MODULATION SYSTEM CONFIGURED TO CONTROL THE MODULATION OF A SIGNAL

Abstract

A modulation system 10 configured to control the modulation of a signal, the system comprising: an optical modulator configured to receive: an input signal consisting of a carrier SOE, SOE1, SOE2, and 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 less than or equal to 90 K, preferably less than or equal to 80 K. Figure to be published with the abbreviation: Fig. 2

Description

Title of the invention: MODULATION SYSTEM CONFIGURED TO CONTROL THE MODULATION OF A SIGNAL FIELD OF INVENTION

[0001] The invention relates to a modulation system configured to control the modulation of an input optical signal STATE OF THE ART

[0002] The conversion of information from the electrical domain to the optical domain involves the use of a modulator.

[0003] It is known to use modulators allowing amplitude modulation.

[0004] An example of amplitude modulation is pulse amplitude modulation, also known as PAM (Pulse Amplitude Modulation). This modulation 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 carrier pulse train are modified according to the sample value of the message signal.

[0005] One type of alternative modulation is quadrature amplitude modulation, also known as QAM (Quadrature Amplitude Modulation). This modulation is a form of carrier modulation achieved by modifying the amplitude of the carrier itself and a quadrature wave based on the information carried by two input signals. A quadrature wave is defined as a wave that is phase-shifted by 90° with respect to the carrier.

[0006] In other words, QAM modulation can be considered as an amplitude modulation of a wave, expressed in complex numbers, by a signal, also expressed in complex numbers. The amplitude and phase of the carrier are simultaneously modified according to the information to be transmitted.

[0007] These two types of modulation are known to include a constellation of 16, 32 or 64 points, as illustrated in figures 1a, 1b and 1e, for the case of quadrature amplitude modulation.

[0008] QAM constellations with a large number of points can be used to obtain a higher data rate. And QAM constellations with a smaller number of points are used to reduce noise induced by modulation and ensure a low bit error rate.

[0009] Figures 1a, 1b, and 1e illustrate a constellation diagram. The constellation diagram is the representation of a signal modulated by a digital modulation such as quadrature amplitude modulation (QAM). The representation is located in a two-dimensional diagram whose axes delimit the complex plane at the symbol sampling instants. The points in the complex plane are the images of the symbols present at that given instant resulting from the modulation. Constellation diagrams can be used to identify the type of interference or distortion in a signal.

[0010] Representing a symbol as a complex number allows us to extract its real (cosine) and imaginary (sine) parts. 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 forms the basis of quadrature modulation.

[0011] 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.

[0012] The constellation diagrams illustrated in Figures 1a, 1b and 1e show the different positions of the states in different quadrature amplitude modulation orders (QAM16, QAM32 and QAM64). The higher the modulation order, the greater the number of points on the QAM constellation diagram.

[0013] As can be seen from these QAM constellation diagrams, as the modulation order increases, the distance between the points in the constellation decreases for a given maximum amplitude. Consequently, small amounts of noise can cause more significant problems as the modulation order increases.

[0014] As the noise level increases due to weak signals, the area covered by a point in the constellation increases. If this area becomes too large, the receiver is unable to determine the position of the transmitted signal on the constellation, leading to errors. It is also observed that the higher the modulation order of the QAM signal, the greater the variation in amplitude of the transmitted signal if a constant distance between the points in the constellation is to be maintained.

[0015] The same principles apply to amplitude pulse modulation, known as PAM modulation. However, PAM constellation diagrams are formed by a plurality of points defined along an axis.

[0016] To determine the number of points in the constellation, it is important to consider 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 and the minimum power of the modulated signal. The extinction ratio of the same amplifier at room temperature is approximately 20 dB.

[0017] The linear zone defines the power range for which the input signal is amplified to a desired gain less, for example, 1 or 3 dB.

[0018] To convert an electrical signal into an optical signal, it is known to use modulators of three types, the Mach-Zehnder modulator (commonly called MZM modulator), the electro-absorbing modulator (commonly called EAM modulator) and the use of a semiconductor amplifier.

[0019] The Mach-Zehnder modulator is an interferometer. An interferometer is an instrument used to generate and study interference fringes. The Mach-Zehnder modulator has an extinction ratio of approximately 25 to 30 dB.

[0020] Nevertheless, the Mach-Zehnder modulator exhibits a significantly reduced extinction ratio in the quasi-linear region of the modulator. This is due to the sinusoidal transfer function of this modulator. This transfer function is conditioned by the voltage of a modulation signal. For such a modulator, the maximum multilevel modulation order does not exceed PAM-16, namely modulation on 16 distinct amplitude levels.

[0021] The electro-absorbing modulator is a reverse-biased diode. The diode is made of semiconductor materials. Varying the bias voltage modifies the absorption of an incident light wave.

[0022] Thus, depending on the variation of the bias voltage, an amplitude modulation of an incident optical signal as a function of an applied inverse voltage is obtained.

[0023] However, such a device has a transfer function which exhibits a non-linearity limiting the extinction rate in the linear part to only 15dB.

[0024] 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, namely modulation on 4 distinct amplitude levels.

[0025] 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.

[0026] Amplifiers are used in virtually all circuits in electronics and optics: they make it possible to raise the voltage of an electrical signal or the power of an optical signal 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 a maximum power sufficient to power a load such as a radio antenna or an electroacoustic speaker.

[0027] An amplifier allows a signal to be amplified over a certain bandwidth. In the case of an electrical circuit, the bandwidth defines a range of frequencies within which the signal can be amplified. In the case of an optical circuit, the bandwidth defines a range of frequencies or wavelengths within which the signal can be amplified, frequency and wavelength being related by the equation f = λ, with f defining the frequency of the light wave (defined in Hz), c defining the speed (defined in ms), and λ defining the wavelength of the background light (defined in m).

[0028] Optical amplification is achieved with forward bias. Amplitude modulation of an incident optical signal can be obtained by varying the bias current. Varying the bias current modifies the gain of the semiconductor optical amplifier.

[0029] The extinction ratio of the solid-state optical amplifier is typically in the order of 10 to 15 dB. For a solid-state optical amplifier or a reflective solid-state optical amplifier, the maximum multilevel modulation order does not exceed PAM-4, namely modulation on 4 distinct amplitude levels.

[0030] 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.

[0031] The invention aims to provide a system to meet these needs.

[0032] BRIEF DESCRIPTION OF THE INVENTION

[0033] To this end, the present invention relates to a modulation system configured to control the modulation of a signal, the system comprising: - an optical modulator configured to receive: • an input signal consisting of a carrier wave, and • a modulation signal, 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 .

[0034] Advantageously, at such a cryogenic temperature, the extinction ratio of the optical modulator is on the order of 50 dB for a current of 100 mA. This allows advantageously increase the gain in the linear region of the optical modulator by approximately 15 dB.

[0035] Advantageously, by placing the optical modulator at such a cryogenic temperature, the maximum multilevel modulation order can reach, for example, PAM-32, namely 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.

[0036] Advantageously, placing the optical modulator at such a cryogenic temperature allows for a reduction of noise at the level of the input signal and the modulation signal.

[0037] 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 called OFDM: "Orthogonal Frequency-Division Multiplexing").

[0038] OFDM is a method of encoding digital signals by orthogonal frequency distribution in the form of a plurality of subcarriers.

[0039] This technique makes it possible to combat frequency-selective channels by enabling low-complexity equalization. These channels manifest themselves particularly in the presence of multiple paths and are all the more detrimental as the transmission rate is high.

[0040] Advantageously, the modulation system may also include 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 laser modulator 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 optical input signal at one terminal and a second optical input signal, identical to the first optical input 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 system is active; and / or the cooling device is passive; and / or the cooling device is direct; and / or the cooling system is indirect; and / or The cooling device includes a temperature controller, the temperature controller being configured to maintain the solid-state 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 solid-state 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 solid-state optical amplifiers or several reflective solid-state optical amplifiers; and / or The cooling system includes a temperature control device for at least two solid-state 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 modulating optical signal and the input optical signal have different polarizations; and / or the wavelength of the input optical signal differs from the wavelength of the modulation 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 system includes: • 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, • a cold spot positioned at a first location on the bar, and • a temperature control device including a temperature sensor located at a second location on the bar. BRIEF DESCRIPTION OF THE FIGURES

[0041] The invention will be better understood in the light of the following description, which is given by way of example only and is not intended to limit the said invention, together with the figures below:

[0042] [Fig.la] is a representation of a constellation diagram of a quadrature amplitude modulation,

[0043] [Fig. 1b] is a representation of a constellation diagram of a quadrature amplitude modulation,

[0044] [Fig. 1] is a representation of a constellation diagram of a quadrature amplitude modulation,

[0045] [Fig.2] is a schematic representation of an interrupt system according to the invention, according to a first embodiment,

[0046] [Fig.3] is a schematic representation of an interrupt system according to the invention, according to a second embodiment,

[0047] [Fig.4] is a schematic representation of an interrupt system according to the invention, according to a third embodiment,

[0048] [Fig.5] is a schematic representation of an interrupt system according to the invention, according to a fourth embodiment,

[0049] [Fig.6] is a schematic representation of an interrupt system according to the invention, according to a fifth embodiment,

[0050] [Fig.7] is a schematic representation of an interrupt system according to the invention, according to a sixth embodiment,

[0051] [Fig.8] is a schematic representation of an interrupt system according to the invention, according to a seventh embodiment,

[0052] [Fig.9] is a schematic representation of an interrupt system according to the invention, according to an eighth embodiment, and

[0053] [Fig. 10] is a schematic representation of an interruption system according to the invention, according to a ninth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0054] The invention relates to a modulation system configured to control the modulation of a signal, the system comprising: - an optical modulator configured to receive: • an input signal consisting of a carrier wave, and • a modulation signal, - 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.

[0055] The optical modulator is configured to receive an input optical signal comprising a carrier whose amplitude can vary.

[0056] The optical modulator can be a laser modulator, such as a laser diode, in the case of direct modulation.

[0057] In an alternative embodiment, the optical modulator is a semiconductor amplifier or a reflective semiconductor amplifier, in the case of indirect modulation.

[0058] 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 determines the wavelength range at which the signal is modulated.

[0059] Figure 2 illustrates a modulation system 10 configured to control the modulation of a signal, the system comprising: - an optical modulator, consisting of a semiconductor amplifier (AMP), configured to receive: • an SOE optical input signal formed by a carrier, and • an SM modulation signal, - 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.

[0060] The signal produced at the output of the optical modulator is a modulated optical signal.

[0061] 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.

[0062] Advantageously, the electrical modulation signal SM can be used to provide power to a modulator in the form of a semiconductor optical amplifier AMP.

[0063] It was surprisingly observed that the AMP semiconductor optical amplifier provided a non-zero gain when subjected to a cryogenic temperature of 10 K or higher, preferably 40 K or higher and 90 K or lower, preferably 80 K or lower, and when a low power supply, on the order of a few milliamperes, was provided.

[0064] Since the AMP semiconductor optical amplifier is not very energy-intensive 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 a QAM16 quadrature modulation.

[0065] Advantageously, when the modulation signal is optical, this allows the latter to be remote.

[0066] In the case of an optical SM modulation signal, the range of wavelengths over which an input signal can be modulated and the modulation options will be different from the ranges of wavelengths and modulation options permitted by a modulation signal in electrical form.

[0067] In the context of an all-optical modulation system, where 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.

[0068] The power of the input optical signal SOE is less 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.

[0069] The modulation signal of a semiconductor amplifier AMP is the signal having the highest power among the input optical signal SOE and the modulation signal SM.

[0070] In one embodiment, the input optical signal power 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).

[0071] The SM modulation signal may have a different polarization than the SOE input optical signal. For example, the SM modulation signal may be in electrical transverse mode, or in magnetic transverse mode respectively, and the SOE input optical signal may be in magnetic transverse mode, or in electrical transverse mode respectively.

[0072] For the remainder of this description, the optical modulator is considered to be 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.

[0073] In the case where the modulation signal is optical, the optical input 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 AMP semiconductor amplifier.

[0074] The AMP semiconductor optical amplifier is a bidirectional optoelectronic component.

[0075] In one embodiment, illustrated in [Fig. 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 terminals arranged on either side of the amplifier. The optical input signals SOE1 and SOE2 are considered to be counter-directional.

[0076] To facilitate understanding of [Fig. 3], the second optical input signal SOE2 and the modulated optical signal SOM have been represented separately to define the direction of propagation of these signals. However, the second optical input signal SOE2 and the modulated optical signal SOM are counter-propagating signals within the same optical fiber.

[0077] 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.

[0078] 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 may differ 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.

[0079] The cooling device 12 of the modulation system 10 is preferably a cryogenic cooling device.

[0080] The cooling device 12 may be indirect. The cooling device is considered indirect when a cooling means does not act directly on the optical modulator but on an element, for example a thermally conductive one, on which the optical modulator is placed. The thermally conductive element, cooled by a cooling means, will in turn cool the optical modulator by thermal conduction.

[0081] An indirect cooling device 12 can, for example, be formed by a thermally conductive rod which is cooled at one of its ends by a cooling means. The rod is configured to receive at least one optical modulator.

[0082] Advantageously, an indirect cooling device can allow a cooling means to be shared for several optical modulators on a thermally conductive bar, for example arranged in different locations.

[0083] Alternatively, the cooling device 12 can be direct. The direct cooling device 12 is a device configured to apply a variation Thermal control is performed directly at the optical modulator.

[0084] 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.

[0085] Advantageously, it is not necessary to use a thermally conductive structure on which the optical modulator(s) would be placed.

[0086] Advantageously, the use of a direct cooling device 12 allows better control of the temperature supplied to at least one optical modulator.

[0087] Also, in the context of a direct cooling device 12, it is easier and faster to compensate for a variation in 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 situated.

[0088] The cooling device 12 can be a passive cooling device.

[0089] For example, a passive cooling device may be a heat sink in contact with the optical modulator. The heat sink radiates outwards from the modulation system, like a radiant heat extraction device. A passive cooling device 12 may also consist of a cooling circuit comprising liquid nitrogen.

[0090] A passive cooling device requires no energy input. Advantageously, the energy consumption for maintaining the optical modulator(s), for example the semiconductor optical amplifier(s) AMP1, AMP2, at a cryogenic temperature is reduced.

[0091] A cooling device 12 can be active. An active cooling device requires an energy input to ensure the 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.

[0092] 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 provide respectively a modulated optical signal SOM1, SOM2.

[0093] At least of the semiconductor optical amplifiers AMP1, AMP2 is cooled by the cooling device.

[0094] In one embodiment, the two semiconductor optical amplifiers AMP1, AMP2 are cooled by the same cooling device 12 or a respective cooling device.

[0095] Advantageously, the cooling device 12 can be shared by using the same cooling device for two semiconductor optical amplifiers AMP1, AMP2.

[0096] 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.

[0097] Alternatively, the two semiconductor optical amplifiers AMP1, AMP2 can be maintained at different temperatures. For example, two semiconductor optical amplifiers AMP1, AMP2 are maintained at temperatures with a difference greater than or equal to 5 K, preferably a difference greater than or equal to 10 K.

[0098] Advantageously, the amplifiers AMP1, AMP2 will modulate the input optical signals SOE1, SOE2 respectively received on different wavelength ranges.

[0099] In one embodiment, illustrated in [Fig.5], the same SM modulation signal is shared for two semiconductor optical amplifiers AMP1, AMP2.

[0100] 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.

[0101] In the same way as in the embodiment illustrated in [Fig. 5], where the SM modulation signal is shared, the input optical signal can also be shared. A single input signal SOE could be split in two and supplied to two solid-state optical amplifiers AMP1, AMP2. Each of the two solid-state optical amplifiers AMP1, AMP2 receives a different SMI, SM2 modulation signal, so as to provide a modulated optical signal SOM1, SOM2 respectively. The modulated optical signals SOM1, SOM2 are different

[0102]

[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 solid-state optical amplifier AMP or a plurality of solid-state optical amplifiers AMP1, AMP2 can form part of an integrated circuit 22, as illustrated in [Fig.6]. The integrated circuit 22 is, for example, a photonic integrated circuit.

[0107] To ensure precise temperature control of 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 include a temperature regulator 14, 14-1, 14-2 (illustrated in [Fig.8]).

[0108] Preferably, the temperature regulator 14, 14-1, 14-2 is configured to maintain the solid-state optical amplifier AMP, AMP1, AMP2 at a target temperature.

[0109] Advantageously, precise temperature control of the semiconductor optical amplifier AMP, AMP1, AMP2 allows precise control over which wavelength range the input signal will be modulated.

[0110] Also, the temperature regulator 14, 14-1, 14-2 compensates for the heat supplied by the modulation signal to the solid-state optical amplifier AMP, AMP1, AMP2. The higher the power of the modulation signal SM, SMI, SM2, the greater the heat transmitted by this signal. Therefore, to ensure proper thermal regulation of the temperature of the optical modulator, for example, the solid-state optical amplifier AMP, AMP1, AMP2, it is important to take into account the thermal impact of the modulation signal SM, SMI, SM2.

[0111] 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].

[0112] Furthermore, the cooling device includes a temperature regulator, the temperature regulator being configured to maintain the solid-state 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.

[0113] Advantageously, precise temperature control of the solid-state optical amplifier AMP can be ensured. By having precise temperature control of the solid-state amplifier AMP, it is possible to control over which wavelength range the input optical signal SOE, SOE1, SOE2 will be modulated.

[0114] Fig. 8 represents 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.

[0115] Such a system, using cooling devices and respective temperature regulators, allows for better control of the temperature of each of the two semiconductor optical amplifiers AMP1, AMP2.

[0116] Figure 9 illustrates one embodiment of the cooling device 14. The cooling device 14 may include: - a bar 16 made of a material having high thermal conductivity on which the N amplifiers are arranged (in the case of [Fig.9], two amplifiers AMP1 and AMP2 are shown), - a cold point 18 arranged at a first location El of the bar 16, and - a temperature regulation device 14 comprising a temperature sensor 20 disposed at a second location E2 of the bar.

[0117] 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.

[0118] In one embodiment, the bar 16 is made of copper.

[0119] The bar can be made of a material having high thermal conductivity and the presence of a cold spot 18 makes it possible to create a temperature gradient between the first place El where the cold source 18 is located and an end E2 of the bar 16.

[0120] With such a temperature gradient, the positioning of the semiconductor optical amplifiers AMP1, AMP2 is important to be at a desired target temperature T1, T2.

[0121] The temperature of the semiconductor optical amplifiers AMP1, AMP2 arranged on the bar 16 is conditioned by their location on the bar 16.

[0122] The cold spot 18 corresponds to a cooling means configured to cool the bar 16 at a particular location on that bar 16, corresponding to the first location EL

[0123] In this way, the amplifiers located closest to the cold point 18 have a colder temperature than the amplifiers furthest from the cold point 18.

[0124] Preferably, the cooling means used is a cryogenic cooler.

[0125] The cold spot 18 is preferentially 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] Positioning a temperature sensor 20 at a second location E2 on the bar 16 makes it possible to determine the temperature of the bar 16 at this second location E2. Since the bar is made of a conductive material, it can be determined from the measurement from 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 located.

[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] If the temperature of at least one solid-state optical amplifier AMP1, AMP2 is different from the desired target temperature T1, T2, the cooling device 12 commands the regulating device 14 to regulate the temperature of the cold spot 18 of the bar 16.

[0129] In another embodiment illustrated in [Fig. 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 regulates the temperature of that amplifier AMP1, AMP2.

[0130] Each of the semiconductor optical amplifiers AMP1, AMP2 is associated with a respective additional thermal source S1, S2. Each of the additional thermal sources S1, S2 is configured to individually regulate the temperature of one of the semiconductor optical amplifiers AMP1, AMP2.

[0131] In one embodiment, the N additional thermal sources are Peltier modules and / or resistors.

[0132] Advantageously, Peltier modules allow the temperatures of the semiconductor optical amplifiers AMP1, AMP2 to be regulated by locally increasing or lowering their temperature.

[0133] Advantageously, the resistors allow the temperatures of the semiconductor optical amplifiers AMP1, AMP2 to be regulated by locally increasing their temperature.

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

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

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

[0137] Many other modifications and variations are self-evident to a person skilled in the art, after consideration of the different 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 "including" 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 shall not be interpreted as a limitation of the scope of the invention.

Claims

Claims

1. Modulation system (10) configured to control the modulation of a signal, the system comprising: - an optical modulator configured to receive: • an input signal formed by a carrier (SOE, SOE1, SOE2), and • 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 and less than or equal to 90 K, and characterized in that the optical modulator is a semiconductor optical amplifier (AMP, AMP1, AMP2) or a reflective semiconductor optical amplifier.

2. The modulation system according to claim 1, characterized in that the modulation signal (SM, SMI, SM2) is an electrical signal.

3. The modulation system according to one of the preceding claims, characterized in that the cooling device (12, 12-1, 12-2) is direct.

4. The modulation system according to claim 1 or 2, characterized in that the cooling device (12, 12-1, 12-2) is indirect.

5. The modulation system according to one of the preceding claims, characterized in that the cooling device (12, 12-1, 12-2) comprises a temperature regulator (14, 14-1, 14-2), the temperature regulator being configured to maintain the semiconductor optical amplifier (AMP, AMP1, AMP2) at a target temperature (Tl, T2) with a margin of ± 500 mK, preferably ± 200 mK.

6. The modulation system according to one of the preceding claims, characterized in that the semiconductor optical amplifier (AMP, AMP1, AMP2) is mounted on an integrated component (22).

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

8. The modulation system according to one of the preceding claims, characterized in that the modulation system comprises several semiconductor optical amplifiers (AMP, AMP1, AMP2) or several reflective semiconductor optical amplifiers.

9. 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).

10. The modulation system according to one of the preceding claims, characterized in that the modulation signal (SM, SMI, SM2) 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.

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