Modulation system configured to control signal modulation

Abstract

The invention relates to a modulation system 10 configured to control the modulation of a signal, the system comprising: - an optical modulator configured to receive: o an input signal formed by a carrier SOE, SOE1, SOE2, and o a modulation signal SM, SM1, SM2, - a cooling device 12, 12-1, 12-2 configured to cool the optical modulator to a temperature greater than or equal to 10 K, preferably greater than or equal to 40 K, and to cool the optical modulator to a temperature less than or equal to 90 K, preferably less than or equal to 80 K.

Description

[0001] MODULATION SYSTEM CONFIGURED TO CONTROL THE

[0002] MODULATION OF A SIGNAL

[0003] FIELD OF THE INVENTION

[0004] The invention relates to a modulation system configured to control the modulation of an input optical signal.

[0005] STATE OF THE ART

[0006] Converting information from the electrical domain to the optical domain involves the use of a modulator.

[0007] US 10,097,281 B1 describes an optoelectronic data link system involving cryogenic cooling. And US 5,271,074 A describes an integrated optical waveguide apparatus.

[0008] It is known to use modulators that allow amplitude modulation.

[0009] An example of amplitude modulation is pulse amplitude modulation, also known as PAM (Pulse Amplitude Modulation). PAM is a form of signal modulation in which the message information is encoded according to the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal.

[0010] An alternative type of modulation is quadrature amplitude modulation, also known as "QAM" (Quadrature Amplitude Modulation). This modulation is a form of modulation of a carrier by modifying the amplitude of the carrier itself and a quadrature wave according to the information carried by two input signals. A quadrature is defined by a wave that is 90° out of phase with the carrier. In other words, QAM can be considered as an amplitude modulation of a wave, expressed in complex, by a signal, expressed in complex. The amplitude and phase of the carrier are simultaneously modified according to the information to be transmitted.

[0011] These two types of modulation are known to comprise a constellation of 16, 32 or 64 points, as illustrated in figures 1a, 1b and 1c, for the case of quadrature amplitude modulation.

[0012] QAM constellations with a large number of points can be used to achieve higher data rates. And QAM constellations with a smaller number of points are used to reduce modulation-induced noise and ensure a low bit error rate.

[0013] Figures 1a, 1b, and 1c illustrate a constellation diagram. A constellation diagram is a representation of a signal modulated by a digital modulation technique such as quadrature amplitude modulation (QAM). The representation is a two-dimensional diagram whose axes delimit the complex plane at the symbol sampling times. The points in the complex plane are the images of the symbols present at that time resulting from the modulation. Constellation diagrams can be used to identify the type of interference or distortion in a signal.

[0014] Representing a symbol as a complex number allows its real (cosine) and imaginary (sine) parts to be extracted. A symbol can therefore be transmitted by modulating two carriers of the same frequency with these components. These are then called quadrature carriers. A coherent detector is capable of demodulating these components separately. The principle of independently modulating two carriers is the basis of quadrature modulation.

[0015] The two components of a symbol taken as a complex number can be visualized in a coordinate system with the real component (I-axis, or "in-phase") as the abscissa and the imaginary component (Q-axis, or "in quadrature") as the ordinate. Displaying all the symbols at a given time in this coordinate system constitutes the constellation diagram. The points in a constellation diagram are called constellation points. The constellation diagrams illustrated in Figures 1a, 1b and 1c show the different positions of the states in different orders of quadrature amplitude modulation (QAM16, QAM32 and QAM64). As the order of modulation increases, the number of points on the QAM constellation diagram increases.

[0016] It can be seen from these QAM constellation diagrams that as the modulation order increases, the distance between constellation points decreases for a given maximum amplitude. Therefore, small amounts of noise can cause larger problems as the modulation order increases.

[0017] As the noise level increases due to weak signals, the area covered by a point in the constellation increases. If it becomes too large, the receiver is unable to determine the position of the transmitted signal in the constellation, which leads to errors. It is also noted that the higher the modulation order of the QAM signal, the greater the variation in amplitude of the transmitted signal if we want to maintain a constant distance between the points in the constellation.

[0018] The same teachings apply to pulse amplitude modulation, known as PAM modulation. However, PAM constellation diagrams are formed by a plurality of points defined along an axis.

[0019] To be able to define the number of points in the constellation, it is important to take into account the linear area and the extinction ratio of the amplifier used as a modulator. The extinction ratio corresponds to the ratio in dB between the maximum power of the modulated signal compared to the minimum power of the modulated signal. The extinction ratio of the same amplifier at room temperature is of the order of 20 dB.

[0020] The linear range defines the power range over which the input signal is amplified to a desired gain minus, for example, 1 or 3 dB.

[0021] To convert an electrical signal into an optical signal, it is known to use three types of modulators: the Mach-Zehnder modulator (commonly called MZM modulator), the electro-absorbing modulator (commonly called EAM modulator) and the use of a semiconductor amplifier. The Mach-Zehnder modulator is an interferometer. An interferometer is an instrument for forming and studying interference fringes. The Mach-Zehnder modulator has an extinction ratio of around 25 to 30 dB.

[0022] However, the Mach-Zehnder modulator exhibits a greatly reduced extinction ratio in the quasi-linear region of the modulator. This is caused by the transfer function of this modulator, which is sinusoidal in shape. This transfer function is conditioned by the voltage of a modulating signal. For such a modulator, the maximum order of multilevel modulation does not exceed PAM-16, i.e., modulation on 16 distinct amplitude levels.

[0023] The electro-absorbing modulator is a reverse-biased diode. The diode is made from semiconductor materials. Varying the bias voltage changes the absorption of an incident light wave.

[0024] Thus, depending on the variation of the bias voltage, an amplitude modulation of an incident optical signal as a function of an applied reverse voltage is obtained.

[0025] However, such a device has a transfer function that exhibits a non-linearity limiting the extinction ratio in the linear part to only 15dB.

[0026] The voltage range over which the electro-absorbing modulator is controlled is significantly lower than that of the Mach-Zehnder modulator. For the electro-absorbing modulator, the maximum multilevel modulation order does not exceed PAM-4, i.e. modulation on 4 distinct amplitude levels.

[0027] An amplifier is an electronic or optoelectronic system that amplifies an electrical or optical signal. The energy required for amplification is drawn from the system's power supply. A perfect amplifier does not distort the input signal: the output signal is an exact replica of the input signal with increased power.

[0028] Amplifiers are used in almost all circuits in electronics and optics: they allow the voltage of an electrical signal or the power of an optical signal to be raised to a level usable by the rest of the system, to increase the output current of a sensor to allow its transmission without interference, to provide sufficient maximum power to power a load such as a radio antenna or an electroacoustic speaker.

[0029] An amplifier is used to amplify a signal over a certain bandwidth. In the case of an electrical circuit, bandwidth defines a range of frequencies over which the signal can be amplified. In the case of an optical circuit, bandwidth defines a range of frequencies or wavelengths over which the signal can be amplified, with frequency and wavelength being related by the equation ' —Â,, with f defining the frequency of the light wave (defined in Hz), c defining the speed (defined in ms-1) and X defining the wavelength of the light wave (defined in m).

[0030] Optical amplification is achieved by forward bias. Amplitude modulation of an incident optical signal can be achieved by varying the bias current. Varying the bias current changes the gain of the semiconductor optical amplifier.

[0031] The extinction ratio of the semiconductor optical amplifier is typically in the order of 10 to 15 dB. For a semiconductor optical amplifier or a reflective semiconductor optical amplifier, the maximum order of multilevel modulation does not exceed PAM-4, i.e. modulation on 4 distinct amplitude levels.

[0032] There is therefore a need to be able to increase the linear area over which the signal can be modulated and the number of constellation points.

[0033] The invention aims to provide a system to meet these needs.

[0034] BRIEF DESCRIPTION OF THE INVENTION

[0035] To this end, the present invention relates to a modulation system configured to control the modulation of a signal, the system comprising:

[0036] • an optical modulator configured to receive: o an input signal formed by a carrier, and o a modulation signal,

[0037] • a cooling device configured to cool the optical modulator to a temperature greater than or equal to 10 K, preferably greater than or equal to 40 K, and to cool the optical modulator to a temperature less than or equal to 90 K, preferably greater than or equal to 80 K.

[0038] Advantageously, at such a cryogenic temperature, the extinction ratio of the optical modulator is of the order of 50 dB for a current of 100 mA. This advantageously makes it possible to increase the gain in the linear zone of the optical modulator by approximately 15 dB.

[0039] Advantageously, by placing the optical modulator at such a cryogenic temperature, the maximum order of multilevel modulation can reach, for example, PAM-32, i.e. modulation on 32 distinct amplitude levels. And the number of points in the constellation can reach at least 256 points in quadrature amplitude modulation, within the framework of electro-optical modulation.

[0040] Advantageously, by placing the optical modulator at such a cryogenic temperature, it is possible to reduce the noise at the level of the input signal and the modulation signal.

[0041] Advantageously, by placing the optical modulator at such a cryogenic temperature, the linearity range of the modulator is increased compared to prior art modulation systems. This allows modulation of input signals whose envelope amplitude is not constant, as in orthogonal frequency division multiplexing (commonly referred to as OFDM).

[0042] OFDM is a method of coding digital signals by orthogonal frequency division in the form of a plurality of subcarriers.

[0043] This technique helps combat frequency-selective channels by enabling low-complexity equalization. These channels occur particularly in the presence of multiple paths and are all the more penalizing when the transmission rate is high.

[0044] Advantageously, the modulation system may also comprise one or more of the following features, considered individually or in all technically possible combinations: the optical modulator is a laser modulator; and / or the optical modulator is a modulator configured to receive a laser signal; and / or the laser modulator is a laser diode; and / or the optical modulator is a modulator configured to receive a laser signal is a laser diode; and / or the optical modulator is a semiconductor optical amplifier or a reflective semiconductor optical amplifier; and / or the modulation signal is an electrical signal; and / or the modulation signal is an optical signal;and / or the semiconductor optical amplifier is a bidirectional component configured to receive a first input optical signal at one terminal and a second input optical signal, identical to the first input optical signal, at another terminal in opposite directions; and / or the input optical signal has a power greater than or equal to -30 dBm and less than or equal to +10 dBm; and / or the cooling device is active; and / or the cooling device is passive; and / or the cooling device is direct; and / or the cooling device is indirect; and / or the cooling device comprises a temperature controller, the temperature controller being configured to maintain the semiconductor optical amplifier at a target temperature with a margin of less than or equal to 500 mK, preferably less than or equal to 200 mK, and greater than or equal to -500 mK, preferably greater than or equal to -200 mK;and / or the semiconductor optical amplifier is mounted on an integrated component; and / or the integrated component is a photonic integrated component; and / or the modulation system comprises several semiconductor optical amplifiers or several reflective semiconductor optical amplifiers; and / or the cooling device comprises a device for regulating the temperature of at least two semiconductor optical amplifiers; and / or at least two semiconductor optical amplifiers are at a different temperature; and / or the modulation signal is a shared modulation signal for each of the semiconductor optical amplifiers; and / or the modulation signal has a bandwidth greater than or equal to 0.01 GHz and less than or equal to 100 GHz, preferably less than or equal to 40 GHz; and / or the optical modulation signal and the input optical signal have different polarizations;and / or the wavelength of the input optical signal differs from the wavelength of the modulating optical signal by at least 0.05 nm, preferably by at least 0.1 nm, preferably by at least 0.5 nm, preferably by at least 1 nm, preferably by at least 1.5 nm and even more preferably by at least 5 nm; and / or the cooling device comprises:;

[0045] • a bar made of a material having a thermal conductivity greater than or equal to 20 watts per meter-kelvin on which the amplifiers are placed,

[0046] • a cold point placed at a first location on the bar, and

[0047] • a temperature regulation device comprising a temperature sensor arranged at a second location on the bar.

[0048] The present invention also relates to a modulation system configured to control the modulation of a signal, the system comprising:

[0049] • an optical modulator configured to receive: o an input signal formed by a carrier, and o a modulation signal,

[0050] • a cooling device configured to cool the optical modulator to a cryogenic temperature.

[0051] BRIEF DESCRIPTION OF THE FIGURES

[0052] The invention will be better understood in light of the following description which is given for information purposes only and which is not intended to limit said invention, accompanied by the figures below: Figure 1a is a representation of a constellation diagram of a quadrature amplitude modulation, Figure 1b is a representation of a constellation diagram of a quadrature amplitude modulation, Figure 1c is a representation of a constellation diagram of a quadrature amplitude modulation, Figure 2 is a schematic representation of an interruption system according to the invention, according to a first embodiment, Figure 3 is a schematic representation of an interruption system according to the invention, according to a second embodiment, Figure 4 is a schematic representation of an interruption system according to the invention, according to a third embodiment,Figure 5 is a schematic representation of an interruption system according to the invention, according to a fourth embodiment, Figure 6 is a schematic representation of an interruption system according to the invention, according to a fifth embodiment, Figure 7 is a schematic representation of an interruption system according to the invention, according to a sixth embodiment, Figure 8 is a schematic representation of an interruption system according to the invention, according to a seventh embodiment, Figure 9 is a schematic representation of an interruption system according to the invention, according to an eighth embodiment, and Figure 10 is a schematic representation of an interruption system according to the invention, according to a ninth embodiment.,

[0053] DETAILED DESCRIPTION OF THE INVENTION

[0054] A modulation system configured to control modulation of a signal is provided, the system comprising:

[0055] • an optical modulator configured to receive: o an input signal formed by a carrier, and o a modulation signal,

[0056] • a cooling device configured to cool the optical modulator to a temperature greater than or equal to 10 K, preferably greater than or equal to 40 K, and less than or equal to 90 K, preferably less than or equal to 80 K.

[0057] The optical modulator is configured to receive an input optical signal comprising a carrier whose amplitude can vary.

[0058] The optical modulator may be a laser modulator, such as a laser diode, in the case of direct modulation. In an alternative embodiment, the optical modulator is a solid-state amplifier or a reflective solid-state amplifier, in the case of indirect modulation.

[0059] The modulation signal has a bandwidth greater than or equal to 0.01 GHz and less than or equal to 100 GHz, preferably less than or equal to 40 GHz. The temperature of the optical modulator conditions the wavelength range at which the signal is modulated.

[0060] Figure 2 illustrates a modulation system 10 configured to control the modulation of a signal, the system comprising:

[0061] • an optical modulator, formed by a semiconductor amplifier AMP, configured to receive: o an optical input signal SOE formed by a carrier, and o a modulation signal SM,

[0062] • a cooling device 12 configured to cool the optical modulator to a temperature greater than or equal to 10 K, preferably greater than or equal to 40 K, and less than or equal to 90 K, preferably less than or equal to 80 K.

[0063] The signal produced at the output of the optical modulator is a modulated optical signal.

[0064] The SM modulation signal can be an electrical signal. Alternatively, the modulation signal is an optical signal. The SM modulation signal provides the modulator with the information necessary to modify the carrier of the input optical signal SOE.

[0065] Advantageously, the electrical modulation signal SM can be used to provide the electrical power supply to a modulator in the form of a semiconductor optical amplifier AMP.

[0066] It was surprisingly noticed that the semiconductor optical amplifier AMP provided a non-zero gain when the latter was subjected to a cryogenic temperature, greater than or equal to 10 K, preferably greater than or equal to 40 K and less than or equal to 90 K, preferably less than or equal to 80 K, and that a low power supply, of the order of a few milliamps was provided.

[0067] Since the AMP semiconductor optical amplifier is low-power at this temperature, it is then possible to replace its power supply via an electrical SM modulation signal with an optical SM modulation signal, for example in the case of QAM16 quadrature modulation.

[0068] Advantageously, when the modulation signal is optical, this allows it to be remote.

[0069] In the case of an optical SM modulation signal, the wavelength range over which an input signal can be modulated and the modulation options may be different from the wavelength ranges and modulation options permitted by a modulation signal in electrical form.

[0070] In an all-optical modulation system, where both the input signal and the modulation signal are optical, the power of the input optical signal SOE is at least 5 dB lower than the power of the modulation signal SM, preferably at least 10 dB lower.

[0071] The power of the input optical signal SOE is lower than the power of the modulation signal so that the semiconductor optical amplifier AMP distinguishes the modulation signal SM from the input optical signal SOE.

[0072] The modulation signal of a solid-state amplifier AMP is the signal with the largest power among the input optical signal SOE and the modulation signal SM.

[0073] In one embodiment, the power of the input optical signal is greater than or equal to -30 dBm, preferably greater than or equal to -10 dBm and less than or equal to +10 dBm, preferably less than or equal to +5 dBm. The dBm is a unit that expresses power in decibels (dB) relative to a reference value of 1 milliwatt (mW).

[0074] The SM modulation signal may have a different polarization than the input optical signal SOE. For example, the SM modulation signal is in transverse electric mode, respectively transverse magnetic mode and the input optical signal SOE is in transverse magnetic mode, respectively transverse electric mode.

[0075] For the remainder of the description, the optical modulator is considered in the form of a semiconductor amplifier AMP. Figures 2 to 10 cover a modulation system according to the invention comprising a semiconductor amplifier AMP. In the case where the modulation signal is optical, the input optical signal and the optical modulation signal can be supplied jointly using a single optical fiber to the optical modulator, for example to one of the terminals of the semiconductor amplifier AMP.

[0076] The AMP semiconductor optical amplifier is a bidirectional optoelectronic component.

[0077] In one embodiment, illustrated in Figure 3, a first optical input signal SOE1 and a second optical input signal SOE2, identical to the first optical input signal SOE1, are supplied to the semiconductor optical amplifier AMP in opposite directions via the terminals arranged on either side of the amplifier. The optical input signals SOE1 and SOE2 are considered counter-directional.

[0078] To facilitate the understanding of Figure 3, the second input optical signal SOE2 and the modulated optical signal SOM have been represented separately to define the propagation direction of these signals. However, the second input optical signal SOE2 and the modulated optical signal SOM are counter-propagating signals at the same optical fiber.

[0079] In one embodiment, the modulation signal SM and the input optical signal SOE have a different polarity and / or are transmitted to two opposite terminals of a semiconductor optical amplifier AMP.

[0080] In another embodiment, the wavelength of the modulation signal and the input optical signal SOE may be different. For example, the wavelength of the modulation signal SM and the input optical signal SOE is different by at least 0.05nm, preferably by at least 0.1nm, preferably by at least 0.5nm, preferably by at least 1nm, preferably by at least 1.5nm and even more preferably by at least 5nm.

[0081] The cooling device 12 of the modulation system 10 is preferably a cryogenic cooling device.

[0082] The cooling device 12 may be indirect. The cooling device is considered indirect in the case where a cooling means does not act directly on the optical modulator but on an element, for example a thermally conductive element on which the optical modulator is arranged. The thermally conductive element, cooled by a cooling means, will in turn cool the optical modulator by thermal conduction.

[0083] An indirect cooling device 12 may for example be formed by a thermally conductive bar which will be cooled at one of its ends by a cooling means. The bar is configured to receive at least one optical modulator.

[0084] Advantageously, an indirect cooling device can make it possible to share a cooling means for several optical modulators on a thermally conductive bar, for example arranged in different locations.

[0085] Alternatively, the cooling device 12 may be direct. The direct cooling device 12 is a device configured to apply a thermal variation directly to the optical modulator. The temperature control is carried out directly at the optical modulator.

[0086] A direct cooling device can be formed by a dedicated cooling means locally cooling the optical modulator(s), for example the semiconductor optical amplifier(s) AMP1, AMP2.

[0087] Advantageously, it is not necessary to use a thermally conductive structure on which the optical modulator(s) would be placed.

[0088] Advantageously, the use of a direct cooling device 12 makes it possible to better control the temperature supplied to the at least one optical modulator.

[0089] Also, in the context of a direct cooling device 12, it is easier and faster to compensate for a variation at the level of an optical modulator. It is not necessary to wait for a conductive element to reach the desired temperature at the location where the optical modulator is arranged.

[0090] The cooling device 12 may be a passive cooling device.

[0091] For example, a passive cooling device may be a radiator in contact with the optical modulator. The radiator radiates outward from the modulation system, such as a radiant thermal energy extraction device. A passive cooling device 12 may also be formed by a cooling circuit comprising liquid nitrogen.

[0092] A passive cooling device is devoid of energy input. Advantageously, the energy consumption to maintain the optical modulator(s), for example the semiconductor optical amplifier(s) AMP1, AMP2 at a cryogenic temperature is reduced.

[0093] A cooling device 12 may be active. An active cooling device requires an energy input to ensure cooling of the optical modulator. Despite the need for an energy input, the temperature regulation of an optical modulator is faster and more reliable due to the control of the cooling device, by regulating its power supply.

[0094] Figure 4 illustrates a modulation device 10 comprising two semiconductor optical amplifiers AMP1, AMP2 or at least two reflective semiconductor optical amplifiers. Each of the two semiconductor optical amplifiers AMP1, AMP2 receives a respective input optical signal SOE1, SO2, each comprising a carrier, and a modulation signal SMI, SM2, so as to respectively provide a modulated optical signal SOM1, SOM2.

[0095] At least semiconductor optical amplifiers AMP1, AMP2 are cooled by the cooling device.

[0096] In one embodiment, both semiconductor optical amplifiers AMP1, AMP2 are cooled by the same cooling device 12 or a respective cooling device.

[0097] Advantageously, the cooling device 12 can be shared by using the same cooling device for two semiconductor optical amplifiers AMP1, AMP2.

[0098] The two semiconductor optical amplifiers AMP1, AMP2 can be maintained at the same temperature, for example when at least two semiconductor optical amplifiers AMP1, AMP2 are mounted in an integrated circuit 22 which is cooled by the cooling device 12. Alternatively, the two semiconductor optical amplifiers AMP1, AMP2 can be maintained at a different temperature. For example, two semiconductor optical amplifiers AMP1, AMP2 are maintained at temperatures having a difference greater than or equal to 5K, preferably a difference greater than or equal to 10K.

[0099] Advantageously, the amplifiers AMP1, AMP2 will modulate the input optical signals SOE1, SOE2 respectively received over different wavelength ranges.

[0100] In one embodiment, illustrated in figure 5, the same modulation signal SM is shared for two semiconductor optical amplifiers AMP1, AMP2.

[0101] Advantageously, in this way the modulation of the input optical signals SOE1, SOE2 can be ensured simultaneously at the level of the semiconductor optical amplifiers AMP1, AMP2.

[0102] In the same way as in the embodiment illustrated in Figure 5, where the modulation signal SM is shared, the input optical signal can be shared. A single input signal SOE could be divided into two and supplied to two semiconductor optical amplifiers AMP1, AMP2. Each of the two semiconductor optical amplifiers AMP1, AMP2 receives a different modulation signal SMI, SM2, so as to respectively provide a modulated optical signal SOM1, SOM2. The modulated optical signals SOM1, SOM2 are different.

[0103] In one embodiment, the input optical signal SOE and the modulation signal SM are respectively shared for at least two amplifiers.

[0104] Advantageously, the same modulated signal can be supplied to separate locations simultaneously.

[0105] In one embodiment, at least one semiconductor optical amplifier AMP, AMP1, AMP2 is a discrete component.

[0106] Alternatively, a single semiconductor optical amplifier AMP or a plurality of semiconductor optical amplifiers AMP1, AMP2 may form part of an integrated circuit 22, as illustrated in FIG. 6. The integrated circuit 22 is, for example, a photonic integrated circuit. To ensure precise control of the temperature of the at least one or each of the semiconductor optical amplifiers AMP1, AMP2 of the modulation system 10, the cooling device 12, 12-1, 12-2 may comprise a temperature regulator 14, 14-1, 14-2 (illustrated in FIG. 8).

[0107] Preferably, the temperature regulator 14, 14-1, 14-2 is configured to maintain the semiconductor optical amplifier AMP, AMP1, AMP2 at a target temperature.

[0108] Advantageously, precise temperature control of the semiconductor optical amplifier AMP, AMP1, AMP2 makes it possible to precisely control over which wavelength range the input signal will be modulated.

[0109] Also, the temperature regulator 14, 14-1, 14-2 allows to compensate the heat supplied by the modulation signal to the semiconductor optical amplifier AMP, AMP1, AMP2. The greater the power of the modulation signal SM, SMI, SM2, the greater the heat transmitted by this signal. Therefore, to ensure the good thermal regulation of the temperature of the optical modulator, for example of the semiconductor optical amplifier AMP, AMP1, AMP2, it is important to take into account the thermal impact of the modulation signal SM, SMI, SM2.

[0110] The temperature controller 14, 14-1, 14-2 can be used to control the temperature of one of the plurality of semiconductor optical amplifiers AMP, AMP1, AMP2, as illustrated in FIG. 7.

[0111] Furthermore, the cooling device comprises a temperature controller, the temperature controller being configured to maintain the semiconductor optical amplifier at a target temperature with a margin less than or equal to 500 mK, preferably less than or equal to 200 mK, and greater than or equal to -500 mK, preferably greater than or equal to -200 mK.

[0112] Advantageously, precise control of the temperature of the semiconductor optical amplifier AMP can be ensured. By having precise control of the temperature of the semiconductor amplifier AMP, it can be controlled over which wavelength range the input optical signal SOE, SOE1, SOE2 will be modulated. Figure 8 shows a modulation system according to the invention in which each of the two semiconductor optical amplifiers AMP1, AMP2 comprises a respective cooling device 12-1, 12-2 and a temperature regulator 14-1, 14-2.

[0113] Such a system, using respective cooling devices and temperature regulators, allows better control of the temperature of each of the two semiconductor optical amplifiers AMP1, AMP2.

[0114] Figure 9 illustrates an embodiment of the cooling device 14. The cooling device 14 may comprise:

[0115] • a bar 16 made of a material having high thermal conductivity on which the N amplifiers are arranged (in the case of figure 9, two amplifiers AMP1 and AMP2 are illustrated),

[0116] • a cold point 18 arranged at a first location El of the bar 16, and

[0117] • a temperature regulation device 14 comprising a temperature sensor 20 arranged at a second location E2 of the bar.

[0118] Preferably, the bar 16 has a thermal conductivity greater than or equal to 20 watts per meter-kelvin. The temperature at different locations of the bar 30 is different.

[0119] In one embodiment, the bar 16 is made of copper.

[0120] The bar may be made of a material having high thermal conductivity and the presence of a cold point 18 makes it possible to create a temperature gradient between the first location E1 where the cold source 18 is arranged and an end E2 of the bar 16.

[0121] With such a temperature gradient, the positioning of the semiconductor optical amplifiers AMP1, AMP2 is important to be at a desired target temperature Tl, T2.

[0122] The temperature of the semiconductor optical amplifiers AMP1, AMP2 arranged on the bar 16 is conditioned by their location on the bar 16.

[0123] The cold point 18 corresponds to a cooling means configured to cool the bar 16 at a particular location of this bar 16, corresponding to the first location EL

[0124] In this way, the amplifiers arranged closest to the cold point 18 have a colder temperature than the amplifiers furthest from the cold point 18. Preferably, the cooling means used is a cryogenic cooler.

[0125] The cold point 18 is preferably positioned at one end of the bar 16 to maximize the temperature gradient between a first end and a second end of the bar 30.

[0126] The positioning of a temperature sensor 20 at a second location E2 of the bar 16 makes it possible to determine the temperature of the bar 16 at this second location E2. The bar being made of a conductive material, it can be determined, from the measurement of the temperature sensor 34, at least approximately the temperature at each point of the bar 16 and more particularly at the positions where the semiconductor optical amplifiers AMP1, AMP2 are arranged.

[0127] Advantageously, from the measurement of the temperature at said second location E2 of the bar 16, the cooling device 12 can determine whether the temperature of the semiconductor optical amplifiers AMP1, AMP2 corresponds to the desired target temperature.

[0128] 51 the temperature of at least one semiconductor optical amplifier AMP1, AMP2 is different from the desired target temperature T1, T2, the cooling device 12 controls the regulating device 14 to regulate the temperature of the cold point 18 of the bar 16.

[0129] In another embodiment illustrated in Figure 10, the cooling device independently controls the temperature T1, T2 of the semiconductor optical amplifiers AMP1, AMP2. If one of the semiconductor optical amplifiers AMP1, AMP2 is not at a desired target temperature, the temperature controller 14 independently controls the temperature of that amplifier AMP1, AMP2.

[0130] Each of the semiconductor optical amplifiers AMP1, AMP2 is associated with a respective additional thermal source SI, S2. Each of the additional thermal sources SI,

[0131] 52 is configured to individually regulate the temperature of one of the semiconductor optical amplifiers AMP1, AMP2.

[0132] In one embodiment, the N additional thermal sources are Peltier modules and / or resistors. Advantageously, the Peltier modules make it possible to regulate the temperatures of the semiconductor optical amplifiers AMP1, AMP2 by locally increasing or lowering their temperature.

[0133] Advantageously, the resistors make it possible to regulate the temperatures of the semiconductor optical amplifiers AMP1, AMP2 by locally increasing their temperature.

[0134] The embodiment, illustrated in Figure 10, is similar to the configuration illustrated in Figure 8, the temperature regulator 14 is however different. The temperature regulator 14 no longer regulates the temperature of the cold point 18 of the bar 16 but directly regulates the temperature of the additional thermal sources S1, S2.

[0135] The embodiment illustrated in Figure 10 may be devoid of the bar 16 and the cold point 18, the thermal sources SI and S2 providing the cold to the semiconductor amplifiers SI, S2.

[0136] The invention has been described above with the help of embodiments shown in the figures, without limitation of the general inventive concept.

[0137] Many other modifications and variations suggest themselves to those skilled in the art, after reflection on the various embodiments illustrated in this application.

[0138] These embodiments are given by way of example and are not intended to limit the scope of the invention, which is determined exclusively by the claims below.

[0139] In the claims, the word "comprising" does not exclude other elements or steps. The mere fact that different features are listed in mutually dependent claims does not indicate that a combination of these features cannot be advantageously used. Finally, any reference used in the claims should not be interpreted as a limitation of the scope of the invention.

Claims

CLAIMS Modulation system (10) configured to control the modulation of a signal, the system comprising: • an optical modulator configured to receive: o an input signal consisting of a carrier (SOE, SOE1, SOE2), and o a modulation signal (SM, SMI, SM2), • A cooling device (12, 12-1, 12-2) configured to cool the optical modulator to a temperature greater than or equal to 10 K, preferably greater than or equal to 40 K, and to cool the optical modulator to a temperature less than or equal to 90 K, preferably less than or equal to 80 K. The modulation system according to claim 1, characterized in that the optical modulator is a semiconductor optical amplifier (AMP, AMP1, AMP2) or a reflective semiconductor optical amplifier. The modulation system according to claim 2, characterized in that the modulation signal (SM, SMI, SM2) is an electrical signal. The modulation system according to claim 1, characterized in that the optical modulator is a modulator configured to receive a laser signal. The modulation system according to claim 4, characterized in that the modulator configured to receive a laser signal is a laser diode.The modulation system according to any one of the preceding claims, characterized in that the cooling device (12, 12-1, 12-2) is direct. The modulation system according to any one of claims 1 to 5, characterized in that the cooling device (12, 12-1, 12-2) is indirect. The modulation system according to any one of claims 2 to 7, characterized in that the cooling device (12, 12-1, 12-2) comprises a temperature regulator. (14, 14-1, 14-2), the temperature controller being configured to maintain the solid-state optical amplifier (AMP, AMP1, AMP2) at a target temperature (T1, T2) with a margin of ± 500 mK, preferably ± 200 mK.

9. The modulation system according to claims 4 to 8, characterized in that the semiconductor optical amplifier (AMP, AMP1, AMP2) is mounted on an integrated component (22).

10. The modulation system according to the preceding claim, characterized in that the integrated component is a photonic integrated component.

11. The modulation system according to claims 4 to 10, characterized in that the modulation system comprises several semiconductor optical amplifiers (AMP, AMP1, AMP2) or several reflective semiconductor optical amplifiers.

12. The modulation system according to the preceding claim, characterized in that the same cooling device (12, 12-1, 12-2) is configured to cool at least two semiconductor optical amplifiers (AMP, AMP1, AMP2).

13. The modulation system according to Tune of the preceding claims, characterized in that the modulation signal (SM, SMI, SM2) has a bandwidth greater than or equal to 0.01GHz and less than or equal to 100 GHz, preferably less than or equal to 40 GHz.

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