Optical System Containing a Reconfigurable Device and Method for Controlling the Optical System

Abstract

Describes an optical system (100) comprising: a reconfigurable optical device (103) with wavelength division multiplexing, comprising a plurality of actuators (A1 - A N ) and having an associated number of optical channels (M) and a number of degrees of freedom (N) lower than the number of optical channels; an optical stimulation source (106) connected to the reconfigurable optical device (103) to provide an optical stimulation signal (S in ), the optical stimulation signal (S in ) having a band including a plurality of wavelengths associated with the optical channels; a photoelectric conversion device (200) configured to receive from the reconfigurable optical device (103) a monitoring optical signal (S in ) corresponding to the optical stimulation signal (S out ), and to provide a set of intensity electrical signals (S EL1 - S ELK ), each intensity electrical signal representing the intensity of the monitoring optical signal (S out ) evaluated at the corresponding wavelength included in the band. The system further includes control means (110) configured to control the plurality of actuators (A1 - A EL1 - S ELK ) according to the set of electrical signals (S N ) and according to a control rule.

Description

Technical Field

[0001] The present disclosure relates to a method for controlling a reconfigurable optical device, which can be used in, for example but not limited to, the telecommunications sector in a reconfigurable optical network. Background Art

[0002] Examples of reconfigurable optical devices are described in US-A-6892021. This document describes an optical gain equalization filter with a waveguide grating router equipped with Mach-Zehnder tunable optical attenuators, each of which is associated with the corresponding wavelength of the optical channel used.

[0003] In addition, the document "Smart dynamic wavelength equalizer with on-chip spectrum analyzer" by Schiffer, P.M.J. et al., IEEE Photonics Technology Letters 12.8 (2000): 1019-1021, describes a dynamic wavelength equalizer using two waveguide grating routers and feedback control using a spectrum analyzer.

[0004] In addition, the document "Design and analysis of a control system for an optical delay-line circuit used as reconfigurable gain equalizer" by Schlipf, T.R. et al., Journal of lightwave technology 21.9 (2003): 1944, describes an open-loop control system for a reconfigurable gain equalizer formed by a two-port lattice optical delay-line circuit.

[0005] Disclosure

[0006] The applicant has noted that the closed-loop control techniques of the prior art are too complex both computationally and in terms of the control circuit structure.

[0007] The problem solved by the present disclosure is to provide an optical system that shows control techniques for the reconfigurable devices of the system itself, which are not particularly computationally burdensome and complex from a structural point of view.

[0008] According to a first aspect, an object of the present disclosure is an optical system and its preferred embodiments.

[0009] Another object of the present disclosure is also a method for controlling an optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present disclosure will be described in detail below by way of example and not limitation with reference to the accompanying drawings:

[0011] - Figure 1 A first embodiment of an optical system including a reconfigurable optical device and a control device is shown;

[0012] - Figure 2 Relates to Figure 1 a numerical simulation of the optical system, and shows the spectrum of the monitoring signal and its sampled version;

[0013] - Figure 3 Relates to Figure 1 a numerical simulation of the optical system, and shows the trends of transfer functions obtained using prior art methods and the method of the present technical solution;

[0014] - Figure 4 Shows Figure 1 a second embodiment of the optical system;

[0015] - Figure 5 Relates to Figure 4 a numerical simulation of the optical system;

[0016] - Figure 6 Relates to Figure 1 a third embodiment of the optical system;

[0017] - Figure 7 Shows an example of a reconfigurable device that can be used in the optical system. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] In this specification, similar or identical elements or components will be denoted by the same reference numerals in the drawings.

[0019] Figure 1 A first embodiment of the optical system 100 is schematically shown, including: a reconfigurable optical device 103, a control device 110, a light source 106, and a photoelectric conversion device 200.

[0020] In particular, the optical system 100 is capable of operating using electromagnetic radiation having a wavelength between 300 nm and 5000 nm, preferably between 1480 nm and 1620 nm.

[0021] For example, the optical system 100 is a system operating in the field of optical communication, particularly in a reconfigurable optical network.

[0022] The reconfigurable optical device 103 (hereinafter referred to as the reconfigurable device) is configured to operate on M optical channels (at least two optical channels) according to the WDM (Wavelength Division Multiplexing) technology, i.e., M optical signals with different wavelength carriers.

[0023] In particular, the reconfigurable device 103 includes at least one tunable optical element Gi (e.g., an optical delay line, a tunable optical coupler, or a tunable attenuator) configured to operate in WDM. As an example, a single tunable optical element Gi with M channels or multiple tunable optical elements Gi operating on M channels can be used.

[0024] The reconfigurable device 103 is also equipped with N actuators A1 - A N , which are associated with the tunable optical element Gi and modify the optical properties (e.g., refractive index and / or attenuation of the medium used to fabricate the reconfigurable device 103) according to the corresponding control signals S1 - S N provided by the control device 110, for example. The reconfigurable device 103 can assume a discrete number of states according to the values of its N state variables θ1, …, θ N , which are controlled by the N control signals S1 - S N .

[0025] Note that the number N of actuators A1 - A N defines the number of degrees of freedom of the reconfigurable device 103, i.e., the number of independent variables required to fully determine the state of the reconfigurable device 103 itself.

[0026] Advantageously, the number N of degrees of freedom of the reconfigurable device 103 is lower than the number M of channels on which the reconfigurable device itself operates.

[0027] The actuators A1 - A N can cause, for example, a change in the optical parameters (e.g., phase or amplitude) of the associated tunable optical element Gi. For example, the following devices can be used as actuators A1 - A N : thermo - optic actuators, electro - optic actuators, piezoelectric actuators, electro - absorption actuators, electro - mechanical actuators, electro - chemical actuators, or all - optical actuators (based or not based on nonlinear optical effects).

[0028] Regarding an exemplary part of a reconfigurable optical network, the reconfigurable device 103 can be, for example: a filter, an equalization filter, a dispersion compensation filter, an FIR filter, an IIR filter, a lattice filter, a binary tree filter.

[0029] For example, the reconfigurable device 103 can be fabricated on an optical platform (or optical chip) using integrated waveguide technology. Some examples of optical platforms that can be used include: semiconductor platforms (such as silicon, indium phosphide, gallium arsenide), amorphous glasses (silicon dioxide, silicon nitride, silicon oxyfluoride, silicon oxycarbide, silicon carbide), polymers, and crystals (lithium niobate), which may be integrated with two-dimensional materials (graphene, silicene), and their possible hybrid integrations.

[0030] According to Figure 1 the example in, the reconfigurable optical device 103 is a device having at least four optical ports. More specifically, the reconfigurable optical device 103 includes an optical input port 101 and an optical output port 102. The optical input port 101 is configured to receive M optical input signals multiplexed as an input signal I, and the optical output port 102 is configured to transmit an optical output signal O. Specifically, as a result of the operation of the reconfigurable optical device 103, the optical output signal O multiplexes M optical output signals.

[0031] In addition, the reconfigurable optical device 103 is equipped with an optical stimulation port 111 connected to a light source 106 and an optical monitoring port 112 connected to a photoelectric conversion device 200.

[0032] A plurality of the M optical input signals in the input signal I occupy an entire wavelength band Δλ, and Δλ identifies the operating wavelength range of the reconfigurable device 103.

[0033] Specifically, referring to the application in the linear mode, in each state identified by the state variables θ1,…,θ N the reconfigurable device 103 behaves as a time-invariant linear system in each state it can assume.

[0034] The transmission of the input signal I from the optical input port 101 to the optical output port 102 can be described by the frequency response H 12,i (f) or equivalently by the wavelength response H 12,i (λ), where the subscript "i" represents the general state presented by the device itself.

[0035] The light source 106 is configured to generate an optical stimulation signal S in provided to the stimulation port 111. The light source 106 is configured to emit optical radiation in a wavelength range greater than or equal to the operating wavelength range Δλ of the reconfigurable device 103. The optical monitoring port 112 is configured to provide a monitored optical signal S out as an output corresponding to the optical stimulation signal S in .

[0036] In the case of an integrated optical device, the light source 106 can be integrated on the same optical platform (i.e., optical chip) as the reconfigurable device 103, or can be external to the platform and connected to the reconfigurable device 103 via an optical fiber.

[0037] Preferably, the light source 106 includes a superluminescent diode (SLD), but other broadband sources can also be used, such as the "amplified spontaneous emission" (ASE) noise of an optical fiber amplifier (e.g., erbium-doped fiber amplifier, EDFA) or a semiconductor optical semiconductor amplifier (SOA), a source of the "supercontinuum laser" type, a laser array (e.g., distributed laser feedback, DFB), a comb spectral array (comb) generated by an optical fiber comb generator or integrated on an optical chip.

[0038] The photoelectric conversion device 200 is configured to receive the monitoring optical signal S out and provide (e.g., on the electrical terminal 108) a set of intensity electrical signals S EL1 -S ELN , each intensity electrical signal representing the intensity of the monitoring signal S evaluated at a corresponding wavelength out . Note that the set of intensity electrical signals S EL1 -S ELN has a cardinality equal to K. Preferably, the cardinality K is equal to N, i.e., the set of intensity electrical signals S EL1 -S ELN has a cardinality equal to the number of degrees of freedom of the reconfigurable device 103.

[0039] Again according to Figure 1 the specific example shown in, the photoelectric conversion device 200 includes a spectral range selector 105 (SP-SL), also referred to hereinafter as a spectral cutter, and a photoelectric converter 104 (DET-ARR). The spectral cutter 105 is equipped with a corresponding optical input port connected to the optical monitoring port 112 to receive the S out monitoring signal, and a plurality of optical output ports 109 (a number K of optical output ports 109, where preferably K = the number of degrees of freedom N).

[0040] The spectral cutter 105 is configured to transmit the selected S outk optical signal to its common k-th output port, which corresponds to a part of the monitoring signal S centered at the k-th wavelength λ k . out

[0041] The selection of the K wavelengths λ to be monitored can be implemented according to different technical and architectural schemes kThe spectral cutter 105. For example, the spectral cutter 105 is a passive device, i.e., it does not require external active control to select λ k wavelength.

[0042] Possible architectures that can be used for the spectral cutter 105 include Array Waveguide Gratings (AWG), echelle gratings, and other types of interference filters, such as Mach Zehnder interferometers, Bragg gratings, ring resonators, and any combination thereof.

[0043] The spectral cutter 105 is preferably fabricated in a waveguide and, for example, integrated on the same optical platform as the reconfigurable optical device 103. The spectral cutter 105 can also be implemented by alternative technologies, such as using discrete optical components in free space, fiber optic components, and combinations thereof.

[0044] According to this example, the optoelectronic converter 104 includes a plurality of optical detectors configured to convert K sampled optical signals S out (λ k ) into K intensity electrical signals S EL1 -S ELK .

[0045] The control device 110 is configured to control a plurality of actuators A1 - A EL1 -S ELK according to the set of intensity electrical signals S N and generate N control signals S1 - S N according to a pre - established control rule.

[0046] Regarding the control rule, for reconfigurable purposes, the control device 110 operates such that the i - th state presented by the reconfigurable device 103 under operating conditions is as close as possible to the i - th "desired" state. For example, the control device 110 uses a method that minimizes the mean square error between the actual transfer function of the reconfigurable device 103 and the desired transfer function of the reconfigurable device 103 to define the plurality of control signals S1 - S N .

[0047] For example, the control device 110 can be implemented by a microcontroller, CPU (Central Processing Unit), FPGA (Field Programmable Gate Array), or DSP (Digital Signal Processor) programmed according to the control method described below.

[0048] Note that the optical system 100 may also include an optical device 300 operatively associated with the reconfigurable optical device 103. For example, the optical device 300 may be an optical amplifier (particularly of the doped fiber type) that allows optical signals to be transmitted over long distances without optoelectronic conversion and regeneration. Optical amplifiers typically operate on a large number of optical signals, for example, on more than a hundred signals.

[0049] According to this example, the reconfigurable optical device 103 may be an equalizer filter configured to equalize the gain band of the erbium-doped fiber of the optical amplifier 300 that does not have a constant gain over the entire frequency range occupied by the signal.

[0050] The use of the reconfigurable equalizer filter 103 allows the optical amplifier 300 to adapt to the needs of the reconfigurable optical network. For example, for an erbium-doped fiber amplifier 300, the reconfigurable equalizer filter 103 may have a degree of freedom N = 20 and operate on a number M = 100 of optical channels.

[0051] Hereinafter, an example of a control method by which the optical system 100 can be used to reconfigure the reconfigurable device 103 will be described.

[0052] Referring to the wavelength domain, the optical output signal O(λ) provided to the optical output port 102 is given by the following expression:

[0053] O(λ) = H 12,i (λ)I(λ) (1)

[0054] where I(λ) is the input signal I, represented in the wavelength domain, and H 12,i (λ) is the predefined wavelength response of the reconfigurable device 103; the subscript "i" represents the general state presented by the device itself related to the transmission of the input signal I from the input optical port 101 to the output optical port 102.

[0055] For ease of understanding the following mathematical notations, in Figure 1 numbers 1, 2, 3, and 4 are added in parentheses at the relevant optical ports of the reconfigurable device 103.

[0056] When there is a request to reconfigure the optical system 100 and particularly the reconfigurable device 103, the control method begins.

[0057] As previously mentioned, the control method monitors and controls the response in the wavelength H 12,i (λ) such that the i-th "effective" state presented by the reconfigurable device 103 in the operating state, defined by the effective wavelength response is as close as possible to the i-th "desired" state defined by the response in H 12,i (λ).

[0058] The optical stimulation signal S generated by the light source 106 in is provided at the input of the stimulation port 111 of the reconfigurable device 103 in order to measure the actual state H i,e (λ) in real time and to evaluate the deviation (i.e., the distance) with respect to the desired state H i,d (λ).

[0059] Note that the desired state H i,d (λ) is pre-identified and stored in a look-up table in the memory of, for example, the control device 110, but it can also be dynamically updated and modified during the operation of the reconfigurable device 103.

[0060] The reconfigurable device 103 receives the stimulation signal S in , and returns the monitoring signal S out (λ) to the optical monitoring port 112; the monitored optical signal S out (λ) is described by the following relationship:[[]]

[0061] S out (λ) = H 34,i (λ) S in (λ) (2)

[0062] When the reconfigurable device 103 is itself in the i-th state associated with the transfer function H 12,i(λ) , the function H 34,i (λ) identifies the transfer function of the reconfigurable device 103 from the stimulation port 111 to the optical monitoring port 112, associated with the transmission from the input optical port 101 to the output optical port 102.

[0063] It should be noted that, for the purposes of the following discussion, the reconfigurable device 103 is considered to have the following characteristics defined according to the transfer function between the optical ports of the device itself:

[0064] - Reciprocity: H mn,i (λ) = H nm,i (λ);

[0065] - Absence of retroreflection on all optical ports (101, 102, 111, 112):

[0066] H 11,i (λ) = H 22,i (λ) = H 33,i (λ) = H 44,i (λ) = 0;

[0067] - No coupling between ports 1 - 4 (H 14,i (λ) = H 41,i (λ) = 0) and no coupling between ports 2 - 3 (H 23,i (λ) = H 32,i (λ) = 0);

[0068] - There is no leakage.

[0069] In the above characteristics, the term "non-existent" should be understood as the above retroreflection, coupling, or loss being zero or negligible for the following discussion.

[0070] As recognized by experts in the field, the above characteristics apply to the following relationship:

[0071] |H 12,i (λ)| 2 +|H 13,i (λ)| 2 = 1

[0072] |H 31i (λ)| 2 +|H 34,i (λ)| 2 = 1

[0073] It can be seen from this that:

[0074] |H 12,i (λ)| 2 = |H 34,i (λ)| 2 (3)

[0075] The relationship (3) shows how the monitored optical signal S 34,i (λ)| 2 associated with the transfer function |H out(λ) provides the same information as the direct monitoring of the optical output signal O(λ) associated with the transfer function |H 12,i (λ)| 2 .

[0076] Given the reciprocity of the reconfigurable device 103, the transfer functions |H 34,i (λ)| 2 and |H 43,i (λ)| 2 are theoretically the same and both can be monitored. However, in practice, it is convenient to use a stimulus signal that propagates in the direction opposite to the signal of interest (backward propagation). In fact, in the case of co-propagating signals, the reconfigurable device 103 may be the cause of crosstalk phenomena and transmit part of the input stimulus signal from port 2 to port 4. Therefore, a backward propagation architecture is preferred, even if it is not the only possible one.

[0077] Since the spectrum of the stimulus signal Sin(λ) is known, the transfer function H 34,i (λ) can be directly derived from the monitored signal S out (λ) (at the monitoring port 112) through the relationship (2).

[0078] Note also that the system 100 operates based on spectral knowledge of only the signal S out (λ), preferably, these K wavelengths are equally spaced, and preferably equal to the number of degrees of freedom N of the device 103 (K = N).

[0079] Note that the K wavelengths of the spectrum of the signal S out (λ) can also be chosen to be greater than the number of degrees of freedom N: K > N. In this case, the system 100 is particularly robust to noise, but more complex than when K equals N.

[0080] On the other hand, by choosing a number K less than the number of degrees of freedom (K < N), the performance of the system 100 is worse than when K ≥ N.

[0081] The number K can be between a minimum value Kmin and a maximum value Kmax. For example, the minimum value can be given by Kmin = N - 20%N or Kmin = N - 5%N. For example, regarding the maximum value, Kmax = N + 100%N, or Kmax = N + 50%N, or Kmax = N + 20%N.

[0082] Regarding the choice of the number K, note that in the system 100, it does not need to be equal to the number of optical channels M, and can also be less than or much less than the number of optical channels M (K < M). For example, when the reconfigurable device 103 is used in an amplification system with M = 130 channels, the number K of monitored wavelengths may be less than 15%, i.e., K < 15%M. Other possible example values are K < 50%M and K < 30%M.

[0083] Depending on the application, considering the trade - off between robustness and complexity, the number K is selected by appropriately combining the above - mentioned relationship regarding the number of degrees of freedom N and the above - mentioned relationship regarding the number of optical channels M.

[0084] In addition, it should be noted that for the control method, it is sufficient to know only the intensity |S out (λ)| 2 of the monitored optical signal without knowing its phase at each wavelength.

[0085] Therefore, the information used by the control device 110 is the intensity of the monitored optical signal:

[0086] |S out (λ k )| 2 (4)

[0087] where the subscript k = 1, 2,...K represents the discrete frequencies at which the spectral power density |S out (λ)| 2 is sampled.

[0088] The spectral cutter 105 receives the monitoring optical signal S out (λ), and transmits to each relevant output port 109 a sampled optical signal S k corresponding to the portion of the monitoring optical signal S out (λ) centered at the k-th wavelength λ out (λ k ). In particular, the spectral cutter 105 provides, on its output ports 109, a plurality of sampled optical signals S S1 -S SK .

[0089] Figure 2 Relates to numerical simulation and shows, for example, the signal S out (λ) for a possible configuration of the reconfigurable device 103, and also shows the portioned version 701 of the signal and its sub-bands S out (λ k ), each having its own band B λ,k .

[0090] Each optical output 109 of the spectral cutter 105 is optically connected to the photodetector of the photoelectric converter 104, which measures the input optical intensity and provides an electrical signal S Elj on the relevant terminal 108. The electrical signal S Elj has a current or voltage proportional to the intensity |S λ,k (λ out )| of the monitoring optical signal S k integrated on its own sub-band B out (λ k ). The photoelectric converter 104 generates N electrical signals S 2 -S EL1 in parallel on a plurality of terminals 108 ELN .

[0091] The plurality of electrical signals S EL1 -S ELN are sent to the control device 110, which monitors in real time the effective frequency response presented by the reconfigurable device 103 under the operating conditions at the k-th wavelength λ k Solve the equation:

[0092]

[0093] The control device 110 compares the current state with the desired state H 12,i (λ), and identifies the control signals S1 - S N, the control signal is applied to the actuators A1 - A of the reconfigurable device 103 through the control terminal 107 N , causing it to enter and remain in the desired state.

[0094] For example, according to the current state and the desired state H 12,i (λ), the control signals S1 - S are determined according to the method of minimizing the mean square error N . However, note that other methods can also be used. An example of the method of minimizing the mean square error will be described later with reference to the simulation of the control method.

[0095] Note that in the initialization stage of the optical system 100, the values of the control signals S1 - S to be applied N can be obtained from a look - up table obtained from the numerical simulation of the reconfigurable device 103. Once these values are applied to the reconfigurable device 103, the above - mentioned method is continued to be applied to make it enter the desired state indicated by the look - up table.

[0096] Simulation

[0097] Figure 3 A numerical simulation related to the effectiveness of the display optical system 100 is involved. A general reconfigurable device 103 with N = 15 degrees of freedom is considered. In the simulation, the reconfiguration of the device 103 has been considered such that its frequency response in the wavelength range between 1528 nm and 1568 nm can exhibit three predefined trends (301, 302, 303). Starting from an arbitrary initial configuration and wishing to make the reconfigurable device 103 operate in the i - th state (301, 302, or 303), the current transfer function of the general state i and the desired transfer function H 12,i (λ) are calculated for the mean square error between them:

[0098]

[0099] For the optimization of the transfer function of the reconfigurable device 103, an alternative cost function expressed by Equation (5) can be used, as well as other optimization algorithms, such as non - linear optimization, genetic algorithms, particle swarm optimization, machine learning, neural networks, and other methods known in the literature.

[0100] In this simulation, we first applied the method of a known technique. According to this method, the transfer functions |H 12,i (λ k )| 2 measured in three different states (301, 302, and 303) of a large number of wavelengths (hollow circles) equal to the number of optical channels (K = M = 130) used in the wavelength range of interest are considered. By applying this traditional method, Figure 3The curve shown by the dashed line in the figure.

[0101] Instead, the control method described with reference to the optical system 100 was applied, and the transfer function |H was measured at a finite number of wavelengths (K = N = 15) equal to the number of degrees of freedom (solid circles) of the reconfigurable device 103. 12,i (λ k )| 2 . By applying the method described for the reference system 100, we obtained Figure 3 the curve shown by the solid line in the figure.

[0102] Figure 3 illustrates how the difference between the dashed curve (conventional method) and the solid curve (system 100 method) is less than 0.2 dB over the entire operating wavelength band, thus confirming the efficiency of the described method.

[0103] According to another implementation of the optical system 100, as Figure 4 schematically shown, the optoelectronic conversion device 200 is implemented by a tunable detector configured to sequentially (i.e., in serial mode) provide the set of intensity electrical signals S to the control device 110 starting from the monitored optical signal S out over time. EL1 -S ELN .

[0104] According to one example, the tunable detector 200 includes a tunable filter 205 having a single optical output 209, followed by a photodetector 204 having a single electrical output 208. The tunable detector 200 is an active device that receives external active control (control signal S CR ) to select the wavelength λ k .

[0105] The optical output 209 of the tunable filter 205 is optically connected to the photodetector 204, which measures the input optical intensity and provides an electrical signal S having a current or voltage proportional to the intensity |S out (λ k )| 2 . ELk .

[0106] By tuning the tunable detector 200 sequentially over time, information about the current transfer function of the reconfigurable device 103 around the frequency of interest can be obtained.

[0107] The electrical signals S EL1 -S ELK sequentially output from the photodetector 204 are sent to the control device 110 and provide monitoring of the actual frequency response of the reconfigurable device 103 under operating conditions.

[0108] Possible architectures that can be used for the tunable filter 205 include: optical ring resonators, Mach-Zehnder interferometers, Bragg gratings, and possible combinations thereof.

[0109] The tunable detector 200 is preferably implemented in a waveguide and preferably integrated on the same optical platform as the reconfigurable optical device 103 already described, or it can be implemented with discrete optical components, fiber optic components, and combinations thereof in free space.

[0110] For example, in order to tune the tunable filter 205, an electrical control signal S CR (generated by the control device 110) can be used, which acts on an actuator (not shown) integrated in the tunable filter 205. These actuators modify the behavior of the tunable filter 205 by modifying the optical parameters of the material medium in which the optical radiation propagates, for example, using the thermo-optic effect, the electro-optic effect, or the elasto-optic effect; alternatively, microelectromechanical actuators (MEMS) can be used to modify the optical radiation path in the device.

[0111] Figure 5 Relates to numerical simulations of the optical system 100 including the tunable filter 205 similar to that Figure 4 described.

[0112] Figure 5 The curve 802 in shows the spectrum of the monitored optical signal S out (λ) of a specific configuration of the reconfigurable optical device 103. Figure 5 Also shown (curve 801) is the "sampling" pattern of the monitored optical signal and its sub-bands, the band B λ,k of which is obtained by the tunable filter 205 that can be tuned over the entire operating band.

[0113] Figure 6 Schematically shows a further optical system 400, which is similar to the optical system 100 already referred to Figure 1 described, but uses a reconfigurable optical device 103 having two ports (input optical port 101 and output optical port 102).

[0114] This further optical system 400 includes a first optical circulator 401 and a second optical circulator 402. The first optical circulator 401 is equipped with a first port 403 for the input signal I and a second port 404 connected to the optical input port 101 of the reconfigurable device 103, and the input signal I can be provided to the reconfigurable device 103. The optical input port 101 of the reconfigurable device 103 is also used, for example, to feed the monitored optical signal S to the second port 404 of the first optical circulator 401. outThe first optical circulator 401 is equipped with a third port 405, and the third port 405 is connected to the spectral cutter 105 to provide the latter with the monitoring optical signal S out .

[0115] The second optical circulator 402 includes a corresponding first port 406 connected to the output port 102 of the reconfigurable device 103. The optical output port 102 is used, for example, to provide the output signal O to the second optical circulator 402 and is also used, for example, to receive the stimulation signal S in .

[0116] The second optical circulator 402 is also equipped with a corresponding second port 407 configured to provide the output signal O and a corresponding third port 408 configured to receive the stimulation signal S in The stimulation signal S in is generated by the light source 106 and is transmitted to the corresponding first port 406, and then is transmitted to the reconfigurable device 103 (through the output port 102).

[0117] In the case where the reconfigurable two-port optical device 103 is reciprocal, the transfer function H 21 is equal to the transfer function H 12 .

[0118] It should be noted that the structure of the reconfigurable two-port optical device 103 having two optical circulators 401 and 402 is also applicable to Figure 4 the structural form of.

[0119] Figure 7 is a schematic diagram of the optical lattice filter 103, which represents an example of the reconfigurable device 103.

[0120] The optical lattice filter 103 includes a plurality of optical couplers K1-K14 and a plurality of actuators Bal1,2...7 and Unbal1,2,...6, which are suitable for introducing delays or imbalances in the optical channels, for a total of thirteen actuators.

[0121] Figure 7 The number of degrees of freedom N of the lattice filter 103 in is equal to 13, that is, equal to the number of actuators used, and the number of optical channels M that can be processed is up to 96. The reconfigurability of the lattice filter 103 can be managed by monitoring only K wavelengths equal to N = 13.

[0122] The optical couplers K1-K14 are examples of the optical elements Gi described in reference Figure 1 and the plurality of actuators Bal 1,2...7 and Unbal 1,2,...6 are examples of the actuators A1-A Figure 1 described in reference N .

[0123] Note that each actuator Bal 1, 2...7 and Unbal 1, 2,...6 acts on the optical behavior of the phase-opposed Kj optical couplers operating in wavelength division multiplexing mode (i.e., it allows multiple optical channels to propagate).

[0124] Typically, the reconfigurable device 103 can be a filter, which includes optical elements Gi: a binary tree or a lattice interferometer, an AWG (arrayed waveguide grating), or a similar structure used as a power splitter, such as a multimode interferometer (MMI), a directional coupler, or a y-branch or the like.

[0125] Note that the above solutions are mainly but not limited to applications in the telecommunications industry, especially in the field of reconfigurable optical networks. Examples of other possible applications of the described teachings are as follows:

[0126] 1) Optical devices for fiber and waveguide sensors, which require a stable optical circuit to process sensor readings,

[0127] 2) Optical devices for distance measurement, such as LIDAR, which require a very wide operating temperature range and can utilize the stability obtained by the present invention.

[0128] 3) Optical paths for 5G wireless networks, which can utilize a photonic circuit to improve the coverage performance of mobile networks, such as using a beamforming network with an integrated photonic circuit controlled by the method described in the present invention.

[0129] 4) Reconfigurable optical paths that can introduce adjustable delay times, such as for optical interferometry, optical tomography, and other applications that require synchronization of the relative delays between two or more optical signals;

[0130] The above optical systems are particularly advantageous in terms of simplicity and performance. In fact, these optical systems allow for the management of their reconfiguration by monitoring a number of signals lower than the number of optical channels on which the system itself operates (i.e., sampling optical signals S S1 -S SK ), thus maintaining the required performance.

[0131] In addition, the described optical systems have the advantages provided by closed-loop control without the high complexity of an actuator system controlled by a control device.

[0132] The lower number of signals to be monitored means a reduction in costs related to the necessary components and the physical size of the control system, and is beneficial for packaging operations.

Claims

1. An optical system (100; 400), comprising: A reconfigurable optical device (103) for wavelength division multiplexing, comprising a plurality of actuators A1 - A N and having an associated number M of optical channels and N degrees of freedom defined by the number of said actuators A1 - A N and less than said number M of optical channels; A stimulation light source (106) connected to the reconfigurable optical device (103) to provide a stimulation optical signal S having a wavelength band including a plurality of wavelengths associated with the optical channels in ; A photoelectric conversion device (200) configured to receive a monitoring optical signal S in generated in response to the stimulation optical signal S out from the reconfigurable optical device (103) and provide a set of intensity electrical signals S EL1 -S ELK where each intensity electrical signal represents the intensity of the monitoring optical signal S out evaluated at a corresponding wavelength included in the band; A control device (110) configured to control the plurality of actuators A1 - A based on the set of intensity electrical signals S EL1 - S ELK and according to a control rule, wherein: the set of intensity electrical signals S N - S EL1 - S ELK has a cardinality K, which is selected based on the number of degrees of freedom N and is included between a first minimum value K1min = N – 20%N and a first maximum value K1max = N + 100%N, and wherein the cardinality K is less than the number M of optical channels.

2. The system (100; 400) according to claim 1, wherein: The base number K is included between a second minimum value K2min = N - 5%N and a second maximum value K2max = N + 50%N; Or The base number K is included between the second minimum value K2min and a third maximum value K3max = N + 20%N.

3. The system (100, 400) according to claim 1, wherein, The base number K is equal to the number N of degrees of freedom.

4. The system (100, 400) according to claim 1, wherein, The control device (110) is configured to: By means of the set of intensity electrical signals S EL1 -S ELK and the stimulation optical signal S in to evaluate the effective transfer function of the reconfigurable optical device (103); Compare the effective transfer function of the reconfigurable optical device (103) with a desired transfer function; Generate the plurality of actuators A1 - A N The plurality of control signals S1 - S N , for enabling the reconfigurable optical device (103) to have the desired transfer function.

5. The system (100; 400) according to claim 4, wherein, The control device (110) is configured to define the plurality of control signals S1-S by using one of the following methods applied to the effective transfer function and the desired transfer function N : method of minimizing the mean square error, nonlinear optimization, genetic algorithm, particle swarm optimization, machine learning, neural network.

6. The system (100; 400) according to claim 1, wherein, The reconfigurable optical device (103) comprises: - An operating input (101; 403) for an input optical signal I, - An operating output (102; 407) for an output optical signal O corresponding to the input optical signal I; - for receiving the stimulation optical signal S in stimulation input (111; 408); - for supplying the monitoring optical signal S out to the monitoring output (112; 405) of the photoelectric conversion device (200).

7. The system (100; 400) according to claim 1, wherein, The photoelectric conversion device (200) comprises: Spectral cutter (105), which includes a plurality of output optical ports (109) and is configured to receive the monitoring optical signal S out and transmit a plurality of sampled optical signals S S1 -S SK to the plurality of output optical ports (109), each sampled optical signal corresponding to a portion of the monitoring optical signal S out ; An optical-electric converter (104) is connected to the plurality of output optical ports (109) for receiving the plurality of sampled optical signals S S1 -S SK , and includes a plurality of electrical terminals (108), the plurality of electrical terminals (108) being configured to transmit the set of intensity electrical signals S EL1 -S ELK to the control device (110).

8. The system (100; 400) according to claim 1, wherein, The photoelectric conversion device (200) comprises: A tunable optical filter (205) configured to receive the monitored optical signal S out and transmit a plurality of sampled optical signals S S1 -S SK to an output optical port (209) via serial transmission, each sampled optical signal S S1 -S SK corresponding to a portion of the monitored optical signal S out ; An optical detector (204), which is connected to the output optical port (209) for receiving the plurality of sampled optical signals S S1 -S SK and includes electrical terminals (208), the electrical terminals (208) being configured to transmit the set of intensity electrical signals S EL1 -S ELK to the control device (110) by serial transmission.

9. The system (400) according to claim 1, wherein, The reconfigurable optical device (103) is a two-port device, comprising an operating input (101) for an input optical signal I and an operating output (102) for an output optical signal O; The system further comprises: A first optical circulator (401) having: a first optical port (403) for receiving the input optical signal I from the outside; a second optical port (404) connected to the operation input (101) for transmitting the input optical signal I to the reconfigurable optical device (103) and receiving the monitoring optical signal S from the reconfigurable optical device (103) out ; a third optical port (405) for transmitting the monitoring optical signal S out to the photoelectric conversion device (200); A second optical circulator (402) having: a respective first optical port (406) connected to the operation output (102); a respective second optical port (407) for externally providing the output optical signal O; for receiving the stimulation optical signal S in and a respective third optical port (408) for transmitting the stimulation optical signal S to the reconfigurable optical device (103) through the operation output (102).

10. The system (100, 400) according to claim 1, wherein, The reconfigurable optical device (103) is a device belonging to the following group: equalization filter, dispersion compensation filter, FIR filter, IIR filter, lattice filter, binary tree filter.

11. The system (100, 400) according to claim 10, wherein, The reconfigurable optical device (103) comprises at least one of the following optical components Gi: binary tree interferometer, lattice interferometer, arrayed waveguide grating AWG, power splitter, multimode interferometer, directional coupler, y-branch.

12. The optical system (100, 400) according to claim 1, wherein, The plurality of actuators A1 - A N comprises at least one of the following actuators: a thermo - optic actuator, an electro - optic actuator, a piezoelectric actuator, an electro - absorption actuator, an electromechanical actuator, an electrochemical actuator, an all - optical actuator based on linear optical effects, and an all - optical actuator based on non - linear optical effects.

13. The optical system (100, 400) according to claim 1, wherein, At least the reconfigurable optical device (103) and the photoelectric conversion device (200) are made by integrated optical technology.

14. The optical system (100, 400) according to claim 1, wherein, The reconfigurable optical device includes a plurality of optical elements Gi that can be adjusted by the plurality of actuators A1 - A N and each optical element is configured to operate according to wavelength - division multiplexing technology.

15. The optical system (100, 400) according to claim 1, wherein, The pump light source (106) is selected from the group comprising: superluminescent diode SLD, ASE noise of an optical fiber amplifier, ASE noise of a semiconductor optical amplifier, supercontinuum laser type light source, laser array, distributed feedback laser DFB, optical fiber comb generator, integrated comb generator on an optical chip.

16. A method for reconfiguring an optical device, comprising: - Provide a reconfigurable optical device (103) for wavelength division multiplexing, which includes a plurality of actuators A1 - A N and has an associated number M of optical channels and N degrees of freedom defined by the number of said actuators A1 - A N and less than the number M of the optical channels; - Transmit the stimulation optical signal S in to the reconfigurable optical device (103), and the stimulation optical signal S in has a wavelength band including a plurality of wavelengths associated with the optical channels; - Receive a monitored optical signal S generated in response to the stimulation optical signal S from the reconfigurable optical device (103), and perform photoelectric conversion by providing a set of intensity electrical signals S in - S out , where each intensity electrical signal represents the intensity of the monitored optical signal S evaluated at a corresponding wavelength included in the wavelength band EL1 - S ELK ; out ​ - Based on the set of intensity electrical signals S EL1 - S ELK and control the plurality of actuators A1 - A according to a control rule N ; Wherein: The set of intensity electrical signals S EL1 -S ELK has a cardinality K, which is selected based on the number of degrees of freedom N and is included between a first minimum value K1min = N - 20%N and a first maximum value K1max = N + 100%N, Wherein the base number K is less than the number M of optical channels.

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