Method and system for controlling the output signals of a first dynamic system and a second dynamic system.

Abstract

A method and control system for controlling the output signals of a system comprising first and second dynamic systems, each receiving first and second input signals and outputting first and second output signals, respectively. The method involves using a first control system to generate a first control signal to compensate the first and second output signals based on the difference between the output signal and a reference signal. A second control system generates one or more second control signals based on the difference between the first output signal and the second output signal. The second control signals are used to further compensate the output signals, and / or the first control system further compensates the output signals based on the second control signals. The first and second control systems have different closed-loop bandwidths, the second being smaller than the first.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling the output signals of a system comprising at least a first dynamic system and a second dynamic system. Furthermore, the present invention relates to a system for controlling the output signals of a system comprising at least a first dynamic system and a second dynamic system. Moreover, the present invention relates to a method and system for performing controlled synchronization, more specifically, controlled synchronization of a first optical signal and a second optical signal. [Background technology]

[0002] Controlling the output signals of dynamic systems is used in a variety of applications. For example, synchronization is a technique in which two or more systems reach agreement on their behavior. Synchronization is an important concept with various applications such as (tele)communications, control, signal processing, quantum computing, etc. The concept of controlled synchronization has been widely studied to achieve identical behavior despite different initial conditions and inputs. In controlled synchronization, one system can be designed to influence the behavior of another system in order to achieve a desired output.

[0003] Controlled synchronization involves forcing two or more systems to exhibit substantially identical behavior despite different inputs and initial conditions. Systems can be linear or nonlinear, and synchronization can be complete or partial. Partial synchronization occurs when certain components or states of a system are synchronized while others remain asynchronous. Complete synchronization, on the other hand, occurs when all components or states of a system are synchronized.

[0004] Various methods have been proposed to achieve controlled synchronization, including adaptive control, feedback control, and sliding mode control. Adaptive control involves adjusting control parameters to adapt to changes in the system. Feedback control involves using feedback signals to modify the system's behavior. Sliding mode control involves designing a sliding surface to force the system to converge to a desired state.

[0005] Controlled synchronization via direct error measurement can be bandwidth-limited in applications where a specific sensor needs to be used to measure the synchronization error, for example, interference measurements with a single-photon detector in quantum interference experiments, or when the control implementation is bandwidth-limited. There is a strong desire to better handle such bandwidth limitations.

[0006] One of the problems is the synchronization error that arises when a system exhibits slight differences in its behavior. These differences can be due to uncertainty, disturbances, or noise. Another problem is robustness, which refers to the ability of synchronization to withstand uncertainty and disturbances. Robustness is important in real-world applications where the system may be exposed to external disturbances. These aspects can also be affected by the bandwidth problem mentioned above.

[0007] In various applications, there are technical problems related to the inability to measure synchronization errors quickly enough. This problem is exacerbated by bandwidth limitations, affecting both the measurement of synchronization errors and the processing of those measurements.

[0008] There are various sources of limited measurement bandwidth, including shot noise, which limits the bandwidth that allows for sufficiently accurate measurements.

[0009] Noise and disturbances, which may arise from external sources or the inherent probabilities of the system, can interfere with synchronization and make it difficult to achieve and maintain a stable synchronized state. Furthermore, the presence of delays in the coupling between systems can also lead to desynchronization, making it difficult to achieve and maintain synchronization.

[0010] Therefore, even when bandwidth limitations exist, there is a need to provide improved control over the output signals of dynamic systems, such as for controlled synchronization which involves forcing two systems to have the same output despite having different input signals and initial conditions (typically close but different). [Overview of the project] [Problems that the invention aims to solve]

[0011] An object of the present invention is to provide a method and system for avoiding at least one of the drawbacks mentioned above.

[0012] An object of the present invention is to improve the control of the output signals of a system including a first dynamic system and a second dynamic system, either additionally or alternatively.

[0013] Additionally, or alternatively, an object of the present invention is to enable controlled synchronization with a bandwidth exceeding the limits of direct synchronization error measurement.

[0014] An objective of the present invention is to improve the synchronization of optical paths, either additionally or alternatively. [Means for solving the problem]

[0015] In contrast, the present invention provides a method for controlling the output signals of a system, comprising at least a first dynamic system and a second dynamic system, wherein the first and second dynamic systems are configured to receive first and second input signals and output first and second output signals, respectively, the method provides a first control system configured to generate first control signals provided to the first and second dynamic systems, respectively, to compensate for the first output signal based on the difference between the first output signal and the first reference signal, and to compensate for the second output signal based on the difference between the second output signal and the second reference signal, and one or more based on the difference between the first output signal and the second output signal The present invention provides a second control system configured to generate a second control signal, wherein the first control system is configured to perform compensation of a first output signal and / or a second output signal based on a second control signal generated by the second control system, and / or the second control system is configured to provide one or more second control signals to at least one of the first dynamic system or the second dynamic system, respectively, to compensate for the first output signal or the second output signal, wherein a first closed-loop bandwidth is associated with the first control system and a second closed-loop bandwidth is associated with the second control system, and the first and second control systems are configured such that the second closed-loop bandwidth is smaller than the first closed-loop bandwidth.

[0016] The advantage is that a higher control bandwidth can be obtained, resulting in lower error between the two transmitted signals. This is very important for a variety of applications, including, but not limited to, signal synchronization.

[0017] This method can handle control of an output signal via bandwidth-limited direct error measurement, for example, due at least partly to the sensor used to measure the synchronization error and / or at least partly to bandwidth limitations in the control implementation.

[0018] When an incoming signal is received, both the first and second dynamic systems can be synchronized with the first and second reference signals using a high-speed controller and high-speed sensors. Any remaining errors between the first and second dynamic systems can then be compensated for. Low-frequency residual errors may occur while attempting to equalize the signal with the reference signal. These errors can be compensated for using additional sensors.

[0019] It should be understood that closed-loop bandwidth can be a characteristic determined by each control system, dynamic system, detector, cabling, etc. The closed-loop bandwidth of a control system can be determined by the characteristics of the system's feedback loop and the components within the loop. The feedback loop in a control system measures the system's output and compares it to the desired input. The difference between the output and input is called the error signal. The feedback loop then uses this error signal to adjust the system's output and minimize the error. The characteristics of components within the feedback loop, such as sensors, amplifiers, and actuators, can also affect the closed-loop bandwidth. For example, if a sensor has a slow response time, the sensor can limit the system's closed-loop bandwidth. Additionally or alternatively, the controller used in the system can also affect the closed-loop bandwidth. A controller with a fast response time can improve the closed-loop bandwidth, while a slow controller can limit it.

[0020] Therefore, the closed-loop bandwidths of the first and second control systems as a whole can be determined by the interaction between their feedback loops and the characteristics of the components and controllers within those loops.

[0021] Optionally, the method and system according to the invention are used for controlled synchronization with a bandwidth beyond the limits of direct synchronization error measurement. The outputs of the first dynamic system and the second dynamic system can be synchronized despite the presence of different uncontrolled inputs to their respective first and second dynamic systems.

[0022] Controlled synchronization refers to the process of ensuring that two systems have the same output despite having different input signals or initial conditions. However, direct error measurement in controlled synchronization can have a limited bandwidth in applications where a particular sensor is used to measure the synchronization error. Also, bandwidth limitations can occur during control implementation. To overcome both problems, the invention proposes first using a high-bandwidth controller to synchronize both signals to a reference signal with low high-frequency content. This approach avoids high-frequency signals in the residual synchronization error, making bandwidth limitations a non-issue, and ensures that controlled synchronization can be achieved by a controller that uses direct error measurement, where either the controller or the error measurement is bandwidth-limited. Synchronization is achieved by applying feedback to the reference signal with a low bandwidth. By selecting a reference signal close to the input signal, the control effort remains limited. This innovation is implemented for two optical inputs to lock the phases of the output light to each other. The proposed approach involves using two controllers with different bandwidths, which goes beyond the current state of the art and provides a synchronization solution for optical synchronization problems.

[0023] When attempting to modify the wavelength of light, the achievable range can be relatively narrow. To achieve the desired wavelength, the reference signal can be adjusted to a value within the range that the actuator can handle. The term "close" indicates a value that fits well within the range of the actuator.

[0024] The second control system can be used for direct and / or indirect control.

[0025] The second control system may perform direct control by (directly) providing one or more second control signals to at least one of the first dynamic system or the second dynamic system to compensate for the first output signal (in the case of the first dynamic system) and / or the second output signal (in the case of the second dynamic system). For example, the second control system may provide the second control signal to one of the following: the first dynamic system and the second dynamic system. In some other embodiments, the second control system may provide a primary second control signal to the first dynamic system and a secondary second control signal to the second dynamic system.

[0026] Additionally or alternatively, the second control system may be configured to perform indirect control, and the first control system may be configured to perform compensation of the first output signal and / or the second output signal further based on the second control signal generated and provided by the second control system.

[0027] The method according to the present disclosure can be employed in a wide range of potential applications. One such application is in synchronization processes that require high bandwidth criteria. It can also be used in optical synchronization processes where accurate synchronization is important. Additionally, the present technology can be utilized in phase-locked photon paths of a quantum internet where maintaining phase coherence is essential for the proper functioning of quantum communication protocols.

[0028] The method can be employed in various applications in the field of quantum technology, for example, for optical phase synchronization in a quantum communication / internet system.

[0029] Optionally, the first control bandwidth is selected such that the high-frequency content in the difference between the first output signal and the second output signal is smaller than the limitation imposed by the controller of the second control system due to that second control bandwidth.

[0030] Acceptably low high-frequency content can be content that is low enough for the second controller to compensate for it.

[0031] This invention makes it possible to achieve controlled synchronization with a bandwidth that exceeds the limits of direct synchronization error measurement. In optical phase synchronization problems, the measurement bandwidth can be limited by the shot noise of direct synchronization error measurement. Classical solutions typically require a high bandwidth for synchronization error measurement. However, the approach according to this disclosure does not require high-bandwidth synchronization error measurement. Instead, it involves a combination of high-bandwidth synchronization with a reference signal and low-bandwidth synchronization efforts from synchronization error measurement. This helps to reduce the complexity of the control signal.

[0032] In conventional technologies, control signals may not be limited by bandwidth. Furthermore, some conventional technologies have not encountered bandwidth limitations that cause control problems due to error signals, and have not involved external inputs.

[0033] Optionally, the first and second reference signals are selected such that the difference between the first and second reference signals and the first and second input signals is less than a threshold.

[0034] Optionally, the first control system is configured to compensate for both the first and second output signals based on a second control signal generated by the second control system, or the first control system is configured to compensate for only one of the first or second output signals based on a second control signal generated by the second control system.

[0035] This method is optionally employed for synchronizing optical paths.

[0036] Optionally, the first and second dynamic systems are optical systems configured to receive first and second optical input signals and output first and second optical output signals, respectively, wherein the first and second optical input signals, the first and second optical output signals, and the first and second reference signals are optical signals induced through an optical path, and the nodes of the first and second control systems, where the signals are added or subtracted, are implemented by measuring the interference amplitude using one or more detectors.

[0037] Optionally, a first control system and a second control system are employed to phase-lock the first and second optical input signals.

[0038] Optionally, the first and second dynamic optical systems are optical phase shifters or optical frequency shifters.

[0039] In some embodiments, the dynamic optical system is configured to function as any other system capable of processing a phase shifter or a time-varying input signal and generating an associated time-varying output signal.

[0040] Optionally, a first dynamic optical system is configured to receive at least two first optical input signals having different wavelengths, and a second dynamic optical system is configured to receive at least two second optical input signals having different wavelengths, the phase difference between at least two first optical input signals and the phase difference between at least two second optical input signals are determined, and the first and / or second control signals are employed in each first and / or second dynamic optical system to apply optical phase shifts to at least two first and / or second optical input signals, respectively, in order to generate at least two first and / or second optical output signals for each first and / or second dynamic optical system.

[0041] Optionally, a first primary control signal is generated by the first control system based on an error signal obtained by interfering the first output signal with the first reference signal at the first detector and then subtracting the second control signal received from the second control system; and a second primary control signal is generated by the first control system based on an error signal obtained by interfering the second output signal with the second reference signal at the second detector and then subtracting the second control signal received from the second control system.

[0042] The first control signal may be generated by a first control system, for example, a first controller of the first control system may generate a primary first control signal, and a second controller of the first control system may generate a secondary first control signal. One or more second control signals may be generated by a second control system.

[0043] Optionally, one or more second control signals are generated by a second control system based on interference between a first output signal and a second output signal, and further based on the phase difference between at least two first optical input signals and the phase difference between at least two second optical input signals.

[0044] The first and second reference signals are different, and are optional.

[0045] The first and second reference signals are the same, at the user's discretion.

[0046] Optionally, the optical phase difference is measured using heterodyne.

[0047] Optionally, the optical phase difference is measured using homodyne.

[0048] The homodyne method is a simpler approach, while heterodyne offers electronic advantages because the signal being measured is around a specific frequency (such as 200 MHz), resulting in less noise than measurements performed around DC. Compared to the simpler homodyne solution, heterodyne may be preferred, for example, to reduce low-frequency noise sources originating from the detector.

[0049] In some embodiments, this method is employed in quantum applications. Quantum information that needs to be compared or combined at two distinct points often depends on the phase of light. Therefore, maintaining a constant optical phase is crucial when combining the information. This presents a synchronization challenge for quantum applications. Synchronization errors can be detected using sensors. The method according to the present invention can be used to maintain synchronization of the optical phase of the optical path.

[0050] Quantum interference is a crucial concept in quantum communication. In quantum communication, quantum interference is used to encode and transmit information through quantum states. For example, in quantum key distribution, two parties can use the interference of quantum states to generate a shared secret key that can be used for secure communication. The parties can create two entangled quantum states and then measure them in a specific way, which yields an interference pattern. The pattern will differ depending on whether an eavesdropper has intercepted the transmission, allowing the parties to detect any attempt at interception. Similarly, in quantum teleportation, quantum interference is used to transmit the quantum state of one system to another system without physically moving the system itself. The quantum state is measured, and the result is used to construct a new quantum state to be transmitted to the receiving system, which is then interfered with by another quantum state to recreate the original state. In both cases, the use of quantum interference enables secure and efficient communication using quantum systems.

[0051] The optical phases and polarizations of light particles from light sources A and B may need to be compared to determine the degree of their similarity. This comparison can then be used to develop communication techniques. In the first step, quantum interference can be generated, resulting in entanglement between the qubits on both sides. This entanglement can then be used for various purposes, such as cryptographic key calculation, communication, and / or exchange.

[0052] In one aspect, the present invention relates to a control system for controlling the output signals of a system, comprising at least a first dynamic system and a second dynamic system, the first and second dynamic systems being configured to receive first and second input signals and output first and second output signals, respectively, wherein the system comprises a first control system configured to generate control signals provided to the first and second dynamic systems, respectively, to compensate for the first output signal based on the difference between the first output signal and the first reference signal, and to compensate for the second output signal based on the difference between the second output signal and the second reference signal, and one The first control system is configured to perform compensation for the first output signal and / or the second output signal based on the second control signal generated by the second control system, and / or the second control system is configured to provide one or more second control signals to at least one of the first or second dynamic systems in order to compensate for the first output signal or the second output signal, with a first closed-loop bandwidth associated with the first control system and a second closed-loop bandwidth associated with the second control system, and the first and second control systems are configured such that the second closed-loop bandwidth is smaller than the first closed-loop bandwidth.

[0053] This invention enables the achievement of higher synchronization bandwidth and results in lower errors between two outgoing signals. This is particularly useful in applications such as optical synchronization and phase-locked photon paths for quantum internets, for example, as it allows the use of in-fringe control even in the presence of large high-frequency differences between incoming signals.

[0054] In one embodiment, the present invention provides a method for controlling the output signals of a system comprising first and second dynamic systems, each receiving first and second input signals and outputting first and second output signals, respectively. The method involves using a first control system to generate a first control signal to compensate the first and second output signals based on the difference between the output signal and a reference signal. A second control system generates one or more second control signals based on the difference between the first output signal and the second output signal. The first control system further compensates the output signals based on the second control signals, and the first and second control systems have different closed-loop bandwidths, with the second being smaller than the first.

[0055] It will be understood that any of the embodiments, features, and options described in terms of methodology apply equally to the system and the described device. It will also be clear that one or more of the above embodiments, features, and options can be combined.

[0056] The present invention will be further illustrated based on exemplary embodiments shown in the drawings. These exemplary embodiments are given as non-limiting examples. It should be noted that the figures are merely schematic representations of embodiments of the present invention given as non-limiting examples.

[0057] In the drawing: [Brief explanation of the drawing]

[0058] [Figure 1] A schematic diagram of the system's embodiment is shown. [Figure 2] A schematic diagram of the system's embodiment is shown. [Figure 3]A schematic diagram of the system's embodiment is shown. [Modes for carrying out the invention]

[0059] Figure 1 shows a schematic diagram of an embodiment of System 1. The control system is used to control the output signals of a system including at least a first dynamic system P1 and a second dynamic system P2, the first and second dynamic systems being configured to receive first and second input signals X1 and X2 and to output first and second output signals Y1 and Y2, respectively. A first control system 3(C1, C2) is provided, configured to generate first control signals, i.e., a primary first control signal U1 and a secondary first control signal U2, provided to the first dynamic system P1 and the second dynamic system P2, respectively, to compensate the first output signal Y1 based on the difference between the first output signal Y1 and a first reference signal R1, and to compensate the second output signal Y2 based on the difference between the second output signal Y2 and a second reference signal R2. A second control system 5(C) is provided, configured to generate one or more second control signals US1 and US2 based on the difference between the first output signal Y1 and the second output signal Y2. The first control system 3 is configured to perform compensation of the first output signal Y1 and / or the second output signal Y2 based on one or more second control signals US1, US2 generated by the second control system 5. The first closed-loop bandwidth is associated with the first control system 3, and the second closed-loop bandwidth is associated with the second control system 5, and the first and second control systems 3 and 5 are configured such that the second closed-loop bandwidth is smaller than the first closed-loop bandwidth.

[0060] The present invention can be applied to various types of dynamic systems. The system does not necessarily have to be an optical system. In some embodiments, the system has inputs and outputs related to optical problems, such as, for example, the analysis of the optical phase of incoming light. In these cases, dynamic systems P1 and P2 can be inserted into the optical path to achieve desired synchronization between y1 and y2. It should be understood that dynamic systems P1 and P2 can be introduced as part of an arrangement to achieve synchronization.

[0061] A control system can be employed for signal synchronization. In this case, the objective is to synchronize Y1 to Y2, even if systems P1 and P2 have different uncontrolled inputs X1 and X2. This method can be applied to optical phase synchronization involving two wavelengths.

[0062] The first control signals (for example, a primary first control signal U1 generated by the first controller C1 of the first control system 3, and a secondary first control signal U2 generated by the second controller C2 of the first control system 3) can be electrical / electronic / digital signals.

[0063] The goal may be to synchronize two signals, Y1 and Y2. This is achieved by first calculating the difference between them, generating a synchronization error E. This can be done by using this error signal in the controller. If the bandwidth of this signal is insufficient, additional measurements may be required to reduce the high-frequency error between Y1 and Y2. This is accomplished by setting signal Y1 to match a reference signal R1 and signal Y2 to match a reference signal R2 before closing the control loop. It can be ensured that Y2 is as similar to R2 as possible.

[0064] In some embodiments, the control system is used for synchronizing the optical path. However, the control system may also be used for other applications, such as non-optical or partially optical applications.

[0065] The control system may be configured to synchronize two systems individually to a reference signal using a high-speed control loop, and then apply slower feedback based on error measurements of the associated synchronization error measurements on the setpoint of the high-speed loop. The present invention is suitable for optical phase locking with multiple wavelengths.

[0066] It is possible to select the same reference signal. However, it is also possible to employ two different reference signals. For example, in the case of optical signals, the reference signals may have wavelengths in the intermediate range. First, R1 can be compared with Y1 (and R2 with Y2, respectively), and then the error can be minimized or reduced by closing the control loop, resulting in a fast loop. However, this process may still leave a residual error between Y1 and Y2, which can be due to various factors such as external disturbances or an imperfect controller. To address this, the signal can be measured continuously, and the setpoints of one or both controllers can be adjusted accordingly. In this scenario, the US1 and US2 paths are employed for this purpose.

[0067] Controllers C1 and C2 may be faster controllers compared to controller C. In some cases, the measured values ​​may be bandwidth-limited. However, additionally or alternatively, it is also possible that the controllers are bandwidth-limited.

[0068] This method enables controlled synchronization over bandwidths exceeding the direct synchronization error measurement limits through the use of an additional reference signal. Problems associated with conventional synchronization methods include limitations imposed by control hardware or measurement bandwidth limitations, such as in optical synchronization where shot noise can occur.

[0069] In some embodiments, a synchronous implementation is performed in which the linearized behavior follows the scheme of Figure 1, so that two control signals U1 and U2 are supplied to plants P1 and P2, which also have input signals X1 and X2, respectively. Based on the dynamics of these plants, output signals Y1 and Y2 are generated, which should be identical in time. Here, signals U1 and U2 are devised by controllers C1 and C2 from error signals E1 and E2 generated by subtracting control signals US1 and US2 and (optionally identical) reference signals R1 and R2 from the output signals Y1 and Y2, while signals US1 and US2 are generated by a low-bandwidth controller C using the difference E between Y1 and Y2.

[0070] In some embodiments, controller C is designed such that either US1 or US2 is zero or not implemented. In such exemplary embodiments, one of the lines carrying US1 and US2 may be omitted, thus simplifying the design of the control system.

[0071] In some embodiments, X1, X2, Y1, Y2, R1, R2 are the phases of optical signals, the added optical portion in the control loop is implemented by measuring interference amplitude, and systems P1, P2 are optical phase or frequency shifters.

[0072] In some embodiments, the process involves subtracting two optical signals R2 and Y2, and then performing electronic subtraction in US2. The optical phase difference can be measured through interference.

[0073] Several techniques are available to adjust the phase, including the use of acousto-optic modulators, fiber stretchers, or electro-optic modulators. For example, the acousto-optic modulator approach involves generating vibrations within a crystal, which reflect light and produce sound waves that result in a phase shift.

[0074] In some embodiments, the phase difference is measured using heterodyne. Alternatively, in some embodiments, the phase difference is measured using homodyne.

[0075] In the embodiment shown in Figure 1, the first control system is configured to perform compensation of the first and / or second output signals based on a second control signal generated by the second control system. However, additionally or alternatively, the second control system may also be configured to provide one or more second control signals to at least one of the first or second dynamic systems in order to compensate for the first or second output signal. In other words, the second control system may also be configured to act directly on one or both of the dynamic systems. Thus, the second control system can be employed for direct and / or indirect control.

[0076] Figure 2 shows a schematic diagram of an embodiment of System 1. The control system shown in Figure 2 can be used to achieve synchronization between Y1' and Y2'. For example, this may involve optical synchronization. However, the present invention is not limited to optical / optical applications.

[0077] The present invention enables controlled synchronization over bandwidths exceeding the limits of direct synchronization error measurement by using one or more additional reference signals. Conventional methods for synchronizing two systems are often limited by the bandwidth of the control hardware or measurement process, which can lead to errors. For example, in optical synchronization processes, shot noise on a single-photon detector can limit the achievable bandwidth. Advantageously, according to this disclosure, a combination of fast and slow feedback loops can be employed.

[0078] Two different wavelengths of light, X1 and X1', and X2 and X2', are used on opposite sides of the system, respectively. The actuators mentioned, such as acousto-optic modulators, can apply the same phase shift to both wavelengths. In some embodiments, the intensity / power on Y1' may be limited, while light with higher intensity / power may be permitted for Y1. Therefore, X1' and Y1' may have lower power (light intensity), but below that, the control system may be applied in parallel for synchronization with the higher power (higher intensity).

[0079] In some embodiments, each optical input comprises two wavelengths, namely X1 and X1', or X2 and X2', where the phase difference between X1 and X1' (or between X2 and X2', respectively) is known or can be approximated, and U1 (or U2, respectively) consists of an optical phase shift applied to PS1 in both X1 and X1' (or applied to PS2 in X2 and X2', respectively) to generate optical signals Y1 and Y1' (or Y2 and Y2'). Here, signals U1 and U2 are brought by controllers C1 and C2 from error signals E1 and E2 generated by interfering Y1 with R1 in detector D1 (and Y2 with R2 in D2, respectively) and subtracting the generated control signals US1 and US2, with reference optical inputs R1 and R2 being used. Signals US1 and US2 are generated by the low-bandwidth controller C using the interference output of detector D, the interference of Y1 and Y2, and a proxy for the phase calculation (X1'-X1)-(X2'-X2) generated by external logic S.

[0080] Advantageously, the present invention may employ a combination of fast and slow feedback loops in a specific order, as well as the introduction of a reference signal. In some embodiments, the phase difference at the input can be determined. While measurement of Y1'-Y2' may not be possible, X1-X1' and X2-X2' are known or estimated.

[0081] In some embodiments, the external logic is configured to perform the measurement directly.

[0082] In some advantageous embodiments, external logic is configured to estimate the relative phase difference between a first and second optical beam induced through a common optical path, the first optical beam having a first wavelength and the second optical beam having a second wavelength different from the first wavelength, and the system comprises a measuring unit configured to perform one or more measurements to measure a value indicating variation in physical path length, and a calculating unit configured to calculate the relative phase difference between the first and second optical beams at a given location in the optical path based on the value indicating variation in physical path length.

[0083] Optionally, a value indicating physical path length variation is determined by measuring the optical path delay of the optical path.

[0084] Optionally, a value indicating physical path length variation is determined by measuring the round-trip time of the optical path.

[0085] Optionally, a third light beam having a third wavelength different from the first and second wavelengths is guided through an optical path, and a value indicating the physical path length is determined based on the relative phase difference between the third light beam and any further light beams guided through the optical path.

[0086] Optionally, a further light beam is a fourth light beam additionally guided through an optical path, the fourth light beam having a different wavelength from the first, second, and third light beams.

[0087] Optionally, the additional light beam corresponds to either the first or second light beam.

[0088] Optionally, the relative phase difference variation Δφ(t) is calculated based on the following relationship.

number

[0089] Optionally, the optical path delay variation ΔT(t) measures the physical path length variation ΔL(t) based on the following relational expression at wavelength λ forward as measured.

Number

[0090] Optionally, the round-trip time variation ΔT rt (t) measures the physical path length variation ΔL(t) based on the following relational expression at wavelengths λ forward , λ backward as measured.

Number

[0091] Optionally, the physical path length variation is determined based on at least one of the following relational expressions.

Number

Number

[0092] Optionally, the optical path is parallel to further adjacent optical paths, the first and second light beams are guided through the optical path, the third and fourth light beams are guided through further optical paths, and the round-trip time, optical path delay, or phase difference between the light at the third and fourth wavelengths is measured with light passing through the further optical path.

[0093] Optionally, the optical path and any adjacent optical paths are encapsulated, at least partially, within the same fiber duct.

[0094] Figure 3 shows a schematic diagram of an embodiment of System 1. The control system shown in Figure 3 may be configured to perform optical synchronization between Y1' and Y2' using optical signals marked with O (gray line) and electronic or digital signals marked with D (black line). Other electrical signals may be used instead of digital signals.

[0095] In some embodiments, measuring the error between Y1' and Y2' may not be feasible (e.g., single photon). Furthermore, the error between Y1 and Y2 may be bandwidth-limited.

[0096] In some embodiments, the optical phase difference is measured heterodyne, and the mixed frequency difference is used to distinguish Y1-US1-R1 from Y1'-US1-R1 from interference at detector D1, Y2-US2-R2 from Y2'-US2-R2 from interference at detector D2, and each of the signals Y1'-Y1, Y2'-Y2, and Y2'-Y1' from interference between y2 and y1 at detector D.

[0097] In some embodiments, the optical phase difference is measured homodyne, and the power difference allows for the distinction of the signals.

[0098] In some embodiments, controller C is designed such that either US1 or US2 is zero or not implemented. If US1 or US2 is chosen to be zero, then a simpler design may be obtained. This can be done by omitting the path C to the US2 control loop. Y1 can be equal to Y2, and it is sufficient to adjust only one of the two signals. Thus, a simpler implementation is to exclude either US1 or US2, while the remaining elements such as R1 and R2 remain unchanged.

[0099] In some cases, actuators have limitations. Therefore, it can be advantageous when both actuators need to perform an equal share of the task (relatively less burden compared to when only one actuator has to perform the adjustment).

[0100] It will be understood that the systems and methods described herein can be used in applications employing quantum interference between paths of light using a single photon detector.

[0101] Some embodiments may be implemented, for example, using a machine or a tangible computer-readable medium or article, which, when executed by a machine, may store instructions or sets of instructions that cause the machine to perform the methods and / or operations according to the embodiment.

[0102] Various embodiments may be implemented using hardware elements, software elements, or a combination of both. Examples of hardware elements may include processors, microprocessors, circuits, application-specific integrated circuits (ASICs), programmable logic devices (PLDs), digital signal processors (DSPs), field-programmable gate arrays (FPGAs), logic gates, registers, semiconductor devices, microchips, and chipsets. Examples of software may include software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, mobile apps, middleware, firmware, software modules, routines, subroutines, functions, computer implementation methods, procedures, software interfaces, application programming interfaces (APIs), methods, instruction sets, computing code, and computer code.

[0103] In this specification, the present invention is described with reference to specific examples of embodiments of the invention. However, it will be apparent that various modifications, alterations, substitutions, and changes can be made therein without departing from the essence of the invention. For the purpose of clarification and concise explanation, features are described herein as part of the same or distinct embodiments, but alternative embodiments having all or some combinations of the features described in these distinct embodiments are also assumed and understood to fall within the framework of the invention, as outlined by the claims. Accordingly, this specification, figures, and examples should be considered illustrative, not restrictive. The invention is intended to encompass all substitutions, modifications, and alterations that fall within the scope of the appended claims. Furthermore, many of the elements described are functional entities that can be implemented as separate or distributed components, or in combination with other components, in any suitable combination and location.

[0104] In the claims, any reference numerals placed in parentheses shall not be construed as limiting the claims. The word “comprising” shall not preclude the existence of other features or steps other than those enumerated in the claims. Furthermore, the words “a” and “an” shall not be construed as limiting to “only one,” but rather as meaning “at least one,” and not precluding plural. The term “and / or” includes any and all combinations of one or more of the associated enumerated items. The mere fact that certain measures are enumerated in different claims shall not imply that combinations of these measures cannot be used to one's advantage.

Claims

1. A method for controlling the output signals of a system, comprising at least a first dynamic system and a second dynamic system, wherein the first and second dynamic systems are configured to receive first and second input signals and output first and second output signals, respectively, wherein the method is To provide a first control system configured to generate first control signals to be provided to the first dynamic system and the second dynamic system, respectively, to compensate the first output signal based on the difference between the first output signal and the first reference signal, and to compensate the second output signal based on the difference between the second output signal and the second reference signal. The present invention includes providing a second control system configured to generate one or more second control signals based on the difference between the first output signal and the second output signal, The first control system is configured to perform compensation for the first output signal and / or the second output signal based on the second control signal generated by the second control system, and / or the second control system is configured to provide one or more second control signals to at least one of the first dynamic system or the second dynamic system in order to compensate for the first output signal or the second output signal, A method in which a first closed-loop bandwidth is associated with the first control system, a second closed-loop bandwidth is associated with the second control system, and the first and second control systems are configured such that the second closed-loop bandwidth is smaller than the first closed-loop bandwidth.

2. The method according to claim 1, wherein the first operating bandwidth is selected such that the high-frequency content in the difference between the first output signal and the second output signal is less than the limit imposed by the controller of the second control system due to the second operating bandwidth.

3. The method according to claim 1 or 2, wherein the first and second reference signals are selected such that the difference between the first and second reference signals and the first and second input signals is less than a threshold.

4. The method according to any one of claims 1 to 3, wherein the first control system is configured to perform compensation for both the first output signal and the second output signal based on the second control signal generated by the second control system, or the first control system is configured to perform compensation for only one of the first output signal or the second output signal based on the second control signal generated by the second control system.

5. The method according to any one of claims 1 to 4, wherein the first and second dynamic systems are optical systems configured to receive first and second optical input signals and output first and second optical output signals, the first and second optical input signals, the first and second optical output signals, and the first and second reference signals are optical signals induced through an optical optical path, and the nodes of the first and second control systems, where the signals are added or subtracted, are implemented by measuring interference amplitude using one or more detectors.

6. The method according to claim 5, wherein the first control system and the second control system are employed to phase-lock the first and second optical input signals.

7. The method according to claim 5 or 6, wherein the first and second dynamic optical systems are optical phase shifters or optical frequency shifters.

8. The method according to any one of claims 5 to 7, wherein the first dynamic optical system is configured to receive at least two first optical input signals having different wavelengths, the second dynamic optical system is configured to receive at least two second optical input signals having different wavelengths, the phase difference between the at least two first optical input signals and the phase difference between the at least two second optical input signals are determined, and the first and / or second control signals are employed in each of the first and / or second dynamic optical systems to apply an optical phase shift to the at least two first and / or second optical input signals, respectively, in order to generate the at least two first and / or second optical output signals of each of the first and / or second dynamic optical systems.

9. The method according to any one of claims 5 to 8, wherein a primary first control signal is generated by the first control system based on an error signal obtained by interfering the first output signal with the first reference signal at a first detector and subtracting the second control signal received from the second control system, and a secondary first control signal is generated by the first control system based on an error signal obtained by interfering the second output signal with the second reference signal at a second detector and subtracting the second control signal received from the second control system.

10. The method according to any one of claims 5 to 9, wherein the one or more second control signals are generated by the second control system based on interference between the first output signal and the second output signal, and further based on the phase difference between the at least two first optical input signals and the phase difference between the at least two second optical input signals.

11. The method according to any one of claims 1 to 10, wherein the first and second reference signals are different.

12. The method according to any one of claims 1 to 10, wherein the first and second reference signals are the same.

13. The method according to any one of claims 5 to 12, wherein the optical phase difference is measured by heterodyne.

14. The method according to any one of claims 5 to 12, wherein the optical phase difference is measured using homodyne.

15. A control system for controlling the output signals of a system, comprising at least a first dynamic system and a second dynamic system, wherein the first and second dynamic systems are configured to receive first and second input signals and output first and second output signals, respectively, wherein the system A first control system configured to generate control signals provided to the first dynamic system and the second dynamic system, respectively, to compensate the first output signal based on the difference between the first output signal and the first reference signal, and to compensate the second output signal based on the difference between the second output signal and the second reference signal. The system includes a second control system configured to generate one or more second control signals based on the difference between the first output signal and the second output signal, The first control system is configured to perform compensation for the first output signal and / or the second output signal based on the second control signal generated by the second control system, and / or the second control system is configured to provide one or more second control signals to at least one of the first dynamic system or the second dynamic system in order to compensate for the first output signal or the second output signal, A control system in which a first closed-loop bandwidth is associated with the first control system, a second closed-loop bandwidth is associated with the second control system, and the first and second control systems are configured such that the second closed-loop bandwidth is smaller than the first closed-loop bandwidth.

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