WO2025086310A1

WO2025086310A1 - Method and system for detecting faults occurring in an optical transport network

Info

Publication number: WO2025086310A1
Application number: PCT/CN2023/127426
Authority: WO
Inventors: Zhiping Jiang; Jian Zhong; Yang LAN
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2023-10-28
Filing date: 2023-10-28
Publication date: 2025-05-01
Anticipated expiration: 2026-04-28

Abstract

System and method for detecting faults of an optical transport link (OTL) of an optical transport network (OTN). The method includes receiving at least one multiplexed signal from the OTL, the at least one multiplexed signal having been generated by a multiplexing device from a first signal comprising a first set of optical channels and a second signal comprising a second set of signals, determining an alternating current power and a direct current power, determining a power ratio of the alternating current power and the direct current power and determining a power ratio indicative of a total number of optical channels among the first and second set that are received with an optical power above a pre-determined threshold at an output of the OTL.

Description

METHOD AND SYSTEM FOR DETECTING FAULTS OCCURRING IN AN OPTICAL TRANSPORT NETWORK

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the first application filed for the instantly disclosed technology.

FIELD OF THE TECHNOLOGY

The present disclosure generally relates to the field of optical communications and, in particular, to methods and systems for method for detecting faults occurring on an optical multiplexing section (OMS) of an optical transport network (OTN) .

BACKGROUND

Typical implementation of optical networks, for example dense wavelength division multiplex (DWDM) networks, involves an enormous number of optical devices and optical communication lines making standard monitoring systems inefficient. Most meshed optical networks include of OADM (Optical Add-Drop Multiplexer) nodes, where wavelength channels can be added/dropped/routed. During routing, any number of channels may be dropped and/or added at OADM nodes.

Optical signal at an output of an OADM node may have a loss of optical power. This may be due to several factors such as fiber cut, fiber bending, optical amplifier failure, etc. Due to amplifier gain coupling and fiber nonlinearities (e.g. Stimulated Raman Scattering) , power change on some channels may affect other channels of the OADM. However, standard systems are not configured to determine if a power loss is occurring on all channels of the OADM node, or only on local channels added at the OADM node. Segregation between the two situations may be beneficial to provide custom reactive action depending on the type of optical power loss.

Therefore, it may be desirable to detect one or more types of optical power loss at an output of an OADM.

SUMMARY

An aspect of the present disclosure is to provide a method for detecting faults of an optical transport link (OTL) of an optical transport network (OTN) . The method includes receiving at least one multiplexed signal from the OTL, the at least one multiplexed signal having been generated by a multiplexing device from a first signal comprising a first set of optical channels and a second signal comprising a second set of signals. The method also includes determining an alternating current power indicative of a bandwidth of the at least one multiplexed signal based on an optical beat noise of the at least one multiplexed signal, determining a direct current power representative of the at least one multiplexed signal based on an average optical power thereof, determining a power ratio of the alternating current power and the direct current power and determining a power ratio indicative of a total number of optical channels among the first and second set that are received with an optical power above a pre-determined threshold at an output of the OTL.

In some implementations, the first signal is received from an optical multiplexing section (OMS) of the OTN. The method further includes locally generating the second signal by a signal generating device communicably connected to the multiplexing assembly.

In some implementations, the method further includes determining a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels in response to determining a variation of the power ratio.

In some implementations, determining direct electric current includes receiving, by a sensing device, the at least one multiplexed signal, amplifying the received at least one multiplexed signal by an electric? amplifier optically connected to an output of the sensing device and calculating the direct electric current according to:
i_DC=Resp×P

where Resp is the responsivity of the sensing device, andis the optical power of the at least one multiplexed signal in which ρ (f) is the optical power spectrum density and f is the optical frequency.

In some implementations, determining the direct electric current includes tapping the output of the optical amplifier by a low-pass filter and converting an output of the low-pass filter by an Analog-to-Digital converter.

In some implementations, determining the optical power noise includes determining:

where ρ is the optical power spectrum density, v is electrical frequency, and B_e is the electric bandwidth of detection.

In some implementations, determining the alternating current power further includes tapping the output of the optical amplifier a Radio-Frequency power sensor, filtering an output of the Radio-Frequency sensor by a low-pass filter and converting an output of the low-pass filter by an Analog-to-Digital converter.

In some implementations, the first optical inlet, the second optical inlet and the multiplexing device are implemented in an Optical Add-Drop Multiplexer (OADM) .

In some implementations, the method further includes, in response to the power ratio being equal to the pre-determined value and the direct electric power being below a pre-determined threshold, determining an occurrence of an overall power loss of the first and second sets of optical channels, and, in response to the power ratio being below the pre-determined value, determining an occurrence of a partial channel drop defined by a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels.

In some implementations, the method further includes, in response to determining an occurrence of an overall power loss, adding additional optical power to the multiplexed signal.

In a second aspect of the present technology, there is provided a multiplexing assembly for an optical transport network (OTN) . The multiplexing assembly includes a first optical inlet for receiving a first optical signal comprising a first set of optical channels, an optical amplifier at the first optical inlet for amplifying the first optical signal upon reception thereof by the multiplexing assembly, a second optical inlet for receiving a second optical signal comprising a second set of optical channels, a multiplexing device for multiplexing the first and second optical signal, an optical outlet for outputting the multiplexed signal to an output optical transport link; and a processing module communicably connected to the optical outlet for receiving the multiplexed signal from the output optical transport link. The processing module is configured to measure an alternating current power indicative of a bandwidth of the multiplexed signal, measure a direct electric current representative of the multiplexed signal, and determine a ratio of the alternating current power and the direct current power, said ratio being indicative of number of optical channels among the first and second set that are received with an optical power above a pre-determined threshold at the processing module.

In some implementations, the first signal is received from an optical multiplexing section (OMS) of the OTN, and the second signal is locally generated by a signal generating device communicably connected to the multiplexing assembly.

In some implementations, the processing module determines a variation of the ratio indicative of a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels.

In some implementations, the processing module includes a sensing device for receiving the multiplexed signal and an optical amplifier optically connected to an output of the sensing device. The processing module determines the direct current based on information received from the sensing device, the direct current being:
i_DC=Resp×P

where Resp is the responsivity of the sensing device, andis the optical power of the at least one multiplexed signal in which ρ (f) is the optical power spectrum density and f is the optical frequency, the alternating current power being:

In some implementations, the multiplexing assembly further includes a low-pass filter operatively connected to the output of the optical amplifier and an Analog-to-Digital converter (ADC) operatively connected to the low-pass filter. The processing module determines the direct current based on signals from the ADC.

In some implementations, the multiplexing assembly further includes a Radio-Frequency power sensor operatively connected to the output of the optical amplifier, a second low-pass filter operatively connected to the Radio-Frequency power sensor and a second ADC operatively connected to the second low-pass filter. The processing module determines the alternating current power based on signals from the second ADC.

In some implementations, the optical amplifier is a transient induced amplifier.

In some implementations, the multiplexing device is a Wavelength Selective Switch (WSS) .

BRIEF DESCRIPTION OF THE FIGURES

The features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIG. 1 is a high-level diagram of an optical transport link (OTL) in accordance with some embodiments of the present technology;

FIG. 2 is a high-level diagram of an Optical Add-Drop Multiplexer (OADM) of the OTL of Fig. 1;

FIG. 3 is a schematic representation of an optical amplifier in accordance with some embodiments of the present technology;

FIG. 4 is a representation of potential faults that may occur on the OTL of FIG. 1;

FIG. 5 is a block diagram of a monitoring system in in accordance with an embodiment of the present technology;

FIG. 6 is a block diagram of a controller of the monitoring system of FIG. 5;

FIG. 7 is a flow diagram of a method for detecting faults occurring optical multiplexing section (OMS) of the OTL of FIG. 1, in accordance with some embodiments of the present technology; and

FIG. 8 is a chart illustrating experimental results of variations of a power ratio in response to variations of the number of optical channels present in a multiplexed signal of an OTL, such as the OTL of FIG. 1.

It is to be understood that throughout the appended drawings and corresponding descriptions, like features are identified by like reference characters. Furthermore, it is also to be understood that the drawings and ensuing descriptions are intended for illustrative purposes only and that such disclosures are not intended to limit the scope of the claims.

DETAILED DESCRIPTION

Various representative embodiments of the described technology will be described more fully hereinafter with reference to the accompanying drawings, in which representative embodiments are shown. The present technology concept may, however, be embodied in many different forms and should not be construed as limited to the representative embodiments set forth herein. Rather, these representative embodiments are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the present technology to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. Like numerals refer to like elements throughout.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. Thus, a first element discussed below could be termed a second element without departing from the teachings of the present technology. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between, ” “adjacent” versus “directly adjacent, ” etc. ) .

The terminology used herein is only intended to describe particular representative embodiments and is not intended to be limiting of the present technology. As used herein, the singular forms “a, ” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising, ” when used in this specification, specify the presence of stated 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 groups thereof.

Moreover, all statements herein reciting principles, aspects, and implementations of the present technology, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof, whether they are currently known or developed in the future. Thus, for example, it will be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the present technology. Similarly, it will be appreciated that any flowcharts, flow diagrams, state transition diagrams, pseudo-code, and the like represent various processes which may be substantially represented in computer-readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

The functions of the various elements shown in the figures, including any functional block labeled as a “controller” , “processor” or “processing unit” , may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software and according to the methods described herein. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. In some embodiments of the present technology, the processor may be a general purpose processor, such as a central processing unit (CPU) or a processor dedicated to a specific purpose, such as a digital signal processor (DSP) . Moreover, explicit use of the term a “processor” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, application specific integrated circuit (ASIC) , field programmable gate array (FPGA) , read-only memory (ROM) for storing software, random access memory (RAM) , and non-volatile storage. Other hardware, conventional and/or custom, may also be included.

Software modules, or simply modules or units which are implied to be software, may be represented herein as any combination of flowchart elements or other elements indicating performance of process steps and/or textual description. Such modules may be executed by hardware that is expressly or implicitly shown, the hardware being adapted to (made to, designed to, or configured to) execute the modules. Moreover, it should be understood that module may include for example, but without being limitative, computer program logic, computer program instructions, software, stack, firmware, hardware circuitry or a combination thereof which provides the required capabilities.

Broadly speaking, the present technology provides a system and a method for detecting faults occurring on an optical multiplexing section (OMS) of an optical transport link (OTL) of an optical transport network (OTN) . As will be described in greater detail herein after, the system disclosed herein is able to segregate between occurrence of an all-channel power drop situation and a partial power drop situation. In the context of the present disclosure, “all-channel power drop” occurs at an output of an OADM when an optical power drop occurs on all of the output optical channels of the OADM, and “partial power drop” occurs when optical power drop occurs on only a subset of the output optical channels of the OADM. The disclosed technology may determine if a power drop is an all-channel power drop or a partial power drop using a single photodetector, thereby providing a cost-effective way to determine a nature of a potential power drop.

With these fundamentals in place, we will now consider some non-limiting examples to illustrate various implementations of aspects of the present disclosure.

Referring now to the drawings, FIG. 1 depicts a conceptual diagram of an optical transport link (OTL) 90 that may be addressed by the systems and methods presented herein. As shown, the OTL 90 typically includes a plurality of optical multiplexing sections (OMSs) 92 for transmitting an optical signal 300. The OTL 90 may include a conventional optical fiber such as, for example, a glass fiber surrounded by one or more coating layers. The OTL 90 may include an optical fiber core which transmits the optical signal 300, and an optical cladding, which confines the optical signal within the optical fiber core. It is also contemplated that light defining the optical signal 300, may be single polarized, dual polarized, or randomly polarized, may have a particular polarization (e.g. linearly polarized, elliptically polarized, or circularly polarized) . In this implementation, a wavelength of the optical signal 300 can be located in one or multiple of the following bands: E-band (1400～1470 nm) , S-band (1470～1520 nm) , C-band (1520～1565 nm) , L-band (1565～1630 nm) , and U-band (1630nm ～ 1680nm) bands.

Each OMS 92 includes optical add-drop multiplexers (OADMs) , such as, for example, a reconfigurable optical add-drop multiplexers (ROADMs) 94 each containing at least one wavelength selective switch (not shown) . The ROADMs 94 may include transmitters, denoted “Tx” , and receivers, denoted “Rx” , to respectively add and drop a given signal from the optical signal 300. Each OMS 92 may then be configured to add, remove, and/or reroute a wavelength of the optical signal 300, via the ROADMs 94. For example and without limitation, each transmitter Tx may be a laser source of a respective wavelength and communicatively connected to a corresponding processing unit (not shown) of the ROADM 94. The laser source may be configured to produce, emit, or radiate pulses of light with certain pulse duration. In certain implementations, one or more transmitters Tx implemented as pulsed laser light sources may include one or more laser diodes, such as but not limited to, Fabry-Perot laser diode, a quantum well laser, a distributed Bragg reflector (DBR) laser, a distributed feedback (DFB) laser, or a vertical-cavity surface-emitting laser (VCSEL) . Just as examples, a given laser diode may be an aluminum-gallium-arsenide (AlGaAs) laser diode, an indium-gallium-arsenide (InGaAs) laser diode, or an indium-gallium-arsenide-phosphide (InGaAsP) laser diode, or any other suitable laser diode. The ROADM 94 may be a passive multiplexer such as, without limitation, a prism-based or a mirror-based multiplexer, or an active multiplexer based on a combination of passive components and tunable detectors, each detector being tuned to a specific frequency. Each OMS 92 is formed from multiple optical transport sections (OTSs) 96, where at each OTS 96 the wavelength remains same.

It is noted that the OTL 90 may incorporate additional optical elements, which may include either or both of active and passive elements/modules, including but not limited to: optical amplifiers, optical filters, wavelength selective switches, arrayed waveguide gratings, optical transmitters, optical receivers, processors and other suitable components. However, for purposes of simplicity, these elements have been omitted from FIG. 1.

Each optical transport section 96, also referred to as a link 96, includes an optical amplifier (e.g., erbium-doped fiber amplifiers (EDFAs) ) and a length of fiber 97. The optical fiber may be of any suitable type such as, for example, single mode optical fiber, multi-mode optical fiber, standard single mode fibers (SSMFs) , large effective area fibers (LEAFs) or the like.

Use of one or more additional optical network elements and modules (which may include either or both of active and passive elements /modules) , such as, for example, optical filters, arrayed waveguide gratings, optical transmitting devices, optical receiving devices, processors and other suitable components along the OTL 90 is also contemplated in alternative embodiments.

It should be noted that a given ROADM 94 may receive more than one optical signal (e.g. two optical signals) , each optical signal being received at a corresponding optical input of the ROADM 94. For example, FIG. 2 is schematic diagram of a ROADM 94 in accordance with non-limiting implementations of the present technology. In this illustrative example, the ROADM 94 includes a first optical input 210 for receiving a first optical signal 202 from a first OMS (noted OMS-A) , and a second optical input 220 for receiving a second optical signal 204 from a second OMS (noted OMS-B) . More specifically, the first signal 202 includes a first set of optical channels, and the second signal 204 includes a second set of optical channels as depicted on FIG. 2.

The ROADM 94 also includes a transmitter 230 for locally adding a third optical signal 206 to an output signal of the ROADM 94. In use, the ROADM 94 includes a multiplexing device 240 for multiplexing the first optical signal 202, the second optical signal 204 and the third optical signal 206. In this implementation, the multiplexing device 240 is a wavelength selective switch (WSS) . More specifically, the ROADM 94 includes a first optical amplifier 210_A for applying power amplification to the first optical signal 202, and a second optical amplifier 210_B for applying power amplification to the second optical signal 204. The amplified first and second optical signals 202, 204 are then directed to the WSS 240.

The ROADM 94 may further include an output optical amplifier 240_A that receives the multiplexed signal from the WSS 240 before the optical signal is outputted from the ROADM 94 at an optical output 240 thereof. In this implementation, the optical output 240 is optically connected to a third OMS (noted OMS-C) . More specifically, the OMS-C defines an optical input at the optical output 240 of the OMS 94 and an optical output 302. In addition, the OMS-C includes an optical amplifier 301 at the optical output 302. In this implementation, a WSS 304 is configured to receive the multiplexed signal 290 at the optical output 302 of the OMS-C.

FIG. 3 is a schematic diagram of an optical amplifier 310 in accordance with some non-limiting implementations of the present technology. In some implementations, the optical amplifiers 210_a, 220_A and 301 are implemented as the optical amplifier 310. The optical amplifier 310 defines an optical input 311 for receiving an optical signal. The optical signal may be carried over a plurality of optical channels received at the optical input 311. The optical amplifier 310 further includes an optic signal generating device 312 configured to generate a placeholder optical signal, or “dummy light signal” , which is an optical signal with optical power but that does not carry information. Broadly speaking, dummy light signals may be added at an OMS head and terminated at an OMS tail to stabilize the OTN. The dummy light signal is then directed to a variable optical attenuator (VOA) 314. The VOA 314 may be used for adjusting a gain level of the dummy light signal by attenuating the dummy light signal propagating therein. The attenuated dummy light signal is further combined with the optical signal received at the optical input 311 by a signal combiner 316 (e.g. a coupler) . The combined optical signal is further directed through a local optical amplifier 318 before being outputted of the optical amplifier 310 at an optical output 319 thereof.

In circumstances when the optical amplifier 310 is implemented at an end, or “tail” of an OMS, the VOA 314 is set to its maximum in normal operation, such that the dummy light signal is completely blocked and does not affect traffic channels (i.e. the optical signal received at the optical input 311) . If there is a fiber cut in the OMS, the power of all optical channels will be reduced. The local optical amplifier 318 is operated in constant output power mode, such that, in the event of a fiber cut in the OMS, the local optical amplifier 318 will increase its gain, so that the output power is maintained. This may facilitate preservation of an integrity of the OMS and the OTN. If the input power drop exceeds a certain threshold, the attenuation of the VOA 314 is reduced to add power from the dummy light signal. In this way, output optical power of the optical amplifier 310 may be maintained. In some implementations, the power drop threshold is selected between 6dB and 10dB.

More specifically, the total power from the channels is kept constant such that a channel replacement operation may be executed in response to a fault occurring in the OTN. Maintaining the total optical power may enable operators to perform transientless switching where little to no transient is induced during replacement operation, therefore all channels can be replaced in one operation. There is thus no need to divide the optical channels into replacement groups.

The present technology addresses the need to separately identify two types of faults occurring in the OTN: an all-channel drop and a partial channel drop. As depicted on FIG. 4, a fiber cut fault occurring on the OMS-C is noted “Fault-A” . This leads to an all-channel drop at the WSS 304. More specifically, all optical channels of the OMS-C experience an optical power drop that is substantially the same for all the optical channels. Another type of fault is a local fault occurring at the transmitter 230 of the ROADM 94, noted “Fault-B” , which leads to a partial channel drop. More specifically, only the optical channels added by the transmitters 230, or “local channels” , experience a power drop upon being transmitted over the OMS-C. In other words, only a subset of the optical channels experiences an optical power drop in the “Fault-B” situation, said subset corresponding to the local channels added by the transmitter 320. In one aspect the present technology may be used to distinguish between the all-channel drop situation and the partial channel drop situation.

FIG. 5 is a schematic diagram of a monitoring system 500 in accordance with some non-limiting implementations of the present technology. The monitoring device 500 may be, for example and without-limitations, implemented at the tail of the OMS-C such as the optical output 302 thereof for distinguishing between the all-channel drop situation and the partial channel drop situation. In use, the monitoring system 500 includes a sensing module 510 that may receive the multiplexed signal 290 from the OMS-C. In this implementation, the sensing module 510 includes a single sensing device 512 that may be photodetector such as a Ge Photodiode, a InGaAs photodiode, etc. In this implementation, the sensing device 512 is a square law detector. The sensing module 510 also includes an amplifier 514 at an output of the sensing device 512. For example, the amplifier 514 may be a transient induced amplifier.

Broadly speaking, once the multiplexed signal 290 is received by the sensing module 510, the monitoring system 500 may determine whether a fault is an all-channel power drop or a partial channel power drop. On the one hand, the averaged photocurrent (or equivalently the voltage) outputted by the sensing module 510 is proportional to the received input optical power of the multiplexed signal 290. On the other hand, different spectral components in optical signals or ASE noise spectra generate beat noise upon photo detection. The beat noise is AC, while the DC normalized AC power depends on the spectral width of its input, or equivalently the number of channels in the input.

Therefore, a power detector may be used to measure the input optical power of the multiplexed signal 290 (i.e. AC power) . Analog-to-Digital converters (ADCs) may be used to convert the DC, AC power into digital domain, and then to calculate the AC/DC power ratio. The monitoring system 500 may thus use the AC/DC power ratio to monitor variation of the number of optical channels in the multiplexed signal 290. The AC/DC power ratio is indicative of a total number of optical channels that are received at the WSS 304 without having experienced a power loss (i.e. that have an optical power above a pre-determined threshold) .

To do so, the monitoring system 500 includes a low-pass filter (LPF) 536 receiving an output of the amplifier 514 to improve the measurement quality, and an Analog-to-Digital converter (ADC) 538 receiving an output of the LPF 536 and outputting a DC current 539. The DC current 539 is given by:
i_DC=Resp×P,

where Resp is the photodetector responsivity, is the optical power of the at least one multiplexed signal in which ρ (f) is the optical power spectrum density and f is the optical frequency, B_o is the optical bandwidth. It should also be noted that power density of the spontaneous-spontaneous beat noise at frequency f may be written as:

where Λ (x) =1-x, if x≤1; Λ (x) =0, if x>1.

The monitoring system 500 includes a DC module 522 receiving the output of the sensing module 510. In use, the DC module 522 prevents direct current frequencies in electric signals. For example, the DC module 522 includes a capacitor and a conductor. The DC module 522 may remove the DC frequency component of the original signal, and only let AC frequencies pass through. The monitoring system 500 also includes a radio frequency (RF) power module 524 for determining a RF power level of the photocurrent generated by the sensing module 510. The monitoring system 500 further includes a second LPF 526 receiving an output of the RF power module 524 to improve the measurement quality, and a second ADC 528 receiving an output of the second LPF 526 and outputting an AC power 529.

The optical bandwidth is usually more than 10 GHz for electrical bandwidth of less than a few GHz (e.g. few hundreds of MHz to a few GHz) . Multiple optical channels could occupy a few THz. Therefore, the spontaneous-spontaneous beat noise is substantially flat. Therefore, the total beat noise power (AC power) within bandwidth B_e may be written as:

where ρ is the optical power spectrum density, v is electrical frequency, and B_e is the electric bandwidth of detection which is much smaller than the optical bandwidth B_o. The equation may be approximated to:

whereis the defined effective optical bandwidth of the multiplexed signal.

The DC power is proportional to the square of the photocurrent of the sensing module 510, the AC/DC power ratio R_AC-DC is thus proportional to a ratio of the bandwidths:

The AC/DC power ratio R_AC-DC is thus inversely proportional to the optical bandwidth B_o. In circumstances of an all-channel power drop, the optical bandwidth B_o does not change. In circumstances of a partial channel power drop however, the effective optical bandwidth B_o decreases. Since the optical bandwidth is proportional to the number of optical channels present in the multiplexed signal 290, the monitoring system 500 may provide indication of a variation in the number of optical channels effectively present in the multiplexed signal 290, thereby providing segregation between all-channel power drop scenario and partial channel power drop scenario.

FIG. 8 is a chart showing experimental results of variations of the AC/DC power ratio R_AC-DC in response to variations of the number of optical channels present in the multiplexed signal 290 (i.e. optical channels having a corresponding optical power above a given power threshold) . In the experiment, each optical channel has a spectral width of 50GHz. The power ratio R_AC-DC is measured as a function of the number of optical channels in the multiplexed signal 290. A sampling scope is used to measure the AC waveform as well as the DC level. The detection bandwidth is around 130MHz, and the sampling rate is 500MHz. Each measurement is obtained using 100k samples, which has a time duration of 100 microseconds at 1GHz sampling rate. A theoretical curve of a ratio between the bandwidths is also illustrated.

For example, a loss of optical power in the set of optical channels of the third optical signal 206 with respect to optical power of set of optical channels of the first and/or second optical signals 202, 204 (i.e. a partial channel power drop) may be determined in response to determining a variation of the power ratio R_AC-DC. For example, if a known number of optical channels is expected to be present at the WSS 304 (e.g. 70 optical channels) , an corresponding expected value of the power ratio R_AC-DC may be determined, for example about 0.000037 for 70 expected optical channels. If the current value of the power ratio R_AC-DC is different than the expected value, then occurrence of a partial channel drop may be determined. For example, if the current value of the power ratio R_AC-DC is about 0.000043, it may be determined that 10 channels are experiencing a loss of optical power out of the 70 optical channels.

In use, the DC current 539 and the AC power 529 are received by a processing module 540 that determines the AC/DC power ratio R_AC-DC. As an example, FIG. 6 is a schematic block diagram of a controller 600 of the processing module 540 according to an embodiment of the present technology. The controller 600 comprises a processor or a plurality of cooperating processors (represented as a processor 604 for simplicity) , a memory device or a plurality of memory devices (represented as a memory device 610 for simplicity) , and an input/output interface 602 allowing the controller 600 to communicate with other components of the monitoring system 500 and/or other components in remote communication with the monitoring system 500. The processor 604 is operatively connected to the memory device 610 and to the input/output interface 602. The memory device 610 includes a storage for storing parameters 614. The memory device 610 may comprise a non-transitory computer-readable medium for storing code instructions 612 that are executable by the processor 604 to allow the controller 600 to perform the various tasks allocated to the controller 600 in methods described herein.

The controller 600 is operatively connected, via the input/output interface 602, to the ADCs 528, 538. The controller 600 executes the code instructions 612 stored in the memory device 610 to implement the various above-described functions that may be present in a particular implementation. FIG. 6 as illustrated represents a non-limiting embodiment in which the controller 602orchestrates operations of the processing module 540. This particular embodiment is not meant to limit the present disclosure and is provided for illustration purposes

FIG. 7 is a flowchart of a method 700 for detecting faults occurring on an optical multiplexing section (OMS) such as the OMS-C. In one or more aspects, the method 700 is performed by the monitoring system 500 communicably and operably connected to a tail of the OMS-C, although some implementational details of the system 500 could vary in different embodiments. In some implementations, one of more operations of the method 700 could be implemented, in whole or in part, by another computer-implemented device. It is also contemplated that the method 700 or one or more operation thereof may be embodied in computer-executable instructions that are stored in a computer-readable medium, such as a non-transitory mass storage device, loaded into memory and executed by a processor, such as the controller 600. Some operations or portions of operations in the flow diagram may be possibly being executed concurrently, omitted or changed in order.

The method 700 begins with receiving, at operation 710, at least one multiplexed signal from the OMS. In use, the multiplexed signal has been generated by a multiplexing device from a first signal comprising a first set of optical channels and a second signal comprising a second set of signals. In this implementation, the multiplexed signal is the multiplexed signal 290 that has been generated by the WSS 240 from the optical channels of the first optical signal 202 and/or the second optical signal 204 multiplexed with the third optical signal 230.

In some implementations, the first signal is received from another OMS (e.g. OMS-A) of the OTN, and the second signal is locally generated by a signal generating device such as the transmitter 230 communicably connected to the multiplexing assembly.

The method 700 continues with determining, at operation 720, an alternating current power indicative of a bandwidth of the at least one multiplexed signal. In this implementation, the alternating current power is the AC power 529.

The method 700 continues with determining, at operation 730, a direct electric power representative of the at least one multiplexed signal. In this implementation, the direct electric power is due to the DC current 539. For example and without limitations, determining direct electric current may include receiving, by a sensing device such as the sensing device 512, the at least one multiplexed signal. The received at least one multiplexed signal, or a signal indicative thereof such as a photocurrent, may be amplified by an amplifier communicably connected to an output of the sensing device. The direct electric current may then be calculated according to:
i_DC=Resp×P

where Resp is the responsivity of the sensing device, andis the optical power of the at least one multiplexed signal in which ρ (f) is the optical power spectrum density and f is the optical frequency. In some implementations, determining the direct electric current comprises tapping the output of the optical amplifier by a low-pass filter and converting an output of the low-pass filter by an Analog-to-Digital converter (ADC) .

In some implementations, the direct electric current is determined by tapping the output of the optical amplifier by a low-pass filter and converting an output of the low-pass filter by an ADC.

The method 700 continues with determining, at operation 740, a power ratio of the alternating current power and the direct electric power. In this implementation, the power ratio is the AC/DC power ratio R_AC-DC. The power ratio indicative of number of optical channels among the first and second set that are received with an optical power above a pre-determined threshold at the output of the OMS.

In some implementations, the method 700 continues with determining a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels in response to determining a variation of the power ratio.

It will be appreciated that at least some of the operations of the method 700 may also be performed by computer programs, which may exist in a variety of forms, both active and inactive. Such as, the computer programs may exist as software program (s) comprised of program instructions in source code, object code, executable code or other formats. Any of the above may be embodied on a computer readable medium, which include storage devices and signals, in compressed or uncompressed form. Representative computer readable storage devices include conventional computer system RAM (random access memory) , ROM (read only memory) , EPROM (erasable, programmable ROM) , EEPROM (electrically erasable, programmable ROM) , and magnetic or optical disks or tapes. Representative computer readable signals, whether modulated using a carrier or not, are signals that a computer system hosting or running the computer program may be configured to access, including signals downloaded through the Internet or other networks. Concrete examples of the foregoing include distribution of the programs on a CD ROM or via Internet download. In a sense, the Internet itself, as an abstract entity, is a computer readable medium. The same is true of computer networks in general.

While the above-described implementations have been described and shown with reference to particular operations performed in a particular order, it will be understood that these steps may be combined, sub-divided, or re-ordered without departing from the teachings of the present technology. At least some of the steps may be executed in parallel or in series. Accordingly, the order and grouping of the steps is not a limitation of the present technology.

It is to be understood that the operations and functionality of the monitoring system 500, its constituent components, and associated processes may be achieved by any one or more of hardware-based, software-based, and firmware-based elements. Such operational alternatives do not, in any way, limit the scope of the present disclosure.

It should be expressly understood that not all technical effects mentioned herein need to be enjoyed in each and every implementation of the present technology.

Modifications and improvements to the above-described implementations of the present technology may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the present technology is therefore intended to be limited solely by the scope of the appended claims.

Claims

A method for detecting faults of an optical transport link (OTL) of an optical transport network (OTN) , the method comprising:

receiving at least one multiplexed signal from the OTL, the at least one multiplexed signal having been generated by a multiplexing device from a first signal comprising a first set of optical channels and a second signal comprising a second set of optical channels;

determining an alternating current power indicative of a bandwidth of the at least one multiplexed signal based on an optical beat noise of the at least one multiplexed signal;

determining a direct current power representative of the at least one multiplexed signal based on an average optical power thereof;

determining a power ratio of the alternating current power and the direct current power; and

determining a power ratio indicative of a total number of optical channels among the first and second set that are received with an optical power above a pre-determined threshold at an output of the OTL.
The method of claim 1, wherein the first signal is received from an optical multiplexing section (OMS) of the OTN, the method further comprising:

locally generating the second signal by a signal generating device communicably connected to the multiplexing assembly.
The method of claim 1 or 2, further comprising:

determining a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels in response to determining a variation of the power ratio.
The method of any one of claims 1 to 3, wherein determining direct current power comprises:

receiving, by a sensing device, the at least one multiplexed signal;

amplifying the received at least one multiplexed signal by an electric amplifier optically connected to an output of the sensing device; and

calculating a direct electric current according to:
i_DC=Resp×P

where Resp is the responsivity of the sensing device, andis the optical power of the at least one multiplexed signal in which ρ (f) is the optical power spectrum density and f is the optical frequency.
The multiplexing assembly of claim 4, wherein determining the direct current power comprises tapping the output of the optical amplifier by a low-pass filter and converting an output of the low-pass filter by an Analog-to-Digital converter.
The method of claim 4 or 5, wherein determining the alternating current power comprises determining:

where ρ is the optical power spectrum density, v is electrical frequency, and B_e is the electric bandwidth of detection.
The method of claim 6, wherein determining the alternating current power further comprises:

tapping the output of the optical amplifier to a Radio-Frequency power sensor;

filtering an output of the Radio-Frequency power sensor by a low-pass filter; and

converting an output of the low-pass filter by an Analog-to-Digital converter.
The method of any one of claims 1 to 7, wherein the first optical inlet, the second optical inlet and the multiplexing device are implemented in an Optical Add-Drop Multiplexer (OADM) .
The method of any one of claims 1 to 8, further comprising:

in response to the power ratio being equal to the pre-determined value and the direct current power being below a pre-determined threshold, determining an occurrence of an overall power loss of the first and second sets of optical channels; and

in response to the power ratio being below the pre-determined value, determining an occurrence of a partial channel drop defined by a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels.
The method of claim 9, further comprising, in response to determining an occurrence of an overall power loss, adding additional optical power to the multiplexed signal.
A multiplexing assembly for an optical transport network (OTN) , the multiplexing assembly comprising:

a first optical inlet for receiving a first optical signal comprising a first set of optical channels;

an optical amplifier at the first optical inlet for amplifying the first optical signal upon reception thereof by the multiplexing assembly;

a second optical inlet for receiving a second optical signal comprising a second set of optical channels;

a multiplexing device for multiplexing the first and second optical signals into a multiplexed signal;

an optical outlet for outputting the multiplexed signal to an output optical transport link; and

a processing module communicably connected to the optical outlet for receiving the multiplexed signal from the output optical transport link, the processing module being configured to:

measure an alternating current power indicative of a bandwidth of the multiplexed signal,

measure a direct current power representative of the multiplexed signal, and

determine a ratio of the alternating current power and the direct current power, said ratio being indicative of number of optical channels among the first and second set that are received with an optical power above a pre-determined threshold at the processing module.
The multiplexing assembly of claim 11, wherein:

the first signal is received from an optical multiplexing section (OMS) of the OTN, and

the second signal is locally generated by a signal generating device communicably connected to the multiplexing assembly.
The multiplexing assembly of claim 11 or 12, wherein the processing module is configured to determine a variation of the ratio indicative of a loss of optical power of the second set of optical channels with respect to optical power of the first set of optical channels.
The multiplexing assembly of any one of claims 11 to 13, wherein the processing module comprises:

a sensing device for receiving the multiplexed signal; and

an optical amplifier optically connected to an output of the sensing device,

the processing module being further configured to determine the direct current based on information received from the sensing device, the direct current being:
i_DC=Resp×P

where Resp is the responsivity of the sensing device, andis the optical power of the at least one multiplexed signal in which ρ (f) is the optical power spectrum density and f is the optical frequency,

the alternating current power being:

where ρ is the optical power spectrum density, v is electrical frequency, and B_e is the electric bandwidth of detection.
The multiplexing assembly of claim 14, further comprising:

a low-pass filter operatively connected to the output of the optical amplifier; and

an Analog-to-Digital converter (ADC) operatively connected to the low-pass filter,

the processing module being further configured to determine the direct current based on signals from the ADC.
The multiplexing assembly of claim 14 or 15, further comprising:

a Radio-Frequency power sensor operatively connected to the output of the optical amplifier;

a second low-pass filter operatively connected to the Radio-Frequency power sensor; and

a second ADC operatively connected to the second low-pass filter, the processing module being further configured to determine the alternating current power based on signals from the second ADC.
The multiplexing assembly of any one of claims 14 to 16, wherein the optical amplifier is a transient induced amplifier.
The multiplexing assembly of any one of claims 11 to 17, wherein the multiplexing device is a Wavelength Selective Switch (WSS) .
The multiplexing assembly of any one of claims 11 to 18, wherein the first optical inlet, the second optical inlet and the multiplexing device are implemented in an Optical Add-Drop Multiplexer (OADM) .