Optical equalization of communication networks

Abstract

A method and apparatus for improving transmission in an optical communication system, the method comprising: receiving an optical signal; equalizing the optical signal using an optical equalization filter to obtain an equalized optical signal; converting the equalized optical signal into an electrical signal; comparing the electrical signal with an expected electrical signal to obtain a comparison result; determining one or more optical parameters to be modified for the optical equalization filter based on the comparison result; determining modifications to be applied to the optical equalization filter based on the optical parameters to be modified; applying the modifications to the optical equalization filter; thereby determining the strain on the optical signal in the electrical domain; and applying modifications in the optical domain to correct the strain on the optical signal.

Description

[Technical Field]

[0001] This application claims priority from U.S. Provisional Patent Application No. 63 / 508,037, filed on 14 June 2023, entitled "OPTICAL EQUALIZATION OF COMMUNICATION NETWORKS," which is incorporated herein by reference.

[0002] This disclosure relates in general to optical communication networks, and more specifically to optical equalization in high-speed communication systems. [Background technology]

[0003] Optical networks, also known as fiber optic communication networks, are used to transmit information from one place to another by sending pulses of light through optical fibers. Light is a form of carrier wave that is modulated to carry information. Fibers are advantageous over electrical cables when high bandwidth, long distance, or resistance to electromagnetic interference is required. This type of communication can transmit voice, video, or any other type of data through local area networks or over long distances.

[0004] However, optical channels are not immune to noise, loss, bandwidth limitations, nonlinearity, and dispersion, which introduce distortion into the transmitted signal. To compensate for this distortion, equalization can be performed, which aims to cancel it out. Therefore, when the channel is equalized, the frequency-domain attributes of the signal at the input are faithfully reproduced at the output.

[0005] The equalizer aims to invert the frequency response of a channel in order to reduce intersymbol interference (ISI).

[0006] Equalization can be pre-emphasis, that is, adapting the transmitter signal to the expected distortion, because in some embodiments, information may be received from the receiver to the transmitter, and therefore the properties of the communication channel are known and can be dynamically compensated for. Thus, pre-emphasis relates to emphasizing desired properties, such as high frequencies. In other embodiments, the correction may be predetermined without considering further information about the channel characteristics.

[0007] As an addition or alternative, post-emphasis correction may be performed on the receiving end. Post-emphasis equalization may use passive components with low power consumption and can operate at different bandwidths. Post-emphasis equalization may provide better results because it ensures that the output signal takes into account the actual distortion of the communication channel. In some embodiments, calibrating the post-emphasis equalizer may be performed by transmitting a given signal, checking the received signal, and adapting the equalizer so that the received signal corresponds to the transmitted signal.

[0008] Some known types of equalization methods include the following: • Feed-forward equalization (FFE) corrects the amplitude of symbols in the transition region and maintains constant transmit power. • Continuous Time Linear Equalization (CTLE) is applied in the receiver to attenuate low-frequency signal components and amplify components around the Nyquist frequency. Decision Feedback Equalization (DFE) is implemented in the receiver to feed back symbol determination to the symbol decoder.

[0009] In some embodiments, equalization may be performed using continuous-time linear equalization (CTLE). In some embodiments, CTLE may be implemented using a finite impulse response (FIR) filter, where the impulse response, or response to any finite-length input, is of finite duration, since it stabilizes to zero in a finite time. Thus, the impulse response of an N-th order discrete-time FIR filter lasts just N samples from the first non-zero element to the last non-zero element before it stabilizes to zero. [Overview of the project] [Problems that the invention aims to solve]

[0010] When implementing an FIR filter, the challenge is to select and implement the coefficients for each tap such that the sum of the samples actuated by the corresponding coefficients reproduces the transmitted signal. [Means for solving the problem]

[0011] An exemplary embodiment of the subject matter disclosed is a method for improving transmission in an optical communication system, comprising: receiving an optical signal; equalizing the optical signal using an optical equalization filter to obtain an equalized optical signal; converting the equalized optical signal into an electrical signal; comparing the electrical signal to an expected electrical signal to obtain a comparison result; determining one or more optical parameters to be modified for the optical equalization filter based on the comparison result; determining modifications to be applied to the optical equalization filter based on the optical parameters to be modified; applying the modifications to the optical equalization filter, thereby determining the strain on the optical signal in the electrical domain; and applying modifications in the optical domain to compensate for the strain on the optical signal. The method may further include repeating the receiving, equalizing, modifying, comparing, determining the optical parameters, and determining the modifications until the difference between the electrical signal and the expected electrical signal falls below a predetermined threshold. In the method, the optical signal is optionally received at the receiving end of an optical communication system after the optical signal has been carried by an optical fiber. In this method, an optical signal is optionally received at the transmitting end of an optical communication system, and an optical signal corresponding to the equalized optical signal is carried to the receiving end via an optical fiber. In this method, each of the optical parameters to be modified affects at least one performance measure selected from the group consisting of bit error rate, symbol error rate, channel impulse response, eye-opening, eye width, eye height, signal rise and fall times, signal-to-noise ratio, and extinction ratio. In this method, the modification is optionally selected from the group consisting of changing the temperature of a thermo-optic phase shifter and applying a reverse bias to a PN depletion phase shifter. In this method, the modification is optionally performed by changing the characteristics of one or more optical equalization filters selected from the group consisting of a delay line, a phase shifter, and a coupler. In this method, the comparison or modification decision is optionally performed using non-invasive components.Within this method, the comparison or modification decision may be performed using one or more methods selected at will from the group consisting of least mean squares (LMS), Gauss-Newton, Levenberg-Marquardt, neural networks, deep neural networks, and reinforcement learning.

[0012] Another exemplary embodiment of the disclosed subject matter is an apparatus for improving transmission in an optical communication system, comprising: an optical equalization filter for receiving an optical signal and outputting an equalized optical signal; an optical-to-electric converter for receiving an equalized optical signal and outputting an electrical signal; a digital signal processor (DSP) for comparing the electrical signal with an expected electrical signal and determining changes to the optical parameters of the optical equalization filter; and a controller for applying modifications to the optical equalization filter to achieve the changes, wherein the apparatus is operable to determine the strain on the optical signal in the electrical domain and to apply modifications in the optical domain to compensate for the strain on the optical signal. In the apparatus, the controller is optionally a microcontroller unit (MCU). The apparatus is optionally located on the receiving side of the optical communication system and receives optical signals carried by optical fibers. Within this device, optical signals are optionally received at the transmitting end of an optical communication system, and the optical signals corresponding to the equalized optical signals are optionally carried to the receiving end via optical fibers. Within this device, the optical parameters to be modified optionally affect one or more items selected from the group consisting of bit error rate, symbol error rate, channel impulse response, eye opening, eye width, eye height, signal rise and fall times, signal-to-noise ratio, and extinction ratio. Within this device, modifications optionally consist of changing the temperature of a thermo-optic phase shifter and applying a reverse bias to a PN depletion phase shifter. Modifications performed within this device by changing the characteristics of an optical equalization filter optionally consist of a group consisting of a delay line, a phase shifter, and a coupler. Within this device, comparisons or modification decisions are optionally performed using non-invasive components.Within the present apparatus, comparison or correction determination is optionally performed using at least one method selected from the group consisting of the least mean square (LMS), Gauss-Newton, neural network, deep neural network, and reinforcement learning.

[0013] The present disclosure will be more fully understood and appreciated from the following detailed description taken in conjunction with the drawings in which corresponding or like numerals or letters indicate corresponding or like components. Unless otherwise specified, the drawings provide exemplary embodiments or aspects of the present disclosure and do not limit the scope of the present disclosure.

Brief Description of the Drawings

[0014] [Figure 1A] FIG. 1 is a schematic diagram of a first embodiment of an optical communication system according to some exemplary embodiments of the present disclosure. [Figure 1B] FIG. 2 is a schematic diagram of a second embodiment of an optical communication system according to some exemplary embodiments of the present disclosure. [Figure 1C] FIG. 3 is a flowchart of steps in a method for improving equalization in an optical communication system according to some exemplary embodiments of the present disclosure. [Figure 2] FIG. 4 is a frequency response graph of a continuous time linear equalizer (CTLE) according to some exemplary embodiments of the present disclosure. [Figure 3] FIG. 5 is a schematic diagram of a general structure of a finite impulse response (FIR) filter according to some exemplary embodiments of the present disclosure. [Figure 4] FIG. 6 is a drawing of an optical FIR filter in the frequency domain according to some exemplary embodiments of the present disclosure. [Figure 5] FIG. 7 is a schematic diagram of an exemplary embodiment of a two-stage filter according to some exemplary embodiments of the present disclosure. [Figure 6A] FIG. 8 is a schematic diagram of a photonic integrated circuit according to some exemplary embodiments of the present disclosure. [Figure 6B]This is a schematic diagram of a two-tap filter according to some exemplary embodiments of the present disclosure. [Figure 6C] This is a schematic diagram of a four-tap filter according to some exemplary embodiments of the present disclosure. [Figure 7A] This figure shows simulated results of applying the present disclosure to optical communication systems using some exemplary embodiments of the present disclosure. [Figure 7B] This figure shows simulated results of applying the present disclosure to optical communication systems using some exemplary embodiments of the present disclosure. [Figure 7C] This figure shows simulated results of applying the present disclosure to optical communication systems using some exemplary embodiments of the present disclosure. [Modes for carrying out the invention]

[0015] One technical problem addressed by this disclosure is the need to improve the quality of signals received at the receiving end of a network in which signals are transmitted as optical pulses through an optical medium.

[0016] Another technical issue of this disclosure is the need to enhance the signal in a post-emphasis manner, i.e., at the receiving end, for example, by using a post-emphasis equalizer.

[0017] Another technical issue of this disclosure is the need to enhance signals using passive components that are more energy-efficient and time-efficient. However, due to the dynamic nature of communication channels, equalization must be adaptable to changing conditions. For example, an equalizer may need to be calibrated at predetermined time intervals, such as 1 millisecond, 1 second, 1 minute, 10 minutes, 1 hour, 1 day, 1 month, etc. Calibration may be performed by transmitting a predetermined signal, such as a predetermined sequence of 1s and 0s, receiving that signal at the receiving end, and enhancing the equalizer so that the acquired signal is the same as the transmitted signal or within an acceptable range of error.

[0018] One technical solution of this disclosure involves equalizing a signal using a post-emphasis photonic device as a filter that operates in the optical domain and adapts the optical signal according to the required response function. Unlike current techniques in which the correction is performed in the digital domain, performing the correction in the optical domain allows for the use of passive components that are energetically efficient, reduce latency, and provide high performance.

[0019] The filter consists of or may comprise a finite impulse response (FIR) filter having a predetermined number of N tap filters. In an FIR filter, each of the N samples is operated using a coefficient (an operation called a stage), and the N stages operate in such a way that they are summed up.

[0020] In some embodiments, each such stage or combination of two or more stages may be generated by a combination of components including a coupler, a delay line, and a phase shifter. Two photoconductive elements pass through their components so that the input light is split between the two waveguide elements.

[0021] The difference in length between waveguides in the delay line determines the filter's bandwidth.

[0022] At least two of the other components may have a heat-retaining element on them, such as a conductive element that heats up when an electrical signal passes through it. Heating the heat-retaining element of a coupler may affect the coupling between two conductors, and heating the heat-retaining element of a phase shifter may affect the phase difference between two photoconductive elements.

[0023] By altering the phase difference and coupling, the received signal can be improved so that the output optical signal best reproduces the input signal or is within an acceptable error rate. If the input signal is an electrical signal, it can be fed into a photodiode to reconstruct the improved optical signal, which will produce an output electrical signal equal to the input signal in response to absorbing photons.

[0024] In some embodiments, the filter may be designed to implement one, two, or more stages by comprising multiple delay lines, couplers, or phase shifters, and it outputs the sum of the products of two or more stages.

[0025] One technical effect of this disclosure relates to an equalizer filter implemented as a photonic device operating in the optical domain at the receiving end of an optical communication network. The equalizer comprises passive components, and therefore it provides low latency. Furthermore, the passive components eliminate the need for complex calculations and therefore reduce the energy requirements of the system.

[0026] Another technical effect of this disclosure relates to adjustable filters that can be fine-tuned according to potentially varying conditions of the communication channel or potentially varying characteristics of the input signal.

[0027] A linear equalizer cannot distinguish between signal, noise, and crosstalk. Therefore, while a linear equalizer can improve intersymbol interference, the signal-to-noise ratio (SNR) remains unchanged. In optical links, the primary source of noise is relative intensity noise related to the laser and modulator (e.g., an electro absorption modulator). Noise power is directly related to the bandwidth of the optical signal. If equalization is implemented after the light is supplied to the photodiode, the photodiode is open to many frequency ranges and introduces a lot of noise that needs to be addressed. Equalization before the photodiode by implementing a filter in the optical domain is useful in controlling the optical bandwidth and improving the SNR at the receiver. Therefore, while a digital equalizer improves intersymbol interference rather than SNR, using this disclosure provides improvement in both. Furthermore, equalization in the optical domain can significantly reduce the latency and power requirements associated with signal processing in the digital domain.

[0028] Another technical effect of this disclosure, without limitation, relates to applying filters using any equalization method, such as DFE, FFE, and CTLE.

[0029] Next, refer to Figure 1A, which shows a schematic diagram of a first embodiment of an optical communication system in which the present disclosure may be implemented.

[0030] The system includes a light source 104, such as a laser light source. A modulator 112, which converts electrical signals to optical signals, can modulate the light source according to digital data 108. Depending on the parameters of the optical beam being manipulated, the modulator 112 may comprise one or more amplitude modulators, phase modulators, and / or polarization modulators. In some embodiments, instead of the external modulation performed by the optical modulator 112, the current driving the light source, such as a laser diode, may be manipulated to modulate the optical beam; this is called direct modulation.

[0031] The modulated light is transmitted to the destination through the optical fiber 116. In non-limiting examples, the optical fiber 116 can be of any required length between 1m and 10km. Although it is considered highly efficient and reliable, the optical fiber 116 can introduce noise, loss, and other distortions.

[0032] The equalization filter 120 may be an optical equalization filter and may be used to correct various distortions in an optical communication system, as detailed below. The coefficients of the equalization filter 120 may be updated by a microcontroller unit (MCU) 124 in response to changes in the characteristics of the optical communication channel comprising components 112, 116, 120 and an optical receiver 128. For example, the equalization filter 120 may be dynamically updated when the error introduced by the optical communication channel comprising components 112, 116, 120, and 128 to a given known signal exceeds an acceptable rate. These coefficients may change the behavior of delay lines, phase shifters, and directional couplers.

[0033] The equalized signal can be provided to an optical receiver 128, such as one or more photodiodes, to acquire an electrical signal 108.

[0034] An electrical signal may be provided to a digital signal processor (DSP) 130 to analyze and improve the signal, for example, by comparing the received signal with a known transmitted signal. The signal may be analyzed for signal quality, level separation, etc., as detailed in relation to Figures 7A-7C. The analysis of the signal may include running an algorithm to determine updated filter coefficients required to compensate for distortion.

[0035] Once a change to the equalization filter is decided, a controller such as a microcontroller unit (MCU) 124 may operate to make the necessary modifications to the equalization filter 120, for example, by updating one or more of the coefficients of the equalization filter 120, which will affect the behavior of the equalization filter 120 and thereby correct the distortion.

[0036] In some embodiments, the optical receiver 128 and the DSP 130, or the DSP 130 and the MCU 124, may be implemented as a single component. Additionally or alternatively, the DSP 130 may include a deserializer.

[0037] The obtained signal can be output as output data 132 that reproduces data 108 up to a certain bit error rate (BER). For example, an acceptable BER is 10 -3 ~10 -15 It could be within a certain range, etc.

[0038] Next, refer to Figure 1B, which shows a second embodiment of an optical communication system in which the present disclosure may be implemented.

[0039] The system in Figure 1B receives digital data 108 as input, and the digital data 108 can be serialized by a serializer 132 to convert it into a series of electrical pulses.

[0040] The sequence of pulses can be converted into a sequence of optical pulses by the electro-optical (E / O) converter 136.

[0041] If the strain introduced by an optical communication channel comprising components 112, 116, 120, and 128 is known, the optical pulse train can be improved by the transmitter equalization filter 140 according to the known strain. The transmitter equalization filter 140 can be modified as needed according to the changing strain by using updated filter coefficients. The modification can be dynamic, periodic, or otherwise.

[0042] The optical signal can be supplied to a divider 148 that divides the energy of the optical signal. The divider 148 may be an asymmetric divider, for example, it may divide the energy into a large portion 151, such as 80%, 90%, 95%, 99%, etc., to the optical fiber 116, and the remainder of the energy, such as 20%, 10%, 5%, 1%, etc., which are returned as feedback. The smaller portion 150 of the energy can be supplied to a photodiode 152 or another optical-electric converter. The resulting signals can be supplied to the DSP 130 and MCU 124 as described above, which will correct the distortion of the transmit equalization filter 140.

[0043] Next, the majority of the energy 151 is transmitted via the optical fiber 116 and can be enhanced by the receiver equalization filter 120, as in the case of Figure 1A above, and the receiver equalization filter 120 can be modified according to the updated filter coefficients as described above. The enhanced signal can be converted into electrical data by the optical receiver converter 128 and processed by the DSP 130, and the result of this processing can be used with the updated filter coefficients 124 and output as a data output 132 that reproduces the data 108 up to a certain bit error rate (BER). For example, an acceptable BER is 10 -3 ~10 -15 It could be within a certain range, etc.

[0044] It will be understood that the receiver equalization filter 120 may be used in addition to or as a substitute for the transmitter equalization filter 140. Thus, the signal may be enhanced before and / or after transmission via the optical fiber 116.

[0045] This disclosure, without limitation, allows for the closure of a feedback loop by adapting the parameters of an optical equalization filter, as described in the disclosed embodiments, such that strain is detected in the electrical domain but corrected in the optical domain. Furthermore, the equalization filter can limit the frequency bandwidth to reduce the power at noisier frequencies sent to the photodetector, thereby improving the required frequency and reducing noise. Correcting the strain in the optical domain enables faster response times because latency depends on the time it takes for light to pass through the system, and that time is negligible. Moreover, correcting in the optical domain eliminates the need for correction in the electrical domain, thereby reducing the energy consumption and cooling requirements of the electronic components.

[0046] Next, refer to Figure 1C, which shows a flowchart of the steps in a method for improving equalization in optical communication systems, according to some exemplary embodiments of the present disclosure.

[0047] In step 160, the optical signal may be received, for example, by the transmitter equalization filter 140 on the transmitting side of the communication system, or by the receiver equalization filter 120 on the receiving side of the communication system.

[0048] In step 164, the optical signal may be equalized using an optical equalization filter, for example by a transmitter equalization filter 140 or a receiver equalization filter 120, in order to obtain an equalized optical signal.

[0049] In step 168, the equalized optical signal can be converted into an electrical signal by, for example, an optical receiver 128, a photodiode 152, etc.

[0050] In step 172, the electrical signal may be compared with the expected electrical signal in order to obtain a comparison result.

[0051] In step 176, based on the comparison results, one or more optical parameters to be modified for the optical equalization filter may be determined. The comparison step 172 and the parameter determination step 176 may be performed by the DSP 130. These parameters may include, but are not limited to, one or more of the following performance metrics: bit error rate, symbol error rate, channel impulse response, eye opening, eye width, eye height, signal rise and fall times, signal-to-noise ratio, extinction ratio, etc. The "eye" parameters will be described in more detail below in relation to Figures 7A to 7C.

[0052] A filter is first designed to implement the required transfer function. An FIR filter can be characterized by a certain number of taps, each tap associated with a filter coefficient value. The impulse response of an FIR filter corresponds to the set of filter coefficient values.

[0053] The difference in length (ΔL) within the phase shift elements of the filter can be calculated based on the following formula.

number

[0054] These coefficient values ​​can be changed to optical delay lines, directional couplers, and phase shifters.

[0055] The directional coupler can be realized as a Mach-Zehnder interferometer (MZI), and thus can be implemented as a cascade of a fixed 3dB coupler acting as a splitter, a phase shifter, and a second 3dB coupler acting as a combiner.

[0056] The design of the FIR filter may involve the use of one or more algorithms or techniques for estimating the channel response and determining appropriate filter coefficients. These methods may include, but are not limited to, the least mean square (LMS), Gauss-Newton, Levenberg-Marquardt, minimum mean square error (MMSE), maximum likelihood estimation, and neural network (NN).

[0057] Then, in step 176, parameter determination may be performed.

[0058] Phase shift in the variable directional coupler

[0059] Two parameters, θ n and φ n can be defined.

[0060] θ n is the normalized phase shift caused by the difference in the lengths of the two arms in each variable directional element (see the variable directional couplers 504, 512, 520 in FIG. 5 below) and the effect of the power applied to the heater in one of those arms. An additional phase shift is caused by a variable directional coupler that can be considered a delay line with a path length difference of zero. Since heating changes the phase, the directional coupling also changes. Thus, θ n represents the variable directional coupling where the arms (501, 502) are theoretically of the same length but may actually exhibit some difference. On the other hand, φ n represents the directional coupling in components (508, 516) with a significant arm difference.

[0061] In the case of low heater power, θ n It depends linearly on power dissipation. For more significant heater power, the phase shift is found to depend quadratically on the applied power. (The coefficient will be obtained as a fitting parameter as part of the device characterization.)

[0062] φ n This is the phase shift caused by heating one of the arms, plus the modulo 2π portion of the phase shift caused by the difference in length. n and φ n Common algorithms for determining the value of include least-squares mean, Gauss-Newton, Levenberg-Marquardt, neural networks (NN), deep neural networks, or other machine learning algorithms related to optimization problems. The calculated phase parameter θ is then used. n and φ n θ is used as a starting value for nonlinear optimization using a real device model, and therefore, n and φ n This is converted into heater power.

[0063] For faster convergence, non-invasive measurements are enabled by adding a heatable element on a short arm of the phase shift element to determine the phase shift. The results aim to provide parameters for fitting the real-world device model response to the desired spectrum.

[0064] In step 180, based on the optical parameters to be modified, the modifications to be applied to the optical equalization filter may be determined. These modifications may include changing the temperature of the thermo-optic phase shifter or applying a reverse bias to the PN depletion phase shifter. To achieve equalization, the received signal is processed through a finite impulse response (FIR) filter. The FIR filter convolves the received signal with the coefficients of its FIR filter, resulting in θ n and φ nThis acquires the power of the heater, thereby effectively adjusting the frequency response to compensate for channel distortion and attenuation.

[0065] In step 184, modifications may be applied to the optical equalization filter to correct its behavior and compensate for strain. The steps of determining and applying the modifications may be performed by the MCU 124. Possible modifications may include, but are not limited to, one or more of the following: changing the temperature of the thermo-optic phase shifter, or applying a reverse bias to the PN depletion phase shifter.

[0066] Please understand that the desired performance may not be achieved by a single iteration as described above. Therefore, the process may be repeated and restarted one or more times in step 160 until the performance, for example, the BER, is within an acceptable range.

[0067] Furthermore, channel characteristics can change over time, which can lead to unwanted performance degradation; therefore, feedback and equalization adaptation may need to be repeated continuously or at least periodically.

[0068] Next, refer to Figure 2, which shows frequency response graphs of CTLE according to some exemplary embodiments of the present disclosure.

[0069] Post-equalization, i.e., applying equalization after the optical pulse has been transmitted through the optical channel, flattens the transfer function of the equalized channel—that is, the product of the transfer function of that channel and the CTLE—over a wider frequency range. Therefore, by placing the CTLE in series with the channel, the equalizer selectively reduces the gain at low frequencies (e.g., by only -5 to -10) while maintaining the gain at higher frequencies, thereby improving the quality of the received signal.

[0070] Next, refer to Figure 3, which shows a schematic diagram of a general structure of an FIR filter implementing CTLE according to some exemplary embodiments of this disclosure.

[0071] A typical FIR filter, often referred to as 300, receives a discrete input signal x[n] as input and outputs y[n] according to the following equation:

number

[0072] b should be applied to the relevant delay signal in order to obtain a satisfactory output signal. i The coefficients 308, 308', and 308'' need to be adjusted to compensate for the distortion introduced by the optical fiber.

[0073] Next, refer to Figure 4, which shows a diagram of an optical FIR filter in the frequency domain implementing an equalization filter according to some exemplary embodiments of the present disclosure.

[0074] A filter, generally referred to as reference number 400, comprises N components, S k Each component, indicated as 404, should be applied to the x[n] input with a corresponding delay to the associated b i It is equivalent to S. k 404 is a combination of three factors: delay lines, phase shifts, and directional decoupling.

[0075] These components are implemented by two optical waveguides 408 and 412. The light can be split between the two waveguides, and the interrelationship between the two waveguides can determine these factors.

[0076] Therefore, the difference in length between line 408 and line 412 shown in pane 424 determines the delay Δτ.

[0077] One of those waveguides, for example waveguide 408, may have a heating element 416 attached to waveguide 408, and the heating element 416 changes the phase φ of the light passing through conductor 408 compared to the original phase when passing through conductor 412, as shown in pane 428. k Change it.

[0078] The distance and structural combination of waveguides 408 and 412, and in particular in area 420 where they are closest to each other, is shown in pane 432, as the directional coupling θ between their conductors. k This is determined. The coupling can also be changed by placing another heatable element (not shown) on one of those conductors in area 420.

[0079] Therefore, by changing the temperature of heating element 416 and / or other heating elements, the phase and coupling between optical conductors change, thereby affecting a specific b i The signal can be changed by injecting a predetermined signal and changing the temperature of the heating element until the output signal corresponds to the input signal. i By adapting this, the system can be dynamically adapted to provide appropriate post-emphasis equalization.

[0080] In some embodiments, a multi-mode interferometer (MMI) coupler may be used instead of a directional coupler.

[0081] Next, refer to Figure 5, which shows a schematic diagram of an exemplary embodiment of a two-stage FIR filter according to some exemplary embodiments of the present disclosure.

[0082] The filter referred to by 500 comprises conductors 501 and 502 and is configured to include three variable directionality couplers, such as 504, 512, and 520, where coupler 504 is responsible for θ0, coupler 512 is responsible for θ1, and coupler 520 is responsible for θ2.

[0083] The filter 500 further comprises a delay line and a phase shifter 508, which includes a phase shift element 507. The delay line and phase shifter 508 is responsible for the phase shift φ, and the delay line and phase shifter 516 is responsible for the delay Δτ. Thus, the combination of the three couplers 504, 512, and 520 and the delay line and phase shifters 508 and 516 provides two combined stages of the FIR filter. Each of these elements comprises a conductive member, such as elements 505, 509, and 513 of the couplers 504, 512, and 520, and elements 507 and 511 of the delay line and phase shifters 508 and 516, respectively. Each of the conductive members 505, 507, 509, 511, and 513 is heated in response to current, thereby changing the coupling, delay, and / or phase of the filter, so that the filter can be adjusted according to the changing conditions of the communication channel and the output signal can be equalized.

[0084] In some embodiments, the conductor 502 may also include additional elements, such as elements 515 and 517 provided in the delay line and phase shifters 508 and 516, respectively.

[0085] Elements 515 and 517 may enable non-invasive measurements and determination of modifications to be applied to the optical equalization filter. Non-invasiveness may allow for faster convergence to the desired signal. The determination of parameter modifications may be carried out using any known method, but is not limited to least squares mean (LMS), Gauss-Newton, or Levenberg-Marquardt. The modifications may also be determined using neural networks, such as convolutional neural networks (CNNs) or deep neural networks (DNNs).

[0086] Please understand that further filters can be designed that include more couplers and optionally additional components, and thus implement filters with a greater number of stages.

[0087] Next, refer to Figure 6A, which shows a schematic diagram of a photonic integrated circuit comprising four filters according to some exemplary embodiments of the present disclosure.

[0088] Therefore, the chip 600 comprises a 5-tap filter 604, 6-tap filters 608 and 612, and a 4-tap filter 616. Although the chip 600 is mounted on silicon nitride, the chip 600 can also be applied in other technologies, including but not limited to silicon and silicon-germanium technologies.

[0089] Figures 6B and 6C show schematic diagrams of a two-tap filter 620 and a four-tap filter 624, respectively, according to some exemplary embodiments of the present disclosure.

[0090] Next, refer to Figures 7A–7C, which show simulated results of applying the present disclosure to an optical communication system using some exemplary embodiments of the present disclosure.

[0091] Figures 7A–7C show diagrams of received signals in an optical communication network. Each of these diagrams may be called an "eye" diagram, which is an oscilloscope display in which a digital signal is repeatedly sampled and applied to the vertical input (y-axis), and a data rate is used to trigger a horizontal sweep (x-axis). In some situations, the pattern may look like a series of eyes between pairs of rails and can be used to evaluate the combined effects of channel noise, dispersion, and intersymbol interference on the performance of a baseband pulse transmission system. From a mathematical standpoint, the eye pattern is a visualization of the probability density function (PDF) of the signal modulo the unit interval (UI). It should be noted that larger empty areas ("eyes") indicate a better signal with less distortion and better separation between signal voltage levels.

[0092] Figure 7A shows a 4-level received signal with an opening ("eye") of 704 and no post-emphasis equalization.

[0093] Figure 7B shows the received signal after applying an electrical filter, following the application of a transimpedance amplifier to the signal after photoelectric conversion, and having an opening of 708.

[0094] Figure 7C shows the signal after applying an optical FIR filter according to this disclosure, having an aperture of 712. It can be seen that aperture 712 is larger than aperture 704 and even larger than aperture 708. Thus, it is clear that applying and adjusting optical filters improves equalization and, therefore, improves the overall performance of the communication network, in addition to providing low latency and high energy efficiency.

[0095] The present invention may be a system, method, and / or a computer program product. The computer program product may include a computer-readable storage medium (or media) having computer-readable program instructions thereon for causing a processor to perform aspects of the present invention.

[0096] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by instruction-executing devices. Computer-readable storage media can be, for example, but are not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any preferred combination thereof. A non-exhaustive list of more specific examples of computer-readable storage media includes portable computer diskettes, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or flash memory, static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital versatile disk (DVD), memory sticks, floppy disks, mechanically encoded devices such as punched cards or grooved raised structures on which instructions are recorded, and any preferred combination thereof. The computer-readable storage media used herein should not be interpreted as being transient signals in themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses passing through fiber optic cables), or electrical signals transmitted through wires.

[0097] The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical transmission fibers, wireless transmitters, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives computer-readable program instructions from the network and forwards them for storage in a computer-readable storage medium within each computing / processing device.

[0098] The computer-readable program instructions for performing the operation of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages ​​such as "C", C#, C++, Java®, Python, Smalltalk, etc. The computer-readable program instructions may run entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, via the Internet using an Internet service provider). In some embodiments, an electronic circuit, including, for example, a programmable logic circuit, a field-programmable gate array (FPGA), or a programmable logic array (PLA), may execute a computer-readable program instruction by personalizing the electronic circuit using state information of a computer-readable program instruction in order to carry out an aspect of the present invention.

[0099] Aspects of the present invention will be described herein with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It will be understood that each block in the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer-readable program instructions.

[0100] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, segment, or portion of instructions comprising one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions described in the blocks may be performed in a different order than that shown in the diagram. For example, two consecutively shown blocks may be executed effectively substantially simultaneously, or they may be executed in reverse order from time to time, depending on the functionality involved. It should also be noted that each block in the block diagram and / or flowchart, and combinations of blocks in the block diagram and / or flowchart, may be implemented by a dedicated hardware-based system that performs a specified function or action, or combines dedicated hardware with computer instructions.

[0101] The technical terms used herein are for illustrative purposes only to describe specific embodiments and do not limit the invention. The singular forms “a,” “an,” and “the” used herein also include the plural form unless the context otherwise clearly indicates. Furthermore, the terms “comprises” and / or “comprising” used herein indicate the presence of the described features, completes, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, completes, steps, actions, elements, components, and / or groups thereof.

[0102] All corresponding structures, materials, actions, and equivalents of all means-plus-function elements or step-plus-function elements in the following claims include any structures, materials, or actions for performing a function in combination with other claimed elements specifically claimed. The description of the present invention is presented for illustrative and explanatory purposes, but is not exhaustive and does not limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The examples have been selected and described to best illustrate the principles and practical applications of the invention and to enable others skilled in the art to understand the invention for various examples with various modifications suitable for specific intended uses.

Claims

1. A method for improving transmission in an optical communication system, The steps include receiving an optical signal and A step of equalizing the optical signal using an optical equalization filter to obtain an equalized optical signal, The steps include converting the equalized optical signal into an electrical signal, To obtain the comparison result, the steps include comparing the electrical signal with the expected electrical signal, The steps include determining at least one optical parameter to be modified for the optical equalization filter based on the comparison results, A step of determining the modification to be applied to the optical equalization filter based on the at least one optical parameter to be modified, The steps include applying the aforementioned modification to the optical equalization filter, This involves the step of determining the strain on the optical signal in the electrical domain, The steps include applying modifications to correct the distortion introduced into the optical signal in the optical domain, and Methods that include...

2. The method according to claim 1, further comprising repeating the steps of receiving, equalizing, converting, comparing, determining the at least one optical parameter, and determining the modification until the difference between the electrical signal and the previously expected electrical signal falls below a predetermined threshold.

3. The method according to claim 1, wherein the optical signal is received at the receiving end of the optical communication system after the optical signal has been transported by an optical fiber.

4. The method according to claim 1, wherein the optical signal is received at the transmitting end of the optical communication system, and an optical signal corresponding to the equalized optical signal is transported to the receiving end by an optical fiber.

5. The method according to claim 1, wherein the at least one optical parameter to be modified affects at least one performance measure selected from the group consisting of bit error rate, symbol error rate, channel impulse response, eye opening, eye width, eye height, signal rise and fall times, signal-to-noise ratio, and extinction ratio.

6. The method according to claim 1, wherein the modification is selected from the group consisting of changing the temperature of a thermo-optic phase shifter and applying a reverse bias to a PN depletion phase shifter.

7. The method according to claim 1, wherein the modification is carried out by changing at least one characteristic of the optical equalization filter, the at least one characteristic being selected from the group consisting of a delay line, a phase shifter, and a coupler.

8. The method according to claim 1, wherein the step of comparing or the step of determining the modification is performed using a non-invasive component.

9. The method according to claim 1, wherein the comparison step or the step of determining the modification is performed using at least one method selected from the group consisting of least squares mean (LMS), Gauss-Newton, neural networks, deep neural networks, and reinforcement learning.

10. A device for improving transmission in an optical communication system, An optical equalization filter for receiving an optical signal and outputting an equalized optical signal, A photo-to-electric converter for receiving the equalized optical signal and outputting an electrical signal, A digital signal processor (DSP) for comparing the aforementioned electrical signal with a predicted electrical signal and determining a change in at least one optical parameter of the optical equalization filter, A controller for applying modifications to the photoequalizer filter in order to achieve the aforementioned changes, Equipped with, The apparatus is capable of determining the strain on the optical signal in the electrical domain and applying modifications in the optical domain to correct the strain on the optical signal.

11. The apparatus according to claim 10, wherein the controller is a microcontroller unit (MCU).

12. The apparatus according to claim 10, wherein the apparatus is located on the receiving side of the optical communication system and receives an optical signal carried by an optical fiber.

13. The apparatus according to claim 10, wherein the optical signal is received at the transmitting side of the optical communication system, and the optical signal corresponding to the equalized optical signal is transported to the receiving side by an optical fiber.

14. The apparatus according to claim 10, wherein the at least one optical parameter to be modified affects at least one performance measure selected from the group consisting of bit error rate, symbol error rate, channel impulse response, eye opening, eye width, eye height, signal rise and fall times, signal-to-noise ratio, and extinction ratio.

15. The apparatus according to claim 10, wherein the modification is selected from the group consisting of changing the temperature of the thermo-optic phase shifter and applying a reverse bias to the PN depletion phase shifter.

16. The apparatus according to claim 10, wherein the modification is carried out by changing at least one characteristic of the optical equalization filter, the at least one characteristic being selected from the group consisting of a delay line, a phase shifter, and a coupler.

17. The apparatus according to claim 10, wherein the comparison or determination of the modification is carried out using non-invasive components.

18. The apparatus according to claim 10, wherein the comparison or determination of the modification is carried out using at least one method selected from the group consisting of least squares mean (LMS), Gauss-Newton, neural networks, deep neural networks, and reinforcement learning.

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