Photonic chip provided with Mach-Zehnder modulator

Abstract

The invention relates to a photonic system provided with a photonic chip made of silicon technology, said photonic chip (10) comprising:-a Mach-Zehnder modulator (100), the modulation parts (105, 106) of which extend over a length L of less than 3 mm; first means (107) for adjusting the operating point; -a semiconductor optical amplifier (SOA) configured to amplify the signal modulated by the Mach-Zehnder modulator, the semiconductor optical amplifier (SOA) such that, when the set phase shift F is adjusted to a range of 0.6 * pi to 0.9 * pi, the optical modulation amplitude associated with the photonic chip is between-2dBm and 6dBm at an output port S placed downstream of the semiconductor optical amplifier (SOA).

Description

Technical Field

[0001] The present invention relates to the field of photonics, and more particularly to integrated photonic chips.

[0002] In particular, the invention relates to a photonic chip provided with a Mach-Zehnder modulator configured to limit optical losses and having a bandwidth (3 dB) better than that of Mach-Zehnder modulators known from the prior art.

[0003] The photonic chip advantageously comprises a light emitter. Background Art

[0004] Optical modulators are widely used in optical transmitters to manipulate optical signals. Among the known optical modulators, Mach-Zehnder modulators are of particular interest when high light modulation speed is required.

[0005] therefore,[ Figure 1 ] shows a prior art Mach-Zehnder modulator 1. The Mach-Zehnder modulator 1 comprises in particular two modulation branches, called a first branch 2 and a second branch 3, which are connected at one end by at least one optical input 4 and at the other end by at least one optical output 5.

[0006] In particular, the two modulation branches 2 and 3 are arranged so that the light beam injected at the optical input end 4 is split into a first beam and a guided second beam by the first branch 2 and the second branch 3 respectively, and so that the first beam and the second beam are recombined at the optical output end.

[0007] The device is also provided with two phase modulators, referred to as first modulator 6 and second modulator 7, for applying a phase shift to the first beam and the second beam, respectively, before they are recombined at the optical output 5. The modification of the phase of one and / or the other of the first beam and the second beam makes it possible in particular to modulate the intensity of the recombined beam at the output of the Mach-Zehnder modulator.

[0008] The Mach-Zehnder device further comprises phase shifting means for applying an additional set phase shift q between the first branch 2 and the second branch 3. Conventionally, this set phase shift is usually equal to pi / 2, which corresponds to an operating point of the Mach-Zehnder device known as "quadrature" in order to linearize the output intensity modulation of the device as much as possible.

[0009] However, consideration of orthogonal operating points limits the performance of Mach-Zehnder devices.

[0010] It is therefore an object of the present invention to provide a photonic chip provided with a Mach-Zehnder modulator having improved performance compared to Mach-Zehnder devices or transmitters known from the prior art. Summary of the invention

[0011] The object of the present invention is achieved at least in part by a photonic system provided with a photonic chip made of silicon technology, the photonic chip comprising:

[0012] - a Mach-Zehnder modulator formed on and / or in a useful layer situated on one face of a support substrate, said Mach-Zehnder modulator comprising two modulation branches, respectively called first branch and second branch, each branch being provided with a modulation portion extending over a length L less than 3 mm;

[0013] - first means for adjusting an operating point of the Mach-Zehnder modulator, the first means being configured to impose an operating point associated with a set phase shift F between the first branch and the second branch;

[0014] - A semiconductor optical amplifier formed on and / or in the useful layer and arranged downstream of the output end of the Mach-Zehnder modulator, the semiconductor optical amplifier being configured to amplify the signal modulated by the Mach-Zehnder modulator, the semiconductor optical amplifier having an optical gain configured such that when the set phase shift F is adjusted within the range of 0.6*pi to 0.9*pi, at the output port S arranged downstream of the semiconductor optical amplifier SOA, the optical modulation amplitude associated with the photonic chip is between -3dBm and 10dBm.

[0015] In one embodiment, the first adjustment means comprises a first heating element configured to locally modify the refractive index of the first branch or the second branch by heating so as to apply the set phase shift F.

[0016] According to an embodiment, the photonic system comprises first control means configured to control the first adjustment means.

[0017] In one embodiment, the first control device includes a first photodetector and a first optical spectrum analyzer.

[0018] According to one embodiment, a Mach-Zehnder modulator comprises a radiation combiner configured to combine first radiation and second radiation phase-modulated by the first branch and the second branch, respectively, the first radiation and the second radiation originating from a splitting of optical radiation before being modulated by one of the modulation branches.

[0019] According to one embodiment, the photonic chip further comprises second means for adjusting the optical gain of the semiconductor optical amplifier, advantageously the second adjusting means comprises a second heating element.

[0020] According to one embodiment, the photonic system comprises a second control device configured to control the second adjustment device, the second control device comprising a second photodetector and a second optical spectrum analyzer.

[0021] According to one embodiment, the radiation combiner comprises two output channels, referred to as the first channel and the second channel, the second channel carrying a semiconductor optical amplifier, the second control device being carried by a second control waveguide optically coupled to the second channel, the coupling being of such a magnitude that the second waveguide extracts at most 10%, advantageously at most 5%, of the optical power flowing in the second channel.

[0022] According to one embodiment, the photonic chip further comprises an optical filter carried by the second channel and located downstream of the semiconductor optical amplifier.

[0023] In one embodiment, the photonic chip includes a laser source configured to inject optical radiation having a wavelength I at an input of a Mach-Zehnder modulator.

[0024] In one embodiment, the laser source is a tunable laser source.

[0025] The present invention also relates to a specific implementation of the photonic system according to the present invention, wherein the intensity of the optical radiation injected by the laser source is strictly less than 10 dB, advantageously less than 7 dB, and wherein the gain of the semiconductor optical amplifier is adjusted so that the intensity of the signal at the output end of the photonic chip is equal to the signal intensity obtained by the photonic chip in the absence of the semiconductor optical amplifier, and radiation with an intensity of 10 dB is injected at the input end of the photonic chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings, in which:

[0027] [ Figure 1 ][ Figure 1 ] is a schematic representation of a Mach-Zehnder device 1 known in the prior art;

[0028] [ Figure 2 ][ Figure 2 ] is a schematic representation of a Mach-Zehnder modulator that can be implemented within the scope of the present invention;

[0029] [ Figure 3 ][ Figure 3] is a schematic representation of a support substrate supporting a waveguide layer on its face, and along a cross-sectional plane perpendicular to the front face;

[0030] [ Figure 4 ][ Figure 4 ] is a graphical representation of the transfer function of a Mach-Zehnder modulator. In particular, the vertical axis (arbitrary units) represents the intensity of the modulated radiation as a function of the operating point F / pi (horizontal axis), wherein the double arrow represents the modulation amplitude for the quadrature operation of the Mach-Zehnder modulator;

[0031] [ Figure 5 ][ Figure 5 ] is a graphical representation of the transfer function of a Mach-Zehnder modulator. In particular, the vertical axis (arbitrary units) represents the power of the modulated radiation as a function of the operating point F / pi (horizontal axis), wherein the double arrow represents the modulation amplitude for operating points of the Mach-Zehnder modulator between 0.6*pi and 0.9*pi;

[0032] [ Figure 6 ][ Figure 6 ] is a graphical representation of an exemplary eye diagram associated with the operation of a Mach-Zehnder modulator;

[0033] [ Figure 7 ][ Figure 7 ] is the spectral characteristic of a Mach-Zehnder modulator modulated near the quadrature point;

[0034] [ Figure 8 ][ Figure 8 ] is the spectral characteristic of a Mach-Zehnder modulator modulated near the carrier suppression point. DETAILED DESCRIPTION

[0035] The invention relates to a photonic system provided with a photonic chip. In particular, the photonic chip according to the invention comprises a Mach-Zehnder modulator. The photonic chip is advantageously used to form a transmitter to which the photonic system may belong.

[0036] therefore,[ Figure 2 ] is a schematic representation of a photonic system 10 provided with a Mach-Zehnder modulator 100 that can be implemented within the scope of the present invention. In particular, the Mach-Zehnder modulator 100 can be formed on or in a layer referred to as the useful layer 200, which is located on the front side 310 of the supporting substrate 300 ([ Figure 3 ]).

[0037] The photonic chip is based on silicon technology. In other words, all the waveguides that form the Mach-Zehnder modulator are made of silicon.

[0038] The support substrate 300 may include any type of material, and more particularly includes a semiconductor material, such as silicon.

[0039] The useful layer 200 may include a semiconductor material, such as silicon or a III-V material. More particularly, the useful layer 200 may be located on a dielectric material layer between the useful layer 200 and a support substrate 300. For example, a Mach-Zehnder modulator may be formed on a silicon-on-insulator substrate.

[0040] The remainder of the description also relates to semiconductor amplifiers SOA, which can be made of III-V semiconductor materials. In particular, SOA can be manufactured via III-V semiconductor-on-silicon technology, SOA hybrid (assembly of prefabricated SOA components with silicon or SiNx waveguides) or hybrid or heterogeneous integration (molecular bonding of III-V semiconductor materials and formation of III-V components). In this regard, a person skilled in the art will be able to refer to the documents [1] and [4] cited at the end of the description.

[0041] According to the terminology of the present invention, the Mach-Zehnder modulator includes two modulation branches, respectively referred to as a first branch 101 and a second branch 102. The first branch 101 and the second branch 102 can be connected at one end of the two through an intermediate optical input terminal 103 and at the other end of the two through an intermediate optical output terminal 104.

[0042] More specifically, the first branch 101 and the second branch 102 each comprise a waveguide, respectively referred to as a first waveguide 101a and a second waveguide 102a. The first branch 101 and the second branch 102 each comprise a modulation section, respectively referred to as a first modulation section 105 and a second modulation section 106. The modulation section of a given modulation branch is configured to modulate the phase of a light beam that can be guided by the modulation branch in question.

[0043] The modulation part of the modulation branch may in particular comprise a section of the waveguide of said branch, called modulation waveguide, and an electrode for applying an electrical potential to said modulation waveguide.

[0044] The modulation section is particularly configured so that the potential applied to the modulation waveguide by the electrode modifies the refractive index of the modulation waveguide in question. This refractive index modification makes it possible to apply a phase shift to the light beam that may be guided by the modulation section in question. In this regard, the modulation waveguide may include a doped silicon waveguide and more specifically a silicon waveguide accommodating a PN junction. The refractive index of such a waveguide can be modulated according to the potential applied to such a waveguide. The document [2] cited at the end of the specification provides an example that a person skilled in the art will be able to implement within the scope of the present invention. However, the present invention is not limited to these aspects and other solutions may be considered by a person skilled in the art. In particular, and by way of example, the first modulation waveguide 108 and the second modulation waveguide 110 may include, for example, a III-V semiconductor transferred to a substrate by bonding.

[0045] Thus, the modulation waveguide and the electrode of the first modulation section 105, respectively called first modulation waveguide 108 and first electrode 109, make it possible to apply a phase modulation, called first phase shift, to the light beam guided by the first branch 101. This first phase shift is in particular modulated by a potential applied by the first electrode 109, called first potential.

[0046] In an equivalent manner, the modulation waveguide and the electrode of the second modulation section 106, respectively referred to as the second modulation waveguide 110 and the second electrode 111, make it possible to apply a phase modulation, referred to as the second phase shift, to the light beam guided by the second branch 102. This second phase shift is in particular modulated by a potential applied by the second electrode 111, referred to as the second potential.

[0047] According to the present invention, the first potential and the second potential can be equal to u(t) / 2 and -u(t) / 2, respectively. Under these conditions, the phase shift applied by the first modulation section 105 and the second modulation section 106 is equal to Mu(t) / 2 and -Mu(t) / 2, respectively (M is the efficiency factor of the modulator).

[0048] The second branch 102 typically comprises a first conditioning device 107 (e.g., a phase shift module) configured to apply, in addition to a phase shift -Mu(t) / 2, a set phase shift F (also referred to as the "operating point" of the Mach-Zehnder modulator, given in radians) to the optical radiation that may be guided by the second branch 102. The two radiations guided by the first branch 101 and the second branch 102, respectively, are then recombined at the intermediate optical output end 104 to form an output beam with an intensity of Iout.

[0049] In this way, optical radiation with an intensity of Iin is injected at the optical input end 103. In particular, the radiation can be generated by a laser source LA, which is for example a tunable laser source, which is configured to inject said optical radiation with a wavelength of Iin into the input end of the Mach-Zehnder modulator. The light beam is split into two beams to be guided by the first branch 101 and the second branch 102, respectively. The radiation guided by the first branch 101 (referred to as the first radiation) undergoes a phase shift equal to Mu(t) / 2, while the radiation guided by the second branch 102 (referred to as the second radiation) undergoes a phase shift equal to -Mu(t) / 2+F. The two radiations guided by the first branch 101 and the second branch 102, respectively, are then recombined at the optical output end 104 to form an output beam with an intensity of Iout. When u(t) varies between 0 and a voltage Vpp (for example, Vpp can be limited to 2V), the intensity Iout can vary between a minimum intensity Imin and a maximum intensity Imax, depending on the phase shift applied between the two modulation sections. [ Figure 4] shows the transfer function of a Mach-Zehnder modulator represented by a sine function (representing the intensity ratio Iout / Iin) as a function of F / pi. In order to ensure a substantially linear behavior of the Mach-Zehnder modulator, the phase shift F is usually fixed to pi / 2 (the operating point is then called "quadrature").

[0050] A Mach-Zehnder modulator is characterized by at least two quantities, including the extinction ratio ER and the bandwidth BW.

[0051] The optical modulation amplitude OMA is also a relevant quantity discussed below.

[0052] The extinction ratio ER (dB) is defined as follows:

[0053]

[0054] For a given modulation voltage Vpp (such as [ Figure 4 ]), Imax and Imin are the maximum achievable intensity and the minimum achievable intensity respectively. This item is generally required to be greater than 4dB.

[0055] The optical modulation amplitude (dB) is defined by the following relationship:

[0056] OMA(dBm)=10*log10(I Max -I Min )

[0057] The modulation amplitude must be greater than or close to 0 dBm, or even greater than 0 dBm. Imax and Imin are expressed in optical mW (optical milliwatts).

[0058] Note that Imax is also determined by the radiation intensity I supplied by the laser to the input of the Mach-Zehnder modulator LA More specifically, I MAX According to the relation I MAX =I LA x IL x cos(F) definition, where IL represents the insertion loss and F is the phase shift (operating point) between the 2 modulation sections.

[0059] Usually, I LA Approximately equal to 10mW (or 10dBm).

[0060] The modulation efficiency of a Mach-Zehnder modulator is quantified by the quantity M. In particular, this quantity M is usually written as the ratio of pi to the term Vpi, where Vpi is the voltage difference to be applied between one and the other of the two modulation sections in order to apply a phase shift p between the first radiation and the second radiation. In this regard, it is known that the term Vpi is inversely proportional to the length L of the modulation section, so that the larger the length L, the better the modulation efficiency.

[0061] However, this situation does have an impact on the insertion loss IL and the bandwidth BW of the Mach-Zehnder modulator. Increasing the length L increases the insertion loss IL and reduces the bandwidth BW of the considered Mach-Zehnder modulator.

[0062] For example, the modulation section formed in the silicon-on-insulator waveguide has the following characteristics

[0063]

[0064] Therefore, as described in the table above, a Mach-Zehnder modulator comprising two modulation sections with a length L of the order of 0.4 cm and operating in quadrature has the following characteristics:

[0065]

[0066] Consider the following specific implementation conditions:

[0067] - applying a modulation voltage of u(t) / 2=-Vpp / 2 to Vpp / 2 to each of the "push / pull" sections (in other words, applying a voltage of u(t) / 2 to one of the modulation sections and a voltage of -u(t) / 2 to the other of the modulation sections, where Vpp=2V);

[0068] -Intensity I at the input of the MZM LA 10dBm (10mW);

[0069] Intensity I MAX and I MIN It is defined by the following relationship:

[0070] I MAX =I LA x IL x cos(F)x(1+cos(M1))

[0071] I MIN =I LA x IL x cos(F)x(1+cos(M2))

[0072] Where M1 = pi / 2 + (Vpp / 2) x (pi / Vpi), and M2 = pi / 2 - (Vpp / 2) x (pi / Vpi)

[0073] These considerations allow us to determine the extinction ratio ER and the optical modulation amplitude OMA, which are tabulated as follows:

[0074] ER 6.6dB OMA -0.7dBm

[0075] In order to increase the bandwidth BW of the Mach-Zehnder modulator, it is recommended to reduce the length L of the modulation section. More particularly, and according to the invention, the length L is less than a predetermined length Lp, the predetermined length being a length below which the bandwidth BW is greater than 35 GHz, advantageously greater than 50 GHz, even more advantageously greater than 60 GHz. By way of example, the predetermined length Lp may be less than or equal to 3 mm, and for example equal to 3 mm. By way of another example, the predetermined length Lp may be less than or equal to 2.5 mm, and for example equal to 2.5 mm. By way of another example, the predetermined length Lp may be less than or equal to 2 mm, and for example equal to 2 mm. By way of another example, the predetermined length Lp may be less than or equal to 1.5 mm, and for example equal to 1.5 mm.

[0076] In particular, it has been demonstrated that a modulation section length L equal to 1 mm gives a BW bandwidth equal to 70 GHz. However, such a Mach-Zehnder modulator implemented in quadrature point (loss of 22 dB / cm and Vpi value = 1.8 V / L(cm)) will have a Vpi of 18 V. Therefore, such a Mach-Zehnder modulator modulated with a modulation voltage Vpp = 2 Vpp will have a reduced extinction ratio. For example, and under the above conditions, if the modulation section length L is equal to 1 mm, the extinction ratio is reduced to 1.5 dB. At the same time, the OMA remains at an acceptable level of 0.2 dBm.

[0077] The extinction ratio is then much lower than the expected rate for error-free light transmission. To overcome this problem, higher modulation voltages can be considered. However, this last consideration can lead to excessive dissipation, which is counterproductive (since dissipation is approximately proportional to (Vpp) 2 Thus, for example, to restore an extinction ratio of 6 dB, 4 times the modulation voltage is required, ie Vpp=8 V, and thus the power consumption is 16 times.

[0078] It is proposed here to collocate a SOA semiconductor optical amplifier with a Mach-Zehnder modulator, where the Mach-Zehnder modulator and the SOA have the following characteristics to ensure low total transmitter power consumption:

[0079] 1- Mach-Zehnder Modulator Characteristics : In order to keep the modulation voltage low (e.g. 2 Vpp) while ensuring a sufficiently high extinction ratio, the operating point of the modulator is shifted. In particular, the operating point can be adjusted to a value between 0.6*pi and 0.9*pi, advantageously between 0.65*pi and 0.85*pi, even more advantageously between 0.7*pi and 0.8*pi ([ Figure 5 ]). Consideration of an operating point within one of the above ranges will increase the extinction ratio ER.

[0080] For example, under these conditions, if L=1 mm, Vpp=2 V and F=0.85 x pi, the extinction ratio ER is 6.6 dB. The optical modulation amplitude OMA associated with such an operating point is adversely affected and in particular becomes equal to -3.2 dBm. This OMA value is insufficient.

[0081] 2- In order to compensate for this reduction in the optical modulation amplitude OMA, it is proposed to implement a semiconductor optical amplifier with an SOA at the output 104 of the Mach-Zehnder modulator. The gain of the semiconductor amplifier SOA is also adjusted to compensate for the losses of the OMA. SOA amplifiers are usually used as repeaters after the signal propagation in the optical fiber to compensate for the propagation losses in the optical fiber (usually after tens of kilometers) [3]. According to the present invention, the semiconductor optical amplifier SOA is integrated in the transmitter, at the output of the Mach-Zehnder modulator. Here, the SOA is implemented with a gain between 3 dB and 20 dB, for example equal to 3 dB or 4.8 dB, or greater than 7 dB, or greater than 100 (i.e. 20 dB).

[0082] The SOA power consumption is still low (approximately 1.2V x 50mA, or about 60mWatt at 7dB gain, or about 1.5V x 120mA at 20dB gain). This additional power consumption is much lower than the additional power consumption associated with using 4 times the modulation voltage (e.g., Vpp=8V compared to Vpp=2V). At a gain of 3dB, the OMA becomes acceptable and equals -0.2dBm. Finally, using the SOA at low gain provides another advantage: low gain implemented by low SOA drive strength results in low noise figure [3].

[0083] Overview of the First Embodiment of the Invention

[0084] The following table shows the characteristics of a Mach-Zehnder modulator known in the prior art:

[0085] I LA =10dBm, L=4mm, BW 30GHz

[0086] Mach-Zehnder modulator operating point F Vpp ER <![CDATA[OMA(I LA =10dBm)]]> 0.5*pi 2V 6.6dB -0.7dBm

[0087] ● According to this implementation, the bandwidth is not enough

[0088] The following table shows the characteristics of a quadrature-operated Mach-Zehnder modulator, where the length of the modulator is reduced to 1 mm (I LA =10dBm, L=1mm, BW 70GHz). This reduction in length L significantly increases the bandwidth.

[0089] Mach-Zehnder modulator operating point F Vpp ER <![CDATA[OMA(I LA =10dBm)]]> 0.5*pi 2V 1.5dB 0.2dBm

[0090] The reduction of the length L provides a considerable bandwidth, but the extinction ratio ER is still insufficient.

[0091] The following table shows the characteristics of a quadrature-operated Mach-Zehnder modulator, where the length of the modulator is reduced to 1 mm (I LA =10dBm, L=1mm, BW 70GHz). The modulation voltage suggested in this example is 4 times that suggested in the previous two tables.

[0092] Mach-Zehnder modulator operating point F Vpp ER <![CDATA[OMA(I LA =10dBm)]]> 0.5*pi 8V 1.5dB 6dBm

[0093] By increasing the modulation voltage Vpp, a respectable extinction ratio can be obtained, but the power consumption of the device in question increases by a factor of 16.

[0094] Suggested Implementation 1:

[0095] The following table shows the characteristics of a quadrature-operated Mach-Zehnder modulator, where the length of the modulator is reduced to 1 mm (I LA =10dBm, L=1mm, BW 70GHz). This example uses a semiconductor optical amplifier (gain of 3dB) and applies a sufficiently low modulation voltage to limit power consumption:

[0096] Mach-Zehnder modulator operating point F SOA Gain Vpp ER <![CDATA[OMA(I LA =10dBm)]]> 0.85*pi 3dB 2V 6.6dB -0.2dBm

[0097] The quality factors BW, ER, OMA are within the specifications, where the overconsumption is reduced by using a low gain SOA (about 40 mW overconsumption).

[0098] The implementation of the present invention reduces the size of the Mach-Zehnder modulator while providing it with a wider bandwidth than modulators known in the prior art.

[0099] In addition, the Mach-Zehnder modulator with low gain SOA ensures low power consumption and low noise figure.

[0100] In a second embodiment, the SOA is used to reduce the intensity of the laser. LA As is known, the lower the laser supply intensity and therefore its light intensity I LA The lower the intensity of the signal amplified at its input, the slower it ages. It is also known that the noise figure of an SOA is lower when the intensity of the signal amplified at its input is lower [3]. Therefore, in the second embodiment of the present invention, it is recommended to set the intensity of the laser light I LA Reduce by 3dB, for example, I LA =7dBm, and this reduction is compensated by increasing the gain of the SOA by 3dB, for example 6dB. The following table summarizes the advantages of this second embodiment.

[0101] For example, the intensity of the optical radiation injected by the laser source (LA) is strictly below 10 dB, advantageously below 7 dB. In this case, the gain of the semiconductor optical amplifier is adjusted so that the intensity of the signal at the output of the photonic chip is equal to the signal intensity obtained by the photonic chip without the semiconductor optical amplifier, and radiation with an intensity of 10 dB is injected at the input of the photonic chip.

[0102] Second embodiment (I LA =7dBm, L = 1mm, BW 70GHz)

[0103] Mach-Zehnder modulator operating point F SOA Gain Vpp ER <![CDATA[OMA(I LA =10dBm)]]> 0.85*pi 6dB 2V 6.6dB -0.2dBm

[0104] The quality factors BW, ER and OMA are within the specifications, where the laser intensity is reduced by 3dB and the power consumption is reduced (additional power consumption is about 60mW) due to the use of a SOA with a gain of 6dB.

[0105] [ Figure 6 ] is a graphical representation of an exemplary eye diagram associated with the operation of a Mach-Zehnder modulator. The eye diagram is based on a radiation intensity I at the input of the Mach-Zehnder modulator of 10 dBm. LA The simulation results are shown in Figure 2.

[0106] For the purpose of this simulation, the length L of the modulation section is equal to 1.5 mm, and the gain of the SOA semiconductor amplifier is equal to 4 (6 dB).

[0107] [ Figure 6 ] is a graphical representation of an exemplary eye diagram associated with the operation of a Mach-Zehnder modulator, where the length L of the modulation section is 1.5 mm and the operating point f is equal to 0.75*pi.

[0108] This configuration gives an extinction ratio ER of 5.7 dB at Vpp = 2 V, and the optical modulation amplitude is equal to 4.1 dBm.

[0109] Although the eye diagram is slightly distorted (due to the choice of a non-orthogonal operating point: F different from pi / 2), it shows good OMA and extinction ratio. Furthermore, the reduction in the length L of the modulation section allows the Mach-Zehnder modulator to have a relatively high bandwidth, in particular over 60 GHz.

[0110] In one embodiment, the first conditioning device 107 comprises a first heating element H F , the first heating element is configured to locally modify the refractive index of the first branch or the second branch by heating so as to apply a set phase shift F.

[0111] Advantageously too, the photonic system 10 comprises first control means which are configured to control the first regulating means 107 .

[0112] The first control means comprise a first photodetector PD1 and a first analyser SA1 . In particular, these first means are configured to electrically collect (partially) and analyse the continuous or modulated signal coming from the Mach-Zehnder modulator 100 .

[0113] The modulator M is connected to the first regulating means 107. In particular, the M modulator may be configured such that the first regulating means 107 applies a modulation phase shift F at a modulation frequency Fd (e.g. equal to 5 kHz). In particular, the phase shift F may be modulated according to the following law: F+F.cos(2p.Fd.t)

[0114] This modulation allows detection of the quadrature point (F=pi / 2) as well as the carrier suppression point (F=pi). In particular, when the first modulation means 107 is modulated at a frequency Fd near the quadrature point, the modulated radiation collected by the first photodetector PD1 section substantially comprises harmonics of the frequency Fd. Figure 7 ] shows the Fourier transform obtained using the first analyser when this is the SA1 spectrum analyser.

[0115] In an equivalent manner, when the first modulation device 107 is modulated at a frequency Fd near the carrier suppression point, the modulated radiation collected by the first photodetector PD1 section substantially comprises harmonics of the frequency 2Fd. Figure 8 ] shows the Fourier transform obtained using the first optical spectrum analyzer SA1.

[0116] The adjustment of the phase shift F within the range of 0.6*pi to 0.9*pi can be achieved by weighting the control signal of the first adjustment means 107 to impose a quadrature point (F=pi / 2) and a carrier suppression point.

[0117] Advantageously, the Mach-Zehnder modulator comprises a radiation combiner CO configured to combine first radiation and second radiation phase-modulated by the first branch and the second branch, respectively, the first radiation and the second radiation originating from the splitting of light with wavelength 1 before being modulated by one of the modulation branches.

[0118] According to a particular embodiment, the radiation combiner CO comprises two output channels, respectively referred to as the first channel V1 and the second channel V2.

[0119] In particular, the first V1 channel may be optically coupled to the first GC1 control guide, while the second channel may carry a SOA solid-state optical amplifier.

[0120] The photonic chip further comprises a second device for adjusting the optical gain of the SOA semiconductor optical amplifier. Advantageously, the second adjusting device comprises a second heating element H. SOA .

[0121] The photonic system comprises second control means configured to control second regulating means, said second control means comprising a second photodetector PD2 and a second optical spectrum analyser SA2.

[0122] Advantageously, the second photodetector PD2 is carried by a second control waveguide GC2 optically coupled to the second channel V2, the coupling being of such magnitude that the second waveguide collects at most 10%, advantageously at most 5%, of the optical power flowing in the second channel V2.

[0123] The photonic chip may further comprise an optical filter FO carried by the second channel (V2) and located downstream of the semiconductor optical amplifier SOA.

[0124] Alternatively, the first photodetector PD1 may be located on the SOA branch. In this case, if the SOA output power collection towards PD2 is equal to the SOA input power collection towards PD1, the SOA gain is equal to the optical power on PD2 / optical power on PD1.

[0125] Complementarily, the photonic chip may further comprise third control means configured to determine the intensity of the radiation delivered by the LA laser source. In particular, these third control means may comprise a third photodetector PD3 configured to partially detect the laser radiation emitted by the laser source LA. The third photodetector PD3 may be coupled to an analyzer that enables the intensity of the optical radiation emitted by the laser source LA to be determined based solely on the third photodetector PD3.

[0126] These third control means are advantageously used to adjust the gain of the semiconductor optical amplifier SOA.

[0127] References

[0128] [1] S. Menezo et al., “Back-Side-On-BOX heterogeneous laser integration for fully integrated photonic circuits on silicon” 45th European Conference on Optical Communication (ECOC 2019), 2019, pp. 1-3, doi:10.1049 / cp.2019.0826;

[0129] [2] Reed, G et al., "Silicon optical modulators" Nature Photonics" 4, 518-526 (2010);

[0130] [3] R.Bonk et al., "Linear semiconductor optical amplifiers foramplification of advanced modulation formats" Opt.Express 20, 9657-9672 (2012);

[0131] [4] P. Kaspar et al., “Hybrid III-V / Silicon SOA in Optical Network Based on Advanced Modulation Formats,” IEEE Photonics Technology Letters, Vol. 27, No. 22, pp. 2383–2386, 15 November 2015.

Claims

1. A photonic system, wherein the photonic system is provided with a photonic chip made by silicon technology, wherein the photonic chip (10) comprises: - a Mach-Zehnder modulator (100) formed on and / or in a useful layer (200) located on one face of a support substrate (300), the Mach-Zehnder modulator comprising two modulation branches, respectively referred to as a first branch (101) and a second branch (102), each branch being provided with a modulation portion (105, 106) extending over a length L less than 3 mm; - first means (107) for adjusting an operating point of the Mach-Zehnder modulator, the first means being configured to impose an operating point associated with a set phase shift F between the first branch (101) and the second branch (102); - a semiconductor optical amplifier (SOA) formed on and / or in the useful layer and arranged downstream of an output end (104) of the Mach-Zehnder modulator (100), the semiconductor optical amplifier (SOA) being configured to amplify a signal modulated by the Mach-Zehnder modulator, the semiconductor optical amplifier (SOA) having an optical gain configured such that when the set phase shift F is adjusted within a range of 0.6pi to 0.9pi, at an output port S arranged downstream of the semiconductor optical amplifier (SOA), an optical modulation amplitude associated with the photonic chip is between -3dBm and 10dBm. 2 . The photonic system according to claim 1 , wherein the first adjustment device comprises a first heating element, which is configured to locally modify the refractive index of the first branch or the second branch by heating so as to apply the set phase shift F. 3 .

3. The photonic system according to claim 1 or 2, wherein the photonic system comprises a first control device configured to control the first adjustment device.

4. The photonic system according to claim 3, wherein the first control device comprises a first photodetector (PD1) and a first optical spectrum analyzer (SA1).

5. A photonic system according to claim 4, wherein the Mach-Zehnder modulator (100) comprises a radiation combiner (104), which is configured to combine first radiation and second radiation phase-modulated by the first branch (101) and the second branch (102), respectively, the first radiation and the second radiation originating from the division of optical radiation before being modulated by one of the modulation branches.

6. The photonic system according to claim 5, wherein the photonic chip (10) further comprises a second device for adjusting the optical gain of the semiconductor optical amplifier (SOA), advantageously, the second adjusting device comprises a second heating element (H SOA ).

7. The photonic system according to claim 6, wherein the photonic system comprises a second control device, the second control device being configured to control the second adjustment device, the second control device comprising a second photodetector (PD2) and a second optical spectrum analyzer (SA2).

8. A photonic system according to claim 7, wherein the radiation combiner comprises two output channels, respectively referred to as a first channel (V1) and a second channel (V2), the second channel (V2) carrying the semiconductor optical amplifier (SOA), the second control device being carried by a second control waveguide (GC2) optically coupled to the second channel (V2), the coupling being of such magnitude that the second waveguide extracts at most 10%, advantageously at most 5%, of the optical power flowing in the second channel (V2).

9. The photonic system according to claim 8, wherein the photonic chip further comprises an optical filter (FO) carried by the first channel (V1) and located downstream of the semiconductor optical amplifier (SOA).

10. A photonic system according to any one of claims 5 to 9, wherein the photonic chip comprises a laser source (LA) configured to inject optical radiation with a wavelength of I into an input of the Mach-Zehnder modulator.

11. The photonic system of claim 10, wherein the laser source is a tunable laser source.

12. A specific implementation of a photonic system according to any one of claims 1 to 11 in combination with claim 10 or 11, wherein the intensity of the optical radiation injected by the laser source (LA) is strictly less than 10 dB, advantageously less than 7 dB, and wherein the gain of the semiconductor optical amplifier is adjusted so that the intensity of the signal at the output end of the photonic chip is equal to the signal intensity obtained by the photonic chip in the absence of the semiconductor optical amplifier, and radiation with an intensity of 10 dB is injected at the input end of the photonic chip.

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