Optical spectrum analysis device and optical spectrum analysis method

Abstract

An apparatus (1) for the analysis of the optical spectrum of an optical signal and a method for the analysis of an optical spectrum utilizing said apparatus, the apparatus (1) comprising an optical filter stage (2) having an optical path (5), a photodetector (17) optically connected downstream of the optical filter stage (2), and an actuator (18) configured to change the optical refractive index of at least one section of the optical path (5), the optical filter stages (2) being cascaded together to change the optical refractive index of each of the optical paths (5). a first Mach-Zehnder interferometer (6) and a first ring resonator (7) forming part of the optical path (5), wherein a difference in optical path (dL0) between the first optical branch (11) and the second optical branch (12) of the first Mach-Zehnder interferometer (6) is greater than zero, and the first Mach-Zehnder interferometer (6) is optically connected to the remainder of the optical path (5) by a single first port (13) of an input optical coupler (9) and by a single second port (14) of an output optical coupler (10).

Description

[Technical Field]

[0001] The present invention relates to an optical spectrum analysis device and an optical spectrum analysis method. [Background technology]

[0002] The present invention belongs to the field of photonics, ie the set of techniques and methods for the generation and / or transmission and / or processing and / or reception of optical signals.

[0003] The term "light" refers not necessarily to electromagnetic radiation that falls strictly within the visible light band (i.e., roughly 400-700 nm), but more generally to radiation that falls within a band broader than the visible light band, including, for example, the near infrared (e.g., wavelengths from about 700 nm to about 2 μm).

[0004] In the field of photonics, optical spectrum analyzers (also called OSAs) are known which are used to analyze the optical spectrum of an optical signal. The expression "optical spectrum" typically refers to the power distribution (expressed, for example, in dBm or watts) of an optical signal as a function of wavelength or frequency. Patent Document 1 discloses an OSA that includes a modulator, an integrated optical filter, and a photodetector. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2017 / 0331550 Summary of the Invention [Problem to be solved by the invention]

[0006] In connection with the aforementioned device for the analysis of optical spectra, the applicant has considered the following (where reference is made hereinafter to the wavelength of an optical signal, similar considerations apply in relation to frequency):

[0007] First of all, the Applicant considers it particularly advantageous to be able to determine the optical spectrum of an optical signal with high resolution, i.e. to determine the optical intensities of a plurality of optical sub-signals each comprising a subrange of wavelengths, where each subrange of wavelengths is as narrow as possible (the sum of the analyzed subranges completely encompasses the wavelength range of the original optical signal), thereby making it possible to obtain an optical spectrum with the desired accuracy and that is as faithful as possible to the effective distribution of optical intensities per unit wavelength of the original optical signal. [Means for solving the problem]

[0008] For this purpose, it is advantageous to manufacture a device for analyzing an optical spectrum comprising at least one optical filter stage of an input optical signal capable of filtering the optical signal in order to allow transmission (e.g., towards a photodetector downstream of the optical filter stage) of only a portion of the optical signal corresponding to the narrowest possible subrange of wavelengths. This leads to the realization of a device in which the optical filter stage is characterized by an overall transfer function (e.g., obtained from the product of the individual transfer functions of the optical filter components realizing the filter stage) that includes a periodic repetition of (single) peaks of desired amplitude (e.g., medium-high amplitude, also known as FWHM); the smaller the amplitude, the higher the achievable resolution.

[0009] The range of wavelengths bounded by these peaks is known as the passband.

[0010] Furthermore, as mentioned above, since the peaks of the overall transfer function repeat periodically, if two (or more) repetitions of said peaks are simultaneously within the band of the optical signal (i.e., the range of wavelengths encompassed by the optical signal), a disturbance in the detected optical intensity will be obtained, since this intensity will not clearly correspond to a single, well-established passband, but to two (or more) passbands. As a result, problems arise in determining the final optical spectrum that actually corresponds to the optical signal.

[0011] Therefore, the applicant has also found it particularly advantageous to obtain an overall transfer function of the optical filter stage such that the distance between two consecutive repetitions of said peaks (known as the free spectral range, also called FSR) is wide (wider than the full bandwidth of the signal).

[0012] Based on the above considerations, the applicant has found that devices known in the above context face various problems and can therefore be improved under one or more aspects.

[0013] For example, in practice, the integrated optical filter of the device described in US Patent Application Publication No. 2017 / 0331550, which comprises two ring resonators arranged in cascade, is subject to practical manufacturing problems, particularly related to the level of structural quality (e.g., very small manufacturing tolerances) that the ring resonators must meet in order to achieve the desired (high) resolution and wide free spectral range. For example, a parameter that characterizes a ring resonator is the ring quality factor, also called Q-factor, which represents the ratio between the free spectral range and the passband of the transfer function of the ring resonator. In other words, a very high Q-factor (typically above 10 4 ,10 5 A ring with a .lambda. of about 1000 .ANG. or even higher typically exhibits a ring resonator with a reduced passband and a wide free spectral range.

[0014] However, ring resonators with such high Q factors are not easy to manufacture and / or find in the market and are very sensitive to manufacturing defects, making these elements very delicate.

[0015] The applicant is therefore faced with the problem of realizing an apparatus for the analysis of optical spectra that has desired operating characteristics (e.g., in terms of resolution and free spectral range) and that is at the same time highly robust and / or structurally simple and / or easy to manufacture and / or operate.

[0016] According to the Applicant, the above problem is solved by an apparatus for the analysis of light spectra according to the appended claims and / or by an apparatus having one or more of the following characteristics:

[0017] According to one aspect, the present invention relates to an apparatus for the analysis of an optical spectrum of an optical signal.

[0018] The device is an optical filter stage having an input port, an output port, and an optical path extending from the input port to the output port; a photodetector optically connected to the optical filter stage downstream of the output port; an actuator coupled to the optical filter stage and configured to change the optical refractive index of at least one section of the optical path of the optical filter stage; Equipped with the optical filter stage comprising a first Mach-Zehnder interferometer and a first ring resonator cascaded together to form respective portions of the optical path; the first Mach-Zehnder interferometer comprises an input optical coupler, an output optical coupler, and first and second optical branches connecting the input optical coupler to the output optical coupler; a difference in the optical paths between the first and second optical branches of the first Mach-Zehnder interferometer is greater than 0; The first Mach-Zehnder interferometer is optically connected to the remainder of the optical path of the optical filter stage by a unique first port of the input optical coupler and by a unique second port of the output optical coupler.

[0019] According to the applicant, an optical filter stage comprising an unbalanced Mach-Zehnder interferometer (i.e., one optical branch has a length greater than the other optical branch) and a ring resonator allows a particularly advantageous synergistic combination of the transfer functions of such optical components, thereby making it possible to obtain an overall transfer function of the optical filter stage having desired properties in terms of resolution and free spectral range (i.e., high resolution and wide free spectral range).

[0020] On the other hand, in practice, an unbalanced MZI can have a transfer function characterized by a single peak that repeats periodically over the desired free spectral range (e.g., a high FSR compared to the typical bandwidth of optical signals analyzed by such devices, such as optical signals used in telecommunications).

[0021] On the other hand, ring resonators make it possible to provide respective transfer functions with peaks (also periodically repeated) characterized by narrow amplitudes (ie very weak peaks).

[0022] In this way, by combining the transfer functions corresponding to the two aforementioned optical components, an overall transfer function (representing the product of the individual transfer functions) is obtained that has a combination of the advantages of the individual transfer functions and can mutually compensate and mitigate their respective disadvantages, thus resulting in an overall transfer function with a wide free spectral range and peaks having small amplitudes (i.e., high resolution), while at the same time providing a number of practical advantages in terms of robustness and ease of implementation and / or operation of the optical filter stage.

[0023] In fact, the MZI itself is not only a highly robust optical component and less sensitive to manufacturing tolerances than a ring resonator, but its presence synergistically allows for a significant relaxation of the constructional constraints of the ring resonator, and therefore does not necessarily have to have both high resolution and a wide free spectral range (i.e., necessarily a high Q factor), but it is sufficient to have (only) the desired resolution (i.e., the amplitude of the peaks is reduced, regardless of their mutual distance), and to make the most of the greater robustness and simplicity of manufacturing and / or discovering and / or using a ring resonator (since a resonator having (only) this property is actually easier to manufacture), and the advantages of the optical filter stage thus obtained.

[0024] Furthermore, the fact that the Mach-Zehnder interferometer is optically connected to the remainder of the optical path of the optical filter stage by only a first port of the input optical coupler and by only a second port of the output optical coupler (typically a port in cross form with respect to the used first port of the input optical coupler) makes it possible to obtain a signal intensity at the photodetector that is already directly representative of the optical intensity of the optical signal in the passband, thus limiting subsequent re-processing steps (e.g., software) of the photodetector signal, such as Fourier transform spectroscopy (FTS) operations, simplifying the functionality of the device and / or reducing the computational effort.

[0025] Finally, the presence of an actuator coupled to the optical filter stage and configured to vary the optical refractive index of at least one section of the optical path of the optical filter stage makes it possible to dynamically vary the passband of the overall transfer function of the optical filter stage so as to be able to scan the entire wavelength range of the optical signal and thus to analyze the entire spectrum of the optical signal.

[0026] "Photodetector" means an optoelectronic component configured to convert a respective optical input signal into an electrical signal (current and / or voltage) that represents the optical intensity of the respective optical input signal.

[0027] The terms "upstream," "downstream," "interposed," "input," "output," and "cascade" refer to the propagation direction of the optical signal under consideration. The term "directly" in combination with "upstream," "downstream," etc., means that there are no further intervening elements (except connecting optical waveguides).

[0028] An "optical coupler" refers to an optical component that can distribute optical power entering a first port between a pair of second output ports. For example, an optical coupler includes a pair of first ports, a pair of second ports, and a pair of optical branches (e.g., semiconductor optical waveguides) that each connect a respective first port to a respective second port, and the two optical branches are optically coupled to each other by respective optical coupling paths interposed between the respective first ports and the respective second ports. Examples of optical couplers include a tunable directional coupler (also called a TDC, from the English "tunable directional coupler"), a power divider, an MMI (multimode interferometer), a Y-branch interferometer, a star coupler, and an MZI.

[0029] In the above aspects, the present invention may have one or more of the following preferred features.

[0030] Preferably, the optical filter stage comprises one or more second Mach-Zehnder interferometers (different from the first Mach-Zehnder interferometer) cascaded to each other and each forming a respective portion of the optical path. Preferably, each second Mach-Zehnder interferometer comprises a respective input optical coupler, a respective output optical coupler, and respective first and second optical branches connecting the respective input optical couplers to the respective output optical couplers, and the difference in the respective optical paths between the respective first and second optical branches is greater than 0. Preferably, the differences in the respective optical paths of the first Mach-Zehnder interferometer and the one or more second Mach-Zehnder interferometers are all different from each other. In this way, it is possible to appropriately combine the transfer functions of each unbalanced MZI to further improve the characteristics of the overall transfer function of the optical filter stage (e.g., in terms of resolution and / or FSR).

[0031] Preferably, each second Mach-Zehnder interferometer is optically connected to the remaining respective portions of the optical path of the optical filter stage by one and only a respective first port of a respective input optical coupler and by one and only a respective second port of a respective output optical coupler. In this way, the introduction of the further MZI does not interfere with the analysis of the optical spectrum in terms of a direct relationship between the measured optical intensity and the effective optical intensity of the filtered optical signal portion.

[0032] Preferably, the unique second port of the output optical coupler of each Mach-Zehnder interferometer is arranged in a cross configuration with respect to the unique first port of the input optical coupler of the respective Mach-Zehnder interferometer. Cross configuration (or "cross port") means that the unique second port belongs to an optical branch of the Mach-Zehnder interferometer different from the optical branch to which the unique first port belongs (and vice versa for "bar doors"). In this way, robust operation of each MZI is achieved even against possible structural defects, since it is possible to achieve, for example, the desired spectral separation (i.e., the transfer function of the MZI is zero outside the respective bandwidth). In this way, the desired overall transfer function of the optical filter stage is obtained.

[0033] Preferably, the one or more second Mach-Zehnder interferometers comprise 2 and / or 19 or less, more preferably 9 or less, and even more preferably 2 or less second Mach-Zehnder interferometers. In this way, the complexity of the apparatus and / or the number of components is limited. The applicant has also realized that the presence of (at least) one ring resonator along the optical path synergistically limits the total number of unbalanced MZIs cascaded in the optical filter stage for a given obtainable resolution and free spectral range.

[0034] Preferably, the first ring resonator is a single ring resonator in the optical filter stage, so the device is structurally simple.

[0035] In one embodiment, the optical filter stage comprises one or more second ring resonators (different from the first ring resonator) cascaded together to each form a respective portion of the optical path. Preferably, the respective microrings of the first ring resonator and each second ring resonator all have different radii. In this way, the overall transfer function of the optical filter stage in terms of resolution and / or free spectral range is further improved.

[0036] In one embodiment, the one or more second ring resonators comprise two and / or no more than seven, more preferably no more than four second ring resonators, in this way limiting the structural complexity of the device.

[0037] Typically, each ring resonator comprises at least one microring (in embodiments, a series of cascaded microrings) optically coupled to two optical waveguides, with each input port and each drop port located on a different optical waveguide relative to the input port (also known as a "drop" port). Preferably, each ring resonator is optically connected to the remainder of the optical path (and possibly further optical paths, as described below) only by its input port and only by its drop port. In this way, the resonators are appropriately positioned to contribute to the overall transfer function of the filter stage.

[0038] Preferably, the optical path difference between the first and second optical branches of the first Mach-Zehnder interferometer is a function of the bandwidth of the optical signal. Preferably, the optical path difference is such that the transfer function of the first Mach-Zehnder interferometer has a free spectral range (FSR) substantially equal to or greater than the width of the bandwidth of the optical signal. In this way, the entire bandwidth of the optical signal is analyzed.

[0039] Preferably, the respective difference in the optical paths of each second Mach-Zehnder interferometer is a function of the difference in the optical paths of the first Mach-Zehnder interferometer, and more preferably is 2 times the difference in the optical paths of the first Mach-Zehnder interferometer. itimes, where i is equal to the order of the respective second Mach-Zehnder interferometer. In this way, the transfer function of each of the ith second MZIs has a free spectral range equal to half the free spectral range of the transfer function of the Mach-Zehnder interferometer having a refractive index i-1 (for i=1, the free spectral range is half the free spectral range of the first MZI, which can be assumed corresponding to i=0). In this way, the condition is advantageously and simply obtained in which the maxima of all peaks except one of the transfer function of the ith MZI are located on the wavelength axis at the valleys of the transfer function of the MZI having a refractive index i-1. In this way, all peaks except one are mutually suppressed, and an overall transfer function with only one peak (corresponding to the coincident maxima of all transfer functions of the individual MZIs) is realized in a structurally simple manner. This makes it possible to optimize the use of MZIs, since the number of MZIs used is limited for given final characteristics of the overall transfer function.

[0040] Preferably, the optical path difference of the first Mach-Zehnder interferometer is 1 μm or more, so that the FSR is comparable to the typical band of optical signals used in the field of telecommunications (e.g., about 1520-1580 nm).

[0041] Preferably, the difference in the optical paths of the first Mach-Zehnder interferometer (and possibly each second Mach-Zehnder interferometer) is 2 mm or less. In this way, the spatial extension of the optical filter stage is limited to the advantage of the overall size of the device (e.g., for particular use on supports of limited dimensions, such as integrated chips).

[0042] Preferably, the radius of the microring of the first ring resonator is a function of the optical path difference of the first Mach-Zehnder interferometer, and more preferably, the perimeter of the microring of the first ring resonator is 2 times the optical path difference of the first Mach-Zehnder interferometer. n+1 In one embodiment, the perimeter of each microring of each second ring resonator is equal to twice the difference in the optical paths of the first Mach-Zehnder interferometers.n+1+m where m is equal to the order of the second ring resonator. In this way, the same considerations as mentioned above regarding half the free spectral range of the MZI are valid, and similar advantages can be obtained with regard to optimizing the use of the ring resonator.

[0043] Preferably, the one or more second Mach-Zehnder interferometers are arranged in series with the first Mach-Zehnder interferometer (i.e., regardless of the total number of MZIs used, the one or more second Mach-Zehnder interferometers are all arranged immediately downstream of the previous MZI without interruption). Preferably, the one or more second ring resonators are arranged in series with the first ring resonator. This simplifies the structure of the device.

[0044] Preferably, the input port of the optical filter stage coincides with the only first port of the input optical coupler of the first Mach-Zehnder interferometer, and the output port of the optical filter stage coincides with the drop port of the first ring resonator (or the last second ring resonator in the series of ring resonators). Preferably, the photodetector is directly optically connected to the output port of the optical filter stage. In this way, the apparatus is simplified.

[0045] Preferably, the device comprises an optical signal pre-processing stage upstream of the optical filter stage (and possible further optical filter stages), which preferably comprises a polarization separator for separating a first polarization component (e.g. an electric transverse polarization component) from a second polarization component (e.g. a magnetic transverse polarization) of the optical signal.

[0046] Preferably, the pre-processing stages comprise respective input ports and respective first and second output ports (one output port for each of the first and second polarization components).

[0047] Preferably, the pre-processing stage includes a polarization rotator for rotating the polarization of the second polarization component of the optical signal (e.g., by 90°). Rotating one of the polarization components (typically the transverse magnetic component) allows the second polarization component to have the same polarization as the first polarization component, while maintaining its respective optical intensity. In this way, it is also possible to analyze the second polarization component using the same analytical device without the need for appropriate modifications and / or calibrations and / or adaptations during use. In this way, the device is versatile and can analyze the optical spectrum of an optical signal (which typically varies over time) regardless of its polarization.

[0048] In a first embodiment, the apparatus includes a further optical coupler (different from the Mach-Zehnder interferometer) interposed between the pre-processing stage and the optical filter stage, with each of the first and second output ports of the pre-processing stage optically connected (directly) to one (and only one) respective first port of the further optical coupler, and the only second port of the further optical coupler optically connected (directly) to an input port of the optical filter stage (preferably directly optically connected to the only first port of the input optical coupler of the first Mach-Zehnder interferometer). Preferably, the apparatus further includes first and second optical switches (e.g., variable optical attenuators or VOAs) interposed, respectively, between the respective first and second output ports of the pre-processing stage and the corresponding first port of the further optical coupler. In this way, a structure is created in a simple and effective manner that can selectively pass only one or other polarization component (electric or magnetic) of an optical input signal toward the optical filter stage for analyzing its corresponding optical spectrum.

[0049] Preferably, the series of Mach-Zehnder interferometers is positioned immediately upstream of the series of ring resonators, thus simplifying the overall structure of the device.

[0050] In a second embodiment, the optical filter stage comprises a first 3 dB optical coupler (different from the Mach-Zehnder interferometer) forming a respective portion of the optical path and interposed between the first Mach-Zehnder interferometer (or one or more second Mach-Zehnder interferometers, if present) and the first ring resonator. Preferably, a first port of one (and only one) of the first 3 dB optical couplers is optically connected (directly) to only one second port of the output optical coupler of the first Mach-Zehnder interferometer (or of each output optical coupler of the second Mach-Zehnder interferometer located at the final position along the respective sequence). Preferably, a second port of one (and only one) of the first 3 dB optical couplers is optically connected (directly) to an input port of the first ring resonator. Preferably, the remaining second ports of the first 3 dB optical couplers are optically connected (directly) to second output ports of the pre-processing stage.

[0051] Preferably, the device comprises a further optical filter stage comprising a further input port, a further output port, and a further optical path extending from the further input port to the further output port. Preferably, the further optical filter stage comprises a first Mach-Zehnder interferometer (and more preferably each second Mach-Zehnder interferometer) common to the optical filter stage, and further ring resonators (different from the first ring resonator and one or more second ring resonators) cascaded to each other to form respective parts of the further optical path. In this way, an optical filter stage is created for each polarization component of the optical signal (propagating along both directions during operation), while keeping the device compact because the first MZI (and possibly each second MZI) is common. The combination of the first MZI and the further ring resonators makes it possible to obtain an overall transfer function of the further optical filter stage having the same advantages as those described above for the optical filter stage.

[0052] In one embodiment, the further optical filter stage comprises a plurality of further ring resonators (comprising further ring resonators). Preferably, the further ring resonator (or possibly a plurality of further ring resonators) comprises one or more, more preferably all, features of the first ring resonator (and possibly one or more second ring resonators) referred to in the further optical filter stage where appropriate. In this way, the desired overall transfer function is obtained.

[0053] Preferably, the apparatus comprises a further photodetector optically connected to a further optical filter stage downstream of the further output port, more preferably to a drop port of the further ring resonator.

[0054] Preferably, the further optical filter stage comprises a second 3 dB optical coupler (different from the Mach-Zehnder interferometer and the first 3 dB optical coupler) forming a respective part of the further optical path and interposed between the first Mach-Zehnder interferometer and the further ring resonator. Preferably, a first port of one (and only one) of the second 3 dB optical couplers is optically connected (directly) to a first output port of the pre-processing stage. Preferably, the remaining first ports of the second 3 dB optical couplers are optically connected (directly) to an input port of the further ring resonator. Preferably, a second port of one (and only one) of the second 3 dB optical couplers is optically connected (directly) to only a first port of the input optical coupler of the first Mach-Zehnder interferometer.

[0055] The aforementioned features of the optical connection of the first and second 3 dB optical couplers make it possible to create, in a structurally simple manner and / or using a limited number of components, a closed-loop device architecture in which a first polarization component is addressed to an optical filter stage and a second polarization component is simultaneously addressed to another optical filter stage with an opposite propagation direction. Applicant has found that, despite the simultaneous presence of both polarization components along a common section of the optical path and a common section of a further optical path created by a Mach-Zehnder interferometer, the polarization components do not interfere with each other, making it possible to simultaneously obtain both of their respective optical spectra. In this way, the device is versatile and functional, with a short spectral scanning cycle.

[0056] Preferably, the radius of each microring of the first ring resonator (and optionally each of the second and further ring resonators) is less than or equal to 500 μm. In this way, the dimensions of the device are contained.

[0057] In a second embodiment, the device preferably comprises an optical isolator located upstream of the pre-processing stage, thus suppressing unwanted signal residues resulting from the closed-loop architecture.

[0058] Preferably, the actuator is also coupled to the further optical filter stage and is configured to change the optical refractive index of at least one section of the further optical path of the further optical filter stage.

[0059] Preferably, the actuator comprises a plurality of sub-actuators, each sub-actuator being coupled to a respective Mach-Zehnder interferometer or a respective ring resonator (to vary the optical refractive index of a respective optical path).

[0060] According to another aspect, the present invention relates to a method for the analysis of an optical spectrum of an optical signal having a band, the method comprising: - providing an apparatus for analysis according to any embodiment of the present invention; - introducing an optical signal as input to the device; - adjusting the optical filter stage (and possibly further optical filter stages) by means of an actuator in order to (continuously) move the passband of the optical filter stage (and possibly further optical filter stages) along the band of the optical signal; - obtaining, for each passband, by means of a photodetector (and possibly also by means of further photodetectors), a respective signal representative of the optical intensity of the optical signal in the passband; - calculating the optical spectrum as a function of the respective signals representing the light intensity; Includes.

[0061] In this way, an optical spectrum is obtained with the desired resolution and structural simplicity.

[0062] Preferably, the method further comprises a deconvolution routine of each signal representing light intensity. Preferably, the deconvolution routine comprises: - determining the overall transfer function of the optical filter stage (and possibly further optical filter stages); - calculating the Fourier transform (for example by means of an FFT algorithm) of the overall transfer function of the optical filter stage (and further optical filter stages); - calculating (for example by means of an FFT algorithm) the Fourier transform of each signal representing the light intensity within the band; - calculating, for each passband, the quotient between the Fourier transform of the respective signal representing the light intensity and the Fourier transform of the total transfer function of the optical filter stage (and any further optical filter stages); - calculating the inverse Fourier transform of the quotient (for example using an FFT algorithm); Includes. In this way, the desired resolution of the optical spectrum is obtained. [Brief explanation of the drawings]

[0063] [Figure 1]1 shows a block diagram of a first embodiment of the device according to the invention; [Figure 2] 2 shows a schematic circuit configuration of the device of FIG. 1; [Figure 3] 2 shows a block diagram of a second embodiment of the device according to the invention; [Figure 4] 4 shows a schematic circuit configuration of the device of FIG. 3; [Figure 5] 10 is a graph illustrating an example of a transfer function of an optical component of an optical filter stage. [Figure 6] An example of an overall transfer function obtained from the transfer function of FIG. 5 is shown in the graph. [Figure 7] 10 shows graphically the results of several simulations of the analytical method according to the present invention. [Figure 8] 10 shows graphically the results of several simulations of the analytical method according to the present invention. [Figure 9] 10 shows graphically the results of several simulations of the analytical method according to the present invention. [Figure 10] 10 shows graphically the results of several simulations of the analytical method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0064] The features and advantages of the present invention will become more apparent from the following detailed description of some embodiments thereof, given as non-limiting examples of the invention, in connection with the accompanying drawings (not to scale):

[0065] The number 1 in the figure indicates an apparatus for the analysis of the optical spectrum of an optical signal.

[0066] The device 1 comprises an optical filter stage 2 (closed dotted line shown in Figures 1 and 3) having an input port 3, an output port 4 and an optical path 5 extending from the input port to the output port.

[0067] The optical filter stage 2 comprises a first Mach-Zehnder interferometer 6 and a first ring resonator 7 cascaded together to form respective parts of the optical path 5 .

[0068] Illustratively, the optical filter stage 2 further comprises two second Mach-Zehnder interferometers 8 cascaded together, each forming a respective portion of the optical path (for a total of three Mach-Zehnder interferometers). Illustratively, the two second Mach-Zehnder interferometers 8 are positioned consecutively in series with the first Mach-Zehnder interferometer 6 (i.e., one interferometer immediately downstream of the previous interferometer).

[0069] The first Mach-Zehnder interferometer 6, and illustratively each second Mach-Zehnder interferometer 8, comprises a respective input optical coupler 9, 9', a respective output optical coupler 10, 10', and a respective first optical branch 11, 11' and second optical branch 12, 12' connecting each input optical coupler 9 to each output optical coupler 10.

[0070] The first Mach-Zehnder interferometer 6, and illustratively each second Mach-Zehnder interferometer 8, is optically connected to the remainder of each of the optical paths 5 of the optical filter stage by a unique first port 13, 13' of a respective input optical coupler 9, 9' and a unique second port 14, 14' of a respective output optical coupler 10, 10'.

[0071] Illustratively, the unique second port 14, 14′ of the output optical coupler 10, 10′ of each Mach-Zehnder interferometer 6, 8 is arranged in a cross configuration with respect to the unique first port 13, 13′ of the input optical coupler 9, 9′ of the respective Mach-Zehnder interferometer (i.e., which belongs to a different optical branch).

[0072] In one embodiment not shown, the only second port of the output optical coupler of each Mach-Zehnder interferometer is a bar port.

[0073] The difference in optical path length dL0 between the first optical branch 11 and the second optical branch 12 of the first Mach-Zehnder interferometer 6, and illustratively the difference in optical path length dL between the first and second optical branches of each second Mach-Zehnder interferometer 8, i are all greater than 0 and are all different from each other.

[0074] Illustratively, the optical path difference dL0 between the first and second optical branches of the first Mach-Zehnder interferometer 6 is a function of the bandwidth of the optical signal to be analyzed (e.g., about 1520 nm to about 1580 nm). More specifically, the optical path difference dL0 is illustratively such that the transfer function FDT0 of the first Mach-Zehnder interferometer 6 (FIG. 5) has a respective free spectral range substantially equal to the width of the bandwidth of the optical signal (in this example, about 60 nm).

[0075] Figure 5 shows the trend of the transfer function FDT0 (expressed in dB) as the wavelength (expressed in μm) changes. In Figure 5, the free spectral range corresponds to the distance between two consecutive valleys of the transfer function FDT0.

[0076] Illustratively, the respective differences dL of the optical paths of the second Mach-Zehnder interferometers 8 i is a function of the optical path difference of the first Mach-Zehnder interferometer 6. In particular, the optical path difference dL of the i-th second Mach-Zehnder interferometer i is illustratively represented by the formula dL i =2 i dL0, where i=1, 2. Thus, illustratively, dL1=2dL0 and dL2=4dL0.

[0077] FIG. 5 also shows the transfer functions of both the second Mach-Zehnder interferometers FDT1 (for i=1) and FDT2 (for i=2). It can be seen how the free spectral range of FDT1 (equal to the distance between two consecutive valleys) is halved relative to the free spectral range of FDT0, and how the free spectral range of FDT2 is half that of FDT1. In this way, within the band of the optical signal, only one wavelength value is obtained at which FDT0, FDT1, and FDT2 each have a matching peak repetition (exemplary, this value corresponds to approximately 1567 nm). As shown in FIG. 5, all remaining repetitions of the peak of FDT1 are located in the valley of FDT0, and all remaining repetitions of the peak of FDT2 are located in the valley of FDT0 or FDT1, thus resulting in a mutual suppression effect.

[0078] Illustratively, the optical path differences of the Mach-Zehnder interferometers are all between 1 μm and 2 mm, including the extreme values.

[0079] Illustratively, the first ring resonator 7 is a single ring resonator of the optical filter stage 2 , illustratively comprising a single microring, an input port 15 and a drop port 16 .

[0080] Illustratively, the first ring resonator 7 is optically connected to the respective remainder of the optical path 5 only by the input port 15 and only by the drop port 16 .

[0081] Illustratively, the input port 3 of the optical filter stage 2 coincides with the only first port 13 of the input optical coupler 9 of the first Mach-Zehnder interferometer 6, and the output port 4 of the optical filter stage 2 coincides with the drop port 16 of the first ring resonator 7.

[0082] Illustratively, the radius R of the microring of the first ring resonator 7 is a function of the optical path length difference of the first Mach-Zehnder interferometer 6. More specifically, the perimeter of the microring of the first ring resonator 7 is illustratively 2 times the optical path difference dL0 of the first Mach-Zehnder interferometer.n+1 times, and n is equal to 2 (i.e., the total number of second Mach-Zehnder interferometers 8). Illustratively, 2πR=8dL0.

[0083] FIG. 5 shows the transfer function of the first ring resonator FDTr, characterized by peaks of reduced amplitude with frequent repetition within the optical signal band. It can be seen that all repetitions of the FDTr peaks, except for the one at 1567 nm, are located in the valleys of FDTr, FDT0, FDT1, or FDT2 and are therefore nullified. This is achieved in a simple manner thanks to the aforementioned relationship between the microring radius R and dL0. In this way, it is possible to obtain the overall transfer function FDTc of the optical filter stage (obtained by the product of FTD0, FDT1, FDT2, and FDTr) shown exemplarily in FIG. 6. It can be observed that FDTc has the desired resolution (corresponding to the amplitude of each peak at 1567 nm) thanks to the first ring resonator, and the desired free spectral range thanks to the first MZI, since only one repetition of the peak is present within the band of the optical signal of interest.

[0084] In one embodiment (not shown), the optical filter stage may comprise one or more second ring resonators (different from the first ring resonator) preferably cascaded in series with the first ring resonator to form respective portions of the optical path, and preferably the radii of the microrings of each of the first ring resonators and the radii of the microrings of each of the second ring resonators are all different from each other.

[0085] Preferably, the perimeter of each microring of each second ring resonator is 2 times the optical path difference of the first Mach-Zehnder interferometer. n+1+m times, where m is equal to the (progressively increasing) order of the second resonator ring.

[0086] The device 1 comprises a photodetector 17 optically connected to the optical filter stage 2 downstream of the output port 4 (the photodetector 17 is illustratively optically connected immediately downstream of the drop port 16).

[0087] The apparatus 1 comprises an actuator 18 coupled to the optical filter stage 2 and configured to change the optical refractive index of at least one section of the optical path 5 of the optical filter stage.

[0088] For example, the actuator may utilize the thermo-optic effect, or the electro-optic effect, or both. In one embodiment, the actuator may be structured to change the optical refractive index in one (or both) of one or more branches of the MZI or ring resonator, for example, as known. In one embodiment, the actuator may be structured to directly change the optical refractive index of one or more of the MZIs directly at the level of one or both of the respective optical couplers, for example, as described in Patent Applications Nos. 102021000025160 and 102021000025166 in the name of the same applicant.

[0089] Illustratively, the device 1 comprises an optical signal pre-processing stage 19 upstream of the optical filter stage. Illustratively, the pre-processing stage 19 comprises a polarization separator 20 for separating a first polarization component TE (e.g., a transverse electric polarization component) from a second polarization component TM (e.g., a transverse magnetic) of the optical signal.

[0090] Illustratively, the pre-processing stage 19 comprises a respective input port 21 and respective first and second output ports 22 and 23 (ports for the first and second polarization components, respectively).

[0091] Illustratively, the pre-processing stage 19 further comprises a polarization rotator 24 for rotating the polarization of the second polarization component TM of the optical signal (eg, by 90°).

[0092] In the first embodiment (FIGS. 1 and 2), the device 1 comprises a further optical coupler 25 (different from a Mach-Zehnder interferometer) interposed between the pre-processing stage 19 and the optical filter stage 2 .

[0093] Illustratively, the first output port 22 and the second output port 23 of the pre-processing stage 19 are each optically connected directly to a respective one and only first port 26 of the further optical coupler 25, and the one and only second port 27 of the further optical coupler 25 is optically connected directly to the input port 3 of the optical filter stage 2, and more particularly to the one and only first port 13 of the input optical coupler 9 of the first Mach-Zehnder interferometer 6.

[0094] Illustratively, the further optical coupler 25 is a tunable balanced Mach-Zehnder interferometer with a splitting ratio that is variable from 0-100.

[0095] Illustratively, the device 1 further comprises a first optical switch 28 and a second optical switch 29 (e.g., a variable optical attenuator or VOA) respectively interposed between the respective first output port 22 and second output port 23 of the pre-processing stage and the corresponding first port 26 of the further optical coupler 25.

[0096] Illustratively, a series of consecutive Mach-Zehnder interferometers are positioned immediately upstream of a first ring resonator 7, with the input port of the first ring resonator being optically connected directly to the sole output port 14' of an output optical coupler 10' of a second Mach-Zehnder interferometer 8 positioned at the final position.

[0097] In a second embodiment (FIGS. 3 and 4), the optical filter stage 2 comprises a first 3 dB optical coupler 30 (different from the Mach-Zehnder interferometer) interposed between the first ring resonator 7 and a second Mach-Zehnder interferometer 8 which form respective parts of the optical path 5 and are arranged in a final position.

[0098] Illustratively, the only first port 31 of the first 3 dB optical coupler 30 is optically connected directly to the only second port 14′ of the output optical coupler 10′ of the second Mach-Zehnder interferometer 8 placed in the final position, the only second port 32 of the first 3 dB optical coupler 30 is optically connected directly to the input port 15 of the first ring resonator 7, and the remaining second port 33 of the first 3 dB optical coupler 30 is optically connected directly to the second output port 23 of the pre-processing stage 19.

[0099] Illustratively, the device 1 comprises a further optical filter stage 40 (bounded by a closed dashed double-dot line) with a further input port 41, a further output port 42 and a further optical path 43 extending from the further input port to the further output port.

[0100] Illustratively, the further optical filter stage 40 comprises both a first Mach-Zehnder interferometer 6 and a second Mach-Zehnder interferometer 8 in common with the optical filter stage 2, and a further ring resonator 44 (different from the first resonator ring 7) cascaded with each other to form respective parts of a further optical path 43.

[0101] Illustratively, the further ring resonator 44 comprises all the features of the first ring resonator 7, with reference to the further optical filter stage 40 where appropriate.

[0102] Illustratively, the apparatus 1 comprises a further photodetector 45 optically connected to the drop port 60 of the further ring resonator 44 .

[0103] Illustratively, the further optical filter stage 40 comprises a second 3 dB optical coupler 46 (different from the Mach-Zehnder interferometer and the first 3 dB optical coupler 30) forming a respective part of the further optical path and interposed between the first Mach-Zehnder interferometer 6 and the further ring resonator 44.

[0104] Illustratively, the only first port 47 of the second 3 dB optical coupler 46 is optically connected directly to the first output port 22 of the pre-processing stage 19, the remaining first port 48 of the second 3 dB optical coupler 46 is optically connected directly to the input port 61 of the further ring resonator 44, and the only second port 49 of the second 3 dB optical coupler is optically connected directly to the only first port 13 of the input optical coupler 9 of the first Mach-Zehnder interferometer 6.

[0105] Exemplarily, the radius of the microrings of the first ring resonator 7 and the further ring resonator is 500 μm or less.

[0106] In the second embodiment, the device 1 exemplarily comprises an optical isolator 50 arranged upstream of the pre-treatment stage 19 .

[0107] In one embodiment (not shown), the further optical filter stage may comprise a number of further ring resonators (similar to the second ring resonator of the optical filter stage).

[0108] Illustratively, the actuator 18 is also coupled to a further optical filter stage 40 and is configured to change the optical refractive index of at least one section of the further optical path of the further optical filter stage.

[0109] Illustratively (not shown), the actuator comprises a respective sub-actuator (for varying the optical refractive index of the respective optical path) for each Mach-Zehnder interferometer and each ring resonator. Illustratively, each sub-actuator may be of a known type (e.g., an electric heater, a pair of electrodes electrically connected to the optical waveguide, etc.).

[0110] Illustratively, the device includes semiconductor optical waveguides for connecting the various optical components described above. Illustratively, the device may be fabricated on any semiconductor photonics platform, such as silicon, silicon-on-insulator, silicon nitride, indium phosphide, silicon carbide, gallium arsenide, lithium niobate, or any other semiconductor waveguide platform.

[0111] In use, the device 1 makes it possible to carry out a method for the analysis of the optical spectrum of an optical signal having a band.

[0112] The method includes introducing an optical signal as input to the device. The optical signal is illustratively filtered by optical filter stage 2 (and possibly a further optical filter stage 40) to allow only a portion of the optical signal corresponding to the passband of the filter to pass towards photodetector 17 (and possibly towards further photodetector 45).

[0113] Referring to the first embodiment of the device described above, the method illustratively includes activating one of the two optical switches 28, 29 to shift only one polarization component at a time towards the further optical coupler 25. The further optical coupler 25 is then adjusted to transmit the maximum bar or cross transition depending on the input polarization component to the optical filter stage. For example, if it is desired to transmit the polarization component TE to the optical filter stage, the first switch 28 is activated to block the transmission of the TM component, and the further optical coupler 25 is adjusted to a cross configuration (so that the TE component passes entirely through another optical coupler). The reverse is true for the TM component. For example, the optical intensity of the TE component may be analyzed only in the optical signal band, followed by the same for the TM component.

[0114] With reference to the aforementioned second embodiment of the device, the method illustratively involves simultaneously analyzing both TE and TM polarization components, which therefore simultaneously pass through the device, in particular the three MZIs, in both propagation directions. For example, the TE component, having passed through the pre-processing stage 19, reaches the second 3 dB optical coupler 46 and is (partially) transmitted to the optical filter stage via the second port 49. Conversely, the TM component, after passing through the three MZIs, reaches the second 3 dB optical coupler 46 through the second port 49 and is (partially) transmitted to the further ring resonator 44 by the remaining first port 48. This is precisely the case for the first 3 dB optical coupler 30.

[0115] Thus, the method includes adjusting the optical filter stage (and possibly further optical filter stages) by the actuator 18 to move the passband of the optical filter stage (and possibly further optical filter stages) along the band of the optical signal (i.e., translating the FDTc in Figure 6 along the horizontal axis of wavelength). Figure 6 shows an example of a shifted overall transfer function FDTct corresponding to the FDTc of the optical filter stage shifted as a result of adjusting the optical filter stage by the actuator 18. Illustratively, it can be seen how the passband of the optical filter stage is moved towards higher wavelength values.

[0116] The optical filter stage may be adjusted, for example, by actuating one or more of the sub-actuators associated with MZIs 6, 8 and the first ring resonator 7 (similarly for further optical filter stages, see the sub-actuators of MZIs 6, 8 and the sub-actuators of the further ring resonator 44). Illustratively, the method may include a step of pre-calibration (e.g. by calibration methods that are known and will not be described in further detail) of the operating points of the sub-actuators.

[0117] Thus, the method includes obtaining, for each passband, by the photodetector (and possibly also by further photodetectors) a respective signal representative of the optical intensity of the optical signal in the passband.

[0118] Finally, the method includes calculating the optical spectrum of the optical signal as a function of each of the aforementioned signals representing light intensity.

[0119] 7 and 8 show the results of some simulations of the method according to the invention (shown with reference only to the component TE, regardless of the embodiment of the device), where the vertical axis represents the optical power (dBm) and the horizontal axis represents the frequency (THz).

[0120] In FIG. 7, the optical input signal IS is simulated as a Dirac delta, while the remaining curves represent the acquired signal AS (i.e., the set of all respective signals representing the optical intensity in the passband).

[0121] In Figure 8, the optical input signal IS is simulated as a wave of variable wavelength intensity characterized by four consecutive distinct peaks and zeroed outside each band. The remaining curves are the respective acquired signals AS.

[0122] In the examples of Figures 7 and 8, it can be seen that the respective acquired signal AS represents a convolution between the optical spectrum of the input optical signal IS and the overall transfer function of the optical filter stage FDTc.

[0123] To further improve the resolution of each acquired signal AS, the method illustratively includes performing a deconvolution routine of the acquired signal AS. This algorithm illustratively includes the following steps: - calculating the Fourier transform of the overall transfer function FDTc of the optical filter stage; - calculating the Fourier transform of the acquired signals AS (i.e. the respective signals representative of the optical intensity in the bands of the optical signal); - calculating for each passband the quotient between the Fourier transform of the acquired signal AS and the Fourier transform of the overall transfer function; - calculating the inverse Fourier transform of the quotient; Includes.

[0124] 9 and 10 show the results of the above-described deconvolution routine applied to the acquired signal AS of Figures 7 and 8, along with the corresponding optical input signal IS (shown as a dashed segment in Figure 9). The vertical axis represents optical intensity in dBm, and the horizontal axis represents frequency in THz.

[0125] Before applying the aforementioned algorithm, it is possible to observe how the resolution of the acquired signal is improved relative to the corresponding signal.

[0126] In FIG. 9, the peak of the acquired signal narrows to approximately match the input optical signal, whereas in FIG. 10, the acquired signal follows the input optical signal substantially exactly.

[0127] In particular, applicants have observed that in the example shown, the deconvolution routine described above has resulted in a resolution of about 10 GHz (FIGS. 7 and 8) down to about 4 GHz (FIGS. 9 and 10). What has been said above with reference to the method and deconvolution routine applies equally to the further optical filter stages.

Claims

1. An apparatus (1) for analyzing the optical spectrum of an optical signal, comprising: an optical filter stage (2) having an input port (3), an output port (4) and an optical path (5) extending from said input port (3) to said output port (4); a photodetector (17) optically connected to said optical filter stage (2) downstream of said output port (4); an actuator (18) coupled to the optical filter stage (2) and configured to change the optical refractive index of at least one section of the optical path (5) of the optical filter stage (2); Equipped with the optical filter stage (2) comprises a first Mach-Zehnder interferometer (6) and a first ring resonator (7) cascaded together to form respective portions of the optical path (5); the first Mach-Zehnder interferometer (6) comprises an input optical coupler (9), an output optical coupler (10), and a first optical branch (11) and a second optical branch (12) connecting the input optical coupler (9) to the output optical coupler (10); The difference in the optical paths between the first optical branch (11) and the second optical branch (12) of the first Mach-Zehnder interferometer (6) (dL ０ ) is greater than 0, the first Mach-Zehnder interferometer (6) is optically connected to the remainder of the optical path (5) of the optical filter stage (2) by a unique first port (13) of the input optical coupler (9) and by a unique second port (14) of the output optical coupler (10); Device (1).

2. The optical filter stage (2) comprises one or more second Mach-Zehnder interferometers (8) cascaded together to each other, each forming a respective portion of the optical path (5), each second Mach-Zehnder interferometer (8) comprising a respective input optical coupler (9'), a respective output optical coupler (10'), and a respective first optical branch (11') and a second optical branch (12') connecting the respective input optical coupler (9') to the respective output optical coupler (10'), and a respective optical path difference (dL) between the respective first optical branch (11') and second optical branch (12'). ｉ 2. The apparatus of claim 1, wherein: ∑ ∑ m ∑ ∑ m ∑ n ...

3. 3. The apparatus (1) according to claim 1, wherein the unique second port (14, 14') of the output optical coupler (10, 10') of each Mach-Zehnder interferometer (6, 8) is arranged in a cross configuration with respect to the unique first port (13, 13') of the input optical coupler (9, 9') of the respective Mach-Zehnder interferometer, the first ring resonator (7) is a single ring resonator of the optical filter stage (2), and the actuator (18) comprises multiple sub-actuators, each sub-actuator being coupled to a respective Mach-Zehnder interferometer (6, 8) or a respective ring resonator (7).

4. The difference in optical path length (dL) between the first optical branch (11) and the second optical branch (12) of the first Mach-Zehnder interferometer (6) ０ ) is a function of the bandwidth of the optical signal, and the difference in optical path (dL ０ 4. The apparatus (1) according to claim 1, wherein the difference between the first and second Mach-Zehnder interferometers (6) is such that a transfer function (FDT0) of the first Mach-Zehnder interferometer (6) has a free spectral range substantially equal to or greater than a width of the band of the optical signal.

5. The respective differences (dL ｉ ) is the difference (dL ０ ) and the difference in optical path length (dL ０ ) 2 ｉ times, where i is equal to the order of each of the second Mach-Zehnder interferometers (8), and the difference in optical path length (dL ０ ) is 1 μm or more, and the difference in the optical paths of the first Mach-Zehnder interferometer and each of the differences in the optical paths of the second Mach-Zehnder interferometers (8) (dL ｉ ) is 2 mm or less, and the radius (R) of the micro ring of the first ring resonator (7) is the difference (dL ０ ) and the perimeter of the microring of the first ring resonator (7) is a function of the difference (dL ０ ) 2 ｎ＋１ 3. The apparatus (1) of claim 2, wherein n is equal to a total number of second Mach-Zehnder interferometers (8).

6. 6. The device (1) according to claim 1, further comprising a pre-processing stage (19) for the optical signal upstream of the optical filter stage (2), the pre-processing stage (19) comprising a polarization separator (20) for separating a first polarization component (TE) from a second polarization component (TM) of the optical signal, the pre-processing stage (19) comprising a respective input port (21) and a respective first output port (22) and a respective second output port (23), the pre-processing stage (19) comprising a polarization rotator (24) for rotating the polarization of the second polarization component (TM) of the optical signal.

7. 7. The apparatus (1) of claim 6, further comprising a further optical coupler (25) interposed between the pre-processing stage (19) and the optical filter stage (2), wherein each of the first output port (22) and second output port (23) of the pre-processing stage (19) is optically connected to a respective first port (26) of the further optical coupler (25), and a sole second port (27) of the further optical coupler (25) is optically connected to the input port (4) of the optical filter stage (2), and wherein the apparatus (1) further comprises a first optical switch (28) and a second optical switch (29) interposed between the respective first output port (22) and second output port (23) of the pre-processing stage (19) and the corresponding first port (26) of the further optical coupler (25).

8. 7. The apparatus according to claim 6, wherein the optical filter stage (2) comprises a first 3 dB optical coupler (30) forming a respective part of the optical path (5) and interposed between the first Mach-Zehnder interferometer (6) and the first ring resonator (7), wherein a unique first port (31) of the first 3 dB optical coupler (30) is optically connected to the unique second port (14) of the output optical coupler (10) of the first Mach-Zehnder interferometer (6), a unique second port (32) of the first 3 dB optical coupler (30) is optically connected to the input port (15) of the first ring resonator (7), and a remaining second port (33) of the first 3 dB optical coupler (30) is optically connected to the second output port (23) of the pre-processing stage (19).

9. a further optical filter stage (40) having a further input port (41), a further output port (42) and a further optical path (43) extending from the further input port to the further output port, the further optical filter stage (40) comprising the first Mach-Zehnder interferometer (6) in common with the optical filter stage (2) and further ring resonators (44) cascaded with each other to form a respective part of the further optical path (43); the device (1) comprises a further photodetector (45) optically connected to the further optical filter stage (40) downstream of the further output port (42); the further optical filter stage (40) comprising a second 3 dB optical coupler (46) forming a respective part of the further optical path (43) and interposed between the first Mach-Zehnder interferometer (6) and the further ring resonator (44); 9. The apparatus (1) of claim 8, wherein a unique first port (47) of a second 3 dB optical coupler (46) is optically connected to the first output port (22) of the pre-processing stage (19), a remaining first port (48) of the second 3 dB optical coupler (46) is optically connected to an input port (61) of the further ring resonator (44), and a unique second port (49) of the second 3 dB optical coupler (46) is optically connected to the unique first port (13) of the input optical coupler (9) of the first Mach-Zehnder interferometer (6), the apparatus (1) comprising an optical isolator (50) arranged upstream of the pre-processing stage (19), and the actuator (18) is also coupled to the further optical filter stage (40) and configured to change the optical refractive index of at least one section of the further optical path (43) of the further optical filter stage (40).

10. 1. A method for analysis of an optical spectrum of an optical signal having a band, comprising: - providing a device (1) for analysis according to any one of claims 1 to 9; - introducing said optical signal as input into said device (1); - adjusting the optical filter stage (2) by means of the actuator (18) to move the passband of the optical filter stage (2) along the band of the optical signal; - obtaining, for each passband, by said photodetector (17), a respective signal representative of the optical intensity of said optical signal in said passband; - calculating said optical spectrum as a function of said respective signals representative of said light intensity; A method comprising:

11. and a deconvolution routine for the signal representing the light intensity, the deconvolution routine comprising: - determining the overall transfer function (FDTc) of said optical filter stage (2); - calculating the Fourier transform of the overall transfer function of the optical filter stage; - calculating the Fourier transform of each of said signals representing the light intensity within said bands; - calculating, for each passband, the quotient between the Fourier transform of the respective signal representing the light intensity and the Fourier transform of the total transfer function (FDTc) of the optical filter stage (2); - calculating the inverse Fourier transform of said quotient; The method of claim 10, comprising:

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