 200 and 240 of FIGS. 2A and 2B, respectively, only one SOA (e.g., the SOA in operation) can be "turned on" while the other SOAs can be turned off to maintain power efficiency within the optical repeater. In some examples, the optical switching circuit can also be configured to switch the drive current to the SOA. Figure 2A and Figure 2B

[0032] In one example, when the SOA 302 fails or is inoperative, the optical switching circuit 301 can select and / or switch to a functioning SOA (e.g., SOA 304, SOA n). It should be appreciated that a passive optical combiner can be used at the output without compromising the noise figure (NF) when the power budget allows for additional loss in the associated system.

[0033] Figure 4 An exemplary redundancy configuration using a combination of optical switches with polarization multiplexing is shown in accordance with an embodiment. According to exemplary embodiments, for each of the two shown amplification paths (e.g., vertical polarization amplification path 402, horizontal polarization amplification path 404), redundancy can be implemented by implementing two or more SOAs coupled to an optical switch, which can be a polarization maintaining (PM) component.

[0034] ​For example, PM optical switch 406 can be configured to select or switch between SOA 408 or SOA 410 to amplify an optical signal that can be input at a polarization beam combiner (PBC) 420. Similarly, in another example, PM optical switch 412 can be configured to select or switch between SOA 414 or SOA 416 to amplify an optical signal. At least in this regard, when using polarization multiplexed amplified optical signals, redundancy can be achieved with the aid of PM optical switches and corresponding SOAs. In some examples, PM optical switches 406 and 412 can also be configured to drive current to the corresponding SOAs. Further, it can be appreciated that, in addition to optical switching techniques, WDM and SOA integration (which will be described further below) can also be used to achieve redundancy of each polarization of an optical signal.

[0035] Figure 5 An exemplary redundant configuration 500 using SOA integration is shown in accordance with an embodiment. As shown, two or more SOAs (e.g., SOA 502, SOA 504, SOA“n”) can be integrated in the same substrate package. For example, SOA integration techniques can include photonic integration that can be performed using various methods (e.g., InP integration, Si integration, Ge-Si integration, hetero integration, etc.). It should be appreciated that one or more of the SOA integration packages or substrates (such as the SOA integration package or substrate with redundant configuration 500 shown) can be implemented or arranged in a repeater of an optical communication system. Figure 4

[0036] According to one embodiment, one or more switching mechanisms can also be implemented within the same SOA integration process. For example, the switching mechanisms can be in the form of optical switching, such as lxN and / or Nx1 optical switching. In another example, the switching mechanisms can be WDM combining or any other suitable form of combined optical paths. In another example, polarization combining can be performed by using a polarization beam combiner and an active polarization rotator that effectively act as a switch. Similar to the above examples, selection of the optical amplification path can be performed by switching between SOAs. In different examples, a particular SOA can be turned on or off to achieve the switching effect. It should be appreciated that passive or active optical combining can be used based at least on optical power budget, system requirements, and system complexity level.

[0037] ​In example embodiments, SOA 502 can be turned on while other SOAs in each repeater are turned off. In the event of a SOA (such as SOA 502) failure in one or more repeaters of the system, the current to SOA 502 can be turned off and power to one or more redundant SOAs (e.g., SOA 504, SOA n) can be turned on. As described, in some examples, the switching can be performed by selectively turning on or off particular SOAs. In different examples, the switching can be performed via one or more optical switches or optical switching circuits.

[0038] Figure 6 An example redundant configuration 600 for an optical digital transmission line having three separate fiber pairs is shown in accordance with an embodiment. Each fiber pair includes a receiver fiber and a transmitter fiber. Further, while three fiber pairs are shown in Figure 6 more or fewer fiber pairs can be implemented.

[0039] As shown, the number of amplified paths in each fiber pair can depend on the number of amplifiers, which can be one or more SOAs. In example embodiments, two or more SOAs for each optical path (e.g., paths associated with a repeater) can be used for redundancy and overall improvement of system reliability. The redundant configuration can be based on any of the examples or embodiments discussed above (e.g., WDM, optical switching, SOA integration). In some examples, a command control channel can be included in the optical digital transmission line, for example, for a redundant configuration using optical switching and integration of SOAs with optical combiners and / or optical switches.

[0040] In one or more of the redundant configurations described above, adjustment of gain and gain tilt can be achieved through temperature control of the SOAs and / or drive current. This can allow for adjustment of gain settings in the system as well as effects of aging and repair in the transmission line. Adjustment of temperature assumes implementation of temperature control of SOAs and command control features for all or a portion of the repeaters in the system. Other ways of controlling the overall gain of the SOAs can be used, including but not limited to variable optical attenuators and optical switches with predetermined optical attenuators or filters.

[0041] Novel and inventive apparatuses, systems, and methods for improving redundancy in semiconductor-based communication systems are disclosed herein. The scope of the disclosure is not limited to the specific embodiments described herein. Indeed, other various embodiments and modifications of the disclosure will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings.

[0042] Accordingly, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of particular implementations in a particular environment for a particular purpose, those of ordinary skill in the art will appreciate that its usefulness is not limited thereto and that it can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below shall be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims

1. An apparatus for redundancy improvement in an optical communication system, comprising: Wavelength division multiplexing (WDM) circuit; A first semiconductor optical amplifier (SOA), wherein the first SOA corresponds to a first operating wavelength; and The second SOA, wherein the second SOA corresponds to the second operating wavelength, and The WDM circuit is configured as follows: (i) Receiving an optical signal at the first operating wavelength and providing the received optical signal to the first SOA to amplify the optical signal, wherein the reception of the optical signal at the first operating wavelength is based on the selection of the first operating wavelength at the transmitter of the terminal in response to an instruction from at least one processor that a fault has occurred at the second SOA, or (ii) Receiving the optical signal at the second operating wavelength and providing the received optical signal to the second SOA to amplify the optical signal, wherein the reception of the optical signal at the second operating wavelength is based on the selection of the second operating wavelength at the transmitter in response to an instruction from the at least one processor that a fault has occurred at the first SOA.

2. The apparatus according to claim 1, further comprising: The third SOA, wherein the third SOA is configured to operate at a third operating wavelength, and The WDM circuit is further configured to: (i) receive the optical signal at the third operating wavelength, and (ii) provide the received optical signal to the third SOA to amplify the optical signal.

3. The apparatus of claim 1, wherein (i) when the first SOA amplifies the optical signal, the first SOA is turned on and the second SOA is turned off, or (ii) when the second SOA amplifies the optical signal, the second SOA is turned on and the first SOA is turned off.

4. The apparatus of claim 1, wherein the instruction on whether a fault has occurred at the first SOA or the second SOA includes the at least one processor further determining whether the first SOA or the second SOA is in a fault mode or is not applying or drawing current.

5. The apparatus of claim 1, wherein the apparatus is an optical repeater.

6. A method for redundancy improvement in an optical communication system, comprising: An optical signal is transmitted to an optical repeater, the optical repeater including at least a first semiconductor optical amplifier (SOA) and a second SOA, wherein the first SOA amplifies the optical signal transmitted at a first operating wavelength; The first SOA in the optical repeater is determined to be non-functional or in a fault mode via at least one processor; The second SOA is selected by selecting a second operating wavelength associated with the second SOA at the transmitter of the terminal in response to an instruction from the at least one processor that a fault has occurred at the first SOA; and The optical signal is transmitted at the second operating wavelength, causing the second SOA to amplify the optical signal.

7. The method of claim 6, wherein the selection of the second SOA comprises transmitting the optical signal at the second operating wavelength via a wavelength division multiplexing (WDM) transmitter.

8. The method of claim 6, wherein the optical repeater comprises a third SOA, and the method further comprises: The processor determines that the second SOA in the optical repeater is not functional or is in a fault mode. The third SOA is selected by selecting a third operating wavelength associated with the third SOA at the transmitter in response to an instruction from the at least one processor indicating a fault has occurred at the second SOA; and A third optical signal is transmitted at the third operating wavelength, causing the third SOA to amplify the third optical signal.

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