Systems and Methods for Coherent Burst Reception

Abstract

The present application relates to a system and method for coherent burst reception. An optical network communication system utilizes a coherent passive optical network (PON). The system includes an optical line terminal (OLT) having a downstream transmitter and an upstream receiver system configured for time-division and wavelength-division coherent detection. The system further includes a splitter in operable communication with the OLT and a plurality of optical network units (ONUs) in operable communication with the splitter. Each of the plurality of ONUs is configured to (i) receive a downstream coherent burst signal from the OLT and (ii) transmit at least one upstream burst signal to the OLT. The upstream receiver system further includes a power control module and a local oscillator (LO) configured to generate an optical LO signal. The power control module is configured to adaptively control the power level of the optical LO signal in real time.

Description

[0001] This application is a divisional application of an application filed on August 2, 2019, with application number 201980065013.8 and invention name “System and method for coherent burst reception”.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 713,691, filed August 2, 2018, which is incorporated herein by reference in its entirety. Technical Field

[0004] The field of the present disclosure relates generally to fiber optic communication networks, and more particularly to access networks capable of transmitting coherent optical signals. Background Art

[0005] The development of high-speed wired (e.g., fiber-to-the-premises (FTTP)) access networks has been driven by new business and technology drivers such as cloud services, 5G wireless transmission, and high-bandwidth 4K / 8K video applications. The growing demand for high-speed data and video services is currently driving access network paradigm bandwidth requirements of up to Gigabits per second (Gb / s) for residential products and up to multi-Gb / s for the enterprise market in optical access networks in the near future. For example, cable operators now regularly provide Gb / s services to residential products, and access bandwidth requirements therefrom are expected to grow to multi-Gb / s speeds in response to increased 4K / 8K video streaming, the expansion of cloud computing, "big data," social media, the Internet of Things (IoT), and mobile data delivery.

[0006] Conventional access network architectures utilize passive optical networks (PONs), such as Gigabit Passive Optical Networks (GPONs) within the ITU-T or Ethernet Passive Optical Networks (EPONs) within the IEEE. PONs can be point-to-multipoint (P2MP) and are often a low-cost alternative to point-to-point Ethernet for medium to large groups. GPON and EPON have some technical differences in signal encapsulation and dynamic bandwidth allocation, but both PON types are capable of carrying data over optical fiber from an optical hub to the customer premises via a passive optical network. Both PON types use baseband digital signaling over the optical fiber to carry information.

[0007] In the P2MP paradigm, PON technology has become one of the main architectures to meet the growing high-capacity demand for end users, which is further demonstrated by the progress in standards bodies developing the next-generation high-speed time-division multiplexing PON (TDM-PON) standard. The IEEE 802.3ca 100G Ethernet PON (EPON) task group is moving towards the standardization of 25 / 50G EPON based on wavelength multiplexing of 25Gbps per single channel. New projects to standardize higher-speed PON (e.g., 50Gbps) have also been proposed in the ITU-T Q2 / SG15 group. As a result, there is a continuous demand for PON evolution to provide higher per-subscriber data rates and wider service and application coverage, while minimizing capital expenditure (CAPEX) and operating expenditure (OPEX) costs, and also increasing the reconfigurability of adjustable solutions.

[0008] High-speed PON systems based on single-wavelength TDM mechanisms have been conventionally used to reduce the number of required optical components and their associated costs, while also conserving wavelength resources. However, the limited sensitivity of these systems has become a significant challenge in the further development of high-speed direct detection-based PON systems with high power budgets.

[0009] Coherent detection technology has provided an effective technique for improving receiver sensitivity. Within the PON paradigm, recent coherent detection solutions have improved receiver sensitivity by coherently beating the signal with a clean local oscillator (LO) signal. These recent solutions support longer distance transmission and a larger number of end users, while also enabling the use of high access speeds in multiple dimensions and more advanced modulation formats with higher spectral efficiency. Coherent technology further enables possible advanced digital signal processing (DSP) technology to achieve the reduction of optical and electrical impairments (e.g., chromatic dispersion (CD), etc.) in the digital domain. However, the main challenge in implementing a TDM PON system based on coherent detection comes from the upstream burst receiver, which also exists in non-coherent TDM-PON systems. In the following text with respect to Figure 1 A conventional TDM-PON system is further described.

[0010] Figure 1 FIG1 is a schematic illustration of a conventional TDM PON system 100. System 100 includes a centralized optical line terminal (OLT) 102, a splitter 104, and a plurality of optical network units (ONUs) 106 (i.e., 1 to n), which can, for example, further communicate with a plurality of users or customer premises (not shown). OLT 102 is typically located within a central office, a communications hub, or the headend of an optical link and is used to convert standard signals from a service provider (not shown) to the frequency and framing used by system 100. It also coordinates multiplexing between conversion devices on ONUs 106. Splitter 104 can represent, for example, a power splitter / combiner.

[0011] exist Figure 1 In the example depicted in FIG, system 100 represents a conventional TDM-PON (e.g., 10G-EPON, 10G-PON (also known as XG-PON), etc.) implementing upstream burst technology, wherein a centralized OLT 102 is operatively connected to a splitter 104 via an optical transmission medium 108 (e.g., single-mode fiber (SMF)), which in turn is operatively connected to ONUs 106 via secondary optical fibers 110 at various locations throughout its passive optical distribution network (ODN). In a conventional TDM PON ODN, the splitter 104 is typically a passive optical power splitter.

[0012] In operation of the system 100, the OLT 102 transmits a downstream burst signal 112 and receives a plurality of upstream burst signals 114. Therefore, the upstream burst signals 114(1), 114(2), 114(2) from different users (i.e., ONUs 106(1), 106(2), 106(n) respectively) arrive at the OLT 102 at different power levels in different time slots, as shown in FIG. Figure 1 As depicted in the embodiments described in . The OLT 102 therefore needs to implement burst clock and data recovery (BCDR) in a relatively short time in order to reduce the overhead length of individual bursts of the upstream burst signal 114. However, the dynamic range of the received power in the upstream direction from the upstream burst signal 114 can typically be greater than 15 dB, which poses a challenge for such conventional architectures. That is, to implement burst mode reception for the upstream burst signal 114, conventional techniques generally require two processing steps 116 (i.e., performed by computer-executable instructions of a processor or by a dedicated hardware unit therefor) to obtain synchronization signal detection: (1) burst gain control 118; and (2) burst data recovery 120.

[0013] Furthermore, in conventional PON systems 100, burst amplification is typically implemented in the electrical domain using a burst-mode limited transimpedance amplifier (TIA). However, this type of TIA electrical domain implementation presents additional challenges, especially with respect to high-speed burst signals above 10 Gb / s. Figures 2A to 2B This TIA challenge is further described.

[0014] Figures 2A to 2B is a schematic illustration of a conventional coherent receiver 200, 202. More specifically, Figure 2A The coherent receiver 200 represents a conventional heterodyne dual-polarization receiver, and Figure 2BThe coherent receiver 202 of FIG. 1 represents a conventional homodyne dual-polarization receiver. The heterodyne coherent receiver 200 includes an optical receiving section 204 (e.g., an optical hybrid and a photodetector (PD)) that receives an input optical signal 206 and an input LO signal 208 and outputs an electrical signal 210 using a plurality of burst TIAs 212 for each electrical signal data path. Figure 2A In the illustrated heterodyne example, two TIAs 212 are shown for two respective output electrical signal data paths 210. Similarly, the homodyne coherent receiver 202 includes an optical receive section 214 that receives an input optical signal 216 and an input LO signal 218 and outputs an electrical signal 220 using multiple burst TIAs 222 for each respective electrical signal data path (i.e., four TIAs 222 for four respective output electrical signal data paths 220). For ease of explanation, optical signal paths are depicted as solid lines, and electrical signal paths are depicted as dashed lines.

[0015] The respective architectures of the coherent receivers 200, 202 are thus challenged by the requirement for multiple burst TIAs for each different electrical data path of the coherent upstream burst receiver. Furthermore, the respective TIAs 212, 222 must also be linear and identical for each such electrical data path 210, 220 (i.e., 2 or 4 burst linear TIAs for the dual-polarization coherent receiver 200 or 202, respectively). Therefore, there is a need for improved techniques for implementing burst amplification through gain control in the optical domain, as opposed to conventional techniques implemented in the electrical domain, so that the requirement for burst TIAs can be relaxed, or even eliminated. Summary of the Invention

[0016] In one embodiment, an optical network communication system utilizes a coherent passive optical network (PON). The system includes an optical line terminal (OLT) having a downstream transmitter and an upstream receiver system configured for time-division and wavelength-division coherent detection. The system further includes a splitter in operable communication with the OLT and a plurality of optical network units (ONUs) in operable communication with the splitter. Each of the plurality of ONUs is configured to (i) receive a downstream coherent burst signal from the OLT and (ii) transmit at least one upstream burst signal to the OLT. The upstream receiver system further includes a power control module and a local oscillator (LO) configured to generate an optical LO signal. The power control module is configured to adaptively control the power level of the optical LO signal in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like reference numerals represent like parts throughout:

[0018] Figure 1It is a schematic illustration of a conventional time division multiplexing passive optical network system.

[0019] Figures 2A to 2B is a schematic illustration of a conventional coherent receiver.

[0020] Figure 3 is a schematic illustration depicting the operating principles of an exemplary coherent receiver system for a coherent passive optical network, according to an embodiment.

[0021] Figures 4A to 4C is a schematic illustration of a local oscillator power control scheme according to one embodiment.

[0022] Figure 5 is a schematic illustration of a feed-forward automatic local oscillator power control scheme according to one embodiment.

[0023] Figure 6 is a schematic illustration of a feedback automatic local oscillator power control scheme according to one embodiment.

[0024] Figure 7 is a schematic illustration of a dynamic bandwidth allocation power control scheme according to one embodiment.

[0025] Figure 8 is a flow chart of an exemplary registration process that may be implemented with the embodiments described herein.

[0026] Figure 9 is a flow diagram of an alternative registration process that may be implemented with the embodiments described herein.

[0027] Figure 10 is a flow chart of an automatic power balancing process that may be implemented with embodiments described herein.

[0028] Figure 11 is a flow chart of a command-based power balancing process that may be implemented with embodiments described herein.

[0029] Unless otherwise indicated, the drawings provided herein are intended to illustrate features of embodiments of the present disclosure. These features are believed to be applicable to a wide variety of systems that incorporate one or more embodiments of the present disclosure. As such, the drawings are not intended to include all conventional features known to those of ordinary skill in the art necessary to practice the embodiments disclosed herein. DETAILED DESCRIPTION

[0030] In the following description and claims, reference will be made to several terms which shall be defined to have the following meanings.

[0031] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0032] "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

[0033] As used herein throughout the specification and claims, approximating language may be applied to modify any quantitative representation that can be varied in a permissible manner without resulting in a change in the basic function to which it is related. Accordingly, a value modified by one or more terms such as "about," "approximately," and "substantially" is not limited to the exact value specified. In at least some cases, approximating language may correspond to the precision of an instrument used to measure the stated value. Here and throughout the specification and claims, range limitations may be combined and / or interchangeable; unless content or language indicates otherwise, such ranges are identified and include all subranges contained therein.

[0034] As used herein, the terms "processor" and "computer," as well as related terms (e.g., "processing device," "computing device," and "controller"), are not limited to those integrated circuits known in the art as computers, but broadly refer to microcontrollers, microcomputers, programmable logic controllers (PLCs), application-specific integrated circuits (ASICs), and other programmable circuits, and these terms are used interchangeably herein. In the embodiments described herein, memory may include, but is not limited to, computer-readable media such as random access memory (RAM) and computer-readable non-volatile media such as flash memory. Alternatively, floppy disks, compact disk read-only memories (CD-ROMs), magneto-optical disks (MODs), and / or digital versatile disks (DVDs) may also be used. Furthermore, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and keyboard. Alternatively, other computer peripherals may be used, including, for example, but not limited to, scanners. Furthermore, in exemplary embodiments, additional output channels may include, but are not limited to, an operator interface monitor.

[0035] Furthermore, as used herein, the terms "software" and "firmware" are interchangeable and include computer programs stored in memory for execution by personal computers, workstations, clients, and servers.

[0036] As used herein, the term "non-transitory computer-readable medium" is intended to refer to any tangible computer-based device implemented in any method or technology for short-term and long-term storage of information such as computer-readable instructions, data structures, program modules and submodules, or other data in any device. Thus, the methods described herein may be encoded as executable instructions embodied in a tangible, non-transitory computer-readable medium, including but not limited to storage devices and memory devices. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. Furthermore, as used herein, the term "non-transitory computer-readable medium" encompasses all tangible computer-readable media, including but not limited to non-transitory computer storage devices, including but not limited to volatile and non-volatile media and removable and non-removable media, such as firmware, physical and virtual storage devices, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, as well as digital means yet to be developed, with the sole exception of transitory propagated signals.

[0037] Furthermore, as used herein, the term "real time" refers to at least one of the following: the time of occurrence of associated events, the time of measurement and scheduled data collection, the time of processing data by a computing device (e.g., a processor), and the time of system response to events and circumstances. In the embodiments described herein, these activities and events occur substantially instantaneously.

[0038] As used herein, a "modem termination system" (MTS) refers to a termination unit that includes one or more of the following: an optical network terminal (ONT), an optical line terminal (OLT), a network termination unit, a satellite termination unit, a cable modem termination system (CMTS), and / or other termination systems that may be referred to individually or collectively as an MTS.

[0039] As used herein, "modem" refers to a modem device, which may be referred to individually or collectively as a modem, including one or more cable modems (CMs), satellite modems, optical network units (ONUs), DSL units, etc.

[0040] As described herein, "PON" generally refers to a passive optical network or system having components labeled according to known naming conventions for similar elements used in conventional PON systems. For example, an OLT may be implemented at an aggregation point such as a headend / hub, and multiple ONUs may be located and operable at multiple end-user, customer premises, or subscriber locations. Thus, "uplink transmission" refers to upstream transmission from an end-user to a headend / hub, and "downlink transmission" refers to downstream transmission from a headend / hub to an end-user, which may be assumed to be generally continuous transmission (unless in power-saving mode or the like).

[0041] In one exemplary embodiment, a system and method for burst coherent reception using LO for coherent detection is described herein. Embodiments of the present invention are generally applicable to burst coherent receivers and are not limited to the above with respect to only Figures 2A to 2B An example of a conventional coherent receiver is described. The innovative burst control techniques of the present application thus represent a substantial improvement over direct detection system approaches, which achieve burst gain control simply by adjusting the gain of an optical preamplifier for the received signal. The present coherent detection system and method presents a new advantageous burst gain control technique that adjusts the optical output power of the LO, thereby directly affecting the coherent gain, and the subsequent output electrical signal level therefrom.

[0042] The systems and methods of the present invention are also particularly useful in situations where different users (e.g., ONUs) are located at different distances from the OLT, where the respective powers of bursts in the received optical signal can be expected to vary over a significantly large dynamic range. Since coherent receivers typically include one or more analog-to-digital converters (ADCs) with a specific quantization range, techniques according to embodiments of the present invention provide yet further improvements over conventional techniques by effectively obtaining equal or similar electrical signal powers for different signals, which results in significantly improved optimal receiver performance.

[0043] Thus, in one exemplary embodiment, an improved method for efficiently implementing burst gain control by adaptively adjusting input LO power is provided. As further described in greater detail below, these improved techniques can be implemented not only with respect to different coherent flapping gain control mechanisms, but also with respect to different coherent operating schemes and principles. According to these innovative embodiments, a lower-cost configuration of electrical components can be advantageously achieved, thereby significantly reducing the system's CAPEX and OPEX.

[0044] In some embodiments, the systems and methods of the present invention need not necessarily completely replace existing power balancing methods in PON systems (e.g., power balancing used in NG-PON2 to adjust ONU transmitter power), but can be advantageously implemented in a complementary manner to improve upon conventional techniques.

[0045] In one embodiment, the systems and methods of the present invention further exploit the inherent properties of coherent beating that are unique to the coherent detection paradigm, thereby achieving still further advantages, including but not limited to: (i) an efficient method for implementing burst gain control in the optical domain based on the unique properties of coherent beating gain in coherent detection; (ii) by implementing burst gain control in the optical domain, the need for burst TIAs in the electrical domain is relaxed or eliminated, thereby significantly reducing the equipment and operating costs of coherent receivers that would otherwise require multiple TIAs; and (iii) by advantageously utilizing a continuous LO signal with constant optical power, LO power control is simplified and costs are further reduced compared to conventional techniques for burst optical amplification of the received signal (e.g., using a burst EDFA as a pre-amplifier for the received signal), whereas the received signal in burst mode will have a high dynamic range.

[0046] Figure 3 is a schematic illustration depicting the operating principles of an exemplary coherent receiver system 300 for a coherent PON (not separately illustrated, also referred to as a CPON). Figure 3 In the embodiment depicted in FIG, the coherent receiver system 300 is shown as being structurally similar to Figure 2B The present invention relates to a homodyne dual-polarization receiver 202 of the present invention, except that the coherent receiver system 300 is configured to implement an adaptive power control technique for optimizing the performance of the coherent receiver system 300. As discussed above, the specific structural configuration of the coherent receiver system 300 is provided by way of illustration and not by way of limitation. The adaptive power control technique described herein is applicable to other coherent detection burst receivers (heterodyne, homodyne, intradyne, etc.) that use LO.

[0047] In an exemplary embodiment, the coherent receiver system 300 (or a portion thereof) is disposed at an OLT (e.g., Figure 1 1 ) within the OLT 102 of FIG. 1 and includes an optical receiving portion 302 configured to receive an input optical signal 304 (e.g., via an SMF) and an LO signal 306 from an LO 308. In this example, the optical receiving portion 302 is further configured to output an electrical signal 310 via a corresponding electrical signal path 312 using a plurality of burst TIAs 314 for each corresponding electrical signal path 312 (e.g., four TIAs 314 for four corresponding electrical signal paths 312 in this example). The input optical signal 304 includes signals from a corresponding plurality of users (e.g., Figure 1 ONU 106, Figure 3 3. Similar to the examples described above, the optical signal paths are again depicted with solid lines, and the electrical signal paths are depicted with dashed lines.

[0048] Exemplary architectures of coherent PON architectures and their corresponding components are described in more detail in U.S. Patent No. 9,912,409, U.S. Patent No. 10,200,123, and co-pending U.S. patent application Ser. No. 15 / 609,461, filed May 31, 2017, to the inventor, the disclosures of all of which are incorporated herein by reference.

[0049] In the exemplary operation of the coherent receiver system 300, the adaptive power control of the LO 308 is innovatively exploited by the inherent coherent detection properties. For example, the amplitude of the electrical signal alternating current (AC) after the photodetector (e.g., output electrical signal 310) depends on the power of the LO signal 306 and the input optical signal 304. Assuming the responsivity is R, the amplitude A of the AC signal after the photodetector is ac It can be expressed as follows:

[0050]

[0051] Among them, P S represents the power of the input optical signal 304 at the optical receiving portion 302, and P LO represents the power of the LO signal 306 at the optical receiving section 302 .

[0052] Nevertheless, because different users generating corresponding bursts 316 may be located at various distances from the optical receiving portion 302, the power P of the burst 316 in the received input optical signal 304 may be greater than or equal to 0. S Can vary within a broad range. Figure 3 In the exemplary embodiment depicted in FIG. 3 , after coherent detection by the optical receiving portion 302, the power P of the LO signal 306 at the LO 308 is controlled according to the following LO To achieve the constant amplitude electrical signal 318:

[0053] P LO ∝(A ac / 2R) 2 / P S (Equation 2)

[0054] That is, according to the exemplary operation of the coherent receiver system 300, contrary to the conventional technique that requires the use of a burst optical preamplifier to change the signal power, the LO power P is controlled. LOIn an exemplary embodiment, the power control of LO 308 is adaptively performed. Thus, through adaptive power control of LO 308, optimal demodulation conditions (e.g., constant-amplitude electrical signals 318) of the received signal (e.g., input optical signal 304) are achieved after coherent detection by coherent receiving section 302, such that the corresponding amplitudes of subsequent corresponding electrical bursts have equal or similar burst amplitudes, i.e., power levels.

[0055] In an exemplary embodiment, the power level P of each burst 316 is determined based on the time. S1 ,P S2 ,P S3 As shown in the LO power graph 320, P can be adaptively controlled. LO , so that P in time LO The power level 322 is related to the burst signal power P at any given time. S1 Inversely related. Figures 4A to 7 Exemplary LO power control techniques are further described.

[0056] Figures 4A to 4C 4 and 5. Schematic illustrations of LO power control schemes 400, 402, and 404, respectively. The power control schemes 400, 402, and 404 represent, for example, methods for implementing a PON system (e.g., Figure 1 The present invention provides an alternative to current techniques for burst LO power control in a PON system 100. One or more of the power control schemes 400, 402, 404 may be particularly useful in situations where different burst lengths in the PON system require burst gain control frequencies above a general frequency range (e.g., tens of megahertz or greater).

[0057] In one embodiment of the first method, Figure 4A The power control scheme 400 is implemented with respect to an LO 406 including a laser source 408 and a power control module 410 in operable communication with the LO 406. In some embodiments, the power control module 410 is a separate component from the LO 406. In other embodiments, the power control module 410 is an integral component of the LO 406. In an exemplary operation of the power control scheme 400, the power control module 410 is used to provide direct control of the laser drive voltage of the laser source 408 to (e.g., adaptively) vary the LO power of an output LO signal 412 from the LO 406. For ease of explanation, the LO 406 may include Figure 4A One or more additional hardware and / or processing components not shown. Figures 4A to 4COf the several exemplary methods depicted in , power control scheme 400 represents the simplest structural and operational setup, but a high performance frequency and chirp controlled laser for laser source 408 may be required in situations where LO frequency drift or chirp may be problematic in related PON systems.

[0058] In one embodiment of the second method, Figure 4B The power control scheme 402 is similar to Figure 4A 4. Power control scheme 402 is similar to power control scheme 400 and is implemented similarly with respect to LO 414 including laser source 416 and power control module 418. However, power control scheme 402 differs from power control scheme 400 in that LO 414 further includes an optical amplifier 420, and power control module 418 is used to control optical amplifier 420, thereby enabling LO 414 to maintain a fixed laser drive voltage for laser source 416. According to power control scheme 402, power control of output LO signal 422 is achieved by adjusting the gain of optical amplifier 420 after laser source 416. In one embodiment, optical amplifier 420 may include one or more of a semiconductor optical amplifier (SOA), a fiber amplifier, or another type of amplifier. According to power control scheme 402, frequency drift issues are effectively addressed, and the use of optical amplifier 420 also provides relatively fast gain control response over a significantly wide frequency range (e.g., tens of megahertz or greater).

[0059] In one embodiment of the third method, Figure 4C The power control scheme 404 is similar to Figure 4B 4. The power control scheme 404 is similar to the power control scheme 402 and is implemented similarly with respect to the LO 424 including the laser source 426 and the optical amplifier 428, and the power control module 430. However, the power control scheme 404 differs from the power control scheme 402 in that the LO 424 further includes an adjustable optical attenuator (VOA) 432 after the optical amplifier 428, and the power control module 430 is used to control the adjustable optical attenuator 432, thereby enabling the LO 424 to maintain both the laser driving voltage of the laser source 426 and the gain of the optical amplifier 428 fixed. According to the power control scheme 404, the power control of the output LO signal 434 is achieved by adjusting the attenuation of the adjustable optical attenuator 432 after the optical amplifier 428, and is particularly effective when the adjustable optical attenuator 432 is a fast-response VOA.

[0060] For ease of explanation, the respective techniques of power control schemes 400, 402, and 404 are described above separately. Nevertheless, those skilled in the art, upon reading and understanding the presently written disclosure, will appreciate that one or more of the power control schemes 400, 402, and 404 can be implemented together in a complementary manner, or that one or more parameters of several of their components can be simultaneously subject to the control of one or more power control modules. For example, in at least one embodiment, each of the laser source, operational amplifier, and adjustable optical attenuator can be in operable communication with a power control module or the same power control module and be subject to the control of the power control module.

[0061] Figure 5 FIG. 5 is a schematic illustration of a feed-forward automatic LO power control scheme 500. In an exemplary embodiment, the power control scheme 500 is implemented relative to a coherent PON system ( Figure 5 In some embodiments, the power control scheme 500 may be incorporated into a coherent receiver system 502 (not shown). Figures 4A to 4C One or more of the power control schemes 400, 402, 404 may be implemented in addition to or in place of the power control schemes 400, 402, 404. Figure 5 In the example depicted in FIG, the coherent receiver system 502 is similar to Figure 3 The coherent receiver system 300 includes an optical receiving portion 504 configured to receive an input optical burst signal 506 (eg, including a plurality of bursts, Figure 5 514) and the LO signal 508 from the LO 510, and outputs the electrical signal 512 through the respective electrical signal paths 514 using a plurality of burst TIAs 516 for each respective electrical signal path 514 (e.g., four TIAs 516 for four respective electrical signal paths 514 in this example).

[0062] In an exemplary embodiment, the coherent receiver system 502 further includes a power control module 518 in operable communication with the LO 510 and at least one optical detector 520 in optical communication with the input optical burst signal 506 and in electrical communication with the power control module 518. In an exemplary operation of the feed-forward power control scheme 500, the optical detector 520 is disposed on the receiver side of the optical receiving portion 504 and extracts / decimates a portion of the received burst of the input burst optical signal 506. In this manner, the optical detector 520 is thereby used to monitor the received optical signal power of the input burst optical signal 506 in real time and feed the monitored power level forward to the power control module 518 to achieve adaptive power control of the LO 510.

[0063] In one embodiment, the power control module 518 includes sufficient processing and memory hardware and / or software to enable the power control module 518 to function as an intelligent unit that controls the power of the LO 510 and the LO signal 508, and adapts the amplitude of subsequent electrical signals 512 to ensure substantially the same output level for corresponding electrical bursts. In some embodiments of the power control scheme 500, an additional overhead may be given to each burst as needed to provide sufficient time for power control.

[0064] In an exemplary embodiment, LO 510 may be Figure 4A LO 406 Figure 4B LO 414 and Figure 4C Any one of the LOs 424 and operates according to its associated power control scheme (or hybrid structure / scheme, as described above). As with the exemplary embodiments described above, the homodyne configuration of the coherent receiver system 502 is depicted for illustrative purposes and not in a limiting sense.

[0065] In at least one embodiment, the power control scheme 500 can be implemented with respect to a coherent PON system including a physical (PHY) layer, and can perform signal power monitoring based on the PHY layer signal power without requiring upper layer information. Where PHY layer signal power monitoring is implemented, the coherent receiver system 502 can further utilize a portion of the received signal (e.g., the received optical burst signal 506) and additional hardware components to achieve a sufficiently fast response, if necessary.

[0066] Figure 6 FIG. 6 is a schematic illustration of a feedback automatic LO power control scheme 600. In an exemplary embodiment, the power control scheme 600 is similar in some respects to the power control scheme 500 and is similar in some respects to the coherent PON system ( Figure 6 The coherent receiver system 602 is implemented as shown in FIG. 6 , which includes an optical receiving portion 604 configured to receive an input optical burst signal 606 (eg, including Figure 6 6) and the LO signal 608 from the LO 610, and outputs the electrical signal 612 through the respective electrical signal paths 614 using a plurality of burst TIAs 616 for each respective electrical signal path 614 (e.g., in this example, four TIAs 616 for four respective electrical signal paths 614). Also similar to the implementation of the power control scheme 500 described above, the coherent receiver system 602 further includes a power control module 618 in operable communication with the LO 610.

[0067] In an exemplary operation of the feedback power control scheme 600, and unlike the feedforward power control scheme 500, the coherent receiver system 602 further includes a feedback loop 620 based on the power of the electrical signal 612 after coherent detection. In one embodiment, the power control module 618 uses the feedback loop 620 to adaptively control the power of the LO 610 until the output electrical signal 612 is within a desired optimal range. In at least one embodiment, the LO 610 is set to an initial LO power value, which can be an average power value based on a power budget calculation for the associated PON system. In some embodiments, each burst frame can further be provided with sufficient overhead to achieve the desired convergence. Similar to the power control scheme 500, the power control scheme 600 can also be incorporated into the power control scheme 610, either separately or in a hybrid manner. Figures 4A to 4C One or more of the power control schemes 400, 402, 404.

[0068] Figure 7 FIG. 7 is a schematic illustration of a dynamic bandwidth allocation (DBA) power control scheme 700. In an exemplary embodiment, the power control scheme 700 is also similar in some aspects to the power control scheme 500 and is similar in some aspects to the coherent PON system ( Figure 7 The coherent receiver system 702 is implemented as shown in FIG. 7 , which includes an optical receiving portion 704 configured to receive an input optical burst signal 706 (eg, including Figure 7 7 and 714. The coherent receiver system 702 receives an LO signal 708 from the LO 710 and outputs an electrical signal 712 through the respective electrical signal paths 714 using a plurality of burst TIAs 716 for each respective electrical signal path 714 (e.g., in this example, four TIAs 716 for four respective electrical signal paths 714). Also similar to the implementation of the power control scheme 500 described above, the coherent receiver system 702 further includes a power control module 718 in operable communication with the LO 710.

[0069] In the exemplary operation of the feedback power control scheme 700, and unlike the feedforward power control scheme 500, the coherent receiver system 702 further includes a DBA unit 720 configured to record the power and link loss information of the coherent PON system and generate a DBA map (MAP). Using the DBA MAP from the DBA unit 720, the coherent upstream burst receiver of the coherent receiver system 702 is positioned at the OLT ( Figure 7 (not shown) can manage upstream bandwidth allocation through DBA MAP.

[0070] In an exemplary embodiment, the OLT further includes a ranging mechanism or ranging capability for measuring the transmission delay of each ONU due to the different locations of different ONUs of the PON system that may be in different locations by utilizing different corresponding distances to the OLT and coherent upstream burst receivers. In this scenario, each ONU can be registered and ranged, and thereby provide relevant delay / distance information for the DBA unit 720. After each ONU is properly registered in the DBA MAP, the ONU can be instructed to transmit only corresponding upstream burst signals that can be controlled by the OLT in a "request grant protocol". Therefore, using the DBA MAP information of the DBA unit 720, the OLT will know the exact location from which each burst is transmitted, and when each such burst will arrive at the OLT. That is, the power of the LO 710 can be adaptively controlled based on the DBA MAP information from the DBA unit 720. Similar to the power control scheme 500, the power control scheme 700 can also be incorporated into the DBA MAP and the OLT 710, respectively, either alone or in a hybrid manner. Figures 4A to 4C One or more of the power control schemes 400, 402, 404.

[0071] In some cases, the link loss during the registration period of one or more of the ONUs will not be known. In this scenario, the DBA power control scheme 700 may be based on MAC layer and PHY layer collaboration (hereinafter with respect to Figure 8 and 9 ) and further implement one or more methods to set LO power and initiate proper registration of ONUs without link loss information.

[0072] Figure 8 is a flow chart of an exemplary registration process 800 that may be implemented using embodiments described herein. In an exemplary embodiment, the process 800 uses a user with a LO (e.g., Figure 3 LO 308 Figure 4A LO 406 Figure 4B LO 414 Figure 4C LO 424 Figure 5 LO 510 Figure 6 LO 610 Figure 7 LO 710) of the smart coherent burst mode receiver (e.g., Figure 3 Coherent receiver system 300, Figure 5 Coherent receiver system 502, Figure 6 Coherent receiver system 602, Figure 7 The coherent receiver system 702) is relatively simple compared to the coherent PON system (e.g., Figure 1 of the system 100) (e.g., Figure 1 OLT 102) and one or more ONUs (e.g., Figure 1Unless described to the contrary, the individual steps of process 800 may be performed in the order described, in a different order, or two or more of the steps may be performed simultaneously.

[0073] In one embodiment, process 800 is performed with Figure 5 The feedforward power control scheme 500 and Figure 6 At least one of the feedback power control schemes 600 is jointly implemented Figure 7 The feed-forward power control scheme 500 and the feedback power control scheme 600, for example, generally require longer response times than the DBA power control scheme 700. That is, whereas the feed-forward power control scheme 500 and the feedback power control scheme 600 will depend on the relative speeds of their respective components, the DBA power control scheme 700 will operate much faster than the other schemes because intelligent processing (e.g., of the power control unit 718 and / or the DBA unit 720) knows in advance when each burst will arrive.

[0074] Thus, when operated in conjunction with the DBA scheme 700 as described herein, the feedforward scheme 500 and the feedback scheme 600 advantageously provide further fine power control due to direct power measurements of the corresponding received signals. The DBA scheme 700 can therefore be described as providing coarse power control relative to the feedforward scheme 500 and / or the feedback scheme 600. Such joint operation of the DBA scheme 700 with the feedforward scheme 500 and / or the feedback scheme 600 can be achieved by a process 800 as further described below.

[0075] In an exemplary embodiment, process 800 begins at step 802, where the OLT broadcasts a "discovery gate" to the coherent PON system for ONU registration. In step 804, at least one ONU (e.g., "ONU-i") responds to the discovery gate broadcast and requests registration with the OLT. In step 806, the OLT performs at least one of the feedforward scheme 500 and the feedback scheme 600 and records the power levels of the registered ONUs for the valid requests. In step 808, the OLT updates the DBA unit (e.g., Figure 7 In an exemplary embodiment of step 808, the OLT further sends the authorization to the ONU.

[0076] In step 810, the ONU sends a registration reply message back to the OLT during a given authorized period. In step 812, the OLT performs (e.g., by Figure 7LO power control is performed by the power control module 718 of the LO 710. In an exemplary embodiment of step 812, the LO power control is further based on the recorded power for the ONU obtained from the DBA unit. In at least one embodiment of step 812, the associated feedforward scheme 500 and / or feedback scheme 600 are further used to fine-tune the LO power level as needed.

[0077] Figure 9 is a flow chart of an alternative registration process 900 that may be implemented using the embodiments described herein. Process 900 is similar to Figure 8 The process 800 is implemented in that the process 900 is implemented with respect to the OLT and one or more ONUs of the coherent PON system. Figure 7 700. However, process 900 differs from process 800 in that process 900 does not necessarily integrate either feedforward power control scheme 500 or feedback power control scheme 600 jointly with DBA power control scheme 700.

[0078] When LO power control is based on DBA, process 900 therefore has specific values for ONU registrations and encounters different power classes or groups of upstream bursts. By exchanging messages between the OLT and ONUs according to different power classes and ONU registrations, process 900 can utilize DBA power control scheme 700 independently of other power control schemes (if desired). Unless otherwise described, the individual steps of process 900 can be performed in the order described, in a different order, or two or more of the steps can be performed simultaneously.

[0079] In an exemplary embodiment, process 900 begins at step 902, where the OLT establishes a relatively wide range of different upstream PON power classes. In step 904, at least one ONU (e.g., "ONU-i") determines or calculates its own power class based on the received power from a particular downstream signal. That is, in step 902, the OLT broadly sets the different upstream burst power classes for the PON, and in step 904, enables the ONU to calculate its own power class based on the downstream (DS) signal from the OLT.

[0080] In step 906, the OLT broadcasts a discovery gate for a specific loss category to the coherent PON system. In step 908, the ONU monitors the discovery gate to check for the specific loss category. Step 910 is a decision step. In step 910, the ONU determines whether the ONU's loss category matches the specific loss category broadcast from the OLT. If the ONU's loss category does not match the specific loss category from the OLT, process 900 returns to step 908.

[0081] However, if in step 910 the ONU determines that its loss class matches a specific loss class from the OLT, process 900 proceeds to step 912, where the ONU responds to the OLT broadcast with a registration request. In step 914, the OLT performs LO power control based on the matched loss class to detect upstream bursts from the ONU. In an exemplary embodiment of step 914, the OLT further obtains accurate power information from the ONU and records the obtained power information (e.g., in Figure 7 In step 916, the ONU registers with the OLT. In an exemplary embodiment of step 916, after the ONU registers, the OLT updates the DBA unit and performs DBA-based LO power control based on the DBA and the recorded link / power information (i.e., according to the DBA power control scheme 700).

[0082] According to the exemplary operational flow of process 900, the ONU will only respond to the discovery gate for its own class of ONU, and the OLT will therefore have reliable and accurate power control information for responding ONUs, regardless of whether the power control information is measured by the OLT itself or reported by the ONU. Therefore, after the ONU registers, the OLT is enabled to perform LO power control based on the updated DBA MAP and significantly more accurate power information.

[0083] According to one or more of the novel embodiments described herein, or combinations and / or sub-combinations thereof, intelligent LO power control processing for coherent burst reception can further implement power balancing techniques at the upstream ONU transmitter. That is, one or more of the current LO power control schemes can be implemented at the OLT side (coherent burst receiver), with power balancing implemented at the ONU side (coherent burst transmitter). As used herein, "power balancing" refers to techniques for controlling transmitter output power at the ONU side to reduce the dynamic range of receiver input power in upstream bursts received at the OLT side.

[0084] In an exemplary embodiment, current power balancing techniques are based on transmitter and receiver power information, and therefore these techniques can be implemented in a manner that is fully complementary to one or all of the LO power control schemes described above. In a typical coherent PON system, given that the dynamic range of the ODN is large, and taking into account the various differences in the laser output power from the corresponding ONUs, the total dynamic range of the received optical power in the upstream can be greater than 20 dB, which can exceed the tuning range in which ONU-side power balancing can be achieved only at the ONU. However, according to current power balancing techniques, the OLT and the ONU can operate cooperatively, so that the tuning range for both power balancing and LO power control can be advantageously reduced. As described below with respect to Figure 10and 11 To further describe, current power balancing techniques may be implemented according to either automatic or command-based mechanisms.

[0085] Figure 10 FIG1 is a flow chart of an automatic power balancing process 1000 that can be implemented using embodiments described herein. In one embodiment, process 1000 represents the functional flow of an automatic mechanism for ONU-side power balancing and OLT-side LO power control. In the exemplary embodiment, process 1000 begins at step 1002, where the OLT broadcasts the OLT's transmitter output power in a downstream signal to the ONUs. In step 1004, at least one ONU (e.g., ONU-i) measures the received optical power. In step 1006, the respective ONU performs automatic power balancing and transmits its resulting burst in an upstream signal. In step 1008, after receiving the power-balanced burst from the ONU, the OLT performs LO power control according to one or more of the schemes described herein.

[0086] According to the exemplary operation of process 1000, the ONU is enabled to automatically power balance its own upstream burst transmissions based on the received power of the downstream signal from the OLT. The OLT is then enabled to implement a desired LO power control scheme for the residual power difference from each burst. In an exemplary embodiment of process 1000, the ONU or OLT may be further configured to periodically perform the relevant steps of process 1000. In some embodiments, since process 1000 is initiated by the OLT, process 1000 may be performed as described above with respect to Figure 8 and 9 The process 1000 may be completed during one or more of the described registration procedures. In other embodiments, the process 1000 may be completed after registration.

[0087] Figure 11 FIG1 is a flow chart of a command-based power balancing process 1100 that may be implemented using embodiments described herein. In one embodiment, process 1100 represents the functional flow of a command-based mechanism for ONU-side power balancing and OLT-side LO power control. The command-based process 1100 is thus different from Figure 10 The process 1000 is automated because both the LO power control and ONU power balancing operations in the process 1100 are based on commands from the OLT, which may, in some cases, require message exchanges between the OLT and the ONU. In an exemplary embodiment of the process 1100, the OLT obtains power information for the ONU in an upstream signal from the ONU (e.g., measurements at the OLT side or reports from the ONU side).

[0088] In an exemplary embodiment, process 1100 begins at step 1102, where an ONU (e.g., ONU-i) reports its power status information to the OLT. In step 1104, the OLT updates the power status information for the reporting ONU. In step 1106, the OLT sets the LO power control value and sends a power balancing command to the reporting ONU. In step 1108, the ONU performs power balancing based on the command received from the OLT. In an exemplary embodiment of step 1108, after power balancing by the ONU, the OLT may perform LO power control according to one or more of the schemes described herein.

[0089] According to the exemplary operation of process 1100, since process 1000 is initiated at the ONU, process 1100 is optimally completed after registration (e.g., according to Figure 9 1100). In one embodiment, the relevant power status information may include one or more of transmitter power, received power, and estimated ODN loss. In at least one embodiment, the OLT may update this information and periodically perform the command-based process 1100.

[0090] According to the novel systems and methods described herein, efficient techniques for achieving received burst gain control are implemented through adaptive adjustment of input LO power. Several different LO power control schemes are described herein and with respect to several different implementations for intelligent control of LO power in coherent optical receivers. These schemes can further be implemented based on complementary novel techniques for ONU registration and cooperative ONU-side power balancing.

[0091] Exemplary embodiments of optical communication systems and methods are described in detail above. While the disclosed systems and methods are not limited to the specific embodiments described herein, the components and / or steps implemented herein may be utilized independently and separately from other components and / or steps described herein. Furthermore, the exemplary embodiments may be implemented and utilized in conjunction with other access networks utilizing optical fiber and coaxial transmission at the end user level.

[0092] As described above, the DOCSIS protocol may be replaced or further include protocols such as EPON, RFoG, GPON, and Satellite Internet Protocol without departing from the scope of the embodiments herein. Embodiments of the present invention are therefore particularly suitable for communication systems that implement the DOCSIS protocol and can be advantageously configured for use in existing 4G and 5G networks, as well as for new radio and next generation network implementations.

[0093] Although the specific features of the various embodiments of the present disclosure may be shown in some drawings and not in other drawings, such illustrative techniques are merely for convenience. According to the principles of the present disclosure, the specific features shown in the drawings may be referenced and / or claimed in conjunction with the features of other drawings.

[0094] Some embodiments involve the use of one or more electronic devices or computing devices. Such devices typically include a processor or controller, such as a general-purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application-specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field programmable gate array (FPGA), a digital signal processing (DSP) device, and / or any other circuit or processor capable of performing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer-readable medium including, but not limited to, a storage device and / or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. The above examples are exemplary only and are therefore not intended to limit the definition and / or meaning of the term "processor" in any way.

[0095] This written description uses examples to disclose embodiments, including the best mode, and also to enable those skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

1. A coherent optical receiver for a coherent network, comprising: a local oscillator (LO) configured to generate a variable power output LO signal, wherein the LO includes a laser source; an optical receiving portion configured to receive an input optical burst signal from the coherent network, the optical receiving portion comprising one or more receiving photodetectors configured to generate an output electrical signal; and a power control module in electrical communication with the LO and configured to provide direct control of the laser drive voltage of the laser source to vary the power level P of the variable power output LO signal from the LO; LO , so that the variable power output LO signal power level P LO is inversely related to the power level of the input optical burst signal.

2. The coherent optical receiver according to claim 1, wherein: The one or more receiving light detectors have a responsivity R, wherein the power level of the variable power output LO signal is determined by P LO Indicated by A, where the amplitude of the output electrical signal is represented by ac denoted by P, and wherein the power level of the input optical burst signal is denoted by P S Indicates that the power level P of the variable power output LO signal LO The following relationship applies:

3. The coherent optical receiver according to claim 1, wherein: The input optical burst signal includes a first burst received during a first time slot and a second burst received in a second time slot different from the first time slot.

4. The coherent optical receiver according to claim 3, wherein: The variable power output LO signal power level P LO and the power level P of the first burst during the first time slot S1 inversely related, and wherein the power level P of the variable power output LO signal LO and the power level P of the second burst during the second time slot S2 Inverse correlation.

5. The coherent optical receiver according to claim 1, wherein: The power control module includes: (i) a control input, and (ii) a control output in electrical communication with the LO to adaptively control a power level of the variable power output LO signal.

6. The coherent optical receiver according to claim 5, further comprising: One or more amplifiers in electrical communication with the output electrical signals of corresponding ones of the one or more receiving photodetectors.

7. The coherent optical receiver according to claim 6, further comprising: A feedback loop electrically connects the control input to the output electrical signal at a location between the one or more receive light detectors and the one or more amplifiers.

8. The coherent optical receiver according to claim 5, further comprising: a monitoring photodetector in direct optical communication with the input optical burst signal from the coherent network and in direct electrical communication with the control input of the power control module, wherein the monitoring light detector is configured to extract a portion of the input optical burst signal and generate a real-time power level of the input optical burst signal as an electrical feed-forward signal to the control input.

9. The coherent optical receiver according to claim 5, further comprising: a dynamic bandwidth allocation (DBA) unit in electrical communication with the control input of the power control module, wherein the DBA unit is configured to record power and link loss information of the coherent network and generate a DBA MAP, And wherein the power control module is further configured to adaptively control the power level of the variable power output LO signal based on MAP information from the DBA MAP received at the control input.

10. The coherent optical receiver according to claim 5, wherein: (i) an initial power level of the variable power output LO signal is an average power value calculated based on a power budget of the coherent network, and (ii) after the initial power level, subsequent power levels of the variable power output LO signal are dynamically derived based on a control output of the power control module.

11. The coherent optical receiver according to claim 9, wherein: The power level of the variable power output LO signal is controlled based at least in part on the position of the coherent optical receiver recorded in the MAP information.

12. A method for discovering a first upstream coherent optical transceiver among a plurality of upstream coherent optical transceivers, the method being performed by a downstream coherent optical transceiver in operable communication with the plurality of upstream coherent optical transceivers via an optical transmission medium in a coherent passive optical network (PON), the downstream coherent optical transceiver comprising a coherent optical receiver according to any one of claims 1 to 11, the method comprising the following steps: sending a discovery message to the plurality of upstream coherent optical transceivers; receiving an upstream power level from the first upstream coherent optical transceiver in response to the transmission; as well as The power level of the LO is dynamically controlled based on the upstream power level received from the first upstream coherent optical transceiver.

13. The method according to claim 12, wherein: The downstream coherent optical transceiver includes an optical line terminal (OLT), and the first upstream coherent optical transceiver includes a first optical network unit (ONU).

14. The method according to claim 13, wherein The dynamically controlling step is performed based on real-time feed-forward extraction of an upstream burst signal from the first ONU provided from the optical transmission medium to the power control module.

15. The method according to claim 13, wherein: The OLT further comprises a dynamic bandwidth allocation (DBA) unit in communication with the power control module, and wherein the method further comprises the step of adjusting a power level of the LO for grant-based upstream bursts from the first ONU based on MAP information from the DBA unit.

16. The method according to claim 12, wherein: The step of dynamically controlling is performed based on a real-time feedback loop from an electrical output signal from a photodetector of the coherent optical receiver prior to amplification and processing to the power control module.

17. The method of claim 12, further comprising, prior to the step of transmitting, the step of setting a plurality of different upstream power loss categories for the coherent PON, and wherein the step of transmitting comprises broadcasting a discovery message for a first loss category among the plurality of different upstream power loss categories.

18. The method according to claim 17, wherein The receiving step includes matching the first ONU with a first loss category.

19. The method according to claim 17, wherein The step of dynamically controlling includes the sub-step of detecting an upstream burst from a first ONU based on a first loss category.

20. The method according to claim 13, wherein The step of transmitting includes transmitting the output power of the OLT, so that the first ONU can automatically adjust the optical power of the upstream burst to the OLT according to the measured value of the transmitted output power.

Images