TECHNICAL FIELD

The disclosure relates generally to data transmission. Moreover, the disclosure relates to a method for (namely, a method of) configuring an optical system for communicating data from an optical transmitter via an optical fibre (namely “fiber” US English) waveguide arrangement to an optical receiver.

BACKGROUND

Contemporary optical communication systems are configured to transmit data through an optical fibre from a first location to a second location; the optical fibre is usually a single-mode fibre (SMF), although a multimode fibre (MMF) could alternatively be used for transmitting the data. There is a quest that always remains for achieving an increased optical channel capacity or spectral efficiency in such optical communication systems. Hence, the optical communication systems are evolving relentlessly to accommodate larger flows of data content that needs to be transmitted through an optical channel. To achieve such high spectral efficiency, system designers are motivated to employ more bandwidth-efficient modulation formats, as well as higher symbol rates.

Next-generation coherent optical transponders are now expected to operate at well over 100 gigabaud (GBd) symbol rates. When providing over 100 GBd symbol rates, there are encountered severe component bandwidth limitations and a need for receiver equalization noise enhancement. To overcome the aforementioned problems, a concept of digital pre-emphasis (DPE) at a transmitter (Tx) is introduced. However, an application of DPE results in increased peak to average power ratio (PAPR) of a signal, which in turn amplifies an effect of quantization noise at a digital-to-analog converter (DAC) used in the transmitter (Tx). This problem is exacerbated as state-of-the-art systems are pushing current electronic and photonic technologies to their bandwidth limits. Fully compensating for transmitter (Tx) response means reaching high-frequency amplification values of up to approximately 15 to 25 decibels (dB), or even up to 25 dB. In this scenario, a benefit of reducing, for example minimizing, inter-symbol interference (ISI) with DPE can be outweighed by degradation due to enhanced quantization noise, thus decreasing overall performance of an optical system.

Existing approaches use empirical brute-force techniques to set up optimally transponders for achieving high bandwidth transmission. However, using the brute-force techniques, configuring a digital signal processing (DSP) is generally much slower to achieve. When the brute-force techniques are used in on-line transponders, an adaptation speed of the on-line transponders is slow whenever a channel condition is changed. Similarly, when the brute-force techniques are used in off-line experiments or simulations, the brute-force techniques require more time to determine an optimal configure for the optical transponders.

Some existing approaches propose a semi-analytical DAC quantization noise model. With a given (or measured) PAPR value of the DAC, an optimal DPE level may be calculated analytically. However, the PAPR is extremely difficult to be measured at the DAC either in online transponders or in offline experiments. For a real data communication product, the semi- analytical DAC quantization noise model is less effective than the brute-force approaches.

Besides DPE, further gains can be made when also applying optical pre-emphasis (OPE) or analog pre-emphasis (APE). When employing OPE or APE at the transmitter (Tx) for overcoming bandwidth limitations, when operating coherent optical transponders over 100 gigabaud (GBd) symbol rates, the noise at a digital-to-analog converter (DAC) used in the transmitter (Tx) is reduced compared to using DPE only. As explained above, empirical brute- force techniques are used to set up optimally transponders, and reply on a feedback signal-to- noise-ration (SNR) information.

Furthermore, water-filling (WF) strategies are used for multi-carrier transmission systems. WF is a joint process with DPE and OPE at the transmitter (Tx). In the online transmission scenarios whenever a channel condition is changed, the convergence of many transmitter (Tx) and receiver (Rx) equalizer wait for the monitored SNR to update the coefficients, such as the entropy loading (EL) and power loading (PL). WF strategy calculation comprises EL and PL strategy calculation. In WF strategy calculation, the key feedback information from receiver (Rx) to the transmitter (TX) is the receiver (Rx) SNR information per sub-carrier. However, the feedback speed of the SNR can be hugely delayed posing the risk of bad transition performance of the transponder. Additionally, such brute-force equalizer coefficients optimization based on the feedback SNR of the receiver (Rx) is very time consuming, which is less practical in a real product, such that the transponder might often work at sub-optimum performance. Therefore, there arises a need to address the aforementioned technical drawbacks in existing systems or technologies in overcoming bandwidth limitations for increasing data communication rate.

SUMMARY

It is an object of the disclosure to provide an improved method for (namely, an improved method of) configuring an optical system to optimize a performance of the optical system to increase a data communication rate that can be achieved therethrough. Moreover, it is an object of the disclosure to predict maintenance requirements of the optical system or potential expected failure of the optical system that uses the aforesaid improved method.

This object is achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

The disclosure provides a method for configuring an optical system for communicating data from an optical transmitter via an optical fibre waveguide arrangement to an optical receiver and the optical system that is designed and manufactured using the aforesaid method.

According to a first aspect, there is provided a method for configuring an optical system for communicating data from an optical transmitter via an optical fibre waveguide arrangement to an optical receiver, wherein configuring the optical system includes using a data processing arrangement to determine at least one of the following: an optimal degree of partial digital preemphasis (DPE) (H _D PE(/)) to be used in the optical system, a number of sub-carriers to be used for communicating the data through the optical fibre waveguide arrangement, a Baudrate per sub-carriers, an optical power to be used for the sub-carriers transmitted via the optical fibre waveguide arrangement, a number and characteristics of equalization taps to be used for implementing the partial digital pre-emphasis (DPE), modulation formats to be used for the data, digital signal processing (DSP) parameters of the optical transmitter to be used, and digital signal processing (DSP) parameters of the optical receiver to be used. The method includes calculating, using the data processing arrangement configured to execute a mathematical model, a signal -to-noise ratio (SNR) obtainable when communicating the data from the optical transmitter to the optical receiver as a function of at least one parameter describing or controlling operating characteristics of component parts of the optical system. The method includes, from calculations of the signal-to-noise (SNR), iteratively determining a combination of values of the at least one parameter that provides a substantially best compromise between the signal-to-noise ratio (SNR) and a data communication rate obtainable for the optical system. For example, the best compromise between the signal-to-noise ratio (SNR) and data communication rate is the respective optimum thereof. The method includes configuring the optical system according to the at least one parameter that provides the substantially best compromise. For example, the optical system is configured according to the at least one parameter that provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate. As an example, the optimum signal-to-noise (SNR) could be the highest achievable SNR, whereas the optimum for the data communication rate could be the biggest data communication rate. However, for some examples the best compromise mentioned above might depend on the optical system design and its requirements.

The method is of advantage in that the method provides an enhanced performance of the optical system that provides a substantially best compromise between the signal-to-noise ratio (SNR) and the data communication rate obtainable for the optical system. For example, the method provides an enhanced performance of the optical system that provides the optimum signal-to- noise ratio (SNR) and the optimum data communication rate obtainable for the optical system. The method increases the signal-to-noise ratio (SNR) and the data communication rate. The method quickly and accurately predicts the signal-to-noise ratio (SNR) based on given filter responses. The method provides a set of optimum parameters for the optical system to increase the data communication rate, thereby reducing iterative sweeping time of hundreds of parameters significantly when configuring the optical system. The method can be implemented in a real product, optionally using software, whenever a channel condition is changed, to accelerate convergence time of an online transceiver. Furthermore, the method estimates performance of transceivers, which gives a reference to the mathematical model in adjusting parameters.

Modulation format comprises entropy loading per sub-carrier. In other words, determination of the modulation format per sub-carrier comprises determination of the different entropy per subcarrier.

The at least one parameter may be selected from a group of parameters including: a pulse shaping ( g(f) ) used in the optical transmitter, a degree of partial digital pre-emphasis (DPE) used in the optical transmitter, an effective number of bits (Enob), a transfer function °f a digital-to-analog converter (DAC) at the optical transmitter, a drive noise spectral density ( ri _dnver ) of the optical transmitter, an amplified spontaneous emission (ASE) noise spectral density (TIASE) of one or more optical cross-connects (OXC), optical amplifiers (EDFA) used along the optical fibre waveguide arrangement, a receiver noise spectral density of the optical receiver, transfer functions of driver and modulator, ^a transfer function of one or more wavelength selective switch , and transfer functions of the optical transmitter and the optical receiver Optionally, the method includes computing the partial digital pre-emphasis (DPE) for the mathematical model based on an inverse of a transfer function of the optical transmitter: where = frequency; a scaling factor that adjusts a ratio of the partial digital pre-emphasis (DPE), and the transfer function of the optical transmitter.

Optionally, the method includes computing the partial digital pre-emphasis (DPE) combined with an optical pre-emphasis (OPE), also referred to as joint digital and optical pre-emphasis, for the mathematical model based on an inverse of a transfer function of the optical transmitter (204) and a transfer function of optical pre-emphasis (OPE): wherein f = frequency; b = is a scaling factor that adjusts the level of partial optical pre-emphasis (OPE), the transfer function of the approximated optical transmitter (204) frequency response, the transfer function partial optical pre-emphasis, scaling factor that adjusts a ratio of the partial digital pre-emphasis (DPE), and the transfer function of the optical transmitter (204).

Optionally, the method includes configuring the mathematical model according to at least one of:

(i) the optical transmitter is modelled to include the digital-to-analog converter (DAC) that is modelled as an additive white Gaussian noise source having a noise variance of variance nDAc (DPE) accounting for noise amplification as a function of the degree of partial digital preemphasis (DPE) H _DPE (f) employed, followed by a filter of the digital-to-analog converter (DAC) having a transfer function H _OAC (/) for representing an electrical bandwidth limitation associated with the optical transmitter;

(ii) the optical transmitter is modelled to include a coherent driver modulator (CDM) that includes a white Gaussian noise source having a variance followed by a filter of the coherent driver modulator (CDM) having a transfer function

(iii) the one or more optical cross-connects (OXC) are modelled as the amplified spontaneous emission (ASE) noise spectral density combined with the one or more wavelength selective switch (WSS) filters having a transfer function

(iii) the optical receiver is modelled to include an additive white Gaussian noise source having a noise variance of variance representing all noise sources of the optical receiver and the optical receiver is modelled to include an analog-to-digital converter (ADC) that is modelled as an additive white Gaussian noise source having a noise variance of variance nADc (Enob) accounting for noise as a function of the effective number of bits (ENOB) of the ADC, followed by a filter of the optical receiver having a transfer function ; and

(iv) the optical receiver is modelled to include a digital signal processing (DSP) equalization. Optionally, the method includes modelling the DAC noise variance, by using the effective number of bits (ENOB) used when communicating via the optical system as an input parameter to the mathematical model, the partial digital pre-emphasis (DPE) applied at the optical transmitter, and a digital-to-analog (DAC) output power loss due to low-frequency signal suppression. A signal-to-noise (SNR) ratio of the DAC is given by:

SNR _DAC (ENOB, H _DPE (f)) where a transfer function for the digital pre-emphasis represents a pre-emphasis in a frequency domain, where is ^a noise power spectrum density as defined by: where

E _s = a power of an optical signal within the optical system, and maximum signal-to-noise ratio (SNR) of the digital-to-analog converter (DAC) of the optical transmitter when digital pre-emphasis (DPE) is not applied, where SNR _max is a function of frequency (f).

Optionally, the method includes computing a signal-to-noise ratio (SNR) of the digital-to- analog converter of the optical transmitter, in a time domain, using a multi-channel SNR computation based on a relationship: where where G is a gap of all sub-channels used in the optical system, where typically

Optionally, the method includes configuring the mathematical model to accommodate an ageing of the optical system, and to adjust the optimal degree of partial digital pre-emphasis to be used in the optical system as a function of the ageing.

Optionally, the method includes adjusting the degree of partial digital pre-emphasis (DPE) individually depending on at least one of: a transmission gain per channel, an amplified spontaneous emission (ASE) noise spectral density (TIASE), a noise present per channel, a transmission per sub-carrier, an expected Baudrate per channel, and transfer functions of the optical transmitter the optical receiver ) and the one or more wavelength selective switches used along the optical fibre waveguide arrangement between the optical transmitter and the optical receiver.

Optionally, the method includes using the mathematical model to predict maintenance requirements of the optical system or potential expected failure of the optical system depending on changes in at least one of the parameters and measurements made to characterize the optical system.

The method optionally includes using a machine learning model to determine the signal-to- noise ratio (SNR) obtainable when communicating the data from the optical transmitter to the optical receiver as the function of the at least one parameter describing or controlling operating characteristics of component parts of the optical system, for configuring the optical system. The machine learning model may be trained with historical signal-to-noise ratios for a plurality of parameters describing or controlling operating characteristics of component parts of historical optical systems under one or more operating conditions.

According to a second aspect, there is provided an optical system that is designed and manufactured using the above method.

According to a third aspect, there is provided an optical system that is configured during operation using the above method.

According to a fourth aspect, there is provided a computer program product comprising a non- transitory computer-readable storage medium having computer-readable instructions stored thereon, the computer-readable instructions being executable by a computerized device including processing hardware to execute the above method. The disclosure provides an approach to resolve technical problems encountered in the prior art, where the technical problems include severe bandwidth limitations due to increased effect of quantization noise at the digital-to-analog converter (DAC) in the transmitter (Tx) while minimizing inter-symbol interference (ISI).

Therefore, in contradistinction to the prior art, according to the method for configuring the optical system provided in the disclosure, the method provides an improved trade-off between increased effect of quantization noise and inter-symbol interference (ISI) minimization. The method increases the data transmission rate and the signal-to-noise ratio (SNR) that is achievable in practice. The method optionally includes determining the partial digital preemphasis (DPE) regardless of a single carrier (SC) or multi-carrier (MC) transmission. The method may be implemented at on-line transponders, to increase the adaptation speed of the on-line transponders whenever the channel condition is changed. The method may be used in off-line experiments or simulations, thereby reducing latency (namely, time elapsed). The method may be implemented either in software or application-specific integrated circuit (ASIC), for example.

These and other aspects of the disclosure will be apparent from implementations of the disclosure described below.

BRIEF DESCRIPTION OF DRAWINGS

Implementations of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram that illustrates a computerized device coupled to an optical system in accordance with an implementation of the disclosure;

FIG. 2 is an exemplary schematic representation of an optical system in accordance with an implementation of the disclosure;

FIG. 3 is an exemplary mathematical model representation of an optical system in accordance with an implementation of the disclosure; FIG. 4 is an exemplary graphical representation that illustrates dependency of an inverse of noise variance of a digital-to-analog converter on digital pre-emphasis (DPE), where in accordance with an implementation of the disclosure;

FIG. 5 is an illustration of an exemplary process of determining optimum transmission parameters for an optical system in offline experiments in accordance with an implementation of the disclosure;

FIG. 5A is another illustration of an exemplary process of determining optimum transmission parameters for an optical system in offline experiments in accordance with an implementation of the disclosure;

FIG. 6 is an illustration of an exemplary process of determining optimum transmission parameters for an online transponder in accordance with an implementation of the disclosure;

FIG. 6A is another illustration of an exemplary process of determining optimum transmission parameters for an online transponder in accordance with an implementation of the disclosure;

FIG. 7 is an exemplary graphical representation of performance of a mathematical model at 100 gigabaud (GBd) symbol rates for a first optical signal-to-noise ratio (OSNR) value and a second optical signal-to-noise ratio (OSNR) value in accordance with an implementation of the disclosure;

FIG. 8 is an exemplary graphical representation of performance of a mathematical model at 112.5 gigabaud (GBd) symbol rates for a first optical signal-to-noise ratio (OSNR) value and a second optical signal-to-noise ratio (OSNR) value in accordance with an implementation of the disclosure;

FIG. 8A is an exemplary graphical representation of performance of a mathematical model at 128 gigabaud (GBd) symbol rates for a first optical signal-to-noise ratio (OSNR) value and a second optical signal-to-noise ratio (OSNR) value in accordance with an implementation of the disclosure;

FIGS. 9A-9C are flow diagrams that illustrate a method for configuring an optical system for communicating data from an optical transmitter via an optical fibre waveguide arrangement, to an optical receiver in accordance with an implementation of the disclosure; and FIG. 10 is an illustration of a computing arrangement for use in implementing implementations of the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

Implementations of the disclosure provide a method for (namely, a method of) configuring an optical system for communicating data from an optical transmitter via an optical fibre waveguide arrangement to an optical receiver, where the optical system is configured according to at least one parameter that provides a substantially best compromise between a signal-to- noise ratio (SNR) and a data communication rate obtainable for the optical system. For example, the optical system is configured according to at least one parameter that provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system. Moreover, implementations of the disclosure provide an optical system that is designed and manufactured or is configured during operation, using the aforesaid method.

To make solutions of the disclosure more comprehensible for a person skilled in the art, the following implementations of the disclosure are described with reference to the accompanying drawings.

Terms such as "a first", "a second", "a third", and "a fourth" (if any) in the summary, claims, and foregoing accompanying drawings of the disclosure are used to distinguish between similar objects and are not necessarily used to describe a specific sequence or order. It should be understood that the terms so used are interchangeable under appropriate circumstances, so that the implementations of the disclosure described herein are, for example, capable of being implemented in sequences other than the sequences illustrated or described herein. Furthermore, the terms "include" and "have" and any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, a method, a system, a product, or a device that includes a series of steps or units, is not necessarily limited to expressly listed steps or units but may include other steps or units that are not expressly listed or that are inherent to such process, method, product, or device.

FIG. 1 is a block diagram 100 that illustrates a computerized device 102 coupled to an optical system 108 in accordance with an implementation of the disclosure. The block diagram 100 includes the computerized device 102 and the optical system 108. The computerized device 102 includes a data processing arrangement 104. Optionally, the optical system 108 can be connected to the data processing arrangement 104. This can be a direct connection of the optical system 108 and the data processing arrangement 104 and may depend on the design and configuration of the computerized device 102.

The optical system 108 is configured, using the data processing arrangement 104, to communicate data from an optical transmitter via an optical fibre waveguide arrangement to an optical receiver. The optical system 108 is configured, using the data processing arrangement 104, to determine at least one of the following: an optimal degree of partial digital pre-emphasis (DPE) ( H _DPE (f )) to be used in the optical system 108, a number of sub-carriers to be used for communicating the data through the optical fibre waveguide arrangement, a Baudrate per subcarriers, an optical power to be used for the sub-carriers transmitted via the optical fibre waveguide arrangement, a number and characteristics of equalization taps to be used for implementing the partial digital pre-emphasis (DPE), modulation formats to be used for the data, digital signal processing (DSP) parameters of the optical transmitter to be used, and digital signal processing (DSP) parameters of the optical receiver to be used.

The computerized device 102 calculates, using the data processing arrangement 104 configured to execute a mathematical model, a signal -to-noise ratio (SNR) obtainable when communicating the data from the optical transmitter to the optical receiver as a function of at least one parameter describing or controlling operating characteristics of component parts of the optical system 108. The computerized device 102, from calculations of the signal -to-noise (SNR), iteratively determines a combination of values of the at least one parameter that provides a substantially best compromise between the signal-to-noise ratio (SNR) and a data communication rate obtainable for the optical system 108. For example, the computerized device 102, from calculations of the signal-to-noise (SNR), iteratively determines a combination of values of the at least one parameter that provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system.

The computerized device 102 configures the optical system 108 according to the at least one parameter that provides the substantially best compromise between the signal-to-noise ratio (SNR) and the data communication rate. For example, the computerized device 102 configures the optical system 108 according to the at least one parameter that provides the optimum signal- to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system. The computerized device 102 may include a memory 106 that stores the mathematical model which is executed by the data processing arrangement 104.

The computerized device 102 optionally includes a machine learning model to determine the signal-to-noise ratio (SNR) obtainable when communicating the data from the optical transmitter to the optical receiver as the function of the at least one parameter describing or controlling operating characteristics of component parts of the optical system 108, for configuring the optical system 108. The machine learning model may be trained with historical signal-to-noise ratios for a plurality of parameters describing or controlling operating characteristics of component parts of historical optical systems under one or more operating conditions.

FIG. 2 is an exemplary schematic representation of an optical system 200 in accordance with an implementation of the disclosure. The optical system 200 includes an optical transmitter digital signal processor (Tx DSP) 202, an optical transmitter 204, an optical fibre waveguide arrangement 206, one or more optical cross-connects (OXC) 208A-N, an optical receiver (Rx) 210, and an optical receiver digital signal processor (Rx DSP) 212. The optical system 200 may include a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC). The optical system 200 may be a coherent optical system. The optical fibre waveguide arrangement 206 is a signal path to communicate data from the optical transmitter 204 to the optical receiver 210. The signal path may be a differential signal path having a pair of component signal lines to conduct differential signals. The optical transmitter digital signal processor (Tx DSP) 202 may generate a transmission signal by modulating a data signal 214 using digital signal processing based on modulation formats. Each modulation format may include a binary phase- shift keying (BPSK), a quadrature phase-shift keying (QPSK), and a 16-quadrature amplitude modulation (16-QAM). The digital-to-analog converter (DAC) may convert the transmission signal into an analog signal. The optical transmitter 204 may generate an optical signal 216 (a non-flat spectrum) based on an output signal of the digital-to-analog converter (DAC). The one or more optical cross-connects (OXC) 208A-N may switch high-speed optical signals between different optical fibres in the optical fibre waveguide arrangement 206. The one or more optical cross-connects (OXC) 208A-N may include a wavelength selective switch (WSS) and one or more optical amplifiers. The one or more optical amplifiers may be an Erbium-doped fibre amplifier (EDFA). The optical receiver (Rx) 210 may receive the optical signal 216 from the optical transmitter 204. The analog-to-digital converter (ADC) may convert the optical signal 216 into a digital signal 218. The optical transmitter digital signal processor (Tx DSP) 202 recovers the data signal 214 by demodulating the digital signal 218 from the analog-to-digital converter (ADC) using the digital signal processing.

Optionally, a partial digital pre-emphasis (DPE) is applied to the optical transmitter (Tx) 204 to improve a signal quality of the data signal 214 at the optical receiver (Rx) 210. The partial digital pre-emphasis (DPE) may be combined with an optical pre-emphasis (OPE).

The partial digital pre-emphasis (DPE) for the mathematical model is computed based on an inverse of a transfer function of the optical transmitter 204: where frequency; α = a scaling factor that adjusts a ratio of the partial digital pre-emphasis (DPE), and H _Tx (/) = the transfer function of the optical transmitter 204.

The partial digital pre-emphasis (DPE) combined with an optical pre-emphasis (OPE) for the mathematical model may be computed based on an inverse of a transfer function of the optical transmitter (204) and a transfer function of the optical pre-emphasis (OPE): wherein frequency; is a scaling factor that adjusts the level of partial optical pre-emphasis (OPE), the transfer function of the approximated optical transmitter (204) frequency response, the transfer function partial optical pre-emphasis, α = a scaling factor that adjusts a ratio of the partial digital pre-emphasis (DPE )H _Tx (f) = the transfer function of the optical transmitter (204).

Applying the partial digital pre-emphasis (DPE) at the optical transmitter (Tx) 204 provides a non- flat spectrum at the output of the optical transmitter (Tx) 204 (shown in FIG. 2) which may provide an improved, for example an optimized, trade-off between an increased peak to average power ratio (PAPR) in the digital-to-analog converter (DAC) and an inter-symbol interference (ISI) compensation.

The optical system 200 may be designed and manufactured according to the optimum transmission parameters. The optimum transmission parameters are (i) an optimal degree of the partial digital pre-emphasis (DPE) ( H _DPE (†)) to be used in the optical system 200, (ii) a number of sub-carriers to be used for communicating the data through the optical fibre waveguide arrangement 206, (iii) a Baudrate per sub-carriers, (iv) an optical power to be used for the subcarriers transmitted via the optical fibre waveguide arrangement 206, (v) a number and characteristics of equalization taps to be used for implementing the partial digital pre-emphasis (DPE), (vi) modulation formats to be used for the data, digital signal processing (DSP) parameters of the optical transmitter (Tx) 204 to be used, and (vii) digital signal processing (DSP) parameters of the optical receiver 210 to be used. Optionally, the optical system 200 is configured during operation according to the optimum transmission parameters.

FIG. 3 is an exemplary mathematical model that provides a representation of an optical system 300 in accordance with an implementation of the disclosure. The optical system 300 may be a coherent optical system. The optical system 300 includes an optical transmitter digital signal processor (Tx DSP) 302, an optical transmitter that includes a digital-to-analog converter (DAC) 304, and a coherent driver modulator (CDM) 306, one or more optical cross-connects (OXC A-N) 308A-N, an optical receiver (Rx) 310, an optical receiver digital signal processor (Rx DSP) 312 and an optical fibre waveguide arrangement 314. The optical system 300 may include an analog-to-digital converter (ADC) at the optical receiver (Rx) 310 side. The mathematical model is configured according to at least one of the optical transmitter digital signal processor (Tx DSP) 302, the optical transmitter, the one or more optical cross-connects (OXC A-N) 308A-N, the optical receiver (Rx) 310, and the optical receiver digital signal processor (Rx DSP) 312. At the optical transmitter side, data symbols (I) are digitally shaped with a given pulse shape g(f) followed by a DPE filter HDEP (f) 316. The optical transmitter may be modelled to include the digital-to-analog converter (DAC) 304 that is modelled as an additive white Gaussian noise source having a noise variance of variance, nDAc (DPE), accounting for noise amplification as a function of the degree of partial digital pre- emphasis (DPE) H _DPE (f) employed, followed by a filter of the digital-to-analog converter (DAC) 304 having a transfer function H _OAC (f ) 318 for representing an electrical bandwidth limitation associated with the optical transmitter. The optical transmitter may be modelled to include the coherent driver modulator (CDM) 306 that includes a white Gaussian noise source having a variance n _Driver , followed by a filter 320 of the coherent driver modulator (CDM) 306 having a transfer function H _COM (f). The one or more optical cross-connects (OXC) 308A-N may be modelled as the amplified spontaneous emission (ASE) noise spectral density (n _ASE ) combined with one or more wavelength selective switch (WSS) filters 322A-N having a transfer function ( H _wss (f )) . The optical receiver 310 may be modelled to include an additive white Gaussian noise source having a noise variance of variance n _Rx representing all noise sources of the optical receiver 310. The optical receiver 310 may be modelled to include the analog-to- digital converter (ADC) that is modelled as an additive white Gaussian noise source having a noise variance of variance n _AOC (Enob ) accounting for noise as a function of an effective number of bits (ENOB) of the ADC, followed by a filter 324 of the optical receiver 310 having a transfer function H _Rx (f). The optical receiver 310 may be modelled to include a digital signal processing (DSP) equalization.

The DAC noise variance, n _OAC (DPE), may be modelled using the effective number of bits (ENOB) used when communicating via the optical system 300 as an input parameter to the mathematical model, the partial digital pre-emphasis (DPE) applied at the optical transmitter, and a digital-to-analog (DAC) output power loss due to low-frequency signal suppression. A signal-to-noise (SNR) ratio of the DAC is given by: wherein a transfer function for the digital pre-emphasis represents a pre-emphasis in a frequency domain. is a noise power spectrum density which is defined by: wherein = a power of an optical signal within the optical system 300, and = a maximum signal -to-noise ratio (SNR.) of the digital-to-analog converter (DAC) 304 of the optical transmitter when digital pre-emphasis (DPE) is not applied where SNR _max is a function of frequency (f).

Optionally, a signal -to-noise ratio (SNR.) of the digital-to-analog converter (DAC) 304 of the optical transmitter, in a time domain, is represented using a multi-channel signal-to-noise ratio (SNR.) computation based on a relationship: wherein wherein G is a gap of all sub-channels used in the optical system 300, wherein typically G = 1. FIG. 4 is an exemplary graphical representation 400 that illustrates a dependency of an inverse of noise variance of a digital-to-analog converter (DAC) (l/n _DAC ) on digital pre-emphasis (DPE), where n accordance with an implementation of the disclosure. In the exemplary graphical representation 400, the partial digital pre-emphasis (DPE) is plotted along an abscissa is plotted along an ordinate Y-axis. The exemplary graphical representation 400 includes markers that indicate l/n _DAC as calculated at an output of a digital to analog converter (DAC) in numerical simulations where inter-symbol interference (ISI) is fully removed. The exemplary graphical representation 400 includes a solid line that corresponds to a mathematical model. A trend of quantization noise is increased due to the digital pre-emphasis (DPE) as the DPE is determined using the mathematical model.

With reference to FIG. 2 and FIG. 3, FIG. 5 and 5 A is an illustration of an exemplary process of determining optimum transmission parameters for an optical system in offline experiments in accordance with an implementation of the disclosure. At a step 502, at least one parameter describing or controlling operating characteristics of component parts of the optical system, is received as an input. The at least one parameter may include a digital-to-analog converter (DAC) noise variance n _DAC (DPE, Enob, NL) which is modelled using an effective number of bits (ENOB), a drive noise spectral density (n _Driver ) of an optical transmitter, an amplified spontaneous emission (ASE) noise spectral density (n _ASE ) of one or more optical cross-connects (OXC) and optical amplifiers (EDFA) used along the optical fibre waveguide arrangement, a noise variance of a transimpedance amplifier (TIA) at the optical receiver (UHA), a noise variance of variance (nADC (Enob, NL)) accounting for noise as a function of the effective number of bits (ENOB) of the ADC, a pulse shaping (g(f)), a transfer function of the optical transmitter (HTxi(f)), a transfer function of one or more wavelength selective switch (WSS) filters (Hwss(f)), and a transfer function of an optical receiver (HRxi(f)). The at least one parameter may be at least one change in a channel condition (for example, changes in number or shapes of wavelength selective switch (WSS) filters, or changes in noise distribution). At a step 504, a mathematical model, based on equations (l)-(4) jointly with the minimum mean square error (MMSE) solution, calculates the optimum transmission parameters via Q signal- to-noise ratio (SNR) vs. digital pre-emphasis (DPE) levels under different combinations of Baud rates, a number of sub-carriers, a transmitter and receiver digital signal processor (TRx DSP) parameters such as partial digital pre-emphasis (DPE) or optical pre-emphasis (OPE) levels, a power of subcarriers, a number and value of equalizer taps under different modulation formats. At a step 506, the mathematical model provides the optimum transmission parameters as an output.

With reference to FIG. 2 and FIG. 3, FIG. 6 and 6 A is an illustration of an exemplary process of determining optimum transmission parameters for an online transponder 600 in accordance with an implementation of the disclosure. At a step 602, at least one parameter describing or controlling operating characteristics of component parts of the online transponder 600 during an operation, is received as an input. The at least one parameter may include a digital-to-analog converter (DAC) noise variance n _DAC (DPE, Enob, NL) which is modelled using an effective number of bits (ENOB), a drive noise spectral density (n _Driver ) of an optical transmitter, an amplified spontaneous emission (ASE) noise spectral density (n _ASE ) of one or more optical cross-connects (OXC) and optical amplifiers (EDFA) used along the optical fibre waveguide arrangement, a noise variance of a transimpedance amplifier (TIA) at the optical receiver (UHA), a noise variance of variance (nADC (Enob, NL)) accounting for noise as a function of the effective number of bits (ENOB) of the ADC, a pulse shaping (g(f)), a transfer function of the optical transmitter (H _Txi (f)), a transfer function of one or more wavelength selective switch (WSS) filters (H _WS s(f)), and a transfer function of an optical receiver (H _Rxi (f)). The at least one parameter may be at least one change in channel condition (for example, changes in number or shapes of wavelength selective switch (WSS) filters, or changes in noise distribution).

At a step 604, a mathematical model, based on equations (l)-(4) jointly with the minimum mean square error (MMSE) solution, is used to calculate the optimum transmission parameters via Q signal-to-noise ratio (SNR) vs. digital pre-emphasis (DPE) levels under different combinations of Baud rates, a number of subcarriers, a transmitter and receiver digital signal processor (TRx DSP) parameters such as partial digital pre-emphasis (DPE) or optical pre-emphasis (OPE) levels, a power of subcarriers, a number and value of equalizer taps under different modulation formats.

In FIG. 6, at a step 606, the mathematical model provides the optimum transmission parameters as an output to the transmitter digital signal processor (Tx DSP) and a receiver digital signal processor (Rx DSP) of the online transponder 600.

In FIG. 6A, at a step 606, the mathematical model provides the optimum transmission parameters as an output to the transmitter digital signal processor (Tx DSP) and a receiver digital signal processor (Rx DSP) of the online transponder 600. In addition to the process shown in Fig. 6, the mathematical model provides the optimum transmission parameters as an output to the wavelength selective switch (WSS). Thus, attenuations at different frequencies for the WSS are indicated.

For both, FIG. 6 and 6 A, the online transponder 600 may be configured during the operation based on the optimum transmission parameters. The transmitter digital signal processor (Tx DSP) and receiver the digital signal processor (Rx DSP) of the online transponder 600 may report results of new convergence to the mathematical model iteratively, if needed. FIG. 7 is an exemplary graphical representation 700 of performance of a mathematical model at 100 gigabaud (GBd) symbol rates for a first optical signal-to-noise ratio (OSNR) value and a second optical signal-to-noise ratio (OSNR) value in accordance with an implementation of the disclosure. In the exemplary graphical representation 700, partial digital pre-emphasis (DPE) is plotted along an abscissa X-axis and signal-to-noise (SNR) is plotted along an ordinate Y-axis. The first optical signal-to-noise ratio (OSNR) value is 39 decibels (dB), and the second optical signal-to-noise ratio (OSNR) value is 22 dB. The mathematical model may accurately determine the signal-to-noise ratio (SNR) at different partial digital pre-emphasis (DPE) levels as shown in FIG. 7. An error between the mathematical model and experiments is smaller than 0.1 dB, namely less than 1% if DPE values higher than 5 dB as shown in FIG. 7. The error between the mathematical model and experiments reaches 0.25 dB (~3%) if the DPE values are below 5 dB as shown in FIG. 7.

FIG. 8 is an exemplary graphical representation 800 of performance of a mathematical model at 112.5 gigabaud (GBd) symbol rates for a first optical signal-to-noise ratio (OSNR) value and a second optical signal-to-noise ratio (OSNR) value in accordance with an implementation of the disclosure. In the exemplary graphical representation 800, partial digital pre-emphasis (DPE) is plotted along an abscissa X-axis and signal-to-noise (SNR) is plotted along an ordinate Y-axis. The first optical signal-to-noise ratio (OSNR) value is 35 decibels (dB), and the second optical signal-to-noise ratio (OSNR) value is 25 dB as shown in FIG. 8. The mathematical model may accurately determine the signal-to-noise ratio (SNR) at different partial digital preemphasis (DPE) levels. An error between the mathematical model and experiments lies between 1% and 5%.

An accuracy of the mathematical model in terms of the maximum signal-to-noise ratio (SNR) (namely, at the optimum digital pre-emphasis (DPE) level), as well as the signal-to-noise ratio (SNR) benefit of the partial digital pre-emphasis (DPE), which are defined as the difference between signal-to-noise ratios (SNRs) at the optimum digital pre-emphasis (DPE) level and full digital pre-emphasis (DPE) levels as shown in Table 1:

The exemplary graphical representation 700 depicting a gain of 0.8 dB is obtained at 100 GBd symbol rates. The exemplary graphical representation 800 depicting the gain is increased up to 2 dB at 112.5 GBd. The partial digital pre-emphasis (DPE) is more beneficial when an impact of bandwidth limitation is more severe in optical communication systems. The DPE levels in the experiment are varied in steps of 2.4 dB for the 112.5 GBd symbol rates and 1.5 dB for the 100 GBd symbol rates, whereas in the mathematical model, the signal-to-noise ratio (SNR) vs. digital pre-emphasis (DPE) level curves are continuous. This result partly accounts for a bigger discrepancy between the mathematical model and the experiment for the 112.5 GBd, in terms of optimum DPE level (as shown in the 3rd column of Table 1).

FIG. 8A is an exemplary graphical representation 801 of performance of a mathematical model at 128 gigabaud (GBd) symbol rates for a first optical signal-to-noise ratio (OSNR) value and a second optical signal-to-noise ratio (OSNR) value in accordance with an implementation of the disclosure. In the exemplary graphical representation 801, partial digital pre-emphasis (DPE) is plotted along an abscissa X-axis and signal-to-noise (SNR) is plotted along an ordinate Y-axis. The first optical signal-to-noise ratio (OSNR) value is 28 decibels (dB), and the circle and square markers represent the experimental measured SNR in cases of using 10 dB optical pre-emphasis (OPE) and 0 dB OPE at 28 dB OSNR. The corresponding solid and dashed lines are the SNR calculated by the mathematical model. The second optical signal-to-noise ratio (OSNR) value is 24 dB as shown in FIG. 8A. The mathematical model may accurately determine the signal-to-noise ratio (SNR) at different joint optical pre-emphasis & partial digital pre-emphasis (J-DOPE) levels. An error between the mathematical model and experiments lies between 1% and 8%, and the error between the mathematical model and experiments lies between l%-2% at the highest SNR ranges.

FIGS. 9A-9C are flow diagrams that illustrate a method for configuring an optical system for communicating data from an optical transmitter via an optical fibre waveguide arrangement, to an optical receiver in accordance with an implementation of the disclosure. Configuring the optical system includes using a data processing arrangement to determine at least one of the following: an optimal degree of partial digital pre-emphasis (DPE) (H _DPE (f)) to be used in the optical system, a number of sub-carriers to be used for communicating the data through the optical fibre waveguide arrangement, a Baudrate per sub-carriers, an optical power to be used for the sub-carriers transmitted via the optical fibre waveguide arrangement, a number and characteristics of equalization taps to be used for implementing the partial digital pre-emphasis (DPE), modulation formats to be used for the data, digital signal processing (DSP) parameters of the optical transmitter to be used, and digital signal processing (DSP) parameters of the optical receiver to be used. At a step 902, a signal-to-noise ratio (SNR) obtainable when communicating the data from the optical transmitter to the optical receiver as the function of the at least one parameter describing or controlling operating characteristics of component parts of the optical system is calculated, using the data processing arrangement configured to execute a mathematical model.

In FIG. 9B, at a step 904, from calculations at the step 902, a combination of values of the at least one parameter that provides a substantially best compromise between the signal-to-noise ratio (SNR) and the data communication rate obtainable for the optical system, are iteratively determined. At a step 906 of FIG. 9B, the optical system is configured according to the at least one parameter that provides the substantially best compromise, or, for example, provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system.

In FIG. 9C, from calculations at the step 902, a combination of values of the at least one parameter that provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system, are iteratively determined. At step 906 of FIG. 9C, the optical system is configured according to the at least one parameter that provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system.

The method is of advantage in that the method provides an enhanced performance of an optical system that provides a substantially best compromise between a signal-to-noise ratio (SNR) and a data communication rate obtainable for the optical system. The method also provides an enhanced performance of an optical system that provides the optimum signal-to-noise ratio (SNR) and the optimum data communication rate obtainable for the optical system. The method increases the signal-to-noise ratio (SNR) and the data communication rate. The method quickly and accurately predicts the signal-to-noise ratio (SNR) based on given filter responses. The method provides a set of optimum parameters for the optical system to increase the data communication rate, thereby reducing sweeping time of hundreds of parameters significantly. The method can be implemented in a real product, may be implemented using executable software, whenever a channel condition is changed, to accelerate convergence time of an online transceiver. Furthermore, the method can be used to estimate a performance of transceivers, which gives a reference to the mathematical model in adjusting parameters.

The at least one parameter may be selected from a group of parameters including: a pulse shaping ( g(f) ) used in the optical transmitter, a degree of partial digital pre-emphasis (DPE) (HORE(G)) used in the optical transmitter, an effective number of bits (Enob) and a transfer function of a digital-to-analog converter (DAC) at the optical transmitter, a drive noise spectral density ( ri _dnver ) of the optical transmitter, an amplified spontaneous emission (ASE) noise spectral density (HASE) of one or more optical cross-connects (OXC), optical amplifiers (EDFA) used along the optical fibre waveguide arrangement, a receiver noise spectral density of the optical receiver, transfer functions of driver and modulator, ^a transfer function of one or more wavelength selective switch and transfer functions of the optical transmitter and the optical receiver Optionally, the method includes computing the partial digital pre-emphasis (DPE) for the mathematical model based on an inverse of a transfer function of the optical transmitter: where scaling factor that adjusts a ratio of the partial digital pre-emphasis (DPE), and the transfer function of the optical transmitter.

Optionally, the method includes computing the partial digital pre-emphasis (DPE) combined with an optical pre-emphasis (OPE) for the mathematical model based on an inverse of a transfer function of the optical transmitter (204) and a transfer function of the optical pre emphasis (OPE): wherein frequency; is a scaling factor that adjusts the level of partial optical pre-emphasis (OPE), the transfer function of the approximated optical transmitter (204) frequency response, the transfer function partial optical pre-emphasis, a = a scaling factor that adjusts a ratio of the partial digital pre-emphasis ( transfer function of the optical transmitter (204). Optionally, the method includes configuring the mathematical model according to at least one of:

(i) the optical transmitter is modelled to include the digital-to-analog converter (DAC) that is modelled as an additive white Gaussian noise source having a noise variance of variance accounting for noise amplification as a function of the degree of partial digital pre emphasis employed, followed by a filter of the digital-to-analog converter (DAC) having a transfer function H _OA (/) for representing an electrical bandwidth limitation associated with the optical transmitter;

(ii) the optical transmitter is modelled to include a coherent driver modulator (CDM) that includes a white Gaussian noise source having a variance n _Driver , followed by a filter of the coherent driver modulator (CDM) having a transfer function

(iii) the one or more optical cross-connects (OXC) are modelled as the amplified spontaneous emission (ASE) noise spectral density (n _ASE ) combined with one or more wavelength selective switch (WSS) filters having a transfer function

(iii) the optical receiver is modelled to include an additive white Gaussian noise source having a noise variance of variance n _Rx representing all noise sources of the optical receiver and the optical receiver is modelled to include an analog-to-digital converter (ADC) that is modelled as an additive white Gaussian noise source having a noise variance of variance accounting for noise as a function of the effective number of bits (ENOB) of the ADC, followed by a filter of the optical receiver having a transfer function H _Rx (f ); and

(iv) the optical receiver is modelled to include a digital signal processing (DSP) equalization.

The method may include modelling the DAC noise variance, n _OA (DPE ) by using the effective number of bits (ENOB) used when communicating via the optical system as an input parameter to the mathematical model, the partial digital pre-emphasis (DPE) applied at the optical transmitter, and a digital-to-analog (DAC) output power loss due to low-frequency signal suppression. A signal -to-noise (SNR) ratio of the DAC is given by: where a transfer function for the digital pre-emphasis represents a pre-emphasis in a frequency domain, where is ^a noise power spectrum density as defined by: where

E _s = a power of an optical signal within the optical system, and

SNR _max = a maximum signal-to-noise ratio (SNR) of the digital-to-analog converter (DAC) of the optical transmitter when digital pre-emphasis (DPE) is not applied, where S is a function of frequency (f).

Optionally, the method includes computing a signal-to-noise ratio (SNR) of the digital-to- analog converter of the optical transmitter, in a time domain, using a multi-channel SNR computation based on a relationship: where where is a gap of all sub-channels used in the optical system, where typically

The method may include configuring the mathematical model to accommodate an ageing of the optical system, and to adjust the optimal degree of partial digital pre-emphasis (DPE) H _DPE (f) to be used in the optical system as a function of the ageing. Optionally, the method includes adjusting the degree of partial digital pre-emphasis (DPE) individually depending on at least one of: a transmission gain per channel, an amplified spontaneous emission (ASE) noise spectral density a noise present per channel, a transmission per sub-carrier, an expected Baud rate per channel, and transfer functions of the optical transmitter the optical receiver ) and the one or more wavelength selective switches used along the optical fibre waveguide arrangement between the optical transmitter and the optical receiver.

The method may include using the mathematical model to predict maintenance requirements of the optical system or potential expected failure of the optical system depending on changes in at least one of the parameters and measurements made to characterize the optical system.

The method may include using a machine learning model to determine the signal-to-noise ratio (SNR) obtainable when communicating the data from the optical transmitter to the optical receiver as the function of the at least one parameter describing or controlling operating characteristics of component parts of the optical system, for configuring the optical system.

The machine learning model may be trained with historical signal-to-noise ratios for a plurality of parameters describing or controlling operating characteristics of component parts of historical optical systems under one or more operating conditions.

FIG. 10 is an illustration of an exemplary computer system 1000 in which the various architectures and functionalities of the various previous implementations may be implemented. As shown, the computer system 1000 includes at least one processor 1004 that is connected to a data bus 1002, wherein the computer system 1000 may be implemented using any suitable protocol, such as PCI (Peripheral Component Interconnect), PCI-Express, AGP (Accelerated Graphics Port), Hyper Transport, or any other bus or point-to-point communication protocol (s). The computer system 1000 also includes a memory 1006

Control logic (software) and data are stored in the memory 1006 which may take a form of random-access memory (RAM). In the disclosure, a single semiconductor platform may refer to a sole unitary semiconductor-based integrated circuit or chip. It should be noted that the term single semiconductor platform may also refer to multi-chip modules with increased connectivity which simulate on-chip modules with increased connectivity which simulate on- chip operation, and make substantial improvements over utilizing a conventional central processing unit (CPU) and bus implementation. Of course, the various modules may also be situated separately or in various combinations of semiconductor platforms per the desires of the user.

The computer system 1000 may also include a secondary storage 1010. The secondary storage 1010 includes, for example, a hard disk drive and a removable storage drive, representing a floppy disk drive, a magnetic tape drive, a compact disk drive, digital versatile disk (DVD) drive, recording device, universal serial bus (USB) flash memory. The removable storage drive at least one of reads from and writes to a removable storage unit in a well-known manner.

Computer programs, or computer control logic algorithms, may be stored in at least one of the memory 1006 and the secondary storage 1010. Such computer programs, when executed, enable the computer system 1000 to perform various functions as described in the foregoing for implementing the method of the disclosure. The memory 1006, the secondary storage 1010, and any other storage are possible examples of computer-readable media.

In an implementation, the architectures and functionalities depicted in the various previous figures may be implemented in the context of the processor 1004, a graphics processor coupled to a communication interface 1012, an integrated circuit (not shown) that is capable of at least a portion of the capabilities of both the processor 1004 and a graphics processor, a chipset (namely, a group of integrated circuits designed to work and sold as a unit for performing related functions, and so forth).

Furthermore, the architectures and functionalities depicted in the various previous-described figures may be implemented in a context of a general computer system, a circuit board system, a game console system dedicated for entertainment purposes, an application-specific system. For example, the computer system 1000 may take the form of a desktop computer, a laptop computer, a server, a workstation, a game console, an embedded computer system (for example, an embedded microcontroller).

Furthermore, the computer system 1000 may take the form of various other devices including, but not limited to a personal digital assistant (PDA) device, a mobile phone device, a smart phone, a television, and so forth. Additionally, although not shown, the computer system 1000 may be coupled to a network (for example, a telecommunications network, a local area network (LAN), a wireless network, a wide area network (WAN) such as the Internet, a peer-to-peer network, a cable network, or the like) for communication purposes through an I/O interface 1008 It should be understood that the arrangement of components illustrated in the figures described are exemplary and that other arrangements may be possible. It should also be understood that the various system components (and means) defined by the claims, described below, and illustrated in the various block diagrams represent components in some systems configured according to the subject matter disclosed herein. For example, one or more of these system components (and means) may be realized, in whole or in part, by at least some of the components illustrated in the arrangements illustrated in the described figures.

In addition, while at least one of these components are implemented at least partially as an electronic hardware component, and therefore constitutes a machine, the other components may be implemented in software that when included in an execution environment constitutes a machine, hardware, or a combination of software and hardware.

Although the disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.