A method for spectral positioning of an optical system, and an optical system for performing the method.

Abstract

The present invention relates to a method for spectral positioning of an optical system, wherein the optical system performs the steps of: adjusting a control signal (V) to generate a digital control signal; processing the digital control signal to generate at least one digital signal referred to as a “first lock signal” representing the power of the principal component or second harmonic of the modulation frequency (Fd) present in the digital control signal; and processing the first lock signal (Vr1) to generate a digital adjustment command, wherein the second step (OP2) is to perform a second step aimed at optimizing the amplitude of the first lock signal (Vr1); and adjusting the digital adjustment command to generate an adjustment command (CLa) and applying the adjustment command to an adjustment device (H1).

Description

Technical Field

[0001]

[0001] The present invention relates to an optical system. More specifically, the present invention relates to a method for spectral positioning of an optical device comprising at least one laser light source and one filter. The filter can be a resonant ring filter, a Mach-Zehnder (MZ) interferometer filter, or can at least partially form a resonant ring modulator or an MZ modulator.

Background Art

[0002]

[0002] The state of the art includes a number of methods for aligning the resonant frequency of an optical filter with the emission frequency of a laser light source. Adjustment of the resonant frequency or the emission frequency can be carried out using a heater placed in proximity to the filter or the laser. The heater is controlled so as to "lock" the system, i.e., to match the emission frequency with the resonant frequency.

[0003]

[0003] In Non-Patent Document 1, a photodetector and a heater are associated with an individual filter within the system. A controller measures the current supplied by the photodetector at regular intervals and incrementally adjusts the heater control to maximize the generated current, thus attempting to align the laser emission frequency with the filter resonant frequency. Individual filters (or groups of filters) within the system have their own control loops (including the heater and the photodetector) and are thus locked individually.

[0004]

[0004] Non-patent document 2 also proposes a method for spectral positioning of a similar optical system, including multiple filters with heaters and a photodetector. According to the approach disclosed in this document, the resonant frequency of the filters is modulated using a square wave modulated signal. For each filter, an analog circuit calculates the product between the signal supplied by the photodetector and the modulated signal, filters out the harmonics, retains only the static portion of this product, and identifies whether the radiated frequency is below or above the resonant frequency according to the sign of this static portion. This information is used to adjust the control applied to the heater to reduce the difference between these two frequencies.

[0005]

[0005] With this approach, each filter in the optical system also has its own control loop (including heater and photodetector) and is therefore individually locked.

[0006]

[0006] When an optical system has several channels, i.e., several resonant frequencies and / or several emission frequencies that need to be locked together, these methods require as many photodetectors as there are channels. The presence of a photodetector for each individual channel to be locked makes the implementation of these approaches particularly complex, especially when the number of channels is large, for example, greater than 10 or 50. In contrast, in the approach where the modulation frequency is applied to a filter and its resonant frequency, multiple filters may be locked to a single emission frequency, but generally, it is preferable to lock each individual filter to its own emission frequency in order to form independent channels.

[0007]

[0007] Non-Patent Literature 3 proposes a technique for simultaneously locking the resonant frequency of an array of ring modulators to spectral lines of a frequency comb optical beam. As is well known, a ring modulator filters selected wavelengths from several wavelengths and modulates those selected wavelengths. In the aforementioned document, the lock is achieved by a single photodetector that taps the power of radiation circulating in an optical bus to which the modulators are coupled and the modulated WDM optical signal circulates. The optimization algorithm utilizes the RF portion of the optical power of the radiation, i.e., the power generated by the modulators, to establish a control signal for a heater associated with each of these modulators, and the control aims to maximize the RF optical power present in the optical bus.

[0008]

[0008] Once the optimization algorithm is initialized, each modulator is continuously tuned in an exhaustive search until a significant gradient is found in the measured RF power. In this respect, the gradient method is responsible for rapid convergence to the best heating bias. During this process, each modulator is locked. Once the last ring modulator is tuned, the algorithm tracks the temperature drift for each ring using the endless gradient method.

[0009]

[0009] The approach following this document is based on the assumption that the RF optical power is maximized when the resonant frequency of the modulator is well matched with the radiation frequency that forms the spectral line of the radiation. For this assumption to be met, it is essential that the data modulated by each modulator is uncorrelated. This approach also requires that the radiation frequencies be well separated from each other by at least 50 GHz in order to avoid several modulators being locked to a single radiation frequency.

[0010]

[0010] Another approach based on the modulation of a single photodetector and filter resonant frequency is presented in Non-Patent Literature 4. However, this approach requires device calibration, which makes the operation of the solution particularly cumbersome. The selection of modulation frequencies proposed in this document leads to the introduction of an error term into the feedback signal. This configuration carries the risk of locking several modulators to a single radiation frequency. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] "Error-free operation of a polarization-insensitive 4λ;x 25 Gbps silicon photonic WDM receiver with closed-loop thermal stabilization of Si microrings", Opt.Express 24, 13204-13209 (2016). [Non-Patent Document 2] "Wavelength Locking and Thermally Stabilizing Microring Resonators Using Dithering Signals", Journal of Lightwave Technology, vol. 32, No. 3, pp. 505-512, Feb.1, 2014. [Non-Patent Document 3] "Simultaneous wavelength locking of microring modulator array with a single monitoring signal", Opt.Express 25,16040-16046 (2017). [Non-Patent Document 4] Maarten Hattink, “Streamlined Architecture for Thermal Control and Stabilization of Cascaded DWDM Micro-Ring Filters Bus”, Optical Fiber Conference, March 6-10, 2022. [Overview of the project]

[0012]

[0011] One object of the present invention is to propose a method for spectral positioning of optical systems that is not limited by the prior art and is different from the prior art. More specifically, one object of the present invention is to propose a spectral positioning system that does not require the same number of photodetectors as the number of channels to be locked. Another object of the present invention is to provide a locking means to avoid multiple filters being locked to a single emission frequency of a multispectral radiation source.

[0013]

[0012] To achieve this objective, the present invention proposes a method for spectral positioning of an optical system, the optical system is - At least one laser light source that generates radiation having at least one radiation frequency, - Multiple filters, each having a resonant frequency, - At least one waveguide configured to optically couple the radiation generated by the laser source to the filter, - A photodetector optically coupled to the waveguide and receiving filtered radiation, wherein the photodetector generates a control signal, - A plurality of tuning devices associated with the laser light source and / or the filter, wherein each tuning device is controlled to modulate the at least one radiation frequency of the laser light source or the resonant frequency of the filter at a modulation frequency, and is controlled to adjust the resonant frequency of the filter.

[0014]

[0013] The above method is as follows: - To generate digital control signals by adjusting control signals, - A first operation which processes the digital control signal to generate at least one digital signal referred to as a "first lock signal" that represents the power of the second harmonic and / or principal component of the modulation frequency present in the digital control signal, - A second operation which processes the first lock signal and generates a digital adjustment command, wherein the second operation aims to optimize the amplitude of the first lock signal, - Perform an operation that includes adjusting the digital adjustment command to generate an adjustment command and applying it to the adjustment device.

[0015]

[0014] According to other advantageous non-limiting features of the present invention, the following may be done, either alone or in any technically feasible combination: - The first lock signal represents the power of the second harmonic of the modulation frequency, and the second operation is designed to maximize the amplitude of the first lock signal, or the first lock signal represents the power of the principal component of the modulation frequency, and the second operation is designed to minimize the amplitude of the first lock signal. - The first lock signal is formed by the ratio of the power of the second harmonic of the modulation frequency to the power of the principal component of the modulation frequency, and the second operation is designed to optimize the amplitude of the first lock signal so that the amplitude of the first lock signal is greater than or equal to a predetermined value. - The first operation generates at least one second lock signal representing the phase of the digital control signal of the principal component of the modulation frequency present in the digital control signal. - The second lock signal corresponds to the difference between the phase of the principal component of the modulation frequency present in the digital control signal and the phase of the modulation signal or reference signal. - The first operation involves the Fourier transform of the digital control signal. - The method includes the step of selecting a single adjustment device from among the adjustment devices, and the selection step is repeated to sequentially select each of the adjustment devices. - The modulation frequencies of the adjustment devices are different from each other. - The adjustment commands are applied to the adjustment devices one optical filter at a time.

[0016]

[0015] According to another aspect, the subject matter of the present invention proposes an optical system for spectral positioning of an optical device, said optical system comprising - at least one laser light source generating radiation having at least one emission frequency, - a plurality of filters each having a resonance frequency, - at least one waveguide configured to optically couple the radiation generated by said laser light source to said filters, - a photodetector optically coupled to said waveguide and receiving filtered radiation, said photodetector generating a control signal, said photodetector, - a plurality of adjustment devices associated with said laser light source and / or said filters, said adjustment devices being controlled to modulate the emission frequency of said laser light source or the resonance frequency of said filters at a modulation frequency, while being controlled to adjust the resonance frequency of said filters, said adjustment devices, - a lock device, and being configured to perform the following operations. i. Adjust said control signal to generate a digital control signal. ii. A first operation of processing said digital control signal to generate at least one digital signal, referred to as a "first lock signal", representing the power of the second harmonic and / or the main component of said modulation frequency present in said digital control signal. iii. A second operation of processing said first lock signal to generate a digital adjustment command, said second operation being aimed at optimizing the amplitude of said first lock signal, said second operation. iv. Adjust said digital adjustment command to generate an adjustment command and apply it to said adjustment device.

[0017] According to another advantageous non - limiting feature of the present invention, the following is done, either alone or according to any technically feasible combination. - The optical system comprises a single photodetector coupled to a waveguide. - The filter is a combined basic filter. - The optical device is a wavelength - tunable laser. - The optical device is an optical router. - The laser source comprises a plurality of lasers emitting a plurality of emission frequencies. - The adjustment device associated with the source laser is controlled to modulate the source emission frequency, and the adjustment device associated with the filter is controlled to adjust the resonance frequency of the filter.

Brief Description of the Drawings

[0018]

[0017] Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings. [Figure 1a]

[0018] It is a schematic diagram of the principle underlying the present invention. [Figure 1b]

[0019] It is a schematic diagram of the principle underlying the present invention. [Figure 1c]

[0020] It is a schematic diagram of the principle underlying the present invention. [Figure 1d]

[0021] It is a schematic diagram of the principle underlying the present invention. [Figure 1e]

[0022] It is a schematic diagram of the principle underlying the present invention. [Figure 1f]

[0024] It is a diagram showing a locking device capable of implementing the method according to the present invention. [Figure 1g]

[0025] It is a diagram showing the first part of a locking device capable of implementing the first operation mode. [Figure 1h]

[0026] It is a diagram showing a modification of the process implemented by the locking device of FIG. 1g. [Figure 1i]

[0027] This figure shows a modified example of the process implemented by the locking device of Figure 1g. [Figure 1j]

[0023] This is a schematic diagram illustrating the fundamental principle of the present invention. [Figure 2a]

[0028] This figure shows a modified example of the first embodiment of the present invention, which uses time-division multiplexing. [Figure 2b]

[0029] This figure shows a modified example of the first embodiment of the present invention, which uses time-division multiplexing. [Figure 2c]

[0030] This figure shows a modified example of the first embodiment of the present invention, which uses time-division multiplexing. [Figure 2d]

[0031]

[0032] This figure shows a modified example of the first embodiment of the present invention that uses time-division multiplexing. [Figure 3a]

[0033] This figure shows a modified example of a second frequency division multiplexed embodiment of the present invention. [Figure 3b]

[0034] This figure shows a modified example of a second frequency division multiplexed embodiment of the present invention. [Figure 3c]

[0035] This figure shows a modified example of a second frequency division multiplexed embodiment of the present invention. [Figure 3d]

[0036]

[0037] This figure shows a modified example of a second frequency division multiplexed embodiment of the present invention. [Figure 4a]

[0038] This figure shows a first embodiment of the method according to the present invention. [Figure 4b]

[0039] This figure shows a first embodiment of the method according to the present invention. [Figure 4c]

[0040] This figure shows a first embodiment of the method according to the present invention. [Figure 4d]

[0041] This figure shows a first embodiment of the method according to the present invention. [Figure 4e]

[0042] This figure shows a first embodiment of the method according to the present invention. [Figure 4f]

[0043] This figure shows a first embodiment of the method according to the present invention. [Figure 4g]

[0044] This figure shows a first embodiment of the method according to the present invention. [Figure 4h]

[0045] This figure shows a first embodiment of the method according to the present invention. [Figure 5a]

[0046] This figure shows a second application example of the method according to the present invention. [Figure 5b]

[0047] This figure shows a second application example of the method according to the present invention. [Figure 6a]

[0048] This figure shows a third application example of the method according to the present invention. [Figure 6b]

[0049]

[0050] This figure shows a third application example of the method according to the present invention. [Modes for carrying out the invention]

[0019]

[0051] Figures 1a, 1b, 1c, 1d, and 1e are schematic diagrams of the fundamental principles of the present invention. In the optical system architecture illustrated in Figure 1a, the light radiation from a tunable laser La is directed to a ring resonator MR that forms a filter at resonant frequency F0 and a photodetector PD downstream of the resonator MR. Therefore, the optical system includes a waveguide WG configured to optically couple the radiation generated by the laser light source La to the filter MR and the photodetector PD.

[0020]

[0052] In the example shown in Figure 1a, the laser light source La is a tunable laser. The term “tunable laser” refers to a laser that produces light emission whose frequency (“radiation frequency”) can be tuned via a device H for tuning the radiation frequency. This tuning device H may be configured to change the light source supply current, operating temperature, optical index, and / or free carrier concentration. A tunable laser may comprise multiple devices for tuning its radiation frequency, such as a tunable current source and a heater for changing the operating temperature of the laser.

[0021]

[0053] A modulator M connected to a laser emission frequency adjustment means is configured to modulate the emission frequency Fla of the light emission emitted by the tunable laser La by a modulation frequency Fd. This modulation frequency Fd, for example 5 kHz, is low compared to the laser emission frequency, for example 200 terahertz. The amplitude of this modulation is also low, on the order of gigahertz. As an example, a modulation amplitude of 1 mA of the laser light source supply current La can result in a variation of the emission frequency FLa on the order of plus or minus 1 GHz. Thus, the frequency of the light emission emitted by the tunable laser La varies around its fundamental frequency FLa with a very low frequency Fd and a low amplitude A (1 GHz). Thus, the laser frequency varies as Fla + Acos(2pi·Fd·t).

[0022]

[0054] The modulator M can be selectively activated via a selection signal SEL; that is, depending on the state of this signal, the modulator M is activated to effectively modulate the laser emission frequency La, or the modulator is deactivated to not modulate the laser emission frequency La.

[0023]

[0055] Figure 1b shows the frequency-domain transfer function T of a filter MR whose spectrum TF has a resonant frequency F0, and the signal V supplied by the photodetector PD when the radiation frequency FLa of the tunable laser La is not locked to the resonant frequency F0 of the resonator MR, but has a higher radiation frequency FLa than the resonant frequency F0. Since the radiation frequency of the tunable laser La lies in the relatively linear portion of the transfer function of the resonator MR, the control signal V supplied by the photodetector PD has a principal component Fd (corresponding to the modulation frequency) that is relatively large in the frequency domain with respect to its harmonics, especially the second harmonic 2*Fd. In addition, the phase Phi of the principal component Fd of the control signal V is reduced; that is, this principal component is in phase with the modulation signal supplied by the modulator M.

[0024]

[0056] Similar to Figure 1b, Figure 1c shows the transfer function T of a filter MR whose spectrum TF has a resonant frequency F0, and the control signal V supplied by the photodetector PD when the emission frequency FLa′ of the tunable laser La matches the resonant frequency F0 of the resonator MR. In this case, the emission frequency FLa′ of the tunable laser La is located in a relatively nonlinear portion of the transfer function of the resonator MR. As a result, the control signal V supplied by the photodetector PD has a second harmonic component 2*Fd that is relatively large with respect to the modulation frequency Fd in the frequency domain.

[0025]

[0057] Finally, Figure 1d shows the frequency-domain transfer function T of the filter MR, whose spectrum TF has a resonant frequency F0, and the control signal V supplied by the photodetector PD when the radiation frequency FLa of the tunable laser La is not locked to the resonant frequency F0 of the resonator MR, but has a radiation frequency Fla'' lower than this resonant frequency F0. Since the radiation frequency of the tunable laser La lies in the relatively linear portion of the transfer function of the resonator MR, the control signal V supplied by the photodetector PD has a principal component Fd that is relatively large in the frequency domain relative to its harmonics, especially the second harmonic 2*Fd. Furthermore, the phase Phi+Pi of the principal component Fd of the control signal V is important, i.e., this principal component is out of phase with the modulated signal provided by the modulator M.

[0026]

[0058] Figure 1j summarizes the results of Figures 1b, 1c, and 1d, and in the upper graph, it shows the change in power present in the principal component Fd and the second harmonic 2*Fd of the signal V supplied by the photodetector when the emission frequency FLa of the tunable laser La is changed and the resonant frequency of the filter remains fixed (or vice versa). Figure 1j also shows the change in phase of the principal component Fd of the signal V supplied by the photodetector in the lower graph.

[0027]

[0059] Returning to the schematic diagram in Figure 1a, the locking device R receives and processes the control signal V supplied by the photodetector PD to generate a command CLa for the tunable laser La to tune its emission frequency and lock to the resonant frequency F0 of the resonator MR. The locking device R also generates a selection signal Sel, which allows the modulator M to be activated or deactivated. Optionally, the locking device may have an additional input V′ for collecting a value representing the power emitted by the laser via a photodetector located upstream of the filter MR in the optical path, for example, near the laser La.

[0028]

[0060] Figure 1f shows the lock device R in one of the operating modes of the lock device. This device comprises a first part R1 suitable for operating the optical system 1 in a first operating mode, during which the modulator M is activated. Thus, in this first mode, the lock device R activates the selection signal Sel. Also in this first mode, the lock device R generates an adjustment command from a first lock signal Vr1 representing the power of the second harmonic of the modulation frequency present in the control signal V. This first operating mode will be described in detail in later sections of this specification, but generally speaking, as described in relation to the descriptions of Figures 1b, 1c, and 1d, this operating mode takes advantage of the fact that the radiated frequency Fla and the resonant frequency F0 coincide when the control signal has the largest second harmonic 2*Fd.

[0029]

[0061] While this operating mode is particularly efficient, the modulator can potentially lead to disruption of the payload data transmission channel.

[0030]

[0062] Furthermore, to avoid continuous operation of the control device in the first operating mode, the lock device R also includes a second part R2 that can operate the optical system 1 in a second operating mode in which the modulator M is deactivated. In this second operating mode, the modulator M is deactivated. Therefore, in this second operating mode, the selection signal Sel is deactivated by the lock device R. Also in this second mode, the lock device R generates an adjustment command CLa from a third lock signal representing the power present in the control signal V. This second part can implement a gradient method, i.e., it can generate an adjustment command CLa aimed at maximizing the control signal V. If the lock device R has an additional input V′ for collecting a quantity representing the power radiated by the laser, the gradient method can be applied to a function that takes into account the control signal V and the additional input V′. This can be the difference V′-V or the ratio V / V′ of these two quantities, which can be maximized or minimized.

[0031]

[0063] The second part R2, capable of implementing the second operating mode, may be a microcontroller, a signal processing microprocessor, an FPGA, or any other computing device. This computing device may be the same as the one operating in the first part R1 of the lock device, as detailed in the following sections of this disclosure. The gradient step implemented by the computing device in the second operating mode is well known in itself and requires no further explanation.

[0032]

[0064] The lock device R also includes a state machine ME that generates a selection signal Sel for switching between two operating modes. For example, the state machine ME can be configured to operate the lock device in a first operating mode for a predetermined period when the system is started, and then switch to a second operating mode.

[0033]

[0065] This switching can be based on criteria other than elapsed time; for example, the lock performance can be judged by when the control signal reaches a target value, or when the measured value extracted from this control signal reaches a target value.

[0034]

[0066] The switch to the second operating mode may be permanent. Alternatively, the state machine ME of the lock device R may alternate between the first and second operating modes periodically or according to changes in performance criteria.

[0035]

[0067] An optical system equipped with such a locking device benefits from both the performance of a first operating mode that locks system 1 into nominal operation and the fact that it is permanently unaffected by transmission interference caused by the operation of modulator M.

[0036] First part R1 of the locking device

[0068] This first part R1 of the lock device, shown in Figure 1g, comprises a first adjustment section for a control signal V supplied by the photodetector PD. This first part includes an amplifier Am, a filter BP, and a digital converter ADC, which supply a digital control signal Vn. In this part, the control signal V supplied by the photodetector PD is received by the amplifier Am, which is, for example, a transimpedance amplifier or a logarithmic amplifier. The amplified control signal V is applied to a filter BP, such as a bandpass filter, over an operating frequency range defined by a minimum cutoff frequency and a maximum cutoff frequency. The operating frequency range is selected to include the modulation frequency and its second harmonic. That is, the maximum cutoff frequency is selected to be at least twice the modulation frequency Fd. The signal generated by the filter is sampled by the ADC (analog-to-digital converter) to generate a digital control signal Vn. The sampling frequency is selected to be greater than twice the maximum cutoff frequency of the filter BP (e.g., 2 to 10 times), i.e., much greater than four times the modulation frequency Fd. For example, if the modulation frequency (or, as will be described later, the maximum modulation frequency if multiple frequencies are used) is 30 kHz, a sampling frequency of 128 kHz or higher may be selected.

[0037]

[0069] The digital control signal Vn is processed by a computing device MP, which is a microcontroller, signal processing microprocessor, FPGA, or any other computing device. The computing device generates at least one digital signal known as the "lock signal" to form an adjustment command CLa for the frequency adjustment device. In the example shown in Figure 1f, this adjustment control CLa is formed by a second adjustment section of the digital adjustment control CLa, which in this case is comprised of a digital-to-analog converter DAC.

[0038]

[0070] Of course, the first and second adjustment units may also include other elements in addition to, or instead of, those elements exemplified in Figure 1g. In particular, the ADC and DAC converters can be integrated into the computing device MP rather than the signal adjustment unit.

[0039]

[0071] In very general terms, the computing device MP performs processing using the results shown in Figures 1b, 1c, and 1d to determine a command CLa applied to the laser radiation frequency adjustment means H, with the aim of maximizing the portion of the signal contained in the second harmonic 2*Fd of the control signal supplied by the photodetector PD. As explained in relation to these Figures 1b, 1c, and 1d, when this portion of the signal contained in the second harmonic 2*Fd is maximized, the system is properly locked, i.e., the radiation frequency Fla matches the resonant frequency F0. As clearly shown in Figure 1j, the proportion of the signal contained in the principal component and the proportion of the signal contained in the second harmonic 2*Fd are related, so one and / or the other can be used as needed. It should also be noted that phase can be used to complement either of these signal proportions.

[0040]

[0072] Generally speaking, the control CLa is determined by optimizing a function that takes into account the proportion of the signal present in the principal components and / or second harmonics 2*Fd of the control signal V, and / or the proportion of the principal component Fd. The optimization criteria may be that the function reaches a target value, falls below a predetermined upper limit, or exceeds a predetermined threshold.

[0041]

[0073] For example, the ratio of the signal present in the second harmonic to the signal present in the principal component Fd can be set to be equal to the target value, or to maximize the target value.

[0042]

[0074] For accuracy, the system is described as "locked" when the selected optimization criteria are met. This corresponds to the case where the radiation frequency Fla and the resonant frequency F0 coincide, or where these frequencies are offset from each other by a specified distance.

[0043]

[0075] Returning to the explanation of Figure 1g, the process implemented by the computing device MP is: - A first operation OP1 processes a digital control signal to generate at least one digital signal Vr1, referred to as the "first lock signal," which represents the power of the second harmonic of the modulation frequency present in the digital control signal Vn. - A second operation OP2 that processes a first lock signal Vr1 to generate a digital adjustment command CLan, the second operation OP2 includes a second operation aimed at optimizing an optimization function with respect to the first lock signal Vr1.

[0044]

[0076] For example, the second processing operation OP2 may aim to maximize the amplitude of the first lock signal Vr1.

[0045]

[0077] Figure 1h shows operations OP1 and OP2 implemented by the computing device MP according to the first approach. The first operation OP1 for processing a digital control signal Vn includes a first time window processing step W followed by a second frequency domain transformation step T. This second step T may be a Fast Fourier Transform, but any other digital transformation in the frequency domain may be preferred. This transformation may provide a spectral distribution of power and phase, but in the first approach shown in Figure 1g, only power information is utilized. As is well known, the purpose of the window processing step W is to determine the portion of the digital control signal Vn to which the frequency transformation is applied, and optionally to adjust this sequence. This may be a simple rectangular window, a Hanning window, or a Hamming window. The length of this time window, i.e., the number of time samples held in the portion of the digital control signal Vn to which the frequency transformation is applied, defines the frequency resolution of the signal generated at the end of the transformation step T, and thus the possibility of identifying the power present in the frequency range. For example, if the sampling frequency is 125 kHz and the length is 1024 samples, the resolution of the digital signal generated by the conversion step T is 125 Hz. Returning to the description of the first operation OP1 shown in Figure 1g, the conversion step T is followed by a selection step S, in which a sample corresponding to the second harmonic 2Fd of the modulated signal Fd is selected from the signal generated by the conversion step. Thus, this selection step S results in the generation of a digital signal Vr1, which will be referred to as the "first lock signal" in the following parts of this specification, and this first lock signal represents the power of the second harmonic of the modulation frequency present in the digital control signal Vn. If the control signal V contains multiple modulated signals, the selection step generates multiple samples, each individual sample corresponding to the second harmonic of one modulated signal, as will be discussed in detail later. In this case, the first operation OP1 provides multiple first lock signals, each individual signal associated with a specific modulated signal.

[0046]

[0078] The first lock signal Vr1 can correspond to the power of the second harmonic of the modulation frequency present in the digital control signal Vn. More generally, this lock signal can correspond to any function whose argument is the power of this second harmonic. In particular, this function can be the ratio of the proportion of the signal at the second harmonic to the proportion of the signal at the fundamental frequency.

[0047]

[0079] Figure 1h also shows a second operation OP2 implemented by the computing device MP according to the first approach. This second operation OP2 processes the first lock signal Vr generated during the first operation OP1. During the first comparison step, the value of sample Vr1(n) of the first lock signal Vr1 generated at time n is compared with the value of sample Vr1(n-1) generated and held at the previous time n-1. Depending on the result of this comparison, the digital adjustment command Clan generated at the previous time n-1 is incremented or decremented by a predetermined increment value Delta to generate this digital command at time n. Thus, it is understood that this second operation OP2 aims to maximize the amplitude of the first lock signal Vr1 (representing the power of the second harmonic of the modulation frequency in the digital control signal Vn) by changing the digital adjustment command Clan upward or downward. If multiple modulated signals are incorporated into the control signal V, and therefore multiple first lock signals Vr1 are generated in the first operation as shown in the previous paragraph, then multiple second operations are executed simultaneously, and in each second operation, the multiple first lock signals Vr1 generated in the first operation are processed.

[0048]

[0080] The second comparison step can be performed in a different way than the simple comparison between two consecutive samples shown in this example, resulting in maximizing the amplitude of the first lock signal Vr1. This comparison step is selected according to the chosen optimization criterion, i.e., maximizing, minimizing, or making the lock signal equal to a predetermined value.

[0049]

[0081] Figure 1i shows operations OP1 and OP2 implemented by the computing device MP according to the second approach. The first operation OP1 for processing the digital control signal Vn includes the same first window processing step W and second frequency domain conversion step T as in the first approach. These steps are followed by two simultaneous selection steps S1 and S2 that generate two lock signals Vr1 and Vr2. The first selection step S1 that generates the first lock signal Vr1 is identical to the selection step in the first approach. During the second selection step S2, a sample corresponding to the phase of the modulation frequency Fd (fundamental wave) is selected from the signal generated by the conversion step. Thus, this selection step S2 results in the generation of a digital signal Vr2, which will be referred to as the "second lock signal" in the following parts of this specification, and which represents the phase of the fundamental wave of the modulation frequency present in the digital control signal Vn.

[0050]

[0082] Figure 1i also shows a second operation OP2 implemented by the computing device MP according to the second approach. This second operation maintains the principle described in detail in the first approach and aims to optimize the amplitude of the first lock signal Vr1 by increasing or decreasing the digital adjustment command Clan. The step of incrementing or decrementing the increment value Delta of the digital adjustment command generated at the previous time n-1 is used to generate this digital command at time n. However, in this second approach, the sign Si applied to the increment value Delta is determined by a comparison step between the second lock signal Vr2 and the phase Phi of the modulated signal. As mentioned above, this phase comparison makes it possible to determine the relative position of the filter's radiation frequency and resonant frequency. The increment value Delta is determined by a metric function f applied to the first lock signal Vr1. As an example, this function may determine the total power measured in the spectrum, or the ratio of the power present in the second harmonic to the power at the fundamental frequency. Of course, it is also possible to define the second lock signal Vr2 as the difference between the phase of the principal component of the modulation frequency present in the digital control signal Vn and the phase Phi of the modulation signal.

[0051]

[0083] If the control signal V incorporates multiple modulated signals, the same principle as the first approach applies, where multiple first and second lock signals Vr1, Vr2 are provided at the end of the first operation OP1, and each pair of lock signals Vr1, Vr2 is processed by instances of the second operation OP2, which are executed simultaneously.

[0052]

[0084] In one modified example, the second operation OP2 can generate a digital adjustment command CLan based solely on the processing of the second lock signal Vr2. This second operation OP2 then generates the command CLan using this second lock signal Vr2. In particular, a first spectral positioning phase based solely on the second lock signal Vr2 and a subsequent second spectral positioning phase based on the first lock signal Vr1 can be considered. In this second phase as well, it is possible to utilize the second lock signal Vr2 as described above.

[0053]

[0085] In concluding this section on the general principles applicable to the first operating mode, it should be noted that applying a sinusoidal modulated signal using modulator M, i.e., applying spectrally pure modulation to the radiated frequency, suppresses the generation of harmonics in the control signal V supplied by photodetector PD (compared to, for example, square wave modulation). Therefore, the harmonics detected by the first portion R1 of lock device R are a good indicator of the lock quality between the radiated frequency and the resonant frequency.

[0054]

[0086] Furthermore, it should be noted that the same locking principle can be applied to a configuration in which the laser emission frequency is fixed and the adjustment device H is associated with the filter MR to adjust the resonant frequency. Such a configuration is shown in Figure 1e. In this case, the adjustment device H may be a heater, which can adjust the operating temperature of the filter and, consequently, the resonant frequency.

[0055]

[0087] Finally, the modulator M does not need to be a separate component from the optical system 1; for example, it can be integrated into the lock device R itself, which then generates the modulated signal and applies it to the tuning device H used for modulating the radiation frequency or the resonant frequency. If the same tuning device H is used for both modulating and tuning the laser's radiation frequency or the filter's resonant frequency, the lock device R can simply add the modulated signal and the control signal and apply this resulting signal to this single tuning device H.

[0056]

[0088] The principle of the first operating mode of the locking device described above is particularly useful when it is necessary to lock multiple elements in the optical system 1 together. This is especially useful when the optical system 1 consists of multiple filters, as shown in Figures 2a, 2c, and 3a. It is also useful when the optical system consists of a filter formed by combining multiple basic filters, as shown in Figures 2b and 3b. In either case, it is preferable to use a single photodetector PD to adjust at least one emission frequency of at least one laser light source La and at least one resonant frequency of at least one filter MR to lock them together.

[0057] Time-division multiplexing

[0089] In a first implementation embodiment of the first operating mode, the optical system 1 comprises a plurality of selectively controllable tuning devices H, each associated with a plurality of filters or a plurality of laser light sources. A spectral positioning method for the optical system 1 includes the step of selecting a single tuning device H associated with a filter on which a locking operation is performed.

[0058]

[0090] In the examples shown in Figures 2a and 2b, multiple microring filters MR1, MR2, and MR3 are coupled to a waveguide WG. In these examples, a laser light source La is located upstream of waveguide WG, WG1, and a photodetector PD is located downstream of this waveguide WG (Figure 2a) or complementary waveguide WG2 (Figure 2b). The photodetector PD is coupled to waveguide WG or the complementary waveguide to capture at least a portion of the light radiation propagating through waveguide WG or the complementary waveguide. In the example shown in Figure 2a, the laser light source La emits radiation with multiple emission frequencies and attempts to tune each filter MR1, MR2, and MR3 to one of the emission frequencies of the laser light source La. In the example shown in Figure 2b, the laser light source emits light radiation with a single emission frequency or multiple emission frequencies and attempts to tune each basic filter MR1, MR2, and MR3 to one of the emission frequencies of the laser light source in order to adjust the overall transfer function of the filters.

[0059]

[0091] The modulator M is preferably spectrally pure and therefore produces a modulated signal Vd having a single modulation frequency Fd. This modulated signal is selectively applied to only one of the regulating devices H, in this case the heaters, by a selection signal Sel.

[0060]

[0092] Simultaneously, the lock device R receives the control signals supplied by the photodetector PD and supplies the control signals CL1, CL2, and CL3 to the selected tuning device H. Thus, the lock device R is configured to control the modulator M and, using the selection signal Sel, select the tuning device H to which the modulation signal Vd and command signals CL1, CL2, and CL3 are applied. Consequently, the lock device selects the filters MR1, MR2, and MR3 whose resonant frequencies are tuned.

[0061]

[0093] Figure 2c shows another implementation example of time-division multiplexing. In this particularly advantageous example, a single radiation frequency is modulated using a modulation signal Vd applied from modulator M to tuning device H associated with the laser of light source La. Lock device R receives control signals V supplied by photodetector PD and controls tuning devices H associated with filters MR1, MR2, and MR3 to adjust and lock the resonant frequencies of these filters to the selected laser radiation frequencies.

[0062]

[0094] The laser light source La comprises multiple lasers La1, La2, and La3, each emitting light with different emission frequencies F1, F2, and F3. Each individual laser can be associated with a tuning device H, which preferably constitutes its current source. The radiation from the lasers is combined by an optical mixer MO to produce multispectral light with multiple emission frequencies. A modulation signal Vd is selectively applied to the tuning device H corresponding to any one of the lasers La1, La2, and La3 of the light source La to modulate the emission frequency of that laser. Simultaneously, a lock device R receives a control signal supplied by a photodetector PD and supplies control signals CL1, CL2, and CL3 to the tuning device H associated with any one of the filters MR1, MR2, and MR3 to lock the filters MR1, MR2, and MR3 to the emission frequencies of the lasers.

[0063]

[0095] Figure 2d shows a modified version of the example shown in Figure 2c, which is suitable when the laser light source La and filters MR1, MR2, and MR3 are composed of separate optical components that cannot communicate with each other. In this modified version, a portion of the multispectral light emission propagating along the waveguide WG is sampled upstream of the multiple filters MR1, MR2, and MR3. The input photodetector PDin measures a portion of this light emission and generates a reference signal Vr, which is supplied to the locking device R.

[0064]

[0096] In this case, the lock device R can combine the information present in the control signal V and the reference signal Vr to generate a first lock signal Vr1 and / or a second lock signal Vr2.

[0065]

[0097] After the reference signal Vr has been transformed in the frequency domain (for example, using the Fast Fourier Transform), these processes can attempt to establish the phase and power present in the fundamental and / or second harmonic of the modulation frequency present in the reference signal Vr.

[0066]

[0098] The first lock signal Vr1 can be constructed as the ratio of the power present in the fundamental frequency (modulation frequency Fd) of the reference signal to the power present in the fundamental frequency of the control signal. Alternatively, the first lock signal Vr1 can be defined as the ratio of the power present in the second harmonic of the modulation frequency Fd of the reference signal Vr to the power present in the second harmonic of the modulation frequency Fd of the control signal V. More generally, the first lock signal Vr1 can be a combination of any information extracted from the control signal V and the reference signal Vr. Using the same principle, it is possible to form a second lock signal Vr2 by combining the phase information at the modulation frequency Fd (fundamental frequency) of the reference signal Vr with the control signal V. This may include taking the phase difference between these two.

[0067]

[0099] The second lock signal Vr2 can correspond to the difference between the phase of the principal component of the modulation frequency Fd present in the digital control signal Vn and the phase of the reference signal (Vr).

[0068]

[0100] In all the time-division multiplexing examples shown in Figures 2a to 2d, the state machine of the locking device R can be configured to set a selection signal Sel that cyclically selects one of the tuning devices H connected to the modulator M during a series of locking periods, typically lasting from a few microseconds to a few milliseconds. During each individual locking period, the locking device R performs the locking operation described above, locking the resonant frequency F0 of the filter or fundamental filter to the laser emission frequency La. At the end of a complete cycle, the individual filters or fundamental filters MR1, MR2, and MR3 are locked to the laser emission frequency La.

[0069] Frequency multiplexing

[0101] In this second implementation embodiment of the first operating mode, the optical system 1 also includes multiple tuning devices H associated with multiple filters MR1, MR2, MR3 and / or multiple lasers La1, LA2, La3, respectively. A locking device R also simultaneously generates multiple control signals CL1, CL2, CL3, each of which is applied to the filter tuning devices H. To enable this, the modulation frequencies Vd1, Ve2, Ve3 applied to the tuning devices H by multiple modulators M1, M3, M3 are different from each other.

[0070]

[0102] Figures 3a to 3d show the optical system 1 of the aforementioned example, comprising multiple microring filters MR1, MR2, and MR3, and heaters H associated with these filters. In the cases of Figures 3a and 3c, the laser La produces radiation with multiple emission frequencies. In the case of Figure 3b, the laser La produces radiation with a single emission frequency. In both examples, a single photodetector PD generates a control signal V.

[0071]

[0103] In the embodiments shown in Figures 3a to 3d, filters or basic filters MR1, MR2, and MR3 are simultaneously locked to the laser emission frequency La by frequency multiplexing. For this purpose, the system comprises multiple modulators M1, M3, and M3, each of which is preferably spectrally pure and thus generates modulated signals Vd1, Ve2, and Vd3 having a single modulation frequency. Since this single modulation frequency is different for each modulator, the resonant frequencies of the filters (Figures 3a and 3b), or the laser emission frequencies (Figures 3c and 3d), can be modulated using different modulation frequencies and placed within the line spectrum generated by the locking device R during the first operation OP1. For example, the modulation frequencies can be configured in the range of 1 kHz to 30 kHz and can be varied in steps. Therefore, in this embodiment, it is not necessary to control the modulators M1, M2, and M3 via a time-selection signal. The modulation frequencies should be selected not only to be different from each other but also to their second harmonics in order to avoid spectral overlap with the second harmonics of other modulation frequencies. In the example shown in Figure 3d, the optical system 1 includes an input photodetector PDin that measures a portion of the light radiation propagating along the waveguide WG upstream of the optical filters MR1, MR2, and MR3 to generate a reference signal Vr supplied to the lock device R.

[0072]

[0104] As described above, the lock device R can generate a first lock signal Vr1 and / or a second lock signal Vr2 by combining the information present in the control signal V and the reference signal Vr.

[0073]

[0105] The processing implemented by the first part R1 of the lock device R is naturally applicable to this embodiment but is based on the same principles described above. In particular, this processing operation makes it possible to identify lines (fundamental and harmonics) in the spectrum, prepare multiple first lock signals, and associate them with each filter. The first part R1 of the lock device R is also configured to implement multiple operations associated with each lock signal to simultaneously generate multiple tuning commands CL1, CL2, and CL3 of the tuning device H associated with filters MR1, MR2, and MR3.

[0074] First application example

[0106] Figure 4a shows an example of an application of optical device 1 that can enjoy the advantages of the spectral positioning method according to the present invention. In this example, the laser light source La consists of a bank of lasers La1, La2, and La3, where each laser emits light with different emission frequencies F1, F2, and F3 from the other lasers. These rays are recombined by a mixer MO to produce multiple rays, each ray having the emission frequencies F1, F2, and F3 coupled. One of these rays is utilized by being coupled, at least partially, to a filter MR and then to a photodetector PD via a waveguide WG. The filter MR has resonant frequencies F0i, F0j, and F0k at regularly spaced intervals.

[0075]

[0107] Each individual laser, La1, La2, and La3, is associated with a current source that generates its respective supply current, and each current source constitutes a laser radiation frequency tuning device in the sense of the present invention. The frequency of the associated lasers is modulated or tuned by modulating or adjusting the current generated by the current source. As described above, the tuning device may take forms other than those illustrated herein.

[0076]

[0108] As shown on the left side of Figure 4b, the emission frequencies of the bank's lasers are not necessarily uniformly frequency-separated, and variations in spectral deviation between laser pairs can be problematic. To compensate for this and obtain the configuration shown on the right side of Figure 4b, the optical device can be fitted with a locking device R that implements the operation constituting the spectral positioning method of the present invention. The locking device R can operate in either a first (time-division multiplexing) mode or a second (frequency-division multiplexing) mode. During operation of the optical system thus formed, the laser emission frequencies are adjusted to the resonant frequency of the filter MR, and the spectral deviation is regularized.

[0077]

[0109] Figure 4c shows a modified example of the first application. The laser light source La has at least one output port (two ports P1 and P2 in Figure 4c), each generating multispectral light emission RLM. Thus, this emission consists of multiple spectral lines separated by a variable spectral interval. At least one of these spectral lines is frequency-modulated, as described in detail in connection with the descriptions of Figures 2c and 3c.

[0078]

[0110] Each individual laser, La1, La2, and La3, is associated with a current source H connected to a modulator M, which forms a means for adjusting its radiation frequency. Lasers La, Lb, and Lc are coupled to an optical mixer MO via a waveguide network located inside the light source La. The multispectral light radiation RLM generated by the optical mixer MO is guided by the internal waveguide network to ports P1 and P2 of the light source La. The multispectral light radiation RLM propagates through external waveguides coupled to these ports P1 and P2.

[0079]

[0111] The external waveguide itself is coupled to ports P1 and P2 of optical components MRA1 and MRA2, which are optically positioned downstream of the light source La. Each optical component comprises multiple optical filters MR, each having an individually tunable resonant frequency.

[0080]

[0112] In the example shown in Figure 4c, two radio frequency modulators MRA1 and MRA2, each implementing a micro-resonator array, are optically connected to two ports p1 and P2 of a laser light source La. As is well known in the field of telecommunications, radio frequency modulators are used to condition individual spectral lines of multispectral light emission in order to transmit information signals using frequency division multiplexing (here, using micro-resonators tuned to each of these lines). However, this aspect of the present invention is not limited to optical components implementing radio frequency modulators, but applies to any optical component with multiple optical filters that are advantageous for locking to the frequency of light emission.

[0081]

[0113] To enable locking of the optical system S, the resonators MR of the resonator network of radio frequency modulators MRA1 and MRA2 are each associated with heaters H, forming tuning devices for adjusting the resonant frequencies of these resonators MR, in particular tuning devices for locking the resonators MR to the spectral lines they are associated with. In this way, the optical components MRA1 and MRA2 can be tuned to the light source La. Furthermore, optically downstream of the optical components MRA1 and MRA2, single monitoring photodetectors PD1 and PD2 are provided to establish electrical signals V1 and V2 representing the multispectral radiation RLM1 and RLM2 generated by these components. For this purpose, it is possible to sample a small amount of this multispectral radiation RLM1 and RLM2 and couple it to the monitoring photodetectors PD1 and PD2.

[0082]

[0114] The locking device R collects signals V1 and V2 supplied by the monitoring photodetectors PD1 and PD2, and generates control signals Cd11, Cd12, Cd13, Cd21, Cd22, and Cd23 that enable the tuning device H to control the optical filters MR that constitute the optical components MRA1 and MRA2, thereby allowing their resonant frequencies to be individually adjusted in order to lock to the radiation frequency of the light source La.

[0083]

[0115] In the optical system 1 including a radio frequency modulator, the objective is to position the resonant frequencies F01, F02, and F03 of the individual micro-resonators to the spectral lines FLa, FLb, and FLc of the multispectral radiation generated by the light source La, in accordance with the configuration shown in Figure 1a, i.e., in the linear portion of the transfer function TF1-TF3 of the micro-resonators MR. Naturally, the objective is to assign different emission lines to the individual micro-resonators. As shown in Figure 4d, the tuning means H associated with the micro-resonator MR is used to adjust the original resonant frequencies F01, F02, and F03 to their respective optimized frequencies F01′, F02′, and F03′.

[0084]

[0116] Figure 4e shows another modification of the example shown in Figure 4c. In this modification, the modulator has an output loss port ("drop port") Pd. The monitoring photodetectors PD1 and PD2 are directly connected to this loss output port Pd.

[0085]

[0117] Figure 4f shows a demodulator, which forms another type of optical component MR1, MRA2 that can be calibrated / locked according to the principles of the present invention. In such a demodulator, the individual microresonators of the microring resonator array MR1-MR3 are located between a first waveguide WG1 and a second waveguide WG2. The first waveguide WG1 has an input port Pin to which the multispectral light radiation to be demodulated can be supplied, and a transmission port Pt. The loss ports of the microresonators MR1, MR2, and MR3 are connected to demodulation photodetectors PDa, PDb, and PDc. Photodetector PD1 is located on the first waveguide WG1 at the transmission port Pt. The individual microresonators MR1-MR3 filter and extract from the multispectral light beam radio frequency signals RF1, RF2, and RF3 carried by the emission frequencies of the multispectral light radiation (hereinafter referred to as "carrier frequencies") FLa, FLb, and FLc, respectively. Heater-like means H1-H3 for adjusting the resonant frequencies F01-F03 are also associated with the individual micro-resonators MR1-MR3.

[0086]

[0118] Figure 4g shows, on the left, the relative positions of the resonant frequencies F01, F02, F03 of filters MR1, MR2, and MR3 before adjustment, and the carrier frequencies FLa, FLb, and FLc. On the right side of Figure 4g, the relative positions of the resonant frequencies F01′, F02′, F03′ after adjustment and the carrier frequencies FLa, FLb, and FLc are shown. This is the relative position of the resonant frequencies F01′, F02′, F03′ after adjustment and the carrier frequencies FLa, FLb, and FLc when the micro-resonators MR1, MR2, and MR3 are intentionally locked to the nearest optical carriers FLa, FLb, and FLc.

[0087]

[0119] Of course, as shown in the schematic diagrams of Figures 2d and 3d, the optical system 1 may also include input photodetectors PDin1 and PDin2, respectively, associated with individual external waveguides upstream of the optical devices MRA1 and MRA2. This modification is shown in Figure 4h. The individual input photodetectors PDin1 and PDin2 generate reference signals Vr and Vr' available by the lock device R, as described in a previous section of this specification.

[0088]

[0120] The modified lock device R shown in Figures 4c, 4e, and 4f operates in time-division multiplexing mode. This modification can also be used for frequency multiplexing, where the modulator generates multiple different modulated signals simultaneously, as shown in Figure 3c.

[0089]

[0121] Regardless of the properties of the optical components MRA1 and MRA2 associated with the light source La, it may be advantageous to engage frequency multiplexing during the system implementation's startup phase and apply different modulation frequencies to the individual emission / carrier frequencies Fla, Flb, and FLc of the multispectral optical emission RLM, respectively. For the sake of simplifying implementation, it is possible to decide to sequentially generate control signals that allow independent control of the tuning devices H of the individual microresonators MR1, MR2, and MR3 in order to tune the resonant frequency of one optical filter at a time. As already mentioned, this implementation method allows control of the association between the microresonators and carrier frequencies, whereas conventional solutions associate multiple microresonators with the same carrier frequency. Once this startup phase is complete, it is possible to decide to generate each control signal simultaneously.

[0090] Second application example

[0122] Figure 5a shows another optical device that can enjoy the advantages of the spectral positioning method according to the present invention. In the figure, the device consists of a tunable laser with a gain zone G and a phase zone P. The phase zone P can be, for example, a heater in the waveguide section, and the gain zone G is, as is well known, supplied with current to cause the optical radiation guided by at least one waveguide WG1, WG2 to radiate between two reflectors PR that define a cavity, these reflectors being partial reflectors that transmit a portion of this radiation, e.g., about 90%. In this optical cavity are two basic filters MR1, MR2, each of which is associated with frequency tuning devices H1, H2, e.g., heaters. These basic filters make it possible to precisely select one of the emission frequencies of the laser resonator (the emission frequency of the laser resonator is usually referred to as the "mode" of the resonator) by tuning the resonant frequency of the individual basic filters to a selected mode of the laser's emission frequency.

[0091]

[0123] The optical device shown in Figure 5a can be adapted to a lock device R that implements both (or at least one) operating modes constituting the spectral positioning method of the present invention. The lock device R can operate without distinction in a first operating mode according to a first implementation (by time-division multiplexing) or in a second operating mode according to a second implementation (by frequency-division multiplexing). During the operation of the optical system thus formed, as shown in Figure 5b, the resonant frequencies of the basic filters MR1 ​​and MR2 are locked to selected emission frequencies CM (cavity modes) of the laser that define their emission modes, respectively.

[0092] Third application example

[0124] Figure 6a shows yet another optical device capable of enjoying the advantages of the spectral positioning method according to the present invention. In the figure, the optical router is equipped with a laser source input coupler, represented here by GCin, for receiving optical radiation emitted by a laser outside the device. The received optical radiation is led to a photodetector PD by a waveguide WG. Along the waveguide WG, between this waveguide and the output couplers GC1out, GC2out, GC3out, a number of filters MR1, MR2, and MR3 are arranged. Each filter is associated with a regulating device H1, H2, and H3, such as a heater.

[0093]

[0125] During operation, the optical device allows the optical radiation received at the input coupler to be directed to the selected output coupler. To enable this selection, the tuning device locks the resonant frequency of the filter associated with the selected output coupler to the emission frequency of the laser radiation. Simultaneously, the resonant frequencies of the other filters associated with the unselected output couplers are misaligned with respect to the emission frequency of the laser source. This operation is shown in Figure 6b, where, as an example, the optical radiation is directed to one output coupler GC3out by locking the emission frequency Fla to the resonant frequency of filter MR3 associated with the selected output coupler GC3out. At the same time, the other two filters MR1 ​​and MR2 are misaligned with respect to the laser emission frequency Fla. In this way, the optical beam propagating through the waveguide WG is coupled to the selected single output coupler.

[0094]

[0126] The optical device shown in Figure 6a can be adapted to the locking device R according to the present invention. The locking device R can operate without distinction in a first operating mode according to a first implementation configuration (by time-division multiplexing) or according to a second implementation configuration (by frequency-division multiplexing). During operation of this optical system established in this way, the resonant frequency of the filter associated with the selected output coupler is locked to the laser emission frequency, while other filters are not aligned.

[0095]

[0127] Naturally, the present invention is not limited to the embodiments described, and alternative embodiments can be added without departing from the scope of the invention as defined by the claims.

[0096]

[0128] In particular, while a resonant ring filter is used in the example, this does not limit the present invention, and it is applicable to any form of filter, such as a Mach-Zehnder (MZ) interferometer filter. This filter can, at least in part, form a modulator, such as a resonant ring modulator or an MZ modulator.

[0097]

[0129] In addition, the waveguide can be an optical fiber, and the laser can be modulated, for example, an external laser whose intensity is modulated.

Claims

1. A method for spectral positioning of an optical system, The optical system (1) is A laser light source (La; La1, La2, La3) that generates radiation having at least one radiation frequency, Multiple filters (MR; MR1, MR2, MR3) each having a resonant frequency, At least one waveguide (WG; WG1, WG2) configured to optically couple the radiation generated by the laser light source (La; La1, La2, La3) to the filter (MR; MR1, MR2, MR3), A photodetector (PD; PD1, PD2) is optically coupled to the waveguide (WG; WG1, WG2) and receives filtered radiation, wherein the photodetector (PD; PD1, PD2) generates control signals (V; V1, V2), A plurality of tuning devices (H) associated with the laser light source (La; La1, La2, La3) and / or the filter (MR1, MR2, MR3), wherein the tuning devices (H) are controlled to modulate the at least one radiation frequency of the laser light source or the resonant frequency of the filter by a modulation frequency (Fd), while being controlled to adjust the resonant frequency of the filter (MR; MR1, MR2, MR3), The aforementioned method, The aforementioned control signals (V; V1, V2) are adjusted to generate a digital control signal (Vn), A first operation (OP1) processes the digital control signal (Vn) to generate at least one digital signal (Vr1) referred to as a "first lock signal" that represents the power of the second harmonic and / or principal component of the modulation frequency (Fd) present in the digital control signal (Vn), A second operation (OP2) processes the first lock signal (Vr1) to generate a digital adjustment command (CLan), wherein the second operation (OP2) aims to optimize the amplitude of the first lock signal (Vr1), and A method for implementing the following: adjusting the aforementioned digital adjustment command (CLan) to generate adjustment commands (CLa; CLa1, CLa2, CLa3) and applying them to the adjustment device (H).

2. The method according to claim 1, wherein the first lock signal (Vr1) represents the power of the second harmonic of the modulation frequency (Fd), and the second operation (OP2) aims to maximize the amplitude of the first lock signal (Vr1), or the first lock signal (Vr1) represents the power of the principal component of the modulation frequency (Fd), and the second operation (OP2) aims to minimize the amplitude of the first lock signal (Vr1).

3. The method according to claim 1 or 2, wherein the first lock signal (Vr1) is formed by the ratio of the power of the second harmonic of the modulation frequency (Fd) to the power of the principal component of the modulation frequency (Fd), and the second operation (OP2) aims to optimize the amplitude of the first lock signal (Vr1) to be greater than or equal to a predetermined value.

4. The method according to any one of claims 1 to 3, wherein the first operation (OP1) generates at least one second lock signal (Vr2) representing the phase of the principal component of the modulation frequency (Fd) present in the digital control signal (Vn).

5. The method according to claim 4, wherein the second lock signal (Vr2) corresponds to the difference between the phase of the principal component of the modulation frequency (Fd) present in the digital control signal (Vn) and the phase of the modulation signal or reference signal (Vr).

6. The method according to any one of claims 1 to 5, comprising the step of selecting one of the adjustment devices (H), wherein the selection step is repeated to sequentially select each of the adjustment devices (H).

7. The method according to any one of claims 1 to 5, wherein the modulation frequencies of the adjustment device (H) are different from each other.

8. The method according to any one of claims 1 to 7, wherein the adjustment command (CLa; CLa1, CLa2, CLa3) is applied to the adjustment device (H) one optical filter at a time.

9. An optical system (1) for spectral positioning of optical devices, A laser light source (La; La1, La2, La3) that generates radiation having at least one radiation frequency, Multiple filters (MR1, MR2, MR3), each having its own resonant frequency, At least one waveguide (WG; WG1, WG2) configured to optically couple the radiation generated by the laser light source (La; La1, La2, La3) to the filter (MR1, MR2, MR3), A photodetector (PD) optically coupled to the waveguide (WG; WG1, WG2) and receiving filtered radiation, wherein the photodetector (PD) generates a control signal (V), A plurality of tuning devices (H) associated with the laser light source (La; La1, La2, La3) and / or the filters (MR1, MR2, MR3), wherein the tuning devices (H) are controlled to modulate the radiation frequency of the laser light source or the resonant frequency of the filters by a modulation frequency (Fd), while also being controlled to adjust the resonant frequency of the filters (MR1, MR2, MR3), and A locking device (R) is provided, The locking device is i. To generate a digital control signal (Vn) by adjusting the aforementioned control signal (V), ii. A first operation (OP1) that processes the digital control signal (Vn) to generate at least one digital signal (Vr1) referred to as a "first lock signal" that represents the power of the second harmonic and / or principal component of the modulation frequency (Fd) present in the digital control signal (Vn), iii. A second operation (OP2) which processes the first lock signal (Vr1) to generate a digital adjustment command (CLan), wherein the second operation (OP2) aims to optimize the amplitude of the first lock signal (Vr1), and iv. Adjusting the digital adjustment command (Clan) to generate adjustment commands (CLa; CLa1, CLa2, CLa3) and applying them to the adjustment device (H), A light system configured to perform [a specific action].

10. The optical system according to claim 9, comprising a single photodetector (PD, PD1, PD2) coupled to a single waveguide (WG; WG1, WG2).

11. The optical system according to claim 9, comprising input photodetectors (PDin; PDin1, PDin2) coupled to waveguides (WG; WG1, WG2) upstream of the plurality of filters (MR1, MR2, MR3).

12. The optical system according to any one of claims 9 to 11, wherein the filter is a coupled basic filter.

13. The optical system according to claim 12, wherein the optical device is a tunable laser.

14. The optical system according to any one of claims 9 to 11, wherein the optical device is an optical router.

15. The optical system according to any one of claims 9 to 11, wherein the laser light source includes a plurality of lasers (La1, La2, La3) that emit a plurality of radiation frequencies.

16. The optical system according to claim 15, wherein a tuning device (H) associated with the lasers (La1, La2, La3) of the light source is controlled to modulate the radiation frequency of the light source, and a tuning device (H) associated with the filters (MR1, MR2, MR3) is controlled to adjust the resonant frequencies of the filters (MR1, MR2, MR3).

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