System and method for topping detection

Abstract

Systems and methods are disclosed for topping detection. The system comprises: (i) a spectral dispersion element for: receiving and dispersing an optical channel signal superimposed with a topping (PT) signal; (ii) at least one photodetector array comprising a first plurality of photodetectors for receiving respective portions of the dispersed optical channel signal and converting the respective portions into a first plurality of respective electrical signals; (iii) at least one analog-to-digital converter (ADC) for converting the first plurality of respective electrical signals into a first plurality of respective digital signals; (iv) a digital signal processor for processing the first plurality of respective digital signals and extracting channel specific information included in the PT signal, and calculating a channel power based on the channel specific information included in the PT signal.

Description

Technical Field

[0001] The present disclosure generally relates to optical networks, and more particularly to systems and methods for pilot tone detection. Background Art

[0002] In addressing high data throughput requirements, fiber - based communication systems (e.g., dense wavelength division multiplexing (DWDM) optical transmission and switching systems) are used to combine multiple optical signals operating at different wavelengths and simultaneously transmit the multiple optical signals at high speed along an optical fiber.

[0003] Optical performance monitoring is typically used to manage high - capacity DWDM optical transmission and switching systems. Generally, optical performance monitoring involves evaluating the quality of a data channel by measuring the optical characteristics of the data channel without directly viewing the transmitted bit sequence. This is a potential mechanism for improving the physical - layer fault management and transmission control of DWDM optical transmission and switching systems.

[0004] In optical communication, typical roles of optical performance monitoring include: ensuring the correct switching of reconfigurable optical add - drop multiplexers, setting the dynamic equalization power levels of optical amplifier gains, and providing system alerts and error warnings for lost or out - of - specification optical channels.

[0005] There are various conventional techniques in the art for monitoring optical performance. These conventional techniques are costly in terms of hardware complexity and implementation.

[0006] Therefore, there is an interest in developing efficient systems and methods for pilot tone (PT) detection for monitoring optical performance while reducing hardware complexity. Summary of the Invention

[0007] Embodiments of the present disclosure are developed based on the developers' understanding of the limitations associated with the prior art. A very common phenomenon in optical communication networks is the stimulated Raman scattering (SRS) effect, which causes energy to transfer from shorter wavelengths to longer wavelengths. SRS occurs between any two wavelengths. Due to SRS, the PT applied to one optical channel signal is also transferred to other optical channel signals, and the PT transferred to another optical channel signal becomes a "ghost tone".

[0008] The severity of SRS - induced ghost tones may depend on many factors, such as the number of optical channel signals, the positions and powers of the optical channel signals, the type of optical fiber, etc. SRS may lead to inaccurate monitoring of optical channel signal power, and even result in missed detection or false detection of optical channel signals.

[0009] To reduce the impact of SRS, various conventional techniques propose separating the optical channel signal into sub-bands, and each sub-band is detected by a separate PT detector. To separate the optical channel signal into sub-bands, conventional techniques rely on expensive hardware components, which may not be cost-effective and are even difficult to scale during implementation.

[0010] Therefore, developers have designed a system and method for PT detection that is based on a spectral dispersion element (such as a prism or grating element) to disperse the received optical signal, and an array of photodetectors is used to process the dispersed optical signal.

[0011] According to a first broad aspect of the present disclosure, there is provided a system for pilot tone (PT) detection, comprising: a spectral dispersion element configured to: receive an optical channel signal superimposed with a pilot tone (PT) signal, and disperse the optical channel signal; at least one array of photodetectors including a first plurality of photodetectors configured to receive respective portions of the dispersed optical channel signal and convert the respective portions into a first plurality of respective electrical signals; at least one analog-to-digital convertor (ADC) configured to convert the first plurality of respective electrical signals into a first plurality of respective digital signals; and a digital signal processor configured to: process the first plurality of respective digital signals and extract channel-specific information included in the PT signal, and calculate a channel power based on the channel-specific information included in the PT signal.

[0012] According to any embodiment of the present disclosure, the system further comprises a plurality of masks superimposed on the first plurality of photodetectors to perform responsivity correction of the first plurality of photodetectors.

[0013] According to any embodiment of the present disclosure, the plurality of masks are opaque metal strips.

[0014] According to any embodiment of the present disclosure, the plurality of masks are opaque plastic strips.

[0015] According to any embodiment of the present disclosure, the system further comprises at least one amplifier to amplify the first plurality of respective electrical signals.

[0016] According to any embodiment of the present disclosure, the at least one array of photodetectors includes a second array of photodetectors including a second plurality of photodetectors configured to receive respective portions of the dispersed optical channel signal and convert the respective portions into a second plurality of respective electrical signals.

[0017] According to any embodiment of the present disclosure, the at least one ADC is further configured to convert the second plurality of corresponding electrical signals into a second plurality of corresponding digital signals.

[0018] According to any embodiment of the present disclosure, the digital signal processor is further configured to: process the second plurality of corresponding digital signals, extract channel-specific information included in the PT signal based on the first plurality of corresponding digital signals and the second plurality of corresponding digital signals, and calculate channel power based on the channel-specific information.

[0019] According to any embodiment of the present disclosure, the at least one photodetector array is positioned on top of the second photodetector array in a manner such that the at least one photodetector array is offset relative to the second photodetector array.

[0020] According to any embodiment of the present disclosure, the system further includes at least one amplifier to amplify the first plurality of corresponding electrical signals and the second plurality of corresponding electrical signals.

[0021] According to any embodiment of the present disclosure, the spectral dispersion element is a prism.

[0022] According to any embodiment of the present disclosure, the spectral dispersion element is a grating element.

[0023] According to a second aspect of the present disclosure, there is provided a method for peak-top detection, including: receiving, by a spectral dispersion element, an optical channel signal superimposed with a peak-top (PT) signal; dispersing, by the spectral dispersion element, the optical channel signal; receiving, by at least one photodetector array including a first plurality of photodetectors, corresponding portions of the dispersed optical channel signal and converting the corresponding portions into a first plurality of corresponding electrical signals; converting, by at least one analog-to-digital converter (ADC), the first plurality of corresponding electrical signals into a first plurality of corresponding digital signals; processing, by a digital signal processor, the first plurality of corresponding digital signals and extracting channel-specific information included in the PT signal; and calculating, by the digital signal processor, channel power based on the channel-specific information included in the PT signal.

[0024] According to any embodiment of the present disclosure, the method further includes: superimposing a plurality of masks on the first plurality of photodetectors to perform responsivity correction on the first plurality of photodetectors.

[0025] According to any embodiment of the present disclosure, the plurality of masks are opaque metal strips.

[0026] According to any embodiment of the present disclosure, the plurality of masks are opaque plastic strips.

[0027] According to any embodiment of the present disclosure, the method further comprises: amplifying the first plurality of corresponding electrical signals by at least one amplifier.

[0028] According to any embodiment of the present disclosure, the method further comprises: receiving, by a second photodetector array including a second plurality of photodetectors, a respective portion of the dispersion optical channel signal, and converting the respective portion into a second plurality of corresponding electrical signals.

[0029] According to any embodiment of the present disclosure, the method further comprises: converting, by the at least one ADC, the second plurality of corresponding electrical signals into a second plurality of corresponding digital signals.

[0030] According to any embodiment of the present disclosure, the method further comprises: processing, by the digital signal processor, the second plurality of corresponding digital signals; extracting, by the digital signal processor, channel specific information included in the PT signal based on the first plurality of corresponding digital signals and the second plurality of corresponding digital signals; and calculating, by the digital signal processor, channel power based on the channel specific information.

[0031] According to any embodiment of the present disclosure, the at least one photodetector array is positioned on top of the second photodetector array in such a way that the at least one photodetector array has an offset relative to the second photodetector array.

[0032] According to any embodiment of the present disclosure, the method further comprises: amplifying the first plurality of corresponding electrical signals and the second plurality of corresponding electrical signals by at least one amplifier.

[0033] According to any embodiment of the present disclosure, the spectral dispersion element is a prism.

[0034] According to any embodiment of the present disclosure, the spectral dispersion element is a grating element. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In conjunction with the accompanying drawings, the features and advantages of the present disclosure will become apparent through the following detailed description, in which:

[0036] Figure 1 A block diagram of an optical network of a dense wavelength division multiplexing (DWDM) optical transmission and switching system according to various non-limiting embodiments of the present disclosure is depicted;

[0037] Figure 2 More details of a link between two nodes of an optical network according to various non-limiting embodiments of the present disclosure are shown;

[0038] Figure 3Shows a representative optical channel signal according to various non - limiting embodiments of the present disclosure, where the PT signal amplitude is modulated on the representative optical channel signal;

[0039] Figure 4 Shows a simplified PT detector configuration according to various non - limiting embodiments of the present disclosure;

[0040] Figure 5 Shows a representative scenario depicting the effect of detecting an optical channel signal in the gap between two adjacent photodetectors (PDs) when the detection resolution of the optical channel signal is very high;

[0041] Figure 6 Shows a representative scenario depicting the effect of detecting an optical channel signal in the gap between two adjacent PDs in the case of a low - resolution spectral dispersion element according to various embodiments of the present disclosure;

[0042] Figure 7 Shows a representative example of multiple PDs superimposed with a mask according to various embodiments of the present disclosure;

[0043] Figure 8 Shows representative simulation results of the performance of a PT detector configuration combining multiple PDs superimposed with a mask according to various non - limiting embodiments of the present invention;

[0044] Figure 9 Shows another PT detector configuration according to various non - limiting embodiments of the present disclosure;

[0045] Figure 10 Shows a flowchart of a process for peak - top (PT) detection according to various embodiments of the present disclosure.

[0046] It should be understood that in all the figures and the corresponding descriptions, the same features are identified by the same reference numerals. Additionally, it should also be understood that the figures and the following descriptions are for illustrative purposes only, and these disclosures are not intended to limit the scope of the claims. Detailed Description

[0047] The present disclosure aims to address at least some of the deficiencies of the current technology. Specifically, the present disclosure describes systems and methods for peak - top (PT) detection.

[0048] Unless otherwise defined or indicated by the context, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the described embodiments belong.

[0049] In the context of this specification, a "controller" is any computer hardware capable of running software suitable for handling relevant tasks in a process. In the context of this specification, the term "client device" is generally associated with the user of the client device. Thus, some (non-limiting) examples of client devices include personal computers (desktop, laptop, netbook, etc.), smartphones, and tablet computers, as well as network devices such as routers, switches, and gateways. It should be noted that a device acting as a client device in the context of the present invention does not exclude a server acting as other client devices. The use of the expression "client device" does not exclude multiple client devices from being used to receive / send, execute, or cause to execute any task or request, or the result of any task or request, or the steps of any method described herein.

[0050] In the context of this specification, unless otherwise expressly specified, words such as "first", "second", "third", etc. are only used to distinguish the nouns they modify from each other, rather than to describe any specific relationship between these nouns. Thus, for example, it should be understood that the use of the terms "first processor" and "third processor" is not intended to imply (for example) any particular order, type, chronological order, hierarchy, or ranking among / within the servers, and their use (by themselves) is not intended to imply that any "second server" must exist in any given situation. Furthermore, as discussed elsewhere in this context, the reference to a "first" element and a "second" element does not exclude the two elements being the same actual real-world element. Thus, for example, in some cases, the "first" server and the "second" server can be the same software and / or hardware, and in other cases, they can be different software and / or hardware.

[0051] It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly or indirectly connected or coupled to the other element, and intermediate elements may also exist. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, no intermediate element exists. Other words used to describe the relationship between elements (e.g., "between" versus "directly between", "adjacent" versus "directly adjacent", etc.) should be interpreted in a similar manner.

[0052] In the context of this specification, when an element is referred to as being "associated with" another element, in some embodiments, the two elements can be directly or indirectly linked, related, connected, coupled, the second element adopting the first element, etc., without limiting the scope of the present disclosure.

[0053] The terms used in this document are only for describing specific representative embodiments and are not intended to limit the technology of the present invention. Unless clearly stated in the context, the singular forms "a", "an", and "the" used herein also include the plural forms. It should also be understood that the terms "comprises" and / or "comprising" used in this specification are used to indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or their combinations.

[0054] The implementations of the technology of the present invention all include at least one of the above-mentioned objectives and / or aspects, but may not include all of these objectives and / or aspects. It should be understood that certain aspects of the technology of the present invention are intended to achieve the above-mentioned objectives, but may not meet this objective, and / or may meet other objectives not specifically described herein.

[0055] The examples and conditional language described herein are mainly for helping the reader understand the principles of the technology of the present invention, rather than limiting its scope to these specifically described examples and conditions. It should be understood that those skilled in the art can design various arrangements, although not explicitly described or shown herein, these arrangements embody the principles of the present technology and are included within its spirit and scope.

[0056] In addition, for the sake of helping understanding, the following description may describe relatively simplified implementations of the technology of the present invention. As those skilled in the art understand, various implementations of the technology of the present invention may have greater complexity.

[0057] In some cases, useful examples that are considered to be modifications of the technology of the present invention may also be listed. This is only for helping understanding, and, similarly, is not for defining the scope of the technology of the present invention or prescribing the boundaries of the technology of the present invention. These modifications are not an exhaustive list, and those skilled in the art can make other modifications while remaining within the scope of the present technology. In addition, in the case where no examples of modifications are presented, it should not be construed that modifications are impossible and / or the described is the only way to implement the element of the present technology.

[0058] Moreover, all descriptions of the principles, aspects, and implementations of the technology of the present invention herein, as well as their specific examples, are intended to include their structural and functional equivalents, whether currently known or developed in the future. Thus, for example, those skilled in the art will understand that any block diagrams herein represent a conceptual view of illustrative circuits embodying the principles of the technology of the present invention. Similarly, it should be understood that any flowcharts, flow diagrams, state transition diagrams, pseudocode, etc. represent various processes that can be substantially represented in a computer-readable medium and thus executed by a computer or processor, whether or not such computer or processor is explicitly shown.

[0059] The functions of the various elements shown in the figures, including any functional blocks labeled "processor" or "processing unit", can be provided by using dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, these functions can be provided by a single dedicated processor, a single shared processor, or multiple individual processors, some of which may be shared. In some embodiments of the technology of the present invention, the processor can be a general-purpose processor, such as a central processing unit (CPU), or a processor dedicated to a specific purpose, such as a graphics processing unit (GPU). Additionally, the explicit use of the terms "processor" or "controller" should not be construed as referring exclusively to hardware capable of executing software and can implicitly include, but is not limited to, digital signal processor (DSP) hardware, network processors, application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile memory. Other conventional and / or custom hardware may also be included.

[0060] Software modules, or modules or units that imply software, can herein be represented by any combination of flowchart elements or other elements indicating the execution of process steps and / or text descriptions. Such modules can be executed by hardware that is explicitly or implicitly shown.

[0061] Using these basic principles, the present disclosure aims to address at least some of the deficiencies of the current technology. Specifically, the present disclosure describes systems and methods for PT detection.

[0062] Now referring to the accompanying drawings, Figure 1FIG. 0 depicts a block diagram of an optical network 100 of a dense wavelength division multiplexing (DWDM) optical transmission and switching system in accordance with various non-limiting embodiments of the present disclosure. Typically, the optical network 100 may have a plurality of nodes 102-1, 102-2, ……, 102-7, and each node (e.g., 102-1, 102-2, ……, 102-7) may include an optical multiplexing section (OMS), and the OMS includes an optical add-drop multiplexer, e.g., a reconfigurable optical add-drop multiplexer (ROADM), and each ROADM includes at least one wavelength selective switch (WSS), a multiplexer, a demultiplexer, etc. Each node (e.g., 102-1, 102-2, ……, 102-7) may be used to add, drop, and / or reroute wavelengths. Each OMS-based node may also include a plurality of optical transport sections (OTSs), where the wavelength remains the same at each OTS.

[0063] Each node (e.g., 102-1, 102-2, ……, 102-7) in the optical network 100 may also incorporate one or more laser light sources that are used to generate, emit, or radiate optical pulses having a specific pulse duration. It is also contemplated that the emitted light may be single-polarized, dual-polarized, or randomly polarized and may have a specific polarization (e.g., linear polarization, elliptical polarization, or circular polarization), depending on the signal format.

[0064] In addition, each node (e.g., 102-1, 102-2, ……, 102-7) in the optical network 100 may incorporate a plurality of optical amplifiers for amplifying optical signals, such as erbium-doped fiber amplifiers (EDFAs). The optical network 100 may also use one or more optical network elements and modules (which may include either or both active elements / modules and passive elements / modules), e.g., filters, WSSs, arrayed waveguide gratings, optical transmitters, optical receivers, processors, and other suitable components. However, for the purposes of simplicity and operability, these elements have been omitted from Figure 1 FIG.

[0065] It is conceivable that nodes in an optical network can be communicatively connected via a link including multiple optical fibers. The optical fibers can be of any suitable type, such as single-mode fibers, multi-mode fibers, standard single mode fibers (SSMF), large effective area fibers (LEAF), etc. The link also includes multiple optical amplifiers, for example, EDFAs. The link between two nodes (such as 102-1 and 102-2) also includes an optical amplifier.

[0066] The optical network devices referred to in this article include one or more passive and / or active optical network components and / or modules of the optical network 100, including but not limited to optical fibers, optical amplifiers, filters, optical links, WSSs, arrayed waveguide gratings, and laser light sources.

[0067] Nodes within the optical network 100 (such as 102-1, 102-2, ……, 102-7) typically transmit signals on one optical wavelength channel among multiple optical wavelength channels. In this disclosure, the term "wavelength channel" refers to a modulated optical signal of a specific wavelength. The wavelength channel is also referred to as a "channel" in this article. Each channel is characterized by a channel bandwidth and a channel center frequency, and is usually defined by a frequency grid.

[0068] As described herein, the term "transmitted optical channel signal" refers to an optical channel signal before it propagates through an optical network device. And, as mentioned herein, the term "received optical channel signal" refers to an optical channel signal after it propagates through an optical network device.

[0069] In the optical network 100, a power tracking (PT) signal with amplitude modulation can be used to monitor the channel power. The "power tracking signal with amplitude modulation" (also referred to as the "PT signal" in this article) is a low-frequency (e.g., kHz to MHz) amplitude / intensity modulation applied to an optical channel signal. The PT signal can include a single or multiple frequencies. The spectral characteristics of the PT signal should not limit the scope of this disclosure.

[0070] The modulation depth of the PT signal is usually very small (e.g., a few percent of the channel power). The PT signal provides an in-band auxiliary channel for performance monitoring.

[0071] Each channel can be modulated with a different PT signal. For example, different modulation frequencies can be applied to different channels. Different spreading sequences can also be applied to the spectrally extended PT signals. Therefore, the power of a specific PT signal can be used to indicate the power of an optical channel signal in a wavelength division multiplexed (WDM) system. The PT signal can also be modulated to carry channel characterization information.

[0072] Figure 2 Shows more details of the link 200 between two nodes 102-1 and 102-2 of the optical network 100 according to various non-limiting embodiments of the present disclosure. Nodes 102-1 and 102-2 may include ROADM 202, optical amplifier 204, transmitter 206, receiver 208, and other components (not shown). The two nodes 102-1 and 102-2 may be connected by an optical fiber 212, and the optical fiber may include an additional optical amplifier 205. The link 200 may also include a PT detector 210 (the details of which will be discussed in the subsequent disclosure). Node 102-1 may receive one or more DWDM signals 214, 216, drop one or more channels from the DWDM signals 214, 216 at the receiver 208, add one or more channels generated by the transmitter 206, and pass through other channels. A WSS or a combination of a WSS and other multiplexer and demultiplexer components (not shown) may be used to add or drop signals. In some cases, the dropped channels will be converted from the optical domain to the electrical domain, while the added channels will be converted from the electrical domain to the optical domain. Otherwise, channel switching or passing is performed within the optical domain.

[0073] In addition to the usual service data modulation, the transmitter 206 may receive a bit stream including channel-specific information such as center wavelength, modulation format, baud rate, spectral shape, source / destination, etc. The transmitter 206 may convert the data bit stream into an encoded data stream and encode the PT signal with the encoded data stream to generate an encoded PT signal. In addition, the transmitter 206 may modulate the amplitude of the optical channel signal with the encoded PT signal. The steps of receiving, converting, encoding, and modulating may be performed by an encoder included in the transmitter 206.

[0074] To improve performance and other operation / maintenance purposes, various optical networks (e.g., optical network 100) require various information, such as per-channel power, channel-specific information (center wavelength, modulation format, baud rate, spectral shape, source / destination, etc.), etc. For this purpose, certain optical networks (e.g., optical network 100) may rely on PT technology.

[0075] There are different types of PT signals. The most common is amplitude modulated PT (AM-PT, or simply PT). The transmitter 206 can apply a small, relatively low frequency (kHz / MHz) amplitude / intensity modulation to the optical signal (GHz). Each optical signal can be applied a unique low frequency PT signal. To detect the PT signal, at least one photodetector (PD) array can be used to detect all optical channel signals without optical demultiplexing. By performing spectral analysis in the electrical domain or an equivalent digital domain, the presence and channel power of all channels can be monitored simultaneously. This provides a low-cost monitoring solution. The PT signal can also be turned on and off to carry channel-specific information. Figure 3 A representative optical channel signal 252 is shown in accordance with various non-limiting embodiments of the present disclosure, where a PT signal 254 is amplitude modulated on the representative optical channel signal 252.

[0076] A very common phenomenon in optical communication networks is the stimulated Raman scattering (SRS) effect, which transfers energy from shorter wavelengths to longer wavelengths. SRS occurs between any two wavelengths. Due to SRS, the PT applied to one optical channel signal will also transfer to other optical channel signals, and the PT transferred to another optical channel signal becomes "ghost tone topping".

[0077] The severity of SRS causing ghost tone topping may depend on many factors, such as the number of optical channel signals, the position and power of the optical channel signals, the fiber type, etc. SRS may cause inaccurate monitoring of the optical channel signal power, and even lead to missed detection or false detection of the optical channel signal.

[0078] To reduce the impact of SRS, various conventional techniques propose separating the optical channel signals into subbands, where each subband is detected by a separate PT detector. To separate the optical channel signals into subbands, conventional techniques rely on expensive hardware components, which may not be cost-effective and are even difficult to scale during implementation.

[0079] Therefore, to monitor optical performance, various embodiments of the present disclosure include a simplified PT detector configuration 400. Figure 4FIG. 400 shows a simplified PT detector configuration according to various non - limiting embodiments of the present disclosure. The PT detector configuration 400 can be implemented similar to the PT detector 210 at one or more locations in the link 200. For example, the PT detector configuration 400 can be located between two nodes 102 - 1 and 102 - 2 of the optical link 200. The PT detector configuration 400 can be used to extract a small optical power from the optical channel signals propagating in the optical fiber 212. The PT detector configuration 400 can determine the PT signals in the optical channel signals and calculate the channel power associated with each optical channel signal.

[0080] In some non - limiting embodiments, the PT detector configuration 400 can include a spectral dispersion element 402, a PD array 404 including a plurality of PDs, a transimpedance amplifier (TIA) 406, an analog - to - digital converter (ADC) 408, and a digital signal processor (DSP) 410. In addition to the above - mentioned components, the PT detector configuration 400 can include a lens 412 to focus the optical channel signals onto the spectral dispersion element 402. It should be noted that the PT detector 400 can include additional components. However, for simplicity, Figure 4 such components are omitted herein.

[0081] Some non - limiting examples of the spectral dispersion element 402 can include a low - resolution grating, a prism, etc. It should be noted that compared with the optical components used to detect optical channel signals in DWDM in conventional optical communication systems, the resolution of the spectral dispersion element 402 can be much lower.

[0082] For example, in a conventional coherent fiber - based optical communication system, the bandwidth of the optical channel signals is on the order of dozens to over 100 GHz. The spectral resolution of an optical spectrum analyzer (OSA) commonly used in a conventional coherent fiber - based optical communication system is typically higher than 0.1 nm (about 12.5 GHz in the C - band), and 0.03 nm (about 3.75 GHz) or even better resolution is routinely used. To ensure the advantages of the OSA, a higher resolution is required, otherwise the optical channel signals may not be correctly resolved and may be confused with adjacent channels. However, in various embodiments of the present disclosure, the spectral resolution of the spectral dispersion element 402 is deliberately chosen to be very low, for example, several nanometers.

[0083] It should be noted that the C band can be centered at 1550 nm. The exact wavelength range may vary depending on the optical communication system used. For example, the C band with 120 * 50 GHz channel spacing can have a wavelength range of 1528 to 1565 (6 THz or approximately 48 nm). The 48 nm wavelength can be divided into 4 subbands (or any other suitable number of subbands), so each subband can have a width of approximately 12 nm. A spectral resolution of a few nanometers may be a suitable choice. Such a low resolution is usually not sufficient in conventional spectral measurements, however, it may be beneficial in various embodiments of the present disclosure. To implement the PT detector configuration 400, very low-cost components may be required.

[0084] The spectral dispersion element 402 can be used to receive the optical channel signal propagating in the optical fiber 212. As previously mentioned, the optical channel signal can be superimposed with the PT signal. The spectral dispersion element 402 can disperse the optical channel signal. Dispersion can be referred to as the spreading of the spectrum of the optical channel signal.

[0085] The spectral dispersion element 402 can provide the dispersed optical channel signal 403 to the PD array 404. As previously mentioned, the PD array 404 can include multiple PDs. Each PD can be used to receive a corresponding portion of the dispersed optical channel signal 403. The PD array 402 can be used to convert the corresponding portions of the dispersed optical signal 403 into a first plurality of corresponding electrical signals 414.

[0086] It should be noted that there can be a certain gap between two adjacent PDs in the PD array 402. In the case where the resolution of the PT detector configuration 400 is high, the portion of the dispersed optical channel signal 403 that falls in the middle of each PD can be detected. However, the portion of the dispersed optical channel signal 403 that falls in the gap between two adjacent PDs may not be correctly detected and may result in inaccurate or missed detections. Additionally, detecting the dispersed optical channel signal 403 at the edge of the PD may be affected by a low signal-to-noise ratio (SNR) and high SRS.

[0087] Figure 5 A representative scenario 500 is shown depicting the effect of detecting an optical channel signal in the gap 502 between two adjacent PDs when the detection resolution of the optical channel signal is very high.

[0088] Therefore, the low resolution of the spectral dispersion element 402 can help the PT detector configuration 400 reduce the influence of the gap 502 between two adjacent PDs and improve the SNR. Figure 6FIG. 600 shows a representative scenario depicting the effect of detecting an optical channel signal in the gap 502 between two adjacent PDs in the case of a low-resolution spectral dispersion element 402, in accordance with various embodiments of the present disclosure. As shown, due to the wide dispersion in the dispersed optical signal 403, the influence of the gap 502 can be reduced.

[0089] Return to Figure 4 , the PD array 404 can forward the first plurality of corresponding electrical signals 414 to the TIA 406. The TIA 406 can be used to amplify the first plurality of corresponding electrical signals 414. The TIA 406 can forward the amplified first plurality of corresponding electrical signals 414 to the ADC 408. The ADC 408 can be used to convert the amplified first plurality of corresponding electrical signals 414 into the first plurality of corresponding digital signals 418.

[0090] The ADC 408 can forward the first plurality of corresponding digital signals 418 to the DSP 418. The DSP 410 can be used to: process the first plurality of corresponding digital signals 418 and extract channel-specific information included in the PT signal, such as center frequency, modulation format, baud rate, spectral shape, spectral information, source / destination, etc. It should be noted that how the DSP 410 extracts the PT signal and decodes the channel-specific information should not limit the scope of the present disclosure. Using the channel-specific information, the DSP 410 can calculate the channel power based on the channel-specific information.

[0091] It should be understood that even at a low resolution of the spectral dispersion element 402, the portion between the gaps 502 in the dispersed optical channel signal 403 can be detected, but for channels located in or around the gap 502, the effective responsivity of the PD array 404 may not be consistent. To further improve the performance of the PT detector configuration 400, in various non-limiting embodiments, the photosensitive area of the PD can be modified. To this end, a plurality of masks can be superimposed on the plurality of PDs of the PD array 404 to correct the responsivity of the plurality of PDs.

[0092] Figure 7 FIG. shows a representative example of a plurality of PDs 700 superimposed with a mask 702, in accordance with various embodiments of the present disclosure. In some embodiments, the mask 702 can be an opaque metal strip. In other embodiments, the mask 702 can be an opaque plastic strip. Figure 8 FIG. 800 shows representative simulation results of the performance of the PT detector configuration 400 incorporating a plurality of PDs 700 superimposed with a mask 702, in accordance with various non-limiting embodiments of the present invention; as shown, the responsivity of the PT detector configuration 400 can be improved by the mask 702.

[0093] Using an effective mask transmission distribution, the effective responsivity can be equalized. For example, for an optical communication system operating with a 48 nm bandwidth, 4 sub-bands, and a 2 nm spectral resolution, simulation results show that the relative responsivity ripple can be reduced to approximately + / -0.2 dB. This residual ripple can be further corrected through calibration.

[0094] In some non-limiting embodiments, to further improve the performance of the PT detector configuration 400 in terms of responsivity, the PT detector configuration 400 may include an additional PD array. Figure 9 A PT detector configuration 900 according to various non-limiting embodiments of the present disclosure is shown. The PT detector configuration 900 may be implemented similar to the PT detector 210 at one or more locations in the link 200. For example, the PT detector configuration 900 may be located between two nodes 102-1 and 102-2 of the optical link 200. The PT detector configuration 900 may be used to extract a small optical power from the optical channel signal propagating in the optical fiber 212. The PT detector configuration 900 may determine the PT signal in the optical channel signal and calculate the channel power associated with each optical channel signal.

[0095] In some non-limiting embodiments, the PT detector configuration 900 may include: a spectral dispersion element 902, a first PD array 904 including a first plurality of PDs, a second PD array 906 including a second plurality of PDs, a TIA 908, an ADC 910, and a DSP 912. In addition to the above components, the PT detector configuration 900 may include a lens 912 to focus the optical channel signal onto the spectral dispersion element 902. It should be noted that the PT detector configuration 900 may include additional components. However, for simplicity, Figure 9 such components are omitted herein.

[0096] Some non-limiting examples of the spectral dispersion element 902 may include a low-resolution grating, a prism, etc.

[0097] The spectral dispersion element 902 may be used to receive the optical channel signal propagating in the optical fiber 212. As previously mentioned, the optical channel signal may be superimposed with the PT signal. The spectral dispersion element 902 may disperse the optical channel signal. The dispersion may be referred to as the expansion of the spectrum of the optical channel signal.

[0098] The spectral dispersion element 902 can provide the dispersed optical channel signal 903 to the first PD array 904 and the second PD array 906. In various embodiments, the first PD array 904 can be positioned on top of the second PD array 906 in such a way that the first PD array 904 can have an offset relative to the second PD array 906. The first PD array 902 can be offset from the second PD array 902 in such a way that the photosensitive regions of the first plurality of PDs associated with the first PD array 904 are located above the gaps between the second plurality of PDs associated with the second PD array 906. In some embodiments, the offset can be at least the size of each PD.

[0099] Each PD in the PD array 904 and the PD array 906 can be used to receive a corresponding portion of the dispersed optical channel signal 903. The PD array 904 can be used to convert the corresponding portion of the dispersed optical signal 903 into a first plurality of corresponding electrical signals 916, and the PD array 906 can be used to convert the corresponding portion of the dispersed optical signal 903 into a second plurality of corresponding electrical signals 918.

[0100] The first PD array 404 and the second PD array 404 can forward the first plurality of corresponding electrical signals 916 and the second plurality of corresponding electrical signals 918 to the TIA 908. The TIA 908 can be used to amplify the first plurality of corresponding electrical signals 916 and the second plurality of corresponding electrical signals 918. The TIA 908 can forward the amplified first plurality of corresponding electrical signals 920 and the amplified second plurality of corresponding electrical signals 922 to the ADC 910. The ADC 910 can be used to convert the amplified first plurality of corresponding electrical signals 920 and the amplified second plurality of corresponding electrical signals 922 into a first plurality of corresponding digital signals 924 and a second plurality of corresponding digital signals 924.

[0101] The ADC 910 can forward the first plurality of corresponding digital signals 924 and the second plurality of corresponding digital signals 924 to the DSP 912. The DSP 912 can be used to: process the first plurality of corresponding digital signals 924 and the second plurality of corresponding digital signals 924, and extract channel-specific information included in the PT signal, such as center frequency, modulation format, baud rate, spectral shape, spectral information, source / destination, etc. It should be noted that how the DSP 912 extracts the PT signal and decodes the channel-specific information should not limit the scope of the present disclosure. Using the channel-specific information, the DSP 912 can calculate the channel power based on the channel-specific information.

[0102] Thus, with PT detector configurations 400 and 900, the operating cost and implementation complexity of PT detection technology can be reduced. Additionally, the techniques discussed in this disclosure can also enable better detection of flexible grid optical channel signals. A flexible grid can mean that the bandwidth and associated center wavelength of an optical channel signal are not fixed but can vary.

[0103] Figure 10 FIG. 1000 is a flowchart of a process for tone - top detection in accordance with various embodiments of the present disclosure. As shown, process 1000 begins at step 1002, in which a spectral dispersion element receives an optical channel signal superimposed with a tone - top (PT) signal. As previously described, spectral dispersion element 402 is used to receive an optical channel signal superimposed with a PT signal.

[0104] Process 1000 proceeds to step 1004, in which the spectral dispersion element disperses the optical channel signal. As previously described, spectral dispersion element 402 is used to disperse the optical channel signal.

[0105] Process 1000 advances to step 1006, in which at least one photodetector array including a first plurality of photodetectors receives a corresponding portion of the dispersed optical channel signal and converts the corresponding portion into a first plurality of corresponding electrical signals. As previously described, at least one photodetector array 404 is used to receive a corresponding portion of the dispersed optical channel signal 403 and convert the corresponding portion into a first plurality of corresponding electrical signals 414.

[0106] Process 1000 moves to step 1008, in which at least one analog - to - digital converter (ADC) converts the first plurality of corresponding electrical signals into a first plurality of corresponding digital signals. As previously described, ADC 406 is used to convert the first plurality of corresponding electrical signals 414 into a first plurality of corresponding digital signals 416.

[0107] Process 1000 advances to step 1010, in which a digital signal processor processes the first plurality of corresponding digital signals and extracts channel - specific information included in the PT signal. As previously described, digital signal processor 410 is used to process the first plurality of corresponding digital signals 416 and extract channel - specific information included in the PT signal.

[0108] Finally, at step 1012, the digital signal processor calculates the channel power based on the channel - specific information included in the PT signal. As previously described, digital signal processor 410 is used to calculate the channel power based on the channel - specific information included in the PT signal.

[0109] It should be understood that the operations and functions of the PT detector configurations 400 and 900, the component parts, and the associated processes can be implemented by any one or more of hardware-based, software-based, and firmware-based elements. Such alternative operations do not limit the scope of the present disclosure in any way.

[0110] It should also be understood that although the embodiments presented herein have been described with reference to specific features and structures, it is apparent that various modifications and combinations can be made without departing from these disclosures. Accordingly, the specification and drawings are to be regarded only as an illustration of the implementations or embodiments and their principles defined by the appended claims, and it is intended to cover any and all modifications, variations, combinations, or equivalents that fall within the scope of the present disclosure.

Claims

1. A system for peak-top detection, characterized in that, it includes: a spectral dispersion element, configured to: receive an optical channel signal superimposed with a peak-top (PT) signal, and disperse the optical channel signal; at least one photodetector array, including a first plurality of photodetectors, the first plurality of photodetectors being configured to receive corresponding portions of the dispersed optical channel signal and convert the corresponding portions into a first plurality of corresponding electrical signals; at least one analog-to-digital converter (ADC), configured to convert the first plurality of corresponding electrical signals into a first plurality of corresponding digital signals; and a digital signal processor, configured to: process the first plurality of corresponding digital signals, extract channel-specific information included in the PT signal, and calculate the channel power based on the channel-specific information included in the PT signal.

2. The system according to claim 1, characterized in that, it further includes a plurality of masks, the plurality of masks being superimposed on the first plurality of photodetectors to perform responsivity correction on the first plurality of photodetectors.

3. The system according to claim 2, characterized in that, the plurality of masks are opaque metal strips.

4. The system according to claim 2, characterized in that, the plurality of masks are opaque plastic strips.

5. The system according to any one of claims 1 to 4, characterized in that, it further includes at least one amplifier to amplify the first plurality of corresponding electrical signals.

6. The system according to claim 1, characterized in that, the at least one photodetector array includes a second photodetector array, the second photodetector array including a second plurality of photodetectors, the second photodetector array being configured to receive corresponding portions of the dispersed optical channel signal and convert the corresponding portions into a second plurality of corresponding electrical signals.

7. The system according to claim 6, characterized in that, the at least one ADC is further configured to convert the second plurality of corresponding electrical signals into a second plurality of corresponding digital signals.

8. The system according to claim 6, characterized in that, the digital signal processor is further configured to: process the second plurality of corresponding digital signals, extract channel-specific information included in the PT signal based on the first plurality of corresponding digital signals and the second plurality of corresponding digital signals, and calculate the channel power based on the channel-specific information.

9. The system according to any one of claims 6 to 8, characterized in that, the at least one photodetector array is positioned on top of the second photodetector array in such a way that the at least one photodetector array has an offset relative to the second photodetector array.

10. The system according to any one of claims 6 to 9, characterized in that, it further includes at least one amplifier to amplify the first plurality of corresponding electrical signals and the second plurality of corresponding electrical signals.

11. The system according to any one of claims 1 to 10, characterized in that, the spectral dispersion element is a prism.

12. The system according to any one of claims 1 to 10, characterized in that, The spectral dispersion element is a grating element.

13. A method for peak-top detection, characterized in that, comprising: receiving, by a spectral dispersion element, an optical channel signal superimposed with a peak-top (PT) signal; dispersing, by the spectral dispersion element, the optical channel signal; receiving, by at least one photodetector array including a first plurality of photodetectors, corresponding portions of the dispersed optical channel signal, and converting the corresponding portions into a first plurality of corresponding electrical signals; converting, by at least one analog-to-digital converter (ADC), the first plurality of corresponding electrical signals into a first plurality of corresponding digital signals; processing, by a digital signal processor, the first plurality of corresponding digital signals, and extracting channel-specific information included in the PT signal; and calculating, by the digital signal processor, a channel power based on the channel-specific information included in the PT signal.

14. The method according to claim 12, characterized in that, further comprising: superimposing a plurality of masks on the first plurality of photodetectors to perform responsivity correction on the first plurality of photodetectors.

15. The method according to claim 14, characterized in that, the plurality of masks are opaque metal strips.

16. The method according to claim 14, characterized in that, the plurality of masks are opaque plastic strips.

17. The method according to any one of claims 13 to 16, characterized in that, further comprising: amplifying, by at least one amplifier, the first plurality of corresponding electrical signals.

18. The method according to claim 13, characterized in that, further comprising: receiving, by a second photodetector array including a second plurality of photodetectors, corresponding portions of the dispersed optical channel signal, and converting the corresponding portions into a second plurality of corresponding electrical signals.

19. The method according to claim 18, characterized in that, further comprising: converting, by the at least one ADC, the second plurality of corresponding electrical signals into a second plurality of corresponding digital signals.

20. The method according to claim 18, characterized in that, further comprising: processing, by the digital signal processor, the second plurality of corresponding digital signals; extracting, by the digital signal processor, channel-specific information included in the PT signal based on the first plurality of corresponding digital signals and the second plurality of corresponding digital signals; and calculating, by the digital signal processor, a channel power based on the channel-specific information.

21. The method according to any one of claims 18 to 20, characterized in that, the at least one photodetector array is positioned on top of the second photodetector array in such a way that the at least one photodetector array has an offset relative to the second photodetector array.

22. The method according to any one of claims 18 to 21, characterized in that, further comprising: amplifying, by at least one amplifier, the first plurality of corresponding electrical signals and the second plurality of corresponding electrical signals.

23. The method according to any one of claims 13 to 22, characterized in that, the spectral dispersion element is a prism.

24. The system according to any one of claims 13 to 22, Characterized in that, the spectral dispersion element is a grating element.

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