Patent Description:
An example of a reconfigurable optical device is described in <CIT>. This document describes an optical gain equaliser filter with a Waveguide Grating Router equipped with Mach-Zehnder adjustable optical attenuators, each associated with a relative wavelength of the optical channels used.

Moreover, document <NPL>, describes a dynamic wavelength equalizer using two WGRs and using feedback control via a spectrum analyzer.

In addition, document <NPL>, describes an open loop control system for a reconfigurable gain equalizer formed by a two-port lattice-form optical delay-line circuit.

The Applicant has noted that the closed loop control techniques of the known art are too complex, both in computational terms and in relation to the structure of the control circuit.

The present invention addresses the problem of providing an optical system that shows control techniques of a reconfigurable device of the system itself that are not particularly onerous computationally and complex from a structural point of view.

According to a first aspect, an object of the present invention is an optical system as described by claim <NUM> and its preferred embodiments as defined by claims <NUM>-<NUM>.

Another object of the present invention is also the method of controlling an optical system as defined by claim <NUM>.

This invention is described in detail below, by way of example and without limitation, with reference to the attached drawings:.

In this description, similar or identical elements or components will be shown in the figures with the same identifying symbol.

<FIG> shows schematically a first embodiment of an optical system <NUM> including: a reconfigurable optical device <NUM>, a control device <NUM> (CONT-DEV), an optical source <NUM> (OP-SR) and an optical-electric conversion device <NUM>.

In particular, optical system <NUM> is such as to operate with electromagnetic radiation at wavelengths between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

For example, optical system <NUM> is a system that operates in the field of optical telecommunications and, in particular, in reconfigurable optical networks.

The reconfigurable optical device <NUM> (shorter, reconfigurable device) is such that it operates according to the WDM (Wevelength Division Multiplexing) technique on a plurality of M optical channels (at least two optical channels) i.e. with M optical signals with carriers at different wavelengths.

In particular, the reconfigurable device <NUM> includes at least one adjustable optical element Gi (such as, for example, an optical delay line, an adjustable optical coupler or an adjustable attenuator) configured to operate in WDM. As an example, a single adjustable optical element Gi with M channels or multiple adjustable optical elements Gi operating on M channels can be used.

The reconfigurable device <NUM> is also equipped with a plurality of N actuators A<NUM>-AN, associated with the adjustable optical elements Gi and such as to modify the optical characteristics (for example, the refractive index and/or the attenuation of the medium from which the adjustable device <NUM> is made) according to the corresponding S<NUM>-SN control signals supplied by the control device <NUM>. The reconfigurable device <NUM> can assume a discrete number of states depending on the value of its N state variables θ<NUM>,. , θN which are controlled by the N control signals S<NUM>-SN.

Note that the N number of A<NUM>-AN actuators defines the number of degrees of freedom of the reconfigurable device <NUM>, i.e. the number of independent variables needed to fully determine the state of the reconfigurable device <NUM> itself.

Advantageously, the number of degrees of freedom N of the reconfigurable device <NUM> is lower than the number of channels M on which the reconfigurable device itself operates.

The actuators A<NUM>-AN can be such as to induce a change in the optical parameters (e.g. phase or amplitude) of the relevant adjustable optical elements Gi. For example, the following devices can be used as actuators A<NUM>-AN: thermo-optical, electro-optical, piezoelectric, electro-absorbent, electro-mechanical, electrochemical or fully optical actuators (based or not on non-linear optical effects).

With regard to the exemplyfying sector of reconfigurable optical networks, the reconfigurable device <NUM> can be, for example: an optical filter, an equalizer filter, a dispersion compensator filter, a FIR filter, an IIR filter, a lattice filter, a binary tree filter.

For example, the reconfigurable <NUM> device can be made using integrated waveguide technology on an optical platform (or optical chip). Some examples of optical platforms that can be used include: semiconductor platforms (e.g. silicon, indium phosphide, gallium arsenide), amorphous glasses (silicon dioxide, silicon nitride, silicon oxyfuride, silicon oxycarbon, silicon carbide), polymers and crystals (lithium niobate), possibly integrated with two-dimensional materials (graphene, silicene), and possible hybrid integrations of the same.

According to the example in <FIG>, the reconfigurable optical device <NUM> is a device with at least four optical ports. More in detail, the reconfigurable optical device <NUM> includes an optical input port <NUM> and an optical output port <NUM>. The optical input optical port <NUM> is configured to receive the plurality of M optical input signals, multiplied into an input signal I, and the optical output optical port <NUM> is configured to transmit an optical output signal O in particular, M optical output signals multiplied, as resulting from the action of the reconfigurable optical device <NUM>.

In addition, the reconfigurable optical device <NUM> is equipped with an optical stimulation port <NUM>, connected to the optical source <NUM>, and an optical monitoring port <NUM>, connected to the optical-electric conversion device <NUM>.

The plurality of the M optical input signals in the input signal I occupies an overall band Δλ, which identifies the working wavelength range for the reconfigurable device <NUM>.

In particular, referring to applications in linear mode, in each of the states identified by state variables θ<NUM>,. , θN the reconfigurable device <NUM> behaves, in each of the states it can assume, as a time-invariant linear system.

The transmission of the input signal I from the optical input port <NUM> to the optical output port <NUM> can be described through the frequency response H<NUM>,i(f) of the reconfigurable device <NUM> or equivalently by the wavelength response H<NUM>,i(λ), where the subscript "i" indicates the generic state assumed by the device itself.

Optical source <NUM> is configured to generate an optical Sin stimulation signal which is supplied to stimulation port <NUM>. Optical source <NUM> is configured to emit optical radiation over a wavelength range greater than or equal to the operating wavelength Δλ range of the reconfigurable device <NUM>. Optical monitoring port <NUM> is configured to provide an optical monitoring signal Sout as the output corresponding to the optical stimulation signal Sin.

In the case of integrated optical devices, the optical source <NUM> can be integrated on the same optical platform (i.e., an optical chip) as the reconfigurable device <NUM> or can be external to that platform and connected to the reconfigurable device <NUM> via an optical fibre.

Preferably the optical source <NUM> includes a superluminescent diode (SLD), but other broadband sources can be used, such as, for example, the "amplified spontaneous emission" noise (ASE noise) of a fibre amplifier (e.g. erbium doped fibre amplifier, EDFA) or a semiconductor optical semiconductor amplifier (SOA), from a "supercontinuum laser" type source, from a laser array (e.g., distributed laser feedback, DFB), a comb spectral array (comb) generated by a fibre comb generator or integrated on an optical chip.

The optical-to-electrical conversion device <NUM> is configured to receive the monitoring optical signal Sout and provide (for example, on electrical terminals <NUM>) a set of electrical intensity signals SEL1-SELN, each representative of an intensity of the monitoring signal Sout evaluated at a relative wavelength. Note that the set of intensity electrical signals SEL1-SELK has a cardinality equal to K. Preferably, this cardinality K is equal to N, i.e. the group of intensity electrical signals SEL1-SELK has a cardinality equal to the number of degrees of freedom of the reconfigurable device <NUM>.

According to the particular example shown again in <FIG>, the optical-electric conversion device <NUM> includes a spectral range selector <NUM> (SP-SL), hereinafter also spectral slicer, and an optical-electric converter <NUM> (DET-ARR). The spectral slicer <NUM> is equipped with a corresponding optical input port connected to the optical monitoring port <NUM> so as to receive the Sout monitoring signal and a plurality of optical output ports <NUM> (a number K optical ports <NUM>, where preferably K = N number of degrees of freedom).

The spectral slicer <NUM> is configured to transmit to its generic k-th output port a selected Soutk optical signal, corresponding to a portion of the monitoring signal Sout centred around a k-th wavelength λk.

The spectral slicer <NUM>, used to select the K wavelengths k to be monitored can be realized according to different technological and architectural solutions. For example, the spectral slicer <NUM> is a passive device that, i.e., does not need an external active control to select the λk wavelengths.

Possible architectures that can be used for the spectral slicer <NUM> include Array Waveguide Gratings" (AWG), echelle gratings and other types of interferometric filters such as Mach Zehnder interferometers, Bragg gratings, ring resonators and any combinations thereof.

The spectral slicer <NUM> is preferably made in waveguide and is, for example, integrated on the same optical platform as the reconfigurable optical device <NUM>. The spectral slicer <NUM> can also be realised with alternative technologies, using for example discrete optical components in free space, optical fibre components and combinations of the same.

According to this example, the <NUM> optical-electric converter comprises a plurality of photo detectors configured to convert the K sampled optical signals Sout(λk) into the K intensity electrical signals SEL1-SELK.

The control device <NUM> is configured to control the plurality of actuators A<NUM>-AN according to said set of intensity electrical signals SEL1-SELK, generating the N control signals S<NUM>-SN, according to a pre-established control law.

With regard to the control law, for reconfigurability purposes, control device <NUM> operates so that the i-th state assumed by the reconfigurable device <NUM>, in operating conditions, is as close as possible to an i-th "desired" state. For example, control device <NUM> is such as to define the plurality of control signals S<NUM>-SN using the method of minimising the mean square error between an actual transfer function of reconfigurable device <NUM> and a desired transfer function of reconfigurable device <NUM>.

The control device <NUM> can be realised, as an example, by means of a microcontroller, a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array) or a DSP (Digital Signal Processor), programmed according to the control methodology described below.

Note that the optical system <NUM> can also include an optical apparatus <NUM> (APP) operationally associated with the reconfigurable optical device <NUM>. For example, the optical apparatus <NUM> can be an optical amplifier (in particular, of the doped fibre type) that allows the long distance transmission of optical signals without optoelectronic conversion and regeneration. Optical amplifiers commonly operate on a large number of optical signals, for example, on more than one hundred signals.

According to this example, the reconfigurable optical device <NUM> can be an equalizer filter configured to equalize the gain band of the erbium doped fibres of the optical amplifier <NUM> that do not have a constant gain over the entire frequency range occupied by the signals.

The use of the reconfigurable equalizer filter <NUM> allows adapting the optical amplifier <NUM> to the needs of a reconfigurable optical network. For example, for the erbium doped fibre optical amplifier <NUM>, the reconfigurable equaliser filter <NUM> can have a number of degrees of freedom N = <NUM> and operate on a number of optical channels M = <NUM>.

In the following, an example of a control method that can be used by the optical system <NUM> to reconfigure the reconfigurable device <NUM> will be described.

Referring to the wavelength domain, the optical output signal O(λ) supplied to optical output port <NUM> is given by the following expression: <MAT> where I(λ) is the input signal I, expressed in the wavelength domain and H<NUM>,i(λ) is the already defined wavelength response of the reconfigurable device <NUM>; the subscript "i" indicates the generic status assumed by the device itself, in relation to the transmission of the input signal I from input optical port <NUM> to output optical port <NUM>.

To facilitate the understanding of the following mathematical notations, in <FIG> the numbers <NUM>, <NUM>, <NUM> and <NUM> have been added in brackets at the relevant optical ports of the reconfigurable device <NUM>.

The control method starts when there is a request to reconfigure optical system <NUM> and in particular reconfigurable device <NUM>.

As already mentioned, the described control method performs monitoring and control of the response in wavelength H<NUM>,i(λ) so that an i-th "effective" state, defined by an effective wavelength response H̃<NUM>,i(λ), assumed by the reconfigurable device <NUM> under operating conditions is as close as possible to an i-th "desired" state, defined by a response in H<NUM>,i(λ).

The optical stimulation signal Sin, generated by the optical source <NUM>, is supplied at the input of stimulation port <NUM> of the reconfigurable device <NUM> in order to measure in real time the actual state Hi,e(λ) and evaluate the deviation (i.e., the distance) with respect to the desired state Hi,d(λ).

Note that the desired Hi,d(λ) states are identified in advance and stored, for example in a lookup table, in a control device memory <NUM>, but can also be updated and modified dynamically during operation of the reconfigurable device <NUM>.

The reconfigurable device <NUM> receives the stimulation signal Sin and returns the monitoring signal Sout(λ) to the optical monitoring port <NUM>; the optical monitoring signal Sout(λ) is described in the following relation: <MAT>.

The function H<NUM>,i(λ) identifies the transfer function of the reconfigurable device <NUM> from the stimulation port <NUM> to the monitoring optical port <NUM>, when the device itself is in the i-th state to which the transfer function H<NUM>,i(λ), is associated, relative to the transmission from the input optical port <NUM> to the output optical port <NUM>.

It should be noted that for the purposes of the following discussion the reconfigurable device <NUM> is considered as having the following properties, defined below according to the transfer functions between the optical ports of the device itself:.

In the properties indicated above, the term "absence" is to be understood in the sense that the retroreflexsion, coupling or losses indicated above are null or negligible for the purposes of the following discussion.

As the expert in the field acknowledges, the above mentioned properties apply to the relationships: <MAT> <MAT> from which it can be seen that: <MAT>.

The relation (<NUM>) shows how the optical monitoring signal Sοut(λ) monitoring, associated with the transfer function |H<NUM>,i(λ)|<NUM>, provides the same information as the direct monitoring of the optical output signal O(λ), associated with the transfer function |H<NUM>,i(λ) |<NUM>.

Given the reciprocity of the reconfigurable device <NUM>, the transfer functions |H<NUM>,i(λ)|<NUM> e |H<NUM>,i(λ)|<NUM> are theoretically identical and both could be monitored. However, in practical cases it is convenient to use a stimulation signal that propagates in the opposite direction (counterpropagant) to the signal of interest. In fact, in case of co-propagant signals, the reconfigurable device <NUM> could be responsible for crosstalk phenomena and transfer part of the input stimulation signal to port <NUM> towards port <NUM>. Therefore, a counterpropagant configuration is preferable even if it is not the only one possible.

Since the spectrum of the Sin(λ) stimulation signal is known, the transfer function H<NUM>,i(λ) can be derived directly from monitoring signal the Sout(λ) (at monitoring port <NUM>) through the relationship (<NUM>).

Note also that system <NUM> operates on the basis of knowledge of the spectrum of the signal Sout(λ) only for a K number of wavelengths, preferably equally spaced, and preferably equal to the number of degrees of freedom N of device <NUM> (K=N).

Note that the K number of the wavelengths at which the spectrumof the signal Sout(λ) is considered can also be chosen to be greater than the number of degrees of freedom N: K>N. In this case, system <NUM> is particularly robust against noise, but is more complex than if K is equal to N.

On the other hand, by choosing the number K less than the number of degrees of freedom (K<N) the system <NUM> performs worse than K≥N.

The K number can be between a minimum Kmin and a maximum Kmax value. For example, the minimum value can be given by Kmin= N - <NUM>% N, or Kmin = N- <NUM>%N. For example, regarding the maximum value, Kmax = N + <NUM>% N, or Kmax = N + <NUM>% N, or Kmax = N + <NUM>% N.

With regard to the choice of the number K, please note that in the system <NUM> it is not required to be equal to the number of optical channels M, but can also be less or much less than the number of optical channels M (K<M). For example, when the reconfigurable device <NUM> is used in an amplification system with M = <NUM> channels, the number of monitored wavelengths K may be less than <NUM>%, i.e. K < <NUM>% M. Other possible example values are, K < <NUM>% M and K < <NUM>% M.

The number K is chosen, depending on the application, by appropriately combining both the above mentioned relations concerning the number of degrees of freedom N and the above mentioned relations concerning the number of optical channels M, considering a compromise between robustness and complexity.

Moreover, it should be noted that for the control method, it is sufficient to know only the intensity of the optical monitoring signal |Sout(λ) |<NUM> and not its phase at various wavelengths.

Therefore, the information that is used by the control device <NUM> is the intensity of the optical monitoring signal: <MAT> where the subscript k =<NUM>,. K indicates the discrete frequency at which the spectral power density |Sout(λ) |<NUM> is sampled.

The spectral slicer <NUM> receives themonitoring optical signal Sout(λ) and transmits to each relevant output port <NUM> a sampled optical signal Sout(λk) corresponding to a portion of the monitoring optical signal Sout(λ) centred around the k-th wavelength λk. In particular, the spectral slicer <NUM> provides on its output ports <NUM> a plurality of sampled optical signals SS1-SSK in parallel mode.

<FIG> refers to a numerical simulation and shows, for example, a spectrum <NUM> of the signal Sout(λ) for a possible configuration of the reconfigurable device <NUM> and also the portioned version <NUM> of the same signal and its sub-bands Sout(λk), each with its own band Bλ,k.

Each optical output <NUM> of the spectral slicer <NUM> is optically connected to a photo detector of the optical-electric converter <NUM> which measures the input optical intensity and provides on a related terminal <NUM> an electrical signal SELj having an electrical current or voltage proportional to the intensity |Sout(λk)|<NUM> of the optical monitoring signal Sout(λk) integrated on its own sub-band Bλ,k. The optical-electric converter <NUM> generates N electrical signals SEL1-SELN, in parallel on the plurality of terminals <NUM>.

The plurality of electrical signals SEL1-SELK is sent to the control device <NUM> which monitors in real time the effective frequency response |H̃<NUM>,i(λk)|<NUM> = |H̃<NUM>,i(λk)|<NUM> assumed by the reconfigurable device <NUM> under operating conditions at k-th wavelength λk solving the equation: <MAT>.

Control device <NUM> compares the current state H̃<NUM>,i(λ) with the desired state H<NUM>,i(λ) and identifies the control signals S<NUM>-SN to be applied, via control terminals <NUM>, to the actuators A<NUM>-AN of the reconfigurable device <NUM> to bring it and keep it in the desired state.

For example, the determination of the control signals S<NUM>-SN can be carried out, on the basis of the current state H̃<NUM>,i(λ) and the desired state H<NUM>,i(λ), according to the method of minimising the mean square error; note however that other methods can also be used. An example of the method of minimizing the mean squared error is described later with reference to a simulation of the control method.

Please note that during an initialisation phase of the optical system <NUM>, the values of the control signals S<NUM>-SN to be applied can be taken from a look up table obtained from numerical simulations of the reconfigurable device <NUM>. Once these values are applied to the reconfigurable device <NUM>, proceed to apply the method described above to bring it to the desired state indicated by the look up table.

<FIG> refers to a numerical simulation showing the effectiveness of the optical system <NUM>. Consider a generic reconfigurable device <NUM> having degrees of freedom N=<NUM>. In the simulation, a reconfiguration of device <NUM> has been considered so that its frequency response, in the wavelength range between <NUM> and <NUM>, can assume three predefined trends (<NUM>, <NUM>, <NUM>). Starting from an arbitrary initial configuration and wanting to bring the reconfigurable device <NUM> to work in the i-th state (<NUM>, <NUM> or <NUM>), the mean square error is calculated: <MAT> between the current transfer function H̃<NUM>,i(λ) and the desired transfer function H<NUM>,i(λ) for the generic state i. For the optimization of the transfer function of the reconfigurable device <NUM> alternative cost functions to those expressed by the equation (<NUM>) can be used, as well as other optimization algorithms, such as non-linear optimization, genetic algorithms, particle swarm optimization, machine learning, neural networks and others known in the literature.

In this simulation we first applied the method of the known technique, according to which the transfer functions |H<NUM>,i(λk)|<NUM> in the three different states (<NUM>, <NUM> and <NUM>) measured in a high number of wavelengths (open circles), equal to the number of optical channels used in the wavelength range of interest (K = M = <NUM>), were taken into account. By applying this conventional method, the curves shown in <FIG> with dashed lines have been obtained.

Applying instead the control methodology described with reference to the optical system <NUM>, the transfer functions |H<NUM>,i(λk)|<NUM> are measured in a limited number of wavelengths (K = N = <NUM>) equal to the number of degrees of freedom of the reconfigurable device <NUM> (full circles). Applying the method described with reference to system <NUM> we obtained the curves shown in <FIG> with the continuous lines.

<FIG> illustrates how the difference between dashed curves (conventional method) and continuous curves (system <NUM> method) is smaller than <NUM> dB across the entire operation band, confirming the efficiency of the method described.

According to another form of realization of the optical system <NUM>, schematically shown in <FIG>, the optical-electrical conversion device <NUM> is realized by means of a tunable monitor configured to supply the control device <NUM> with the set of electrical signals of intensity SEL1-SELN in a sequential way over time (i.e. in serial mode), starting from the optical monitoring signal Sout.

This tunable detector <NUM> includes, according to an example, a tunable optical filter <NUM> (TUN-FIL) with a single optical output <NUM> followed by a photodetector <NUM> (DET) with a single electrical output <NUM>. The tunable detector <NUM> is an active device that receives an external active control (an SCR control signal) to select λk wavelengths.

Optical output <NUM> of the tunable optical filter <NUM> is optically connected to the photodetector <NUM> which measures the input optical intensity and provides an electrical signal SELk with a current or voltage proportional to the intensity |Sout(λk)|<NUM>.

By sequentially tuning the tunable detector <NUM> over time it is possible to obtain information on the current transfer function H̃<NUM>,i(λ) of the reconfigurable device <NUM>, around all the frequencies of interest.

The electrical SEL1-SELK signals output sequentially from the <NUM> photodetector are sent to control device <NUM> and provide monitoring of the actual frequency response H̃<NUM>,i(λ) of the reconfigurable device <NUM>, under operating conditions.

Possible architectures that can be used for the tunable optical filter <NUM> include: optical ring resonators, Mach Zehnder interferometers, Bragg gratings, and possible combinations of these.

The tunable detector <NUM> is preferably realized in waveguide and is preferably integrated on the same photonic platform as the reconfigurable optical device <NUM>, already described, or it can be realized with discrete optical components in free space, optical fibre components and combinations of the same.

For example, for tuning the tunable optical filter <NUM>, the electrical control signal SCR (generated by the control device <NUM>) can be used, which acts on actuators (not shown) integrated in the tunable optical filter <NUM>. These actuators modify the behaviour of the tunable filter <NUM> by modifying the optical parameters of the material medium in which the light radiation propagates exploiting, for example, the thermo-optical effect, the electro-optical effect, or the elasto-optical effect; alternatively, micromechanical actuators (MEMS) can be used which modify the path of the light radiation in the device.

<FIG> refers to a numerical simulation of an optical system <NUM> similar to that described in <FIG>, including the tunable optical filter <NUM>.

The curve <NUM> in <FIG> shows the spectrum of the optical monitoring signal Sout(λ) for a particular configuration of the reconfigurable optical device <NUM>. <FIG> also shows (curve <NUM>) the "sampled" version of the optical monitoring signal and its sub-band, with its band Bλ,k as obtained through the tunable filter <NUM>, capable of tuning across the entire operation band.

<FIG> schematically shows a further optical system <NUM>, similar to optical system <NUM> already described with reference to <FIG>, but using a reconfigurable optical device <NUM> with two ports (input optical port <NUM> and output optical port <NUM>).

The further optical system <NUM> comprises a first circulator <NUM> and a second optical circulator <NUM>. The first optical circulator <NUM> is equipped with a first port <NUM> for the input signal I and a second port <NUM>, connected to the optical input port <NUM> of the reconfigurable device <NUM> to which the input signal I can be supplied. The optical input port <NUM> of the reconfigurable device <NUM> is also such as to feed the second port <NUM> of the first optical circulator <NUM> with the monitoring optical signal Sout. The first <NUM> circulator is equipped with a third port <NUM> connected to the spectral slicer <NUM> to supply the latter with the optical monitoring signal Sout.

The second optical circulator <NUM> includes a relative first port <NUM> connected to output port <NUM> of the reconfigurable device <NUM>. The optical output port <NUM> is such as to supply the output signal O to the second optical circulator <NUM> and is also such as to receive the stimulation signal Sin.

The second optical circulator <NUM> is also equipped with a relative second port <NUM>, configured to supply the output signal O, and a relative third port <NUM>, configured to receive the stimulation signal Sin generated by the optical source <NUM> and to be transmitted to the corresponding first port <NUM>, then to the reconfigurable device <NUM> (via output port <NUM>).

If the case that the reconfigurable two-port optical device <NUM> is reciprocal, the transfer function H<NUM> is equal to the transfer function H<NUM>.

It should be noted that the structure that has the reconfigurable two-port optical device <NUM>, equipped with the two optical circulators <NUM> and <NUM>, is also applicable to the form of construction in <FIG>.

<FIG> is a schematic representation of an optical lattice filter <NUM>, indicative of an example of a reconfigurable device <NUM>.

The optical lattice filter <NUM> comprises a plurality of optical couplers K1-K14 and a plurality of actuators Bal <NUM>, <NUM>. <NUM> and Unbal <NUM>, <NUM>,. <NUM>, suitable for introducing delays or imbalances in the optical channels, for a total of thirteen actuators.

The lettice filter <NUM> in <FIG> has a number of degrees of freedom N equal to <NUM>, i.e. equal to the number of actuators used, and can handle up to a number M of optical channels equal to <NUM>. It is possible to manage the reconfigurability of the lattice filter <NUM> by monitoring only a K number of wavelengths equal to N= <NUM>.

The optical couplers K1-K14 are an example of the optical elements Gi described with reference to <FIG> and the plurality of actuators Bal <NUM>, <NUM>. <NUM> and Unbal <NUM>, <NUM>,. <NUM> are an example of the A<NUM>-AN actuators described with reference to <FIG>.

Note that each of the actuators Bal <NUM>, <NUM>. <NUM> and Unbal <NUM>, <NUM>,. <NUM> acts on the optical behaviour of a corresponding Kj optical coupler which operates in WDM mode, i.e. it allows the propagation of several optical channels.

In general, the reconfigurable device <NUM> can be an optical filter that includes as optical elements Gi: binary tree or lattice interferometers, AWG (Arrayed Waveguide Gratings) or similar structures that use as power dividers, for example, MultiMode Interferometers (MMI), directional couplers, or y-branches or similar.

Please note that the solution described above is mainly, but not exclusively, applied in the telecommunications industry, specifically in the field of reconfigurable optical networks. Examples of other possible applications of the lessons described are:.

The optical systems described above are particularly advantageous in terms of simplicity and performance. In fact, these optical systems allow managing their reconfiguration by monitoring a number of signals (i.e. sampled optical signals SS1-SSK) lower than the number of optical channels on which the system itself operates, maintaining the desired performance.

Moreover, the described optical systems have the advantages offered by closed circuit control without requiring a high complexity of the actuator system controlled by the control device.

Claim 1:
Optical system (<NUM>; <NUM>) comprising:
a reconfigurable wavelength division multiplexing optical device (<NUM>) comprising a plurality of actuators (A<NUM>-AN) and having an associated number M of optical channels M and a number N of degrees of freedom defined by the number of said actuators (A<NUM>-AN) and less than said number M of optical channels;
a stimulating optical source (<NUM>) connected to said reconfigurable optical device (<NUM>) to provide a stimulation optical signal (Sin) having a wavelength band including a plurality of wavelengths associated to the optical channels;
an optical-electric conversion device (<NUM>) configured to receive from said reconfigurable optical device (<NUM>) an optical monitoring signal (Sout) produced in response to the stimulation optical signal (Sin) and to provide a group of intensity electric signals (SEL1-SELK), each representative of an intensity of the monitoring optical signal (Sout) evaluated at a respective wavelength included in said band;
a control device (<NUM>) configured to control the plurality of actuators (A<NUM>-AN) as a function of said group of electric signals (SEL1-SELK)and according to a control law, wherein: the group of intensity electric signals (SEL1-SELK)has a cardinality K selected on the basis of said number of degrees of freedom N and comprised between a first minimum value K1min = N - <NUM>% N and a first maximum value K1max = N + <NUM>% N.