Modulation system configured to control modulation of a signal - Patent application

Abstract

A modulation system 10 configured to control modulation of a signal, comprising an optical modulator configured to receive input signals SOE, SOE1, SOE2 formed by a carrier wave and modulation signals SM, SM1, SM2, and cooling devices 12, 12-1, 12-2 configured to cool the optical modulator to a temperature of 10 K or more, preferably 40 K or more, and to cool the optical modulator to a temperature of 90 K or less, preferably 80 K or less.

Description

[Technical field]

[0001] The present invention relates to a modulation system configured to control the modulation of an optical input signal. [Background technology]

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

[0003] US Patent No. 5,399,663 describes an optoelectronic data link system with cryogenic cooling, and US Patent No. 5,399,663 discloses an integrated optical waveguiding device.

[0004] It is known to use a modulator which allows amplitude modulation.

[0005] One example of amplitude modulation is Pulse Amplitude Modulation (PAM), a form of signal modulation in which message information is encoded according to the amplitude of a series of signal pulses. It is an analog pulse modulation method in which the amplitude of a series of carrier pulses is modified according to the sample values ​​of the message signal.

[0006] An alternative type of modulation is quadrature amplitude modulation, also known as "QAM" (an old term for "Quadrature Amplitude Modulation"). This modulation is a form of modulation of a carrier wave by modifying the amplitude of the carrier wave itself and of an orthogonal wave according to the information carried by the two input signals. Quadrature is defined by a wave that is 90 degrees out of phase with the carrier wave.

[0007] In other words, QAM modulation can be thought of as a complex wave amplitude modulation by a complex signal: the amplitude and phase of the carrier wave are simultaneously modified according to the information to be transmitted.

[0008] These two types of modulation are known to include 16, 32 or 64 point constellations, such as those shown in Figures 1a, 1b and 1c, for the case of quadrature amplitude modulation.

[0009] 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.

[0010] Figures 1a, 1b and 1c show constellation diagrams. A constellation diagram is a representation of a signal modulated by a digital modulation such as quadrature amplitude modulation (QAM). The representation is mapped onto a two-dimensional diagram whose axes define the extent of the complex plane at the symbol sampling instants. The points in the complex plane are images of the symbols present at this given instant resulting from the modulation. Constellation diagrams can be used to identify types of interference or distortion in the signal.

[0011] Representing a symbol as a complex number makes it possible 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. They are then called orthogonal carriers. A coherent detector has the ability to demodulate these components separately. The principle of independently modulating two carriers forms the basis of orthogonal modulation.

[0012] The two components of a symbol considered to be a complex number can be visualized in a coordinate system with the real component as the abscissa (I-axis, or "in-phase") and the imaginary component as the ordinate (Q-axis, or "quadrature"). Displaying all the symbols at a given time in this coordinate system constructs a constellation diagram. The points in the constellation diagram are called constellation points.

[0013] The constellation diagrams shown in Figures 1a, 1b and 1c show different positions of the states for different quadrature amplitude modulation orders (QAM16, QAM32 and QAM64). The more the modulation order increases, the more points there are in the QAM constellation diagram.

[0014] It can be seen in these QAM constellation diagrams that as the modulation order increases, the distance between the points of the constellation for a given maximum amplitude decreases. Thus, small amounts of noise can cause bigger problems as the modulation order increases.

[0015] The higher the noise level caused by a weak signal, the more area is covered by one point in the constellation. If it becomes too large, the receiver will not be able to determine the position of the transmitted signal on the constellation, resulting in errors. It should also be noted that the higher the modulation order of the QAM signal, the larger the amplitude variations of the transmitted signal will be, if it is desired to maintain a constant distance between the points of the constellation.

[0016] The same teachings also apply to amplitude pulse modulation, also called Pam modulation, however the Pam constellation diagram is formed by a number of points defined along an axis.

[0017] To be able to define the number of points in the constellation, it is important to take into account the linear area and extinction ratio of the amplifier used as a modulator. The extinction ratio corresponds to the ratio in dB of the maximum power of the modulated signal to the minimum power of the modulated signal. The extinction ratio of the same amplifier at room temperature is about 20 dB.

[0018] The linear area defines the range of power, within which the input signal will be amplified to a desired gain minus, for example, 1 or 3 dB.

[0019] It is known to use three types of modulators to convert an electrical signal into an optical signal: a Mach-Zehnder modulator (commonly referred to as an MZM modulator), an electro-absorption modulator (commonly referred to as an EAM modulator), and the use of solid-state amplifiers.

[0020] A Mach-Zehnder modulator is an interferometer. An interferometer is a tool for creating and studying interference patterns. A Mach-Zehnder modulator has an extinction ratio of about 25 to 30 dB.

[0021] However, Mach-Zehnder modulators have a greatly reduced extinction rate in the quasi-linear area 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 the modulating signal. For such modulators, the highest order of multilevel modulation does not exceed PAM-16, i.e. modulation with 16 distinct amplitude levels.

[0022] An electroabsorption modulator is an inverted polarized diode made from semiconductor materials. Changing the bias voltage changes its absorption of the incident light wave.

[0023] Thus, varying the bias voltage results in an amplitude modulation of the incident optical signal by the applied reverse voltage.

[0024] However, such devices have a transfer function with nonlinearity that limits the extinction rate in the linear part to only 15 dB.

[0025] The voltage range over which an electroabsorption modulator can be driven is much lower than that of a Mach-Zehnder modulator. For electroabsorption modulators, the highest order of multilevel modulation does not exceed PAM-4, i.e. modulation at four distinct amplitude levels.

[0026] 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: its output is an exact replica of the input with increased power.

[0027] Amplifiers are used in almost every circuit in electronics and optics: they can increase the voltage of an electrical signal or the power of an optical signal to a level that can be used by the rest of the system, increase the output current of a sensor to allow interference-free transmission, or provide a maximum power sufficient to power a load such as a radio antenna or an electro-acoustic enclosure.

[0028] An amplifier amplifies a signal up to a certain bandwidth. For electrical circuits, the bandwidth defines the range of frequencies over which the signal can be amplified. For optical circuits, the passband defines the range of frequencies or wavelengths over which the signal can be amplified, and frequency and wavelength are expressed by the equation:

number

[0029] Optical amplification is obtained in the forward polarization. Amplitude modulation of the incident optical signal can be obtained by varying the bias current. Changing the bias current changes the gain of the solid-state optical amplifier.

[0030] The extinction ratio of solid-state optical amplifiers is typically in the range of 10 to 15 dB. For solid-state optical amplifiers or reflective solid-state optical amplifiers, the highest order of multilevel modulation does not exceed PAM-4, i.e. modulation with four distinct amplitude levels.

[0031] There is therefore a need to be able to increase the linear area and the number of constellation points over which a signal can be modulated.

[0032] It is an object of the present invention to provide a system for meeting these needs. [Prior art documents] [Patent documents]

[0033] [Patent Document 1] U.S. Patent No. 10,097,281 [Patent Document 2] U.S. Patent No. 5,271,074 Summary of the Invention

[0034] To this end, the present invention relates to a modulation system adapted to control the modulation of a signal, the system comprising: an optical modulator configured to receive: - an input signal formed by a carrier wave, and - modulated signal, A cooling device configured to cool the optical modulator to a temperature of 10 K or more, preferably 40 K or more, and configured to cool the optical modulator to a temperature of 90 K or less, preferably 80 K or more.

[0035] Advantageously, at such cryogenic temperatures, the extinction ratio of the optical modulator is approximately 50 dB for a current of 100 mA, which advantageously makes it possible to increase the gain in the linear area of ​​the optical modulator by approximately 15 dB.

[0036] Advantageously, by placing the optical modulator at such cryogenic temperatures, the highest order of multilevel modulation can be reached, for example PAM-32, i.e. modulation with 32 distinct amplitude levels, and the number of points in the constellation can reach at least 256 points in quadrature amplitude modulation, as part of the electro-optical modulation.

[0037] Advantageously, by subjecting the optical modulator to such cryogenic temperatures, noise at the input signal and modulated signal levels can be reduced.

[0038] Advantageously, by subjecting the optical modulator to such cryogenic temperatures, the linearity range of the modulator is increased compared to prior art modulation systems, which allows modulation of input signals whose envelope amplitudes are not constant, such as in Orthogonal Frequency-Division Multiplexing (commonly called OFDM: Orthogonal Frequency-Division Multiplexing).

[0039] OFDM is a method for encoding a digital signal by orthogonal frequency division in the form of multiple subcarriers.

[0040] This technique allows for a low-complexity equalization, thereby making it possible to combat frequency-selective channels, which appear especially when multiple paths exist and which are even more detrimental to higher transmission rates.

[0041] Advantageously, the modulation system may comprise one or more of the following features, taken individually or in any technically possible combination: 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 and is a laser diode; and / or - the optical modulator is a semiconductor optical amplifier or a reflective semiconductor optical amplifier; and / or the modulated signal is an electrical signal, and / or the modulated 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 the opposite direction; 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 regulator, the temperature regulator being configured to maintain the semiconductor optical amplifier at the target temperature with a margin of 500 mK or less, preferably 200 mK or less, and a margin of −500 mK or more, preferably −200 mK or more; 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 a plurality of semiconductor optical amplifiers or a plurality of reflective semiconductor optical amplifiers; and / or the cooling device comprises a device for adjusting the temperature of the at least two semiconductor optical amplifiers; and / or at least two semiconductor optical amplifiers are at different temperatures; and / or - the modulating signal is a shared modulating signal of each semiconductor optical amplifier; and / or the modulated signal has a bandwidth of 0.01 GHz or more and 100 GHz or less, preferably 40 GHz or less; 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 modulated 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: A bar made of a material having a thermal conductivity of at least 20 watts per metre Kelvin on which the amplifier is placed, a cold spot arranged at a first position on the bar, and A temperature control device including a temperature sensor disposed at a second location on the bar.

[0042] 1. A modulation system configured to control modulation of a signal, comprising: an optical modulator configured to receive: - an input signal formed by a carrier wave, and - modulated signal, A cooling device configured to cool the optical modulator to a cryogenic temperature. A modulation system comprising:

[0043] The invention will be better understood in the light of the following description, accompanied by the following figures, given merely by way of indication and not intended to limit said invention: [Brief description of the drawings]

[0044] [Figure 1a] 1 is a representation of a constellation diagram for quadrature amplitude modulation. [Figure 1b] 1 is a representation of a constellation diagram for quadrature amplitude modulation. [Figure 1c] 1 is a representation of a constellation diagram for quadrature amplitude modulation. [Diagram 2] 1 is a schematic diagram of an interrupt system according to the present invention according to a first embodiment; [Diagram 3] FIG. 2 is a schematic diagram of an interrupt system according to the present invention according to a second embodiment; [Figure 4] FIG. 4 is a schematic diagram of an interrupt system according to the present invention, according to a third embodiment; [Diagram 5] FIG. 10 is a schematic diagram of an interrupt system according to the present invention, according to a fourth embodiment; [Figure 6] FIG. 10 is a schematic diagram of an interrupt system according to the present invention, according to a fifth embodiment; [Figure 7] FIG. 13 is a schematic diagram of an interrupt system according to the present invention, according to a sixth embodiment; [Figure 8]FIG. 13 is a schematic diagram of an interrupt system according to the present invention, according to a seventh embodiment; [Figure 9] FIG. 13 is a schematic diagram of an interrupt system according to the present invention, according to an eighth embodiment. [Figure 10] FIG. 13 is a schematic diagram of an interrupt system according to the present invention, according to a ninth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] 1. A modulation system configured to control modulation of a signal, comprising: an optical modulator configured to receive: - an input signal formed by a carrier wave, and - modulated signal, A cooling device configured to cool the optical modulator to a temperature of 10 K or more, preferably 40 K or more, and 90 K or less, preferably 80 K or less. A modulation system comprising:

[0046] The optical modulator is configured to receive an input optical signal that includes a carrier whose amplitude can be varied.

[0047] The optical modulator can be a laser modulator, e.g. a laser diode, in the case of direct modulation.

[0048] In an alternative embodiment, the optical modulator is a semiconductor amplifier or a reflective semiconductor amplifier in the case of indirect modulation.

[0049] The modulating signal has a bandwidth greater than 0.01 GHz and less than 100 GHz, preferably less than 40 GHz. The temperature of the optical modulator conditions the wavelength range over which the signal is modulated.

[0050] FIG. 2 shows a modulation system 10 configured to control the modulation of a signal, the system comprising: an optical modulator formed by an amplifier semiconductor amplifier configured to receive: - an input optical signal SOE formed by a carrier wave, and - SM modulated signal, A cooling device 12 configured to cool the optical modulator to a temperature above 10K, preferably above 40K, and below 90K, preferably below 80K.

[0051] The signal produced at the output of the optical modulator is a modulated optical signal.

[0052] The modulating signal SM can be an electrical signal. Alternatively, it is an optical signal. The modulating signal SM provides the modulator with the necessary information for the modification of the carrier of the input optical signal SOE.

[0053] Advantageously, the modulated electrical signal SM may be used to provide power to the modulator in the form of a solid state optical amplifier.

[0054] Surprisingly, it has been found that the amplifier semiconductor optical amplifier provides non-zero gain when subjected to cryogenic temperatures of above 10 K, preferably above 40 K, and below 90 K, preferably below 80 K, and provides low power supply, of about a few milliamps.

[0055] Since the amplifier semiconductor optical amplifier consumes very little energy at this temperature, it is then possible to replace its power supply via an electrical SM modulated signal with an optical SM modulated signal, for example in the case of QAM16 quadrature modulation.

[0056] Advantageously, when the modulating signal is optical, this allows the latter to be cancelled out.

[0057] In the case of an optical SM modulated signal, the range of wavelengths and modulation options at which the input signal may be modulated may differ from the wavelength range and modulation options allowed by the modulated signal in electrical form.

[0058] In an all-optical modulation system, where the input signal and the modulating signal are optical, the power of the input optical signal SOE is at least 5 dB lower, preferably at least 10 dB lower, than the power of the modulating signal SM.

[0059] The power of the input optical signal SOE is less than the power of the modulated signal so that the solid-state optical amplifier distinguishes the modulated signal SM from the input optical signal SOE.

[0060] The modulating signal of the solid-state amplifier AMP is the signal having the highest power among the input optical signal SOE and the modulating signal SM.

[0061] 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, where dBm is a unit expressing power in decibels (dB) relative to a reference value of 1 milliwatt (mW).

[0062] The modulation signal SM may have a different polarization than that of the input optical signal SOE, for example, the modulation signal SM may be in a transverse electric mode, respectively a transverse magnetic mode, and the input optical signal SOE may be in a transverse magnetic mode, respectively a transverse electric mode.

[0063] For the remaining description, the optical modulator is considered in the form of a semiconductor amplifier amplifier.Figures 2 to 10 feature a modulation system according to the invention comprising a semiconductor amplifier amplifier.

[0064] If the modulating signal is optical, the input optical signal and the optical modulating signal may be provided jointly using a single optical fiber to an optical modulator, for example at one of the terminals of a solid-state amplifier.

[0065] Amplifiers Solid-state optical amplifiers are bidirectional optoelectronic components.

[0066] In one embodiment, shown in Figure 3, a first input optical signal SOE1 and a second input optical signal SOE2, which is identical to the first input optical signal SOE1, are provided to a semiconductor optical amplifier in opposite directions via terminals located on either side of the amplifier. The input optical signals SOE1 and SOE2 are considered to be in opposite directions.

[0067] 3, the second input optical signal SOE2 and the modulated optical signal SOM are shown separately to define the direction of propagation of these signals. However, the second input optical signal SOE2 and the modulated optical signal SOM are counter-propagating signals in the same optical fiber.

[0068] In one embodiment, the modulated signal SM and the input optical signal SOe have different polarities and / or are transmitted to two opposite ends of a solid-state optical amplifier amplifier.

[0069] In another embodiment, the wavelengths of the modulation signal and the input optical signal SOE may differ, for example, the wavelengths of the modulation signal SM and the input optical signal SOe differ by at least 0.05 nm, preferably at least 0.1 nm, preferably at least 0.5 nm, preferably at least 1 nm, preferably at least 1.5 nm, and even more preferably at least 5 nm.

[0070] The cooling device 12 of the modulation system 10 is preferably a cryogenic cooling device.

[0071] The cooling device 12 may also be indirect. A cooling device is considered indirect if it does not act directly on the light modulator, but on an element on which the light modulator is placed, e.g. thermally conductive. The thermally conductive element, cooled by the cooling means, will then cool the light modulator by thermal conduction.

[0072] The indirect cooling device 12 may for example be formed by a thermally conductive bar which is to be cooled at one of its ends by a cooling means, the bar being configured to receive at least one light modulator.

[0073] Advantageously, an indirect cooling device may make it possible to pool the cooling means for several light modulators, for example arranged at different positions, on a thermally conductive bar.

[0074] Alternatively, the cooling device 12 may be direct. A direct cooling device 12 is a device configured to apply a thermal variation directly to the optical modulator. Temperature control is performed directly at the optical modulator.

[0075] A direct cooling device may be formed by dedicated cooling means for locally cooling one or more optical modulators, for example one or more semiconductor optical amplifiers AMP1, AMP2.

[0076] Advantageously, there is no need to resort to a conductive thermal structure on which the light modulator is to be disposed.

[0077] Advantageously, the use of a direct cooling device 12 allows for greater control over the temperature supplied to the at least one optical modulator.

[0078] Also, as part of the direct cooling device 12, it is easier and faster to compensate for variations in the light modulator without having to wait for the conductive elements at the location where the light modulator is placed to reach a desired temperature.

[0079] The cooling device 12 can be a passive cooling device.

[0080] For example, the passive cooling device can be a radiator in contact with the light modulator, which radiates to the outside of the modulation system, for example a device for extracting thermal energy by radiation. The passive cooling device 12 can also be formed by a cooling circuit containing liquid nitrogen.

[0081] Passive cooling devices have no energy input. Advantageously, the power consumption for maintaining the optical modulators, e.g., semiconductor optical amplifiers AMP1, AMP2, at cryogenic temperatures is reduced.

[0082] The cooling device 12 may 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 the optical modulator is faster and more reliable due to the control of the cooling device by adjusting its power supply.

[0083] 4 shows 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 including a carrier and a modulation signal SM1, SM2, respectively, to provide a modulated optical signal SOM1, SOM2, respectively.

[0084] At least one of the semiconductor optical amplifiers AMP1 and AMP2 is cooled by a cooling device.

[0085] In one embodiment, the two semiconductor optical amplifiers AMP1, AMP2 are cooled by the same cooling device 12 or by respective cooling devices.

[0086] Advantageously, the cooling device 12 can be shared, using the same cooling device for the two semiconductor optical amplifiers AMP1, AMP2.

[0087] The two semiconductor optical amplifiers AMP1, AMP2 can be maintained at the same temperature, for example when the at least two semiconductor optical amplifiers AMP1, AMP2 are implemented in an integrated circuit 22 that is cooled by a cooling device 12.

[0088] Alternatively, the two semiconductor optical amplifiers AMP1 and AMP2 can be maintained at different temperatures. For example, the two solid-state optical amplifiers AMP1 and AMP2 are maintained at temperatures with a deviation of 5K or more, preferably a deviation of 10K or more.

[0089] Advantageously, amplifiers AMP1, AMP2 will modulate the received input optical signals SOE1, SOE2 respectively over different wavelength ranges.

[0090] In one embodiment, shown in FIG. 5, the same modulated signal SM is pooled for two semiconductor optical amplifiers AMP1, AMP2.

[0091] Advantageously, in this way modulation of the input optical signals SOE1, SOE2 can be ensured simultaneously in the semiconductor optical amplifiers AMP1, AMP2.

[0092] The input optical signal may be shared in the same manner as in the embodiment shown in Fig. 5, where the modulating signal SM is shared. A single input signal SOE may be split in two and fed to two solid-state optical amplifiers AMP1, AMP2. Each of the two semiconductor optical amplifiers AMP1, AMP2 receives a different modulating signal SM1, SM2 to provide a modulated optical signal SOM1, SOM2, respectively. The modulated optical signals SOM1, SOM2 are different.

[0093] In one embodiment, the input optical signal SOE and the modulated signal SM are respectively shared for at least two amplifiers.

[0094] Advantageously, the same modulated signal may be provided at the separate locations at the same time.

[0095] In one embodiment, at least one of the semiconductor optical amplifiers AMP1, AMP2 are separate components.

[0096] Alternatively, a single solid-state optical amplifier AMP or multiple solid-state optical amplifiers AMP1, AMP2 may form part of an integrated circuit 22, as shown in Figure 6. Integrated circuit 22 may be, for example, a photonic integrated circuit.

[0097] 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 devices 12, 12-1, 12-2 may include temperature regulators 14, 14-1, 14-2 (shown in FIG. 8).

[0098] Preferably, the temperature regulators 14, 14-1, 14-2 are configured to maintain the semiconductor optical amplifiers AMP1, AMP2 at a target temperature.

[0099] Advantageously, precise control of the temperature of the semiconductor optical amplifiers AMP1, AMP2 allows precise control of the wavelength range over which the input signal will be modulated.

[0100] The temperature regulators 14, 14-1, 14-2 also make it possible to counteract the heat provided by the modulating signals to the semiconductor optical amplifiers AMP1, AMP2. The higher the power of the modulating signals SM, SM1, SM2, the more heat is provided by these signals. It is therefore important to take into account the thermal effect of the modulating signals SM, SM1, SM2 in order to ensure good thermal regulation of the temperature of the optical modulators, e.g. the semiconductor optical amplifiers AMP1, AMP2.

[0101] The temperature controllers 14, 14-1, 14-2 may be used to control the temperature of one of a plurality of semiconductor optical amplifiers, AMP1, AMP2, as shown in FIG.

[0102] Furthermore, the cooling device comprises a temperature regulator, the temperature regulator being configured to maintain the semiconductor optical amplifier at a target temperature with a margin of 500 mK or less, preferably 200 mK or less, and -500 mK or more, preferably -200 mK or more.

[0103] Advantageously, precise control of the temperature of the semiconductor optical amplifier amplifier can be ensured. By having precise control of the temperature of the solid-state amplifier amplifier, it can control the wavelength range over which the input optical signals SOE, SOE1, SOE2 will be modulated.

[0104] FIG. 8 shows a modulation system according to the invention, in which each of two semiconductor optical amplifiers AMP1, AMP2 is provided with a respective cooling device 12-1, 12-2 and a temperature regulator 14-1, 14-2.

[0105] 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.

[0106] 9 shows one example of the cooling device 14. The cooling device 14 may include: a bar 16 made of a material with high thermal conductivity, on which N amplifiers are arranged (in the case of FIG. 9 two amplifiers AMP1 and AMP2 are shown), a cold spot 18 arranged at a first position E1 of the bar 16, and A temperature regulating device 14 comprising a temperature sensor 20 arranged at a second position E2 of the bar.

[0107] Preferably, the bar 16 has a thermal conductivity of 20 watts per metre per kelvin or greater. The temperature at different positions of the bar 30 is different.

[0108] In one embodiment, the bar 16 is made of copper.

[0109] The bar may be made of a material with high thermal conductivity, and the presence of the cold spot 18 makes it possible to create a temperature gradient between a first location where the cold source 18 is located and one end of the bar 16.

[0110] With such a temperature gradient, the positioning of the semiconductor optical amplifiers AMP1 and AMP2 is important to be at the desired target temperatures T1 and T2.

[0111] The temperatures of the semiconductor optical amplifiers AMP1, AMP2 arranged on the rod 16 are conditioned by their positions on the rod 16.

[0112] The cold spot 18 corresponds to cooling means arranged to cool the bar 16 at a particular location of this bar 16 corresponding to the first location E1.

[0113] In this manner, the amplifiers located closest to the cold spot 18 will have a lower temperature than the amplifiers furthest from the cold spot 18 .

[0114] Preferably the cooling means used is a cryocooler.

[0115] The cold spot 18 is preferably located at one end of the bar 16 so as to maximize the temperature gradient between the first and second ends of the bar 30 .

[0116] The positioning of the temperature sensor 20 at the second position E2 of the bar 16 makes it possible to determine the temperature of the bar 16 at this second position E2. Since the bar is made of an electrically conductive material, it is possible to determine from the measurements of the temperature sensor 34 the approximate temperature at least at each point of the bar, and more specifically at the positions where the AMP1, AMP2 semiconductor optical amplifiers are located.

[0117] Advantageously, from the temperature measurement at said second position E2 of the rod 16, the cooling device 12 is able to determine whether the temperature of the semiconductor optical amplifiers AMP1, AMP2 corresponds to a desired target temperature.

[0118] If the temperature of at least one semiconductor optical amplifier AMP1, AMP2 differs from a desired target temperature T1, T2, the cooling device 12 controls the regulating device 14 to regulate the temperature of the cold spot 18 of the bar 16.

[0119] 10, the cooling device independently controls the temperatures T1, T2 of the semiconductor optical amplifiers AMP1, AMP2. If one of the semiconductor optical amplifiers AMP1, AMP2 is not at the desired target temperature, the temperature regulator 14 independently adjusts the temperature of this amplifier AMP1, AMP2.

[0120] Each of the semiconductor optical amplifiers AMP1, AMP2 is associated with a respective additional heat source S1, S2, each of which is configured to individually regulate the temperature of one of the semiconductor optical amplifiers AMP1, AMP2.

[0121] In one embodiment, the N additional heat sources are Peltier modules and / or resistors.

[0122] Advantageously, the Peltier module makes it possible to regulate the temperature of the semiconductor optical amplifiers AMP1, AMP2 by locally increasing or decreasing their temperature.

[0123] Advantageously, the resistors make it possible to regulate the temperature of the semiconductor optical amplifiers AMP1, AMP2 by locally increasing their temperature.

[0124] The embodiment shown in Figure 10 is similar to the configuration shown in Figure 8, but with a different temperature controller 14. The temperature controller 14 no longer regulates the temperature of the cold spot 18 of the rod 16, but directly regulates the temperature of the additional heat sources S1, S2.

[0125] The embodiment shown in FIG. 10 may not have the bar 16 and cold spot 18, and the heat sources S1 and S2 provide cold air to the semiconductor amplifiers S1, S2.

[0126] The invention has been described above using the embodiments shown in the drawings, without limiting the general inventive concept.

[0127] Numerous other modifications and variations will occur to those skilled in the art after consideration of the different embodiments presented in this application.

[0128] These examples are given by way of illustration and are not intended to limit the scope of the invention, which is determined exclusively by the claims that follow.

[0129] In the claims, the word "comprising" does not exclude other elements or steps. The mere fact that different features are recited in mutually dependent claims does not indicate that a combination of these features cannot be used to advantage. Finally, any reference signs used in the claims shall not be interpreted as limiting the scope of the invention.

Claims

1. A modulation system (10) configured to control modulation of a signal, comprising: An input signal (SOE, SOE1, SOE2) formed by a carrier wave, and Modulation signal (SM, SM1, SM2) an optical modulator configured to receive A cooling device (12, 12-1, 12-2) configured to cool the optical modulator to a temperature of 10 K or more, preferably 40 K or more, and to cool the optical modulator to a temperature of 90 K or less, preferably 80 K or less; A modulation system (10) comprising:

2. 2. 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.

3. A modulation system according to claim 2, characterized in that said modulation signals (SM, SM1, SM2) are electrical signals.

4. 2. The modulation system of claim 1, wherein the optical modulator is a modulator configured to receive a laser signal.

5. 5. The modulation system of claim 4, wherein the modulator configured to receive the laser signal is a laser diode.

6. Modulation system according to any one of the preceding claims, characterized in that the cooling device (12, 12-1, 12-2) is direct.

7. Modulation system according to any one of the preceding claims, characterized in that the cooling device (12, 12-1, 12-2) is indirect.

8. 8. The modulation system according to claim 2, characterized in that the cooling device (12, 12-1, 12-2) comprises a temperature regulator (14, 14-1, 14-2) configured to maintain the semiconductor optical amplifiers (AMP, AMP1, AMP2) at a target temperature (T1, T2) with a margin of ±500 mK, preferably ±200 mK.

9. 9. Modulation system according to any one of claims 4 to 8, characterized in that the semiconductor optical amplifiers (AMP, AMP1, AMP2) are mounted in an integrated component (22).

10. 10. The modulation system of claim 9, wherein the integrated component is a photonic integrated component.

11. 11. The modulation system according to claim 4, characterized in that the modulation system comprises a plurality of semiconductor optical amplifiers (AMP, AMP1, AMP2) or a plurality of reflective semiconductor optical amplifiers.

12. A modulation system according to claim 11, characterized in that the same cooling device (12, 12-1, 12-2) is adapted to cool at least two semiconductor optical amplifiers (AMP, AMP1, AMP2).

13. 13. A modulation system according to any one of the preceding claims, characterized in that the modulating signals (SM, SM1, SM2) have a bandwidth of >0.01 GHz and <100 GHz, preferably <40 GHz.

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